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A thorough review of trace amine-associated receptors that discusses the historical evolution of this research particularly well is that of Grandy. | 1 | Biochemistry |
Dysfunctional or altered levels of carbaminohemoglobin do not generally cause disease or disorders. Carbaminohemoglobin is a part of the carbon dioxide transport process in the body. The levels of this protein can decrease and increase based on factors that regulate the protein in the body.
A way that carbaminohemoglobin can be associated with disease is when there is a change in its level caused by a pre-existing condition or imbalance in the respiratory and metabolic systems of the human body.
Some of these existing medical conditions can be the following:
# Respiratory acidosis: This condition is characterized by a build up of carbon dioxide in the blood, which leads to a drop in the blood's pH. This occurs when there is an impairment in the gas exchange process, such as respiratory failure.
# Hypoventilation: This type of condition can result in higher levels of carbaminohemoglobin. This condition can be caused by many factors, such as central nervous system disorders, and even some medications. | 1 | Biochemistry |
Coprostanol and its derivative epicoprostanol are used in archaeological and paleoenvironmental studies as indicators of past human activity due to their longevity in soils and strong association with production in the human gut. Researchers have used the presence of coprostanol to identify archaeological features such as cesspits or landscape activities like manuring. Variations in the concentration of coprostanol over time can be used to create human population reconstructions within a specific depositional environment. | 2 | Environmental Chemistry |
Benzoyl peroxide and hydrogen peroxide are used as bleaching and "maturing" agents for treating flour to make its grain release gluten more easily; the alternative is letting the flour slowly oxidize by air, which is too slow for the industrialized era. Benzoyl peroxide is an effective topical medication for treating most forms of acne. | 0 | Organic Chemistry |
Carbohydrate conformation refers to the overall three-dimensional structure adopted by a carbohydrate (saccharide) molecule as a result of the through-bond and through-space physical forces it experiences arising from its molecular structure. The physical forces that dictate the three-dimensional shapes of all molecules—here, of all monosaccharide, oligosaccharide, and polysaccharide molecules—are sometimes summarily captured by such terms as "steric interactions" and "stereoelectronic effects" (see below).
Saccharide and other chemical conformations can be reasonably shown using two-dimensional structure representations that follow set conventions; these capture for a trained viewer an understanding of the three-dimensional structure via structure drawings (see organic chemistry article, and "3D Representations" section in molecular geometry article); they are also represented by stereograms on the two dimensional page, and increasingly using 3D display technologies on computer monitors.
Formally and quantitatively, conformation is captured by description of a molecule's angles—for example, sets of three sequential atoms (bond angles) and four sequential atoms (torsion angles, dihedral angles), where the locations and angular directions of non-bonding lone pair electrons must sometimes also be taken into account.
Conformations adopted by saccharide molecules in response to the physical forces arising from their bonding and nonbonding electrons, modified by the molecule's interactions with its aqueous or other solvent environment, strongly influence their reactivity with and recognition by other molecules (processes which in turn can alter conformation). Chemical transformations and biological signalling mediated by conformation-dependent molecular recognition between molecules underlie all essential processes in living organisms. | 0 | Organic Chemistry |
Safranines are the azonium compounds of symmetrical 2,8-dimethyl-3,7-diaminophenazine. They are obtained by the joint oxidation of one molecule of a para-diamine with two molecules of a primary amine; by the condensation of para-aminoazo compounds with primary amines, and by the action of para-nitrosodialkylanilines with secondary bases such as diphenylmetaphenylenediamine. They are crystalline solids showing a characteristic green metallic lustre; they are readily soluble in water and dye red or violet. They are strong bases and form stable monacid salts. Their alcoholic solution shows a yellow-red fluorescence.
Phenosafranine is not very stable in the free state; its chloride forms green plates. It can be readily diazotized, and the diazonium salt when boiled with alcohol yields aposafranine or benzene induline, CHN. Friedrich Kehrmann showed that aposafranine could be diazotized in the presence of cold concentrated sulfuric acid, and the diazonium salt on boiling with alcohol yielded phenylphenazonium salts. Aposafranone, CHNO, is formed by heating aposafranine with concentrated hydrochloric acid. These three compounds are perhaps to be represented as ortho- or as para-quinones. The "safranine" of commerce is an ortho-tolusafranine. The first aniline dye-stuff to be prepared on a manufacturing scale was mauveine, which was obtained by Sir William Henry Perkin by heating crude aniline with potassium dichromate and sulfuric acid.
Mauveine was converted to parasafranine (1,8-dimethylsafranine) by Perkin in 1878 by oxidative/reductive loss of the 7N-para-tolyl group.
Another well known safranin is phenosafranine (C.I. 50200, 3,7-diamino-5-phenylphenazinium chloride) widely used as a histological dye, photosensitizer and redox probe. | 3 | Analytical Chemistry |
Organic Preparations and Procedures International is a bimonthly scientific journal focusing on organic chemists engaged in synthesis. Topics include original preparative chemistry in association with the synthesis of organic and organometallic compounds. | 0 | Organic Chemistry |
Acetic acid bacteria (AAB) incompletely oxidize sugars and alcohols, usually glucose and ethanol, to acetic acid, in a process called AAB oxidative fermentation (AOF). After glycolysis, the produced pyruvate is broken down to acetaldehyde by pyruvate decarboxylase, which in turn is oxidized to acetic acid by acetaldehyde dehydrogenase. Ethanol is first oxidized to acetaldehyde by alcohol dehydrogenase, which is then converted to acetic acid. Both of these processes either generate NAD(P)H, or shuttle electrons into the electron transport chain via ubiquinol. This process is exploited in the use of acetic acid bacteria to produce vinegar. | 1 | Biochemistry |
Bubble nucleation happens when the a volatile becomes saturated. Actually the bubbles are composed of molecules that tend to aggregate spontaneously in a process called homogeneous nucleation. The surface tension acts on the bubbles shrinking the surface and forces them back to the liquid. The nucleation process is greater when the space to fit is irregular and the volatile molecules can ease the effect of surface tension. The nucleation can occur thanks to the presence of solid crystals, which are stored in the magma chamber. They are perfect potential nucleation sites for bubbles. If there is no nucleation in the magma the bubbles formation might appear really late and magma becomes significantly supersaturated. The balance between supersaturation pressure and bubble's radii expressed by this equation: ∆P=2σ/r, where ∆P is 100 MPa and σ is the surface tension. If the nucleation starts later when the magma is very supersaturated, the distance between bubbles becomes smaller. Essentially if the magma rises rapidly to the surface, the system will be more out of equilibrium and supersaturated. When the magma rises there is competition between adding new molecules to the existing ones and creating new ones. The distance between molecules characterizes the efficiency of volatiles to aggregate to the new or existing site. Crystals inside magma can determine how bubbles grow and nucleate. | 9 | Geochemistry |
An S2 reaction occurs when a nucleophile displaces a leaving group residing on a molecule from the backside of the leaving group. This displacement or substitution results in the formation of a substitution product with inversion of stereochemical configuration. The nucleophile forms a bond with its lone pair as the electron source. The electron sink which ultimately accepts the electron density is the nucleofuge (leaving group), with bond forming and bond breaking occurring simultaneously at the transition state (marked with a double-dagger). The rates of S2 reactions are dependent on the concentration of the haloalkane and the nucleophile.
Because an S2 reaction proceeds with the substitution of a leaving group with a nucleophile, the S designation is used. Because this mechanism proceeds with the interaction of two species at the transition state, it is referred to as a bimolecular process, resulting in the S2 designation. An S2 reaction is a concerted process, which means that the bonds are breaking and forming concurrently. Thus, the electron movement shown by the arrow pushing is happening simultaneously. An S2 reaction has one step. | 0 | Organic Chemistry |
The energy of photons (, which includes Planck's constant) emitted when electrons incident on a substance using an electron beam with a constant energy () relax to a lower energy unoccupied state () is given by the conservation of energy as:
By measuring and , the unoccupied state () of the surface can be found. | 7 | Physical Chemistry |
When a plant is attacked, it emits GLVs into the environment through the air. How a plant responds depends on the type of damage involved. Plants respond differently to damage from a purely mechanical source and damage from herbivores. Mechanical damage tends to cause damage-associated molecular patterns (DAMPs) involving plant-derived substances and breakdown products. Herbivore-associated molecular patterns (HAMPs) involve characteristic molecules left by different types of herbivores when feeding. The oral secretions of herbivores appear to play an essential role in triggering the release of species-specific herbivore-induced plant volatiles. Wounds from herbivores, and mechanical wounds that have been treated with herbivore oral secretions, both trigger the release of higher quantities of plant volatiles than mechanical damage.
Volatile blends are proposed to convey a variety of information to insects and plants. "Each plant species and even each plant genotype releases its own specific blend, and the quantities and ratios in which they are released also vary with the arthropod that is feeding on a plant and may even provide information on the time of day that feeding occurs." In addition to GLVs, herbivore induced plant volatiles (HIPVs) include terpenes, ethylene, methyl salicylate and other VOCs.
GLVs activate the expression of genes related to the plants' defense mechanisms.
Different antagonists trigger different expression of genes and the biosynthesis of signaling peptides which mediate systemic defense responses. | 1 | Biochemistry |
Mark Twains Roughing It', published in 1872, provides an informative early description of Mono Lake in its natural condition in the 1860s. Twain found the lake to be lying "in a lifeless, treeless, hideous desert... the loneliest place on earth." | 2 | Environmental Chemistry |
MALS is most commonly used for the characterization of mass and size of molecules in solution. Early implementations of MALS such as those discussed by Bruno H. Zimm in his paper "Apparatus and Methods for Measurement and Interpretation of the Angular Variation of Light Scattering; Preliminary Results on Polystyrene Solutions" involved using a single detector rotated about a sample contained within a transparent vessel. MALS measurements from non-flowing samples such as this are commonly referred to as "batch measurements". By creating samples at several known low concentrations and detecting scattered light about the sample at varying angles, one can create a Zimm plot by plotting : vs where c is the concentration of the sample and k is a stretch factor used to put kc and into the same numerical range.
When plotted one can extrapolate to both zero angle and zero concentration, and analysis of the plot will give the mean square radius of the sample molecules from the initial slope of the c=0 line and the molar mass of the molecule at the point where both concentration and angle equal zero. Improvements to the Zimm plot, which incorporate all collected data (commonly referred to as a "global fit"), have largely replaced the Zimm plot in modern batch analyses. | 7 | Physical Chemistry |
Cold filter plugging point (CFPP) is the lowest temperature, expressed in degrees Celsius (°C), at which a given volume of diesel type of fuel still passes through a standardized filtration device in a specified time when cooled under certain conditions. This test gives an estimate for the lowest temperature that a fuel will give trouble free flow in certain fuel systems. This is important as in cold temperate countries, a high cold filter plugging point will clog up vehicle engines more easily.
The test is important in relation to the use of additives that allow spreading the usage of winter diesel at temperatures below the cloud point. The tests according to EN 590 show that a CloudPoint of +1 °C can have a CFPP −10 °C. Current additives allow a CFPP of −20 °C to be based on diesel fuel with a CloudPoint of −7 °C.
The trustworthiness of the EN 590 have been criticized as being too low for modern diesel motors – the German ADAC has run a test series on customary winter diesel in a cold chamber. All diesel brands did exceed the legal minimum by 3 to 11 degrees in the laboratory according to the legal DIN test. One of the real diesel motors however stopped working even before the legal minimum was reached, presumably due to an undersized filter heater. Notably the experiments did not show a direct correlation between the CFPP value of the mineral oil and the cold start capability of the diesel motors – hence the automobile club suggest the creation of a new test standard. | 7 | Physical Chemistry |
NASAs Dragonfly' lander/aircraft concept is proposed to launch in 2025 and would seek evidence of biosignatures on the organic-rich surface and atmosphere of Titan, as well as study its possible prebiotic primordial soup. Titan is the largest moon of Saturn and is widely believed to have a large subsurface ocean consisting of a salty brine. In addition, scientists believe that Titan may have the conditions necessary to promote prebiotic chemistry, making it a prime candidate for biosignature discovery. | 2 | Environmental Chemistry |
The origin of diastereoselectivity in reductions of chiral ketones has been extensively analyzed and modeled. According to a model advanced by Felkin, diastereoselectivity is controlled by the relative energy of the three transition states I, II, and III. Transition state I is favored in the absence of polar groups on the α carbon, and stereoselectivity increases as the size of the achiral ketone substituent (R) increases. Transition state III is favored for reductions of alkyl ketones in which R is an electron-withdrawing group, because the nucleophile and electron-withdrawing substituent prefer to be as far away from one another as possible.
Diastereoselectivity in reductions of cyclic ketones has also been studied. Conformationally flexible ketones undergo axial attack by the hydride reagent, leading to the equatorial alcohol. Rigid cyclic ketones, on the other hand, undergo primarily equatorial attack to afford the axial alcohol. Preferential equatorial attack on rigid ketones has been rationalized by invoking "steric approach control"—an equatorial approach of the hydride reagent is less sterically hindered than an axial approach. The preference for axial attack on conformationally flexible cyclic ketones has been addressed by a model put forth by Felkin and Anh. The transition state for axial attack (IV) suffers from steric strain between any axial substituents and the incoming hydride reagent. The transition state for equatorial attack (V) suffers from torsional strain between the incoming hydride reagent and adjacent equatorial hydrogens. The difference between these two strain energies determines which direction of attack is favored, and when R is small, torsional strain in V dominates and the equatorial alcohol product is favored. | 0 | Organic Chemistry |
If lichens are exposed to air pollutants at all times, without any deciduous parts, they are unable to avoid the accumulation of pollutants. Also lacking stomata and a cuticle, lichens may absorb aerosols and gases over the entire thallus surface from which they may readily diffuse to the photobiont layer. Because lichens do not possess roots, their primary source of most elements is the air, and therefore elemental levels in lichens often reflect the accumulated composition of ambient air. The processes by which atmospheric deposition occurs include fog and dew, gaseous absorption, and dry deposition. Consequently, environmental studies with lichens emphasize their feasibility as effective biomonitors of atmospheric quality.
Not all lichens are equally sensitive to air pollutants, so different lichen species show different levels of sensitivity to specific atmospheric pollutants. The sensitivity of a lichen to air pollution is directly related to the energy needs of the mycobiont, so that the stronger the dependency of the mycobiont on the photobiont, the more sensitive the lichen is to air pollution. Upon exposure to air pollution, the photobiont may use metabolic energy for repair of its cellular structures that would otherwise be used for maintenance of its photosynthetic activity, therefore leaving less metabolic energy available for the mycobiont. The alteration of the balance between the photobiont and mycobiont can lead to the breakdown of the symbiotic association. Therefore, lichen decline may result not only from the accumulation of toxic substances, but also from altered nutrient supplies that favor one symbiont over the other.
This interaction between lichens and air pollution has been used as a means of monitoring air quality since 1859, with more systematic methods developed by William Nylander in 1866. | 2 | Environmental Chemistry |
1,1,1,2-Tetrafluoroethane (also known as norflurane (INN), R-134a, Klea 134a, Freon 134a, Forane 134a, Genetron 134a, Green Gas, Florasol 134a, Suva 134a, HFA-134a, or HFC-134a) is a hydrofluorocarbon (HFC) and haloalkane refrigerant with thermodynamic properties similar to R-12 (dichlorodifluoromethane) but with insignificant ozone depletion potential and a lower 100-year global warming potential (1,430, compared to R-12's GWP of 10,900). It has the formula CFCHF and a boiling point of −26.3 °C (−15.34 °F) at atmospheric pressure. R-134a cylinders are colored light blue. A phaseout and transition to HFO-1234yf and other refrigerants, with GWPs similar to CO, began in 2012 within the automotive market. | 2 | Environmental Chemistry |
Stripping is commonly used in industrial applications to remove harmful contaminants from waste streams. One example would be the removal of TBT and PAH contaminants from harbor soils. The soils are dredged from the bottom of contaminated harbors, mixed with water to make a slurry and then stripped with steam. The cleaned soil and contaminant rich steam mixture are then separated. This process is able to decontaminate soils almost completely.
Steam is also frequently used as a stripping agent for water treatment. Volatile organic compounds are partially soluble in water and because of environmental considerations and regulations, must be removed from groundwater, surface water, and wastewater. These compounds can be present because of industrial, agricultural, and commercial activity. | 3 | Analytical Chemistry |
Using the appropriate reagent and conditions, alkyl, alkenyl, allylic, and α-keto sulfones may be reduced in good yield and high stereoselectivity (where applicable). Appropriate conditions for the reduction of these classes of sulfones are discussed below.
Alkyl sulfones may be reduced with sodium or lithium in liquid ammonia; however, the strongly basic conditions of these dissolving metal reductions represent a significant disadvantage. In alcoholic solvents, magnesium metal and a catalytic amount of mercury(II) chloride may be used. A wide variety of functional groups are unaffected by these conditions, including many that are transformed by dissolving metal reductions. Reductive desulfonylation with these reagents does not occur in reactions of β-hydroxy sulfones, due to the poor leaving group ability of the hydroxyl group.
A significant issue associated with the reduction of allylic sulfones is transposition of the allylic double bond, which occurs in varying amounts during reductions by metal amalgams. and tin hydrides Palladium-catalyzed reductive desulfonylations of allylic sulfones do not have this issue, and afford allylic sulfones with high site and stereoselectivity.
Aluminum amalgam (Al/Hg) may be used for the chemoselective reduction of α-sulfonylated carbonyl groups. Carboxylic acid derivatives, acetals, thioacetals, amines, alcohols, and isolated double bonds are all inert to Al/Hg. Selective desulfonylation may be carried out on β-hydroxy sulfones without reductive elimination.
Transition metal catalysis is also useful for the stereospecific reduction of alkenyl sulfones. In the presence of an excess of a Grignard reagent, a palladium(II) or nickel(II) catalyst, and a phosphorus or nitrogen ligand, alkenyl sulfones are converted to the corresponding alkenes stereospecifically in good yield. On the other hand, dissolving metal and metal amalgam reductions are not stereoselective in general. Palladium catalysis is generally superior to nickel catalysis, giving higher yields and stereoselectivities.
Alkyl and alkenyl sulfones with good leaving groups in the β position undergo elimination under reductive conditions to afford alkenes or alkynes. The Julia olefination exploits this process for the synthesis of alkenes from alkyl sulfones and carbonyl compounds. Addition of an α-sulfonyl anion to a carbonyl compound, followed by quenching with an acyl or sulfonyl chloride, leads to a β-acyloxy or -sulfonyloxy sulfone, which undergoes elimination under reductive conditions. Sodium amalgam may be used to accomplish the elimination step; however, the combination of samarium(II) iodide and HMPA is milder than strongly basic sodium amalgam and leads to higher yields in reductive elimination processes. | 0 | Organic Chemistry |
Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased acidity and dissociation of a proton.
There are two main types of molecules that release protons upon illumination: photoacid generators (PAGs) and photoacids (PAHs). PAGs undergo proton photodissociation irreversibly, while PAHs are molecules that undergo proton photodissociation and thermal reassociation. In this latter case, the excited state is strongly acidic, but reversible. | 5 | Photochemistry |
An interesting way of achieving chiral distinction on a CSP is the use of selectors with chiral cavity. These chiral selectors are attached to the stationary phase support material. In this category, there are basically three types of cavity chiral selectors namely cyclodextrins, crown ethers and macrocyclic glycopeptide antibiotics. Among these cyclodextrin based CSP is popular. In this type of CSPs the enantioselective guest-host interaction governs the chiral distinction. | 4 | Stereochemistry |
Around one-third of the human population drinks water from groundwater resources. Of this, about 10%, approximately three hundred million people, obtain water from groundwater resources that are heavily contaminated with arsenic or fluoride. These trace elements derive mainly from minerals. Maps locating potential problematic wells are available. | 1 | Biochemistry |
Dissolving in seawater increases the hydrogen ion () concentration in the ocean, and thus decreases ocean pH, as follows:
In shallow coastal and shelf regions, a number of factors interplay to affect air-ocean exchange and resulting pH change. These include biological processes, such as photosynthesis and respiration, as well as water upwelling. Also, ecosystem metabolism in freshwater sources reaching coastal waters can lead to large, but local, pH changes.
Freshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.
The absorption of CO from the atmosphere does not affect the ocean's alkalinity. This is important to know in this context as alkalinity is the capacity of water to resist acidification. Ocean alkalinity enhancement has been proposed as one option to add alkalinity to the ocean and therefore buffer against pH changes. | 9 | Geochemistry |
Oil sampling is a procedure for collecting a volume of fluid from lubricated or hydraulic machinery for the purpose of oil analysis. Much like collecting forensic evidence at a crime scene, when collecting an oil sample, it is important to ensure that procedures are used to minimize disturbance of the sample during and after the sampling process. Oil samples are typically drawn into a small, clean bottle which is sealed and sent to a laboratory for analysis. | 3 | Analytical Chemistry |
Due to the crucial role of base, specific amines must be added in excess or as solvent for the reaction to proceed. It has been discovered that secondary amines such as piperidine, morpholine, or diisopropylamine in particular can react efficiently and reversibly with trans– complexes by substituting one ligand. The equilibrium constant of this reaction is dependent on R, X, a factor for basicity, and the amine's steric hindrance. The result is competition between the amine and the alkyne group for this ligand exchange, which is why the amine is generally added in excess to promote preferential substitution. | 0 | Organic Chemistry |
Enumerating or counting structural isomers in general is a difficult problem, since one must take into account several bond types (including delocalized ones), cyclic structures, and structures that cannot possibly be realized due to valence or geometric constraints, and non-separable tautomers.
For example, there are nine structural isomers with molecular formula CHO having different bond connectivities. Seven of them are air-stable at room temperature, and these are given in the table below.
Two structural isomers are the enol tautomers of the carbonyl isomers (propionaldehyde and acetone), but these are not stable. | 4 | Stereochemistry |
For gene knockout investigations, RNA interference (RNAi), a more recent method, also known as gene silencing, has gained popularity. In RNA interference (RNAi), messenger RNA for a particular gene is inactivated using small interfering RNA (siRNA) or short hairpin RNA (shRNA). This effectively stops the gene from being expressed. Oncogenes like Bcl-2 and p53, as well as genes linked to neurological disease, genetic disorders, and viral infections, have all been targeted for gene silencing utilizing RNA interference (RNAi). | 1 | Biochemistry |
Lees father was a painter in Taiwan. His mother was an elementary school teacher, and his elder brother, Yuan-Chuan Lee, has been a professor in at Johns Hopkins University for 40 years, awarded the honor Special Chair Lectureship in Academia Sinica in Taiwan. Besides, his younger brother, Yuan-Pern Lee, also awarded this honor. Lees sister, Chi-Mei Lee has served as a professor in National Chung Hsing University.
In 2003, he was one of 22 Nobel Laureates who signed the Humanist Manifesto. | 7 | Physical Chemistry |
In a multicomponent system, where the vapor and liquid consist of more than one type of compounds, describing the equilibrium state is more complicated. For all components in the system, the equilibrium state between the two phases is described by the following equations:
:; and
where and are the temperature and pressure for each phase, and and are the partial molar Gibbs free energy also called chemical potential (units of energy per amount of substance) within the liquid and vapor, respectively, for each phase. The partial molar Gibbs free energy is defined by:
where is the (extensive) Gibbs free energy, and is the amount of substance of component . | 7 | Physical Chemistry |
With increasing number of fluorine atoms on the same (geminal) carbon the other bonds become stronger and shorter. This can be seen by the changes in bond length and strength (BDE) for the fluoromethane series, as shown on the table below; also, the partial charges (q and q) on the atoms change within the series. The partial charge on carbon becomes more positive as fluorines are added, increasing the electrostatic interactions, and ionic character, between the fluorines and carbon. | 0 | Organic Chemistry |
Levomilnacipran (brand name Fetzima) is an antidepressant which was approved in the United States in 2013 for the treatment of major depressive disorder (MDD) in adults. It is the levorotatory enantiomer of milnacipran, and has similar effects and pharmacology, acting as a serotonin–norepinephrine reuptake inhibitor (SNRI). | 4 | Stereochemistry |
Due to the fact that translation elongation is an irreversible process, there are few known mechanisms of its regulation. However, it has been shown that translational efficiency is reduced via diminished tRNA pools, which are required for the elongation of polypeptides. In fact, the richness of these tRNA pools are susceptible to change through cellular oxygen supply. | 1 | Biochemistry |
In theoretical thermodynamics, respected authors vary in their approaches to the definition of quantity of heat transferred. There are two main streams of thinking. One is from a primarily empirical viewpoint (which will here be referred to as the thermodynamic stream), to define heat transfer as occurring only by specified macroscopic mechanisms; loosely speaking, this approach is historically older. The other (which will here be referred to as the mechanical stream) is from a primarily theoretical viewpoint, to define it as a residual quantity calculated after transfers of energy as macroscopic work, between two bodies or closed systems, have been determined for a process, so as to conform with the principle of conservation of energy or the first law of thermodynamics for closed systems; this approach grew in the twentieth century, though was partly manifest in the nineteenth. | 7 | Physical Chemistry |
Quinones form a quinhydrone species by formation of hydrogen bonding between ρ-quinone and ρ-hydroquinone. An equimolar mixture of ρ-quinones and ρ-hydroquinone in contact with an inert metallic electrode, such as antimony, forms what is known as a quinhydrone electrode. Such devices can be used to measure the pH of solutions. Quinhydrone electrodes provide fast response times and high accuracy. However, it can only measure pH in the range of 1 to 9 and the solution must not contain a strong oxidizing or reducing agent.
A platinum wire electrode is immersed in a saturated aqueous solution of quinhydrone, in which there is the following equilibrium
: + 2H +2e.
The potential difference between the platinum electrode and a reference electrode is dependent on the activity, , of hydrogen ions in the solution.
: (Nernst equation) | 3 | Analytical Chemistry |
Human perilipin-1 is composed by 522 amino acids, which add up to a molecular mass of 55.990 kDa. It presents an estimated number of 15 phosphorylation sites (residues 81, 85, 126, 130, 132, 137, 174, 299, 301, 382, 384, 408, 436, 497, 499 and 522) from which 3 -those in bold- have been suggested to be relevant for stimulated-lipolysis through PKA phosphorylation - they correspond respectively to PKA Phosphorylation sites 1, 5 and 6. A compositional bias of Glutamic acid can be found between residues 307 and 316. Its secondary structure has been suggested to be conformed exclusively by partially hydrophobic α-helixes, as well as the respective coils and bends.
Whereas perilipin-1 is coded by a single gene, alternative mRNA splicing processes can lead to three protein isoforms (Perilipin A, B and C). Both Perilipin A and B present common N-terminal regions, differing in the C-terminal ones. Concretely, beginning from the N-terminal of Perilipin-1, a PAT domain—characteristic of its protein family—can be found, followed by an also characteristic repeated sequence of 13 residues which form amphipathic helixes with an active role in linking membranes and a 4-helix bundle before the C-terminal carbon. In Perilipin A, lipophile nature is conferred by the slightly hydrophobic amino acids concentrated in the central 25% of the sequence, region that anchors the protein to the core of the lipid droplet. | 1 | Biochemistry |
ILs can replace water as the electrolyte in metal-air batteries. ILs are attractive because of their low vapor pressure. Furthermore, ILs have an electrochemical window of up to six volts (versus 1.23 for water) supporting more energy-dense metals. Energy densities from 900 to 1600 watt-hours per kilogram appear possible. | 7 | Physical Chemistry |
The FeS ferredoxin from Clostridium pasteurianum (Cp2FeFd; ) has been recognized as distinct protein family on the basis of its amino acid sequence, spectroscopic properties of its iron–sulfur cluster and the unique ligand swapping ability of two cysteine ligands to the [FeS] cluster. Although the physiological role of this ferredoxin remains unclear, a strong and specific interaction of Cp2FeFd with the molybdenum-iron protein of nitrogenase has been revealed. Homologous ferredoxins from Azotobacter vinelandii (Av2FeFdI; ) and Aquifex aeolicus (AaFd; ) have been characterized. The crystal structure of AaFd has been solved. AaFd exists as a dimer. The structure of AaFd monomer is different from other FeS ferredoxins. The fold belongs to the α+β class, with first four β-strands and two α-helices adopting a variant of the thioredoxin fold. UniProt categorizes these as the "2Fe2S Shethna-type ferredoxin" family. | 5 | Photochemistry |
In 1860, Edward Frankland was the first to report the preparation and isolation of a boronic acid. Ethylboronic acid was synthesized by a two-stage process. First, diethylzinc and triethyl borate reacted to produce triethylborane. This compound then oxidized in air to form ethylboronic acid. Several synthetic routes are now in common use, and many air-stable boronic acids are commercially available.
Boronic acids typically have high melting points. They are prone to forming anhydrides by loss of water molecules, typically to give cyclic trimers. | 0 | Organic Chemistry |
Normal–phase chromatography was one of the first kinds of HPLC that chemists developed, but has decreased in use over the last decades. Also known as normal-phase HPLC (NP-HPLC), this method separates analytes based on their affinity for a polar stationary surface such as silica; hence it is based on analyte ability to engage in polar interactions (such as hydrogen-bonding or dipole-dipole type of interactions) with the sorbent surface. NP-HPLC uses a non-polar, non-aqueous mobile phase (e.g., chloroform), and works effectively for separating analytes readily soluble in non-polar solvents. The analyte associates with and is retained by the polar stationary phase. Adsorption strengths increase with increased analyte polarity. The interaction strength depends not only on the functional groups present in the structure of the analyte molecule, but also on steric factors. The effect of steric hindrance on interaction strength allows this method to resolve (separate) structural isomers.
The use of more polar solvents in the mobile phase will decrease the retention time of analytes, whereas more hydrophobic solvents tend to induce slower elution (increased retention times). Very polar solvents such as traces of water in the mobile phase tend to adsorb to the solid surface of the stationary phase forming a stationary bound (water) layer which is considered to play an active role in retention. This behavior is somewhat peculiar to normal phase chromatography because it is governed almost exclusively by an adsorptive mechanism (i.e., analytes interact with a solid surface rather than with the solvated layer of a ligand attached to the sorbent surface; see also reversed-phase HPLC below). Adsorption chromatography is still somewhat used for structural isomer separations in both column and thin-layer chromatography formats on activated (dried) silica or alumina supports.
Partition- and NP-HPLC fell out of favor in the 1970s with the development of reversed-phase HPLC because of poor reproducibility of retention times due to the presence of a water or protic organic solvent layer on the surface of the silica or alumina chromatographic media. This layer changes with any changes in the composition of the mobile phase (e.g., moisture level) causing drifting retention times.
Recently, partition chromatography has become popular again with the development of Hilic bonded phases which demonstrate improved reproducibility, and due to a better understanding of the range of usefulness of the technique. | 3 | Analytical Chemistry |
The zero-phonon line and the phonon sideband jointly constitute the line shape of individual light absorbing and emitting molecules (chromophores) embedded into a transparent solid matrix. When the host matrix contains many chromophores, each will contribute a zero-phonon line and a phonon sideband to the absorption and emission spectra. The spectra originating from a collection of identical chromophores in a matrix is said to be inhomogeneously broadened because each chromophore is surrounded by a somewhat different matrix environment which modifies the energy required for an electronic transition. In an inhomogeneous distribution of chromophores, individual zero-phonon line and phonon sideband positions are therefore shifted and overlapping.
Figure 1 shows the typical line shape for electronic transitions of individual chromophores in a solid matrix. The zero-phonon line is located at a frequency ω’ determined by the intrinsic difference in energy levels between ground and excited state as well as by the local environment. The phonon sideband is shifted to a higher frequency in absorption and to a lower frequency in fluorescence. The frequency gap Δ between the zero-phonon line and the peak of the phonon side band is determined by Franck–Condon principles.
The distribution of intensity between the zero-phonon line and the phonon side band is strongly dependent on temperature. At room temperature there is enough thermal energy to excite many phonons and the probability of zero-phonon transition is close to zero. For organic chromophores in organic matrices, the probability of a zero-phonon electronic transition only becomes likely below about 40 kelvins, but depends also on the strength of coupling between the chromophore and the host lattice. | 7 | Physical Chemistry |
Ionic liquids' low volatility effectively eliminates a major pathway for environmental release and contamination.
Ionic liquids' aquatic toxicity is as severe as or more so than many current solvents.
Ultrasound can degrade solutions of imidazolium-based ionic liquids with hydrogen peroxide and acetic acid to relatively innocuous compounds.
Despite low vapor pressure many ionic liquids are combustible. | 7 | Physical Chemistry |
Glycosylation is the process by which a carbohydrate is covalently attached to a target macromolecule, typically proteins and lipids. This modification serves various functions. For instance, some proteins do not fold correctly unless they are glycosylated. In other cases, proteins are not stable unless they contain oligosaccharides linked at the amide nitrogen of certain asparagine residues. The influence of glycosylation on the folding and stability of glycoprotein is twofold. Firstly, the highly soluble glycans may have a direct physicochemical stabilisation effect. Secondly, N-linked glycans mediate a critical quality control check point in glycoprotein folding in the endoplasmic reticulum. Glycosylation also plays a role in cell-to-cell adhesion (a mechanism employed by cells of the immune system) via sugar-binding proteins called lectins, which recognize specific carbohydrate moieties. Glycosylation is an important parameter in the optimization of many glycoprotein-based drugs such as monoclonal antibodies. Glycosylation also underpins the ABO blood group system. It is the presence or absence of glycosyltransferases which dictates which blood group antigens are presented and hence what antibody specificities are exhibited. This immunological role may well have driven the diversification of glycan heterogeneity and creates a barrier to zoonotic transmission of viruses. In addition, glycosylation is often used by viruses to shield the underlying viral protein from immune recognition. A significant example is the dense glycan shield of the envelope spike of the human immunodeficiency virus.
Overall, glycosylation needs to be understood by the likely evolutionary selection pressures that have shaped it. In one model, diversification can be considered purely as a result of endogenous functionality (such as cell trafficking). However, it is more likely that diversification is driven by evasion of pathogen infection mechanism (e.g. Helicobacter attachment to terminal saccharide residues) and that diversity within the multicellular organism is then exploited endogenously.
Glycosylation can also module the thermodynamic and kinetic stability of the proteins. | 0 | Organic Chemistry |
A mirror does not just produce an image of what would be there without it; it also changes the light distribution in the halfspace in front of and behind the mirror. A mirror hanging on the wall makes the room brighter because additional light sources appear in the mirror image. However, the appearance of additional light does not violate the conservation of energy principle, because some light no longer reaches behind the mirror, as the mirror simply re-directs the light energy. In terms of the light distribution, the virtual mirror image has the same appearance and the same effect as a real, symmetrically arranged half-space behind a window (instead of the mirror). Shadows may extend from the mirror into the halfspace before it, and vice versa. | 4 | Stereochemistry |
* Gel permeation chromatography (also known as size-exclusion chromatography)
* Light scattering measurements such as dynamic light scattering
* Direct measurement via mass spectrometry, using matrix-assisted laser desorption/ionization (MALDI) or electrospray ionization with tandem mass spectrometry (ESI-MS/MS) | 7 | Physical Chemistry |
Supramolecular complexes are formed by non-covalent interactions between two chemical moieties, which can be described as an host and a guest. Most commonly, the interacting species are held together by hydrogen bonds. The definition excludes compounds formed by electrostatic interactions, which are called ion pairs.
In solution, the host H, guest G, and complexes HG, will be in equilibrium with each other. In the simplest case, p=q=1, the equilibrium can be written as
The value of the equilibrium constant, K, for this reaction can, in principle, be determined by any of the techniques described below. Some examples are shown in the following table.
The Gibbs free energy change, , for this reaction is the sum of an enthalpy term, and an entropy term .
Both and values can be determined at a given temperature, , by means of Isothermal titration calorimetry. For an example, see Sessler. et.al. In that example a macrocyclic ring with 4 protonated nitrogen atoms encapsulates a chloride anion; illustrations of ITC data and a titration curve are reproduced in Steed&Atwood. (pp 15–16) The value of the equilibrium constant and the stoichiometry of the species formed were found to be strongly solvent-dependent. With nitromethane solutions values of ΔH = 8.55 kJmol and ΔS = -9.1 JKmol were obtained. | 6 | Supramolecular Chemistry |
There are a variety of probes with different membrane and shaft length combinations available. The molecular weight cutoff of commercially available microdialysis probes covers a wide range of approximately 6-100kD, but also 1MD is available. While water-soluble compounds generally diffuse freely across the microdialysis membrane, the situation is not as clear for highly lipophilic analytes, where both successful (e.g. corticosteroids) and unsuccessful microdialysis experiments (e.g. estradiol, fusidic acid) have been reported. However, the recovery of water-soluble compounds usually decreases rapidly if the molecular weight of the analyte exceeds 25% of the membrane’s molecular weight cutoff. | 1 | Biochemistry |
Charles Thomas Beer (18 November 1915 – 15 June 2010) was a Canadian organic chemist who helped in the discovery of vinblastine.
Born in Leigh, Dorset, England, he received a D.Phil. in chemistry from Oxford in 1948. He came to North America in the early 1950s to the department of medical research at the University of Western Ontario to work with Robert L. Noble. Together they isolated the anti-cancer drug vinblastine from the leaves of the Madagascar periwinkle plant (vinca rosea) at the University of Western Ontario in 1958. The discovery of vinblastine is generally considered a milestone in the development of chemotherapy.
In 1960, he became professor of biochemistry at the University of British Columbia. After his retirement, he remained an honorary senior research scientist in the department of cancer endocrinology at the British Columbia Cancer Agency.
In 1997, he was inducted into the Canadian Medical Hall of Fame. In 2003, he was made a Member of the Order of Canada | 0 | Organic Chemistry |
The bifidus factor might be lacto-N-biose I [LNB], which is a derivative of mucin sugars. However, the exact structure and mechanism behind the bifidus factor remains unknown.
The bacteria would break down lactic acid and acetic acid. The environment of the intestine would become acidic, preventing the growth of any harmful pathogens. The function of LBN is unknown and it is possible that oligosaccharides with terminals of Galβ1-3GlcNAc are the bifidus factors.
Bifidobacteria might suppress infections in infants and children. | 1 | Biochemistry |
Søren Peter Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, known for the introduction of the concept of pH, a scale for measuring acidity and alkalinity. | 3 | Analytical Chemistry |
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
The process is called anodizing because the part to be treated forms the anode electrode of an electrolytic cell. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. Anodic films can also be used for several cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add reflected light wave interference effects.
Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminium alloys, although processes also exist for titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum. Iron or carbon steel metal exfoliates when oxidized under neutral or alkaline micro-electrolytic conditions; i.e., the iron oxide (actually ferric hydroxide or hydrated iron oxide, also known as rust) forms by anoxic anodic pits and large cathodic surface, these pits concentrate anions such as sulfate and chloride accelerating the underlying metal to corrosion. Carbon flakes or nodules in iron or steel with high carbon content (high-carbon steel, cast iron) may cause an electrolytic potential and interfere with coating or plating. Ferrous metals are commonly anodized electrolytically in nitric acid or by treatment with red fuming nitric acid to form hard black Iron(II,III) oxide. This oxide remains conformal even when plated on wiring and the wiring is bent.
Anodizing changes the microscopic texture of the surface and the crystal structure of the metal near the surface. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodized aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from ageing and wear, but more susceptible to cracking from thermal stress. | 8 | Metallurgy |
The main use of pyridine is as a precursor to the herbicides paraquat and diquat. The first synthesis step of insecticide chlorpyrifos consists of the chlorination of pyridine. Pyridine is also the starting compound for the preparation of pyrithione-based fungicides. Cetylpyridinium and laurylpyridinium, which can be produced from pyridine with a Zincke reaction, are used as antiseptic in oral and dental care products. Pyridine is easily attacked by alkylating agents to give N-alkylpyridinium salts. One example is cetylpyridinium chloride.
It is also used in the textile industry to improve network capacity of cotton. | 0 | Organic Chemistry |
Organic chemicals such as lactic acid and citric acid have been used to etch metals and create products as early as 400 BCE, when vinegar was used to corrode lead and create the pigment ceruse, also known as white lead. Most modern chemical milling methods involve alkaline etchants; these may have been used as early as the first century CE.
Armor etching, using strong mineral acids, was not developed until the fifteenth century. Etchants mixed from salt, charcoal, and vinegar were applied to plate armor that had been painted with a maskant of linseed-oil paint. The etchant would bite into the unprotected areas, causing the painted areas to be raised into relief. Etching in this manner allowed armor to be decorated as if with precise engraving, but without the existence of raised burrs; it also prevented the necessity of the armor being softer than an engraving tool. Late in the seventeenth century, etching became used to produce the graduations on measuring instruments; the thinness of lines that etching could produce allowed for the production of more precise and accurate instruments than were possible before. Not long after, it became used to etch trajectory information plates for cannon and artillery operators; paper would rarely survive the rigors of combat, but an etched plate could be quite durable. Often such information (normally ranging marks) was etched onto equipment such as stiletto daggers or shovels.
In 1782, the discovery was made by John Senebier that certain resins lost their solubility to turpentine when exposed to light; that is, they hardened. This allowed the development of photochemical milling, where a liquid maskant is applied to the entire surface of a material, and the outline of the area to be masked created by exposing it to UV light. Photo-chemical milling was extensively used in the development of photography methods, allowing light to create impressions on metal plates.
One of the earliest uses of chemical etching to mill commercial parts was in 1927, when the Swedish company Aktiebolaget Separator patented a method of producing edge filters by chemically milling the gaps in the filters. Later, around the 1940s, it became widely used to machine thin samples of very hard metal; photo-etching from both sides was used to cut sheet metal, foil, and shim stock to create shims, recording heat frets, and other components. | 8 | Metallurgy |
There exist several variants of the stable carbenes above where one of the nitrogen atoms adjacent to the carbene center (the α nitrogens) has been replaced by an alternative heteroatom, such as oxygen, sulfur, or phosphorus.
In particular, the formal substitution of sulfur for one of the nitrogens in imidazole would yield the aromatic heterocyclic compound thiazole. A thiazole based carbene (analogous to the carbene postulated by Breslow) has been prepared and characterised by X-ray crystallography. Other non-aromatic aminocarbenes with O, S and P atoms adjacent (i.e. alpha) to the carbene centre have been prepared, for example, thio- and oxyiminium based carbenes have been characterised by X-ray crystallography.
Since oxygen and sulfur are divalent, steric protection of the carbenic centre is limited especially when the N–C–X unit is part of a ring. These acyclic carbenes have diagnostic C NMR chemical shift values between 250 and 300 ppm for the carbenic carbon, further downfield than any other types of stable carbene. X-ray structures have shown N–C–X bond angles of around 104° and 109° respectively.
Carbenes that formally derive from imidazole-2-ylidenes by substitution of sulfur, oxygen, or other chalcogens for both α-nitrogens are expected to be unstable, as they have the potential to dissociate into an alkyne (RC≡CR) and a carbon dichalcogenide (X=C=X). | 0 | Organic Chemistry |
In the US, tolerances for the amount of pesticide residue that may remain on food are set by the EPA, and measures are taken to keep pesticide residues below the tolerances. The US EPA has a web page for the allowable tolerances. In order to assess the risks associated with pesticides on human health, the EPA analyzed individual pesticide active ingredients as well as the common toxic effect that groups of pesticides have, called the cumulative risk assessment. Limits that the EPA sets on pesticides before approving them includes a determination of how often the pesticide should be used and how it should be used, in order to protect the public and the environment. In the US, the Food and Drug Administration (FDA) and USDA also routinely check food for the actual levels of pesticide residues.
A US organic food advocacy group, the Environmental Working Group, is known for creating a list of fruits and vegetables referred to as the Dirty Dozen; it lists produce with the highest number of distinct pesticide residues or most samples with residue detected in USDA data. This list is generally considered misleading and lacks scientific credibility because it lists detections without accounting for the risk of the usually small amount of each residue with respect to consumer health. In 2016, over 99% of samples of US produce had no pesticide residue or had residue levels well below the EPA tolerance levels for each pesticide. | 2 | Environmental Chemistry |
In physics, maximum entropy thermodynamics (colloquially, MaxEnt thermodynamics) views equilibrium thermodynamics and statistical mechanics as inference processes. More specifically, MaxEnt applies inference techniques rooted in Shannon information theory, Bayesian probability, and the principle of maximum entropy. These techniques are relevant to any situation requiring prediction from incomplete or insufficient data (e.g., image reconstruction, signal processing, spectral analysis, and inverse problems). MaxEnt thermodynamics began with two papers by Edwin T. Jaynes published in the 1957 Physical Review. | 7 | Physical Chemistry |
Three main classes of reactions can be explained by the Curtin–Hammett principle: either the more or less stable conformer may react more quickly, or they may both react at the same rate. | 7 | Physical Chemistry |
The presence of sea foam in the marine environment plays a number of ecological roles including providing sources of food and creating habitat. As a food source, sea foam with a stable composition is more important ecologically, as it is able to persist longer and can transport nutrients within the marine environment. Longer decay times result in a higher chance that energy contained in sea foam will move up the food web into higher trophic levels. In the Bay of Fundy for example, a tube-dwelling amphipod, Corophium volutator, can potentially attain 70% of its nutritional requirements from the sugars and amino acids derived from sea foam in its environment. At times however, the sea foam was found to be toxic to this species. It is thought that high concentrations of phenolics and/or the occasional presence of heavy metals or pesticides incorporated into the sea foam from the sea surface contributed to its toxicity. On the west coast of Cape Peninsula, South Africa, sea foam often occurs in nearshore marine areas with large kelp beds during periods of strong westerly winds. It is thought that the foam generated in these conditions is an important food source for local organisms due to the presence of organic detritus in the sea foam. | 9 | Geochemistry |
Trabectedin is composed of three tetrahydroisoquinoline moieties, eight rings including one 10-membered heterocyclic ring containing a cysteine residue, and seven chiral centers. | 0 | Organic Chemistry |
The editing involves cytidine deaminase that deaminates a cytidine base into a uridine base. An example of C-to-U editing is with the apolipoprotein B gene in humans. Apo B100 is expressed in the liver and apo B48 is expressed in the intestines. In the intestines, the mRNA has a CAA sequence edited to be UAA, a stop codon, thus producing the shorter B48 form.
C-to-U editing often occurs in the mitochondrial RNA of flowering plants. Different plants have different degrees of C-to-U editing; for example, eight editing events occur in mitochondria of the moss Funaria hygrometrica, whereas over 1,700 editing events occur in the lycophytes Isoetes engelmanii. C-to-U editing is performed by members of the pentatricopeptide repeat (PPR) protein family. Angiosperms have large PPR families, acting as trans -factors for cis -elements lacking a consensus sequence; Arabidopsis has around 450 members in its PPR family. There have been a number of discoveries of PPR proteins in both plastids and mitochondria. | 1 | Biochemistry |
The most basic aryl group is phenyl, which is made up of a benzene ring with one of its hydrogen atom replaced by some substituent, and has the molecular formula . Note that a phenyl group is not the same as a benzyl group, the latter consisting of a phenyl group attached to a methyl group and a molecular formula of .
To name compounds containing phenyl groups, the phenyl group can be taken to be the parent hydrocarbon and be represented by the suffix Alternatively, the phenyl group could be treated as the substituent, being described within the name as "phenyl". This is usually done when the group attached to the phenyl group consists of six or more carbon atoms.
As an example, consider a hydroxyl group connected to a phenyl group. In this case, if the phenyl group were taken to be the parent hydrocarbon, the compound would be named hydroxybenzene. Alternatively, and more commonly, the hydroxyl group could be taken as the parent group and the phenyl group treated as the substituent, resulting in the more familiar name phenol. | 0 | Organic Chemistry |
When dealing with gases, fugacity, f, is used rather than activity. However, whereas activity is dimensionless, fugacity has the dimension of pressure. A consequence is that chemical potential has to be defined in terms of a standard pressure, p</sup>:
By convention p</sup> is usually taken to be 1 bar.
Fugacity can be expressed as the product of partial pressure, p, and a fugacity coefficient, Φ:
Fugacity coefficients are dimensionless and can be obtained experimentally at specific temperature and pressure, from measurements of deviations from ideal gas behaviour. Equilibrium constants are defined in terms of fugacity. If the gases are at sufficiently low pressure that they behave as ideal gases, the equilibrium constant can be defined as a quotient of partial pressures.
An example of gas-phase equilibrium is provided by the Haber–Bosch process of ammonia synthesis.
:N + 3 H 2 NH;
This reaction is strongly exothermic, so the equilibrium constant decreases with temperature. However, a temperature of around 400 °C is required in order to achieve a reasonable rate of reaction with currently available catalysts. Formation of ammonia is also favoured by high pressure, as the volume decreases when the reaction takes place. The same reaction, nitrogen fixation, occurs at ambient temperatures in nature, when the catalyst is an enzyme such as nitrogenase. Much energy is needed initially to break the nitrogen–nitrogen triple bond even though the overall reaction is exothermic.
Gas-phase equilibria occur during combustion and were studied as early as 1943 in connection with the development of the V2 rocket engine.
The calculation of composition for a gaseous equilibrium at constant pressure is often carried out using ΔG values, rather than equilibrium constants. | 7 | Physical Chemistry |
The Molecular Ancestry Network (MANET) database is a bioinformatics database that maps evolutionary relationships of protein architectures directly onto biological networks. It was originally developed by Hee Shin Kim, Jay E. Mittenthal and Gustavo Caetano-Anolles in the Department of Crop Sciences of the University of Illinois at Urbana-Champaign.
MANET traces for example the ancestry of individual metabolic enzymes in metabolism with bioinformatic, phylogenetic, and statistical methods. MANET currently links information in the Structural Classification of Proteins (SCOP) database, the metabolic pathways database of the Kyoto Encyclopedia of Genes and Genomes (KEGG), and phylogenetic reconstructions describing the evolution of protein fold architecture at a universal level. The database has been updated to reflect evolution of metabolism at the level of protein fold families. MANET literally "paints" the ancestries of enzymes derived from rooted phylogenetic trees directly onto over one hundred metabolic pathways representations, paying homage to one of the fathers of impressionism. It also provides numerous functionalities that enable searching specific protein folds with defined ancestry values, displaying the distribution of enzymes that are painted, and exploring quantitative details describing individual protein folds. This permits the study of global and local metabolic network architectures, and the extraction of evolutionary patterns at global and local levels.
A statistical analysis of the data in MANET showed for example a patchy distribution of ancestry values assigned to protein folds in each subnetwork, indicating that evolution of metabolism occurred globally by widespread recruitment of enzymes. MANET was used recently to sort out enzymatic recruitment processes in metabolic networks and propose that modern metabolism originated in the purine nucleotide metabolic subnetwork. The database is useful for the study of metabolic evolution. | 1 | Biochemistry |
Surface modification has gained a lot of interest in recent years for a variety of applications. An example of the application of free radical polymerizations to forming new architectures is through RAFT polymerizations which result in dithioester end groups. These dithioesters can be reduced to the thiol which can be immobilized on a metal surface; this is important for applications in electronics, sensing and catalysis. The schematic below demonstrates the immobilization of copolymers onto a gold surface as reported for poly(sodium 4-styrenesulfonate) by the McCormick group at the University of Southern Mississippi. | 7 | Physical Chemistry |
Aldol reactions may proceed by two distinct mechanisms. Carbonyl compounds, such as aldehydes and ketones, can be converted to enols or enol ethers. These species, being nucleophilic at the α-carbon, can attack especially reactive protonated carbonyls such as protonated aldehydes. This is the enol mechanism. Carbonyl compounds, being carbon acids, can also be deprotonated to form enolates, which are much more nucleophilic than enols or enol ethers and can attack electrophiles directly. The usual electrophile is an aldehyde, since ketones are much less reactive. This is the enolate mechanism.
Despite the attractiveness of the aldol manifold, there are several problems that need to be addressed to render the process catalytic and effective. The first problem is a thermodynamic one: most aldol reactions are reversible. Furthermore, the equilibrium is also just barely on the side of the products in the case of simple aldehyde–ketone aldol reactions. If the conditions are particularly harsh (e.g.: NaOMe/MeOH/reflux), condensation may occur. However if an Aldol addition is desired, this can usually be avoided with mild reagents and low temperatures (e.g., LDA (a strong base), THF, −78 °C). Although aldol addition usually proceeds to near completion under irreversible conditions, the isolated aldol adducts are sensitive to base-induced retro-aldol cleavage to return starting materials. In contrast, retro-aldol condensations are rare, but possible. This is the basis of the catalytic strategy of class I aldolases in nature, as well as numerous small-molecule amine catalysts. | 0 | Organic Chemistry |
The spontaneous redox reactions of a conventional battery produce electricity through the different reduction potentials of the cathode and anode in the electrolyte. However, electrolysis requires an external source of electrical energy to induce a chemical reaction, and this process takes place in a compartment called an electrolytic cell. | 7 | Physical Chemistry |
The fundamental problem of cartography is that no map from the sphere to the plane can accurately represent both angles and areas. In general, area-preserving map projections are preferred for statistical applications, while angle-preserving (conformal) map projections are preferred for navigation.
Stereographic projection falls into the second category. When the projection is centered at the Earth's north or south pole, it has additional desirable properties: It sends meridians to rays emanating from the origin and parallels to circles centered at the origin. | 3 | Analytical Chemistry |
The influx of micrometeoroids also contributes to the composition of regolith (planetary/lunar soil) on other bodies in the Solar System. Mars has an estimated annual micrometeoroid influx of between 2,700 and 59,000 t/yr. This contributes to about 1 m of micrometeoritic content to the depth of the Martian regolith every billion years. Measurements from the Viking program indicate that the Martian regolith is composed of 60% basaltic rock and 40% rock of meteoritic origin. The lower-density Martian atmosphere allows much larger particles than on Earth to survive the passage through to the surface, largely unaltered until impact. While on Earth particles that survive entry typically have undergone significant transformation, a significant fraction of particles entering the Martian atmosphere throughout the 60 to 1200-μm diameter range probably survive unmelted. | 9 | Geochemistry |
* Chemists' Club of New York, 1974
* Pharmaceutical Society of Japan, 1973
* Chemical Society of Japan, 2002
* Royal Society of Chemistry, UK, 1983
* Chairman Organic Division of the American Chemical Society, 1966–1967 | 0 | Organic Chemistry |
In the semiconductor industry sputtering is used to etch the target. Sputter etching is chosen in cases where a high degree of etching anisotropy is needed and selectivity is not a concern. One major drawback of this technique is wafer damage and high voltage use. | 7 | Physical Chemistry |
*1,2-dipolar compounds have the opposite charges on adjacent atoms.
*1,3-dipolar compounds have the charges separated over three atoms. They are reactants in 1,3-dipolar cycloadditions.
*Also 1,4-dipolars, 1,5-dipolars, and so on exist. | 0 | Organic Chemistry |
Zero-order ultrasensitivity was first described by Albert Goldbeter and Daniel Koshland, Jr in 1981 in a paper in the Proceedings of the National Academy of Sciences. They showed using mathematical modeling that modification of enzymes operating outside of first order kinetics required only small changes in the concentration of the effector to produce larger changes in the amount of modified protein. This amplification provided added sensitivity in biological control, and implicated the importance of this in many biological systems.
Many biological processes are binary (ON-OFF), such as cell fate decisions, metabolic states, and signaling pathways. Ultrasensitivity is a switch that helps decision-making in such biological processes. For example, in apoptotic process, a model showed that a positive feedback of inhibition of caspase 3 (Casp3) and Casp9 by inhibitors of apoptosis can bring about ultrasensitivity (bistability). This positive feedback cooperates with Casp3-mediated feedback cleavage of Casp9 to generate irreversibility in caspase activation (switch ON), which leads to cell apoptosis. Another model also showed similar but different positive feedback controls in Bcl-2 family proteins in apoptotic process.
Recently, Jeyeraman et al. have proposed that the phenomenon of ultrasensitivity may be further subdivided into three sub-regimes, separated by sharp stimulus threshold values: OFF, OFF-ON-OFF, and ON. Based on their model, they proposed that this sub-regime of ultrasensitivity, OFF-ON-OFF, is like a switch-like adaption which can be accomplished by coupling N phosphorylation–dephosphorylation cycles unidirectionally, without any explicit feedback loops.
Other recent work has emphasized that not only is the topology of networks important for creating ultrasensitivity responses, but that their composition (enzymes vs. transcription factors) strongly affects whether they will exhibit robust ultrasensitivity. Mathematical modeling suggests for a broad array of network topologies that a combination of enzymes and transcription factors tends to provide more robust ultrasensitivity than that seen in networks composed entirely of transcription factors or composed entirely of enzymes. | 1 | Biochemistry |
Gammaretroviral and lentiviral vectors for gene therapy have been developed that mediate stable genetic modification of treated cells by chromosomal integration of the transferred vector genomes. This technology is of use, not only for research purposes, but also for clinical gene therapy aiming at the long-term correction of genetic defects, e.g., in stem and progenitor cells. Retroviral vector particles with tropism for various target cells have been designed. Gammaretroviral and lentiviral vectors have so far been used in more than 300 clinical trials, addressing treatment options for various diseases. Retroviral mutations can be developed to make transgenic mouse models to study various cancers and their metastatic models. | 1 | Biochemistry |
The valence isomers are not restricted to isomers of benzene. Valence isomers are also seen in the series (CH). Due to the larger number of units, the number of possible valence isomers is also greater and at least 21: | 4 | Stereochemistry |
When an electrically conductive electrode placed without a direct connection, in the same electrolyte, between an anode and cathode in an electrochemical cell with sufficient voltage being applied; the electrode will experience simultaneous cathodic and anodic reaction at both extremes. This means, the conductive electrode will become a bipolar electrode (BPE); an electrically conductive material in contact with an ionically conductive electrolyte with no direct electronic connection with power supply, that promotes electrochemical (reduction and oxidation) reactions at its both ends (poles); which mean it is a cathode and anode at the same time. This occurs due to: | 7 | Physical Chemistry |
There are three basic configurations in which these agents are stored. The first are self-contained munitions like projectiles, cartridges, mines, and rockets; these can contain propellant and/or explosive components. The next form are aircraft-delivered munitions. Together they constitute the two forms that have been weaponized and are ready for their intended use. The U.S. stockpile consisted of 39% of these weapon ready munitions. The final of the three forms are raw agent housed in one-ton containers. The remaining 61% of the stockpile was in this form. Whereas these chemicals exist in liquid form at normal room temperature, the sulfur mustards H and HD freeze in temperatures below . Mixing lewisite with distilled mustard lowers the freezing point to .
Higher temperatures are a bigger concern because the possibility of an explosion increases as the temperatures rise. A fire at one of these facilities would endanger the surrounding community as well as the personnel at the installations. Perhaps more so for the community having much less access to protective equipment and specialized training. The Oak Ridge National Laboratory conducted a study to assess capabilities and costs for protecting civilian populations during related emergencies, and the effectiveness of expedient, in-place shelters. | 1 | Biochemistry |
Mefloquine is used as a treatment for chloroquine-sensitive or resistant Plasmodium falciparum malaria, and is deemed a reasonable alternative for uncomplicated chloroquine-resistant Plasmodium vivax malaria. It is one of several drugs recommended by the United States' Centers for Disease Control and Prevention.
It is not recommended for severe malaria infections, particularly infections from P. falciparum, which should be treated with intravenous antimalarials. Mefloquine does not eliminate parasites in the liver phase of the disease, and people with P. vivax malaria should be treated with a second drug that is effective for the liver phase, such as primaquine. | 4 | Stereochemistry |
The molecular composition of a biomaterial determines the physical and chemical properties of a biomaterial. These compositions create complex structures that allow the biomaterial to function, and therefore are necessary to define and understand in order to develop a biomaterial. biomaterials can be designed to replicate natural organisms, a process known as biomimetics. The structure of a biomaterial can be observed at different at different levels to better understand a materials properties and function. | 1 | Biochemistry |
Calmodulin plays an important role in the activation of phosphorylase kinase, which ultimately leads to glucose being cleaved from glycogen by glycogen phosphorylase.
Calmodulin also plays an important role in lipid metabolism by affecting calcitonin. Calcitonin is a polypeptide hormone that lowers blood Ca levels and activates Gs protein cascades that leads to the generation of cAMP. The actions of calcitonin can be blocked by inhibiting the actions of calmodulin, suggesting that calmodulin plays a crucial role in the activation of calcitonin. | 1 | Biochemistry |
Elimination, bimolecular reactions are one step, concerted reaction where both base and substrate participate in the rate limiting step. In an E2 mechanism, a base takes a proton near the leaving group, forcing the electrons down to make a double bond, and forcing off the leaving group-all in one concerted step. The rate law depends on the first order concentration of two reactants, making it a 2nd order (bimolecular) elimination reaction. Factors that affect the rate determining step are stereochemistry, leaving groups, and base strength.
A theory, for an E2 reaction, by Joseph Bunnett suggests the lowest pass through the energy barrier between reactants and products is gained by an adjustment between the degrees of C-H and C-X rupture at the transition state. The adjustment involves much breaking of the bond more easily broken, and a small amount of breaking of the bond which requires more energy. This conclusion by Bunnett is a contradiction from the Hammond postulate. The Hammond postulate is the opposite of what Bunnett theorized. In the transition state of a bond breaking step it involves little breaking when the bond is easily broken and much breaking when it is difficult to break. Despite these differences, the two postulates are not in conflict since they are concerned with different sorts of processes. Hammond focuses on reaction steps where one bond is made or broken, or the breaking of two or more bonds occur simultaneously. The E2 theory transition state concerns a process when bond formation or breaking are not simultaneous. | 7 | Physical Chemistry |
The inhabitants of Ban Na Di were casting bronze from to 200 AD, using the lost-wax technique to manufacture bangles. Bangles made by the lost-wax process are characteristic of northeast Thailand. Some of the bangles from Ban Na Di revealed a dark grey substance between the central clay core and the metal, which on analysis was identified as an unrefined form of insect wax. It is likely that decorative items, like bracelets and rings, were made by cire perdue at Non Nok Tha and Ban Chiang. There are technological and material parallels between northeast Thailand and Vietnam concerning the lost-wax technique. The sites exhibiting artifacts made by the lost-mould process in Vietnam, such as the Dong Son drums, come from the Dong Son, and Phung Nguyen cultures, such as one sickle and the figure of a seated individual from Go Mun (near Phung Nguyen, the Bac Bo Region), dating to the Go Mun phase (end of the General B period, up until the 7th century BC). | 8 | Metallurgy |
Bainite can essentially be regarded as martensite that tempers during the course of transformation. It forms at a higher temperature than martensite, and even the latter can autotemper. Because the transformation temperature is higher, the austenite itself is mechanically weak so that the shape deformation due to bainite is relaxed by the plastic deformation of the adjacent austenite. As a consequence, the growing plate of bainite is confronted by a forest of dislocations that eventually terminates its growth even before the plate has hit an austenite grain boundary. Plates of bainite can therefore be smaller than those of martensite in the same steel. The transformation then proceeds by a sub-unit mechanism involving the successive nucleation of new plates. | 8 | Metallurgy |
In Gaunts and Yus works, some derivatives of drug molecules and biologically active compounds were successfully functionalized in their meta-position. For instance, meta-arylated derivatives of anti-inflammatory drugs (S)-ibruprofen and (S)-naproxen were synthesized with copper catalyzed C–H arylation. Meta-olefinated biologically important biphenyl, amino acid and Baclofen derivatives have been accessed by remote C–H activation assisted by the "end-on" template. These demonstrate the potential applications of meta-selective C–H functionalization in medicinal chemistry. | 0 | Organic Chemistry |
Stable isotope ratios of trace metals can be used to answer a variety of questions spanning diverse fields, including oceanography, geochemistry, biology, medicine, anthropology and astronomy. In addition to their modern applications, trace metal isotopic compositions can provide insight into ancient biogeochemical processes operated on Earth. These signatures arise because the processes that form and modify samples are recorded in the trace metal isotopic compositions of the samples. By analyzing and understanding trace metal isotopic compositions in biological, chemical or geological materials, one can answer questions such as the sources of nutrients for phytoplankton in the ocean, processes that drove the formation of geologic structures, the diets of modern or ancient organisms, and accretionary processes that took place in the early Solar System. Trace metal stable isotope biogeochemistry is still an emerging field, yet each trace metal isotope system has clear, powerful applications to diverse and important questions. Important heavy metal isotope systems are discussed (in order of increasing atomic mass) in the proceeding sections. | 9 | Geochemistry |
Ribosomal RNA (rRNA) intergenic spacer analysis (RISA) is a method of microbial community analysis that provides a means of comparing differing environments or treatment impacts without the bias imposed by culture- dependent approaches. RISA involves PCR amplification of a region of the rRNA gene operon between the small (16S) and large (23S) subunits called the intergenic spacer region ISR.
By using oligonucleotide primers targeted to conserved regions in the 16S and 23S genes, RISA fragments can be generated from most of the dominant bacteria in an environmental sample. While the majority of the rRNA operon serves a structural function, portions of the 16S-23S intergenic region can encode tRNAs depending on the bacterial species. However the taxonomic value of the ISR lies in the significant heterogeneity in both length and nucleotide sequence. In RISA, we attempt to exploit the length heterogeneity of the ISR, which has been shown to range between 150 and 1500 bp with the majority of the ISR lengths being between 150 and 500 bp.
The resulting PCR product will be a mixture of fragments contributed by several dominant community members. This product is electrophoresed in a polyacrylamide gel, and the DNA is visualized following staining. The result is a complex banding pattern that provides a community-specific profile, with each DNA band corresponding to a bacterial population on the original assemblage. | 1 | Biochemistry |
Chemical potential is the partial molar free energy. The potential, μ, of the ith species in a chemical reaction is the partial derivative of the free energy with respect to the number of moles of that species, N:
A general chemical equilibrium can be written as
n are the stoichiometric coefficients of the reactants in the equilibrium equation, and m are the coefficients of the products. The value of δG for these reactions is a function of the chemical potentials of all the species.
The chemical potential, μ, of the ith species can be calculated in terms of its activity, a.
μ is the standard chemical potential of the species, R is the gas constant and T is the temperature. Setting the sum for the reactants j to be equal to the sum for the products, k, so that δG(Eq) = 0:
Rearranging the terms,
This relates the standard Gibbs free energy change, ΔG</sup> to an equilibrium constant, K, the reaction quotient of activity values at equilibrium.
It follows that any equilibrium of this kind can be characterized either by the standard free energy change or by the equilibrium constant. In practice concentrations are more useful than activities. Activities can be calculated from concentrations if the activity coefficient are known, but this is rarely the case. Sometimes activity coefficients can be calculated using, for example, Pitzer equations or Specific ion interaction theory. Otherwise conditions must be adjusted so that activity coefficients do not vary much. For ionic solutions this is achieved by using a background ionic medium at a high concentration relative to the concentrations of the species in equilibrium.
If activity coefficients are unknown they may be subsumed into the equilibrium constant, which becomes a concentration quotient. Each activity a is assumed to be the product of a concentration, [A], and an activity coefficient, γ:
This expression for activity is placed in the expression defining the equilibrium constant.
By setting the quotient of activity coefficients, Γ, equal to one, the equilibrium constant is defined as a quotient of concentrations.
In more familiar notation, for a general equilibrium
:α A + β B ... σ S + τ T ...
This definition is much more practical, but an equilibrium constant defined in terms of concentrations is dependent on conditions. In particular, equilibrium constants for species in aqueous solution are dependent on ionic strength, as the quotient of activity coefficients varies with the ionic strength of the solution.
The values of the standard free energy change and of the equilibrium constant are temperature dependent. To a first approximation, the van 't Hoff equation may be used.
This shows that when the reaction is exothermic (ΔH</sup>, is independent of temperature, which is a good approximation only over a small temperature range. Thermodynamic arguments can be used to show that
where C is the heat capacity at constant pressure. | 7 | Physical Chemistry |
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrogen sulfide) or ferrous ions as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon from carbon dioxide through chemosynthesis, are phylogenetically diverse. Groups that include conspicuous or biogeochemically important taxa include the sulfur-oxidizing Gammaproteobacteria, the Campylobacterota, the Aquificota, the methanogenic archaea, and the neutrophilic iron-oxidizing bacteria.
Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single-carbon molecules. Two categories can be distinguished. In the rare sites where hydrogen molecules (H) are available, the energy available from the reaction between CO and H (leading to production of methane, CH) can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized. This may occur with or without the presence of oxygen.
Many chemosynthetic microorganisms are consumed by other organisms in the ocean, and symbiotic associations between chemosynthesizers and respiring heterotrophs are quite common. Large populations of animals can be supported by chemosynthetic secondary production at hydrothermal vents, methane clathrates, cold seeps, whale falls, and isolated cave water.
It has been hypothesized that anaerobic chemosynthesis may support life below the surface of Mars, Jupiter's moon Europa, and other planets. Chemosynthesis may have also been the first type of metabolism that evolved on Earth, leading the way for cellular respiration and photosynthesis to develop later. | 1 | Biochemistry |
This mechanism is found very commonly in everyday life, including central heating, air conditioning, steam turbines, and in many other machines. Forced convection is often encountered by engineers designing or analyzing heat exchangers, pipe flow, and flow over a plate at a different temperature than the stream (the case of a shuttle wing during re-entry, for example). | 7 | Physical Chemistry |
At Eli Lilly in the 1960s, Schmiegel and Bryan Molloy, with the help of David Wong, searched for a compound to combat depression. Because depression and similar psychiatric disorders are associated with reduced serotonin levels, they focused their approach on prohibiting serotonin reuptake. During a regular nerve signal transmission, a neurotransmitter such as serotonin travels from a presynaptic neuron to a postsynaptic neuron; the neurotransmitter returns to the presynaptic neuron after fulfilling its function, the reuptake process. Therefore, slowing and diminishing serotonin reuptake boosts serotonin levels in the brain.
The scientists based their search on the template of the antihistamine drug diphenhydramine hydrochloride, commonly known as Benadryl. After many failures, the research team synthesized a group of compounds called aryloxyphenylpropylamines. Upon testing, a member of the group, fluoxetine hydrochloride, proved to affect only the neurotransmitter serotonin. This compound became the first selective serotonin reuptake inhibitor (SSRI) and the active ingredient in the vastly popular and effective drug Prozac. | 0 | Organic Chemistry |
Light sheet fluorescence microscopy or selective plane imaging microscopy (SPIM) uses illumination that is done perpendicularly to the direction of observation, by using a thin sheet of (laser) light. Under certain conditions, this illumination principle can be combined with fluorescence correlation spectroscopy, to allow spatially resolved imaging of the mobility and interactions of fluorescing particles such as GFP labelled proteins inside living biological samples. | 7 | Physical Chemistry |
García Mancheño has received the following honors and awards during her career:
* 2019 invited speaker at Fulbright-Cottrell Junior Faculty Professional Development Workshop in Göttingen
* 2018 invited speaker at Fulbright-Cottrell Junior Faculty Professional Development Workshop in Berlin
* 2017 European Research Council Consolidator Grant (CoG). Frontiers in Catalytic Anion-Binding Chemistry (Max funding of €1,997,763)
*2016 ORCHEM Prize from the Liebig-Vereinigung für Organische Chemie of the Gesellschaft Deutscher Chemiker | 0 | Organic Chemistry |
*2020 Laura Gagliardi
*2019 Daniel M. Neumark
*2016 Mark A. Ratner
*2015 Xiaoliang Sunney Xie
*2014 Henry F. Schaefer III
*2013 William E. Moerner
*2012 David Chandler
*2011 Louis E. Brus
*2010 George Schatz
*2009 Richard J. Saykally
*2008 Michael L. Klein
*2007 John T. Yates, Jr.
*2006 Donald Truhlar
*2005 Stephen Leone
*2004 William Carl Lineberger
*2003 William H. Miller
*2002 Giacinto Scoles
*2001 John Ross
*2000 Peter G. Wolynes
*1999 Jesse L. Beauchamp
*1998 Graham R. Fleming
*1997 Robin M. Hochstrasser
*1996 Ahmed Zewail
*1995 John C. Tully
*1994 William A. Klemperer
*1993 F. Sherwood Rowland
*1992 Frank H. Stillinger
*1991 Richard N. Zare
*1990 Harden M. McConnell
*1989 Gabor A. Somorjai
*1988 Rudolph A. Marcus
*1987 Harry G. Drickamer
*1986 Yuan T. Lee
*1985 Stuart A. Rice
*1984 B. Seymour Rabinovitch
*1983 George C. Pimentel
*1982 Peter M. Rentzepis
*1981 Richard B. Bernstein
*1976 Robert W. Zwanzig
*1975 Herbert S. Gutowsky
*1974 Walter H. Stockmayer
*1973 William N. Lipscomb, Jr.
*1972 Clyde A. Hutchison, Jr.
*1971 Norman Davidson
*1969 Paul J. Flory
*1968 George B. Kistiakowsky
*1967 Joseph E. Mayer
*1966 Joseph O. Hirschfelder
*1965 Lars Onsager
*1964 Henry Eyring
*1963 Robert S. Mulliken
*1962 E. Bright Wilson, Jr. | 7 | Physical Chemistry |
The standard free-energy scale is measured in electron-volts, and the nE° = 0 value is usually the pure, neutral element. The Frost diagram normally shows free-energy values above and below nE° = 0 and is scaled in integers. The y axis of the graph displays the free energy. Increasing stability (lower free energy) is lower on the graph, so the higher free energy and higher on the graph an element is, the more unstable and reactive it is.
The oxidation state of the element is shown on the x axis of the Frost diagram. Oxidation states are unitless and are also scaled in positive and negative integers. Most often, the Frost diagram displays oxidation number in increasing order, but in some cases it is displayed in decreasing order. The neutral, pure element with a free energy of zero (nE° = 0) also has an oxidation state equal to zero. However, the energy of some allotropes may not be zero.
The slope of the line therefore represents the standard potential between two oxidation states. In other words, the steepness of the line shows the tendency for those two reactants to react and form the lowest-energy product. There is a possibility of having either a positive or negative slope. A positive slope between two species indicates a tendency for an oxidation reaction, while a negative slope between two species indicates a tendency for reduction. For example, if the manganese in [HMnO] has an oxidation state of +6 and nE° = 4, and in MnO the oxidation state is +4 and nE° = 0, then the slope Δy/Δx is 4/2 = 2, yielding the standard potential of +2. The stability of any terms can be similarly found by this graph. | 7 | Physical Chemistry |
Henry Cavendish showed that water was composed of oxygen and hydrogen in 1781. The first decomposition of water into hydrogen and oxygen, by electrolysis, was done in 1800 by English chemist William Nicholson and Anthony Carlisle. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is composed of two parts hydrogen and one part oxygen.
Gilbert Newton Lewis isolated the first sample of pure heavy water in 1933.
The properties of water have historically been used to define various temperature scales. Notably, the Kelvin, Celsius, Rankine, and Fahrenheit scales were, or currently are, defined by the freezing and boiling points of water. The less common scales of Delisle, Newton, Réaumur, and Rømer were defined similarly. The triple point of water is a more commonly used standard point today. | 2 | Environmental Chemistry |
See below. Most stars, including the Sun, generate energy over most of their lives by fusing hydrogen into heavier elements; yet such fusion of light hydrogen (protium) has never been successful in the conditions attainable on Earth. Thus, all artificial fusion, including the hydrogen fusion in hydrogen bombs, requires heavy hydrogen (deuterium, tritium, or both). | 9 | Geochemistry |
In organometallic chemistry, a tuck-in complex usually refers to derivatives of Cp* ligands wherein a methyl group is deprotonated and the resulting methylene attaches to the metal. The C–CH–M angle is acute. The term "tucked in" was coined to describe derivatives of organotungsten complexes. Although most "tucked-in" complexes are derived from Cp* ligands, other pi-bonded rings undergo similar reactions. | 0 | Organic Chemistry |
The term "ultra-deep" can sometimes also refer to higher coverage (>100-fold), which allows for detection of sequence variants in mixed populations. In the extreme, error-corrected sequencing approaches such as Maximum-Depth Sequencing can make it so that coverage of a given region approaches the throughput of a sequencing machine, allowing coverages of >10^8. | 1 | Biochemistry |
For what concern the Samburu-Buffalo Springs, five weeks after the rainy season had started, the grass became rich in nutrients and the females were most likely to conceive, giving birth 22 months later, just in time for another rainy season to provide nutrients to the grass they would have eaten: the cycle could restart.
The research also pointed out how developed is the competition between elephants and cattle: during the typical wet season diet of elephants, the overgrazing by cattle caused the grass to be very short, resulting in a limited access to it for elephants, out-competing them. This situation could have influenced the elephants' ability to bulk up for pregnancy. | 9 | Geochemistry |
M receptors are found in the CNS.
M receptors work via G receptors to decrease cAMP in the cell and, thus, produce generally inhibitory effects. Possible bronchospasm may result if stimulated by muscarinic agonists | 1 | Biochemistry |
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