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DEAD is a reagent in the Mitsunobu reaction where it forms an adduct with phosphines (usually triphenylphosphine) and assists the synthesis of esters, ethers, amines and thioethers from alcohols. Reactions normally result in the inversion of molecular symmetry.
DEAD was used in the original 1967 article by Oyo Mitsunobu, and his 1981 review on the use of diethyl azodicarboxylate is a top-cited chemistry article. The Mitsunobu reaction has several applications in the synthesis of natural products and pharmaceuticals.
In the above reaction, which is assisted either by DEAD or DIAD (diisopropyl azodicarboxylate), thymidine 1 transforms to the derivative 2. The latter easily converts to zidovudine 4 (also known as azidothymidine or AZT), an important antiviral drug, used among others in the treatment of AIDS. Another example of pharmaceutical application of DEAD-assisted Mitsunobu reaction is the synthesis of bis[(pivaloyloxy)methyl [PIVz] derivative of 2-deoxy-5-fluorouridine 5-monophosphate (FdUMP), which is a potent antitumor agent. | 0 | Organic Chemistry |
Radiofrequency (RF) induced evaporative cooling is the most common method for evaporatively cooling atoms in a magneto-optical trap (MOT). Consider trapped atoms laser cooled on a |F=0 |F=1 transition. The magnetic sublevels of the |F=1 state (|m= -1,0,1) are degenerate for zero external field. The confining magnetic quadrupole field, which is zero at the center of the trap and nonzero everywhere else, causes a Zeeman shift in atoms which stray from the trap center, lifting the degeneracy of the three magnetic sublevels. The interaction energy between the total spin angular momentum of the trapped atom and the external magnetic field depends on the projection of the spin angular momentum onto the z-axis, and is proportional toFrom this relation it can be seen that only the |m=-1 magnetic sublevel will have a positive interaction energy with the field, that is to say, the energy of atoms in this state increases as they migrate from the trap center, making the trap center a point of minimum energy, the definition of a trap. Conversely, the energy of the |m=0 state is unchanged by the field (no trapping), and the |m=1 state actually decreases in energy as it strays from the trap center, making the center a point of maximum energy. For this reason |m=-1 is referred to as the trapping state, and |m=0,1 the non-trapping states.
From the equation for the magnetic field interaction energy, it can also be seen that the energies of the |m=1,-1 states shift in opposite directions, changing the total energy difference between these two states. The |m=-1|m=1 transition frequency therefore experiences a Zeeman shift. With this in mind, the RF evaporative cooling scheme works as follows: the size of the Zeeman shift of the -1+1 transition depends on the strength of the magnetic field, which increases radially outward from the trap center. Those atoms which are coldest move within a small region around the trap center, where they experience only a small Zeeman shift in the -1+1 transition frequency. Warm atoms, however, spend time in regions of the trap much further from the center, where the magnetic field is stronger and the Zeeman shift therefore larger. The shift induced by magnetic fields on the scale used in typical MOTs is on the order of MHz, so that a radiofrequency source can be used to drive the -1+1 transition. The choice of frequency for the RF source corresponds to a point on the trapping potential curve at which atoms experience a Zeeman shift equal to the frequency of the RF source, which then drives the atoms to the anti-trapping |m=1 magnetic sublevel and immediately exits the trap. Lowering the RF frequency is therefore equivalent to lowering the dashed line in the figure, effectively reducing the depth of the potential well. For this reason the RF source used to remove these energetic atoms is often referred to as an "RF knife," as it effectively lowers the height of the trapping potential to remove the most energetic atoms from the trap, "cutting" away the high energy tail of the trap's energy distribution. This method was famously used to cool a cloud of rubidium atoms below the condensation critical temperature to form the first experimentally observed Bose-Einstein condensate (BEC) | 7 | Physical Chemistry |
Vat level and drum speed are the two basic operating parameters for any rotary vacuum drum filter. These parameters are adjusted dependently to each other to optimize the filtration performance.
Valve level determines the proportion filter cycle in the filter. The filter cycle consist of the filter drum rotation, release of cake formation from slurry and the drying period for the cake formation shown in figure 1. By default, operate the vat at its maximum level to maximise the rate of filtration. Reduce vat level if discharged solid is in the form of thin and slimy cake or if the discharged solid is very thick.
Decrease in the vat level eventually leads to a decrease in the portion of the drum being submerge under the slurry, more surface exposure for the cake dying surface hence, larger cake formation to dry time ratio. This result in less moisture content of formed solid and lessen the thickness of the form solid. In addition to operating at lower vat level, the flow rate per drum revolution decreases and ultimately thinner cake formation occurs. In the case of pre coat discharge the filter aid efficiency increases.
Drum speed is the driving factor for the filter output and its units is in the form of minutes per drum revolution. At steady operating conditions, adjusting the drum speed gives a proportional relationship with the filter throughput as shown as in figure 2. | 3 | Analytical Chemistry |
Unable to pursue his career, Schwab emigrated from Nazi Germany to Greece in 1939, He and Elly married in Athens in the same year. With the connections of his wife, both started research work in the industrial chemistry laboratory of the recently founded Kanellopoulos Institute of Chemistry and Agriculture in Piraeus.
For the following years he spent in Greece, Schwab (known in Greek as Γεώργιος Σβαμπ, ) came to view Greece as "his second fatherland".
While in the Kanellopoulos Institute, a sui generis research institution for contemporary Greece, he was allowed to pursue purely scientific work; indeed Schwab had a fruitful 11-year stay marked by a series of incidental discoveries as well as systematic studies continuing his previous work on catalysis.
Schwab was in a difficult situation during the Axis occupation of Greece, when he once again faced danger from the German occupying forces due to his Jewish background. In 1942, the German authorities refused to renew his German passport. Georg-Maria escaped the fate of his brother, Josef-Maria Schwab – who died as a forced labourer in Organisation Todt, by keeping a low profile in Greece and getting an exemption from the 1943 order for German citizens to return to Germany with the help of an official at the German Embassy in Athens.
After the liberation of Greece (1944), Schwab was able to resume his research at the Kanellopoulos Institute, until he was offered the Professorship of Physical Chemistry at the Technical University of Athens in 1949. He kept the position and taught the subject for the next 10 years. | 7 | Physical Chemistry |
Complementarity allows information found in DNA or RNA to be stored in a single strand. The complementing strand can be determined from the template and vice versa as in cDNA libraries. This also allows for analysis, like comparing the sequences of two different species. Shorthands have been developed for writing down sequences when there are mismatches (ambiguity codes) or to speed up how to read the opposite sequence in the complement (ambigrams). | 1 | Biochemistry |
In vertebrates, the region of the mRNA that codes for the signal peptide (i.e. the signal sequence coding region, or SSCR) can function as an RNA element with specific activities. SSCRs promote nuclear mRNA export and the proper localization to the surface of the endoplasmic reticulum. In addition SSCRs have specific sequence features: they have low adenine-content, are enriched in certain motifs, and tend to be present in the first exon at a frequency that is higher than expected. | 1 | Biochemistry |
Selected area (electron) diffraction (abbreviated as SAD or SAED) is a crystallographic experimental technique typically performed using a transmission electron microscope (TEM). It is a specific case of electron diffraction used primarily in material science and solid state physics as one of the most common experimental techniques. Especially with appropriate analytical software, SAD patterns (SADP) can be used to determine crystal orientation, measure lattice constants or examine its defects. | 3 | Analytical Chemistry |
In one dimension, a differential form
is exact if and only if has an antiderivative (but not necessarily one in terms of elementary functions). If has an antiderivative and let be an antiderivative of so , then obviously satisfies the condition for exactness. If does not have an antiderivative, then we cannot write with for a differentiable function so is inexact. | 7 | Physical Chemistry |
More complex rate laws have been described as being mixed order if they approximate to the laws for more than one order at different concentrations of the chemical species involved. For example, a rate law of the form represents concurrent first order and second order reactions (or more often concurrent pseudo-first order and second order) reactions, and can be described as mixed first and second order. For sufficiently large values of [A] such a reaction will approximate second order kinetics, but for smaller [A] the kinetics will approximate first order (or pseudo-first order). As the reaction progresses, the reaction can change from second order to first order as reactant is consumed.
Another type of mixed-order rate law has a denominator of two or more terms, often because the identity of the rate-determining step depends on the values of the concentrations. An example is the oxidation of an alcohol to a ketone by hexacyanoferrate (III) ion [Fe(CN)] with ruthenate (VI) ion (RuO) as catalyst. For this reaction, the rate of disappearance of hexacyanoferrate (III) is
This is zero-order with respect to hexacyanoferrate (III) at the onset of the reaction (when its concentration is high and the ruthenium catalyst is quickly regenerated), but changes to first-order when its concentration decreases and the regeneration of catalyst becomes rate-determining.
Notable mechanisms with mixed-order rate laws with two-term denominators include:
* Michaelis-Menten kinetics for enzyme-catalysis: first-order in substrate (second-order overall) at low substrate concentrations, zero order in substrate (first-order overall) at higher substrate concentrations; and
* the Lindemann mechanism for unimolecular reactions: second-order at low pressures, first-order at high pressures. | 7 | Physical Chemistry |
* Respiratory tract infections (such as tonsillitis, pharyngitis, and lobar pneumonia) caused by group A beta-hemolytic streptococci and S. pneumoniae (formerly D. pneumonia).
* Otitis media caused by group A beta-hemolytic streptococci, S. pneumoniae, H. influenzae, and staphylococci.
* Skin and skin structure infections caused by staphylococci (penicillin-susceptible and penicillin-resistant) and beta-hemolytic streptococci.
* Urinary tract infections, including prostatitis, caused by E. coli, P. mirabilis and Klebsiella species. | 4 | Stereochemistry |
Unsuccessful transfer or abortive transfer is any bacterial DNA transfer from donor cells to recipient cells that fails to survive transduction and conjugation. In all cases, the transferred fragment could be diluted during the proliferation phase. Failures in the integration of the transferred DNA in the genetic material of the recipient cells may be due to:
*Failure of the incoming DNA to form a circular molecule;
*Post-circularisation, the circular molecule is wrong for maintenance, making this transfer occurs as plasmids. Genes that are located on the corresponding part of the DNA can express in the recipient cells. | 1 | Biochemistry |
Deviations from ideality can be described by the use of Margules functions or activity coefficients. A single Margules parameter may be sufficient to describe the properties of the solution if the deviations from ideality are modest; such solutions are termed regular.
In contrast to ideal solutions, where volumes are strictly additive and mixing is always complete, the volume of a non-ideal solution is not, in general, the simple sum of the volumes of the component pure liquids and solubility is not guaranteed over the whole composition range. By measurement of densities, thermodynamic activity of components can be determined. | 7 | Physical Chemistry |
The Historical Metallurgy Society is a British learned society providing an international forum for exchange of information and research in historical metallurgy. It was founded as the Historical Metallurgy Group in 1963. All aspects of the history of metals and associated materials are covered from prehistory to the present, from processes and production through technology and economics to archaeology and conservation.
The Historical Metallurgy Society origins were partly a response to the damage and destruction of many historically important metallurgical sites. Conservation, research and protection remain important parts of the society’s role.
Each year the society holds a two-day conference (usually in the United Kingdom) with a program of papers covering a particular area of metallurgical interest. In addition to this, it also runs other day meetings.
The Historical Metallurgy Society publishes Historical Metallurgy an internationally recognised peer-reviewed journal, published annually in two parts. The society also issues a newsletter The Crucible three times a year, and has published edited collections based on the papers given at several of its conferences in an Occasional Papers series.
The Historical Metallurgy Society is a company limited by guarantee (no. 1442508) and a registered charity (no. 279314). | 8 | Metallurgy |
VMAT research began in 1958 when Nils-Åke Hillarp discovered secretory vesicles. In the 1970s, scientists like Arvid Carlsson recognized the need to understand how transport systems and ion gradients work in different organisms in order to explore new treatment options such as reserpine (RES). Researchers discovered inhibitors that blocked the uptake of neurotransmitters into vesicles, suggesting the existence of VMATs. A decade later, molecular genetic tools have improved methods for protein identification. Scientists have used these tools to analyze DNA and amino acid sequences, and discovered that transporters in bacteria and humans were very similar, which emphasized the importance and universality of transporters. The transporters were first structurally identified by cloning VMATs in rats. The VMAT were first isolated and purified in bovine chromaffin granules, in both its native and denatured forms. | 1 | Biochemistry |
The complex is commercially available but can also be generated by the dissolution of diborane in THF. Alternatively, it can be prepared by the oxidation of sodium borohydride with iodine in THF.
The complex can reduce carboxylic acids to alcohols and is a common route for the reduction of amino acids to amino alcohols (e.g. valinol). It adds across alkenes to give organoboron compounds that are useful intermediates. The following organoboron reagents are prepared from borane-THF: [[9-Borabicyclo(3.3.1)nonane|9-borabicyclo[3.3.1]nonane]], Alpine borane, diisopinocampheylborane. It is also used as a source of borane (BH) for the formation of adducts. | 0 | Organic Chemistry |
If homopolymer repeats of the same nucleotide (e.g. ) are present on the template strand (strand to be sequenced) then multiple introduced nucleotides are incorporated and more hydrogen ions are released in a single cycle. This results in a greater pH change and a proportionally greater electronic signal. This is a limitation of the system in that it is difficult to enumerate long repeats. This limitation is shared by other techniques that detect single nucleotide additions such as pyrosequencing. Signals generated from a high repeat number are difficult to differentiate from repeats of a similar but different number; e.g., homorepeats of length 7 are difficult to differentiate from those of length 8.
Another limitation of this system is the short read length compared to other sequencing methods such as Sanger sequencing or pyrosequencing. Longer read lengths are beneficial for de novo genome assembly. Ion Torrent semiconductor sequencers produce an average read length of approximately 400 nucleotides per read.
The throughput is currently lower than that of other high-throughput sequencing technologies, although the developers hope to change this by increasing the density of the chip. | 1 | Biochemistry |
Much of the development of 3D optical data storage has been carried out in universities. The groups that have provided valuable input include:
*Peter T. Rentzepis was the originator of this field, and has recently developed materials free from destructive readout.
*Watt W. Webb codeveloped the two-photon microscope in Bell Labs, and showed 3D recording on photorefractive media.
*Masahiro Irie developed the diarylethene family of photochromic materials.
*Yoshimasa Kawata, Satoshi Kawata, and Zouheir Sekkat have developed and worked on several optical data manipulation systems, in particular involving poled polymer systems.
*Kevin C Belfield is developing photochemical systems for 3D optical data storage by the use of resonance energy transfer between molecules, and also develops high two–photon cross-section materials.
*Seth Marder performed much of the early work developing logical approaches to the molecular design of high two–photon cross-section chromophores.
*Tom Milster has made many contributions to the theory of 3D optical data storage.
*Robert McLeod has examined the use of microholograms for 3D optical data storage.
*Min Gu has examined confocal readout and methods for its enhancement. | 5 | Photochemistry |
Exemestane is known chemically as 6-methylideneandrosta-1,4-diene-3,17-dione. Like the aromatase inhibitors formestane and atamestane, exemestane is a steroid that is structurally similar to 4-androstenedione, the natural substrate of aromatase. It is distinguished from the natural substance only by the methylidene group in position 6 and an additional double bond in position 1.
Pure exemestane is a white to off-white powder that is soluble in DMSO to at least 20 mg/mL. Optical rotation [α] is +250 to 300° (per g/100 cm and decimetre at 589 nm wavelength). | 4 | Stereochemistry |
Glyceraldehyde-3-phosphate can double up to form larger sugar molecules like glucose and fructose. These molecules are processed, and from them, the still larger sucrose, a disaccharide commonly known as table sugar, is made, though this process takes place outside of the chloroplast, in the cytoplasm.
Alternatively, glucose monomers in the chloroplast can be linked together to make starch, which accumulates into the starch grains found in the chloroplast.
Under conditions such as high atmospheric CO concentrations, these starch grains may grow very large, distorting the grana and thylakoids. The starch granules displace the thylakoids, but leave them intact.
Waterlogged roots can also cause starch buildup in the chloroplasts, possibly due to less sucrose being exported out of the chloroplast (or more accurately, the plant cell). This depletes a plant's free phosphate supply, which indirectly stimulates chloroplast starch synthesis.
While linked to low photosynthesis rates, the starch grains themselves may not necessarily interfere significantly with the efficiency of photosynthesis, and might simply be a side effect of another photosynthesis-depressing factor. | 5 | Photochemistry |
NAPPA uses DNA template that has already been immobilized onto the same protein capture surface. The DNA template is biotinylated and is bound to avidin that is pre-coated onto the protein capture surface. Newly synthesized proteins which are tagged with GST are then immobilized next to the template DNA by binding to the adjacent polyclonal anti-GST capture antibody that is also pre-coated onto the capture surface. The main drawback of this method is the extra and tedious preparation steps at the beginning of the process: (1) the cloning of cDNAs in an expression-ready vector; and (2) the need to biotinylate the plasmid DNA but not to interfere with transcription. Moreover, the resulting protein array is not ‘pure’ because the proteins are co-localized with their DNA templates and capture antibodies. | 1 | Biochemistry |
Acetyl-CoA is a metabolic intermediate that is involved in many metabolic pathways in an organism. It is produced during the breakdown of glucose, fatty acids, and amino acids, and is used in the synthesis of many other biomolecules, including cholesterol, fatty acids, and ketone bodies. Acetyl-CoA is also a key molecule in the citric acid cycle, which is a series of chemical reactions that occur in the mitochondria of cells and is responsible for generating energy in the form of ATP.
In addition, acetyl-CoA is a precursor for the biosynthesis of various acetyl-chemicals, acting as an intermediate to transfer an acetyl group during the biosynthesis of those acetyl-chemicals. Acetyl-CoA is also involved in the regulation of various cellular mechanisms by providing acetyl groups to target amino acid residues for post-translational acetylation reactions of proteins. | 1 | Biochemistry |
The first metal carbene complex to have been reported was Chugaev's red salt, first synthesized as early as 1925, although it was never identified to be a carbene complex. The characterization of (CO)5W(COCH3(Ph)) in the 1960s is often cited as the starting point of the area and Ernst Otto Fischer, for this and other achievements in organometallic chemistry, was awarded the 1973 Nobel Prize in Chemistry. In 1968, Hans-Werner Wanzlick and Karl Öfele separately reported metal-bonded N-heterocyclic carbenes. The synthesis and characterization of ((CH)CCH)Ta=CHC(CH) by Richard R. Schrock in 1974 marked the first metal alkylidene complex. In 1991, Anthony J. Arduengo synthesized and crystallized the first persistent carbene, an NHC with large adamantane alkyl groups, accelerating the field of N-heterocarbene ligands to its current use. | 0 | Organic Chemistry |
Nowadays, several Calphad softwares are available - in a framework of computational thermodynamics - to simulate solidification in systems with more than two components; these have recently been defined as Calphad Tools for the Metallurgy of Solidification. In recent years, Calphad-based methodologies have reached maturity in several important fields of metallurgy, and especially in solidification-related processes such as semi-solid casting, 3d printing, and welding, to name a few. While there are important studies devoted to the progress of Calphad methodology, there is still space for a systematization of the field, which proceeds from the ability of most Calphad-based software to simulate solidification curves and includes both fundamental and applied studies on solidification, to be substantially appreciated by a wider community than today. The three applied fields mentioned above could be widened by specific successful examples of simple modeling related to the topic of this issue, with the aim of widening the application of simple and effective tools related to Calphad and Metallurgy. See also "Calphad Tools for the Metallurgy of Solidification" in an ongoing issue of an Open Journal. https://www.mdpi.com/journal/metals/special_issues/Calphad_Solidification
Given a specific chemical composition, using a software for computational thermodynamics - which might be open or commercial - the calculation of the Scheil curve is possible if a thermodynamic database is available. A good point in favour of some specific commercial softwares is that the install is easy indeed and you can use it on a windows based system - for instance with students or for self training.
One should get some open, chiefly binary, databases (extension *.tdb), one could find - after registering - at Computational Phase Diagram Database (CPDDB) of the National Institute for Materials Science of Japan, NIMS https://cpddb.nims.go.jp/index_en.html. They are available - for free - and the collection is rather complete; in fact currently 507 binary systems are available in the thermodynamic data base (tdb) format.
Some wider and more specific alloy systems partly open - with tdb compatible format - are available with minor corrections for Pandat use at Matcalc https://www.matcalc.at/index.php/databases/open-databases. | 8 | Metallurgy |
The asymmetric cyanohydrin reaction of benzaldehyde with trimethylsilylcyanide is made possible by employment of (R)-Binol at 1–10% catalyst loading. This ligand firsts reacts with a lithium alkoxy compound to form a lithium binaphtholate Complex.
The chemist Urech in 1872 was the first to synthesize cyanohydrins from ketones with alkali cyanides and acetic acid and therefore this reaction also goes by the name of Urech cyanohydrin method. | 0 | Organic Chemistry |
Δ-capnellene, also referred to simply as capnellene in the literature, is a monounsaturated hydrocarbon of the molecular formula CH. It features a tricyclic skeleton, a geminal dimethyl group, a tertiary methyl group, and an exocyclic methylene group.
Capnellene is also a sesquiterpene, a class of terpenes that are natural semiochemicals. However, it is a non-isoprenoid sesquiterpene, meaning that unlike most sesquiterpenes its structure is not based on a repeated isoprene unit. Capnellene is the presumed biosynthetic precursor to the capnellanols, a group of alcohols based on the capnellene skeleton that are also produced by Capnella imbricata, however the biosynthesis of these compounds has not yet been elucidated. | 0 | Organic Chemistry |
Richmond, located in the San Francisco Bay Area, is an evolving, multi-cultural community that has transformed itself from an over-polluted industrial town to a pioneer in an environmental justice movement. The city has been host to numerous oil refineries, including the Chevron Corporation refinery, which opened in 1901 under the ownership of Pacific Coast Oil. The Chevron Refinery is a leading source of air quality violations in the state of California. Richmond residents are also exposed to pollution from the Santa Fe train line and the presence of heavy traffic and diesel trucks along the Richmond Parkway. However, residents are most concerned with air pollution health impacts from the Chevron Refinery. In 1999, Richmond measure significantly higher on Air Quality Indices (AQI) (an indicator of how polluted is air is) compared to national level. Air pollution emission from the Chevron refinery includes benzene, ethylbenzene, toluene, xylene, nitrous dioxide, and sulfur dioxide, which are known to cause elevated cancer risks and respiratory illness. Rates of child and adult asthma are especially elevated among Richmond residents.
Richmond residents have struggled to improve local air quality. The city has a significant non-white, low-income population. According to 2010 U.S. Census, of Richmond's 103,701 person populations, “one in six residents lives below the federal poverty level, and more than eight in 10 are people of color. In North Richmond, next to one of the nation’s largest refineries, 97 percent of residents are non-white and nearly one in four live in poverty”. Low-income communities have differential access to political power, and their collective political voice is often less able to contest decisions impacting industrial operations. The combination of poverty, poor access to clean air, and poor political power can result in inequality in which communities of color bear a disproportionate burden of pollution and, therefore, suffer from greater environmental health risks.
Because Richmond is an air pollution hotspot, Richmond residents have applied different strategies since the 1980s to try to improve local air quality. The first EJ movement in the area started in the late 1980s, when the activist tried to stop construction of a garbage incinerator near North Richmond. Sixteen years later, local citizen utilizes “Bucket Brigades” to document a handful of criteria air pollutants such as sulfur dioxide (SO), carbon monoxide (CO), nitrogen dioxide (NO), and ozone (O).This study involves citizens to actively collecting the samples of emissions from Chevron's refineries, especially during accidents, fires, leaks, and explosions. The “sniffers” alert the “samplers” to collect the air samples when they notice a problem. The “samplers” then contact the Coordinator to check the bucket and perform the paperwork before submitting the samples to the Laboratory, in which the results will be reported to CBE, an environmental justice organization. The “Bucket Brigades” did not only raise the awareness local citizens to fight against the air pollution in their area but also their participation.
As the number of activists and participants grew in numbers, their position in the battle against environmental injustice was further fortified with the election Green-party mayor of Richmond, Gayle McLaughlin, as well as three new council members sympathetic to their cause in 2008. In July 2008, despite the council failing to halt the Chevron's plan to build more refineries in the area due to rising gasoline prices during that time, the council succeeded to acquire $61 million from the oil company for community programs.
Due to great forces from the local communities and fellow EJ activists in Richmond area, Chevron has been making progress to embrace cleaner environment. In 2005, local activists managed to convince Bay Area Air Quality Management District to tighten the air pollution regulations by increasing the frequency of fines of facility incidents. Since then, Chevron has been flaring 10 times less than before. On top of that, Chevron has invested $150 million for building gas turbine in order to reduce air emission, increase energy efficiency, as well as provide most electrical and steam power Chevron requires to operate. | 2 | Environmental Chemistry |
Materials supporting quantum spin liquid states may have applications in data storage and memory. In particular, it is possible to realize topological quantum computation by means of spin-liquid states. Developments in quantum spin liquids may also help in the understanding of high temperature superconductivity. | 7 | Physical Chemistry |
The cAMP response element CREB is closely related to the cell decision to proliferate or not. Cells that are forced to overexpress AKT increase the amount of CREB and proliferation compared to wild type cells. These cells also express less glial and neural cell markers such as GFAP or β-tubulin. This is because CREB is a transcription factor that influences the transcription of cyclin A which promotes proliferation. For example, adult hippocampal neural progenitor cells need abeyance as stem cells to differentiate later. This is regulated by Shh. Shh works through a slow protein synthesis dependence, which stimulates other cascades that work synergistically with the PI3K/AKT pathway to induce proliferation. Then, the other pathway can be turned off and the effects of the PI3K/AKT pathway become insufficient in stopping differentiation. The specifics of this pathway are unknown. | 1 | Biochemistry |
Nutrients are important to the growth and survival of living organisms, and hence, are essential for development and maintenance of healthy ecosystems. Humans have greatly influenced the phosphorus cycle by mining phosphate rock. For millennia, phosphorus was primarily brought into the environment through the weathering of phosphate containing rocks, which would replenish the phosphorus normally lost to the environment through processes such as runoff, albeit on a very slow and gradual time-scale. Since the 1840s, when the technology to mine and extract phosphorus became more prevalent, approximately 110 Tg of phosphorus has been added to the environment. This trend doesn't appear to be slowing down as from 1900-2022, the amount of phosphorus mined globally has increased 72-fold, with an expected annual increase of 4%. Most of this mining is done in order to produce fertilizers which can be used on a global scale. However, at the rate humans are mining, the geological system can not restore what is lost quickly enough. Thus, researchers are examining ways to better recycle phosphorus in the environment, with one promising application including the use of microorganisms. Regardless, humans have had a powerful impact on the phosphorus cycle with wide-reaching implications about food security, eutrophication, and the overall availability of the nutrient.
Repeated application of liquid hog manure in excess to crop needs can have detrimental effects on soil phosphorus status. Also, application of biosolids may increase available phosphorus in soil. In poorly drained soils or in areas where snowmelt can cause periodic waterlogging, reducing conditions can be attained in 7–10 days. This causes a sharp increase in phosphorus concentration in solution and phosphorus can be leached. In addition, reduction of the soil causes a shift in phosphorus from resilient to more labile forms. This could eventually increase the potential for phosphorus loss. This is of particular concern for the environmentally sound management of such areas, where disposal of agricultural wastes has already become a problem. It is suggested that the water regime of soils that are to be used for organic wastes disposal is taken into account in the preparation of waste management regulations. | 9 | Geochemistry |
Esketamine was introduced for medical use as an anesthetic in Germany in 1997, and was subsequently marketed in other countries. In addition to its anesthetic effects, the medication showed properties of being a rapid-acting antidepressant, and was subsequently investigated for use as such. Esketamine received a breakthrough designation from the for treatment-resistant depression (TRD) in 2013 and major depressive disorder (MDD) with accompanying suicidal ideation in 2016. In November 2017, it completed phase III clinical trials for treatment-resistant depression in the United States. Johnson & Johnson filed a Food and Drug Administration (FDA) New Drug Application (NDA) for approval on 4 September 2018; the application was endorsed by an FDA advisory panel on 12 February 2019, and on 5 March 2019, the FDA approved esketamine, in conjunction with an oral antidepressant, for the treatment of depression in adults. In August 2020, it was approved by the U.S. Food and Drug Administration (FDA) with the added indication for the short-term treatment of suicidal thoughts.
Since the 1980s, closely associated ketamine has been used as a club drug also known as "Special K" for its trip-inducing side effects. | 4 | Stereochemistry |
The choice of culture medium might affect the physiological relevance of findings from cell culture experiments due to the differences in the nutrient composition and concentrations. A systematic bias in generated datasets was recently shown for CRISPR and RNAi gene silencing screens (especially for metabolic genes), and for metabolic profiling of cancer cell lines. For example, a stronger dependence on ASNS (asparagine synthetase) was found in cell lines cultured in DMEM, which lacks asparagine, compared to cell lines cultured in RPMI or F12 (containing asparagine). Avoiding such bias might be achieved by using a uniform media for all screened cell lines, and ideally, using a growth medium that better represents the physiological levels of nutrients. Recently, such media types, as Plasmax and Human Plasma Like Medium (HPLM), were developed. | 1 | Biochemistry |
As of 2006, there were no studies demonstrating "drug liking" scores of oral levomethamphetamine that are similar to racemic methamphetamine or dextromethamphetamine in either recreational users or medicinal users.
In recent years, tighter controls in Mexico on certain methamphetamine precursors like ephedrine and pseudoephedrine has led to a greater percentage of illicit meth from Mexican drug cartels consisting of a higher ratio of levomethamphetamine to dextromethamphetamine within batches of racemic meth. | 4 | Stereochemistry |
Freezing is almost always an exothermic process, meaning that as liquid changes into solid, heat and pressure are released. This is often seen as counter-intuitive, since the temperature of the material does not rise during freezing, except if the liquid were supercooled. But this can be understood since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing is a latent heat, and is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid.
Low-temperature helium is the only known exception to the general rule. Helium-3 has a negative enthalpy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative enthalpy of fusion below 0.8 K. This means that, at appropriate constant pressures, heat must be added to these substances in order to freeze them. | 1 | Biochemistry |
The surface temperature of a single layer
The frequency domain solution for a semi-infinite solid which is heated by a point source with angular frequency can be expressed by the following equation.
where (1)
(Λ: thermal conductivity of the solid, D: thermal diffusivity of the solid, r: radial coordinate)
In a typical time-domain thermoreflectance experiment, the co-aligned laser beams have cylindrical symmetry, therefore the
Hankel Transform can be used to simplify the computation of the convolution of equation (1) with the distributions of the laser intensities.
(The Hankel transform is an integral transform equivalent to a two-dimensional Fourier transform with a radially symmetric integral kernel)
Here g(r) is radially symmetric and by the definition of Hankel transform using Eq. (1),
Since the pump and probe beams used here have Gaussian distribution, the radius of the pump and probe beam are and respectively.
The surface is heated by the pump laser beam with the intensity , i.e.
where is the amplitude of the heat absorbed by the sample at frequency .
Then the Hankel transform of is
Then the distributions of temperature oscillations at the surface is the inverse Hankel transforms of the product and , i.e.
The surface temperatures are measured due to the change in the reflectivity with the temperature , i.e. ,
while this change is measured by the changes in the reflected intensity of a probe laser beam.
The probe laser beam measures a weighted average of the temperature , i.e.
(6a)
This last integral (6a) can be simplified to an integral over :
(6b)
The surface temperature of a layered structure
In the similar way, frequency domain solution for the surface temperature of a layered structure can be acquired. Instead of Eq. (2), Eq. (7) will be used for a layered structure.
(Λn: thermal conductivity of nth layer, Dn: thermal diffusivity of nth layer, Ln: thickness of nth layer)
Using Eqs. (6) and (7), we can calculate the changes of temperature of a layered structure.
Modeling of data acquired in time-domain thermoreflectance
The acquired data from time-domain thermoreflectance experiments are required to be compared with the model.
(Q: quality factor of the resonant circuit)
This calculated Vf/V0 would be compared with the measured one. | 7 | Physical Chemistry |
PIPES has two pKa values. One pKa (6.76 at 25 °C) is near the physiological pH which makes it useful in cell culture work. Its effective buffering range is 6.1-7.5 at 25 °C. The second pKa value is at 2.67 with a buffer range of from 1.5-3.5. PIPES has been documented minimizing lipid loss when buffering glutaraldehyde histology in plant and animal tissues. Fungal zoospore fixation for fluorescence microscopy and electron microscopy were optimized with a combination of glutaraldehyde and formaldehyde in PIPES buffer. It has a negligible capacity to bind divalent ions. | 1 | Biochemistry |
*Olfaction: In terrestrial vertebrates, olfaction occurs in the nose. Volatile chemical stimuli enter the nose and eventually reach the olfactory epithelium which houses the chemoreceptor cells known as olfactory sensory neurons often referred to as OSNs. Embedded in the olfactory epithelium are three types of cells: supporting cells, basal cells, and OSNs. While all three types of cells are integral to normal function of the epithelium, only OSN serve as receptor cells, i.e. responding to the chemicals and generating an action potential that travels down the olfactory nerve to reach the brain. In insects, antennae act as distance chemoreceptors. For example, antennae on moths are made up of long feathery hairs that increase sensory surface area. Each long hair from the main antenna also has smaller sensilla that are used for volatile olfaction. Since moths are mainly nocturnal animals, the development of greater olfaction aids them in navigating the night.
*Gustation: In many terrestrial vertebrates, the tongue serves as the primary gustatory sensory organ. As a muscle located in the mouth, it acts to manipulate and discern the composition of food in the initial stages of digestion. The tongue is rich in vasculature, allowing the chemoreceptors located on the top surface of the organ to transmit sensory information to the brain. Salivary glands in the mouth allow for molecules to reach chemoreceptors in an aqueous solution. The chemoreceptors of the tongue fall into two distinct superfamilies of G protein-coupled receptors. GPCRs are intramembrane proteins than bind to an extracellular ligand- in this case chemicals from food- and begin a diverse array of signaling cascades that can result in an action potential registering as input in an organisms brain. Large quantities of chemoreceptors with discrete ligand-binding domains provide for the five basic tastes: sour, salty, bitter, sweet, and savory. The salty and sour tastes work directly through the ion channels, the sweet and bitter taste work through G protein-coupled receptors, and the savory sensation is activated by glutamate.Gustatory chemosensors are not just present on the tongue but also on different cells of the gut epithelium where they communicates the sensory information to several effector systems involved in the regulation of appetite, immune responses, and gastrointestinal motility.
*Contact Chemoreception: Contact chemoreception is dependent on the physical contact of the receptor with the stimulus. The receptors are short hairs or cones that have a single pore at, or close to the tip of the projection. They are known as uniporous receptors. Some receptors are flexible, while others are rigid and do not bend with contact. They are mostly found in the mouthparts, but can also occur on the antennae or legs of some insects. There is a collection of dendrites located near the pores of the receptors, yet the distribution of these dendrites changes depending on the organism being examined. The method of transduction of the signal from the dendrites differs depending on the organism and the chemical it is responding to.
When inputs from the environment are significant to the survival of the organism, the input must be detected. As all life processes are ultimately based on chemistry it is natural that detection and passing on of the external input will involve chemical events. The chemistry of the environment is, of course, relevant to survival, and detection of chemical input from the outside may well articulate directly with cell chemicals.
Chemoreception is important for the detection of food, habitat, conspecifics including mates, and predators. For example, the emissions of a predator's food source, such as odors or pheromones, may be in the air or on a surface where the food source has been. Cells in the head, usually the air passages or mouth, have chemical receptors on their surface that change when in contact with the emissions. It passes in either chemical or electrochemical form to the central processor, the brain or spinal cord. The resulting output from the CNS (central nervous system) makes body actions that will engage the food and enhance survival. | 3 | Analytical Chemistry |
Alkoxide ligands are often nucleophilic. They often undergo insertion reactions with unsaturated substrates such as carbon dioxide and isocyanates . | 0 | Organic Chemistry |
Though it was initially dubbed "mysterious protein", recent empirical studies are gradually starting to unveil some of seipins most compelling physiological functions. Among these, the following have been identified: central regulation of energy homeostasis, lipid catabolism (essential for adipocyte differentiation), lipid storage and lipid droplet maintenance, as well as prevention of ectopic lipid droplet formation in non-adipose tissues. Additionally, mutations of BSCL2 have been recently linked to the Silver syndrome (hereditary spastic periplegia type 17) and Celias encephalopathy. | 1 | Biochemistry |
Catecholaminergic means "related to catecholamines". The catecholamine neurotransmitters include dopamine, epinephrine (adrenaline), and norepinephrine (noradrenaline).
A catecholaminergic agent (or drug) is a chemical which functions to directly modulate the catecholamine systems in the body or brain. Examples include adrenergics and dopaminergics. | 1 | Biochemistry |
Photoinhibition can also be induced with short flashes of light using either a pulsed laser or a xenon flash lamp. When very short flashes are used, the photoinhibitory efficiency of the flashes depends on the time difference between the flashes. This dependence has been interpreted to indicate that the flashes cause photoinhibition by inducing recombination reactions in PSII, with subsequent production of singlet oxygen. The interpretation has been criticized by noting that the photoinhibitory efficiency of xenon flashes depends on the energy of the flashes even if such strong flashes are used that they would saturate the formation of the substrate of the recombination reactions. | 5 | Photochemistry |
Although ethers resist hydrolysis, they are cleaved by hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers typically afford methyl halides:
:ROCH + HBr → CHBr + ROH
These reactions proceed via onium intermediates, i.e. [RO(H)CH]Br.
Some ethers undergo rapid cleavage with boron tribromide (even aluminium chloride is used in some cases) to give the alkyl bromide. Depending on the substituents, some ethers can be cleaved with a variety of reagents, e.g. strong base.
Despite these difficulties the chemical paper pulping processes are based on cleavage of ether bonds in the lignin. | 0 | Organic Chemistry |
DNAzymes have found practical use in metal biosensors. A DNAzyme based biosensor for lead ion was used to detect lead ion in water in St. Paul Public Schools in Minnesota. Furthermore, DNAzymes have been used in combination of aptamers and nucleic acid bioreceptors for the development of a multiplex bioassay. | 7 | Physical Chemistry |
The enantiopure synthesis of levopropylhexedrine may be accomplished in a two step reaction. The first step is the Wenker synthesis of the relevant aziridine. The second step is the simple catalytic hydrogenation of the propylhexedrine-aziridine. | 4 | Stereochemistry |
* 1982 Ledlie Prize, Harvard University
* 1988 Wallace P. Rowe Award, National Institute of Allergy and Infectious Diseases
* 1990 Louisa Gross Horwitz Prize (with Don Wiley and Michael Rossmann), Columbia University
* 1990 Harvey Lecturer, The Harvey Society, New York
* 1995 George Ledlie Prize, Harvard University
* 1997 ICN International Prize in Virology
* 2001 Paul Ehrlich and Ludwig Darmstaedter Prize (with Michael Rossmann)
* 2005 Bristol-Myers Squibb Award for Distinguished Achievement in Infectious Diseases Research
* 2006 Gregori Aminoff Prize in Crystallography (with David Stuart)
* 2007 UCSD/Merck Life Sciences Achievement Award
* 2011 William Silen Lifetime Achievement in Mentoring Award, Harvard Medical School
* 2012 Pauling Lectureship, Stanford University
* 2014 Elected as a Foreign Member of the Royal Society of London.
* 2015 The Welch Award in Chemistry
* 2015 Honorary Doctorate in Medicine, University of Milan
* 2018 48th Rosenstiel Award for research on proteins and viruses. | 1 | Biochemistry |
In its coil state, the radius of gyration of the macromolecule scales as its chain length to the three-fifths power. As it passes through the coil–globule transition, it shifts to scaling as chain length to the half power (at the transition) and finally to the one third power in the collapsed state. The direction of the transition is often specified by the constructions coil-to-globule or globule-to-coil transition. | 7 | Physical Chemistry |
Tritrophic interactions in plant defense against herbivory describe the ecological impacts of three trophic levels on each other: the plant, the herbivore, and its natural enemies. They may also be called multitrophic interactions when further trophic levels, such as soil microbes, endophytes, or hyperparasitoids (higher-order predators) are considered. Tritrophic interactions join pollination and seed dispersal as vital biological functions which plants perform via cooperation with animals.
Natural enemies—predators, pathogens, and parasitoids that attack plant-feeding insects—can benefit plants by hindering the feeding behavior of the harmful insect. It is thought that many plant traits have evolved in response to this mutualism to make themselves more attractive to natural enemies. This recruitment of natural enemies functions to protect against excessive herbivory and is considered an indirect plant defense mechanism. Traits attractive to natural enemies can be physical, as in the cases of domatia and nectaries; or chemical, as in the case of induced plant volatile chemicals that help natural enemies pinpoint a food source.
Humans can take advantage of tritrophic interactions in the biological control of insect pests. | 1 | Biochemistry |
The branched-chain fatty acid synthesizing system uses α-keto acids as primers. This system is distinct from the branched-chain fatty acid synthetase that utilizes short-chain acyl-CoA esters as primers. α-Keto acid primers are derived from the transamination and decarboxylation of valine, leucine, and isoleucine to form 2-methylpropanyl-CoA, 3-methylbutyryl-CoA, and 2-methylbutyryl-CoA, respectively. 2-Methylpropanyl-CoA primers derived from valine are elongated to produce even-numbered iso-series fatty acids such as 14-methyl-pentadecanoic (isopalmitic) acid, and 3-methylbutyryl-CoA primers from leucine may be used to form odd-numbered iso-series fatty acids such as 13-methyl-tetradecanoic acid. 2-Methylbutyryl-CoA primers from isoleucine are elongated to form anteiso-series fatty acids containing an odd number of carbon atoms such as 12-Methyl tetradecanoic acid. Decarboxylation of the primer precursors occurs through the branched-chain α-keto acid decarboxylase (BCKA) enzyme. Elongation of the fatty acid follows the same biosynthetic pathway in Escherichia coli used to produce straight-chain fatty acids where malonyl-CoA is used as a chain extender. The major end products are 12–17 carbon branched-chain fatty acids and their composition tends to be uniform and characteristic for many bacterial species.
BCKA decarboxylase and relative activities of α-keto acid substrates
The BCKA decarboxylase enzyme is composed of two subunits in a tetrameric structure (AB) and is essential for the synthesis of branched-chain fatty acids. It is responsible for the decarboxylation of α-keto acids formed by the transamination of valine, leucine, and isoleucine and produces the primers used for branched-chain fatty acid synthesis. The activity of this enzyme is much higher with branched-chain α-keto acid substrates than with straight-chain substrates, and in Bacillus species its specificity is highest for the isoleucine-derived α-keto-β-methylvaleric acid, followed by α-ketoisocaproate and α-ketoisovalerate. The enzyme's high affinity toward branched-chain α-keto acids allows it to function as the primer donating system for branched-chain fatty acid synthetase.
Factors affecting chain length and pattern distribution
α-Keto acid primers are used to produce branched-chain fatty acids that, in general, are between 12 and 17 carbons in length. The proportions of these branched-chain fatty acids tend to be uniform and consistent among a particular bacterial species but may be altered due to changes in malonyl-CoA concentration, temperature, or heat-stable factors (HSF) present. All of these factors may affect chain length, and HSFs have been demonstrated to alter the specificity of BCKA decarboxylase for a particular α-keto acid substrate, thus shifting the ratio of branched-chain fatty acids produced. An increase in malonyl-CoA concentration has been shown to result in a larger proportion of C17 fatty acids produced, up until the optimal concentration (≈20μM) of malonyl-CoA is reached. Decreased temperatures also tend to shift the fatty-acid distribution slightly toward C17 fatty-acids in Bacillus species. | 1 | Biochemistry |
Seven autotrophic carbon fixation pathways are known. The Calvin cycle fixes carbon in the chloroplasts of plants and algae, and in the cyanobacteria. It also fixes carbon in the anoxygenic photosynthesis in one type of Pseudomonadota called purple bacteria, and in some non-phototrophic Pseudomonadota.
Of the five other autotrophic pathways, two are known only in bacteria (the reductive citric acid cycle and the 3-hydroxypropionate cycle), two only in archaea (two variants of the 3-hydroxypropionate cycle), and one in both bacteria and archaea (the reductive acetyl CoA pathway). | 5 | Photochemistry |
Cell signaling or cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Signaling can occur through direct cell contact or endocrine, paracrine, and autocrine signaling. Direct cell-cell contact is when a receptor on a cell binds a molecule that is attached to the membrane of another cell. Endocrine signaling occurs through molecules secreted into the bloodstream. Paracrine signaling uses molecules diffusing between two cells to communicate. Autocrine is a cell sending a signal to itself by secreting a molecule that binds to a receptor on its surface. Forms of communication can be through:
* Ion channels: Can be of different types such as voltage or ligand gated ion channels. They allow for the outflow and inflow of molecules and ions.
* G-protein coupled receptor (GPCR): Is widely recognized to contain seven transmembrane domains. The ligand binds on the extracellular domain and once the ligand binds, this signals a guanine exchange factor to convert GDP to GTP and activate the G-α subunit. G-α can target other proteins such as adenyl cyclase or phospholipase C, which ultimately produce secondary messengers such as cAMP, Ip3, DAG, and calcium. These secondary messengers function to amplify signals and can target ion channels or other enzymes. One example for amplification of a signal is cAMP binding to and activating PKA by removing the regulatory subunits and releasing the catalytic subunit. The catalytic subunit has a nuclear localization sequence which prompts it to go into the nucleus and phosphorylate other proteins to either repress or activate gene activity.
* Receptor tyrosine kinases: Bind growth factors, further promoting the tyrosine on the intracellular portion of the protein to cross phosphorylate. The phosphorylated tyrosine becomes a landing pad for proteins containing an SH2 domain allowing for the activation of Ras and the involvement of the MAP kinase pathway. | 1 | Biochemistry |
Stable, isolable, diradicals include singlet oxygen and triplet oxygen. Other important diradicals are certain carbenes, nitrenes, and their main group elemental analogues. Lesser known diradicals are nitrenium ions, carbon chains and organic so-called non-Kekulé molecules in which the electrons reside on different carbon atoms. Main group cyclic structures can also exhibit diradicals, such as disulfur dinitride, or diradical character, such as diphosphadiboretanes. In inorganic chemistry, both homoleptic and heteroleptic 1,2-dithiolene complexes of d transition metal ions show a large degree of diradical character in the ground state. | 0 | Organic Chemistry |
Gunzbergs test is a chemical test used for detecting the presence of hydrochloric acid. Gunzbergs reagent is made by dissolving two grams of phloroglucinol and one gram of vanillin in 100 millilitres of 95% ethanol. Hydrochloric acid catalyses Gunzberg's reagent to form a red complex. | 3 | Analytical Chemistry |
The mechanisms that damage kidneys during hypothermic storage can be sub-divided as follows:
# Injury to the metabolic processes of the cell caused by:
## Cold
## Anoxia when the kidney is warm both before and after the period of hypothermic storage.
## Failure to supply the correct nutrients.
## Toxin accumulation in the perfusate.
## Toxic damage from the storage fluid.
## Washout of essential substrates from the kidney cells.
# Injury to nuclear DNA.
# Mechanical injury to the vascular system of the kidney during hypothermic perfusion.
# Post reimplantation injury. | 1 | Biochemistry |
Pump–probe microscopy can also measure stimulated emission. In this case, the pump beam drives the electron to an excited state. Then the electron emits a photon when exposed to the probe beam. This interaction increases the probe signal at the detector site. | 7 | Physical Chemistry |
The third law of thermodynamics states: As the temperature of a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.
This law of thermodynamics is a statistical law of nature regarding entropy and the impossibility of reaching absolute zero of temperature. This law provides an absolute reference point for the determination of entropy. The entropy determined relative to this point is the absolute entropy. Alternate definitions include "the entropy of all systems and of all states of a system is smallest at absolute zero," or equivalently "it is impossible to reach the absolute zero of temperature by any finite number of processes".
Absolute zero, at which all activity would stop if it were possible to achieve, is −273.15 °C (degrees Celsius), or −459.67 °F (degrees Fahrenheit), or 0 K (kelvin), or 0° R (degrees Rankine). | 7 | Physical Chemistry |
Boyles law, also referred to as the Boyle–Mariotte law or Mariottes law (especially in France), is an empirical gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as:
Mathematically, Boyle's law can be stated as:
or
where is the pressure of the gas, is the volume of the gas, and is a constant.
Boyle's law states that when the temperature of a given mass of confined gas is constant, the product of its pressure and volume is also constant. When comparing the same substance under two different sets of conditions, the law can be expressed as:
showing that as volume increases, the pressure of a gas decreases proportionally, and vice versa.
Boyle's law is named after Robert Boyle, who published the original law in 1662. An equivalent law is Mariotte’s law named after French physicist Edme Mariotte. | 7 | Physical Chemistry |
The photochlorination of benzene proceeds also via a radical chain reaction:
In some applications, the reaction is carried out at 15 to 20 °C. At a conversion of 12 to 15% the reaction is stopped and the reaction mixture is worked up. | 5 | Photochemistry |
LAP proteins are expressed in a variety of marine organisms as a method of coping with the osmotic threat high salinity poses to the cell. During bouts of high salinity, LAP begins the catalysis of proteins in order to release amino acids into the cell in an attempt to balance the high ion concentrations in the external environment. | 1 | Biochemistry |
For surfaces which are not black bodies, one has to consider the (generally frequency dependent) emissivity factor . This factor has to be multiplied with the radiation spectrum formula before integration. If it is taken as a constant, the resulting formula for the power output can be written in a way that contains as a factor:
This type of theoretical model, with frequency-independent emissivity lower than that of a perfect black body, is often known as a grey body. For frequency-dependent emissivity, the solution for the integrated power depends on the functional form of the dependence, though in general there is no simple expression for it. Practically speaking, if the emissivity of the body is roughly constant around the peak emission wavelength, the gray body model tends to work fairly well since the weight of the curve around the peak emission tends to dominate the integral. | 7 | Physical Chemistry |
John Walshe first described the use of penicillamine in Wilsons disease in 1956. He had discovered the compound in the urine of patients (including himself) who had taken penicillin, and experimentally confirmed that it increased urinary copper excretion by chelation. He had initial difficulty convincing several world experts of the time (Denny Brown and Cumings) of its efficacy, as they held that Wilsons disease was not primarily a problem of copper homeostasis but of amino acid metabolism, and that dimercaprol should be used as a chelator. Later studies confirmed both the copper-centered theory and the efficacy of -penicillamine. Walshe also pioneered other chelators in Wilson's such as triethylene tetramine and tetrathiomolybdate.
Penicillamine was first synthesized by John Cornforth under supervision of Robert Robinson.
Penicillamine has been used in rheumatoid arthritis since the first successful case in 1964. | 4 | Stereochemistry |
The journal is abstracted and indexed in several databases including:
* Science Citation Index
* Web of Science
* Polymer Contents
According to the Journal Citation Reports, the journal has a 2022 impact factor of 11.2. | 0 | Organic Chemistry |
Photochemical reduction involves chemical reduction (redox) generated from the photoexcitation of another molecule, called a photosensitizer. To harness the sun's energy, the photosensitizer must be able to absorb light within the visible and ultraviolet spectrum.
Molecular sensitizers that meet this criterion often include a metal center, as the d-orbital splitting in organometallic species often falls within the energy range of far-UV and visible light. The reduction process begins with excitation of the photosensitizer, as mentioned. This causes the movement of an electron from the metal center into the functional ligands. This movement is termed a metal-to-ligand charge transfer (MLCT). Back-electron transfer from the ligands to the metal after the charge transfer, which yields no net result, is prevented by including an electron-donating species in solution. Successful photosensitizers have a long-lived excited state, usually due to the interconversion from singlet to triplet states, that allow time for electron donors to interact with the metal center.
Common donors in photochemical reduction include triethylamine (TEA), triethanolamine (TEOA), and 1-benzyl-1,4-dihydronicotinamide (BNAH).
After excitation, CO coordinates or otherwise interacts with the inner coordination sphere of the reduced metal. Common products include formic acid, carbon monoxide, and methanol. Note that light absorption and catalytic reduction may occur at the same metal center or on different metal centers. That is, a photosensitizer and catalyst may be tethered through an organic linkage that provides for electronic communication between the species. In this case, the two metal centers form a bimetallic supramolecular complex. And, the excited electron that had resided on the functional ligands of photosensitizer passes through the ancillary ligands to the catalytic center, which becomes a one-electron reduced (OER) species. The advantage of dividing the two processes among different centers is in the ability to tune each center for a particular task, whether through selecting different metals or ligands. | 5 | Photochemistry |
Quinapril, sold under the brand name Accupril by the Pfizer corporation. It a medication used to treat high blood pressure (hypertension), heart failure, and diabetic kidney disease. It is a first line treatment for high blood pressure. It is taken by mouth.
Common side effects include headaches, dizziness, feeling tired, and cough. Serious side effects may include liver problems, low blood pressure, angioedema, kidney problems, and high blood potassium. Use in pregnancy and breastfeeding is not recommended. It is among a class of drugs called ACE inhibitors and works by decreasing renin-angiotensin-aldosterone system activity.
Quinapril was patented in 1980 and came into medical use in 1989. It is available as a generic medication. In 2020, it was the 253rd most commonly prescribed medication in the United States, with more than 1million prescriptions. | 4 | Stereochemistry |
Oxidation of diisopinocampheylborane with basic hydrogen peroxide gives isopincampheol. Methanolysis gives methoxydiisopinocampheylborane | 0 | Organic Chemistry |
The Biogeochemistry Department, headed by Ralf Conrad, is focused on the microbial metabolism and biogeochemical matter cycling in soil. Soil microbial metabolism plays an important role in the global cycling of matter and — through the formation of atmospheric trace gases such as methane and nitrous oxide — also influences the climate on Earth. The department examines the role of soil microorganisms in carbon and nitrogen cycling, particularly in chemically well-defined processes such as the production and consumption of methane, the oxidation of ammonia, or denitrification. There are four research leaders in charge of six research groups and two project groups:
Research Groups<br />
Ralf Conrad
* Methanogenic degradation
* Microbial metabolism of trace gases
Andreas Brune
* Microbial ecology of the termite gut
* Microbial symbioses
Werner Liesack
* Molecular biology and ecology of methanotrophs
* Environmental genomics and transcriptomics
Project Group<br />
Peter Frenzel
* Methane oxidation
* Biogeochemistry and microbial ecology of wetlands | 9 | Geochemistry |
The mimic poison frog Ranitomeya (Dendrobates) imitator is polymorphic, with a striped morph that imitates the black and yellow striped morph of Ranitomeya variabilis, a spotted morph that imitates the largely blue-green highland spotted morph also of R. variabilis, and a banded morph that imitates the red and black banded Ranitomeya summersi.
R. imitator has thus apparently evolved in separate populations to resemble different targets, i.e. it has changed to resemble (adverged on) those target species, rather than both R. imitator and the other species mutually converging in the way that Müller supposed for tropical butterflies.
Such advergence may be common. The mechanism was proposed by the entomologist F. A. Dixey in 1909 and has remained controversial; the evolutionary biologist James Mallet, reviewing the situation in 2001, suggested that in Müllerian mimicry, advergence may be more common than convergence. In advergent evolution, the mimicking species responds to predation by coming to resemble the model more and more closely. Any initial benefit is thus to the mimic, and there is no implied mutualism, as there would be with Müllers original convergence theory. However, once model and mimic have become closely similar, some degree of mutual protection becomes likely. This theory would predict that all mimicking species in an area should converge on a single pattern of coloration. This does not appear to happen in nature, however, as Heliconius' butterflies form multiple Müllerian mimicry rings in a single geographical area. The finding implies that additional evolutionary forces are probably at work. | 1 | Biochemistry |
The main advantage of electroforming is that it accurately replicates the external shape of the mandrel. Generally, machining a cavity accurately is more challenging than machining a convex shape, however the opposite holds true for electroforming because the mandrel's exterior can be accurately machined and then used to electroform a precision cavity.
Compared to other basic metal forming processes (casting, forging, stamping, deep drawing, machining and fabricating) electroforming is very effective when requirements call for extreme tolerances, complexity or light weight. The precision and resolution inherent in the photo-lithographically produced conductive patterned substrate, allows finer geometries to be produced to tighter tolerances while maintaining superior edge definition with a near optical finish. Electroformed metal can be extremely pure, with superior properties over wrought metal due to its refined crystal structure. Multiple layers of electroformed metals can be bonded together, or to different substrate materials to produce complex structures with "grown-on" flanges and bosses.
Tolerances of 1.5 to 3 nanometres have been reported.
A wide variety of shapes and sizes can be made by electroforming, the principal limitation being the need to part the product from the mandrel. Since the fabrication of a product requires only a single model or mandrel, low production quantities can be made economically. | 8 | Metallurgy |
LDH in humans uses His(193) as the proton acceptor, and works in unison with the coenzyme (Arg99 and Asn138), and substrate (Arg106; Arg169; Thr248) binding residues. The His(193) active site, is not only found in the human form of LDH, but is found in many different animals, showing the convergent evolution of LDH. The two different subunits of LDH (LDHA, also known as the M subunit of LDH, and LDHB, also known as the H subunit of LDH) both retain the same active site and the same amino acids participating in the reaction. The noticeable difference between the two subunits that make up LDHs tertiary structure is the replacement of alanine (in the M chain) with a glutamine (in the H chain). This tiny but notable change is believed to be the reason the H subunit can bind NAD faster, and the M subunits catalytic activity isnt reduced in the presence of acetylpyridine adenine dinucleotide, whereas the H subunits activity is reduced fivefold. | 1 | Biochemistry |
The process is similar to that of homebrewing wine. If done slowly, it requires rigorous hygiene and filtering of the product. If brewed fast, specialized dried yeasts are available in amounts to drive the fermentation process through before bacterial infiltration can take place, in about three days. In Finnish the latter are called pikahiiva (lit. quick-yeast), and they are sold in about a hundred gramme packs dry, as opposed to the live standard pack of brewer's yeast of 50g wet.
Properly made kilju is a clear, colorless or off-white liquid with no discernible taste other than that of ethanol. It can be produced by natural settling of the yeast over time, but nowadays various fining agents are used to hasten the process as well.
Kilju is often produced improperly by home brewers who allow contaminants to disrupt fermentation or do not adequately filter or rack the liquid, or do not use a fining agent. The latter mistakes result in yeast being suspended, causing the mixture to be cloudy rather than clear. The yeast is not harmful, but can yield an unpleasant taste and intestinal discomfort. It is also a common mistake to leave the carbon dioxide produced by fermentation into the suspension, so that the yeast provides it with nucleation sites, keeping the yeast up in the solution. Proper technique calls for airing the product after fermentation, stirring, and perhaps for fining agents such as microsilica or various semipolar proteinaceacous or carbohydrate agents. | 1 | Biochemistry |
In chemistry, the carbon-hydrogen bond ( bond) is a chemical bond between carbon and hydrogen atoms that can be found in many organic compounds. This bond is a covalent, single bond, meaning that carbon shares its outer valence electrons with up to four hydrogens. This completes both of their outer shells, making them stable.
Carbon–hydrogen bonds have a bond length of about 1.09 Å (1.09 × 10 m) and a bond energy of about 413 kJ/mol (see table below). Using Pauling's scale—C (2.55) and H (2.2)—the electronegativity difference between these two atoms is 0.35. Because of this small difference in electronegativities, the bond is generally regarded as being non-polar. In structural formulas of molecules, the hydrogen atoms are often omitted. Compound classes consisting solely of bonds and bonds are alkanes, alkenes, alkynes, and aromatic hydrocarbons. Collectively they are known as hydrocarbons.
In October 2016, astronomers reported that the very basic chemical ingredients of life—the carbon-hydrogen molecule (CH, or methylidyne radical), the carbon-hydrogen positive ion () and the carbon ion ()—are the result, in large part, of ultraviolet light from stars, rather than in other ways, such as the result of turbulent events related to supernovae and young stars, as thought earlier. | 0 | Organic Chemistry |
Frame Lake is irregularly shaped, with a northern section and a southern section along a north-northeast to south-southwest axis approximately long, connected by a narrower central passage midway along its length where a wide peninsula extends from the western shore and an arm extends roughly to the east, curving northward. At their widest shorelines, both sections are roughly the same distance apart. Five small islands are located within the lake, three in the northern section and two in the southern section. Its total surface area is .
The lake lies at an elevation of . Surrounding terrain is gently undulating, with some of the small hills nearby cresting as high as and one of the islands rising to . Two unnamed streams drain into the lake south of the peninsula on the western side. The northerly of the two rises from drainage ditches surrounding the runways at Yellowknife Airport to the west, draining Robinson's Pond on the way to Frame Lake; the southerly has largely been channelized, draining Range Lake to the west, itself fed by a stream of similarly short length flowing into it from the west.
Surrounding terrain, as well as that of the islands, is primarily taiga forest, amid mostly bare outcrops of Canadian Shield bedrock typical of the Yellowknife area. Bare rock predominates on the shoreline, except for some shallow bays with weed beds. On the eastern shore, near the southern end of the lake, is an overgrown sandy area called McNiven Beach, after the city's first mayor.
The developed areas of Yellowknife form a "V" around the lake. On the eastern side, and the southern shore of the arm, is New Town, the citys modern downtown. Public buildings such as City Hall, the Royal Canadian Mounted Polices local headquarters, and the Canadian Forces Northern Area Headquarters Yellowknife are situated along the south side of the arm, their associated lawns coming almost to the edge of the lake.
South of City Hall along the lake shore is Somba Ke Park, open space with the only totally developed portion of shoreline. Beyond it, the taiga and bedrock buffer the lake from the city, except for the dead end of residential Matonabee Road. The Frame Lake Trail, a partially paved pathway in length, closely follows the shoreline past an extensive area of forest. Just south of McNiven Beach is a recreational facility with an arena and pool, again close to the waters edge.
At the south end, another residential neighborhood comes near the lake, after which a rocky area buffers Stanton Regional Hospital. Commercial strip development along Old Airport Road also comes close, and the road itself runs alongside part of the lakes southwestern shore for . After it curves away to the west, the northwestern side and northern end of the lake are all taiga and bedrock between Frame and nearby Robinsons Pond and Jackfish Lake, with just the trail alongside.
Amid a park-like setting on the northeastern corner of the lake, and the northern shore of the western arm, stand two other large public buildings: the Prince of Wales Northern Heritage Centre and Northwest Territories Legislative Assembly Building. The two are connected via paths and driveways through the intervening taiga and bedrock. A causeway carries the Frame Lake Trail across the tip of the arm, where the Northern Frontier Visitor Centre overlooks the lake. | 2 | Environmental Chemistry |
The Kerr/CFT correspondence is an extension of the AdS/CFT correspondence or gauge-gravity duality to rotating black holes (which are described by the Kerr metric).
The duality works for black holes whose near-horizon geometry can be expressed as a product of AdS and a single compact coordinate. The AdS/CFT duality then maps this to a two-dimensional conformal field theory (the compact coordinate being analogous to the S factor in Maldacena's original work), from which the correct Bekenstein entropy can then be deduced.
The original form of the duality applies to black holes with the maximum value of angular momentum, but it has now been speculatively extended to all lesser values. | 7 | Physical Chemistry |
The particle size distribution of milled coal depends partly on the rank of the coal, which determines its brittleness, and on the handling, crushing and milling it has undergone. Generally coal is utilised in furnaces and coking ovens at a certain size, so the crushability of the coal must be determined and its behaviour quantified. It is necessary to know these data before coal is mined, so that suitable crushing machinery can be designed to optimise the particle size for transport and use. | 3 | Analytical Chemistry |
Methyl chloroformate is a chemical compound with the chemical formula . It is the methyl ester of chloroformic acid. It is an oily colorless liquid, although aged samples appear yellow. It is also known for its pungent odor. | 0 | Organic Chemistry |
The moisture sorption properties of food products are recognized as critical factors in determining their storage, stability, processing and application performance. DVS is also used to measure moisture and flavor diffusion properties for packaging and barrier applications. Further, moisture sorption plays critical roles in the storage and performance of agricultural products like pesticides, herbicides, fertilizers, and seeds. | 7 | Physical Chemistry |
The synthesis of polycatenanes is considered a very challenging task. The formation of poly-[2]-catenanes can be achieved by polymerization of functionalized [2]-catenanes. Also the synthesis of [3]-catenanes, [5]-catenanes, [6]-catenanes and [7]-catenanes is reported in many articles. The synthesis of poly-[n]-catenanes has instead some practical issues. To this purpose, molecular dynamic simulation is very used as a tool for the design of the optimal synthetic path toward the desired product by predicting the final topology.
There are two main synthetic routes: the Statistical approach and the Template-Directed approach.
The statistical approach is based on a stochastic methodology. When the reactants are together, there is a probability that they will fit together first and then close on top of each other in a process of cyclization. The catenation of two rings into a catenane is already complex, thus, as expected, the interlocking of multiple cycles into a polycatenane is statistically improbable. Being an unfavored entropically process the product is obtained in very small amount. Also, the cyclization process requires high dilutions, but the elongation of the chain is favored at high concentrations, making the synthesis even more difficult.
The Template directed approach is based on the host-guest interactions that can direct the cyclization of pre-organized linear unit upon the existing macrocycle. These interactions can be hydrogen bonds, π-π interactions, hydrophobic interactions or metal ions coordinations. In this way the synthesis can be enthalpy-driven, obtaining quantitative results.
The yield and selectivity are restrained by the kinetic or thermodynamic control of the reaction.
Generally the kinetic control induces the formation of a product after short reaction times because it is favoued by irreversible reactions (or equilibrium reaction moved very much toward the formation of the products). The thermodynamic product is obtained for longer reaction times for reversible processes. In this case the units have the time to rearrange themselves toward the most stable state, in a sort of error-checking process. This is obtained by breaking covalent and coordination bonds and forming the most stable ones. | 6 | Supramolecular Chemistry |
The iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. The iodine clock reaction exists in several variations, which each involve iodine species (iodide ion, free iodine, or iodate ion) and redox reagents in the presence of starch. Two colourless solutions are mixed and at first there is no visible reaction. After a short time delay, the liquid suddenly turns to a shade of dark blue due to the formation of a triiodide–starch complex. In some variations, the solution will repeatedly cycle from colorless to blue and back to colorless, until the reagents are depleted. | 7 | Physical Chemistry |
In both prokaryotes and eukaryotes signal sequences may act co-translationally or post-translationally.
The co-translational pathway is initiated when the signal peptide emerges from the ribosome and is recognized by the signal-recognition particle (SRP). SRP then halts further translation (translational arrest only occurs in Eukaryotes) and directs the signal sequence-ribosome-mRNA complex to the SRP receptor, which is present on the surface of either the plasma membrane (in prokaryotes) or the ER (in eukaryotes). Once membrane-targeting is completed, the signal sequence is inserted into the translocon. Ribosomes are then physically docked onto the cytoplasmic face of the translocon and protein synthesis resumes.
The post-translational pathway is initiated after protein synthesis is completed. In prokaryotes, the signal sequence of post-translational substrates is recognized by the SecB chaperone protein that transfers the protein to the SecA ATPase, which in turn pumps the protein through the translocon. Although post-translational translocation is known to occur in eukaryotes, it is poorly understood. It is known that in yeast post-translational translocation requires the translocon and two additional membrane-bound proteins, Sec62 and Sec63. | 1 | Biochemistry |
Metal complexes are known to catalyze alkyne trimerization to give arenes. These reactions have been used to prepare arene complexes. Illustrative is the reaction of [Co(mesitylene)] with 2-butyne to give [Co(CMe)]. | 0 | Organic Chemistry |
The greatest danger of tailings ponds is dam failure, with the most publicized failure in the U.S. being the failure of a coal slurry dam in the West Virginia Buffalo Creek Flood of 1972, which killed 125 people; other collapses include the Ok Tedi environmental disaster in New Guinea, which destroyed the fishery of the Ok Tedi River. On average, worldwide, there is one big accident involving a tailings dam each year.
Other disasters caused by tailings dam failures are, the 2000 Baia Mare cyanide spill and the Ajka alumina plant accident. In 2015, the iron ore tailings dam failure at the Germano mine complex in Minas Gerais, Brazil, was the country's biggest environmental disaster. The dam breach caused the death of 19 people due to flooding of tailings slime downstream and affected some 400 km of the Doce river system with toxic effluence and out into the Atlantic Ocean. | 8 | Metallurgy |
Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability. More controversially, hyperconjugation is proposed by quantum mechanical modeling to be a better explanation for the preference of the staggered conformation rather than the old textbook notion of steric hindrance. | 7 | Physical Chemistry |
Cram was born and raised in Chester, Vermont, to a Scottish immigrant father, and a German immigrant mother. His father died before Cram turned four, leaving him the only male in a family of five. He grew up on Aid to Dependent Children, and learned to work at an early age, doing jobs such as picking fruit, tossing newspapers, and painting houses, while bartering for piano lessons. By the time he turned eighteen, he had worked at least eighteen different jobs.
Cram attended the Winwood High School in Long Island, N.Y.
From 1938 to 1941, he attended Rollins College in Winter Park, Florida on a national honorary scholarship, where he worked as an assistant in the chemistry department, and was active in theater, chapel choir, Lambda Chi Alpha, Phi Society, and Zeta Alpha Epsilon. It was at Rollins that he became known for building his own chemistry equipment. In 1941, he graduated from Rollins College with a BS in chemistry.
In 1942, he graduated from the University of Nebraska–Lincoln with a MS in organic chemistry, with Norman O. Cromwell serving as his thesis adviser. His subject was "Amino ketones, mechanism studies of the reactions of heterocyclic secondary amines with -bromo-, -unsaturated ketones."
In 1947, Cram graduated from Harvard University with a PhD in organic chemistry, with Louis Fieser serving as the adviser on his dissertation on "Syntheses and reactions of 2-(ketoalkyl)-3-hydroxy-1,4-naphthoquinones" | 4 | Stereochemistry |
The phase-down mandated by the AIM Act will lead to R-410A's replacement by other refrigerants beginning in 2022. Alternative refrigerants are available, including hydrofluoroolefins, hydrocarbons (such as propane R-290 and isobutane R-600A), and even carbon dioxide (R-744, GWP = 1). The alternative refrigerants have much lower GWP than R-410A. | 2 | Environmental Chemistry |
The CC chemokine (or β-chemokine) proteins have two adjacent cysteines (amino acids), near their amino terminus.
There have been at least 27 distinct members of this subgroup reported for mammals, called CC chemokine ligands (CCL)-1 to -28; CCL10 is the same as CCL9. Chemokines of this subfamily usually contain four cysteines (C4-CC chemokines), but a small number of CC chemokines possess six cysteines (C6-CC chemokines). C6-CC chemokines include CCL1, CCL15, CCL21, CCL23 and CCL28. CC chemokines induce the migration of monocytes and other cell types such as NK cells and dendritic cells.
Examples of CC chemokine include monocyte chemoattractant protein-1 (MCP-1 or CCL2) which induces monocytes to leave the bloodstream and enter the surrounding tissue to become tissue macrophages.
CCL5 (or RANTES) attracts cells such as T cells, eosinophils and basophils that express the receptor CCR5.
Increased CCL11 levels in blood plasma are associated with aging (and reduced neurogenesis) in mice and humans. | 1 | Biochemistry |
It is often noted that beer served by gravity (that is, directly from a tap in the cask) is less heavily carbonated than the same beer served via a hand-pump (or beer-engine). This is because beer is pressured on its way to the point of service by the action of the beer engine, which causes carbon dioxide to dissolve in the beer. This then comes out of solution once the beer has left the pump, causing a higher level of perceptible condition in the beer. | 7 | Physical Chemistry |
Mandelonitrile, with the formula CHCH(OH)CN, occurs in small amounts in the pits of some fruits. Related cyanogenic glycosides are known, such as amygdalin.
Glycolonitrile, also called hydroxyacetonitrile or formaldehyde cyanohydrin, is the organic compound with the formula HOCHCN. It is the simplest cyanohydrin, being derived from formaldehyde. | 0 | Organic Chemistry |
Although it is relatively simple to demonstrate that the electron and proton begin and end in different orbitals, it is more difficult to prove that they do not move sequentially. The main evidence that PCET exists is that a number of reactions occur faster than expected for the sequential pathways. In the initial electron transfer (ET) mechanism, the initial redox event has a minimum thermodynamics barrier associate with the first step. Similarly, the initial proton transfer (PT) mechanism has a minimum barrier associated with the protons initial pK. Variations on these minimum barriers are also considered. The important finding is that there are a number of reactions with rates greater than these minimum barriers would permit. This suggests a third mechanism lower in energy; the concerted PCET has been offered as this third mechanism. This assertion has also been supported by the observation of unusually large kinetic isotope effects (KIE).
A typical method for establishing PCET pathway is to show that the individual ET and PT pathways operate at higher activation energy than the concerted pathway. | 7 | Physical Chemistry |
Daily experience shows that T-symmetry does not hold for the behavior of bulk materials. Of these macroscopic laws, most notable is the second law of thermodynamics. Many other phenomena, such as the relative motion of bodies with friction, or viscous motion of fluids, reduce to this, because the underlying mechanism is the dissipation of usable energy (for example, kinetic energy) into heat.
The question of whether this time-asymmetric dissipation is really inevitable has been considered by many physicists, often in the context of Maxwells demon. The name comes from a thought experiment described by James Clerk Maxwell in which a microscopic demon guards a gate between two halves of a room. It only lets slow molecules into one half, only fast ones into the other. By eventually making one side of the room cooler than before and the other hotter, it seems to reduce the entropy of the room, and reverse the arrow of time. Many analyses have been made of this; all show that when the entropy of room and demon are taken together, this total entropy does increase. Modern analyses of this problem have taken into account Claude E. Shannons relation between entropy and information. Many interesting results in modern computing are closely related to this problem—reversible computing, quantum computing and physical limits to computing, are examples. These seemingly metaphysical questions are today, in these ways, slowly being converted into hypotheses of the physical sciences.
The current consensus hinges upon the Boltzmann–Shannon identification of the logarithm of phase space volume with the negative of Shannon information, and hence to entropy. In this notion, a fixed initial state of a macroscopic system corresponds to relatively low entropy because the coordinates of the molecules of the body are constrained. As the system evolves in the presence of dissipation, the molecular coordinates can move into larger volumes of phase space, becoming more uncertain, and thus leading to increase in entropy. | 7 | Physical Chemistry |
Identification of predictive biomarkers of efficacy for tumor types that are sensitive to mTOR inhibitors remains a major issue.
Possible predictive biomarkers for tumor response to mTOR inhibitors, as have been described in glioblastoma, breast and prostate cancer cells, may be the differential expression of mTOR pathway proteins, PTEN, AKT, and S6. Thus, this data is based on preclinical assays, based on in vitro cultured tumor cell lines, which suggest that the effects of mTOR inhibitors may be more pronounced in cancers displaying loss of PTEN functions or PIK3CA mutations. However, the use of PTEN, PIK3CA mutations, and AKT–phospho status for predicting rapalog sensitivity has not been fully validated in clinic. To date, attempts to identify biomarkers of rapalog response have been unsuccessful. | 1 | Biochemistry |
Glomalin is hypothesized to improve soil aggregate stability and decrease soil erosion. However, since glomalin can not be adequate quantified in soil, studies usually analyze the GRSPs extract, which is a complex mixture including proteins and other substances.
GRSPs, the mixture of proteins and humic substances, are a significant component of soil organic matter and act to bind mineral particles together, improving soil quality. GRSPs have been investigated for its carbon and nitrogen storing properties, including as a potential method of carbon sequestration. Sampled GRSP takes 7–42 years to biodegrade and is thought to contribute up to 30 percent of the soil carbon where mycorrhizal fungi is present. The highest levels of GRSP were found in volcanic soils of Hawaii and Japan. Concentrations of glomalin in soil were correlated with the primary productivity of an ecosystem. A strong correlation has been found between GRSP and soil aggregate water stability in a wide variety of soils where organic material is the main binding agent, although the mechanism is not known. | 9 | Geochemistry |
A living organism is a thermodynamic system of an active type (in which energy transformations occur), striving for a stable nonequilibrium thermodynamic state. The nonequilibrium thermodynamic state in plants is achieved by continuous alternation of phases of solar energy consumption as a result of photosynthesis and subsequent biochemical reactions, as a result of which adenosine triphosphate (ATP) is synthesized in the daytime, and the subsequent release of energy during the splitting of ATP mainly in the dark. Thus, one of the conditions for the existence of life on Earth is the alternation of light and dark time of day.
In animals, the processes of alternating cycles of biochemical reactions of ATP synthesis and cleavage occur automatically. Moreover, the processes of alternating cycles of biochemical reactions at the levels of organs, systems and the whole organism, for example, respiration, heart contractions and others occur with different periods and externally manifest themselves in the form of biorhythms. At the same time, the stability of the nonequilibrium thermodynamic state, optimal under certain conditions of vital activity, is provided by feedback systems through the regulation of biochemical reactions in accordance with the Lyapunov stability theory. This principle of vital activity was formulated by B. Dobroborsky in the form of the 2nd law of thermodynamics of biological systems in the following wording:
The stability of the nonequilibrium thermodynamic state of biological systems is ensured by the continuous alternation of phases of energy consumption and release through controlled reactions of synthesis and cleavage of ATP.
The following consequences follow from this law:
1. In living organisms, no process can occur continuously, but must alternate with the opposite direction: inhalation with exhalation, work with rest, wakefulness with sleep, synthesis with cleavage, etc.
2. The state of a living organism is never static, and all its physiological and energy parameters are always in a state of continuous fluctuations relative to the average values both in frequency and amplitude.
This principle of functioning of living organisms provides them with the properties of phenotypic adaptation and a number of others. | 7 | Physical Chemistry |
Addition of achiral allylmetals to aldehydes forms a chiral alcohol, the stereochemical outcome of this reaction is determined by the chirality of the α-carbon on the aldehyde substrate (Figure "Substrate control: addition of achiral allylmetals to α-chiral aldehydes"). The allylmetal reagents used include boron, tin and titanium.
Cram’s rule explains the stereoselectivity by considering the transition state depicted in figure 3. In the transition state the oxygen lone pair is able to interact with the boron centre whilst the allyl group is able to add to the carbon end of the carbonyl group. The steric demand of this transition state is minimized by the α-carbon configuration holding the largest group away from (trans to) the congested carbonyl group and the allylmetal group approaching past the smallest group on the α-carbon centre. In the example below (Figure "An example of substrate controlled addition of achiral allyl-boron to α-chiral aldehyde"), (R)-2-methylbutanal (1) reacts with the allylboron reagent (2) with two possible diastereomers of which the (R, R)-isomer is the major product. The Cram model of this reaction is shown with the carbonyl group placed trans to the ethyl group (the large group) and the allyl boron approaching past the hydrogen (the small group). The structure is shown in Newman projection. In this case the nucleophilic addition reaction happens at the face where the hydrogen (the small group) is, producing the (R, R)-isomer as the major product. | 4 | Stereochemistry |
In winter conditions, or in cold climates, when the temperature falls below , the crystallization of ice in the pores of concrete is also a physical mechanism (change of state) responsible for the volumetric expansion of a substance exerting a high tensile strength inside the concrete matrix. When the tensile strength of concrete is exceeded, cracks appear. Adding an air entrainment agent during the mixing of fresh concrete induces the formation of tiny air bubbles in the fresh concrete slurry. This creates numerous small air-filled micro-cavities in the hardened concrete serving as empty volume reserve to accommodate the volumetric expansion of ice and delays the moment tensile stress will develop. Air entrainment makes concrete more workable during placement, and increases its durability when hardened, particularly in climates subject to freeze-thaw cycles. | 8 | Metallurgy |
In oral rehydration therapy, electrolyte drinks containing sodium and potassium salts replenish the body's water and electrolyte concentrations after dehydration caused by exercise, excessive alcohol consumption, diaphoresis (heavy sweating), diarrhea, vomiting, intoxication or starvation. Athletes exercising in extreme conditions (for three or more hours continuously, e.g. a marathon or triathlon) who do not consume electrolytes risk dehydration (or hyponatremia).
A home-made electrolyte drink can be made by using water, sugar and salt in precise proportions. It is important to include glucose (sugar) to utilise the co-transport mechanism of sodium and glucose. Commercial preparations are also available for both human and veterinary use.
Electrolytes are commonly found in fruit juices, sports drinks, milk, nuts, and many fruits and vegetables (whole or in juice form) (e.g., potatoes, avocados). | 7 | Physical Chemistry |
Potential of a cell assembled of two electrodes can be determined from the two individual electrode potentials using
: however , it depends.
or, equivalently,
This follows from the IUPAC definition of the electric potential difference of a galvanic cell, according to which the electric potential difference of a cell is the difference of the potentials of the electrodes on the right and the left of the galvanic cell. When is positive, then positive electrical charge flows through the cell from the left electrode (anode) to the right electrode (cathode). | 7 | Physical Chemistry |
MAPs bind to the tubulin subunits that make up microtubules to regulate their stability. A large variety of MAPs have been identified in many different cell types, and they have been found to carry out a wide range of functions. These include both stabilizing and destabilizing microtubules, guiding microtubules towards specific cellular locations, cross-linking microtubules and mediating the interactions of microtubules with other proteins in the cell.
Within the cell, MAPs bind directly to the tubulin dimers of microtubules. This binding can occur with either polymerized or depolymerized tubulin, and in most cases leads to the stabilization of microtubule structure, further encouraging polymerization. Usually, it is the C-terminal domain of the MAP that interacts with tubulin, while the N-terminal domain can bind with cellular vesicles, intermediate filaments or other microtubules. MAP-microtubule binding is regulated through MAP phosphorylation. This is accomplished through the function of the microtubule-affinity-regulating-kinase (MARK) protein. Phosphorylation of the MAP by the MARK causes the MAP to detach from any bound microtubules. This detachment is usually associated with a destabilization of the microtubule causing it to fall apart. In this way the stabilization of microtubules by MAPs is regulated within the cell through phosphorylation. | 1 | Biochemistry |
The derivation of the method proceeds as follows. First we introduce rank-one (separable)
approximation to the potential
The integral equation for the rank-one part of potential is easily soluble. The full solution of the original problem can therefore be expressed as
in terms of new function . This function is solution of modified Lippmann–Schwinger equation
with
The remainder potential term is transparent for incoming wave
i. e. it is weaker operator than the original one.
The new problem thus obtained for is of the same form as the original one and we can repeat the procedure.
This leads to recurrent relations
It is possible to show that the T-matrix of the original problem can be expressed in the form of chain fraction
where we defined
In practical calculation the infinite chain fraction is replaced by finite one assuming that
This is equivalent to assuming that the remainder solution
is negligible. This is plausible assumption, since the remainder potential has all vectors
in its null space and it can be shown that this potential converges to zero and the chain fraction converges to the exact T-matrix. | 7 | Physical Chemistry |
In the United Kingdom, regulation of contaminated land comes from Part IIA of the Environmental Protection Act 1990; responsibility falls on local authorities to create a "contaminated land register". For sites with dubious past and present uses the Local Planning Authority may ask for a desktop study, which is sometimes implemented as a condition in planning applications. However by definition land that is derelict or underused is highly unlikely to be determined as contaminated land – especially due to risks to human health.
The key regulation of brownfield land is through the land use planning system when a new land use is being considered. | 2 | Environmental Chemistry |
There is great potential for RNA interference (RNAi) to be used therapeutically to reversibly silence any gene. For RNAi to realize its therapeutic potential, small interfering RNA (siRNA) must be delivered to the site of action in the cells of target tissues. But finding safe and efficient delivery mechanisms is a major obstacle to achieving the full potential of siRNA-based therapies. Unmodified siRNA is unstable in the bloodstream, has the potential to cause immunogenicity, and has difficulty readily navigating cell membranes. As a result, chemical alterations and/or delivery tools are needed to safely transfer siRNA to its site of action.
There are three main techniques of delivery for siRNA that differ on efficiency and toxicity. | 1 | Biochemistry |
A dead zone exists in the Lower St. Lawrence River area from east the Saguenay River to east of Baie Comeau, greatest at depths over and noticed since the 1930s. The main concern for Canadian scientists is the impact on fish found in the area. | 9 | Geochemistry |
Zymology, also known as zymurgy, is an applied science that studies the biochemical process of fermentation and its practical uses. Common topics include the selection of fermenting yeast and bacteria species and their use in brewing, wine making, fermenting milk, and the making of other fermented foods. | 1 | Biochemistry |
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