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In figure at left, the various segments that form the epitope have been shown to be continuously collinear, meaning that they have been shown as sequential; however, for the situation being discussed here (i.e., the antigen recognition by the B cell), this explanation is too simplistic. Such epitopes are known as sequential or linear epitopes, as all the amino acids on them are in the same sequence (line). This mode of recognition is possible only when the peptide is small (about six to eight amino acids long), and is employed by the T cells (T lymphocytes).
However, the B memory/naive cells recognize intact proteins present on the pathogen surface. In this situation, the protein in its tertiary structure is so greatly folded that some loops of amino acids come to lie in the interior of the protein, and the segments that flank them may lie on the surface. The paratope on the B cell receptor comes in contact only with those amino acids that lie on the surface of the protein. The surface amino acids may actually be discontinuous in the proteins primary structure, but get juxtaposed owing to the complex protein folding patterns (as in the adjoining figure). Such epitopes are known as conformational' epitopes and tend to be longer (15–22 amino acid residues) than the linear epitopes. Likewise, the antibodies produced by the plasma cells belonging to the same clone would bind to the same conformational epitopes on the pathogen proteins.
The binding of a specific antigen with corresponding BCR molecules results in increased production of the MHC-II molecules. This assumes significance as the same does not happen when the same antigen would be internalized by a relatively nonspecific process called pinocytosis, in which the antigen with the surrounding fluid is "drunk" as a small vesicle by the B cell. Hence, such an antigen is known as a nonspecific antigen and does not lead to activation of the B cell, or subsequent production of antibodies against it. | 1 | Biochemistry |
Retinaldehyde is a retinol (vitamin A) derivative responsible for vision. It binds rhodopsin, a well-characterized GPCR that binds all-cis retinal in its inactive state. Upon photoisomerization by a photon the cis-retinal is converted to trans-retinal causing activation of rhodopsin which ultimately leads to depolarization of the neuron thereby enabling visual perception. | 1 | Biochemistry |
While magnets can be used to localize magnetic nanoparticles to desired cells, this mechanism may be difficult to maintain in practice. The nanoparticles can be concentrated in 2D space such as on a culture plate or at the surface of the body, but it can be more difficult to localize them in the 3D space of the body. Magnetofection does not work well for organs or blood vessels far from the surface of the body, since the magnetic field weakens as distance increases. In addition, the user must consider the frequency and timing of applying the magnetic field, as the particles will not necessarily stay in the desired location once the magnet is removed. | 1 | Biochemistry |
The function of protein paucimannosylation remains largely unexplored in vertebrates. Recent literature however has emerged demonstrating that paucimannosylation play roles in mediating pathophysiological processes such as in inflammation, pathogen infection, cancer and in the development of stem cells and in normal homeostasis. For example, elevated expression of paucimannosidic proteins was shown in Mycobacterium tuberculosis infected macrophages, during preclampsia and on Tamm-Horsfall proteins secreted by human urothelial cells during urinary tract infections suggesting the involvement of paucimannosylation in those conditions. Additionally, sputum from individuals suffering from cystic fibrosis and airway infections were also observed to be rich in paucimannosidic proteins. Furthermore, paucimannosylation was reported to be prominent features of human neutrophils and in monocytes and macrophages. Recent literature have also demonstrated elevated signatures of paucimannosidic proteins associated with a range of human cancers including brain, breast, blood, melanoma, non-melanoma, liver, ovarian and prostate cancers. Enriched paucimannosidic glycoepitopes were found in the tumours when compared to the adjacent non-tumour tissues. Literature have also reported the presence of paucimannosylation in embryonic stem cells and neuronal stem cells, suggesting potential functional role(s) in these cells. Notably, deficiency of hexosaminidases results in clinically significant Tay-Sachs and Sandhoff diseases, which also implicates Hex and paucimannosidic proteins in those conditions.
Endogenous and exogenous binding partners of mammalian paucimannosidic glycans have been suggested, including the macrophage mannose receptor (CD206) and dectin-2. Other putative endogenous paucimannosidic protein receptors such as dectin-1, DC-SIGN and DC-SIGNR have been proposed, but experimental support is still lacking. Exogeneous binders of paucimannosidic glycans such as the Escherichia coli FimH and P. aeruginosa PA-IIL were also reported to play important roles in the adhesion and pathophysiology of these opportunistic pathogens. | 1 | Biochemistry |
Many other industries take into account distribution coefficients, for example in the formulation of make-up, topical ointments, dyes, hair colors and many other consumer products. | 7 | Physical Chemistry |
Although the glyoxalase pathway is the main metabolic system that reduces methylglyoxal levels in the cell, other enzymes have also been found to convert methylglyoxal into non-AGE producing species: specifically, 99% of MG is processed by glyoxalase metabolism, while less than 1% is metabolized into hydroxyacetone by aldo-keto reductases (AKRs) or into pyruvate by aldehyde dehydrogenases (ALDH). Other reactions have been found to produce MG that also feeds into the glyoxalase pathway. These reactions include catabolism of threonine and acetone, peroxidation of lipids, autoxidation of glucose, and degradation of glycated proteins. | 1 | Biochemistry |
Methanesulfonic anhydride (MsO) is the acid anhydride of methanesulfonic acid. Like methanesulfonyl chloride (MsCl), it may be used to generate mesylates (methanesulfonyl esters). | 0 | Organic Chemistry |
The ratio of activities of a solute, A in an aqueous/organic system will remain constant and independent of the total quantity of A (hence ), so at any given temperature:
Distribution constants are useful as they allow the calculation of the concentration of remaining analyte in the solution, even after a number of solvent extractions have occurred. They also provide guidance in choosing the most efficient way to conduct an extractive separation.
Thus, the concentration of A remaining in an aqueous solution after i extractions with an organic solvent can be found using:
(where [A] is the concentration of A remaining after extracting V millilitres of solution with the original concentration of [A] with i portions of the organic solvent, each with a volume of V). | 3 | Analytical Chemistry |
Knowledge base annotation is done based on the information of gene attribute, protein function and its metabolism. In this type of annotation more emphasis is given to genetic variation that disrupts the protein function domain, protein-protein interaction and biological pathway. The non-coding region of genome contain many important regulatory elements including promoter, enhancer and insulator, any kind of change in this regulatory region can change the functionality of that protein. The mutation in DNA can change the RNA sequence and then influence the RNA secondary structure, RNA binding protein recognition and miRNA binding activity. | 1 | Biochemistry |
When iron is in contact with water and oxygen, it rusts. If salt is present, for example in seawater or salt spray, the iron tends to rust more quickly, as a result of chemical reactions. Iron metal is relatively unaffected by pure water or by dry oxygen. As with other metals, like aluminium, a tightly adhering oxide coating, a passivation layer, protects the bulk iron from further oxidation. The conversion of the passivating ferrous oxide layer to rust results from the combined action of two agents, usually oxygen and water.
Other degrading solutions are sulfur dioxide in water and carbon dioxide in water. Under these corrosive conditions, iron hydroxide species are formed. Unlike ferrous oxides, the hydroxides do not adhere to the bulk metal. As they form and flake off from the surface, fresh iron is exposed, and the corrosion process continues until either all of the iron is consumed or all of the oxygen, water, carbon dioxide or sulfur dioxide in the system are removed or consumed.
When iron rusts, the oxides take up more volume than the original metal; this expansion can generate enormous forces, damaging structures made with iron. See economic effect for more details. | 8 | Metallurgy |
The Calvin cycle, also known as the dark reactions, is a series of biochemical reactions that fixes CO into G3P sugar molecules and uses the energy and electrons from the ATP and NADPH made in the light reactions. The Calvin cycle takes place in the stroma of the chloroplast.
While named "the dark reactions", in most plants, they take place in the light, since the dark reactions are dependent on the products of the light reactions. | 5 | Photochemistry |
Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na, K, Ca, and/or Cl to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter.
When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand-gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response.
These receptor proteins are typically composed of at least two different domains: a transmembrane domain which includes the ion pore, and an extracellular domain which includes the ligand binding location (an allosteric binding site). This modularity has enabled a divide and conquer approach to finding the structure of the proteins (crystallising each domain separately). The function of such receptors located at synapses is to convert the chemical signal of presynaptically released neurotransmitter directly and very quickly into a postsynaptic electrical signal. Many LICs are additionally modulated by allosteric ligands, by channel blockers, ions, or the membrane potential. LICs are classified into three superfamilies which lack evolutionary relationship: cys-loop receptors, ionotropic glutamate receptors and ATP-gated channels. | 1 | Biochemistry |
HRI (encoded in humans by the gene EIF2AK1) also dimerizes in order to autophosphorylate and activate. This activation is dependent on the presence of heme. HRI has two domains that heme may bind to, including one on the N-terminus and one on the kinase insertion domain. The presence of heme causes a disulfide bond to form between the monomers of HRI, resulting in the structure of an inactive dimer. However, when heme is absent, HRI monomers form an active dimer through non-covalent interactions. Therefore, the activation of this kinase is dependent on heme deficiency. HRI activation can also occur due to other stressors such as heat shock, osmotic stress and proteasome inhibition. Activation of HRI in response to these stressors does not depend on heme, but rather relies on the help of two heat shock proteins (HSP90 and HSP70). HRI is mainly found in the precursors of red blood cells, and has been observed to increase during erythropoiesis. | 1 | Biochemistry |
Pseudoephedrine amides undergo deprotonation by a strong base such as lithium diisopropylamide (LDA) to give the corresponding (Z)-enolates. Alkylation of these lithium enolates proceeds with high facial selectivity.
<br />
The diastereoselectivity is believed to result from a configuration wherein one face of the lithium enolate is blocked by the secondary lithium alkoxide and the solvent molecules associated with that lithium cation. In accordance with this proposal, it has been observed that the diastereoselectivity of the alkylation step is highly dependent on the amount of lithium chloride present and on the solvent, tetrahydrofuran (THF). Typically, 4 to 6 equivalents of lithium chloride are sufficient to saturate a solution of enolate in THF at the reaction molarity.
<br />
One primary advantage of asymmetric alkylation with pseudoephedrine amides is that the amide enolates are typically nucleophilic enough to react with primary and even secondary halides at temperatures ranging from –78 °C to 0 °C. Construction of quaternary carbon centers by alkylation of α-branched amide enolates is also possible, though the addition of DMPU is necessary for less reactive electrophiles. | 4 | Stereochemistry |
The initial and rate limiting step involving the electrophilic activation of RHC-H by a Pt center to produce a Pt-CHR species and a proton. The mechanism of this activation is debated. One possibility is the oxidative addition of a sigma coordinated C-H bond followed by the reductive removal of the proton. Another is a sigma-bond metathesis involving the formation of the M-C bond and a H-Cl or H-O bond. Regardless it is this step that kinetically imparts the chemoselectivity to the overall transformation. Stronger, more electron-rich bonds are activated preferentially over weaker, more electron-poor bonds of species that have already been partially oxidized. This avoids a problem that plagues many partial oxidation processes, namely, the over-oxidation of substrate to thermodynamic sinks such as HO and CO.
In the next step the Pt-CHR complex is oxidized by [PtCl] to a Pt-CHR complex. There have been multiple studies to find a replacement oxidant that is less expensive than [PtCl] or a method to regenerate [PtCl]. It would be most advantageous to develop an electron train which would use oxygen as the ultimate oxidant. It is important that the oxidant preferentially oxidizes the Pt-CHR species over the initial Pt species since Pt complexes will not electrophilically activate a C-H bond of the alkane (although Pt complexes electrophilically substitute hydrogens in aromatics - see refs. and ). Such premature oxidation shuts down the catalysis.
Finally the Pt-CHR undergoes nucleophilic attack by OH or Cl with the departure of Pt complex to regenerate the catalyst. | 0 | Organic Chemistry |
The thermal effective mass of electrons in a metal is the apparent mass due to interactions with the periodic potential of the crystal lattice, with phonons (e.g. phonon drag), and interaction with other electrons. The resulting effective mass of electrons contributes to the electronic heat capacity of the metal, leading to deviations from the heat capacity of a free electron gas. | 8 | Metallurgy |
It has been uncertain for a long time whether metal carbonyl hydrides contain a direct metal-hydrogen bond, although this has been suspected by Hieber for HFe(CO). The precise structure cannot be identified by X-ray diffraction, particularly the length of a possible metal-hydrogen bond remained uncertain. The exact structure of the metal carbonyl hydrides has been determined by using neutron diffraction and nuclear magnetic resonance spectroscopy. | 0 | Organic Chemistry |
The complete mathematical model describing electromigration consists of several partial differential equations (PDEs) which need to be solved for three-dimensional geometrical domains representing segments of an interconnect structure. Such a mathematical model forms the basis for simulation of electromigration in modern technology computer aided design (TCAD) tools.
Use of TCAD tools for detailed investigations of electromigration induced interconnect degradation is gaining importance. Results of TCAD studies in combination with reliability tests lead to modification of design rules improving the interconnect resistance to electromigration. | 7 | Physical Chemistry |
Once quantitative counts of each transcript are available, differential gene expression is measured by normalising, modelling, and statistically analysing the data. Most tools will read a table of genes and read counts as their input, but some programs, such as cuffdiff, will accept binary alignment map format read alignments as input. The final outputs of these analyses are gene lists with associated pair-wise tests for differential expression between treatments and the probability estimates of those differences. | 1 | Biochemistry |
Simultaneous use of the one- and two-hybrid methods (that is, simultaneous protein–protein and protein–DNA interaction) is known as a one-two-hybrid approach and expected to increase the stringency of the screen. | 1 | Biochemistry |
On a per molecule basis, it is considered to be the most potent greenhouse gas present in Earth's atmosphere, having a global warming potential of about 18,000 times that of carbon dioxide. The chemical is predicted to have a lifetime of 800 years in the atmosphere. However, the current concentration of trifluoromethylsulfur pentafluoride remains at a level that is unlikely to measurably contribute to global warming. The presence of the gas in the atmosphere is attributed to anthropogenic sources, possibly a by-product of the manufacture of fluorochemicals, originating from reactions of SF with fluoropolymers used in electronic devices and in microchips, or the formation can be associated with high voltage equipment created from SF (a breakdown product of high voltage equipment) reacting with CF to form the CFSF molecule. | 2 | Environmental Chemistry |
Signatures of mass-anomalous sulfur isotope fractionation preserved in the rock record have been an important piece of evidence for understanding the Great Oxidation Event, the sudden rise of oxygen on the ancient Earth. Nonzero values of ΔS and ΔS are present in the sulfur-bearing minerals of Precambrian rock formed greater than 2.45 billion years ago, but completely absent from rock less than 2.09 billion years old. Multiple mechanisms have been proposed for how oxygen prevents the fingerprints of mass-anomalous fractionation from being created and preserved; nevertheless, all studies of ΔS and ΔS records conclude that oxygen was essentially absent from Earth's atmosphere prior to 2.45 billion years ago. | 9 | Geochemistry |
Tanning facilities are ubiquitous in the US, although the figures are in decline. In a study in the US published in 2002, there was a higher density in colder areas with a lower median income and higher proportion of whites. A study in 1997 found an average of 50.3 indoor-tanning facilities in 20 US cities (13.89 facilities for every 100,000 residents); the highest was 134 in Minneapolis, MN, and the lowest four in Honolulu, Hawaii. In 2006 a study of 116 cities in the US found 41.8 facilities on average, a higher density than either Starbucks or McDonalds. Of the countrys 125 top colleges and universities in 2014, 12% had indoor-tanning facilities on campus and 42.4% in off-campus housing, 96% of the latter free of charge to the tenants.
There are fewer professional salons than tanning facilities; the latter includes tanning beds in gyms, spas and similar. According to the FDA, citing the Indoor Tanning Association, there were 25,000 tanning salons in 2010 in the US (population 308.7 million in 2010). Mailing-list data suggest there were 18,200 in September 2008 and 12,200 in September 2015, a decline of 30 percent. According to Chris Sternberg of the American Suntanning Association, the figures are 18,000 in 2009 and 9,500 in 2016.
The South West Public Health Observatory found 5,350 tanning salons in the UK in 2009: 4,492 in England (population 52.6 million in 2010), 484 in Scotland (5.3 million), 203 in Wales (3 million) and 171 in Northern Ireland (1.8 million). | 5 | Photochemistry |
Oligosaprobes include some green and diatomaceous algae, flowering plants (for example, European white water lilies), some rotifers, Bryozoa, sponges, mollusks of the genus Dreissena, cladocerans (daphnids, bithotrephes), dragonfly and mayfly larvae, sterlets, trout, minnows, and newts.
Oligosaprobes also embrace a few saprophytes, including bacteria (scores and hundreds per 1 cu mm of water) and organisms that feed on bacteria. The term “oligosaprobe” is usually applied only to freshwater organisms. | 9 | Geochemistry |
The Vuilleumier cycle was patented by a Swiss-American engineer named Rudolph Vuilleumier in 1918. The purpose of Vuilleumier's machine was to create a heat pump that would use heat at high temperature as energy input. The Vuilleumier cycle...The Vuilleumier cycle is a thermodynamic cycle with applications in low-temperature cooling. In some respects it resembles a Stirling cycle or engine, although it has two "displacers" with a mechanical linkage connecting them as compared to one in the Stirling cycle. The hot displacer is larger than the cold displacer. The coupling maintains the appropriate phase difference. The displacers do no workthey are not pistons. Thus no work is required in an ideal case to operate the cycle. In reality friction and other losses mean that some work is required.
Devices operating on this cycle have been able to produce temperatures as low as 15 K using liquid nitrogen to pre-cool. Without precooling 77 K was reached with a heat flow of 1 W.
The cycle was first patented by Vuilleumier in 1918 [https://www.google.com/patents/US1275507 with patent US1275507], and again in Leiden by KW Taconis in 1951. In March 2014, the Vuilleumier Cycle was tested in application with updating conventional HVAC (heating, ventilation, and air-conditioning) systems by utilizing the cycle's proposed thermodynamic process of moving heat energy, and having results of increased output efficiencies coupled with a reduced carbon footprint. This work was completed by ThermoLift (http://www.tm-lift.com/), a company based out of the Advanced Energy Research and Technology Center at Stony Brook University, with collaboration from the US Department of Energy and the New York State Energy Research and Development Authority (NYSERDA). This work culminated in the demonstration of the ThermoLift system at Oak Ridge National Laboratory in August, 2018. The demonstration showed that the ThermoLift technology (TCHP), is able to achieve coefficients of performance (COP) for the cycle that well exceeded the DOE’s target COPs for cold-climate heat pumps (although not at all exceeding Geothermal heat pump efficiencies). Furthermore, due to the nature of the TCHP, there is no significant capacity decrease as the inlet temperature to the cold HX decreases. | 7 | Physical Chemistry |
Jostel's TSH index can be calculated with
from equilibrium serum concentrations of thyrotropin (TSH), free T4 (FT4) and a correction coefficient derived from the logarithmic standard model (β = 0.1345).
An alternative standardised form (standardised TSH index or sTSHI) is calculated with.
as a z-transformed value incorporating mean (2.7) and standard deviation (0.676) of TSHI in a reference population | 1 | Biochemistry |
Discontinuous recrystallization is heterogeneous; there are distinct nucleation and growth stages. It is common in materials with low stacking-fault energy. Nucleation then occurs, generating new strain-free grains which absorb the pre-existing strained grains. It occurs more easily at grain boundaries, decreasing the grain size and thereby increasing the amount of nucleation sites. This further increases the rate of discontinuous dynamic recrystallization.
Discontinuous Dynamic Recrystallization has 5 main characteristics:
* Recrystallization does not occur until the threshold strain has been reached
* The stress-strain curve may have several peaks – there is not a universal equation
* Nucleation generally occurs along pre-existing grain boundaries
* Recrystallization rates increase as the initial grain size decreases
* There is a steady grain size which is approached as recrystallization proceeds
Discontinuous dynamic recrystallization is caused by the interplay of work hardening and recovery. If the annihilation of dislocations is slow relative to the rate at which they are generated, dislocations accumulate. Once critical dislocation density is achieved, nucleation occurs on grain boundaries. Grain boundary migration, or the atoms transfer from a large pre-existing grain to a smaller nucleus, allows the growth of the new nuclei at the expense of the pre-existing grains. The nucleation can occur through the bulging of existing grain boundaries. A bulge forms if the subgrains abutting a grain boundary are of different sizes, causing a disparity in energy from the two subgrains. If the bulge achieves a critical radius, it will successfully transition to a stable nucleus and continue its growth. This can be modeled using Cahn’s theories pertaining to nucleation and growth.
Discontinuous dynamic recrystallization commonly produces a ‘necklace’ microstructure. Since new grain growth is energetically favorable along grain boundaries, new grain formation and bulging preferentially occurs along pre-existing grain boundaries. This generates layers of new, very fine grains along the grain boundary initially leaving the interior of the pre-existing grain unaffected. As the dynamic recrystallization continues, it consumes the unrecrystallized region. As deformation continues, the recrystallization does not maintain coherency between layers of new nuclei, producing a random texture. | 8 | Metallurgy |
How chitin interacts with the immune system of plants and animals has been an active area of research, including the identity of key receptors with which chitin interacts, whether the size of chitin particles is relevant to the kind of immune response triggered, and mechanisms by which immune systems respond. Chitin is deacetylated chemically or enzymatically to produce chitosan, a highly biocompatible polymer which has found a wide range of applications in the biomedical industry. Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.
Chitin and chitosan are under development as scaffolds in studies of how tissue grows and how wounds heal, and in efforts to invent better bandages, surgical thread, and materials for allotransplantation. Sutures made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.
Chitosan has been demonstrated and proposed to make a reproducible form of biodegradable plastic. Chitin nanofibers are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, drug delivery and medicine.
Chitin has been proposed for use in building structures, tools, and other solid objects from a composite material, combining chitin with Martian regolith. To build this, the biopolymers in the chitin are suggested as the binder for the regolith aggregate to form a concrete-like composite material. The authors believe that waste materials from food production (e.g. scales from fish, exoskeletons from crustaceans and insects, etc.) could be put to use as feedstock for manufacturing processes. | 1 | Biochemistry |
Radon-222 has been classified by International Agency for Research on Cancer as being carcinogenic to humans. In September 2009, the World Health Organization released a comprehensive global initiative on radon that recommended a reference level of 100 Bq/m for radon, urging establishment or strengthening of radon measurement and mitigation programs as well as development building codes requiring radon prevention measures in homes under construction.
Elevated lung cancer rates have been reported from a number of cohort and case-control studies of underground miners exposed to radon and its decay products but the main confounding factor in all miners' studies is smoking and dust. Up to the most of regulatory bodies there is sufficient evidence for the carcinogenicity of radon and its decay products in humans for such exposures. However, the discussion about the opposite results is still going on, especially a recent retrospective case-control study of lung cancer risk showed substantial cancer rate reduction between 50 and 123 Bq per cubic meter relative to a group at zero to 25 Bq per cubic meter. Additionally, the meta-analysis of many radon studies, which independently show radon risk increase, gives no confirmation of that conclusion: the joined data show log-normal distribution with the maximal value in zero risk of lung cancer below 800 Bq per cubic meter.
The primary route of exposure to radon and its progeny is inhalation. Radiation exposure from radon is indirect. The health hazard from radon does not come primarily from radon itself, but rather from the radioactive products formed in the decay of radon. The general effects of radon to the human body are caused by its radioactivity and consequent risk of radiation-induced cancer. Lung cancer is the only observed consequence of high concentration radon exposures; both human and animal studies indicate that the lung and respiratory system are the primary targets of radon daughter-induced toxicity.
Radon has a short half-life (3.8 days) and decays into other solid particulate radium-series radioactive nuclides.
Two of these decay products, polonium-218 and 214, present a significant radiologic hazard.
If the gas is inhaled, the radon atoms decay in the airways or the lungs, resulting in radioactive polonium and ultimately lead atoms attaching to the nearest tissue. If dust or aerosol is inhaled that already carries radon decay products, the deposition pattern of the decay products in the respiratory tract depends on the behaviour of the particles in the lungs. Smaller diameter particles diffuse further into the respiratory system, whereas the larger—tens to hundreds of micron-sized—particles often deposit higher in the airways and are cleared by the body's mucociliary staircase. Deposited radioactive atoms or dust or aerosol particles continue to decay, causing continued exposure by emitting energetic alpha radiation with some associated gamma radiation too, that can damage vital molecules in lung cells,
by either creating free radicals or causing DNA breaks or damage,
perhaps causing mutations that sometimes turn cancerous. In addition, through ingestion and blood transport, following crossing of the lung membrane by radon, radioactive progeny may also be transported to other parts of the body.
The risk of lung cancer caused by smoking is much higher than the risk of lung cancer caused by indoor radon. Radiation from radon has been attributed to increase of lung cancer among smokers too. It is generally believed that exposure to radon and cigarette smoking are synergistic; that is, that the combined effect exceeds the sum of their independent effects. This is because the daughters of radon often become attached to smoke and dust particles, and are then able to lodge in the lungs.
It is unknown whether radon causes other types of cancer, but recent studies suggest a need for further studies to assess the relationship between radon and leukemia.
The effects of radon, if found in food or drinking water, are unknown. Following ingestion of radon dissolved in water, the biological half-life for removal of radon from the body ranges from 30 to 70 minutes. More than 90% of the absorbed radon is eliminated by exhalation within 100 minutes, By 600 minutes, only 1% of the absorbed amount remains in the body. | 2 | Environmental Chemistry |
Human chorionic gonadotropin can be used as a tumor marker, as its β subunit is secreted by some cancers including seminoma, choriocarcinoma, teratoma with elements of choriocarcinoma, other germ cell tumors, hydatidiform mole, and islet cell tumor. For this reason, a positive result in males can be a test for testicular cancer. The normal range for men is between 0-5 mIU/mL. Combined with alpha-fetoprotein, β-HCG is an excellent tumor marker for the monitoring of germ cell tumors. | 1 | Biochemistry |
Gravitational work is defined by the force on a body measured in a gravitational field. It may cause a generalized displacement in the form of change of the spatial distribution of the matter within the system. The system gains internal energy (or other relevant cardinal quantity of energy, such as enthalpy) through internal friction. As seen by the surroundings, such frictional work appears as mechanical work done on the system, but as seen by the system, it appears as transfer of energy as heat. When the system is in its own state of internal thermodynamic equilibrium, its temperature is uniform throughout. If the volume and other extensive state variables, apart from entropy, are held constant over the process, then the transferred heat must appear as increased temperature and entropy; in a uniform gravitational field, the pressure of the system will be greater at the bottom than at the top.
By definition, the relevant cardinal energy function is distinct from the gravitational potential energy of the system as a whole; the latter may also change as a result of gravitational work done by the surroundings on the system. The gravitational potential energy of the system is a component of its total energy, alongside its other components, namely its cardinal thermodynamic (e.g. internal) energy and its kinetic energy as a whole system in motion. | 7 | Physical Chemistry |
The addition of polyethylene glycol (PEG) to the process causes silica particles to aggregate into a macroporous continuous block, allowing access to a monolithic morphology. PEG polymers with allyl or silyl end groups with a molecular weight of greater than 2000 g mol are required. The Stöber process is initiated under neutral pH conditions, so that the PEG polymers will congregate around the outside of the growing particles, providing stabilization. Once the aggregates are sufficiently large, the PEG-stabilized particles will contact and irreversibly fuse together by "sticky aggregation" between the PEG chains. This continues until complete flocculation of all the particles has occurred and the monolith has been formed, at which point the monolith may be calcined and the PEG removed, resulting in a macroporous silica monolith. Both particle size and sticky aggregation can be controlled by varying the molecular weight and concentration of PEG. | 7 | Physical Chemistry |
In organosulfur chemistry, thioacetals are the sulfur (thio-) analogues of acetals (). There are two classes: the less-common monothioacetals, with the formula , and the dithioacetals, with the formula (symmetric dithioacetals) or (asymmetric dithioacetals).
The symmetric dithioacetals are relatively common. They are prepared by condensation of thiols () or dithiols (two groups) with aldehydes (). These reactions proceed via the intermediacy of hemithioacetals ():
#Thiol addition to give hemithioacetal:
#Thiol addition with loss of water to give dithioacetal:
Such reactions typically employ either a Lewis acid or Brønsted acid as catalyst.
Dithioacetals generated from aldehydes and either 1,2-ethanedithiol or 1,3-propanedithiol are especially common among this class of molecules for use in organic synthesis.
The carbonyl carbon of an aldehyde is electrophilic and therefore susceptible to attack by nucleophiles, whereas the analogous central carbon of a dithioacetal is not electrophilic. As a result, dithioacetals can serve as protective groups for aldehydes.
Far from being unreactive, and in a reaction unlike that of aldehydes, that carbon can be deprotonated to render it nucleophilic:
The inversion of polarity between and is referred to as umpolung. The reaction is commonly performed using the 1,3-dithiane. The lithiated intermediate can be used for various nucleophilic bond-forming reactions, and then the dithioketal hydrolyzed back to its carbonyl form. This overall process, the Corey–Seebach reaction, gives the synthetic equivalent of an acyl anion. | 0 | Organic Chemistry |
The dual tiling is called an order-7-3 floret pentagonal tiling, and is related to the floret pentagonal tiling. | 4 | Stereochemistry |
The "push" in the intercropping scheme is provided by the plants that emit volatile chemicals (kairomones) which repel stemborer moths and drive them away from the main crop (maize or sorghum). The most commonly used species of push plants are legumes of the genus Desmodium (e.g. silverleaf Desmodium, D. uncinatum, and greenleaf Desmodium, D. intortum). The Desmodium is planted in between the rows of maize or sorghum, where they emit volatile chemicals (such as (E)-β-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene) that repel the stemborer moths. These semiochemicals are also produced in grasses such as maize when they are damaged by insect herbivores, which may explain why they are repellent to stemborers. Being a low-growing plant, Desmodium does not interfere with the growth of crops, but can suppress weeds and help improve soil quality by increasing soil organic matter content, fixing nitrogen, and stabilizing soils from erosion. It also serves as a highly nutritious animal feed and effectively suppresses striga weeds through an allelopathic mechanism. Another plant showing good repellent properties is molasses grass (Melinis minutiflora), a nutritious animal feed with tick-repelling and stemborer larval parasitoid attractive properties. | 1 | Biochemistry |
Cadet's fuming liquid was a red-brown oily liquid prepared in 1760 by the French chemist Louis Claude Cadet de Gassicourt (1731-1799) by the reaction of potassium acetate with arsenic trioxide. It consisted mostly of dicacodyl (((CH)As)) and cacodyl oxide (((CH)As)O).
The global reaction (mass balance) corresponding to the oxide formation is the following:
These were the first organometallic substances prepared; as such, Cadet has been regarded as the father of organometallic chemistry.
This liquid develops white fumes when exposed to air, resulting in a pale flame producing carbon dioxide, water, and arsenic trioxide. It has a nauseating and very disagreeable garlic-like odor.
Around 1840, Robert Bunsen did much work on characterizing the compounds in the liquid and its derivatives. His research was important in the development of radical theory. | 7 | Physical Chemistry |
Fluorescence cross-correlation spectroscopy (FCCS) has several applications in the field of biophysics and biochemistry. Fluorescence cross-correlation spectroscopy (FCCS) is a powerful technique that enables the investigation of interactions between various types of biomolecules, including proteins, nucleic acids, and lipids.
FCCS is one of the few techniques that can provide information about protein-protein interactions at a specific time and location within a living cell. FCCS can be used to study the dynamics of biomolecules in living cells, including their diffusion rates and localization.
This can provide insights into the function and regulation of cellular processes. Unlike fluorescence resonance energy transfer, FCCS does not have a distance limit for interactions making it suitable for probing large complexes. However, FCCS requires active diffusion of the complexes through the microscope focus on a relatively short time scale, typically seconds. FCCS allows for measuring simple molecular stoichiometries and binding constants. | 7 | Physical Chemistry |
Evekeo is an FDA-approved medication that contains racemic amphetamine sulfate (i.e., 50% levoamphetamine sulfate and 50% dextroamphetamine sulfate). It is approved for the treatment of narcolepsy, ADHD, and exogenous obesity. The orally disintegrating tablets are approved for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents aged six to 17 years of age. | 4 | Stereochemistry |
There are two main types of inorganic carbon that are found in the oceans. Dissolved inorganic carbon (DIC) is made up of bicarbonate (HCO), carbonate (CO) and carbon dioxide (including both dissolved CO and carbonic acid HCO). DIC can be converted to particulate inorganic carbon (PIC) through precipitation of CaCO (biologically or abiotically). DIC can also be converted to particulate organic carbon (POC) through photosynthesis and chemoautotrophy (i.e. primary production). DIC increases with depth as organic carbon particles sink and are respired. Free oxygen decreases as DIC increases because oxygen is consumed during aerobic respiration.
Particulate inorganic carbon (PIC) is the other form of inorganic carbon found in the ocean. Most PIC is the CaCO that makes up shells of various marine organisms, but can also form in whiting events. Marine fish also excrete calcium carbonate during osmoregulation.
Some of the inorganic carbon species in the ocean, such as bicarbonate and carbonate, are major contributors to alkalinity, a natural ocean buffer that prevents drastic changes in acidity (or pH). The marine carbon cycle also affects the reaction and dissolution rates of some chemical compounds, regulates the amount of carbon dioxide in the atmosphere and Earth's temperature. | 9 | Geochemistry |
The Joback method is an extension of the Lydersen method and uses very similar groups, formulas, and parameters for the three properties the Lydersen already supported (critical temperature, critical pressure, critical volume).
Joback extended the range of supported properties, created new parameters and modified slightly the formulas of the old Lydersen method. | 7 | Physical Chemistry |
The human trace amine-associated receptors are a group of six G protein-coupled receptors (i.e., TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) that – with exception for TAAR1 – are expressed in the human olfactory epithelium. In humans and other animals, TAARs in the olfactory epithelium function as olfactory receptors that detect volatile amine odorants, including certain pheromones; these TAARs putatively function as a class of pheromone receptors involved in the olfactive detection of social cues.
A review of studies involving non-human animals indicated that TAARs in the olfactory epithelium can mediate attractive or aversive behavioral responses to a receptor agonist. This review also noted that the behavioral response evoked by a TAAR can vary across species (e.g., TAAR5 mediates attraction to trimethylamine in mice and aversion to trimethylamine in rats). In humans, hTAAR5 presumably mediates aversion to trimethylamine, which is known to act as an hTAAR5 agonist and to possess a foul, fishy odor that is aversive to humans; however, hTAAR5 is not the only olfactory receptor that is responsible for trimethylamine olfaction in humans. hTAAR5-mediated trimethylamine aversion has not been examined in published research. | 1 | Biochemistry |
The development of facile chemical glycosylation protocols is essential to synthesizing complex oligosaccharides. Among many diverse type of glycosidic linkages, the 1,2-cis-β-glycoside, which exists in many biologically relevant glycoconjugates and oligosaccharides, is arguably one of the most difficult to synthesize. The challenges in constructing β-mannose linkage have been well documented in several reviews. To date, a few laboratories have devised efficient methodologies to overcome these synthetic hurdles, and achieved varying degrees of success. Of those elegant approaches, a highly stereoselective β-mannosylation protocol developed by Crich and co-workers was realized as a breakthrough in β-mannoside synthesis. This strategy is based on the initial activation of α-mannosyl sulfoxides 1 with triflic anhydride (TfO) using DTBMP (2,6-di-tert-butyl-4-methylpyridine) as a base, followed by nucleophilic substitution of glycosyl acceptors (HOR) to provide the 1,2-cis-β-glycoside 2 in good yield and selectivity (Scheme 1). | 0 | Organic Chemistry |
From the start Fulmer was a commercial enterprise aiming to make a surplus for investment in its own development. It received no grant or membership fees. Its income was solely from projects, each with defined objectives and time and cost limits agreed with individual sponsors from Government or Industry. Normally, the project contract would provide that all results would belong in confidence to the sponsor, who would also own any patents arising from the investigation. | 8 | Metallurgy |
MDCs are utilized in seawater desalination by primarily acting as a precursor treatment for electrodialysis (ED) due to the inefficiency in salinity removal due to biofouling and membrane scaling by the complex ion composition. Studies show that efficacy of MDC systems diminish over 5000 hours due to membrane scaling such as calcium and potassium accumulation, increasing ohmic resistance and reducing ion exchange through the membrane. However, by utilizing MDCs as a precursor treatment for electrodialysis, results show that system time is reduced by 25% and energy expenditure decreases by 45.3%. Reduction in external resistance increases desalination efficiency to as high as 74%, as demonstrated in upflow microbial desalination cells (UMDC), but increased membrane scaling on the ion exchange membranes by calcium and magnesium accumulation, resulting in a higher internal ohmic resistance and decrease in overall desalination of seawater. With the application of an osmotic MFC (OsMFC) in conjunction with the UMDC as an initial pretreatment of biosolid removal and desalination, 85% of oxygen demand and approximately 97% of salts was reduced after secondary treatment. Subsequent treatment by traditional BES systems such as electrodialysis can function as a more effective system for desalination, provisioning energy demands by the output energy obtained from the MDC pretreatment. | 7 | Physical Chemistry |
Regarding the volume-temperature relationship, Gay-Lussac attributed his findings to Jacques Charles because he used much of Charless unpublished data from 1787 – hence, the law became known as Charless law or the Law of Charles and Gay-Lussac.
Amontonss, Charles, and Boyles law form the combined gas law. These three gas laws in combination with Avogadros law can be generalized by the ideal gas law.
Gay-Lussac used the formula acquired from ΔV/V = αΔT to define the rate of expansion α for gases. For air, he found a relative expansion ΔV/V = 37.50% and obtained a value of α = 37.50%/100 °C = 1/266.66 °C which indicated that the value of absolute zero was approximately 266.66 °C below 0 °C. The value of the rate of expansion α is approximately the same for all gases and this is also sometimes referred to as Gay-Lussacs Law. See the introduction to this article, and Charless Law. | 7 | Physical Chemistry |
In metallurgical processes tank leaching is a hydrometallurgical method of extracting valuable material (usually metals) from ore. | 8 | Metallurgy |
Minigastrin (also mini gastrin) is a form of gastrin. Its sequence is H-Leu-Glu-Glu-Glu-Glu-Glu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2.
Minigastrin is a potential therapeutic agent for thyroid carcinoma by targeting cancer-promoting cholecystokinin receptors. | 1 | Biochemistry |
The PHLPP isoforms (PH domain and Leucine rich repeat Protein Phosphatases) are a pair of protein phosphatases, PHLPP1 and PHLPP2, that are important regulators of Akt serine-threonine kinases (Akt1, Akt2, Akt3) and conventional/novel protein kinase C (PKC) isoforms. PHLPP may act as a tumor suppressor in several types of cancer due to its ability to block growth factor-induced signaling in cancer cells.
PHLPP dephosphorylates Ser-473 (the hydrophobic motif) in Akt, thus partially inactivating the kinase.
In addition, PHLPP dephosphorylates conventional and novel members of the protein kinase C family at their hydrophobic motifs, corresponding to Ser-660 in PKCβII. | 1 | Biochemistry |
In the specific case of antibodies (Ab) binding to antigen (Ag), usually the term affinity constant refers to the association constant.
This chemical equilibrium is also the ratio of the on-rate (k or k) and off-rate (k or k) constants. Two antibodies can have the same affinity, but one may have both a high on- and off-rate constant, while the other may have both a low on- and off-rate constant. | 7 | Physical Chemistry |
Tris(tert-butoxy)silanethiol is a silicon compound containing three tert-butoxy groups and a rare Si–S–H functional group. This colourless compound serves as an hydrogen donor in radical chain reactions. It was first prepared by alcoholysis of silicon disulfide and purified by distillation:
:3 (CH)COH + SiS → [(CH)CO]SiSH + HS
Since 1962 it was thoroughly studied including its acid-base properties and coordination chemistry with metal ions. It coordinates to metal ions via the sulfur and oxygen donor atoms. | 0 | Organic Chemistry |
A crystallization adjutant is a material used to promote crystallization, normally in a context where a material does not crystallize naturally from a pure solution. | 3 | Analytical Chemistry |
Electropolishing, also known as electrochemical polishing, anodic polishing, or electrolytic polishing (especially in the metallography field), is an electrochemical process that removes material from a metallic workpiece, reducing the surface roughness by levelling micro-peaks and valleys, improving the surface finish. Electropolishing is often compared to, but distinctly different from, electrochemical machining. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating. It may be used in lieu of abrasive fine polishing in microstructural preparation. | 8 | Metallurgy |
The control of enzymatic browning has always been a challenge for the food industry. A variety of approaches are used to prevent or slow down enzymatic browning of foods, each method aimed at targeting specific steps of the chemical reaction. The different types of enzymatic browning control can be classified into two large groups: physical and chemical. Usually, multiple methods are used. The use of sulfites (powerful anti-browning chemicals) have been reconsidered due to the potential hazards that it causes along with its activity. Much research has been conducted regarding the exact types of control mechanisms that take place when confronted with the enzymatic process. Besides prevention, control over browning also includes measures intended to recover the food color after its browning. For instance, ion exchange filtration or ultrafiltration can be used in winemaking to remove the brown color sediments in the solution. | 1 | Biochemistry |
The Schöllkopf method or Schöllkopf Bis-Lactim Amino Acid Synthesis is a method in organic chemistry for the asymmetric synthesis of chiral amino acids. The method was established in 1981 by Ulrich Schöllkopf. In it glycine is a substrate, valine a chiral auxiliary and the reaction taking place an alkylation. | 0 | Organic Chemistry |
Pro-oxidants are chemicals that induce oxidative stress, either by generating reactive oxygen species or by inhibiting antioxidant systems. The oxidative stress produced by these chemicals can damage cells and tissues, for example, an overdose of the analgesic paracetamol (acetaminophen) can fatally damage the liver, partly through its production of reactive oxygen species.
Some substances can serve as either antioxidants or pro-oxidants, depending on conditions. Some of the important conditions include the concentration of the chemical and if oxygen or transition metals are present. While thermodynamically very favored, reduction of molecular oxygen or peroxide to superoxide or hydroxyl radical respectively is spin forbidden. This greatly reduces the rates of these reactions, thus allowing aerobic life to exist. As a result, the reduction of oxygen typically involves either the initial formation of singlet oxygen, or spin–orbit coupling through a reduction of a transition-series metal such as manganese, iron, or copper. This reduced metal then transfers the single electron to molecular oxygen or peroxide. | 1 | Biochemistry |
The major benefits of ion semiconductor sequencing are rapid sequencing speed and low upfront and operating costs. This has been enabled by the avoidance of modified nucleotides and optical measurements.
Because the system records natural polymerase-mediated nucleotide incorporation events, sequencing can occur in real-time. In reality, the sequencing rate is limited by the cycling of substrate nucleotides through the system. Ion Torrent Systems Inc., the developer of the technology, claims that each incorporation measurement takes 4 seconds and each run takes about one hour, during which 100-200 nucleotides are sequenced. If the semiconductor chips are improved (as predicted by Moore’s law), the number of reads per chip (and therefore per run) should increase.
The cost of acquiring a pH-mediated sequencer from Ion Torrent Systems Inc. at time of launch was priced at around $50,000 USD, excluding sample preparation equipment and a server for data analysis. The cost per run is also significantly lower than that of alternative automated sequencing methods, at roughly $1,000. | 1 | Biochemistry |
The most common side effects are fine tremor, anxiety, headache, muscle cramps, dry mouth, and palpitation. Other symptoms may include tachycardia, arrhythmia, flushing of the skin, myocardial ischemia (rare), and disturbances of sleep and behaviour. Rarely occurring, but of importance, are allergic reactions of paradoxical bronchospasms, urticaria (hives), angioedema, hypotension, and collapse. High doses or prolonged use may cause hypokalemia, which is of concern especially in patients with kidney failure and those on certain diuretics and xanthine derivatives.
Salbutamol metered dose inhalers have been described as the "single biggest source of carbon emissions from NHS medicines prescribing" due to the propellants used in the inhalers. Dry powder inhalers are recommended as a low-carbon alternative. | 4 | Stereochemistry |
Peters served as the chemistry departments graduate student advisor from 1969 to 1971 where he recruited the departments largest incoming class. His research has focused on the mechanistic and synthetic properties of the oxidation and reduction of halogenated organic compounds and electrocatalysis in organic synthesis. Peters was still actively teaching up to the time he suffered a fall during spring break 2020 and was taken to a hospital. | 3 | Analytical Chemistry |
Due to the high energy of C−F bonds, hexafluoroethane is nearly inert and thus acts as an extremely stable greenhouse gas, with an atmospheric lifetime of 10,000 years (other sources: 500 years). It has a global warming potential (GWP) of 9200 and an ozone depletion potential (ODP) of 0. Hexafluoroethane is included in the IPCC list of greenhouse gases.
Hexafluoroethane did not exist in significant amounts in the environment prior to industrial-scale manufacturing. Atmospheric concentration of hexafluoroethane reached 3 pptv at the start of the 21st century. Its absorption bands in the infrared part of the spectrum cause a radiative forcing of about 0.001 W/m. | 2 | Environmental Chemistry |
The third piece has a fractured top surface, which indicates that a fourth piece of the original pillar is missing. Klaus Roessler (1995) estimated the length of this piece at . Henry Cousens hypothesized that the fourth piece had a garuda figure (the Paramara royal emblem) or a trishula (trident) at the top. As Bhoja was a Shaivite king, R. Balasubramaniam analyzed Shaivite iconography to conclude that the top had a trishula.
Balasubramaniam also theorizes that an iron pillar in front of Mandus Jami Masjid might be a re-shaped version of the Dhar pillars missing piece. This pillar is called Allaudins Sang' (spear) after Alauddin Khalji. | 8 | Metallurgy |
The zinc–bromine flow battery (Zn-Br2) is the oldest flow battery chemistry, with John Doyle's patent US224404 filed on September 29, 1879. Zn-Br2 batteries have relatively high specific energy, and they were demonstrated as power sources for electric cars in the 1970s.
Walther Kangro, an Estonian chemist working in Germany, was the first to demonstrate in the 1950s flow batteries based fully on dissolved transition metal ions: Ti–Fe and Cr–Fe. After some initial experimentations with Ti–Fe RFB NASA and some other groups in Japan and elsewhere selected Cr–Fe chemistry for further development. In order to reduce the effect of time-varying concentration during RFB cycling, mixed solutions (i.e. comprising both chromium and iron species in the negolyte and in the posolyte) were used. Among disadvantages of the Cr–Fe chemistry are: hydrate isomerism (i.e. the equilibrium between electrochemically active Cr3+ chloro-complexes and inactive hexa-aqua complex, which can be alleviated by adding chelating amino-ligands) and hydrogen evolution on the negode (which is mitigated by adding Pb salts for increasing the H2 overvoltage and Au salts for catalyzing the chromium electrode reaction).
In the late 1980s, Sum, Rychcik and Skyllas-Kazacos at the University of New South Wales (UNSW) in Australia demonstrated the advantages of all-vanadium RFB chemistry, such as the existence of four oxidation states within the electrochemical voltage window of the graphite-aqueous acid interface, and thus the elimination of the mixing dilution, detrimental in Cr–Fe RFBs. UNSW filed several patents related to VRFBs, that were later licensed to Japanese, Thai and Canadian corporations, which tried to commercialize this technology with variable success.
In 2022, Dalian, China began operating a 400 MWh, 100 MW vanadium flow battery, then the largest of its type. | 7 | Physical Chemistry |
Grignard reagents or Grignard compounds are chemical compounds with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . They are a subclass of the organomagnesium compounds.
Grignard compounds are popular reagents in organic synthesis for creating new carbon–carbon bonds. For example, when reacted with another halogenated compound in the presence of a suitable catalyst, they typically yield and the magnesium halide as a byproduct; and the latter is insoluble in the solvents normally used. In this aspect, they are similar to organolithium reagents.
Grignard reagents are rarely isolated as solids. Instead, they are normally handled as solutions in solvents such as diethyl ether or tetrahydrofuran using air-free techniques. Grignard reagents are complex with the magnesium atom bonded to two ether ligands as well as the halide and organyl ligands.
The discovery of the Grignard reaction in 1900 was recognized with the Nobel Prize awarded to Victor Grignard in 1912. | 0 | Organic Chemistry |
This photosystem is known as PSI because it was discovered before Photosystem II, although future experiments showed that Photosystem II is actually the first enzyme of the photosynthetic electron transport chain. Aspects of PSI were discovered in the 1950s, but the significance of these discoveries was not yet recognized at the time. Louis Duysens first proposed the concepts of Photosystems I and II in 1960, and, in the same year, a proposal by Fay Bendall and Robert Hill assembled earlier discoveries into a coherent theory of serial photosynthetic reactions. Hill and Bendall's hypothesis was later confirmed in experiments conducted in 1961 by the Duysens and Witt groups. | 5 | Photochemistry |
Phosgene oxime can be prepared by reduction of chloropicrin using a combination of tin metal and hydrochloric acid as the source of the active hydrogen reducing agent:
The observation of a transient violet color in the reaction suggests intermediate formation of trichloronitrosomethane (ClCNO). Early preparations, using stannous chloride as the reductant, also started with chloropicrin.
The compound is electrophilic and thus sensitive to nucleophiles, including bases, which destroy it:
Phosgene oxime has been used to prepare heterocycles that contain N-O bonds, such as isoxazoles.
Dehydrohalogenation upon contact with mercuric oxide generates chlorine fulminate, a reactive nitrile oxide: | 1 | Biochemistry |
# Removal of the smear layer and etching of dentine
# Priming of the dentine surface
# Bonding of the primed dentine surface to the restorative material | 7 | Physical Chemistry |
pComb3H, a derivative of pComb3 optimized for expression of human fragments, is a phagemid used to express proteins such as zinc finger proteins and antibody fragments on phage pili for the purpose of phage display selection.
For the purpose of phage production, it contains the bacterial ampicillin resistance gene (for B-lactamase), allowing the growth of only transformed bacteria. | 1 | Biochemistry |
The reaction steps are reversible reactions and the reaction is driven to completion by removal of water e.g. by azeotropic distillation, molecular sieves or titanium tetrachloride. Primary amines react through an unstable hemiaminal intermediate which then splits off water.
Secondary amines do not lose water easily because they do not have a proton available and instead they often react further to an aminal:
or when an α-carbonyl proton is present to an enamine:
In acidic environment the reaction product is an iminium salt by loss of water.
This reaction type is found in many Heterocycle preparations for example the Povarov reaction and the Friedländer-synthesis to quinolines. | 0 | Organic Chemistry |
A beam of electrons is fired at a sample. The beam causes each element in the sample to emit X-rays at a characteristic frequency; the X-rays can then be detected by the electron microprobe. The size and current density of the electron beam determines the trade-off between resolution and scan time and/or analysis time. | 3 | Analytical Chemistry |
A Piper diagram is a graphic procedure proposed by Arthur M. Piper in 1944 for presenting water chemistry data to help in understanding the sources of the dissolved constituent salts in water. This procedure is based on the premise that cations and anions in water are in such amounts to assure the electroneutrality of the dissolved salts, in other words the algebraic sum of the electric charges of cations and anions is zero.
A Piper diagram is a graphical representation of the chemistry of a water sample or samples.
The cations and anions are shown by separate ternary plots. The apexes of the cation plot are calcium, magnesium and sodium plus potassium cations. The apexes of the anion plot are sulfate, chloride and carbonate plus hydrogen carbonate anions. The two ternary plots are then projected onto a diamond. The diamond is a matrix transformation of a graph of the anions (sulfate + chloride/ total anions) and cations (sodium + potassium/total cations).
The Piper diagram is suitable for comparing the ionic composition of a set of water samples, but does not lend itself to spatial comparisons. For geographical applications, the Stiff diagram and Maucha diagram are more applicable, because they can be used as markers on a map. Colour coding of the background of the Piper diagram allows linking Piper Diagrams and maps
Water samples shown on the Piper diagram can be grouped in hydrochemical facies. The cation and anion triangles can be separated in regions based on the dominant cation(s) or anion(s) and their combination creates regions in the diamond shaped part of the diagram. | 7 | Physical Chemistry |
An mRNA molecule is said to be monocistronic when it contains the genetic information to translate only a single protein chain (polypeptide). This is the case for most of the eukaryotic mRNAs. On the other hand, polycistronic mRNA carries several open reading frames (ORFs), each of which is translated into a polypeptide. These polypeptides usually have a related function (they often are the subunits composing a final complex protein) and their coding sequence is grouped and regulated together in a regulatory region, containing a promoter and an operator. Most of the mRNA found in bacteria and archaea is polycistronic, as is the human mitochondrial genome. Dicistronic or bicistronic mRNA encodes only two proteins. | 1 | Biochemistry |
Single reversible solid oxide cells can be arranged in series to form stacks. Single stacks can be then arranged in modules to reach power capabilities in the order of kilowatts or megawatts.
One of the most challenging aspects in designing large rSOC systems for energy storage purposes is the thermal integration. When the rSOC is operated in electrolysis mode, thermal power is needed for the operation of the system. Thermal power must be provided at two different temperature levels. Heat is needed for water operation, and additional heat at high temperature may be needed if the SOEC modality is endothermic. The latter requirement can be avoided if the rSOC is operated with an exothermic reaction in SOEC modality, with a negative effect on the roundtrip efficiency. On the other hand, when the rSOC is operated in fuel cell mode, the reaction is characterized by a high exothermicity. A number of works in the scientific literature have proposed the exploitation of a Thermal energy storage (TES) to ease the thermal integration of the system.
Excess heat from the SOFC operation can be recovered and stored in a TES, and later used for the SOEC operation. Thermal energy storage typologies and heat transfer fluids that have been considered for this purpose are those used for Concentrated solar power (CSP) technologies. Diathermic oil can be used to store heat at relatively low temperature (for instance, 180°C) and exploited for water evaporation. Alternatively, phase-change materials characterized by high fusion points can be used to store heat at high temperature and enable the endothermic operation in the electrolysis mode. In this case, usually, rSOCs operate at different temperature levels in the two modalities (for example, 850°C in SOFC mode and 800°C in SOEC mode).
If carbonaceous chemistries are employed, the beneficial effect of methane synthesis inside the cell can be exploited to reduce the heat request of the electrolysis mode. In this regard, systems operating at high pressure and lower temperature (20 bar and 650°C) have been proposed to reduce or even eliminate the thermal power requirement of the rSOC system. Alternatively, the production of methane can be favored in external reactors. The methanation reaction is exothermic and favored at low temperature.
The syngas that produced by the co-electrolysis can undergo a further reaction in one or multiple methanation reactors to produce methane and generate low-temperature heat for water evaporation. In addition, the formation of methane in such systems may be beneficial to the size of the tanks used for storing the fuels. In fact, methane is characterized by a higher volumetric energy density than hydrogen in the gaseous form.
When computing the roundtrip efficiencies of rSOC systems, the definition must take into account the net electric consumption (or additional electric production) of other components inside the system. The set of these component is regarded as balance of plant (BOP), and may comprehend pumps, compressors, expanders or fans, needed for fluid circulation and processing inside the system. Therefore, the system roundtrip efficiency can be defined as:
where:
* is the electric power produced in SOFC mode;
* is the electric power consumed in SOEC mode;
* is the net electric power consumption (negative) or production (positive) by the BOP in FC mode;
* is the net electric power consumption (negative) or production (positive) by the BOP in EC mode.
The roundtrip efficiencies achievable with rSOC systems operating with steam and hydrogen can reach values in the order of 60%. On the other hand, systems exploiting the beneficial effects of methane formation, either inside the rSOC or in external reactors, can reach rountrip efficiencies in the order of 70% and beyond. | 7 | Physical Chemistry |
The water balances are calculated for each reservoir separately as shown in the article Hydrology (agriculture). The excess water leaving one reservoir is converted into incoming water for the next reservoir.<br>
The three soil reservoirs can be assigned a different thickness and storage coefficients, to be given as input data.<br>
In a particular situation, the transition zone or the aquifer need not be present. Then, it must be given a minimum thickness of 0.1 m.<br>
The depth of the water table, calculated from the water balances, is assumed to be the same for the whole area. If this assumption is not acceptable, the area must be divided into separate units.<br>
Under certain conditions, the height of the water table influences the water balance components. For example, a rise of the water table towards the soil surface may lead to an increase of evaporation, surface runoff, and subsurface drainage, or a decrease of percolation losses from canals. This, in turn, leads to a change of the water balance, which again influences the height of the water table, etc.<br>
This chain of reactions is one of the reasons why Saltmod has been developed into a computer program. It takes a number of repeated calculations (iterations) to find the correct equilibrium of the water balance, which would be a tedious job if done by hand. Other reasons are that a computer program facilitates the computations for different water management options over long periods of time (with the aim to simulate their long-term effects) and for trial runs with varying parameters. | 9 | Geochemistry |
The gradient of the line between any two points on a Frost diagram gives the potential for the reaction. A species that lies in a peak, above the gradient of the two points on either side, denotes a species unstable with respect to disproportionation, and a point that falls below the gradient of the line joining its two adjacent points lies in a thermodynamic sink, and is intrinsically stable. | 7 | Physical Chemistry |
Immersed in water, extremely water repellent (super-hydrophobic), structured surfaces trap air between the structures and this air-layer is maintained for a period of time. A silvery shine, due to the reflection of light at the interface of air and water, is visible on the submerged surfaces.
Long lasting air layers also occur in aquatic arthropods which breathe via a physical gill (plastron) e. g. the water spider (Argyroneta) and the saucer bug (Aphelocheirus) Air layers are presumably also conducive to the reduction of friction in fast moving animals under water, as is the case for the back swimmer Notonecta.
The best known examples for long term air retention under water are the floating ferns of genus Salvinia. About ten species of very diverse sizes are found in lentic water in all warmer regions of the earth, one widely spread species (S. natans) found in temperate climates can be even found in Central Europe. The ability to retain air is presumably a survival technique for these plants. The upper side of the floating leaves is highly water repellent and possesses highly complex and species-specific very distinctive hairs. Some species present multicellular free-standing hairs of 0.3–3 mm length (e. g. S. cucullata) while on others, two hairs are connected at the tips (e.g. S. oblongifolia). S. minima and S. natans have four free standing hairs connected at a single base. The Giant Salvinia (S. molesta), as well as S. auriculata, and other closely related species, display the most complex hairs: four hairs grow on a shared shaft; they are connected at their tips. These structures resemble microscopic eggbeaters and are therefore referred to as “eggbeater trichomes”. The entire leaf surface, including the hairs, is covered with nanoscale wax crystals which are the reason for the water repellent properties of the surfaces. These leaf surfaces are therefore a classical example of a “hierarchical structuring“.
The egg-beater hairs of Salvinia molesta and closely related species (e.g. S. auriculata) show an additional remarkable property. The four cells at the tip of each hair (the anchor cells), as opposed to the rest of the hair, are free of wax and therefore hydrophilic; in effect, wettable islands surrounded by a super-hydrophobic surface. This chemical heterogeneity, the Salvinia paradox, enables a pinning of the air water interface to the plant and increases the pressure and longtime stability of the air layer.
The air retaining surface of the floating fern does not lead to a reduction in friction. The ecological extremely adaptable Giant Salvinia (S. molesta) is one of the most important invasive plants in all tropical and subtropical regions of the earth and is the cause of economic as well as ecological problems. Its growth rate might be the highest of all vascular plants. In the tropics and under optimal conditions, S. molesta can double its biomass within four days. The Salvinia effect, described here, most likely plays an essential role in its ecological success; the multilayered floating plant mats presumably maintain their function of gas exchange within the air-layer. | 7 | Physical Chemistry |
In organic chemistry, hydrocyanation is a process for conversion of alkenes to nitriles. The reaction involves the addition of hydrogen cyanide and requires a catalyst. This conversion is conducted on an industrial scale for the production of precursors to nylon. | 0 | Organic Chemistry |
Caesium acetate or cesium acetate is an ionic caesium compound with the molecular formula CHCOOCs. It is a white solid that may be formed by the reaction of caesium hydroxide or caesium carbonate with acetic acid. | 0 | Organic Chemistry |
During plant photosynthesis, 2 equivalents of glycerate 3-phosphate (GP; also known as 3-phosphoglycerate) are produced by the first step of the light-independent reactions when ribulose 1,5-bisphosphate (RuBP) and carbon dioxide are catalysed by the rubisco enzyme. The GP is converted to D-glyceraldehyde 3-phosphate (G3P) using the energy in ATP and the reducing power of NADPH as part of the Calvin cycle. This returns ADP, phosphate ions Pi, and NADP+ to the light-dependent reactions of photosynthesis for their continued function.
RuBP is regenerated for the Calvin cycle to continue.
G3P is generally considered the prime end-product of photosynthesis and it can be used as an immediate food nutrient, combined and rearranged to form monosaccharide sugars, such as glucose, which can be transported to other cells, or packaged for storage as insoluble polysaccharides such as starch. | 5 | Photochemistry |
If two systems, and , have identical intensive variables, a thermodynamic operation of wall removal can compose them into a single system, , with the same intensive variables. If, for example, their internal energies are in the ratio , then the composed system, , has internal energy in the ratio of to that of the system . By the inverse thermodynamic operation, the system can be split into two subsystems in the obvious way. As usual, these thermodynamic operations are conducted in total ignorance of the microscopic states of the systems. More particularly, it is characteristic of macroscopic thermodynamics that the probability vanishes, that the splitting operation occurs at an instant when system is in the kind of extreme transient microscopic state envisaged by the Poincaré recurrence argument. Such splitting and recomposition is in accord with the above defined additivity of extensive variables. | 7 | Physical Chemistry |
Alkylation in biology causes DNA damage. It is the transfer of alkyl groups to the nitrogenous bases. It is caused by alkylating agents such as EMS (Ethyl Methyl Sulphonate). Bifunctional alkyl groups which have two alkyl groups in them cause cross linking in DNA. Alkylation damaged ring nitrogen bases are repaired via the Base Excision Repair (BER) pathway. | 0 | Organic Chemistry |
The Tulkun is a whale-like creature native to Pandoras ocean. They are similar to Earths whales and possess a form of sentience with their own language, laws, and philosophy which makes them capable of bonding with Navi in a more spiritual way than other animals. Each member of the Metkayina Clan forms a life-long bond with a tulkun as a spirit brother/sister. Once violent creatures who continually warred with one another, they are now completely pacifistic, refusing to kill even to defend themselves. As such they banish those who commit violence. They are introduced in Avatar: The Way of Water, in which humans have begun hunting them to harvest their brain enzymes for creating anti-aging remedies called amrita. Jake Sullys son, Lo'ak, bonds with an outcast tulkun named Payakan after he is banished for killing the whalers who killed his mother. | 1 | Biochemistry |
Certain household materials and substances can be seen to exhibit the property:
* Ordinary pressure-sensitive tape ("Scotch tape") displays a glowing line where the end of the tape is being pulled away from the roll. Soviet scientists observed in 1953 that unpeeling a roll of tape in a vacuum produced X-rays. The mechanism of X-ray generation was studied further in 2008. Similar X-ray emissions have also been observed with metals.
* Opening an envelope sealed with polymer glue may generate light that can be viewed as blue flashes in darkness.
* When sugar crystals are crushed, tiny electrical fields are created, separating positive and negative charges that create sparks while trying to reunite. Wint-O-Green Life Savers work especially well for creating such sparks, because wintergreen oil (methyl salicylate) is fluorescent and converts ultraviolet light into blue light.
A diamond may begin to glow while being rubbed; this occasionally happens to diamonds while a facet is being ground or the diamond is being sawn during the cutting process. Diamonds may fluoresce blue or red. Some other minerals, such as quartz, are triboluminescent, emitting light when rubbed together.
Triboluminescence as a biological phenomenon is observed in mechanical deformation and contact electrification of epidermal surface of osseous and soft tissues, during chewing food, at friction in joints of vertebrae, during sexual intercourse, and during blood circulation.
Water jet abrasive cutting of ceramics (e.g., tiles) creates a yellow/orange glow at the point of impact of very high-speed flow. | 5 | Photochemistry |
Apamin is the smallest neurotoxin polypeptide known, and the only one that passes the blood-brain barrier. Apamin thus reaches its target organ, the central nervous system. Here it inhibits small-conductance Ca-activated K channels (SK channels) in neurons. These channels are responsible for the afterhyperpolarizations that follow action potentials, and therefore regulate the repetitive firing frequency.
Three different types of SK channels show different characteristics. Only SK2 and SK3 are blocked by apamin, whereas SK1 is apamin insensitive. SK channels function as a tetramer of subunits. Heteromers have intermediate sensitivity. SK channels are activated by the binding of intracellular Ca to the protein calmodulin, which is constitutively associated to the channel. Transport of potassium ions out of the cell along their concentration gradient causes the membrane potential to become more negative. The SK channels are present in a wide range of excitable and non-excitable cells, including cells in the central nervous system, intestinal myocytes, endothelial cells, and hepatocytes.
Binding of apamin to SK channels is mediated by amino acids in the pore region as well as extracellular amino acids of the SK channel. It is likely that the inhibition of SK channels is caused by blocking of the pore region, which hinders the transport of potassium ions. This will increase the neuronal excitability and lower the threshold for generating an action potential. Other toxins that block SK channels are tamapin and scyllatoxin. | 1 | Biochemistry |
Common components of a phase diagram are lines of equilibrium or phase boundaries, which refer to lines that mark conditions under which multiple phases can coexist at equilibrium. Phase transitions occur along lines of equilibrium. Metastable phases are not shown in phase diagrams as, despite their common occurrence, they are not equilibrium phases.
Triple points are points on phase diagrams where lines of equilibrium intersect. Triple points mark conditions at which three different phases can coexist. For example, the water phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a stable equilibrium ( and a partial vapor pressure of ). The pressure on a pressure-temperature diagram (such as the water phase diagram shown) is the partial pressure of the substance in question.
The solidus is the temperature below which the substance is stable in the solid state. The liquidus is the temperature above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus; within the gap, the substance consists of a mixture of crystals and liquid (like a "slurry").
Working fluids are often categorized on the basis of the shape of their phase diagram. | 7 | Physical Chemistry |
Plant roots acidify soil by releasing protons and organic acids so as to chemically weather soil minerals. Decaying remains of dead plants on soil may also form organic acids which contribute to soil acidification. Acidification from leaf litter on the O-horizon is more pronounced under coniferous trees such as pine, spruce and fir, which return fewer base cations to the soil, rather than under deciduous trees; however, soil pH differences attributed to vegetation often preexisted that vegetation, and help select for species which tolerate them. Calcium accumulation in existing biomass also strongly affects soil pH - a factor which can vary from species to species. | 9 | Geochemistry |
This enzyme is encoded by MTHFD1L and reversibly interconverts ADP + phosphate + 10-formyltetrahydrofolate to ATP + formate + tetrahydrofolate. | 1 | Biochemistry |
An organogel is a non-crystalline, non-glassy thermoreversible (thermoplastic) solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network. The liquid can be, for example, an organic solvent, mineral oil, or vegetable oil. The solubility and particle dimensions of the structurant are important characteristics for the elastic properties and firmness of the organogel. Often, these systems are based on self-assembly of the structurant molecules. (An example of formation of an undesired thermoreversible network is the occurrence of wax crystallization in petroleum.)
Organogels have potential for use in a number of applications, such as in pharmaceuticals, cosmetics, art conservation, and food. | 7 | Physical Chemistry |
Agmatine hypoglycemic effects are the result of simultaneous modulation of several molecular mechanisms involved in blood glucose regulation. | 1 | Biochemistry |
The Toxicity/Residue Database is maintained by the U.S. EPA and is a database for the prediction of toxicity of organic and inorganic chemicals to aquatic organisms. This data base was developed by the EPA Duluth office and became operational in 1999. The data base is derived from more than 500 peer-reviewed references and is a collection of their findings on roughly 200 chemicals and 190 species both marine and fresh water. Data regarding organism response endpoints or effects are measured as the concentration of chemical in the tissue of the test organism at the time which effects such as lethality, metabolic depression, or increased respiration occur. More than 3,000 effects may be queried from a small piece of downloaded software to gather survival, growth or reproductive endpoint effect data. | 1 | Biochemistry |
The process of separating mixtures of chemical compounds by passing them through a column that contains a solid stationary phase that was eluted with a mobile phase (column chromatography) was well known at that time. Chromatographic separation was considered to occur by an adsorption process whereby compounds adhered to a solid media and were washed off the column with a solvent, mixture of solvents, or solvent gradient. In contrast, Martin and Synge developed and described a chromatographic separation process whereby compounds were partitioned between two liquid phases similar to the separatory funnel liquid-liquid separation dynamic. This was an important departure, both in theory and inder equilibrium conditions. Martin and Synge initially attempted to devise a method of performing a sequential liquid-liquid extraction with serially connected glass vessels that functioned as separatory funnels. The seminal article presenting their early studies described a rather complicated instrument that allowed partitioning of amino acids between water and chloroform phases. The process was termed "counter-current liquid-liquid extraction." Martin and Synge described the theory of this technique in reference to continuous fractional distillation described by Randall and Longtin. This approach was deemed too cumbersome, so they developed a method of absorbing water onto silica gel as the stationary phase and using a solvent, such as chloroform, as the mobile phase. This work was published in 1941 as "a new form of chromatogram employing two liquid phases." The article describes both the theory in terms of the partition coefficient of a compound, and the application of the process to the separation of amino acids on a water-impregnated silica column eluted with a water:chloroform:n-butanol solvent mixture. | 3 | Analytical Chemistry |
Within statistical mechanics, the LCST may be modeled theoretically via the lattice fluid model, an extension of Flory–Huggins solution theory, that incorporates vacancies, and thus accounts for variable density and compressibility effects. | 7 | Physical Chemistry |
Carbaminohemoglobin (carbaminohaemoglobin BrE) (COHb, also known as carbhemoglobin and carbohemoglobin) is a compound of hemoglobin and carbon dioxide, and is one of the forms in which carbon dioxide exists in the blood. Twenty-three percent of carbon dioxide is carried in blood this way (70% is converted into bicarbonate by carbonic anhydrase and then carried in plasma, 7% carried as free CO, dissolved in plasma). | 1 | Biochemistry |
Ants typically use trail pheromones to coordinate roles like nest defense and foraging. Ants can produce a trail of defensive secretions that trigger an alarm response within their nestmates. In regards to foraging, an ant can communicate the quality of a food source to its colony; the more rewarding a food source is, the higher the concentration of the trail produced. Additionally, some species, like Lasius niger ants, can "eavesdrop" on the trails produced by another species in order to procure food.
Myrmicine ants produce their trail pheromones through their poison glands. The major component in the trail pheromones secreted by Pristomyrex pungens is 6-n-pentyl-2-pyrone; several monoterpenes were also found in the secretion, but they provided only marginal effects when combined with the former. The major components found in the secretions of Aphaenogaster rudis include anabaseine, anabasine, and 2,3'-bipyridyl, though the third contributes less than the other two. When secreted, this trail pheromone does not recruit ants directly from their nest; instead, worker ants may stumble upon to the trail unintentionally and follow it thereafter to the food source. | 1 | Biochemistry |
In oxidative phosphorylation, electrons are transferred from an electron donor such as NADH to an acceptor such as O through an electron transport chain, releasing energy. In photophosphorylation, the energy of sunlight is used to create a high-energy electron donor which can subsequently reduce oxidized components and couple to ATP synthesis via proton translocation by the electron transport chain.
Photosynthetic electron transport chains, like the mitochondrial chain, can be considered as a special case of the bacterial systems. They use mobile, lipid-soluble quinone carriers (phylloquinone and plastoquinone) and mobile, water-soluble carriers (cytochromes). They also contain a proton pump. The proton pump in all photosynthetic chains resembles mitochondrial Complex III. The commonly-held theory of symbiogenesis proposes that both organelles descended from bacteria. | 1 | Biochemistry |
* Depurination is caused by hydrolysis and results in loss if the purine base of a nucleic acid. DNA is more prone to this, as the transition state in the depurination reaction has much greater energy in RNA.
* Tautomerization is a chemical reaction that is primarily relevant in the behavior of amino acids and nucleic acids. Both of which are correlated to DNA and RNA. The process of tautomerization of DNA bases occurs during DNA replication. The ability for the wrong tautomer of one of the standard nucleic bases to mispair causes a mutation during the process of DNA replication which can be cytotoxic or mutagenic to the cell. These mispairings can result in transition, transversion, frameshift, deletion, and/or duplication mutations. Some diseases that result from tautomerization induced DNA lesions include Kearns-Sayre syndrome, Fragile X syndrome, Kennedy disease, and Huntington's disease.
* Cytosine deamination commonly occurs under physiological conditions and essentially is the deamination of cytosine. This process yields uracil as its product, which is not a base pair found within DNA. This process causes extensive DNA damage. The rate of this process is slowed down significantly in double-stranded DNA compared to single-stranded DNA. | 1 | Biochemistry |
Chitin is a good inducer of plant defense mechanisms for controlling diseases. It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields. | 1 | Biochemistry |
* Deepening of the voice
* Growth of facial and body hair
* Male-pattern baldness
* Enlargement of the clitoris
* Breast atrophy – possible shrinking and/or softening of breasts | 1 | Biochemistry |
In operating batteries and fuel cells, charge transfer coefficient is the parameter that signifies the fraction of overpotential that affects the current density. This parameter has had a mysterious significance in electrochemical kinetics for over three quarters of the previous century. It can also be said that charge transfer coefficient is the heart of electrode kinetics. | 7 | Physical Chemistry |
The earliest polymerizations of fluorene were oxidative polymerization with AlCl or FeCl, and more commonly electropolymerization. Electropolymerization is an easy route to obtain thin, insoluble conducting polymer films. However, this technique has a few disadvantages in that it does not provide controlled chain growth polymerizations, and processing and characterization are difficult as a result of its insolubility. Oxidative polymerization produces a similarly poor site-selectivity on the monomer for chain growth resulting in poor control over the regularity of the polymers structure. However, oxidative polymerization does produce soluble polymers (from side-chain containing monomers) which are more easily characterized with nuclear magnetic resonance. | 7 | Physical Chemistry |
Pseudocopulation is achieved when a flower successfully mimics the appearance and the pheromones emitted by the female of an insect species. The chemicals emitted by the mimicking species work to draw these pollinators to the plant and increase the number of visits to and time spent on the flower. This increases the chances that pollen will efficiently stick to the organism or that pollen already stuck to it is transferred to the plant.
In one study on mining bees (Andrena nigroaenea) and spider orchids (Ophrys sphegodes Mill.) it was found that unpollinated spider orchids emitted odours that consisted of hydrocarbons that were an exact match for the odours released by virgin female bees. As a result, male mining bees are extremely attracted to the flowers of the spider orchid, triggering more quick visits to the flower and in some cases the male bees attempt copulation, either getting themselves sufficiently covered in pollen or successfully transferring it to another plant. | 1 | Biochemistry |
This method is designed to be robust where the other methods don't even provide any results in particular. As such, it is indispensable, since it is the only way to use the sessile drop technique on very high surface energy solids. Its major drawback is the fact that it is far more complex, both in its mathematics and experimentally. The Schultz theory requires one to account for many more factors, as there is now the unusual interaction of the probe liquid phase with the surrounding liquid. | 7 | Physical Chemistry |
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