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Kodesomes are liposomes that have been decorated with FSL Kode constructs. These have been used to deposit FSL constructs onto microplates to create diagnostic assays. They also have the potential for therapeutic use. | 1 | Biochemistry |
Monalkylphosphinic acids have the formula OP(OH)(H)R, with the simplest example being methylphosphinic acid.
Phosphinic acid adds to Michael acceptors, for example with acrylamide it gives H(HO)P(O)CHCHC(O)NH. | 0 | Organic Chemistry |
Surprisals add where probabilities multiply. The surprisal for an event of probability is defined as . If is then surprisal is in nats, bits, or so that, for instance, there are bits of surprisal for landing all "heads" on a toss of coins.
Best-guess states (e.g. for atoms in a gas) are inferred by maximizing the average surprisal (entropy) for a given set of control parameters (like pressure or volume ). This constrained entropy maximization, both classically and quantum mechanically, minimizes Gibbs availability in entropy units where is a constrained multiplicity or partition function.
When temperature is fixed, free energy () is also minimized. Thus if and number of molecules are constant, the Helmholtz free energy (where is energy and is entropy) is minimized as a system "equilibrates." If and are held constant (say during processes in your body), the Gibbs free energy is minimized instead. The change in free energy under these conditions is a measure of available work that might be done in the process. Thus available work for an ideal gas at constant temperature and pressure is where and (see also Gibbs inequality).
More generally the work available relative to some ambient is obtained by multiplying ambient temperature by relative entropy or net surprisal defined as the average value of where is the probability of a given state under ambient conditions. For instance, the work available in equilibrating a monatomic ideal gas to ambient values of and is thus , where relative entropy
The resulting contours of constant relative entropy, shown at right for a mole of Argon at standard temperature and pressure, for example put limits on the conversion of hot to cold as in flame-powered air-conditioning or in the unpowered device to convert boiling-water to ice-water discussed here. Thus relative entropy measures thermodynamic availability in bits. | 7 | Physical Chemistry |
Bis(pinacolato)diboron is a covalent compound containing two boron atoms and two pinacolato ligands. It has the formula [(CH)COB]; the pinacol groups are sometimes abbreviated as "pin", so the structure is sometimes represented as Bpin. It is a colourless solid that is soluble in organic solvents. It is a commercially available reagent for making pinacol boronic esters for organic synthesis. Unlike some other diboron compounds, Bpin is not moisture-sensitive and can be handled in air. | 0 | Organic Chemistry |
PBMCs were separated from blood on Ficoll-Paque by differential centrifugation and were suspended in 24-well tissue culture plates culture medium. Different dilutions of PBMCs were incubated at 37 °C with 5% . Culture supernatants were collected at 24, 48, 72, and 96 h after incubation and the supernatants were test against BCG or PPD by ELISA. The ELISA titer indicate the positive or negative result. | 1 | Biochemistry |
Somatomedins are a group of proteins produced predominantly by the liver when growth hormones act on target tissue. Somatomedins inhibit the release of growth hormones by acting directly on anterior pituitary and by stimulating the secretion of somatostatin from the hypothalamus.
Somatomedins are a group of proteins that promote cell growth and division in response to stimulation by growth hormone (GH), also known as somatotropin (STH).
Somatomedins have similar biological effects to somatotropin.
In addition to their actions that stimulate growth, somatomedins also stimulate production of somatostatin, which suppresses growth hormone release. Thus, levels of somatomedins are controlled via negative feedback through the intermediates of somatostatin and growth hormone. Somatomedins are produced in many tissues and have autocrine and paracrine actions in addition to their endocrine action. The liver is thought to be the predominant source of circulating somatomedins.
Three forms include:
* Somatomedin A, which is another name for insulin-like growth factor 2 (IGF-2)
* Somatomedin B, which is derived from vitronectin
* Somatomedin C, which is another name for insulin-like growth factor 1 (IGF-1) | 1 | Biochemistry |
Proper explanation of optical trapping behavior depends upon the size of the trapped particle relative to the wavelength of light used to trap it. In cases where the dimensions of the particle are much greater than the wavelength, a simple ray optics treatment is sufficient. If the wavelength of light far exceeds the particle dimensions, the particles can be treated as electric dipoles in an electric field. For optical trapping of dielectric objects of dimensions within an order of magnitude of the trapping beam wavelength, the only accurate models involve the treatment of either time dependent or time harmonic Maxwell equations using appropriate boundary conditions. | 1 | Biochemistry |
Synthetic molecular motors are molecular machines capable of continuous directional rotation under an energy input. Although the term "molecular motor" has traditionally referred to a naturally occurring protein that induces motion (via protein dynamics), some groups also use the term when referring to non-biological, non-peptide synthetic motors. Many chemists are pursuing the synthesis of such molecular motors.
The basic requirements for a synthetic motor are repetitive 360° motion, the consumption of energy and unidirectional rotation. The first two efforts in this direction, the chemically driven motor by Dr. T. Ross Kelly of Boston College with co-workers and the light-driven motor by Ben Feringa and co-workers, were published in 1999 in the same issue of Nature.
As of 2020, the smallest atomically precise molecular machine has a rotor that consists of four atoms. | 6 | Supramolecular Chemistry |
The tongue is skeletal muscle on the floor of the mouth of most vertebrates, that manipulates food for chewing (mastication) and swallowing (deglutition). It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is used to roll food particles into a bolus before being transported down the esophagus through peristalsis.
The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract. | 1 | Biochemistry |
Overflow metabolism refers to the seemingly wasteful strategy in which cells incompletely oxidize their growth substrate (e.g. glucose) instead of using the respiratory pathway, even in the presence of oxygen. As a result of employing this metabolic strategy, cells excrete (or "overflow") metabolites like lactate, acetate and ethanol. Incomplete oxidation of growth substrates yields less energy (e.g. ATP) than complete oxidation through respiration, and yet overflow metabolism—known as the Warburg effect in the context of cancer and the Crabtree effect in the context of yeast—occurs ubiquitously among fast-growing cells, including bacteria, fungi and mammalian cells.
Based on experimental studies of acetate overflow in Escherichia coli, recent research has offered a general explanation for the association of overflow metabolism with fast growth. According to this theory, the enzymes required for respiration are more costly than those required for partial oxidation of glucose. That is, if the cell were to produce enough of these enzymes to support fast growth with respiratory metabolism, it would consume much more energy, carbon and nitrogen (per unit time) than supporting fast growth with an incompletely oxidative metabolism (e.g. fermentation). Given that cells have limited energy resources and fixed physical volume for proteins, there is thought to be a trade-off between efficient energy capture through central metabolism (i.e. respiration) and fast growth achieved through high central-metabolic fluxes (e.g. through fermentation as in yeast).
As an alternative explanation, it was suggested that cells could be limited by the rate with which they can dissipate Gibbs energy to the environment. Using combined thermodynamic and stoichiometric metabolic models in flux balance analyses with (i) growth maximization as objective function and (ii) an identified limit in the cellular Gibbs energy dissipation rate, correct predictions of physiological parameters, intracellular metabolic fluxes and metabolite concentrations were achieved. | 1 | Biochemistry |
This type of BCA assay seems to only be available from Thermo Fisher Scientific. Reportedly it uses "the same copper reduction method as the traditional BCA Protein Assay with a unique [proprietary] copper chelator.", that absorbs at 480 nm instead of 562 nm. This proprietor chelator and presumed optimized Biuret reaction formulation allows the assay to provide rapid (<5 min) results without the 37˚C+ incubation of the original BCA assay. However the assay has a different interference profile from other non-protein components. The Pierce Quantitative Colorimetric Peptide Assay (now owned by and available from Thermo Fisher Scientific) appears to use a similar or identical 480 nm absorbing proprietary copper chelator. | 1 | Biochemistry |
The basic apparatus comprises an optical microscope, a light source and some fluorescent probe. Fluorescent emission is contingent upon absorption of a specific optical wavelength or color which restricts the choice of lamps. Most commonly, a broad spectrum mercury or xenon source is used in conjunction with a color filter. The technique begins by saving a background image of the sample before photobleaching. Next, the light source is focused onto a small patch of the viewable area either by switching to a higher magnification microscope objective or with laser light of the appropriate wavelength. The fluorophores in this region receive high intensity illumination which causes their fluorescence lifetime to quickly elapse (limited to roughly 10 photons before extinction). Now the image in the microscope is that of a uniformly fluorescent field with a noticeable dark spot. As Brownian motion proceeds, the still-fluorescing probes will diffuse throughout the sample and replace the non-fluorescent probes in the bleached region. This diffusion proceeds in an ordered fashion, analytically determinable from the diffusion equation. Assuming a Gaussian profile for the bleaching beam, the diffusion constant D can be simply calculated from:
where w is the radius of the beam and t is the "Characteristic" diffusion time. | 1 | Biochemistry |
In contrast to traditional combinatorial synthesis where a library of catalysts were first generated and later screened (as in the two above approaches), dynamic combinatorial library approach utilizes a mixture of multicomponent building blocks that reversibly form library of catalysts. With out a template, the library consists of a roughly equal mixture of different combination of building blocks. In the presence of a template which is either a starting material or a TSA, the combination that provides the best binding to the template is thermodynamically favorable and thus that combination is more prevalent than other library members. The biased ratio of the desired catalyst to other combinatorial products could then be frozen by terminating the reversibility of the equilibrium by means such as change in temperature, pH, or radiation to yield the optimal catalyst. For example, Lehn et al. used this method to create a dynamic combinatorial library of imine inhibitor from a set of amines and a set of aldehydes. After some time, the equilibrium was terminated by an addition of NaBHCN to afford the desired catalyst. | 6 | Supramolecular Chemistry |
The prevailing view that single ion activities are unmeasurable, or perhaps even physically meaningless, has its roots in the work of Edward A. Guggenheim in the late 1920s. However, chemists have not given up the idea of single ion activities. For example, pH is defined as the negative logarithm of the hydrogen ion activity. By implication, if the prevailing view on the physical meaning and measurability of single ion activities is correct it relegates pH to the category of thermodynamically unmeasurable quantities. For this reason the International Union of Pure and Applied Chemistry (IUPAC) states that the activity-based definition of pH is a notional definition only and further states that the establishment of primary pH standards requires the application of the concept of primary method of measurement tied to the Harned cell. Nevertheless, the concept of single ion activities continues to be discussed in the literature, and at least one author purports to define single ion activities in terms of purely thermodynamic quantities. The same author also proposes a method of measuring single ion activity coefficients based on purely thermodynamic processes. | 7 | Physical Chemistry |
Multi-state modeling of biomolecules refers to a series of techniques used to represent and compute the behaviour of biological molecules or complexes that can adopt a large number of possible functional states.
Biological signaling systems often rely on complexes of biological macromolecules that can undergo several functionally significant modifications that are mutually compatible. Thus, they can exist in a very large number of functionally different states. Modeling such multi-state systems poses two problems: The problem of how to describe and specify a multi-state system (the "specification problem") and the problem of how to use a computer to simulate the progress of the system over time (the "computation problem"). To address the specification problem, modelers have in recent years moved away from explicit specification of all possible states, and towards rule-based modeling that allow for implicit model specification, including the κ-calculus, BioNetGen, the Allosteric Network Compiler and others. To tackle the computation problem, they have turned to particle-based methods that have in many cases proved more computationally efficient than population-based methods based on ordinary differential equations, partial differential equations, or the Gillespie stochastic simulation algorithm. Given current computing technology, particle-based methods are sometimes the only possible option. Particle-based simulators further fall into two categories: Non-spatial simulators such as StochSim, DYNSTOC, RuleMonkey, and NFSim
and spatial simulators, including Meredys, SRSim and MCell. Modelers can thus choose from a variety of tools; the best choice depending on the particular problem. Development of faster and more powerful methods is ongoing, promising the ability to simulate ever more complex signaling processes in the future. | 1 | Biochemistry |
An alternative and promising chemistry for rSOCs is that one involving ammonia conversion to hydrogen and nitrogen. Ammonia has great potential as hydrogen carrier, due to its higher volumetric density with respect to hydrogen itself, and it can be directly fed to SOFCs. It has been demonstrated that ammonia-fed SOFCs operate through successive ammonia decomposition and hydrogen oxidation:
Ammonia decomposition has been demonstrated to be slightly more efficient than simple hydrogen oxidation, confirming the great potential of ammonia as a fuel other than an energy carrier.
Unfortunately, ammonia cannot be directly synthesized on the fuel electrode of a rSOC, because the equilibrium reaction
is completely shifted towards the left at their higher than 600°C working temperature. For this reason, for clean ammonia production, hydrogen production via electrolysis must be coupled with nitrogen production from air with hydrogen oxidation and subsequent water separation. | 7 | Physical Chemistry |
Nonribosomal peptides are synthesized by one or more specialized nonribosomal peptide-synthetase (NRPS) enzymes. The NRPS genes for a certain peptide are usually organized in one operon in bacteria and in gene clusters in eukaryotes. However the first fungal NRP to be found was ciclosporin. It is synthesized by a single 1.6MDa NRPS. The enzymes are organized in modules that are responsible for the introduction of one additional amino acid. Each module consists of several domains with defined functions, separated by short spacer regions of about 15 amino acids.
The biosynthesis of nonribosomal peptides shares characteristics with the polyketide and fatty acid biosynthesis. Due to these structural and mechanistic similarities, some nonribosomal peptide synthetases contain polyketide synthase modules for the insertion of acetate or propionate-derived subunits into the peptide chain.
Note that as many as 10% percent of bacterial NRPS are not laid out as large modular proteins, but as separate enzymes. Some NRPS modules deviate from the standard domain structure, and some extra domains have been described. There are also NRPS enzymes that serve as a scaffold for other modifications to the substrate to incorporate unusual amino acids. | 1 | Biochemistry |
Conjugated Schiff bases absorb strongly in the UV-visible region of the electromagnetic spectrum. This absorption is the basis of the anisidine value, which is a measure of oxidative spoilage for fats and oils. | 0 | Organic Chemistry |
Capping of the pre-mRNA involves the addition of 7-methylguanosine (mG) to the 5 end. To achieve this, the terminal 5 phosphate requires removal, which is done with the aid of enzyme RNA triphosphatase. The enzyme guanosyl transferase then catalyses the reaction, which produces the diphosphate 5 end. The diphosphate 5 end then attacks the alpha phosphorus atom of a GTP molecule in order to add the guanine residue in a 55 triphosphate link. The enzyme (guanine-N-)-methyltransferase ("cap MTase") transfers a methyl group from S-adenosyl methionine to the guanine ring. This type of cap, with just the (mG) in position is called a cap 0 structure. The ribose of the adjacent nucleotide may also be methylated to give a cap 1. Methylation of nucleotides downstream of the RNA molecule produce cap 2, cap 3 structures and so on. In these cases the methyl groups are added to the 2' OH groups of the ribose sugar.
The cap protects the 5 end of the primary RNA transcript from attack by ribonucleases that have specificity to the 35' phosphodiester bonds. | 1 | Biochemistry |
The activity of malate–aspartate shuttle is modulated by arginine methylation of malate dehydrogenase 1 (MDH1). Protein arginine N-methyltransferase CARM1 methylates and inhibits MDH1 by disrupting its dimerization, which represses malate–aspartate shuttle and inhibits mitochondria respiration of pancreatic cancer cells. | 1 | Biochemistry |
In genetics and molecular biology, a corepressor is a molecule that represses the expression of genes. In prokaryotes, corepressors are small molecules whereas in eukaryotes, corepressors are proteins. A corepressor does not directly bind to DNA, but instead indirectly regulates gene expression by binding to repressors.
A corepressor downregulates (or represses) the expression of genes by binding to and activating a repressor transcription factor. The repressor in turn binds to a gene's operator sequence (segment of DNA to which a transcription factor binds to regulate gene expression), thereby blocking transcription of that gene. | 1 | Biochemistry |
The word gas was first used by the early 17th-century Flemish chemist Jan Baptist van Helmont. He identified carbon dioxide, the first known gas other than air. Van Helmonts word appears to have been simply a phonetic transcription of the Ancient Greek word – the g in Dutch being pronounced like ch in "loch" (voiceless velar fricative, ) – in which case Van Helmont simply was following the established alchemical usage first attested in the works of Paracelsus. According to Paracelsuss terminology, chaos meant something like .
An alternative story is that Van Helmonts term was derived from "gahst (or geist), which signifies a ghost or spirit". That story is given no credence by the editors of the Oxford English Dictionary'. In contrast, the French-American historian Jacques Barzun speculated that Van Helmont had borrowed the word from the German , meaning the froth resulting from fermentation. | 7 | Physical Chemistry |
The world's first iron pillar was the Iron pillar of Delhi—erected at the times of Chandragupta II Vikramaditya (375–413), often considered as one of the finest pieces of ancient metallurgy. The swords manufactured in Indian workshops find written mention in the works of Muhammad al-Idrisi (flourished 1154). Indian Blades made of Damascus steel found their way into Persia. European scholars—during the 14th century—studied Indian casting and metallurgy technology.
Indian metallurgy under the Mughal emperor Akbar (reign: 1556–1605) produced excellent small firearms. Gommans (2002) holds that Mughal handguns were probably stronger and more accurate than their European counterparts.
Srivastava & Alam (2008) comment on Indian coinage of the Mughal Empire (established: April 21, 1526 - ended: September 21, 1857) during Akbar's regime:
Statues of Nataraja and Vishnu were cast during the reign of the imperial Chola dynasty (200–1279) in the 9th century. The casting could involve a mixture of five metals: copper, zinc, tin, gold, and silver.
Considered great feat in metallurgy, the hollow, Seamless, celestial globe was invented in Kashmir by Ali Kashmiri ibn Luqman in 998 AH (1589-90 CE), and twenty other such globes were later produced in Lahore and Kashmir during the Mughal Empire. These Indian metallurgists pioneered the method of lost-wax casting, and disguised plugs, in order to produce these globes. | 8 | Metallurgy |
One of the simplest reactions entails condensation of formaldehyde and dimethylamine. This reaction produces first the carbinolamine (a hemiaminal) and bis(dimethylamino)methane ():
The reaction of formaldehyde with carbazole, which is weakly basic, proceed similarly:
Again, this carbinol converts readily to the methylene-linked bis(carbazole). | 0 | Organic Chemistry |
Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Important examples include the sandwich and half-sandwich complexes, respectively, Cr(CH) and [[(Benzene)ruthenium dichloride dimer|[RuCl(CH)]]]. | 2 | Environmental Chemistry |
Gag/pol translational readthrough site (or Retroviral readthrough element) is a cis-regulatory element found in retroviruses. The readthrough site facilitates the mechanism of translation readthrough of the stop codon at the gag-pol junction producing the gag and pol fusion protein in certain retroviruses.
Retroviruses whose gag and pol genes are in the same reading frame often depend upon approximately 5% read-through of the gag UAG termination codon to form the gag-pol polyprotein. This readthrough is usually dependent on a pseudoknot located eight nucleotides downstream of the stop codon (UAG). Sequence conservation is found in the second pseudoknot loop. | 1 | Biochemistry |
These processes involve high-temperature blending of iron ore and coal powder, with a little limestone to reduce the acidity of the ore. Processes such as Carl Wilhelm Siemens', based on the use of a short drum, first appeared at the end of the 19th century. The tool used then evolved into a long tubular rotary kiln, inspired by those used in cement works, as in the Basset process, developed in the 1930s.
A process of historic importance is the Krupp-Renn. Developed in the 1930s, there were as many as 38 furnaces in 1945 which, although they only had a capacity of 1 Mt/year at the time, were installed all over the world. This process was improved and inspired the German Krupp-CODIR furnaces and the Japanese Kawasaki and Koho processes. Both Japanese processes integrate a pelletizing unit for steel by-products upstream of the rotary furnaces. Two units of each process were built between 1968 (Kawasaki) and 1975 (Koho).
The ACCAR process, developed in the late 1960s and used confidentially until 1987, uses a mixture of 80% coal and 20% oil or gas: the hydrocarbons, although more expensive, enrich the reducing gas with hydrogen. The German Krupp-CODIR process, operational since 1974, has had little more success: only three units have been commissioned. Finally, Indian steelmakers are behind the SIIL, Popurri, Jindal, TDR and OSIL processes, which are simply variants developed to meet specific technical and economic constraints.
Other processes, built on the same principle, failed to develop, such as the Strategic-Udy, consisting of a single plant commissioned in 1963 and shut down in 1964.
The SL/RN process, developed in 1964, dominated coal-fired processes in 2013. In 1997, it accounted for 45% of pre-reduced coal production. In 2012, however, production capacity for this process had fallen to just 1.8 Mt/year, out of a total of 17.06 Mt attributed to coal-fired processes. | 8 | Metallurgy |
Small nuclear RNA (snRNA) and small nucleolar RNA (snoRNA) are widely known to guide the nucleotide modifications and processing of rRNA. Both snRNA and snoRNA are categorized into a class of small RNA molecules that are present in the nucleus. However, they vary a lot by function. snRNA are 80-350nucletides long while snoRNA are 80-1000 nucleotides long in yeast. snRNA plays a critical role in regulating the pre-mRNA silencing. On the other hand, snoRNAs are involved in mRNA editing, modification of the rRNA and tRNA, and genome imprinting. Major function of snoRNA includes the maturation of rRNA during ribosomal formation. Small nuclear and small nucleolar RNAs are critical components of snRNPs and snoRNPs and play an essential role in the maturation of, respectively, mRNAs and rRNAs within the nucleus of eukaryotic cells. Both snRNA and snoRNA are involved in modifying RNA just after transcription. snRNA can be found in splicing speckles and Cajal bodies of the nucleus of the cell.snRNA and snoRNA requires a phosphorylated adaptor for nuclear export (PHAX) to get transported to the site of action within the nucleus. | 1 | Biochemistry |
Metal sulfides (e.g., pyrite FeS, arsenopyrite FeAsS, chalcopyrite CuFeS) are normally processed by chemical oxidation either in aqueous media or at high temperatures. In fact, most base metals, e.g., aluminium, chromium, must be (electro)chemically reduced at high temperatures by which the process entails a high energy demand, and sometimes large volumes of aqueous waste is generated. In aqueous media chalcopyrite, for instance, is more difficult to dissolve chemically than covellite and chalcocite due to surface effects (formation of polysulfide species,). The presence of Cl ions has been suggested to alter the morphology of any sulfide surface formed, allowing the sulfide mineral to leach more easily by preventing passivation. DESs provide a high Cl ion concentration and low water content, whilst reducing the need for either high additional salt or acid concentrations, circumventing most oxide chemistry. Thus, the electrodissolution of sulfide minerals has demonstrated promising results in DES media in absence of passivation layers, with the release into the solution of metal ions which could be recovered from solution.
During extraction of copper from copper sulfide minerals with Ethaline, chalcocite (CuS) and covellite (CuS) produce a yellow solution, indicating that [CuCl] complex are formed. Meanwhile, in the solution formed from chalcopyrite, Cu and Cu species co-exist in solution due to the generation of reducing Fe species at the cathode. The best selective recovery of copper (>97 %) from chalcopyrite can be obtained with a mixed DES of 20 wt.% ChCl-oxalic acid and 80 wt.% Ethaline. | 8 | Metallurgy |
The analytical and approximated solutions should now be compared in order to decide when it is valid to use the steady state approximation. The analytical solution transforms into the approximate one when because then and Therefore, it is valid to apply the steady state approximation only if the second reaction is much faster than the first ( is a common criterion), because that means that the intermediate forms slowly and reacts readily so its concentration stays low.
The graphs show concentrations of A (red), B (green) and C (blue) in two cases, calculated from the analytical solution.
When the first reaction is faster it is not valid to assume that the variation of [B] is very small, because [B] is neither low or close to constant: first A transforms into B rapidly and B accumulates because it disappears slowly. As the concentration of A decreases its rate of transformation decreases, at the same time the rate of reaction of B into C increases as more B is formed, so a maximum is reached when <br />From then on the concentration of B decreases.
When the second reaction is faster, after a short induction period during which the steady state approximation does not apply, the concentration of B remains low (and more or less constant in an absolute sense) because its rates of formation and disappearance are almost equal and the steady state approximation can be used.
The equilibrium approximation can sometimes be used in chemical kinetics to yield similar results to the steady state approximation. It consists in assuming that the intermediate arrives rapidly at chemical equilibrium with the reactants. For example, Michaelis-Menten kinetics can be derived assuming equilibrium instead of steady state. Normally the requirements for applying the steady state approximation are laxer: the concentration of the intermediate is only needed to be low and more or less constant (as seen, this has to do only with the rates at which it appears and disappears) but it is not required to be at equilibrium. | 7 | Physical Chemistry |
The old MIL-F-14256 and QQ-S-571 standards defined fluxes as:
*R (rosin)
*RMA (rosin mildly activated)
*RA (rosin activated)
*WS (water-soluble)
Any of these categories may be no-clean, or not, depending on the chemistry selected and the standard that the manufacturer requires. | 8 | Metallurgy |
Sulfolene, or butadiene sulfone is a cyclic organic chemical with a sulfone functional group. It is a white, odorless, crystalline, indefinitely storable solid, which dissolves in water and many organic solvents. The compound is used as a source of butadiene. | 0 | Organic Chemistry |
Even though photoemission can occur from any material, it is most readily observed from metals and other conductors. This is because the process produces a charge imbalance which, if not neutralized by current flow, results in the increasing potential barrier until the emission completely ceases. The energy barrier to photoemission is usually increased by nonconductive oxide layers on metal surfaces, so most practical experiments and devices based on the photoelectric effect use clean metal surfaces in evacuated tubes. Vacuum also helps observing the electrons since it prevents gases from impeding their flow between the electrodes.
As sunlight, due to atmosphere's absorption, does not provide much ultraviolet light, the light rich in ultraviolet rays used to be obtained by burning magnesium or from an arc lamp. At the present time, mercury-vapor lamps, noble-gas discharge UV lamps and radio-frequency plasma sources, ultraviolet lasers, and synchrotron insertion device light sources prevail.
The classical setup to observe the photoelectric effect includes a light source, a set of filters to monochromatize the light, a vacuum tube transparent to ultraviolet light, an emitting electrode (E) exposed to the light, and a collector (C) whose voltage V can be externally controlled.
A positive external voltage is used to direct the photoemitted electrons onto the collector. If the frequency and the intensity of the incident radiation are fixed, the photoelectric current I increases with an increase in the positive voltage, as more and more electrons are directed onto the electrode. When no additional photoelectrons can be collected, the photoelectric current attains a saturation value. This current can only increase with the increase of the intensity of light.
An increasing negative voltage prevents all but the highest-energy electrons from reaching the collector. When no current is observed through the tube, the negative voltage has reached the value that is high enough to slow down and stop the most energetic photoelectrons of kinetic energy K. This value of the retarding voltage is called the stopping potential or cut off potential V. Since the work done by the retarding potential in stopping the electron of charge e is eV, the following must hold eV = K
The current-voltage curve is sigmoidal, but its exact shape depends on the experimental geometry and the electrode material properties.
For a given metal surface, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This frequency is called the threshold frequency. Increasing the frequency of the incident beam increases the maximum kinetic energy of the emitted photoelectrons, and the stopping voltage has to increase. The number of emitted electrons may also change because the probability that each photon results in an emitted electron is a function of photon energy.
An increase in the intensity of the same monochromatic light (so long as the intensity is not too high), which is proportional to the number of photons impinging on the surface in a given time, increases the rate at which electrons are ejected—the photoelectric current I—but the kinetic energy of the photoelectrons and the stopping voltage remain the same. For a given metal and frequency of incident radiation, the rate at which photoelectrons are ejected is directly proportional to the intensity of the incident light.
The time lag between the incidence of radiation and the emission of a photoelectron is very small, less than 10 second. Angular distribution of the photoelectrons is highly dependent on polarization (the direction of the electric field) of the incident light, as well as the emitting materials quantum properties such as atomic and molecular orbital symmetries and the electronic band structure of crystalline solids. In materials without macroscopic order, the distribution of electrons tends to peak in the direction of polarization of linearly polarized light. The experimental technique that can measure these distributions to infer the materials properties is angle-resolved photoemission spectroscopy. | 7 | Physical Chemistry |
The R/S system is an important nomenclature system for denoting enantiomers. This approach labels each chiral center R or S according to a system by which its substituents are each assigned a priority, according to the Cahn–Ingold–Prelog priority rules (CIP), based on atomic number. When the center is oriented so that the lowest-priority substituent of the four is pointed away from the viewer, the viewer will then see two possibilities: if the priority of the remaining three substituents decreases in clockwise direction, it is labeled R (for right); if it decreases in counterclockwise direction, it is S (for left).
(R) or (S) is written in italics and parentheses. If there are multiple chiral carbons, e.g. (1R,4S), a number specifies the location of the carbon preceding each configuration.
The R/S system also has no fixed relation to the system. For example, the side-chain one of serine contains a hydroxyl group, −OH. If a thiol group, −SH, were swapped in for it, the labeling would, by its definition, not be affected by the substitution. But this substitution would invert the molecules R/S labeling, because the CIP priority of CHOH is lower than that for COH but the CIP priority of CHSH is higher than that for COH. For this reason, the system remains in common use in certain areas of biochemistry, such as amino acid and carbohydrate chemistry, because it is convenient to have the same chiral label for the commonly occurring structures of a given type of structure in higher organisms. In the system, nearly all naturally occurring amino acids are all , while naturally occurring carbohydrates are nearly all . All proteinogenic amino acids are S, except for cysteine, which is R'. | 4 | Stereochemistry |
Based on the functions of the cytokine, the IL-10 family can be separated into three subfamily groups. IL-10 subfamily cytokine selects the innate and adaptive immune response and can prevent the function to reduce tissue damage. The IL-20 subfamily of cytokine works on tissues in the stroma and epithelial cells to bring out the mechanism of innate defense that manages the attack of extracellular pathogens. The IL-28 subfamily of cytokine are type III interferon (IFN) family. This subfamily share intersecting biology and signaling pathways with type I IFN family cytokines but the difference is that the type III INF family cytokines prefer to target the tissues of the epithelial cell. | 1 | Biochemistry |
A hydrophilic molecule or portion of a molecule is one whose interactions with water and other polar substances are more thermodynamically favorable than their interactions with oil or other hydrophobic solvents. They are typically charge-polarized and capable of hydrogen bonding. This makes these molecules soluble not only in water but also in other polar solvents.
Hydrophilic molecules (and portions of molecules) can be contrasted with hydrophobic molecules (and portions of molecules). In some cases, both hydrophilic and hydrophobic properties occur in a single molecule. An example of these amphiphilic molecules is the lipids that comprise the cell membrane. Another example is soap, which has a hydrophilic head and a hydrophobic tail, allowing it to dissolve in both water and oil.
Hydrophilic and hydrophobic molecules are also known as polar molecules and nonpolar molecules, respectively. Some hydrophilic substances do not dissolve. This type of mixture is called a colloid.
An approximate rule of thumb for hydrophilicity of organic compounds is that solubility of a molecule in water is more than 1 mass % if there is at least one neutral hydrophile group per 5 carbons, or at least one electrically charged hydrophile group per 7 carbons.
Hydrophilic substances (ex: salts) can seem to attract water out of the air. Sugar is also hydrophilic, and like salt is sometimes used to draw water out of foods. Sugar sprinkled on cut fruit will "draw out the water" through hydrophilia, making the fruit mushy and wet, as in a common strawberry compote recipe. | 6 | Supramolecular Chemistry |
Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase chain reaction (PCR). It is primarily used to measure the amount of a specific RNA. This is achieved by monitoring the amplification reaction using fluorescence, a technique called real-time PCR or quantitative PCR (qPCR). Confusion can arise because some authors use the acronym RT-PCR to denote real-time PCR. In this article, RT-PCR will denote Reverse Transcription PCR. Combined RT-PCR and qPCR are routinely used for analysis of gene expression and quantification of viral RNA in research and clinical settings.
The close association between RT-PCR and qPCR has led to metonymic use of the term qPCR to mean RT-PCR. Such use may be confusing, as RT-PCR can be used without qPCR, for example to enable molecular cloning, sequencing or simple detection of RNA. Conversely, qPCR may be used without RT-PCR, for example to quantify the copy number of a specific piece of DNA. | 1 | Biochemistry |
The mechanism of action of armodafinil is unknown. Armodafinil (R-(−)-modafinil) has pharmacological properties almost identical to those of modafinil (a mixture of R-(−)- and (S)-(+)-modafinil). The (R)- and (S)-enantiomers have similar pharmacological action in animals. Armodafinil has wake-promoting actions similar to sympathomimetic agents including amphetamine and methylphenidate, although its pharmacologic profile is not identical to that of the sympathomimetic amines. Armodafinil is an indirect dopamine receptor agonist; it binds in vitro to the dopamine transporter (DAT) and inhibits dopamine reuptake. For modafinil, this activity has been associated in vivo with increased extracellular dopamine levels. In genetically engineered mice lacking the dopamine transporter, modafinil lacked wake-promoting activity, suggesting that this activity was DAT-dependent. However, the wake-promoting effects of modafinil, unlike those of amphetamine, were not antagonized by the dopamine receptor antagonist haloperidol in rats. In addition, alpha-methyl-p-tyrosine, an inhibitor of dopamine synthesis, blocks the action of amphetamine but does not block locomotor activity induced by modafinil.
In addition to its wake-promoting effects and ability to increase locomotor activity in animals, according to Nuvigil prescribing information from manufacturer Cephalon, armodafinil produces psychoactive and euphoric effects, alterations in mood, perception, thinking, and feelings typical of other central nervous system (CNS) stimulants in humans. Armodafinil, like racemic modafinil, may also possess reinforcing properties, as evidenced by its self-administration in monkeys previously trained to administer cocaine; armodafinil was also partially discriminated as stimulant-like. A Cephalon-founded study in which patients were administered modafinil, methylphenidate, and a placebo found that modafinil produces "psychoactive and euphoric effects and feelings consistent with [methylphenidate]." | 4 | Stereochemistry |
Phosphonium ylides are used in the Wittig reaction, a method used to convert ketones and especially aldehydes to alkenes. The positive charge in these Wittig reagents is carried by a phosphorus atom with three phenyl substituents and a bond to a carbanion. Ylides can be stabilised or non-stabilised. A phosphonium ylide can be prepared rather straightforwardly. Typically, triphenylphosphine is allowed to react with an alkyl halide in a mechanism analogous to that of an S2 reaction. This quaternization forms an alkyltriphenylphosphonium salt, which can be isolated or treated in situ with a strong base (in this case, butyllithium) to form the ylide.
Due to the S2 mechanism, a less sterically hindered alkyl halide reacts more favorably with triphenylphosphine than an alkyl halide with significant steric hindrance (such as tert-butyl bromide). Because of this, there will typically be one synthetic route in a synthesis involving such compounds that is more favorable than another.
Phosphorus ylides are important reagents in organic chemistry, especially in the synthesis of naturally occurring products with
biological and pharmacological activities. Much of the interest in the coordination properties of a-keto stabilized phosphorus
ylides stems from their coordination versatility due to the presence of different functional groups in their molecular structure. | 0 | Organic Chemistry |
Bases (e.g. sodium bicarbonate) or acids (e.g. citric acid) are sometimes used as cutting agents. An individual base solution and acid solution can help determine if the substance contains an acid or base respectively, if an acid–base reaction will occur. | 3 | Analytical Chemistry |
Classical thermodynamics considers three main kinds of thermodynamic processes: (1) changes in a system, (2) cycles in a system, and (3) flow processes.
(1) A Thermodynamic process is a process in which the thermodynamic state of a system is changed. A change in a system is defined by a passage from an initial to a final state of thermodynamic equilibrium. In classical thermodynamics, the actual course of the process is not the primary concern, and often is ignored. A state of thermodynamic equilibrium endures unchangingly unless it is interrupted by a thermodynamic operation that initiates a thermodynamic process. The equilibrium states are each respectively fully specified by a suitable set of thermodynamic state variables, that depend only on the current state of the system, not on the path taken by the processes that produce the state. In general, during the actual course of a thermodynamic process, the system may pass through physical states which are not describable as thermodynamic states, because they are far from internal thermodynamic equilibrium. Non-equilibrium thermodynamics, however, considers processes in which the states of the system are close to thermodynamic equilibrium, and aims to describe the continuous passage along the path, at definite rates of progress.
As a useful theoretical but not actually physically realizable limiting case, a process may be imagined to take place practically infinitely slowly or smoothly enough to allow it to be described by a continuous path of equilibrium thermodynamic states, when it is called a "quasi-static" process. This is a theoretical exercise in differential geometry, as opposed to a description of an actually possible physical process; in this idealized case, the calculation may be exact.
A really possible or actual thermodynamic process, considered closely, involves friction. This contrasts with theoretically idealized, imagined, or limiting, but not actually possible, quasi-static processes which may occur with a theoretical slowness that avoids friction. It also contrasts with idealized frictionless processes in the surroundings, which may be thought of as including purely mechanical systems; this difference comes close to defining a thermodynamic process.
(2) A cyclic process carries the system through a cycle of stages, starting and being completed in some particular state. The descriptions of the staged states of the system are not the primary concern. The primary concern is the sums of matter and energy inputs and outputs to the cycle. Cyclic processes were important conceptual devices in the early days of thermodynamical investigation, while the concept of the thermodynamic state variable was being developed.
(3) Defined by flows through a system, a flow process is a steady state of flows into and out of a vessel with definite wall properties. The internal state of the vessel contents is not the primary concern. The quantities of primary concern describe the states of the inflow and the outflow materials, and, on the side, the transfers of heat, work, and kinetic and potential energies for the vessel. Flow processes are of interest in engineering. | 7 | Physical Chemistry |
The full stack for DNA computing looks very similar to a traditional computer architecture. At the highest level, a C-like general purpose programming language is expressed using a set of chemical reaction networks (CRNs). This intermediate representation gets translated to domain-level DNA design and then implemented using a set of DNA strands. In 2010, [http://www.dna.caltech.edu/~winfree/ Erik Winfrees group] showed that DNA can be used as a substrate to implement arbitrary chemical reactions. This opened the way to design and synthesis of biochemical controllers since the expressive power of CRNs is equivalent to a Turing machine. Such controllers can potentially be used in vivo' for applications such as preventing hormonal imbalance. | 1 | Biochemistry |
Two GGPP molecules condense via phytoene synthase (PSY), forming the 15-cis isomer of phytoene. PSY belongs to the squalene/phytoene synthase family and is homologous to squalene synthase that takes part in steroid biosynthesis. The subsequent conversion of phytoene into all-trans-lycopene depends on the organism. Bacteria and fungi employ a single enzyme, the bacterial phytoene desaturase (CRTI) for the catalysis. Plants and cyanobacteria however utilize four enzymes for this process. The first of these enzymes is a plant-type phytoene desaturase which introduces two additional double bonds into 15-cis-phytoene by dehydrogenation and isomerizes two of its existing double bonds from trans to cis producing 9,15,9’-tri-cis-ζ-carotene. The central double bond of this tri-cis-ζ-carotene is isomerized by the zeta-carotene isomerase Z-ISO and the resulting 9,9'-di-cis-ζ-carotene is dehydrogenated again via a ζ-carotene desaturase (ZDS). This again introduces two double bonds, resulting in 7,9,7’,9’-tetra-cis-lycopene. CRTISO, a carotenoid isomerase, is needed to convert the cis-lycopene into an all-trans lycopene in the presence of reduced FAD.
This all-trans lycopene is cyclized; cyclization gives rise to carotenoid diversity, which can be distinguished based on the end groups. There can be either a beta ring or an epsilon ring, each generated by a different enzyme (lycopene beta-cyclase [beta-LCY] or lycopene epsilon-cyclase [epsilon-LCY]). α-Carotene is produced when the all-trans lycopene first undergoes reaction with epsilon-LCY then a second reaction with beta-LCY; whereas β-carotene is produced by two reactions with beta-LCY. α- and β-Carotene are the most common carotenoids in the plant photosystems but they can still be further converted into xanthophylls by using beta-hydrolase and epsilon-hydrolase, leading to a variety of xanthophylls. | 5 | Photochemistry |
Electrochemical kinetics is the field of electrochemistry that studies the rate of electrochemical processes. This includes the study of how process conditions, such as concentration and electric potential, influence the rate of oxidation and reduction (redox) reactions that occur at the surface of an electrode, as well as an investigation into electrochemical reaction mechanisms. Two accompanying processes are involved in the electrochemical reaction and influence the overall reaction rate:
* electron transfer at the interface between the electrode and the electrolyte
* transport of the redox species from the interior of the solution to the surface of the electrode; the transport can occur by diffusion, convection and migration.
Contributors to this field include Alexander Frumkin, John Alfred Valentine Butler, Max Volmer, and Julius Tafel. | 7 | Physical Chemistry |
The natural bite angle (β) of diphosphines, obtained using molecular mechanics calculations, is defined as the preferred chelation angle determined only by ligand backbone and not by metal valence angles (Figure 3).
Both steric bite angle effect and the electronic bite angle effects are recognized. The steric bite angle effect involves the steric interactions between ligands or between a ligand and a substrate. The electronic bite angle effect, on the other hand, relates to the electronic changes that occur when the bite angle is modified. This effect is sensitive to the hybridization of metal orbitals. This flexibility range accounts for the diverse conformations of the ligand with energies slightly above the strain energy of the natural bite angle.
The bite angle of a diphosphine ligand also indicates the distortion from the ideal geometry of a complex based on VSEPR models. Octahedral and square planar complexes prefer angles near 90° while tetrahedral complexes prefer angles near 110°. Since catalysts often interconvert between various geometries, the rigidity of the chelate ring can be decisive. A bidentate phosphine with a natural bite angle of 120° may preferentially occupy two equatorial sites in a trigonal bipyramidal complex whereas a bidentate phosphine with a natural bite angle of 90° may preferentially occupy apical-equatorial positions. Diphosphine ligands with bite angles of over 120° are obtained using a bulky, stiff diphosphine backbones. Diphosphines of wide bite angles are used in some industrial processes. | 0 | Organic Chemistry |
Fluoroform, or trifluoromethane, is the chemical compound with the formula . It is a hydrofluorocarbon as well as being apart of the haloforms, a class of compounds with the formula (X = halogen) with C symmetry. Fluoroform is used in diverse applications in organic synthesis. It is not an ozone depleter but is a greenhouse gas. | 2 | Environmental Chemistry |
There are disadvantages to GPC, however. First, there is a limited number of peaks that can be resolved within the short time scale of the GPC run. Also, as a technique GPC requires around at least a 10% difference in molecular weight for a reasonable resolution of peaks to occur. In regards to polymers, the molecular masses of most of the chains will be too close for the GPC separation to show anything more than broad peaks. Another disadvantage of GPC for polymers is that filtrations must be performed before using the instrument to prevent dust and other particulates from ruining the columns and interfering with the detectors. Although useful for protecting the instrument, there is the possibility of the pre-filtration of the sample removing higher molecular weight sample before it can be loaded on the column. Another possibility to overcome these issues is the separation by field-flow fractionation (FFF). | 3 | Analytical Chemistry |
This is the earliest theory specifically for grain boundaries, in which McLean uses a model of P solute atoms distributed at random amongst N lattice sites and p solute atoms distributed at random amongst n independent grain boundary sites. The total free energy due to the solute atoms is then:
where E and e are energies of the solute atom in the lattice and in the grain boundary, respectively and the kln term represents the configurational entropy of the arrangement of the solute atoms in the bulk and grain boundary. McLean used basic statistical mechanics to find the fractional monolayer of segregant, , at which the system energy was minimized (at the equilibrium state), differentiating G with respect to p, noting that the sum of p and P is constant. Here the grain boundary analogue of Langmuir adsorption at free surfaces becomes:
Here, is the fraction of the grain boundary monolayer available for segregated atoms at saturation, is the actual fraction covered with segregant, is the bulk solute molar fraction, and is the free energy of segregation per mole of solute.
Values of were estimated by McLean using the elastic strain energy, , released by the segregation of solute atoms. The solute atom is represented by an elastic sphere fitted into a spherical hole in an elastic matrix continuum. The elastic energy associated with the solute atom is given by:
where is the solute bulk modulus, is the matrix shear modulus, and and are the atomic radii of the matrix and impurity atoms, respectively. This method gives values correct to within a factor of two (as compared with experimental data for grain boundary segregation), but a greater accuracy is obtained using the method of Seah and Hondros, described in the following section. | 7 | Physical Chemistry |
The coffee-ring pattern is detrimental when uniform application of a dried deposit is required, such as in printed electronics. It can be suppressed by adding elongated particles, such as cellulose fibers, to the spherical particles that cause the coffee-ring effect. The size and weight fraction of added particles may be smaller than those of the primary ones.
It is also reported that controlling flow inside a droplet is a powerful way to generate a uniform film; for example, by harnessing solutal Marangoni flows occurring during evaporation.
Mixtures of low boiling point and high boiling point solvents were shown to suppress the coffee ring effect, changing the shape of a deposited solute from a ring-like to a dot-like shape.
Control of the substrate temperature was shown to be an effective way to suppress the coffee ring formed by droplets of water-based PEDOT:PSS solution. On a heated hydrophilic or hydrophobic substrate, a thinner ring with an inner deposit forms, which is attributed to Marangoni convection.
Control of the substrate wetting properties on slippery surfaces can prevent the pinning of the drop contact line, which will, therefore, suppress the coffee ring effect by reducing the number of particles deposited at the contact line. Drops on superhydrophobic or liquid impregnated surfaces are less likely to have a pinned contact line and will suppress ring formation. Drops with an oil ring formed at the drop contact line have high mobility and can avoid the ring formation on hydrophobic surfaces.
Alternating voltage electrowetting may suppress coffee stains without the need to add surface-active materials. Reverse particle motion may also reduce the coffee-ring effect because of the capillary force near the contact line. The reversal takes place when the capillary force prevails over the outward coffee-ring flow by the geometric constraints. | 7 | Physical Chemistry |
Deprotonation of sulfonium and oxosulfonium salts affords ylides, of structure RS−C−R′ and RS(O)−C−R′. While sulfonium ylides, for instance in the Johnson–Corey–Chaykovsky reaction used to synthesize epoxides, are sometimes drawn with a C=S double bond, e.g., RS=CR′, the ylidic carbon–sulfur bond is highly polarized and is better described as being ionic. Sulfonium ylides are key intermediates in the synthetically useful Stevens rearrangement. Thiocarbonyl ylides (RR′C=S−C−RR′) can form by ring-opening of thiiranes, photocyclization of aryl vinyl sulfides, as well as by other processes. | 9 | Geochemistry |
In metallurgy, a shape-memory alloy (SMA) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It is also known in other names such as memory metal, memory alloy, smart metal, smart alloy, and muscle wire. The "memorized geometry" can be modified by fixating the desired geometry and subjecting it to a thermal treatment, for example a wire can be taught to memorize the shape of a coil spring.
Parts made of shape-memory alloys can be lightweight, solid-state alternatives to conventional actuators such as hydraulic, pneumatic, and motor-based systems. They can also be used to make hermetic joints in metal tubing, and it can also replace a sensor-actuator closed loop to control water temperature by governing hot and cold water flow ratio. | 8 | Metallurgy |
Adenoviral E1A-associated protein of 300kDa (p300) and the CREB-binding protein (CBP) make up the next family of HATs. This family of HATs contain HAT domains that are approximately 500 residues long and contain bromodomains as well as three cysteine-histidine rich domains that help with protein interactions. These HATs are known to acetylate all of the histone subunits in the nucleosome. They also have the ability to acetylate and mediate non-histone proteins involved in transcription and are also involved in the cell-cycle, differentiation and apoptosis. | 0 | Organic Chemistry |
Singlet fission is a spin-allowed process, unique to molecular photophysics, whereby one singlet excited state is converted into two triplet states. The phenomenon has been observed in molecular crystals, aggregates, disordered thin films, and covalently-linked dimers, where the chromophores are oriented such that the electronic coupling between singlet and the double triplet states is large. Being spin allowed, the process can occur very rapidly (on a picosecond or femtosecond timescale) and out-compete radiative decay (that generally occurs on a nanosecond timescale) thereby producing two triplets with very high efficiency. The process is distinct from intersystem crossing, in that singlet fission does not involve a spin flip, but is mediated by two triplets coupled into an overall singlet. It has been proposed that singlet fission in organic photovoltaic devices could improve the photoconversion efficiencies. | 7 | Physical Chemistry |
Some azides are valuable as bioorthogonal chemical reporters, molecules that can be "clicked" to see the metabolic path it has taken inside a living system.
The antiviral drug zidovudine (AZT) contains an azido group. | 0 | Organic Chemistry |
He carried out his doctoral studies at Yale University in New Haven, Connecticut, United States, obtaining his Ph.D. in 1961 under the tutorship of Prof. F.M. Richards. He did post doctoral work with Prof. Fritz Lipmann at Rockefeller University and with Marshall Warren Nirenberg at NIH.
During the 1960s, his research was focused on protein synthesis, a field in which he made crucial contributions. In the 1970s he was a pioneer in studying the mechanism of hormonal induction of oocyte maturation. His later research is focused in two ubiquitous protein kinases, CK1 and CK2, involved in the phosphorylation of key cellular proteins.
He devoted much of his life to organizing activities for the scientific integration in Latin America especially through organizing series of training courses in molecular biology techniques, and through the creation of the Latin American Network of Biological Sciences.
In recent years, Doctor Allende has been an promoter of science education through his personal commitment in several projects, like the Science Education Inquiry Based program, funded by the University of Chile, and through his participation in the Allende-Connelly Foundation, founded by him and his wife.
Though he retired from active science in 2009, he remains a professor at the Faculty of Medicine. He was also Research Vice President of the University of Chile.
He published his autobiography in 2010. | 1 | Biochemistry |
Glucose sensing and signaling in budding yeast is similar to the mammalian system in many ways. However, there are also significant differences. Mammalian cells regulate their glucose uptake via hormones (i.e. insulin and glucagon) or intermediary metabolites. In contrast, yeast as a unicellular organism does not depend on hormones but on nutrients in the medium. The presence of glucose induces a conformational change in the membrane proteins Snf3/Rgt2 or Gpr1, and regulates expression of genes involved in glucose metabolism. | 1 | Biochemistry |
Chang et al., realized that further increase in resolution could be gained if one carefully analyzed the results of each spot detected by the CCD camera. Under the microchannel plate amplification typical in most laboratories, each such spot was 5-10 pixels in diameter. By programming a microprocessor to examine each of up to 200 spots per laser shot to determine the center of the distribution of each spot, Chang et al. were able to further increase the velocity resolution to the equivalent of one pixel out of the 256-pixel radius of the CCD chip. | 7 | Physical Chemistry |
In the process of transcription (by any polymerase), there are three main stages:
#Initiation: the construction of the RNA polymerase complex on the gene's promoter with the help of transcription factors
#Elongation: the actual transcription of the majority of the gene into a corresponding RNA sequence
#Termination: the cessation of RNA transcription and the disassembly of the RNA polymerase complex. | 1 | Biochemistry |
The MPTP was originally discovered by Haworth and Hunter in 1979 and has been found to be involved in neurodegeneration, hepatotoxicity from Reye-related agents, cardiac necrosis and nervous and muscular dystrophies among other deleterious events inducing cell damage and death.
MPT is one of the major causes of cell death in a variety of conditions. For example, it is key in neuronal cell death in excitotoxicity, in which overactivation of glutamate receptors causes excessive calcium entry into the cell. MPT also appears to play a key role in damage caused by ischemia, as occurs in a heart attack and stroke. However, research has shown that the MPT pore remains closed during ischemia, but opens once the tissues are reperfused with blood after the ischemic period, playing a role in reperfusion injury.
MPT is also thought to underlie the cell death induced by Reye's syndrome, since chemicals that can cause the syndrome, like salicylate and valproate, cause MPT. MPT may also play a role in mitochondrial autophagy. Cells exposed to toxic amounts of Ca ionophores also undergo MPT and death by necrosis. | 1 | Biochemistry |
Haifuki-ho (灰吹法; literally "ash-blowing method"), also known as Lead-silver separation method (Korean: 연은분리법; Hanja: 鉛銀分離法) is a method of silver mining developed in Joseon dynasty of Korea in the 16th century and spread to China and Feudal Japan. The industrial process involved cupellation, and was a contributing factor to the large amount of silver traditionally exported by Japan. | 8 | Metallurgy |
Amidines are much more basic than amides and are among the strongest uncharged/unionized bases.
Protonation occurs at the sp-hybridized nitrogen. This occurs because the positive charge can be delocalized onto both nitrogen atoms. The resulting cationic species is known as an amidinium ion and possesses identical C-N bond lengths. | 0 | Organic Chemistry |
Cancer-based research into co-receptors includes the investigation of growth factor activated co-receptors, such as Transforming Growth Factor (TGF-β) co-receptors. Expression of the co-receptor endoglin, which is expressed on the surface of tumor cells, is correlated with cell plasticity and the development of tumors.
Another co-receptor of TGF-β is CD8. Although the exact mechanism is still unknown, CD8 co-receptors have been shown to enhance T-cell activation and TGF-β-mediated immune suppression.
TGF-β has been shown to influence the plasticity of cells through integrin and focal adhesion kinase. The co-receptors of tumor cells and their interaction with T-cells provide important considerations for tumor immunotherapy.
Recent research into co-receptors for p75, such as the sortilin co-receptor, has implicated sortilin in connection to neurotrophins, a type of nerve growth factor.
The p75 receptor and co-receptors have been found to influence the aggressiveness of tumors, specifically via the ability of neurotrophins to rescue cells from certain forms of cell death.
Sortilin, the p75 co-receptor, has been found in natural killer cells, but with only low levels of neurotrophin receptor. The sortilin co-receptor is believed to work with a neurotrophin homologue that can also cause neurotrophin to alter the immune response. | 1 | Biochemistry |
A modern steel plant employs very few people per tonne, compared to the past. In South Korea, Posco employs 29,648 people to produce 28 million tonnes.
During the period 1974 to 1999, the steel industry had drastically reduced employment all around the world. In the US, it was down from 521,000 to 153,000. In Japan, from 459,000 to 208,000; Germany from 232,000 to 78,000; UK from 197,000 to 31,000; Brazil from 118,000 to 59,000; South Africa from 100,000 to 54,000. South Korea already had a low figure. It was only 58,000 in 1999. The steel industry had reduced its employment around the world by more than 1,500,000 in 25 years. | 8 | Metallurgy |
Eukaryotic initiation factors (eIFs) are proteins or protein complexes involved in the initiation phase of eukaryotic translation. These proteins help stabilize the formation of ribosomal preinitiation complexes around the start codon and are an important input for post-transcription gene regulation. Several initiation factors form a complex with the small 40S ribosomal subunit and Met-tRNA called the 43S preinitiation complex (43S PIC). Additional factors of the eIF4F complex (eIF4A, E, and G) recruit the 43S PIC to the five-prime cap structure of the mRNA, from which the 43S particle scans 5-->3 along the mRNA to reach an AUG start codon. Recognition of the start codon by the Met-tRNA promotes gated phosphate and eIF1 release to form the 48S preinitiation complex (48S PIC), followed by large 60S ribosomal subunit recruitment to form the 80S ribosome. There exist many more eukaryotic initiation factors than prokaryotic initiation factors, reflecting the greater biological complexity of eukaryotic translation. There are at least twelve eukaryotic initiation factors, composed of many more polypeptides, and these are described below. | 1 | Biochemistry |
Epothilone D, with the generic drug name utidelone, was approved in China in 2021 for the treatment of metastatic breast cancer. Utidelone has shown benefits in a phase III breast cancer trial when added to capecitabine.
One synthetic analog, ixabepilone, was approved in October 2007 by the United States Food and Drug Administration for use in the treatment of aggressive metastatic or locally advanced breast cancer that no longer responds to currently available chemotherapies. In November 2008, the EMEA refused a marketing authorization for ixabepilone.
Epothilone B, with the generic drug name patupilone, was proven to contain potent in vivo anticancer activities at tolerated dose levels in several human xenograft models. As a result, patupilone and various analogs underwent various clinical phases.
Patupilone and the fully synthetic sagopilone were tested in phase II trials and BMS-310705 was tested in phase I trials). Patupilone failed a phase III trial for ovarian cancer in 2010.
Results of a phase III trial with ixabepilone (BMS-247550) in combination with capecitabine in metastatic breast cancer have been announced (2007 – leading to FDA approval). | 0 | Organic Chemistry |
The limiting equivalent conductivity of solutions based on mixed solvents like water alcohol has minima depending on the nature of alcohol. For methanol the minimum is at 15 molar % water, and for the ethanol at 6 molar % water. | 7 | Physical Chemistry |
Flotation is one of the unit processes used to separate the bituminous component of oil sands as part of the process of oil extraction. Some of the bitumen is not recovered in the primary separation vessel and reports to the tailings. These tailings are typically retreated in a scavenging operation to try to recover some of the remaining bitumen.
Three industrial-size single downcomer Jameson Cells were sold by Xstrata Technology to Shell Canada in 2007 for a large scale pilot plant project and eight 500 mm downcomers were sold to Syncrude Limited in 2008. In the latter case, the downcomers were used to treat middlings in an existing tertiary oil recovery vessel in a bitumen recovery process patented by Syncrude. | 8 | Metallurgy |
Lab Tests Online (now Testing.com) is a peer-reviewed non-profit web resource about clinical laboratory testing. The site provides information on clinical lab tests as well as conditions that are managed or diagnosed by lab tests. Lab Tests Online also provides summaries of recommendations by age, feature articles on lab-related topics, and news items of patient interest. All contents are reviewed and approved by an Editorial Review Board composed of laboratory professionals before being posted to the site.
The site was launched in 2001 by the American Association for Clinical Chemistry, the scientific society for clinical laboratory science and is a collaboration with other professional societies representing the laboratory medicine community. The website is mirrored on other sites in other countries and is available via mobile apps in several countries.
In January 2021, AACC’s Lab Tests Online (labtestsonline.org) was acquired by OneCare Media. In November of 2021, LabTestsOnline.org was rebranded to Testing.com. | 1 | Biochemistry |
The nuclear cross section of a nucleus is used to describe the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger probability of interaction. The standard unit for measuring a nuclear cross section (denoted as σ) is the barn, which is equal to , or . Cross sections can be measured for all possible interaction processes together, in which case they are called total cross sections, or for specific processes, distinguishing elastic scattering and inelastic scattering; of the latter, amongst neutron cross sections the absorption cross sections are of particular interest.
In nuclear physics it is conventional to consider the impinging particles as point particles having negligible diameter. Cross sections can be computed for any nuclear process, such as capture scattering, production of neutrons, or nuclear fusion. In many cases, the number of particles emitted or scattered in nuclear processes is not measured directly; one merely measures the attenuation produced in a parallel beam of incident particles by the interposition of a known thickness of a particular material. The cross section obtained in this way is called the total cross section and is usually denoted by a σ or σ.
Typical nuclear radii are of the order 10 m. Assuming spherical shape, we therefore expect the cross sections for nuclear reactions to be of the order of or (i.e., 1 barn). Observed cross sections vary enormously: for example, slow neutrons absorbed by the (n, ) reaction show a cross section much higher than 1,000 barns in some cases (boron-10, cadmium-113, and xenon-135), while the cross sections for transmutations by gamma-ray absorption are in the region of 0.001 barn. | 7 | Physical Chemistry |
Instead of using sulfated molecules or the fairly big Buckminster fullerenes recently it became possible to synthesize crystals from the hydrocarbon picene and phenanthrene. Doping the crystal picene and phenanthrene with alkali metals such as potassium or rubidium and annealing for several days leads to superconductivity with transition temperatures up to . For AxPhenanthrene, the superconductivity is possible unconventional. Both phenanthrene and picene are called phenanthrene-edge-type polycyclic aromatic hydrocarbon. The increasing number of benzene rings results in higher T. | 0 | Organic Chemistry |
Different grains and their orientations can be observed using scanning electron microscope (SEM) techniques such as electron backscatter diffraction (EBSD) or polarized optical microscopy (POM). Samples are initially cold- or hot-rolled to introduce a high degree of dislocation density, and then deformed at different strain rates so that dynamic recrystallization occurs. The deformation may be in the form of compression, tension, or torsion. The grains elongate in the direction of applied stress and the misorientation angle of subgrain boundaries increases. | 8 | Metallurgy |
This modeling technique compares the gene sequence of an unknown protein with sequences of proteins with known structures. Depending on the degree of similarity between the sequences, the structure of the known protein can be used as a model for solving the structure of the unknown protein. Highly accurate modeling is considered to require at least 50% amino acid sequence identity between the unknown protein and the solved structure. 30-50% sequence identity gives a model of intermediate-accuracy, and sequence identity below 30% gives low-accuracy models. It has been predicted that at least 16,000 protein structures will need to be determined in order for all structural motifs to be represented at least once and thus allowing the structure of any unknown protein to be solved accurately through modeling. One disadvantage of this method, however, is that structure is more conserved than sequence and thus sequence-based modeling may not be the most accurate way to predict protein structures. | 1 | Biochemistry |
Neurogranin is a calmodulin-binding protein expressed primarily in the brain, particularly in dendritic spines, and participating in the protein kinase C signaling pathway. Neurogranin has recently been found in aortic endothelial cells and cardiomyocytes. Neurogranin is the main postsynaptic protein regulating the availability of calmodulin, binding to it in the absence of calcium. Phosphorylation by protein kinase C lowers its binding ability. NRGN gene expression is controlled by thyroid hormones. Human neurogranin consists of 78 amino acids.
One study tells of potential link of neurogranin gene to the heightened risk of schizophrenia in males, another study gives evidence of lowered neurogranin immunoreactivity in the brains of people suffering from schizophrenia.
Neurogranin concentration in cerebrospinal fluid (CSF) is further discussed as marker for synaptic dysfunction in age-related neurodegeneration. It has also been shown to be specifically increased in patients with Alzheimers disease. Especially the ratio of CSF neurogranin trunc P75 and the beta-secretase BACE1 is suggested as potential marker for cognitive deterioration in the progress of Alzheimers disease.
Prior to its identification in the bovine and rat brain in 1991, neurogranin was known as a putative protein kinase C-phosphorylated protein named p17. Human neurogranin was cloned in 1997 and turned out to be 96% identical to the rat protein. | 1 | Biochemistry |
Flow injection analysis (FIA), was introduced in 1975 by Ruzicka and Hansen, The first generation of FIA technology, termed flow injection (FI), was inspired by the AutoAnalyzer technique invented by Skeggs in early 1950s. While Skeggs' AutoAnalyzer uses air segmentation to separate a flowing stream into numerous discrete segments to establish a long train of individual samples moving through a flow channel, FIA systems separate each sample from subsequent sample with a carrier reagent. While the AutoAnalyzer mixes sample homogeneously with reagents, in all FIA techniques sample and reagents are merged to form a concentration gradient that yields analysis results.
FIA methods can be used for both fast reactions as well as slow reactions. For slow reactions, a heater is often utilized. The reaction does not need to reach completion since all samples and standards are given the same period to react. For typical assays commonly measured with FIA (e.g., nitrite, nitrate, ammonia, phosphate) it is not uncommon to have a throughput of 60-120 samples per hour.
FIA methods are limited by the amount of time necessary to obtain a measurable signal since travel time through the tubing tends to broaden peaks to the point where samples can merge with each other. As a general rule, FIA methods should not be used if an adequate signal cannot be obtained within two minutes, and preferably less than one. Reactions that need longer reaction times should be segmented. However, considering the number of FIA publications and wide variety of uses of FIA for serial assays, the "one minute" time limitation does not seem to be a serious limitation for most real life assays. Yet, assays based on slow chemical reactions have to be carried either in stopped flow mode ( SIA) or by segmenting the flow.
OI Analytical, in its gas diffusion amperometric total cyanide method, uses a segmented flow injection analysis technique that allows reaction times of up to 10 minutes by flow injection analysis.
Technicon experimented with FIA long before it was championed by Ruzicka and Hansen. Andres Ferrari reported that analysis was possible without bubbles if flow rates were increased and tubing diameters decreased. In fact, Skegg's first attempts at the auto analyzer did not segment. Technicon chose to not pursue FIA because it increased reagent consumption and the cost of analysis.
The second generation of the FIA technique, called sequential injection analysis (SIA), was conceived in 1990 by Ruzicka and Marshal, and has been further developed and miniaturized over the course of the following decade. It uses flow programming instead of the continuous flow regime (as used by CFA and FIA), that allows the flow rate and flow direction to be tailored to the need of individual steps of analytical protocol. Reactants are mixed by flow reversals and a measurement is carried out while the reaction mixture is arrested within the detector by stopping the flow. Microminiaturized chromatography is carried out on microcolumns that are automatically renewed by microfluidic manipulations. The discrete pumping and metering of microliter sample and reagent volumes used in SI only generates waste per each sample injection. The enormous volume of FI and SI literature documents the versatility of FI and SI and their usefulness for routine assays (in soil, water, environmental, biochemical and biotechnological assays) has demonstrated their potential to be used as a versatile research tool. | 3 | Analytical Chemistry |
Numerous compounds adopt this geometry, examples being especially numerous for transition metal complexes. The noble gas compound xenon tetrafluoride adopts this structure as predicted by VSEPR theory. The geometry is prevalent for transition metal complexes with d configuration, which includes Rh(I), Ir(I), Pd(II), Pt(II), and Au(III). Notable examples include the anticancer drugs cisplatin, [PtCl(NH)], and carboplatin. Many homogeneous catalysts are square planar in their resting state, such as Wilkinsons catalyst and Crabtrees catalyst. Other examples include Vaskas complex and Zeises salt. Certain ligands (such as porphyrins) stabilize this geometry. | 4 | Stereochemistry |
Vaporization (from liquid to gas) is divided into two types: vaporization on the surface of the liquid is called evaporation, and vaporization at the boiling point with formation of bubbles in the interior of the liquid is called boiling. However there is no such distinction for the solid-to-gas transition, which is always called sublimation in both corresponding cases. | 3 | Analytical Chemistry |
The study of vitriols (hydrated sulfates of various metals forming glassy minerals from which sulfuric acid can be derived) began in ancient times. Sumerians had a list of types of vitriol that they classified according to the substances color. Some of the earliest discussions on the origin and properties of vitriol is in the works of the Greek physician Dioscorides (first century AD) and the Roman naturalist Pliny the Elder (23–79 AD). Galen also discussed its medical use. Metallurgical uses for vitriolic substances were recorded in the Hellenistic alchemical works of Zosimos of Panopolis, in the treatise Phisica et Mystica', and the Leyden papyrus X. | 7 | Physical Chemistry |
The first sperm banks began as early as 1964 in Iowa, USA and Tokyo, Japan and were established for a medical therapeutic approach to support individuals who were infertile. As a result, over 1 million babies were born within 40 years.
Sperm banks provide the opportunity for individuals to have a child who otherwise would not be able to conceive naturally. This includes, but is not limited to, single women, same-sexed couples, and couples where one partner is infertile.
Where a sperm bank provides fertility services directly to a recipient woman, it may employ different methods of fertilization using donor sperm in order to optimize the chances of a pregnancy. Sperm banks do not provide a cure for infertility in individuals who produce non-viable sperm. Nevertheless, the increasing range of services available through sperm banks enables people to have choices over challenges with reproduction.
Individuals may choose an anonymous donor who will not be a part of family life, or they may choose known donors who may be contacted later in life by the donor children. People may choose to use a surrogate to bear their children, using eggs provided by the person and sperm from a donor. Sperm banks often provide services which enable an individual to have subsequent pregnancies by the same donor, but equally, people may choose to have children by a number of different donors. Sperm banks sometimes enable an individual to choose the sex of their child, enabling even greater control over the way families are planned. Sperm banks increasingly adopt a less formal approach to the provision of their services thereby enabling people to take a relaxed approach to their own individual requirements.
Men who donate semen through a sperm bank provide an opportunity for others who cannot have children on their own. Sperm donors may or may not have legal obligations or responsibilities to the child conceived through this route. Whether a donor is anonymous or not, this factor is important in allowing sperm banks to recruit sperm donors and to use their sperm to produce whatever number of pregnancies from each donor as are permitted where they operate, or alternatively, whatever number they decide.
In many parts of the world sperm banks are not allowed to be established or to operate. Where sperm banks are allowed to operate they are often controlled by local legislation which is primarily intended to protect the unborn child, but which may also provide a compromise between the conflicting views which surround their operation. A particular example of this is the control which is often placed on the number of children which a single donor may father and which may be designed to protect against consanguinity. However, such legislation usually cannot prevent a sperm bank from supplying donor sperm outside the jurisdiction in which it operates, and neither can it prevent sperm donors from donating elsewhere during their lives. There is an acute shortage of sperm donors in many parts of the world and there is obvious pressure from many quarters for donor sperm from those willing and able to provide it to be made available as safely and as freely as possible. | 1 | Biochemistry |
Grev Brook; Bill Bowyer; David Davies; Mike Dewey; Bill Flavell; Philipp Gross; Eddie Sugars; GI Williams | 8 | Metallurgy |
N-philes are group of radical molecules which are specifically attracted to the C=N bonds, defying often the selectivity rules of electrophilic attack. N-philes can often masquerade as electrophiles, where acyl radicals are excellent examples which interact with pi electrons of aryl groups. | 0 | Organic Chemistry |
Epoxidation with dioxiranes refers to the synthesis of epoxides from alkenes using three-membered cyclic peroxides, also known as dioxiranes.
Dioxiranes are three-membered cyclic peroxides containing a weak oxygen-oxygen bond. Although they are able to effect oxidations of heteroatom functionality and even carbon-hydrogen bonds, they are most widely used as epoxidizing agents of alkenes. Dioxiranes are electrophilic oxidants that react more quickly with electron-rich than electron-poor double bonds; however, both classes of substrates can be epoxidized within a reasonable time frame. Dioxiranes may be prepared and isolated or generated in situ from ketones and potassium peroxymonosulfate (Oxone). In situ preparations may be catalytic in ketone, and if the ketone is chiral, enantioselective epoxidation takes place. The functional group compatibility of dioxiranes is limited somewhat, as side oxidations of amines and sulfides are rapid. Nonetheless, protocols for dioxirane oxidations are entirely metal free. The most common dioxiranes employed for synthesis are dimethyl dioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD). | 0 | Organic Chemistry |
In 1857 Rudolf Clasius published The Nature of the Motion which We Call Heat. In it he derived the relation for the pressure, , in a gas with particles per unit volume (number density), mass , and mean square speed . He then noted that using the classical laws of Boyle and Charles one could write with a constant of proportionality. Hence temperature was proportional to the average kinetic energy of the particles. This article inspired further work based on the twin ideas that substances are composed of indivisible particles, and that heat is a consequence of the particle motion as governed by Newton's laws. The work, known as the kinetic theory of gases, was done principally by James Clerk Maxwell, and Ludwig Boltzmann. At about the same time J. Willard Gibbs also contributed, and advanced it by converting it into statistical mechanics.
This environment influenced Johannes Diderik van der Waals. After initially pursuing a teaching credential, he was accepted for doctoral studies at the University of Leiden under Pieter Rijke. This led, in 1873, to a dissertation that provided a simple, particle based, equation that described the gas–liquid change of state, the origin of a critical temperature, and the concept of corresponding states. The equation is based on two premises, first that fluids are composed of particles with non-zero volumes, and second that at a large enough distance each particle exerts an attractive force on all other particles in its vicinity. These forces were called by Boltzmann van der Waals cohesive forces.
In 1869 Irish professor of chemistry Thomas Andrews at Queens University Belfast in a paper entitled On the Continuity of the Gaseous and Liquid States of Matter', displayed an experimentally obtained set of isotherms of carbonic acid, HCO, that showed at low temperatures a jump in density at a certain pressure, while at higher temperatures there was no abrupt change; the figure can be seen here. Andrews called the isotherm at which the jump just disappeared the critical point. Given the similarity of the titles of this paper and van der Waals subsequent thesis one might think that van der Waals set out to develop a theoretical explanation of Andrews experiments. However the opposite is true, van der Waals began work by trying to determine a mollecular attraction that appeared in Laplaces theory of capillarity, and only after establishing his equation tested it using Andrews results.
By 1877 sprays of both liquid oxygen and liquid nitrogen had been produced, and a new field of research, low temperature physics, had been opened. The van der Waals equation played a part in all this especially with respect to the liquefaction of hydrogen and helium which was finally achieved in 1908. From measurements of and in two states with the same density, the van der Waals equation produces the values and . Thus from two such measurements of pressure and temperature one could determine and , and from these values calculate the expected critical pressure, temperature, and molar volume. Goodstein summarized this contribution of the van der Waals equation as follows:
Van der Waals was awarded the Nobel Prize in 1910, in recognition of the contribution of his formulation of this "equation of state for gases and liquids".
As noted previously, modern day studies of first order phase changes make use of the van der Waals equation together with the Gibbs criterion, equal chemical potential of each phase, as a model of the phenomenon. This model has an analytic coexistence (saturation) curve expressed parametrically, , that was first obtained by Plank, known to Gibbs, and later derived in a beautifully simple and elegant manner by Lekner. A summary of Lekner's solution is presented in a subsequent section, and a more complete discussion in the Maxwell construction. | 7 | Physical Chemistry |
Catalytic resonance theory is constructed on the Sabatier principle of catalysis developed by French chemistry Paul Sabatier. In the limit of maximum catalytic performance, the surface of a catalyst is neither too strong nor too weak. Strong binding results in an overall catalytic reaction rate limitation due to product desorption, while weak binding catalysts are limited in the rate of surface chemistry. Optimal catalyst performance is depicted as a volcano peak using a descriptor of the chemical reaction defining different catalytic materials. Experimental evidence of the Sabatier principle was first demonstrated by Balandin in 1960.
The concept of catalytic resonance was proposed on dynamic interpretation of the Sabatier volcano reaction plot. As described, extension of either side of the volcano plot above the peak defines the timescales of the two rate-limiting phenomena such as surface reaction(s) or desorption. For binding energy oscillation amplitudes that extend across the volcano peak, the amplitude endpoints intersect the transiently accessible faster timescales of independent reaction phenomena. At the conditions of sufficiently fast binding energy oscillation, the transient binding energy variation frequency matches the natural frequencies of the reaction and the rate of overall reaction achieves turnover frequencies greatly in excess of the volcano plot peak. | 7 | Physical Chemistry |
The LE cell was discovered in bone marrow in 1948 by Hargraves et al. In 1957 Holborow et al. first demonstrated ANA using indirect immunofluorescence. This was the first indication that processes affecting the cell nucleus were responsible for SLE. In 1959 it was discovered that serum from individuals with SLE contained antibodies that precipitated with saline extracts of nuclei, known as extractable nuclear antigens (ENAs). This led to the characterisation of ENA antigens and their respective antibodies. Thus, anti-Sm and anti-RNP antibodies were discovered in 1966 and 1971, respectively. In the 1970s, the anti-Ro/anti-SS-A and anti-La/anti-SS-B antibodies were discovered. The Scl-70 antibody was known to be a specific antibody to scleroderma in 1979, however the antigen (topoisomerase-I) was not characterised until 1986. The Jo-1 antigen and antibody were characterised in 1980. | 1 | Biochemistry |
To make equations of the previous section applicable to the states belonging to the continuum spectrum, they should be rewritten in terms of matrix elements of the momentum . In absence of magnetic field, the Hamiltonian can be written as , and calculating a commutator in the basis of eigenfunctions of results in the relation between matrix elements
Next, calculating matrix elements of a commutator in the same basis and eliminating matrix elements of , we arrive at
Because , the above expression results in a sum rule
where are oscillator strengths for quantum transitions between the states and . This is the Thomas-Reiche-Kuhn sum rule, and the term with has been omitted because in confined systems such as atoms or molecules the diagonal matrix element due to the time inversion symmetry of the Hamiltonian . Excluding this term eliminates divergency because of the vanishing denominator. | 7 | Physical Chemistry |
# The Grunwald–Winstein equation cannot fit all data for different kinds of solvent mixtures. The combinations are limited to certain systems and only to nucleophilic solvents.
# For many reactions and nucleophilic solvent systems, the relationships are not fully linear. This derives from the growing S2 reaction character within the mechanism. | 7 | Physical Chemistry |
In August 2018, scientists announced new observations regarding the rapid transformation of fluid deuterium from an insulating to a metallic form below 2000 K. Remarkable agreement is found between the experimental data and the predictions based on quantum Monte Carlo simulations, which is expected to be the most accurate method to date. This may help researchers better understand giant gas planets, such as Jupiter, Saturn and related exoplanets, since such planets are thought to contain a lot of liquid metallic hydrogen, which may be responsible for their observed powerful magnetic fields. | 7 | Physical Chemistry |
On October 4, 2010, the Ajka alumina plant in Hungary had an incident where the western dam of its red mud reservoir collapsed. The reservoir was filled with 700,000 m of a mixture of red mud and water with a pH of 12. The mixture was released into the valley of Torna river and flooded parts of the city of Devecser and the villages of Kolontár and Somlóvásárhely. The incident resulted in 10 deaths, more than a hundred injuries, and contamination in lakes and rivers. | 8 | Metallurgy |
Biomarkers validated by genetic and molecular biology methods can be classified into three types.
* Type 0 — Natural history markers
* Type 1 — Drug activity markers
* Type 2 — Surrogate markers | 1 | Biochemistry |
Cram and Reetz demonstrated that 1,3-stereocontrol is possible if the reaction proceeds through an acyclic transition state. The reaction of β-alkoxy aldehyde with allyltrimethylsilane showed good selectivity for the anti-1,3-diol, which was explained by the Cram polar model. The polar benzyloxy group is oriented anti to the carbonyl to minimize dipole interactions and the nucleophile attacks anti- to the bulkier (R) of the remaining two substituents. | 4 | Stereochemistry |
Silicon in nature is typically bonded to oxygen, in a tetravalent oxidation state. The major forms of solid Si are silicate minerals and amorphous silica, whereas in aqueous solutions the dominant forms are orthosilicic acid and its dissociated species. There are three stable isotopes of Si, associated with the following mean natural abundances: Si– 92.23%, Si– 4.67%, and Si– 3.10%. The isotopic composition of Si is often formulated by the delta notation, as the following:
The reference material (standard) for defining the δSi of a sample is the National Bureau of Standards (NBS) 28 Sand Quartz, which has been certified and distributed by the National Institute of Standards and Technology (NIST), and is also named NIST RM 8546. Currently, there are four main analytical methods for the measurement of Si isotopes: Gas Source Isotope-Ratio Mass Spectrometry (GC-IRMS), Secondary Ion Mass Spectrometry (SIMS), Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC–IPC–MS), and Laser Ablation MC–ICP–MS. | 9 | Geochemistry |
Azines are a functional class of organic compounds with the connectivity RRC=N-N=CRR. These compounds are the product of the condensation of hydrazine with ketones and aldehydes, although in practice they are often made by alternative routes. Ketazines are azines derived from ketones. For example, acetone azine is the simplest ketazine. Aldazines are azines derived from aldehydes. | 0 | Organic Chemistry |
Using multi-spectral imaging it is possible to read illegible papyrus, such as the burned papyri of the Villa of the Papyri or of Oxyrhynchus, or the Archimedes palimpsest. The technique involves taking pictures of the illegible document using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion can be found for distinguishing ink from paper on the papyrus surface.
Simple NUV sources can be used to highlight faded iron-based ink on vellum. | 5 | Photochemistry |
The nonradiative process for heat generation of organic PTAs is different from that of inorganic PTAs such as metals and semiconductors which is related with surface plasmon resonance. As shown in the figure, conjugated polymers are first activated to the excited state (S1) under light irradiation and then excited state (S1) decays back to the ground state (S0) via three processes: (I) emitting a photon (fluorescence), (II) intersystem crossing, and (III) nonradiative relaxation (heat generation). Because these three pathways of the S1 decaying back to the S0 are usually competitive in photosensitive materials, light emitting and intersystem crossing must be efficiently reduced in order to increase the heat generation and improve the photothermal conversion efficiency. For conjugated polymers, on the one hand, their unique structures lead to closed stacking of the molecular sensitizers with highly frequent intermolecular collisions which can efficiently quench the fluorescence and intersystem crossing, and thus enhance the yield of nonradiative relaxation. On the other hand, compared with monomeric phototherapeutic molecules, conjugated polymers possess higher stability in vivo against disassembly and photobleaching, longer blood circulation time, and more accumulation at tumor site due to the enhanced permeability and retention (EPR) effect. Therefore, conjugated polymers have high photothermal conversion efficiency and a large amount of heat generation. One of the most widely used equations to calculate photothermal conversion efficiency (η) of organic PTAs is as follows:
η = (hAΔΤ-Qs)/I(1-10)
where h is the heat transfer coefficient, A is the container surface area, ΔΤ means the maximum temperature change in the solution, A means the light absorbance, I is the laser power density, and Qs is the heat associated with the light absorbance of the solvent.
Furthermore, various efficient methods, especially donor-acceptor (D-A) strategy, have been designed to enhance the photothermal conversion efficiency and heat generation of conjugated polymers. The D-A assembly system in the conjugated polymers contributes to strong intermolecular electron transfer from the donor to the acceptor, thus bringing efficient fluorescence and intersystem crossing quenching, and improved heat generation. In addition, the HOMO-LUMO gap of the D−A conjugated polymers can be easily tuned through changing the selection of electron donor (ED) and electron acceptor (EA) moieties, and thus D−A structured polymers with extremely low band gap can be developed to improve the NIR absorption and photothermal conversion efficiency of CPs. | 5 | Photochemistry |
Moroidin has shown to have anti-mitotic properties, chiefly by inhibiting the polymerization of tubulin. Tubulin protein polymers are the major component of microtubules. During mitosis, microtubules form the organizing structure called the mitotic apparatus, which captures, aligns, and separates chromosomes. The proper alignment and separation of chromosomes is critical to ensure that cells divide their genetic material equally between daughter cells. Failure to attach chromosomes to the mitotic apparatus activates the mitotic checkpoint, preventing cells from entering anaphase to proceed with cell division. Agents that disrupt microtubules therefore inhibit mitosis through activation of this checkpoint.
Moroidin and its related compounds, the celogentins, inhibit tubulin polymerization. Of this family, celogentin C is the most potent (IC 0.8×10 M), and it is more potent than the anti-mitotic agent vinblastine (IC 3.0×10). Moroidin has the same potency as vinblastine. Because of this biological activity, compounds in this family have potential as anti-cancer agents.
The mechanism of tubulin disruption is not known, but the degree of biological activity has been linked to the structure of the right-hand ring containing the Trp-His linkage. Moroidin and the celogentins can be divided into three groups according to structural similarity of the right-hand ring. Celogentin C, the most potent compound, has a unique right-hand ring containing a proline residue. Moroidin and its analogous celogentins all have activity comparable to that of vinblastine, and a third group of celogentins all have reduced activity. In contrast, stephanotic acid, a cyclic compound analogous only to the left-hand ring and containing the same Leu-His linkage, has no anti-mitotic activity.
Other anti-tubulin agents used as chemotherapy agents have painful side effects known as neuropathy when the drugs are exposed to tissue. Although the exact mechanism for the cause of neuropathy is unknown, it is thought to be related to the degradation of microtubules, which are essential components of neurons. | 0 | Organic Chemistry |
Supercritical fluid chromatography (SFC) is a form of normal phase chromatography that uses a supercritical fluid such as carbon dioxide as the mobile phase. It is used for the analysis and purification of low to moderate molecular weight, thermally labile molecules and can also be used for the separation of chiral compounds. Principles are similar to those of high performance liquid chromatography (HPLC); however, SFC typically utilizes carbon dioxide as the mobile phase. Therefore, the entire chromatographic flow path must be pressurized. Because the supercritical phase represents a state whereby bulk liquid and gas properties converge, supercritical fluid chromatography is sometimes called convergence chromatography. The idea of liquid and gas properties convergence was first envisioned by Giddings. | 3 | Analytical Chemistry |
The Kirkendall effect was discovered by Ernest Kirkendall and Alice Smigelskas in 1947, in the course of Kirkendalls ongoing research into diffusion in brass. The paper in which he discovered the famous effect was the third in his series of papers on brass diffusion, the first being his thesis. His second paper revealed that zinc diffused more quickly than copper in alpha-brass, which led to the research producing his revolutionary theory. Until this point, substitutional and ring methods were the dominant ideas for diffusional motion. Kirkendalls experiment produced evidence of a vacancy diffusion mechanism, which is the accepted mechanism to this day. At the time it was submitted, the paper and Kirkendalls ideas were rejected from publication by Robert Franklin Mehl, director of the Metals Research Laboratory at Carnegie Institute of Technology (now Carnegie Mellon University). Mehl refused to accept Kirkendalls evidence of this new diffusion mechanism, and denied publication for over six months, only relenting after a conference was held and several other researchers confirmed Kirkendall's results. | 8 | Metallurgy |
Diffuse clouds are of astronomical interest because they play a primary role in the evolution and thermodynamics of ISM. Observation of the abundant atomic hydrogen in 21 cm has shown good signal-to-noise ratio in both emission and absorption. Nevertheless, HI observations have a fundamental difficulty when are directed to low mass regions of the hydrogen nucleus, as the center part of a diffuse cloud: Thermal width of hydrogen lines are the same order as the internal velocities structures of interest, so clouds components of various temperatures and central velocities are indistinguishable in the spectrum. Molecular lines observations in principle doesnt suffer from these problems. Unlike HI, molecules generally have excitation temperature T , so that emission is very weak even from abundant species. CO and HO are considered to be the most easily studied candidate molecules. CO has transitions in a region of the spectrum (wavelength HO has the 18 cm emission, line convenient for absorption observations. Observation studies provide the most sensitive means of detections of molecules with sub thermal excitation, and can give the opacity of the spectral line, which is a central issue to model the molecular region.
Studies based in the kinematic comparison of HO and HI absorption lines from diffuse clouds are useful in determining their physical conditions, especially because heavier elements provide higher velocity resolution. | 2 | Environmental Chemistry |
15-Crown-5 can be synthesized using a modified Williamson ether synthesis:
:(CHOCHCHCl) + O(CHCHOH) + 2 NaOH → (CHCHO) + 2 NaCl + 2 HO
It also forms from the cyclic oligomerization of ethylene oxide in the presence of gaseous boron trifluoride. | 6 | Supramolecular Chemistry |
There are a number of ASTM analytical test methods to determine amine value. A number of states in the United States have adopted their own test methods but they are based on ASTM methods. Although there are similarities with the method it is not the same as an acid value.
* ASTM D2073 - This is a potentiometric method.
* ASTM D2074-07
* ASTM D2896 - potentiometric method with perchloric acid.
* ASTM D6979-03 | 3 | Analytical Chemistry |
Subsets and Splits