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Ionic interactions involve the attraction of ions or molecules with full permanent charges of opposite signs. For example, sodium fluoride involves the attraction of the positive charge on sodium (Na) with the negative charge on fluoride (F). However, this particular interaction is easily broken upon addition to water, or other highly polar solvents. In water ion pairing is mostly entropy driven; a single salt bridge usually amounts to an attraction value of about ΔG =5 kJ/mol at an intermediate ion strength I, at I close to zero the value increases to about 8 kJ/mol. The ΔG values are usually additive and largely independent of the nature of the participating ions, except for transition metal ions etc.
These interactions can also be seen in molecules with a localized charge on a particular atom. For example, the full negative charge associated with ethoxide, the conjugate base of ethanol, is most commonly accompanied by the positive charge of an alkali metal salt such as the sodium cation (Na). | 6 | Supramolecular Chemistry |
When photon energies are as high as the electron rest energy of , yet another process, Compton scattering, may occur. Above twice this energy, at , pair production is also more likely. Compton scattering and pair production are examples of two other competing mechanisms.
Even if the photoelectric effect is the favoured reaction for a particular interaction of a single photon with a bound electron, the result is also subject to quantum statistics and is not guaranteed. The probability of the photoelectric effect occurring is measured by the cross section of the interaction, σ. This has been found to be a function of the atomic number of the target atom and photon energy. In a crude approximation, for photon energies above the highest atomic binding energy, the cross section is given by:
Here Z is the atomic number and n is a number which varies between 4 and 5. The photoelectric effect rapidly decreases in significance in the gamma-ray region of the spectrum, with increasing photon energy. It is also more likely from elements with high atomic number. Consequently, high-Z materials make good gamma-ray shields, which is the principal reason why lead (Z = 82) is preferred and most widely used. | 7 | Physical Chemistry |
The pK of DMSO is 35, which leads NaDMSO to be a powerful Brønsted base. NaDMSO is used in the generation of phosphorus and sulfur ylides. NaDMSO in DMSO is especially convenient in the generation of dimethyloxosulfonium methylide and dimethylsulfonium methylide. | 0 | Organic Chemistry |
Expression of paired receptors is common in many types of leukocytes, especially myeloid cells and natural killer (NK) cells. Activation of NK cells is a complex regulatory process modulated by a number of different paired receptor families coexpressed in this cell type. In some cases, only one member of the pair is expressed in a cell type. Expression of the paired members in a single cell type may vary with time, or the proteins may differ in subcellular localization, resulting in variations in signaling. Expression in NK cells can be stochastic, resulting in unique variations in receptor repertoire.
Some paired receptors are expressed outside the immune system, for example in neurons, endothelium, and epithelium but in many examples, wide tissue distribution can be observed. | 1 | Biochemistry |
Variation in methylation states of DNA can alter gene expression levels significantly. Methylation variation usually occurs through the action of DNA methylases. When the change is heritable, it is considered epigenetic. When the change in information status is not heritable, it would be a somatic epitype. The effective information content has been changed by means of the actions of a protein or proteins on DNA, but the primary DNA sequence is not altered. | 1 | Biochemistry |
Using a volume integral on dimensions, the density of states is:
The Fermi energy is obtained by looking for the number density of particles:
To get:
where is the corresponding d-dimensional volume, is the dimension for the internal Hilbert space. For the case of spin-½, every energy is twice-degenerate, so in this case .
A particular result is obtained for , where the density of states becomes a constant (does not depend on the energy): | 7 | Physical Chemistry |
ADAM17 is understood to be involved in the processing of tumor necrosis factor alpha (TNF-α) at the surface of the cell, and from within the intracellular membranes of the trans-Golgi network. This process, which is also known as shedding, involves the cleavage and release of a soluble ectodomain from membrane-bound pro-proteins (such as pro-TNF-α), and is of known physiological importance. ADAM17 was the first sheddase to be identified, and is also understood to play a role in the release of a diverse variety of membrane-anchored cytokines, cell adhesion molecules, receptors, ligands, and enzymes.
Cloning of the TNF-α gene revealed it to encode a 26 kDa type II transmembrane pro-polypeptide that becomes inserted into the cell membrane during its maturation. At the cell surface, pro-TNF-α is biologically active, and is able to induce immune responses via juxtacrine intercellular signaling. However, pro-TNF-α can undergo a proteolytic cleavage at its Ala76-Val77 amide bond, which releases a soluble 17kDa extracellular domain (ectodomain) from the pro-TNF-α molecule. This soluble ectodomain is the cytokine commonly known as TNF-α, which is of pivotal importance in paracrine signaling. This proteolytic liberation of soluble TNF-α is catalyzed by ADAM17.
Recently, ADAM17 was discovered as a crucial mediator of resistance to radiotherapy. Radiotherapy can induce a dose-dependent increase of furin-mediated cleavage of the ADAM17 proform to active ADAM17, which results in enhanced ADAM17 activity in vitro and in vivo. It was also shown that radiotherapy activates ADAM17 in non-small cell lung cancer, which results in shedding of multiple survival factors, growth factor pathway activation, and radiotherapy-induced treatment resistance.
ADAM17 may play a prominent role in the Notch signaling pathway, during the proteolytic release of the Notch intracellular domain (from the Notch1 receptor) that occurs following ligand binding. ADAM17 also regulates the MAP kinase signaling pathway by regulating shedding of the EGFR ligand amphiregulin in the mammary gland. ADAM17 also has a role in the shedding of L-selectin, a cellular adhesion molecule. | 1 | Biochemistry |
Hydrogen cyanide, discovered in the late 18th century, was used in the 1880s for the fumigation of citrus trees in California. Its use spread to other countries for the fumigation of silos, goods wagons, ships, and mills. Its light weight and rapid dispersal meant its application had to take place under tents or in enclosed areas. Research by Fritz Haber of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry led to the founding in 1919 of Deutsche Gesellschaft für Schädlingsbekämpfung mbH (Degesch), a state-controlled consortium formed to investigate military use of the chemical. Chemists at Degesch added a cautionary eye irritant to a less volatile cyanide compound which reacted with water in the presence of heat to become hydrogen cyanide. The new product was marketed as the pesticide Zyklon (cyclone). As a similar formula had been used as a weapon by the Germans during World War I, Zyklon was soon banned.
Deutsche Gold- und Silber-Scheideanstalt (German Gold and Silver Refinery; Degussa) became sole owners of Degesch in 1922. There, beginning in 1922, , Bruno Tesch, and others worked on packaging hydrogen cyanide in sealed canisters along with a cautionary eye irritant and adsorbent stabilizers such as diatomaceous earth. The new product was also labelled as Zyklon, but it became known as Zyklon B to distinguish it from the earlier version. Heerdt was named the inventor of Zyklon B in the Degesch patent application (number DE 438818) dated 20 June 1922. The Deutsches Patent- und Markenamt awarded the patent on 27 December 1926. Beginning in the 1920s, Zyklon B was used at U.S. Customs facilities along the Mexican border to fumigate the clothing of border crossers. | 1 | Biochemistry |
Chichinin, Einfeld, Maul, and Gericke replaced the phosphor screen by a time-resolving delay line anode in order to be able to measure all three components of the initial product momentum vector simultaneously for each individual product particle arriving at the detector. This technique allows one to measure the three-dimensional product momentum vector distribution without having to rely on mathematical reconstruction methods which require the investigated systems to be cylindrically symmetric. Later, velocity mapping was added to 3D imaging. 3D techniques have been used to characterize several elementary photodissociation processes and bimolecular chemical reactions. | 7 | Physical Chemistry |
Targeted temperature management is used during open-heart surgery because it decreases the metabolic needs of the brain, heart, and other organs, reducing the risk of damage to them. The patient is given medication to prevent shivering. The body is then cooled to 25–32 °C (79–89 °F). The heart is stopped and an external heart-lung pump maintains circulation to the patient's body. The heart is cooled further and is maintained at a temperature below 15 °C (60 °F) for the duration of the surgery. This very cold temperature helps the heart muscle to tolerate its lack of blood supply during the surgery. | 1 | Biochemistry |
The main effect of chloride ions on reinforced concrete is to cause pitting corrosion of the steel reinforcement bars (rebar). It is a surreptitious and dangerous form of localized corrosion because the rebar sections can be decreased to the point that the steel reinforcement are no longer capable to withstand to the tensile efforts they are supposed to resist by design. When the rebar sections are too small or the rebar are locally broken, the reinforcements are lost, and concrete is no longer reinforced concrete.
Chlorides, particularly calcium chloride, have been used to shorten the setting time of concrete.
However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength, as well as attacking the steel reinforcement present in most concrete. The ten-storey Queen Elizabeth hospital in Kota Kinabalu contained a high percentage of chloride causing early failure. | 8 | Metallurgy |
In biochemistry, p represents the partial pressure of a gas required to achieve 50% saturation of a particular proteins binding sites. Values of p are negatively correlated with substrate affinity; lower values correspond to higher affinity and vice versa. The term is analogous to the Michaelis–Menten constant (K'), which identifies the concentration of substrate required for an enzyme to achieve 50% of its maximum reaction velocity.
The concept of p is derived from considering the fractional saturation of a protein by a gas. Imagine myoglobin, a protein which is able to bind a single molecule of oxygen, as per the reversible reaction below, whose equilibrium constant K (which is also a dissociation constant, since it describes a reversible association-dissociation event) is equal to the product of the concentrations (at equilibrium) of free myoglobin and free oxygen, divided by the concentration of myoglobin-oxygen complex.
The fractional saturation Y of the myoglobin is what proportion of the total myoglobin concentration is made up of oxygen-bound myoglobin, which can be rearranged as the concentration of free oxygen over the sum of that concentration and the dissociation constant K. Since diatomic oxygen is a gas, its concentration in solution can be thought of as a partial pressure.
From defining the p as the partial pressure at which the fractional saturation is 50%, we can deduce that it is in fact equal to the dissociation constant K.
For example, myoglobins p for O is 130 pascals while the P for adult hemoglobin is 3.5 kPa. Thus, when O partial pressure is low, hemoglobin-bound O is more readily transferred to myoglobin. Myoglobin, found in high concentrations in muscle tissue, can then transfer the oxygen to muscle tissue muscle fibers, where it will be used in the generation of energy to fuel muscle contraction. Another example is that of human fetal hemoglobin, which has a higher affinity (lower P') than adult hemoglobin, and therefore allows uptake of oxygen across the placental diffusion barrier. | 1 | Biochemistry |
Source: [http://www.aps.org/programs/honors/prizes/langmuir.cfm American Physical Society] and [https://www.acs.org/content/acs/en/funding-and-awards/awards/national/bytopic/irving-langmuir-award-in-chemical-physics.html American Chemical Society] | 7 | Physical Chemistry |
Drugs have long been considered crucial targets for transmitter-gated ion channels. The majority of medications utilized to treat schizophrenia, anxiety, depression, and sleeplessness work at chemical synapses, and many of these pharmaceuticals function by binding to transmitter-gated channels. For instance, some drugs like barbiturates and tranquilizers bind to GABA receptors and enhance the inhibitory effect of GABA neurotransmitter. Thus, reduced concentration of GABA enables the opening of Cl- channels.
Furthermore, psychoactive drugs could potentially target many other synaptic signalling machinery components. In fact, numerous neurotransmitters are released by Na+-driven carriers and are subsequently removed from the synaptic cleft. By inhibiting such carriers, synaptic transmission is strengthened as the action of the transmitter is prolonged. For example, Prozac is one of antidepressant medications that works by preventing the absorption of serotonin neurotransmitter. Also, other antidepressants operate by inhibiting the reabsorption of both serotonin and norepinephrine. | 1 | Biochemistry |
A Lot (formerly Loth) was an old unit of measurement for the relative fineness to gross weight in metallurgy and especially in coinage until the 19th century. A Lot was thus a proportion of the precious metal content in a piece of metal. It was used in the four main monetary systems of Germany: Austrian, South German, North German and Hamburg.
The lot was defined as the sixteenth part of a Mark. For example, in silver, the total weight was divided into 16 (proportional) Lots until about 1857, according to which a "12-Lot" silver alloy (750 silver) contained 12/16 = or 75% by weight of silver and 25% of another metal (usually copper). A 14-Lot silver alloy (), on the other hand, corresponded to 875 silver. For refinement, a Lot was further divided into 18 grains. Thus 14 Lots, 4 grains fine then correspond to a fineness of 888.89 ‰ = (14 + 4 / 18) / 16 = (252 + 4)/288, i.e. 256/288 grains.
The German proportional measure, the Lot, was finally replaced on 1 January 1888 in the German Empire by the proportional measure, permille (thousandths). | 8 | Metallurgy |
According to equation (10), the minimum required entropy change (right term) for the summation of the positive entropy changes decreases when T increases. As an example, performing the same numerical application but with T equals to 2000K would give a twice lower value (around 140 kJ/mol), which allows thermochemical cycles with only two reactions. Such processes can be realistically coupled with concentrated solar power technologies like Solar Updraft Tower. As an example in Europe, this is the goal of the Hydrosol-2 project (Greece, Germany (German Aerospace Center), Spain, Denmark, England) and of the researches of the solar department of the ETH Zurich and the Paul Scherrer Institute (Switzerland).
Examples of reactions satisfying high entropy changes are metal oxide dissociations, as the products have more excitation levels due to their gaseous state (metal vapors and oxygen) than the reactant (solid with crystalline structure, so symmetry dramatically reduces the number of different excitation levels). Consequently, these entropy changes can often be larger than the water-splitting one and thus a reaction with a negative entropy change is required in the thermochemical process so that Eq.(5) is satisfied. Furthermore, assuming similar stabilities of the reactant (ΔH°) for both thermolysis and oxide dissociation, a larger entropy change in the second case explained again a lower reaction temperature (Eq.(3)).
Let us assume two reactions, with positive (1 subscript, at T) and negative (2 subscript, at T°) entropy changes. An extra property can be derived in order to have T strictly lower than the thermolysis temperature: The standard thermodynamic values must be unevenly distributed among the reactions .
Indeed, according to the general equations (2) (spontaneous reaction), (4) and (5), one must satisfy,
Hence, if ΔH° is proportional to ΔH° by a given factor, and if ΔS° and ΔS° follow a similar law (same proportionality factor), the inequality (17) is broken (equality instead, so T equals to the water thermolysis temperature). | 7 | Physical Chemistry |
A biosurvey, or biological survey, is a scientific study of organisms to assess the condition of an ecological resource, such as a water body. | 2 | Environmental Chemistry |
The health effects of radon are harmful, and include an increased chance of lung cancer. Radon is a radioactive, colorless, odorless, tasteless noble gas, which has been studied by a number of scientific and medical bodies for its effects on health. A naturally-occurring gas formed as a decay product of radium, radon is one of the densest substances that remains a gas under normal conditions, and is considered to be a health hazard due to its radioactivity. Its most stable isotope, radon-222, has a half-life of 3.8 days. Due to its high radioactivity, it has been less well studied by chemists, but a few compounds are known.
Radon-222 is formed as part of the uranium series i.e. the normal radioactive decay chain of uranium-238 that terminates in lead-206. Uranium has been present since the Earth was formed, and its most common isotope has a very long half-life (4.5 billion years), which is the time required for one-half of uranium to break down. Thus, uranium and radon will continue to occur for millions of years at about the same concentrations as they do now.
Radon is responsible for the majority of public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics and basements. It can also be found in some spring waters and hot springs.
According to a 2003 report EPAs Assessment of Risks from Radon in Homes' from the United States Environmental Protection Agency, epidemiological evidence shows a clear link between lung cancer and high concentrations of radon, with 21,000 radon-induced U.S. lung cancer deaths per year—second only to cigarette smoking. Thus in geographic areas where radon is present in heightened concentrations, radon is considered a significant indoor air contaminant. | 2 | Environmental Chemistry |
Contraindications include:
* Pregnancy
* Impaired renal and liver function
* Patients with a history of angioedema related to previous treatment with an ACE inhibitor
* Hypersensitivity to Quinapril | 4 | Stereochemistry |
Calculations of the IMFP are mostly based on the algorithm (full Penn algorithm, FPA) developed by Penn, experimental optical constants or calculated optical data (for compounds). The FPA considers an inelastic scattering event and the dependence of the energy-loss function (EFL) on momentum transfer which describes the probability for inelastic scattering as a function of momentum transfer. | 7 | Physical Chemistry |
To obtain the desired measurement of , it is not sufficient to just measure .
The temperature at the reference junctions must be already known.
Two strategies are often used here:
* "Ice bath" method: The reference junction block is immersed in a semi-frozen bath of distilled water at atmospheric pressure. The precise temperature of the melting point phase transition acts as a natural thermostat, fixing to 0 °C.
* Reference junction sensor (known as ""): The reference junction block is allowed to vary in temperature, but the temperature is measured at this block using a separate temperature sensor. This secondary measurement is used to compensate for temperature variation at the junction block. The thermocouple junction is often exposed to extreme environments, while the reference junction is often mounted near the instrument's location. Semiconductor thermometer devices are often used in modern thermocouple instruments.
In both cases the value is calculated, then the function is searched for a matching value. The argument where this match occurs is the value of : | 8 | Metallurgy |
The photoelectric effect will cause spacecraft exposed to sunlight to develop a positive charge. This can be a major problem, as other parts of the spacecraft are in shadow which will result in the spacecraft developing a negative charge from nearby plasmas. The imbalance can discharge through delicate electrical components. The static charge created by the photoelectric effect is self-limiting, because a higher charged object does not give up its electrons as easily as a lower charged object does. | 7 | Physical Chemistry |
An excess of free fatty acids in liver cells plays a role in Nonalcoholic Fatty Liver Disease (NAFLD). In the liver, it is the type of fatty acid, not the quantity, that determines the extent of the lipotoxic effects. In hepatocytes, the ratio of monounsaturated fatty acids and saturated fatty acids leads to apoptosis and liver damage. There are several potential mechanisms by which the excess fatty acids can cause cell death and damage. They may activate death receptors, stimulate apoptotic pathways, or initiate cellular stress response in the endoplasmic reticulum. These lipotoxic effects have been shown to be prevented by the presence of excess triglycerides within the hepatocytes. | 1 | Biochemistry |
The Imd pathway is a broadly-conserved NF-κB immune signalling pathway of insects and some arthropods that regulates a potent antibacterial defence response. The pathway is named after the discovery of a mutation causing severe immune deficiency (the gene was named "Imd" for "immune deficiency"). The Imd pathway was first discovered in 1995 using Drosophila fruit flies by Bruno Lemaitre and colleagues, who also later discovered that the Drosophila Toll gene regulated defence against Gram-positive bacteria and fungi. Together the Toll and Imd pathways have formed a paradigm of insect immune signalling; as of September 2, 2019, these two landmark discovery papers have been cited collectively over 5000 times since publication on Google Scholar.
The Imd pathway responds to signals produced by Gram-negative bacteria. Peptidoglycan recognition proteins (PGRPs) sense DAP-type peptidoglycan, which activates the Imd signalling cascade. This culminates in the translocation of the NF-κB transcription factor Relish, leading to production of antimicrobial peptides and other effectors. Insects lacking Imd signalling either naturally or by genetic manipulation are extremely susceptible to infection by a wide variety of pathogens and especially bacteria. | 1 | Biochemistry |
When water flows through cracks present in concrete, water may dissolve various minerals present in the hardened cement paste or in the aggregates, if the solution is unsaturated with respect to them. Dissolved ions, such as calcium (Ca), are leached out and transported in solution some distance. If the physico-chemical conditions prevailing in the seeping water evolve with distance along the water path and water becomes supersaturated with respect to certain minerals, they can further precipitate, making calthemite deposits (predominately calcium carbonate) inside the cracks, or at the concrete outer surface. This process can cause the self-healing of fractures in particular conditions.
Fagerlund (2000) determined that, “About 15% of the lime has to be dissolved before strength is affected. This corresponds to about 10% of the cement weight, or almost all of the initially formed Ca(OH).” Therefore, a large amount of "calcium hydroxide" (Ca(OH)) must be leached from the concrete before structural integrity is affected. The other issue however is that leaching away Ca(OH) may allow the corrosion of reinforcing steel to affect structural integrity. | 8 | Metallurgy |
In 1986, the N-end rule was elucidated, and it states that the identity of the amino acid at the N-terminus of the protein's amino acid sequence determines the half-life of the protein. In an effort to determine the effects of arginylation on the half-life of proteins, several studies were performed using modified yeast proteins. These studies revealed that when proteins were engineered to include N-termini which had been arginylated, the modified proteins were metabolically unstable. Furthermore, it was also discovered that protein ubiquitination and degradation become more likely to occur when a protein is arginylated. The evidence gathered from these experiments make it clear that arginylation in vivo leads to the degradation of proteins with asparagine and glutamine residues at their N-termini.
However, there have also been several recent studies which have shown that protein degradation may not be the prevalent function of arginylation, but that this modification may also be important for certain proteins to function correctly. For instance, when arginylation occurs on beta amyloid proteins, the proteins are guided into their proper alpha helical shape and are also prevented from misfolding and aggregating. Another protein which benefits from arginylation is calreticulin because when modified, its role during endoplasmic reticulum stress is facilitated, rather than it being removed from cells entirely. As both degradation and facilitation effects of arginylation have been identified and studied, it is clear that arginylation has an important role in protein regulation within cells. | 1 | Biochemistry |
The EPOC effect is greatest soon after the exercise is completed and decays to a lower level over time. One experiment, involving exertion above baseline, found EPOC increasing metabolic rate to an excess level that decays to 13% three hours after exercise, and 4% after 16 hours, for the studied exercise dose. Another study, specifically designed to test whether the effect existed for more than 16 hours, conducted tests for 48 hours after the conclusion of the exercise and found measurable effects existed up to the 38-hour post-exercise measurement, for the studied exercise dose. | 1 | Biochemistry |
Hollow fiber membranes are ubiquitously used in industrial separations, especially the filtration of drinking water.
Industrial water filters are mainly equipped with ultrafiltration hollow fiber membranes. Domestic water filtration systems have microfiltration hollow fiber membranes. In microfiltration a membrane pore diameter of 0.1 micrometers cuts-off microorganisms like germs and bacteria, Giardia cysts and other intestinal parasites, as well removing sediments. Ultrafiltration membranes are capable of removing not only bacteria, but also viruses.
Hollow fibers are commonly used substrates for specialized bioreactor systems, with the ability of some hollow fiber cartridges to culture billions of anchorage-dependent cells within a relatively low (<100 mL) bioreactor volume.
Hollow fibers can be used for drug efficacy testing in cancer research, as an alternative to the traditional, but more expensive, xenograft model.
Hollow fiber membranes are used in Membrane oxygenators in extracorporeal membrane oxygenation which oxygenates blood, replacing lungs in critically ill patients. | 7 | Physical Chemistry |
geWorkbench (genomics Workbench) is an open-source software platform for integrated genomic data analysis. It is a desktop application written in the programming language Java. geWorkbench uses a component architecture. , there are more than 70 plug-ins available, providing for the visualization and analysis of gene expression, sequence, and structure data.
geWorkbench is the Bioinformatics platform of MAGNet, the National Center for the Multi-scale Analysis of Genomic and Cellular Networks, one of the 8 National Centers for Biomedical Computing funded through the NIH Roadmap (NIH Common Fund). Many systems and structure biology tools developed by MAGNet investigators are available as geWorkbench plugins. | 1 | Biochemistry |
Buffering Mechanisms such as molecular titration can generate ultrasensitivity. In vitro, this can be observed for the simple mechanism:
Where the monomeric form of A is active and it can be inactivated by binding B to form the heterodimer AB. When the concentration of ( = [B] + [AB]) is much greater than the , this system exhibits a threshold determined by the concentration of . At concentrations of ( = [A] +[AB]), lower than , B acts as a buffer to free A and nearly all A will be found as AB. However, at the equivalence point, when ≈ , can no longer buffer the increase in , so a small increase in causes a large increase in A. The strength of the ultrasensitivity of [A] to changes in is determined by /. Ultrasensitivity occurs when this ratio is greater than one and is increased as the ratio increases. Above the equivalence point, and A are again linearly related.
In vivo, the synthesis of A and B as well as the degradation of all three components complicates generation of ultrasensitivity. If the synthesis rates of A and B are equal this system still exhibits ultrasensitivity at the equivalence point.
One example of a buffering mechanism is protein sequestration, which is a common mechanism found in signalling and regulatory networks. In 2009, Buchler and Cross constructed a synthetic genetic network that was regulated by protein sequestration of a transcriptional activator by a dominant-negative inhibitor. They showed that this system results in a flexibile ultrasensitive response in gene expression. It is flexible in that the degree of ultrasensitivity can be altered by changing expression levels of the dominant-negative inhibitor. Figure 1 in their article illustrates how an active transcription factor can be sequestered by an inhibitor into the inactive complex AB that is unable to bind DNA. This type of mechanism results in an "all-or-none" response, or ultransensitivy, when the concentration of the regulatory protein increases to the point of depleting the inhibitor. Robust buffering against a response exists below this concentration threshold, and when it is reached any small increase in input is amplified into a large change in output. | 1 | Biochemistry |
Difficulties have been encountered in the definition of the technological parameters that drive the process.
Two broad categories of generators, also known as power supplies, are in use on EDM machines commercially available: the group based on RC circuits and the group based on transistor-controlled pulses.
In both categories, the primary parameters at setup are the current and frequency delivered. In RC circuits, however, little control is expected over the time duration of the discharge, which is likely to depend on the actual spark-gap conditions (size and pollution) at the moment of the discharge. Also, the open circuit voltage (i.e. the voltage between the electrodes when the dielectric is not yet broken) can be identified as steady state voltage of the RC circuit.
In generators based on transistor control, the user is usually able to deliver a train of pulses of voltage to the electrodes. Each pulse can be controlled in shape, for instance, quasi-rectangular. In particular, the time between two consecutive pulses and the duration of each pulse can be set. The amplitude of each pulse constitutes the open circuit voltage. Thus, the maximum duration of discharge is equal to the duration of a pulse of voltage in the train. Two pulses of current are then expected not to occur for a duration equal or larger than the time interval between two consecutive pulses of voltage.
The maximum current during a discharge that the generator delivers can also be controlled. Because other sorts of generators may also be used by different machine builders, the parameters that may actually be set on a particular machine will depend on the generator manufacturer. The details of the generators and control systems on their machines are not always easily available to their user. This is a barrier to describing unequivocally the technological parameters of the EDM process. Moreover, the parameters affecting the phenomena occurring between tool and electrode are also related to the controller of the motion of the electrodes.
A framework to define and measure the electrical parameters during an EDM operation directly on inter-electrode volume with an oscilloscope external to the machine has been recently proposed by Ferri et al. These authors conducted their research in the field of μ-EDM, but the same approach can be used in any EDM operation. This would enable the user to estimate directly the electrical parameters that affect their operations without relying upon machine manufacturer's claims. When machining different materials in the same setup conditions, the actual electrical parameters of the process are significantly different. | 8 | Metallurgy |
In the classical mechanics framework, a rough surface, such as a machined metal surface, randomizes the probability distribution function governing the incoming particles, leading to net momentum loss of the particle flux. | 7 | Physical Chemistry |
FMRFamide, a neuropeptide involved in cardiac activity regulation, is found in Biomphalaria glabrata, a species of a freshwater snail best known for its role as the intermediate host for the human-infecting trematode parasite Schistosoma mansoni.
This freshwater snail species is used as a model organism, in other words, a non-human species which is extensively studied to understand a biological phenomenon, with the expectation that discoveries made in the model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to research human disease when human experimentation would be unfeasible or unethical. | 1 | Biochemistry |
The theory propounded was summarized by Stephen Berry, a chemist; "describing the following causal chain: the properties of the chemical elements dictate the types of monomers that can be formed in prebiotic syntheses, which then dictate the properties of the occurring polymers, which finally dictate the properties of the first eobionts and all succeeding cells." Kenyon's work was about virus production.
Intelligent design proponent Stephen C. Meyer says that the book provided a new approach which came to be known as "Self-organization".
Kenyon began to doubt his theory in the mid-1970s after a student posed the question to him as to how the first proteins could have been assembled without specific genetic instructions. On a fellowship at the Graduate Theological Union in Berkeley during the 1969–1970 academic year, he reviewed literature on the relationship of science and religion. He began to rethink his Christian faith, and explored the topic further in a 1974 sabbatical at the University of Oxford. In 1976, a student gave him a book by the young Earth creationist A. E. Wilder-Smith, and "Eventually, several other books and articles by neo-creationists came to my attention. I read some of Henry Morris’ books, in particular, The Genesis Flood. Im not a geologist, and I dont agree with everything in that book, but what stood out was that here was a scientific statement giving a very different view of earth history. Though the book doesnt deal with the subject of the origin of life per se, it had the effect of suggesting that it is possible to have a rational alternative explanation of the past." In 1976 he wrote a new section for Morris and Whitcombs The Genesis Flood: The Biblical Record and Its Scientific Implications. In the 1982 foreword he wrote to What Is Creation Science? by Morris and Gary Parker, Kenyon said that he no longer accepted the pro-evolution arguments in Biochemical Predestination. At the Edwards v. Aguillard trial he provided an affidavit in support of creation science and noted the book as one of his publications. Kenyon subsequently became a co-author of Of Pandas and People which rebranded creation science as intelligent design. | 1 | Biochemistry |
Mitogen-activated protein kinases are catalytically inactive in their base form. In order to become active, they require (potentially multiple) phosphorylation events in their activation loops. This is conducted by specialized enzymes of the STE protein kinase group. In this way protein dynamics can induce a conformational change in the structure of the protein via long-range allostery.
In the case of classical MAP kinases, the activation loop contains a characteristic TxY (threonine-x-tyrosine) motif (TEY in mammalian ERK1 and ERK2, TDY in ERK5, TPY in JNKs, TGY in p38 kinases) that needs to be phosphorylated on both the threonine and the tyrosine residues in order to lock the kinase domain in a catalytically competent conformation. In vivo and in vitro, phosphorylation of tyrosine oftentimes precedes phosphorylation of threonine, although phosphorylation of either residue can occur in the absence of the other.
This tandem activation loop phosphorylation (that was proposed to be either distributive or processive, dependent on the cellular environment) is performed by members of the Ste7 protein kinase family, also known as MAP2 kinases. MAP2 kinases in turn, are also activated by phosphorylation, by a number of different upstream serine-threonine kinases (MAP3 kinases). Because MAP2 kinases display very little activity on substrates other than their cognate MAPK, classical MAPK pathways form multi-tiered, but relatively linear pathways. These pathways can effectively convey stimuli from the cell membrane (where many MAP3Ks are activated) to the nucleus (where only MAPKs may enter) or to many other subcellular targets.
In comparison to the three-tiered classical MAPK pathways, some atypical MAP kinases appear to have a more ancient, two-tiered system. ERK3 (MAPK6) and ERK4 (MAPK4) were recently shown to be directly phosphorylated and thus activated by PAK kinases (related to other MAP3 kinases). In contrast to the classical MAP kinases, these atypical MAPKs require only a single residue in their activation loops to be phosphorylated. The details of NLK and ERK7 (MAPK15) activation remain unknown.
Inactivation of MAPKs is performed by a number of phosphatases. A very conserved family of dedicated phosphatases is the so-called MAP kinase phosphatases (MKPs), a subgroup of dual-specificity phosphatases (DUSPs). As their name implies, these enzymes are capable of hydrolyzing the phosphate from both phosphotyrosine and the phosphothreonine residues. Since removal of either phosphate groups will greatly reduce MAPK activity, essentially abolishing signaling, some tyrosine phosphatases are also involved in inactivating MAP kinases (e.g. the phosphatases HePTP, STEP and PTPRR in mammals). | 1 | Biochemistry |
TET dioxygenase isoforms include at least two isoforms of TET1, one of TET2 and three isoforms of TET3. The full-length canonical TET1 isoform appears virtually restricted to early embryos, embryonic stem cells and primordial germ cells (PGCs). The dominant TET1 isoform in most somatic tissues, at least in the mouse, arises from alternative promoter usage which gives rise to a short transcript and a truncated protein designated TET1s. The isoforms of TET3 are the full length form TET3FL, a short form splice variant TET3s, and a form that occurs in oocytes and neurons designated TET3o. TET3o is created by alternative promoter use and contains an additional first N-terminal exon coding for 11 amino acids. TET3o only occurs in oocytes and neurons and is not expressed in embryonic stem cells or in any other cell type or adult mouse tissue tested. Whereas TET1 expression can barely be detected in oocytes and zygotes, and TET2 is only moderately expressed, the TET3 variant TET3o shows extremely high levels of expression in oocytes and zygotes, but is nearly absent at the 2-cell stage. It is possible that TET3o, high in neurons, oocytes and zygotes at the one cell stage, is the major TET enzyme utilized when very large scale rapid demethylations occur in these cells. | 1 | Biochemistry |
Complementing alkylation reactions are the reverse, dealkylations. Prevalent are demethylations, which are prevalent in biology, organic synthesis, and other areas, especially for methyl ethers and methyl amines. | 0 | Organic Chemistry |
The nano guitar illustrates inaudible technology that is not meant for musical entertainment. The application of frequencies generated by nano-objects is called sonification. Such objects can represent numerical data and provide support for information processing activities of many different kinds that produce synthetic non-verbal sounds. Since the manufacture of the nano-guitar, researchers in the lab headed by Dr. Craighead have built even tinier devices. One thought is that they may be useful as tiny scales to measure tinier particles, such as bacteria, which may aid in diagnosis. | 6 | Supramolecular Chemistry |
The diffuse series is a series of spectral lines in the atomic emission spectrum caused when electrons jump between the lowest p orbital and d orbitals of an atom. The total orbital angular momentum changes between 1 and 2. The spectral lines include some in the visible light, and may extend into ultraviolet or near infrared. The lines get closer and closer together as the frequency increases never exceeding the series limit. The diffuse series was important in the development of the understanding of electron shells and subshells in atoms. The diffuse series has given the letter d to the d atomic orbital or subshell.
The diffuse series has values given by
The series is caused by transitions from the lowest P state to higher energy D orbitals.
One terminology to identify the lines is: 1P-mD But note that 1P just means the lowest P state in the valence shell of an atom and that the modern designation would start at 2P, and is larger for higher atomic numbered atoms.
The terms can have different designations, mD for single line systems, mδ for doublets and md for triplets.
Since the Electron in the D subshell state is not the lowest energy level for the alkali atom (the S is) the diffuse series will not show up as absorption in a cool gas, however it shows up as emission lines.
The Rydberg correction is largest for the S term as the electron penetrates the inner core of electrons more.
The limit for the series corresponds to electron emission, where the electron has so much energy it escapes the atom.
In alkali metals the P terms are split and . This causes the spectral lines to be doublets, with a constant spacing between the two parts of the double line.
This splitting is called fine structure. The splitting is larger for atoms with higher atomic number. The splitting decreases towards the series limit. Another splitting occurs on the redder line of the doublet. This is because of splitting in the D level and . Splitting in the D level has a lesser amount than the P level, and it reduces as the series limit is approached. | 7 | Physical Chemistry |
Chiral oxocarbenium ions have been exploited to carry out highly diastereoselective and enantioselective acetate aldol
addition reactions. The oxocarbenium ion is used as an electrophile in the reaction. When the methyl group increases in size, the diastereoselevtivity increases. | 0 | Organic Chemistry |
Among the thousands of species of plant pathogenic microorganisms, only a small minority have the capacity to infect a broad range of plant species. Most pathogens instead exhibit a high degree of host-specificity. Non-host plant species are often said to express non-host resistance. The term host resistance is used when a pathogen species can be pathogenic on the host species but certain strains of that plant species resist certain strains of the pathogen species. The causes of host resistance and non-host resistance can overlap. Pathogen host range is determined, among other things, by the presence of appropriate effectors that allow colonization of a particular host. Pathogen host range can change quite suddenly if, for example, the pathogen's capacity to synthesize a host-specific toxin or effector is gained by gene shuffling/mutation, or by horizontal gene transfer. | 1 | Biochemistry |
Sulfur bloom refers to the migration of sulfur, usually as S, to the surface of a rubber article either before or after vulcanization. Blooming is undesirable in rubber processing. When sulfur bloom appears before vulcanization, the rubber is deprived of the crosslinking agent. Sulfur bloom after vulcanization indicates incomplete vulcanization. In rubber processing, ingredients other than sulfur can "bloom", including antioxidants, fatty acids, and accelerators. | 7 | Physical Chemistry |
Agricultural chemistry is the chemistry, especially organic chemistry and biochemistry, as they relate to agriculture. Agricultural chemistry embraces the structures and chemical reactions relevant in the production, protection, and use of crops and livestock. Its applied science and technology aspects are directed towards increasing yields and improving quality, which comes with multiple advantages and disadvantages. | 1 | Biochemistry |
Signs Of LIfe Detector (SOLID) is an analytical instrument under development to detect extraterrestrial life in the form of organic biosignatures obtained from a core drill during planetary exploration.
The instrument is based on fluorescent immunoassays and it is being developed by the Spanish Astrobiology Center (CAB) in collaboration with the NASA Astrobiology Institute. SOLID is currently undergoing testing for use in astrobiology space missions that search for common biomolecules that may indicate the presence of extraterrestrial life, past or present. The system was validated in field tests and engineers are looking into ways to refine the method and miniaturize the instrument further. | 1 | Biochemistry |
Such materials include semiconductors that can be photoactivated like many solar cells, biological systems such as those used in photosynthesis, and small molecules with suitable absorptions and redox states. | 5 | Photochemistry |
After amplification with PCR, samples are loaded into a gel (either agarose or polyacrylamide) for gel electrophoresis. The differing sizes created through random amplification will separate along the gel in a repeatable manner depending on the sample source. This creates a distinct DNA fingerprint.
Unlike traditional PCR analysis, RAPD does not require any specific knowledge of the DNA sequence of the target organism: the identical 10-mer primers will or will not amplify a segment of DNA, depending on positions that are complementary to the primers sequence. For example, no fragment is produced if primers annealed too far apart or 3 ends of the primers are not facing each other. Therefore, if a mutation has occurred in the template DNA at the site that was previously complementary to the primer, a PCR product will not be produced, resulting in a different pattern of amplified DNA segments on the gel. | 1 | Biochemistry |
The Gmelin database is a large database of organometallic and inorganic compounds updated quarterly. It is based on the German publication Gmelins Handbuch der anorganischen Chemie ("Gmelins Handbook of Inorganic Chemistry") which was originally published by Leopold Gmelin in 1817; the last print edition, the 8th, appeared in the 1990s. Although published over many decades, the printed series was not uniform in coverage or currency. Some elements are represented only by decades-old and not updated slim summary volumes. Others (Fe, B, S, F, U, etc.) have numerous supplements. Most later supplement volumes focused on an elements organic complexes. Each volume lists its literature coverage date.
The database currently contains every compound/reaction discovered between 1772 and 1995, amounting to 1.5 million compounds and 1.3 million different reactions, with over 85,000 titles, keywords and abstracts. It has over 800 different data fields on subjects such as the compounds' electric, magnetic, thermal, crystal and physiological information.
The Gmelin database is maintained by Elsevier MDL. It is the sister database to the Beilstein database, which deals with organic chemicals and reactions; both are now part of the Reaxys system. The Gmelin database is less complete and less up-to-date than the handbook; the printed book is consequently kept available. | 0 | Organic Chemistry |
Mixtures of different solvents can have interesting features like anomalous conductivity (electrolytic) of particular lyonium ions and lyate ions generated by molecular autoionization of protic and aprotic solvents due to Grotthuss mechanism of ion hopping depending on the mixing ratios. Examples may include hydronium and hydroxide ions in water and water alcohol mixtures, alkoxonium and alkoxide ions in the same mixtures, ammonium and amide ions in liquid and supercritical ammonia, alkylammonium and alkylamide ions in ammines mixtures, etc.... | 3 | Analytical Chemistry |
Solid-state NMR techniques have the potential to yield detailed information about the dynamics of individual amino acid residues within a membrane protein. However, the techniques can require large amounts (100–200 mg) of isotopically labeled proteins and are most informative when applied to small proteins where spectroscopic assignments are possible. | 1 | Biochemistry |
Is the linkage of chemical reactions in a way that the product of one reaction becomes the substrate of another reaction.
* This allows organisms to utilize energy and resources efficiently. For example, in cellular respiration, energy released by the breakdown of glucose is coupled in the synthesis of ATP. | 1 | Biochemistry |
The structure of P700 consists of a heterodimer with two distinct chlorophyll molecules, most notably chlorophyll a and chlorophyll a’, giving it an additional name of “special pair”. Inevitably, however, the special pair of P700 behaves as if it were just one unit. This species is vital due to its ability to absorb light energy with a wavelength approximately between 430 nm-700 nm, and transfer high-energy electrons to a series of acceptors that are situated near it, like Fe-S complex, Ferridoxyn(FD), which have a . | 5 | Photochemistry |
The POCIS device was developed and patented by Jimmie D. Petty, James N. Huckins, and David A. Alvarez, of the Columbia Environmental Research Center. Integrative passive samplers are an effective way to monitor the concentration of organic contaminants in aquatic systems over time. Most aquatic monitoring programs rely on collecting individual samples, often called grab samples, at a specific time. The grab sampling method is associated with many disadvantages that can be resolved by passive sampling techniques. When contaminants are present in trace amounts, grab sampling may require the collection of large volumes of water. Also, lab analysis of the sample can only provide a snapshot of contaminant levels at the time of collection. This approach therefore has drawbacks when monitoring in environments where water contamination varies over time and episodic contamination events occur. Passive sampling techniques have been able to provide a time-integrated sample of water contamination with low detection limits and in situ extraction of analytes. | 3 | Analytical Chemistry |
Low-emissivity windows in houses are a more complicated technology, since they must have low emissivity at thermal wavelengths while remaining transparent to visible light. To reduce the heat transfer from a surface, such as a glass window, a clear reflective film with a low emissivity coating can be placed on the interior of the surface. "Low-emittance (low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow". By adding this coating we are limiting the amount of radiation that leaves the window thus increasing the amount of heat that is retained inside the window. | 7 | Physical Chemistry |
RNA aptamers can be designed to act as antagonists, agonists, or so-called ”RNA decoy aptamers." In the case of antagonists, the RNA aptamer is used either to prevent binding of a certain protein to its cell membrane receptor or to prevent the protein from performing its activity by binding to the proteins target. Currently, the only RNA aptamer-based therapies that have advanced to clinical trials act as antagonists. When RNA aptamers are designed to act as agonists, they promote immune cell activation as a co-stimulatory molecule, thus aiding in the mobilization of the bodys own defense system. For RNA decoy aptamers, the synthetic RNA aptamer resembles a native RNA molecule. As such, proteins(s) which bind to the native RNA target instead bind to the RNA aptamer, possibly interfering with the biomolecular pathway of a particular disease. In addition to their utility as direct therapeutic agents, RNA aptamers are also being considered for other therapeutic roles. For instance, by conjugating the RNA aptamer to a drug compound, the RNA aptamer can act as a targeted delivery system for that drug. Such RNA aptamers are known as ApDCs. Additionally, through conjugation to radioisotope or a fluorescent dye molecule, RNA aptamers may be useful in diagnostic imaging.
Because of the SELEX process utilized to select RNA aptamers, RNA aptamers can be generated for many potential targets. By directly introducing the RNA aptamers to the target during SELEX, a very selective, high-affinity, homogeneous pool of RNA aptamers can be produced. As such, RNA aptamers can be made to target small peptides and proteins, as well as cell fragments, whole cells, and even specific tissues. Examples of RNA aptamer molecular targets and potential targets include vascular endothelial growth factor, osteoblasts, and C-X-C Chemokine Ligand 12 (CXCL2).
An example of an RNA aptamer therapy includes Pegaptanib (aka Macugen ® ), the only FDA-approved RNA aptamer treatment. Originally approved in 2004 to treat age-related macular degeneration, Pegaptanib is a 28 nucleotide RNA aptamer that acts as a VEGF antagonist. However, it is not as effective as antibody-based treatments such as bevacizumab and ranibizumab. Another example of an RNA aptamer therapeutic is NOX-A12, a 45 nucleotide RNA aptamer that is in clinical trials for chronic lymphocytic leukemia, pancreatic cancer, as well as other cancers. NOX-A12 acts as antagonist for CXCL12/SDF-1, a chemokine involved in tumor growth. | 1 | Biochemistry |
Color–flavor locking (CFL) is a phenomenon that is expected to occur in ultra-high-density strange matter, a form of quark matter. The quarks form Cooper pairs, whose color properties are correlated with their flavor properties in a one-to-one correspondence between three color pairs and three flavor pairs. According to the Standard Model of particle physics, the color-flavor-locked phase is the highest-density phase of three-flavor colored matter. | 7 | Physical Chemistry |
Nitrile oxides have the chemical formula . Their general structure is . The R stands for any group (typically organyl, e.g., acetonitrile oxide , hydrogen in the case of fulminic acid , or halogen, e.g., chlorine fulminate ). They and are used in 1,3-dipolar cycloadditions. They undergo type 1 dyotropic rearrangement to isocyanates. Nitrile oxides can be synthesised by dehydrogenation of oximes or by dehydration of nitroalkanes. They can be used to synthesise isoxazoles. | 0 | Organic Chemistry |
Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ultraviolet lamps are employed. Organic photochemistry has proven to be a very useful synthetic tool. Complex organic products can be obtained simply. | 5 | Photochemistry |
In crystallography, the orientations of crystal axes and faces in three-dimensional space are a central geometric concern, for example in the interpretation of X-ray and electron diffraction patterns. These orientations can be visualized as in the section Visualization of lines and planes above. That is, crystal axes and poles to crystal planes are intersected with the northern hemisphere and then plotted using stereographic projection. A plot of poles is called a pole figure.
In electron diffraction, Kikuchi line pairs appear as bands decorating the intersection between lattice plane traces and the Ewald sphere thus providing experimental access to a crystal's stereographic projection. Model Kikuchi maps in reciprocal space, and fringe visibility maps for use with bend contours in direct space, thus act as road maps for exploring orientation space with crystals in the transmission electron microscope. | 3 | Analytical Chemistry |
Strong measurements (both classical and quantum) are certainly disturbing, causing asymmetry due to the second law of thermodynamics. However,
noninvasive measurements should not disturb the evolution, so they are expected to be time-symmetric. Surprisingly, it is true only in classical physics but not in quantum physics, even in a thermodynamically invariant equilibrium state. This type of asymmetry is independent of CPT symmetry but has not yet been confirmed experimentally due to extreme conditions of the checking proposal. | 7 | Physical Chemistry |
The Allen–Millar–Trippett rearrangement is a ring expansion reaction in which a cyclic phosphine is transformed into a cyclic phosphine oxide. This name reaction, first reported in the 1960s by David W. Allen, Ian T. Millar, and Stuart Trippett, occurs by alkylation or acylation of the phosphorus, followed by reaction with hydroxide to give a rearranged product. The hydroxide first attacks the phosphonium atom, followed by collapse to the phosphine oxide with one of the groups migrating off of the phosphorus. | 0 | Organic Chemistry |
As the name suggests, trishomoaromatics are defined as containing one additional methylene bridge compared to bishomoaromatics, therefore containing three of these homoconjugate bridges in total. Just like semibullvalene, there is still much debate as to the extent of the homoaromatic character of trishomoaromatics. While theoretically they are homoaromatic, these compounds show a stabilization of no more than 5% of benzene due to delocalization. | 7 | Physical Chemistry |
The final loaded carbon is removed from the machinery and extracted with a hot alkaline solution of cyanide. The elute solution passes through an electrowinning cell where the gold metal is deposited. The solution then passes back through the loaded carbon, extracting more gold and other metals. This process continues until the carbon has been stripped of its metals.
The cathodes (wire wool, now plated with gold and other metals) are removed and placed in sulfuric, hydrochloric, or nitric acid. The acid burns off the wire wool and other metals such as copper, and leaves a sediment of gold and a solution of acid and dissolved silver. The acid and silver are drained off, after which the gold sediment is washed with water numerous times. | 8 | Metallurgy |
In organic chemistry, thioacyl chloride is a functional group of the type RC(S)Cl, where R is an organic substituent. Thioacyl chlorides are analogous to acid chlorides, but much rarer and less robust. The best studied is thiobenzoyl chloride, a purple oil first prepared by chlorination of dithiobenzoic acid with a combination of chlorine and thionyl chloride.
A more modern preparation employs phosgene as the chlorinating agent, this also generates carbonyl sulfide as a by-product.
PhCSH + COCl → PhC(S)Cl + HCl + COS
The most common thioacyl chloride is thiophosgene. | 0 | Organic Chemistry |
O-linked glycopeptides recently have been shown to exhibit excellent CNS permeability and efficacy in multiple animal models with disease states. In addition one of the most intriguing aspects thereof is the capability of O-glycosylation to extend half life, decrease clearance, and improve PK/PD thereof the active peptide beyond increasing CNS penetration. The innate utilization of sugars as solubilizing moieties in Phase II and III metabolism (glucuronic acids) has remarkably allowed an evolutionary advantage in that mammalian enzymes are not directly evolved to degrade O glycosylated products on larger moieties.
The peculiar nature of O-linked glycopeptides is that there are numerous examples which are CNS penetrant. The fundamental basis of this effect is thought to involve "membrane hopping" or "hop diffusion". The non-brownian motion driven "hop diffusion" process is thought to occur due to discontinuity of the plasma membrane. "Hop diffusion" notably combines free diffusion and intercomparmental transitions. Recent examples notably include high permeability of met-enkephalin analogs amongst other peptides. The full mOR agonist pentapeptide DAMGO is also CNS penetrant upon introduction of glycosylation. | 0 | Organic Chemistry |
The genes required for the synthesis of cysteine are coded for on the cys regulon. The integration of sulfur is positively regulated by CysB. Effective inducers of this regulon are N-acetyl-serine (NAS) and very small amounts of reduced sulfur. CysB functions by binding to DNA half sites on the cys regulon. These half sites differ in quantity and arrangement depending on the promoter of interest. There is however one half site that is conserved. It lies just upstream of the -35 site of the promoter. There are also multiple accessory sites depending on the promoter. In the absence of the inducer, NAS, CysB will bind the DNA and cover many of the accessory half sites. Without the accessory half sites the regulon cannot be transcribed and cysteine will not be produced. It is believed that the presence of NAS causes CysB to undergo a conformational change. This conformational change allows CysB to bind properly to all the half sites and causes the recruitment of the RNA polymerase. The RNA polymerase will then transcribe the cys regulon and cysteine will be produced.
Further regulation is required for this pathway, however. CysB can down regulate its own transcription by binding to its own DNA sequence and blocking the RNA polymerase. In this case NAS will act to disallow the binding of CysB to its own DNA sequence. OAS is a precursor of NAS, cysteine itself can inhibit CysE which functions to create OAS. Without the necessary OAS, NAS will not be produced and cysteine will not be produced. There are two other negative regulators of cysteine. These are the molecules sulfide and thiosulfate, they act to bind to CysB and they compete with NAS for the binding of CysB. | 1 | Biochemistry |
Dozens of congenital metabolic diseases also known as inborn errors of metabolism (IEM) are now detectable by newborn screening tests, especially the testing using gas chromatography–mass spectrometry. GC–MS can determine compounds in urine even in minor concentration. These compounds are normally not present but appear in individuals suffering with metabolic disorders. This is increasingly becoming a common way to diagnose IEM for earlier diagnosis and institution of treatment eventually leading to a better outcome. It is now possible to test a newborn for over 100 genetic metabolic disorders by a urine test at birth based on GC–MS.
In combination with isotopic labeling of metabolic compounds, the GC–MS is used for determining metabolic activity. Most applications are based on the use of C as the labeling and the measurement of C-C ratios with an isotope ratio mass spectrometer (IRMS); an MS with a detector designed to measure a few select ions and return values as ratios. | 3 | Analytical Chemistry |
In chemistry, a radical clock is a chemical compound that assists in the indirect methodology to determine the kinetics of a free-radical reaction. The radical-clock compound itself reacts at a known rate, which provides a calibration for determining the rate of another reaction.
Many organic mechanisms involve intermediates that cannot be identified directly but which are inferred from trapping reactions. When such intermediates are radicals, their lifetimes can be deduced from radical clocks. An alternative, perhaps more direct approach involves generation and isolation of the intermediates by flash photolysis and pulse radiolysis, but such methods are time-consuming and require expensive equipment. With an indirect approach of radical clocks, one can still obtain relative or absolute rate constants without the need for instruments or equipment beyond those normally needed for the reaction being studied. | 7 | Physical Chemistry |
The dystrophin-associated protein complex, also known as the dystrophin-associated glycoprotein complex is a multiprotein complex that includes dystrophin and the dystrophin-associated proteins. It is one of the two protein complexes that make up the costamere in striated muscle cells. The other complex is the integrin-vinculin-talin complex. | 1 | Biochemistry |
Human EH3 is a recently characterized protein with epoxy hydrolase activity for metabolizing epoxyeicosatrienoic acids (EETs) and vernolic acids (leukotoxins) to their corresponding diols; in these capacities they may thereby limit the cell signaling activity of the EETs and contribute to the toxicity of the leukotoxins. mRNA for EH3 is most strongly expressed in the lung, skin, and upper gastrointestinal tract tissues of mice. The function of EH3 in humans, mice, or other mammals has not yet been determined although the gene for EH3 has been validated as being hypermethylated on CpG sites in its promoter region in human prostate cancer tissue, particularly in the tissues of more advanced or morphologically-based (i.e. Gleason score) more aggressive cancers; this suggests that the gene silencing of EH3 due to this hypermethylation may contribute to the onset and/or progression of prostate cancer. Similar CpG site hypermethylations in the promoter of for the EH3 gene have been validated for other cancers. This promoter methylation pattern, although not yet validated, was also found in human malignant melanoma. | 1 | Biochemistry |
In 1992, Hunter was jointly awarded the Meldola Medal and Prize by the Royal Society of Chemistry. It is awarded to a British chemist who was under 32 years of age for promising original investigations in chemistry. In 1999, he was jointly awarded the Corday–Morgan Medal and Prize by the Royal Society of Chemistry. It is awarded for the most meritorious contributions to chemistry. In 2008, he was elected a Fellow of the Royal Society (FRS), the premier learned society for science in the United Kingdom. | 0 | Organic Chemistry |
Nitrification inhibitors are also of interest from an environmental standpoint because of the production of nitrates and nitrous oxide from the process of nitrification. Nitrous oxide (NO), although its atmospheric concentration is much lower than that of CO has a global warming potential of about 300 times greater than carbon dioxide and contributes 6% of planetary warming due to greenhouse gases. This compound is also notable for catalyzing the breakup of ozone in the stratosphere. Nitrates, a toxic compound for wildlife and livestock and a product of nitrification, are also of concern.
Soil, consisting of polyanionic clays and silicates, generally has a net anionic charge. Consequently, ammonium (NH) binds tightly to the soil but nitrate ions (NO) do not. Because nitrate is more mobile, it leaches into groundwater supplies through agricultural runoff. Nitrates in groundwater can affect surface water concentrations, either through direct groundwater-surface water interactions (e.g., gaining stream reaches, springs), or from when it is extracted for surface use. As an example, much of the drinking water in the United States comes from groundwater, but most wastewater treatment plants discharge to surface water.
Wildlife such as amphibians, freshwater fish, and insects are sensitive to nitrate levels, and have been known to cause death and developmental anomalies in affected species. Nitrate levels also contribute to eutrophication, a process in which large algal blooms reduce oxygen levels in bodies of water and lead to death in oxygen-consuming creatures due to anoxia. Nitrification is also thought to contribute to the formation of photochemical smog, ground level ozone, acid rain, changes in species diversity, and other undesirable processes. In addition, nitrification inhibitors have also been shown to suppress the oxidation of methane (CH), a potent greenhouse gas, to CO. Both nitrapyrin and acetylene are shown to be especially strong suppressors of both processes, although the modes of action distinguishing them are unclear. | 1 | Biochemistry |
Phenols form a complex with ferric ions. This complex has an intense colour, which may vary from blue, green or even red depending upon the nature of the phenol. As an example using the chemical phenol itself:
: 6 PhOH + Fe → [Fe(OPh)] | 3 | Analytical Chemistry |
Nanoparticles used as carriers for nucleic acids are mostly iron oxides. These iron oxides can be generated by precipitation from acidic iron-salt solutions upon addition of appropriate bases. The magnetic nanoparticles have an approximate size of 100 nm and are additionally coated with biological polymers to allow loading of nucleic acids. Particles and nucleic acids form complexes by ionic interaction of the negatively charged nucleic acid and the positively charged surface of the magnetic nanoparticle. | 1 | Biochemistry |
The attraction between cationic and anionic sites is a noncovalent, or intermolecular interaction which is usually referred to as ion pairing or salt bridge.
It is essentially due to electrostatic forces, although in aqueous medium the association is driven by entropy and often even endothermic. Most salts form crystals with characteristic distances between the ions; in contrast to many other noncovalent interactions, salt bridges are not directional and show in the solid state usually contact determined only by the van der Waals radii of the ions.
Inorganic as well as organic ions display in water at moderate ionic strength I similar salt bridge as association ΔG values around 5 to 6 kJ/mol for a 1:1 combination of anion and cation, almost independent of the nature (size, polarizability, etc.) of the ions. The ΔG values are additive and approximately a linear function of the charges, the interaction of e.g. a doubly charged phosphate anion with a single charged ammonium cation accounts for about 2x5 = 10 kJ/mol. The ΔG values depend on the ionic strength I of the solution, as described by the Debye-Hückel equation, at zero ionic strength one observes ΔG = 8 kJ/mol. | 6 | Supramolecular Chemistry |
There is ongoing research on how Genetic variants in the CYP21A2 gene may lead to pathogenic conditions. A variant of this gene has been reported to cause autosomal dominant posterior polar cataract, suggesting that steroid 21-hydroxylase may be involved in the extra-adrenal biosynthesis of aldosterone and cortisol in the lens of the eye. | 1 | Biochemistry |
Some sperm banks enable recipients to choose the sex of their child, through methods of sperm sorting. Although the methods used do not guarantee 100% success, the chances of being able to select the gender of a child are held to be considerably increased.
One of the processes used is the swim up method, whereby a sperm extender is added to the donor's freshly ejaculated sperm and the test-tube is left to settle. After about half-an-hour, the lighter sperm, containing the male chromosome pair (XY), will have swum to the top, leaving the heavier sperm, containing the female chromosome pair (XX), at the bottom, thus allowing selection and storage according to sex.
The alternative process is the Percoll Method which is similar to the swim up method but involves additionally the centrifuging of the sperm in a similar way to the washing of samples produced for IUI inseminations, or for IVF purposes.
Sex selection is not permitted in a number of countries, including the UK. | 1 | Biochemistry |
The transport of Mg into Paramecium has been characterised largely by R. R. Preston and his coworkers. Electrophysiological techniques on whole Paramecium were used to identify and characterise Mg currents in a series of papers before the gene was cloned by Haynes et al. (2002).
The open reading frame for the XNTA gene is 1707 bp in size, contains two introns and produces a predicted protein of 550 amino acids. The protein has been predicted to contain 11 TM domains and also contains the α1 and α2 motifs (see figure) of the SLC8 (Na+/Ca exchanger) and SLC24 (K+ dependent Na+/Ca exchanger) human solute transport proteins. The XntAp is equally similar to the SLC8 and SLC24 protein families by amino acid sequence, but the predicted TM topology is more like that of SLC24, but the similarity is at best weak and the relationship is very distant. The AtMHX protein from plants also shares a distant relationship with the SLC8 proteins.
The figure shows the predicted TM topology of XntAp. Adapted from Haynes et al. (2002), this figure shows the computer predicted membrane topology of XntAp in Paramecium. The orientation in the membrane was determined using HMMTOP. The TM domains are shown in light blue, the α1 and α2 domains are shown in green. The orientation in the membrane and the positions of the N- and C-termini are indicated and the figure is not drawn to scale.
The Mg-dependent currents carried by XntAp are kinetically like that of a channel protein and have an ion selectivity order of Mg > Co, Mn > Ca — a series again very similar to that of CorA. Unlike the other transport proteins reported so far, XntAp is dependent on intracellular Ca. The transport is also dependent on ΔΨ, but again Mg is not transported to equilibrium, being limited to approximately 0.4 mM free Mg in the cytoplasm. The existence of an intracellular compartment with a much higher free concentration of Mg (8 mM) was supported by the results. | 1 | Biochemistry |
Household ammonia can be used. A couple of drops are placed on the flesh. For example, Boletus spadiceus gives a fleeting blue to blue-green reaction. | 3 | Analytical Chemistry |
Oceanic anoxic events have had many important consequences. It is believed that they have been responsible for mass extinctions of marine organisms both in the Paleozoic and Mesozoic. The early Toarcian and Cenomanian-Turonian anoxic events correlate with the Toarcian and Cenomanian-Turonian extinction events of mostly marine life forms. Apart from possible atmospheric effects, many deeper-dwelling marine organisms could not adapt to an ocean where oxygen penetrated only the surface layers.
An economically significant consequence of oceanic anoxic events is the fact that the prevailing conditions in so many Mesozoic oceans has helped produce most of the world's petroleum and natural gas reserves. During an oceanic anoxic event, the accumulation and preservation of organic matter was much greater than normal, allowing the generation of potential petroleum source rocks in many environments across the globe. Consequently, some 70 percent of oil source rocks are Mesozoic in age, and another 15 percent date from the warm Paleogene: only rarely in colder periods were conditions favorable for the production of source rocks on anything other than a local scale. | 9 | Geochemistry |
Although theoretically, any living cell might be used as the background to a two-hybrid analysis, there are practical considerations that dictate which is chosen. The chosen cell line should be relatively cheap and easy to culture and sufficiently robust to withstand application of the investigative methods and reagents. The latter is especially important for doing high-throughput studies. Therefore the yeast S. cerevisiae has been the main host organism for two-hybrid studies. However it is not always the ideal system to study interacting proteins from other organisms. Yeast cells often do not have the same post translational modifications, have a different codon use or lack certain proteins that are important for the correct expression of the proteins. To cope with these problems several novel two-hybrid systems have been developed. Depending on the system used agar plates or specific growth medium is used to grow the cells and allow selection for interaction. The most common used method is the agar plating one where cells are plated on selective medium to see of interaction takes place. Cells that have no interaction proteins should not survive on this selective medium. | 1 | Biochemistry |
Copper was probably the first metal mined and crafted by humans. It was originally obtained as a native metal and later from the smelting of ores. Earliest estimates of the discovery of copper suggest around 9000 BC in the Middle East. It was one of the most important materials to humans throughout the Chalcolithic and Bronze Ages. Copper beads dating from 6000 BC have been found in Çatalhöyük, Anatolia and the archaeological site of Belovode on the Rudnik mountain in Serbia contains the world's oldest securely dated evidence of copper smelting from 5000 BC. It was recognised as an element by Louis Guyton de Morveau, Antoine Lavoisier, Claude Berthollet, and Antoine-François de Fourcroy in 1787.
It is believed that lead smelting began at least 9,000 years ago, and the oldest known artifact of lead is a statuette found at the temple of Osiris on the site of Abydos dated around 3800 BC. It was recognised as an element by Guyton de Morveau, Lavoisier, Berthollet, and Fourcroy in 1787.
The earliest gold artifacts were discovered at the site of Wadi Qana in the Levant. Silver is estimated to have been discovered in Asia Minor shortly after copper and gold.
There is evidence that iron was known from before 5000 BC. The oldest known iron objects used by humans are some beads of meteoric iron, made in Egypt in about 4000 BC. The discovery of smelting around 3000 BC led to the start of the Iron Age around 1200 BC and the prominent use of iron for tools and weapons. It was recognised as an element by Guyton de Morveau, Lavoisier, Berthollet, and Fourcroy in 1787.
Tin was first smelted in combination with copper around 3500 BC to produce bronze (and thus giving place to the Bronze Age (except in some places which did not experience a significant Bronze Age, passing directly from the Neolithic Stone Age to the Iron Age)). Kestel, in southern Turkey, is the site of an ancient Cassiterite mine that was used from 3250 to 1800 BC. The oldest artifacts date from around 2000 BC. It was recognised as an element by Guyton de Morveau, Lavoisier, Berthollet, and Fourcroy in 1787. | 8 | Metallurgy |
FCCS measures the coincident green and red intensity fluctuations of distinct molecules that correlate if green and red labeled particles move together through a predefined confocal volume. To perform fluorescence cross-correlation spectroscopy (FCCS), samples of interest are first labeled with fluorescent probes of different colours. The FCCS setup typically includes a confocal microscope, two laser sources, and two detectors. The confocal microscope is used to focus the laser beams and collect the fluorescence signals. The signals from the detectors are then collected and recorded over time. Data analysis involves cross-correlating the signals to determine the degree of correlation between the two fluorescent probes. This information can be used to extract data on the stoichiometry and binding constants of molecular complexes, as well as the timing and location of interactions within living cells. | 7 | Physical Chemistry |
The strength of a synapse has been defined by Bernard Katz as the product of (presynaptic) release probability pr, quantal size q (the postsynaptic response to the release of a single neurotransmitter vesicle, a quantum), and n, the number of release sites. "Unitary connection" usually refers to an unknown number of individual synapses connecting a presynaptic neuron to a postsynaptic neuron.
The amplitude of postsynaptic potentials (PSPs) can be as low as 0.4 mV to as high as 20 mV. The amplitude of a PSP can be modulated by neuromodulators or can change as a result of previous activity. Changes in the synaptic strength can be short-term, lasting seconds to minutes, or long-term (long-term potentiation, or LTP), lasting hours. Learning and memory are believed to result from long-term changes in synaptic strength, via a mechanism known as synaptic plasticity. | 1 | Biochemistry |
The term pewter covers a variety of alloys consisting primarily of tin. As a pure metal, tin is much too soft to use for most practical purposes. However, during the Bronze Age, tin was a rare metal in many parts of Europe and the Mediterranean, so it was often valued higher than gold. To make jewellery, cutlery, or other objects from tin, workers usually alloyed it with other metals to increase strength and hardness. These metals were typically lead, antimony, bismuth or copper. These solutes were sometimes added individually in varying amounts, or added together, making a wide variety of objects, ranging from practical items such as dishes, surgical tools, candlesticks or funnels, to decorative items like ear rings and hair clips.
The earliest examples of pewter come from ancient Egypt, around 1450 BC. The use of pewter was widespread across Europe, from France to Norway and Britain (where most of the ancient tin was mined) to the Near East. The alloy was also used in China and the Far East, arriving in Japan around 800 AD, where it was used for making objects like ceremonial vessels, tea canisters, or chalices used in shinto shrines. | 8 | Metallurgy |
Homochirality is the geometric uniformity of materials composed of chiral (non-mirror-symmetric) units. Living organisms use molecules that have the same chirality (handedness): with almost no exceptions, amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 (racemic) mixture of both forms. Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction; asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, statistical fluctuations during racemic synthesis, and spontaneous symmetry breaking.
Once established, chirality would be selected for. A small bias (enantiomeric excess) in the population can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.
Homochirality may have started in outer space, as on the Murchison meteorite the amino acid L-alanine is more than twice as frequent as its D form, and L-glutamic acid is more than three times as abundant as its D counterpart. Amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, as found in living organisms, suggesting an abiogenic origin of these compounds.
In 2010, an experiment by Robert Root-Bernstein shows that "two D-RNA-oligonucleotides having inverse base sequences (D-CGUA and D-AUGC) and their corresponding L-RNA-oligonucleotides (L-CGUA and L-AUGC) were synthesized and their affinity determined for Gly and eleven pairs of L- and D-amino acids". This suggests that homochirality, including codon directionality, might have "emerged as a function of the origin of the genetic code". | 9 | Geochemistry |
Administration of neuromuscular blocking agents (NMBA) during anesthesia can facilitate endotracheal intubation. This can decrease the incidence of postintubation hoarseness and airway injury.
Short-acting neuromuscular blocking agents are chosen for endotracheal intubation for short procedures (< 30minutes), and neuromonitoring is required soon after intubation. Options include succinylcholine, rocuronium or vecuronium if sugammadex is available for rapid reversal block.
Any short or intermediate acting neuromuscular blocking agents can be applied for endotracheal intubation for long procedures (≥ 30 minutes). Options include succinylcholine, rocuronium, vecuronium, mivacurium, atracurium and cisatracurium. The choice among these NMBA depends on availability, cost and patient parameters that affect drug metabolism.
Intraoperative relaxation can be maintained as necessary with additional dose of nondepolarizing NMBA.
Among all NMBA, Succinylcholine establish the most stable and fastest intubating conditions, thus is considered as the preferred NMBA for rapid sequence induction and intubation (RSII). Alternatives for succinylcholine for RSII include high dose rocuronium (1.2mg/kg which is a 4 X ED95 dose), or avoidance of NMBAs with a high dose remifentanil intubation. | 1 | Biochemistry |
Due to MoOPH's steric bulk, preferential attack at the O–O bond occurs from the less hindered enolate face in the absence of stereoelectronic factors.
In addition, nitriles with acidic alpha protons can be converted directly to cyanohydrins; however, in the case of branched nitriles, this reaction directly affords the ketone.
In the case of sulfones, alpha-hydroxylation leads directly to the ketone or aldehyde.
Common byproducts of the alpha-hydroxylation tend to include overoxidation to the corresponding dicarbonyl or intermolecular aldol reaction of the starting material. Procedures to prevent side reactions include the inverse addition of the enolate to MoOPH or careful control of the temperature (-78 to -20 °C). Notable miscellaneous reactions include MoOPH’s ability to oxidize alkylboranes directly to the alcohol with net stereo-retention.
MoOPH has also been shown to oxidize N-trimethylsilyl amides directly to the hydroxamic acid. | 0 | Organic Chemistry |
Cryo crystallography enables X-ray data collection at cryogenic temperatures, typically 100 K.
*Crystals are transferred from the solution they have grown in (called mother liquor) to a solution with a cryo-protectant to prevent ice formation.
*Crystals are mounted in a glass fiber (as opposed to a capillary.)
*Crystals are cooled by dipping directly into liquid nitrogen and then placed in a cryo cold stream.
*Cryo cooled macromolecular crystals show reduced radiation damage by more than 70 times that at room temperature. | 3 | Analytical Chemistry |
Key to modeling the topology of a material are the special points along k-vector of the Brillouin zone, accounting for the accurate depiction of the density of states emerging from the electronics of the material. Density functional theory (DFT) analyses predicted an indirect band gap of 0.158 eV in the β-BiI phase with the valence and conduction band maxima localized at the Γ and M k-space points, respectively. Interestingly enough, the major contributors to the band structure around the Fermi level are bismuth's p orbitals of even and odd parity, thus giving the gerade and ungerade points of symmetry. | 7 | Physical Chemistry |
Neurotransmitters bind to ionotropic receptors on postsynaptic neurons, either causing their opening or closing. The variations in the quantities of neurotransmitters released from the presynaptic neuron may play a role in regulating the effectiveness of synaptic transmission. In fact, the concentration of cytoplasmic calcium is involved in regulating the release of neurotransmitters from presynaptic neurons.
The chemical transmission involves several sequential processes:
# Synthesizing neurotransmitters within the presynaptic neuron.
# Loading the neurotransmitters into secretory vesicles.
# Controlling the release of neurotransmitters into the synaptic cleft.
# Binding of neurotransmitters to postsynaptic receptors.
# Ceasing the activity of the released neurotransmitters. | 1 | Biochemistry |
Metallurgists study the microscopic and macroscopic structure of metals using metallography, a technique invented by Henry Clifton Sorby.
In metallography, an alloy of interest is ground flat and polished to a mirror finish. The sample can then be etched to reveal the microstructure and macrostructure of the metal. The sample is then examined in an optical or electron microscope, and the image contrast provides details on the composition, mechanical properties, and processing history.
Crystallography, often using diffraction of x-rays or electrons, is another valuable tool available to the modern metallurgist. Crystallography allows identification of unknown materials and reveals the crystal structure of the sample. Quantitative crystallography can be used to calculate the amount of phases present as well as the degree of strain to which a sample has been subjected. | 8 | Metallurgy |
Because methylmercury is formed in aquatic systems, and because it is not readily eliminated from organisms, it is biomagnified in aquatic food chains from bacteria, to plankton, through macroinvertebrates, to herbivorous fish and to piscivorous (fish-eating) fish. At each step in the food chain, the concentration of methylmercury in the organism increases. The concentration of methylmercury in the top-level aquatic predators can reach a level a million times higher than the level in the water. This is because methylmercury has a half-life of about 72 days in aquatic organisms resulting in its bioaccumulation within these food chains. Organisms, including humans, fish-eating birds, and fish-eating mammals such as otters and cetaceans (i.e. whales and dolphins) that consume fish from the top of the aquatic food chain receive the methylmercury that has accumulated through this process, plus the toxins in their habitat. Fish and other aquatic species are the main source of human methylmercury exposure.
The concentration of mercury in any given fish depends on the species of fish, the age and size of the fish and the type of water body in which it is found. In general, fish-eating fish such as shark, swordfish, marlin, larger species of tuna, walleye, largemouth bass, and northern pike, have higher levels of methylmercury than herbivorous fish or smaller fish such as tilapia and herring. Within a given species of fish, older and larger fish have higher levels of methylmercury than smaller fish. Fish that develop in water bodies that are more acidic also tend to have higher levels of methylmercury. | 0 | Organic Chemistry |
Hydroamination is well-established technology for generating fragrances from myrcene. In this conversion, diethylamine adds across the diene substituent, the reaction being catalyzed by lithium diethylamide. Intramolecular hydroaminations were reported by Tobin J. Marks in 1989 using metallocene derived from rare-earth metals such as lanthanum, lutetium, and samarium. Catalytic rates correlated inversely with the ionic radius of the metal, perhaps as a consequence of steric interference from the ligands. In 1992, Marks developed the first chiral hydroamination catalysts by using a chiral auxiliary, which were the first hydroamination catalysts to favor only one specific stereoisomer. Chiral auxiliaries on the metallocene ligands were used to dictate the stereochemistry of the product. The first non-metallocene chiral catalysts were reported in 2003, and used bisarylamido and aminophenolate ligands to give higher enantioselectivity. | 0 | Organic Chemistry |
A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences). Telomeres are a widespread genetic feature most commonly found in eukaryotes. In most, if not all species possessing them, they protect the terminal regions of chromosomal DNA from progressive degradation and ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break. | 1 | Biochemistry |
Phycochromes are a subclass of phycobiliprotein that was initially recognised only as light sensory pigments in cyanobacteria. They are now deemed to constitute of all possible photoreversibly photochromic pigments, regardless of function. They are also found in red algae. In a series of journal articles written by G.S. and L.O. Björn, it was reported that phycochromes a, b, c and d were discovered by scientists who fractionated samples of blue-green algae using electrofocusing. The fractions with isoelectric points at or around 4.6 seemed analogous to phytochromes in that they possessed photochromic properties, yet were sensitive to light of shorter wavelengths. All four phycochromes except phycochrome c were extracted from the blue-green algae Tolypothrix distorta; whereas phycochrome a was also found in Phormidium luridum, Nostoc muscorum 1453/12 and Anacystis nidulans; and phycochrome c was extracted from Nostoc muscorum A and Tolypothrix tenuis. | 1 | Biochemistry |
In organic chemistry, alpha-elimination refers to reactions of this type:
:RCHX → RC: + HX
The reaction is employed to generate carbenes and nitrenes. The formation of dichlorocarbene from chloroform is an example.
Alpha eliminations contrasts with beta eliminations, which are commonly used to generate alkenes:
:RCHCXR → RC=CR + HX
Both alpha- and beta-eliminations typically require strong base. | 0 | Organic Chemistry |
The amount of negative charge from deprotonation of clay hydroxy groups or organic matter depends on the pH of the surrounding solution. Increasing the pH (i.e. decreasing the concentration of H cations) increases this variable charge, and therefore also increases the cation-exchange capacity. | 9 | Geochemistry |
Source:
*1946 – David E. Green
*1947 – Van R. Potter
*1948 – Albert L. Lehninger
*1949 – Henry A. Lardy
*1950 – Britton Chance
*1951 – Arthur Kornberg
*1952 – Bernard L. Horecker
*1953 – Earl R. Stadtman
*1954 – Alton Meister
*1955 – Paul D. Boyer
*1956 – Merton F. Utter
*1957 – G. Robert Greenberg
*1958 – Eugene P. Kennedy
*1959 – Minor J. Coon
*1960 – Arthur Pardee
*1961 – Frank M. Huennekens
*1962 – Jack L. Strominger
*1963 – Charles Gilvarg
*1964 – Marshall Nirenberg
*1965 – Frederic M. Richards
*1966 – Samuel B. Weiss
*1967 – P. Roy Vagelos & Salih J. Wakil
*1968 – William J. Rutter
*1969 – Robert T. Schimke
*1970 – Herbert Weissbach
*1971 – Jack Preiss
*1972 – Ekkehard K. F. Bautz
*1973 – Howard M. Temin
*1974 – Michael J. Chamberlin
*1975 – Malcolm L. Gefter
*1976 – Michael S. Brown & Joseph L. Goldstein
*1977 – Stephen J. Benkovic
*1978 – Paul Schimmel
*1979 – Frederik C. Hartman
*1980 – Thomas A. Steitz
*1981 – Daniel V. Santi
*1982 – Richard R. Burgess
*1983 – Paul L. Modrich
*1984 – Robert T.N. Tjian
*1985 – Thomas R. Cech
*1986 – JoAnne Stubbe
*1987 – Gregory Petsko
*1988 – John W. Kozarich
*1989 – Kenneth A. Johnson
*1990 – James A. Wells
*1991 – Ronald Vale
*1992 – Carl O. Pabo
*1993 – Michael H. Gelb
*1994 – Donald Hilvert
*1995 – Gerald F. Joyce
*1996 – P. Andrew Karplus
*1997 – Daniel Herschlag
*1998 – Ronald T. Raines
*1999 – David W. Christianson
*2000 – Eric T. Kool
*2001 – Ruma Banerjee
*2002 – Karin Musier-Forsyth
*2003 – Dorothee Kern
*2004 – Wilfred A. van der Donk
*2005 – Nicole S. Sampson
*2006 – James Berger
*2007 – Neil L. Kelleher
*2008 – Carsten Krebs
*2009 – Virginia Cornish
*2010 – Vahe Bandarian
*2011 – Sarah O’Connor
*2012 – Jin Zhang
*2013 – Kate Carroll
*2014 – Hening Lin
*2015 – Douglas Mitchell
*2016 – Michelle C. Chang
*2017 – Emily Balskus
*2018 – Mohammad Seyedsayamdost
*2019 – Kenichi Yokoyama
*2020 – Rahul Kohli
*2021 – Amie K. Boal | 1 | Biochemistry |
From intravenous (IV) animal studies the toxic dose (LD) of palytoxin via IV for humans has been estimated by extrapolation to be between 2.3 and 31.5 micrograms (µg) of palytoxin. An acute oral reference dose has been suggested to be 64 µg for a person with weight of 60 kg. Acute reference dose means a dose that can be safely ingested over a short period of time, usually during one meal or one day.
In comparison to IV injection, the toxicity of palytoxin in various animals via intramuscular and subcutaneous injections are 2.5 and 4–30 times higher, respectively. Upon ingestion the toxicity in animals has been 200 times less than via IV. In the table below, there are listed some LD values for partially pure palytoxin obtained from different Palythoa. These values represent the amount of palytoxin required to kill half of the test animals. Values are in micrograms (µg) per kilogram of the animal's weight and have been measured 24 hours after the initial exposure.
An early toxicological characterization classified palytoxin as "relatively non-toxic" after intragastric administration to rats. The lethal dose (LD) was greater than 40 µg/kg. The LD after parenteral administration was lower than 1 µg/kg. However the doubtful purity of this study increased because of uncertainty concerning the toxicological data. In 1974, the structure of palytoxin was not completely elucidated and the molecular weight was a lot higher (3300 Da instead of 2681 Da). A 2004 study discovered an LD of 510 µg/kg after intragastric administration in mice, but histological or biochemical information was missing. (Rhodes and Munday, 2004) Furthermore, palytoxin was not lethal to mice given an oral dose of 200 µg/kg. It was also found that palytoxin is very toxic after intraperitoneal injection. The LD in mice was less than 1 µg/kg. Because toxin-producing organisms spread to temperate climates and palytoxin-contaminated shellfish were discovered in the Mediterranean Sea a study was done to better define the toxic effects of palytoxin after oral exposure in mice. Palytoxin was lethal from 600 µg/kg doses. The number of deaths were dose-dependent and the LD calculated to be 767 µg/kg. This is comparable to the LD of 510 µg/kg referred by Munday (2008). The toxicity was not different if the mice had some food in their stomach. The oral toxicity is several times lower than the intraperitoneal toxicity. One of the possible causes of this behavior is that palytoxin is a very big hydrophilic molecule and therefore the absorption could be less efficient through the gastrointestinal tract than through the peritoneum. A recent study by Fernandez et al. further investigated on this issue using an in vitro model of intestinal permeability with differentiated monolayers of human colonic Caco-2 cells, confirming that palytoxin was unable to cross the intestinal barrier significantly, despite the damage the toxin exerted on cells and on the integrity of the monolayer. The same study also revealed that palytoxin does not affect tight-junctions on such cells. Palytoxin is most toxic after intravenous injection. The LD in mice is 0.045 µg/kg and in rats 0.089 µg/kg. In other mammals (rabbits, dogs, monkeys and guinea pigs) the LD is ranged between 0.025 and 0.45 µg/kg. They all died in several minutes from heart failure. The lethal dose for mice by the intratracheal route is above 2 µg/kg in 2 hours. Palytoxin is also very toxic after intramuscular or subcutaneous injection. No toxicity is found after intrarectal administration. Palytoxin is not lethal when topically applied to skin or eyes. Palytoxin can travel in water vapor and cause poisoning by inhalation.
In this context, despite an increase in reports of palytoxin contaminated seafood in temperate waters (i.e., Mediterranean Sea), there are no validated and accepted protocols for the detection and quantification of this class of biomolecules. However, in recent years, many methodologies have been described with particular attention on the development of new techniques for the ultrasensitive detection of palytoxin in real matrix such as mussels and microalgae (based on LC-MS-MS or immunoassay). | 0 | Organic Chemistry |
In physical chemistry, when referring to surface processes, saturation denotes the degree at which a binding site is fully occupied. For example, base saturation refers to the fraction of exchangeable cations that are base cations. | 0 | Organic Chemistry |
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