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Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, who worked on butterflies in the rainforests of Brazil.
Batesian mimicry is the most commonly known and widely studied of mimicry complexes, such that the word mimicry is often treated as synonymous with Batesian mimicry. There are many other forms however, some very similar in principle, others far separated. It is often contrasted with Müllerian mimicry, a form of mutually beneficial convergence between two or more harmful species. However, because the mimic may have a degree of protection itself, the distinction is not absolute. It can also be contrasted with functionally different forms of mimicry. Perhaps the sharpest contrast here is with aggressive mimicry where a predator or parasite mimics a harmless species, avoiding detection and improving its foraging success.
The imitating species is called the mimic, while the imitated species (protected by its toxicity, foul taste or other defenses) is known as the model. The predatory species mediating indirect interactions between the mimic and the model is variously known as the [signal] receiver, dupe or operator. By parasitising the honest warning signal of the model, the Batesian mimic gains an advantage, without having to go to the expense of arming itself. The model, on the other hand, is disadvantaged, along with the dupe. If impostors appear in high numbers, positive experiences with the mimic may result in the model being treated as harmless. At higher frequency there is also a stronger selective advantage for the predator to distinguish mimic from model. For this reason, mimics are usually less numerous than models, an instance of frequency-dependent selection. Some mimetic populations have evolved multiple forms (polymorphism), enabling them to mimic several different models and thereby to gain greater protection. Batesian mimicry is not always perfect. A variety of explanations have been proposed for this, including limitations in predators' cognition.
While visual signals have attracted most study, Batesian mimicry can employ deception of any of the senses; some moths mimic the ultrasound warning signals sent by unpalatable moths to bat predators, constituting auditory Batesian mimicry, while some weakly electric fish appear to mimic the electrolocation signals of strongly electric fish, probably constituting electrical mimicry. | 1 | Biochemistry |
* CRC atlas of spectral data and physical constants for organic compounds, Volume 3 (1975)
* Infrared and Raman Spectroscopy, Part 1 (1976)
* Chemical applications of Raman spectroscopy (1981)
* The Analytical approach (1983)
* 1985 International Conference on Fourier and Computerized Infrared Spectroscopy (1985)
* Handbook of data on organic compounds, Volume 11 (1992) | 3 | Analytical Chemistry |
Often it is the colour of freshwater or how clear or hazy the water is that is the most obvious visual characteristic. Unfortunately neither colour nor turbidity are strong indicators of the overall chemical composition of water. However both colour and turbidity reduce the amount of light penetrating the water and can have significant impact on algae and macrophytes. Some algae in particular are highly dependent on water with low colour and turbidity.
Many rivers draining high moor-lands overlain by peat have a very deep yellow brown colour caused by dissolved humic acids. | 2 | Environmental Chemistry |
Within the field of biochemistry, 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) also known as toxopyrimidine together with its mono phosphate (HMP-P) and pyrophosphate (HMP-PP) esters are biogenetic precursors to the important biochemical cofactor thiamine pyrophosphate (TPP), a derivative of thiamine (vitamin B).
HMP, HMP-P and HMP-PP are found along with thiamine forms in a wide variety of living organisms. Thiamine in various salt, formulation and biological matrix forms are used to supplement human and animal diets because these organisms lack the capability to produce it. Methodologies are being sought for biotechnology-based production of thiamine forms and for increasing thiamine content in food sources. | 1 | Biochemistry |
The Joint Center for Artificial Photosynthesis (JCAP), founded in 2010, is a (DOE) Energy Innovation Hub whose primary mission is to find a cost-effective method to produce fuels using only sunlight, water, and carbon-dioxide. The program has a budget of $122M over five years, subject to Congressional appropriation.
The Director of JCAP is Professor Harry Atwater of Caltech and its two main centers are located at the California Institute of Technology and the Lawrence Berkeley National Laboratory. In addition, JCAP has partners from Stanford University, the University of California at Berkeley, University of California at Santa Barbara, University of California at Irvine, the University of California at San Diego, and Stanford Linear Accelerator. In addition, JCAP also serves as a hub for other solar fuels research teams across the United States, including 20 DOE Energy Frontier Research Center.
In Obamas 2011 State of the Union address, he mentioned the Joint Center for Artificial Photosynthesis. Specifically, he said, "Were issuing a challenge. Were telling Americas scientists and engineers that if they assemble teams of the best minds in their fields, and focus on the hardest problems in clean energy, well fund the Apollo projects of our time. At the California Institute of Technology, theyre developing a way to turn sunlight and water into fuel for our cars". | 5 | Photochemistry |
The Mössbauer isomeric shift is the shift seen in gamma-ray spectroscopy when one compares two different nuclear isomeric states in two different physical, chemical or biological environments, and is due to the combined effect of the recoil-free Mössbauer transition between the two nuclear isomeric states and the transition between two atomic states in those two environments.
The isomeric shift on atomic spectral lines depends on the electron wave function ψ and on the difference δφ of electrostatic potentials φ of the two isomeric states.
For a given nuclear isomer in two different physical or chemical environments (different physical phases or different chemical combinations), the electron wave functions are also different. Therefore, on top of the isomeric shift on atomic spectral lines, which is due to the difference of the two nuclear isomer states, there will be a shift between the two environments (because of the experimental arrangement, these are called source (s) and absorber (a)). This combined shift is the Mössbauer isomeric shift, and it is described mathematically by the same formalism as the nuclear isomeric shift on atomic spectral lines, except that instead of one electron wave function, that in the source ψ, one deals with the difference between the electron wave function in the source ψ and the electron wave function in the absorber ψ:
The first measurement of the isomeric shift in gamma spectroscopy with the help of the Mössbauer effect was reported in 1960, two years after its first experimental observation in atomic spectroscopy. By measuring this shift, one obtains important and extremely precise information, both about the nuclear isomer states and about the physical, chemical or biological environment of the atoms, represented by the electronic wave functions.
Under its Mössbauer variant, the isomeric shift has found important applications in domains as different as atomic physics, solid-state physics, nuclear physics, chemistry, biology, metallurgy, mineralogy, geology, and lunar research. For further literature, see also.
The nuclear isomeric shift has also been observed in muonic atoms, that is, atoms in which a muon is captured by the excited nucleus and makes a transition from an atomic excited state to the atomic ground state in a time shorter than the lifetime of the excited isomeric nuclear state. | 7 | Physical Chemistry |
Cyclopropyl cyanide is prepared by the reaction of 4-chlorobutyronitrile with a strong base, such as sodium amide in liquid ammonia. | 7 | Physical Chemistry |
By targeting proteins, heavy metals have been known to disrupt the function and activity carried out by proteins. It is important to note that heavy metals fall into categories consisting of transition metals as well as a select amount of metalloid. These metals, when interacting with native, folded proteins, tend to play a role in obstructing their biological activity. This interference can be carried out in a different number of ways. These heavy metals can form a complex with the functional side chain groups present in a protein or form bonds to free thiols. Heavy metals also play a role in oxidizing amino acid side chains present in protein. Along with this, when interacting with metalloproteins, heavy metals can dislocate and replace key metal ions. As a result, heavy metals can interfere with folded proteins, which can strongly deter protein stability and activity. | 1 | Biochemistry |
The most popular methods rely on adsorbing floral VOCs on an adsorbent material such as SPME fibers or cartridges by pumping air sampled around inflorescences through the adsorbent material.
It is also possible to extract chemicals stocked in petals by immersing them in a solvent and then analyze the liquid residue. This is more adapted to the study of heavier organic compounds, and/or VOCs that are stored in floral tissue before being emitted into air. | 1 | Biochemistry |
Among the superconducting graphite intercalation compounds, exhibits the highest critical temperature T = 11.5 K, which further increases under applied pressure (15.1 K at 8 GPa). Superconductivity in these compounds is thought to be related to the role of an interlayer state, a free electron like band lying roughly above the Fermi level; superconductivity only occurs if the interlayer state is occupied. Analysis of pure using a high quality ultraviolet light revealed to conduct angle-resolved photoemission spectroscopy measurements. The opening of a superconducting gap in the π* band revealed a substantial contribution to the total electron–phonon-coupling strength from the π*-interlayer interband interaction. | 6 | Supramolecular Chemistry |
Recent work has demonstrated that the scope of "soft" nucleophiles can be expanded to include some pronucleophiles that have much higher than ~ 25. Some of these "soft" nucleophiles have ranging all the way to 32, and even more basic pronucleophiles (~44) have been shown to act as soft nucleophiles with the addition of Lewis acids that help to facilitate deprotonation. The improved pKa range of "soft" nucleophiles is critical because these nucleophiles are the only ones that have been explored for enantioselective reactions until very recently (although non-enantioselective reactions of "hard" nucleophiles have been known for some time). By increasing the scope of pronucleophiles that act as "soft" nucleophiles, these substrates can also be incorporated into enantioselective reactions using previously reported and well characterized methods. | 0 | Organic Chemistry |
Melainabacteria can be found in a range of environments, including soil, water, and animal habitats. They can be often be found in the gut of humans and in the respiratory tract, oral environments, and skin surface, though rarely. Melainabacteria is often found in natural environments such as groundwater aquifers and lake sediment, as well as soil and bioreactors. Melainabacteria are also found in the aphotic zone of aquatic environments such as lake sediment and aquifers. Cyanobacteria bloom in freshwater systems as a result of excess nutrients and high temperatures, resulting in a scum on the water surface that resembles spilled paint. Because Melainabacteria and Cyanobacteria are related, it has raised concern because Melainabacteria thrive in groundwater systems. The genomes of Melainabacteria were found to be bigger when found in aquifer systems and algal cultivation ponds than when in the mammalian gut environment. | 2 | Environmental Chemistry |
*1989 – Fellow, the Royal Swedish Academy of Sciences
*2009 – Honorary doctor, Monash University, Melbourne
*2012 – Knut Schmidt-Nielsen Prize Lecture, International Union of Physiological Sciences
*2013 – Honorary doctor, Royal Veterinary College, London
*2013 – European Lipid Research Award, EuroFedLipid
*2014 – Honorary doctor, Buckingham University, Buckingham, UK
*2014 – King's Medal (12th size), the Order of the Seraphims
*2016 – Prize for Scientific Reviews, Experimental Biology and American Physiological Society
*2016 – Recipient of the Order of the Rising Sun, Gold and Silver Star, Japan
*2017 – Fellow, Academia Europaea | 1 | Biochemistry |
Recent advances in the understanding of biomolecules enabled their application to numerous fields like medicine, diagnostics, biocatalysis and materials. Synthetically modified biomolecules can have diverse functionalities, such as tracking cellular events, revealing enzyme function, determining protein biodistribution, imaging specific biomarkers, and delivering drugs to targeted cells. Bioconjugation is a crucial strategy that links these modified biomolecules with different substrates. Besides applications in biomedical research, bioconjugation has recently also gained importance in nanotechnology such as bioconjugated quantum dots. | 1 | Biochemistry |
Isothiocyanates occur widely in nature and are of interest in food science and medical research. Vegetable foods with characteristic flavors due to isothiocyanates include bok choy, broccoli, cabbage, cauliflower, kale, wasabi, horseradish, mustard, radish, Brussels sprouts, watercress, papaya seeds, nasturtiums, and capers. These species generate isothiocyanates in different proportions, and so have different, but recognizably related, flavors. They are all members of the order Brassicales, which is characterized by the production of glucosinolates, and of the enzyme myrosinase, which acts on glucosinolates to release isothiocyanates.
* Sinigrin is the precursor to allyl isothiocyanate
* Glucotropaeolin is the precursor to benzyl isothiocyanate
* Gluconasturtiin is the precursor to phenethyl isothiocyanate
* Glucoraphanin is the precursor to sulforaphane | 0 | Organic Chemistry |
The basic principle of displacement chromatography is: there are only a finite number of binding sites for solutes on the matrix (the stationary phase), and if a site is occupied by one molecule, it is unavailable to others. As in any chromatography, equilibrium is established between molecules of a given kind bound to the matrix and those of the same kind free in solution. Because the number of binding sites is finite, when the concentration of molecules free in solution is large relative to the dissociation constant for the sites, those sites will mostly be filled. This results in a downward-curvature in the plot of bound vs free solute, in the simplest case giving a Langmuir isotherm. A molecule with a high affinity for the matrix (the displacer) will compete more effectively for binding sites, leaving the mobile phase enriched in the lower-affinity solute. Flow of mobile phase through the column preferentially carries off the lower-affinity solute and thus at high concentration the higher-affinity solute will eventually displace all molecules with lesser affinities. | 3 | Analytical Chemistry |
For equibiaxial extension in the and directions, the principal stretches are . From incompressibility . Hence .
Therefore,
The left Cauchy–Green deformation tensor can then be expressed as
If the directions of the principal stretches are oriented with the coordinate basis vectors, we have
The engineering strain is . The engineering stress is | 7 | Physical Chemistry |
In West Africa, copper was used as medium of exchange, symbols of status and kingship, jewelry, and ritual purposes; this was a part of Bantu tradition prior to their expansion into Central Africa. The use of copper in the Iron Age of Central Africa was produced because of indigenous or internal demand rather than those from outside, and it is thought to be a sensitive sign of political and social change.
Copper appeared to be a prestigious metal in Central and Southern Africa. In Central Africa copper has been found in places where copper is not produced, implying some sort of commerce. Also the majority of artifacts found suggest that the primary use for copper in the area was for decorative purposes. The available evidence shows that prior to fifteenth century Zimbabwean Iron Age site also placed higher value in copper than gold, though the date may have to be pushed with recent carbon dates.
It is thought that through trade with India and later Portugal Zimbabwe started to value gold as prestige metal, however it did not replace copper. Archaeological and documentary sources may skew the record in favor of nonperishable elements of culture and not give enough credit to pastoral and mixed farming activities that were needed to sustain these Iron Age populations. They do make it clear that copper was an important part of the exchange economies of Central and Southern Africa. The site of Bosutswe is evidence that copper and other precious metals were vital to trade in the area.
Tswana towns of the pre-colonial period in South Africa, such as the Tlokwa capital at Marothodi near the Pilanesberg National Park, demonstrate a continuation of native copper production into the early nineteenth century. In this period, archaeological research suggests that copper production had intensified significantly to meet growing regional demands. | 8 | Metallurgy |
Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz or vycor, since ordinary glass absorbs UV‑C. These lamps emit ultraviolet light with two peaks in the UV‑C band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm. The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UV‑C power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–40 watts of total UV output. They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies. | 5 | Photochemistry |
In 1903, Eichengrün co-developed the first soluble form of cellulose acetate with Theodore Becker. He developed processes for the manufacture of cellulose acetate materials and devoted the rest of his life to the technical and economic development of plastics, lacquers, enamels, and artificial fibers based on cellulose acetate. During World War I his relatively non-inflammable synthetic cellulose acetate lacquers were important in the aircraft industry. He also pioneered the influential technique of injection moulding. In 1904, he created and patented the first safety film with Becker, (cellulose diacetate) from a process they devised in 1901 for the direct acetylation of cellulose at a low temperature to prevent its degradation, which permitted the degree of acetylation to be controlled, thereby avoiding total conversion to its triacetate. Cellit was a stable, non-brittle cellulose acetate polymer that could be dissolved in acetone for further processing. It was used to manufacture cellulose diacetate cinematographic film, which Eastman Kodak and the Pathé Frères began to use in 1909. Cellulose acetate film became the standard in the 1950s, preferred over the highly flammable and unstable film stock produced from Nitrocellulose. | 5 | Photochemistry |
Primary treatment for wastewater or drinking water includes settling in a sedimentation chamber to remove as much of the solid matter as possible before applying additional treatments. The amount removed is controlled by the hydraulic residence time (HRT). When water flows through a volume at a slower rate, less energy is available to keep solid particles entrained in the stream and there is more time for them to settle to the bottom. Typical HRTs for sedimentation basins are around two hours, although some groups recommend longer times to remove micropollutants such as pharmaceuticals and hormones.
Disinfection is the last step in the tertiary treatment of wastewater or drinking water. The types of pathogens that occur in untreated water include those that are easily killed like bacteria and viruses, and those that are more robust such as protozoa and cysts. The disinfection chamber must have a long enough HRT to kill or deactivate all of them. | 9 | Geochemistry |
Steric effects of the alkyl substituents on the carbonyl reactant have been shown to affect both the rates and yields of Büchner–Curtius–Schlotterbeck reaction. Table 1 shows the percent yield of the ketone and epoxide products as well as the relative rates of reaction for the reactions between several methyl alkyl ketones and diazomethane.
The observed decrease in rate and increase in epoxide yield as the size of the alkyl group becomes larger indicates a steric effect. | 0 | Organic Chemistry |
An article investigating the structural basis of interactions between clinically relevant antibiotics and the 50S ribosome appeared in Nature in October 2001. High-resolution X-ray crystallography established that these antibiotics associate only with the 23S rRNA of a ribosomal subunit, and no interactions are formed with a subunit's protein portion. The article stresses that the results show "the importance of putative Mg ions for the binding of some drugs". | 1 | Biochemistry |
MPSS is a method for determining expression levels of mRNA by counting the number of individual mRNA molecules produced by each gene. It is "open ended" in the sense that the identity of the RNAs to be measured are not pre-determined as they are with gene expression microarrays.
A sample of mRNA are first converted to complementary DNA (cDNA) using reverse transcriptase, which makes subsequent manipulations easier. These cDNA are fused to a small oligonucleotide "tag" which allows the cDNA to be PCR amplified and then coupled to microbeads. After several rounds of sequence determination, using hybridization of fluorescent labeled probes, a sequence signature of ~16–20 bp is determined from each bead. Fluorescent imaging captures the signal from all of the beads, while affixed to a 2-dimensional surface, so DNA sequences are determined from all the beads in parallel. There is some amplification of the starting material so, in the end, approximately 1,000,000 sequence reads are obtained per experiment. | 1 | Biochemistry |
The temperature jump method is a technique used in chemical kinetics for the measurement of very rapid reaction rates. It is one of a class of chemical relaxation methods pioneered by the German physical chemist Manfred Eigen in the 1950s. In these methods, a reacting system initially at equilibrium is perturbed rapidly and then observed as it relaxes back to equilibrium. In the case of temperature jump, the perturbation involves rapid heating which changes the value of the equilibrium constant, followed by relaxation to equilibrium at the new temperature.
The heating usually involves discharging of a capacitor (in the kV range) through a small volume (< 1 mL) of a conducting solution containing the molecule/reaction to be studied. In some versions of the apparatus used, the solution is heated instead by the output of a pulsed laser which emits in the near infra-red. When laser heating is employed, the solution need not be conducting. In both cases, the temperature of the solution is caused to rise by a small amount in microseconds (or less in the case of laser heating). This allows the study of the shift in equilibrium of reactions that equilibrate in milliseconds (or microseconds with laser temperature jump), these changes most commonly being observed using absorption spectroscopy or fluorescence spectroscopy. Due to the small volumes involved the temperature of the solution returns to that of its surroundings in minutes.
The fractional extent of the reaction (i.e. the percentage change in concentration of a measurable species) depends on the molar enthalpy change (ΔH°) between the reactants and products and the equilibrium position. If K is the equilibrium constant and dT is the change in temperature then the enthalpy change is given by the Van 't Hoff equation:
where R is the universal gas constant and T is the absolute temperature. When a single step in a reaction is perturbed in a temperature jump experiment, the reaction follows a single exponential decay function with time constant equal to a function of the forward (k) and reverse (k) rate constants. For the perturbation of a simple equilibrium which is first order in both directions, the reciprocal of the time constant equals the sum of the two rate constants
The two rate constants can be determined from the values of and the equilibrium constant :, yielding two equations for two unknowns.
In more complex reaction networks, when multiple reaction steps are perturbed, then the reciprocal time constants are given by the eigenvalues of the characteristic rate equations. The ability to observe intermediate steps in a reaction pathway is one of the attractive features of this technology.
Related chemical relaxation methods include pressure jump, electric field jump and pH jump. | 7 | Physical Chemistry |
The simplest methods of chemical analysis are those measuring chemical elements without respect to their form. Elemental analysis for oxygen, as an example, would indicate a concentration of 890 g/L (grams per litre) of water sample because oxygen (O) has 89% mass of the water molecule (HO). The method selected to measure dissolved oxygen should differentiate between diatomic oxygen and oxygen combined with other elements. The comparative simplicity of elemental analysis has produced a large amount of sample data and water quality criteria for elements sometimes identified as heavy metals. Water analysis for heavy metals must consider soil particles suspended in the water sample. These suspended soil particles may contain measurable amounts of metal. Although the particles are not dissolved in the water, they may be consumed by people drinking the water. Adding acid to a water sample to prevent loss of dissolved metals onto the sample container may dissolve more metals from suspended soil particles. Filtration of soil particles from the water sample before acid addition, however, may cause loss of dissolved metals onto the filter. The complexities of differentiating similar organic molecules are even more challenging.
Making these complex measurements can be expensive. Because direct measurements of water quality can be expensive, ongoing monitoring programs are typically conducted and results released by government agencies. However, there are local volunteer programs and resources available for some general assessment. Tools available to the general public include on-site test kits, commonly used for home fish tanks, and biological assessment procedures. | 3 | Analytical Chemistry |
Receptor-linked tyrosine kinases, such as the epidermal growth factor receptor (EGFR), are activated by extracellular ligands, such as the epidermal growth factor (EGF). Binding of EGF to the EGFR activates the tyrosine kinase activity of the cytoplasmic domain of the receptor. The EGFR becomes phosphorylated on tyrosine residues. Docking proteins such as GRB2 contain an SH2 domain that binds to the phosphotyrosine residues of the activated receptor. GRB2 binds to the guanine nucleotide exchange factor SOS by way of the two SH3 domains of GRB2. When the GRB2-SOS complex docks to phosphorylated EGFR, SOS becomes activated. Activated SOS then promotes the removal of GDP from a member of the Ras subfamily (most notably H-Ras or K-Ras). The Ras protein can then bind GTP and become active.
Apart from EGFR, other cell surface receptors that can activate this pathway via GRB2 include Trk A/B, Fibroblast growth factor receptor (FGFR) and PDGFR. | 1 | Biochemistry |
When the weights have been correctly derived from estimates of experimental error, the expectation value of is 1. It is therefore very useful to estimate experimental errors and derive some reasonable weights from them as this is an absolute indicator of the goodness of fit.
When unit weights are used, it is implied that all observations have the same variance. is expected to be equal to that variance. | 7 | Physical Chemistry |
Kubista began his academic career in 1991 as an Assistant Professor in the Department of Physical Chemistry at Chalmers University of Technology. From 1993 to 1997, he served as an Associate Professor in the Department of Biochemistry at the same institution. Following this, he held the position of Professor in the Department of Biochemistry at Chalmers University of Technology from 1997 to 2006. Since 2007, he is the Head of the Department of Gene Expression at the Institute of Biotechnology, BIOCEV, Czech Academy of Sciences. | 1 | Biochemistry |
One of the most well discussed, and detrimental, embrittlement is hydrogen embrittlement in metals. There are multiple ways that hydrogen atoms can diffuse into metals, including from environment or during processing (eg. electroplating). The exact mechanism that causes hydrogen embrittlement is still not determined, but many theories are proposed and are still undergoing verification. Hydrogen atoms are likely to diffuse to grain boundaries of metals, which becomes a barrier for dislocation motion and builds up stress near the atoms. When the metal is stressed, the stress is concentrated near the grain boundaries due to hydrogen atoms, allowing a crack to nucleate and propagate along the grain boundaries to relieve the built-up stress.
There are many ways to prevent or reduce the impact of hydrogen embrittlement in metals. One of the more conventional ways is to place coatings around the metal, which will act as diffusion barriers that prevents hydrogen from being introduced from the environment into the material. Another way is to add traps or absorbers in the alloy which takes into the hydrogen atom and forms another compound. | 8 | Metallurgy |
The type III partition system is the most recently discovered partition system. It is composed of tubulin-like GTPase termed TubZ, and the CBP is termed TubR.
Amino-acid sequence identity can go down to 21% for TubZ proteins.
The mechanism is similar to a treadmill mechanism:
# Multiple TubR dimer binds to the centromere-like region stbDRs of the plasmids.
# Contact between TubR and filament of treadmilling TubZ polymer. TubZ subunits are lost from the - end and are added to the + end.
# TubR-plasmid complex is pulled along the growing polymer until it reaches the cell pole.
# Interaction with membrane is likely to trigger the release of the plasmid.
The net result being transport of partition complex to the cell pole. | 1 | Biochemistry |
The general mathematical concept embodied in a Wigner–Seitz cell is more commonly called a Voronoi cell, and the partition of the plane into these cells for a given set of point sites is known as a Voronoi diagram.
The cell may be chosen by first picking a lattice point. After a point is chosen, lines are drawn to all nearby lattice points. At the midpoint of each line, another line is drawn normal to each of the first set of lines. The smallest area enclosed in this way is called the Wigner–Seitz primitive cell.
For a 3-dimensional lattice, the steps are analogous, but in step 2 instead of drawing perpendicular lines, perpendicular planes are drawn at the midpoint of the lines between the lattice points.
As in the case of all primitive cells, all area or space within the lattice can be filled by Wigner–Seitz cells and there will be no gaps.
Nearby lattice points are continually examined until the area or volume enclosed is the correct area or volume for a primitive cell. Alternatively, if the basis vectors of the lattice are reduced using lattice reduction only a set number of lattice points need to be used. In two-dimensions only the lattice points that make up the 4 unit cells that share a vertex with the origin need to be used. In three-dimensions only the lattice points that make up the 8 unit cells that share a vertex with the origin need to be used. | 3 | Analytical Chemistry |
In analytical chemistry, a chiral derivatizing agent (CDA), also known as a chiral resolving reagent, is a derivatization reagent that is a chiral auxiliary used to convert a mixture of enantiomers into diastereomers in order to analyze the quantities of each enantiomer present and determine the optical purity of a sample. Analysis can be conducted by spectroscopy or by chromatography. Some analytical techniques such as HPLC and NMR, in their most commons forms, cannot distinguish enantiomers within a sample, but can distinguish diastereomers. Therefore, converting a mixture of enantiomers to a corresponding mixture of diastereomers can allow analysis. The use of chiral derivatizing agents has declined with the popularization of chiral HPLC. Besides analysis, chiral derivatization is also used for chiral resolution, the actual physical separation of the enantiomers. | 4 | Stereochemistry |
When the receptor is inactive, the GEF domain may be bound to an also inactive α-subunit of a heterotrimeric G-protein. These "G-proteins" are a trimer of α, β, and γ subunits (known as Gα, Gβ, and Gγ, respectively) that is rendered inactive when reversibly bound to Guanosine diphosphate (GDP) (or, alternatively, no guanine nucleotide) but active when bound to guanosine triphosphate (GTP). Upon receptor activation, the GEF domain, in turn, allosterically activates the G-protein by facilitating the exchange of a molecule of GDP for GTP at the G-protein's α-subunit. The cell maintains a 10:1 ratio of cytosolic GTP:GDP so exchange for GTP is ensured. At this point, the subunits of the G-protein dissociate from the receptor, as well as each other, to yield a Gα-GTP monomer and a tightly interacting Gβγ dimer, which are now free to modulate the activity of other intracellular proteins. The extent to which they may diffuse, however, is limited due to the palmitoylation of Gα and the presence of an isoprenoid moiety that has been covalently added to the C-termini of Gγ.
Because Gα also has slow GTP→GDP hydrolysis capability, the inactive form of the α-subunit (Gα-GDP) is eventually regenerated, thus allowing reassociation with a Gβγ dimer to form the "resting" G-protein, which can again bind to a GPCR and await activation. The rate of GTP hydrolysis is often accelerated due to the actions of another family of allosteric modulating proteins called regulators of G-protein signaling, or RGS proteins, which are a type of GTPase-activating protein, or GAP. In fact, many of the primary effector proteins (e.g., adenylate cyclases) that become activated/inactivated upon interaction with Gα-GTP also have GAP activity. Thus, even at this early stage in the process, GPCR-initiated signaling has the capacity for self-termination. | 1 | Biochemistry |
The phenomenon of electromigration has been known for over 100 years, having been discovered by the French scientist Gerardin. The topic first became of practical interest during the late 1960s when packaged ICs first appeared. The earliest commercially available ICs failed in a mere three weeks of use from runaway electromigration, which led to a major industry effort to correct this problem. The first observation of electromigration in thin films was made by I. Blech. Research in this field was pioneered by a number of investigators throughout the fledgling semiconductor industry. One of the most important engineering studies was performed by Jim Black of Motorola, after whom Black's equation is named. At the time, the metal interconnects in ICs were still about 10 micrometres wide. Currently interconnects are only hundreds to tens of nanometers in width, making research in electromigration increasingly important. | 7 | Physical Chemistry |
After finishing school, Hammond began working at Howe & Leeds Wholesale West India Goods Store on Boston's Long Wharf. The same year, he became a clerk with J. W. Blodgett & Co.
Hammond attended the Massachusetts Institute of Technology as a special student on the chemistry of paper manufacturing.
After moving to Maine part-time, in 1853 he accepted a position at his uncle Samuel Dennis Warrens S. D. Warren Paper Mill in Cumberland Mills. By 1857, he was superintendent, a role in which remained for five years. His next position was as the mills agent.
In 1874, Hammond and Warren bought the rights to Yarmouth Paper Company, in Yarmouth, Maine, at the towns Third Falls. They renamed it Forest Paper Company. Beginning with a single wooden building, the facility expanded to ten buildings covering as many acres, including a span over the Royal River to Factory Island. Two bridges to it were also constructed. In 1909, the year following Hammonds death, it was the largest such mill in the world, employing 275 people. Hammond also worked at the S. D. Warren mill until 1876, before transferring full-time to Yarmouth as the manager of the new business. The mill became known as a pioneer in the processing of soda pulp.
Hammond retired from active business on January 1, 1906. | 8 | Metallurgy |
The TET proteins also have activities that are independent of DNA demethylation. These include, for instance, TET2 interaction with O-linked N-acetylglucosamine (O-GlcNAc) transferase to promote histone O-GlcN acylation to affect transcription of target genes. | 1 | Biochemistry |
The spectral shape and intensity of the optical signals from the NV centers are sensitive to external perturbation, such as temperature, strain, electric and magnetic field. However, the use of spectral shape for sensing those perturbation is impractical, as the diamond would have to be cooled to cryogenic temperatures to sharpen the NV signals. A more realistic approach is to use luminescence intensity (rather than lineshape), which exhibits a sharp resonance when a microwave frequency is applied to diamond that matches the splitting of the ground-state levels. The resulting optically detected magnetic resonance signals are sharp even at room temperature, and can be used in miniature sensors. Such sensors can detect magnetic fields of a few nanotesla or electric fields of about 10 V/cm at kilohertz frequencies after 100 seconds of averaging. This sensitivity allows detecting a magnetic or electric field produced by a single electron located tens of nanometers away from an NV center.
Using the same mechanism, the NV centers were employed in scanning thermal microscopy to measure high-resolution spatial maps of temperature and thermal conductivity (see image).
Because the NV center is sensitive to magnetic fields, it is being actively used in scanning probe measurements to study myriad condensed matter phenomena both through measuring a spatially varying magnetic field or inferring local currents in a device.
Another possible use of the NV centers is as a detector to measure the full mechanical stress tensor in the bulk of the crystal. For this application, the stress-induced splitting of the zero-phonon-line is exploited, and its polarization properties. A robust frequency-modulated radio receiver using the electron-spin-dependent photoluminescence that operated up to 350 °C demonstrates the possibility for use in extreme conditions.
In addition to the quantum optical applications, luminescence from the NV centers can be applied for imaging biological processes, such as fluid flow in living cells. This application relies on good compatibility of diamond nano-particles with the living cells and on favorable properties of photoluminescence from the NV centers (strong intensity, easy excitation and detection, temporal stability, etc.). Compared with large single-crystal diamonds, nanodiamonds are cheap (about 1 USD per gram) and available from various suppliers. NV centers are produced in diamond powders with sub-micrometre particle size using the standard process of irradiation and annealing described above. Due to the relatively small size of nanodiamond, NV centers can be produced by irradiating nanodiamond of 100 nm or less with medium energy H+ beam. This method reduces the required ion dose and reaction, making it possible to mass produce fluorescent nanodiamonds in ordinary laboratory. Fluorescent nanodiamond produced with such method is bright and photostable, making it excellent for long-term, three dimensional tracking of single particle in living cell. Those nanodiamonds are introduced in a cell, and their luminescence is monitored using a standard fluorescence microscope.
Stimulated emission from the NV center has been demonstrated, though it could be achieved only from the phonon side-band (i.e. broadband light) and not from the ZPL. For this purpose, the center has to be excited at a wavelength longer than ~650 nm, as higher-energy excitation ionizes the center.
The first continuous-wave room-temperature maser has been demonstrated. It used 532-nm pumped NV centers held within a high Purcell factor microwave cavity and an external magnetic field of 4300 G. Continuous maser oscillation generated a coherent signal at ~9.2 GHz.
The NV center can have a very long spin coherence time approaching the second regime. This is advantageous for applications in quantum sensing and quantum communication. Disadvantageous for these applications is the long radiative lifetime (~12 ns
) of the NV center and the strong phonon sideband in its emission spectrum. Both issues can be addressed by putting the NV center in an optical cavity. | 7 | Physical Chemistry |
Tramadol induces analgesic effects through a variety of different targets on the noradrenergic system, serotoninergic system, and opioid receptors system. Tramadol exists as a racemic mixture, the positive enantiomer inhibits serotonin reuptake while the negative enantiomer inhibits noradrenaline re-uptake, by binding to and blocking the transporters. Tramadol has also been shown to act as a serotonin releasing agent. Both enantiomers of tramadol are agonists of the μ-opioid receptor and its M1 metabolite, O-desmetramadol, is also a μ-opioid receptor agonist but is 6 times more potent than tramadol itself. All these effects work synergistically to induce analgesia.
Tramadol has been found to possess these actions:
* Agonist of the μ-opioid receptor (MOR) and to a far lesser extent of the δ-opioid receptor (DOR) and κ-opioid receptor (KOR)
* Serotonin reuptake inhibitor (SRI) and norepinephrine reuptake inhibitor; hence, an SNRI
* Serotonin 5-HT receptor antagonist
* M and M muscarinic acetylcholine receptor antagonist
* α7 nicotinic acetylcholine receptor antagonist
* NMDA receptor antagonist (very weak)
* TRPA1 inhibitor
Tramadol acts on the opioid receptors through its major active metabolite desmetramadol, which has as much as 700-fold higher affinity for the MOR relative to tramadol. Moreover, tramadol itself has been found to possess no efficacy in activating the MOR in functional activity assays, whereas desmetramadol activates the receptor with high intrinsic activity (E equal to that of morphine). As such, desmetramadol is exclusively responsible for the opioid effects of tramadol. Both tramadol and desmetramadol have pronounced selectivity for the MOR over the DOR and KOR in terms of binding affinity.
Tramadol is well-established as an SRI. In addition, a few studies have found that it also acts as a serotonin releasing agent (1–10 μM), similar in effect to fenfluramine. The serotonin releasing effects of tramadol could be blocked by sufficiently high concentrations of the serotonin reuptake inhibitor 6-nitroquipazine, which is in accordance with other serotonin releasing agents such as fenfluramine and MDMA. However, two more recent studies failed to find a releasing effect of tramadol at respective concentrations up to 10 and 30 μM. In addition to serotonergic activity, tramadol is also a norepinephrine reuptake inhibitor. It is not a norepinephrine releasing agent. Tramadol does not inhibit the reuptake or induce the release of dopamine.
A positron emission tomography imaging study found that single oral 50-mg and 100-mg doses of tramadol to human volunteers resulted in 34.7% and 50.2% respective mean occupation of the serotonin transporter (SERT) in the thalamus. The estimated median effective dose (ED) for SERT occupancy hence was 98.1 mg, which was associated with a plasma tramadol level of about 330 ng/ml (1,300 nM). The estimated maximum daily dosage of tramadol of 400 mg (100 mg ) would result in as much as 78.7% occupancy of the SERT (in association with a plasma concentration of 1,220 ng/ml or 4,632 nM). This is close to that of SSRIs, which occupy the SERT by 80% or more.
Peak plasma concentrations during treatment with clinical dosages of tramadol have generally been found to be in the range of 70 to 592 ng/ml (266–2,250 nM) for tramadol and 55 to 143 ng/ml (221–573 nM) for desmetramadol. The highest levels of tramadol were observed with the maximum oral daily dosage of 400 mg per day divided into one 100-mg dose every 6 hours (i.e., four 100-mg doses evenly spaced out per day). Some accumulation of tramadol occurs with chronic administration; peak plasma levels with the maximum oral daily dosage (100 mg ) are about 16% higher and the area-under-the-curve levels 36% higher than following a single oral 100-mg dose. Positron emission tomography imaging studies have reportedly found that tramadol levels are at least four-fold higher in the brain than in plasma. Conversely, brain levels of desmetramadol "only slowly approach those in plasma". The plasma protein binding of tramadol is only 4–20%; hence, almost all tramadol in circulation is free, thus bioactive. | 4 | Stereochemistry |
*The wallpaper group of a pattern is invariant under isometries and uniform scaling (similarity transformations).
*Translational symmetry is preserved under arbitrary bijective affine transformations.
*Rotational symmetry of order two ditto; this means also that 4- and 6-fold rotation centres at least keep 2-fold rotational symmetry.
*Reflection in a line and glide reflection are preserved on expansion/contraction along, or perpendicular to, the axis of reflection and glide reflection. It changes p6m, p4g, and p3m1 into cmm, p3m1 into cm, and p4m, depending on direction of expansion/contraction, into pmm or cmm. A pattern of symmetrically staggered rows of points is special in that it can convert by expansion/contraction from p6m to p4m.
Note that when a transformation decreases symmetry, a transformation of the same kind (the inverse) obviously for some patterns increases the symmetry. Such a special property of a pattern (e.g. expansion in one direction produces a pattern with 4-fold symmetry) is not counted as a form of extra symmetry.
Change of colors does not affect the wallpaper group if any two points that have the same color before the change, also have the same color after the change, and any two points that have different colors before the change, also have different colors after the change.
If the former applies, but not the latter, such as when converting a color image to one in black and white, then symmetries are preserved, but they may increase, so that the wallpaper group can change. | 3 | Analytical Chemistry |
Direct enantiomer separation involves the formation of a transient rather than covalent diastereomeric complexation between the chiral selector/discriminator and the analyte (drug enantiomer). In this approach, the subtle energy differences between the reversibly formed noncovalent diastereomeric complexes are exploited for chiral recognition. The direct chromatographic enantiomer separation may be achieved in two different ways, the chiral mobile phase additive and chiral stationary phase mode. | 4 | Stereochemistry |
Martha Austin Phelps was an American chemist who conducted research in measuring metal concentrations and developed several analytical protocols to do so. She also worked on the early development of ester synthesis. In between conducting research, she worked as school teacher teaching chemistry and physics. She finished her career as an activist in women's academic clubs. Her chemistry career lasted approximately 10 years, resulting in 15 publications, which set her apart as one of the most skilled female chemists within the first generation of women chemists in the United States. | 3 | Analytical Chemistry |
In physics, the super Tonks–Girardeau gas represents an excited quantum gas phase with strong attractive interactions in a one-dimensional spatial geometry.
Usually, strongly attractive quantum gases are expected to form dense particle clusters and lose all gas-like properties. But in 2005, it was proposed by Stefano Giorgini and co-workers that there is a many-body state of attractively interacting bosons that does not decay in one-dimensional systems. If prepared in a special way, this lowest gas-like state should be stable and show new quantum mechanical properties.
Particles in a super-Tonks gas should be strongly correlated and show long range order with a Luttinger liquid parameter K<1. Since each particle occupies a certain volume, the gas properties are similar to a classical gas of hard rods. Despite the mutual attraction, the single particle wave functions separate and the bosons behave similar to fermions with repulsive, long-range interaction.
To prepare the super-Tonks–Girardeau phase it is necessary to increase the repulsive interaction strength all the way through the Tonks–Girardeau regime up to infinity. Sudden switching from infinitely strong repulsive to infinitely attractive interactions stabilizes the gas against collapse and connects the ground state of the Tonks gas to the excited state of the super-Tonks gas. | 7 | Physical Chemistry |
In chloroplasts of the moss Physcomitrella patens, the DNA mismatch repair protein Msh1 interacts with the recombinational repair proteins RecA and RecG to maintain chloroplast genome stability. In chloroplasts of the plant Arabidopsis thaliana the RecA protein maintains the integrity of the chloroplast's DNA by a process that likely involves the recombinational repair of DNA damage. | 5 | Photochemistry |
Butadiene, cyclooctadiene, and norbornadiene are well-studied chelating agents. Trienes and even some tetraenes can bind to metals through several adjacent carbon centers. Common examples of such ligands are cycloheptatriene and cyclooctatetraene. The bonding is often denoted using the hapticity formalism. Keto-alkenes are tetrahapto ligands that stabilize highly unsaturated low valent metals as found in (benzylideneacetone)iron tricarbonyl and tris(dibenzylideneacetone)dipalladium(0). | 0 | Organic Chemistry |
Adhesive materials fill the voids or pores of the surfaces and hold surfaces together by interlocking. Other interlocking phenomena are observed on different length scales. Sewing is an example of two materials forming a large scale mechanical bond, velcro forms one on a medium scale, and some textile adhesives (glue) form one at a small scale. | 6 | Supramolecular Chemistry |
Emerging technologies are aiming to combine pooled CRISPR screens with the detailed resolution of massively parallel single-cell RNA-sequencing (RNA-seq). Studies utilising “CRISP-seq”, “CROP-seq”, and “PERTURB-seq” have demonstrated rich genomic readouts, accurately identifying gene expression signatures for individual gene knockouts in a complex pool of cells. These methods have the added benefit of producing transcriptional profiles of the sgRNA-induced cells. | 1 | Biochemistry |
It remains a challenge to develop good single-phase multiferroics with large magnetization and polarization and strong coupling between them at room temperature. Therefore, composites combining magnetic materials, such as FeRh, with ferroelectric materials, such as PMN-PT, are an attractive and established route to achieving multiferroicity. Some examples include magnetic thin films on piezoelectric PMN-PT substrates and Metglass/PVDF/Metglass trilayer structures. Recently an interesting layer-by-layer growth of an atomic-scale multiferroic composite has been demonstrated, consisting of individual layers of ferroelectric and antiferromagnetic LuFeO alternating with ferrimagnetic but non-polar LuFeO in a superlattice.
A new promising approach are core-shell type ceramics where a magnetoelectric composite is formed in-situ during synthesis. In the system (BiFeCoO)-(BiKTiO) (BFC-BKT) very strong ME coupling has been observed on a microscopic scale using PFM under magnetic field. Furthermore, switching of magnetization via electric field has been observed using MFM. Here, the ME active core-shell grains consist of magnetic CoFeO (CFO) cores and a (BiFeO)-(BiKTiO) (BFO-BKT) shell where core and shell have an epitaxial lattice structure. The mechanism of strong ME coupling is via magnetic exchange interaction between CFO and BFO across the core-shell interface, which results in an exceptionally high Neel-Temperature of 670 K of the BF-BKT phase. | 7 | Physical Chemistry |
The Lemieux–Johnson or Malaprade–Lemieux–Johnson oxidation is a chemical reaction in which an olefin undergoes oxidative cleavage to form two aldehyde or ketone units. The reaction is named after its inventors, Raymond Urgel Lemieux and William Summer Johnson, who published it in 1956.
The reaction proceeds in a two step manner, beginning with dihydroxylation of the alkene by osmium tetroxide, followed by a Malaprade reaction to cleave the diol using periodate. Excess periodate is used to regenerate the osmium tetroxide, allowing it to be used in catalytic amounts. The Lemieux–Johnson reaction ceases at the aldehyde stage of oxidation and therefore produces the same results as ozonolysis.
The classical Lemieux–Johnson oxidation often generates many side products, resulting in low reaction yields; however the addition of non-nucleophilic bases, such as 2,6-lutidine, can improve on this.
OsO may be replaced with a number of other Osmium compounds. Periodate may also be replaced with other oxidising agents, such as oxone. | 0 | Organic Chemistry |
Unlike DNA editing, which is permanent, the effects of RNA editing − including potential off-target mutations in RNA − are transient and are not inherited. RNA editing is therefore considered to be less risky. Furthermore, it may only require a guide RNA by using the ADAR protein already found in humans and many other eukaryotes' cells instead of needing to introduce a foreign protein into the body. | 1 | Biochemistry |
1,3 Diaxial interactions occur when the non-hydrogen substituent on a cyclohexane occupies the axial position. This axial substituent is in the eclipsed position with the axial substituents on the 3-carbons relative to itself (there will be two such carbons and thus two 1,3 diaxial interactions). This eclipsed position increases the steric strain on the cyclohexane conformation and the confirmation will shift towards a more energetically favorable equilibrium.
Gauche interactions occur when a non-hydrogen substituent on a cyclohexane occupies the equatorial position. The equatorial substituent is in a staggered position with the 2-carbons relative to itself (there will be two such carbons and thus two 1,2 gauche interactions). This creates a dihedral angle of ~60°. This staggered position is generally preferred to the eclipsed positioning. | 4 | Stereochemistry |
Riboses 2 hydroxy group reacts with the phosphate linked 3 hydroxy group, making RNA too unstable to be used or synthesized reliably. To overcome this, a ribose analogue can be used. The most common RNA analogues are 2-O-methyl-substituted RNA, locked nucleic acid (LNA) or bridged nucleic acid (BNA), morpholino, and peptide nucleic acid (PNA). Although these oligonucleotides have a different backbone sugar—or, in the case of PNA, an amino acid residue in place of the ribose phosphate—they still bind to RNA or DNA according to Watson and Crick pairing while being immune to nuclease activity. They cannot be synthesized enzymatically and can only be obtained synthetically using the phosphoramidite strategy or, for PNA, other methods of peptide synthesis. | 1 | Biochemistry |
Reductive elimination is sensitive to a variety of factors including: 1) metal identity and electron density; 2) sterics; 3) participating ligands; 4) coordination number; 5) geometry; and 6) photolysis/oxidation. Additionally, because reductive elimination and oxidative addition are reverse reactions, any sterics or electronics that enhance the rate of reductive elimination must thermodynamically hinder the rate of oxidative addition. | 0 | Organic Chemistry |
miRBase is considered to be the gold-standard miRNA database—it stores miRNA sequences detected by thousand of experiments. In this database each miRNA is associated with a miRNA precursor and with one or two mature miRNA (-5p and -3p). In the past it had always been said that the same miRNA precursor generates the same miRNA sequences. However, the advent of deep sequencing has now allowed researchers to detect a huge variability in miRNA biogenesis, meaning that from the same miRNA precursor many different sequences can be generated potentially have different targets, or even lead to opposite changes in mRNA expression. | 1 | Biochemistry |
The normal coordinates, denoted as Q, refer to the positions of atoms away from their equilibrium positions, with respect to a normal mode of vibration. Each normal mode is assigned a single normal coordinate, and so the normal coordinate refers to the "progress" along that normal mode at any given time. Formally, normal modes are determined by solving a secular determinant, and then the normal coordinates (over the normal modes) can be expressed as a summation over the cartesian coordinates (over the atom positions). The normal modes diagonalize the matrix governing the molecular vibrations, so that each normal mode is an independent molecular vibration. If the molecule possesses symmetries, the normal modes "transform as" an irreducible representation under its point group. The normal modes are determined by applying group theory, and projecting the irreducible representation onto the cartesian coordinates. For example, when this treatment is applied to CO, it is found that the C=O stretches are not independent, but rather there is an O=C=O symmetric stretch and an O=C=O asymmetric stretch:
* symmetric stretching: the sum of the two C–O stretching coordinates; the two C–O bond lengths change by the same amount and the carbon atom is stationary. Q = q + q
* asymmetric stretching: the difference of the two C–O stretching coordinates; one C–O bond length increases while the other decreases. Q = q − q
When two or more normal coordinates belong to the same irreducible representation of the molecular point group (colloquially, have the same symmetry) there is "mixing" and the coefficients of the combination cannot be determined a priori. For example, in the linear molecule hydrogen cyanide, HCN, The two stretching vibrations are
* principally C–H stretching with a little C–N stretching; Q = q + a q (a << 1)
* principally C–N stretching with a little C–H stretching; Q = b q + q (b << 1)
The coefficients a and b are found by performing a full normal coordinate analysis by means of the Wilson GF method. | 7 | Physical Chemistry |
While it was known that the different enantiomers of a drug could have different activities, with significant early work being done by Arthur Robertson Cushny, this was not accounted for in early drug design and testing. However, following the thalidomide disaster the development and licensing of drugs changed dramatically.
First synthesized in 1953, thalidomide was widely prescribed for morning sickness from 1957 to 1962, but was soon found to be seriously teratogenic, eventually causing birth defects in more than 10,000 babies. The disaster prompted many countries to introduce tougher rules for the testing and licensing of drugs, such as the Kefauver-Harris Amendment (US) and Directive 65/65/EEC1 (EU).
Early research into the teratogenic mechanism, using mice, suggested that one enantiomer of thalidomide was teratogenic while the other possessed all the therapeutic activity. This theory was later shown to be incorrect and has now been superseded by a body of research. However it raised the importance of chirality in drug design, leading to increased research into enantioselective synthesis. | 4 | Stereochemistry |
The European Synchrotron Radiation Facility (ESRF) as well as many other synchrotron facilities as the three major synchrotron user facilities in the United States all have beamlines equipped with laser heating systems. The respective beamlines with laser heating systems are at the ESRF ID27, ID18, and ID24; at the Advanced Photon Source (APS), 13-ID-D GSECARS and 16-ID-B HP-CAT; at the National Synchrotron Light Source, X17B3; and at the Advanced Light Source, 12.2.2. Laser heating has become a routine technique in high-pressure science but the reliability of temperature measurement is still controversial. | 7 | Physical Chemistry |
Polyethers are generally polymers containing ether linkages in their main chain. The term polyol generally refers to polyether polyols with one or more functional end-groups such as a hydroxyl group. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties.
Crown ethers are cyclic polyethers. Some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are extremely large and are known as cyclic or ladder polyethers.
The phenyl ether polymers are a class of aromatic polyethers containing aromatic cycles in their main chain: polyphenyl ether (PPE) and poly(p-phenylene oxide) (PPO). | 0 | Organic Chemistry |
Differentiating healthy versus cancerous bladder cells with metabolic footprinting.
Footprinting, in combination with other techniques, for early recognition of outbreak and strain characterization.
Studying aging with C. elegans exometabolomics.
Extracellular metabolite analysis to evaluate pathogenic mechanism of intracellular protozoal parasite. | 1 | Biochemistry |
The Joback method (often named Joback/Reid method) predicts eleven important and commonly used pure component thermodynamic properties from molecular structure only. | 7 | Physical Chemistry |
While cerium anomalies in coal are usually negative, they can rarely be positive as well. This can occur during volcanic eruptions when volcanic ash is weathered into mafic tuffs with positive Ce-anomalies. The Pavlovka deposit in Far East Russia has large positive Ce-anomalies in its Fe-Mn oxyhydroxide ores. Because cerium is one of only two REEs that can obtain an oxidation number of +4, Ce is absorbed into Mn(IV) oxides instead of other REEs and this results in a positive Ce-anomaly. | 9 | Geochemistry |
Avogadros hypothesis (as it was known originally) was formulated in the same spirit of earlier empirical gas laws like Boyles law (1662), Charless law (1787) and Gay-Lussacs law (1808). The hypothesis was first published by Amadeo Avogadro in 1811, and it reconciled Dalton atomic theory with the "incompatible" idea of Joseph Louis Gay-Lussac that some gases were composite of different fundamental substances (molecules) in integer proportions. In 1814, independently from Avogadro, André-Marie Ampère published the same law with similar conclusions. As Ampère was more well known in France, the hypothesis was usually referred there as Ampère's hypothesis, and later also as Avogadro–Ampère hypothesis or even Ampère–Avogadro hypothesis.
Experimental studies carried out by Charles Frédéric Gerhardt and Auguste Laurent on organic chemistry demonstrated that Avogadros law explained why the same quantities of molecules in a gas have the same volume. Nevertheless, related experiments with some inorganic substances showed seeming exceptions to the law. This apparent contradiction was finally resolved by Stanislao Cannizzaro, as announced at Karlsruhe Congress in 1860, four years after Avogadros death. He explained that these exceptions were due to molecular dissociations at certain temperatures, and that Avogadro's law determined not only molecular masses, but atomic masses as well. | 7 | Physical Chemistry |
Tendril perversion is a geometric phenomenon sometimes observed in helical structures in which the direction of the helix transitions between left-handed and right-handed. Such a reversal of chirality is commonly seen in helical plant tendrils and telephone handset cords.
The phenomenon was known to Charles Darwin, who wrote in 1865,
The term "tendril perversion" was coined by Alain Goriely and Michael Tabor in 1998 based on the word perversion found in 19th-century science literature. "Perversion" is a transition from one chirality to another and was known to James Clerk Maxwell, who attributed it to topologist J. B. Listing.
Tendril perversion can be viewed as an example of spontaneous symmetry breaking, in which the strained structure of the tendril adopts a configuration of minimum energy while preserving zero overall twist.
Tendril perversion has been studied both experimentally and theoretically. Gerbode et al. have made experimental studies of the coiling of cucumber tendrils. A detailed study of a simple model of the physics of tendril perversion was made by McMillen and Goriely in the early 2000s. Liu et al. showed in 2014 that "the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section."
Generalized tendril perversions were put forward by Silva et al., to include perversions that can be intrinsically produced in elastic filaments, leading to a multiplicity of geometries and dynamical properties. | 4 | Stereochemistry |
In the absence of hypoxic conditions (i.e. physiological levels of oxygen), cancer cells preferentially convert glucose to lactate, according to Otto H. Warburg, who believed that aerobic glycolysis was the key metabolic change in cancer cell malignancy. The "Warburg effect" was later coined to describe this metabolic shift. Warburg thought this change in metabolism was due to mitochondrial "respiration injury", but this interpretation was questioned by other researchers in 1956 showing that intact and functional cytochromes detected in most tumor cells clearly speak against a general mitochondrial dysfunction. Furthermore, Potter et al. and several other authors provided significant evidence that oxidative phosphorylation and a normal Krebs cycle persist in the vast majority malignant tumors, adding to the growing body of evidence that most cancers exhibit the Warburg effect while maintaining a proper mitochondrial respiration. Dang et al. in 2008 provided evidence that the tumor tissue sections used in Warburgs experiments should have been thinner for the oxygen diffusion constants employed, implying that the tissue slices studied were partially hypoxic and the calculated critical diffusion distance was of 470 micrometers. As a result, endless debates and discussions about Warburgs discovery took place and have piqued the interest of scientists all over the world, which has helped bring attention to cell metabolism in cancer and immune cells and the use of modern technology to discover what these pathways are and how they are modified as well as potential therapeutic targets. | 1 | Biochemistry |
Analytical light scattering (ALS), also loosely referred to as SEC-MALS, is the implementation of static light scattering (SLS) and dynamic light scattering (DLS) techniques in an online or flow mode. A typical ALS instrument consists of an HPLC/FPLC chromatography system coupled in-line with appropriate light scattering and refractive index detectors. The advantage of ALS over conventional steady-state light scattering methods is that it allows separation of molecules/macromolecules on a chromatography column prior to analysis with light scattering detectors. Accordingly, ALS enables one to determine hydrodynamic properties of a single monodisperse species as opposed to bulk or average measurements on a sample afforded by conventional light scattering. | 7 | Physical Chemistry |
Floral scent, or flower scent, is composed of all the volatile organic compounds (VOCs), or aroma compounds, emitted by floral tissue (e.g. flower petals). Other names for floral scent include, aroma, fragrance, floral odour or perfume. Flower scent of most flowering plant species encompasses a diversity of VOCs, sometimes up to several hundred different compounds. The primary functions of floral scent are to deter herbivores and especially folivorous insects (see Plant defense against herbivory), and to attract pollinators. Floral scent is one of the most important communication channels mediating plant-pollinator interactions, along with visual cues (flower color, shape, etc.). | 1 | Biochemistry |
Many PDRC thin films have been developed which have demonstrated very high solar reflectance and heat emittance. However, films with precise patterns or structures are not scalable "due to the cost and technical difficulties inherent in large-scale precise lithography," as per Khan et al., or "due to complex nanoscale lithography/synthesis and rigidity," as per Zhou et al.
The polyacrylate hydrogel film from the later study has broader applications, including potential uses in building construction and large-scale thermal management systems. This research focuses on a polyacrylate film developed for hybrid passive cooling. The film uses sodium polyacrylate, a low-cost industrial material, to achieve high solar reflectance and high mid-infrared emittance. A significant aspect of this material is its ability to absorb atmospheric moisture, enabling it to provide both radiative and evaporative cooling. This dual mechanism allows for efficient cooling even under varying atmospheric conditions, including high humidity or limited access to clear skies.
Some researchers have attempted to overcome this with various methods:
* Zhang et al. (2020), facile microstamping method film on low-cost polymer PDMS, solar reflectance 95%, heat emittance 96%, daytime temperature reduction up to 5.1 °C, "promising for scale-up production."
* Zhang et al. (2021), low-cost film developed with a phase inversion process using cellulose acetate and calcium silicate, solar reflectance 97.3%, heat emittance 97.2%, daytime temperature reduction up to 7.3 °C below ambient (average net cooling power of 90.7 W m), "a low-cost, scalable composite film with novel dendritic cell like structures," tested in Qingdao.
* Fan et al. (2022), eco-friendly preparation of superhydrophobic porous polydimethylsiloxane (PDMS) radiative cooling film, daytime temperature reduction up to 11.52 °C below ambient, "the film is promising to be widely used for long-term cooling for outdoor applications."
* Nie et al. (2022), composite film made of fluorine-free reagents and particles, solar reflectance 85%, heat emittance 95%, daytime temperature reduction average 12.2 °C, manufactured with "a simple preparation process, which has characteristics of low-cost environmental friendliness and excellent machinal durability," tested in Hubei.
* Zhong et al. (2023), hierarchical flexible fibrous cellulose (wood pulp) film, solar reflectance 93.8%, heat emittance 98.3%, daytime temperature reduction up to 11.3 °C below ambient, study is "the first time to realize high crystallinity and hierarchical microstructures in regenerated cellulose materials by the self-assembly of cellulose macromolecules at the molecular level," which "will provide new perspectives for the development of flexible cellulose materials." | 7 | Physical Chemistry |
Termination of elongation depends on eukaryotic release factors. The process is similar to that of bacterial termination, but unlike bacterial termination, there is a universal release factor, eRF1, that recognizes all three stop codons. Upon termination, the ribosome is disassembled and the completed polypeptide is released. eRF3 is a ribosome-dependent GTPase that helps eRF1 release the completed polypeptide. The human genome encodes a few genes whose mRNA stop codon are surprisingly leaky: In these genes, termination of translation is inefficient due to special RNA bases in the vicinity of the stop codon. Leaky termination in these genes leads to translational readthrough of up to 10% of the stop codons of these genes. Some of these genes encode functional protein domains in their readthrough extension so that new protein isoforms can arise. This process has been termed functional translational readthrough. | 1 | Biochemistry |
Translation initiation is the process by which the ribosome and its associated factors bind to an mRNA and are assembled at the start codon. This process is defined as either cap-dependent, in which the ribosome binds initially at the 5 cap and then travels to the stop codon, or as cap-independent, where the ribosome does not initially bind the 5 cap. | 1 | Biochemistry |
It is possible to modify Tebbe's reagent through the use of different ligands. This can alter the reactivity of the complex, allowing for a broader range of reactions. For example, cyclopropanation can be achieved using a chlorinated analogue. | 0 | Organic Chemistry |
Potassium ethyl xanthate (KEX) is an organosulfur compound with the chemical formula . It is a pale yellow powder that is used in the mining industry for the separation of ores. It is a potassium salt of ethyl xanthic acid. | 8 | Metallurgy |
When using different types of microspheres, SAT is capable of simultaneously testing multiple variables, such as DNA and proteins, in a given sample. This allows SAT to analyze variety of molecular targets during a single reaction. The common nucleic acid detection method includes direct DNA hybridization. The direct DNA hybridization approach is the simplest suspension array assay whereby 15 to 20 bp DNA oligonucleotides attached to microspheres are amplified using PCR. This is the optimized probe length as it minimizes the melting temperature variation among different probes during probe-target hybridization. After amplifying one DNA oligoprobe of interest, it can be used to create 100 different probes on 100 different sets of microspheres, each with the capability of capturing 100 potential targets (if using a 100-plex array). Similarly, target DNA samples are usually PCR amplified and labeled. Hybridization between the capture probe and the target DNA is achieved by melting and annealing complementary target DNA sequences to their capture probes located on the microspheres. After washing to remove non-specific binding between sequences, only strongly paired probe-targets will remain hybridized. | 1 | Biochemistry |
The idea for anti-Stokes cooling was first advanced by Pringsheim in 1929. While Doppler cooling lowers the translational temperature of a sample, anti-Stokes cooling decreases the vibrational or phonon excitation of a medium. This is accomplished by pumping a substance with a laser beam from a low-lying energy state to a higher one with subsequent emission to an even lower-lying energy state. The principal condition for efficient cooling is that the anti-Stokes emission rate to the final state be significantly larger than that to other states as well as the nonradiative relaxation rate. Because vibrational or phonon energy can be many orders of magnitude larger than the energy associated with Doppler broadening, the efficiency of heat removal per laser photon expended for anti-Stokes cooling can be correspondingly larger than that for Doppler cooling. The anti-Stokes cooling effect was first demonstrated by Djeu and Whitney in CO gas. The first anti-Stokes cooling in a solid was demonstrated by Epstein et al. in 1980, in a ytterbium doped fluoride glass sample.
Potential practical applications for anti-Stokes cooling of solids include radiation balanced solid state lasers and vibration-free optical refrigeration. | 7 | Physical Chemistry |
For a long time, cyanobacteria were considered incapable of performing non-photochemical quenching (NPQ) as a photoprotective mechanism, relying instead on a mechanism of energy redistribution between the two photosynthetic reaction centers, PSII and PSI, known as "state transitions".
OCP is found in a majority of cyanobacterial genomes, with remarkable conservation of its amino acid sequence, implying evolutionary constraints to preserve an important function. Mutant cells engineered to lack OCP photobleach under high light and become photoinhibited more rapidly under fluctuating light. Under nutrient stress conditions, which are expected to be norm in marine environments, photoprotective mechanisms such as OCP become important even at lower irradiances.
This protein is not found in chloroplasts, and appears to be specific to cyanobacteria. | 5 | Photochemistry |
Rare but severe diseases such as mitochondrial myopathies are associated with dysfunctional human ADP/ATP translocase. Mitochondrial myopathies (MM) refer to a group of clinically and biochemically heterogeneous disorders that share common features of major mitochondrial structural abnormalities in skeletal muscle. The major morphological hallmark of MM is ragged, red fibers containing peripheral and intermyofibrillar accumulations of abnormal mitochondria. In particular, autosomal dominant progressive external ophthalmoplegia (adPEO) is a common disorder associated with dysfunctional ADP/ATP translocase and can induce paralysis of muscles responsible for eye movements. General symptoms are not limited to the eyes and can include exercise intolerance, muscle weakness, hearing deficit, and more. adPEO shows Mendelian inheritance patterns but is characterized by large-scale mitochondrial DNA (mtDNA) deletions. mtDNA contains few introns, or non-coding regions of DNA, which increases the likelihood of deleterious mutations. Thus, any modification of ADP/ATP translocase mtDNA can lead to a dysfunctional transporter, particularly residues involved in the binding pocket which will compromise translocase efficacy. MM is commonly associated with dysfunctional ADP/ATP translocase, but MM can be induced through many different mitochondrial abnormalities. | 1 | Biochemistry |
The translational invariance of a crystal lattice is described by a set of unit cell, direct lattice basis vectors (contravariant or polar) called a, b, and c, or equivalently by the lattice parameters, i.e. the magnitudes of the vectors, called a, b and c, and the angles between them, called α (between b and c), β (between c and a), and γ (between a and b). Direct lattice vectors have components measured in distance units, like meters (m) or angstroms (Å).
A lattice vector is indexed by its coordinates in the direct lattice basis system and is generally placed between square brackets []. Thus a direct lattice vector , or , is defined as . Angle brackets ⟨⟩ are used to refer to a symmetrically equivalent class of lattice vectors (i.e. the set of vectors generated by an action of the lattice's symmetry group). In the case of a cubic lattice, for instance, ⟨100⟩ represents [100], [010], [001], [00], [00] and [00] because each of these vectors is symmetrically equivalent under a 90 degree rotation along an axis. A bar over a coordinate is equivalent to a negative sign (e.g., ).
The term "zone axis" more specifically refers to the direction of a direct-space lattice vector. For example, since the [120] and [240] lattice vectors are parallel, their orientations both correspond the ⟨120⟩ zone of the crystal. Just as a set of lattice planes in direct space corresponds to a reciprocal lattice vector in the complementary space of spatial frequencies and momenta, a "zone" is defined as a set of reciprocal lattice planes in frequency space that corresponds to a lattice vector in direct space.
The reciprocal space analog to a zone axis is a "lattice plane normal" or "g-vector direction". Reciprocal lattice vectors (one-form or axial) are Miller-indexed using coordinates in the reciprocal lattice basis instead, generally between round brackets () (similar to square brackets [] for direct lattice vectors). Curly brackets {} (not to be confused with a mathematical set) are used to refer to a symmetrically equivalent class of reciprocal lattice vectors, similar to angle brackets ⟨⟩ for classes of direct lattice vectors.
Here, , , and , where the unit cell volume is ( denotes a dot product and a cross product). Thus a reciprocal lattice vector or has a direction perpendicular to a crystallographic plane and a magnitude equal to the reciprocal of the spacing between those planes, measured in spatial frequency units, e.g. of cycles per angstrom (cycles/Å).
A useful and quite general rule of crystallographic "dual vector spaces in 3D", e.g. reciprocal lattices, is that the condition for a direct lattice vector [uvw] (or zone axis) to be perpendicular to a reciprocal lattice vector (hkl) can be written with a dot product as . This is true even if, as is often the case, the basis vector set used to describe the lattice is not Cartesian. | 3 | Analytical Chemistry |
m + n + o + p − q = 2 + 20 + 0 + 0 + 0 = 22 SEPs are required; 16 BH units provide 16 pairs; four shared boron atoms provide 6 pairs, which describes why is stable as a neutral species. | 7 | Physical Chemistry |
The production of trichloroacetonitrile by dehydration of trichloroacetamide was first described in 1873 by L. Bisschopinck at the Katholieke Universiteit Leuven.
Trichloroacetonitrile can be obtained by chlorination of acetonitrile on a zinc, copper and alkaline earth metal halide-impregnated activated carbon catalyst at 200–400 °C with a 54% yield.
The high temperatures required by this process favours the formation of byproducts, such as tetrachloromethane. In contrast, the chlorination of acetonitrile saturated with hydrogen chloride leads to pure trichloroacetonitrile even at 50–80 °C in good yields.
Like other halogenated acetonitriles, trichloroacetonitrile is produced from organic substances such as algae, humic acids and proteinaceous material in the disinfecting chlorination of water from natural sources. | 0 | Organic Chemistry |
Selecting an internal standard in inductively coupled plasma spectroscopy can be difficult, because signals from the sample matrix can overlap with those belonging to the analyte. Yttrium is a common internal standard that is naturally absent in most samples. It has both a mid-range mass and emission lines that don't interfere with many analytes. The intensity of the yttrium signal is what the signal from the analyte gets compared to.
In Inductively coupled plasma-mass spectrometry (ICP-MS), species with a similar mass to the analyte usually serve as good internal standards, though not in every case. Factors that also contribute to the effectiveness of an internal standard in ICP-MS include how close its ionization potential, change in enthalpy, and change in entropy are to the analyte.
Inductively coupled plasma-optical emission spectroscopy (ICP-OES) internal standards can be selected by observing how the analyte and internal standard signals change with varying experimental conditions. This includes making adjustments to the sample matrix or instrumentation settings and evaluating whether the selected internal standard is reacting in the same way the analyte is. | 3 | Analytical Chemistry |
Learning and memory have levels of permanence, differing from other mental processes such as thought, language, and consciousness, which are temporary in nature. Learning and memory can be either accumulated slowly (multiplication tables) or rapidly (touching a hot stove), but once attained, can be recalled into conscious use for a long time. Rats subjected to one instance of contextual fear conditioning create an especially strong long-term memory. At 24 hours after training, 9.17% of the genes in the genomes of rat hippocampus neurons were found to be differentially methylated. This included more than 2,000 differentially methylated genes at 24 hours after training, with over 500 genes being demethylated. Similar results to that in the rat hippocampus were also obtained in mice with contextual fear conditioning.
The hippocampus region of the brain is where contextual fear memories are first stored (see Figure), but this storage is transient and does not remain in the hippocampus. In rats contextual fear conditioning is abolished when the hippocampus is subjected to hippocampectomy just one day after conditioning, but rats retain a considerable amount of contextual fear when hippocampectomy is delayed by four weeks. In mice, examined at 4 weeks after conditioning, the hippocampus methylations and demethylations were reversed (the hippocampus is needed to form memories but memories are not stored there) while substantial differential CpG methylation and demethylation occurred in cortical neurons during memory maintenance. There were 1,223 differentially methylated genes in the anterior cingulate cortex (see Figure) of mice four weeks after contextual fear conditioning. Thus, while there were many methylations in the hippocampus shortly after memory was formed, all these hippocampus methylations were demethylated as soon as four weeks later.
Li et al. reported one example of the relationship between expression of a TET protein, demethylation and memory while using extinction training. Extinction training is the disappearance of a previously learned behavior when the behavior is not reinforced.
A comparison between infralimbic prefrontal cortex (ILPFC) neuron samples derived from mice trained to fear an auditory cue and extinction-trained mice revealed dramatic experience-dependent genome-wide differences in the accumulation of 5-hmC in the ILPFC in response to learning. Extinction training led to a significant increase in TET3 messenger RNA levels within cortical neurons. TET3 was selectively activated within the adult neo-cortex in an experience-dependent manner.
A short hairpin RNA (shRNA) is an artificial RNA molecule with a tight hairpin turn that can be used to silence target gene expression via RNA interference. Mice trained in the presence of TET3-targeted shRNA showed a significant impairment in fear extinction memory. | 1 | Biochemistry |
Wu Yundong () is a Chinese chemist. He is a theoretical organic chemist based in the Hong Kong University of Science and Technology and holds a concurrent position in Peking University. He was born 10 May 1957 in Liyang, Jiangsu, China. He graduated with a BS from Lanzhou University in 1982 and received his PhD in 1986 from the University of Pittsburgh, working with Kendall N. Houk in computational organic chemistry. He went on to become a research associate in University of California Los Angeles from 1989 to 1992, before beginning his independent research career in Hong Kong.
Professor Wu has received numerous awards in his career; in December 2005, he was elected as an Academician of the prestigious Chinese Academy of Sciences. His research interest focuses mainly on the elucidation of reaction mechanisms, protein-protein interactions/aggregations (Alzheimer's disease etc.) and conformational features of natural and unnatural peptides. | 0 | Organic Chemistry |
Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects.
Important concepts advanced by supramolecular chemistry include molecular self-assembly, molecular folding, molecular recognition, host–guest chemistry, mechanically-interlocked molecular architectures, and dynamic covalent chemistry. The study of non-covalent interactions is crucial to understanding many biological processes that rely on these forces for structure and function. Biological systems are often the inspiration for supramolecular research. | 6 | Supramolecular Chemistry |
The ndhF fragment has been a very useful tool in phylogenetic reconstruction at a number of taxonomic levels. | 5 | Photochemistry |
The rhodium-catalyzed hydroboration reaction is thought to be initiated with the dissociation of a triphenylphosphine from the Rh(I) centre. Oxidative addition of the B-H bond of the borane reagent to this 14 e species is then followed by coordination of the alkene to the 16e Rh(III) hydride complex. Subsequent migratory insertion of the alkene into the rhodium-hydride bond can give two regioisomeric alkyl rhodium(III) boride complexes. Reductive elimination of the boronate ester regenerates the catalyst. Catalyst prepared and handled under anaerobic condition reverses the selectivity to favor the secondary boronate ester. What has been debated is the coordination of the alkene. In the dissociative mechanism, proposed by Männig and Nöth, and supported by Evans and Fu the coordination is accompanied by the loss of one triphenylphosphine ligand.
In the associative mechanism (see below), proposed by Burgess et al., the alkene binds trans to the chloride without dissociation of a triphenylphosphine ligand. The mechanism has been studied by computational methods. Dorigo and Schleyer excluded the associative mechanism by an ab initio study on the dissociative mechanism, whereas Musaev and co-workers support the associative mechanism. | 0 | Organic Chemistry |
Resistance, , is proportional to the distance, , between the electrodes and is inversely proportional to the cross-sectional area of the sample, (noted on the Figure above). Writing (rho) for the specific resistance, or resistivity.
In practice the conductivity cell is calibrated by using solutions of known specific resistance, , so the individual quantities and need not be known precisely, but only their ratio. If the resistance of the calibration solution is , a cell-constant, defined as the ratio of and ( = ), is derived.
The specific conductance (conductivity), (kappa) is the reciprocal of the specific resistance.
Conductivity is also temperature-dependent.
Sometimes the conductance (reciprocical of the resistance) is denoted as = . Then the specific conductance (kappa) is: | 7 | Physical Chemistry |
Prigogine's theorem is a theorem of non-equilibrium thermodynamics, originally formulated by Ilya Prigogine.
The formulation of Prigogine's theorem is:
According to this theorem, the stationary state of a linear non-equilibrium system (under conditions that prevent the achievement of an equilibrium state) corresponds to the minimum entropy production. If there are no such obstacles, then the production of entropy reaches its absolute minimum - zero. A linear system means the fulfillment of linear phenomenological relationships between thermodynamic flows and driving forces. The coefficients of proportionality in the relationships between flows and driving forces are called phenomenological coefficients.
The theorem was proved by Prigogine in 1947 from the Onsager relations. Prigogines theorem is valid if the kinetic coefficients in the Onsager relations are constant (do not depend on driving forces and flows); for real systems, it is valid only approximately, so the minimum entropy production for a stationary state is not such a general principle as the maximum entropy for an equilibrium state. It has been experimentally established that Onsagers linear relations are valid in a fairly wide range of parameters for heat conduction and diffusion processes (for example, Fouriers law, Ficks law). For chemical reactions, the linear assumption is valid in a narrow region near the state of chemical equilibrium. The principle is also violated for systems odd with respect to time reversal. | 7 | Physical Chemistry |
pH is defined in terms of the activity of the hydrogen ion
:pH = −log {H}
In the approximation of ideal behaviour, activity is replaced by concentration. pH is measured by means of a glass electrode, a mixed equilibrium constant, also known as a Brønsted constant, may result.
:HL L + H;
It all depends on whether the electrode is calibrated by reference to solutions of known activity or known concentration. In the latter case the equilibrium constant would be a concentration quotient. If the electrode is calibrated in terms of known hydrogen ion concentrations it would be better to write p[H] rather than pH, but this suggestion is not generally adopted. | 7 | Physical Chemistry |
An E1 elimination occurs when a proton adjacent to a positive charge leaves and generates a double bond.
Because initial formation of a cation is necessary for E1 reactions to occur, E1 reactions are often observed as side reactions to S1 mechanisms.
E1 eliminations proceed with the Elimination of a leaving group leading to the E designation. Because this mechanism proceeds with the initial dissociation of a single starting material forming a carbocation, this process is considered a uni-molecular reaction. The involvement of only 1 species in the initial phase of the reaction enhances the mechanistic designation to E1. | 0 | Organic Chemistry |
Threading bases structural modeling on fold similarities rather than sequence identity. This method may help identify distantly related proteins and can be used to infer molecular functions. | 1 | Biochemistry |
Fetal alcohol spectrum disorder (FASD), formerly referred to as fetal alcohol syndrome, presents as craniofacial malformations, neurobehavioral disorders and mental disabilities, all attributed to exposing human embryos to alcohol during fetal development. The risk of FASD depends on the amount consumed, the frequency of consumption, and the points in pregnancy at which the alcohol is consumed. Ethanol is a known teratogen, i.e., causes birth defects. Ethanol is metabolized by alcohol dehydrogenase enzymes into acetaldehyde. The subsequent oxidation of acetaldehyde into acetate is performed by aldehyde dehydrogenase enzymes. Given that retinoic acid (RA) regulates numerous embryonic and differentiation processes, one of the proposed mechanisms for the teratogenic effects of ethanol is a competition for the enzymes required for the biosynthesis of RA from vitamin A. Animal research demonstrates that in the embryo, the competition takes place between acetaldehyde and retinaldehyde for aldehyde dehydrogenase activity. In this model, acetaldehyde inhibits the production of retinoic acid by retinaldehyde dehydrogenase. Ethanol-induced developmental defects can be ameliorated by increasing the levels of retinol, retinaldehyde, or retinaldehyde dehydrogenase. Thus, animal research supports the reduction of retinoic acid activity as an etiological trigger in the induction of FASD. | 1 | Biochemistry |
Yttria-stabilized zirconia (YSZ) is a ceramic in which the cubic crystal structure of zirconium dioxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO) and "yttria" (YO), hence the name. | 7 | Physical Chemistry |
A variety of mechanical adaptations, such as tip geometry and surface roughness, to aid in neural implant design have been investigated and implemented in recent years. The geometry of an electrode affects the shape of the electric field emitted. The electric field shape, in turn, affects the current density produced by the electrode. Determining optimum surface roughness for neural implants proves to be a challenging topic. Smooth surfaces may be preferable to rougher ones as they may decrease the likelihood of bacterial adsorption and infection. Smooth surfaces would also make it more difficult for the initiation of a corrosion cell. However, creating a rougher, porous surface, may prove beneficial for at least two reasons: decreased potential polarization at the electrode surface as a result of increased surface area and decreased current density, and a decrease in fibrous tissue encapsulation thickness due to opportunity for tissue ingrowth. It has been determined that if interconnected pores with sizes between 25 and 150 micrometers, ingrowth of tissue can occur and can decrease the exterior tissue encapsulation thickness by a factor of approximately 10 (compared to a smooth electrode such as polished platinum-iridium). | 7 | Physical Chemistry |
His group has also been involved in the development of a novel technique: Laser Vaporization Controlled Condensation (LVCC) for the synthesis of a variety of semiconductor, metal and metal oxide nanoparticles. His research lab is currently focused on the applications of graphene in heterogeneous catalysis and energy conversion, and he developed novel microwave and laser methods for the synthesis of nanoparticle catalysts supported on graphene. The recent discovery of efficient photo-thermal energy conversion by graphene-based materials by El-Shall's group has resulted in the development of new materials for efficient solar water desalination and the removal of heavy metals from contaminated water. | 7 | Physical Chemistry |
Leukocytes or white blood cells destroy abnormal cells and also provide protection against bacteria and other foreign matter. These interactions are transitory in nature but are crucial as an immediate immune response. To fight infection, leukocytes must move from the blood into the affected tissues. This movement into tissues is called extravasation. It requires successive forming and breaking of cell-cell interactions between the leukocytes and the endothelial cells that line blood vessels. These cell-cell interactions are mediated mainly by a group of Cell Adhesion Molecules (CAMs) called selectins.
T helper cells, central to the immune system, interact with other leukocytes by releasing signals known as cytokines which activate and stimulate the proliferation of B cells and killer T cells. T helper cells also directly interact with macrophages, cells that engulf foreign matter and display antigens on its surface. T-helper cells that possess the appropriate receptors can bind to these antigens and proliferate resulting in T-helper cells that have the ability to identify the same antigens. | 1 | Biochemistry |
Human genes encoding KRAB-ZFPs include KOX1/ZNF10, KOX8/ZNF708, ZNF43, ZNF184, ZNF91, HPF4, HTF10 and HTF34. | 1 | Biochemistry |
Liquefaction processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), or for the storage of gases, for example: LPG, and in refrigeration and air conditioning. There the gas is liquefied in the condenser, where the heat of vaporization is released, and evaporated in the evaporator, where the heat of vaporization is absorbed. Ammonia was the first such refrigerant, and is still in widespread use in industrial refrigeration, but it has largely been replaced by compounds derived from petroleum and halogens in residential and commercial applications.
Liquid oxygen is provided to hospitals for conversion to gas for patients with breathing problems, and liquid nitrogen is used in the medical field for cryosurgery, by inseminators to freeze semen, and by field and lab scientists to preserve samples. Liquefied chlorine is transported for eventual solution in water, after which it is used for water purification, sanitation of industrial waste, sewage and swimming pools, bleaching of pulp and textiles and manufacture of carbon tetrachloride, glycol and numerous other organic compounds as well as phosgene gas.
Liquefaction of helium (He) with the precooled Hampson–Linde cycle led to a Nobel Prize for Heike Kamerlingh Onnes in 1913. At ambient pressure the boiling point of liquefied helium is . Below 2.17 K liquid He becomes a superfluid (Nobel Prize 1978, Pyotr Kapitsa) and shows characteristic properties such as heat conduction through second sound, zero viscosity and the fountain effect among others.
The liquefaction of air is used to obtain nitrogen, oxygen, and argon and other atmospheric noble gases by separating the air components by fractional distillation in a cryogenic air separation unit. | 7 | Physical Chemistry |
In an early example of the use of a chiral auxiliary in asymmetric synthesis, E. J. Corey and coworkers conducted an asymmetric Diels-Alder reaction between (−)-8-phenylmenthol acrylate ester and 5-benzyloxymethylcyclopentadiene. The cycloaddition product was carried forward to the iodolactone shown below, an intermediate in the classic Corey synthesis of the prostaglandins. It is proposed that the back face of the acrylate is blocked by the auxiliary, so that cycloaddition occurs at the front face of the alkene.
(−)-8-phenylmenthol can be prepared from either enantiomer of pulegone,
though neither route is very efficient. Because of the widespread utility of the 8-phenylmenthol auxiliary, alternative compounds that are more easily synthesized, such as trans-2-phenyl-1-cyclohexanol
and trans-2-(1-pheyl-1-methylethyl)cyclohexanol have been explored. | 4 | Stereochemistry |
This proof of the Hellmann–Feynman theorem requires that the wave function be an eigenfunction of the Hamiltonian under consideration; however, it is also possible to prove more generally that the theorem holds for non-eigenfunction wave functions which are stationary (partial derivative is zero) for all relevant variables (such as orbital rotations). The Hartree–Fock wavefunction is an important example of an approximate eigenfunction that still satisfies the Hellmann–Feynman theorem. Notable example of where the Hellmann–Feynman is not applicable is for example finite-order Møller–Plesset perturbation theory, which is not variational.
The proof also employs an identity of normalized wavefunctions – that derivatives of the overlap of a wave function with itself must be zero. Using Dirac's bra–ket notation these two conditions are written as
The proof then follows through an application of the derivative product rule to the expectation value of the Hamiltonian viewed as a function of : | 6 | Supramolecular Chemistry |
Many agrochemicals are toxic, and agrichemicals in bulk storage may pose significant environmental and/or health risks, particularly in the event of accidental spills. In many countries, use of agrichemicals is highly regulated. Government-issued permits for purchase and use of approved agrichemicals may be required. Significant penalties can result from misuse, including improper storage resulting in spillage. On farms, proper storage facilities and labeling, emergency clean-up equipment and procedures, and safety equipment and procedures for handling, application and disposal are often subject to mandatory standards and regulations. Usually, the regulations are carried out through the registration process.
For instance, bovine somatotropin, though widely used in the United States, is not approved in Canada and some other jurisdictions as there are concerns for the health of cows using it. | 2 | Environmental Chemistry |
Dna2 endonuclease does not have a specific structure and their properties are not well characterized, but could be referred as single-stranded DNA with free ends (ssDNA). Dna2 endonuclease is essential to cleave long DNA flaps that leave FEN1 during the Okazaki Process. Dna2 endonuclease is responsible for the removal of the initiator RNA segment on Okazaki Fragments. Also, Dna2 endonuclease has a pivotal role in the intermediates created during diverse DNA metabolisms and is functional in telomere maintenance.
Dna2 endonuclease becomes active when a terminal RNA segment attaches at the 5’ end, because it translocates in the 5’ to 3’ direction. In the presence of a single stranded DNA-binding protein RPA, the DNA 5 flaps become too long, and the nicks no longer fit as substrate for FEN1. This prevents the FEN1 from removing the 5′-flaps. Thus, Dna2s role is to reduce the 3′ end of these fragments, making it possible for FEN1 to cut the flaps, and the Okazaki fragment maturation more efficient. During the Okazaki Process, Dna2 helicase and endonuclease are inseparable. Dna2 Endonuclease does not depend on the 5’-tailed fork structure of its activity. Unproductive binding has been known to create blocks to FEN1 cleavage and tracking. It is known that ATP reduces activity, but promotes the release of the 3’-end label. Studies have suggested that a new model of Dna2 Endonuclease and FEN1 are partially responsible in Okazaki fragment maturation. | 1 | Biochemistry |
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