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Concentrated sulfuric acid has a powerful dehydrating property, removing water () from other chemical compounds such as table sugar (sucrose) and other carbohydrates, to produce carbon, steam, and heat. Dehydration of table sugar (sucrose) is a common laboratory demonstration. The sugar darkens as carbon is formed, and a rigid column of black, porous carbon called a carbon snake may emerge as shown in the figure.
Similarly, mixing starch into concentrated sulfuric acid gives elemental carbon and water. The effect of this can be seen when concentrated sulfuric acid is spilled on paper, which is composed of cellulose; the cellulose reacts to give a burnt appearance in which the carbon appears much like soot that results from fire.
Although less dramatic, the action of the acid on cotton, even in diluted form, destroys the fabric.
The reaction with copper(II) sulfate can also demonstrate the dehydration property of sulfuric acid. The blue crystals change into white powder as water is removed: | 7 | Physical Chemistry |
The gel fragment is placed in a dialysis tube that is permeable to fluids but impermeable to molecules at the size of DNA, thus preventing the DNA from passing through the membrane when soaked in TE buffer. An electric field is established around the tubing (in a way similar to gel electrophoresis) long enough so that the DNA is removed from the gel but remains in the tube. The tube solution can then be pipetted out and will contain the desired DNA with minimal background. | 1 | Biochemistry |
According to R. Balasubramaniam and A. V. Ramesh Kumar (2003), the pillar shows "excellent" atmospheric corrosion resistance.
Ray et al. (1997) analyzed portions of the two smaller fragments. Their analysis revealed the following chemical composition (weight %):
Balasubramaniam (2002) also obtained a small portion of the pillar with ASI's permission, and used an electron probe microanalyzer to analyze its chemical composition. He found that "the composition varied from one location to another":
The typical composition of the slag was 55.8% iron, 27.8% silicon, 16.3% phosphorus, and 0.1% manganese. | 8 | Metallurgy |
Fractional crystallization is the removal and segregation from a melt of mineral precipitates, which changes the composition of the melt. This is one of the most important geochemical and physical processes operating within the Earth's crust and mantle.
Fractional crystallization in silicate melts (magmas) is a very complex process compared to chemical systems in the laboratory because it is affected by a wide variety of phenomena. Prime amongst these are the composition, temperature, and pressure of a magma during its cooling.
The composition of a magma is the primary control on which mineral is crystallized as the melt cools down past the liquidus. For instance in mafic and ultramafic melts, the MgO and SiO contents determine whether forsterite olivine is precipitated or whether enstatite pyroxene is precipitated.
Two magmas of similar composition and temperature at different pressure may crystallize different minerals. An example is high-pressure and high-temperature fractional crystallization of granites to produce single-feldspar granite, and low-pressure low-temperature conditions which produce two-feldspar granites.
The partial pressure of volatile phases in silicate melts is also of prime importance, especially in near-solidus crystallization of granites. | 9 | Geochemistry |
Figures 1 and 2 show two-dimensional projections of a phase diagram. In the pressure-temperature phase diagram (Fig. 1) the boiling curve separates the gas and liquid region and ends in the critical point, where the liquid and gas phases disappear to become a single supercritical phase.
The appearance of a single phase can also be observed in the density-pressure phase diagram for carbon dioxide (Fig. 2). At well below the critical temperature, e.g., 280 K, as the pressure increases, the gas compresses and eventually (at just over 40 bar) condenses into a much denser liquid, resulting in the discontinuity in the line (vertical dotted line). The system consists of 2 phases in equilibrium, a dense liquid and a low density gas. As the critical temperature is approached (300 K), the density of the gas at equilibrium becomes higher, and that of the liquid lower. At the critical point, (304.1 K and 7.38 MPa (73.8 bar)), there is no difference in density, and the 2 phases become one fluid phase. Thus, above the critical temperature a gas cannot be liquefied by pressure. At slightly above the critical temperature (310 K), in the vicinity of the critical pressure, the line is almost vertical. A small increase in pressure causes a large increase in the density of the supercritical phase. Many other physical properties also show large gradients with pressure near the critical point, e.g. viscosity, the relative permittivity and the solvent strength, which are all closely related to the density. At higher temperatures, the fluid starts to behave more like an ideal gas, with a more linear density/pressure relationship, as can be seen in Figure 2. For carbon dioxide at 400 K, the density increases almost linearly with pressure.
Many pressurized gases are actually supercritical fluids. For example, nitrogen has a critical point of 126.2 K (−147 °C) and 3.4 MPa (34 bar). Therefore, nitrogen (or compressed air) in a gas cylinder above this pressure is actually a supercritical fluid. These are more often known as permanent gases. At room temperature, they are well above their critical temperature, and therefore behave as a nearly ideal gas, similar to CO at 400 K above. However, they cannot be liquified by mechanical pressure unless cooled below their critical temperature, requiring gravitational pressure such as within gas giants to produce a liquid or solid at high temperatures. Above the critical temperature, elevated pressures can increase the density enough that the SCF exhibits liquid-like density and behaviour. At very high pressures, an SCF can be compressed into a solid because the melting curve extends to the right of the critical point in the P/T phase diagram. While the pressure required to compress supercritical CO into a solid can be, depending on the temperature, as low as 570 MPa, that required to solidify supercritical water is 14,000 MPa.
The Fisher–Widom line, the Widom line, or the Frenkel line are thermodynamic concepts that allow to distinguish liquid-like and gas-like states within the supercritical fluid. | 7 | Physical Chemistry |
In March 1996, a group of scientists at Lawrence Livermore National Laboratory reported that they had serendipitously produced the first identifiably metallic hydrogen for about a microsecond at temperatures of thousands of kelvins, pressures of over , and densities of approximately . The team did not expect to produce metallic hydrogen, as it was not using solid hydrogen, thought to be necessary, and was working at temperatures above those specified by metallization theory. Previous studies in which solid hydrogen was compressed inside diamond anvils to pressures of up to , did not confirm detectable metallization. The team had sought simply to measure the less extreme electrical conductivity changes they expected. The researchers used a 1960s-era light-gas gun, originally employed in guided missile studies, to shoot an impactor plate into a sealed container containing a half-millimeter thick sample of liquid hydrogen. The liquid hydrogen was in contact with wires leading to a device measuring electrical resistance. The scientists found that, as pressure rose to , the electronic energy band gap, a measure of electrical resistance, fell to almost zero. The band gap of hydrogen in its uncompressed state is about , making it an insulator but, as the pressure increases significantly, the band gap gradually fell to . Because the thermal energy of the fluid (the temperature became about due to compression of the sample) was above , the hydrogen might be considered metallic. | 7 | Physical Chemistry |
Photo-Induced Cross-Linking of Unmodified Proteins (PICUP) is a protein cross-linking method by visible light irradiation of a photocatalyst in the presence of an electron acceptor and the protein of interest. Irradiation results in a highly reactive protein radical that forms a covalent bond between the amino acid side chains of the proteins to be linked. Cross-linking methods developed prior to PICUP, including the use of physical, oxidative, and chemical cross-linkers, often require more time and result in protein byproducts. In addition, the cross-linked protein yield is very low due to the multifunctionality of the cross-linking reagents.
The process was invented (US6613582B1) in 1999 to utilize protein cross-linking techniques to analyze the interactions between polypeptides as well as structural differences proteins undergo in a catalytic pathway. The techniques in the 20th century were not sufficient to be applied to cross-link fast and transient changes of these proteins in high yield. PICUP allowed for rapid (<1 second) and high production of covalently-linked proteins in close proximity with each other. | 1 | Biochemistry |
The Schikorr reaction can occur in the process of anaerobic corrosion of iron and carbon steel in various conditions.
Anaerobic corrosion of metallic iron to give iron(II) hydroxide and hydrogen:
:3 (Fe + 2 HO → Fe(OH) + H)
followed by the Schikorr reaction:
:3 Fe(OH) → FeO + 2 HO + H
give the following global reaction:
:3 Fe + 6 HO → FeO + 2 HO + 4 H
:3 Fe + 4 HO → FeO + 4 H
At low temperature, the anaerobic corrosion of iron can give rise to the formation of "green rust" (fougerite) an unstable layered double hydroxide (LDH). In function of the geochemical conditions prevailing in the environment of the corroding steel, iron(II) hydroxide and green rust can progressively transform in iron(II,III) oxide, or if bicarbonate ions are present in solution, they can also evolve towards more stable carbonate phases such as iron carbonate (FeCO), or iron(II) hydroxycarbonate (Fe(OH)(CO), chukanovite) isomorphic to copper(II) hydroxycarbonate (Cu(OH)(CO), malachite) in the copper system. | 8 | Metallurgy |
The carboxy-terminal domain (CTD) of RNA polymerase II is that portion of the polymerase that is involved in the initiation of DNA transcription, the capping of the RNA transcript, and attachment to the spliceosome for RNA splicing. The CTD typically consists of up to 52 repeats (in humans) of the sequence Tyr-Ser-Pro-Thr-Ser-Pro-Ser. The carboxy-terminal repeat domain (CTD) is essential for life. Cells containing only RNAPII with none or only up to one-third of its repeats are inviable.
The CTD is an extension appended to the C terminus of RPB1, the largest subunit of RNA polymerase II. It serves as a flexible binding scaffold for numerous nuclear factors, determined by the phosphorylation patterns on the CTD repeats. Each repeat contains an evolutionary conserved and repeated heptapeptide, Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7, which is subjected to reversible phosphorylations during each transcription cycle. This domain is inherently unstructured yet evolutionarily conserved, and in eukaryotes it comprises from 25 to 52 tandem copies of the consensus repeat heptad. As the CTD is frequently not required for general transcription factor (GTF)-mediated initiation and RNA synthesis, it does not form a part of the catalytic essence of RNAPII, but performs other functions. | 1 | Biochemistry |
Perdeuteration of one component of a multi-component system can provide contrast for neutron scattering experiments, where the contrast obtained by using deuterated solvents is insufficient. | 7 | Physical Chemistry |
In geochemistry, the primitive mantle (also known as the bulk silicate Earth) is the chemical composition of the Earth's mantle during the developmental stage between core-mantle differentiation and the formation of early continental crust. The chemical composition of the primitive mantle contains characteristics of both the crust and the mantle. | 9 | Geochemistry |
There are two types of VMATs expressed in humans: VMAT1 and VMAT2. VMAT1 is expressed mainly in large dense-core vesicles (LDCVs) of the peripheral nervous system. VMAT1 may be found in neuroendocrine cells, particularly chromaffin and enterochromaffin granules, which are primarily found in the medulla of the adrenal glands.
VMAT2 favors expression in a variety of monoaminergic cells of the central nervous system, such as the brain, sympathetic nervous system, mast cells, It is prevalent in β-cells, expressed in blood platelets, and co-expressed in chromaffin cells. Expression of the two transporters in internal organs seems to differ between species: only VMAT1 is expressed in rat adrenal medulla cells, whereas VMAT2 is the major transporter in bovine adrenal medulla cells. | 1 | Biochemistry |
Development of the chromatogram is done by allowing the solvent to travel down the paper. Here, the mobile phase is placed in a solvent holder at the top. The spot is kept at the top and solvent flows down the paper from above. | 3 | Analytical Chemistry |
Early micro-fossils may have come from a hot world of gases such as methane, ammonia, carbon dioxide, and hydrogen sulfide, toxic to much current life. Analysis of the tree of life places thermophilic and hyperthermophilic bacteria and archaea closest to the root, suggesting that life may have evolved in a hot environment. The deep sea or alkaline hydrothermal vent theory posits that life began at submarine hydrothermal vents. William Martin and Michael Russell have suggested "that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments".
These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-mafic olivine with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see iron–sulfur world theory. These are exothermic reactions. | 9 | Geochemistry |
Since facultative anaerobes are able to grow in both the presence and absence of oxygen, they can survive in many different environments, adapt easily to changing conditions, and thus have a selective advantage over other bacteria. As a result, most life-threatening pathogens are facultative anaerobes.
The ability of facultative anaerobic pathogens to survive without oxygen is important since their infection is shown to reduce oxygen levels in their host's gut tissue. Moreover, the ability of facultative anaerobes to limit oxygen levels at infection sites is beneficial to them and other bacteria, as dioxygen can form reactive oxygen species (ROS). These species are toxic to bacteria and can damage their DNA, among other constituents. | 1 | Biochemistry |
In DSSC, electrodes consisted of sintered semiconducting nanoparticles, mainly TiO or ZnO. These nanoparticle DSSCs rely on trap-limited diffusion through the semiconductor nanoparticles for the electron transport. This limits the device efficiency since it is a slow transport mechanism. Recombination is more likely to occur at longer wavelengths of radiation. Moreover, sintering of nanoparticles requires a high temperature of about 450 °C, which restricts the fabrication of these cells to robust, rigid solid substrates. It has been proven that there is an increase in the efficiency of DSSC, if the sintered nanoparticle electrode is replaced by a specially designed electrode possessing an exotic nanoplant-like morphology. | 5 | Photochemistry |
For pure substances so that . In a single phase () condition of a pure component system, two variables (), such as temperature and pressure, can be chosen independently to be any pair of values consistent with the phase. However, if the temperature and pressure combination ranges to a point where the pure component undergoes a separation into two phases (), decreases from 2 to 1. When the system enters the two-phase region, it becomes no longer possible to independently control temperature and pressure.
In the phase diagram to the right, the boundary curve between the liquid and gas regions maps the constraint between temperature and pressure when the single-component system has separated into liquid and gas phases at equilibrium. The only way to increase the pressure on the two phase line is by increasing the temperature. If the temperature is decreased by cooling, some of the gas condenses, decreasing the pressure. Throughout both processes, the temperature and pressure stay in the relationship shown by this boundary curve unless one phase is entirely consumed by evaporation or condensation, or unless the critical point is reached. As long as there are two phases, there is only one degree of freedom, which corresponds to the position along the phase boundary curve.
The critical point is the black dot at the end of the liquid–gas boundary. As this point is approached, the liquid and gas phases become progressively more similar until, at the critical point, there is no longer a separation into two phases. Above the critical point and away from the phase boundary curve, and the temperature and pressure can be controlled independently. Hence there is only one phase, and it has the physical properties of a dense gas, but is also referred to as a supercritical fluid.
Of the other two-boundary curves, one is the solid–liquid boundary or melting point curve which indicates the conditions for equilibrium between these two phases, and the other at lower temperature and pressure is the solid–gas boundary.
Even for a pure substance, it is possible that three phases, such as solid, liquid and vapour, can exist together in equilibrium (). If there is only one component, there are no degrees of freedom () when there are three phases. Therefore, in a single-component system, this three-phase mixture can only exist at a single temperature and pressure, which is known as a triple point. Here there are two equations , which are sufficient to determine the two variables T and p. In the diagram for CO the triple point is the point at which the solid, liquid and gas phases come together, at 5.2 bar and 217 K. It is also possible for other sets of phases to form a triple point, for example in the water system there is a triple point where ice I, ice III and liquid can coexist.
If four phases of a pure substance were in equilibrium (), the phase rule would give , which is meaningless, since there cannot be −1 independent variables. This explains the fact that four phases of a pure substance (such as ice I, ice III, liquid water and water vapour) are not found in equilibrium at any temperature and pressure. In terms of chemical potentials there are now three equations, which cannot in general be satisfied by any values of the two variables T and p, although in principle they might be solved in a special case where one equation is mathematically dependent on the other two. In practice, however, the coexistence of more phases than allowed by the phase rule normally means that the phases are not all in true equilibrium. | 7 | Physical Chemistry |
The Wikipedia page Metabolic pathway defines a pathway as "a metabolic pathway is a linked series of chemical reactions occurring within a cell". This means that any sequence of reactions can be labeled a metabolic pathway. However, as metabolism was being uncovered, groups of reactions were assigned specific labels, such as glycolysis, Krebs Cycle, or Serine biosynthesis. Often the categorization was based on common chemistry or identification of an input and output. For example, serine biosynthesis starts at 3-phosphoglycerate and ends at serine. This is a somewhat ad hoc means for defining pathways, particularly when pathways are dynamic structures, changing as environmental result in changes in gene expression. For example, the Kreb Cycle is often not cyclic as depicted in textbooks. In E. coli and other bacteria, it is only cyclic during aerobic growth on acetate or fatty acids. Instead, under anaerobiosis, its enzymes function as two distinct biosynthetic pathways producing succinyl-CoA and α-ketoglutarate.
It has therefore been proposed to define a pathway as either a single elementary mode or some combination of elementary modes. The added advantage is that the set of elementary modes is unique and non-decomposable to simpler pathways. A single elementary mode can therefore be thought of as an elementary pathway. Note that the set of elementary modes will change as the set of expressed enzymes change during transitions from one cell state to another.
Elementary modes, therefore, provide an unambiguous definition of a pathway. | 1 | Biochemistry |
In its earliest form, liquid chromatography was used to separate the pigments of chlorophyll by a Russian botanist. Decades later, other chemists used the procedure for the study of carotins. Liquid chromatography was then used for the isolation of small molecules and organic compounds like amino acids, and most recently has been used in peptide and DNA research. Monolith columns have been instrumental in advancing the field of biomolecular research.
In recent trade shows and international meetings for HPLC, interest in column monoliths and biomolecular applications has grown steadily, and this correlation is no coincidence. Monoliths have been shown to possess great potential in the “omics” fields- genomics, proteomics, metabolomics, and pharmacogenomics, among others. The reductionist approach to understanding the chemical pathways of the body and reactions to different stimuli, like drugs, are essential to new waves of healthcare like personalized medicine.
Pharmacogenomics studies how responses to pharmaceutical products differ in efficacy and toxicity based on variations in the patients genome; it is a correlation of drug response to gene expression in a patient. Jeremy K. Nicholson of the Imperial College, London, used a postgenomic viewpoint to understand adverse drug reactions and the molecular basis of human disesase. His group studied gut microbial metabolic profiles and were able to see distinct differences in reactions to drug toxicity and metabolism even among various geographical distributions of the same race. Affinity monolith chromatography provides another approach to drug response measurements. David Hage at the University of Nebraska binds ligands to monolithic supports and measures the equilibrium phenomena of binding interactions between drugs and serum proteins. A monolith-based approach at the University of Bologna, Italy, is currently in use for high-speed screening of drug candidates in the treatment of Alzheimers. In 2003, Regnier and Liu of Purdue University described a multi-dimensional LC procedure for identifying single nucleotide polymorphisms (SNPs) in proteins. SNPs are alterations in the genetic code that can sometimes cause changes in protein conformation, as is the case with sickle cell anemia. Monoliths are particularly useful in these kinds of separations because of their superior mass transport capabilities, low backpressures coupled with faster flow rates, and relative ease of modification of the support surface.
Bioseparations on a production scale are enhanced by monolith column technologies as well. The fast separations and high resolving power of monoliths for large molecules means that real-time analysis on production fermentors is possible. Fermentation is well known for its use in making alcoholic beverages, but is also an essential step in the production of vaccines for rabies and other viruses. Real-time, on-line analysis is critical for monitoring of production conditions, and adjustments can be made if necessary. Boehringer Ingelheim Austria has validated a method with cGMP (commercial good manufacturing practices) for production of pharmaceutical-grade DNA plasmids. They are able to process 200L of fermentation broth on an 800mL monolith. At BIA Separations, processing time of the tomato mosaic virus decreased considerably from the standard five days of manually intensive work to equivalent purity and better recovery in only two hours with a monolith column. Other viruses have been purified on monoliths as well.
Another area of interest for HPLC is forensics. GC-MS (Gas Chromatography-Mass Spectroscopy) is generally considered the gold standard for forensic analysis. It is used in conjunction with online databases for rapid analysis of compounds in tests for blood alcohol, cause of death, street drugs, and food analysis, especially in poisoning cases. Analysis of buprenorphine, a heroin substitute, demonstrated the potential utility of multidimensional LC as a low-level detection method. HPLC methods can measure this compound at 40 ng/mL, compared to GC-MS at 0.5 ng/mL, but LC-MS-MS can detect buprenorphine at levels as low as 0.02 ng/mL. The sensitivity of multidimensional LC is therefore 2000 times greater than that of conventional HPLC. | 3 | Analytical Chemistry |
As at 2017, the company operated the following stations:
*Alexandria Station, Northern Territory
* Boomarra Station, Queensland
* Coolullah Station, Queensland
*Coorabulka Station, Queensland
* Cungelella Station, Queensland
*Glenormiston Station, Queensland
* Goldsborough Station, Queensland
*Kynuna Station (includes Dagworth Station), Queensland
* Landsborough Station, Queensland
*Marion Downs Station, Queensland
*Mittiebah Station, Northern Territory
*Monkira Station, Queensland
*Portland Downs Station, Queensland
* Wainui Feedlot and Farm, Queensland
Other properties that the company has owned include:
*Gordon Downs, Queensland | 2 | Environmental Chemistry |
Bis(trimethylsilyl)amine (also known as hexamethyldisilazane and HMDS) is an organosilicon compound with the molecular formula [(CH)Si]NH. The molecule is a derivative of ammonia with trimethylsilyl groups in place of two hydrogen atoms. An electron diffraction study shows that silicon-nitrogen bond length (173.5 pm) and Si-N-Si bond angle (125.5°) to be similar to disilazane (in which methyl groups are replaced by hydrogen atoms) suggesting that steric factors are not a factor in regulating angles in this case. This colorless liquid is a reagent and a precursor to bases that are popular in organic synthesis and organometallic chemistry. Additionally, HMDS is also increasingly used as molecular precursor in chemical vapor deposition techniques to deposit silicon carbonitride thin films or coatings. | 0 | Organic Chemistry |
* left hand side of Navier–Stokes equations minus body force (per unit volume) acting on fluid.
* this relation is derived using this relationship which is alternative form of continuity equation | 7 | Physical Chemistry |
According to the rules exposed above, the phenanthrene molecule admits two different resonance structures: one of them presents a single circle in the center of the molecule, with each of the two adjacent rings having two double bonds; the other one has the two peripheral rings each with one circle, and the central ring with one double bond. According to Clar's rule, this last resonance structure gives the most important contribution to the determination of the properties of phenanthrene. | 7 | Physical Chemistry |
In the human genome, all genes get transcribed into RNA because that's how the molecular gene is defined. (See Gene.) The transcriptome consists of coding regions of mRNA plus non-coding UTRs, introns, non-coding RNAs, and spurious non-functional transcripts.
Several factors render the content of the transcriptome difficult to establish. These include alternative splicing, RNA editing and alternative transcription among others. Additionally, transcriptome techniques are capable of capturing transcription occurring in a sample at a specific time point, although the content of the transcriptome can change during differentiation. The main aims of transcriptomics are the following: "catalogue all species of transcript, including mRNAs, non-coding RNAs and small RNAs; to determine the transcriptional structure of genes, in terms of their start sites, 5′ and 3′ ends, splicing patterns and other post-transcriptional modifications; and to quantify the changing expression levels of each transcript during development and under different conditions".
The term can be applied to the total set of transcripts in a given organism, or to the specific subset of transcripts present in a particular cell type. Unlike the genome, which is roughly fixed for a given cell line (excluding mutations), the transcriptome can vary with external environmental conditions. Because it includes all mRNA transcripts in the cell, the transcriptome reflects the genes that are being actively expressed at any given time, with the exception of mRNA degradation phenomena such as transcriptional attenuation. The study of transcriptomics, (which includes expression profiling, splice variant analysis etc.), examines the expression level of RNAs in a given cell population, often focusing on mRNA, but sometimes including others such as tRNAs and sRNAs. | 1 | Biochemistry |
Biochemical Predestination is a 1969 book by Dean H. Kenyon and Gary Steinman which argued in support of biochemical evolution.
In the book, Kenyon and Steinman conclude that "Life might have been biochemically predestined by the properties of attraction that exist between its chemical parts, especially between amino acids in proteins." They argued that life originated with the chemical properties of amino acids causing them to be attracted to each other, forming long protein chains, most important in every living cell. Kenyon believed that proteins were directly formed by attraction between amino acids without DNA coding, and that these were derivatives from non-living raw chemicals in a conducive environment.
In 1976 Kenyon was persuaded by the young Earth creationist arguments of A. E. Wilder-Smith. In the 1982 foreword he wrote to What Is Creation Science? by Henry M. Morris and Gary Parker, Kenyon said that he no longer accepted the pro-evolution arguments in Biochemical Predestination. At the Edwards v. Aguillard trial he provided an affidavit in support of creation science and noted the book as one of his publications. In 1989 Kenyon became a co-author of Of Pandas and People which rebranded creation science as intelligent design. | 1 | Biochemistry |
The stereochemical outcome of a glycosylation reaction may in certain cases be affected by the type of protecting group employed at position 2 of the glycosyl donor. A participating group, typically one with a carboxyl group present, will predominantly result in the formation of a β-glycoside. Whereas a non-participating group, a group usually without a carboxyl group, will often result in an α-glycoside.
Below it can be seen that having an acetyl protecting group at position 2 allows for the formation for an acetoxonium ion intermediate that blocks attack to the bottom face of the ring therefore allowing for the formation of the β-glycoside predominantly.
Alternatively, the absence of a participating group at position 2 allows for either attack from the bottom or top face. Since the α-glycoside product will be favoured by the anomeric effect, the α-glycoside usually predominates. | 0 | Organic Chemistry |
Transmetalation involves the exchange of two metals between organic molecules by a redox exchange mechanism. For example, transmetalations often form a reaction between an organolithium reagent and a metal salt. | 0 | Organic Chemistry |
In chemistry, an amine oxide, also known as an amine N-oxide or simply N-oxide, is a chemical compound that has the chemical formula . It contains a nitrogen-oxygen coordinate covalent bond with three additional hydrogen and/or substituent-groups attached to nitrogen. Sometimes it is written as or, alternatively, as .
In the strict sense, the term amine oxide applies only to oxides of tertiary amines. Sometimes it is also used for the analogous derivatives of primary and secondary amines.
Examples of amine oxides include pyridine-N-oxide, a water-soluble crystalline solid with melting point 62–67 °C, and N-methylmorpholine N-oxide, which is an oxidant. | 0 | Organic Chemistry |
The term bulk material analyzer is the generic noun for that device which fits around a conveyor belt and conducts real-time elemental analysis of the material on the belt. Other names often found for such a device include belt analyzer, crossbelt analyzer and elemental analyzer. This product first found popularity in the cement industry during the 1990s, and today most new cement plants include at least one analyzer, if not two. | 3 | Analytical Chemistry |
The so-called inner sphere mechanism entails coordination of the alkene to the metal center. Other characteristics of this mechanism include a tendency for a homolytic splitting of dihydrogen when more electron-rich, low-valent metals are present while electron-poor, high valent metals normally exhibit a heterolytic cleavage of dihydrogen assisted by a base.
The diagram below depicts purposed mechanisms for catalytic hydrogenation with rhodium complexes which are inner sphere mechanisms. In the unsaturated mechanism, the chiral product formed will have the opposite mode compared to the catalyst used. While the thermodynamically favoured complex between the catalyst and the substrate is unable to undergo hydrogenation, the unstable, unfavoured complex undergoes hydrogenation rapidly. The dihydride mechanism on the other hand sees the complex initially hydrogenated to the dihydride form. This subsequently allows for the coordination of the double bond on the non-hindered side. Through insertion and reductive elimination, the product's chirality matches that of the ligand.
The preference for producing one enantiomer instead of another in these reactions is often explained in terms of steric interactions between the ligand and the prochiral substrate. Consideration of these interactions has led to the development of quadrant diagrams where "blocked" areas are denoted with a shaded box, while "open" areas are left unfilled. In the modeled reaction, large groups on an incoming olefin will tend to orient to fill the open areas of the diagram, while smaller groups will be directed to the blocked areas and hydrogen delivery will then occur to the back face of the olefin, fixing the stereochemistry. Note that only part of the chiral phosphine ligand is shown for the sake of clarity. | 0 | Organic Chemistry |
This category groups pages related to the spliceosome, which is a loose conglomerate of protein and RNA responsible for the correct splicing of mRNA. | 1 | Biochemistry |
Martin Schoell attended University of Munich for his undergraduate career in 1961 and in 1964 attended the University Clausthal, Germany for graduate school where he obtained a PhD in geochemistry. While at the University Clausthal, in 1966 Schoell delivered his Diplomarbeit (Masters Thesis) on the geochemistry of strontium in a deposit of barite. Later, in 1981, Schoell continued his education in Germany by obtaining his Habilitation (the highest possible academic degree offered in German academia). Schoell was mentored by Wolfgang Stahl, who inspired Schoells interest in hydrogen isotope geochemistry with respect to natural gas research. | 9 | Geochemistry |
Primordial fluctuations, density variations in the early universe, are quantified by a power spectrum which gives the power of the variations as a function of spatial scale. | 7 | Physical Chemistry |
The upcasting (up-casting, upstream, or upward casting) is a method of either vertical or horizontal continuous casting of rods and pipes of various profiles (cylindrical, square, hexagonal, slabs etc.) of 8-30mm in diameter. Copper (Cu), bronze (Cu·Sn alloy), nickel alloys are usually used because of greater casting speed (in case of vertical upcasting) and because of better physical features obtained. The advantage of this method is that metals are almost oxygen-free and that the rate of product crystallization (solidification) may be adjusted in a crystallizer - a high-temperature resistant device that cools a growing metal rod or pipe by using water.
The method is comparable to Czochralski method of growing silicon (Si) crystals, which is a metalloid. | 8 | Metallurgy |
Most applications of hydrothermal liquefaction operate at temperatures between 250-550 °C and high pressures of 5-25 MPa as well as catalysts for 20–60 minutes, although higher or lower temperatures can be used to optimize gas or liquid yields, respectively. At these temperatures and pressures, the water present in the biomass becomes either subcritical or supercritical, depending on the conditions, and acts as a solvent, reactant, and catalyst to facilitate the reaction of biomass to bio-oil.
The exact conversion of biomass to bio-oil is dependent on several variables:
* Feedstock composition
* Temperature and heating rate
* Pressure
* Solvent
* Residence time
* Catalysts | 0 | Organic Chemistry |
In a closed system, there is a difference observed in the anomeric effect for different substituents on a cyclohexane or tetrahydropyran ring (Y=Oxygen). When X=OH, the generic anomeric effect can be seen, as previously explained. When X=CN, the same results are seen, where the equatorial position is preferred on the cyclohexane ring, but the axial position is preferred on the tetrahydropyran ring. This is consistent with the anomeric effect stabilization. When X=F, the anomeric effect is in fact observed for both rings. However, when X=NH, no anomeric effect stabilization is observed and both systems prefer the equatorial position. This is attributed to both sterics and an effect called the reverse anomeric effect (see below). | 7 | Physical Chemistry |
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein.
mRNA is created during the process of transcription, where an enzyme (RNA polymerase) converts the gene into primary transcript mRNA (also known as pre-mRNA). This pre-mRNA usually still contains introns, regions that will not go on to code for the final amino acid sequence. These are removed in the process of RNA splicing, leaving only exons, regions that will encode the protein. This exon sequence constitutes mature mRNA. Mature mRNA is then read by the ribosome, and the ribosome creates the protein utilizing amino acids carried by transfer RNA (tRNA). This process is known as translation. All of these processes form part of the central dogma of molecular biology, which describes the flow of genetic information in a biological system.
As in DNA, genetic information in mRNA is contained in the sequence of nucleotides, which are arranged into codons consisting of three ribonucleotides each. Each codon codes for a specific amino acid, except the stop codons, which terminate protein synthesis. The translation of codons into amino acids requires two other types of RNA: transfer RNA, which recognizes the codon and provides the corresponding amino acid, and ribosomal RNA (rRNA), the central component of the ribosome's protein-manufacturing machinery.
The concept of mRNA was developed by Sydney Brenner and Francis Crick in 1960 during a conversation with François Jacob. In 1961, mRNA was identified and described independently by one team consisting of Brenner, Jacob, and Matthew Meselson, and another team led by James Watson. While analyzing the data in preparation for publication, Jacob and Jacques Monod coined the name "messenger RNA". | 1 | Biochemistry |
ETF-QO consists of one structural domain with three functional domains packed in close proximity: a FAD domain, a 4Fe4S cluster domain, and a UQ-binding domain. FAD is in an extended conformation and is buried deeply within its functional domain. Multiple hydrogen bonds and a positive helix dipole modulate the redox potential of FAD and can possibly stabilize the anionic semiquinone intermediate. The 4Fe4S cluster is also stabilized by extensive hydrogen bonding around the cluster and its cysteine components. Ubiquinone binding is achieved through a deep hydrophobic binding pocket which is a different mode than other UQ-binding proteins such as succinate-Q oxidoreductase. Although ETF-QO is an integral membrane protein, it does not traverse the entire membrane unlike other UQ-binding proteins. | 1 | Biochemistry |
One of main contributions of SNPs in clinical research is genome-wide association study (GWAS). Genome-wide genetic data can be generated by multiple technologies, including SNP array and whole genome sequencing. GWAS has been commonly used in identifying SNPs associated with diseases or clinical phenotypes or traits. Since GWAS is a genome-wide assessment, a large sample site is required to obtain sufficient statistical power to detect all possible associations. Some SNPs have relatively small effect on diseases or clinical phenotypes or traits. To estimate study power, the genetic model for disease needs to be considered, such as dominant, recessive, or additive effects. Due to genetic heterogeneity, GWAS analysis must be adjusted for race. | 1 | Biochemistry |
The primary sequence for FAM227B is isoform 1 with accession number: NP_689860.2. It is 508 amino acids long. There are 30 isoforms. The molecular weight is 59.9kD and the isoelectric point is predicted to be high, around 10. Compared to other proteins in humans, FAM227B has high abundance of Phenylalanine and Glycine and low abundance levels of Valine. The protein is predicted to be in the nuclear region of the cell. There is a bipartite nuclear localization signal at RKLERYGEFLKKYHKKK, and three other nuclearization signals at HKKK, KKKK, and PKKTKIK. There is also a vacuolar targeting motif at TLPI. An FWWh region, where h signifies hydrophobic, runs from amino acids 135-296 in Homo sapiens FAM227B isoform 1. The function of this region is still unknown. | 1 | Biochemistry |
Orthophosphate ion can be conveniently thermometrically titrated with magnesium ions in the presence of ammonium ion. An aliquot of sample is buffered to approximately pH10 with an NH/NHCl solution.
The reaction:
: Mg + NH + PO ↔ MgNHPO↓
Is exothermic. CV's of under 0.1 have been achieved in test applications. The procedure is suitable for the determination of orthophosphate in fertilizers and other products. | 3 | Analytical Chemistry |
Annulenes are monocyclic hydrocarbons that contain the maximum number of non-cumulated or conjugated double bonds (mancude). They have the general formula CH (when n is an even number) or CH (when n is an odd number). The IUPAC accepts the use of annulene nomenclature in naming carbocyclic ring systems with 7 or more carbon atoms, using the name [n]annulene for the mancude hydrocarbon with n carbon atoms in its ring, though in certain contexts (e.g., discussions of aromaticity for different ring sizes), smaller rings (n = 3 to 6) can also be informally referred to as annulenes. Using this form of nomenclature 1,3,5,7-cyclooctatetraene is [8]annulene and benzene is [6]annulene (and occasionally referred to as just annulene).
The discovery that [18]annulene possesses a number of key properties associated with other aromatic molecules was an important development in the understanding of aromaticity as a chemical concept.
In the related annulynes, one double bond is replaced by a triple bond. | 7 | Physical Chemistry |
Sterlite Industries ("Sterlite"), a subsidiary of Vedanta Resources, built a copper smelter in Tuticorin using an ISASMELT furnace and Peirce-Smith converters. The smelter was commissioned in 1996 and was designed to produce 60,000 t/y of copper (450,000 t/y of copper concentrate), but by increasing the oxygen content of the lance air and making modifications to other equipment, the ISASMELT furnace feed rate was increased to the point where the smelter was producing 180,000 t/y of copper.
Sterlite commissioned a new ISASMELT furnace in May 2005 that was designed to treat 1.3 million t/y of copper concentrate, and the smelters production capacity was expanded to 300,000 t/y of copper. The new plant reached its design capacity, measured over a three-month period, six months after it started treating its first feed. Vedantas website states that the new ISASMELT furnace was successfully ramped up "in a record period of 45 days".
Since then Sterlite decided to further expand its copper production by installing a third ISASMELT smelter and new refinery using IsaKidd technology. The new smelter has a design capacity of 1.36 million t/y of copper concentrate (containing 400,000 t/y of copper), processed through a single ISASMELT furnace. | 8 | Metallurgy |
Mediator is involved in "looping" of chromatin, which brings distant regions of a chromosome into closer physical proximity. The ncRNA-a mentioned above is involved in such looping. Enhancer RNAs (eRNAs) can function similarly.
In addition to the looping of euchromatin, mediator appears to be involved in formation or maintenance of heterochromatin at centromeres and telomeres. | 1 | Biochemistry |
A vacuum ceramic filter is designed to separate liquids from solids for dewatering of ore concentrates purposes. The device consists of a rotator, slurry tank, ceramic filter plate, distributor, discharge scraper, cleaning device, frame, agitating device, pipe system, vacuum system, automatic acid dosing system, automatic lubricating system, valve and discharge chute. The operation and construction principle of vacuum ceramic filter resemble those of a conventional disc filter, but the filter medium is replaced by a finely porous ceramic disc. The disc material is inert, has a long operational life and is resistant to almost all chemicals. Performance can be optimized by taking into account all those factors which affect the overall efficiency of the separation process. Some of the variables affecting the performance of a vacuum ceramic filter include the solid concentration, speed rotation of the disc, slurry level in the feed basin, temperature of the feed slurry, and the pressure during dewatering stages and filter cake formation. | 3 | Analytical Chemistry |
It has been established that cationic macromolecules in general destabilize the cell membrane, which can lead to lysis and cell death. The common conclusion present in current work echoes this observation: increasing dendrimer molecular weight and surface charge (both being generation-dependent) increases their cytotoxic behavior.
Initial studies on PAMAM toxicity showed that PAMAM was less toxic (in some cases, much less so) than related dendrimers, exhibiting minimal cytotoxicity across multiple toxicity screens, including tests of metabolic activity (MTT assay), cell breakdown (LDH assay), and nucleus morphology (DAPI staining). However, in other cell lines, the MTT assay and several other assays revealed some cytotoxicity. These disparate observations could be due to differences in sensitivity of the various cell lines used in each study to PAMAM; although cytotoxicity for PAMAM varies among cell lines, they remain less toxic than other dendrimer families overall.
More recently, a series of studies by Mukherjee et al. have shed some light on the mechanism of PAMAM cytotoxicity, providing evidence that the dendrimers break free of their encapsulating membrane (endosome) after being absorbed by the cell, causing harm to the cell's mitochondria and eventually leading to cell death. Further elucidation of the mechanism of PAMAM cytotoxicity would help resolve the dispute as to precisely how toxic the dendrimers are.
In relation to neuronal toxicity, fourth generation PAMAM has been shown to break down calcium transients, altering neurotransmitter vesicle dynamics and synaptic transmission. All of the above can be prevented by replacing the surface amines with folate or polyethylene glycol.
It has also been shown that PAMAM dendrimers cause rupturing of red blood cells, or hemolysis. Thus, if PAMAM dendrimers are to be considered in biological applications that involve dendrimers or dendrimer complexes traveling through the bloodstream, the concentration and generation number of unmodified PAMAM in the bloodstream should be taken into account. | 6 | Supramolecular Chemistry |
Sir Robert Howson Pickard FRS (27 September 1874 – 18 October 1949) was a chemist who did pioneering work in stereochemistry and also for the cotton industry in Lancashire. He was also involved in educational administration and was Vice Chancellor of the University of London from 1937-1939. He was Principal of Battersea Polytechnic (which later became the University of Surrey) from 1920 to 1927. | 4 | Stereochemistry |
AKT is downstream to PI3K and is inhibited by Ipatasertib. Akt is an AGC-family kinase and a central, integral signaling node of the PAM pathway. There are three Akt isozymes, Akt1, Akt2 and Akt3. Small-molecule inhibitors of Akt1 could be especially useful to target tumors with a high prevalence of Akt1 E17K activating mutations, which is observed in 4–6% of breast cancers and 1–2% of colorectal cancer. Research towards Akt inhibition has focused on inhibition of two distinct binding sites:
* the allosteric pocket of the inactive enzyme, and
* the ATP binding site.
Allosteric Akt inhibitors, highlighted by MK-2206, have been extensively evaluated in a clinical setting; Recently, additional allosteric Akt inhibitors have been identified. ARQ-092, is a potent pan-Akt inhibitor which can inhibit tumor growth preclinically and is currently in Phase I clinical studies. | 1 | Biochemistry |
The term polyol is used for various chemistries of the molecular backbone. Polyols may be reacted with diisocyanates or polyisocyanates to produce polyurethanes. MDI finds considerable use in PU foam production. Polyurethanes are used to make flexible foam for mattresses and seating, rigid foam insulation for refrigerators and freezers, elastomeric shoe soles, fibers (e.g. Spandex), coatings, sealants and adhesives.
The term polyol is also attributed to other molecules containing hydroxyl groups. For instance, polyvinyl alcohol is (CHCHOH) with n hydroxyl groups where n can be in the thousands. Cellulose is a polymer with many hydroxyl groups, but it is not referred to as a polyol. | 7 | Physical Chemistry |
In chemistry, an arsaalkyne is chemical compound with a triple bond between carbon and arsenic. These organoarsenic compounds are rare, especially in comparison with the phosphaalkynes. The parent HCAs has been characterized spectroscopically, otherwise the only arsaalkynes have bulky organic substituents. | 0 | Organic Chemistry |
The metal reagents used in this reaction include lithium bromide and silver acetate. In this method, the metal coordinates to the nitrogen in order to activate the substrate for deprotonation. Another way to form azomethine ylides from imines is by prototropy and by alkylation. | 0 | Organic Chemistry |
Boyles law states that at constant temperature' the volume of a given mass of a dry gas is inversely proportional to its pressure.
Most gases behave like ideal gases at moderate pressures and temperatures. The technology of the 17th century could not produce very high pressures or very low temperatures. Hence, the law was not likely to have deviations at the time of publication. As improvements in technology permitted higher pressures and lower temperatures, deviations from the ideal gas behavior became noticeable, and the relationship between pressure and volume can only be accurately described employing real gas theory. The deviation is expressed as the compressibility factor.
Boyle (and Mariotte) derived the law solely by experiment. The law can also be derived theoretically based on the presumed existence of atoms and molecules and assumptions about motion and perfectly elastic collisions (see kinetic theory of gases). These assumptions were met with enormous resistance in the positivist scientific community at the time, however, as they were seen as purely theoretical constructs for which there was not the slightest observational evidence.
Daniel Bernoulli (in 1737–1738) derived Boyles law by applying Newtons laws of motion at the molecular level. It remained ignored until around 1845, when John Waterston published a paper building the main precepts of kinetic theory; this was rejected by the Royal Society of England. Later works of James Prescott Joule, Rudolf Clausius and in particular Ludwig Boltzmann firmly established the kinetic theory of gases and brought attention to both the theories of Bernoulli and Waterston.
The debate between proponents of energetics and atomism led Boltzmann to write a book in 1898, which endured criticism until his suicide in 1906. Albert Einstein in 1905 showed how kinetic theory applies to the Brownian motion of a fluid-suspended particle, which was confirmed in 1908 by Jean Perrin. | 7 | Physical Chemistry |
Once the presence of certain substances in a sample is known, the study of their absolute or relative abundance could help in determining specific properties. Knowing the composition of a sample is very important, and several ways have been developed to make it possible, like gravimetric and volumetric analysis. Gravimetric analysis yields more accurate data about the composition of a sample than volumetric analysis but also takes more time to perform in the laboratory. Volumetric analysis, on the other hand, doesnt take that much time and can produce satisfactory results. Volumetric analysis can be simply a titration based in a neutralization reaction but it can also be a precipitation or a complex forming reaction as well as a titration based in a redox reaction. However, each method in quantitative analysis has a general specification, in neutralization reactions, for example, the reaction that occurs is between an acid and a base, which yields a salt and water, hence the name neutralization. In the precipitation reactions the standard solution is in the most cases silver nitrate which is used as a reagent to react with the ions present in the sample and to form a highly insoluble precipitate. Precipitation methods are often called simply as argentometry. In the two other methods the situation is the same. Complex forming titration is a reaction that occurs between metal ions and a standard solution that is in the most cases EDTA (Ethylene Diamine Tetra Acetic acid). In the redox titration that reaction is carried out between an oxidizing agent and a reduction agent. There are some more methods like Liebig method / Dumas method / Kjeldahl's method and Carius method for estimation of organic compounds.
For example, quantitative analysis performed by mass spectrometry on biological samples can determine, by the relative abundance ratio of specific proteins, indications of certain diseases, like cancer. | 3 | Analytical Chemistry |
In epigenetics, proline isomerization is the effect that cis-trans isomerization of the amino acid proline has on the regulation of gene expression. Similar to aspartic acid, the amino acid proline has the rare property of being able to occupy both cis and trans isomers of its prolyl peptide bonds with ease. Peptidyl-prolyl isomerase, or PPIase, is an enzyme very commonly associated with proline isomerization due to their ability to catalyze the isomerization of prolines. PPIases are present in three types: cyclophilins, FK507-binding proteins, and the parvulins. PPIase enzymes catalyze the transition of proline between cis and trans isomers and are essential to the numerous biological functions controlled and affected by prolyl isomerization (i.e. cell signalling, protein folding, and epigenetic modifications) Without PPIases, prolyl peptide bonds will slowly switch between cis and trans isomers, a process that can lock proteins in a nonnative structure that can affect render the protein temporarily ineffective. Although this switch can occur on its own, PPIases are responsible for most isomerization of prolyl peptide bonds. The specific amino acid that precedes the prolyl peptide bond also can have an effect on which conformation the bond assumes. For instance, when an aromatic amino acid is bonded to a proline the bond is more favorable to the cis conformation. Cyclophilin A uses an "electrostatic handle" to pull proline into cis and trans formations. Most of these biological functions are affected by the isomerization of proline when one isomer interacts differently than the other, commonly causing an activation/deactivation relationship. As an amino acid, proline is present in many proteins. This aids in the multitude of effects that isomerization of proline can have in different biological mechanisms and functions. | 4 | Stereochemistry |
One of the first examples of encapsulating a structure at the molecular level was demonstrated by Donald Cram and coworkers; they were able to isolate highly unstable, antiaromatic cyclobutadiene at room temperature by encapsulating it within a hemicarcerand. Isolation of cyclobutadiene allowed chemists to experimentally confirm one of the most fundamental predictions of the rules of aromaticity.
In another example the cage consists of a gallium tetrahedral cluster compound stabilized by 6 bidentate catechol amide ligands residing at the tetrahedron edges. The guest is a 16 electron and thus very reactive ruthenium metallocene (an organometallic catalyst) with a cyclopentadienyl ligand (red) and a 1,3,7-octatriene ligand (blue). The total charge for this anion is 11 and the counterions are 5 tetramethyl ammonium cations and 6 potassium cations. The ruthenium compound decomposes in water within minutes but encapsulated it survives in water for weeks.
Large metalla-assemblies, known as metallaprisms, contain a conformationally flexible cavity that allows them to host a variety of guest molecules. These assemblies have shown promise as agents of drug delivery to cancer cells.
An application of encapsulation is controlling reactivity, spectroscopy, and structure. For instance, excited state reactivity of free 1-phenyl-3-tolyl-2-proponanone (abbreviated A-CO-B) yields products A-A, B-B, and AB, which result from decarbonylation followed by random recombination of radicals A• and B•. Whereas, the same substrate upon encapsulation reacts to yield the controlled recombination product A-B, and rearranged products (isomers of A-CO-B).
Other applications:
* the encapsulation of filaments of a self-assembling bi-copper complex in polymer nanowires. | 6 | Supramolecular Chemistry |
The phenotype of each individual is modeled as the gene expression pattern at time . It is represented by a state vector in this model.
whose element denotes the expression state of gene i at time t. In the original Wagner model,
where 1 represents the gene is expressed while -1 implies the gene is not expressed. The expression pattern can only be ON or OFF. The continuous expression pattern between -1 (or 0) and 1 is also implemented in some other variants. | 1 | Biochemistry |
Enzyme induction is a process in which a molecule (e.g. a drug) induces (i.e. initiates or enhances) the expression of an enzyme.
Enzyme inhibition can refer to
* the inhibition of the expression of the enzyme by another molecule
* interference at the enzyme-level, basically with how the enzyme works. This can be competitive inhibition, uncompetitive inhibition, non-competitive inhibition or partially competitive inhibition.
If the molecule induces enzymes that are responsible for its own metabolism, this is called auto-induction (or auto-inhibition if there is inhibition). These processes are particular forms of gene expression regulation.
These terms are of particular interest to pharmacology, and more specifically to drug metabolism and drug interactions. They also apply to molecular biology. | 1 | Biochemistry |
Solar-blind imaging can be used to detect corona discharge, in electrical infrastructure. Missile exhaust can be detected from the troposphere or ground. Also when looking down on the Earth from space, the Earth appears dark in this range, so rockets can be easily detected from above once they pass the ozone layer.
Israel, People's Republic of China, Russia, South Africa, United Kingdom, and United States are developing this technology. | 5 | Photochemistry |
Some necessary apparatus include:
* crucible (or similar porcelain or metal dishes)
* muffled furnace
* hot plate
* the sample | 3 | Analytical Chemistry |
Other than standard fluorescence optical tweezers are now being built with multiple color Confocal, Widefield, STED, FRET, TIRF or IRM.
This allows applications such as measuring: protein/DNA localization binding, protein folding, condensation, motor protein force generation, visualization of cytoskeletal filaments and motor dynamics, microtubule dynamics, manipulating liquid droplet (rheology) or fusion. These setups are difficult to build and traditionally are found in non correlated academic setups. In the recent years even home builders (both biophysics and general biologists) are converting to the alternative and are acquiring total correlated solution with easy data acquisition and data analysis. | 1 | Biochemistry |
Desorption/ionization on silicon (DIOS) is a soft laser desorption method used to generate gas-phase ions for mass spectrometry analysis. DIOS is considered the first surface-based surface-assisted laser desorption/ionization (SALDI-MS) approach. Prior approaches were accomplished using nanoparticles in a matrix of glycerol, while DIOS is a matrix-free technique in which a sample is deposited on a nanostructured (porous silicon) surface and the sample desorbed directly from the nanostructured surface through the adsorption of laser light energy. DIOS has been used to analyze organic molecules, metabolites, biomolecules and peptides, and, ultimately, to image tissues and cells. | 3 | Analytical Chemistry |
Deuterium has been shown to lengthen the period of oscillation of the circadian clock when dosed in rats, hamsters, and Gonyaulax dinoflagellates. In rats, chronic intake of 25% DO disrupts circadian rhythmicity by lengthening the circadian period of suprachiasmatic nucleus-dependent rhythms in the brain's hypothalamus. Experiments in hamsters also support the theory that deuterium acts directly on the suprachiasmatic nucleus to lengthen the free-running circadian period. | 9 | Geochemistry |
TEs are found in almost all life forms, and the scientific community is still exploring their evolution and their effect on genome evolution. It is unclear whether TEs originated in the last universal common ancestor, arose independently multiple times, or arose once and then spread to other kingdoms by horizontal gene transfer. While some TEs confer benefits on their hosts, most are regarded as selfish DNA parasites. In this way, they are similar to viruses. Various viruses and TEs also share features in their genome structures and biochemical abilities, leading to speculation that they share a common ancestor.
Because excessive TE activity can damage exons, many organisms have acquired mechanisms to inhibit their activity. Bacteria may undergo high rates of gene deletion as part of a mechanism to remove TEs and viruses from their genomes, while eukaryotic organisms typically use RNA interference to inhibit TE activity. Nevertheless, some TEs generate large families often associated with speciation events. Evolution often deactivates DNA transposons, leaving them as introns (inactive gene sequences). In vertebrate animal cells, nearly all 100,000+ DNA transposons per genome have genes that encode inactive transposase polypeptides. The first synthetic transposon designed for use in vertebrate (including human) cells, the Sleeping Beauty transposon system, is a Tc1/mariner-like transposon. Its dead ("fossil") versions are spread widely in the salmonid genome and a functional version was engineered by comparing those versions. Human Tc1-like transposons are divided into Hsmar1 and Hsmar2 subfamilies. Although both types are inactive, one copy of Hsmar1 found in the SETMAR gene is under selection as it provides DNA-binding for the histone-modifying protein. Many other human genes are similarly derived from transposons. Hsmar2 has been reconstructed multiple times from the fossil sequences.
The frequency and location of TE integrations influence genomic structure and evolution and affect gene and protein regulatory networks during development and in differentiated cell types. Large quantities of TEs within genomes may still present evolutionary advantages, however. Interspersed repeats within genomes are created by transposition events accumulating over evolutionary time. Because interspersed repeats block gene conversion, they protect novel gene sequences from being overwritten by similar gene sequences and thereby facilitate the development of new genes. TEs may also have been co-opted by the vertebrate immune system as a means of producing antibody diversity. The V(D)J recombination system operates by a mechanism similar to that of some TEs. TEs also serve to generate repeating sequences that can form dsRNA to act as a substrate for the action of ADAR in RNA editing.
TEs can contain many types of genes, including those conferring antibiotic resistance and the ability to transpose to conjugative plasmids. Some TEs also contain integrons, genetic elements that can capture and express genes from other sources. These contain integrase, which can integrate gene cassettes. There are over 40 antibiotic resistance genes identified on cassettes, as well as virulence genes.
Transposons do not always excise their elements precisely, sometimes removing the adjacent base pairs; this phenomenon is called exon shuffling. Shuffling two unrelated exons can create a novel gene product or, more likely, an intron.
Some non-autonomous DNA TEs found in plants can capture coding DNA from genes and shuffle them across the genome. This process can duplicate genes in the genome (a phenomenon called transduplication), and can contribute to generate novel genes by exon shuffling. | 1 | Biochemistry |
Thermoplastic starch represents the most widely used bioplastic, constituting about 50 percent of the bioplastics market. Simple starch bioplastic film can be made at home by gelatinizing starch and solution casting. Pure starch is able to absorb humidity, and is thus a suitable material for the production of drug capsules by the pharmaceutical sector. However, pure starch-based bioplastic is brittle. Plasticizer such as glycerol, glycol, and sorbitol can also be added so that the starch can also be processed thermo-plastically. The characteristics of the resulting bioplastic (also called "thermoplastic starch") can be tailored to specific needs by adjusting the amounts of these additives. Conventional polymer processing techniques can be used to process starch into bioplastic, such as extrusion, injection molding, compression molding and solution casting. The properties of starch bioplastic is largely influenced by amylose/amylopectin ratio. Generally, high-amylose starch results in superior mechanical properties. However, high-amylose starch has less processability because of its higher gelatinization temperature and higher melt viscosity.
Starch-based bioplastics are often blended with biodegradable polyesters to produce starch/polylactic acid, starch/polycaprolactone or starch/Ecoflex (polybutylene adipate-co-terephthalate produced by BASF) blends. These blends are used for industrial applications and are also compostable. Other producers, such as Roquette, have developed other starch/polyolefin blends. These blends are not biodegradable, but have a lower carbon footprint than petroleum-based plastics used for the same applications.
Starch is cheap, abundant, and renewable.
Starch-based films (mostly used for packaging purposes) are made mainly from starch blended with thermoplastic polyesters to form biodegradable and compostable products. These films are seen specifically in consumer goods packaging of magazine wrappings and bubble films. In food packaging, these films are seen as bakery or fruit and vegetable bags. Composting bags with this films are used in selective collecting of organic waste. Further, starch-based films can be used as a paper.
Starch-based nanocomposites have been widely studied, showing improved mechanical properties, thermal stability, moisture resistance, and gas barrier properties. | 7 | Physical Chemistry |
SCCmec, or staphylococcal cassette chromosome mec, is a mobile genetic element of Staphylococcus bacterial species. This genetic sequence includes the mecA gene coding for resistance to the antibiotic methicillin and is the only known way for Staphylococcus strains to spread the gene in the wild by horizontal gene transfer. SCCmec is a 21 to 60 kb long genetic element that confers broad-spectrum β-lactam resistance to MRSA. Moreover, additional genetic elements like Tn554, pT181, and pUB110 can be found in SCCmec, which have the capability to render resistance to various non-β-lactam drugs. | 1 | Biochemistry |
By combining substances with pK values differing by only two or less and adjusting the pH, a wide range of buffers can be obtained. Citric acid is a useful component of a buffer mixture because it has three pK values, separated by less than two. The buffer range can be extended by adding other buffering agents. The following mixtures (McIlvaine's buffer solutions) have a buffer range of pH 3 to 8.
A mixture containing citric acid, monopotassium phosphate, boric acid, and diethyl barbituric acid can be made to cover the pH range 2.6 to 12.
Other universal buffers are the Carmody buffer and the Britton–Robinson buffer, developed in 1931. | 7 | Physical Chemistry |
Phosphine is used for pest control, but its usage is strictly regulated due to high toxicity. Gas from phosphine has high mortality rate and has caused deaths in Sweden and other countries.
Because the previously popular fumigant methyl bromide has been phased out in some countries under the Montreal Protocol, phosphine is the only widely used, cost-effective, rapidly acting fumigant that does not leave residues on the stored product. Pests with high levels of resistance toward phosphine have become common in Asia, Australia and Brazil. High level resistance is also likely to occur in other regions, but has not been as closely monitored. Genetic variants that contribute to high level resistance to phosphine have been identified in the dihydrolipoamide dehydrogenase gene. Identification of this gene now allows rapid molecular identification of resistant insects. | 0 | Organic Chemistry |
Siderophores have applications in medicine for iron and aluminum overload therapy and antibiotics for improved targeting. Understanding the mechanistic pathways of siderophores has led to opportunities for designing small-molecule inhibitors that block siderophore biosynthesis and therefore bacterial growth and virulence in iron-limiting environments.
Siderophores are useful as drugs in facilitating iron mobilization in humans, especially in the treatment of iron diseases, due to their high affinity for iron. One potentially powerful application is to use the iron transport abilities of siderophores to carry drugs into cells by preparation of conjugates between siderophores and antimicrobial agents. Because microbes recognize and utilize only certain siderophores, such conjugates are anticipated to have selective antimicrobial activity. An example is the cephalosporin antibiotic cefiderocol.
Microbial iron transport (siderophore)-mediated drug delivery makes use of the recognition of siderophores as iron delivery agents in order to have the microbe assimilate siderophore conjugates with attached drugs. These drugs are lethal to the microbe and cause the microbe to apoptosise when it assimilates the siderophore conjugate. Through the addition of the iron-binding functional groups of siderophores into antibiotics, their potency has been greatly increased. This is due to the siderophore-mediated iron uptake system of the bacteria. | 1 | Biochemistry |
Only one example is known, bis(trifluoromethyl)phosphinous acid, (CF)POH. It is prepared in several steps from phosphorus trichloride (Et = ethyl):
:PCl + 2 EtNH → PClNEt + EtNHCl
:2 P(NEt) + PClNEt + 2 CFBr → P(CF)NEt + 2 BrClP(NEt)
:P(CF)NEt + HO → P(CF)OH + HNEt | 0 | Organic Chemistry |
In crystallography, a Strukturbericht designation or Strukturbericht type is a system of detailed crystal structure classification by analogy to another known structure. The designations were intended to be comprehensive but are mainly used as supplement to space group crystal structures designations, especially historically. Each Strukturbericht designation is described by a single space group, but the designation includes additional information about the positions of the individual atoms, rather than just the symmetry of the crystal structure. While Strukturbericht symbols exist for many of the earliest observed and most common crystal structures, the system is not comprehensive, and is no longer being updated. Modern databases such as Inorganic Crystal Structure Database index thousands of structure types directly by the prototype compound (i.e. "the NaCl structure" instead of "the B1 structure"). These are essentially equivalent to the old Stukturbericht designations. | 3 | Analytical Chemistry |
In two-dimensional space there are 5 Bravais lattices, grouped into four lattice systems, shown in the table below. Below each diagram is the Pearson symbol for that Bravais lattice.
Note: In the unit cell diagrams in the following table the lattice points are depicted using black circles and the unit cells are depicted using parallelograms (which may be squares or rectangles) outlined in black. Although each of the four corners of each parallelogram connects to a lattice point, only one of the four lattice points technically belongs to a given unit cell and each of the other three lattice points belongs to one of the adjacent unit cells. This can be seen by imagining moving the unit cell parallelogram slightly left and slightly down while leaving all the black circles of the lattice points fixed.
The unit cells are specified according to the relative lengths of the cell edges (a and b) and the angle between them (θ). The area of the unit cell can be calculated by evaluating the norm , where a and b are the lattice vectors. The properties of the lattice systems are given below: | 3 | Analytical Chemistry |
In cycloalkanes, each carbon is bonded nonpolar covalently to two carbons and two hydrogen. The carbons have sp hybridization and should have ideal bond angles of 109.5°. Due to the limitations of cyclic structure, however, the ideal angle is only achieved in a six carbon ring — cyclohexane in chair conformation. For other cycloalkanes, the bond angles deviate from ideal.
Molecules with a high amount of ring strain consist of three, four, and some five-membered rings, including: cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, [1,1,1]propellanes, [2,2,2]propellanes, epoxides, aziridines, cyclopentenes, and norbornenes. These molecules have bond angles between ring atoms which are more acute than the optimal tetrahedral (109.5°) and trigonal planar (120°) bond angles required by their respective sp and sp bonds. Because of the smaller bond angles, the bonds have higher energy and adopt more p-character to reduce the energy of the bonds. In addition, the ring structures of cyclopropanes/enes and cyclclobutanes/enes offer very little conformational flexibility. Thus, the substituents of ring atoms exist in an eclipsed conformation in cyclopropanes and between gauche and eclipsed in cyclobutanes, contributing to higher ring strain energy in the form of van der Waals repulsion.
monocycles
*cyclopropane (29 kcal/mol), CH — the C-C-C bond angles are 60° whereas tetrahedral 109.5° bond angles are expected. The intense angle strain leads to nonlinear orbital overlap of its sp orbitals. Because of the bond's instability, cyclopropane is more reactive than other alkanes. Since any three points make a plane and cyclopropane has only three carbons, cyclopropane is planar. The H-C-H bond angle is 115° whereas 106° is expected as in the CH groups of propane.
*cyclobutane (26.3 kcal/mol), CH — if cyclobutane were completely square planar, its bond angles would be 90° whereas tetrahedral 109.5° bond angles are expected. However, the actual C-C-C bond angle is 88° because it has a slightly folded form to relieve some torsional strain at the expense of slightly more angle strain. The high strain energy of cyclobutane is primarily from angle strain.
*cyclopentane (7.4 kcal/mol), CH — if it was a completely regular planar pentagon its bond angles would be 108°, but tetrahedral 109.5° bond angles are expected. However, it has an unfixed puckered shape that undulates up and down.
*cyclohexane (1.3 kcal/mol), CH — Although the chair conformation is able to achieve ideal angles, the unstable half-chair conformation has angle strain in the C-C-C angles which range from 109.86° to 119.07°.
Bicyclics
*[[Bicyclobutane|bicyclo[1.1.0]butane]] (66.3 kcal/mol),
*[[housane|bicyclo[1.2.0]pentane]] (54.7 kcal/mol),
*[[bicyclo[1.3.0]hexane]] (26 kcal/mol),
*norbornane (16.6 kcal/mol),
Ring strain can be considerably higher in bicyclic systems. For example, bicyclobutane, CH, is noted for being one of the most strained compounds that is isolatable on a large scale; its strain energy is estimated at 63.9 kcal mol (267 kJ mol).
Cyclopropane has a lesser amount of ring strain since it has the least amount of unsaturation; as a result, increasing the amount of unsaturation leads to greater ring strain. For example, cyclopropene has a greater amount of ring strain than cyclopropane because it has more unsaturation. | 7 | Physical Chemistry |
Straight-chain alkanes take the suffix "-ane" and are prefixed depending on the number of carbon atoms in the chain, following standard rules. The first few are:
For example, the simplest alkane is methane, and the nine-carbon alkane is named nonane. The names of the first four alkanes were derived from methanol, ether, propionic acid and butyric acid, respectively. The rest are named with a Greek numeric prefix, with the exceptions of nonane which has a Latin prefix, and undecane which has mixed-language prefixes.
Cyclic alkanes are simply prefixed with "cyclo-": for example, is cyclobutane (not to be confused with butene) and is cyclohexane (not to be confused with hexene).
Branched alkanes are named as a straight-chain alkane with attached alkyl groups. They are prefixed with a number indicating the carbon the group is attached to, counting from the end of the alkane chain. For example, , commonly known as isobutane, is treated as a propane chain with a methyl group bonded to the middle (2) carbon, and given the systematic name 2-methylpropane. However, although the name 2-methylpropane could be used, it is easier and more logical to call it simply methylpropane – the methyl group could not possibly occur on any of the other carbon atoms (that would lengthen the chain and result in butane, not propane) and therefore the use of the number "2" is unnecessary.
If there is ambiguity in the position of the substituent, depending on which end of the alkane chain is counted as "1", then numbering is chosen so that the smaller number is used. For example, (isopentane) is named 2-methylbutane, not 3-methylbutane.
If there are multiple side-branches of the same size alkyl group, their positions are separated by commas and the group prefixed with multiplier prefixes depending on the number of branches. For example, (neopentane) is named 2,2-dimethylpropane. If there are different groups, they are added in alphabetical order, separated by commas or hyphens. The longest possible main alkane chain is used; therefore 3-ethyl-4-methylhexane instead of 2,3-diethylpentane, even though these describe equivalent structures. The di-, tri- etc. prefixes are ignored for the purpose of alphabetical ordering of side chains (e.g. 3-ethyl-2,4-dimethylpentane, not 2,4-dimethyl-3-ethylpentane). | 0 | Organic Chemistry |
Hicks' research focuses largely on the development and implementation of mass spectrometric methods for protein identification and characterization. Recent work in the Hicks Lab has focused primarily on two areas. The first is the study of post-translational modifications and their role in regulation and development. The second involves a novel analytical pipeline for the discovery and characterization of antimicrobial peptides.
Hicks research in post-translational modifications typically employs bottom-up proteomics using label-free quantification. Much of this research involves the model organism C. reinhardtii, an important organism in biofuel research due to its tendency to accumulate triacylglycerols. The Hicks Lab has studied the phosphoproteome of C. reinhardtii in order to examine underlying biological processes. Work has also been done to understand cell regulatory pathways, especially the algal analog of the mammalian TOR pathway. To a similar end, Hicks group has extended its work to examine how the reversible oxidation of thiols plays a role in signaling and effector-triggered immunity.
The increasing threat of antimicrobial resistance has produced a need for novel antimicrobial agents. The Hicks Lab has investigated antimicrobial peptides as a potential source for new antibiotics. Recent work has involved the development of a comprehensive analytical approach using LC-MS for the identification of novel antimicrobial peptides from botanical, fungal, and bacterial sources. | 3 | Analytical Chemistry |
Iodic acid crystallises from acidic solution as orthorhombic α- in space group P222. The structure consists of pyramidal molecules linked by hydrogen bonding and intermolecular iodine-oxygen interactions. The I=O bond lengths are 1.81 Å while the I–OH distance is 1.89 Å. Several other polymorphs have been reported, including an orthorhombic γ form in space group Pbca and an orthorhombic δ form in space group P222. All of the polymorphs contain pyramidal molecules, hydrogen bonding and I···O interactions, but differ in packing arrangement. | 3 | Analytical Chemistry |
P1 is a temperate bacteriophage that infects Escherichia coli and some other bacteria. When undergoing a lysogenic cycle the phage genome exists as a plasmid in the bacterium unlike other phages (e.g. the lambda phage) that integrate into the host DNA. P1 has an icosahedral head containing the DNA attached to a contractile tail with six tail fibers.
The P1 phage has gained research interest because it can be used to transfer DNA from one bacterial cell to another in a process known as transduction. As it replicates during its lytic cycle it captures fragments of the host chromosome. If the resulting viral particles are used to infect a different host the captured DNA fragments can be integrated into the new hosts genome. This method of in vivo genetic engineering was widely used for many years and is still used today, though to a lesser extent. P1 can also be used to create the P1-derived artificial chromosome cloning vector which can carry relatively large fragments of DNA. P1 encodes a site-specific recombinase, Cre, that is widely used to carry out cell-specific or time-specific DNA recombination by flanking the target DNA with loxP' sites (see Cre-Lox recombination). | 1 | Biochemistry |
There are several methods for preparing aldehydes, but the dominant technology is hydroformylation. Illustrative is the generation of butyraldehyde by hydroformylation of propene: | 0 | Organic Chemistry |
Liquid hydrophilic chemicals complexed with solid chemicals can be used to optimize solubility of hydrophobic chemicals. | 6 | Supramolecular Chemistry |
In chemistry imidines are a rare functional group, being the nitrogen analogues of anhydrides and imides. They were first reported by Adolf Pinner in 1883, but did not see significant investigation until the 1950s, when Patrick Linstead and John Arthur Elvidge developed a number of compounds.
Imidines may be prepared in a modified Pinner reaction, by passing hydrogen chloride into an alcoholic solution of their corresponding di-nitriles (i.e. succinonitrile, glutaronitrile, adiponitrile) to give imino ethers which then condense when treated with ammonia. As a result, most structures are cyclic.
The compounds are highly moisture sensitive and can be converted into imides upon exposure to water. | 0 | Organic Chemistry |
Fluorescent materials are also very widely used in numerous applications in molecular biology, often as "tags" which bind themselves to a substance of interest (for example, DNA), so allowing their visualization.
Thousands of moth and insect collectors all over the world use various types of black lights to attract moth and insect specimens for photography and collecting. It is one of the preferred light sources for attracting insects and moths at night. Black light can also be used to see animal excreta such as urine and vomit that is not always visible to the naked eye. | 5 | Photochemistry |
The ionization equilibrium of an acid or a base is affected by a solvent change. The effect of the solvent is not only because of its acidity or basicity but also because of its dielectric constant and its ability to preferentially solvate and thus stabilize certain species in acid-base equilibria. A change in the solvating ability or dielectric constant can thus influence the acidity or basicity.
In the table above, it can be seen that water is the most polar-solvent, followed by DMSO, and then acetonitrile. Consider the following acid dissociation equilibrium:
:HA A + H
Water, being the most polar-solvent listed above, stabilizes the ionized species to a greater extent than does DMSO or Acetonitrile. Ionization - and, thus, acidity - would be greatest in water and lesser in DMSO and Acetonitrile, as seen in the table below, which shows pK values at 25 °C for acetonitrile (ACN) and dimethyl sulfoxide (DMSO) and water. | 7 | Physical Chemistry |
The American Society for Biochemistry and Molecular Biology (ASBMB) is a learned society that was founded on December 26, 1906, at a meeting organized by John Jacob Abel (Johns Hopkins University). The roots of the society were in the American Physiological Society, which had been formed some 20 years earlier. ASBMB is the US member of the International Union of Biochemistry and Molecular Biology.
The ASBMB was originally called the American Society of Biological Chemists, before obtaining its current name in 1987. The society is based in Rockville, Maryland. ASBMB's mission is to advance the science of biochemistry and molecular biology through publication of scientific and educational journals, the organization of scientific meetings, advocacy for funding of basic research and education, support of science education at all levels, and by promoting the diversity of individuals entering the scientific workforce. The organization currently has over 12,000 members. | 1 | Biochemistry |
The physical and mathematical basics of electron charge transfer absent chemical bonds leading to pseudocapacitance was developed by Rudolph A. Marcus. Marcus Theory explains the rates of electron transfer reactions—the rate at which an electron can move from one chemical species to another. It was originally formulated to address outer sphere electron transfer reactions, in which two chemical species change only in their charge, with an electron jumping. For redox reactions without making or breaking bonds, Marcus theory takes the place of Henry Eyring's transition state theory which was derived for reactions with structural changes. Marcus received the Nobel Prize in Chemistry in 1992 for this theory. | 7 | Physical Chemistry |
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl () group of an alcohol), and the word is a blend of "thio-" with "alcohol".
Many thiols have strong odors resembling that of garlic or rotten eggs. Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans () or mercapto compounds, a term introduced in 1832 by William Christopher Zeise and is derived from the Latin (capturing mercury) because the thiolate group () bonds very strongly with mercury compounds. | 0 | Organic Chemistry |
In the late 1960s it was discovered that illuminated organic dyes can generate electricity at oxide electrodes in electrochemical cells. In an effort to understand and simulate the primary processes in photosynthesis the phenomenon was studied at the University of California at Berkeley with chlorophyll extracted from spinach (bio-mimetic or bionic approach). On the basis of such experiments electric power generation via the dye sensitization solar cell (DSSC) principle was demonstrated and discussed in 1972. The instability of the dye solar cell was identified as a main challenge. Its efficiency could, during the following two decades, be improved by optimizing the porosity of the electrode prepared from fine oxide powder, but the instability remained a problem.
A modern n-type DSSC, the most common type of DSSC, is composed of a porous layer of titanium dioxide nanoparticles, covered with a molecular dye that absorbs sunlight, like the chlorophyll in green leaves. The titanium dioxide is immersed under an electrolyte solution, above which is a platinum-based catalyst. As in a conventional alkaline battery, an anode (the titanium dioxide) and a cathode (the platinum) are placed on either side of a liquid conductor (the electrolyte).
The working principle for n-type DSSCs can be summarized into a few basic steps. Sunlight passes through the transparent electrode into the dye layer where it can excite electrons that then flow into the conduction band of the n-type semiconductor, typically titanium dioxide. The electrons from titanium dioxide then flow toward the transparent electrode where they are collected for powering a load. After flowing through the external circuit, they are re-introduced into the cell on a metal electrode on the back, also known as the counter electrode, and flow into the electrolyte. The electrolyte then transports the electrons back to the dye molecules and regenerates the oxidized dye.
The basic working principle above, is similar in a p-type DSSC, where the dye-sensitised semiconductor is of p-type nature (typically nickel oxide). However, instead of injecting an electron into the semiconductor, in a p-type DSSC, a hole flows from the dye into the valence band of the p-type semiconductor.
Dye-sensitized solar cells separate the two functions provided by silicon in a traditional cell design. Normally the silicon acts as both the source of photoelectrons, as well as providing the electric field to separate the charges and create a current. In the dye-sensitized solar cell, the bulk of the semiconductor is used solely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte.
The dye molecules are quite small (nanometer sized), so in order to capture a reasonable amount of the incoming light the layer of dye molecules needs to be made fairly thick, much thicker than the molecules themselves. To address this problem, a nanomaterial is used as a scaffold to hold large numbers of the dye molecules in a 3-D matrix, increasing the number of molecules for any given surface area of cell. In existing designs, this scaffolding is provided by the semiconductor material, which serves double-duty. | 5 | Photochemistry |
After ingestion, ethyl eicosapentaenoic acid (E-EPA) is metabolized to eicosapentaenoic acid (EPA). EPA is absorbed in the small intestine and enters circulation. Peak plasma concentration occurs about five hours after ingestion, and the half-life is about 89 hours. EPA is lipolyzed mostly in the liver. | 1 | Biochemistry |
A pheromone (from Greek phero "to bear" + hormone from Greek – "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Their use among insects has been particularly well documented. In addition, some vertebrates and plants communicate by using pheromones. A notable example of pheromone usage to indicate sexual receptivity in insects can be seen in the female Dawsons burrowing bee, which uses a particular mixture of cuticular hydrocarbons to signal sexual receptivity to mating, and then another mixture to indicate sexual disinterest. These hydrocarbons, in association with other chemical signals produced in the Dufours gland, have been implicated in male repulsion signaling as well.
The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in 1959, based on the Greek word pherein (to transport) and hormone (to stimulate). They are also sometimes classified as ecto-hormones. German Biochemist Adolf Butenandt characterized the first such chemical, Bombykol (a chemically well-characterized pheromone released by the female silkworm to attract mates). | 1 | Biochemistry |
A gasket used in a diamond anvil cell experiment is a thin metal foil, typically 0.3 mm in thickness, which is placed in between the diamonds. Desirable materials for gaskets are strong, stiff metals such as rhenium or tungsten. Steel is frequently used as a cheaper alternative for low pressure experiments. The above-mentioned materials cannot be used in radial geometries where the x-ray beam must pass through the gasket. Since they are not transparent to X-rays, if X-ray illumination through the gasket is required, lighter materials such as beryllium, boron nitride, boron or diamond are used as a gasket. Gaskets are preindented by the diamonds and a hole is drilled in the center of the indentation to create the sample chamber. | 7 | Physical Chemistry |
A method that is the less well-known is the metabisulfite method, in which metabisulfite is placed at the bottom of a beaker and 12.6 molar concentration hydrochloric acid is added. The resulting gas is bubbled through nitric acid, which will release brown/red vapors of nitrogen dioxide as the reaction proceeds. The completion of the reaction is indicated by the ceasing of the fumes. This method does not produce an inseparable mist, which is quite convenient.
Burning sulfur together with saltpeter (potassium nitrate, ), in the presence of steam, has been used historically. As saltpeter decomposes, it oxidizes the sulfur to , which combines with water to produce sulfuric acid.
Alternatively, dissolving sulfur dioxide in an aqueous solution of an oxidizing metal salt such as copper(II) or iron(III) chloride:
Two less well-known laboratory methods of producing sulfuric acid, albeit in dilute form and requiring some extra effort in purification. A solution of copper(II) sulfate can be electrolyzed with a copper cathode and platinum/graphite anode to give spongy copper at cathode and evolution of oxygen gas at the anode, the solution of dilute sulfuric acid indicates completion of the reaction when it turns from blue to clear (production of hydrogen at cathode is another sign):
More costly, dangerous, and troublesome yet novel is the electrobromine method, which employs a mixture of sulfur, water, and hydrobromic acid as the electrolytic solution. The sulfur is pushed to bottom of container under the acid solution. Then the copper cathode and platinum/graphite anode are used with the cathode near the surface and the anode is positioned at the bottom of the electrolyte to apply the current. This may take longer and emits toxic bromine/sulfur bromide vapors, but the reactant acid is recyclable. Overall, only the sulfur and water are converted to sulfuric acid and hydrogen (omitting losses of acid as vapors):
: (electrolysis of aqueous hydrogen bromide)
: (initial tribromide production, eventually reverses as depletes)
: (bromine reacts with sulfur to form disulfur dibromide)
: (oxidation and hydration of disulfur dibromide)
Prior to 1900, most sulfuric acid was manufactured by the lead chamber process. As late as 1940, up to 50% of sulfuric acid manufactured in the United States was produced by chamber process plants.
In the early to mid 19th century "vitriol" plants existed, among other places, in Prestonpans in Scotland, Shropshire and the Lagan Valley in County Antrim Ireland, where it was used as a bleach for linen. Early bleaching of linen was done using lactic acid from sour milk but this was a slow process and the use of vitriol sped up the bleaching process. | 7 | Physical Chemistry |
The biosynthesis of N-linked glycans occurs via 3 major steps:
#Synthesis of dolichol-linked precursor oligosaccharide
#En bloc transfer of precursor oligosaccharide to protein
#Processing of the oligosaccharide
Synthesis, en bloc transfer and initial trimming of precursor oligosaccharide occurs in the endoplasmic reticulum (ER). Subsequent processing and modification of the oligosaccharide chain are carried out in the Golgi apparatus.
The synthesis of glycoproteins is thus spatially separated in different cellular compartments. Therefore, the type of N-glycan synthesized, depends on its accessibility to the different enzymes present within these cellular compartments.
However, in spite of the diversity, all N-glycans are synthesized through a common pathway with a common core glycan structure.
The core glycan structure is essentially made up of two N-acetyl glucosamine and three mannose residues. This core glycan is then elaborated and modified further, resulting in a diverse range of N-glycan structures. | 0 | Organic Chemistry |
In a common FPLC strategy, a resin is chosen that the protein of interest will bind to by a charge interaction while in buffer A (the running buffer) but become dissociated and return to solution in buffer B (the elution buffer). A mixture containing one or more proteins of interest is dissolved in 100% buffer A and pumped into the column. The proteins of interest bind to the resin while other components are carried out in the buffer. The total flow rate of the buffer is kept constant; however, the proportion of buffer B (the "elution" buffer) is gradually increased from 0% to 100% according to a programmed change in concentration (the "gradient"). At some point during this process each of the bound proteins dissociates and appears in the eluant. The eluant passes through two detectors which measure salt concentration (by conductivity) and protein concentration (by absorption of ultraviolet light at a wavelength of 280 nm). As each protein is eluted, it appears in the eluant as a "peak" in protein concentration, and can be collected for further use. | 3 | Analytical Chemistry |
Exogenous antigens are antigens that have entered the body from the outside, for example, by inhalation, ingestion or injection. The immune system's response to exogenous antigens is often subclinical. By endocytosis or phagocytosis, exogenous antigens are taken into the antigen-presenting cells (APCs) and processed into fragments. APCs then present the fragments to T helper cells (CD4) by the use of class II histocompatibility molecules on their surface. Some T cells are specific for the peptide:MHC complex. They become activated and start to secrete cytokines, substances that activate cytotoxic T lymphocytes (CTL), antibody-secreting B cells, macrophages and other particles.
Some antigens start out as exogenous and later become endogenous (for example, intracellular viruses). Intracellular antigens can be returned to circulation upon the destruction of the infected cell. | 1 | Biochemistry |
An STR multiplex system is used to identify specific short tandem repeats (STRs). STR polymorphisms are genetic markers that may be used to identify a DNA sequence.
The FBI analyses 13 specific STR loci for their database. These may be used in many areas of genetics in addition to their forensic uses.
One can think of a STR multiplex system as a collection of specific STRs which are positionally conserved on a target genome. Hence these can be used as markers. A number of different STRs along with their loci in a particular genome can be used for genotyping.
For example, the STR multiplex system AmpFlSTR Profiler Plus which analyses nine different STRs (3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820) plus Amelogenin for sex determination is used for human identification purposes. | 1 | Biochemistry |
Classically, it converts carboxylic acids to acyl chlorides:
The reaction mechanism has been investigated: | 0 | Organic Chemistry |
Upon heating to 420 °C, it rearranges to form the meta isomer. The para isomer is produced by heating to temperatures above 600 °C. | 7 | Physical Chemistry |
The Golm Metabolome Database (GMD) is a gas chromatography (GC) – mass spectrometry (MS) reference library dedicated to metabolite profiling experiments and comprises mass spectral and retention index (RI) information for non-annotated mass spectral tags (MSTs, mass spectral information with retention time attached indices) together with data of a multitude of already identified metabolites and reference substances. The GMD is hosted at the Max Planck Institute of Molecular Plant Physiology in Golm district of Potsdam, Germany. | 0 | Organic Chemistry |
These circuits can be modelled in silico to predict the dynamics of a genetic system. Having constructed a computational model of the natural circuit of interest, one can use the model to make testable predictions about circuit performance. When designing a synthetic circuit for a specific engineering task, a model is useful for identifying necessary connections and parameter operating regimes that give rise to a desired functional output. Similarly, when studying a natural circuit, one can use the model to identify the parts or parameter values necessary for a desired biological outcome. In other words, computational modelling and experimental synthetic perturbations can be used to probe biological circuits. However, the structure of the circuits have shown to not be a reliable indicator of the function that the regulatory circuit provides for the larger cellular regulatory network. | 1 | Biochemistry |
In chemistry, autoprotolysis is a chemical reaction in which a proton is transferred between two identical molecules, one of which acts as a Brønsted acid, releasing a proton which is accepted by the other molecule acting as a Brønsted base. For example, water undergoes autoprotolysis in the self-ionization of water reaction. It is a type of molecular autoionization.
Any solvent that contains both acidic hydrogen and lone pairs of electrons to accept can undergo autoprotolysis.
For example, ammonia in its purest form may undergo autoprotolysis:
Another example is acetic acid: | 7 | Physical Chemistry |
Luciferases can be produced in the lab through genetic engineering for a number of purposes. Luciferase genes can be synthesized and inserted into organisms or transfected into cells. As of 2002, mice, silkworms, and potatoes are just a few of the organisms that have already been engineered to produce the protein.
In the luciferase reaction, light is emitted when luciferase acts on the appropriate luciferin substrate. Photon emission can be detected by light sensitive apparatus such as a luminometer or an optical microscope with a CCD camera. This allows observation of biological processes. Since light excitation is not needed for luciferase bioluminescence, there is minimal autofluorescence and therefore the bioluminescent signal is virtually background-free. Therefore, as little as 0.02 pg can still be accurately measured using a standard scintillation counter.
In biological research, luciferase is commonly used as a reporter to assess the transcriptional activity in cells that are transfected with a genetic construct containing the luciferase gene under the control of a promoter of interest. Additionally, proluminescent molecules that are converted to luciferin upon activity of a particular enzyme can be used to detect enzyme activity in coupled or two-step luciferase assays. Such substrates have been used to detect caspase activity and cytochrome P450 activity, among others.
Luciferase can also be used to detect the level of cellular ATP in cell viability assays or for kinase activity assays. Luciferase can act as an ATP sensor protein through biotinylation. Biotinylation will immobilize luciferase on the cell-surface by binding to a streptavidin-biotin complex. This allows luciferase to detect the efflux of ATP from the cell and will effectively display the real-time release of ATP through bioluminescence. Luciferase can additionally be made more sensitive for ATP detection by increasing the luminescence intensity by changing certain amino acid residues in the sequence of the protein.
Whole organism imaging (referred to as in vivo when intact or, otherwise called ex vivo imaging for example of living but explanted tissue) is a powerful technique for studying cell populations in live plants or animals, such as mice. Different types of cells (e.g. bone marrow stem cells, T-cells) can be engineered to express a luciferase allowing their non-invasive visualization inside a live animal using a sensitive charge-couple device camera (CCD camera).This technique has been used to follow tumorigenesis and response of tumors to treatment in animal models. However, environmental factors and therapeutic interferences may cause some discrepancies between tumor burden and bioluminescence intensity in relation to changes in proliferative activity. The intensity of the signal measured by in vivo imaging may depend on various factors, such as -luciferin absorption through the peritoneum, blood flow, cell membrane permeability, availability of co-factors, intracellular pH and transparency of overlying tissue, in addition to the amount of luciferase.
Luciferase is a heat-sensitive protein that is used in studies on protein denaturation, testing the protective capacities of heat shock proteins. The opportunities for using luciferase continue to expand. | 1 | Biochemistry |
Prelog attended elementary school in Sarajevo, but in 1915, as a child, Prelog moved to Zagreb (then part of the Austro-Hungary) with his parents. In Zagreb he graduated from elementary school. At first, he attended gymnasium in Zagreb, but soon afterwards, his father got a job in Osijek, so he continued his education there. He spent two years in Osijek gymnasium, where he became interested in chemistry under the influence of his professor Ivan Kuria.
In 1922, as a 16-year-old boy, his first scientific work was published in the German scientific journal Chemiker Zeitung. The article concerned an analytical instrument used in chemical labs. Prelog completed his high school education in Zagreb in 1924. Following his fathers wishes, he moved to Prague, where he received his diploma in chemical engineering from the Czech Technical University in 1928. He received his Sc.D in 1929. His teacher was Emil Votoček, while his assistant and mentor Rudolf Lukeš introduced him to the world of organic chemistry.
Upon leaving the Czech Technical University, Prelog worked in the plant laboratory of the private firm of G.J. Dríza in Prague; few academic positions were available due to the Great Depression. Prelog was in charge of the production of rare chemicals that were not commercially available at that time. He worked for Driza from 1929 until 1935. During the time, he got his first doctoral candidate, a company owner at Driza. He performed research in his spare time, investigating alkaloids in cacao bark. | 4 | Stereochemistry |
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