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Ampicillin is an antibiotic belonging to the aminopenicillin class of the penicillin family. The drug is used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B streptococcal infection in newborns. It is used by mouth, by injection into a muscle, or intravenously.
Common side effects include rash, nausea, and diarrhea. It should not be used in people who are allergic to penicillin. Serious side effects may include Clostridium difficile colitis or anaphylaxis. While usable in those with kidney problems, the dose may need to be decreased. Its use during pregnancy and breastfeeding appears to be generally safe.
Ampicillin was discovered in 1958 and came into commercial use in 1961. It is on the World Health Organization's List of Essential Medicines. The World Health Organization classifies ampicillin as critically important for human medicine. It is available as a generic medication. | 4 | Stereochemistry |
Many CF-containing metal complexes have been prepared, and some are useful for trifluoromethylation. The most obvious reagent is CFLi, which can be generated by lithium-iodide exchange. This compound is however unstable even at low temperatures. It degrades to lithium fluoride and difluorocarbene. Trifluoromethyl copper(I) reagents are more useful. These reagents are generated in situ by reaction of CFI with copper powder in polar solvents. Hg(CF), prepared by decarboxylation of the trifluoroacetate, has proven useful for the trifluoromethylation of other metals, although for low-temperature reactions it may prove useful to transmetallate to bis(trifluoromethyl)cadmium. | 0 | Organic Chemistry |
1,1,2-Trichloro-1,2,2-trifluoroethane, also called trichlorotrifluoroethane (often abbreviated as TCTFE) or CFC-113, is a chlorofluorocarbon. It has the formula . This colorless, volatile liquid is a versatile solvent. | 2 | Environmental Chemistry |
Enantiomers of a chiral drug often interact in an enantioselective way in a chiral environment. This may be offered by different biotic substances (viz. proteins, nucleic acids, phospholipids and oligosaccharides). They are made up of chiral building blocks that are put together in space in handed conformations. These biological targets function as receptors for the drug enantiomers. So, at the binding sites of these receptors, enantiomers will be seen as different chemical species. The three point attachment model (Easson & Stedman model) can be used to see how chiral discrimination works. Figure depicts how the enantiomers of a drug interact with receptors in a way that depends on the drug's shape.
This model was made for chiral drugs with a single stereogenic center. It says that there are three binding sites in the receptor (B, C and D) that match the drugs pharmacophoric groups (B, C, D). A three-point fit (good fit) is possible for the eutomer at BB, CC and DD(Fig. A). Even though the distomer is the wrong enantiomer, it can fit either a one-point interaction (bad fit), or a two-point attachment (CC and DD') with the same receptor site as shown in (Fig. B).
Eutomer is the version that works the way you want it to, and distomer is the version that doesnt work or works in a way you dont want it to. Most of the time, the mirror-image versions have different binding affinities. In the eutomer, the ligands or moiety around a stereogenic element have more binding energy than in the distomer. When the eutomer goes through chiral inversion, it loses its ability to bind to a biological receptor. Because of these enantiospecific interactions, therapeutic and toxicological properties are enantioselective So, the stereo-stability of chiral drugs may have big effects on the process of making new drugs, especially when it comes to how pharmaceutical, pharmacokinetic, and pharmacodynamic information is read and understood. At every stage of designing, making, and testing a drug for safety, chiral inversion must be taken into account. | 4 | Stereochemistry |
Cholesterol uptake by cells instigates inflammation, affecting both the central nervous system and the peripheral systems. This phenomenon involves the aggregation of inflammatory proteins. For instance, in the context of TLR4, cholesterol prompts receptor dimerization. Similarly, with TNF alpha, the substrate facilitates the enzyme's binding. Subsequent hydrolysis yields soluble cytokines, contributing to the inflammatory response.
During an inflammatory response cholesterol is loaded into immune cells including macrophages. The cholesterol is a signal that activates cytokine production and other inflammatory responses. Cholesterol's role in inflammation is central to many diseases. | 1 | Biochemistry |
A sand bath is a common piece of laboratory equipment made from a container filled with heated sand. It is used to evenly heat another container, most often during a chemical reaction.
A sand bath is most commonly used in conjunction with a hot plate or heating mantle. A beaker is filled with sand or metal pellets (called shot) and is placed on the plate or mantle. The reaction vessel is then partially covered by sand or pellets. The sand or shot then conducts the heat from the plate to all sides of the reaction vessel.
This technique allows a reaction vessel to be heated throughout with minimal stirring, as opposed to heating the bottom of the vessel and waiting for convection to heat the remainder, cutting down on both the duration of the reaction and the possibility of side reactions that may occur at higher temperatures.
A variation on this theme is the water bath in which the sand is replaced with water. It can be used to keep a reaction vessel at the temperature of boiling water until all water is evaporated (see Standard enthalpy change of vaporization).
Sand baths are one of the oldest known pieces of laboratory equipment, having been used by the alchemists. In Arabic alchemy, a sand bath was known as a qadr. In Latin alchemy, a sand bath was called balneum siccum, balneum cineritium, or balneum arenosum. | 7 | Physical Chemistry |
The carrier gas is sent through the central channel and into the very hot plasma. The sample is then exposed to radio frequency which converts the gas into a plasma. The high temperature of the plasma is sufficient to cause a very large portion of the sample to form ions. This fraction of ionization can approach 100% for some elements (e.g. sodium), but this is dependent on the ionization potential. A fraction of the formed ions passes through a ~1 mm hole (sampler cone) and then a ~0.4 mm hole (skimmer cone). The purpose of which is to allow a vacuum that is required by the mass spectrometer.
The vacuum is created and maintained by a series of pumps. The first stage is usually based on a roughing pump, most commonly a standard rotary vane pump. This removes most of the gas and typically reaches a pressure of around 133 Pa. Later stages have their vacuum generated by more powerful vacuum systems, most often turbomolecular pumps. Older instruments may have used oil diffusion pumps for high vacuum regions. | 3 | Analytical Chemistry |
Histone acetylation and deacetylation are the processes by which the lysine residues within the N-terminal tail protruding from the histone core of the nucleosome are acetylated and deacetylated as part of gene regulation.
Histone acetylation and deacetylation are essential parts of gene regulation. These reactions are typically catalysed by enzymes with "histone acetyltransferase" (HAT) or "histone deacetylase" (HDAC) activity. Acetylation is the process where an acetyl functional group is transferred from one molecule (in this case, acetyl coenzyme A) to another. Deacetylation is simply the reverse reaction where an acetyl group is removed from a molecule.
Acetylated histones, octameric proteins that organize chromatin into nucleosomes, the basic structural unit of the chromosomes and ultimately higher order structures, represent a type of epigenetic marker within chromatin. Acetylation removes the positive charge on the histones, thereby decreasing the interaction of the N termini of histones with the negatively charged phosphate groups of DNA. As a consequence, the condensed chromatin is transformed into a more relaxed structure that is associated with greater levels of gene transcription. This relaxation can be reversed by deacetylation catalyzed by HDAC activity. Relaxed, transcriptionally active DNA is referred to as euchromatin. More condensed (tightly packed) DNA is referred to as heterochromatin. Condensation can be brought about by processes including deacetylation and methylation. | 0 | Organic Chemistry |
Terfenol-D, an alloy of the formula (x ≈ 0.3), is a magnetostrictive material. It was initially developed in the 1970s by the Naval Ordnance Laboratory in the United States. The technology for manufacturing the material efficiently was developed in the 1980s at Ames Laboratory under a U.S. Navy-funded program. It is named after terbium, iron (Fe), Naval Ordnance Laboratory (NOL), and the D comes from dysprosium. | 8 | Metallurgy |
SPE is in fact a method of chromatography, in the sense of having a mobile phase, carrying mixtures through a stationary phase, packed inside a column. The chromatographic process is harnessed to create a solid-liquid extractive technique—allowing separation of a mixture of components by taking advantage of large differences between the solid and liquid phase K, or equilibrium constant, for each component in the mixture. The chemical considerations for the selection of stationary and mobile phases are similar to those for liquid column chromatography and many of the adsorbents/materials used are the same. The theory, procedures, and aims are different, however, and as an extractive technique it has a unique niche in modern chemical science. | 3 | Analytical Chemistry |
The borax method of gold extraction has been used by artisanal gold miners in the Benguet area north of Manila in the Philippines for more than 30 years. Some believe it was in practice as early as the 1900s. The method is increasingly being seen as a safe alternative to the widespread use of toxic mercury in artisanal gold mining today. About 30% of the world's mercury emissions comes from small scale mining. Efforts are being made to revive the method and spread its use. As of 2012, around 15,000 artisanal gold miners in a small area of Luzon, the main island in the northern portion of the Philippines, use this method exclusively. The mineral is inexpensive and easily available, and the miners have reportedly found that more gold is recovered through its use. | 8 | Metallurgy |
Common cutting agents:
* Sugar: Brix refractometers are used to determine sugar content. Traditional handheld refractometers are cheap and can be used to measure whole percentages. Digital handheld refractometers are used to determine percentages in decimal values. | 3 | Analytical Chemistry |
An alternative method for analyzing the autocorrelation function can be achieved through an inverse Laplace transform known as CONTIN developed by Steven Provencher. The CONTIN analysis is ideal for heterodisperse, polydisperse, and multimodal systems that cannot be resolved with the cumulant method. The resolution for separating two different particle populations is approximately a factor of five or higher and the difference in relative intensities between two different populations should be less than 1:10. | 7 | Physical Chemistry |
Recent research suggests that patients with elevated basal levels of CRP are at an increased risk of diabetes, hypertension and cardiovascular disease. A study of over 700 nurses showed that those in the highest quartile of trans fat consumption had blood levels of CRP that were 73% higher than those in the lowest quartile. Although one group of researchers indicated that CRP may be only a moderate risk factor for cardiovascular disease, this study (known as the Reykjavik Study) was found to have some problems for this type of analysis related to the characteristics of the population studied, and there was an extremely long follow-up time, which may have attenuated the association between CRP and future outcomes. Others have shown that CRP can exacerbate ischemic necrosis in a complement-dependent fashion and that CRP inhibition can be a safe and effective therapy for myocardial and cerebral infarcts; this has been demonstrated in animal models and humans.
It has been hypothesized that patients with high CRP levels might benefit from use of statins. This is based on the JUPITER trial that found that elevated CRP levels without hyperlipidemia benefited. Statins were selected because they have been proven to reduce levels of CRP. Studies comparing effect of various statins in hs-CRP revealed similar effects of different statins. A subsequent trial however failed to find that CRP was useful for determining statin benefit.
In a meta-analysis of 20 studies involving 1,466 patients with coronary artery disease, CRP levels were found to be reduced after exercise interventions. Among those studies, higher CRP concentrations or poorer lipid profiles before beginning exercise were associated with greater reductions in CRP.
To clarify whether CRP is a bystander or active participant in atherogenesis, a 2008 study compared people with various genetic CRP variants. Those with a high CRP due to genetic variation had no increased risk of cardiovascular disease compared to those with a normal or low CRP. A study published in 2011 shows that CRP is associated with lipid responses to low-fat and high-polyunsaturated fat diets. | 1 | Biochemistry |
Degenerate gases are gases composed of fermions such as electrons, protons, and neutrons rather than molecules of ordinary matter. The electron gas in ordinary metals and in the interior of white dwarfs are two examples. Following the Pauli exclusion principle, there can be only one fermion occupying each quantum state. In a degenerate gas, all quantum states are filled up to the Fermi energy. Most stars are supported against their own gravitation by normal thermal gas pressure, while in white dwarf stars the supporting force comes from the degeneracy pressure of the electron gas in their interior. In neutron stars, the degenerate particles are neutrons.
A fermion gas in which all quantum states below a given energy level are filled is called a fully degenerate fermion gas. The difference between this energy level and the lowest energy level is known as the Fermi energy. | 7 | Physical Chemistry |
The crushed ore is irrigated with a dilute alkaline cyanide solution. The solution containing the dissolved precious metals in a pregnant solution continues percolating through the crushed ore until it reaches the liner at the bottom of the heap where it drains into a storage (pregnant solution) pond. After separating the precious metals from the pregnant solution, the dilute cyanide solution (now called "barren solution") is normally re-used in the heap-leach-process or occasionally sent to an industrial water treatment facility where the residual cyanide is treated and residual metals are removed. In very high rainfall areas, such as the tropics, in some cases there is surplus water that is then discharged to the environment, after treatment, posing possible water pollution if treatment is not properly carried out.
The production of one gold ring through this method, can generate 20 tons of waste material.
During the extraction phase, the gold ions form complex ions with the cyanide:
Recuperation of the gold is readily achieved with a redox-reaction:
The most common methods to remove the gold from solution are either using activated carbon to selectively absorb it, or the Merrill-Crowe process where zinc powder is added to cause a precipitation of gold and zinc. The fine product can be either doré (gold-silver bars) or zinc-gold sludge that is then refined elsewhere. | 8 | Metallurgy |
Dimethylaminomethylene cation is described as a resonance hybrid of the carbocation and an iminium cation:
The atoms are coplanar. The cation is isoelectronic with isobutene. | 0 | Organic Chemistry |
In addition to the use of the multiprotein complexes listed above, gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles. Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective. | 1 | Biochemistry |
Hydrophilic solids, which include many solids of biological origin, can readily absorb water. Polar interactions between water and the molecules of the solid favor partition of the water into the solid, which can allow significant absorption of water vapor even in relatively low humidity. | 7 | Physical Chemistry |
Because many polymers are composed of primarily of hydrocarbon chains with at most slightly polar functional groups, they tend to have low surface energies and thus adsorb rather poorly. While this can be advantageous for some applications, modification of polymer surfaces is crucial for many other applications in which adhering a substrate to its surface is vital for optimal performance. For example, many applications utilize polymers as structural components, but which degrade rapidly when exposed to weather or other sources of wear. Therefore, coatings must be used which protect the structural layer from damage. However, the poor adhesive properties of nonpolar polymers makes it difficult to adsorb the protective coating onto its surface. These types of problems make the measurement and control of surface energies important to development of useful technologies.
The Gibbs energy of adsorption, , can be determined from the adsorption equilibrium constant:
Because is negative for a spontaneous process and positive for a nonspontaneous process, it can be used to understand the tendency for different compounds to adsorb to a surface. In addition, it can be divided into a combination of two components:
which are the Gibbs energies of physisorption and chemisorption, respectively. Many polymer applications, such as those which use polytetrafluoroethylene (PTFE, or Teflon) require the use of a surface with specific physisorption properties toward one type of material, while being firmly adhered in place to a different type of material. Because the physisorption energy is so low for these types of materials, chemisorption is used to form covalent bonds between the polymer coating and the surface of the object (such as a pan) which holds it in place. Because the relative magnitudes of chemisorption processes are generally much greater than magnitudes of physisorption processes, this forms a strong bond between the polymer and the surface it is chemically adhered to, while allowing the polymer to retain its physisorption characteristics toward other materials.
Experimentally, the enthalpy and entropy of adsorption are often used to fine-tune the adsorption properties of a material. The enthalpy of adsorption can be determined from constant pressure calorimetry:
where:
: is the heat exchanged,
: is the integral molar enthalpy of adsorption,
: is the number of moles adsorbed.
From the enthalpy of adsorption, the entropy of adsorption can be calculated:
where:
: is the integral molar entropy of adsorption,
: is the temperature in kelvins.
Together, these are used to understand the driving forces behind adsorption processes. | 7 | Physical Chemistry |
DNA fragmentation is often necessary prior to library construction or subcloning for DNA sequences. A variety of methods involving the mechanical breakage of DNA have been employed where DNA is fragmented by laboratory personnel. Such methods include sonication, needle shear, nebulisation, point-sink shearing and passage through a pressure cell.
* Restriction digest is the intentional laboratory breaking of DNA strands. It is an enzyme-based treatment used in biotechnology to cut DNA into smaller strands in order to study fragment length differences among individuals or for gene cloning. This method fragments DNA either by the simultaneous cleavage of both strands, or by generation of nicks on each strand of dsDNA to produce dsDNA breaks.
* Acoustic shearing of the transmission of high-frequency acoustic energy waves delivered to a DNA library. The transducer is bowl shaped so that the waves converge at the target of interest.
* Nebulization forces DNA through a small hole in a nebulizer unit, which results in the formation of a fine mist that is collected. Fragment size is determined by the pressure of the gas used to push the DNA through the nebulizer, the speed at which the DNA solution passes through the hole, the viscosity of the solution, and the temperature.
* Sonication, a type of hydrodynamic shearing, subjects DNA to acoustic cavitation and hydrodynamic shearing by exposure to brief periods of sonication, usually resulting in 700bp fragments. For DNA fragmentation, sonication is commonly applied at burst cycles using a probe-type sonicator.
* Point-sink shearing, a type of hydrodynamic shearing, uses a syringe pump to create hydrodynamic shear forces by pushing a DNA library through a small abrupt contraction. About 90% of fragment lengths fall within a two-fold range.
* Needle shearing creates shearing forces by passing DNA libraries through small gauge needle. The DNA pass through a gauge needle several times to physically tear the DNA into fine pieces.
* French pressure cells pass DNA through a narrow valve under high pressure to create high shearing forces. With a French press, the shear force can be carefully modulated by adjusting the piston pressure. The Press provides a single pass through the point of maximum shear force, limiting damage to delicate biological structures due to repeated shear, as occurs in other disruption methods.
* In transposome mediated fragmentation (tagmentation) transposomes are prepared with DNA that is afterwards cut so that the transposition events result in fragmented DNA with adapters (instead of an insertion). The relative concentration of transposomes and DNA must be appropriate. | 1 | Biochemistry |
A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other small water crustaceans that are present in many water bodies can be monitored for changes (biochemical, physiological, or behavioural) that may indicate a problem within their ecosystem. Bioindicators can tell us about the cumulative effects of different pollutants in the ecosystem and about how long a problem may have been present, which physical and chemical testing cannot.
A biological monitor or biomonitor is an organism that provides quantitative information on the quality of the environment around it. Therefore, a good biomonitor will indicate the presence of the pollutant and can also be used in an attempt to provide additional information about the amount and intensity of the exposure.
A biological indicator is also the name given to a process for assessing the sterility of an environment through the use of resistant microorganism strains (e.g. Bacillus or Geobacillus). Biological indicators can be described as the introduction of a highly resistant microorganisms to a given environment before sterilization, tests are conducted to measure the effectiveness of the sterilization processes. As biological indicators use highly resistant microorganisms, any sterilization process that renders them inactive will have also killed off more common, weaker pathogens. | 2 | Environmental Chemistry |
The biosphere is 22% oxygen by volume, present mainly as a component of organic molecules (CHNO) and water. | 5 | Photochemistry |
The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The gas emerging from the hot end can reach temperatures of , and the gas emerging from the cold end can reach . It has no moving parts and is considered an environmentally friendly technology because it can work solely on compressed air and does not use Freon. Its efficiency is low, however, counteracting its other environmental advantages.
Pressurised gas is injected tangentially into a swirl chamber near one end of a tube, leading to a rapid rotation—the first vortex—as it moves along the inner surface of the tube to the far end. A conical nozzle allows gas specifically from this outer layer to escape at that end through a valve. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. Gas from the inner vortex transfers energy to the gas in the outer vortex, so the outer layer is hotter at the far end than it was initially. The gas in the central vortex is likewise cooler upon its return to the starting-point, where it is released from the tube. | 7 | Physical Chemistry |
The rocks on the plains of Gusev are a type of basalt. They contain the minerals olivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes (geologists would say they have vesicles and vugs).
Much of the soil on the plains came from the breakdown of the local rocks. Fairly high levels of nickel were found in some soils; probably from meteorites.
Analysis shows that the rocks have been slightly altered by tiny amounts of water. Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds. All the rocks contain a fine coating of dust and one or more harder rinds of material. One type can be brushed off, while another needed to be ground off by the Rock Abrasion Tool (RAT).
There are a variety of rocks in the Columbia Hills (Mars), some of which have been altered by water, but not by very much water.
The dust in Gusev Crater is the same as dust all around the planet. All the dust was found to be magnetic. Moreover, Spirit found the magnetism was caused by the mineral magnetite, especially magnetite that contained the element titanium. One magnet was able to completely divert all dust hence all Martian dust is thought to be magnetic. The spectra of the dust was similar to spectra of bright, low thermal inertia regions like Tharsis and Arabia that have been detected by orbiting satellites. A thin layer of dust, maybe less than one millimeter thick covers all surfaces. Something in it contains a small amount of chemically bound water. | 9 | Geochemistry |
There are three molecules that serve as chelator agents that bond to arsenic. These three are British Anti-Lewisite (BAL, Dimercaprol), succimer (DMSA) and Unithiol (DMPS).
When these agents chelate inorganic arsenic, it is converted into an organic form of arsenic because it is bound to the organic chelating agent. The sulfur atoms of the thiol groups are the site of interaction with arsenic. This is because the thiol groups are nucleophilic while the arsenic atoms are electrophilic. Once bound to the chelating agent the molecules can be excreted, and therefore free inorganic arsenic atoms are removed from the body.
Other chelating agents can be used, but may cause more side effects than British Anti-Lewisite (BAL, Dimercaprol), succimer (DMSA) and (DMPS). DMPS and DMSA also have a higher therapeutic index than BAL.
These drugs are efficient for acute poisoning of arsenic, which refers to the instantaneous effects caused by arsenic poisoning. For example, headaches, vomiting or sweating are some of the common examples of an instantaneous effect. In comparison, chronic poisonous effects arise later on, and unexpectedly such as organ damage. Usually it is too late to prevent them once they appear. Therefore, action should be taken as soon as acute poisonous effects arise. | 1 | Biochemistry |
Willard's research interests focused on analytical chemistry and quantitative analysis of inorganic substances. With student G. Frederick Smith, he was particularly productive in studying perchloric acid and periodic acid salts. In addition, he is credited with important work in determining precise atomic weights of chemical elements such as lithium, silver, and antimony, and with development of metal alloy techniques. | 3 | Analytical Chemistry |
Most floral VOCs belong to three main chemical classes. VOCs in the same chemical class are synthesized from a shared precursor, but the biochemical pathway is specific for each VOC and often varies from one plant species to another.
Terpenoids (or isoprenoids) are derived from isoprene and synthesized via the mevalonate pathway or the erythritol phosphate pathway. They represent the majority of floral VOCs and are often the most abundant compounds in floral scent blends.
The second chemical class is composed of the fatty acid derivatives synthesized from acetyl-CoA, most of which are known as green leaf volatiles, because they are also emitted by vegetative parts (i.e.: leaves and stems) of plants, and sometimes higher in abundance than from floral tissue.
The third chemical class is composed of benzenoids/phenylpropanoids, also known as aromatic compounds; they are synthesized from phenylalanine. | 1 | Biochemistry |
A sample of cells, either derived from an in vitro cell culture or from an in vivo test subject is dispersed into individual cells and suspended in molten low-melting-point agarose at 37 °C. This mono-suspension is cast on a microscope slide. A glass cover slip is held at an angle and the mono-suspension is applied to the point of contact between the coverslip and the slide. As the coverslip is lowered onto the slide the molten agarose spreads to form a thin layer. The agarose is gelled at 4 °C and the coverslip removed.
The agarose forms a matrix of carbohydrate fibres that encapsulate the cells, anchoring them in place. The agarose is considered to be osmotic-neutral, therefore solutions can penetrate the gel and affect the cells without cells shifting position.
In an in vitro study the cells would be exposed to a test agent – typically UV light, ionising radiation, or a genotoxic chemical – to induce DNA damage in the encapsulated cells. For calibration, hydrogen peroxide is usually used to provide a standardized level of DNA damage. | 1 | Biochemistry |
In 2003, ATSDR released public health assessments that evaluated the potential health effects of pollution left behind by the United States Navy in Vieques, Puerto Rico. The public health assessments noted that residents of the island were exposed to environmental contamination at such low levels that no harmful health effects were expected, and the agency concluded that there was "no apparent public health hazard." In 2009, however, ATSDR announced that it had identified gaps in environmental data and planned to take a "fresh look" at Vieques by reviewing studies on the island. | 1 | Biochemistry |
Deoxycytidine triphosphate (dCTP) is a nucleoside triphosphate that contains the pyrimidine base cytosine. The triphosphate group contains high-energy phosphoanhydride bonds, which liberate energy when hydrolized.
DNA polymerase enzymes use this energy to incorporate deoxycytidine into a newly synthesized strand of DNA. A chemical equation can be written that represents the process:
: (DNA) + dCTP ↔ (DNA)-C + PP
That is, dCTP has the PP (pyrophosphate) cleaved off and the dCMP is incorporated into the DNA strand at the 3' end.
Subsequent hydrolysis of the PP drives the equilibrium of the reaction toward the right side, i.e. incorporation of the nucleotide in the growing DNA chain.
Like other nucleoside triphosphates, manufacturers recommend that dCTP be stored in aqueous solution at −20 °C. | 1 | Biochemistry |
Cannabinoidergic, or cannabinergic, means "working on the endocannabinoid neurotransmitters". As with terms such as dopaminergic and serotonergic, related proteins and cellular components involved endocannabinoid signaling, such as the cannabinoid (CB) receptor, as well as exogenous compounds, such as phytocannabinoids or other cannabinoids which modulate the activity of endocannabinoid system, can be described as cannabinoidergic. | 1 | Biochemistry |
The extent of boiling-point elevation can be calculated by applying Clausius–Clapeyron relation and Raoult's law together with the assumption of the non-volatility of the solute. The result is that in dilute ideal solutions, the extent of boiling-point elevation is directly proportional to the molal concentration (amount of substance per mass) of the solution according to the equation:
: = K · b</big>
where the boiling point elevation, is defined as T − T.
* K, the ebullioscopic constant, which is dependent on the properties of the solvent. It can be calculated as K = RTM/ΔH, where R is the gas constant, and T is the boiling temperature of the pure solvent [in K], M is the molar mass of the solvent, and ΔH is the heat of vaporization per mole of the solvent.
* b is the colligative molality, calculated by taking dissociation into account since the boiling point elevation is a colligative property, dependent on the number of particles in solution. This is most easily done by using the van t Hoff factor i as b = b · i, where b is the molality of the solution. The factor i' accounts for the number of individual particles (typically ions) formed by a compound in solution. Examples:
** i = 1 for sugar in water
** i = 1.9 for sodium chloride in water, due to the near full dissociation of NaCl into Na and Cl (often simplified as 2)
** i = 2.3 for calcium chloride in water, due to nearly full dissociation of CaCl into Ca and 2Cl (often simplified as 3)
Non integer i factors result from ion pairs in solution, which lower the effective number of particles in the solution.
Equation after including the van 't Hoff factor
: = K · b · i</big>
At high concentrations, the above formula is less precise due to nonideality of the solution. If the solute is also volatile, one of the key assumptions used in deriving the formula is not true, since it derived for solutions of non-volatile solutes in a volatile solvent. In the case of volatile solutes it is more relevant to talk of a mixture of volatile compounds and the effect of the solute on the boiling point must be determined from the phase diagram of the mixture. In such cases, the mixture can sometimes have a boiling point that is lower than either of the pure components; a mixture with a minimum boiling point is a type of azeotrope. | 7 | Physical Chemistry |
A widely publicized study suggested that humans can detect more than one trillion different odors. This finding has been disputed. Critics argued that the methodology used for the estimation was fundamentally flawed, showing that applying the same argument for better-understood sensory modalities, such as vision or audition, leads to wrong conclusions. Other researchers have also showed that the result is extremely sensitive to the precise details of the calculation, with small variations changing the result over dozens of orders of magnitude, possibly going as low as a few thousand. The authors of the original study have argued that their estimate holds as long as it is assumed that odor space is sufficiently high-dimensional. | 1 | Biochemistry |
The term was used as early as 1973, when scientist Carl Sagan described it and other human chauvinisms that limit imagination of possible extraterrestrial life. It suggests that human beings, as carbon-based life forms who have never encountered any life that has evolved outside the Earth's environment, may find it difficult to envision radically different biochemistries. | 1 | Biochemistry |
Crystallographic features of HCP systems, such as vectors and atomic plane families, can be described using a four-value Miller index notation ( hkil ) in which the third index i denotes a convenient but degenerate component which is equal to −h − k. The h, i and k index directions are separated by 120°, and are thus not orthogonal; the l component is mutually perpendicular to the h, i and k index directions. | 3 | Analytical Chemistry |
In particle tracking, the trajectories of a set of particles are measured, typically by applying particle tracking algorithms to movies.[http://www.physics.emory.edu/~weeks/idl/] Particle tracking has the advantage that all the dynamical information is maintained in the measurement, unlike FCS where correlation averages the dynamics to a single smooth curve. The advantage is apparent in systems showing complex diffusion, where directly computing the mean squared displacement allows straightforward comparison to normal or power law diffusion. To apply particle tracking, the particles have to be distinguishable and thus at lower concentration than required of FCS. Also, particle tracking is more sensitive to noise, which can sometimes affect the results unpredictably. | 7 | Physical Chemistry |
Besides anchoring cells to the ECM, laminins are also involved in the signalling of cells and other components of the ECM. Even though there is not a general mechanism that applies to all laminins in signalling, there are some common pathways that can be seen in more than one isoform of laminin. For example, the PI3K/AKT pathway is used by laminin-111 (promotes cell-survival), 511 (prevents apoptosis with laminin 521), and 521 (stabilizes pluripotency of human embryonic stem cells). The pathway begins with the adhesion of the cell to the ECM for activation of the lipid-associated PI3K. Once PI3K is activated, it will localize AKT that is in the cytoplasm to the cell membrane where AKT is then phosphorylated to promote cell survival. | 0 | Organic Chemistry |
Absolute size-exclusion chromatography (ASEC) is a technique that couples a light scattering instrument, most commonly multi-angle light scattering (MALS) or another form of static light scattering (SLS), but possibly a dynamic light scattering (DLS) instrument, to a size-exclusion chromatography system for absolute molar mass and/or size measurements of proteins and macromolecules as they elute from the chromatography system.
The definition of “absolute” in this case is that calibration of retention time on the column with a set of reference standards is not required to obtain molar mass or the hydrodynamic size, often referred to as hydrodynamic diameter (D in units of nm). Non-ideal column interactions, such as electrostatic or hydrophobic surface interactions that modulate retention time relative to standards, do not impact the final result. Likewise, differences between conformation of the analyte and the standard have no effect on an absolute measurement; for example, with MALS analysis, the molar mass of inherently disordered proteins are characterized accurately even though they elute at much earlier times than globular proteins with the same molar mass, and the same is true of branched polymers which elute late compared to linear reference standards with the same molar mass. Another benefit of ASEC is that the molar mass and/or size is determined at each point in an eluting peak, and therefore indicates homogeneity or polydispersity within the peak. For example, SEC-MALS analysis of a monodisperse protein will show that the entire peak consists of molecules with the same molar mass, something that is not possible with standard SEC analysis.
Determination of molar mass with SLS requires combining the light scattering measurements with concentration measurements. Therefore SEC-MALS typically includes the light scattering detector and either a differential refractometer or UV/Vis absorbance detector. In addition, MALS determines the rms radius R of molecules above a certain size limit, typically 10 nm. SEC-MALS can therefore analyze the conformation of polymers via the relationship of molar mass to R. For smaller molecules, either DLS or, more commonly, a differential viscometer is added to determine hydrodynamic radius and evaluate molecular conformation in the same manner.
In SEC-DLS, the sizes of the macromolecules are measured as they elute into the flow cell of the DLS instrument from the size exclusion column set. The hydrodynamic size of the molecules or particles are measured and not their molecular weights. For proteins a Mark-Houwink type of calculation can be used to estimate the molecular weight from the hydrodynamic size.
A major advantage of DLS coupled with SEC is the ability to obtain enhanced DLS resolution. Batch DLS is quick and simple and provides a direct measure of the average size, but the baseline resolution of DLS is a ratio of 3:1 in diameter. Using SEC, the proteins and protein oligomers are separated, allowing oligomeric resolution. Aggregation studies can also be done using ASEC. Though the aggregate concentration may not be calculated with light scattering (an online concentration detector such as that used in SEC-MALS for molar mass measurement also determines aggregate concentration), the size of the aggregate can be measured, only limited by the maximum size eluting from the SEC columns.
Limitations of ASEC with DLS detection include flow-rate, concentration, and precision. Because a correlation function requires anywhere from 3–7 seconds to properly build, a limited number of data points can be collected across the peak. ASEC with SLS detection is not limited by flow rate and measurement time is essentially instantaneous, and the range of concentration is several orders of magnitude larger than for DLS. However, molar mass analysis with SEC-MALS does require accurate concentration measurements. MALS and DLS detectors are often combined in a single instrument for more comprehensive absolute analysis following separation by SEC. | 1 | Biochemistry |
Many aspects of academic research and industrial research such as in pharmaceuticals, health products, and many others relies on accurate water analysis to identify substances of potential use, to refine those substances and to ensure that when they are manufactured for sale that the chemical composition remains consistent. The analytical methods used in these area can be very complex and may be specific to the process or area of research being conducted and may involve the use of bespoke analytical equipment. | 9 | Geochemistry |
Junwang Tang, MAE, FRSC and FIMMM, is the Founding Director of Industrial Catalysis Center, and Carbon Neutrality Chair Professor of Materials Chemistry and Catalysis at the Department of Chemical Engineering, Tsinghua University and Visiting Professor at University College London (UCL). He also served as the Director of the University Material Hub at UCL (2016–2019). | 5 | Photochemistry |
Several theoretical models exist to predict the order of duplication and specialisation events, but the actual process is more intertwined and fuzzy (§ Reconstructed enzymes below). On one hand, gene amplification results in an increase in enzyme concentration, and potentially freedom from a restrictive regulation, therefore increasing the reaction rate (v) of the promiscuous activity of the enzyme making its effects more pronounced physiologically ("gene dosage effect"). On the other, enzymes may evolve an increased secondary activity with little loss to the primary activity ("robustness") with little adaptive conflict (§ Robustness and plasticity below). | 1 | Biochemistry |
Galvanic corrosion is an electrochemical process whereby one metal corrodes preferentially to another when both metals are in electrical contact with each other in the presence of an electrolyte, such as moisture and salts. This is because the dissimilar metals have different electrode potentials. The potential difference between the dissimilar metals is the driving force for the accelerated attack on the metal with the lower galvanic number (i.e., the anode). Over time, the anode metal dissolves into the electrolyte.
Metals are ranked according to galvanic numbers as a qualitative measure of their nobility. These numbers qualify the resistance to corrosion of any metal when in contact with other metals. A larger difference in the galvanic number between two metals in contact with each other indicates a greater potential for corrosion.
The galvanic numbers of the most common metals used in construction are ranked as follows: 1. aluminium; 2. zinc; 3. steel; 4. iron; 5. stainless steel - active; 6. tin; 7. lead; 8. copper; 9. stainless steel - passive.
Galvanic corrosion is a primary concern with metal roof maintenance. Marine environments present an additional concern due to the higher concentration of salts in the air and water.
Copper is one of the most noble metals. It will not be harmed by contact with other metals but it will cause corrosion to some other metals if contacted directly. The principal metals of concern regarding direct contact with copper are aluminium, light-gauge steel, and zinc. Aluminium and steel flashings and galvanized steel fasteners should not be used with copper. Runoff from a copper roof corrodes aluminium and steel guttering. It is not necessary to isolate copper from lead, tin or many stainless steels under most circumstances.
When it is not possible to avoid contact, an effective method of material separation is required. If paints or coatings are used for isolation, they should be compatible with both metals. Bituminous or zinc chromate primers can be used between copper and aluminium. Bituminous, zinc chromate, or a red lead primer can be effective in separating copper from iron and other ferrous metals. Taping or gasketing with non-absorptive materials or sealants are effective in separating copper from all other metals. In areas with severe exposure, lead or similar gasketing materials should be used, except between copper and aluminium. Water draining from copper surfaces should be prevented from exposure to aluminium and galvanized steel as traces of copper salts may accelerate corrosion. In some cases, anodizing may protect thicker aluminium, such as aluminium window system mullions. | 8 | Metallurgy |
Lisinopril is typically used for the treatment of high blood pressure, congestive heart failure, and diabetic nephropathy and after acute myocardial infarction (heart attack). Lisinopril is part of the ACE inhibitors drug class. Lisinopril is indicated for the treatment of hypertension, adjunctive therapy for heart failure, and acute myocardial infarction. | 4 | Stereochemistry |
A-values provide another measure of the bulk of substituents. A-values are derived from equilibrium measurements of monosubstituted cyclohexanes. The extent that a substituent favors the equatorial position gives a measure of its bulk. | 4 | Stereochemistry |
In a fluidized-bed roaster, finely ground sulfide concentrates are suspended and oxidized in feedstock bed supported on an air column. As in the suspension roaster, the reaction rates for desulfurization are more rapid than in the older multiple-hearth processes. Fluidized-bed roasters operate under a pressure slightly lower than atmospheric and at temperatures averaging . In the fluidized-bed process, no additional fuel is required after ignition has been achieved. The major advantages of this roaster are greater throughput capacities, greater sulfur removal capabilities, and lower maintenance. | 8 | Metallurgy |
* Endomycetales (yeasts): Candida albicans, Candida cylindracea, Candida melibiosica, Candida parapsilosis, and Candida rugosa. | 1 | Biochemistry |
*The main criticism applied to the yeast two-hybrid screen of protein–protein interactions are the possibility of a high number of false positive (and false negative) identifications. The exact rate of false positive results is not known, but earlier estimates were as high as 70%. This also, partly, explains the often found very small overlap in results when using a (high throughput) two-hybrid screening, especially when using different experimental systems.
The reason for this high error rate lies in the characteristics of the screen:
*Certain assay variants overexpress the fusion proteins which may cause unnatural protein concentrations that lead to unspecific (false) positives.
*The hybrid proteins are fusion proteins; that is, the fused parts may inhibit certain interactions, especially if an interaction takes place at the N-terminus of a test protein (where the DNA-binding or activation domain is typically attached).
*An interaction may not happen in yeast, the typical host organism for Y2H. For instance, if a bacterial protein is tested in yeast, it may lack a chaperone for proper folding that is only present in its bacterial host. Moreover, a mammalian protein is sometimes not correctly modified in yeast (e.g., missing phosphorylation), which can also lead to false results.
*The Y2H takes place in the nucleus. If test proteins are not localized to the nucleus (because they have other localization signals) two interacting proteins may be found to be non-interacting.
*Some proteins might specifically interact when they are co-expressed in the yeast, although in reality they are never present in the same cell at the same time. However, in most cases it cannot be ruled out that such proteins are indeed expressed in certain cells or under certain circumstances.
Each of these points alone can give rise to false results. Due to the combined effects of all error sources yeast two-hybrid have to be interpreted with caution. The probability of generating false positives means that all interactions should be confirmed by a high confidence assay, for example co-immunoprecipitation of the endogenous proteins, which is difficult for large scale protein–protein interaction data. Alternatively, Y2H data can be verified using multiple Y2H variants or bioinformatics techniques. The latter test whether interacting proteins are expressed at the same time, share some common features (such as gene ontology annotations or certain network topologies), have homologous interactions in other species. | 1 | Biochemistry |
*2001: Outstanding President Prize by The Chinese Academy of Sciences.
*2003–2005: Japan Society for the Promotion of Science (JSPS) Fellowship by Japan Society for the Promotion of Science.
*2008: Young Scientist Award for research on renewable solar energy by The International Association of Catalysis Societies.
*2014: Runner-up of the Global Innovator of the Year by IChemE.
*2018: IPS Scientist Award in the 22nd International Conference on Chemical Conversion and Storage of Solar Energy.
*2019: Winner of the IChemE Global Business Start-Up Award 2019 and Runner-up of the IChemE Global Oil and Gas Award 2019 .
*2021: Winder of the IChemE Innovative Product Global Award.
*2021: Winner of the 2021 Corday-Morgan Prize from the Royal Society of Chemistry.
*2021: Winner of the IChemE Medal Round: The Andrew Medal.
*2021 IChemE Innovative Product Award, IChemE
*2021 Member of the Academy of Europe
*2022 IChemE Global Oil and Gas Award
*2022 Fellow of Institute of Materials, Minerals and Mining | 5 | Photochemistry |
According to Etymology Online, the verb assay means "to try, endeavor, strive, test the quality of"; from Anglo-French assaier, from assai (noun), from Old French essai, "trial". Thus the noun assay means "trial, test of quality, test of character" (from mid-14th century), from Anglo-French assai; and its meaning "analysis" is from the late 14th century.
For assay of currency coins this literally meant analysis of the purity of the gold or silver (or whatever the precious component) that represented the true value of the coin. This might have translated later (possibly after the 14th century) into a broader usage of "analysis", e.g., in pharmacology, analysis for an important component of a target inside a mixture—such as the active ingredient of a drug inside the inert excipients in a formulation that previously was measured only grossly by its observable action on an organism (e.g., a lethal dose or inhibitory dose). | 1 | Biochemistry |
A thermodynamic instrument is any device for the measurement of thermodynamic systems. In order for a thermodynamic parameter or physical quantity to be truly defined, a technique for its measurement must be specified. For example, the ultimate definition of temperature is "what a thermometer reads". The question follows – what is a thermometer?
There are two types of thermodynamic instruments: the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of a thermodynamic system. A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. | 7 | Physical Chemistry |
Silicon wafers are treated with solutions of electronic-grade hydrofluoric acid in water, buffered water, or alcohol. One of the relevant reactions is simply removal of silicon oxides:
:SiO + 4 HF → SiF + 2 HO
The key reaction however is the formation of the hydrosilane functional group.
atomic force microscope (AFM) has been used to manipulate hydrogen-terminated silicon surfaces. | 6 | Supramolecular Chemistry |
In earlier years it was thought that apamin was a rather nontoxic compound (LD = 15 mg/kg in mice) compared to the other compounds in bee venom. The current lethal dose values of apamin measured in mice are given below. There are no data known specific for humans.
Intraperitoneal (mouse) LD: 3.8 mg/kg
Subcutaneous (mouse) LD: 2.9 mg/kg
Intravenous (mouse) LD: 4 mg/kg
Intracerebral (mouse) LD: 1800 ng/kg
Parenteral (mouse) LD: 600 mg/kg | 1 | Biochemistry |
The austrapede (Tspìng in Navi) is a Pandoran creature that resembles a cross between an ostrich, a pink flamingo and the herbivorous dinosaur Parasaurolophus. The Austrapede has yellow-orange skin with faint purple striping, a long, flat beak, and a flat tail reaching down to its feet. Unlike other Pandoran birds and its relative, the great austrapede, the austrapedes wings have shrunken down to small, vestigial appendages, and much of its height is made up by its legs and neck. Austrapedes flap their wings when frightened. The austrapedes are impulsive, fidgety creatures whose emotions spread quickly from one individual to the other by a form of mimicry. Relatively small by Pandoran standards, Austrapedes generally pose little threat to other creatures, and are sometimes affectionate to Navi. They first appear in the musical, Toruk – The First Flight'. | 1 | Biochemistry |
The Van 't Hoff isotherm can be used to determine the temperature dependence of the Gibbs free energy of reaction for non-standard state reactions at a constant temperature:
where is the Gibbs free energy of reaction under non-standard states at temperature , is the Gibbs free energy for the reaction at , is the extent of reaction, and is the thermodynamic reaction quotient. Since , the temperature dependence of both terms can be described by Van tHoff equations as a function of T'. This finds applications in the field of electrochemistry. particularly in the study of the temperature dependence of voltaic cells.
The isotherm can also be used at fixed temperature to describe the Law of Mass Action. When a reaction is at equilibrium, and . Otherwise, the Van 't Hoff isotherm predicts the direction that the system must shift in order to achieve equilibrium; when , the reaction moves in the forward direction, whereas when , the reaction moves in the backwards direction. See Chemical equilibrium. | 7 | Physical Chemistry |
Action potentials are most commonly initiated by excitatory postsynaptic potentials from a presynaptic neuron. Typically, neurotransmitter molecules are released by the presynaptic neuron. These neurotransmitters then bind to receptors on the postsynaptic cell. This binding opens various types of ion channels. This opening has the further effect of changing the local permeability of the cell membrane and, thus, the membrane potential. If the binding increases the voltage (depolarizes the membrane), the synapse is excitatory. If, however, the binding decreases the voltage (hyperpolarizes the membrane), it is inhibitory. Whether the voltage is increased or decreased, the change propagates passively to nearby regions of the membrane (as described by the cable equation and its refinements). Typically, the voltage stimulus decays exponentially with the distance from the synapse and with time from the binding of the neurotransmitter. Some fraction of an excitatory voltage may reach the axon hillock and may (in rare cases) depolarize the membrane enough to provoke a new action potential. More typically, the excitatory potentials from several synapses must work together at nearly the same time to provoke a new action potential. Their joint efforts can be thwarted, however, by the counteracting inhibitory postsynaptic potentials.
Neurotransmission can also occur through electrical synapses. Due to the direct connection between excitable cells in the form of gap junctions, an action potential can be transmitted directly from one cell to the next in either direction. The free flow of ions between cells enables rapid non-chemical-mediated transmission. Rectifying channels ensure that action potentials move only in one direction through an electrical synapse. Electrical synapses are found in all nervous systems, including the human brain, although they are a distinct minority. | 7 | Physical Chemistry |
The choice of aryl halide or pseudohalide substrate (sp-carbon) is one of the factors that mainly influence the reactivity of the Sonogashira catalytic system. The reactivity of halides is higher towards iodine, and vinyl halides are more reactive than analogous aryl halides. The coupling of aryl iodides proceeds at room temperature, while aryl bromides require heating.
This difference in reactivity can be exploited to selectively couple an aryl iodide but not an aryl bromide, by performing the reaction at room temperature. An example is the symmetrical Sonogashira coupling of two equivalents of 1-bromo-4-iodobenzene with trimethylsilylacetylene (with the trimethylsilyl group removed in-situ) to form bis(4-bromophenyl)acetylene.
Aryl triflates can also be employed instead of aryl halides. | 0 | Organic Chemistry |
The Union Carbide (UCC) process, also known as low-pressure oxo process (LPO), relies on a rhodium catalyst dissolved in high-boiling thick oil, a higher molecular weight condensation product of the primary aldehydes, for the hydroformylation of propene. The reaction mixture is separated in a falling film evaporator from volatile components. The liquid phase is distilled and butyraldehyde is removed as head product while the catalyst containing bottom product is recycled to the process. The process is carried out at about 1.8 MPa and 95–100 °C. | 0 | Organic Chemistry |
The first report of the BCCP structure was made by biochemists F. K. Athappilly and W. A. Hendrickson in 1995. It can be thought of as a long β-hairpin structure, with four pairs of antiparallel β-strands that wrap around a central hydrophobic core. The biotinylation motif Met-Lys-Met is located at the tip of the β-hairpin structure. Rotations around the CαCβ bond of this Lys residue contribute to the swinging-arm model. The connection to the rest of the enzyme at the N-terminus of BCCP core is located at the opposite end of the structure from the biotin moiety. Rotations around this region contribute to the swinging-domain model, and the N1′ atom of biotin is ~ 40 Å from this pivot point. This gives a range of ~ 80 Å for the swinging-domain model, and the BC–CT active site distances observed so far are between 40 and 80 Å. In addition, the linker before the BCCP core in the holoenzyme could also be flexible, which would give further reach for the biotin N1′ atom.
The structures of biotin-accepting domains from E. coli BCCP-87 and the 1.3S subunit of P. shermanii TC were determined by both X-ray crystallography and nuclear magnetic resonance studies. (Athappilly and Hendrickson, 1995; Roberts et al., 1999; Reddy et al., 1998). These produced essentially the same structures that are structurally related to the lipoyl domains of 2-oxo acid dehydrogenase multienzyme complexes (Brocklehurst and Perham, 1993; Dardel et al., 1993), which similarly undergo an analogous post-translational modification. These domains form a flattened β-barrel structure comprising two four-stranded β-sheets with the N- and C-terminal residues close together at one end of the structure. At the other end of the molecule, the biotinyl- or lipoyl-accepting lysine resides on a highly exposed, tight hairpin loop between β4 and β5 strands. The structure of the domain is stabilized by a core of hydrophobic residues, which are important structural determinants. Conserved glycine residues occupy β-turns linking the β-strands.
The structure of the Biotin-accepting domain consists of BCCP-87 which contains a seven-amino-acid insertion common to certain prokaryotic acetyl-CoA carboxylases but not present in other biotindomains (Chapman-Smith and Cronan, 1999). This region of the peptide adopts a thumb structure between the β2 and β3 strands and, interestingly, forms direct contacts with the biotin moiety in both the crystal and solution structures (Athappilly and Hendrickson, 1995; Roberts et al., 1999). It has been proposed that this thumb may function as a mobile lid for either, or possibly both, the biotin carboxylase or carboxyl- transferase active sites in the biotin-dependent enzyme (Cronan, 2001). The function of this lid could aid to prevent solvation of the active sites, thereby aiding in the transfer of CO from carboxybiotin to acetyl CoA. Secondly, the thumb is required for dimerization of BCCP, necessary for the formation of the active acetyl CoA carboxylase complex (Cronan, 2001). In conclusion, the thumb functions to inhibit the aberrant lipoylation of the target lysine by lipoyl protein ligase (Reche and Perham, 1999). Removal of the thumb by mutagenesis rendered BCCP-87 a favorable substrate for lipoylation but abolished biotinylation (Reche and Perham, 1999). The thumb structure, however, is not a highly conserved feature amongst all biotin domains. Many biotin-dependent enzymes do not contain this insertion, including all five mammalian enzymes. However, it appears the interactions between biotin and protein might be a conserved feature and important for catalysis as similar contacts have been observed in the "thumbless" domains from P. shermanii transcarboxylase (Jank et al., 2002) and the biotinyl/lipoyl attachment protein of B. subtilis (Cui et al., 2006). The significance of this requires further investigation but it is possible that the mechanism employed by the biotin enzymes may involve noncovalent interactions between the protein and the prosthetic group. | 1 | Biochemistry |
Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars (such as O- and B-type) emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m in vacuum.
The atmosphere blocks about 77% of the Suns UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches the Earths surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. Almost no UVC reaches the Earth's surface. The fraction of UVA and UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. On "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by Rayleigh scattering in the same way as the visible blue light from those parts of the sky. UVB also plays a major role in plant development, as it affects most of the plant hormones. During total overcast, the amount of absorption due to clouds is heavily dependent on the thickness of the clouds and latitude, with no clear measurements correlating specific thickness and absorption of UVA and UVB.
The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air. | 5 | Photochemistry |
Actaplanin is a complex of broad-spectrum antibiotics made by Actinoplanes bacteria. Research carried out by a group in Eli Lilly and Co. in 1984 identified several actaplanins using high-performance liquid chromatography. Actaplanins A, B, B, B, C and G were shown to be composed of the same peptide core, an amino sugar, and varying amounts of glucose, mannose, and rhamnose. | 0 | Organic Chemistry |
Two research groups reported trifluoromethylations of diazonium salts in 2013. Goossen reported the preparation of a complex from CuSCN, , and . In contrast, Fu reported the trifluoromethylation using Umemotos reagent (S'-trifluoromethyldibenzothiophenium tetrafluoroborate) and Cu powder (Gattermann-type conditions). They can be described by the following equation:
The bracket indicates that other ligands on copper are likely present but are omitted. | 0 | Organic Chemistry |
In 2016, some 90 organizations, representing over US$2.5 trillion of purchasing power, requested that their suppliers disclose information on how they are approaching climate and water risks and opportunities. Data was gathered from over 4,000 suppliers worldwide, who reported over US$12 billion worth of savings from emission reduction activities. | 2 | Environmental Chemistry |
Prenatal virilization of a genetically female fetus can occur when an excessive amount of androgen is produced by the fetal adrenal glands or is present in maternal blood. In the severest form of congenital adrenal hyperplasia, complete masculinization of a genetically female fetus results in an apparently normal male anatomy with no palpable testes. More often, the virilization is partial and the genitalia are ambiguous.
It can also be associated with progestin-induced virilisation. | 1 | Biochemistry |
Bioaerosols (short for biological aerosols) are a subcategory of particles released from terrestrial and marine ecosystems into the atmosphere. They consist of both living and non-living components, such as fungi, pollen, bacteria and viruses. Common sources of bioaerosols include soil, water, and sewage.
Bioaerosols are typically introduced into the air via wind turbulence over a surface. Once in the atmosphere, they can be transported locally or globally: common wind patterns/strengths are responsible for local dispersal, while tropical storms and dust plumes can move bioaerosols between continents. Over ocean surfaces, bioaerosols are generated via sea spray and bubbles.
Bioaerosols can transmit microbial pathogens, endotoxins, and allergens to which humans are sensitive. A well-known case was the meningococcal meningitis outbreak in sub-Saharan Africa, which was linked to dust storms during dry seasons. Other outbreaks linked to dust events including Mycoplasma pneumonia and tuberculosis.
Another instance was an increase in human respiratory problems in the Caribbean that may have been caused by traces of heavy metals, microorganism bioaerosols, and pesticides transported via dust clouds passing over the Atlantic Ocean. | 7 | Physical Chemistry |
Chrome Azurol S is a histological dye used in biomedical research.
Chrome Azural S (CAS) is a common spectrophotometric reagent for detection of certain metals like aluminum which can be toxic in excess and can contribute to people with neurodegenerative disorders. CAS is used to provide quantitative and qualitative information on molecules of interest like aluminum and siderophores. Qualitatively a color change can be observed while also allowing to quantitatively determine concentration of certain ions. | 1 | Biochemistry |
Excessive dephosphorylation of the membrane ATPases and proton pumps in the gastrointestinal tract leads to higher secretory rates of caustic peptic acids. These result in heartburn and esophagitis. In combination with Helicobacter pylori infection, peptic ulcer disease is caused by the elevated pH dephosphorylation elicits.
The microtubule-associated protein tau is abnormally hyperphosphorylated when isolated from the brain of patients who suffer from Alzheimers disease. This is due to the dysfunction of dephosphorylation mechanisms at specific amino acids on the tau protein. Tau dephosphorylation is catalysed by protein phosphatase-2A and phosphatase-2B. Deficiency or modification of one or both proteins may be involved in abnormal phosphorylation of tau in Alzheimers disease
Dephosphorylation has also been linked to cardiac disease, particularly the alteration of actin-myosin interactions that are key for providing the underlying force of a heartbeat. Dephosphorylation is a key part of the myosin cycling kinetics that directly control the actin-myosin interactions. When the dephosphorylation process is interrupted, calcium dependent cardiac contraction is impaired or fully disabled.
Research has also suggested that modifications to dephosphorylation impact physiological processes implicated in Diabetes mellitus. The kinetics of dephosphorylation of insulin receptor substrate-1/2, Akt, and ERK1/2, phosphoproteins are shown to be involved in insulin receptor signaling, and in vitro models demonstrate that changes to dephosphorylation kinetics impact upstream and downstream insulin stimulation. | 1 | Biochemistry |
Each instrument used in analytical chemistry has a useful working range. This is the range of concentration (or mass) that can be adequately determined by the instrument, where the instrument provides a useful signal that can be related to the concentration of the analyte.
All instruments have an upper and a lower working limit. Concentrations below the working limit do not provide enough signal to be useful, and concentrations above the working limit provide too much signal to be useful. When calibrating an instrument for use, the experimenter must be familiar with both the lower and upper working range of the chosen instrument; results obtained from a sample of concentration outside the working range are often statistically uncertain. | 3 | Analytical Chemistry |
All living surfaces are decorated with a diverse range of complex molecules, which are key modulators of chemical communications and other functions such as protection, adhesion, infectivity, apoptosis, etc. Functional-Spacer-Lipid (FSL) Kode constructs can be synthesized to mimic the bioactive components present on biological surfaces, and then re-present them in novel ways.
The architecture of an FSL Kode construct, as implicit in the name, consists of three components - a functional head group, a spacer, and a lipid tail. This structure is analogous to a Lego minifigure in that, they have three structural components, with each component having a separate purpose. In the examples shown in all the figures, a Lego minifig has been used for the analogy. However, it should be appreciated that this is merely a representation and the true structural similarity is significantly varied between Lego minifigures and FSL Kode constructs (fig 1). The functional group of an FSL is equivalent to a Lego minifigure head, with both being at the extremity and carrying the character functional components. The spacer of the FSL is equivalent to the body of the Lego minifigure and the arms on the minifigure are representative of substitutions which may be engineered into the chemical makeup of the spacer. The lipid of the FSL anchors it to lipid membranes and gives the FSL construct its amphiphatic nature which can cause it to self-assemble. Because the lipid tail can act directly as an anchor it is analogous to the legs of a Lego minifigure. | 1 | Biochemistry |
The Virtual breakdown mechanism is a concept in the field of electrochemistry. In electrochemical reactions, when the cathode and the anode are close enough to each other (i.e., so-called "nanogap electrochemical cells"), the double layer of the regions from the two electrodes is overlapped, forming a large electric field uniformly distributed inside the entire electrode gap. Such high electric fields can significantly enhance the ion migration inside bulk solutions and thus increase the entire reaction rate, akin to the "breakdown" of the reactant(s). However, it is fundamentally different from the traditional "breakdown".
The Virtual breakdown mechanism was discovered in 2017 when researchers studied pure water electrolysis based on deep-sub-Debye-length nanogap electrochemical cells. Furthermore, researchers found the relation of the gap distance between cathodes and anodes to the performance of electrochemical reactions. | 7 | Physical Chemistry |
In generic terms, electrochemical potential is the mechanical work done in bringing 1 mole of an ion from a standard state to a specified concentration and electrical potential. According to the IUPAC definition, it is the partial molar Gibbs energy of the substance at the specified electric potential, where the substance is in a specified phase. Electrochemical potential can be expressed as
where:
* is the electrochemical potential of species i, in J/mol,
* μ is the chemical potential of the species i, in J/mol,
* z is the valency (charge) of the ion i, a dimensionless integer,
* F is the Faraday constant, in C/mol,
* Φ is the local electrostatic potential, in V.
In the special case of an uncharged atom, z = 0, and so = μ.
Electrochemical potential is important in biological processes that involve molecular diffusion across membranes, in electroanalytical chemistry, and industrial applications such as batteries and fuel cells. It represents one of the many interchangeable forms of potential energy through which energy may be conserved.
In cell membranes, the electrochemical potential is the sum of the chemical potential and the membrane potential. | 7 | Physical Chemistry |
The protein encoded by this gene was initially named CA-related protein because of sequence similarity to other known carbonic anhydrase genes. However, the gene product lacks carbonic anhydrase activity (i.e., the reversible hydration of carbon dioxide). The gene product continues to carry a carbonic anhydrase designation based on clear sequence identity to other members of the carbonic anhydrase gene family. The absence of CA8 gene transcription in the cerebellum of the lurcher mutant in mice with a neurologic defect suggests an important role for this acatalytic form. | 1 | Biochemistry |
Apart from its usage in sensing acids and fluoride anions, PPA has been used in sensing Pd(0) metal by employing allyl chloroformate as a terminating end cap. This has been reported by Phillips and his research group, where they used an allyl formate endcap that stoichiometrically depolymerized within minutes upon its exposure to a catalytic amount of tetrakis(triphenylphosphine)palladium(0) (Pd(PPh)). | 7 | Physical Chemistry |
Esomeprazole, sold under the brand name Nexium [or Neksium] among others, is a medication which reduces stomach acid. It is used to treat gastroesophageal reflux disease, peptic ulcer disease, and Zollinger–Ellison syndrome. Its effectiveness is similar to that of other proton pump inhibitors (PPIs). It is taken by mouth or injection into a vein.
Common side effects include headache, constipation, dry mouth, and abdominal pain. Serious side effects may include angioedema, Clostridium difficile infection, and pneumonia. Use in pregnancy appears to be safe, while safety during breastfeeding is unclear. Esomeprazole is the (S)-(−)-enantiomer (or less specifically the S-isomer) of omeprazole. It works by blocking H/K-ATPase in the parietal cells of the stomach.
It was patented in 1993 and approved for medical use in 2000. It is available as a generic medication and sold over the counter in a number of countries. In 2021, it was the 125th most commonly prescribed medication in the United States, with more than 4million prescriptions. It is also available in lower dose formulations without a prescription in the United States, the United Kingdom as well as Australia, Canada, and New Zealand. | 4 | Stereochemistry |
The PEP carboxylase enzyme is present in plants and some types of bacteria, but not in fungi or animals (including humans). The genes vary between organisms, but are strictly conserved around the active and allosteric sites discussed in the mechanism and regulation sections. Tertiary structure of the enzyme is also conserved.
The crystal structure of PEP carboxylase in multiple organisms, including Zea mays (maize), and Escherichia coli has been determined. The overall enzyme exists as a dimer-of-dimers: two identical subunits closely interact to form a dimer through salt bridges between arginine (R438 - exact positions may vary depending on the origin of the gene) and glutamic acid (E433) residues. This dimer assembles (more loosely) with another of its kind to form the four subunit complex. The monomer subunits are mainly composed of alpha helices (65%), and have a mass of 106kDa each. The sequence length is about 966 amino acids.
The enzyme active site is not completely characterized. It includes a conserved aspartic acid (D564) and a glutamic acid (E566) residue that non-covalently bind a divalent metal cofactor ion through the carboxylic acid functional groups. This metal ion can be magnesium, manganese or cobalt depending on the organism, and its role is to coordinate the phosphoenolpyruvate molecule as well as the reaction intermediates. A histidine (H138) residue at the active site is believed to facilitate proton transfer during the catalytic mechanism. | 5 | Photochemistry |
Casting and forging are traditional metallurgical processing techniques that can be used to generate both polycrystalline and monocrystalline products. Polycrystalline casts offer higher fracture resistance, while monocrystalline casts offer higher creep resistance.
Jet turbine engines employ both crystalline component types to take advantage of their individual strengths. The disks of the high-pressure turbine, which are near the central hub of the engine are polycrystalline. The turbine blades, which extend radially into the engine housing, experience a much greater centripetal force, necessitating creep resistance, typically adopting monocrystalline or polycrystalline with a preferred crystal orientation. | 8 | Metallurgy |
The crossed molecular beam technique was developed by Dudley Herschbach and Yuan T. Lee, for which they were awarded the 1986 Nobel Prize in Chemistry. While the technique was demonstrated in 1953 by Taylor and Datz of Oak Ridge National Laboratory, Herschbach and Lee refined the apparatus and began probing gas-phase reactions in unprecedented detail.
Early crossed beam experiments investigated alkali metals such as potassium, rubidium, and cesium. When the scattered alkali metal atoms collided with a hot metal filament, they ionized, creating a small electric current. Because this detection method is nearly perfectly efficient, the technique was quite sensitive. Unfortunately, this simple detection system only detects alkali metals. New techniques for detection were needed to analyze main group elements.
Detecting scattered particles through a metal filament gave a good indication of angular distribution but has no sensitivity to kinetic energy. In order to gain insight into the kinetic energy distribution, early crossed molecular beam apparatuses used a pair of slotted disks placed between the collision center and the detector. By controlling the rotation speed of the disks, only particles with a certain known velocity could pass through and be detected. With information about the velocity, angular distribution, and identity of the scattered species, useful information about the dynamics of the system can be derived.
Later improvements included the use of quadrupole mass filters to select only the products of interest, as well as time-of-flight mass spectrometers to allow easy measurement of kinetic energy. These improvements also allowed the detection of a vast array of compounds, marking the advent of the "universal" crossed molecular beam apparatus.
The inclusion of supersonic nozzles to collimate the gases expanded the variety and scope of experiments, and the use of lasers to excite the beams (either before impact or at the point of reaction) further broadened the applicability of this technique. | 7 | Physical Chemistry |
With primary amines, thionyl chloride gives sulfinylamine derivatives (RNSO), one example being N-sulfinylaniline. Thionyl chloride reacts with primary formamides to form isocyanides and with secondary formamides to give chloroiminium ions; as such a reaction with dimethylformamide will form the Vilsmeier reagent.
By an analogous process primary amides will react with thionyl chloride to form imidoyl chlorides, with secondary amides also giving chloroiminium ions. These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides, they are also exploited in the Bischler–Napieralski reaction as a means of forming isoquinolines.
Primary amides will continue on to form nitriles if heated (Von Braun amide degradation).
Thionyl chloride has also been used to promote the Beckmann rearrangement of oximes. | 0 | Organic Chemistry |
The advantage of nanofluidic devices is from its feasibility to be integrated with electronic circuitry. Because they are built using the same manufacturing technology, it is possible to make a nanofluidic system with digital integrated circuit on a single chip. Therefore, the control and manipulation of particles in the electrolyte can be achieved in a real-time.
Fabrication of nano-channels is categorized into top-down and bottom-up methods. Top-down methods are the conventional processes utilized in the IC industry and Microelectromechanical systems research. It begins with photolithography on a bulk silicon wafer. Bottom-up methods, in contrast, starts with atoms or molecules with intrinsic nano-scaled dimension. By organize and combine these building blocks together, it is able to form a nanostructures as small as only a few nanometers. | 7 | Physical Chemistry |
Nuclear reaction analysis (NRA) is a nuclear method of nuclear spectroscopy in materials science to obtain concentration vs. depth distributions for certain target chemical elements in a solid thin film. | 7 | Physical Chemistry |
Lake surface temperatures fluctuate between in winter, and in summer. From 1979 to 2011 annual rainfall was at the lake, and at Cerro La Laguna, the highest part of the catchment. The residence time of water in the lake is therefore 35 ± 6 days assuming homogeneous water mixing. In actuality the lake is strongly stratified and dimictic, being composed of a highly turbid and poorly mineralized epilimnion, over a 5 °C cooler, highly mineralized hypolimnion. Most of the water therefore only restrict its circulation to the epilimnion, with an average residence time of 18 ± 3 days, assuming a constant mean depth of the termocline of . The lake usually homogenizes in January or February, sometimes very rapidly.
The lake is fed by several streams, most noticeably by the Paná River in the west, which is born from the junction of Chijuljá and Requenzal creeks. Other streams (Los Lavaderos, Chicojgual, Cerro Caj Coj) contribute very little to the lake water budget. Some springs feed the lake either directly near the shoreline (for example near Panconsul cave), or through the extensive marshlands that surround the lake. Lake Chichoj drains to Río El Desagüe, a tributary of the Cahabón River, which it joins after sinking into a cave for several hundreds of meters. Some of the sewage of San Cristál Verapaz is rerouted away from the lake and flows in a pipe through the marshlands before being emptied into Río El Desagüe, downstream of lake Chichoj.
The lake results from the coalescence of at least three dolines, likely resulting from the dissolution of gypsum at depth. The occurrence of gypsum is evidenced by a cluster of sulfate-bearing springs that dot the active trace of the Chixoy Polochic fault, 2 km south of the lake in the chixoy river valley, where they form large travertine fans. Discharge at these springs is much larger than what their upslope catchments can provide. The catchment of Lake Chichój is the closest catchment susceptible to provide water to these springs, and it lies above the springs. | 2 | Environmental Chemistry |
Duke University did a study where they dosed a loblolly pine plantation with elevated levels of . The studies showed that the pines did indeed grow faster and stronger. They were also less prone to damage during ice storms, which is a factor that limits loblolly growth farther north. The forest did relatively better during dry years. The hypothesis is that the limiting factors in the growth of the pines are nutrients such as nitrogen, which is in deficit on much of the pine land in the Southeast. In dry years, however, the trees do not bump up against those factors since they are growing more slowly because water is the limiting factor. When rain is plentiful trees reach the limits of the site's nutrients and the extra is not beneficial. Most forest soils in Southeastern region are deficient in nitrogen and phosphorus as well as trace minerals. Pine forests often sit on land that was used for cotton, corn or tobacco. Since these crops depleted originally shallow and infertile soils, tree farmers must work to improve soils. | 2 | Environmental Chemistry |
All physical and chemical systems in the universe follow the second law of thermodynamics and proceed in a downhill, i.e., exergonic, direction. Thus, left to itself, any physical or chemical system will proceed, according to the second law of thermodynamics, in a direction that tends to lower the free energy of the system, and thus to expend energy in the form of work. These reactions occur spontaneously.
A chemical reaction is endergonic when non spontaneous. Thus in this type of reaction the Gibbs free energy increases. The entropy is included in any change of the Gibbs free energy. This differs from an endothermic reaction where the entropy is not included. The Gibbs free energy is calculated with the Gibbs–Helmholtz equation:
where:
: = temperature in kelvins (K)
: = change in the Gibbs free energy
: = change in entropy (at 298 K) as
: = change in enthalpy (at 298 K) as
A chemical reaction progresses non spontaneously when the Gibbs free energy increases, in that case the is positive. In exergonic reactions the is negative and in endergonic reactions the is positive:
: exergonic
: endergonic
where equals the change in the Gibbs free energy after completion of a chemical reaction. | 7 | Physical Chemistry |
Alkalinity roughly refers to the molar amount of bases in a solution that can be converted to uncharged species by a strong acid. For example, 1 mole of in solution represents 1 molar equivalent, while 1 mole of is 2 molar equivalents because twice as many H ions would be necessary to balance the charge. The total charge of a solution always equals zero. This leads to a parallel definition of alkalinity that is based upon the charge balance of ions in a solution.
Certain ions, including Na, K, Ca, Mg, Cl, , and are "conservative" such that they are unaffected by changes in temperature, pressure or pH. Others such as are affected by changes in pH, temperature, and pressure. By isolating the conservative ions on one side of this charge balance equation, the nonconservative ions which accept or donate protons and thus define alkalinity are clustered on the other side of the equation.
This combined charge balance and proton balance is called total alkalinity. Total alkalinity is not (much) affected by temperature, pressure, or pH, and is thus itself a conservative measurement, which increases its usefulness in aquatic systems. All anions except and have low concentrations in Earth's surface water (streams, rivers, and lakes). Thus carbonate alkalinity, which is equal to is also approximately equal to the total alkalinity in surface water. | 9 | Geochemistry |
Sunset yellow is used in foods, condoms, cosmetics, and drugs. Sunset yellow FCF is used as an orange or yellow-orange dye. For example, it is used in candy, desserts, snacks, sauces, and preserved fruits.
Sunset yellow is often used in conjunction with E123, amaranth, to produce a brown colouring in both chocolates and caramel. | 3 | Analytical Chemistry |
The generation of a transmembrane electrical potential through ion movement across a cell membrane drives biological processes like nerve conduction, muscle contraction, hormone secretion, and sensation. By convention, physiological voltages are measured relative to the extracellular region; a typical animal cell has an internal electrical potential of (−70)–(−50) mV.
An electrochemical gradient is essential to mitochondrial oxidative phosphorylation. The final step of cellular respiration is the electron transport chain, composed of four complexes embedded in the inner mitochondrial membrane. Complexes I, III, and IV pump protons from the matrix to the intermembrane space (IMS); for every electron pair entering the chain, ten protons translocate into the IMS. The result is an electric potential of more than . The resulting flux of protons back into the matrix powers the efforts of ATP synthase to combine inorganic phosphate and ADP.
Similar to the electron transport chain, the light-dependent reactions of photosynthesis pump protons into the thylakoid lumen of chloroplasts to drive the synthesis of ATP. The proton gradient can be generated through either noncyclic or cyclic photophosphorylation. Of the proteins that participate in noncyclic photophosphorylation, photosystem II (PSII), plastiquinone, and cytochrome bf complex directly contribute to generating the proton gradient. For each four photons absorbed by PSII, eight protons are pumped into the lumen.
Several other transporters and ion channels play a role in generating a proton electrochemical gradient. One is TPK, a potassium channel that is activated by Ca and conducts K from the thylakoid lumen to the stroma, which helps establish the electric field. On the other hand, the electro-neutral K efflux antiporter (KEA) transports K into the thylakoid lumen and H into the stroma, which helps establish the pH gradient. | 7 | Physical Chemistry |
The observation of the color of metal-electride solutions is generally attributed to Humphry Davy. In 1807–1809, he examined the addition of grains of potassium to gaseous ammonia (liquefaction of ammonia was invented in 1823). James Ballantyne Hannay and J. Hogarth repeated the experiments with sodium in 1879–1880. W. Weyl in 1864 and C. A. Seely in 1871 used liquid ammonia, whereas Hamilton Cady in 1897 related the ionizing properties of ammonia to that of water. Charles A. Kraus measured the electrical conductance of metal ammonia solutions and in 1907 attributed it to the electrons liberated from the metal. In 1918, G. E. Gibson and W. L. Argo introduced the solvated electron concept. They noted based on absorption spectra that different metals and different solvents (methylamine, ethylamine) produce the same blue color, attributed to a common species, the solvated electron. In the 1970s, solid salts containing electrons as the anion were characterized. | 0 | Organic Chemistry |
Activated GPCRs cause a conformational change in the attached G protein complex, which results in the G alpha subunit's exchanging GDP for GTP and separation from the beta and gamma subunits. The G alpha subunit, in turn, activates adenylyl cyclase, which quickly converts ATP into cAMP. This leads to the activation of the cAMP-dependent pathway. This pathway can also be activated downstream by directly activating adenylyl cyclase or PKA.
Molecules that activate cAMP pathway include:
* cholera toxin - increases cAMP levels
* forskolin - a diterpene natural product that activates adenylyl cyclase
* caffeine and theophylline inhibit cAMP phosphodiesterase, which degrades cAMP - thus enabling higher levels of cAMP than would otherwise be had.
* bucladesine (dibutyryl cAMP, db cAMP) - also a phosphodiesterase inhibitor
* pertussis toxin, which increases cAMP levels by inhibiting Gi to its GDP (inactive) form. This leads to an increase in adenylyl cyclase activity, thereby increasing cAMP levels, which can lead to an increase in insulin and therefore hypoglycemia | 1 | Biochemistry |
Loss-of-function mutations in females can lead to infertility. In 46, XY individuals severe inactivation can cause male pseudohermaphroditism, as fetal Leydig cells during may not respond and thus interfere with masculinization. Less severe inactivation can result in hypospadias or a micropenis. | 1 | Biochemistry |
Many classes of compounds with C–O–C linkages are not considered ethers: Esters (R–C(=O)–O–R′), hemiacetals (R–CH(–OH)–O–R′), carboxylic acid anhydrides (RC(=O)–O–C(=O)R′).
There are compounds which, instead of C in the linkage, contain heavier group 14 chemical elements (e.g., Si, Ge, Sn, Pb). Such compounds are considered ethers as well. Examples of such ethers are silyl enol ethers (containing the linkage), disiloxane (the other name of this compound is disilyl ether, containing the linkage) and stannoxanes (containing the linkage). | 0 | Organic Chemistry |
Rhenium and osmium are siderophile elements which are present at very low abundances in the crust. Rhenium undergoes radioactive decay to produce osmium. The ratio of non-radiogenic osmium to radiogenic osmium throughout time varies.
Rhenium prefers to enter sulfides more readily than osmium. Hence, during melting of the mantle, rhenium is stripped out, and prevents the osmium–osmium ratio from changing appreciably. This locks in an initial osmium ratio of the sample at the time of the melting event. Osmium–osmium initial ratios are used to determine the source characteristic and age of mantle melting events. | 9 | Geochemistry |
Arslantepe was first investigated by the French archaeologist Louis Delaporte from 1932 to 1939. From 1946 to 1951 Claude F.A. Schaeffer carried out some soundings.
The first Italian excavations at the site of Arslantepe started in 1961, and were conducted under the direction of Professors Piero Meriggi and Salvatore M. Puglisi until 1968. The choice of the site was initially due to their desire to investigate the Neo-Hittite phases of occupation at the site, a period in which Malatya was the capital of one of the most important reigns born after the destruction of the Hittite Empire in its most eastern borders. Majestic remains of this period had been known from Arslantepe since the 1930s after they were brought to light by a French expedition. The Hittitologist Meriggi only took part in the first few campaigns and later left the direction to Puglisi, a palaeoethnologist, who expanded and regularly conducted yearly investigations under regular permit from the Turkish government. Alba Palmieri took over the supervision of the excavation during the 1970s. In the early 21st century, the archaeological investigation was led by Marcella Frangipane. | 8 | Metallurgy |
The existence of discrete inheritable units was first suggested by Gregor Mendel (1822–1884). From 1857 to 1864, in Brno, Austrian Empire (todays Czech Republic), he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2 combinations where n is the number of differing characteristics in the original peas. Although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. This description prefigured Wilhelm Johannsens distinction between genotype (the genetic material of an organism) and phenotype (the observable traits of that organism). Mendel was also the first to demonstrate independent assortment, the distinction between dominant and recessive traits, the distinction between a heterozygote and homozygote, and the phenomenon of discontinuous inheritance.
Prior to Mendels work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilization process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan ("all, whole") and genesis ("birth") / genos ("origin"). Darwin used the term gemmule' to describe hypothetical particles that would mix during reproduction.
Mendels work went largely unnoticed after its first publication in 1866, but was rediscovered in the late 19th century by Hugo de Vries, Carl Correns, and Erich von Tschermak, who (claimed to have) reached similar conclusions in their own research. Specifically, in 1889, Hugo de Vries published his book Intracellular Pangenesis, in which he postulated that different characters have individual hereditary carriers and that inheritance of specific traits in organisms comes in particles. De Vries called these units "pangenes" (Pangens in German), after Darwins 1868 pangenesis theory.
Twenty years later, in 1909, Wilhelm Johannsen introduced the term gene and in 1906, William Bateson, that of genetics while Eduard Strasburger, amongst others, still used the term pangene for the fundamental physical and functional unit of heredity. | 1 | Biochemistry |
Recent research has focused on the in-place remediation of trichloroethylene in soil and groundwater using potassium permanganate instead of removal for off-site treatment and disposal. Naturally occurring bacteria have been identified with the ability to degrade TCE. Dehalococcoides sp. degrade trichloroethylene by reductive dechlorination under anaerobic conditions. Under aerobic conditions, Pseudomonas fluorescens can co-metabolize TCE. Soil and groundwater contamination by TCE has also been successfully remediated by chemical treatment and extraction. The bacteria Nitrosomonas europaea can degrade a variety of halogenated compounds including trichloroethylene. Toluene dioxygenase has been reported to be involved in TCE degradation by Pseudomonas putida. In some cases, Xanthobacter autotrophicus can convert up to 51% of TCE to CO and . | 2 | Environmental Chemistry |
In molecular biology, intercellular adhesion molecules (ICAMs) and vascular cell adhesion molecule-1 (VCAM-1) are part of the immunoglobulin superfamily. They are important in inflammation, immune responses and in intracellular signalling events. The ICAM family consists of five members, designated ICAM-1 to ICAM-5. They are known to bind to leucocyte integrins CD11/CD18 such as LFA-1 and Macrophage-1 antigen, during inflammation and in immune responses. In addition, ICAMs may exist in soluble forms in human plasma, due to activation and proteolysis mechanisms at cell surfaces.
Mammalian intercellular adhesion molecules include:
* ICAM-1
* ICAM2
* ICAM3
* ICAM4
* ICAM5 | 1 | Biochemistry |
Blood samples for BAC analysis are typically obtained by taking a venous blood sample from the arm. A variety of methods exist for determining blood-alcohol concentration in a blood sample. Forensic laboratories typically use headspace-gas chromatography combined with mass spectrometry or flame ionization detection, as this method is accurate and efficient. Hospitals typically use enzyme multiplied immunoassay, which measures the co-enzyme NADH. This method is more subject to error but may be performed rapidly in parallel with other blood sample measurements.
In Germany, BAC is determined by measuring the serum level and then converting to whole blood by dividing by the factor 1.236. This calculation underestimates BAC by 4% to 10% compared to other methods. | 1 | Biochemistry |
Reductive elimination of square planar complexes can progress through a variety of mechanisms: dissociative, nondissociative, and associative. Similar to octahedral complexes, a dissociative mechanism for square planar complexes initiates with loss of a ligand, generating a three-coordinate intermediate that undergoes reductive elimination to produce a one-coordinate metal complex. For a nondissociative pathway, reductive elimination occurs from the four-coordinate system to afford a two-coordinate complex. If the eliminating ligands are trans to each other, the complex must first undergo a trans to cis isomerization before eliminating. In an associative mechanism, a ligand must initially associate with the four-coordinate metal complex to generate a five-coordinate complex that undergoes reductive elimination synonymous to the dissociation mechanism for octahedral complexes. | 0 | Organic Chemistry |
Self-propulsion is the autonomous displacement of nano-, micro- and macroscopic natural and artificial objects, containing their own means of motion. Self-propulsion is driven mainly by interfacial phenomena. Various mechanisms of self-propelling have been introduced and investigated, which exploited phoretic effects, gradient surfaces, breaking the wetting symmetry of a droplet on a surface, the Leidenfrost effect, the self-generated hydrodynamic and chemical fields originating from the geometrical confinements, and soluto- and thermo-capillary Marangoni flows. Self-propelled system demonstrate a potential as micro-fluidics devices and micro-mixers. Self-propelled liquid marbles have been demonstrated. | 7 | Physical Chemistry |
In molecular biology, subcloning is a technique used to move a particular DNA sequence from a parent vector to a destination vector.
Subcloning is not to be confused with molecular cloning, a related technique. | 1 | Biochemistry |
Natta first used polymerization catalysts based on titanium chlorides to polymerize propylene and other 1-alkenes. He discovered that these polymers are crystalline materials and ascribed their crystallinity to a special feature of the polymer structure called stereoregularity.
The concept of stereoregularity in polymer chains is illustrated in the picture on the left with polypropylene. Stereoregular poly(1-alkene) can be isotactic or syndiotactic depending on the relative orientation of the alkyl groups in polymer chains consisting of units −[CH−CHR]−, like the CH groups in the figure. In the isotactic polymers, all stereogenic centers CHR share the same configuration. The stereogenic centers in syndiotactic polymers alternate their relative configuration. A polymer that lacks any regular arrangement in the position of its alkyl substituents (R) is called atactic. Both isotactic and syndiotactic polypropylene are crystalline, whereas atactic polypropylene, which can also be prepared with special Ziegler–Natta catalysts, is amorphous. The stereoregularity of the polymer is determined by the catalyst used to prepare it. | 7 | Physical Chemistry |
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