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Most common imides are prepared by heating dicarboxylic acids or their anhydrides and ammonia or primary amines. The result is a condensation reaction:
: (RCO)O + R′NH → (RCO)NR′ + HO
These reactions proceed via the intermediacy of amides. The intramolecular reaction of a carboxylic acid with an amide is far faster than the intermolecular reaction, which is rarely observed.
They may also be produced via the oxidation of amides, particularly when starting from lactams.
: R(CO)NHCHR + 2 [O] → R(CO)N(CO)R + HO
Certain imides can also be prepared in the isoimide-to-imide Mumm rearrangement. | 0 | Organic Chemistry |
Several international standards classify coals by their rank, where increasing rank corresponds to coal with a higher carbon content. The rank of coal is correlated with its geologic history, as described in Hilt's law.
In the ASTM system, any coal with more than 69% fixed carbon is classified by its content of carbon and volatiles. Coal with less than 69% fixed carbon is classified by its heating value. Volatiles and carbon are on a dry mineral free base; heating value is based on the moisture content as mined, but without any free water.
The ISO also has a coal ranking system, though its subdivisions do not align with the ASTM standard. | 3 | Analytical Chemistry |
IUPAC uses the prefix "isocyano" for the systematic nomenclature of isocyanides: isocyanomethane, isocyanoethane, isocyanopropane, etc.
The sometimes used old term "carbylamine" conflicts with systematic nomenclature. An amine always has three single bonds, whereas an isocyanide has only one single and one multiple bond.
The isocyanamide functional group consists of a amino group attached to an isocyano moiety.
for nomenclature as suffix of isonitrile or prefix of isocyano is used depending upon priority table. | 0 | Organic Chemistry |
The complex is a large integral membrane protein composed of several metal prosthetic sites and 14 protein subunits in mammals. In mammals, eleven subunits are nuclear in origin, and three are synthesized in the mitochondria. The complex contains two hemes, a cytochrome a and cytochrome a, and two copper centers, the Cu and Cu centers. In fact, the cytochrome a and Cu form a binuclear center that is the site of oxygen reduction. Cytochrome c, which is reduced by the preceding component of the respiratory chain (cytochrome bc1 complex, Complex III), docks near the Cu binuclear center and passes an electron to it, being oxidized back to cytochrome c containing Fe. The reduced Cu binuclear center now passes an electron on to cytochrome a, which in turn passes an electron on to the cytochrome a>-Cu binuclear center. The two metal ions in this binuclear center are 4.5 Å apart and coordinate a hydroxide ion in the fully oxidized state.
Crystallographic studies of cytochrome c oxidase show an unusual post-translational modification, linking C6 of Tyr(244) and the ε-N of His(240) (bovine enzyme numbering). It plays a vital role in enabling the cytochrome a- Cu binuclear center to accept four electrons in reducing molecular oxygen and four protons to water. The mechanism of reduction was formerly thought to involve a peroxide intermediate, which was believed to lead to superoxide production. However, the currently accepted mechanism involves a rapid four-electron reduction involving immediate oxygenoxygen bond cleavage, avoiding any intermediate likely to form superoxide. | 1 | Biochemistry |
The Gaia hypothesis posits that the Earth is a self-regulating complex system involving the biosphere, the atmosphere, the hydrospheres and the pedosphere, tightly coupled as an evolving system. The hypothesis contends that this system as a whole, called Gaia, seeks a physical and chemical environment optimal for contemporary life.
Gaia evolves through a cybernetic feedback system operated by the biota, leading to broad stabilization of the conditions of habitability in a full homeostasis. Many processes in the Earths surface, essential for the conditions of life, depend on the interaction of living forms, especially microorganisms, with inorganic elements. These processes establish a global control system that regulates Earths surface temperature, atmosphere composition and ocean salinity, powered by the global thermodynamic disequilibrium state of the Earth system.
The existence of a planetary homeostasis influenced by living forms had been observed previously in the field of biogeochemistry, and it is being investigated also in other fields like Earth system science. The originality of the Gaia hypothesis relies on the assessment that such homeostatic balance is actively pursued with the goal of keeping the optimal conditions for life, even when terrestrial or external events menace them. | 9 | Geochemistry |
The helicity of a particle is positive ("right-handed") if the direction of its spin is the same as the direction of its motion. It is negative ("left-handed") if the directions of spin and motion are opposite. So a standard clock, with its spin vector defined by the rotation of its hands, has left-handed helicity if tossed with its face directed forwards.
Mathematically, helicity is the sign of the projection of the spin vector onto the momentum vector: "left" is negative, "right" is positive.
The chirality of a particle is more abstract: It is determined by whether the particle transforms in a right- or left-handed representation of the Poincaré group.
For massless particles – photons, gluons, and (hypothetical) gravitons – chirality is the same as helicity; a given massless particle appears to spin in the same direction along its axis of motion regardless of point of view of the observer.
For massive particles – such as electrons, quarks, and neutrinos – chirality and helicity must be distinguished: In the case of these particles, it is possible for an observer to change to a reference frame moving faster than the spinning particle, in which case the particle will then appear to move backwards, and its helicity (which may be thought of as "apparent chirality") will be reversed. That is, helicity is a constant of motion, but it is not Lorentz invariant. Chirality is Lorentz invariant, but is not a constant of motion: a massive left-handed spinor, when propagating, will evolve into a right handed spinor over time, and vice versa.
A massless particle moves with the speed of light, so no real observer (who must always travel at less than the speed of light) can be in any reference frame where the particle appears to reverse its relative direction of spin, meaning that all real observers see the same helicity. Because of this, the direction of spin of massless particles is not affected by a change of inertial reference frame (a Lorentz boost) in the direction of motion of the particle, and the sign of the projection (helicity) is fixed for all reference frames: The helicity of massless particles is a relativistic invariant (a quantity whose value is the same in all inertial reference frames) which always matches the massless particle's chirality.
The discovery of neutrino oscillation implies that neutrinos have mass, so the photon is the only confirmed massless particle; gluons are expected to also be massless, although this has not been conclusively tested. Hence, these are the only two particles now known for which helicity could be identical to chirality, and only the photon has been confirmed by measurement. All other observed particles have mass and thus may have different helicities in different reference frames. | 4 | Stereochemistry |
Several applications have been developed that interrogate SNPs by hybridizing complementary DNA probes to the SNP site. The challenge of this approach is reducing cross-hybridization between the allele-specific probes. This challenge is generally overcome by manipulating the hybridization stringency conditions. | 1 | Biochemistry |
GPCRs include one or more receptors for the following ligands:
sensory signal mediators (e.g., light and olfactory stimulatory molecules);
adenosine, bombesin, bradykinin, endothelin, γ-aminobutyric acid (GABA), hepatocyte growth factor (HGF), melanocortins, neuropeptide Y, opioid peptides, opsins, somatostatin, GH, tachykinins, members of the vasoactive intestinal peptide family, and vasopressin;
biogenic amines (e.g., dopamine, epinephrine, norepinephrine, histamine, serotonin, and melatonin);
glutamate (metabotropic effect);
glucagon;
acetylcholine (muscarinic effect);
chemokines;
lipid mediators of inflammation (e.g., prostaglandins, prostanoids, platelet-activating factor, and leukotrienes);
peptide hormones (e.g., calcitonin, C5a anaphylatoxin, follicle-stimulating hormone [FSH], gonadotropin-releasing hormone [GnRH], neurokinin, thyrotropin-releasing hormone [TRH], and oxytocin);
and endocannabinoids.
GPCRs that act as receptors for stimuli that have not yet been identified are known as orphan receptors.
However, in contrast to other types of receptors that have been studied, wherein ligands bind externally to the membrane, the ligands of GPCRs typically bind within the transmembrane domain. However, protease-activated receptors are activated by cleavage of part of their extracellular domain. | 1 | Biochemistry |
A relatively new topography-related technique (first published in 1996) is the so-called reticulography. Based on white-beam topography, the new aspect consists in placing a fine-scaled metallic grid ("reticule") between sample and detector. The metallic grid lines are highly absorbing, producing dark lines in the recorded image. While for flat, homgeneous sample the image of the grid is rectilinear, just as the grid itself, strongly deformed grid images may occur in the case of tilted or strained sample. The deformation results from Bragg angle changes (and thus different directions of propagation of the diffracted beams) due to lattice parameter differences (or tilted crystallites) in the
sample. The grid serves to split the diffracted beam into an array of microbeams, and to backtrace the propagation of each individual microbeam onto the sample surface. By recording reticulographic images at several sample-to-detector distances, and appropriate data processing, local distributions of misorientation across the sample surface can be derived. | 3 | Analytical Chemistry |
Giovanni Aldini, Galvanis nephew, continued his uncles work after Luigi Galvani died in 1798. In 1803, Aldini performed a famous public demonstration of the electro-stimulation technique of deceased limbs on the corpse of an executed criminal George Foster at Newgate in London. The Newgate Calendar describes what happened when the galvanic process was used on the body:
Galvani has been called the father of electrophysiology. The debate between Galvani and Volta "would result in the creation of electrophysiology, electromagnetism, electrochemistry and the electric battery." | 7 | Physical Chemistry |
The protein-rich, alkaline, aqueous fluid within the inner chloroplast membrane and outside of the thylakoid space is called the stroma, which corresponds to the cytosol of the original cyanobacterium. Nucleoids of chloroplast DNA, chloroplast ribosomes, the thylakoid system with plastoglobuli, starch granules, and many proteins can be found floating around in it. The Calvin cycle, which fixes CO into G3P takes place in the stroma. | 5 | Photochemistry |
Oxygen evolution is the process of generating molecular oxygen (O) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distilling liquefied air. | 5 | Photochemistry |
The Moon stands out as being very depleted in volatiles.
The Moon not only lacks water and atmospheric gases, but also lacks moderately volatile elements such as K, Na, and Cl. The Earth's K/U ratio is 12,000, while the Moon has a K/U ratio of only 2,000. This difference suggests that the material that formed the Moon was subjected to temperatures considerably higher than the Earth.
The prevailing theory is that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, about 20 to 100 million years after the Solar System coalesced. This is called the Giant-impact hypothesis.
It is hypothesized that most of the outer silicates of the colliding body would be vaporized, whereas a metallic core would not. Hence, most of the collisional material sent into orbit would consist of silicates, leaving the coalescing Moon deficient in iron. The more volatile materials that were emitted during the collision probably would escape the Solar System, whereas silicates would tend to coalesce.
The ratios of the Moon's volatile elements are not explained by the giant-impact hypothesis. If the giant-impact hypothesis is correct, they must be due to some other cause. | 9 | Geochemistry |
E. coli cell lysate containing the cellular components required for transcription and translation are used in this in vitro method of protein production. The advantage of such system is that protein may be produced much faster than those produced in vivo since it does not require time to culture the cells, but it is also more expensive. Vectors used for E. coli expression can be used in this system although specifically designed vectors for this system are also available. Eukaryotic cell extracts may also be used in other cell-free systems, for example, the wheat germ cell-free expression systems. Mammalian cell-free systems have also been produced. | 1 | Biochemistry |
In 2022, Vietnam was the second-largest PV module producer, only behind China, with its production capacity rising to 24.1 GW, marking a significant 47% increase from the 16.4 GW produced in 2021. Vietnam accounts for 6.4% of the world's photovoltaic production. | 7 | Physical Chemistry |
If the model is not acceptable, a variety of other models should be examined to find one that best fits the experimental data, within experimental error. The main difficulty is with the so-called minor species. These are species whose concentration is so low that the effect on the measured quantity is at or below the level of error in the experimental measurement. The constant for a minor species may prove impossible to determine if there is no means to increase the concentration of the species. | 7 | Physical Chemistry |
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as "the single most important operation used for the recovery and upgrading of sulfide ores". The development of froth flotation has improved the recovery of valuable minerals, such as copper- and lead-bearing minerals. Along with mechanized mining, it has allowed the economic recovery of valuable metals from much lower-grade ore than previously. | 8 | Metallurgy |
Buccianti is the co-author, with Fabio Rosso, Fabio Vlacci, of the three-volume Italian book Metodi matematici e statistici nelle scienze della terra (2000). She is co-editor of Compositional Data Analysis in the Geosciences: From Theory to Practice (Geological Society, 2006) and Compositional Data Analysis: Theory and Applications (Wiley, 2011). | 9 | Geochemistry |
Rewriting the above result for the pressure as , we may combine it with the ideal gas law
where is the Boltzmann constant and the absolute temperature defined by the ideal gas law, to obtain
which leads to a simplified expression of the average translational kinetic energy per molecule,
The translational kinetic energy of the system is times that of a molecule, namely . The temperature, is related to the translational kinetic energy by the description above, resulting in
which becomes
Equation () is one important result of the kinetic theory:
The average molecular kinetic energy is proportional to the ideal gas laws absolute temperature'.
From equations () and (), we have
Thus, the product of pressure and volume per mole is proportional to the average
translational molecular kinetic energy.
Equations () and () are called the "classical results", which could also be derived from statistical mechanics;
for more details, see:
The equipartition theorem requires that kinetic energy is partitioned equally between all kinetic degrees of freedom, D. A monotatomic gas is axially symmetric about each spatial axis, so that D = 3 comprising translational motion along each axis. A diatomic gas is axially symmetric about only one axis, so that D = 5, comprising translational motion along three axes and rotational motion along two axes. A polyatomic gas, like water, is not radially symmetric about any axis, resulting in D = 6, comprising 3 translational and 3 rotational degrees of freedom.
Because the equipartition theorem requires that kinetic energy is partitioned equally, the total kinetic energy is
Thus, the energy added to the system per gas particle kinetic degree of freedom is
Therefore, the kinetic energy per kelvin of one mole of monatomic ideal gas (D = 3) is
where is the Avogadro constant, and R is the ideal gas constant.
Thus, the kinetic energy per unit kelvin of an ideal monoatomic gas can be calculated easily:
* per mole: 12.47 J / K
* per molecule: 20.7 yJ / K = 129 μeV / K
At standard temperature (273.15 K), the kinetic energy can also be obtained:
* per mole: 3406 J
* per molecule: 5.65 zJ = 35.2 meV.
At higher temperatures (typically thousands of kelvins), vibrational modes become active to provide additional degrees of freedom, creating a temperature-dependence on D and the total molecular energy. Quantum statistical mechanics is needed to accurately compute these contributions. | 7 | Physical Chemistry |
The macroscopic theory of van der Waals theory has many experimental validations. Among which, some of the most notable ones are Derjaguin (1960); Derjaguin, Abrikosova and Lifshitz (1956) and Israelachvili and Tabor (1973), who measured the balance of forces between macroscopic bodies of glass, or glass and mica; Haydon and Taylor (1968), who measured the forces across bilayers by measuring their contact angle; and lastly Shih and Parsegian (1975), who investigated Van der Waals potentials between heavy alkali-metal atoms and gold surfaces using atomic-beam-deflection. | 7 | Physical Chemistry |
The pK of [HDABCO] (the protonated derivative) is 8.8, which is almost the same as ordinary alkylamines. The nucleophilicity of the amine is high because the amine centers are unhindered. It is sufficiently basic to promote a variety of coupling reactions. | 0 | Organic Chemistry |
Aside from the academic world, during all these years, George Hammond, "made many public speeches on controversial themes, both political (e.g., the invasion of Cambodia, delivered in 1971 at a public rally on Caltechs Olive Walk) and scientific (e.g., the future of chemistry)" Many of these controversial speeches affected his career negatively. For example, after his speech at Olive Walk, president Richard Nixons administration removed his name from nomination for a major NSF post. Nevertheless, he did not back down and continued to criticize the government, and not limiting to delivering speeches, he wrote a letter to the editor of a newspaper saying: “A June 30 front-page article describes the potential bonanza in arms sales to new members as the North Atlantic Treaty Organization expands. I was favorably inclined toward expansion because of my naive assumption that bringing most of the nations of Europe and North America together as a cooperating group would decrease the likelihood of war. I cannot believe this will be the case if a prerequisite for entry is that countries buy new armaments from present members. At whom will the guns be aimed? Russia? Then we will probably re-create the cold war." The way this excerpt was written says many things about George Hammond, starting with his passionate character. Hammond fought for everything he believed in. He cared about his nation and he was also a little reckless about the consequences he could suffer for defying the government. Also, in the excerpt, a sarcastic side of Hammond can be perceived, a man of strong character with the ability to recognize when he is wrong. | 7 | Physical Chemistry |
Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic variables of the body or system, such as volume or pressure. | 7 | Physical Chemistry |
There are three major techniques for the site-specific mapping of pseudouridine in RNA, called Pseudo-seq, Ψ-seq and PSI-seq. All these methods are based on the unique reaction between pseudouridine and N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate (CMCT). The RNA to be analyzed is fragmented and incubated with CMCT. Even if CMCT can form covalent bonds with U, G and Ψ residues, only Ψ-CMC is resistant to alkaline hydrolysis (U-CMC and G-CMC get hydrolyzed). Next, reverse transcription is done to obtain a cDNA library, with the cDNAs terminating one nucleotide downstream the pseudouridine residue. Next generation sequencing of the cDNA library will indicate where the modified pseudouridine residue is located in the RNA. In order to do this, two cDNA libraries are prepared, one in which the RNA has undergone CMC treatment and the other one without CMC treatment. Differences in the length of the reads between the two libraries will indicate where the Ψ residues are. Another method is called CeU-Seq, which uses a biotinylated derivative of CMCT. This enables the purification and enrichment of biotinylated transcripts (transcripts modified with pseudouridine) with streptavidin columns, therefore reducing the library size and increasing sensitivity.
Other pseudouridine detection methods include site-specific cleavage and radioactive-labeling followed by ligation-assisted extraction and thin-layer chromatography (SCARLET) and mass spectrometry. | 1 | Biochemistry |
Endogenous retroviruses are not formally included in this classification system, and are broadly classified into three classes, on the basis of relatedness to exogenous genera:
* Class I are most similar to the gammaretroviruses
* Class II are most similar to the betaretroviruses and alpharetroviruses
* Class III are most similar to the spumaviruses. | 1 | Biochemistry |
Sunset yellow FCF is known as FD&C yellow No. 6 in the US and is approved for use in coloring food, drugs, and cosmetics with an acceptable daily intake of 3.75 mg/kg. | 3 | Analytical Chemistry |
An insertion reaction is a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity e.g.:
The term only refers to the result of the reaction and does not suggest a mechanism. Insertion reactions are observed in organic, inorganic, and organometallic chemistry. In cases where a metal-ligand bond in a coordination complex is involved, these reactions are typically organometallic in nature and involve a bond between a transition metal and a carbon or hydrogen. It is usually reserved for the case where the coordination number and oxidation state of the metal remain unchanged. When these reactions are reversible, the removal of the small molecule from the metal-ligand bond is called extrusion or elimination.
There are two common insertion geometries— 1,1 and 1,2 (pictured above). Additionally, the inserting molecule can act either as a nucleophile or as an electrophile to the metal complex. These behaviors will be discussed in more detail for CO, nucleophilic behavior, and SO, electrophilic behavior. | 0 | Organic Chemistry |
Both the lower pH and higher aluminium concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pH lower than 5 most fish eggs will not hatch and lower pH can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.
However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75% of the acidic lakes and about 50% of the acidic streams". Lakes hosted by silicate basement rocks are more acidic than lakes within limestone or other basement rocks with a carbonate composition (i.e. marble) due to buffering effects by carbonate minerals, even with the same amount of acid rain.
Sulfur dioxide and nitrous oxide concentration has many implication on aquatic ecosystems, including acidity change, increased nitrogen and aluminum content, and altering biogeochemical processes. Typically, sulfur dioxide and nitrous oxide do not have direct physiological effects upon exposure; most effects are developed by accumulation and prolonged exposure of these gases in the environment, modifying soil and water chemistry. | 2 | Environmental Chemistry |
The presence of color in water does not necessarily indicate that the water is not drinkable. Water with high water clarity is generally more cyan in color due to low concentrations of particles and/or dissolved substances. Color-causing particulate substances can be easily removed by filtration. Color-causing dissolved substances such as tannins are only toxic to animals in large concentration.
Color from dissolved substances is not removed by typical water filters; however the use of coagulants may succeed in trapping the color-causing compounds within the resulting precipitate.
Other factors can affect the color seen:
*Particles and solutes can absorb light, as in tea or coffee. Green algae in rivers and streams often lend a blue-green color. The Red Sea has occasional blooms of red Trichodesmium erythraeum algae.
*Particles in water can scatter light. The Colorado River is often muddy red because of suspended reddish silt in the water—this gives the river its name, from Spanish , . Some mountain lakes and streams with finely ground rock, such as glacial flour, are turquoise. Light scattering by suspended matter is required in order that the blue light produced by water's absorption can return to the surface and be observed. Such scattering can also shift the spectrum of the emerging photons toward the green, a color often seen when water laden with suspended particles is observed. | 3 | Analytical Chemistry |
Many biochemists predicted when examining K. C. Nicolaou's biomimetic synthesis of the endiandric acid cascade that enzymes aided this reaction in the biosynthesis. The biomimetic series determined that this process took place synthetically through a series of Diels-Alder cyclization reactions and therefore led researches to believe that Diels-Alderase assisted the formation of endiandric acid C.
Although it has been discovered since then that many famous cyclization reactions like that of lovastatin do result from the Diels-Alderase they have determine that the endiandric acid cascade does not involve enzymes but rather spontaneously undergoes ring formation from a derivative of bisnoryangonin 5, which results from both the shikimate and acetic pathways. The 4-hydroxycinnamoyl-CoA, compound 2, is the precursor that comes from the shikimate pathway. Two units of malonyl CoA are then added to through the acetate pathway 3. Compound 3 is then reduced to the di-enol form that tautomerizes to give the bisnoryangonin 5. A small amount of compound 5 can be isolated, however S-adenosyl methionine methylates most of it and gives yangonin 6. It has been proposed that a bisnoryangonin derivative 7, is then reduced by dehydrogenase to give the polyene precursor 8, that goes through spontaneous 8π conrotatory, 6π disrotatory, and [4+2] cyclization reactions to form endiandric acid C. This proposal is supported by the fact that endiandric acids naturally occur as racemic mixtures and not in an enantiomerically pure form, which should happen if enzymes mediate this process. The Diels-Alder reaction itself is a powerful reaction that can give cyclic compounds with many stereogenic centers. | 0 | Organic Chemistry |
The Tebbe reagent is used in organic synthesis for carbonyl methylidenation.
This conversion can also be effected using the Wittig reaction, although the Tebbe reagent is more efficient especially for sterically encumbered carbonyls. Furthermore, the Tebbe reagent is less basic than the Wittig reagent and does not give the β-elimination products.
Methylidenation reactions also occur for aldehydes as well as esters, lactones and amides. The Tebbe reagent converts esters and lactones to enol ethers and amides to enamines. In compounds containing both ketone and ester groups, the ketone selectively reacts in the presence of one equivalent of the Tebbe reagent.
The Tebbe reagent methylidenates carbonyls without racemizing a chiral α carbon. For this reason, the Tebbe reagent has found applications in reactions of sugars where maintenance of stereochemistry can be critical.
The Tebbe reagent reacts with acid chlorides to form titanium enolates by replacing Cl. | 0 | Organic Chemistry |
When a neurotransmitter is released at a synapse, it reaches its highest concentration inside the narrow space of the synaptic cleft, but some of it is certain to diffuse away before being reabsorbed or broken down. If it diffuses away, it has the potential to activate receptors that are located either at other synapses or on the membrane away from any synapse. The extrasynaptic activity of a neurotransmitter is known as volume transmission. It is well established that such effects occur to some degree, but their functional importance has long been a matter of controversy.
Recent work indicates that volume transmission may be the predominant mode of interaction for some special types of neurons. In the mammalian cerebral cortex, a class of neurons called neurogliaform cells can inhibit other nearby cortical neurons by releasing the neurotransmitter GABA into the extracellular space. Along the same vein, GABA released from neurogliaform cells into the extracellular space also acts on surrounding astrocytes, assigning a role for volume transmission in the control of ionic and neurotransmitter homeostasis. Approximately 78% of neurogliaform cell boutons do not form classical synapses. This may be the first definitive example of neurons communicating chemically where classical synapses are not present. | 1 | Biochemistry |
The theory presents simple mechanistic rules that describe the uptake and allocation of energy (and nutrients) and the consequences for physiological organization throughout an organism's life cycle, including the relationships of energetics with aging and effects of toxicants. Assumptions of the DEB theory are delineated in an explicit way, the approach clearly distinguishes mechanisms associated with intra‐ and interspecific variation in metabolic rates, and equations for energy flows are mathematically derived following the principles of physics and simplicity.
Cornerstones of the theory are:
* conservation of mass, energy and time,
* relationships between surface area and volume
* stoichiometric constraints on production
* organizational uncoupling of metabolic modules (assimilation, dissipation, growth)
* strong and weak homeostasis (composition of compartments is constant; composition of the organism is constant when the food is constant)
* substrate(s) from the environment is/are first converted to reserve(s) before being used for further metabolism
The theory specifies that an organism is made up two main compartments: (energy) reserve and structure. Assimilation of energy is proportional to surface area of the structure, and maintenance is proportional to its volume. Reserve does not require maintenance. Energy mobilization will depend on the relative amount of the energy reserve, and on the interface between reserve and structure. Once mobilized, the energy is split into two branches:
* a fixed proportion (termed kappa, κ) is allocated to growth (increase of structural mass) and maintenance of structure, while
* the remaining proportion (1- κ) is allocated to processes of maturation (increase in complexity, installation of regulation systems, preparation for reproduction) and maintaining the level of attained maturity (including, e.g., maintenance of defense systems).
The κ-rule therefore states that the processes of growth and maturation do not directly compete. Maintenance needs to be paid before allocating energy to other processes.
In the context of energy acquisition and allocation, the theory recognizes three main developmental stages: embryo, which does not feed or reproduce, juvenile, which feeds but does not reproduce, and adult, which both feeds and is allocating energy to reproduction. Transitions between these life stages occur at events specified as birth and puberty, which are reached when energy invested into maturation (tracked as level of maturity<nowiki/>) reaches a certain threshold. Maturity does not increase in the adult stage, and maturity maintenance is proportional to maturity.
Biochemical composition of reserve and structure is considered to be that of generalised compounds, and is constant (the assumption of strong homeostasis) but not necessarily identical. Biochemical transformation from food to reserve (assimilation), and from reserve to structure (growth) include overhead costs. These overheads, together with processes of somatic and maturity maintenance and reproduction overheads (inefficiencies in transformation from reserve to reproductive material), all contribute to the consumption of oxygen and production of carbon dioxide, i.e. metabolism. | 1 | Biochemistry |
Wu Yangjie (; born 1 January 1928) is a Chinese organic chemist and a professor at Zhengzhou University. He is an academician of the Chinese Academy of Sciences. | 0 | Organic Chemistry |
Small RNA sequencing (Small RNA-Seq) is a type of RNA sequencing based on the use of NGS technologies that allows to isolate and get information about noncoding RNA molecules in order to evaluate and discover new forms of small RNA and to predict their possible functions. By using this technique, it is possible to discriminate small RNAs from the larger RNA family to better understand their functions in the cell and in gene expression. Small RNA-Seq can analyze thousands of small RNA molecules with a high throughput and specificity. The greatest advantage of using RNA-seq is represented by the possibility of generating libraries of RNA fragments starting from the whole RNA content of a cell. | 1 | Biochemistry |
Before monosaccharide units are incorporated into glycoproteins, polysaccharides, or lipids in living organisms, they are typically first "activated" by being joined via a glycosidic bond to the phosphate group of a nucleotide such as uridine diphosphate (UDP), guanosine diphosphate (GDP), thymidine diphosphate (TDP), or cytidine monophosphate (CMP). These activated biochemical intermediates are known as sugar nucleotides or sugar donors. Many biosynthetic pathways use mono- or oligosaccharides activated by a diphosphate linkage to lipids, such as dolichol. These activated donors are then substrates for enzymes known as glycosyltransferases, which transfer the sugar unit from the activated donor to an accepting nucleophile (the acceptor substrate). | 0 | Organic Chemistry |
Chlorarachniophytes are a rare group of organisms that also contain chloroplasts derived from green algae, though their story is more complicated than that of the euglenophytes. The ancestor of chlorarachniophytes is thought to have been a eukaryote with a red algal derived chloroplast. It is then thought to have lost its first red algal chloroplast, and later engulfed a green alga, giving it its second, green algal derived chloroplast.
Chlorarachniophyte chloroplasts are bounded by four membranes, except near the cell membrane, where the chloroplast membranes fuse into a double membrane. Their thylakoids are arranged in loose stacks of three. Chlorarachniophytes have a form of polysaccharide called chrysolaminarin, which they store in the cytoplasm, often collected around the chloroplast pyrenoid, which bulges into the cytoplasm.
Chlorarachniophyte chloroplasts are notable because the green alga they are derived from has not been completely broken down—its nucleus still persists as a nucleomorph found between the second and third chloroplast membranes—the periplastid space, which corresponds to the green alga's cytoplasm. | 5 | Photochemistry |
* The bicinchoninic acid assay tests for proteins
* The Biuret test tests for proteins and polypeptides
* Bradford protein assay measures protein quantitatively
* The Phadebas amylase test determines alpha-amylase activity | 3 | Analytical Chemistry |
The PACMAD clade (previously PACCMAD, PACCAD, or PACC) is one of two major lineages (or clades) of the true grasses (Poaceae), regrouping six subfamilies and about 5700 species, more than half of all true grasses. Its sister group is the BOP clade. The PACMAD lineage is the only group within the grasses in which the C photosynthesis pathway has evolved; studies have shown that this happened independently multiple times.
The name of the clade comes from the first initials of the included subfamilies Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, and Danthonioideae. It has no defined taxonomic rank but is used frequently because it refers to a well-defined monophyletic group with a distinct ecology.
Phylogeny of the PACMAD clade, with photosynthetic pathways for each subfamily: | 5 | Photochemistry |
Because the fluorescent secondary molecule is applied after capture of the free receptor from solution (Figure 2) the binding constants measured using a kinetic exclusion assay are for unmodified molecules in solution and thus more accurately reflects endogenous binding interactions than methods requiring modification (typically labeling or immobilization) before measurement. Kinetic exclusion assays have been performed using unpurified molecules, in serum, and have measured binding to cell membrane proteins on intact whole cell which brings the measured binding interactions closer to their endogenous state.
Molecules suited for measurement by KinExA are antibodies, recombinant proteins, small molecules, aptamers, lipids, nanobodies, and toxins.
Kinetic exclusion assay have also been applied for concentration immunoassay, where it has proven capable of providing the maximum theoretical, K limited, sensitivity. An example of this technique has been employed for sensitive detection of environmental contaminants i<nowiki/>n near real-time. | 1 | Biochemistry |
In single-phase heat transfer, convection is often the dominant mechanism of heat transfer. For adiabatic flow where the flow receives heat, the temperature of the coolant changes as it flows. An example of single-phase heat transfer is a gas-cooled reactor and molten-salt reactor.
The most convenient way for characterizing the single-phase heat transfer is based on an empirical approach, where the temperature difference between the wall and bulk flow can be obtained from the heat transfer coefficient. The heat transfer coefficient depends on several factors: mode of heat transfer (e.g., internal or external flow), type of fluid, geometry of the system, flow regime (e.g., laminar or turbulent flow), boundary condition, etc.
Examples of heat transfer correlations are Dittus-Boelter correlation (turbulent forced convection), Churchill & Chu (natural convection). | 7 | Physical Chemistry |
Nitrogen-vacancy centers are typically produced from single substitutional nitrogen centers (called C or P1 centers in diamond literature) by irradiation followed by annealing at temperatures above 700 °C. A wide range of high-energy particles is suitable for such irradiation, including electrons, protons, neutrons, ions, and gamma photons. Irradiation produces lattice vacancies, which are a part of NV centers. Those vacancies are immobile at room temperature, and annealing is required to move them. Single substitutional nitrogen produces strain in the diamond lattice; it therefore efficiently captures moving vacancies, producing the NV centers.
During chemical vapor deposition of diamond, a small fraction of single substitutional nitrogen impurity (typically <0.5%) traps vacancies generated as a result of the plasma synthesis. Such nitrogen-vacancy centers are preferentially aligned to the growth direction. Delta doping of nitrogen during CVD growth can be used to create two-dimensional ensembles of NV centers near the diamond surface for enhanced sensing or simulation.
Diamond is notorious for having a relatively large lattice strain. Strain splits and shifts optical transitions from individual centers resulting in broad lines in the ensembles of centers. Special care is taken to produce extremely sharp NV lines (line width ~10 MHz) required for most experiments: high-quality, pure natural or better synthetic diamonds (type IIa) are selected. Many of them already have sufficient concentrations of grown-in NV centers and are suitable for applications. If not, they are irradiated by high-energy particles and annealed. Selection of a certain irradiation dose allows tuning the concentration of produced NV centers such that individual NV centers are separated by micrometre-large distances. Then, individual NV centers can be studied with standard optical microscopes or, better, near-field scanning optical microscopes having sub-micrometre resolution. | 7 | Physical Chemistry |
The areas are saturated with unexploded shells (including many gas shells), grenades, and rusting ammunition. Soils were heavily polluted by lead, mercury, chlorine, arsenic, various dangerous gases, acids, and human and animal remains. The area was also littered with ammunition depots and chemical plants. The land of the Western Front is covered in old trenches and shell holes.
Each year, numerous unexploded shells are recovered from former WWI battlefields in what is known as the iron harvest. According to the Sécurité Civile, the French agency in charge of the land management of Zone Rouge, 300 to 700 more years at this current rate will be needed to clean the area completely. Some experiments conducted in 2005–06 discovered up to 300 shells per hectare (120 per acre) in the top of soil in the worst areas.
Areas where 99% of all plants still die remain off limits (for example, two small pieces of land close to Ypres and the Woëvre), as arsenic constitutes up to 175,907 mg (175.9 g) per kilogramme of soil samples because arsenical shells were destroyed in the 1920s. | 2 | Environmental Chemistry |
MALDI techniques typically employ the use of UV lasers such as nitrogen lasers (337 nm) and frequency-tripled and quadrupled Nd:YAG lasers (355 nm and 266 nm respectively).
Infrared laser wavelengths used for infrared MALDI include the 2.94 μm Er:YAG laser, mid-IR optical parametric oscillator, and 10.6 μm carbon dioxide laser. Although not as common, infrared lasers are used due to their softer mode of ionization. IR-MALDI also has the advantage of greater material removal (useful for biological samples), less low-mass interference, and compatibility with other matrix-free laser desorption mass spectrometry methods. | 1 | Biochemistry |
Two oligonucleotides are used for this step (Figure 1: Adapter oligos). One of the oligonucleotides contains a 12-nucleotide single-stranded random tag sequence followed by a fixed 5' nucleotide sequence (black sequence in Figure 1). In this step, oligonucleotides are annealed in a complementary region by incubation at the required temporal condition. | 1 | Biochemistry |
Aside from ethylene oxide, most epoxides are generated by treating alkenes with peroxide-containing reagents, which donate a single oxygen atom. Safety considerations weigh on these reactions because organic peroxides are prone to spontaneous decomposition or even combustion.
Metal complexes are useful catalysts for epoxidations involving hydrogen peroxide and alkyl hydroperoxides. Peroxycarboxylic acids, which are more electrophilic, convert alkenes to epoxides without the intervention of metal catalysts. In specialized applications, other peroxide-containing reagents are employed, such as dimethyldioxirane. Depending on the mechanism of the reaction and the geometry of the alkene starting material, cis and/or trans epoxide diastereomers may be formed. In addition, if there are other stereocenters present in the starting material, they can influence the stereochemistry of the epoxidation. Metal-catalyzed epoxidations were first explored using tert-butyl hydroperoxide (TBHP). Association of TBHP with the metal (M) generates the active metal peroxy complex containing the MOOR group, which then transfers an O center to the alkene.
Organic peroxides are used for the production of propylene oxide from propylene. Catalysts are required as well. Both t-butyl hydroperoxide and ethylbenzene hydroperoxide can be used as oxygen sources. | 0 | Organic Chemistry |
Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrins. Bilin (also called bilichrome) was named as a bile pigment of mammals, but can also be found in lower vertebrates, invertebrates, as well as red algae, green plants and cyanobacteria. Bilins can range in color from red, orange, yellow or brown to blue or green.
In chemical terms, bilins are linear arrangements of four pyrrole rings (tetrapyrroles). In human metabolism, bilirubin is a breakdown product of heme. A modified bilane is an intermediate in the biosynthesis and uroporphyrinogen III from porphobilinogen.
Examples of bilins are found in animals (cardinal examples are bilirubin and biliverdin), and phycocyanobilin, the chromophore of the photosynthetic pigment phycocyanin, in algae and plants. In plants, bilins also serve as the photopigments of the photoreceptor protein phytochrome. An example of an invertebrate bilin is micromatabilin, which is responsible for the green color of the Green Huntsman Spider, Micrommata virescens. | 1 | Biochemistry |
Select filter cloth based on the type filter aid used (refer Filter aid selection), adjust the advancing knife to optimize the knife advance rate per drum revolution. (Detail explained in Advance blade section) | 3 | Analytical Chemistry |
Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.
Hyperpolarization is often caused by efflux of K (a cation) through K channels, or influx of Cl (an anion) through Cl channels. On the other hand, influx of cations, e.g. Na through Na channels or Ca through Ca channels, inhibits hyperpolarization. If a cell has Na or Ca currents at rest, then inhibition of those currents will also result in a hyperpolarization. This voltage-gated ion channel response is how the hyperpolarization state is achieved. In neurons, the cell enters a state of hyperpolarization immediately following the generation of an action potential. While hyperpolarized, the neuron is in a refractory period that lasts roughly 2 milliseconds, during which the neuron is unable to generate subsequent action potentials. Sodium-potassium ATPases redistribute K and Na ions until the membrane potential is back to its resting potential of around –70 millivolts, at which point the neuron is once again ready to transmit another action potential. | 7 | Physical Chemistry |
A microwave spectrometer can be most simply constructed using a source of microwave radiation, an absorption cell into which sample gas can be introduced and a detector such as a superheterodyne receiver. A spectrum can be obtained by sweeping the frequency of the source while detecting the intensity of transmitted radiation. A simple section of waveguide can serve as an absorption cell. An important variation of the technique in which an alternating current is applied across electrodes within the absorption cell results in a modulation of the frequencies of rotational transitions. This is referred to as Stark modulation and allows the use of phase-sensitive detection methods offering improved sensitivity. Absorption spectroscopy allows the study of samples that are thermodynamically stable at room temperature. The first study of the microwave spectrum of a molecule () was performed by Cleeton & Williams in 1934. Subsequent experiments exploited powerful sources of microwaves such as the klystron, many of which were developed for radar during the Second World War. The number of experiments in microwave spectroscopy surged immediately after the war. By 1948, Walter Gordy was able to prepare a review of the results contained in approximately 100 research papers. Commercial versions of microwave absorption spectrometer were developed by Hewlett-Packard in the 1970s and were once widely used for fundamental research. Most research laboratories now exploit either Balle-Flygare or chirped-pulse Fourier transform microwave (FTMW) spectrometers. | 7 | Physical Chemistry |
The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label GFP traditionally refers to the protein first isolated from the jellyfish Aequorea victoria and is sometimes called avGFP. However, GFPs have been found in other organisms including corals, sea anemones, zoanithids, copepods and lancelets.
The GFP from A. victoria has a major excitation peak at a wavelength of 395 nm and a minor one at 475 nm. Its emission peak is at 509 nm, which is in the lower green portion of the visible spectrum. The fluorescence quantum yield (QY) of GFP is 0.79. The GFP from the sea pansy (Renilla reniformis) has a single major excitation peak at 498 nm. GFP makes for an excellent tool in many forms of biology due to its ability to form an internal chromophore without requiring any accessory cofactors, gene products, or enzymes / substrates other than molecular oxygen.
In cell and molecular biology, the GFP gene is frequently used as a reporter of expression. It has been used in modified forms to make biosensors, and many animals have been created that express GFP, which demonstrates a proof of concept that a gene can be expressed throughout a given organism, in selected organs, or in cells of interest. GFP can be introduced into animals or other species through transgenic techniques, and maintained in their genome and that of their offspring. To date, GFP has been expressed in many species, including bacteria, yeasts, fungi, fish and mammals, including in human cells. Scientists Roger Y. Tsien, Osamu Shimomura, and Martin Chalfie were awarded the 2008 Nobel Prize in Chemistry on 10 October 2008 for their discovery and development of the green fluorescent protein.
Most commercially available genes for GFP and similar fluorescent proteins are around 730 base-pairs long. The natural protein has 238 amino acids. Its molecular mass is 27 kD. Therefore, fusing the GFP gene to the gene of a protein of interest can significantly increase the proteins size and molecular mass, and can impair the proteins natural function or change its location or trajectory of transport within the cell. | 1 | Biochemistry |
An array of technical manuals, maps, databases, and other forms of guidance for identifying, sampling, and/or managing acid sulfate soils have been published by Federal and State/Territory governments over the years. National Acid sulfate soils guidance: a synthesis provides a summary of available guidance. It is recommended that those not familiar with available guidance first consult this document. An overview is also available on the Commonwealth Water Quality Australia website. Key, publicly available resources are described below. | 9 | Geochemistry |
The most common source of new genes in eukaryotic lineages is gene duplication, which creates copy number variation of an existing gene in the genome. The resulting genes (paralogs) may then diverge in sequence and in function. Sets of genes formed in this way compose a gene family. Gene duplications and losses within a family are common and represent a major source of evolutionary biodiversity. Sometimes, gene duplication may result in a nonfunctional copy of a gene, or a functional copy may be subject to mutations that result in loss of function; such nonfunctional genes are called pseudogenes.
"Orphan" genes, whose sequence shows no similarity to existing genes, are less common than gene duplicates. The human genome contains an estimate 18 to 60 genes with no identifiable homologs outside humans. Orphan genes arise primarily from either de novo emergence from previously non-coding sequence, or gene duplication followed by such rapid sequence change that the original relationship becomes undetectable. De novo genes are typically shorter and simpler in structure than most eukaryotic genes, with few if any introns. Over long evolutionary time periods, de novo gene birth may be responsible for a significant fraction of taxonomically restricted gene families.
Horizontal gene transfer refers to the transfer of genetic material through a mechanism other than reproduction. This mechanism is a common source of new genes in prokaryotes, sometimes thought to contribute more to genetic variation than gene duplication. It is a common means of spreading antibiotic resistance, virulence, and adaptive metabolic functions. Although horizontal gene transfer is rare in eukaryotes, likely examples have been identified of protist and alga genomes containing genes of bacterial origin. | 1 | Biochemistry |
A third, non-fusion protein may be co-expressed with two fusion proteins. Depending on the investigation, the third protein may modify one of the fusion proteins or mediate or interfere with their interaction.
Co-expression of the third protein may be necessary for modification or activation of one or both of the fusion proteins. For example, S. cerevisiae possesses no endogenous tyrosine kinase. If an investigation involves a protein that requires tyrosine phosphorylation, the kinase must be supplied in the form of a tyrosine kinase gene.
The non-fusion protein may mediate the interaction by binding both fusion proteins simultaneously, as in the case of ligand-dependent receptor dimerization.
For a protein with an interacting partner, its functional homology to other proteins may be assessed by supplying the third protein in non-fusion form, which then may or may not compete with the fusion-protein for its binding partner. Binding between the third protein and the other fusion protein will interrupt the formation of the reporter expression activation complex and thus reduce reporter expression, leading to the distinguishing change in phenotype. | 1 | Biochemistry |
The IIR publishes two professional Directories: a [https://iifiir.org/en/directory/laboratories Laboratory Directory], which lists more than 300 laboratories in 55 countries; an [https://iifiir.org/en/directory/experts Expertise Directory], which lists over 300 international experts in the refrigeration sector. | 7 | Physical Chemistry |
Adenoviruses are viruses that carry their genetic material in the form of double-stranded DNA. They cause respiratory, intestinal, and eye infections in humans (especially the common cold). When these viruses infect a host cell, they introduce their DNA molecule into the host. The genetic material of the adenoviruses is not incorporated (transient) into the host cell's genetic material. The DNA molecule is left free in the nucleus of the host cell, and the instructions in this extra DNA molecule are transcribed just like any other gene. The only difference is that these extra genes are not replicated when the cell is about to undergo cell division so the descendants of that cell will not have the extra gene.
As a result, treatment with the adenovirus will require re-administration in a growing cell population although the absence of integration into the host cell's genome should prevent the type of cancer seen in the SCID trials. This vector system has been promoted for treating cancer and indeed the first gene therapy product to be licensed to treat cancer, Gendicine, is an adenovirus. Gendicine, an adenoviral p53-based gene therapy was approved by the Chinese food and drug regulators in 2003 for treatment of head and neck cancer. Advexin, a similar gene therapy approach from Introgen, was turned down by the US Food and Drug Administration (FDA) in 2008.
Concerns about the safety of adenovirus vectors were raised after the 1999 death of Jesse Gelsinger while participating in a gene therapy trial. Since then, work using adenovirus vectors has focused on genetically limited versions of the virus. | 1 | Biochemistry |
In aqueous solution, oxyanions with high charge can undergo condensation reactions, such as in the formation of the dichromate ion, :
The driving force for this reaction is the reduction of electrical charge density on the anion and the elimination of the hydronium () ion. The amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction. It is an example of an acid–base reaction with the monomeric oxyanion acting as a base and the condensed oxyanion acting as its conjugate acid. The reverse reaction is a hydrolysis reaction, as a water molecule, acting as a base, is split. Further condensation may occur, particularly with anions of higher charge, as occurs with adenosine phosphates.
The conversion of ATP to ADP is a hydrolysis reaction and is an important source of energy in biological systems.
The formation of most silicate minerals can be viewed as the result of a de-condensation reaction in which silica reacts with a basic oxide, an acid–base reaction in the Lux–Flood sense. | 7 | Physical Chemistry |
Using either Pd–Cu or Cu catalysts Yang et al. reported the first example of decarboxylative C–P cross-coupling. | 0 | Organic Chemistry |
In materials science, the Zener–Hollomon parameter, typically denoted as Z, is used to relate changes in temperature or strain-rate to the stress-strain behavior of a material. It has been most extensively applied to the forming of steels at increased temperature, when creep is active. It is given by
where is the strain rate, Q is the activation energy, R is the gas constant, and T is the temperature. The Zener–Hollomon parameter is also known as the temperature compensated strain rate, since the two are inversely proportional in the definition. It is named after Clarence Zener and John Herbert Hollomon, Jr. who established the formula based on the stress-strain behavior in steel.
When plastically deforming a material, the flow stress depends heavily on both the strain-rate and temperature. During forming processes, Z may help determine appropriate changes in strain-rate or temperature when the other variable is altered, in order to keep material flowing properly. Z has also been applied to some metals over a large range of strain rates and temperatures and shown comparable microstructures at the end-of-processing, as long as Z remained similar. This is because the relative activity of various deformation mechanisms is typically inversely proportional to temperature or strain-rate, such that decreasing strain rate or increasing temperature will increase Z and promote plastic deformation. | 8 | Metallurgy |
Ethylene oxide is widely used to generate detergents and surfactants by ethoxylation. Its hydrolysis affords ethylene glycol. It is also used for sterilisation of medical instruments and materials.
The reaction of epoxides with amines is the basis for the formation of epoxy glues and structural materials. A typical amine-hardener is triethylenetetramine (TETA). | 0 | Organic Chemistry |
The two most prevalent shape-memory alloys are copper-aluminium-nickel and nickel-titanium (NiTi), but SMAs can also be created by alloying zinc, copper, gold and iron.
Although iron-based and copper-based SMAs, such as Fe-Mn-Si, Cu-Zn-Al and Cu-Al-Ni, are commercially available and cheaper than NiTi, NiTi-based SMAs are preferable for most applications due to their stability and practicability as well as their superior thermo-mechanical performance. SMAs can exist in two different phases, with three different crystal structures (i.e. twinned martensite, detwinned martensite, and austenite) and six possible transformations. The thermo-mechanic behavior of the SMAs is governed by a phase transformation between the austenite and the martensite.
; M is the temperature at which the transition to martensite completes upon cooling. Accordingly, during heating A and A are the temperatures at which the transformation from martensite to austenite starts and finishes.
Applying a mechanical load to the martensite leads to a re-orientation of the crystals, referred to as “de-twinning”, which results in a deformation which is not recovered (remembered) after releasing the mechanical load. De-twinning starts at a certain stress σ and ends at σ above which martensite continue exhibiting only elastic behavior (as long as the load is below the yield stress). The memorized deformation from detwinning is recovered after heating to austenite.
The phase transformation from austenite to martensite can also occur at constant temperature by applying a mechanical load above a certain level. The transformation is reversed when the load is released.
The transition from the martensite phase to the austenite phase is only dependent on temperature and stress, not time, as most phase changes are, as there is no diffusion involved. Similarly, the austenite structure receives its name from steel alloys of a similar structure. It is the reversible diffusionless transition between these two phases that results in special properties. While martensite can be formed from austenite by rapidly cooling carbon-steel, this process is not reversible, so steel does not have shape-memory properties.
In this figure the vertical axis represents the martensite fraction. The difference between the heating transition and the cooling transition gives rise to hysteresis where some of the mechanical energy is lost in the process. The shape of the curve depends on the material properties of the shape-memory alloy, such as the alloy's composition and work hardening. | 8 | Metallurgy |
A 2019 review conducted on the potential nootropic effects of modafinil in healthy, non-sleep-deprived individuals revealed the following: a) while studies using basic testing paradigms demonstrated that modafinil enhances executive function, only half of these studies showed improvements in attention, learning, and memory, with a few studies even reporting impairments in divergent creative thinking; b) modafinil displayed small levels of enhancement in attention, executive functions, and learning abilities; c) no substantial side effects or mood changes were observed; d) the available evidence showed limited evidence for modafinil as a cognitive enhancer outside of its use for sleep-deprived populations.
A 2020 review reported that modafinil has a modest effect on memory updating, but the effect is small and may not accurately reflect the perception that it is useful as a cognitive enhancer, as there is insufficient evidence to support such a claim. | 4 | Stereochemistry |
Cefapirin (INN, also spelled cephapirin) is an injectable, first-generation cephalosporin antibiotic. It is marketed under the trade name Cefadyl. Production for use in humans has been discontinued in the United States.
It also has a role in veterinary medicine as Metricure, an intrauterine preparation, and combined with prednisolone in Mastiplan, an intramammary preparation. Both are licensed in cattle. | 4 | Stereochemistry |
S-Adenosyl--homocysteine (SAH) is the biosynthetic precursor to homocysteine. SAH is formed by the demethylation of S-adenosyl--methionine. Adenosylhomocysteinase converts SAH into homocysteine and adenosine. | 1 | Biochemistry |
Self-replicating stretches of eukaryotic genomes known as retrotransposons utilize reverse transcriptase to move from one position in the genome to another via an RNA intermediate. They are found abundantly in the genomes of plants and animals. Telomerase is another reverse transcriptase found in many eukaryotes, including humans, which carries its own RNA template; this RNA is used as a template for DNA replication.
Initial reports of reverse transcriptase in prokaryotes came as far back as 1971 in France (Beljanski et al., 1971a, 1972) and a few years later in the USSR (Romashchenko 1977). These have since been broadly described as part of bacterial Retrons, distinct sequences that code for reverse transcriptase, and are used in the synthesis of msDNA. In order to initiate synthesis of DNA, a primer is needed. In bacteria, the primer is synthesized during replication.
Valerian Dolja of Oregon State argues that viruses, due to their diversity, have played an evolutionary role in the development of cellular life, with reverse transcriptase playing a central role. | 1 | Biochemistry |
ScBC (x = 0.27, y = 1.1, z = 0.2) has an orthorhombic crystal structure with space group Pbam (No. 55) and lattice constants of a = 1.73040(6), b = 1.60738(6) and c = 1.44829(6) nm. This phase is indicated as ScBC (phase IV) in the phase diagram of figure 17. This rare orthorhombic structure has 78 atomic positions in the unit cell: seven partially occupied Sc sites, four C sites, 66 B sites including three partially occupied sites and one B/C mixed-occupancy site. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table IX.
More than 500 atoms are available in the unit cell. In the crystal structure, there are six structurally independent icosahedra I1–I6, which are constructed from B1–B12, B13–B24, B25–B32, B33–B40, B41–B44 and B45–B56 sites, respectively; B57–B62 sites form a B polyhedron. The ScBC crystal structure is layered, as shown in figure 26. This structure has been described in terms of two kinds of boron icosahedron layers, L1 and L2. L1 consists of the icosahedra I3, I4 and I5 and the C65 "dimer", and L2 consists of the icosahedra I2 and I6. I1 is sandwiched by L1 and L2 and the B polyhedron is sandwiched by L2.
An alternative description is based on the same B(B)supericosahedron as in the YB structure. In the YB crystal structure, the supericosahedra form 3-dimensional boron framework as shown in figure 5. In this framework, the neighboring supericosahedra are rotated 90° with respect to each other. On the contrary, in ScBC the supericosahedra form a 2-dimensional network where the 90° rotation relation is broken because of the orthorhombic symmetry. The planar projections of the supericosahedron connection in ScBC and YB are shown in figures 27a and b, respectively. In the YB crystal structure, the neighboring 2-dimensional supericosahedron connections are out-of-phase for the rotational relation of the supericosahedron. This allows 3-dimensional
stacking of the 2-dimensional supericosahedron connection while maintaining the cubic symmetry.
The B boron cluster occupies the large space between four supericosahedra as described in the REB section. On the other hand, the 2-dimensional supericosahedron networks in the ScBC crystal structure stack in-phase along the z-axis. Instead of the B cluster, a pair of the I2 icosahedra fills the open space staying within the supericosahedron network, as shown in figure 28 where the icosahedron I2 is colored in yellow.
All Sc atoms except for Sc3 reside in large spaces between the supericosahedron networks, and the Sc3 atom occupies a void in the network as shown in figure 26. Because of the small size of Sc atom, the occupancies of the Sc1–Sc5 sites exceed 95%, and those of Sc6 and Sc7 sites are approximately 90% and 61%, respectively (see table IX). | 3 | Analytical Chemistry |
To separate nucleic acids by TGGE, the following steps must be performed: preparing and pouring the gels, electrophoresis, staining, and elution of DNA. Because a buffered system must be chosen, it is important that the system remain stable within the context of increasing temperature. Thus, urea is typically utilized for gel preparation; however, researchers need to be aware that the amount of urea used will affect the overall temperature required to separate the DNA. The gel is loaded, the sample is placed on the gel according to the type of gel that is being run—i.e. parallel or perpendicular—the voltage is adjusted and the sample can be left to run. Depending on which type of TGGE is to be run, either perpendicular or parallel, varying amounts of sample need to be prepared and loaded. A larger amount of one sample is used with perpendicular, while a smaller amount of many samples are used with parallel TGGE. Once the gel has been run, the gel must be stained to visualize the results. While there are a number of stains that can be used for this purpose, silver staining has proven to be the most effective tool. The DNA can be eluted from the silver stain for further analysis through PCR amplification. | 1 | Biochemistry |
Another potential solid-state refrigeration technique and a relatively new area of study comes from a special property of super elastic materials. These materials undergo a temperature change when experiencing an applied mechanical stress (called the elastocaloric effect). Since super elastic materials deform reversibly at high strains, the material experiences a flattened elastic region in its stress-strain curve caused by a resulting phase transformation from an austenitic to a martensitic crystal phase.
When a super elastic material experiences a stress in the austenitic phase, it undergoes an exothermic phase transformation to the martensitic phase, which causes the material to heat up. Removing the stress reverses the process, restores the material to its austenitic phase, and absorbs heat from the surroundings cooling down the material.
The most appealing part of this research is how potentially energy efficient and environmentally friendly this cooling technology is. The different materials used, commonly shape-memory alloys, provide a non-toxic source of emission free refrigeration. The most commonly studied materials studied are shape-memory alloys, like nitinol and Cu-Zn-Al. Nitinol is of the more promising alloys with output heat at about 66 J/cm and a temperature change of about 16–20 K. Due to the difficulty in manufacturing some of the shape memory alloys, alternative materials like natural rubber have been studied. Even though rubber may not give off as much heat per volume (12 J/cm ) as the shape memory alloys, it still generates a comparable temperature change of about 12 K and operates at a suitable temperature range, low stresses, and low cost.
The main challenge however comes from potential energy losses in the form of hysteresis, often associated with this process. Since most of these losses comes from incompatibilities between the two phases, proper alloy tuning is necessary to reduce losses and increase reversibility and efficiency. Balancing the transformation strain of the material with the energy losses enables a large elastocaloric effect to occur and potentially a new alternative for refrigeration. | 7 | Physical Chemistry |
In electromagnetism, the Townsend discharge or Townsend avalanche is an ionisation process for gases where free electrons are accelerated by an electric field, collide with gas molecules, and consequently free additional electrons. Those electrons are in turn accelerated and free additional electrons. The result is an avalanche multiplication that permits significantly increased electrical conduction through the gas. The discharge requires a source of free electrons and a significant electric field; without both, the phenomenon does not occur.
The Townsend discharge is named after John Sealy Townsend, who discovered the fundamental ionisation mechanism by his work circa 1897 at the Cavendish Laboratory, Cambridge. | 7 | Physical Chemistry |
In metazoans, small interfering RNAs (siRNAs) processed by Dicer are incorporated into a complex known as the RNA-induced silencing complex or RISC. This complex contains an endonuclease that cleaves perfectly complementary messages to which the siRNA binds. The resulting mRNA fragments are then destroyed by exonucleases. siRNA is commonly used in laboratories to block the function of genes in cell culture. It is thought to be part of the innate immune system as a defense against double-stranded RNA viruses. | 1 | Biochemistry |
Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old. More recent studies also suggest that photosynthesis may have begun about 3.4 billion years ago, though the first direct evidence of photosynthesis comes from thylakoid membranes preserved in 1.75-billion-year-old cherts.
Oxygenic photosynthesis is the main source of oxygen in the Earth's atmosphere, and its earliest appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around two billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic, using water as an electron donor, which is oxidized to molecular oxygen in the photosynthetic reaction center. | 5 | Photochemistry |
In physics, a "coffee ring" is a pattern left by a puddle of particle-laden liquid after it evaporates. The phenomenon is named for the characteristic ring-like deposit along the perimeter of a spill of coffee. It is also commonly seen after spilling red wine. The mechanism behind the formation of these and similar rings is known as the coffee ring effect or in some instances, the coffee stain effect, or simply ring stain. | 7 | Physical Chemistry |
As found by Brooks, et al., while lactate is disposed of mainly through oxidation and only a minor fraction supports gluconeogenesis, lactate is the main gluconeogenic precursor during sustained exercise.
Brooks demonstrated in his earlier studies that little difference in lactate production rates were seen in trained and untrained subjects at equivalent power outputs. What was seen, however, was more efficient clearance rates of lactate in the trained subjects suggesting an upregulation of MCT protein.
Local lactate use depends on exercise exertion. During rest, approximately 50% of lactate disposal take place through lactate oxidation whereas in time of strenuous exercise (50-75% VO2 max) approximately 75-80% of lactate is used by the active cell, indicating lactate’s role as a major contributor to energy conversion during increased exercise exertion. | 1 | Biochemistry |
Despite the fact that the process of chemosynthesis has been known for more than a hundred years, its significance and importance are still relevant today in the transformation of chemical elements in biogeochemical cycles. Today, the vital processes of nitrifying bacteria, which lead to the oxidation of ammonia to nitric acid, require scientific substantiation and additional research. The ability of bacteria to convert inorganic substances into organic ones suggests that chemosynthetics can accumulate valuable resources for human needs.
Chemosynthetic communities in different environments are important biological systems in terms of their ecology, evolution and biogeography, as well as their potential as indicators of the availability of permanent hydrocarbon- based energy sources. In the process of chemosynthesis, bacteria produce organic matter where photosynthesis is impossible. Isolation of thermophilic sulfate-reducing bacteria Thermodesulfovibrio yellowstonii and other types of chemosynthetics provides prospects for further research. Thus, the importance of chemosynthesis remains relevant for use in innovative technologies, conservation of ecosystems, human life in general. The role of Sergey Winogradsky in discovering the phenomenon of chemosynthesis is underestimated and needs further research and popularization. | 1 | Biochemistry |
In 1887, Heinrich Rudolf Hertz discovered but could not explain the photoelectric effect, which was later explained in 1905 by Albert Einstein (Nobel Prize in Physics 1921). Two years after Einsteins publication, in 1907, P.D. Innes experimented with a Röntgen tube, Helmholtz coils, a magnetic field hemisphere (an electron kinetic energy analyzer), and photographic plates, to record broad bands of emitted electrons as a function of velocity, in effect recording the first XPS spectrum. Other researchers, including Henry Moseley, Rawlinson and Robinson, independently performed various experiments to sort out the details in the broad bands. After WWII, Kai Siegbahn and his research group in Uppsala (Sweden) developed several significant improvements in the equipment, and in 1954 recorded the first high-energy-resolution XPS spectrum of cleaved sodium chloride (NaCl), revealing the potential of XPS. A few years later in 1967, Siegbahn published a comprehensive study of XPS, bringing instant recognition of the utility of XPS and also the first hard X-ray photoemission experiments, which he referred to as Electron Spectroscopy for Chemical Analysis (ESCA). In cooperation with Siegbahn, a small group of engineers (Mike Kelly, Charles Bryson, Lavier Faye, Robert Chaney) at Hewlett-Packard in the US, produced the first commercial monochromatic XPS instrument in 1969. Siegbahn received the Nobel Prize for Physics in 1981, to acknowledge his extensive efforts to develop XPS into a useful analytical tool. In parallel with Siegbahns work, David Turner at Imperial College London (and later at Oxford University) developed ultraviolet photoelectron spectroscopy (UPS) for molecular species using helium lamps. | 7 | Physical Chemistry |
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel. | 4 | Stereochemistry |
R3D measured ionizing and non-ionizing radiation as well as cosmic radiation reaching the biological samples located on the EXPOSE-E. Due to errors in data transmission or temporary termination of EXPOSE power, not all data could be acquired. Radiation was not constant during the mission. At regular intervals of about 2 months, low or almost no radiation was encountered. The radiation dose during the mission was 1823.98 MJ m−2 for PAR, 269.03 MJ m−2 for UVA, 45.73 MJ m−2 for UVB, or 18.28 MJ m−2 for UVC. Registered sunshine duration during the mission was about 152 days (about 27% of mission time). The surface of EXPOSE was most likely turned away from the Sun for considerably longer time.
The highest daily averaged absorbed dose rate of 426 μGy per day came from the South Atlantic Anomaly (SAA) region of the inner radiation belt; galactic cosmic rays (GCR) delivered a daily absorbed dose rate of 91.1 μGy per day, and the outer radiation belt (ORB) source delivered 8.6 μGy per day. | 1 | Biochemistry |
11β-hydroxylase is a steroidogenic enzyme, i.e. the enzyme involved in the metabolism of steroids. The enzyme is primarily localized in the zona glomerulosa and zona fasciculata of the adrenal cortex. The enzyme functions by introducing a hydroxyl group at carbon position 11β on the steroid nucleus, thereby facilitating the conversion of certain steroids.
Humans have two isozymes with 11β-hydroxylase activity: CYP11B1 and CYP11B2.
CYP11B1 (11β-hydroxylase) is expressed at high levels and is regulated by ACTH, while CYP11B2 (aldosterone synthase) is usually expressed at low levels and is regulated by angiotensin II. In addition to the 11β-hydroxylase activity, both isozymes have 18-hydroxylase activity. The CYP11B1 isozyme has strong 11β-hydroxylase activity, but the activity of 18-hydroxylase is only one-tenth of CYP11B2. The weak 18-hydroxylase activity of CYP11B1 explains why an adrenal with suppressed CYP11B2 expression continues to synthesize 18-hydroxycorticosterone.
Here are some of the steroids, grouped by catalytic activity of the CYP11B1 isozyme:
* strong activity:
** 11-deoxycortisol to cortisol,
** 11-deoxycorticosterone to corticosterone;
* medium activity:
** progesterone to 11β-hydroxyprogesterone,
** 17α-hydroxyprogesterone to 21-deoxycortisol,
** androstenedione to 11β-hydroxyandrostenedione;
** testosterone to 11β-hydroxytestosterone,
* weak activity:
** corticosterone to 18-hydroxycorticosterone,
** cortisol to 18-hydroxycortisol. | 1 | Biochemistry |
The Uhp system uptakes phosphorylated hexose sugars into bacteria. The system is triggered by phosphorylated hexose sugars on the outside of the cell. UhpC binds to the phosphorylated hexose, which allows the phosphorylation of UhpB on one of its cytoplasmic histidines. This facilitates the phosphorylation of an aspartate on UhpA, and the phosphorylated UhpA activates the transcription of UhpT. UhpT then facilitates the transport of the phosphorylated hexose sugars into the cell. | 1 | Biochemistry |
Volatilizing roasting, involves oxidation at elevated temperatures of the ores, to eliminate impurity elements in the form of their volatile oxides. Examples of such volatile oxides include AsO, SbO, ZnO and sulfur oxides. Careful control of the oxygen content in the roaster is necessary, as excessive oxidation can form non-volatile oxides. | 8 | Metallurgy |
Multiple isomorphous replacement (MIR), where heavy atoms are inserted into structure (usually by synthesizing proteins with analogs or by soaking) | 3 | Analytical Chemistry |
High through-put methods exist to help streamline the large number of experiments required to explore the various conditions that are necessary for successful crystal growth. There are numerous commercial kits available for order which apply preassembled ingredients in systems guaranteed to produce successful crystallization. Using such a kit, a scientist avoids the hassle of purifying a protein and determining the appropriate crystallization conditions.
Liquid-handling robots can be used to set up and automate large number of crystallization experiments simultaneously. What would otherwise be slow and potentially error-prone process carried out by a human can be accomplished efficiently and accurately with an automated system. Robotic crystallization systems use the same components described above, but carry out each step of the procedure quickly and with a large number of replicates. Each experiment utilizes tiny amounts of solution, and the advantage of the smaller size is two-fold: the smaller sample sizes not only cut-down on expenditure of purified protein, but smaller amounts of solution lead to quicker crystallizations. Each experiment is monitored by a camera which detects crystal growth. | 3 | Analytical Chemistry |
15-Crown-5 is a crown ether with the formula (CHO). It is a cyclic pentamer of ethylene oxide that forms complex with various cations, including sodium (Na) and potassium (K); however, it is complementary to Na and thus has a higher selectivity for Na ions. | 6 | Supramolecular Chemistry |
In 2014 based on their research on the northern United States Atlantic marine continental margins from Cape Hatteras to Georges Bank, a group of scientists from the US Geological Survey, the Department of Geosciences, Mississippi State University, Department of Geological Sciences, Brown University and Earth Resources Technology, found widespread leakage of methane from the seafloor, but they did not assign specific dates, beyond suggesting that some of the seeps were more than 1000 years old. In March 2017, a meta-analysis by the USGS Gas Hydrates Project concluded:
In June 2017, scientists from the Center for Arctic Gas Hydrate (CAGE), Environment and Climate at the University of Tromsø, published a study describing over a hundred ocean sediment craters, some 300 meters wide and up to 30 meters deep, formed due to explosive eruptions, attributed to destabilizing methane hydrates, following ice-sheet retreat during the last glacial period, around 15,000 years ago, a few centuries after the Bølling–Allerød warming. These areas around the Barents Sea, still seep methane today, and still existing bulges with methane reservoirs could eventually have the same fate. Later that same year, the Arctic Council published SWIPA 2017 report, where it cautioned "Arctic sources and sinks of greenhouse gases are still hampered by data and knowledge gaps."
In 2018, a perspective piece devoted to tipping points in the climate system suggested that the climate change contribution from methane hydrates would be "negligible" by the end of the century, but could amount to on the millennial timescales. In 2021, the IPCC Sixth Assessment Report no longer included methane hydrates in the list of potential tipping points, and says that "it is very unlikely that CH4 emissions from clathrates will substantially warm the climate system over the next few centuries." The report had also linked terrestrial hydrate deposites to gas emission craters discovered in the Yamal Peninsula in Siberia, Russia beginning in July 2014, but noted that since terrestrial gas hydrates predominantly form at a depth below 200 metres, a substantial response within the next few centuries can be ruled out. Likewise, a 2022 assessment of tipping points described methane hydrates as a "threshold-free feedback" rather than a tipping point. | 6 | Supramolecular Chemistry |
Eoxin A4, also known as 14,15-leukotriene A4, is an eoxin. Cells make eoxins by metabolizing arachidonic acid with a 15-lipoxygenase enzyme to form 15(S)-hydroperoxyeicosapentaenoic acid (i.e. 15(S)-HpETE). This product is then converted serially to eoxin A4 (i.e. EXA4), EXC4, EXD4, and EXE4 by LTC4 synthase, an unidentified gamma-glutamyltransferase, and an unidentified dipeptidase, respectively, in a pathway which appears similar if not identical to the pathway which forms leukotreines, i.e. LTA4, LTC4, LTD4, and LTE4. This pathway is schematically shown as follows:
EXA is viewed as an intracellular-bound, short-lived intermediate which is rapidly metabolized to the down-stream eoxins. The eoxins down stream of EXA4 are secreted from their parent cells and, it is proposed but not yet proven, serve to regulate allergic responses and the development of certain cancers (see Eoxins). | 1 | Biochemistry |
Cytidine residues, modified once to m5C (discussed above), can be further modified: either oxidised once for 5-hydroxylmethylcytidine (hm5C), or oxidised twice for 5-formylcytidine (f5C). Arising from the oxidative processing of m5C enacted in mammals by ten-eleven translocation (TET) family enzymes, hm5C is known to occur in all three kingdoms and to have roles in regulation. While 5-hydroxymethylcytidine (hm5dC) is known to be found in DNA in a widespread manner, hm5C is also found in organisms for which no hm5dC has been detected, indicating it is a separate process with distinct regulatory stipulations. To observe the in vivo addition of methyl groups to cytosine RNA residues followed by oxidative processing, mice can be fed on a diet incorporating particular isotopes and these be traced by LC-MS/MS analysis. Since the metabolic pathway from nutritional intake to nucleotide incorporation is known to progress from dietary methionine --> S-adenosylmethionine (SAM) --> methyl group on RNA base, the labelling of dietary methionine with C and D means these will end up in hm5C residues that have been altered since the addition of these into the diet. In contrast to m5C, a large quantity of hm5C modifications have been recorded within coding sequences. | 1 | Biochemistry |
A direct repeat occurs when a sequence is repeated with the same pattern downstream. There is no inversion and no reverse complement associated with a direct repeat. The nucleotide sequence written in bold characters signifies the repeated sequence. It may or may not have intervening nucleotides.
Linguistically, a typical direct repeat is comparable to rhyming, as in "time on a dime". | 1 | Biochemistry |
Spectroscopists customarily refer to the spectrum arising from a given ionization state of a given element by the element's symbol followed by a Roman numeral. The numeral I is used for spectral lines associated with the neutral element, II for those from the first ionization state, III for those from the second ionization state, and so on. For example, "He I" denotes lines of neutral helium, and "C IV" denotes lines arising from the third ionization state, C, of carbon. This notation is used for example to retrieve data from the [http://physics.nist.gov/PhysRefData/ASD/levels_form.html NIST Atomic Spectrum Database]. | 7 | Physical Chemistry |
Dexpramipexole was originally identified as a candidate therapy for amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease by James Bennett, M.D., Ph.D., then of the University of Virginia.
The drug was initially investigated in ALS by Knopp Biosciences and Biogen Idec. A 2010 Phase II clinical trial showed a slowing of ALS disease progression and mortality benefits. In January 2013, Biogen Idec discontinued its development of dexpramipexole in ALS due to lack of efficacy in the Phase III study.
As a result of observing eosinophil lowering in the ALS trials, Knopp pivoted dexpramipexole clinical development to eosinophil associated diseases. In subsequent clinical trials, dexpramipexole significantly reduced eosinophil counts and glucocorticoid requirements in patients with hypereosinophilic syndrome and significantly reduced blood and tissue eosinophil counts in patients with chronic rhinosinusitis with nasal polyps. | 4 | Stereochemistry |
Usually, the amine reacts as the nucleophile with another organic compound acting as the electrophile. This sense of reactivity may be reversed for some electron-deficient amines, including oxaziridines, hydroxylamines, oximes, and other N–O substrates. When the amine is used as an electrophile, the reaction is called electrophilic amination. Electron-rich organic substrates that may be used as nucleophiles for this process include carbanions and enolates. | 0 | Organic Chemistry |
As mentioned above, the noise due to the Brownian fluctuations of the bead increases with length. Robust sequencing tests have yet to be performed to determine the maximum read length of this system. However, the ligation of a 7-mer in the middle of a 1241 nucleotide-long hairpin was successfully detected, suggesting that the current system is sufficient to sequence up to ~500 bp. | 1 | Biochemistry |
NMMO monohydrate is used as a solvent in the lyocell process to produce lyocell fiber. It dissolves cellulose to form a solution called dope, and the cellulose is reprecipitated in a water bath to produce a fiber. The process is similar but not analogous to the viscose process. In the viscose process, cellulose is made soluble by conversion to its xanthate derivatives. With NMMO, cellulose is not derivatized but dissolves to give a homogeneous polymer solution. The resulting fiber is similar to viscose; this was observed, for example, for Valonia cellulose microfibrils. Dilution with water causes the cellulose to reprecipitate, i.e. the solvation of cellulose with NMMO is a water sensitive process.
Cellulose remains insoluble in most solvents because it has a strong and highly structured intermolecular hydrogen bonding network, which resists common solvents. NMMO breaks the hydrogen bonding network that keeps cellulose insoluble in water and other solvents. Similar solubility has been obtained in a few solvents, particularly a mix of lithium chloride in dimethyl acetamide and some hydrophilic ionic liquids. | 0 | Organic Chemistry |
Solventogenic Clostridium species have a biphasic metabolism composed of an acidogenic phase and a solventogenic phase. During acidogenesis, these bacteria are able to convert several carbon sources into organic acids, commonly butyrate and acetate. As acid accumulates, cells begin to assimilate the organic acids to solvents. In Clostridium acetobutylicum, a model solventogenic Clostridium species, a combination of low pH and high undisociated butyrate, referred to as the "pH-acid effect", triggers the metabolic shift from acidogenesis to solventogenesis. | 1 | Biochemistry |
The non-dispersive infrared analysis (NDIR) method offers the only practical interference-free method for detecting CO in TOC analysis. The principal advantage of using NDIR is that it directly and specifically measures the CO generated by oxidation of the organic carbon in the oxidation reactor, rather than relying on a measurement of a secondary, corrected effect, such as used in conductivity measurements.
A traditional NDIR detector relies upon flow-through-cell technology, where the oxidation product flows into and out of the detector continuously. A region of absorption of infrared light specific to CO, usually around 4.26 µm (2350 cm), is measured over time as the gas flows through the detector. A second reference measurement that is non-specific to CO is also taken concentration in the detector at that moment. As the gas continues to flow into and out of the detector cell the sum of the measurements results in a peak that is integrated and correlated to the total CO concentration in the sample aliquot.
A new advance of NDIR technology is static pressurized concentration (SPC). The exit valve of the NDIR is closed to allow the detector to become pressurized. Once the gases in the detector have reached equilibrium, the concentration of the CO is analyzed. This pressurization of the sample gas stream in the NDIR, a patented technique, allows for increased sensitivity and precision by measuring the entirety of the oxidation products of the sample in one reading, compared to flow-through cell technology. The output signal is proportional to the concentration of CO in the carrier gas, from the oxidation of the sample aliquot. UV/ Persulfate oxidation combined with NDIR detection provides good oxidation of organics, low instrument maintenance, good precision at ppb levels, relatively fast sample analysis time and easily accommodates multiple applications, including purified water (PW), water for injection (WFI), CIP, drinking water and ultra-pure water analyses. | 3 | Analytical Chemistry |
The Kharasch addition is an organic reaction and a metal-catalysed free radical addition of CXCl compounds (X = Cl, Br, H) to alkenes. The reaction is used to append trichloromethyl or dichloromethyl groups to terminal alkenes. The method has attracted considerable interest, but it is of limited value because of narrow substrate scope and demanding conditions.
The basic reaction proceeds through the CXCl free radical. Examples of organohalides are carbon tetrachloride and chloroform. Radicals are often generated by abstraction of a halide radical by a metal ion. The addition is an anti-Markovnikov addition. Early work linked the addition to olefin polymerization and is therefore considered a first step into what was to become atom transfer radical polymerization.
An example of Kharasch addition is the synthesis of 1,1,3-trichloro-n-nonane from 1-octene and chloroform using an iron-based catalyst. | 0 | Organic Chemistry |
Mill scale, often shortened to just scale, is the flaky surface of hot rolled steel, consisting of the mixed iron oxides iron(II) oxide (, wüstite), iron(III) oxide (, hematite), and iron(II,III) oxide (, magnetite).
Mill scale is formed on the outer surfaces of plates, sheets or profiles when they are produced by passing red hot iron or steel billets through rolling mills. Mill scale is bluish-black in color. It is usually less than thick, and initially adheres to the steel surface and protects it from atmospheric corrosion provided no break occurs in this coating.
Because it is electrochemically cathodic to steel, any break in the mill scale coating will cause accelerated corrosion of steel exposed at the break. Mill scale is thus a boon for a while, until its coating breaks due to handling of the steel product or due to any other mechanical cause.
Mill scale becomes a nuisance when the steel is to be processed. Any paint applied over it is wasted, since it will come off with the scale as moisture-laden air gets under it. Thus mill scale can be removed from steel surfaces by flame cleaning, pickling, or abrasive blasting, which are all tedious operations that consume energy. This is why shipbuilders and steel fixers used to leave steel and rebar delivered freshly rolled from mills out in the open to allow it to weather until most of the scale fell off due to atmospheric action. Nowadays, most steel mills can supply their product with mill scale removed and steel coated with shop primers over which welding or painting can be done safely.
Mill scale generated in rolling mills will be collected and sent to a sinter plant for recycling. | 8 | Metallurgy |
DNA separation by silica adsorption is a method of DNA separation that is based on DNA molecules binding to silica surfaces in the presence of certain salts and under certain pH conditions. | 1 | Biochemistry |
Antisense transcripts are stretches of non coding mRNA that are complementary to the coding sequence. Genome wide studies have shown that RNA antisense transcripts occur commonly within nature. They are generally believed to increase the coding potential of the genetic code and add an overall layer of complexity to gene regulation. So far, it is known that 40% of the human genome is transcribed in both directions, underlining the potential significance of reverse transcription.
It has been suggested that complementary regions between sense and antisense transcripts would allow generation of double stranded RNA hybrids, which may play an important role in gene regulation. For example, hypoxia-induced factor 1α mRNA and β-secretase mRNA are transcribed bidirectionally, and it has been shown that the antisense transcript acts as a stabilizer to the sense script. | 1 | Biochemistry |
Liquids can form solutions with gases, solids, and other liquids.
Two liquids are said to be miscible if they can form a solution in any proportion; otherwise they are immiscible. As an example, water and ethanol (drinking alcohol) are miscible whereas water and gasoline are immiscible. In some cases a mixture of otherwise immiscible liquids can be stabilized to form an emulsion, where one liquid is dispersed throughout the other as microscopic droplets. Usually this requires the presence of a surfactant in order to stabilize the droplets. A familiar example of an emulsion is mayonnaise, which consists of a mixture of water and oil that is stabilized by lecithin, a substance found in egg yolks. | 7 | Physical Chemistry |
If the underlying infertility is related to abnormalities in spermatogenesis, it is plausible, but too early to examine that male offspring are at higher risk for sperm abnormalities.
IVF does not seem to confer any risks regarding cognitive development, school performance, social functioning, and behaviour. Also, IVF infants are known to be as securely attached to their parents as those who were naturally conceived, and IVF adolescents are as well-adjusted as those who have been naturally conceived.
Limited long-term follow-up data suggest that IVF may be associated with an increased incidence of hypertension, impaired fasting glucose, increase in total body fat composition, advancement of bone age, subclinical thyroid disorder, early adulthood clinical depression and binge drinking in the offspring. It is not known, however, whether these potential associations are caused by the IVF procedure in itself, by adverse obstetric outcomes associated with IVF, by the genetic origin of the children or by yet unknown IVF-associated causes. Increases in embryo manipulation during IVF result in more deviant fetal growth curves, but birth weight does not seem to be a reliable marker of fetal stress.
IVF, including ICSI, is associated with an increased risk of imprinting disorders (including Prader–Willi syndrome and Angelman syndrome), with an odds ratio of 3.7 (95% confidence interval 1.4 to 9.7).
An IVF-associated incidence of cerebral palsy and neurodevelopmental delay are believed to be related to the confounders of prematurity and low birthweight. Similarly, an IVF-associated incidence of autism and attention-deficit disorder are believed to be related to confounders of maternal and obstetric factors.
Overall, IVF does not cause an increased risk of childhood cancer. Studies have shown a decrease in the risk of certain cancers and an increased risks of certain others including retinoblastoma, hepatoblastoma and rhabdomyosarcoma. | 1 | Biochemistry |
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