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Angle-resolved low-coherence interferometry (a/LCI) is an emerging biomedical imaging technology which uses the properties of scattered light to measure the average size of cell structures, including cell nuclei. The technology shows promise as a clinical tool for in situ detection of dysplastic, or precancerous tissue. | 7 | Physical Chemistry |
Artificial seawater (abbreviated ASW) is a mixture of dissolved mineral salts (and sometimes vitamins) that simulates seawater. Artificial seawater is primarily used in marine biology and in marine and reef aquaria, and allows the easy preparation of media appropriate for marine organisms (including algae, bacteria, plants and animals). From a scientific perspective, artificial seawater has the advantage of reproducibility over natural seawater since it is a standardized formula. Artificial seawater is also known as synthetic seawater and substitute ocean water. | 9 | Geochemistry |
Unlike the widely used automotive antifreeze, ethylene glycol, AFPs do not lower freezing point in proportion to concentration. Rather, they work in a noncolligative manner. This phenomenon allows them to act as an antifreeze at concentrations 1/300th to 1/500th of those of other dissolved solutes. Their low concentration minimizes their effect on osmotic pressure. The unusual properties of AFPs are attributed to their selective affinity for specific crystalline ice forms and the resulting blockade of the ice-nucleation process. | 1 | Biochemistry |
In the presence of palladium acetate under 1-30 bar of CO, simple aromatic compounds convert to aromatic carboxylic acids. A PSiP-pincer ligand (5) promotes carboxylation of allene without using pre-functionalized substrates. Catalyst regeneration, EtAl was added to do transmetallation with palladium. Catalyst is regenerated by the following β-H elimination. Apart from terminal allenes, some of internal allenes are also tolerated in this reaction, generating allyl carboxylic acid with the yield between 54% and 95%. This system was also applied to 1,3-diene, generating carboxylic acid in 1,2 addition fashion. In 2015, Iwasawa et al. reported the germanium analogue (6) and combined CO source together with hydride source to formate salts.
Palladium has shown huge power to catalyze C-H functionalization. If the Pd-C intermediate in carboxylation reaction comes from C-H activation, such methodology must promote metal catalyzed carboxylation to a much higher level in utility. Iwasawa and co-workers reported direct carboxylation by styrenyl C-H activation generating coumarin derivatives. Benzene rings with different electronic properties and some heteroaromatic rings are tolerated in this reaction with yield from 50% to 90%. C-H activation was demonstrated by crystallography study. | 0 | Organic Chemistry |
Due to its surface property, sucrose esters are used in pharmaceutical research as a stabilizer or a surfactant on vesicles for drug delivery systems. | 0 | Organic Chemistry |
After DNA has been separated and purified by standard biochemical methods, one has a sample in a jar much like in the figure at the top of this article. Below are the main steps involved in generating structural information from X-ray diffraction studies of oriented DNA fibers that are drawn from the hydrated DNA sample with the help of molecular models of DNA that are combined with crystallographic and mathematical analysis of the X-ray patterns. | 4 | Stereochemistry |
Source:
* 1991 Chris H. Greene: "For his many contributions to atomic and molecular theory including studies of resonance vibronic processes, multiple electron excitations, photo-absorption in external fields, and threshold effects of long range forces."
* 1993 Timothy E. Chupp: "For his contributions to the development of high density polarized noble gases by spin exchange with optically pumped alkali atoms and in particular for his leadership and use of polarized 3He as a target for fundamental experiments in nuclear physics."
* 1995 Randall G. Hulet: "For his contributions to a broad range of important problems in atomic and optical physics including cavity quantum electrodynamics, quantum jumps, ion storage, and laser cooling of atoms. In the latter field, in particular for his demonstration of multiphoton cooling involving Doppleron resonances in neutral Lithium and his collision experiments with cooled Lithium vapor."
* 1997 Eric Allin Cornell and Wolfgang Ketterle: "For achieving Bose-Einstein condensation of an atomic gas, for creating techniques for studying the Bose condensate, and for measuring the physical properties of the weakly interacting atomic Bose gas."
* 1999 Mark G. Raizen: "For his pioneering advances in the experimental study of atom optics, and especially for the insightful connections he has developed between this discipline and studies of chaotic dynamics, condensed matter physics, and dissipative quantum systems."
* 2001 Christopher Monroe: "For his pivotal experiments that implemented quantum logic using trapped atomic ions, and for his fundamental studies of coherence and decoherence in entangled quantum systems."
* 2003 Mark A. Kasevich: "For developing atom interferometer inertial sensors with unprecedented precision, and for pioneering studies of Bose-Einstein condensates, especially the achievement of non-classical spin states and the demonstration of a mode-locked atom laser."
* 2005 Deborah Jin:
* 2007 Jun Ye: "For advances in precision measurement, including techniques for stabilizing and measuring optical frequencies, controlling the phase of femtosecond laser pulses, and measuring molecular transitions."
* 2009 Mikhail Lukin: "For pioneering theoretical and experimental work at the interface between quantum optics, quantum information processing, and the quantum many body problem."
* 2011 Cheng Chin: "For pioneering work in strongly interacting Fermi gas and few body physics including the discovery of the Effimov effect."
* 2013 Markus Greiner: "For seminal contributions to the field of ultracold atoms, including the observation of the superfluid-to-Mott-insulator transition, the study of the BEC-BCS cross over for fermions, and the development of imaging techniques for atoms in optical lattices with single-atom resolution"
* 2015 Ian Spielman: "For the development of quantum simulations using ultra-cold atoms, creation of synthetic electromagnetic fields, demonstration of synthetic spinorbit coupling, and applications to studying new physical systems."
* 2017 Martin Zwierlein: "For seminal studies of ultracold Fermi gases, including precision measurements of the equation of state, the observation of superfluidity, solitons, vortices, and polarons, the realization of a microscope for fermions in a lattice; and the production of chemically stable polar molecules."
* 2019 Kang-Kuen Ni: "For seminal work on ultracold molecules, including original contributions to the understanding of chemical reactions in the quantum regime, deterministic creation of individual molecules with optical tweezers, and development of novel, high-precision techniques to interrogate and control the complete set of internal molecular resources."
* 2021 Monika Schleier-Smith: "For seminal work in quantum optics and for discoveries at the intersection of AMO, condensed matter, and quantum information, including original contributions to spin squeezing in optical cavities, engineering long-range interactions for quantum simulations, and metrology, and for theoretical development of a measurement protocol related to the scrambling of quantum information."
* 2023 Adam M. Kaufman: "For seminal developments in optical tweezer arrays and clocks based on alkaline earth atoms, with applications to metrology and quantum information processing." | 7 | Physical Chemistry |
A majority of silver nanoparticles in consumer products go down the drain and are eventually released into sewer systems and reach wastewater treatment plants. Primary screening and grit removal in wastewater treatment does not completely filter out silver nanoparticles, and coagulation treatment may lead to further condensation into wastewater sludge. The secondary wastewater treatment process involves suspended growth systems which allow bacteria to decompose organic matter within the water. Any silver nanoparticles still suspended in the water may collect on these microbes, potentially killing them due to their antimicrobial effects. After passing through both treatment processes, the silver nanoparticles are eventually deposited into the environment.
A majority of the submerged portions of wastewater treatment plants are anoxic and rich in sulfur. During the wastewater treatment process, silver nanoparticles either remain the same, are converted into free silver ions, complex with ligands, or agglomerate. Silver nanoparticles can also attach to wastewater biosolids found in both the sludge and the effluent. Silver ions in wastewater are removed efficiently because of their strong complexation with chloride or sulfide.
A majority of the silver found in wastewater treatment plant effluent is associated with reduced sulfur as organic thiol groups and inorganic sulfides. Silver nanoparticles also tend to accumulate in activated sludge, and the dominant form of the silver found in sewage sludge is AgS. Therefore, most of the silver found in wastewater treatment plants is in the form of silver nanoparticles or silver precipitates such as AgS and AgCl.
The amount of silver precipitate formed depends on silver ion release, which increases with increasing dissolved oxygen concentration and decreasing pH. Silver ions account for approximately 1% of total silver after silver nanoparticles are suspended in aerated water. In anoxic wastewater treatment environments, silver ion release is therefore often negligible, and most of the silver nanoparticles in wastewater remain in the original silver nanoparticle form. The presence of natural organic matter can also decrease oxidative dissolution rates and therefore the release rate of free silver ions. The slow oxidation of silver nanoparticles may enable new pathways for its transfer into the environment. | 2 | Environmental Chemistry |
In these cycles and engines the working fluid is always a gas (i.e., there is no phase change):
*Carnot cycle (Carnot heat engine)
*Ericsson cycle (Caloric Ship John Ericsson)
*Stirling cycle (Stirling engine, thermoacoustic devices)
*Internal combustion engine (ICE):
**Otto cycle (e.g. gasoline/petrol engine)
**Diesel cycle (e.g. Diesel engine)
**Atkinson cycle (Atkinson engine)
**Brayton cycle or Joule cycle originally Ericsson cycle (gas turbine)
**Lenoir cycle (e.g., pulse jet engine)
**Miller cycle (Miller engine) | 7 | Physical Chemistry |
Preventative measures have been recommended that are intended to decrease the risk of accidental ingestion of caustic substances including:
* Keeping caustic substances in locked cabinets or on upper shelves
* Not storing chemical substances in food or drink containers
* Not keeping large amounts of detergent in the home
* Not mentioning a drug as "candy" when giving it as medication
* Keeping the phone number for poison control in the home
* Keeping caustic substances in labelled containers | 8 | Metallurgy |
Yeast artificial chromosomes (YACs) are linear DNA molecules containing the necessary features of an authentic yeast chromosome, including telomeres, a centromere, and an origin of replication. Large inserts of DNA can be ligated into the middle of the YAC so that there is an “arm” of the YAC on either side of the insert. The recombinant YAC is introduced into yeast by transformation; selectable markers present in the YAC allow for the identification of successful transformants. YACs can hold inserts up to 2000kb, but most YAC libraries contain inserts 250-400kb in size. Theoretically there is no upper limit on the size of insert a YAC can hold. It is the quality in the preparation of DNA used for inserts that determines the size limit. The most challenging aspect of using YAC is the fact they are prone to rearrangement. | 1 | Biochemistry |
The study of thermodynamical systems has developed into several related branches, each using a different fundamental model as a theoretical or experimental basis, or applying the principles to varying types of systems. | 7 | Physical Chemistry |
There is a fast and a slow carbon cycle. The fast cycle operates in the biosphere and the slow cycle operates in rocks. The fast or biological cycle can complete within years, moving carbon from atmosphere to biosphere, then back to the atmosphere. The slow or geological cycle may extend deep into the mantle and can take millions of years to complete, moving carbon through the Earth's crust between rocks, soil, ocean and atmosphere.
The fast carbon cycle involves relatively short-term biogeochemical processes between the environment and living organisms in the biosphere (see diagram at start of article). It includes movements of carbon between the atmosphere and terrestrial and marine ecosystems, as well as soils and seafloor sediments. The fast cycle includes annual cycles involving photosynthesis and decadal cycles involving vegetative growth and decomposition. The reactions of the fast carbon cycle to human activities will determine many of the more immediate impacts of climate change.
The slow (or deep) carbon cycle involves medium to long-term geochemical processes belonging to the rock cycle (see diagram on the right). The exchange between the ocean and atmosphere can take centuries, and the weathering of rocks can take millions of years. Carbon in the ocean precipitates to the ocean floor where it can form sedimentary rock and be subducted into the Earths mantle. Mountain building processes result in the return of this geologic carbon to the Earths surface. There the rocks are weathered and carbon is returned to the atmosphere by degassing and to the ocean by rivers. Other geologic carbon returns to the ocean through the hydrothermal emission of calcium ions. In a given year between 10 and 100 million tonnes of carbon moves around this slow cycle. This includes volcanoes returning geologic carbon directly to the atmosphere in the form of carbon dioxide. However, this is less than one percent of the carbon dioxide put into the atmosphere by burning fossil fuels. | 5 | Photochemistry |
End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, they are functional groups that are at the very ends of a macromolecule or oligomer (IUPAC). In polymer synthesis, like condensation polymerization and free-radical types of polymerization, end-groups are commonly used and can be analyzed by nuclear magnetic resonance (NMR) to determine the average length of the polymer. Other methods for characterization of polymers where end-groups are used are mass spectrometry and vibrational spectrometry, like infrared and raman spectroscopy. These groups are important for the analysis of polymers and for grafting to and from a polymer chain to create a new copolymer. One example of an end group is in the polymer poly(ethylene glycol) diacrylate where the end-groups are circled. | 7 | Physical Chemistry |
In the English literature this reaction is sometimes called Baeyer–Drewsn reaction, although the author of the original paper was spelled Drewsn. | 0 | Organic Chemistry |
The introduction of lasers in atomic manipulation experiments was the precursor to the laser cooling proposals in the mid 1970s. Laser cooling was proposed separately in 1975 by two different research groups: Hänsch and Schawlow,
and Wineland and Dehmelt. Both proposals outlined the simplest laser cooling process, known as Doppler cooling, where laser light below an atom's resonant frequency is repeatedly absorbed and the velocity distribution of the atoms is reduced.
In 1977 Ashkin submitted a paper which describes how Doppler cooling could be used to provide the necessary damping to load atoms into an optical trap. In this work he emphasized how this process could allow for long spectroscopic measurements without the atoms escaping the trap and proposed the overlapping of optical traps in order to study interactions between different atoms. | 7 | Physical Chemistry |
For each thermodynamic potential, there are thermodynamic variables that need to be held constant to specify the potential value at a thermodynamical equilibrium state, such as independent variables for a mathematical function. These variables are termed the natural variables of that potential. The natural variables are important not only to specify the potential value at the equilibrium, but also because if a thermodynamic potential can be determined as a function of its natural variables, all of the thermodynamic properties of the system can be found by taking partial derivatives of that potential with respect to its natural variables and this is true for no other combination of variables. If a thermodynamic potential is not given as a function of its natural variables, it will not, in general, yield all of the thermodynamic properties of the system.
The set of natural variables for each of the above four thermodynamic potentials is formed from a combination of the , , , variables, excluding any pairs of conjugate variables; there is no natural variable set for a potential including the - or - variables together as conjugate variables for energy. An exception for this rule is the − conjugate pairs as there is no reason to ignore these in the thermodynamic potentials, and in fact we may additionally define the four potentials for each species. Using IUPAC notation in which the brackets contain the natural variables (other than the main four), we have:
If there is only one species, then we are done. But, if there are, say, two species, then there will be additional potentials such as and so on. If there are dimensions to the thermodynamic space, then there are unique thermodynamic potentials. For the most simple case, a single phase ideal gas, there will be three dimensions, yielding eight thermodynamic potentials. | 7 | Physical Chemistry |
DIDs are sensitive to a broad range of components.
In air separation plants, they are used to detect the components ; ; ; ; in argon product in ppm range.
DIDs are non-destructive detectors. They do not destroy or consume the components they detect. Therefore, they can be used before other detectors in multiple-detector configurations.
DIDs are an improvement over helium ionization detectors in that they contain no radioactive source. | 3 | Analytical Chemistry |
Progesterone plays a role in early human sexual differentiation. Placental progesterone is the feedstock for the 5α-dihydrotestosterone (DHT) produced via the backdoor pathway found operating in multiple non-gonadal tissues of the fetus, whereas deficiencies in this pathway lead to undervirilization of the male fetus, resulting in incomplete development of the male genitalia. DHT is a potent androgen that is responsible for the development of male genitalia, including the penis and scrotum.
During early fetal development, the undifferentiated gonads can develop into either testes or ovaries. The presence of the Y chromosome leads to the development of testes. The testes then produce testosterone, which is converted to DHT via the enzyme 5α-reductase. DHT is a potent androgen that is responsible for the masculinization of the external genitalia and the development of the prostate gland. Progesterone, produced by the placenta during pregnancy, plays a role in fetal sexual differentiation by serving as a precursor molecule for the synthesis of DHT via the backdoor pathway. In the absence of adequate levels of steroidogenic enzymes during fetal development, the backdoor pathway for DHT synthesis can become deficient, leading to undermasculinization of the male fetus. This can result in the development of ambiguous genitalia or even female genitalia in some cases. Therefore, both DHT and progesterone play crucial roles in early fetal sexual differentiation, with progesterone acting as a precursor molecule for DHT synthesis and DHT promoting the development of male genitalia. | 0 | Organic Chemistry |
The classic method of nonlinear absorption used by microscopists is conventional two-photon fluorescence, in which two photons from a single source interact to excite a photoelectron. The electron then emits a photon as it transitions back to its ground state. This microscopy method has been revolutionary in biological sciences because of its inherent three-dimensional optical sectioning capabilities.
Two-photon absorption is inherently a nonlinear process: fluorescent output intensity is proportional to the square of the excitation light intensity. This ensures that fluorescence is only generated within the focus of a laser beam, as the intensity outside of this plane is insufficient to excite a photoelectron.
However, this microscope modality is inherently limited by the number of biological molecules that can undergo both two-photon excitation and fluorescence.
Pump–probe microscopy circumvents this limitation by directly measuring excitation light. This expands the number of potential targets to any molecule capable of two-photon absorption, even if it does not fluoresce upon relaxation. The method modulates the amplitude of a pulsed laser beam, referred to as the pump, to bring the target molecule to an excited state. This will then affect the properties of a second coherent beam, referred to as the probe, based on the interaction of the two beams with the molecule. These properties are then measured by a detector to form an image. | 7 | Physical Chemistry |
An oil dispersant is a mixture of emulsifiers and solvents that helps break oil into small droplets following an oil spill. Small droplets are easier to disperse throughout a water volume, and small droplets may be more readily biodegraded by microbes in the water. Dispersant use involves a trade-off between exposing coastal life to surface oil and exposing aquatic life to dispersed oil. While submerging the oil with dispersant may lessen exposure to marine life on the surface, it increases exposure for animals dwelling underwater, who may be harmed by toxicity of both dispersed oil and dispersant. Although dispersant reduces the amount of oil that lands ashore, it may allow faster, deeper penetration of oil into coastal terrain, where it is not easily biodegraded. | 2 | Environmental Chemistry |
Hydrocarbon utilizing microorganisms, mostly Cladosporium resinae and Pseudomonas aeruginosa and sulfate reducing bacteria, colloquially known as "HUM bugs", are commonly present in jet fuel. They live in the water-fuel interface of the water droplets, form dark black/brown/green, gel-like mats, and cause microbial corrosion to plastic and rubber parts of the aircraft fuel system by consuming them, and to the metal parts by the means of their acidic metabolic products. They are also incorrectly called algae due to their appearance. FSII, is added to fuel as a growth retardant. There are about 250 kinds of bacteria that can live in jet fuel, but fewer than a dozen are meaningfully harmful. | 8 | Metallurgy |
In organic chemistry, pyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom (a heterocycle). There may be other carbons external to the ring. The name derives from its similarity to the oxygen heterocycle pyran, but the pyranose ring does not have double bonds. A pyranose in which the anomeric (hydroxyl group) at C(l) has been converted into an OR group is called a pyranoside. | 0 | Organic Chemistry |
The composition of Mars covers the branch of the geology of Mars that describes the make-up of the planet Mars. | 9 | Geochemistry |
Damage and subsequent dysfunction in mitochondria is an important factor in a range of human diseases due to their influence in cell metabolism. Mitochondrial disorders often present as neurological disorders, including autism. They can also manifest as myopathy, diabetes, multiple endocrinopathy, and a variety of other systemic disorders. Diseases caused by mutation in the mtDNA include Kearns–Sayre syndrome, MELAS syndrome and Lebers hereditary optic neuropathy. In the vast majority of cases, these diseases are transmitted by a female to her children, as the zygote derives its mitochondria and hence its mtDNA from the ovum. Diseases such as Kearns-Sayre syndrome, Pearson syndrome, and progressive external ophthalmoplegia are thought to be due to large-scale mtDNA rearrangements, whereas other diseases such as MELAS syndrome, Lebers hereditary optic neuropathy, MERRF syndrome, and others are due to point mutations in mtDNA.
It has also been reported that drug tolerant cancer cells have an increased number and size of mitochondria which suggested an increase in mitochondrial biogenesis. A 2022 study in Nature Nanotechnology has reported that cancer cells can hijack the mitochondria from immune cells via physical tunneling nanotubes.
In other diseases, defects in nuclear genes lead to dysfunction of mitochondrial proteins. This is the case in Friedreichs ataxia, hereditary spastic paraplegia, and Wilsons disease. These diseases are inherited in a dominance relationship, as applies to most other genetic diseases. A variety of disorders can be caused by nuclear mutations of oxidative phosphorylation enzymes, such as coenzyme Q10 deficiency and Barth syndrome. Environmental influences may interact with hereditary predispositions and cause mitochondrial disease. For example, there may be a link between pesticide exposure and the later onset of Parkinsons disease. Other pathologies with etiology involving mitochondrial dysfunction include schizophrenia, bipolar disorder, dementia, Alzheimers disease, Parkinson's disease, epilepsy, stroke, cardiovascular disease, chronic fatigue syndrome, retinitis pigmentosa, and diabetes mellitus.
Mitochondria-mediated oxidative stress plays a role in cardiomyopathy in type 2 diabetics. Increased fatty acid delivery to the heart increases fatty acid uptake by cardiomyocytes, resulting in increased fatty acid oxidation in these cells. This process increases the reducing equivalents available to the electron transport chain of the mitochondria, ultimately increasing reactive oxygen species (ROS) production. ROS increases uncoupling proteins (UCPs) and potentiate proton leakage through the adenine nucleotide translocator (ANT), the combination of which uncouples the mitochondria. Uncoupling then increases oxygen consumption by the mitochondria, compounding the increase in fatty acid oxidation. This creates a vicious cycle of uncoupling; furthermore, even though oxygen consumption increases, ATP synthesis does not increase proportionally because the mitochondria are uncoupled. Less ATP availability ultimately results in an energy deficit presenting as reduced cardiac efficiency and contractile dysfunction. To compound the problem, impaired sarcoplasmic reticulum calcium release and reduced mitochondrial reuptake limits peak cytosolic levels of the important signaling ion during muscle contraction. Decreased intra-mitochondrial calcium concentration increases dehydrogenase activation and ATP synthesis. So in addition to lower ATP synthesis due to fatty acid oxidation, ATP synthesis is impaired by poor calcium signaling as well, causing cardiac problems for diabetics.
Mitochondria also modulate processes such as testicular somatic cell development, spermatogonial stem cell differentiation, luminal acidification, testosterone production in testes, and more. Thus, dysfunction of mitochondria in spermatozoa can be a cause for infertility.
In efforts to combat mitochondrial disease, mitochondrial replacement therapy (MRT) has been developed. This form of in vitro fertilization uses donor mitochondria, which avoids the transmission of diseases caused by mutations of mitochondrial DNA. However, this therapy is still being researched and can introduce genetic modification, as well as safety concerns. These diseases are rare but can be extremely debilitating and progressive diseases, thus posing complex ethical questions for public policy. | 1 | Biochemistry |
NMR spectroscopic research includes the following steps:
*Extraction of carbohydrate material (for natural glycans)
*Chemical removal of moieties masking regularity (for polymers)
*Separation and purification of carbohydrate material (for 2D NMR experiments, 10 mg or more is recommended)
*Sample preparation (usually in DO)
*Acquisition of 1D spectra
*Planning, acquisition and processing of other NMR experiments (usually requires from 5 to 20 hours)
*Assignment and interpretation of spectra (see exemplary figure)
*If a structural problem could not be solved: chemical modification/degradation and NMR analysis of products
*Acquisition of spectra of the native (unmasked) compound and their interpretation based on modified structure
*Presentation of results | 0 | Organic Chemistry |
acid is a member of the carboxylic acid family of organic compounds. It is a structural analog of butyric acid with a hydroxyl functional group and a methyl substituent located on its beta carbon. By extension, other structural analogs include acid and acid. | 1 | Biochemistry |
<section begin=sampling />
The complexity of water quality as a subject is reflected in the many types of measurements of water quality indicators. Some measurements of water quality are most accurately made on-site, because water exists in equilibrium with its surroundings. Measurements commonly made on-site and in direct contact with the water source in question include temperature, pH, dissolved oxygen, conductivity, oxygen reduction potential (ORP), turbidity, and Secchi disk depth.
Sampling of water for physical or chemical testing can be done by several methods, depending on the accuracy needed and the characteristics of the contaminant. Sampling methods include for example simple random sampling, stratified sampling, systematic and grid sampling, adaptive cluster sampling, grab samples, semi-continuous monitoring and continuous, passive sampling, remote surveillance, remote sensing, and biomonitoring. The use of passive samplers greatly reduces the cost and the need of infrastructure on the sampling location.
Many contamination events are sharply restricted in time, most commonly in association with rain events. For this reason "grab" samples are often inadequate for fully quantifying contaminant levels. Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or discharge intervals.<section end=sampling />
More complex measurements are often made in a laboratory requiring a water sample to be collected, preserved, transported, and analyzed at another location. | 3 | Analytical Chemistry |
As part of the post-September 11 drive towards increased capability in homeland security and public health preparedness, traditional GC–MS units with transmission quadrupole mass spectrometers, as well as those with cylindrical ion trap (CIT-MS) and toroidal ion trap (T-ITMS) mass spectrometers have been modified for field portability and near real-time detection of chemical warfare agents (CWA) such as sarin, soman, and VX. These complex and large GC–MS systems have been modified and configured with resistively heated low thermal mass (LTM) gas chromatographs that reduce analysis time to less than ten percent of the time required in traditional laboratory systems. Additionally, the systems are smaller, and more mobile, including units that are mounted in mobile analytical laboratories (MAL), such as those used by the United States Marine Corps Chemical and Biological Incident Response Force MAL and other similar laboratories, and systems that are hand-carried by two-person teams or individuals, much ado to the smaller mass detectors. Depending on the system, the analytes can be introduced via liquid injection, desorbed from sorbent tubes through a thermal desorption process, or with solid-phase micro extraction (SPME). | 3 | Analytical Chemistry |
Self-assembled monolayers (SAMs) are formed by chemisorbing reactive reagents with metal surfaces. A famous example involves thiols (RS-H) adsorbing onto the surface of gold. This process forms strong Au-SR bonds and releases H. The densely packed SR groups protect the surface. | 7 | Physical Chemistry |
In E. coli amino acid starvation inhibited DNA replication at the initiation stage at oriC, most probably owing to the lack of the DnaA replication initiation protein. In B. subtilis, the replication arrest due to (p)ppGpp accumulation is caused by the binding of an Rtp protein to specific sites about 100-200kb away from oriC in both directions. DNA primase (DnaG) was directly inhibited by (p)ppGpp. Unlike E. coli, B. subtilis accumulates more pppGpp than ppGpp; the more abundant nucleotide is a more-potent DnaG inhibitor. ppGpp can bind with Obg protein which belongs to the conserved, small GTPase protein family. Obg protein interacts with several regulators (RsbT, RsbW, RsbX) necessary for the stress activation of sigma B. | 1 | Biochemistry |
The neutral monomer , as well as the other neutral gold trihalide species, has not been isolated in the gas phase which indicates the coordination number three is not favored. Predominantly, gold(III) displays square planar coordination corresponding to a preferred coordination number of four.
Specifically, in solution gold(III) trihalides have the tendency to add a fourth ligand to form the more preferred four-coordinate complex. With respect to gold tribromide, it is common to purchase gold(III) bromide hydrate, , where the central gold atom exhibits a coordination number of four, rather than the anhydrous form of the compound, which exhibits a coordination number of three.
Alternatively, if there is no addition of a fourth ligand, gold tribromide will oligomerize to form the halogen-bridged dimer complex mentioned previously.
Furthermore, like gold(III) chloride, gold tribromide is a Lewis acid and can form several complexes. For example, in the presence of hydrobromic acid, the dimer dissolves and bromoauric acid is formed.
The dimer also undergoes hydrolysis rapidly in moist air. | 3 | Analytical Chemistry |
Golden rice is a recombinant variety of rice that has been engineered to express the enzymes responsible for β-carotene biosynthesis. This variety of rice holds substantial promise for reducing the incidence of vitamin A deficiency in the world's population. Golden rice is not currently in use, pending the resolution of regulatory and intellectual property issues. | 1 | Biochemistry |
Piperidine is produced by hydrogenation of pyridine with a nickel-, cobalt-, or ruthenium-based catalyst at elevated temperatures. The hydrogenation of pyridine to piperidine releases 193.8 kJ·mol, which is slightly less than the energy of the hydrogenation of benzene (205.3 kJ·mol).
Partially hydrogenated derivatives are obtained under milder conditions. For example, reduction with lithium aluminium hydride yields a mixture of 1,4-dihydropyridine, 1,2-dihydropyridine, and 2,5-dihydropyridine. Selective synthesis of 1,4-dihydropyridine is achieved in the presence of organometallic complexes of magnesium and zinc, and (Δ3,4)-tetrahydropyridine is obtained by electrochemical reduction of pyridine. Birch reduction converts pyridine to dihydropyridines. | 0 | Organic Chemistry |
Halocarbons are less prolific compounds developed for diverse uses throughout industry; for example as solvents and refrigerants. Nevertheless, the buildup of relatively small concentrations (parts per trillion) of chlorofluorocarbon, hydrofluorocarbon, and perfluorocarbon gases in the atmosphere is responsible for about 10% of the total direct radiative forcing from all long-lived greenhouse gases (year 2019); which includes forcing from the much larger concentrations of carbon dioxide and methane. Chlorofluorocarbons also cause stratospheric ozone depletion. International efforts are ongoing under the Montreal Protocol and Kyoto Protocol to control rapid growth in the industrial manufacturing and use of these environmentally potent gases. For some applications more benign alternatives such as hydrofluoroolefins have been developed and are being gradually introduced. | 5 | Photochemistry |
Geminal dithiols have the formula RR'C(SH). They are derived from aldehydes and ketones by the action of hydrogen sulfide. Their stability contrasts with the rarity of geminal diols. Examples include methanedithiol, ethane-1,1-dithiol, and cyclohexane-1,1-dithiol. Upon heating, gem-dithiols often release hydrogen sulfide, giving the transient thioketone or thial, which typically convert to oligomers. | 0 | Organic Chemistry |
The AMoN measures ambient ammonia gas concentrations over a two-week period via a Radiello®-passive sampler, which is a simple diffusive sampler that offers higher capacity and faster sampling rates than other devices. Therefore, AMoN can provide reliable data to aid in meeting air quality policies and administration needs. AMoN collects data biweekly to determine the spatial variability and seasonality of ammonia concentrations. | 2 | Environmental Chemistry |
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration. The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in solutions. The molar (amount) concentration has variants, such as normal concentration and osmotic concentration. Dilution is reduction of concentration, e.g. by adding solvent to a solution. The verb to concentrate means to increase concentration, the opposite of dilute. | 3 | Analytical Chemistry |
An MTC provides traceability and assurance to the end user about the quality of the steel used and the process used to produce it.
Typically a European MTC will be produced to EN 10204. High quality steels for pressure vessel of structural purposes will be declared to 2.1 or 2.2 or certificated to 3.1 or 3.2. (EDIT: type is declared not by chapter in the document, but by type name, so edited the numbering)
The MTC will specify the type of certificate, the grade of steel and any addenda. It will also specify the results of chemical and physical examination to allow the purchaser or end user to compare the plate to the requirements of the relevant standards. | 8 | Metallurgy |
Originally developed in the 1970s by French neuroscientist Michel Jouvet and Lafon Laboratories, modafinil has been prescribed in France since 1994, and was approved for medical use in the United States in 1998.
Concerns have been raised about the growing use of modafinil as a "smart drug" or cognitive enhancer among healthy individuals who use it with the aim to improve concentration and memory. In 2003, modafinil sales were skyrocketing, with some experts concerned that it had become a tempting pick-me-up for people looking for an extra edge in a productivity-obsessed society. The cost of modafinil varied depending on factors such as location and insurance coverage, still, in 2004, the price of modafinil in the US was around $120 or more per monthly supply. However, the availability of generic versions has increased since then and may have driven down prices.
In 2020, modafinil was the 302nd most commonly prescribed medication in the United States, with just over prescriptions.
the global sales figures for modafinil are not known. Still, modafinil sold under the brand name Provigil accounted for over 40% of Cephalon's global turnover for several years, according to the information published in 2020. | 4 | Stereochemistry |
For many years mutations of the seipin gene were associated with a loss of function, such as in CGL (see above). However, recent studies show that mutations such as N88S and S90L seem to have a gain-of-toxic-function which may result in autosomal dominant motor neuron diseases and distal hereditary motor neuropathy, such as Silver syndrome and distal hereditary motor neuropathy type V.
Owing to the wide clinical spectrum of these mutations, it has been proposed to collectively refer to seipin-related motor neuron diseases as seipinopathies.
Symptoms can vary and include: developmental regression of motor and cognitive skills in the first years of life leading to death (encephalopathy), muscle weakness and spasticity in lower limbs (spastic paraplegia type XVII), weakness of distal muscles of upper limbs (distal hereditary motor neuropathy type V) as well as wasting of the hand muscles (in both cases). Complex forms of seipinopathies may include deafness, dementia or mental retardation. | 1 | Biochemistry |
The 7 crystal systems consist of 32 crystal classes (corresponding to the 32 crystallographic point groups) as shown in the following table below:
The point symmetry of a structure can be further described as follows. Consider the points that make up the structure, and reflect them all through a single point, so that (x,y,z) becomes (−x,−y,−z). This is the inverted structure. If the original structure and inverted structure are identical, then the structure is centrosymmetric. Otherwise it is non-centrosymmetric. Still, even in the non-centrosymmetric case, the inverted structure can in some cases be rotated to align with the original structure. This is a non-centrosymmetric achiral structure. If the inverted structure cannot be rotated to align with the original structure, then the structure is chiral or enantiomorphic and its symmetry group is enantiomorphic.
A direction (meaning a line without an arrow) is called polar if its two-directional senses are geometrically or physically different. A symmetry direction of a crystal that is polar is called a polar axis. Groups containing a polar axis are called polar. A polar crystal possesses a unique polar axis (more precisely, all polar axes are parallel). Some geometrical or physical property is different at the two ends of this axis: for example, there might develop a dielectric polarization as in pyroelectric crystals. A polar axis can occur only in non-centrosymmetric structures. There cannot be a mirror plane or twofold axis perpendicular to the polar axis, because they would make the two directions of the axis equivalent.
The crystal structures of chiral biological molecules (such as protein structures) can only occur in the 65 enantiomorphic space groups (biological molecules are usually chiral). | 3 | Analytical Chemistry |
Minimise the lateral pressure of the strings by adjusting the alignment tine bar to avoid the string being cut off. Have ceramic tube place over each aligning tine bar to act as bearing surface for the strings. | 3 | Analytical Chemistry |
The competition between energy and entropy makes liquids difficult to model at the molecular level, as there is no idealized "reference state" that can serve as a starting point for tractable theoretical descriptions. Mathematically, there is no small parameter from which one can develop a systematic perturbation theory. This situation contrasts with both gases and solids. For gases, the reference state is the ideal gas, and the density can be used as a small parameter to construct a theory of real (nonideal) gases (see virial expansion). For crystalline solids, the reference state is a perfect crystalline lattice, and possible small parameters are thermal motions and lattice defects. | 7 | Physical Chemistry |
A typical action potential begins at the axon hillock with a sufficiently strong depolarization, e.g., a stimulus that increases V. This depolarization is often caused by the injection of extra sodium cations into the cell; these cations can come from a wide variety of sources, such as chemical synapses, sensory neurons or pacemaker potentials.
For a neuron at rest, there is a high concentration of sodium and chloride ions in the extracellular fluid compared to the intracellular fluid, while there is a high concentration of potassium ions in the intracellular fluid compared to the extracellular fluid. The difference in concentrations, which causes ions to move from a high to a low concentration, and electrostatic effects (attraction of opposite charges) are responsible for the movement of ions in and out of the neuron. The inside of a neuron has a negative charge, relative to the cell exterior, from the movement of K out of the cell. The neuron membrane is more permeable to K than to other ions, allowing this ion to selectively move out of the cell, down its concentration gradient. This concentration gradient along with potassium leak channels present on the membrane of the neuron causes an efflux of potassium ions making the resting potential close to E ≈ –75 mV. Since Na ions are in higher concentrations outside of the cell, the concentration and voltage differences both drive them into the cell when Na channels open. Depolarization opens both the sodium and potassium channels in the membrane, allowing the ions to flow into and out of the axon, respectively. If the depolarization is small (say, increasing V from −70 mV to −60 mV), the outward potassium current overwhelms the inward sodium current and the membrane repolarizes back to its normal resting potential around −70 mV. However, if the depolarization is large enough, the inward sodium current increases more than the outward potassium current and a runaway condition (positive feedback) results: the more inward current there is, the more V increases, which in turn further increases the inward current. A sufficiently strong depolarization (increase in V) causes the voltage-sensitive sodium channels to open; the increasing permeability to sodium drives V closer to the sodium equilibrium voltage E≈ +55 mV. The increasing voltage in turn causes even more sodium channels to open, which pushes V still further towards E. This positive feedback continues until the sodium channels are fully open and V is close to E. The sharp rise in V and sodium permeability correspond to the rising phase of the action potential.
The critical threshold voltage for this runaway condition is usually around −45 mV, but it depends on the recent activity of the axon. A cell that has just fired an action potential cannot fire another one immediately, since the Na channels have not recovered from the inactivated state. The period during which no new action potential can be fired is called the absolute refractory period. At longer times, after some but not all of the ion channels have recovered, the axon can be stimulated to produce another action potential, but with a higher threshold, requiring a much stronger depolarization, e.g., to −30 mV. The period during which action potentials are unusually difficult to evoke is called the relative refractory period. | 7 | Physical Chemistry |
Moreso than other enzymes in the Calvin cycle, SBPase levels have a significant impact on plant growth, photosynthetic ability, and response to environmental stresses. Small decreases in SBPase activity result in decreased photosynthetic carbon fixation and reduced plant biomass. Specifically, decreased SBPase levels result in stunted plant organ growth and development compared to wild-type plants, and starch levels decrease linearly with decreases in SBPase activity, suggesting that SBPase activity is a limiting factor to carbon assimilation. This sensitivity of plants to decreased SBPase activity is significant, as SBPase itself is sensitive to oxidative damage and inactivation from environmental stresses. SBPase contains several catalytically relevant cysteine residues that are vulnerable to irreversible oxidative carbonylation by reactive oxygen species (ROS), particularly from hydroxyl radicals created during the production of hydrogen peroxide. Carbonylation results in SBPase enzyme inactivation and subsequent growth retardation due to inhibition of carbon assimilation. Oxidative carbonylation of SBPase can be induced by environmental pressures such as chilling, which causes an imbalance in metabolic processes leading to increased production of reactive oxygen species, particularly hydrogen peroxide. Notably, chilling inhibits SBPase and a related enzyme, fructose bisphosphatase, but does not affect other reductively activated Calvin cycle enzymes.
The sensitivity of plants to synthetically reduced or inhibited SBPase levels provides an opportunity for crop engineering. There are significant indications that transgenic plants which overexpress SBPase may be useful in improving food production efficiency by producing crops that are more resilient to environmental stresses, as well as have earlier maturation and higher yield. Overexpression of SBPase in transgenic tomato plants provided resistance to chilling stress, with the transgenic plants maintaining higher SBPase activity, increased carbon dioxide fixation, reduced electrolyte leakage and increased carbohydrate accumulation relative to wild-type plants under the same chilling stress. It is also likely that transgenic plants would be more resilient to osmotic stress caused by drought or salinity, as the activation of SBPase is shown to be inhibited in chloroplasts exposed to hypertonic conditions, though this has not been directly tested. Overexpression of SBPase in transgenic tobacco plants resulted in enhanced photosynthetic efficiency and growth. Specifically, transgenic plants exhibited greater biomass and improved carbon dioxide fixation, as well as an increase in RuBisCO activity. The plants grew significantly faster and larger than wild-type plants, with increased sucrose and starch levels. | 5 | Photochemistry |
Applied Geochemistry is a monthly peer-reviewed scientific journal published by Elsevier on behalf of the International Association of GeoChemistry. It covers research on environmental and regional geochemistry and was established in 1986. It is published by Elsevier and from 2012 to 2022 the editor-in-chief was Michael Kersten. He was succeeded by Zimeng Wang in 2023. | 9 | Geochemistry |
The Nickelodeon television series SpongeBob SquarePants features a copepod named Sheldon J. Plankton as a recurring character. | 2 | Environmental Chemistry |
Silent Information Regulator (SIR) proteins are involved in regulating gene expression. SIR proteins organize heterochromatin near telomeres, ribosomal DNA (rDNA), and at silent loci including hidden mating type loci in yeast. The SIR family of genes encodes catalytic and non-catalytic proteins that are involved in de-acetylation of histone tails and the subsequent condensation of chromatin around a SIR protein scaffold. Some SIR family members are conserved from yeast to humans. | 1 | Biochemistry |
Synthetic primers, sometimes known as oligos, are chemically synthesized oligonucleotides, usually of DNA, which can be customized to anneal to a specific site on the template DNA. In solution, the primer spontaneously hybridizes with the template through Watson-Crick base pairing before being extended by DNA polymerase. The ability to create and customize synthetic primers has proven an invaluable tool necessary to a variety of molecular biological approaches involving the analysis of DNA. Both the Sanger chain termination method and the “Next-Gen” method of DNA sequencing require primers to initiate the reaction. | 1 | Biochemistry |
The Bradford protein assay (also known as the Coomassie protein assay) was developed by Marion M. Bradford in 1976. It is a quick and accurate spectroscopic analytical procedure used to measure the concentration of protein in a solution. The reaction is dependent on the amino acid composition of the measured proteins. | 3 | Analytical Chemistry |
Primary energy sources are transformed in energy conversion processes to more convenient forms of energy that can directly be used by society, such as electrical energy, refined fuels, or synthetic fuels such as hydrogen fuel. In the field of energetics, these forms are called energy carriers and correspond to the concept of "secondary energy" in energy statistics. | 7 | Physical Chemistry |
The chloralkali process is a large scale application that uses electrocatalysts. This technology supplies most of the chlorine and sodium hydroxide required by many industries. The cathode is a mixed metal oxide clad titanium anode (also called a dimensionally stable anode). | 7 | Physical Chemistry |
The method has mainly been developed for detecting the various phenotypes of metastatic castration-resistant prostate cancer. It requires the usage of patient-derived xenografts for enrichment of ctDNA in blood for further analysis. After WGS, the method utilizes the tool Griffin for inspection of local promoter coverage, nucleosome positioning, fragment size analysis, and composite trancription factor binding sites plus open chromatin sites of ctDNA reads. It also checks the histone modifications and applies dimensionality reduction on the found sites to identify putative promoter, enhancer, and gene repressive heterochromatic marks. To interrogate the chromatine phasing, distance between open chromatin regions, the method uses TritonNP, newly developed software, that uses Fourier transforms and band-pass filters. XGBoost is utilized for classification on cancer subtype with using the features detected in previous steps | 1 | Biochemistry |
The catalytic cracking process involves the presence of solid acid catalysts, usually silica-alumina and zeolites. The catalysts promote the formation of carbocations, which undergo processes of rearrangement and scission of C-C bonds. Relative to thermal cracking, cat cracking proceeds at milder temperatures, which saves energy. Furthermore, by operating at lower temperatures, the yield of alkenes is diminished. Alkenes cause instability of hydrocarbon fuels.
Fluid catalytic cracking is a commonly used process, and a modern oil refinery will typically include a cat cracker, particularly at refineries in the US, due to the high demand for gasoline. The process was first used around 1942 and employs a powdered catalyst. During WWII, the Allied Forces had plentiful supplies of the materials in contrast to the Axis Forces, which suffered severe shortages of gasoline and artificial rubber. Initial process implementations were based on low activity alumina catalyst and a reactor where the catalyst particles were suspended in a rising flow of feed hydrocarbons in a fluidized bed.
In newer designs, cracking takes place using a very active zeolite-based catalyst in a short-contact time vertical or upward-sloped pipe called the "riser". Pre-heated feed is sprayed into the base of the riser via feed nozzles where it contacts extremely hot fluidized catalyst at . The hot catalyst vaporizes the feed and catalyzes the cracking reactions that break down the high-molecular weight oil into lighter components including LPG, gasoline, and diesel. The catalyst-hydrocarbon mixture flows upward through the riser for a few seconds, and then the mixture is separated via cyclones. The catalyst-free hydrocarbons are routed to a main fractionator for separation into fuel gas, LPG, gasoline, naphtha, light cycle oils used in diesel and jet fuel, and heavy fuel oil.
During the trip up the riser, the cracking catalyst is "spent" by reactions which deposit coke on the catalyst and greatly reduce activity and selectivity. The "spent" catalyst is disengaged from the cracked hydrocarbon vapors and sent to a stripper where it contacts steam to remove hydrocarbons remaining in the catalyst pores. The "spent" catalyst then flows into a fluidized-bed regenerator where air (or in some cases air plus oxygen) is used to burn off the coke to restore catalyst activity and also provide the necessary heat for the next reaction cycle, cracking being an endothermic reaction. The "regenerated" catalyst then flows to the base of the riser, repeating the cycle.
The gasoline produced in the FCC unit has an elevated octane rating but is less chemically stable compared to other gasoline components due to its olefinic profile. Olefins in gasoline are responsible for the formation of polymeric deposits in storage tanks, fuel ducts and injectors. The FCC LPG is an important source of C-C olefins and isobutane that are essential feeds for the alkylation process and the production of polymers such as polypropylene. | 0 | Organic Chemistry |
Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydrogen atom within the compound. The phenomenon of tautomerization is called tautomerism, also called desmotropism. Tautomerism is for example relevant to the behavior of amino acids and nucleic acids, two of the fundamental building blocks of life.
Care should be taken not to confuse tautomers with depictions of "contributing structures" in chemical resonance. Tautomers are distinct chemical species that can be distinguished by their differing atomic connectivities, molecular geometries, and physicochemical and spectroscopic properties, whereas resonance forms are merely alternative Lewis structure (valence bond theory) depictions of a single chemical species, whose true structure is a quantum superposition, essentially the "average" of the idealized, hypothetical geometries implied by these resonance forms. | 4 | Stereochemistry |
The evidence that arsenic may be a beneficial nutrient at trace levels below the background to which living organisms are normally exposed has been reviewed. Some organoarsenic compounds found in nature are arsenobetaine and arsenocholine, both being found in many marine organisms. Some As-containing nucleosides (sugar derivatives) are also known. Several of these organoarsenic compounds arise via methylation processes. For example, the mold Scopulariopsis brevicaulis produces significant amounts of trimethylarsine if inorganic arsenic is present. The organic compound arsenobetaine is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations. In clean environments, the edible mushroom species Cyanoboletus pulverulentus hyperaccumulates arsenic in concentrations reaching even 1,300 mg/kg in dry weight; cacodylic acid is the major As compound. A very unusual composition of organoarsenic compounds was found in deer truffles (Elaphomyces spp.). The average person's intake is about 10–50 µg/day. Values about 1000 µg are not unusual following consumption of fish or mushrooms; however, there is little danger in eating fish since this arsenic compound is nearly non-toxic.
A topical source of arsenic are the green pigments once popular in wallpapers, e.g. Paris green. A variety of illness have been blamed on this compound, although its toxicity has been exaggerated.
Trimethylarsine, once known as Gosio's gas, is an intensely malodorous organoarsenic compound that is commonly produced by microbial action on inorganic arsenic substrates.
Arsenic (V) compounds are easily reduced to arsenic (III) and could have served as an electron acceptor on primordial Earth. Lakes that contain a substantial amount of dissolved inorganic arsenic, harbor arsenic-tolerant biota. | 1 | Biochemistry |
Using chiral phosphines as spectator ligands, catalysts have been developed for catalytic asymmetric hydrosilation. A well studied reaction is the addition of trichlorosilane to styrene to give 1-phenyl-1-(trichlorosilyl)ethane:
:ClSiH + PhCH=CH → (Ph)(CH)CHSiCl
Nearly perfect enantioselectivities (ee's) can be achieved using palladium catalysts supported by binaphthyl-substituted monophosphine ligands. | 7 | Physical Chemistry |
Part of the extraordinary potential of hyrax middens as palaeoenvironmental archives is the large range of proxies that are contained within them. Initially, when their diachronic nature was less evident, they were viewed as the poor relation to the better studied pack rat middens. While pack rat middens are rich in identifiable macrofossils, which can be directly dated and provide high taxonomic resolution, hyrax middens are poor in macroremains. Those that are found are almost exclusively masticated material that has been incorporated into the deposits as faecal pellets. While some studies have analysed these midden components, more recent work suggests that this approach does not maximise the full potential of hyrax middens as palaeoenvironmental archives
Hyrax middens contain a suite of proxies that have the potential to provide clear insights into past climate and vegetation change. Working within the context of the middens’ stratigraphy, and building on robust chronologies indicating predictable and consistent accumulation rates, sampling methodologies are now more akin to those applied to speleothems rather than to packrat middens. Whereas the early focus was on small (N), as the relative roles of climatic forcing versus vegetation dynamics related to competitive processes within an ecosystem can be better resolved, resulting in a fuller and more reliable understanding of palaeoenvironmental dynamics | 9 | Geochemistry |
One of the more interesting applications of hydrogenases is to produce hydrogen, due its capacity to catalyze its redox reaction:
In the field of hydrogen production, the incorporation of chemical compounds in electrochemical devices to produce molecular hydrogen has been a topic of huge interest in the recent years due to the possibility of using hydrogen as a replacement of the fossil fuels as an energetic carrier. This approach of using materials inspired by natural models to do the same function as their natural counterparts is called bio-mimetic approach. Nowadays this approach has received a big impulse due to the availability of high-resolution crystal structures of several hydrogenases obtained with different techniques. The technical details of these hydrogenases are stored in electronic databases at disposition to who may be interested.
This information has allowed scientists to determine the important parts of the enzyme necessary to catalyze the reaction and determine the pathway of the reaction in a very detailed way. Which allow to have a very good comprehension of what is necessary to catalyze the same reaction using artificial components. | 1 | Biochemistry |
This pathway has a significant effect in the way genes are translated, restricting the amount of gene expression. It is still a new field in genetics, but its role in research has already led scientists to uncover numerous explanations for gene regulation. Studying nonsense-mediated decay has allowed scientists to determine the causes for certain heritable diseases and dosage compensation in mammals. | 1 | Biochemistry |
There are several ways of reducing and preventing this form of corrosion.
* Electrically insulate the two metals from each other. If they are not in electrical contact, no galvanic coupling will occur. This can be achieved by using non-conductive materials between metals of different electropotential. Piping can be isolated with a spool of pipe made of plastic materials, or made of metal material internally coated or lined. It is important that the spool be a sufficient length to be effective. For reasons of safety, this should not be attempted where an electrical earthing system uses the pipework for its ground or has equipotential bonding.
* Metal boats connected to a shore line electrical power feed will normally have to have the hull connected to earth for safety reasons. However the end of that earth connection is likely to be a copper rod buried within the marina, resulting in a steel-copper "battery" of about 0.5 V. Additionally, the hull of each boat is connected to the hull of all other boats, resulting in further "batteries" between propellers (which may be made of bronze) and steel hulls, which may cause corrosion of the expensive propellers. For such cases, the use of a galvanic isolator is essential, typically two semiconductor diodes in series, in parallel with two diodes conducting in the opposite direction (antiparallel). This device is inserted in the protective earth connection between the hull and the shoreline protective conductor. This prevents any current in the protective conductor while the applied voltage is less than 1.4 V (i.e. 0.7 V per diode), but allows a full current in the case of an electrical fault. There will still be a very minor leakage of current through the diodes, which may result in slightly faster corrosion than normal.
* Ensure there is no contact with an electrolyte. This can be done by using water-repellent compounds such as greases, or by coating the metals with an impermeable protective layer, such as a suitable paint, varnish, or plastic. If it is not possible to coat both, the coating should be applied to the more noble, the material with higher potential. This is advisable because if the coating is applied only on the more active material, in case of damage to the coating there will be a large cathode area and a very small anode area, and for the exposed anodic area the corrosion rate will be correspondingly high.
* Using antioxidant paste is beneficial for preventing corrosion between copper and aluminium electrical connections. The paste consists of a lower nobility metal than aluminium or copper.
* Choose metals that have similar electropotentials. The more closely matched the individual potentials, the smaller the potential difference and hence the smaller the galvanic current. Using the same metal for all construction is the easiest way of matching potentials.
* Electroplating or other plating can also help. This tends to use more noble metals that resist corrosion better. Chrome, nickel, silver and gold can all be used. Galvanizing with zinc protects the steel base metal by sacrificial anodic action.
* Cathodic protection uses one or more sacrificial anodes made of a metal which is more active than the protected metal. Alloys of metals commonly used for sacrificial anodes include zinc, magnesium, and aluminium. This approach is commonplace in water heaters and many buried or immersed metallic structures.
* Cathodic protection can also be applied by connecting a direct current (DC) electrical power supply to oppose the corrosive galvanic current. (See .) | 8 | Metallurgy |
The eIF4F complex is composed of three subunits: eIF4A, eIF4E, and eIF4G. Each subunit has multiple human isoforms and there exist additional eIF4 proteins: eIF4B and eIF4H.
eIF4G is a 175.5-kDa scaffolding protein that interacts with eIF3 and the Poly(A)-binding protein (PABP), as well as the other members of the eIF4F complex. eIF4E recognizes and binds to the 5' cap structure of mRNA, while eIF4G binds PABP, which binds the poly(A) tail, potentially circularizing and activating the bound mRNA. eIF4Aa DEAD box RNA helicaseis important for resolving mRNA secondary structures.
eIF4B contains two RNA-binding domainsone non-specifically interacts with mRNA, whereas the second specifically binds the 18S portion of the small ribosomal subunit. It acts as an anchor, as well as a critical co-factor for eIF4A. It is also a substrate of S6K, and when phosphorylated, it promotes the formation of the pre-initiation complex. In vertebrates, eIF4H is an additional initiation factor with similar function to eIF4B. | 1 | Biochemistry |
The white rot fungus Phanerochaete chrysosporium can remove up to 80% of phenolic compounds from coking waste water. | 0 | Organic Chemistry |
Drosatos received his B.Sc. from the department of biology at the Aristotle University of Thessaloniki, Greece in 2000. In 2000, he continued with graduate studies at the Molecular Biology-Biomedicine graduate program of the department of biology and the medical school of the University of Crete. He received his M.Sc. in 2002 and his Ph.D. in molecular biology-biomedicine in 2007. During his graduate studies (2002–2007) he was a visiting research scholar in the laboratory of Vassilis I. Zannis at Boston University Medical School. Following his graduation with a PhD in molecular biology-biomedicine in 2007, he joined the laboratory of Ira J. Goldberg at Columbia University, where he pursued post-doctoral training until 2012, when he was promoted to associate research scientist in the department of medicine at Columbia University. In 2014 he joined the faculty of the Lewis Katz School of Medicine at Temple University as an assistant professor in pharmacology and in 2020, he was promoted to associate professor with tenure in cardiovascular sciences (primary affiliation). In 2022, he was recruited at the University of Cincinnati College of Medicine, which he joined as the Ohio Eminent Scholar and Professor of Pharmacology and Systems Physiology | 1 | Biochemistry |
Potential antitumor and antiviral drugs. The Anderson-type polyoxomolybdates and heptamolybdates exhibit activity for suppressing the growth of some tumors. In the case of (NHPr)[MoO], activity appears related to its redox properties. The Wells-Dawson structure can efficiently inhibit amyloid β (Aβ) aggregation in a therapeutic strategy for Alzheimer's disease. antibacterial and antiviral uses. | 7 | Physical Chemistry |
A myc tag is a polypeptide protein tag derived from the c-myc gene product that can be added to a protein using recombinant DNA technology. It can be used for affinity chromatography, then used to separate recombinant, overexpressed protein from wild type protein expressed by the host organism. It can also be used in the isolation of protein complexes with multiple subunits.
A myc tag can be used in many different assays that require recognition by an antibody and was originally identified in 1985. If there is no antibody against the studied protein, adding a myc-tag allows one to follow the protein with an antibody against the Myc epitope. Examples are cellular localization studies by immunofluorescence or detection by Western blotting.
The peptide sequence of the myc-tag is (in 1- and 3-letter codes, respectively): EQKLISEEDL and Glu-Gln-Lys-Leu-Ile-Ser-Glu-Glu-Asp-Leu. The tag is approximately 1202 daltons in atomic mass and has 10 amino acids.
It can be fused to the C-terminus and the N-terminus of a protein. It is advisable not to fuse the myc-tag directly behind the signal peptide of a secretory protein, since it can interfere with translocation into the secretory pathway.
A monoclonal antibody against the myc epitope, named 9E10, is available from the non-commercial Developmental Studies Hybridoma Bank. | 1 | Biochemistry |
Vsevolod Vasilyevich Perekalin (; 27 February 1913, Saint Petersburg – 7 January 1998, Saint Petersburg) was a Soviet and Russian organic chemist, Doktor nauk. He created the drug known as Phenibut. | 0 | Organic Chemistry |
Thiomers are able to reversibly open tight junctions. The responsible mechanism seems to be based on the inhibition of protein tyrosine phosphatase being involved in the closing process of tight junctions. Due to thiolation the permeation enhancing effect of polymers such as polyacrylic acid or chitosan can be up to 10-fold improved. In comparison to most low molecular weight permeation enhancers, thiolated polymers offer the advantage of not being absorbed from the mucosal membrane. Hence, their permeation enhancing effect can be maintained for a comparatively longer period of time and systemic toxic side effects of the auxiliary agent can be excluded. | 7 | Physical Chemistry |
In an investigation performed by Luo et al., Escherichia coli strains were utilized to examine how the metabolism of propionyl-CoA could potentially lead to the production of 3-hydroxypropionic acid (3-HP). It was shown that a mutation in a key gene involved in the pathway, succinate CoA-transferase, led to a significant increase in 3-HP. However, this is still a developing field and information on this topic is limited. | 1 | Biochemistry |
Agmatine, also known as 4-aminobutyl-guanidine, was discovered in 1910 by Albrecht Kossel. It is a chemical substance which is naturally created from the amino acid arginine. Agmatine has been shown to exert modulatory action at multiple molecular targets, notably: neurotransmitter systems, ion channels, nitric oxide (NO) synthesis and polyamine metabolism and this provides bases for further research into potential applications. | 1 | Biochemistry |
The first compound of the homolog row of nitriles, the nitrile of formic acid, hydrogen cyanide was first synthesized by C. W. Scheele in 1782. In 1811 J. L. Gay-Lussac was able to prepare the very toxic and volatile pure acid.
Around 1832 benzonitrile, the nitrile of benzoic acid, was prepared by Friedrich Wöhler and Justus von Liebig, but due to minimal yield of the synthesis neither physical nor chemical properties were determined nor a structure suggested. In 1834 Théophile-Jules Pelouze synthesized propionitrile, suggesting it to be an ether of propionic alcohol and hydrocyanic acid.
The synthesis of benzonitrile by Hermann Fehling in 1844 by heating ammonium benzoate was the first method yielding enough of the substance for chemical research.
Fehling determined the structure by comparing his results to the already known synthesis of hydrogen cyanide by heating ammonium formate. He coined the name "nitrile" for the newfound substance, which became the name for this group of compounds. | 0 | Organic Chemistry |
A nuclear run-on assay is conducted to identify the genes that are being transcribed at a certain time point. Approximately one million cell nuclei are isolated and incubated with labeled nucleotides, and genes in the process of being transcribed are detected by hybridization of extracted RNA to gene specific probes on a blot. Garcia-Martinez et al. (2004) developed a protocol for the yeast S. cerevisiae (Genomic run-on, GRO) that allows for the calculation of transcription rates (TRs) for all yeast genes to estimate mRNA stabilities for all yeast mRNAs.
Alternative microarray methods have recently been developed, mainly PolII RIP-chip: RNA immunoprecipitation of RNA polymerase II with phosphorylated C-terminal domain directed antibodies and hybridization on a microarray slide or chip (the word chip in the name stems from "ChIP-chip" where a special Affymetrix GeneChip was required). A comparison of methods based on run-on and ChIP-chip has been made in yeast (Pelechano et al., 2009). A general correspondence of both methods has been detected but GRO is more sensitive and quantitative. It has to be considered that run-on only detects elongating RNA polymerases whereas ChIP-chip detects all present RNA polymerases, including backtracked ones.
Attachment of new RNA polymerase to genes is prevented by inclusion of sarkosyl. Therefore only genes that already have an RNA polymerase will produce labeled transcripts. RNA transcripts that were synthesized before the addition of the label will not be detected as they will lack the label. These run on transcripts can also be detected by purifying labeled transcripts by using antibodies that detect the label and hybridizing these isolated transcripts with gene expression arrays or by next generation sequencing (GRO-Seq).
Run on assays have been largely supplanted with Global Run on assays that use next generation DNA sequencing as a readout platform. These assays are known as GRO-Seq and provide an incredibly detailed view of genes engaged in transcription with quantitative levels of expression. Array based methods for analyzing Global run on (GRO) assays are being replaced with Next Generation Sequencing which eliminates the design of probes against gene sequences. Sequencing will catalog all transcripts produced even if they are not reported in databases. GRO-seq involves the labeling of newly synthesized transcripts with bromouridine (BrU). Cells or nuclei are incubated with BrUTP in the presence of sarkosyl, which prevents the attachment of RNA polymerase to the DNA. Therefore only RNA polymerase that are already on the DNA before the addition of sarkosyl will produce new transcripts that will be labeled with BrU. The labeled transcripts are captured with anti-BrU antibody labeled beads, converted to cDNAs and then sequenced by Next Generation DNA sequencing. The sequencing reads are then aligned to the genome and number of reads per transcript provide an accurate estimate of the number of transcripts synthesized. | 1 | Biochemistry |
Homotopic groups in a chemical compound are equivalent groups. Two groups A and B are homotopic if the molecule remains achiral when the groups are interchanged with some other atom (such as bromine) while the remaining parts of the molecule stay fixed. Homotopic atoms are always identical, in any environment. Homotopic NMR-active nuclei have the same chemical shift in an NMR spectrum. For example, the four hydrogen atoms of methane (CH) are homotopic with one another, as are the two hydrogens or the two chlorines in dichloromethane (CHCl). | 4 | Stereochemistry |
The conventional semi-classical model describes the photosynthetic energy transfer process as one in which excitation energy hops from light-capturing pigment molecules to reaction center molecules step-by-step down the molecular energy ladder.
The effectiveness of photons of different wavelengths depends on the absorption spectra of the photosynthetic pigments in the organism. Chlorophylls absorb light in the violet-blue and red parts of the spectrum, while accessory pigments capture other wavelengths as well. The phycobilins of red algae absorb blue-green light which penetrates deeper into water than red light, enabling them to photosynthesize in deep waters. Each absorbed photon causes the formation of an exciton (an electron excited to a higher energy state) in the pigment molecule. The energy of the exciton is transferred to a chlorophyll molecule (P680, where P stands for pigment and 680 for its absorption maximum at 680 nm) in the reaction center of photosystem II via resonance energy transfer. P680 can also directly absorb a photon at a suitable wavelength.
Photolysis during photosynthesis occurs in a series of light-driven oxidation events. The energized electron (exciton) of P680 is captured by a primary electron acceptor of the photosynthetic electron transport chain and thus exits photosystem II. In order to repeat the reaction, the electron in the reaction center needs to be replenished. This occurs by oxidation of water in the case of oxygenic photosynthesis. The electron-deficient reaction center of photosystem II (P680*) is the strongest biological oxidizing agent yet discovered, which allows it to break apart molecules as stable as water.
The water-splitting reaction is catalyzed by the oxygen-evolving complex of photosystem II. This protein-bound inorganic complex contains four manganese ions, plus calcium and chloride ions as cofactors. Two water molecules are complexed by the manganese cluster, which then undergoes a series of four electron removals (oxidations) to replenish the reaction center of photosystem II. At the end of this cycle, free oxygen () is generated and the hydrogen of the water molecules has been converted to four protons released into the thylakoid lumen (Dolai's S-state diagrams).
These protons, as well as additional protons pumped across the thylakoid membrane coupled with the electron transport chain, form a proton gradient across the membrane that drives photophosphorylation and thus the generation of chemical energy in the form of adenosine triphosphate (ATP). The electrons reach the P700 reaction center of photosystem I where they are energized again by light. They are passed down another electron transport chain and finally combine with the coenzyme and protons outside the thylakoids to form NADPH. Thus, the net oxidation reaction of water photolysis can be written as:
The free energy change () for this reaction is 102 kilocalories per mole. Since the energy of light at 700 nm is about 40 kilocalories per mole of photons, approximately 320 kilocalories of light energy are available for the reaction. Therefore, approximately one-third of the available light energy is captured as NADPH during photolysis and electron transfer. An equal amount of ATP is generated by the resulting proton gradient. Oxygen as a byproduct is of no further use to the reaction and thus released into the atmosphere. | 5 | Photochemistry |
The second phase of the $170 million Human Microbiome Project was focused on integrating patient data to different omic datasets, considering host genetics, clinical information and microbiome composition. The phase one focused on characterization of communities in different body sites. Phase 2 focused in the integration of multiomic data from host & microbiome to human diseases. Specifically, the project used multiomics to improve the understanding of the interplay of gut and nasal microbiomes with type 2 diabetes, gut microbiomes and inflammatory bowel disease and vaginal microbiomes and pre-term birth. | 1 | Biochemistry |
*Hilal-i-Imtiaz (2003)
*Sitara-e-Imtiaz (1999)
* President, Pakistan Materials Research Society
*Fellow, Pakistan Institute of Metallurgical Engineers
*Fellow of Pakistan Nuclear Society | 7 | Physical Chemistry |
Being a powerful oxidizing acid, nitric acid reacts with many organic materials, and the reactions may be explosive. The hydroxyl group will typically strip a hydrogen from the organic molecule to form water, and the remaining nitro group takes the hydrogen's place. Nitration of organic compounds with nitric acid is the primary method of synthesis of many common explosives, such as nitroglycerin and trinitrotoluene (TNT). As very many less stable byproducts are possible, these reactions must be carefully thermally controlled, and the byproducts removed to isolate the desired product.
Reaction with non-metallic elements, with the exceptions of nitrogen, oxygen, noble gases, silicon, and halogens other than iodine, usually oxidizes them to their highest oxidation states as acids with the formation of nitrogen dioxide for concentrated acid and nitric oxide for dilute acid.
Concentrated nitric acid oxidizes Iodine|, White phosphorus|, and Octasulfur| into Iodic acid|, Phosphoric acid|, and Sulfuric acid|, respectively. Although it reacts with graphite and amorphous carbon, it does not react with diamond; it can separate diamond from the graphite that it oxidizes. | 3 | Analytical Chemistry |
The blister copper is put into an anode furnace, a furnace that refines the blister copper to anode-grade copper in two stages by removing most of the remaining sulfur and iron, and then removing oxygen introduced during the first stage. This second stage, often referred to as poling is done by blowing natural gas, or some other reducing agent, through the molten copper oxide. When this flame burns green, indicating the copper oxidation spectrum, the oxygen has mostly been burned off. This creates copper at about 99% pure. | 8 | Metallurgy |
LINE-1 (L1) retrotransposons make up a significant portion of the human genome, with an estimated 500,000 copies per genome. Genes encoding for human LINE1 usually have their transcription inhibited by methyl groups binding to its DNA carried out by PIWI proteins and enzymes DNA methyltransferases. L1 retrotransposition can disrupt the nature of genes transcribed by pasting themselves inside or near genes which could in turn lead to human disease. LINE1s can only retrotranspose in some cases to form different chromosome structures contributing to differences in genetics between individuals. There is an estimate of 80–100 active L1s in the reference genome of the Human Genome Project, and an even smaller number of L1s within those active L1s retrotranspose often. L1 insertions have been associated with tumorigenesis by activating cancer-related genes oncogenes and diminishing tumor suppressor genes.
Each human LINE1 contains two regions from which gene products can be encoded. The first coding region contains a leucine zipper protein involved in protein-protein interactions and a protein that binds to the terminus of nucleic acids. The second coding region has a purine/pyrimidine nuclease, reverse transcriptase and protein rich in amino acids cysteines and histidines. The end of the human LINE1, as with other retrotransposons is adenine-rich.
Human L1 actively retrotransposes in the human genome. A recent study identified 1,708 somatic L1 retrotransposition events, especially in colorectal epithelial cells. These events occur from early embryogenesis and retrotransposition rate is substantially increased during colorectal tumourigenesis. | 1 | Biochemistry |
Droplet countercurrent chromatography (DCCC or DCC) was introduced in 1970 by Tanimura, Pisano, Ito, and Bowman. DCCC is considered to be a form of liquid-liquid separation, which includes countercurrent distribution and countercurrent chromatography, that employs a liquid stationary phase held in a collection of vertical glass columns connected in series. The mobile phase passes through the columns in the form of droplets. The DCCC apparatus may be run with the lower phase stationary and the upper phase being introduced to the bottom of each column. Or it may be run with the upper phase stationary and the lower phase being introduced from the top of the column. In both cases, the work of gravity is allowed influence the two immiscible liquids of different densities to form the signature droplets that rise or descend through the column. The mobile phase is pumped at a rate that will allow droplets to form that maximize the mass transfer of a compound between the upper and lower phases. Compounds that are more soluble in the upper phase will travel quickly through the column, while compounds that are more soluble in the stationary phase will linger. Separation occurs because different compounds distribute differently, in a ratio called the partition coefficient, between the two phases.
The biphasic solvent system must be carefully formulated so that it will perform appropriately in the DCCC column. The solvent system must form two phases without excess emulsification in order to form droplets. The densities of the two phases must also be sufficiently different so that the phases will move past each other in the column. Many DCCC solvent systems contain both chloroform and water. The solvent system used in the seminal publication was made from chloroform, acetic acid, and aqueous 0.1 M hydrochloric acid. Many subsequent solvents systems were made with chloroform, methanol, and water which is sometimes represented as a ChMWat solvent system. Solvent systems formulated with n-butanol, water and a modifier such as acetic acid, pyridine or n-propanol have also enjoyed some success in DCCC. In some cases, non-aqueous biphasic solvent systems such as acetonitrile and methanol have been utilized.
The main difference between DCCC and other types of countercurrent chromatography techniques is that there is no vigorous mixing of phases to enhance the mass transfer of compounds that allows them to distribute between the two phases. In 1951 Kies and Davis described an apparatus similar to the DCCC. They created a series of open tubes that were arranged in a cascade to either drip a more dense phase through a less dense stationary phase or, conversely, a less dense phase could be introduced into the bottom of the tube to dribble through the more dense phase. In 1954, a fractionation column was introduced by Kepes the resembled a CCC column divided into chambers with perforated plastic disks. Similar DCCC-type instruments have been created by A. E. Kostanyan and collaborators which employ vertical columns that are divided into partitions with porous disks. Once the columns are filled with stationary phase, the mobile phase is pumped through, not continuously but, in pulses. The solvent motion created by a pulsed pumping action creates the mixing and settling that is common to most all forms of countercurrent chromatography. | 3 | Analytical Chemistry |
The recent identification of several antimicrobial compounds from the secretions of animal dermal scent glands may be the beginning of a promising new area of drug development. Assuming functional analogs of these lead compounds can be synthesized and found to be effective in vivo, the potential exists for producing new antimicrobial agents against pathogenic skin microorganisms. | 1 | Biochemistry |
Organic matter plays an important role in drinking water and wastewater treatment and recycling, natural aquatic ecosystems, aquaculture, and environmental rehabilitation. It is therefore important to have reliable methods of detection and characterisation, for both short- and long-term monitoring. A variety of analytical detection methods for organic matter have existed for up to decades, to describe and characterise organic matter. These include, but are not limited to: total and dissolved organic carbon, mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, UV-Visible spectroscopy, and fluorescence spectroscopy. Each of these methods has its own advantages and limitations. | 0 | Organic Chemistry |
Despite being used in 90% of gold production: gold cyanidation is controversial due to the toxic nature of cyanide. Although aqueous solutions of cyanide degrade rapidly in sunlight, the less-toxic products, such as cyanates and thiocyanates, may persist for some years. The famous disasters have killed few people — humans can be warned not to drink or go near polluted water, but cyanide spills can have a devastating effect on rivers, sometimes killing everything for several miles downstream. The cyanide is soon washed out of river systems and, as long as organisms can migrate from unpolluted areas upstream, affected areas can soon be repopulated. According to Romanian authorities, in the Someș river below Baia Mare, the plankton returned to 60% of normal within 16 days of the spill; the numbers were not confirmed by Hungary or Yugoslavia.
Famous cyanide spills include:
Such spills have prompted fierce protests at new mines that involve use of cyanide, such as Roşia Montană in Romania, Lake Cowal in Australia, Pascua Lama in Chile, and Bukit Koman in Malaysia. | 8 | Metallurgy |
Gene guns are mostly used with plant cells. However, there is much potential use in humans and other animals as well. | 1 | Biochemistry |
Complexes with three bidentate ligands or two cis bidentate ligands can exist as enantiomeric pairs. Examples are shown below. | 4 | Stereochemistry |
The interactions of the soil's micropores and macropores are important to soil chemistry, as they allow for the provision of water and gaseous elements to the soil and the surrounding atmosphere. Macropores help transport molecules and substances in and out of the micropores. Micropores are comprised within the aggregates themselves. | 9 | Geochemistry |
When the temperature of a system changes, the Henry constant also changes. The temperature dependence of equilibrium constants can generally be described with the van t Hoff equation, which also applies to Henrys law constants:
where is the enthalpy of dissolution. Note that the letter in the symbol refers to enthalpy and is not related to the letter for Henrys law constants. This applies to the Henrys solubility ratio, ; for Henry's volatility ratio,, the sign of the right-hand side must be reversed.
Integrating the above equation and creating an expression based on at the reference temperature = 298.15 K yields:
The van 't Hoff equation in this form is only valid for a limited temperature range in which does not change much with temperature (around 20K of variations).
The following table lists some temperature dependencies:
Solubility of permanent gases usually decreases with increasing temperature at around room temperature. However, for aqueous solutions, the Henrys law solubility constant for many species goes through a minimum. For most permanent gases, the minimum is below 120 °C. Often, the smaller the gas molecule (and the lower the gas solubility in water), the lower the temperature of the maximum of the Henrys law constant. Thus, the maximum is at about 30 °C for helium, 92 to 93 °C for argon, nitrogen and oxygen, and 114 °C for xenon. | 7 | Physical Chemistry |
The B3 DNA binding domain (DBD) is a highly conserved domain found exclusively in transcription factors (≥40 species) () combined with other domains (). It consists of 100-120 residues, includes seven beta strands and two alpha helices that form a DNA-binding pseudobarrel protein fold (); it interacts with the major groove of DNA. | 1 | Biochemistry |
Propionyl-CoA is a coenzyme A derivative of propionic acid. It is composed of a 24 total carbon chain (without the coenzyme, it is a 3 carbon structure) and its production and metabolic fate depend on which organism it is present in. Several different pathways can lead to its production, such as through the catabolism of specific amino acids or the oxidation of odd-chain fatty acids. It later can be broken down by propionyl-CoA carboxylase or through the methylcitrate cycle. In different organisms, however, propionyl-CoA can be sequestered into controlled regions, to alleviate its potential toxicity through accumulation. Genetic deficiencies regarding the production and breakdown of propionyl-CoA also have great clinical and human significance. | 1 | Biochemistry |
The U.S. Standard Atmosphere, 1976 (USSA1976) defines the gas constant R as:
:R = = .
Note the use of kilomoles, with the resulting factor of in the constant. The USSA1976 acknowledges that this value is not consistent with the cited values for the Avogadro constant and the Boltzmann constant. This disparity is not a significant departure from accuracy, and USSA1976 uses this value of R for all the calculations of the standard atmosphere. When using the ISO value of R, the calculated pressure increases by only 0.62 pascal at 11 kilometers (the equivalent of a difference of only 17.4 centimeters or 6.8 inches) and 0.292 Pa at 20 km (the equivalent of a difference of only 33.8 cm or 13.2 in).
Also note that this was well before the 2019 SI redefinition, through which the constant was given an exact value. | 7 | Physical Chemistry |
When the host and guest molecules combine to form a single complex, the equilibrium is represented as
and the equilibrium constant, K, is defined as
where [X] denotes the concentration of a chemical species X (all activity coefficients are assumed to have a numerical values of 1).
The mass-balance equations, at any data point,
where and represent the total concentrations, of host and guest, can be reduced to a single quadratic equation in, say, [G] and so can be solved analytically for any given value of K. The concentrations [H] and [HG] can then derived.
The next step in the calculation is to calculate the value, , of a quantity corresponding to the quantity observed . Then, a sum of squares, U, over all data points, np, can be defined as
and this can be minimized with respect to the stability constant value, K, and a parameter such the chemical shift of the species HG (nmr data) or its molar absorbency (uv/vis data). The minimization can be performed in a spreadsheet application such as EXCEL by using the in-built SOLVER utility.
This procedure is applicable to 1:1 adducts. | 6 | Supramolecular Chemistry |
Charles Bonner Harris (April 24, 1940, in New York City – March 10, 2020, in Berkeley, California) was an American physical chemist. | 7 | Physical Chemistry |
In bacteria, HMP-P arises by conversion of the purine biosynthetic precursor 5-aminoimidazole ribotide (AIR) through the action of enzymes such as phosphomethylpyrimidine synthase, a member of the radical SAM superfamily. Studies using isotopically labelled AIR have shown which atoms carry into the product. Mechanisms by which this occurs are not yet known with certainty.
In yeasts, HMP-P is derived from metabolites of histidine and pyridoxine. Some of these transformations appear to be catalyzed by radical SAM enzymes. Isotopically labelled precursors have been used to investigate this biogenesis. Mechanisms of the transformations are unknown.
In Salmonella, HMP-P can be derived independently of purine biogenesis when AICAR is available.
In algae, thiamine forms and precursors are scavenged by uptake from water of exogenous products from other organisms. In higher plants, thiamine biogenesis resembles that of bacteria. In some circumstances, thiamine forms and precursors may be obtained through symbiotic relationships with microorganisms in the soil.
Genes relevant for transformations in the biogenesis of HMP-P, HET-P, and TPP have been identified in various organisms and some of the proteins resulting from their expression have been characterized. Biosynthesis of TPP is feedback inhibited through actions of a riboswitch.
Research is ongoing towards understanding biochemistry involved and towards facilitating technologies of socioeconomic value for supply of thiamine in various forms. | 1 | Biochemistry |
Maximum valences for the elements are based on the data from list of oxidation states of the elements. They are shown by the color code at the bottom of the table. | 3 | Analytical Chemistry |
Conventionally, redox reactions of coordination complexes are assumed to be metal-centered. The reduction of MnO to MnO is described by the change in oxidation state of manganese from 7+ to 6+. The oxide ligands do not change in oxidation state, remaining 2-. Oxide is an innocent ligand. Another example of conventional metal-centered redox couple is
[[Cobalt(III) hexammine chloride|Co(NH)]]/[Co(NH)]. Ammonia is innocent in this transformation.
Redox non-innocent behavior of ligands is illustrated by nickel bis(stilbenedithiolate) ([Ni(SCPh)]). As all bis(1,2-dithiolene) complexes of nd metal ions, three oxidation states can be identified: z = 2-, 1-, and 0. If the ligands are always considered to be dianionic (as is done in formal oxidation state counting), then z = 0 requires that that nickel has a formal oxidation state of +IV. The formal oxidation state of the central nickel atom therefore ranges from +II to +IV in the above transformations (see Figure). However, the formal oxidation state is different from the real (spectroscopic) oxidation state based on the (spectroscopic) metal d-electron configuration. The stilbene-1,2-dithiolate behaves as a redox non-innocent ligand, and the oxidation processes actually take place at the ligands rather than the metal. This leads to the formation of ligand radical complexes. The charge-neutral complex (z =0), showing a partial singlet diradical character, is therefore better described as a Ni derivative of the radical anion SCPh. The diamagnetism of this complex arises from anti-ferromagnetic coupling between the unpaired electrons of the two ligand radicals.
Another example is higher oxidation states of copper complexes of diamido phenyl ligands that are stabilized by intramolecular multi center hydrogen bonding | 0 | Organic Chemistry |
The main use of litmus is to test whether a solution is acidic or basic, as blue litmus paper turns red under acidic conditions, and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at . Neutral litmus paper is purple. Wet litmus paper can also be used to test for water-soluble gases that affect acidity or basicity; the gas dissolves in the water and the resulting solution colors the litmus paper. For instance, ammonia gas, which is alkaline, turns red litmus paper blue. While all litmus paper acts as pH paper, the opposite is not true.
Litmus can also be prepared as an aqueous solution that functions similarly. Under acidic conditions, the solution is red, and under alkaline conditions, the solution is blue.
Chemical reactions are other than acid–base can also cause a color change to litmus paper. For instance, chlorine gas turns blue litmus paper white; the litmus dye is bleached because hypochlorite ions are present. This reaction is irreversible, so the litmus is not acting as an indicator in this situation. | 3 | Analytical Chemistry |
Ferric iron () is a widespread anaerobic terminal electron acceptor both for autotrophic and heterotrophic organisms. Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase. Model organisms include Shewanella putrefaciens and Geobacter metallireducens. Since some ferric iron-reducing bacteria (e.g. G. metallireducens) can use toxic hydrocarbons such as toluene as a carbon source, there is significant interest in using these organisms as bioremediation agents in ferric iron-rich contaminated aquifers.
Although ferric iron is the most prevalent inorganic electron acceptor, a number of organisms (including the iron-reducing bacteria mentioned above) can use other inorganic ions in anaerobic respiration. While these processes may often be less significant ecologically, they are of considerable interest for bioremediation, especially when heavy metals or radionuclides are used as electron acceptors. Examples include:
* Manganic ion () reduction to manganous ion ()
* Selenate () reduction to selenite () and selenite reduction to inorganic selenium (Se)
* Arsenate () reduction to arsenite ()
* Uranyl ion () reduction to uranium dioxide () | 1 | Biochemistry |
In water treatment plants, organic halides are adsorbed using GAC or PAC in agitated tanks. The loaded carbon is separated using a membrane made out of materials like polypropylene or cellulose nitrate. Measuring the AOX levels into and out of the treatment zone shows a drop in organic halide concentrations. Some processes use a two-step GAC filtration to remove AOX precursors, and thus reduce the amount of AOX in treated waters. A two step filtration process consists of two GAC filters in series. The first filter is loaded with exhausted GAC, while the second filter is loaded with fresh GAC. This set up is preferred for its increased efficiency and higher throughput capacity. The GAC is replaced cyclically and the extracted organic halide-carbon mixture is then sent for subsequent biological or chemical treatment such as ozonation to regenerate the GAC. Often, these chemical treatments, while effective, pose economical challenges to the treatment plants. | 2 | Environmental Chemistry |
The electrophilic addition reaction of hydrogen bromide to 1,3-butadiene above room temperature leads predominantly to the thermodynamically more stable 1,4 adduct, 1-bromo-2-butene, but decreasing the reaction temperature to below room temperature favours the kinetic 1,2 adduct, 3-bromo-1-butene.
:The rationale for the differing selectivities is as follows: Both products result from Markovnikov protonation at position 1, resulting in a resonance-stabilized allylic cation. The 1,4 adduct places the larger Br atom at a less congested site and includes a more highly substituted alkene moiety, while the 1,2 adduct is the result of the attack by the nucleophile (Br) at the carbon of the allylic cation bearing the greatest positive charge (the more highly substituted carbon is the most likely place for the positive charge). | 7 | Physical Chemistry |
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