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7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD) is a bicyclic strong guanidine base (pK = 25.43 in CHCN and pK = 17.9 in THF). mTBD, like [[Triazabicyclodecene|1,5,7-triazabicyclo[4.4.0]dec-5-ene]] and other guanidine super bases, can be used as a catalyst in a variety of chemical reactions. It also reacts with CO, which could make it useful for carbon capture and storage.
When brought into contact with some acids, mTBD reacts to form an ionic liquid. Some of these ionic liquids can dissolve cellulose. | 0 | Organic Chemistry |
The binding of oxygen is affected by molecules such as carbon monoxide (for example, from tobacco smoking, exhaust gas, and incomplete combustion in furnaces). CO competes with oxygen at the heme binding site. Hemoglobins binding affinity for CO is 250 times greater than its affinity for oxygen, meaning that small amounts of CO dramatically reduce hemoglobins ability to deliver oxygen to the target tissue. Since carbon monoxide is a colorless, odorless and tasteless gas, and poses a potentially fatal threat, carbon monoxide detectors have become commercially available to warn of dangerous levels in residences. When hemoglobin combines with CO, it forms a very bright red compound called carboxyhemoglobin, which may cause the skin of CO poisoning victims to appear pink in death, instead of white or blue. When inspired air contains CO levels as low as 0.02%, headache and nausea occur; if the CO concentration is increased to 0.1%, unconsciousness will follow. In heavy smokers, up to 20% of the oxygen-active sites can be blocked by CO.
In similar fashion, hemoglobin also has competitive binding affinity for cyanide (CN), sulfur monoxide (SO), and sulfide (S), including hydrogen sulfide (HS). All of these bind to iron in heme without changing its oxidation state, but they nevertheless inhibit oxygen-binding, causing grave toxicity.
The iron atom in the heme group must initially be in the ferrous (Fe) oxidation state to support oxygen and other gases' binding and transport (it temporarily switches to ferric during the time oxygen is bound, as explained above). Initial oxidation to the ferric (Fe) state without oxygen converts hemoglobin into "hemiglobin" or methemoglobin, which cannot bind oxygen. Hemoglobin in normal red blood cells is protected by a reduction system to keep this from happening. Nitric oxide is capable of converting a small fraction of hemoglobin to methemoglobin in red blood cells. The latter reaction is a remnant activity of the more ancient nitric oxide dioxygenase function of globins. | 7 | Physical Chemistry |
On the basis of Mössbauer spectroscopic analysis, green rust minerals are suspected to occur as minerals in certain bluish-green soils that are formed in alternating redox conditions, and turn ochre once exposed to air. The green rust has been conjectured to be present in the form of the mineral fougerite. | 8 | Metallurgy |
Jani Ingram is a professor of chemistry and biochemistry at Northern Arizona University. Ingram researches the chemistry and health impacts of environmental pollutants, especially uranium and arsenic. Ingram is a member of the Navajo tribe, and the Naneesht’ezhi clan. She leads the Bridging Arizona Native American Students to Bachelor's Degrees (NIH Bridges to Baccalaureate) program and the Native American Cancer Prevention Program. She promotes educational and professional opportunities for Native American students in chemistry through a number of initiatives and for this work was awarded the 2018 American Chemical Society Award for Encouraging Disadvantaged Students into Careers in the Chemical Sciences. | 3 | Analytical Chemistry |
In theoretical chemistry, Marcus theory is a theory originally developed by Rudolph A. Marcus, starting in 1956, to explain the rates of electron transfer reactions – the rate at which an electron can move or jump from one chemical species (called the electron donor) to another (called the electron acceptor). It was originally formulated to address outer sphere electron transfer reactions, in which the two chemical species only change in their charge with an electron jumping (e.g. the oxidation of an ion like Fe/Fe), but do not undergo large structural changes. It was extended to include inner sphere electron transfer contributions, in which a change of distances or geometry in the solvation or coordination shells of the two chemical species is taken into account (the Fe-O distances in Fe(HO) and Fe(HO) are different).
For electron transfer reactions without making or breaking bonds Marcus theory takes the place of Eyrings transition state theory which has been derived for reactions with structural changes. Both theories lead to rate equations of the same exponential form. However, whereas in Eyring theory the reaction partners become strongly coupled in the course of the reaction to form a structurally defined activated complex, in Marcus theory they are weakly coupled and retain their individuality. It is the thermally induced reorganization of the surroundings, the solvent (outer sphere) and the solvent sheath or the ligands (inner sphere) which create the geometrically favourable situation prior' to and independent of the electron jump.
The original classical Marcus theory for outer sphere electron transfer reactions demonstrates the importance of the solvent and leads the way to the calculation of the Gibbs free energy of activation, using the polarization properties of the solvent, the size of the reactants, the transfer distance and the Gibbs free energy of the redox reaction. The most startling result of Marcus' theory was the "inverted region": whereas the reaction rates usually become higher with increasing exergonicity of the reaction, electron transfer should, according to Marcus theory, become slower in the very negative domain. Scientists searched the inverted region for proof of a slower electron transfer rate for 30 years until it was unequivocally verified experimentally in 1984.
R. A. Marcus received the Nobel Prize in Chemistry in 1992 for this theory. Marcus theory is used to describe a number of important processes in chemistry and biology, including photosynthesis, corrosion, certain types of chemiluminescence, charge separation in some types of solar cells and more. Besides the inner and outer sphere applications, Marcus theory has been extended to address heterogeneous electron transfer. | 7 | Physical Chemistry |
The level of complementarity of the mRNA SD sequence to the ribosomal ASD greatly affects the efficiency of translation initiation. Richer complementarity results in higher initiation efficiency. It is worth noting that this only holds up to a certain point - having too rich of a complementarity is known to paradoxically decrease the rate of translation as the ribosome then happens to be bound too tightly to proceed downstream.
The optimal distance between the RBS and the start codon is variable - it depends on the portion of the SD sequence encoded in the actual RBS and its distance to the start site of a consensus SD sequence. Optimal spacing increases the rate of translation initiation once a ribosome has been bound. The composition of nucleotides in the spacer region itself was also found to affect the rate of translation initiation in one study. | 1 | Biochemistry |
Beta particle-emitting substances sometimes exhibit a weak radiation with continuous spectrum that is due to bremsstrahlung (see the "outer bremsstrahlung" below). In this context, bremsstrahlung is a type of "secondary radiation", in that it is produced as a result of stopping (or slowing) the primary radiation (beta particles). It is very similar to X-rays produced by bombarding metal targets with electrons in X-ray generators (as above) except that it is produced by high-speed electrons from beta radiation. | 7 | Physical Chemistry |
The direct reduction of iron ore principle was tested in the late 19th century using high-temperature stirring of ore powder mixed with coal and a small amount of limestone to adjust the ores acidity. Carl Wilhelm Siemens direct reduction process, which was sporadically employed in the United States and United Kingdom in the 1880s, is particularly noteworthy. This process is based on using a 3-meter in diameter and similarly lengthy drum with a horizontal axis for blowing gases preheated by two regenerators.
The metallurgy industry underwent much research regarding the implementation of rotary tubular furnaces, inspired by similar equipment used in cement works. The Basset process, developed during the 1930s, is capable of even producing molten cast iron. In the 1920s, German metallurgist , head of the metallurgy department at the and professor at the Clausthal University of Technology, explored the metallurgical applications of this type of furnace. He filed a series of patents for removing volatile metals from steel raw materials.
During the 1930s Johannsen initiated the development of direct-reduction iron production. The first installation underwent testing from 1931 to 1933 at the Gruson plant in Magdeburg. Research on the Krupp-Renn process continued until 1939 at the Krupp facility in Essen-Borbeck. The process, named after the Krupp company that created it and the , translating to "low furnace," displayed potential. As a result, Krupp procured patents overseas to safeguard the invention after 1932. | 8 | Metallurgy |
Molecular self-assembly underlies the construction of biologic macromolecular assemblies and biomolecular condensates in living organisms, and so is crucial to the function of cells. It is exhibited in the self-assembly of lipids to form the membrane, the formation of double helical DNA through hydrogen bonding of the individual strands, and the assembly of proteins to form quaternary structures. Molecular self-assembly of incorrectly folded proteins into insoluble amyloid fibers is responsible for infectious prion-related neurodegenerative diseases. Molecular self-assembly of nanoscale structures plays a role in the growth of the remarkable β-keratin lamellae/setae/spatulae structures used to give geckos the ability to climb walls and adhere to ceilings and rock overhangs. | 6 | Supramolecular Chemistry |
An eluotropic series is listing of various compounds in order of eluting power for a given adsorbent. The "eluting power" of a solvent is largely a measure of how well the solvent can "pull" an analyte off the adsorbent to which it is attached. This often happens when the eluent adsorbs onto the stationary phase, displacing the analyte. Such series are useful for determining necessary solvents needed for chromatography of chemical compounds. Normally such a series progresses from non-polar solvents, such as n-hexane, to polar solvents such as methanol or water. The order of solvents in an eluotropic series depends both on the stationary phase as well as on the compound used to determine the order. | 3 | Analytical Chemistry |
Hydrolysis of isothiouronium salts gives thiols.
:[RSC(NH)]X + NaOH → RSH + OC(NH) + NaX
Isothiouronium salts in which the sulfur has been alkylated, such as S-methylisothiourea hemisulfate (CAS number: 867-44-7), will convert amines into guanidinium groups. This approach is sometimes called the Rathke synthesis after Bernhard Rathke who first reported it in 1881.
: RNH + [MeSC(NH)]X → RNC(NH)]X + MeSH
Chelating resins with isothiouronium groups are used to recover mercury and other noble metals including platinum from solutions. | 0 | Organic Chemistry |
The replication of technique in copper production includes a vast number of possibilities in trying to recreate what has been found through archaeological excavation. Tylecote and Boydell have experimented on possible explanations for the levels of iron found in certain copper objects and the possibility of removing excess iron through the re-melting of the copper. Crew has also done experimental work on iron to show possible loss in iron mass due to the processes involved with working the metal from bloom to billet which concluded with a loss of 75% in slag, impurities, and iron metal. | 8 | Metallurgy |
The polyniobates, polytantalates, and vanadates are derived, formally at least, from highly charged [MO] precursors. For Nb and Ta, most common members are (M = Nb, Ta), which adopt the Lindqvist structure. These octaanions form in strongly basic conditions from alkali melts of the extended metal oxides (MO), or in the case of Nb even from mixtures of niobic acid and alkali metal hydroxides in aqueous solution. The hexatantalate can also be prepared by condensation of peroxotantalate in alkaline media. These polyoxometalates display an anomalous aqueous solubility trend of their alkali metal salts inasmuch as their Cs and Rb salts are more soluble than their Na and Li salts. The opposite trend is observed in group 6 POMs.
The decametalates with the formula (M = Nb, Ta) are isostructural with decavanadate. They are formed exclusively by edge-sharing {MO} octahedra (the structure of decatungstate comprises edge-sharing and corner-sharing tungstate octahedra). | 7 | Physical Chemistry |
Complex I is the first enzyme of the mitochondrial electron transport chain. There are three energy-transducing enzymes in the electron transport chain - NADH:ubiquinone oxidoreductase (complex I), Coenzyme Q – cytochrome c reductase (complex III), and cytochrome c oxidase (complex IV). Complex I is the largest and most complicated enzyme of the electron transport chain.
The reaction catalyzed by complex I is:
:NADH + H + CoQ + 4H→ NAD + CoQH + 4H
In this process, the complex translocates four protons across the inner membrane per molecule of oxidized NADH, helping to build the electrochemical potential difference used to produce ATP. Escherichia coli complex I (NADH dehydrogenase) is capable of proton translocation in the same direction to the established Δψ, showing that in the tested conditions, the coupling ion is H. Na transport in the opposite direction was observed, and although Na was not necessary for the catalytic or proton transport activities, its presence increased the latter. H was translocated by the Paracoccus denitrificans complex I, but in this case, H transport was not influenced by Na, and Na transport was not observed. Possibly, the E. coli complex I has two energy coupling sites (one Na independent and the other Nadependent), as observed for the Rhodothermus marinus complex I, whereas the coupling mechanism of the P. denitrificans enzyme is completely Na independent. It is also possible that another transporter catalyzes the uptake of Na. Complex I energy transduction by proton pumping may not be exclusive to the R. marinus enzyme. The Na/H antiport activity seems not to be a general property of complex I. However, the existence of Na-translocating activity of the complex I is still in question.
The reaction can be reversed – referred to as aerobic succinate-supported NAD reduction by ubiquinol – in the presence of a high membrane potential, but the exact catalytic mechanism remains unknown. Driving force of this reaction is a potential across the membrane which can be maintained either by ATP-hydrolysis or by complexes III and IV during succinate oxidation.
Complex I may have a role in triggering apoptosis. In fact, there has been shown to be a correlation between mitochondrial activities and programmed cell death (PCD) during somatic embryo development.
Complex I is not homologous to Na-translocating NADH Dehydrogenase (NDH) Family ([http://tcdb.org/search/result.php?tc=3.D.1 TC# 3.D.1]), a member of the Na transporting Mrp superfamily.
As a result of a two NADH molecule being oxidized to NAD+, three molecules of ATP can be produced by Complex V (ATP synthase) downstream in the respiratory chain. | 1 | Biochemistry |
Carbon nucleophiles are often organometallic reagents such as those found in the Grignard reaction, Blaise reaction, Reformatsky reaction, and Barbier reaction or reactions involving organolithium reagents and acetylides. These reagents are often used to perform nucleophilic additions.
Enols are also carbon nucleophiles. The formation of an enol is catalyzed by acid or base. Enols are ambident nucleophiles, but, in general, nucleophilic at the alpha carbon atom. Enols are commonly used in condensation reactions, including the Claisen condensation and the aldol condensation reactions. | 7 | Physical Chemistry |
In crystallography, goniometers are used for measuring angles between crystal faces. They are also used in X-ray diffraction to rotate the samples. The groundbreaking investigations of physicist Max von Laue and colleagues into the atomic structure of crystals in 1912 involved a goniometer. | 7 | Physical Chemistry |
Aldehyde molecules have a central carbon atom that is connected by a double bond to oxygen, a single bond to hydrogen and another single bond to a third substituent, which is carbon or, in the case of formaldehyde, hydrogen. The central carbon is often described as being sp-hybridized. The aldehyde group is somewhat polar. The bond length is about 120–122 picometers. | 0 | Organic Chemistry |
Cantilever enhanced photoacoustic spectroscopy enables the detection of small amount of trace gases which is vital in many applications. Photoacoustic spectroscopy is one of the most sensitive optical detection schemes. It is based on detecting a gas specific acoustic wave generated that originates from the absorption of light in the medium. The sensitivity of the traditional membrane microphones is limited by electrical noise and the nonlinearity of the displacement of the mechanical sensor at high optical power levels. Conventional membrane microphones can be replaced with optically measured micromechanical cantilevers to enhance sensitivity.
__TOC__ | 7 | Physical Chemistry |
If the chromatographic separation can be modified to prevent coelution of suppressing species then other approaches need not be considered. The effect of chromatographic modification may be evaluated using the detector response monitoring under constant infusion approach described previously. | 3 | Analytical Chemistry |
In high energy particle physics nucleon-lepton scattering, the semi-inclusive deep inelastic scattering (SIDIS) is a method to obtain information on the nucleon structure. It expands the traditional method of deep inelastic scattering (DIS). In DIS, only the scattered lepton is detected while the remnants of the shattered nucleon are ignored (inclusive experiment). In SIDIS, a high momentum hadron, a.k.a. as the leading hadron is detected in addition to the scattered lepton. This allows us to obtain additional details about the scattering process kinematics. | 7 | Physical Chemistry |
FTIR is an analytical method which uses an infrared laser focused on a spot on the glass phase of the melt inclusion to determine an absorption (or extinction) coefficient for either HO and CO associated with wavelengths for each species depending on the parent lithology that contained the melt inclusion. | 9 | Geochemistry |
A common pathological cause for a high BMR is fever, since a rise in body temperature increases the rate of cellular metabolic reactions. It is estimated that for every degree Fahrenheit of rise in body temperature, the BMR increases by 7 percent.
Thyroid disease also has a marked effect on BMR, since thyroid hormones regulate the rate of cellular metabolism. Hyperthyroidism—in which there is an increase in the production of thyroid hormones—leads to a high BMR, while hypothyroidism—in which thyroid hormones are depleted—causes a low BMR.
Prolonged periods of abnormal nutrition cause an adaptive change in BMR; this helps the body to maintain a stable body weight in response to the change in food supply. In prolonged malnutrition, the BMR declines, while in prolonged overnutrition, the BMR is increased. Cancer sometimes causes an increase in BMR, perhaps because the cancer cells that form tumors have a high level of metabolic activity. | 1 | Biochemistry |
Protein analysis using microPIXE allow for the determination of the elemental composition of liquid and crystalline proteins. microPIXE can quantify the metal content of protein molecules with a relative accuracy of between 10% and 20%.
The advantage of microPIXE is that given a protein of known sequence, the X-ray emission from sulfur can be used as an internal standard to calculate the number of metal atoms per protein monomer. Because only relative concentrations are calculated there are only minimal systematic errors, and the results are totally internally consistent.
The relative concentrations of DNA to protein (and metals) can also be measured using the phosphate groups of the bases as an internal calibration. | 7 | Physical Chemistry |
Ketone bodies are produced mainly in the mitochondria of liver cells, and synthesis can occur in response to an unavailability of blood glucose, such as during fasting. Other cells, e.g. human astrocytes, are capable of carrying out ketogenesis, but they are not as effective at doing so. Ketogenesis occurs constantly in a healthy individual. Ketogenesis in healthy individuals is ultimately under the control of the master regulatory protein AMPK, which is activated during times of metabolic stress, such as carbohydrate insufficiency. Its activation in the liver inhibits lipogenesis, promotes fatty acid oxidation, switches off acetyl-CoA carboxylase, turns on malonyl-CoA decarboxylase, and consequently induces ketogenesis. Ethanol is a potent AMPK inhibitor and therefore can cause significant disruptions in the metabolic state of the liver, including halting of ketogenesis, even in the context of hypoglycemia.
Ketogenesis takes place in the setting of low glucose levels in the blood, after exhaustion of other cellular carbohydrate stores, such as glycogen. It can also take place when there is insufficient insulin (e.g. in type 1 (and less commonly type 2) diabetes), particularly during periods of "ketogenic stress" such as intercurrent illness.
The production of ketone bodies is then initiated to make available energy that is stored as fatty acids. Fatty acids are enzymatically broken down in β-oxidation to form acetyl-CoA. Under normal conditions, acetyl-CoA is further oxidized by the citric acid cycle (TCA/Krebs cycle) and then by the mitochondrial electron transport chain to release energy. However, if the amounts of acetyl-CoA generated in fatty-acid β-oxidation challenge the processing capacity of the TCA cycle; i.e. if activity in TCA cycle is low due to low amounts of intermediates such as oxaloacetate, acetyl-CoA is then used instead in biosynthesis of ketone bodies via acetoacetyl-CoA and β-hydroxy-β-methylglutaryl-CoA (HMG-CoA). Furthermore, since there is only a limited amount of coenzyme A in the liver, the production of ketogenesis allows some of the coenzyme to be freed to continue fatty-acid β-oxidation. Depletion of glucose and oxaloacetate can be triggered by fasting, vigorous exercise, high-fat diets or other medical conditions, all of which enhance ketone production. Deaminated amino acids that are ketogenic, such as leucine, also feed TCA cycle, forming acetoacetate & ACoA and thereby produce ketones. Besides its role in the synthesis of ketone bodies, HMG-CoA is also an intermediate in the synthesis of cholesterol, but the steps are compartmentalised. Ketogenesis occurs in the mitochondria, whereas cholesterol synthesis occurs in the cytosol, hence both processes are independently regulated. | 1 | Biochemistry |
Water has as much propensity to form hydrogen bonds as any group in a polypeptide. During a folding and association process, peptide and amino acid groups exchange hydrogen bonds with water. Thus, hydrogen bonding does not have a strong stabilizing effect on protein adsorption in an aqueous medium. | 1 | Biochemistry |
The poly(A) tail acts as the binding site for poly(A)-binding protein. Poly(A)-binding protein promotes export from the nucleus and translation, and inhibits degradation. This protein binds to the poly(A) tail prior to mRNA export from the nucleus and in yeast also recruits poly(A) nuclease, an enzyme that shortens the poly(A) tail and allows the export of the mRNA. Poly(A)-binding protein is exported to the cytoplasm with the RNA. mRNAs that are not exported are degraded by the exosome. Poly(A)-binding protein also can bind to, and thus recruit, several proteins that affect translation, one of these is initiation factor-4G, which in turn recruits the 40S ribosomal subunit. However, a poly(A) tail is not required for the translation of all mRNAs. Further, poly(A) tailing (oligo-adenylation) can determine the fate of RNA molecules that are usually not poly(A)-tailed (such as (small) non-coding (sn)RNAs etc.) and thereby induce their RNA decay. | 1 | Biochemistry |
Like all other beta-lactam antibiotics, mezlocillin inhibits the third and last stage of bacterial cell wall synthesis by binding to penicillin binding proteins. This ultimately leads to cell lysis. | 4 | Stereochemistry |
ETQ-QO links the oxidation of fatty acids and some amino acids to oxidative phosphorylation in the mitochondria. Specifically, it catalyzes the transfer of electrons from electron transferring flavoprotein (ETF) to ubiquinone, reducing it to ubiquinol. The entire sequence of transfer reactions is as follows:
Acyl-CoA → Acyl-CoA dehydrogenase → ETF → ETF-QO → UQ → Complex III. | 1 | Biochemistry |
Within the focus of bioengineering, various cell modification methods are utilized to alter inherent properties of cells such as growth density, growth rate, growth yield, temperature resistance, freezing tolerance, chemical sensitivity, and vulnerability to pathogens. For example, in 1988 one group of researchers from the Illinois Institute of Technology successfully expressed a Vitreoscilla hemoglobin gene in E. Coli to create a strain that was more tolerant to low-oxygen conditions such as those found in high density industrial bioreactors. | 1 | Biochemistry |
An exercise mimetic is a drug that mimics some of the biological effects of physical exercise. Exercise is known to have an effect in preventing, treating, or ameliorating the effects of a variety of serious illnesses, including cancer, type 2 diabetes, cardiovascular disease, and psychiatric and neurological diseases such as Alzheimer's disease. As of 2021, no drug is known to have the same benefits.
Known biological targets affected by exercise have also been targets of drug discovery, with limited results. These known targets include:
The majority of the effect of exercise in reducing cardiovascular and all-cause mortality cannot be explained via improvements in quantifiable risk factors, such as blood cholesterol. This further increases the challenge of developing an effective exercise mimetic. Moreover, even if a broad spectrum exercise mimetic were invented, it is not necessarily the case that its public health effects would be superior to interventions to increase exercise in the population. | 1 | Biochemistry |
Hemithioacetals ordinarily readily dissociate into thiol and aldehyde, however, some have been isolated. In general, these isolable hemithioacetals are cyclic, which disfavors dissociation, and can often be further stabilized by the presence of acid. An important class are S-glycosides, such as octylthioglucoside, which are formed by a reaction between thiols and sugars. Other examples include 2-hydroxytetrahydrothiophene and the anti-HIV drug Lamivudine. Another class of isolable hemithioacetals are derived from carbonyl groups that form stable hydrates. For example, thiols react with hexafluoroacetone trihydrate to give hemithioacetals, which can be isolated. | 0 | Organic Chemistry |
The IUBMB is associated with the journals IUBMB Life, Biochemistry and Molecular Biology Education (formerly Biochemical Education), BioFactors, Biotechnology and Applied Biochemistry, Molecular Aspects of Medicine and Trends in Biochemical Sciences. The publishing program supports the IUBMB's mission of fostering growth and advancement of biochemistry and molecular biology as the foundation from which the biomolecular sciences derive their basic ideas and techniques in the service of humanity. | 1 | Biochemistry |
In contrast to elution chromatography, solutes separated in displacement mode form sharp-edged zones rather than spreading peaks. Zone boundaries in displacement chromatography are self-sharpening: if a molecule for some reason gets ahead of its band, it enters a zone in which it is more strongly retained, and will then run more slowly until its zone catches up. Furthermore, because displacement chromatography takes advantage of the non-linearity of the isotherms, loadings are deliberately high; more material can be separated on a given column, in a given time, with the purified components recovered at significantly higher concentrations. Retention conditions can still be adjusted, but the displacer controls the migration rate of the solutes. The displacer is selected to have higher affinity for the stationary phase than does any of the solutes being separated, and its concentration is set to approach saturation of the stationary phase and to give the desired migration rate of the concentration wave. High-retention conditions can be employed without gradient operation, because the displacer ensures removal of all solutes of interest in the designed run time.
Because of the concentrating effect of loading the column under high-retention conditions, displacement chromatography is well suited to purify components from dilute feed streams. However, it is also possible to concentrate material from a dilute stream at the head of a chromatographic column and then switch conditions to elute the adsorbed material in conventional isocratic or gradient modes. Therefore, this approach is not unique to displacement chromatography, although the higher loading capacity and less dilution allow greater concentration in displacement mode.
A disadvantage of displacement chromatography is that non-idealities always give rise to an overlap zone between each pair of components; this mixed zone must be collected separately for recycle or discard to preserve the purity of the separated materials. The strategy of adding spacer molecules to form zones between the components (sometimes termed "carrier displacement chromatography") has been investigated and can be useful when suitable, readily removable spacers are found. Another disadvantage is that the raw chromatogram, for instance a plot of absorbance or refractive index vs elution volume, can be difficult to interpret for contiguous zones, especially if the displacement train is not fully developed. Documentation and troubleshooting may require additional chemical analysis to establish the distribution of a given component. Another disadvantage is that the time required for regeneration limits throughput.
According to John C. Fords article in the Encyclopedia of Chromatography', theoretical studies indicate that at least for some systems, optimized overloaded elution chromatography offers higher throughput than displacement chromatography, though limited experimental tests suggest that displacement chromatography is superior (at least before consideration of regeneration time). | 3 | Analytical Chemistry |
For multicomponent solutions, apparent molar properties can be defined in several ways. For the volume of a ternary (3-component) solution with one solvent and two solutes as an example, there would still be only one equation , which is insufficient to determine the two apparent volumes. (This is in contrast to partial molar properties, which are well-defined intensive properties of the materials and therefore unambiguously defined in multicomponent systems. For example, partial molar volume is defined for each component i as .)
One description of ternary aqueous solutions considers only the weighted mean apparent molar volume of the solutes, defined as
where is the solution volume and the volume of pure water.
This method can be extended for mixtures with more than 3 components.
The sum of products molalities – apparent molar volumes of solutes in their binary solutions equals the product between the sum of molalities of solutes and apparent molar volume in ternary of multicomponent solution mentioned above.
Another method is to treat the ternary system as pseudobinary and define the apparent molar volume of each solute with reference to a binary system containing both other components: water and the other solute. The apparent molar volumes of each of the two solutes are then
: and
The apparent molar volume of the solvent is:
However, this is an unsatisfactory description of volumetric properties.
The apparent molar volume of two components or solutes considered as one pseudocomponent or is not to be confused with volumes of partial binary mixtures with one common component V, V which mixed in a certain mixing ratio form a certain ternary mixture V or V.
Of course the complement volume of a component in respect to other components of the mixture can be defined as a difference between the volume of the mixture and the volume of a binary submixture of a given composition like:
There are situations when there is no rigorous way to define which is solvent and which is solute like in the case of liquid mixtures (say water and ethanol) that can dissolve or not a solid like sugar or salt. In these cases apparent molar properties can and must be ascribed to all components of the mixture. | 7 | Physical Chemistry |
Charles law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles law is:
This relationship of direct proportion can be written as:
So this means:
where:
* is the volume of the gas,
* is the temperature of the gas (measured in kelvins), and
* is a non-zero constant.
This law describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the law can be written as:
The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion. | 7 | Physical Chemistry |
In organic chemistry, a dioxazolone is a cyclic carbonate incorporated into CNO ring. It is an uncommon heterocyclic compound. They arise by the phosgenation of hydroxamic acids:
:RC(O)NHOH + COCl → RC=NOCO + 2 HCl
Although dioxazolones are often explosive, they are of interest as precursors to isocyanates:
:RC=NOCO → R-N=C=O + CO
Dioxazolones have attracted attention as reagents for the preparation of amides. | 0 | Organic Chemistry |
Photolysis occurs in the atmosphere as part of a series of reactions by which primary pollutants such as hydrocarbons and nitrogen oxides react to form secondary pollutants such as peroxyacyl nitrates. See Photochemical smog.
The two most important photodissociation reactions in the troposphere are firstly:
which generates an excited oxygen atom which can react with water to give the hydroxyl radical:
The hydroxyl radical is central to atmospheric chemistry as it initiates the oxidation of hydrocarbons in the atmosphere and so acts as a detergent.
Secondly the reaction:
is a key reaction in the formation of tropospheric ozone.
The formation of the ozone layer is also caused by photodissociation. Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (), splitting them into individual oxygen atoms (atomic oxygen). The atomic oxygen then combines with unbroken to create ozone, . In addition, photolysis is the process by which CFCs are broken down in the upper atmosphere to form ozone-destroying chlorine free radicals. | 5 | Photochemistry |
Ff phages have been engineered for applications such as remediation, electrochemical, photovoltaic, catalytic, sensing and digital memory devices, especially by Angela Belcher and colleagues. | 1 | Biochemistry |
When the days sky is overcast, sunlight passes through the turbidity layer of the clouds, resulting in scattered, diffuse light on the ground (sunbeam). This exhibits Mie scattering instead of Tyndall scattering because the cloud droplets are larger than the wavelength of the light and scatters all colors approximately equally. When the daytime sky is cloudless, the skys color is blue due to Rayleigh scattering instead of Tyndall scattering because the scattering particles are the air molecules, which are much smaller than the wavelengths of visible light. Similarly, the term Tyndall effect is incorrectly applied to light scattering by large, macroscopic dust particles in the air as due to their large size, they do not exhibit Tyndall scattering. | 7 | Physical Chemistry |
Sheldon Cooper, a fictional physicist from the television series The Big Bang Theory, appeared on the cover of a fictional issue of the journal. | 7 | Physical Chemistry |
Acyl ligands are intermediates in many carbonylation reactions, which are important in some catalytic reactions. Metal acyls arise usually via insertion of carbon monoxide into metal–alkyl bonds. Metal acyls also arise from reactions involving acyl chlorides with low-valence metal complexes or by the reaction of organolithium compounds with metal carbonyls. Metal acyls are often described by two resonance structures, one of which emphasizes the basicity of the oxygen center. O-alkylation of metal acyls gives Fischer carbene complexes. | 0 | Organic Chemistry |
Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. The leaf is a vital source of energy production for the plant, and plants have evolved protection against animals that consume leaves, such as tannins, chemicals which hinder the digestion of proteins and have an unpleasant taste. Animals that are specialized to eat leaves are known as folivores.
Some species have cryptic adaptations by which they use leaves in avoiding predators. For example, the caterpillars of some leaf-roller moths will create a small home in the leaf by folding it over themselves. Some sawflies similarly roll the leaves of their food plants into tubes. Females of the Attelabidae, so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. Other herbivores and their predators mimic the appearance of the leaf. Reptiles such as some chameleons, and insects such as some katydids, also mimic the oscillating movements of leaves in the wind, moving from side to side or back and forth while evading a possible threat. | 5 | Photochemistry |
The reflection operation is carried out with respect to symmetry elements known as planes of symmetry or mirror planes. Each such plane is denoted as (sigma). Its orientation relative to the principal axis of the molecule is indicated by a subscript. The plane must pass through the molecule and cannot be completely outside it.
*If the plane of symmetry contains the principal axis of the molecule (i.e., the molecular -axis), it is designated as a vertical mirror plane, which is indicated by a subscript ().
*If the plane of symmetry is perpendicular to the principal axis, it is designated as a horizontal mirror plane, which is indicated by a subscript ().
*If the plane of symmetry bisects the angle between two 2-fold axes perpendicular to the principal axis, it is designated as a dihedral mirror plane, which is indicated by a subscript ().
Through the reflection of each mirror plane, the molecule must be able to produce an identical image of itself. | 7 | Physical Chemistry |
Opposite to false positives, false negative biosignatures arise in a scenario where life may be present on another planet, but some processes on that planet make potential biosignatures undetectable. This is an ongoing problem and area of research in preparation for future telescopes that will be capable of observing exoplanetary atmospheres. | 2 | Environmental Chemistry |
Cells were first seen in 17th-century Europe with the invention of the compound microscope. In 1665, Robert Hooke referred to the building blocks of all living organisms as "cells" (published in Micrographia) after looking at a piece of cork and observing a cell-like structure; however, the cells were dead. They gave no indication to the actual overall components of a cell. A few years later, in 1674, Anton Van Leeuwenhoek was the first to analyze live cells in his examination of algae. Many years later, in 1831, Robert Brown discovered the nucleus. All of this preceded the cell theory which states that all living things are made up of cells and that cells are organisms' functional and structural units. This was ultimately concluded by plant scientist Matthias Schleiden and animal scientist Theodor Schwann in 1838, who viewed live cells in plant and animal tissue, respectively. 19 years later, Rudolf Virchow further contributed to the cell theory, adding that all cells come from the division of pre-existing cells. Viruses are not considered in cell biology – they lack the characteristics of a living cell and instead are studied in the microbiology subclass of virology. | 1 | Biochemistry |
Phytoremediation is the use of plant-based technologies to decontaminate an area.
Most land plants can form a symbiotic relationship with fungi which is advantageous for both organisms. This relationship is called mycorrhiza. Researchers found that phytoremediation is enhanced by mycorrhizae. Mycorrhizal fungis symbiotic relationships with plant roots help with the uptake of nutrients and the plants ability to resist biotic and abiotic stress factors such as heavy metals bioavailable in the rhizosphere. Arbuscular mycorrhizal fungi (AMF) produce proteins that bind heavy metals and thereby decrease their bioavailability. The removal of soil contaminants by mycorrhizal fungi is called mycorrhizoremediation.
Mycorrhizal fungi, especially AMF, can greatly improve the phytoremediation capacity of some plants. This is mostly due to the stress the plants suffer because of the pollutants is greatly reduced in the presence of AMF, so they can grow more and produce more biomass. The fungi also provide more nutrition, especially phosphorus, and promote the overall health of the plants. The mycelium's quick expansion can also greatly extend the rhizosphere influence zone (hyphosphere), providing the plant with access to more nutrients and contaminants. Increasing the rhizosphere overall health also means a rise in the bacteria population, which can also contribute to the bioremediation process.
This relationship has been proven useful with many pollutants, such as Rhizophagus intraradices and Robinia pseudoacacia in lead contaminated soil, Rhizophagus intraradices with Glomus versiforme inoculated into vetiver grass for lead removal, AMF and Calendula officinalis in cadmium and lead contaminated soil, and in general was effective in increasing the plant bioremediation capacity for metals, petroleum fuels, and PAHs. In wetlands AMF greatly promote the biodegradation of organic pollutants like benzene-, methyl tert-butyl ether- and ammonia from groundwater when inoculated into Phragmites australis. | 2 | Environmental Chemistry |
Deprotonation of enolizable ketones, aromatic alcohols, aldehydes, and esters gives enolates. With strong bases, the deprotonation is quantitative. Typically enolates are generated from using lithium diisopropylamide (LDA).
Often, as in conventional Claisen condensations, Mannich reactions, and aldol condensations, enolates are generated in low concentrations with alkoxide bases. Under such conditions, they exist in low concentrations, but they still undergo reactions with electrophiles. Many factors affect the behavior of enolates, especially the solvent, additives (e.g. diamines), and the countercation (Li vs Na, etc.). For unsymmetrical ketones, methods exist to control the regiochemistry of the deprotonation.
The deprotonation of carbon acids can proceed with either kinetic or thermodynamic reaction control. For example, in the case of phenylacetone, deprotonation can produce two different enolates. LDA has been shown to deprotonate the methyl group, which is the kinetic course of the deprotonation. To ensure the production of the kinetic product, a slight excess (1.1 equiv) of lithium diisopropylamide is used, and the ketone is added to the base at −78 °C. Because the ketone is quickly and quantitatively converted to the enolate and base is present in excess at all times, the ketone is unable to act as a proton shuttle to catalyze the gradual formation of the thermodynamic product. A weaker base such as an alkoxide, which reversibly deprotonates the substrate, affords the more thermodynamically stable benzylic enolate.
Enolates can be trapped by acylation and silylation, which occur at oxygen. Silyl enol ethers are common reagents in organic synthesis as illustrated by the Mukaiyama aldol reaction: | 0 | Organic Chemistry |
Escitalopram discontinuation, particularly abruptly, may cause certain withdrawal symptoms such as "electric shock" sensations, colloquially called "brain shivers" or "brain zaps" by those affected. Frequent symptoms in one study were dizziness (44%), muscle tension (44%), chills (44%), confusion or trouble concentrating (40%), amnesia (28%), and crying (28%). Very slow tapering was recommended. There have been spontaneous reports of discontinuation of Lexapro and other SSRIs and SNRIs, especially when abrupt, leading to dysphoric mood, irritability, agitation, anxiety, headache, lethargy, emotional lability, insomnia, and hypomania. Other symptoms such as panic attacks, hostility, aggressiveness, impulsivity, akathisia (psychomotor restlessness), mania, worsening of depression, and suicidal ideation can emerge when the dose is adjusted down. | 4 | Stereochemistry |
The folding of proteins from a primary (linear) sequence of amino acids to a three-dimensional structure is directed by all types of non-covalent interactions, including the hydrophobic forces and formation of intramolecular hydrogen bonds. Three-dimensional structures of proteins, including the secondary and tertiary structures, are stabilized by formation of hydrogen bonds. Through a series of small conformational changes, spatial orientations are modified so as to arrive at the most energetically minimized orientation achievable. The folding of proteins is often facilitated by enzymes known as molecular chaperones. Sterics, bond strain, and angle strain also play major roles in the folding of a protein from its primary sequence to its tertiary structure.
Single tertiary protein structures can also assemble to form protein complexes composed of multiple independently folded subunits. As a whole, this is called a protein's quaternary structure. The quaternary structure is generated by the formation of relatively strong non-covalent interactions, such as hydrogen bonds, between different subunits to generate a functional polymeric enzyme. Some proteins also utilize non-covalent interactions to bind cofactors in the active site during catalysis, however a cofactor can also be covalently attached to an enzyme. Cofactors can be either organic or inorganic molecules which assist in the catalytic mechanism of the active enzyme. The strength with which a cofactor is bound to an enzyme may vary greatly; non-covalently bound cofactors are typically anchored by hydrogen bonds or electrostatic interactions. | 6 | Supramolecular Chemistry |
A Bpin (pinacolatoboron) group, of use in Suzuki-Miyaura cross coupling reactions, can be installed by reaction of a diazonium salt with bis(pinacolato)diboron in the presence of benzoyl peroxide (2 mol %) as an initiator:. Alternatively similar borylation can be achieved using transition metal carbonyl complexes including dimanganese decacarbonyl. | 0 | Organic Chemistry |
Anionic and cationic surfactants can be determined thermometrically by titrating one type against the other. For instance, benzalkonium chloride (a quaternary-type cationic surfactant) may be determined in cleaners and algaecides for swimming pools and spas by titrating with a standard solution of sodium dodecyl sulfate. Alternatively, anionic surfactants such as sodium lauryl sulfate can be titrated with cetyl pyridinium chloride. | 3 | Analytical Chemistry |
The simple relationship between amino acid sequence and DNA recognition of the TALE binding domain allows for the efficient engineering of proteins. In this case, artificial gene synthesis is problematic because of improper annealing of the repetitive sequence found in the TALE binding domain. One solution to this is to use a publicly available software program (DNAWorks) to calculate oligonucleotides suitable for assembly in a two step PCR oligonucleotide assembly followed by whole gene amplification. A number of modular assembly schemes for generating engineered TALE constructs have also been reported. Both methods offer a systematic approach to engineering DNA binding domains that is conceptually similar to the modular assembly method for generating zinc finger DNA recognition domains. | 1 | Biochemistry |
Bitumen is a commonly recycled material in the construction industry. The two most common recycled materials that contain bitumen are reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS). RAP is recycled at a greater rate than any other material in the United States, and typically contains approximately 5–6% bitumen binder. Asphalt shingles typically contain 20–40% bitumen binder.
Bitumen naturally becomes stiffer over time due to oxidation, evaporation, exudation, and physical hardening. For this reason, recycled asphalt is typically combined with virgin asphalt, softening agents, and/or rejuvenating additives to restore its physical and chemical properties. | 7 | Physical Chemistry |
He is the Director of Center for Chemistry at the Space-Time Limit, a National Science Foundation Center for Chemical Innovation. He graduated from University of Southern California with B.S. degrees in Chemistry followed by Ph.D. degree in chemistry from Northwestern University. Following a postdoctoral fellowship at Cornell University, he joined the University of California as Chemistry faculty in 1983. He served as the Chair of the Chemistry Department (2004-2007) at UC Irvine.
He is a Foreign Member of the National Academy of Sciences of Armenia, and a Fellow of American Physical Society, American Association for the Advancement of Sciences. His teaching and research has been recognized with awards including the Humboldt Prize (1996), USC Distinguished Alumnus (2007), Charles Bennett Service Through Chemistry Award of ACS (2008) ACS Award in Experimental Physical Chemistry (2014), Honorary Doctorate from the University of Jyväskylä, Finland (2016).
His recent scientific contributions include creating a single-molecule sensor and developing tools to confine the light to atomic dimensions. His team visualized the internal structure of single molecules and imaging the normal vibrational modes of single molecules. | 7 | Physical Chemistry |
Antoine Lavoisier considered that radiation of heat was concerned with the condition of the surface of a physical body rather than the material of which it was composed. Lavoisier described a poor radiator to be a substance with a polished or smooth surface as it possessed its molecules lying in a plane closely bound together thus creating a surface layer of caloric fluid which insulated the release of the rest within. He described a great radiator to be a substance with a rough surface as only a small amount of molecules held caloric in within a given plane allowing for greater escape from within. Count Rumford would later cite this explanation of caloric movement as insufficient to explain the radiation of cold becoming a point of contention for the theory as a whole.
In his first memoir, Augustin-Jean Fresnel responded to a view he extracted from a French translation of Isaac Newtons Optics'. He says that Newton imagined particles of light traversing space uninhibited by the caloric medium filling it, and refutes this view (never actually held by Newton) by saying that a body under illumination would increase indefinitely in heat.
In Marc-Auguste Pictet's famous experiment of 1790, it was reported that a thermometer detected a lower temperature when a set of mirror were used to focus "frigorific rays" from a cold object.
In 1791, Pierre Prevost a colleague of Pictet, introduced the concept of radiative equilibrium, wherein all objects both radiates and absorb heat. When an object is cooler than its surroundings, it absorbs more heat than it emits, causing its temperature to increase until it reaches equilibrium. Even at equilibrium, it continues to radiate heat, balancing absorption and emission.
The discovery of infrared radiation is ascribed to astronomer William Herschel. Herschel published his results in 1800 before the Royal Society of London. Herschel used a prism to refract light from the sun and detected the calorific rays, beyond the red part of the spectrum, as an increase in the temperature recorded on a thermometer in that region. | 7 | Physical Chemistry |
Prior to the emergence of underwater cabled observatories, oceanographers and other researchers studying the global ocean tended to rely on the use of research vessels and manned submersibles in order to collect data. This was followed by a shift toward Remote Operated Vehicles (ROV's) and space-based research satellites. The limitation to these methods was that they were either not cost-effective, or data could only be collected for short durations. While the importance of expedition-based exploration was recognized, a solution was needed.
In 1987, the concept of utilizing high-power, high-bandwidth underwater cabled observatories emerged as a long-term, cost-effective solution for conducting real-time monitoring of ocean systems.
In the early 1990s, the United States and Canada formed an agreement to develop a plate-scale submarine electro-optically cabled ocean observatory in the northeast Pacific Ocean. This region is home to the smallest of Earth's tectonic plates – the Juan de Fuca plate. The small size and close coastal proximity of the Juan de Fuca plate presents a unique opportunity to observe the dynamic systems in submarine volcano regions.
The partnership between the U.S. and Canada developed into a plan to build a Canadian cabled array that would cover the upper 1/3 of the Juan de Fuca plate, and a U.S. system spanning the lower 2/3 of the plate (cite). Together, this plate-scale observatory would be called NEPTUNE (Northeast Pacific Time Series Underwater Networked Experiments) and would provide continuous observations for 25 years.
By the mid-2000s, NEPTUNE Canada had received full funding and their cabled array was completed and online by 2009. It was brought under the umbrella network of Ocean Networks Canada (ONC). Meanwhile, NEPTUNE U.S. was renamed to Regional Scale Nodes and became a component of the OOI. It is slated for completion in 2014. Both NEPTUNE Canada and RSN will be integrated through the ONC's digital infrastructure and the OOI Cyberinfrastructure providing real-time access to anyone connected to the Internet. | 9 | Geochemistry |
*2023 Peter R. Griffiths
*2022 Martin Zanni
*2021 Rohit Bhargava
*2020 Volker Deckert
*2019 Ji-Xin Cheng
*2018 Peter Hamm
*2017 Roberto Merlin
*2016 Thomas Elsaesser
*2013 Xiaoliang Sunney Xie
*2012 Keith A. Nelson
*2011 Isao Noda
*2009 Michael D. Fayer
*2008 Richard P. Van Duyne
*2007 Jonathan Tennyson
*2006 Hai-Lung Dai
*2003 Shaul Mukamel
*2001 Lester Andrews
*2000 Donald Levy
*1999 Mitsuo Tasumi
*1998 Takeshi Oka
*1997 Robin Hochstrasser
*1995 Giacinto Scoles
*1994 Herbert L. Strauss
*1992 Richard Saykally
*1990 Robert W. Field
*1989 Marilyn E. Jacox
*1988 Andreas C. Albrecht
*1987 C. Bradley Moore
*1986 Wolfgang Kaiser
*1984 Jon T. Hougen
*1980 George C. Pimentel
*1979 E. Bright Wilson
*1978 Bryce L. Crawford, Jr.
*1976 Richard C. Lord | 7 | Physical Chemistry |
In 2009, Larhlimi and Bockmayr presented a new approach called "minimal metabolic behaviors" for the analysis of metabolic networks. Like elementary modes or extreme pathways, these are uniquely determined by the network, and yield a complete description of the flux cone. However, the new description is much more compact. In contrast with elementary modes and extreme pathways, which use an inner description based on generating vectors of the flux cone, MMBs are using an outer description of the flux cone. This approach is based on sets of non-negativity constraints. These can be identified with irreversible reactions, and thus have a direct biochemical interpretation. One can characterize a metabolic network by MMBs and the reversible metabolic space. | 1 | Biochemistry |
The function of liver glycogen is to maintain glucose homeostasis, generating glucose via glycogenolysis to compensate for the decrease of glucose levels that can occur between meals. Thanks to the presence of the glucose-6-phosphatase enzyme, the hepatocytes are capable of turning glycogen to glucose, releasing it into blood to prevent hypoglycemia.
In skeletal muscle, glycogen is used as an energy source for muscle contraction during exercise. The different functions of glycogen in muscle or liver make the regulation mechanisms of its metabolism differ in each tissue. These mechanisms are based mainly on the differences on structure and on the regulation of the enzymes that catalyze synthesis, glycogen synthase (GS), and degradation, glycogen phosphorylase (GF). | 1 | Biochemistry |
TFA is a heterodimer with two subunits: one large unprocessed (subunit 1, or alpha/beta; gene name ) and one small (subunit 2, or gamma; gene name ). It was originally believed to be a heterotrimer of an alpha (p35), a beta (p19) and a gamma subunit (p12). In humans, the sizes of the encoded proteins are approximately 55 kD and 12 kD. Both genes are present in species ranging from humans to yeast, and their protein products interact to form a complex composed of a beta barrel domain and an alpha helical bundle domain. It is the N-terminal and C-terminal regions of the large subunit that participate in interactions with the small subunit. These regions are separated by another domain whose sequence is always present in large subunits from various species but whose size varies and whose sequence is poorly conserved. A second gene encoding a large TFA subunit has been found in some higher eukaryotes. This gene, ALF/TFIIAtau (gene name ) is expressed only in oocytes and spermatocytes, suggesting it has a TFA-like regulatory role for gene expression only in germ cells. | 1 | Biochemistry |
In a study of 5000 oxides, only 13% of them satisfy all of the last 4 rules, indicating limited universality of Pauling's rules. | 4 | Stereochemistry |
Substrates for RuBisCO are ribulose-1,5-bisphosphate and carbon dioxide (distinct from the "activating" carbon dioxide). RuBisCO also catalyses a reaction of ribulose-1,5-bisphosphate and molecular oxygen (O) instead of carbon dioxide ().
Discriminating between the substrates and O is attributed to the differing interactions of the substrates quadrupole moments and a high electrostatic field gradient. This gradient is established by the dimer form of the minimally active RuBisCO, which with its two components provides a combination of oppositely charged domains required for the enzymes interaction with O and . These conditions help explain the low turnover rate found in RuBisCO: In order to increase the strength of the electric field necessary for sufficient interaction with the substrates’ quadrupole moments, the C- and N- terminal segments of the enzyme must be closed off, allowing the active site to be isolated from the solvent and lowering the dielectric constant. This isolation has a significant entropic cost, and results in the poor turnover rate. | 5 | Photochemistry |
In multivariate calculus, a differential or differential form is said to be exact or perfect (exact differential), as contrasted with an inexact differential, if it is equal to the general differential for some differentiable function in an orthogonal coordinate system (hence is a multivariable function whose variables are independent, as they are always expected to be when treated in multivariable calculus).
An exact differential is sometimes also called a total differential, or a full differential, or, in the study of differential geometry, it is termed an exact form.
The integral of an exact differential over any integral path is path-independent, and this fact is used to identify state functions in thermodynamics. | 7 | Physical Chemistry |
Interferometric microscopy or imaging interferometric microscopy is the concept of microscopy which
is related to holography, synthetic-aperture imaging, and off-axis-dark-field illumination techniques.
Interferometric microscopy allows enhancement of resolution of optical microscopy due to interferometric (holographic)
registration of several partial images (amplitude and phase) and the numerical combining. | 7 | Physical Chemistry |
Biological photovoltaic systems are defined by the type of light harvesting material that they employ, and the mode of electron transfer from the biological material to the anode. | 7 | Physical Chemistry |
The vacuum ultraviolet (V‑UV) band (100–200 nm) can be generated by non-linear 4 wave mixing in gases by sum or difference frequency mixing of 2 or more longer wavelength lasers. The generation is generally done in gasses (e.g. krypton, hydrogen which are two-photon resonant near 193 nm) or metal vapors (e.g. magnesium). By making one of the lasers tunable, the V‑UV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the V‑UV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. Difference frequency mixing (i.e., ) has an advantage over sum frequency mixing because the phase matching can provide greater tuning.
In particular, difference frequency mixing two photons of an (193 nm) excimer laser with a tunable visible or near IR laser in hydrogen or krypton provides resonantly enhanced tunable V‑UV covering from 100 nm to 200 nm. Practically, the lack of suitable gas / vapor cell window materials above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable V‑UV wavelengths down to 75 nm was achieved using window-free configurations. | 5 | Photochemistry |
Janus kinase (JAK) is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. They were initially named "just another kinase" 1 and 2 (since they were just two of many discoveries in a PCR-based screen of kinases), but were ultimately published as "Janus kinase". The name is taken from the two-faced Roman god of beginnings, endings and duality, Janus, because the JAKs possess two near-identical phosphate-transferring domains. One domain exhibits the kinase activity, while the other negatively regulates the kinase activity of the first. | 1 | Biochemistry |
The most fundamental formula for Joule heating is the generalized power equation:
where
* is the power (energy per unit time) converted from electrical energy to thermal energy,
* is the current travelling through the resistor or other element,
* is the voltage drop across the element.
The explanation of this formula () is:
Assuming the element behaves as a perfect resistor and that the power is completely converted into heat, the formula can be re-written by substituting Ohm's law, , into the generalized power equation:
where R is the resistance.
Voltage can be increased in DC circuits by connecting batteries or solar panels in series. | 7 | Physical Chemistry |
Copper has played a role in architecture for thousands of years. For example, in ancient Egypt, massive doors to the temple of Amen-Re at Karnak were clad with copper. In the 3rd Century B.C., copper roof shingles were installed atop of the Lowa Maha Paya Temple in Sri Lanka. And the Romans used copper as roof covering for the Pantheon in 27 B.C.
Centuries later, copper and its alloys were integral in medieval architecture. The doors of the Church of the Nativity at Bethlehem (6th century) are covered with plates of bronze, cut out in patterns. Those of Hagia Sophia at Constantinople, of the 8th and 9th century, are wrought in bronze. Bronze doors on the Aachen Cathedral in Germany date back to about 800 A.D. Bronze baptistery doors at the Cathedral of Florence were completed in 1423 A.D. by Ghiberti.
The copper roof of Hildesheim Cathedral, installed in 1280 A.D., survives to this day. And the roof at Kronborg, one of northern Europes most important Renaissance castles that was immortalized as Elsinore Castle in Shakespeares Hamlet, was installed in 1585 A.D. The copper on the tower was renovated in 2009.
For years, copper was reserved mainly for public institutions, such as churches, government buildings, and universities. Copper roofs are often one of the most architecturally distinguishable features of these structures.
Today, architectural copper is used in roofing systems, flashings and copings, rain gutters and downspouts, building expansion joints, wall cladding, domes, spires, vaults, and various other design elements. Simultaneously, the metal has evolved from a weather barrier and exterior design element into indoor building environments where it is changing the way commercial and residential interiors are decorated.
In the 21st century, the use of copper continues to evolve in the indoor environment. Its recently proven antimicrobial properties reduce pathogenic bacterial loads on such products as handrails, bedrails, bathroom fixtures, counter tops, etc. These antimicrobial copper-based products are now being incorporated into public facilities (hospitals, nursing homes, mass transit facilities) as well as in residential buildings because of the public health benefits. (For main article, see: Antimicrobial copper-alloy touch surfaces.) | 8 | Metallurgy |
Eutrophication and harmful algal blooms can have economic impacts due to increasing water treatment costs, commercial fishing and shellfish losses, recreational fishing losses (reductions in harvestable fish and shellfish), and reduced tourism income (decreases in perceived aesthetic value of the water body). Water treatment costs can be increased due to decreases in water transparency (increased turbidity). There can also be issues with color and smell during drinking water treatment. | 2 | Environmental Chemistry |
An estimate of V̇O max is based on maximum and resting heart rates. In the Uth et al. (2004) formulation, it is given by:
This equation uses the ratio of maximum heart rate (HR) to resting heart rate (HR) to predict V̇O max. The researchers cautioned that the conversion rule was based on measurements on well-trained men aged 21 to 51 only, and may not be reliable when applied to other sub-groups. They also advised that the formula is most reliable when based on actual measurement of maximum heart rate, rather than an age-related estimate.
The Uth constant factor of 15.3 is given for well-trained men. Later studies have revised the constant factor for different populations. According to Voutilainen et al. 2020, the constant factor should be 14 in around 40-year-old normal weight never-smoking men with no cardiovascular diseases, bronchial asthma, or cancer.
Every 10 years of age reduces the coefficient by one, as well as does the change in body weight from normal weight to obese or the change from never-smoker to current smoker. Consequently, V̇O max of 60-year-old obese current smoker men should be estimated by multiplying the HR to HR ratio by 10. | 1 | Biochemistry |
Confirmation that DNA is the genetic material which is cause of infection came from the Hershey–Chase experiment. They used E.coli and bacteriophage for the experiment. This experiment is also known as blender experiment, as kitchen blender was used as a major piece of apparatus. Alfred Hershey and Martha Chase demonstrated that the DNA injected by a phage particle into a bacterium contains all information required to synthesize progeny phage particles. They used radioactivity to tag the bacteriophages protein coat with radioactive sulphur and DNA with radioactive phosphorus, into two different test tubes respectively. After mixing bacteriophage and E.coli into the test tube, the incubation period starts in which phage transforms the genetic material in the E.coli cells. Then the mixture is blended or agitated, which separates the phage from E.coli cells. The whole mixture is centrifuged and the pellet which contains E.coli cells was checked and the supernatant was discarded. The E.coli' cells showed radioactive phosphorus, which indicated that the transformed material was DNA not the protein coat.
The transformed DNA gets attached to the DNA of E.coli and radioactivity is only seen onto the bacteriophage's DNA. This mutated DNA can be passed to the next generation and the theory of Transduction came into existence. Transduction is a process in which the bacterial DNA carry the fragment of bacteriophages and pass it on the next generation. This is also a type of horizontal gene transfer. | 1 | Biochemistry |
Various CBRNE (Chemical, Biological, Radiological, Nuclear, and Explosive) weapons can be used for area denial, as long as the agent is long-lasting. Fallout from nuclear weapons might be used in such a role. While never actually employed in this form, its use had been suggested by Douglas MacArthur during the Korean War, who proposed spreading radioactive waste across transportation corridors to inhibit the movement of Chinese and North Korean forces.
Anthrax spores can contaminate the ground for long periods of time, thus providing a form of area denial. However, the short-term (tactical) effects are likely to be low - the psychological effects on an opponent would likely be more significant.
The massive use of defoliants such as Agent Orange can be used as an interdiction measure because they leave areas empty of any form of vegetation cover. In the desert-like terrain that ensues, it is impossible for the enemy to travel without being seen, and there is little cover in case of an attack, especially from the air.
Many chemical weapons also produce toxic effects on any personnel in an affected area. However, this usually has no tactical value, as the effects of indirect exposure do not develop fast or substantially enough - though again, the psychological effect upon an enemy aware of the chemical usage may be considerable. There are however some chemical agents that are by design non-degrading, such as the nerve agent VX. Sulfur mustard (mustard gas) was extensively used by both German and allied forces on the west front in World War I as an effective area-denial weapon, usually through contaminating large land stripes by extensive shelling with HD/Gelbkreuz ordnance. Since sulfur mustard is very persistent, involatile, hard-to-decontaminate and highly effective in inflicting debilitating casualties at even low doses, this tactic proved to be very effective. | 1 | Biochemistry |
Laminins are non-collagenous proteins found in basement membranes and form networks through non-covalent self-interactions. Nidogens (also known as entactins) are sulfated monomeric glycoproteins that are ubiquitously present in basement membranes of higher organisms. Nidogens help with the formation of the basement. With both laminins and nidogens present, both interact with each other to have a stoichiometry relationship of 1:1 in a complex. In order to study the short arm of laminin γ1, photo methionine introduced both to nidogen-1, laminin γ1 LEb2-4, and laminin γ1 short arm to see if this photo-cross linking method could map out the structure. MS/MS analysis was done before cross-linking to find only 13-25% of methionines had been incorporated, but once UV-A-induced or another cross-linker, BSG-mediated cross-linked (a homobifunctional cross-linker), the percentage of photo-methionine's had increased to 35%. Both cross-linkers had shown extra structural insight both computationally and experimentally to help with understanding the functions. | 5 | Photochemistry |
The most common of these uses a group contribution method and is termed cLogP. It has been shown that the log P of a compound can be determined by the sum of its non-overlapping molecular fragments (defined as one or more atoms covalently bound to each other within the molecule). Fragmentary log P values have been determined in a statistical method analogous to the atomic methods (least-squares fitting to a training set). In addition, Hammett-type corrections are included to account of electronic and steric effects. This method in general gives better results than atomic-based methods, but cannot be used to predict partition coefficients for molecules containing unusual functional groups for which the method has not yet been parameterized (most likely because of the lack of experimental data for molecules containing such functional groups). | 7 | Physical Chemistry |
It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise. Alternatively, a superconductor is called unconventional if the superconducting order parameter transforms according to a non-trivial irreducible representation of the point group or space group of the system. | 7 | Physical Chemistry |
Mander completed a BSc degree at the University of Auckland, New Zealand in 1960, followed by an MSc degree in 1961 from the same institution.
He then moved to Australia in 1962 to undertake a PhD degree at the University of Sydney before committing to an initial postdoctoral fellowship at the University of Michigan. Mander then moved to Caltech in 1965 (after his PhD had been conferred) for an additional two years. | 0 | Organic Chemistry |
He received his degree at the University of Barcelona in 1944, his doctorate in Madrid, and finished his training at Harvard University in 1951. In 1944 he formed a team at the Spanish National Research Council. His work has largely been in kinetics and organic chemistry. | 0 | Organic Chemistry |
Urethane (ethyl carbamate) was once produced commercially in the United States as a chemotherapy agent and for other medicinal purposes. It was found to be toxic and largely ineffective. It is occasionally used in veterinary medicine in combination with other drugs to produce anesthesia. | 0 | Organic Chemistry |
Beyond its canonical role in the SIR complex, SIR2 also plays a role in rDNA repression. As part of the cells regulation mechanism, rDNA repeats are excised from the chromosome so they cannot be expressed. SIR2 forms a complex with NET1 (a nuclear protein) and CDC14 (a phosphatase) to form the regulator of nucleolar silencing and telophase (RENT) complex. The RENT complex sequesters excised rDNA in extrachromosomal circles, preventing recombination. Accumulation of these circles has been linked to premature aging. Sirtuin 2 (SIRT2), SIR2s human analog, has also been linked to age-related disease. | 1 | Biochemistry |
UCP1 belongs to the UCP family which are transmembrane proteins that decrease the proton gradient generated in oxidative phosphorylation. They do this by increasing the permeability of the inner mitochondrial membrane, allowing protons that have been pumped into the intermembrane space to return to the mitochondrial matrix and hence dissipating the proton gradient. UCP1-mediated heat generation in brown fat uncouples the respiratory chain, allowing for fast substrate oxidation with a low rate of ATP production. UCP1 is related to other mitochondrial metabolite transporters such as the adenine nucleotide translocator, a proton channel in the mitochondrial inner membrane that permits the translocation of protons from the mitochondrial intermembrane space to the mitochondrial matrix. UCP1 is restricted to brown adipose tissue, where it provides a mechanism for the enormous heat-generating capacity of the tissue.
UCP1 is activated in the brown fat cell by fatty acids and inhibited by nucleotides. Fatty acids are released by the following signaling cascade: Sympathetic nervous system terminals release Norepinephrine onto a Beta-3 adrenergic receptor on the plasma membrane. This activates adenylyl cyclase, which catalyses the conversion of ATP to cyclic AMP (cAMP). cAMP activates protein kinase A, causing its active C subunits to be freed from its regulatory R subunits. Active protein kinase A, in turn, phosphorylates triacylglycerol lipase, thereby activating it. The lipase converts triacylglycerols into free fatty acids, which activate UCP1, overriding the inhibition caused by purine nucleotides (GDP and ADP). During the termination of thermogenesis, thermogenin is inactivated and residual fatty acids are disposed of through oxidation, allowing the cell to resume its normal energy-conserving state.
UCP1 is very similar to the ATP/ADP Carrier protein, or Adenine Nucleotide Translocator (ANT). The proposed alternating access model for UCP1 is based on the similar ANT mechanism. The substrate comes in to the half open UCP1 protein from the cytoplasmic side of the membrane, the protein closes the cytoplasmic side so the substrate is enclosed in the protein, and then the matrix side of the protein opens, allowing the substrate to be released into the mitochondrial matrix. The opening and closing of the protein is accomplished by the tightening and loosening of salt bridges at the membrane surface of the protein. Substantiation for this modelling of UCP1 on ANT is found in the many conserved residues between the two proteins that are actively involved in the transportation of substrate across the membrane. Both proteins are integral membrane proteins, localized to the inner mitochondrial membrane, and they have a similar pattern of salt bridges, proline residues, and hydrophobic or aromatic amino acids that can close or open when in the cytoplasmic or matrix state. | 1 | Biochemistry |
De Novo biosynthesis of a pyrimidine is catalyzed by three gene products CAD, DHODH and UMPS. The first three enzymes of the process are all coded by the same gene in CAD which consists of carbamoyl phosphate synthetase II, aspartate carbamoyltransferase and dihydroorotase. Dihydroorotate dehydrogenase (DHODH) unlike CAD and UMPS is a mono-functional enzyme and is localized in the mitochondria. UMPS is a bifunctional enzyme consisting of orotate phosphoribosyltransferase (OPRT) and orotidine monophosphate decarboxylase (OMPDC). Both, CAD and UMPS are localized around the mitochondria, in the cytosol. In Fungi, a similar protein exists but lacks the dihydroorotase function: another protein catalyzes the second step.
In other organisms (Bacteria, Archaea and the other Eukaryota), the first three steps are done by three different enzymes. | 1 | Biochemistry |
Photosynthetic carbohydrate synthesis in plants and certain bacteria is an anabolic process that produces glucose, cellulose, starch, lipids, and proteins from CO. It uses the energy produced from the light-driven reactions of photosynthesis, and creates the precursors to these large molecules via carbon assimilation in the photosynthetic carbon reduction cycle, a.k.a. the Calvin cycle. | 1 | Biochemistry |
When the box contains N non-interacting fermions of spin ½, it is interesting to calculate the energy in the thermodynamic limit, where N is so large that the quantum numbers n, n, n can be treated as continuous variables.
With the vector , each quantum state corresponds to a point in n-space with energy
With denoting the square of the usual Euclidean length .
The number of states with energy less than E + E is equal to the number of states that lie within a sphere of radius in the region of n-space where n, n, n are positive. In the ground state this number equals the number of fermions in the system:
The factor of two expresses the two spin states, and the factor of 1/8 expresses the fraction of the sphere that lies in the region where all n are positive.
The Fermi energy is given by
Which results in a relationship between the Fermi energy and the number of particles per volume (when L is replaced with V):
This is also the energy of the highest-energy particle (the th particle), above the zero point energy . The th particle has an energy of
The total energy of a Fermi sphere of fermions (which occupy all energy states within the Fermi sphere) is given by:
Therefore, the average energy per particle is given by: | 7 | Physical Chemistry |
Triglycerides are formed from the esterification of 3 molecules of fatty acids with one molecule of trihydric alcohol, glycerol (glycerine or trihydroxy propane). In the process, 3 molecules of water are eliminated. The word "triglyceride" refers to the number of fatty acids esterified to one molecule of glycerol.
In triglycerides, the three fatty acids are rarely similar and are thus called pure fats. For example, tripalmitin, tristearin, etc. | 1 | Biochemistry |
Investigators have hypothesized that the PHLPP isoforms may play roles in cancer, for several reasons. First, the genetic loci coding for PHLPP1 and 2 are commonly lost in cancer. The region including PHLPP1, 18q21.33, commonly undergoes loss of heterozygosity (LOH) in colon cancers, while 16q22.3, which includes the PHLPP2 gene, undergoes LOH in breast and ovarian cancers, Wilms tumors, prostate cancer and hepatocellular carcinoma. Second, experimental overexpression of PHLPP in cancer cell lines tends to decrease apoptosis and increase proliferation, and stable colon and glioblastoma cell lines overexpressing PHLPP1 show decreased tumor formation in xenograft models. Recent studies have also shown that Bcr-Abl, the fusion protein responsible for chronic myelogenous leukemia (CML), downregulates PHLPP1 and PHLPP2 levels, and that decreasing PHLPP levels interferes with the efficacy of Bcr-Abl inhibitors, including Gleevec, in CML cell lines.
Finally, both Akt and PKC are known to be tumor promoters, suggesting that their negative regulator PHLPP may act as a tumor suppressor. | 1 | Biochemistry |
If the illuminated area selected by the aperture covers many differently oriented crystallites, their diffraction patterns superimpose forming an image of concentric rings. The ring diffractogram is typical for polycrystalline samples, powders or nanoparticles. Diameter of each ring corresponds to interplanar distance of a plane system present in the sample. Instead of information about individual grains or the sample orientation, this diffractogram provides more of a statistical information for instance about overall crystallinity or texture. Textured materials are characteristic by a non-uniform intensity distribution along the ring circumference despite crystallinity sufficient for generating smooth rings. Ring diffractograms can be also used to discriminate between nanocrystalline and amorphous phases.
Not all the features depicted in the diffraction image are necessarily wanted. The transmitted beam is often too strong and needs to be shadowed with a beam-stopper in order to protect the camera. The beam-stopper typically shadows part of the useful information as well. Towards the rings center, the background intensity also gradually increases lowering the contrast of diffraction rings. Modern analytical software allows to minimize such unwanted image features and together with other functionalities improves the image readability it helps with image interpretation. | 3 | Analytical Chemistry |
Sedative hypnotic drugs including eszopiclone are more commonly prescribed to the elderly than to younger patients despite benefits of medication being generally unimpressive.
In 2015, the American Geriatrics Society reviewed the safety information about eszopiclone and similar drugs and concluded that the "nonbenzodiazepine, benzodiazepine receptor agonist hypnotics (eszopiclone, zaleplon, zolpidem) are to be avoided without consideration of duration of use because of their association with harms balanced with their minimal efficacy in treating insomnia."
The review made this determination both because of the relatively large dangers to elderly individuals from zolpidem and other "z-drugs" together with the fact the drugs have "minimal efficacy in treating insomnia." This was a change from the 2012 AGS recommendation, which suggested limiting use to 90 days or less. The review stated: "the 90‐day‐use caveat [was] removed from nonbenzodiazepine, benzodiazepine receptor agonist hypnotics, resulting in an unambiguous avoid statement (without caveats) because of the increase in the evidence of harm in this area since the 2012 update."
An extensive review of the medical literature regarding the management of insomnia and the elderly found that there is considerable evidence of the effectiveness and durability of non-drug treatments for insomnia in adults of all ages and that these interventions are underutilized. Compared with the benzodiazepines, the nonbenzodiazepine sedative-hypnotics, including eszopiclone appeared to offer few, if any, significant clinical advantages in efficacy or tolerability in elderly persons. It was found that newer agents with novel mechanisms of action and improved safety profiles, such as the melatonin receptor agonists, hold promise for the management of chronic insomnia in elderly people. Long-term use of sedative-hypnotics for insomnia lacks an evidence base and has traditionally been discouraged for reasons that include concerns about such potential adverse drug effects as cognitive impairment (anterograde amnesia), daytime sedation, motor incoordination, and increased risk of motor vehicle accidents and falls. In addition, the effectiveness and safety of long-term use of these agents remain to be determined. It was concluded that more research is needed to evaluate the long-term effects of treatment and the most appropriate management strategy for elderly persons with chronic insomnia.
A 2009 meta-analysis found a higher rate of infections. | 4 | Stereochemistry |
The ability of a surface to self-clean commonly depends on the hydrophobicity or hydrophilicity of the surface. Whether cleaning aqueous or organic matter from a surface, water plays an important role in the self-cleaning process. Specifically, the contact angle of water on the surface is an important characteristic that helps determine the ability of a surface to self-clean. This angle is affected by the roughness of the surface and the following models have been developed to describe the "stickiness" or wettability of a self-cleaning surface. | 7 | Physical Chemistry |
Discoveries of the microwave spectra of a considerable number of molecules prove the existence of rather complex molecules in the interstellar clouds, and provides the possibility to study dense clouds, which are obscured by the dust they contain. The HO molecule has been observed in the interstellar medium since 1963 through its 18-cm transitions. In the subsequent years HO was observed by its rotational transitions at far infrared wavelengths, mainly in the Orion region. Because each rotational level of HO is split in by lambda doubling, astronomers can observe a wide variety of energy states from the ground state. | 2 | Environmental Chemistry |
Propane-1,3-dithiol is the parent member of this series. It is employed as a reagent in organic chemistry, since it forms 1,3-dithianes upon treatment with ketones and aldehydes. When derived from aldehydes, the methyne () group is sufficiently acidic that it can be deprotonated and the resulting anion can be C-alkylated. The process is the foundation of the umpolung phenomenon.
Like 1,2-ethanedithiol, propanedithiol forms complexes with metals, for example with triiron dodecacarbonyl:
A naturally occurring 1,3-dithiol is dihydrolipoic acid.
1,3-Dithiols oxidize to give 1,2-dithiolanes. | 0 | Organic Chemistry |
Scattering experiments are a common method for learning about crystals. Such experiments typically involve a probe (e.g. X-rays or neutrons) and a crystalline solid. A well-characterized probe propagating towards the crystal may interact and scatter away in a particular manner. Mathematical expressions relating the scattering pattern, properties of the probe, properties of the experimental apparatus, and properties of the crystal then allow one to derive desired features of the crystalline sample.
The following derivation is based on chapter 14 of Simons The Oxford Solid State Basics and on the report Atomic Displacement Parameter Nomenclature by Trueblood et al. (available under #External links). It is recommended to consult these sources for a more explicit discussion. Background on the quantum mechanics involved may be found in Sakurai and Napolitanos Modern Quantum Mechanics.
Scattering experiments often consist of a particle with initial crystal momentum incident on a solid. The particle passes through a potential distributed in space, , and exits with crystal momentum . This situation is described by Fermis golden rule, which gives the probability of transition per unit time, , to the energy eigenstate from the energy eigenstate due to the weak perturbation caused by our potential .
By inserting a complete set of position states, then utilizing the plane-wave expression relating position and momentum, we find that the matrix element is simply a Fourier transform of the potential.
Above, the length of the sample is denoted by . We now assume that our solid is a periodic crystal with each unit cell labeled by a lattice position vector . Position within a unit cell is given by a vector such that the overall position in the crystal may be expressed as . Because of the translational invariance of our unit cells, the potential distribution of every cell is identical and . | 7 | Physical Chemistry |
Since natural amino acid residues are usually present in large quantities, it is often difficult to modify one single site. Strategies targeting the termini of protein have been developed, because they greatly enhanced the site selectivity of protein modification. One of the N- termini modifications involves the functionalization of the terminal amino acid. The oxidation of N-terminal serine and threonine residues are able to generate N-terminal aldehyde, which can undergo further bioorthogonal reactions (shown in the first reaction in Figure 4). Another type of modification involves the condensation of N-terminal cysteine with aldehyde, generating thiazolidine that is stable at high pH (second reaction in Figure 4). Using pyridoxal phosphate (PLP), several N-terminal amino acids can undergo transamination to yield N-terminal aldehyde, such as glycine and aspartic acid (third reaction in Figure 4).
An example of C-termini modification is the native chemical ligation (NCL), which is the coupling between a C-terminal thioester and a N-terminal cysteine (Figure 5). | 1 | Biochemistry |
Sulfuric acid produced by microorganisms will interact with the surface of the structure material. For ordinary Portland cement, it reacts with the calcium hydroxide in concrete to form calcium sulfate. This change simultaneously destroys the polymeric nature of calcium hydroxide and substitutes a larger molecule into the matrix causing pressure and spalling of the adjacent concrete and aggregate particles. The weakened crown may then collapse under heavy overburden loads. Even within a well-designed sewer network, a rule of thumb in the industry suggests that 5% of the total length may/will suffer from biogenic corrosion. In these specific areas, biogenic sulfide corrosion can deteriorate metal or several millimeters per year of concrete (see Table).
For calcium aluminate cements, processes are completely different because they are based on another chemical composition. At least three different mechanisms contribute to the better resistance to biogenic corrosion:
* The first barrier is the larger acid neutralizing capacity of calcium aluminate cements vs. ordinary Portland Cement; one gram of calcium aluminate cement can neutralize around 40% more acid than a gram of ordinary Portland Cement. For a given production of acid by the biofilm, a calcium aluminate cement concrete will last longer.
* The second barrier is due to the precipitation, when the surficial pH gets below 10, of a layer of alumina gel (AH3 in cement chemistry notation). AH3 is a stable compound down to a pH of 4 and it will form an acid-resistant barrier as long as the surface pH is not lowered below 3-4 by the bacterial activity.
* The third barrier is the bacteriostatic effect locally activated when the surface reaches pH values less than 3–4. At this level, the alumina gel is no longer stable and will dissolve, liberating aluminum ions. These ions will accumulate in the thin biofilm. Once the concentration reaches 300-500 ppm, it will produce a bacteriostatic effect on bacteria metabolism. In other word, bacteria will stop oxidizing the sulfur from HS to produce acid, and the pH will stop decreasing.
A mortar made of calcium aluminate cement combined with
calcium aluminate aggregates, i.e. a 100% calcium aluminate material, will last much longer as aggregates can also limit microorganisms’ growth and inhibits the acid generation at the source itself. | 8 | Metallurgy |
Pregnanediol, or 5β-pregnane-3α,20α-diol, is an inactive metabolic product of progesterone. A test can be done to measure the amount of pregnanediol in urine, which offers an indirect way to measure progesterone levels in the body.
From the urine of pregnant women from London clinics, Guy Frederic Marrian isolated a substance that contained two hydroxyl groups and could be converted into a diacetate with acetic anhydride. However, the formula had not been clearly clarified. Almost at the same time, Adolf Butenandt at the Chemical University Laboratory in Göttingen investigated the constituents of pregnant urine and clarified the structure of the diol. The name pregnandiol, coined by Butenandt, is derived from the Latin verb praegnans (pregnant) or the English pregnant and pregnancy. This gave rise to the name pregnane for the underlying parent hydrocarbon.
In 1936, Venning and Browne demonstrated the presence of pregnanediol, specifically the glucuronide of pregnanediol in pregnancy urine. Their study extracted pregnanediol from pregnancy urine and revealed that pregnanediol concentration in urine indicates the amount of progesterone excreted. Since progesterone levels indicate the functionality of a corpus luteum, and pregnanediol concentration represents 40-45% of the progesterone excreted, estimations of pregnanediol reveal the functionality of a corpus luteum. However, pregnanediol concentrations vary with menstrual cycle phases, so it is essential to consider the menstrual cycle phase when examining them. Furthermore, current research has demonstrated that pregnanediol concentration in urine is also a measure of ovarian activity. | 1 | Biochemistry |
Calorimetry may be used to monitor the course of a reaction, since the instantaneous heat flux of the reaction, which is directly related to the enthalpy change for the reaction, is monitored. Reaction calorimetry may be classified as a differential technique since the primary data collected are proportional to rate vs. time. From these data, the starting material or product concentration over time may be obtained by simply taking the integral of a polynomial fit to the experimental curve.
While reaction calorimetry is less frequently employed than a number of other techniques, it has found use as an effective tool for catalyst screening. Reaction calorimetry has also been applied as an efficient method for mechanistic study of individual reactions including the prolinate-catalyzed α-amination of aldehydes and the palladium catalyzed Buchwald-Hartwig amination reaction. | 7 | Physical Chemistry |
Restriction endonucleases, also known as restriction enzymes are enzymes that cleave the sugar-phosphate backbone of the DNA at specific nucleotides sequences that are usually four to six nucleotides long. Studies performed by Horton and colleagues have shown that the mechanism by which these enzymes cleave the DNA involves base flipping as well as bending the DNA and the expansion of the minor groove. In 2006, Horton and colleagues, x-ray crystallography evidence was presented showing that the restriction endonuclease HinP1I utilizes base flipping in order to recognize its target sequence. This enzyme is known to cleave the DNA at the palindromic tetranucleotide sequence G↓CGC. | 1 | Biochemistry |
Polymer scattering experiments are one of the main scientific methods used in chemistry, physics and other sciences to study the characteristics of polymeric systems: solutions, gels, compounds and more. As in most scattering experiments, it involves subjecting a polymeric sample to incident particles (with defined wavelengths), and studying the characteristics of the scattered particles: angular distribution, intensity polarization and so on. This method is quite simple and straightforward, and does not require special manipulations of the samples which may alter their properties, and hence compromise exact results.
As opposed to crystallographic scattering experiments, where the scatterer or "target" has very distinct order, which leads to well defined patterns (presenting Bragg peaks for example), the stochastic nature of polymer configurations and deformations (especially in a solution), gives rise to quite different results. | 7 | Physical Chemistry |
The AFM-IR technique based on a pulsed infrared laser source was commercialized by Anasys Instruments, a company founded by Reading, Hammiche and Pollock in the United Kingdom in 2004; a sister, United States corporation was founded a year later. Anasys Instruments developed its product with support from the National Institute of Standards and Technology and the National Science Foundation. Since free electron lasers are rare and available only at select institutions, a key to enabling a commercial AFM-IR was to replace them with a more compact type of infrared source. Following the lead given by Hammiche et al in 2001 and Hill et al in 2008, Anasys Instruments introduced an AFM-IR product in early 2010, using a tabletop laser source based on a nanosecond optical parametric oscillator. The OPO source enabled nanoscale infrared spectroscopy over a tuning range of roughly 1000–4000 cm or 2.5-10 μm.
The initial product required samples to be mounted on infrared-transparent prisms, with the infrared light being directed from below in the manner of Dazzi et al. For best operation, this illumination scheme required thin samples, with optimal thickness of less than 1 μm, prepared on the surface of the prism. In 2013, Anasys released an AFM-IR instrument based on the work of Hill et al. that supported top-side illumination. "By eliminating the need to prepare samples on infrared-transparent prisms and relaxing the restriction on sample thickness, the range of samples that could be studied was greatly expanded. The CEO of Anasys Instruments recognised this achievement by calling it " an exciting major advance" in a letter written to the university and included in the final report of EPSRC project EP/C007751/1. The UEA technique went on to become Anasys Instruments' flagship product. | 3 | Analytical Chemistry |
While a single subject/animal is perfused with multiple concentrations during the no-net-flux method, multiple subjects are perfused with a single concentration during the dynamic no-net-flux (DNNF) method. Data from the different subjects/animals is then combined at each time point for regression analysis allowing determination of the recovery over time. The design of the DNNF calibration method has proven very useful for studies that evaluate the response of endogenous compounds, such as neurotransmitters, to drug challenge. | 1 | Biochemistry |
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