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A photolabile protecting group (PPG; also known as: photoremovable, photosensitive, or photocleavable protecting group) is a chemical modification to a molecule that can be removed with light. PPGs enable high degrees of chemoselectivity as they allow researchers to control spatial, temporal and concentration variables with light. Control of these variables is valuable as it enables multiple PPG applications, including orthogonality in systems with multiple protecting groups. As the removal of a PPG does not require chemical reagents, the photocleavage of a PPG is often referred to as "traceless reagent processes", and is often used in biological model systems and multistep organic syntheses. Since their introduction in 1962, numerous PPGs have been developed and utilized in a variety of wide-ranging applications from protein science to photoresists. Due to the large number of reported protecting groups, PPGs are often categorized by their major functional group(s); three of the most common classifications are detailed below. | 5 | Photochemistry |
In organic chemistry, hydroamination is the addition of an bond of an amine across a carbon-carbon multiple bond of an alkene, alkyne, diene, or allene. In the ideal case, hydroamination is atom economical and green. Amines are common in fine-chemical, pharmaceutical, and agricultural industries. Hydroamination can be used intramolecularly to create heterocycles or intermolecularly with a separate amine and unsaturated compound. The development of catalysts for hydroamination remains an active area, especially for alkenes. Although practical hydroamination reactions can be effected for dienes and electrophilic alkenes, the term hydroamination often implies reactions metal-catalyzed processes. | 0 | Organic Chemistry |
In electrospray ionization (ESI), coeluted matrix components can influence signal intensity through a competition for available charges and for the access to the droplet surface for gas-phase emission, thus creating the so-called matrix effects. Matrix effects can occur at different stages of the interfacing process leading to unpredictably enhanced or suppressed signal response. Direct-EI interface, using a gas phase ionization technique, can eliminate most matrix effects observed with ESI. In fact, it is influenced neither by the mobile phase nor by other matrix components so that the signal response is always proportional only to analyte concentration. This simplifies sample preparation procedures that can be very complex and time-consuming prior to ESI. | 3 | Analytical Chemistry |
In antiquity, pewter was tin alloyed with lead and sometimes also copper. Older pewters with higher lead content are heavier, tarnish faster, and their oxidation has a darker, silver-gray color. Pewters containing lead are no longer used in items that will come in contact with the human body (such as cups, plates, or jewelry), due to the toxicity of lead. Modern pewters are available that are completely free of lead, although many pewters containing lead are still being produced for other purposes.
A typical European casting alloy contains 94% tin, 1% copper and 5% antimony. A European pewter sheet would contain 92% tin, 2% copper, and 6% antimony. Asian pewter, produced mostly in Malaysia, Singapore, and Thailand, contains a higher percentage of tin, usually 97.5% tin, 1% copper, and 1.5% antimony. This makes the alloy slightly softer.
The term Mexican pewter is used for any of various alloys of aluminium that are used for decorative items.
Pewter is also used to imitate platinum in costume jewelry. | 8 | Metallurgy |
Triphenyl tetrazolium chloride, TTC, or simply tetrazolium chloride (with the formula 2,3,5-triphenyl-2H-tetrazolium chloride) is a redox indicator commonly used in biochemical experiments especially to indicate cellular respiration. It is a white crystalline powder, soluble in water, ethanol and acetone but insoluble in ether. | 3 | Analytical Chemistry |
Many countries, including India, France and Germany, have underground deposits of iron ore in dust form (blue dust). Such iron ore cannot be directly charged in a blast furnace. In the early 20th century, sinter technology was developed for converting ore fines into lumpy material chargeable in blast furnaces. Sinter technology took 30 years to gain acceptance in the iron-making domain, but now plays an important role. Initially developed to generate steel, it is now a means of using metallurgical waste generated in steel plants to enhance blast furnace operation and reducing waste. The largest sinter plant is located in Chennai, India, and employs 10,000 people. | 8 | Metallurgy |
Several technologies are related to soil vapor extraction. As noted above, various soil-heating remediation technologies (e.g., electrical resistive heating, in situ vitrification) require a soil gas collection component, which may take the form of SVE and/or a surface barrier (i.e., hood). Bioventing is a related technology, the goal of which is to introduce additional oxygen (or possibly other reactive gases) into the subsurface to stimulate biological degradation of the contamination. In situ air sparging is a remediation technology for treating contamination in groundwater. Air is injected and "sparged" through the groundwater and then collected via soil vapor extraction wells. | 2 | Environmental Chemistry |
Metals are predominantly accumulated in the roots causing an unbalanced shoot to root ratio of metal concentrations in most plants. However, in hyperaccumulators, the shoot to root ratio of metal concentrations are abnormally higher in the leaves and much lower in the roots. As this process occurs, metals are efficiently shuttled from the root to the shoot as an enhanced ability in order to protect the roots from metal toxicity.
Delving into tolerance: Throughout the research of hyperaccumulation, there is a conundrum with tolerance. There are several different understandings of tolerance associated with accumulation; however, there are a few similarities. Evidence has conveyed that the traits of tolerance and accumulation are separate to each other and are moderated by genetic and physiological mechanisms. Moreover, the physiological mechanisms, in relation to tolerance, are classified as exclusion: when the movement of metals at the interfaces of soil/root or root/shoot are blocked, or accumulation: when the uptake of metals that have been rendered as non-toxic are allowed into the aerial plant parts.
Characteristics from certain physiological elements:
There are certain characteristics that are specific to certain species. For example, when presented with a low supply of zinc, Thlaspi caerulescens had higher zinc concentrations accumulated compared to other non-accumulator plant species. Further evidence indicated that when T. caerulescens were grown on soil with an adequate amount of contamination, the species accumulated an amount of zinc that was 24-60 times more than Raphanus sativus (radish) had accumulated. Additionally, the capacity to experimentally manipulate soil metal concentrations with soil amendments has allowed researchers to identify the maximum soil concentrations that hyperaccumulation species can tolerate and the minimum soil concentrations in order to reach hyperaccumulation. Furthermore, with these findings, two distinct categories of hyperaccumulation arose, active and passive hyperaccumulation. Active hyperaccumulation is attained by relatively low soil concentrations. Passive hyperaccumulation is induced by exceedingly high soil concentrations. | 2 | Environmental Chemistry |
Alba, a green-fluorescent rabbit, was created by a French laboratory commissioned by Eduardo Kac using GFP for purposes of art and social commentary. The US company Yorktown Technologies markets to aquarium shops green fluorescent zebrafish (GloFish) that were initially developed to detect pollution in waterways. NeonPets, a US-based company has marketed green fluorescent mice to the pet industry as NeonMice. Green fluorescent pigs, known as Noels, were bred by a group of researchers led by Wu Shinn-Chih at the Department of Animal Science and Technology at National Taiwan University. A Japanese-American Team created green-fluorescent cats as proof of concept to use them potentially as model organisms for diseases, particularly HIV. In 2009 a South Korean team from Seoul National University bred the first transgenic beagles with fibroblast cells from sea anemones. The dogs give off a red fluorescent light, and they are meant to allow scientists to study the genes that cause human diseases like narcolepsy and blindness. | 1 | Biochemistry |
Even though Staudinger ligation is a suitable bioconjugation in living cells without major toxicity, the phosphines sensitivity to air oxidation and its poor solubility in water significantly hinder its efficiency. The copper(I) catalyzed azide-alkyne coupling has reasonable reaction rate and efficiency under physiological conditions, but copper poses significant toxicity and sometimes interferes with protein functions in living cells. In 2004, chemist Carolyn R. Bertozzis lab developed a metal free [3+2] cycloaddition using strained cyclooctyne and azide. Cyclooctyne, which is the smallest stable cycloalkyne, can couple with azide through [3+2] cycloaddition, leading to two regioisomeric triazoles (Figure 12). The reaction occurs readily at room temperature and therefore can be used to effectively modify living cells without negative effects. It has also been reported that the installation of fluorine substituents on a cyclic alkyne can greatly accelerate the reaction rate. | 1 | Biochemistry |
The TRAFAC class of G domain proteins is named after the prototypical member, the translation factor G proteins. They play roles in translation, signal transduction, and cell motility. | 1 | Biochemistry |
The lactate shuttle hypothesis also explains the balance of lactate production in the cytosol, via glycolysis or glycogenolysis, and lactate oxidation in the mitochondria (described below). | 1 | Biochemistry |
To illustrate the processes, consider the case of dissolving a weak acid, HA, in water. The pH can be calculated using an ICE table. Note that in this example, we are assuming that the acid is not very weak, and that the concentration is not very dilute, so that the concentration of [OH] ions can be neglected. This is equivalent to the assumption that the final pH will be below about 6 or so. See pH calculations for more details.
First write down the equilibrium expression.
The columns of the table correspond to the three species in equilibrium.
The first row shows the reaction, which some authors label R and some leave blank.
The second row, labeled I, has the initial conditions: the nominal concentration of acid is C and it is initially undissociated, so the concentrations of A and H are zero.
The third row, labeled C, specifies the change that occurs during the reaction. When the acid dissociates, its concentration changes by an amount , and the concentrations of A and H both change by an amount . This follows from consideration of mass balance (the total number of each atom/molecule must remain the same) and charge balance (the sum of the electric charges before and after the reaction must be zero).
Note that the coefficients in front of the "x" correlate to the mole ratios of the reactants to the product. For example, if the reaction equation had 2 H ions in the product, then the "change" for that cell would be "2x"
The fourth row, labeled E, is the sum of the first two rows and shows the final concentrations of each species at equilibrium.
It can be seen from the table that, at equilibrium, [H] = x.
To find x, the acid dissociation constant (that is, the equilibrium constant for acid-base dissociation) must be specified.
Substitute the concentrations with the values found in the last row of the ICE table.
With specific values for C and K this quadratic equation can be solved for x. Assuming that pH = −log[H] the pH can be calculated as pH = −logx.
If the degree of dissociation is quite small, C ≫ x and the expression simplifies to
and pH = (pK − log C). This approximate expression is good for pK values larger than about 2 and concentrations high enough. | 7 | Physical Chemistry |
GC-VUV can be used for bulk compositional analysis because compounds share spectral shape characteristics within a class. Proprietary software applies fitting procedures to quickly determine the relative contribution of each compound category present in a sample. Retention index information is used to limit the amount of VUV library searching and fitting performed for each analyte, enabling the automated data processing routine to be completed quickly. Compound class or specific compound concentrations can be reported as either mass or volume percent.
GC-VUV bulk compound characterization was first applied to the analysis of paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) hydrocarbons in gasoline streams. It is suitable for use with finished gasoline, reformate, reformer feed, FCC, light naphtha, and heavy naphtha samples. A typical chromatographic analysis is displayed in Figure 7. The inset shows how the analyte spectral response is fit with VUV library spectra for the selected time slice. A report detailing the carbon number breakdown within each PIONA compound class, as well as the relative mass or volume percent of classes, is shown. A table with mass % and carbon number data from a gasoline sample can be seen in Figure 8. Compound class characterization utilizes a method known as time interval deconvolution (TID), which has recently been applied to the analysis of terpenes. | 7 | Physical Chemistry |
The Joule–Thomson coefficient, , is of practical importance because the two end states of a throttling process () lie on a constant enthalpy curve. Although ideal gases, for which , do not change temperature in such a process, real gases do, and it is important in applications to know whether they heat up or cool down.
This coefficient can be found in terms of the previously described derivatives as,
so when is positive the gas temperature decreases when it passes through a throttle, and if it is negative the temperature increases. Therefore the condition defines a curve that separates the region of the plane where from the region where it is less than zero. This curve is called the inversion curve, and its equation is . Using the expression for derived previously for the van der Waals equation this is
Note that for there will be cooling for or in terms of the critical temperature . As Sommerfeld noted, "This is the case with air and with most other gases. Air can be cooled at will by repeated expansion and can finally be liquified."
The inversion curve can be found by solving its equation for , and substituting into the vdW equation. This produces , where, for simplicity, have been replaced by .
The maximum of this, quadratic, curve occurs, with , for
which gives , or , and the corresponding . The zeros of the inversion curve , are, making use of the quadratic formula, , or and ( and ). In terms of the dimensionless variables, the zeros are at and , while the maximum is , and occurs at . Note from Fig. 5 that there is an overlap between the saturation curve and the inversion curve plotted there.
This region is shown enlarged in the right hand graph of the figure. Therefore a van der Waals gas can be liquified by passing it through a throttle under the proper conditions; real gases are liquified in this way. | 7 | Physical Chemistry |
The main application of DVS is to measure water sorption isotherms. In general, a vapor sorption isotherm shows the equilibrium amount of vapor sorbed as a function of steady state relative vapor pressure at a constant temperature. For water sorption isotherms, water-relative vapor pressure is more commonly expressed as relative humidity. This is accomplished in a DVS measurement by exposing a sample to a series of step changes in relative humidity and monitoring the mass change as a function of time. The sample mass must be allowed to reach gravimetric equilibrium at each step change in humidity before progressing to the next humidity level. Then, the equilibrium mass values at each relative humidity step are used to generate the isotherm. Isotherms are typically divided into two components: sorption for increasing humidity steps, and desorption for decreasing humidity steps. Sorption can be further divided into adsorption (sorbate located on the surface) and absorption (sorbate penetrates the bulk). | 7 | Physical Chemistry |
The United States became interested in gas turbine development around 1905. From 1910-1915, austenitic ( γ phase) stainless steels were developed to survive high temperatures in gas turbines. By 1929, 80Ni-20Cr alloy was the norm, with small additions of Ti and Al. Although early metallurgists did not know it yet, they were forming small γ' precipitates in Ni-based superalloys. These alloys quickly surpassed Fe- and Co-based superalloys, which were strengthened by carbides and solid solution strengthening.
Although Cr was great for protecting the alloys from oxidation and corrosion up to 700 °C, metallurgists began decreasing Cr in favor of Al, which had oxidation resistance at much higher temperatures. The lack of Cr caused issues with hot corrosion, so coatings needed to be developed.
Around 1950, vacuum melting became commercialized, which allowed metallurgists to create higher purity alloys with more precise composition.
In the 60s and 70s, metallurgists changed focus from alloy chemistry to alloy processing. Directional solidification was developed to allow columnar or even single-crystal turbine blades. Oxide dispersion strengthening could obtain very fine grains and superplasticity. | 8 | Metallurgy |
Friedels salt plays a main role in the binding and retention of chloride anions in cement and concrete. However, Friedels salt remains a poorly understood phase in the CaO–AlO–CaCl–HO system. A sufficient understanding of the Friedel's salt system is essential to correctly model the reactive transport of chloride ions in reinforced concrete structures affected by chloride attack and steel reinforcement corrosion. It is also important to assess the long-term stability of salt-saturated Portland cement-based grouts to be used in engineering structures exposed to seawater or concentrated brine as it is the case for radioactive waste disposal in deep salt formations.
Another reason to study AFm phases and the Friedel's salt system is their tendency to bind, trap and to immobilise toxic anions, such as , , and , or the long-lived radionuclide I, in cementitious materials. Their characterization is important to conceive anion getters and to assess the retention capacity of cementitious buffer and concrete barriers used for radioactive waste disposal. | 3 | Analytical Chemistry |
Bay muds occur in bays and estuaries throughout the temperate regions of the world. In North America, prominent instances are: (a) the Stellwagen Bank formed 16,000 to 9000 BCE by glaciation of Cape Cod Bay in Massachusetts, (b) Florida Bay, (c) in California Morro Bay and San Francisco Bay and (d) Knik & Turnagain Arms in Anchorage, Alaska. In the United Kingdom large bay mud occurrences are found at Morecambe Bay, Bridgwater Bay and Bristol Bay. Straddling Denmark, the Netherlands and Germany is the Wadden Sea, a major formation underlain by bay muds.
In Asia the Chongming Dongtan Nature Reserve in Shanghai, China, is an example of a large scale bay mud formation. The Atlantic coast of Africa holds the Banc dArguin, a World Heritage nature preserve in the country of Mauritania. Banc dArguin is a vast area underlain by bay mud. | 2 | Environmental Chemistry |
The conservative nature of gene deserts confirms that these stretches of noncoding bases are essential to proper functioning. Indeed, a wide range of studies on irregularities in the noncoding genes discovered several associations to genetic diseases. One of the most studied gene deserts is the 8q24 region. Early genome wide association studies were focused on the 8q24 region (residing on chromosome 8) due to the abnormally high rates of SNPs that seem to occur in the region. These studies found that the region was linked to increased risks for a variety of cancers, notably in the prostate, breast, ovaries, colonic, and pancreas. Using inserts of the gene desert into bacterial artificial chromosomes, one study was able to produce enhancer activity in certain regions, which were isolated via cloning systems. This study successfully identified an enhancer sequence hidden in the region. Within this enhancer sequence, an SNP that conferred risk for prostate cancer, labeled SNP s6983267, was discovered in diseased mice. However, the 8q24 region is not solely limited to conferred risks of prostate cancer. A study in 2008 screened human subjects (and controls) with variations in the gene desert region, discovering five different regions that conferred different risks when affected by different SNPs. This study used identified SNP markers in the gene desert to identify risk conference from each of the regions to a specific tissue expression. Although these risks were successfully linked to various forms of cancer, Ghoussaini, M., et al. note their uncertainty in whether the SNPs functioned merely as markers or were the direct causants of the cancers.
These varied effects occur due to the different interactions between the SNPs in this region and MYC promoters of different organs. The MYC promoter, which is located at a short distance downstream of the 8q24 region, is perhaps the most studied oncogene due to its association with a myriad of diseases. Normal functioning of the MYC promoter ensures that cells divide regularly. The study postulates that the 8q region, which underwent a chromosomal translocation in humans, could have moved an essential enhancer for the MYC promoter. This areas around this region could have been subjected to recombination that may have hidden the essential MYC enhancer within the gene desert through time, although its enhancing effects are still very much retained. This analysis stems from disease associations observed in several mice species where this region is retained at proximity to the MYC promoter. Thus, the 8q24 gene desert should have been somewhat linked to the MYC promoter. The desert resembles a stable gene desert that has had very little recombination after the translocation event. Thus, a potential hypothesis is that SNPs affecting this region disrupt the important tissue-specific genes with the stable gene desert, which could explain the risks of cancer in various tissue forms. This effect of hidden enhancer elements can also be observed in other locations in the genome. For instance, SNPs in the 5p13.1 deregulate the PTGER4 coding region, leading to Crohn's Disease. Another affected region in the 9p21 gene desert causes several coronary artery diseases. However, none of these risk-conferring gene deserts seem to be affected as much as the 8q24 regions. Current studies are still unsure about the SNP-affected processes in the 8q24 region that result in particularly amplified responses to the MYC promoter. With the aid of a more accessible population and more specific markers for genome wide association mapping, an increasing number of risk alleles are now being marked in gene deserts, where small, isolated, and seemingly-unimportant regions of genes may moderate important genes. | 1 | Biochemistry |
Pump–probe imaging is ideal for the study and characterization of nanomaterials, such as graphene, nanocubes, nanowires, and a variety of semiconductors, due to their large susceptibilities but weak fluorescence. In particular, single-walled carbon nanotubes have been extensively studied and imaged with submicrometer resolution, providing details about carrier dynamics, photophysical, and photochemical properties. | 7 | Physical Chemistry |
The term human equivalent is used in a number of different contexts. This term can refer to human equivalents of various comparisons of animate and inanimate things. | 1 | Biochemistry |
Reversed phase SPE separates analytes based on their polarity. The stationary phase of a reversed phase SPE cartridge is derivatized with hydrocarbon chains, which retain compounds of mid to low polarity due to the hydrophobic effect. The analyte can be eluted by washing the cartridge with a non-polar solvent, which disrupts the interaction of the analyte and the stationary phase.
A stationary phase of silicon with carbon chains is commonly used. Relying on mainly non-polar, hydrophobic interactions, only non-polar or very weakly polar compounds will adsorb to the surface. | 3 | Analytical Chemistry |
GFP has a beta barrel structure consisting of eleven β-strands with a pleated sheet arrangement, with an alpha helix containing the covalently bonded chromophore 4-(p-hydroxybenzylidene)imidazolidin-5-one (HBI) running through the center. Five shorter alpha helices form caps on the ends of the structure. The beta barrel structure is a nearly perfect cylinder, 42Å long and 24Å in diameter (some studies have reported a diameter of 30Å), creating what is referred to as a "β-can" formation, which is unique to the GFP-like family. HBI, the spontaneously modified form of the tripeptide Ser65–Tyr66–Gly67, is nonfluorescent in the absence of the properly folded GFP scaffold and exists mainly in the un-ionized phenol form in wtGFP. Inward-facing sidechains of the barrel induce specific cyclization reactions in Ser65–Tyr66–Gly67 that induce ionization of HBI to the phenolate form and chromophore formation. This process of post-translational modification is referred to as maturation. The hydrogen-bonding network and electron-stacking interactions with these sidechains influence the color, intensity and photostability of GFP and its numerous derivatives. The tightly packed nature of the barrel excludes solvent molecules, protecting the chromophore fluorescence from quenching by water. In addition to the auto-cyclization of the Ser65-Tyr66-Gly67, a 1,2-dehydrogenation reaction occurs at the Tyr66 residue. Besides the three residues that form the chromophore, residues such as Gln94, Arg96, His148, Thr203, and Glu222 all act as stabilizers. The residues of Gln94, Arg96, and His148 are able to stabilize by delocalizing the chromophore charge. Arg96 is the most important stabilizing residue due to the fact that it prompts the necessary structural realignments that are necessary from the HBI ring to occur. Any mutation to the Arg96 residue would result in a decrease in the development rate of the chromophore because proper electrostatic and steric interactions would be lost. Tyr66 is the recipient of hydrogen bonds and does not ionize in order to produce favorable electrostatics. | 1 | Biochemistry |
The theoretical framework underpinning FTMW spectroscopy is analogous to that used to describe FT-NMR spectroscopy. The behaviour of the evolving system is described by optical Bloch equations. First, a short (typically 0-3 microsecond duration) microwave pulse is introduced on resonance with a rotational transition. Those molecules that absorb the energy from this pulse are induced to rotate coherently in phase with the incident radiation. De-activation of the polarisation pulse is followed by microwave emission that accompanies decoherence of the molecular ensemble. This free induction decay occurs on a timescale of 1-100 microseconds depending on instrument settings. Following pioneering work by Dicke and co-workers in the 1950s, the first FTMW spectrometer was constructed by Ekkers and Flygare in 1975. | 7 | Physical Chemistry |
Hermann Emil Fischer won the Nobel Prize in Chemistry (1902) for his work in determining the structure of the -aldohexoses. However, the linear, free-aldehyde structures that Fischer proposed represent a very minor percentage of the forms that hexose sugars adopt in solution. It was Edmund Hirst and Clifford Purves, in the research group of Walter Haworth, who conclusively determined that the hexose sugars preferentially form a pyranose, or six-membered, ring. Haworth drew the ring as a flat hexagon with groups above and below the plane of the ring – the Haworth projection.
A further refinement to the conformation of pyranose rings came when Sponsler and Dore (1926) realized that Sachse's mathematical treatment of six-membered rings could be applied to their X-ray structure of cellulose. It was determined that the pyranose ring is puckered, to allow all of the carbon atoms of the ring to have close to the ideal tetrahedral geometry. | 0 | Organic Chemistry |
A glacier can exert a sufficient amount of pressure on its lower surface to lower the melting point of its ice. The melting of the ice at the glacier's base allows it to move from a higher elevation to a lower elevation. Liquid water may flow from the base of a glacier at lower elevations when the temperature of the air is above the freezing point of water. | 7 | Physical Chemistry |
In general ketones () take the suffix "-one" (pronounced own, not won) with a suffixed position number: is pentan-2-one. If a higher precedence suffix is in use, the prefix "oxo-" is used: is 3-oxohexanal. | 0 | Organic Chemistry |
Non-sequential double ionization is a process whose mechanism differs (in any detail) from the sequential one. For example, both the electrons leave the system simultaneously (as in alkaline earth atoms, see below), the second electron's liberation is assisted by the first electron (as in noble gas atoms, see below), etc.
The phenomenon of non-sequential double ionization was experimentally discovered by Suran and Zapesochny for alkaline earth atoms as early as 1975.
Despite extensive studies, the details of double ionization in alkaline earth atoms remain unknown. It is supposed that double ionization in this case is realized by transitions of both the electrons through the spectrum of autoionizing atomic states, located between the first and second ionization potentials.
For noble gas atoms, non-sequential double ionization was first observed by L'Huillier.
The interest to this phenomenon grew rapidly after it was rediscovered
in infrared fields and for higher intensities. Multiple ionization has also been observed.
The mechanism of non-sequential double ionization in noble gas atoms differs from the one in alkaline earth atoms. For noble gas atoms in infrared laser fields, following one-electron ionization, the liberated electron can recollide
with the parent ion.
This electron acts as an "atomic antenna", absorbing the
energy from the laser field between ionization and recollision and
depositing it into the parent ion. Inelastic scattering on the
parent ion results in further collisional excitation and/or
ionization. This mechanism is known as the three-step model of non-sequential double ionization, which is also closely related to the three step model of high harmonic generation.
Dynamics of double ionization within the three-step model strongly depends on the laser field intensity. The maximum energy (in atomic units) gained by the recolliding electron from the laser field is , where
is the ponderomotive energy, is the laser field strength, and is the laser frequency. Even when is far below ionization potential experiments have observed correlated ionization.
As opposed to the high- regime ()
in the low- regime () the assistance of the laser field during the
recollision is vital.
Classical and quantum analysis
of the low- regime
demonstrates the following two ways of electron ejection after the recollision: First, the two electrons can be freed with little time delay compared to the quarter-cycle of the driving laser field. Second, the time delay between the ejection of the
first and the second electron is of the order of the quarter-cycle of the driving field. In these two cases, the electrons appear in different quadrants of the correlated spectrum. If following the recollision, the electrons are ejected
nearly simultaneously, their parallel momenta have equal signs,
and both electrons are driven by the laser field in the same
direction toward the detector
. If after the recollision, the electrons are ejected with a substantial delay (quarter-cycle or
more), they end up going in the opposite directions. These two types of dynamics produce distinctly different correlated spectra (compare experimental results
with | 7 | Physical Chemistry |
Haploid cells are one of two mating types (a or α), and respond to the mating pheromone produced by haploid cells of the opposite mating type, and can mate with cells of the opposite mating type. Haploid cells cannot undergo meiosis. Diploid cells do not produce or respond to either mating pheromone and do not mate, but can undergo meiosis to produce four haploid cells.
Like the differences between haploid a and α cells, different patterns of gene repression and activation are responsible for the phenotypic differences between haploid and diploid cells. In addition to the specific a and α transcriptional patterns, haploid cells of both mating types share a haploid transcriptional pattern which activates haploid-specific genes (such as HO) and represses diploid-specific genes (such as IME1). Similarly, diploid cells activate diploid-specific genes and repress haploid-specific genes.
The different gene expression patterns of haploids and diploids are again due to the MAT locus. Haploid cells only contain one copy of each of the 16 chromosomes and thus can only possess one allele of MAT (either MATa or MATα), which determines their mating type. Diploid cells result from the mating of an a cell and an α cell, and thus possess 32 chromosomes (in 16 pairs), including one chromosome bearing the MATa allele and another chromosome bearing the MATα allele. The combination of the information encoded by the MATa allele (the a1 gene) and the MATα allele (the α1 and α2 genes) triggers the diploid transcriptional program. Similarly, the presence of only a single allele of MAT, whether it is MATa or MATα, triggers the haploid transcriptional program.
The alleles present at the MAT locus are sufficient to program the mating behaviour of the cell. For example, using genetic manipulations, a MATa allele can be added to a MATα haploid cell. Despite having a haploid complement of chromosomes, the cell now has both the MATa and MATα alleles, and will behave like a diploid cell: it will not produce or respond to mating pheromones, and when starved will attempt to undergo meiosis, with fatal results. Similarly, deletion of one copy of the MAT locus in a diploid cell, leaving only a single MATa or MATα allele, will cause a cell with a diploid complement of chromosomes to behave like a haploid cell. | 1 | Biochemistry |
SPINA-GD correlates to the T4-T3 conversion rate in slow tissue pools, as determined with isotope-based measurements in healthy volunteers. It was also shown that GD correlates with resting energy expenditure, body mass index and thyrotropin levels in humans, and that it is reduced in nonthyroidal illness with hypodeiodination. Multiple studies demonstrated SPINA-GD to rise after initiation of substitution therapy with selenium, a trace element that is essential for the synthesis of deiodinases. Conversely, it was observed that SPINA-GD is reduced in persons positive for autoantibodies to selenoprotein P, which is assumed to be involved in transport and storage of selenium. | 1 | Biochemistry |
A refrigeration device passes a working substance through successive stages, overall constituting a cycle. This may be brought about not by moving or changing separating walls around an unmoving body of working substance, but rather by moving a body of working substance to bring about exposure to a cyclic succession of unmoving unchanging walls. The effect is virtually a cycle of thermodynamic operations. The kinetic energy of bulk motion of the working substance is not a significant feature of the device, and the working substance may be practically considered as nearly at rest. | 7 | Physical Chemistry |
Animals that commonly cause injury to plants include pests such as insects, mites, and nematodes. These variously bite or abrade plant parts such as leaves, stems, and roots, or as is common among the true bugs, pierce the plants surface and suck plant juices. The resulting injuries may admit plant pathogens such as bacteria and fungi, which may extend the injury. Caterpillar larvae of agricultural pests such as cabbage white butterflies (Pieridae) can completely defoliate Brassica' crops.
Molluscs such as snails graze on plants including grasses and forbs, abrading them with their rasp-like radula; they can inflict substantial damage to crops.
Grazing mammals including livestock such as cattle, too, bite off or break parts of plants including grasses, forbs, and forest trees, causing injury, and again, potentially admitting pathogens. | 1 | Biochemistry |
When retroviruses have integrated their own genome into the germ line, their genome is passed on to a following generation. These endogenous retroviruses (ERVs), contrasted with exogenous ones, now make up 5–8% of the human genome. Most insertions have no known function and are often referred to as "junk DNA". However, many endogenous retroviruses play important roles in host biology, such as control of gene transcription, cell fusion during placental development in the course of the germination of an embryo, and resistance to exogenous retroviral infection. Endogenous retroviruses have also received special attention in the research of immunology-related pathologies, such as autoimmune diseases like multiple sclerosis, although endogenous retroviruses have not yet been proven to play any causal role in this class of disease.
While transcription was classically thought to occur only from DNA to RNA, reverse transcriptase transcribes RNA into DNA. The term "retro" in retrovirus refers to this reversal (making DNA from RNA) of the usual direction of transcription. It still obeys the central dogma of molecular biology, which states that information can be transferred from nucleic acid to nucleic acid but cannot be transferred back from protein to either protein or nucleic acid. Reverse transcriptase activity outside of retroviruses has been found in almost all eukaryotes, enabling the generation and insertion of new copies of retrotransposons into the host genome. These inserts are transcribed by enzymes of the host into new RNA molecules that enter the cytosol. Next, some of these RNA molecules are translated into viral proteins. The proteins encoded by the gag and pol genes are translated from genome-length mRNAs into Gag and Gag–Pol polyproteins. In example, for the gag gene; it is translated into molecules of the capsid protein, and for the pol gene; it is translated into molecules of reverse transcriptase. Retroviruses need a lot more of the Gag proteins than the Pol proteins and have developed advanced systems to synthesize the required amount of each. As an example, after Gag synthesis nearly 95 percent of the ribosomes terminate translation, while other ribosomes continue translation to synthesize Gag–Pol. In the rough endoplasmic reticulum glycosylation begins and the env gene is translated from spliced mRNAs in the rough endoplasmic reticulum, into molecules of the envelope protein. When the envelope protein molecules are carried to the Golgi complex, they are divided into surface glycoprotein and transmembrane glycoprotein by a host protease. These two glycoprotein products stay in close affiliation, and they are transported to the plasma membrane after further glycosylation.
It is important to note that a retrovirus must "bring" its own reverse transcriptase in its capsid, otherwise it is unable to utilize the enzymes of the infected cell to carry out the task, due to the unusual nature of producing DNA from RNA.
Industrial drugs that are designed as protease and reverse-transcriptase inhibitors are made such that they target specific sites and sequences within their respective enzymes. However these drugs can quickly become ineffective due to the fact that the gene sequences that code for the protease and the reverse transcriptase quickly mutate. These changes in bases cause specific codons and sites with the enzymes to change and thereby avoid drug targeting by losing the sites that the drug actually targets.
Because reverse transcription lacks the usual proofreading of DNA replication, a retrovirus mutates very often. This enables the virus to grow resistant to antiviral pharmaceuticals quickly, and impedes the development of effective vaccines and inhibitors for the retrovirus.
One difficulty faced with some retroviruses, such as the Moloney retrovirus, involves the requirement for cells to be actively dividing for transduction. As a result, cells such as neurons are very resistant to infection and transduction by retroviruses. This gives rise to a concern that insertional mutagenesis due to integration into the host genome might lead to cancer or leukemia. This is unlike Lentivirus, a genus of Retroviridae, which are able to integrate their RNA into the genome of non-dividing host cells. | 1 | Biochemistry |
Gessner et al. first revealed a synthetic route for stabilized ketenyl anion using metalated ylides in 2022. In their paper, upon introducing CO, metalated ylide with posassium cation exchange CO with phosphine group R, also known for carbonylation of ylide. Their isolated ketenyl anion [K(PPh(=S)CCO] is stable solid for a week under inert atmosphere, and its crystal structure was characterized. An alternate synthetic pathway for synthesizing ketenyl anion from ylide, shown in Figure 2, includes sulfuration on diphenylphosphine group, deprotonation on carbon center, and CO substitution in exchange of triphenylphosphine leaving. This synthesis resulted in 88% isolation of the product. Later in their studies, the ketenyl anion product upon carbonylation can be selective by changing electron-withdrawing ability on a certain leaving group and Lewis acidity of coordinated alkali metal cation. In their example with ylide containing phosphine group and tosyl group (Ts), Gessner et al. was able to produce the ketenyl anion product more selective by modifying those parameters, shown in Figure 2. As R group is more electron-withdrawing group, it becomes more likely to leave than tosyl group. For example, changing R group from cyclohexyl group (Cy) to phenyl group (Ph) favored the ketenyl anion product with R group leaving by 76%. This is because phenyl group is less electron rich and less nucleophilic compared to cyclohexyl group, resulting in more stable by itself. For alkali metal cation trend, when triphenylphosphine group is present, changing from M = Li to M = K favored in phosphine group leaving by 9%. Although it is a small effect compared to leaving group effect, this is due to Lewis acidity on metal cations because a stronger Lewis acidic metal cation (Li > K in Lewis acidity) attracts tosyl group to interact, resulting in increasing leaving group ability.
Inoue et al. presented synthetic route of stabilizing ketene via silica-carbonyl anion, silicon analogue of ketene. They motivated this goals from recent reactivity study of silylene and disilane activating CO and isolating intermediate, hypothesizing that silica-ketenyl anion is also capable to stabilize ketene. While Gessner et al. uses ylides to accept CO, Inoue et al. uses silylene anion with another silyl group substituted to afford insertion of CO or carbonylation at room temperature in exchange of silyl group.
Liu et al. had another approach to stabilize and isolate ketene by using carbene coordinated by phosphinidene. Carbene coordinated by 2,6-diisopropylphenyl(Dipp)-substituted phosphinidene and dinitrogen (N) perform N/CO ligand exchange. The starting material is similar to N-heterocyclic carbene with bulky substituents, invented by Bertrand. In their studies, this reaction is concerted and thermodynamically favorable (-47.4 kcal/mol relative to N-coordinated carbene) on coordinating CO ligand to NHC. This product is stable at room temperature inert atmosphere for a month, and no decomposition while heating in THF at 80 °C for 12 hours was observed. | 0 | Organic Chemistry |
In biological research, transgenic fruit flies (Drosophila melanogaster) are model organisms used to study the effects of genetic changes on development. Fruit flies are often preferred over other animals due to their short life cycle and low maintenance requirements. They also have a relatively simple genome compared to many vertebrates, with typically only one copy of each gene, making phenotypic analysis easy. Drosophila have been used to study genetics and inheritance, embryonic development, learning, behavior, and aging. The discovery of transposons, in particular the p-element, in Drosophila provided an early method to add transgenes to their genome, although this has been taken over by more modern gene-editing techniques.
Due to their significance to human health, scientists are looking at ways to control mosquitoes through genetic engineering. Malaria-resistant mosquitoes have been developed in the laboratory by inserting a gene that reduces the development of the malaria parasite and then use homing endonucleases to rapidly spread that gene throughout the male population (known as a gene drive). This approach has been taken further by using the gene drive to spread a lethal gene. In trials the populations of Aedes aegypti mosquitoes, the single most important carrier of dengue fever and Zika virus, were reduced by between 80% and by 90%. Another approach is to use a sterile insect technique, whereby males genetically engineered to be sterile out compete viable males, to reduce population numbers.
Other insect pests that make attractive targets are moths. Diamondback moths cause US$4 to $5 billion of damage each year worldwide. The approach is similar to the sterile technique tested on mosquitoes, where males are transformed with a gene that prevents any females born from reaching maturity. They underwent field trials in 2017. Genetically modified moths have previously been released in field trials. In this case a strain of pink bollworm that were sterilized with radiation were genetically engineered to express a red fluorescent protein making it easier for researchers to monitor them.
Silkworm, the larvae stage of Bombyx mori, is an economically important insect in sericulture. Scientists are developing strategies to enhance silk quality and quantity. There is also potential to use the silk producing machinery to make other valuable proteins. Proteins currently developed to be expressed by silkworms include; human serum albumin, human collagen α-chain, mouse monoclonal antibody and N-glycanase. Silkworms have been created that produce spider silk, a stronger but extremely difficult to harvest silk, and even novel silks. | 1 | Biochemistry |
The Mond gas was used primarily during the early 20th century, and its process was further developed by the Power Gas Corporation as the Lymn system; however, the gas has been widely forgotten.
The use of coal gases has become far less popular due to the adoption of natural gas in the 1960s. Natural gases were better for the environment because they burned more cleanly than other fuels such as coal and oil and could also be transported more safely and efficiently over sea. | 7 | Physical Chemistry |
Hoffman nucleation theory is a theory developed by John D. Hoffman and coworkers in the 1970s and 80s that attempts to describe the crystallization of a polymer in terms of the kinetics and thermodynamics of polymer surface nucleation. The theory introduces a model where a surface of completely crystalline polymer is created and introduces surface energy parameters to describe the process. Hoffman nucleation theory is more of a starting point for polymer crystallization theory and is better known for its fundamental roles in the Hoffman–Weeks lamellar thickening and Lauritzen–Hoffman growth theory. | 7 | Physical Chemistry |
Acetate esters and acetamides are generally prepared by acetylations. Acetylations are often used in making C-acetyl bonds in Friedel-Crafts reactions. Carbanions and their equivalents are susceptible to acetylations. | 0 | Organic Chemistry |
Cells are oval-shaped, non-motile and stain Gram-negative. Strictly anaerobic organism. Chemo-organotrophic. Mucolytic in pure culture. | 1 | Biochemistry |
The need for fluorescently tracking RNA rose as its roles in complex cellular functions has grown to not only include mRNA, rRNA, and tRNA, but also RNAi, siRNA, snoRNA, and lncRNA, among others. Spinach is a synthetically derived RNA aptamer born out of the need for a way of studying the role of RNAs at the cellular level. This aptamer was created using Systematic Evolution for Ligands by EXponential enrichment, or SELEX, which is also known as in vitro evolution. The aptamer was designed to be an RNA mimic of green fluorescent protein (GFP); similar to GFP for proteins, Spinach can be used for the fluorescently labeling RNA and tracking it in vivo. A method for inserting the Spinach sequence after an RNA sequence of interest is readily available.
GFP’s fluorophore is made up of three cyclized amino acids within the beta-barrel structure: Serine65-Tyrosine66-Glycine67. This structure, 4-hydroxybenzylidene imidazolinone (HBI) was the basis for the synthetic analogue used in the SELEX studies. Many derivatives of this structure were screened using SELEX, but the chosen fluorophore, 3,5-difluoro-4-hydroxybenzylidene imidazolinone (DFHBI), showed the best selective fluorescence with high quantum yield (0.72) when bound to the RNA sequence 24-2, deemed Spinach.
It was determined that DFHBI only binds Spinach in the phenolate form. At pH < 6.0, both the phenolic and phenolate forms are detected. At pH = 6.0, only the phenolate peak is detected. DFHBI is also incredibly robust and resists photobleaching over a long period of time as compared to HBI and EGFP. It is believed that the free exchange of bound and unbound ligand allows for this persistence. As the fluorophore of GFP and its derivatives are covalently bound to/a part of the protein, free exchange cannot happen and thus photobleaching results.
Spinach is an 84-nucleotide-long structure with two helical strands and an internal bulge with a G-quadruplex motif. It is at this G-quadruplex that the fluorophore binds. Based on crystallographic data, massive rearrangement of the adjacent bases occurs once the fluorophore binds to accommodate the molecule. This binding is favorable, however, as it promotes base-stacking in a normally unstable region, i.e. the internal bulge. Similar to GFP, the DFHBI is also dehydrated, which would help with its high quantum yield.
Spinach has also been adapted for sensing proteins or molecules in vivo. An adapted structure, which includes two binding sites, limits fluorescence of the aptamer to (1) the fluorophore and (2) the protein or small molecule. | 1 | Biochemistry |
The two families above can be seen as special cases of a broader class of compounds which have a carbenic atom bridging two nitrogen atoms. A range of such diaminocarbenes have been prepared principally by Roger Alder's research group. In some of these compounds, the N–C–N unit is a member of a five- or six-membered non-aromatic ring, including a bicyclic example. In other examples, the adjacent nitrogens are connected only through the carbenic atom, and may or may not be part of separate rings.
Unlike the aromatic imidazol-2-ylidenes or triazol-5-ylidenes, these carbenes appear not to be thermodynamically stable, as shown by the dimerisation of some unhindered cyclic and acyclic examples. Studies suggest that these carbenes dimerise via acid catalysed dimerisation (as in the Wanzlick equilibrium).
Diaminocarbenes have diagnostic C NMR chemical shift values between 230 and 270 ppm for the carbenic atom. The X-ray structure of dihydroimidazole-2-ylidene shows a N–C–N bond angle of about 106°, whilst the angle of the acyclic carbene is 121°, both greater than those seen for imidazol-2-ylidenes. | 0 | Organic Chemistry |
To distinguish whether the geometry of the coordination center is trigonal bipyramidal or square pyramidal, the (originally just ) parameter was proposed by Addison et al.:
where: are the two greatest valence angles of the coordination center.
When is close to 0 the geometry is similar to square pyramidal, while if is close to 1 the geometry is similar to trigonal bipyramidal: | 3 | Analytical Chemistry |
Ashish Arora is an Indian structural biologist and a senior scientist at Central Drug Research Institute. He did his postgraduate studies at Rajasthan University and post-doctoral work at the Max Planck Institute for Biophysical Chemistry, Goettingen, and University of Virginia, Charlottesville, VA, before joining the Central Drug Research Institute in 2002. He is known for his studies on Protein NMR Spectroscopy and the pathogenesis of diseases such as tuberculosis and visceral leishmaniasis, commonly known as Kala Azar and has delivered invited speeches at various seminars. The Department of Biotechnology of the Government of India awarded him the National Bioscience Award for Career Development, one of the highest Indian science awards, for his contributions to biosciences, in 2011. He is also a recipient of the 2010 Prof. B. K. Bachhawat Memorial Young Scientist Award of the National Academy of Sciences, India. | 1 | Biochemistry |
Sustainable development requires the promotion of environmental management and a constant search for new technologies to treat vast quantities of wastes generated by increasing anthropogenic activities. Biotreatment, the processing of wastes using living organisms, is an environmentally friendly, relatively simple and cost-effective alternative to physico-chemical clean-up options. Confined environments, such as bioreactors, have been engineered to overcome the physical, chemical and biological limiting factors of biotreatment processes in highly controlled systems. The great versatility in the design of confined environments allows the treatment of a wide range of wastes under optimized conditions. To perform a correct assessment, it is necessary to consider various microorganisms having a variety of genomes and expressed transcripts and proteins. A great number of analyses are often required. Using traditional genomic techniques, such assessments are limited and time-consuming. However, several high-throughput techniques originally developed for medical studies can be applied to assess biotreatment in confined environments. | 2 | Environmental Chemistry |
Denitrification is the reduction of nitrates back into nitrogen gas (), completing the nitrogen cycle. This process is performed by bacterial species such as Pseudomonas and Paracoccus, under anaerobic conditions. They use the nitrate as an electron acceptor in the place of oxygen during respiration. These facultatively (meaning optionally) anaerobic bacteria can also live in aerobic conditions. Denitrification happens in anaerobic conditions e.g. waterlogged soils. The denitrifying bacteria use nitrates in the soil to carry out respiration and consequently produce nitrogen gas, which is inert and unavailable to plants. Denitrification occurs in free-living microorganisms as well as obligate symbionts of anaerobic ciliates. | 1 | Biochemistry |
The following sections outline the method of MeDIP coupled with either high-resolution array hybridization or high-throughput sequencing. Each DNA detection method will also briefly describe post-laboratory processing and analysis. Different post-processing of the raw data is required depending on the technology used to identify the methylated sequences. This is analogous to data generated using ChIP-chip and ChIP-seq. | 1 | Biochemistry |
The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1. This forms an intramolecular hemiacetal. If reaction is between the C-4 hydroxyl and the aldehyde, a furanose is formed instead. The pyranose form is thermodynamically more stable than the furanose form, which can be seen by the distribution of these two cyclic forms in solution. | 0 | Organic Chemistry |
The FCC and HCP packings are the densest known packings of equal spheres with the highest symmetry (smallest repeat units).
Denser sphere packings are known, but they involve unequal sphere packing.
A packing density of 1, filling space completely, requires non-spherical shapes, such as honeycombs.
Replacing each contact point between two spheres with an edge connecting the centers of the touching spheres produces tetrahedrons and octahedrons of equal edge lengths.
The FCC arrangement produces the tetrahedral-octahedral honeycomb.
The HCP arrangement produces the gyrated tetrahedral-octahedral honeycomb.
If, instead, every sphere is augmented with the points in space that are closer to it than to any other sphere, the duals of these honeycombs are produced: the rhombic dodecahedral honeycomb for FCC, and the trapezo-rhombic dodecahedral honeycomb for HCP.
Spherical bubbles appear in soapy water in a FCC or HCP arrangement when the water in the gaps between the bubbles drains out. This pattern also approaches the rhombic dodecahedral honeycomb or trapezo-rhombic dodecahedral honeycomb. However, such FCC or HCP foams of very small liquid content are unstable, as they do not satisfy Plateau's laws. The Kelvin foam and the Weaire–Phelan foam are more stable, having smaller interfacial energy in the limit of a very small liquid content.
There are two types of interstitial holes left by hcp and fcc conformations; tetrahedral and octahedral void. Four spheres surround the tetrahedral hole with three spheres being in one layer and one sphere from the next layer. Six spheres surround an octahedral voids with three spheres coming from one layer and three spheres coming from the next layer. Structures of many simple chemical compounds, for instance, are often described in terms of small atoms occupying tetrahedral or octahedral holes in closed-packed systems that are formed from larger atoms.
Layered structures are formed by alternating empty and filled octahedral planes. Two octahedral layers usually allow for four structural arrangements that can either be filled by an hpc of fcc packing systems. In filling tetrahedral holes a complete filling leads to fcc field array. In unit cells, hole filling can sometimes lead to polyhedral arrays with a mix of hcp and fcc layering. | 3 | Analytical Chemistry |
In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero (−273.15 °C or −459.67 °F). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically.
More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.
Bose–Einstein condensate was first predicted, generally, in 1924–1925 by Albert Einstein, crediting a pioneering paper by Satyendra Nath Bose on the new field now known as quantum statistics. In 1995, the Bose–Einstein condensate was created by Eric Cornell and Carl Wieman of the University of Colorado Boulder using rubidium atoms; later that year, Wolfgang Ketterle of MIT produced a BEC using sodium atoms. In 2001 Cornell, Wieman, and Ketterle shared the Nobel Prize in Physics "for the achievement of Bose–Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates". | 7 | Physical Chemistry |
* Trp arylation
Multiple methods have been reported to achieve tryptophan C–H arylation, where diverse electrophiles such as aryl halides and aryl boronic acids (an example shown below) have been used to transfer the aryl groups.
However, current tryptophan C–H arylation reaction conditions remain relatively harsh, requiring organic solvents, low pH and/or high temperatures.
* Cys arylation
Free thiols has been considered unfavorable for Pd-mediated reactions due to Pd-catalyst decomposition. However, Pd oxidative addition complexes (OACs) supported by dialkylbiaryl phosphine ligands have shown to work efficiently towards cysteine S-arylation.
The first example is the use of Pd OAC with RuPhos: The Pd complex resulting from the oxidative addition of aryl halides or trifluoromethanesulfonates and using RuPhos as the ligand could chemoselectively modify cysteines in various buffer with 5% organic co-solvent under neutral pH. This method has been shown to modify peptides and proteins, achieve peptide macrocyclization (by using bis-palladium reagent and peptides with two unprotected cysteines) and synthesizing antibody-drug conjugates (ADCs). Changing the ligand to sSPhos supports the Pd complex to be sufficiently water soluble to achieve cysteine S-arylation under cosolvent-free aqueous conditions.
There are other applications of this method where the Pd complexes were generated as Pd-peptide OACs by introducing 4-halophenylalanine into peptides during SPPS to achieve peptide-peptide or peptide-protein ligation.
Alternate to directly oxidative addition to the peptide, the Pd OACs could also be transferred to the protein through amine-selective acylation reaction via NHS ester. The latter has been applied to selectively label surface lysine residues of a protein (forming Pd-protein OACs) and oligonucleotides (forming Pd-oligonucleotide OACs), which could then be linked to cysteine-containing peptides or proteins.
Another example of protein-protein cross-coupling is achieved through converting cysteine residues into an electrophilic S-aryl–Pd–X OAC by utilizing an intramolecular oxidative addition strategy.
* Lys arylation
Similar to cysteine, lysine N-arylation could be achieved through Pd OACs with different dialkylbiaryl phosphine ligands. Due to weaker nucleophilicity and slower reductive elimination rate compared to cysteine, the selection of supporting ligands is shown to be critical. The bulky BrettPhos and t-BuBrettPhos ligands in conjunction with mildly basic sodium phenoxide have been used as the strategy to functionalize lysines on peptide substrates. The reaction happens in mild conditions and is selective over most other nucleophilic amino acid residues. | 1 | Biochemistry |
Hai-Lung Dai is a Taiwanese-born American physical chemist and university administrator. He currently is the Laura H. Carnell Professor of Chemistry and Vice President for International Affairs at Temple University in Philadelphia, Pennsylvania, in the United States. | 7 | Physical Chemistry |
The United States Congress has recognized that pseudoephedrine is used in the illegal manufacture of methamphetamine. In 2005, the Committee on Education and the Workforce heard testimony concerning education programs and state legislation designed to curb this illegal practice.
Attempts to control the sale of the drug date back to 1986, when federal officials at the Drug Enforcement Administration (DEA) first drafted legislation, later proposed by Senator Bob Dole, that would have placed a number of chemicals used in the manufacture of illicit drugs under the Controlled Substances Act. The bill would have required each transaction involving pseudoephedrine to be reported to the government, and federal approval of all imports and exports. Fearing this would limit legitimate use of the drug, lobbyists from over the counter drug manufacturing associations sought to stop this legislation from moving forward, and were successful in exempting from the regulations all chemicals that had been turned into a legal final product, such as Sudafed.
Prior to the passage of the Combat Methamphetamine Epidemic Act of 2005, sales of the drug became increasingly regulated, as DEA regulators and pharmaceutical companies continued to fight for their respective positions. The DEA continued to make greater progress in their attempts to control pseudoephedrine as methamphetamine production skyrocketed, becoming a serious problem in the western United States. When purity dropped, so did the number of people in rehab and people admitted to emergency rooms with methamphetamine in their systems. This reduction in purity was usually short lived, however, as methamphetamine producers eventually found a way around the new regulations.
Congress passed the Combat Methamphetamine Epidemic Act of 2005 (CMEA) as an amendment to the renewal of the USA Patriot Act. Signed into law by president George W. Bush on 6 March 2006, the act amended , concerning the sale of pseudoephedrine-containing products. The law mandated two phases, the first needing to be implemented by 8 April 2006, and the second to be completed by 30 September 2006. The first phase dealt primarily with implementing the new buying restrictions based on amount, while the second phase encompassed the requirements of storage, employee training, and record keeping. Though the law was mainly directed at pseudoephedrine products it also applies to all over-the-counter products containing ephedrine, pseudoephedrine, and phenylpropanolamine, their salts, optical isomers, and salts of optical isomers.
Pseudoephedrine was defined as a "scheduled listed chemical product" under (45(A)). The act included the following requirements for merchants ("regulated sellers") who sell such products:
* Required a retrievable record of all purchases, identifying the name and address of each party, to be kept for two years
* Required verification of proof of identity of all purchasers
* Required protection and disclosure methods in the collection of personal information
* Required reports to the Attorney General of any suspicious payments or disappearances of the regulated products
* Required training of employees with regard to the requirements of the CMEA. Retailers must self-certify as to training and compliance.
* The non-liquid dose form of regulated products may only be sold in unit dose blister packs
* Regulated products must be stored behind the counter or in a locked cabinet in such a way as to restrict public access
* Sales limits (per customer):
** Daily sales limit—must not exceed 3.6 grams of pseudoephedrine base without regard to the number of transactions
** 30-day (not monthly) sales limit—must not exceed 7.5 grams of pseudoephedrine base if sold by mail order or "mobile retail vendor"
** 30-day purchase limit—must not exceed 9 grams of pseudoephedrine base. (A misdemeanor possession offense under for the person who buys it.)
The requirements were revised in the Methamphetamine Production Prevention Act of 2008 to require that a regulated seller of scheduled listed chemical products may not sell such a product unless the purchaser:
* Presents a government issued photographic identification; and
* Signs the written logbook with their name, address, and time and date of the sale | 4 | Stereochemistry |
Alkylresorcinols can be found in cereals.
2,4-Bis(4-hydroxybenzyl)phenol is a phenolic compound found in the orchids Gastrodia elata and Galeola faberi. | 0 | Organic Chemistry |
In organic chemistry, the bromine test is a qualitative test for the presence of unsaturation (carbon-to-carbon double or triple bonds), phenols and anilines.
An unknown sample is treated with a small amount of elemental bromine in an organic solvent, being
as dichloromethane or carbon tetrachloride. Presence of unsaturation and/or phenol or aniline in the sample is shown by disappearance of the deep brown coloration of bromine when it has reacted with the unknown sample. The formation of a brominated phenol (i.e. 2,4,6-tribromophenol) or aniline (i.e. 2,4,6-tribromoaniline) in form of a white precipitate indicates that the unknown was a phenol or aniline. The more unsaturated an unknown is, the more bromine it reacts with, and the less coloured the solution will appear.
Should the brown colour not disappear, possibly due to the presence of an alkene which doesn't react, or reacts very slowly with, bromine, the potassium permanganate test should be performed, in order to determine the presence or absence of the alkene. The iodine value is a way to determine the presence of unsaturation quantitatively.
The bromine test is a simple qualitative test. Modern spectroscopic methods (e.g. NMR and infrared spectroscopy) are better at determining the structural features and identity of unknown compounds. | 0 | Organic Chemistry |
*"Synthesis of Jeewanu, the Protocell." Bahadur, Krishna. (In English) Ram Narain Lal Beni Prasad, New Katra, Allahabad-211002 (U.P) India. ASIN: B0007JHWU0 (1966)
*"Origin of Life: A Functional Approach." Bahadur K. and Ranganayaki S.Ram Narain Lal Beni Prasad, New Katra, Allahabad-211002(U.P), India, (1981) | 9 | Geochemistry |
Superhydrophobic surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The contact angles of a water droplet exceeds 150°. This is referred to as the lotus effect, and is primarily a physical property related to interfacial tension, rather than a chemical property. | 6 | Supramolecular Chemistry |
The coordination number of systems with disorder cannot be precisely defined.
The first coordination number can be defined using the radial distribution function g(r):
where r is the rightmost position starting from r = 0 whereon g(r) is approximately zero, r is the first minimum. Therefore, it is the area under the first peak of g(r).
The second coordination number is defined similarly:
Alternative definitions for the coordination number can be found in literature, but in essence the main idea is the same. One of those definition are as follows: Denoting the position of the first peak as r,
The first coordination shell is the spherical shell with radius between r and r around the central particle under investigation. | 4 | Stereochemistry |
Organometallic compounds find wide use in commercial reactions, both as homogenous catalysts and as stoichiometric reagents. For instance, organolithium, organomagnesium, and organoaluminium compounds, examples of which are highly basic and highly reducing, are useful stoichiometrically but also catalyze many polymerization reactions.
Almost all processes involving carbon monoxide rely on catalysts, notable examples being described as carbonylations. The production of acetic acid from methanol and carbon monoxide is catalyzed via metal carbonyl complexes in the Monsanto process and Cativa process. Most synthetic aldehydes are produced via hydroformylation. The bulk of the synthetic alcohols, at least those larger than ethanol, are produced by hydrogenation of hydroformylation-derived aldehydes. Similarly, the Wacker process is used in the oxidation of ethylene to acetaldehyde.
Almost all industrial processes involving alkene-derived polymers rely on organometallic catalysts. The world's polyethylene and polypropylene are produced via both heterogeneously via Ziegler–Natta catalysis and homogeneously, e.g., via constrained geometry catalysts.
Most processes involving hydrogen rely on metal-based catalysts. Whereas bulk hydrogenations (e.g., margarine production) rely on heterogeneous catalysts, for the production of fine chemicals such hydrogenations rely on soluble (homogenous) organometallic complexes or involve organometallic intermediates. Organometallic complexes allow these hydrogenations to be effected asymmetrically.
Many semiconductors are produced from trimethylgallium, trimethylindium, trimethylaluminium, and trimethylantimony. These volatile compounds are decomposed along with ammonia, arsine, phosphine and related hydrides on a heated substrate via metalorganic vapor phase epitaxy (MOVPE) process in the production of light-emitting diodes (LEDs). | 0 | Organic Chemistry |
The general equation for for species in a mixture of components is:
with
There are several different equation forms for and , the most general of which are shown above. | 7 | Physical Chemistry |
There is an association between high intake of heme iron sourced from meat and increased risk of colorectal cancer.
The American Institute for Cancer Research (AICR) and World Cancer Research Fund International (WCRF) concluded in a 2018 report that there is limited but suggestive evidence that foods containing heme iron increase risk of colorectal cancer. A 2019 review found that heme iron intake is associated with increased breast cancer risk. | 1 | Biochemistry |
Anti-graffiti coatings can be invisible to the naked eye. There are two different categories of anti-graffiti coatings. The first, sacrificial coatings, are applied to a surface and then removed when graffiti is applied. The surface underneath will be left clean and a new sacrificial coating can be applied. The other type of coating are permanent coatings that prevent graffiti from adhering to a surface in the first place.
Newer coatings are made of charged polymeric materials that form a gel on the surface of the building or substrate. Some of the most important characteristics of anti-graffiti coatings are:
* Sufficient adherence without damage to substrates
* Hydrophobicity (water repellence)
* Environmentally friendly composition and processing
* Resistance to UV aging and weathering
* Good cleaning efficiency | 7 | Physical Chemistry |
Though the Cram and Felkin–Anh models differ in the conformers considered and other assumptions, they both attempt to explain the same basic phenomenon: the preferential addition of a nucleophile to the most sterically favored face of a carbonyl moiety. However, many examples exist of reactions that display stereoselectivity opposite of what is predicted by the basic tenets of the Cram and Felkin–Anh models. Although both of the models include attempts to explain these reversals, the products obtained are still referred to as "anti-Felkin" products. One of the most common examples of altered asymmetric induction selectivity requires an α-carbon substituted with a component with Lewis base character (i.e. O, N, S, P substituents). In this situation, if a Lewis acid such as Al-iPr or Zn is introduced, a bidentate chelation effect can be observed. This locks the carbonyl and the Lewis base substituent in an eclipsed conformation, and the nucleophile will then attack from the side with the smallest free α-carbon substituent. If the chelating R group is identified as the largest, this will result in an "anti-Felkin" product.
This stereoselective control was recognized and discussed in the first paper establishing the Cram model, causing Cram to assert that his model requires non-chelating conditions. An example of chelation control of a reaction can be seen here, from a 1987 paper that was the first to directly observe such a "Cram-chelate" intermediate, vindicating the model:
Here, the methyl titanium chloride forms a Cram-chelate. The methyl group then dissociates from titanium and attacks the carbonyl, leading to the anti-Felkin diastereomer.
A non-chelating electron-withdrawing substituent effect can also result in anti-Felkin selectivity. If a substituent on the α-carbon is sufficiently electron withdrawing, the nucleophile will add anti- relative to the electron withdrawing group, even if the substituent is not the largest of the 3 bonded to the α-carbon. Each model offers a slightly different explanation for this phenomenon. A polar effect was postulated by the Cornforth model and the original Felkin model, which placed the EWG substituent and incoming nucleophile anti- to each other in order to most effectively cancel the dipole moment of the transition structure.
This Newman projection illustrates the Cornforth and Felkin transition state that places the EWG anti- to the incoming nucleophile, regardless of its steric bulk relative to R and R.
The improved Felkin–Anh model, as discussed above, makes a more sophisticated assessment of the polar effect by considering molecular orbital interactions in the stabilization of the preferred transition state. A typical reaction illustrating the potential anti-Felkin selectivity of this effect, along with its proposed transition structure, is pictured below: | 4 | Stereochemistry |
The strength of non-covalent interactions in a mechanically interlocked molecular architecture increases as compared to the non-mechanically bonded analogues. This increased strength is demonstrated by the necessity of harsher conditions to remove a metal template ion from catenanes as opposed to their non-mechanically bonded analogues. This effect is referred to as the "catenand effect". The augmented non-covalent interactions in interlocked systems compared to non-interlocked systems has found utility in the strong and selective binding of a range of charged species, enabling the development of interlocked systems for the extraction of a range of salts. This increase in strength of non-covalent interactions is attributed to the loss of degrees of freedom upon the formation of a mechanical bond. The increase in strength of non-covalent interactions is more pronounced on smaller interlocked systems, where more degrees of freedom are lost, as compared to larger mechanically interlocked systems where the change in degrees of freedom is lower. Therefore, if the ring in a rotaxane is made smaller the strength of non-covalent interactions increases, the same effect is observed if the thread is made smaller as well. | 6 | Supramolecular Chemistry |
While at University of Michigan, Omar M. Yaghi (currently at UCBerkeley) and Adrien P Cote published the first paper of COFs in 2005, reporting a series of 2D COFs. They reported the design and successful synthesis of COFs by condensation reactions of phenyl diboronic acid (CH[B(OH)]) and hexahydroxytriphenylene (CH(OH)). Powder X-ray diffraction studies of the highly crystalline products having empirical formulas (CHBO)·(CH) (COF-1) and CHBO (COF-5) revealed 2-dimensional expanded porous graphitic layers that have either staggered conformation (COF-1) or eclipsed conformation (COF-5). Their crystal structures are entirely held by strong bonds between B, C, and O atoms to form rigid porous architectures with pore sizes ranging from 7 to 27 Angstroms. COF-1 and COF-5 exhibit high thermal stability (to temperatures up to 500 to 600 °C), permanent porosity, and high surface areas (711 and 1590 square meters per gram, respectively).
The synthesis of 3D COFs has been hindered by longstanding practical and conceptual challenges until it was first achieved in 2007 by Omar M. Yaghi and colleagues, which received the Newcomb Cleveland Prize. The research team synthesized and designed the first 3D-COF ever; COF-103 and COF-108, helping unleash this new field. Unlike 0D and 1D systems, which are soluble, the insolubility of 2D and 3D structures precludes the use of stepwise synthesis, making their isolation in crystalline form very difficult. This first challenge, however, was overcome by judiciously choosing building blocks and using reversible condensation reactions to crystallize COFs. | 6 | Supramolecular Chemistry |
Epstein's coefficient of difference is based on the differences in polarity and size between replaced pairs of amino acids. This index that distincts the direction of exchange between amino acids, described by 2 equations:
when smaller hydrophobic residue is replaced by larger hydrophobic or polar residue
when polar residue is exchanged or larger residue is replaced by smaller | 1 | Biochemistry |
1,1,1-Trichloroethane was first reported by Henri Victor Regnault in 1840. Industrially, it is usually produced in a two-step process from vinyl chloride. In the first step, vinyl chloride reacts with hydrogen chloride at 20-50 °C to produce 1,1-dichloroethane:
:CH=CHCl + HCl → CHCHCl
This reaction is catalyzed by a variety of Lewis acids, mainly aluminium chloride, iron(III) chloride, or zinc chloride. The 1,1-dichloroethane is then converted to 1,1,1-trichloroethane by reaction with chlorine under ultraviolet irradiation:
:CHCHCl + Cl → CHCCl + HCl
This reaction proceeds at 80-90% yield, and the hydrogen chloride byproduct can be recycled to the first step in the process. The major side-product is the related compound 1,1,2-trichloroethane, from which the 1,1,1-trichloroethane can be separated by distillation.
A somewhat smaller amount of 1,1,1-trichloroethane is produced from the reaction of 1,1-dichloroethene and hydrogen chloride in the presence of an iron(III) chloride catalyst:
:CH=CCl + HCl → CHCCl
1,1,1-Trichloroethane is sold with stabilizers because it is unstable with respect to dehydrochlorination and attacks some metals. Stabilizers comprise up to 8% of the formulation, including acid scavengers (epoxides, amines) and complexants. | 2 | Environmental Chemistry |
Danishefskys diene (Kitahara diene) is an organosilicon compound and a diene with the formal name trans'-1-methoxy-3-trimethylsilyloxy-buta-1,3-diene named after Samuel J. Danishefsky. Because the diene is very electron-rich it is a very reactive reagent in Diels-Alder reactions. This diene reacts rapidly with electrophilic alkenes, such as maleic anhydride. The methoxy group promotes highly regioselective additions. The diene is known to react with amines, aldehydes, alkenes and alkynes. Reactions with imines and nitro-olefins have been reported.
It was first synthesized by the reaction of trimethylsilyl chloride with 4-methoxy-3-buten-2-one and zinc chloride:
The diene has two features of interest: the substituents promote regiospecific addition to unsymmetrical dienophiles and the resulting adduct is amenable to further functional group manipulations after the addition reaction. High regioselectivity is obtained with unsymmetrical alkenes with a preference for a 1,2-relation of the ether group with the electron-deficient alkene-carbon. All this is exemplified in this aza Diels-Alder reaction:
In the cycloaddition product, the silyl ether is a synthon for a carbonyl group through the enol. The methoxy group is susceptible to an elimination reaction enabling the formation of a new alkene group.
Applications in asymmetric synthesis have been reported. Derivatives have been reported. | 0 | Organic Chemistry |
Inclusion compounds are often molecules, whereas . Intercalation compounds are not 3-dimensional, unlike clathrate compounds. Photolytically-sensitive caged compounds have been examined as containers for releasing a drug or reagent.
Zeolites are another type of crystalline structures that form a framework with cavities in which guest species can reside. Unlike clathrates, zeolites are defined by the tetrahedra linking of four oxygen atoms surrounding a cation. The guests are also not required to fill the open cavities. Zeolite structures are defined by the diverse building units of the framework, as opposed to cavity structures in clathrates. Similar applications have been explored.
Silica clathrasil are compounds structurally similar to clathrate hydrates with a SiO framework and can be found in a range of marine sediment. | 6 | Supramolecular Chemistry |
Renal lipotoxicity occurs when excess long-chain nonesterified fatty acids are stored in the kidney and proximal tubule cells. It is believed that these fatty acids are delivered to the kidneys via serum albumin. This condition leads to tubulointerstitial inflammation and fibrosis in mild cases, and to kidney failure and death in severe cases. The current accepted treatments for lipotoxicity in renal cells are fibrate therapy and intensive insulin therapy. | 1 | Biochemistry |
Almost half of the genes of the bacterium E. coli that are repressed during cold shock are similarly repressed when Gyrase is blocked by the antibiotic Novobiocin. Moreover, during cold shocks, the density of nucleoids increases, and the protein gyrase and the nucleoid become colocalized (which is consistent with a reduction in DNA relaxation). This is evidence that the reduction of negative supercoiling of the DNA is one of the main mechanisms responsible for the blocking of transcription of half of the genes that conduct the cold shock transcriptional response program of bacteria. Based on this, a stochastic model of this process has been proposed. This model is illustrated in the figure, where reactions 1 represent transcription and its locking due to supercoiling. Meanwhile, reactions 2 to 4 model, respectively, translation, and RNA and protein degradation. | 1 | Biochemistry |
Nearly 180 sites in all were used for this process, having a furnace, a forge or both between the 15th century and 18th century. Waterpower was the means of operating the bellows in the blast furnaces and for operating bellows and helve hammers in finery forges. Scattered through the Weald are ponds still to be found called ’Furnace Pond’ or ’Hammer Pond’. The iron was used for making household utensils, nails and hinges; and for casting cannon. The first blast furnace was recorded at Buxted in 1490.
The industry was at its peak towards the end of Queen Elizabeth Is reign. Most works were small, but at Brenchley one ironmaster employed 200 men. Most of them would have been engaged in mining ore and cutting wood (for charcoal), as the actual ironworks only required a small workforce. The wars fought during the reign of Henry VIII increased the need for armaments, and the Weald became the centre of an armaments industry. Cast-iron cannon were made in the Weald from 1543 when Buxteds Ralf Hogge cast the first iron cannon for his unlikely employer: a Sussex vicar who was gunstonemaker to the king.
In the 16th century and the early 17th century, the Weald was a major source of iron for manufacture in London, peaking at over 9000 tons per year in the 1590s. However, after 1650, Wealden production became increasingly focused on the production of cannon; and bar iron was only produced for local consumption. This decline may have begun as early as the 1610s, when Midland ironware began to be sold in London. Certainly after Swedish iron began to be imported in large quantities after the Restoration, Wealden bar iron seems to have been unable to compete in the London market.
Cannon production was a major activity in the Weald until the end of the Seven Years War, but a cut in the price paid by the Board of Ordnance drove several Wealden ironmasters into bankruptcy. They were unable to match the much lower price that was acceptable to the Scottish Carron Company, whose fuel was coke. A few ironworks continued operating on a very small scale. With no local source of mineral coal, the Wealden iron industry was unable to compete with the new coke-fired ironworks of the Industrial Revolution. The last to close was the forge at Ashburnham. Little survives of the furnace and forge buildings, although there are still scores of the industrys hammer and furnace ponds scattered throughout the Weald.
Steel production was never widespread in the Weald, with most high quality steel being imported from Spain, the Middle East, or Germany. A steel forge was built upstream from Newbridge Furnace on Ashdown Forest around 1505 but had ceased production by 1539. The Sydney family, with mills at Robertsbridge forge and at Sandhurst in Kent, produced steel using skilled German workers, but faced strong competition from German suppliers. In the 17th century a steel forge existed at Warbleton in Sussex. | 8 | Metallurgy |
An electrochemical cell is a device that produces an electric current from energy released by a spontaneous redox reaction. This kind of cell includes the Galvanic cell or Voltaic cell, named after Luigi Galvani and Alessandro Volta, both scientists who conducted experiments on chemical reactions and electric current during the late 18th century.
Electrochemical cells have two conductive electrodes (the anode and the cathode). The anode is defined as the electrode where oxidation occurs and the cathode is the electrode where the reduction takes place. Electrodes can be made from any sufficiently conductive materials, such as metals, semiconductors, graphite, and even conductive polymers. In between these electrodes is the electrolyte, which contains ions that can freely move.
The galvanic cell uses two different metal electrodes, each in an electrolyte where the positively charged ions are the oxidized form of the electrode metal. One electrode will undergo oxidation (the anode) and the other will undergo reduction (the cathode). The metal of the anode will oxidize, going from an oxidation state of 0 (in the solid form) to a positive oxidation state and become an ion. At the cathode, the metal ion in solution will accept one or more electrons from the cathode and the ion's oxidation state is reduced to 0. This forms a solid metal that electrodeposits on the cathode. The two electrodes must be electrically connected to each other, allowing for a flow of electrons that leave the metal of the anode and flow through this connection to the ions at the surface of the cathode. This flow of electrons is an electric current that can be used to do work, such as turn a motor or power a light.
A galvanic cell whose electrodes are zinc and copper submerged in zinc sulfate and copper sulfate, respectively, is known as a Daniell cell.
The half reactions in a Daniell cell are as follows:
:Zinc electrode (anode): Zn → Zn + 2 e
:Copper electrode (cathode): Cu + 2 e → Cu
In this example, the anode is the zinc metal which is oxidized (loses electrons) to form zinc ions in solution, and copper ions accept electrons from the copper metal electrode and the ions deposit at the copper cathode as an electrodeposit. This cell forms a simple battery as it will spontaneously generate a flow of electric current from the anode to the cathode through the external connection. This reaction can be driven in reverse by applying a voltage, resulting in the deposition of zinc metal at the anode and formation of copper ions at the cathode.
To provide a complete electric circuit, there must also be an ionic conduction path between the anode and cathode electrolytes in addition to the electron conduction path. The simplest ionic conduction path is to provide a liquid junction. To avoid mixing between the two electrolytes, the liquid junction can be provided through a porous plug that allows ion flow while minimizing electrolyte mixing. To further minimize mixing of the electrolytes, a salt bridge can be used which consists of an electrolyte saturated gel in an inverted U-tube. As the negatively charged electrons flow in one direction around this circuit, the positively charged metal ions flow in the opposite direction in the electrolyte.
A voltmeter is capable of measuring the change of electrical potential between the anode and the cathode.
The electrochemical cell voltage is also referred to as electromotive force or emf.
A cell diagram can be used to trace the path of the electrons in the electrochemical cell. For example, here is a cell diagram of a Daniell cell:
:Zn | Zn (1 M) || Cu (1 M) | Cu
First, the reduced form of the metal to be oxidized at the anode (Zn) is written. This is separated from its oxidized form by a vertical line, which represents the limit between the phases (oxidation changes). The double vertical lines represent the saline bridge on the cell. Finally, the oxidized form of the metal to be reduced at the cathode, is written, separated from its reduced form by the vertical line. The electrolyte concentration is given as it is an important variable in determining the exact cell potential. | 7 | Physical Chemistry |
Shingling was a stage in the production of bar iron or steel, in the finery and puddling processes. As with many ironmaking terms, this is derived from the French - cinglage.
The product of the finery was a bloom or loop (from old Frankish luppa or lopp, meaning a shapeless mass); that of the puddling furnace was a puddled ball. In each case, this needed to be consolidated by hammering it into a more regular shape. This was done manually with heavy hammers; later by a waterwheel or steam powered hammers, leading to modern power hammers. The result was an oblong-shaped iron product similar in appearance to shingles used on roofs. In the finery, this was part of the work of the finer; during puddling, it was done by a special workman called the shingler. The iron (or steel) then had to be further shaped (drawn out) under the hammer or rolled in a rolling mill to produce a bar. In more recent times, the process was carried out using mechanical jaws to squeeze the puddled ball into shape. | 8 | Metallurgy |
When a nucleus has a spin quantum number, I, greater than 1/2 it has a quadrupole moment. In that case, coupling of nuclear spin angular momentum with rotational angular momentum causes splitting of the rotational energy levels. If the quantum number J of a rotational level is greater than I, levels are produced; but if J is less than I, levels result. The effect is one type of hyperfine splitting. For example, with N () in HCN, all levels with J > 0 are split into 3. The energies of the sub-levels are proportional to the nuclear quadrupole moment and a function of F and J. where , . Thus, observation of nuclear quadrupole splitting permits the magnitude of the nuclear quadrupole moment to be determined.
This is an alternative method to the use of nuclear quadrupole resonance spectroscopy. The selection rule for rotational transitions becomes | 7 | Physical Chemistry |
In molecular biology and genetics, transcription coregulators are proteins that interact with transcription factors to either activate or repress the transcription of specific genes. Transcription coregulators that activate gene transcription are referred to as coactivators while those that repress are known as corepressors. The mechanism of action of transcription coregulators is to modify chromatin structure and thereby make the associated DNA more or less accessible to transcription. In humans several dozen to several hundred coregulators are known, depending on the level of confidence with which the characterisation of a protein as a coregulator can be made. One class of transcription coregulators modifies chromatin structure through covalent modification of histones. A second ATP dependent class modifies the conformation of chromatin. | 1 | Biochemistry |
The Ruhr Valley provided an excellent location for the German iron and steel industry because of the availability of raw materials, coal, transport, a skilled labor force, nearby markets, and an entrepreneurial spirit that led to the creation of many firms, often in close conjunction with coal mines. By 1850 the Ruhr had 50 iron works with 2,813 full-time employees. The first modern furnace was built in 1849. The unification of Germany in 1871 gave further impetus to rapid growth, as the German Empire started to catch up with Britain. From 1880 to World War I, the industry of the Ruhr area consisted of numerous enterprises, each working on a separate level of production. Mixed enterprises could unite all levels of production through vertical integration, thus lowering production costs. Technological progress brought new advantages as well. These developments set the stage for the creation of combined business concerns.
The leading firm was Friedrich Krupp AG run by the Krupp family. Many diverse, large-scale family firms such as Krupps reorganized in order to adapt to the changing conditions and meet the economic depression of the 1870s, which reduced the earnings in the German iron and steel industry. Krupp reformed his accounting system to better manage his growing empire, adding a specialized bureau of calculation as well as a bureau for the control of times and wages. The rival firm GHH quickly followed, as did Thyssen AG, which had been founded by August Thyssen in 1867. Germany became Europes leading steel-producing nation in the late 19th century, thanks in large part to the protection from American and British competition afforded by tariffs and cartels.
By 1913 American and German exports dominated the world steel market, and Britain slipped to third place. German steel production grew explosively from 1 million metric tons in 1885 to 10 million in 1905 and peaked at 19 million in 1918. In the 1920s Germany produced about 15 million tons, but output plunged to 6 million in 1933. Under Nazi rule, steel output peaked at 22 million tons in 1940, then dipped to 18 million in 1944 under Allied bombing.
The merger of four major firms into the German Steel Trust (Vereinigte Stahlwerke) in 1926 was modeled on the U.S. Steel corporation in the U.S. The goal was to move beyond the limitations of the old cartel system by incorporating advances simultaneously inside a single corporation. The new company emphasized rationalization of management structures and modernization of the technology; it employed a multi-divisional structure and used return on investment as its measure of success. It represented the "Americanization" of the German steel industry because its internal structure, management methods, use of technology, and emphasis on mass production. The chief difference was that consumer capitalism as an industrial strategy did not seem plausible to German steel industrialists.
In iron and steel and other industries, German firms avoided cut-throat competition and instead relied on trade associations. Germany was a world leader because of its prevailing "corporatist mentality", its strong bureaucratic tradition, and the encouragement of the government. These associations regulated competition and allowed small firms to function in the shadow of much larger companies.
With the need to rebuild the bombed-out infrastructure after the Second World War, Marshall Plan (1948–51) enabled West Germany to rebuild and modernize its mills. It produced 3 million tons of steel in 1947, 12 million in 1950, 34 million in 1960 and 46 million in 1970. East Germany produced about a tenth as much. | 8 | Metallurgy |
The word patina comes from the Italian patina (shallow layer of deposit on a surface), derived from the Latin patĭna (pan, shallow dish). Figuratively, patina can refer to any fading, darkening, or other signs of age, which are felt to be natural or unavoidable (or both).
The chemical process by which a patina forms or is deliberately induced is called patination, and a work of art coated by a patina is said to be patinated. | 8 | Metallurgy |
Ovomucin is a glycoprotein found mainly in egg whites, as well as in the chalaza and vitelline membrane. The protein makes up around 2-4% of the protein content of egg whites; like other members of the mucin protein family, ovomucin confers gel-like properties. It is composed of two subunits, alpha-ovomucin (MUC5B) and beta-ovomucin (MUC6), of which the beta subunit is much more heavily glycosylated. | 1 | Biochemistry |
VAMAS6 - vanillin synthase - VanY protein domain - Var1 protein domain - vax2os1 - vector - VEK-30 protein domain - vinorine hydroxylase - vitamin B12-transporting ATPase - vitamin D binding protein domain III - vitelline membrane outer layer protein I (VMO-I) - | 1 | Biochemistry |
The oxygen effect has particular importance in external beam radiation therapy where the killing of tumour cells with photon and electron beams in well oxygenated regions can be up to three times greater than in a poorly vasculated portion of the tumour.
Besides tumour hypoxia, the oxygen effect is also relevant to hypoxia conditions present in the normal physiology of stem cell niches such as the endosteum adjacent to bone in bone marrow and the epithelium layer of the intestine. In addition, there are non-malignant diseases where oxygenated tissues can become hypoxic such as in stenosed coronary arteries associated with cardiovascular disease. | 1 | Biochemistry |
James A. Shapiro argues that a superset of these examples should be classified as natural genetic engineering and are sufficient to falsify the central dogma. While Shapiro has received a respectful hearing for his view, his critics have not been convinced that his reading of the central dogma is in line with what Crick intended. | 1 | Biochemistry |
This is an example of a system with several phases, which at ordinary temperatures are two solids and a gas. There are three chemical species (CaCO, CaO and CO) and one reaction:
: CaCO CaO + CO.
The number of components is then 3 - 1 = 2. | 7 | Physical Chemistry |
The optimal conditions for TMM cycloadditions depend on both the TMM source and two-atom component. However, a few general principles for each of the TMM sources have emerged.
Reactions of diazenes should employ degassed solvents to avoid radical reactions with oxygen. Tetrahydrofuran (THF) at reflux is the most commonly employed solvent system, but photodissociation conditions at low temperature may also be used.
Reactions employing polar MCPs are usually carried out in a polar solvent to facilitate formation of the TMM intermediate. Although rigorous exclusion of air and water is not required, it is generally preferred.
For transition-metal catalyzed MCP reactions, the choice of catalyst and ligand system is key. Generally, phosphine or phosphite ligands are required in conjunction with a palladium(0) or nickel(0) source; the most common are Pd(dba) and Ni(cod). Tri(isopropyl)phosphine is the most common ligand used with palladium, and triarylphosphites are usually added in nickel-catalyzed reactions.
For transition-metal catalyzed reactions of silylated allylic acetates, the most commonly used catalyst system is palladium(II) acetate and tri(isopropyl)phosphite. Reactions are usually carried out in THF at temperatures ranging from 60 to 110 °C. The choice of solvent or leaving group may affect the course of the reaction. | 0 | Organic Chemistry |
Improving the resolution and enhancing the instrumentation with user-friendly hardware and software will make AFM/NSOM coupled with IR/Raman a useful characterization tool in many areas including biomedical, materials and life sciences. For example, this technique was used in detecting the spin-cast thin film of poly(dimethylsiloxane) with polystyrene on it by scanning the tip over the sample. The shape and size of polystyrene fragments was detected at a high spatial resolution due to its high absorption at specific resonance frequencies. Other examples include inorganic boron nitride thin films characterization with IR-NSOM. The images of single molecule rhodamine 6G (Rh-6G) was obtained with a spatial resolution of 50 nm. These techniques can be also used in numerous biological related applications including the analysis of plant materials, bone, and single cells. Biological application was demonstrated by detecting details of conformation changes of cholesteryl-oleate caused by FEL irradiation with a spatial resolution below the diffraction limit. Researchers also used Raman/NSOM in tracking the formation of energy-storing polymer polyhydroxybutyrate in bacteria Rhodobacter capsulatus.
This characterization tool may also help in the kinetic studies on physical and chemical processes at a wide variety of surfaces giving chemical specificity via IR spectroscopy as well as high-resolution imaging via AFM. For example, the study of the hydrogen termination of Si (100) surface was performed by studying the absorbance of Si-O bond to characterize the reaction between silicon surface and atmospheric oxygen. Studies were also conducted where the reactivity of a polymer, a 1000-nm-thick poly-(tert-butylmethacrylate) (PTBMA) combined with a photochemically modified 500-nm-thick poly(methacrylic acid) (PMAA), with water vapor depicted the different absorption bands before and after water uptake by the polymer. Not only the increased swell of PMAA (280 nm) was observed but also the different absorption ability of water was shown by the different transmission of IR light at a much smaller dimension (<500 nm). These results are related to polymer, chemical and biological sensors, and tissue engineering and artificial organ studies. Because of their high spatial resolution, NSOM/AFM-Raman/IR techniques can be used for measuring the width of multilayer films, including layers which are too small (in the x and y directions) to be probed with conventional IR or Raman spectroscopy. | 7 | Physical Chemistry |
Van Krevelen diagrams are graphical plots developed by
Dirk Willem van Krevelen (chemist and professor of fuel technology at the TU Delft) and used to assess the origin and maturity of kerogen and petroleum. The diagram cross-plots the hydrogen:carbon atomic ratio as a function of the oxygen:carbon atomic ratio.
Beginning around 2003, the diagrams are often used to visualize data from mass spectrometry analysis, used for mixtures other than kerogen and petroleum. For example, the diagrams have been used in one analysis of the components in Scotch whiskey. | 9 | Geochemistry |
It was produced industrially from paraformaldehyde and a mixture of chlorosulfonic acid and sulfuric acid. It is also produced as a byproduct in the Blanc chloromethylation reaction, formed when formaldehyde (the monomer, paraformaldehyde or formalin) and concentrated hydrochloric acid are mixed, and is a known impurity in technical grade chloromethyl methyl ether.
Because of their carcinogenic potency, the industrial production of chloromethyl ethers ended in most countries in the early 1980s. Bis(chloromethyl) ether was no exception to this with production in the U.S.A. ending in 1982. | 0 | Organic Chemistry |
Powder diffraction patterns of very small single crystals, or crystallites, are subject to size-dependent peak broadening, which, below a certain size, renders powder diffraction fingerprinting useless. In this case, peak resolution is only possible in 3D reciprocal space,
i.e. by applying single-crystal electron diffraction techniques.
High-Resolution Transmission Electron Microscopy (HRTEM) provides images and diffraction patterns of nanometer sized crystallites. Fourier transforms of HRTEM images and electron diffraction patterns both supply information about the projected reciprocal lattice geometry
for a certain crystal orientation, where the projection axis coincides with the optical axis of the microscope.
Projected lattice geometries can be represented by so-called ‘lattice-fringe fingerprint plots’ (LFFPs), also called angular covariance plots. The horizontal axis of such a plot is given in reciprocal lattice length and is limited by the point resolution of the microscope. The vertical axis is defined as acute angle between Fourier transformed lattice fringes or electron diffraction spots. A 2D data point is defined by the length of a reciprocal lattice vector and its (acute) angle with another reciprocal lattice vector. Sets of 2D data points that obey Weiss's zone law are subsets of the entirety of data points in an LFFP. A suitable search-match algorithm using LFFPs, therefore, tries to find matching zone axis subsets in the database. It is, essentially, a variant of a lattice matching algorithm.
In the case of electron diffraction patterns, structure factor amplitudes can be used, in a later step, to further discern among a selection of candidate structures (so-called structure factor fingerprinting). Structure factor amplitudes from electron diffraction data are far less reliable than their counterparts from X-ray single-crystal and powder diffraction data. Existing precession electron diffraction techniques greatly improve the quality of structure factor amplitudes, increase their number and, thus, make structure factor amplitude information much more useful for the fingerprinting process.
Fourier transforms of HRTEM images, on the other hand, supply information not only about the projected reciprocal lattice geometry and structure factor amplitudes, but also structure factor phase angles. After crystallographic image processing, structure factor phase angles are far more reliable than structure factor amplitudes. Further discernment of candidate structures is then mainly based on structure factor phase angles and, to a lesser extent, structure factor amplitudes (so-called structure factor fingerprinting). | 7 | Physical Chemistry |
*ARPES, Angle-resolved photoemission spectroscopy
*UPS, Ultraviolet photoelectron spectroscopy
*PES, Photoemission spectroscopy
*ZEKE, Zero electron kinetic energy spectroscopy
*AES, Auger electron spectroscopy
*EDS, Energy-dispersive X-ray spectroscopy, (EDX or EDXRF)
*PEEM, Photoelectron emission microscopy | 7 | Physical Chemistry |
In veterinary medicine, ampicillin is used in cats, dogs, and farm animals to treat:
* Anal gland infections
* Cutaneous infections, such as abscesses, cellulitis, and pustular dermatitis
* E. coli and Salmonella infections in cattle, sheep, and goats (oral form). Ampicillin use for this purpose had declined as bacterial resistance has increased.
* Mastitis in sows
* Mixed aerobic–anaerobic infections, such as from cat bites
* Multidrug-resistant Enterococcus faecalis and E. faecium
* Prophylactic use in poultry against Salmonella and sepsis from E. coli or Staphylococcus aureus
* Respiratory tract infections, including tonsilitis, bovine respiratory disease, shipping fever, bronchopneumonia, and calf and bovine pneumonia
* Urinary tract infections in dogs
Horses are generally not treated with oral ampicillin, as they have low bioavailability of beta-lactams.
The half-life in animals is around that same of that in humans (just over an hour). Oral absorption is less than 50% in cats and dogs, and less than 4% in horses. | 4 | Stereochemistry |
Enalapril, sold under the brand name Vasotec among others, is an ACE inhibitor medication used to treat high blood pressure, diabetic kidney disease, and heart failure. For heart failure, it is generally used with a diuretic, such as furosemide. It is given by mouth or by injection into a vein. Onset of effects are typically within an hour when taken by mouth and last for up to a day.
Common side effects include headache, tiredness, feeling lightheaded with standing, and cough. Serious side effects include angioedema and low blood pressure. Use during pregnancy is believed to result in harm to the baby. It is in the angiotensin-converting-enzyme (ACE) inhibitor family of medications.
Enalapril was patented in 1978, and came into medical use in 1984. It is on the World Health Organization's List of Essential Medicines. In 2021, it was the 278th most commonly prescribed medication in the United States, with more than 800,000 prescriptions. It is available as a generic medicine. | 4 | Stereochemistry |
Complexes of salen per se are poorly soluble in organic solvents. Substitution of the organic framework increases the solubility of the complex. An example is the salpn ligand, derived from 1,2-diaminopropane instead of ethylenediamine, which is used as a metal deactivating additive in motor oils and motor fuel.
The presence of bulky groups adjacent to the phenoxide group can give complexes with enhanced catalytic activity. These substituents suppress formation of dimers. For these reasons, salen ligands derived from 3,5-di-tert-butylsalicylaldehyde have received particular scrutiny.
Chirality may be introduced into the ligand either via the diamine backbone, via the phenyl ring, or both. For example, condensation of the C-symmetric trans-1,2-diaminocyclohexane with 3,5-di-tert-butylsalicylaldehdye gives a ligand that forms complexes with Cr, Mn, Co, Al, which have proven useful for asymmetric transformations. For an example, see the Jacobsen epoxidation, which is catalyzed by a chiral manganese-salen complex: | 0 | Organic Chemistry |
In light, low cGMP levels close Na and Ca channels, reducing intracellular Na and Ca.
During recovery (dark adaptation), the low Ca levels induce recovery (termination of the phototransduction cascade), as follows:
# Low intracellular Ca causes Ca to dissociate from guanylate cyclase activating protein (GCAP). The liberated GCAP ultimately restores depleted cGMP levels, which re-opens the cGMP-gated cation channels (restoring dark current).
# Low intracellular Ca causes Ca to dissociate from GTPase-activating protein (GAP), also known as regulator of G protein signaling. The liberated GAP deactivates transducin, terminating the phototransduction cascade (restoring dark current).
# Low intracellular Ca makes intracellular Ca-recoverin-RK dissociate into Ca and recoverin and rhodopsin kinase (RK). The liberated RK then phosphorylates the Metarhodopsin II, reducing its binding affinity for transducin. Arrestin then completely deactivates the phosphorylated-metarhodopsin II, terminating the phototransduction cascade (restoring dark current).
# Low intracellular Ca make the Ca/calmodulin complex within the cGMP-gated cation channels more sensitive to low cGMP levels (thereby, keeping the cGMP-gated cation channel open even at low cGMP levels, restoring dark current)
In more detail:
GTPase Accelerating Protein (GAP) of RGS (regulators of G protein signaling) interacts with the alpha subunit of transducin, and causes it to hydrolyse its bound GTP to GDP, and thus halts the action of phosphodiesterase, stopping the transformation of cGMP to GMP. This deactivation step of the phototransduction cascade (the deactivation of the G protein transducer) was found to be the rate limiting step in the deactivation of the phototransduction cascade.
In other words: Guanylate Cyclase Activating Protein (GCAP) is a calcium binding protein, and as the calcium levels in the cell have decreased, GCAP dissociates from its bound calcium ions, and interacts with Guanylate Cyclase, activating it. Guanylate Cyclase then proceeds to transform GTP to cGMP, replenishing the cell's cGMP levels and thus reopening the sodium channels that were closed during phototransduction.
Finally, Metarhodopsin II is deactivated. Recoverin, another calcium binding protein, is normally bound to Rhodopsin Kinase when calcium is present. When the calcium levels fall during phototransduction, the calcium dissociates from recoverin, and rhodopsin kinase is released and phosphorylates metarhodopsin II, which decreases its affinity for transducin. Finally, arrestin, another protein, binds the phosphorylated metarhodopsin II, completely deactivating it. Thus, finally, phototransduction is deactivated, and the dark current and glutamate release is restored. It is this pathway, where Metarhodopsin II is phosphorylated and bound to arrestin and thus deactivated, which is thought to be responsible for the S2 component of dark adaptation. The S2 component represents a linear section of the dark adaptation function present at the beginning of dark adaptation for all bleaching intensities. | 1 | Biochemistry |
Single-molecule techniques impacted optics, electronics, biology, and chemistry. In the biological sciences, the study of proteins and other complex biological machinery was limited to ensemble experiments that nearly made impossible the direct observation of their kinetics. For example, it was only after single molecule fluorescence microscopy was used to study kinesin-myosin pairs in muscle tissue that direct observation of the walking mechanisms were understood. These experiments, however, have for the most part been limited to in vitro studies, as useful techniques for live cell imaging have yet to be fully realized. The promise of single molecule in vivo imaging, however, brings with it an enormous potential to directly observe bio-molecules in native processes. These techniques are often targeted for studies involving low-copy proteins, many of which are still being discovered. These techniques have also been extended to study areas of chemistry, including the mapping of heterogeneous surfaces. | 7 | Physical Chemistry |
* Fulbright Scholar in Marine Resources, Portugal (2020)
*A.G. Huntsman Award for Excellence in Marine Science (2019)
* Fellow, American Geophysical Union (2018)
* Fellow, Association for the Sciences of Limnology and Oceanography (ASLO, 2016)
* Dansgaard Award, AGU mid-career Paleoceanography Award (2015)
*Fellow, Geochemical Society (2014)
* American Geophysical Union's Rachel Carson Lecture (2013)
*Excellence Chair of the Prof. Dr. Werner Petersen Foundation from GEOMAR
* American Geophysical Union's Ocean Sciences Early Career Award (2004) | 9 | Geochemistry |
Another possible model for fusion pore formation is the protein-lined pore theory. In this model, after activation of synaptotagmin by calcium, several SNARE complexes come together to form a ring structure, with synaptobrevin forming the pore in the vesicle membrane and Syntaxin forming the pore in the cell membrane. As the initial pore expands it incorporates lipids from both bilayers, eventually resulting in complete fusion of the two membranes. The SNARE complex has a much more active role in the protein-lined pore theory; because the pore consists initially entirely of SNARE proteins, the pore is easily able to undergo intercellular regulation, making fluctuation and "kiss-and-run" mechanisms easily attainable.
A protein-lined pore perfectly meets all the observed requirements of the early fusion pore, and while some data does support this theory, sufficient data does not exist to pronounce it the primary method of fusion. A protein-lined pore requires at least five copies of the SNARE complex while fusion has been observed with as few as two.
In both theories the function of the SNARE complex remains largely unchanged, and the entire SNARE complex is necessary to initiate fusion. It has, however, been proven that in vitro Syntaxin per se is sufficient to drive spontaneous calcium independent fusion of synaptic vesicles containing v-SNAREs. This suggests that in Ca-dependent neuronal exocytosis synaptotagmin is a dual regulator, in absence of Ca ions to inhibit SNARE dynamics, while in presence of Ca ions to act as agonist in the membrane fusion process. | 1 | Biochemistry |
Some studies have used interesting comparisons in order to probe the energetic stability of the 2-norbornyl cation provided by its delocalized nature. Comparing the rearrangement between the 3-methyl-2-norbornyl cation and the 2-methyl-2-norbornyl cation to that between the tertiary and secondary isopentane carbocations, one finds that the change in enthalpy is about 6 kcal/mol less for the norbornyl system. Since the major difference between these two reversible rearrangements is the amount of delocalization possible in the electronic ground state, one can attribute the stabilization of the 3-methyl-2-norbornyl cation to its non-classical nature. However, some experimental studies failed to observe this stabilization in solvolysis reactions.
Other studies on the stability of the 2-norbornyl cation have shown that the alkyl substitutions at carbon 1 or 2 force the system to be decidedly classical. Tertiary carbocations are much more stable than their secondary counterparts and therefore do not need to adopt delocalized bonding in order to reach the lowest possible potential energy. | 7 | Physical Chemistry |
After the absolute structure was determined, lineatin quickly attracted considerable synthetic interests due to its natural occurrence, biological activity, and unique structural features. A few routes describing the total synthesis of lineatin was proposed with yields of 0.5–2%. Recently, a new total synthesis route that adopted a photochemical [2 + 2] cycloaddition approach to construct diastereoselective cyclobutene and a regiocontrolled oxymercuration reaction was proposed. This route achieved in synthesizing highly pure (+)-lineatin (> 99.5% ee) through 14 steps and resulted in 14% overall yield from a homochiral 2(5H)-furanone. (Figure 1 showed the basic outline of this approach). | 0 | Organic Chemistry |
* Ciliata: Oxytricha and Stylonychia, Paramecium, Tetrahymena, Oxytrichidae and probably Glaucoma chattoni.
* Dasycladaceae: Acetabularia, and Batophora.
* Diplomonadida: Hexamita inflata, Diplomonadida ATCC50330, and ATCC50380. | 1 | Biochemistry |
Because a large portion of the pairs of a and b contain zeros in one or both conditions, they are impossible to plot as-is on a log scale. Other MA plotting functions artificially include these condition-unique points in the plot by spreading them vertically as a "smear" on the left or horizontally as a "[https://web.archive.org/web/20110825045150/http://projetos.inpa.gov.br/i3geo/pacotes/r/win/library/graphics/html/rug.html rug]" at the very top and bottom of the plot. In an RA plot, by contrast, the uniques are included via addition a small epsilon factor (between .1 and .5) which places them in a more statistically appropriate location in the plot. | 1 | Biochemistry |
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