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A dipole can align to stabilize or destabilize the formation or loss of a charge, thereby decreasing (if stabilized) or increasing (if destabilized) the activation barrier to a chemical event. Field effects can therefore tune the acidity or basicity of bonds within their fields by donating or withdrawing charge density. With respect to acidity, a common trend to note is that, inductively, an electron-withdrawing substituent in the vicinity of an acidic proton will lower the pKa (i.e. increase the acidity) and, correspondingly, an electron-donating substituent will raise the pKa. The reorganization of charge due to field effects will have the same result. An electric dipole field propagated through the space around, or in the middle of, a molecule in the direction of an acidic proton will decrease the acidity, while a dipole pointed away will increase the acidity and concomitantly elongate the X-H bond. These effects can therefore help to tune the acidity/basicity of a molecule to protonate/deprotonate a specific compound, or enhance hydrogen bond-donor ability for molecular recognition or anion sensing applications. Field effects have also been shown in substituted arenes to dominate the electrostatic potential maps, which are maps of electron density used to explain intermolecular interactions. | 7 | Physical Chemistry |
An isotopic tracer, (also "isotopic marker" or "isotopic label"), is used in chemistry and biochemistry to help understand chemical reactions and interactions. In this technique, one or more of the atoms of the molecule of interest is substituted for an atom of the same chemical element, but of a different isotope (like a radioactive isotope used in radioactive tracing). Because the labeled atom has the same number of protons, it will behave in almost exactly the same way as its unlabeled counterpart and, with few exceptions, will not interfere with the reaction under investigation. The difference in the number of neutrons, however, means that it can be detected separately from the other atoms of the same element.
Nuclear magnetic resonance (NMR) and mass spectrometry (MS) are used to investigate the mechanisms of chemical reactions. NMR and MS detects isotopic differences, which allows information about the position of the labeled atoms in the products' structure to be determined. With information on the positioning of the isotopic atoms in the products, the reaction pathway the initial metabolites utilize to convert into the products can be determined. Radioactive isotopes can be tested using the autoradiographs of gels in gel electrophoresis. The radiation emitted by compounds containing the radioactive isotopes darkens a piece of photographic film, recording the position of the labeled compounds relative to one another in the gel.
Isotope tracers are commonly used in the form of isotope ratios. By studying the ratio between two isotopes of the same element, we avoid effects involving the overall abundance of the element, which usually swamp the much smaller variations in isotopic abundances. Isotopic tracers are some of the most important tools in geology because they can be used to understand complex mixing processes in earth systems. Further discussion of the application of isotopic tracers in geology is covered under the heading of isotope geochemistry.
Isotopic tracers are usually subdivided into two categories: stable isotope tracers and radiogenic isotope tracers. Stable isotope tracers involve only non-radiogenic isotopes and usually are mass-dependent. In theory, any element with two stable isotopes can be used as an isotopic tracer. However, the most commonly used stable isotope tracers involve relatively light isotopes, which readily undergo fractionation in natural systems. See also isotopic signature. A radiogenic isotope tracer involves an isotope produced by radioactive decay, which is usually in a ratio with a non-radiogenic isotope (whose abundance in the earth does not vary due to radioactive decay). | 7 | Physical Chemistry |
In the future alternative marker technologies will need to be used more often to, at the least, assuage concerns about their persistence into the final product. It is also possible that markers will be replaced entirely by future techniques which use removable markers, and others which do not use markers at all, instead relying on co-transformation, homologous recombination, and recombinase-mediated excision. | 1 | Biochemistry |
In freshwater or estuarine systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia, levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species. Nitrate toxicity remains a subject of debate.
In most cases of excess nitrate concentrations in aquatic systems, the primary sources are wastewater discharges, as well as surface runoff from agricultural or landscaped areas that have received excess nitrate fertilizer. The resulting eutrophication and algae blooms result in anoxia and dead zones. As a consequence, as nitrate forms a component of total dissolved solids, they are widely used as an indicator of water quality. | 0 | Organic Chemistry |
For the past 30 years, isothermal titration calorimetry has been used in a wide array of fields. In the old days, this technique was used to determine fundamental thermodynamic values for basic small molecular interactions. In recent years, ITC has been used in more industrially applicable areas, such as drug discovery and testing synthetic materials. Although it is still heavily used in fundamental chemistry, the trend has shifted over to the biological side, where label-free and buffer independent values are relatively harder to achieve. | 7 | Physical Chemistry |
Astressin-B is a nonselective corticotropin releasing hormone antagonist that reduces the synthesis of adrenocorticotropic hormone and cortisol.
It reduces the synthesis of adrenocorticotropic hormone and improves the sexual drive of rats under stressing conditions.
Astressin-B is able to delay the emptying of solid food in mice. Astressin-B can prevent the release of adrenocorticotropic hormone in mice due to shock, alcohol and endotoxemia.
Treatment with astressin-B caused the sudden growth of hair in mice bred for a propensity for stress. | 1 | Biochemistry |
In the sense that DNA replication must occur if genetic material is to be provided for the progeny of any cell, whether somatic or reproductive, the copying from DNA to DNA arguably is the fundamental step in information transfer. A complex group of proteins called the replisome performs the replication of the information from the parent strand to the complementary daughter strand. | 1 | Biochemistry |
Archaeal transcription shares eukaryotic and bacterial ties. With eukaryotes, it shares similarities with its initiation factors that help transcription identify appropriate sequences such as TATA box homologs as well as factors that maintain transcription elongation. However, additional transcription factors similar to those found in bacteria are needed for the whole process to occur.
In terms of transcription termination, the archaeal genome is unique in that it is sensitive to both intrinsic termination and factor-dependent termination. Bioinformatic analysis has shown that approximately half of the genes and operons in Archaea arrange themselves into signals or contain signals for intrinsic termination. Archaeal RNA polymerase is responsive to intrinsic signals both in vivo and in vitro such as the poly-U-rich regions. However, unlike bacterial intrinsic termination, no specific RNA structure or hairpin is needed. The surrounding environment and other genome factors can still influence the termination.
Factor-dependent termination in archaea is also distinct from factor-dependent termination in bacteria. The terminational factor aCASP1 (also known as FttA) recognizes poly-U-rich regions, probably cooperating with the "intrinsic" mode to achieve more efficient termination. | 1 | Biochemistry |
β-Oxidation of unsaturated fatty acids poses a problem since the location of a cis-bond can prevent the formation of a trans-Δ bond which is essential for continuation of β-Oxidation as this conformation is ideal for enzyme catalysis. This is handled by additional two enzymes, Enoyl CoA isomerase and 2,4 Dienoyl CoA reductase.
β-oxidation occurs normally until the acyl CoA (because of the presence of a double bond) is not an appropriate substrate for acyl CoA dehydrogenase, or enoyl CoA hydratase:
* If the acyl CoA contains a cis-Δ bond, then cis-Δ-Enoyl CoA isomerase will convert the bond to a trans-Δ bond, which is a regular substrate.
* If the acyl CoA contains a cis-Δ double bond, then its dehydrogenation yields a 2,4-dienoyl intermediate, which is not a substrate for enoyl CoA hydratase. However, the enzyme 2,4 Dienoyl CoA reductase reduces the intermediate, using NADPH, into trans-Δ-enoyl CoA. This compound is converted into a suitable intermediate by 3,2-Enoyl CoA isomerase and β-Oxidation continues. | 1 | Biochemistry |
Gene therapy is a promising treatment for a number of diseases where a "normal" gene carried by the vector is inserted into the genome, to replace an "abnormal" gene or supplement the expression of particular gene. Viral vectors are generally used but other nonviral methods of delivery are being developed. The treatment is still a risky option due to the viral vector used which can cause ill-effects, for example giving rise to insertional mutation that can result in cancer. However, there have been promising results. | 1 | Biochemistry |
The term amphibolism () is used to describe a biochemical pathway that involves both catabolism and anabolism. Catabolism is a degradative phase of metabolism in which large molecules are converted into smaller and simpler molecules, which involves two types of reactions. First, hydrolysis reactions, in which catabolism is the breaking apart of molecules into smaller molecules to release energy. Examples of catabolic reactions are digestion and cellular respiration, where sugars and fats are broken down for energy. Breaking down a protein into amino acids, or a triglyceride into fatty acids, or a disaccharide into monosaccharides are all hydrolysis or catabolic reactions. Second, oxidation reactions involve the removal of hydrogens and electrons from an organic molecule. Anabolism is the biosynthesis phase of metabolism in which smaller simple precursors are converted to large and complex molecules of the cell. Anabolism has two classes of reactions. The first are dehydration synthesis reactions; these involve the joining of smaller molecules together to form larger, more complex molecules. These include the formation of carbohydrates, proteins, lipids and nucleic acids. The second are reduction reactions, in which hydrogens and electrons are added to a molecule. Whenever that is done, molecules gain energy.
The term amphibolism was proposed by B. Davis in 1961 to emphasise the dual metabolic role of such pathways. These pathways are considered to be central metabolic pathways which provide, from catabolic sequences, the intermediates which form the substrate of the metabolic processes. | 1 | Biochemistry |
Sodium amide induces the loss of two equivalents of hydrogen bromide from a vicinal dibromoalkane to give a carbon–carbon triple bond, as in a preparation of phenylacetylene.
Usually two equivalents of sodium amide yields the desired alkyne. Three equivalents are necessary in the preparation of a terminal alkynes because the terminal CH of the resulting alkyne protonates an equivalent amount of base.
Hydrogen chloride and ethanol can also be eliminated in this way, as in the preparation of 1-ethoxy-1-butyne. | 0 | Organic Chemistry |
The first step in Gateway cloning is the preparation of a Gateway Entry clone. There are a few different ways to make entry clone.
# Gateway attB1 and attB2 sequences are added to the 5 and 3 end of a gene fragment, respectively, using gene-specific PCR primers and PCR amplification. The PCR amplification products are then mixed with a proprietary mixture of plasmids called Gateway "Donor vectors" (Invitrogen terminology) and proprietary "BP Clonase" enzymes. The enzyme mix catalyzes the recombination and insertion of the PCR product containing the attB sequence into the attP recombination sites in the Gateway Donor vector. When the cassette is part of the target plasmid, it is referred to as an "Entry clone" in Gateway nomenclature and the recombination sequences are referred to as Gateway "attL" type.
# A short end containing attL is added using the TOPO method, a technique in which DNA fragments are cloned into specific vectors without the need for DNA ligases.
# The desired DNA sequence can be cloned into a multicloning site containing attL using restriction enzyme.
The second step in Gateway cloning is the preparation of a Gateway Destination vector. It is important to choose the target vector that best suits your target when preparing the expression clone. The gene cassette in the Gateway Entry clone can then be simply and efficiently transferred into any Gateway Destination vector (Invitrogen nomenclature for any Gateway plasmid that contains Gateway “attR” recombination sequences and elements such as promoters and epitope tags, but not ORFs) using the proprietary enzyme mix, “LR Clonase”. Thousands of Gateway Destination plasmids have been made and are freely shared amongst researchers across the world. Gateway Destination vectors are similar to classical expression vectors containing multiple cloning sites, before the insertion of a gene of interest, using restriction enzyme digestion and ligation. Gateway Destination vectors are commercially available from Invitrogen, EMD (Novagen) and Covalys.
The third step in Gateway cloning is the preparation of express your gene of interest. Make sure to use sequencing or a restriction digest to check the integrity of your expression clone. Once your construct is working, you can transform or transfect the cells you intend to employ in your investigations.
Since Gateway cloning uses patented recombination sequences, and proprietary enzyme mixes available only from Invitrogen, the technology does not allow researchers to switch vendors and contributes to the lock-in effect of all such patented procedures.
To summarize the different steps involved in Gateway cloning:
* Gateway BP reaction: PCR-product with flanking att B sites (this step can also use other methods of DNA isolation, such as restriction-digestion) + Donor vector containing attP sites + BP clonase => Gateway Entry clone, containing att L sites, flanking gene of interest
* Gateway LR reaction: Entry clone containing att L sites + Destination vector containing att R sites, and promoters and tags + LR clonase => Expression clone containing attB sites, flanking gene of interest, ready for gene expression. | 1 | Biochemistry |
Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame).
Thermal spraying can provide thick coatings (approx. thickness range is 20 microns to several mm, depending on the process and feedstock), over a large area at high deposition rate as compared to other coating processes such as electroplating, physical and chemical vapor deposition. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites. They are fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge is usually used as the source of energy for thermal spraying. Resulting coatings are made by the accumulation of numerous sprayed particles. The surface may not heat up significantly, allowing the coating of flammable substances.
Coating quality is usually assessed by measuring its porosity, oxide content, macro and micro-hardness, bond strength and surface roughness. Generally, the coating quality increases with increasing particle velocities. | 8 | Metallurgy |
* R.J. Talling, R.J. Dashwood, M. Jackson, D. Dye, [https://www.sciencedirect.com/science/article/pii/S1359645408008082 On the mechanism of superelasticity in Gum metal], Acta Materialia, Volume 57, Issue 4, 2009, Pages 1188-1198, ISSN 1359-6454, doi: 10.1016/j.actamat.2008.11.013.
* N.G. Jones, R.J. Dashwood, M. Jackson, D. Dye, [https://www.sciencedirect.com/science/article/pii/S1359645409002559 β Phase decomposition in Ti–5Al–5Mo–5V–3Cr], Acta Materialia, Volume 57, Issue 13, 2009, Pages 3830-3839, ISSN 1359-6454, doi: 10.1016/j.actamat.2009.04.031.
* N.G. Jones, R.J. Dashwood, D. Dye, M. Jackson, [https://www.sciencedirect.com/science/article/pii/S0921509308001007 Thermomechanical processing of Ti–5Al–5Mo–5V–3Cr], Materials Science and Engineering: A, Volume 490, Issues 1–2, 2008, Pages 369-377, ISSN 0921-5093, doi: 10.1016/j.msea.2008.01.055.
* K.M. Rahman, V.A. Vorontsov, D. Dye, [https://www.sciencedirect.com/science/article/pii/S1359645415001081 The effect of grain size on the twin initiation stress in a TWIP steel], Acta Materialia, Volume 89, 2015, Pages 247-257, ISSN 1359-6454, doi: 10.1016/j.actamat.2015.02.008. | 8 | Metallurgy |
It is important to note that A-values do not predict the physical size of a molecule, only the steric effect. For example, the tert-butyl group (A-value=4.9) has a larger A-value than the trimethylsilyl group (A-value=2.5), yet the tert-butyl group actually occupies less space. This difference can be attributed to the longer length of the carbon–silicon bond as compared to the carbon–carbon bond of the tert-butyl group. The longer bond allows for less interactions with neighboring substituents, which effectively makes the trimethylsilyl group less sterically hindering, thus, lowering its A-value. This can also be seen when comparing the halogens. Bromine, iodine, and chlorine all have similar A-values even though their atomic radii differ. A-values then, predict the apparent size of a substituent, and the relative apparent sizes determine the differences in steric effects between compounds. Thus, A-values are useful tools in determining compound reactivity in chemical reactions. | 4 | Stereochemistry |
In addition to the scanning forms of Fourier-transform spectrometers, there are a number of stationary or self-scanned forms. While the analysis of the interferometric output is similar to that of the typical scanning interferometer, significant differences apply, as shown in the published analyses. Some stationary forms retain the Fellgett multiplex advantage, and their use in the spectral region where detector noise limits apply is similar to the scanning forms of the FTS. In the photon-noise limited region, the application of stationary interferometers is dictated by specific consideration for the spectral region and the application. | 7 | Physical Chemistry |
Metastasis is a major cause of cancer deaths, and strategies to prevent or halt invasion are lacking. One study showed that autocrine PDGFR signaling plays an essential role in epithelial-mesenchymal transition (EMT) maintenance in vitro, which is known to correlate well with metastasis in vivo. The authors showed that the metastatic potential of oncogenic mammary epithelial cells required an autocrine PDGF/PDGFR signaling loop, and that cooperation of autocrine PDGFR signaling with oncogenic was required for survival during EMT. Autocrine PDGFR signaling also contributes to maintenance of EMT, possibly through activation of STAT1 and other distinct pathways. In addition, expression of PDGFRα and -β correlated with invasive behavior in human mammary carcinomas. This indicates the numerous pathways through which autocrine signaling can regulate metastatic processes in a tumor. | 1 | Biochemistry |
In the iron and steel industry, direct reduction is a set of processes for obtaining iron from iron ore, by reducing iron oxides without melting the metal. The resulting product is pre-reduced iron ore.
Historically, direct reduction was used to obtain a burr in a low furnace. At the beginning of the 20th century, this process was abandoned in favor of the blast furnace, which produces iron in two stages (reduction-melting to produce cast iron, followed by refining in a converter).
However, various processes were developed in the course of the 20th century and, since the 1970s, the production of pre-reduced iron ore has undergone remarkable industrial development, notably with the rise of the Midrex process. Designed to replace the blast furnace, these processes have so far only proved profitable in certain economic contexts, which still limits this sector to less than 5% of world steel production. | 8 | Metallurgy |
There is no limit to the number of possible organic reactions and mechanisms. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types. Some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway. This overview isn't intended to include every single organic reaction. Rather, it is intended to cover the basic reactions.
In condensation reactions a small molecule, usually water, is split off when two reactants combine in a chemical reaction. The opposite reaction, when water is consumed in a reaction, is called hydrolysis. Many polymerization reactions are derived from organic reactions. They are divided into addition polymerizations and step-growth polymerizations.
In general the stepwise progression of reaction mechanisms can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition to intermediates and products. | 0 | Organic Chemistry |
Abiotic factors that can damage plants include heat, freezing, flooding, lightning strikes, ozone gas, and pollutant chemicals.
Heat can kill any plant, given a sufficient temperature. Alpine plants tend to die at around 47 Celsius; temperate plants at around 51 Celsius; and tropical plants at nearly 58 Celsius: but there is some overlap depending on species. Similarly among cereal crops, temperate barley and oat die at around 49 Celsius, but tropical maize at 55 Celsius.
Freezing affects plants variously, according to each species' ability to resist frost damage. Many forbs, including many garden flowers, are tender with little tolerance to frost, and die or are seriously damaged when frozen. Many woody plants are able to supercool, with tough buds and stems containing molecules that lower the freezing point or help to prevent the nucleation of ice crystals, and cell walls that mechanically protect cells against freezing.
Flooding of soil quickly kills or injures many plants. The leaves become yellow (chlorosis) and die, progressively up the stem, within about five days after the roots are flooded. The roots lose the ability to absorb water and nutrients.
Lightning strikes kill or injure plants, from root crops like beet and potato, which are instantly cooked in the ground, to trees such as coconut, through effects such as sudden heat and pressure shock waves created when water inside the plant flashes to steam. This can rupture stems and scorch any plant parts.
Ozone, a gas, causes injury to leaves at concentrations from as little as 0.1 part per million in the atmosphere, such as may be found in or near large cities.
It is one of many pollutant chemicals that can damage plants. | 1 | Biochemistry |
IUPAC nomenclature is used in scientific publications, and in writings where precise identification of the substance is important. In naming simple alcohols, the name of the alkane chain loses the terminal e and adds the suffix -ol, e.g., as in "ethanol" from the alkane chain name "ethane". When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the -ol: propan-1-ol for , propan-2-ol for . If a higher priority group is present (such as an aldehyde, ketone, or carboxylic acid), then the prefix hydroxy-is used, e.g., as in 1-hydroxy-2-propanone (). Compounds having more than one hydroxy group are called polyols. They are named using suffixes -diol, -triol, etc., following a list of the position numbers of the hydroxyl groups, as in propane-1,2-diol for CHCH(OH)CHOH (propylene glycol).
In cases where the hydroxy group is bonded to an sp carbon on an aromatic ring, the molecule is classified separately as a phenol and is named using the IUPAC rules for naming phenols. Phenols have distinct properties and are not classified as alcohols. | 0 | Organic Chemistry |
Detonation gun spraying like any other industrial process carries with it a number of safety hazards that need to be managed correctly in order to ensure operator safety whilst in use. These safety precautions primarily fall into the following categories and the hazard minimisation techniques suggested, in some cases have a positive effect on the resultant detonation spray coating. For example, having to automate the spraying process means that a very even and consistent spray coating can be achieved. | 8 | Metallurgy |
The COLUMBUS PROGRAMS maintain a program unique style that distinguish itself from most other quantum chemistry programs.
The program suite is a collection of a number of programs coded in Fortran, each can be executed independently. These programs communicate through files. Perl scripts are provided to prepare input files and to link these programs together to perform common tasks such as single point energy calculation, geometry optimization, normal mode analysis, etc. This style provides very high degree of flexibility which is embraced by advanced users. The open style allows new components to be added to the program suite with ease. However, such flexibility also increased the complexity of input file preparation and execution, making it very difficult for new users. | 7 | Physical Chemistry |
The total Hamiltonian of an atom in a magnetic field is
where is the unperturbed Hamiltonian of the atom, and is the perturbation due to the magnetic field:
where is the magnetic moment of the atom. The magnetic moment consists of the electronic and nuclear parts; however, the latter is many orders of magnitude smaller and will be neglected here. Therefore,
where is the Bohr magneton, is the total electronic angular momentum, and is the Landé g-factor.
A more accurate approach is to take into account that the operator of the magnetic moment of an electron is a sum of the contributions of the orbital angular momentum and the spin angular momentum , with each multiplied by the appropriate gyromagnetic ratio:
where and (the latter is called the anomalous gyromagnetic ratio; the deviation of the value from 2 is due to the effects of quantum electrodynamics). In the case of the LS coupling, one can sum over all electrons in the atom:
where and are the total spin momentum and spin of the atom, and averaging is done over a state with a given value of the total angular momentum.
If the interaction term is small (less than the fine structure), it can be treated as a perturbation; this is the Zeeman effect proper. In the Paschen–Back effect, described below, exceeds the LS coupling significantly (but is still small compared to ). In ultra-strong magnetic fields, the magnetic-field interaction may exceed , in which case the atom can no longer exist in its normal meaning, and one talks about Landau levels instead. There are intermediate cases which are more complex than these limit cases. | 7 | Physical Chemistry |
Precipitation of minerals is affected by water solubility within silicate melts, which typically exists as hydroxyl groups bound to Si or Group 1 and Group 2 cations in concentrations ranging from approximately 6-7 wt. %. Specifically, the equilibrium of water and dissolved oxygen yields hydroxides, where the K has been approximated between 0.1 and 0.3.
This inherent solubility is low yet varies greatly depending on the pressure of the system. Rhyolitic magmas have the highest solubility, ranging from approximately 0% at the surface to nearly 10% at 1100 °C and 5 kbar. Degassing occurs when hydrous magma is uplifted, gradually converting the dissolved water to aqueous phase. This aqueous phase is typically abundant in volatiles, metals (copper, lead, zinc, silver and gold), and Group 1 and Group 2 cations. Dependent on which cation the hydroxyl is bound to, it significantly impacts the properties of a volcanic eruption, particularly its explosiveness. During unusually high temperature and pressure conditions exceeding 374 °C and 218 bar, water enters a supercritical fluid state and becomes no longer a liquid or a gas. | 9 | Geochemistry |
With non-covalent imprinting, interaction forces between template molecule and functional monomer are the same as the interaction forces between the polymer matrix and analyte. The forces involved in this procedure can include hydrogen bonds, dipole dipole interactions, and induced dipole forces. This method is the most widely used approach to create MIPs due to easy preparation and the wide variety of functional monomers that can be bound to the template molecule. Among the functional groups, methacrylic acid is the most commonly used compound due to its ability to interact with other functional groups. Another way to alternate the non-covalent interaction between the template molecule and polymer is through the technique ‘bite and switch’ developed by Professor Sergey A. Piletsk<nowiki/>y and Sreenath Subrahmanyam. In this process, functional groups first non-covalently bond with the binding site, but during the rebinding step, the polymer matrix forms irreversible covalent bonds with the target molecule. | 6 | Supramolecular Chemistry |
In 2005, the water supply to the city of Harbin in China with a population of almost nine million people, was cut off because of a major benzene exposure. Benzene leaked into the Songhua River, which supplies drinking water to the city, after an explosion at a China National Petroleum Corporation (CNPC) factory in the city of Jilin on 13 November 2005.
When plastic water pipes are subject to high heat, the water may be contaminated with benzene. | 2 | Environmental Chemistry |
Eslicarbazepine acetate was developed by the Portuguese pharmaceutical company Bial. In early 2009, Bial sold the marketing rights in Europe to the Japanese company Eisai. The drug was approved in the European Union in April 2009 under the trade names Zebinix and Exalief, but was marketed only under the first name. In the US it is marketed by Sunovion (formerly Sepracor) and was approved in November 2013. | 4 | Stereochemistry |
At 16 billion Scoville units, resiniferatoxin is rather toxic and can inflict chemical burns in minute quantities. The primary action of resiniferatoxin is to activate sensory neurons responsible for the perception of pain. It is currently the most potent TRPV1 agonist known, with ~500x higher binding affinity for TRPV1 than capsaicin, the active ingredient in hot chili peppers such as those produced by Capsicum annuum. For rats, LD50 through oral ingestion is 148.1 mg/kg. It causes severe burning pain in sub-microgram (less than 1/1,000,000th of a gram) quantities when ingested orally. | 0 | Organic Chemistry |
In 2021, dextrorphan was identified in >75% of sludge samples taken from 12 wastewater treatment plants in California. The same study associated dextrorphan with estrogenic activity by using predictive modelling, before observing it in in vitro. | 4 | Stereochemistry |
Cells secrete ATP to communicate with other cells in a process called purinergic signalling. ATP serves as a neurotransmitter in many parts of the nervous system, modulates ciliary beating, affects vascular oxygen supply etc. ATP is either secreted directly across the cell membrane through channel proteins or is pumped into vesicles which then fuse with the membrane. Cells detect ATP using the purinergic receptor proteins P2X and P2Y. | 1 | Biochemistry |
Chitin-glucan complex (CGC) is a copolymer (polysaccharide) that makes up fungal cell walls, consisting of covalently-bonded chitin and branched 1,3/1,6-ß-D-glucan. CGCs are alkaline-insoluble. Different species of fungi have different structural compositions of chitin and β-glucan making up the CGCs in their cell walls. Soil composition and other environmental factors can also affect the ratio of chitin to β-glucan found in the CGC. Fungal cell walls may also contain chitosan-glucan complexes, which are similar copolymers but have chitosan instead of chitin. Chitin and chitosan are closely related molecules: greater than 40% of the polymer chain of chitin is made of acetylated glucosamine units, whereas greater than 60% of chitosan is made of deacetylated glucosamine units.
In their natural form, CGCs provide structural support to the fungal cell wall. Biomedical applications of CGCs have been studied, including the immunostimulant properties of A. fumigatus, as well as successful antibacterial activity against S. typhimurium by CGCs from A. niger and M. rouxii. There is some evidence that CGCs can act as an effective prebiotic, as it was tested on growing 100 different bifidobacterial strains as well as on rats in vivo. CGCs have many industrial applications, such as in food, cosmetics, and textiles industries, because they can be prepared easily without toxins. As food additives, they are commonly used due to their ability to adsorb heavy metal ions. Additionally, CGCs are produced in high volume industrially because they can be broken down into their constitutive components by hydrolysis, producing pure chitin (or chitosan) and β-glucans.
Rather than being produced from animal parts, pure chitin can be extracted from the cell walls of the fungus Pichia pastoris, recently classified as Komagataella pastoris. Unlike chitin extracted from crustaceans, for example, this chitin contains no heavy metals. A study revealed that the complex exhibits traces of α-chitin in the molecular structure via x-ray diffraction. The similarities in structure and physical properties suggest that the complex is a suitable alternative to crustacean-based chitin as fungi are a more feasible and reliable source of raw materials. | 1 | Biochemistry |
Nervous system control over hormone release is based in the hypothalamus, from which the neurons that populate the pariventricular and arcuate nuclei originate. These neurons project to the median eminence, where they secrete releasing hormones into the hypophysial portal system connecting the hypothalamus with the pituitary gland. There, they dictate endocrine function via the four Hypothalamic-Pituitary-Glandular axes. Recent studies have begun to offer evidence that many pituitary hormones which have been observed to be released episodically are preceded by pulsatile secretion of their associated releasing hormone from the hypothalamus in a similar pulsatile fashion. Novel research into the cellular mechanisms associated with pituitary hormone pulsatility, such as that observed for Leutinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), have indicated similar pulses into the hypophyseal vessels of Gonadotropin Releasing Hormone (GnRH). | 1 | Biochemistry |
Polymers that can crystallize are (with the exception of PP) guarantee to obtain this effect, mainly due to their ordering capacity, which is reflected in the crystallinity, the crystals have affinity for their constituent elements and form new bonds these achieve anchoring forces that give stability to the temporary form. | 7 | Physical Chemistry |
Anoxic conditions result from a combination of environmental conditions including density stratification, inputs of organic material or other reducing agents, and physical barriers to water circulation. In fjords, shallow sills at the entrance may prevent circulation, while at continental boundaries, circulation may be especially low while organic material input from production at upper levels is exceptionally high. In wastewater treatment, the absence of oxygen alone is indicated anoxic while the term anaerobic is used to indicate the absence of any common electron acceptor such as nitrate, sulfate or oxygen.
When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water, is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate. This results in the byproduct of hydrogen sulfide (HS), a chemical toxic to most biota and responsible for the characteristic "rotten egg" smell and dark black sediment color:
:2 CHO + → 2 + HS + chemical energy
These sulfides will mostly be oxidized to either sulfates (~90%) in more oxygen-rich water or precipitated and converted into pyrite (~10%), according to the following chemical equations:
Some chemolithotrophs can also facilitate the oxidation of hydrogen sulfide into elemental sulfur, according to the following chemical equation:
:HS + O → S + HO
Anoxia is quite common in muddy ocean bottoms where there are both high amounts of organic matter and low levels of inflow of oxygenated water through the sediment. Below a few centimeters from the surface the interstitial water (water between sediment) is oxygen free.
Anoxia is further influenced by biochemical oxygen demand (BOD), which is the amount of oxygen used by marine organisms in the process of breaking down organic matter. BOD is influenced by the type of organisms present, the pH of the water, temperature, and the type of organic matter present in the area. BOD is directly related to the amount of dissolved oxygen available, especially in smaller bodies of water such as rivers and streams. As BOD increases, available oxygen decreases. This causes stress on larger organisms. BOD comes from natural and anthropogenic sources, including: dead organisms, manure, wastewater, and urban runoff. | 9 | Geochemistry |
Copper indium gallium selenide (CIGS) is a direct band gap material. It has the highest efficiency (~20%) among all commercially significant thin film materials (see CIGS solar cell). Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. Recent developments at IBM and Nanosolar attempt to lower the cost by using non-vacuum solution processes. | 7 | Physical Chemistry |
Yulia Sister entered the Department of Chemistry of the University of Kishinev in the fall 1954. While asked by Professor , who interviewed the applicants to the Department, why she has chosen this Department, she explained that thanks to her school teacher she fell in love with chemistry. At the University Yulia was involved in various campus activities, and served as an editor of the faculty newspaper "Chemist". Since her second year at the university she became a member of the student scientific society and was engaged in the research of compounds called heteropolyacids. In 1959 Sister successfully defended her Master's thesis "Precipitation chromatography of heteropolyacids." and graduated with honors from the University of Kishinev.
Upon completion of the studies Sister was assigned to the laboratory of analytical chemistry headed by Professor Yuri Lyalikov. The laboratory was a part of the Institute of Chemistry at the Moldavian branch of the Academy of Sciences of the USSR, which became the Academy of Sciences of Moldova in 1961. Working in this laboratory allowed the young chemist Sister to begin her research with new polarographic methods. In order to carry out analysis of organic compounds by the means of alternating-current (ac) polarography Yulia built with her own hands a polarograph and received the first polarograms. Sister was the first in Moldova (with Y. S. Lyalikov), who applied the methods of ac polarography and second harmonic ac polarography for analyzing organic compounds. Then, together with the physicist Vil Senkevich, they assembled an automatic device, and only later began the serial production of polarographs in the USSR. In the early 1960s Yulia published her first research articles. In 1967 she received her Ph.D. from the Institute of Chemistry of the Moldavian Academy of Sciences.
Through 25 years of research at the Institute of Chemistry Sister dealt with a wide range of topics. Her ecology oriented research included analysis of pesticides in environmental samples, food items and biological mediums. She participated in research and analysis of suspensions and was involved in analyzing new organic compounds. Sister made a substantial contribution to the development of such methods as the second harmonic ac polarography, the difference polarography with magnetic recording, the chromatopolarography. For about 20 years Yulia Sister served as a consultant on the use of the polarographic method in biology at the Department of Human and Animal Physiology of the University of Kishinev.
In 1984 Yulia Sister was invited to work with the Institute of Technology and Development where she soon headed the laboratory of physical and chemical methods. The Institute was affiliated to a research and production association in the Ialoveni (formerly Kutuzov). Sister and her laboratory were using a variety of research methods and among them the high-performance liquid chromatography being at that time a new approach in the laboratories of the country. She also contributed as a board member of Moldavian branch of the Mendeleev Chemical Society and led the program "Young Chemist" in the Moldavian Republic. Many of her students, the former young chemists, became later scientists and managers of respectable companies. | 3 | Analytical Chemistry |
The development of an analytical instrument that utilizes the reduction-oxidation (redox) chemistry of oxygen in the presence of dissimilar metal electrodes was introduced during the 1950s. This redox electrode (also known as dissolved oxygen sensor) utilized an oxygen-permeable membrane to allow the diffusion of the gas into an electrochemical cell and its concentration determined by polarographic or galvanic electrodes. This analytical method is sensitive and accurate to down to levels of ± 0.1 mg/L dissolved oxygen. Calibration of the redox electrode of this membrane electrode still requires the use of the Henry's law table or the Winkler test for dissolved oxygen. | 3 | Analytical Chemistry |
One mechanism proposed for the oxidation of adsorbed organics from solution is the production of hydroxyl radical by the valence holes migrating to the surface and reacting with adsorbed hydroxyl groups, resulting in a very strong oxidizing radical. Identification of hydroxylated oxidation intermediates and hydroxyl radicals supports this proposed mechanism, however this does not negate the possibility of the direct oxidation of the organic reactant by the valence holes because similar intermediates would be expected in either case. Some photo-oxidation reactions are shown below. | 7 | Physical Chemistry |
Because of the ambiguity of the term valence, other notations are currently preferred. Beside the lambda notation, as used in the IUPAC nomenclature of inorganic chemistry, oxidation state is a more clear indication of the electronic state of atoms in a molecule.
The oxidation state of an atom in a molecule gives the number of valence electrons it has gained or lost. In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an electronegative atom).
Elements in a high oxidation state have an oxidation state higher than +4, and also, elements in a high valence state (hypervalent elements) have a valence higher than 4. For example, in perchlorates , chlorine has 7 valence bonds (thus, it is heptavalent, in other words, it has valence 7), and it has oxidation state +7; in ruthenium tetroxide , ruthenium has 8 valence bonds (thus, it is octavalent, in other words, it has valence 8), and it has oxidation state +8.
In some molecules, there is a difference between valence and oxidation state for a given atom. For example, in disulfur decafluoride molecule , each sulfur atom has 6 valence bonds (5 single bonds with fluorine atoms and 1 single bond with the other sulfur atom). Thus, each sulfur atom is hexavalent or has valence 6, but has oxidation state +5. In the dioxygen molecule , each oxygen atom has 2 valence bonds and so is divalent (valence 2), but has oxidation state 0. In acetylene , each carbon atom has 4 valence bonds (1 single bond with hydrogen atom and a triple bond with the other carbon atom). Each carbon atom is tetravalent (valence 4), but has oxidation state −1. | 3 | Analytical Chemistry |
An example of the Grignard reaction is a key step in the (non-stereoselective) industrial production of Tamoxifen (currently used for the treatment of estrogen receptor positive breast cancer in women): | 0 | Organic Chemistry |
Leopold Ružička (; born Lavoslav Stjepan Ružička; 13 September 1887 – 26 September 1976) was a Croatian-Swiss scientist and joint winner of the 1939 Nobel Prize in Chemistry "for his work on polymethylenes and higher terpenes" "including the first chemical synthesis of male sex hormones." He worked most of his life in Switzerland, and received eight doctorates honoris causa in science, medicine, and law; seven prizes and medals; and twenty-four honorary memberships in chemical, biochemical, and other scientific societies. | 0 | Organic Chemistry |
The major disadvantage to the DSSC design is the use of the liquid electrolyte, which has temperature stability problems. At low temperatures the electrolyte can freeze, halting power production and potentially leading to physical damage. Higher temperatures cause the liquid to expand, making sealing the panels a serious problem. Another disadvantage is that costly ruthenium (dye), platinum (catalyst) and conducting glass or plastic (contact) are needed to produce a DSSC. A third major drawback is that the electrolyte solution contains volatile organic compounds (or VOC's), solvents which must be carefully sealed as they are hazardous to human health and the environment. This, along with the fact that the solvents permeate plastics, has precluded large-scale outdoor application and integration into flexible structure.
Replacing the liquid electrolyte with a solid has been a major ongoing field of research. Recent experiments using solidified melted salts have shown some promise, but currently suffer from higher degradation during continued operation, and are not flexible. | 5 | Photochemistry |
The Yukawa–Tsuno equation, first developed in 1959, is a linear free-energy relationship in physical organic chemistry. It is a modified version of the Hammett equation that accounts for enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds. This equation does so by introducing a new term to the original Hammett relation that provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive or negative) in its transition state. The Yukawa–Tsuno equation can take the following forms:
where and represent the rate constants for an X-substituted and unsubstituted compound, respectively; represents the Hammett reaction constant; represents the Hammett substituent constant; and represent the Hammett substituent constants for reactions in which positive or negative charges are built up at the reactive center, respectively; and represents the Yukawa–Tsuno parameter. | 7 | Physical Chemistry |
Shq1, a protein thought to play a role in the stabilization and/or production of box H/ACA snoRNA, is still uncharacterized. It has been proposed that Shq1, along with Naf1p, is involved in the initial steps of the biogenesis of H/ACA box snoRNPs (box H/ACA snoRNAs form complexes with proteins, thereby forming snoRNPs) because of its association with certain snoRNP proteins during the snoRNP’s maturation, while showing very little association with the mature snoRNP complex. Despite the known involvement of Shq1 in H/ACA box snoRNP's production, the exact function of this protein in the overall rRNA processing pathway is still unknown. | 1 | Biochemistry |
In July 2022, concerns were raised by Matthew Schrag, a Vanderbilt University neuroscientist, that certain images in the 2006 Nature paper were manipulated in the paper co-authored by Ashes postdoctoral Sylvain Lesné, whom she hired in 2002. These concerns were published in an article in Science authored by Charles Piller which questioned the association between the Aβ*56 protein and dementia symptoms. Ashe stated in July 2022 via email that "it is devastating to discover that a colleague may have misled me and the scientific community [... it is also] distressing that a major scientific journal has blatantly misrepresented the implications of my work." Ashe has stated that the edited images, which she agrees "should not have occurred", do not change the conclusions of the paper. No image inconsistencies have been found in other work published by Ashe without' Lesné as a co-author.
UMN is investigating the reports as of May 2023. The editors of Nature responded with a July 14, 2022 note stating they were aware of and investigating the concerns raised, that a "further editorial response [would] follow as soon as possible", and that "readers are advised to use caution when using results reported therein". The NIH, where Schrag lodged the whistleblower report, is also investigating the matter. Retraction Watch states that Ashe co-authored with Lesné other disputed papers, and that the authors in the disputed work do not overlap except for two from UMN Department of Neuroscience.
In May of 2023, the Star Tribune reported that Ashe was using new techniques to re-do the work reported in the 2006 Nature study, and that she stated "its my responsibility to establish the truth of what weve published". | 1 | Biochemistry |
* This is an irreversible physical immobilization technique which can be considered as a physical restriction of enzyme in a specified area/space. It can be used for raising mechanical stability and can be also used for the reduction of leaching events of enzymes. Since the enzyme in this process does not interact chemically with the polymer/ material of the support fibers/lattice, it remains protected from denaturation with time.
* Basically, the enzyme is trapped in insoluble beads or microspheres, such as calcium alginate beads. However, these insoluble substances hinder the arrival of the substrate, and the exit of products. | 4 | Stereochemistry |
Because peanut agglutinin specifically binds a particular carbohydrate sequence it finds use in a range of methods for cell biology and biochemistry. For example in PNA-affinity chromatography the binding specificity of peanut agglutinin is used to isolate glycosylated molecules which have the sugar sequence Gal-β(1-3)-GalNAc. Peanut agglutinin activity is inhibited by lactose and galactose which compete for the binding site.
Other uses include:
* Potent anti-T cell activity.
* Distinguishing between human lymphocyte subsets.
* Identification of cone cell inner and outer segments and to a lesser extent rod cell inner segments in the mammalian retina.
* Tumour tissue determination for transitional mucosa malignancies.
* Identification of mammalian-infective metacyclic promastigote Leishmania major parasites from other life cycle forms also found in the sandfly host.
* Identification of the outer acrosome membrane in sperm, indicating acrosome integrity. | 1 | Biochemistry |
The ores of base metals are often sulfides. In recent centuries, reverberatory furnaces have been used to keep the charge being smelted separately from the fuel. Traditionally, they were used for the first step of smelting: forming two liquids, one an oxide slag containing most of the impurities, and the other a sulfide matte containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 meters long, 3 meters high, and 10 meters wide. Fuel is burned at one end to melt the dry sulfide concentrates (usually after partial roasting) which are fed through openings in the roof of the furnace. The slag floats over the heavier matte and is removed and discarded or recycled. The sulfide matte is then sent to the converter. The precise details of the process vary from one furnace to another depending on the mineralogy of the ore body.
While reverberatory furnaces produced slags containing very little copper, they were relatively energy inefficient and off-gassed a low concentration of sulfur dioxide that was difficult to capture; a new generation of copper smelting technologies has supplanted them. More recent furnaces exploit bath smelting, top-jetting lance smelting, flash smelting, and blast furnaces. Some examples of bath smelters include the Noranda furnace, the Isasmelt furnace, the Teniente reactor, the Vunyukov smelter, and the SKS technology. Top-jetting lance smelters include the Mitsubishi smelting reactor. Flash smelters account for over 50% of the world's copper smelters. There are many more varieties of smelting processes, including the Kivset, Ausmelt, Tamano, EAF, and BF. | 8 | Metallurgy |
In biochemistry, the Corey-Pauling rules are a set of three basic statements that govern the secondary nature of proteins, in particular, the CO-NH peptide link. They were originally proposed by Robert Corey and Linus Pauling.
The rules are as follows:
#The atoms in a peptide link all lie on the same plane.
#The nitrogen, hydrogen, and oxygen atoms in a hydrogen bond are approximately in a straight line.
#The carbon-oxygen and nitrogen-hydrogen groups are all involved in bonding. | 4 | Stereochemistry |
Anthocyanins are thought to be subject to physiochemical degradation in vivo and in vitro. Structure, pH, temperature, light, oxygen, metal ions, intramolecular association, and intermolecular association with other compounds (copigments, sugars, proteins, degradation products, etc.) generally are known to affect the color and stability of anthocyanins. B-ring hydroxylation status and pH have been shown to mediate the degradation of anthocyanins to their phenolic acid and aldehyde constituents. Indeed, significant portions of ingested anthocyanins are likely to degrade to phenolic acids and aldehyde in vivo, following consumption. This characteristic confounds scientific isolation of specific anthocyanin mechanisms in vivo. | 3 | Analytical Chemistry |
Single colour reflectometry (SCORE), formerly known as imaging Reflectometric Interferometry (iRIf) and 1-lambda Reflectometry, is a physical method based on interference of monochromatic light at thin films, which is used to investigate (bio-)molecular interactions. The obtained binding curves using SCORE provide detailed information on kinetics and thermodynamics of the observed interaction(s) as well as on concentrations of the used analytes. These data can be relevant for pharmaceutical screening and drug design, biosensors and other biomedical applications, diagnostics, and cell-based assays. | 7 | Physical Chemistry |
Progesterone is a naturally occurring pregnane steroid and is also known as pregn-4-ene-3,20-dione. It has a double bond (4-ene) between the C4 and C5 positions and two ketone groups (3,20-dione), one at the C3 position and the other at the C20 position. | 0 | Organic Chemistry |
Chlorprothixene, sold under the brand name Truxal among others, is a typical antipsychotic of the thioxanthene group. | 4 | Stereochemistry |
Terpenes and terpenoids of many kinds are found in resinous plants such as the conifers. They are aromatic and serve to repel herbivores. Their scent makes them useful in essential oils, whether for perfumes such as rose and lavender, or for aromatherapy. Some have had medicinal uses: thymol is an antiseptic and was once used as a vermifuge (anti-worm medicine). | 1 | Biochemistry |
After recognizing an antigen, an antigen-presenting cell such as the macrophage or B lymphocyte engulfs it completely by a process called phagocytosis. The engulfed particle, along with some material surrounding it, forms the endocytic vesicle (the phagosome), which fuses with lysosomes. Within the lysosome, the antigen is broken down into smaller pieces called peptides by proteases (enzymes that degrade larger proteins). The individual peptides are then complexed with major histocompatibility complex class II (MHC class II) molecules located in the lysosome – this method of "handling" the antigen is known as the exogenous or endocytic pathway of antigen processing in contrast to the endogenous or cytosolic pathway, which complexes the abnormal proteins produced within the cell (e.g. under the influence of a viral infection or in a tumor cell) with MHC class I molecules.
An alternate pathway of endocytic processing had also been demonstrated wherein certain proteins like fibrinogen and myoglobin can bind as a whole to MHC-II molecules after they are denatured and their disulfide bonds are reduced (breaking the bond by adding hydrogen atoms across it). The proteases then degrade the exposed regions of the protein-MHC II-complex. | 1 | Biochemistry |
Also known as Transposable element#DNA transposons DNA transposons], these employ a strategy by which the transposon is excised from its position via transposase, and re-integrated elsewhere in the genome. These can be identified by the following:
* TIRs, terminal inverted repeats, which allow transposase to recognize the transposon and excise/reintegrate it
* TSDs, target site duplications, which are generated during re-integration and are thought to add to the difficulties in recognizing transposons
Those DNA transposons lacking the coding necessary to synthesize transposase function non-autonomously, likely piggy-backing off of the machinery generated by neighboring transposons of the same class. An example of this would be MITEs, miniature inverted repeat transposable elements, which, while having both TIRs and TSDs, cannot produce transposase. These are particularly prevalent in plants, and are thought to be derived from deletions in the more autonomous DNA transposons. Similarly, these types of transposons can become non-autonomous by capturing or replicating pieces of host DNA. | 1 | Biochemistry |
The hammerhead titanothere (Angtsìk in Navi) is a large hexapodal herbivore whose massive, low-slung head features bony projections on either side of the skull, similar to those of hammerhead sharks and their bodies resemble the Brontotheres of Earth. These protrusions are often used to push and destroy objects: a single sideways thrust of the neck being sufficient to down a significantly sized tree. The titanothere has exceedingly thick, gray skin. There is a small "fan" feather structure on the head that it flares up as a warning symbol seen in the film and in the video game. The creature, which resembles a cross between a rhinoceros and a hammerhead shark, is easily aroused. Its hide is impervious to small arms fire, though firing on it is known to anger it. This massive, grazing creature travels in moderately large herds or packs of 10–20 animals. Avatar creature designer Yuri Bartoli explained about the creatures colorful threat display: "Originally, the hammerhead just had to be a huge creature, big enough that even a thanator would think twice about attacking one. A threat display is meant to be seen, so it required bright colors that would stand out against its more muted body". It is moderately social, but also extremely territorial and hierarchical. A soft ungulate mouth is protected by a rigid, beak-like jaw structure. The species is scientifically known as Titanotheris hammercephalis. In the climax of the film, a group of hammerhead titanothere assist the Navi in their battle against Colonel Miles Quaritch's army. | 1 | Biochemistry |
Orgel diagrams are correlation diagrams which show the relative energies of electronic terms in transition metal complexes, much like Tanabe–Sugano diagrams. They are named after their creator, Leslie Orgel. Orgel diagrams are restricted to only show weak field (i.e. high spin) cases, and offer no information about strong field (low spin) cases. Because Orgel diagrams are qualitative, no energy calculations can be performed from these diagrams; also, Orgel diagrams only show the symmetry states of the highest spin multiplicity instead of all possible terms, unlike a Tanabe–Sugano diagram. Orgel diagrams will, however, show the number of spin allowed transitions, along with their respective symmetry designations. In an Orgel diagram, the parent term (P, D, or F) in the presence of no ligand field is located in the center of the diagram, with the terms due to that electronic configuration in a ligand field at each side. There are two Orgel diagrams, one for d, d, d, and d configurations and the other with d, d, d, and d configurations.
In an Orgel diagram, lines with the same Russell–Saunders terms will diverge due to the non-crossing rule, but all other lines will be linear. Also, for the D Orgel diagram, the left side contains d and d tetrahedral and d and d octahedral complexes. The right side contains d and d tetrahedral and d and d octahedral complexes. For the F Orgel diagram, the left side contains d and d tetrahedral and d and d octahedral complexes. The right side contains d and d tetrahedral and d and high spin d octahedral complexes. | 7 | Physical Chemistry |
These are extremely light-sensitive vacuum tubes with a coated photocathode inside the envelope. The photo cathode contains combinations of materials such as cesium, rubidium, and antimony specially selected to provide a low work function, so when illuminated even by very low levels of light, the photocathode readily releases electrons. By means of a series of electrodes (dynodes) at ever-higher potentials, these electrons are accelerated and substantially increased in number through secondary emission to provide a readily detectable output current. Photomultipliers are still commonly used wherever low levels of light must be detected. | 7 | Physical Chemistry |
Sulfate reduction in the seabed is strongly focused toward near-surface sediments with high depositional rates along the ocean margins. The benthic marine sulfur cycle is therefore sensitive to anthropogenic influence, such as ocean warming and increased nutrient loading of coastal seas. This stimulates photosynthetic productivity and results in enhanced export of organic matter to the seafloor, often combined with low oxygen concentration in the bottom water (Rabalais et al., 2014; Breitburg et al., 2018). The biogeochemical zonation is thereby compressed toward the sediment surface, and the balance of organic matter mineralization is shifted from oxic and suboxic processes toward sulfate reduction and methanogenesis (Middelburg and Levin, 2009).
* cable bacteria
The sulfur cycle in marine environments has been well-studied via the tool of sulfur isotope systematics expressed as δS. The modern global oceans have sulfur storage of 1.3 × 10 g, mainly occurring as sulfate with the δS value of +21‰. The overall input flux is 1.0 × 10 g/year with the sulfur isotope composition of ~3‰. Riverine sulfate derived from the terrestrial weathering of sulfide minerals (δS = +6‰) is the primary input of sulfur to the oceans. Other sources are metamorphic and volcanic degassing and hydrothermal activity (δS = 0‰), which release reduced sulfur species (e.g., HS and S). There are two major outputs of sulfur from the oceans. The first sink is the burial of sulfate either as marine evaporites (e.g., gypsum) or carbonate-associated sulfate (CAS), which accounts for 6 × 10 g/year (δS = +21‰). The second sulfur sink is pyrite burial in shelf sediments or deep seafloor sediments (4 × 10 g/year; δS = -20‰). The total marine sulfur output flux is 1.0 × 10 g/year which matches the input fluxes, implying the modern marine sulfur budget is at steady state. The residence time of sulfur in modern global oceans is 13,000,000 years.
In modern oceans, Hydrogenovibrio crunogenus, Halothiobacillus, and Beggiatoa are primary sulfur oxidizing bacteria, and form chemosynthetic symbioses with animal hosts. The host provides metabolic substrates (e.g., CO, O, HO) to the symbiont while the symbiont generates organic carbon for sustaining the metabolic activities of the host. The produced sulfate usually combines with the leached calcium ions to form gypsum, which can form widespread deposits on near mid-ocean spreading centers.
Hydrothermal vents emit hydrogen sulfide that support the carbon fixation of chemolithotrophic bacteria that oxidize hydrogen sulfide with oxygen to produce elemental sulfur or sulfate. | 9 | Geochemistry |
PCBs originating from Monsanto Chemical Company in Anniston, Alabama, were dumped into Snow Creek, which then spread to Choccolocco Creek, then Logan Martin Lake. In the early 2000s, class action lawsuits were settled by local land owners, including those on Logan Martin Lake, and Lay Reservoir (downstream on the Coosa River), for the PCB pollution. Donald Stewart, former Senator from Alabama, first learned of the concerns of hundreds of west Anniston residents after representing a church which had been approached about selling its property by Monsanto. Stewart went on to be the pioneer and lead attorney in the first and majority of cases against Monsanto and focused on residents in the immediate area known to be most polluted. Other attorneys later joined in to file suits for those outside the main immediate area around the plant; one of these was the late Johnnie Cochran.
In 2007, the highest pollution levels remained concentrated in Snow and Choccolocco Creeks. Concentrations in fish have declined and continue to decline over time; sediment disturbance, however, can resuspend the PCBs from the sediment back into the water column and food web. | 2 | Environmental Chemistry |
UDP-glucuronic acid is a sugar used in the creation of polysaccharides and is an intermediate in the biosynthesis of ascorbic acid (except in primates and guinea pigs). It also participates in the heme degradation process of human.
It is made from UDP-glucose by UDP-glucose 6-dehydrogenase (EC 1.1.1.22) using NAD+ as a cofactor. It is the source of the glucuronosyl group in glucuronosyltransferase reactions. | 1 | Biochemistry |
The Wong–Sandler mixing rule is a thermodynamic mixing rule used for vapor–liquid equilibrium and liquid-liquid equilibrium calculations.
__TOC__ | 7 | Physical Chemistry |
In organic chemistry, alkyl nitrites are a group of organic compounds based upon the molecular structure , where R represents an alkyl group. Formally they are alkyl esters of nitrous acid. They are distinct from nitro compounds ().
The first few members of the series are volatile liquids; methyl nitrite and ethyl nitrite are gaseous at room temperature and pressure. The compounds have a distinctive fruity odor. Another frequently encountered nitrite is amyl nitrite (3-methylbutyl nitrite).
Alkyl nitrites were initially, and largely still are, used as medications and chemical reagents, a practice which began in the late 19th century. In their use as medicine, they are often inhaled for relief of angina and other heart-related symptoms of disease. However, when referred to as "poppers", alkyl nitrites represent recreational drugs. | 0 | Organic Chemistry |
The modern non-stick pans were made using a coating of Teflon (polytetrafluoroethylene or PTFE). PTFE was invented serendipitously by Roy Plunkett in 1938, while working for a joint venture of the DuPont company. The substance was found to have several unique properties, including very good corrosion-resistance and the lowest coefficient of friction of any substance yet manufactured. PTFE was first used to make seals resistant to the uranium hexafluoride gas used in development of the atomic bomb during World War II, and was regarded as a military secret. Dupont registered the Teflon trademark in 1944 and soon began planning for post-war commercial use of the new product.
By 1951 Dupont had developed applications for Teflon in commercial bread and cookie-making; however, the company avoided the market for consumer cookware due to potential problems associated with release of toxic gases if stove-top pans were overheated in inadequately ventilated spaces. While working at DuPont, NYU Tandon School of Engineering alumnus John Gilbert was asked to evaluate a newly developed material called Teflon. His experiments using the fluorinated polymer as a surface coating for pots and pans helped usher in a revolution in non-stick cookware.
A few years later, a French engineer had begun coating his fishing gear with Teflon to prevent tangles. His wife Colette suggested using the same method to coat her cooking pans. The idea was successful and a French patent was granted for the process in 1954. The Tefal company was formed in 1956 to manufacture non-stick pans. | 7 | Physical Chemistry |
High levels of mixed-function oxidase activity have been studied for their activation effects in human colon carcinoma cell lines, to study the susceptibility to certain cancers. The research has been successful in mice but remains inconclusive in humans. | 1 | Biochemistry |
* An array or slide is a collection of features spatially arranged in a two dimensional grid, arranged in columns and rows.
* Block or subarray: a group of spots, typically made in one print round; several subarrays/ blocks form an array.
* Case/control: an experimental design paradigm especially suited to the two-colour array system, in which a condition chosen as control (such as healthy tissue or state) is compared to an altered condition (such as a diseased tissue or state).
* Channel: the fluorescence output recorded in the scanner for an individual fluorophore and can even be ultraviolet.
* Dye flip or dye swap or fluor reversal: reciprocal labelling of DNA targets with the two dyes to account for dye bias in experiments.
* Scanner: an instrument used to detect and quantify the intensity of fluorescence of spots on a microarray slide, by selectively exciting fluorophores with a laser and measuring the fluorescence with a filter (optics) photomultiplier system.
* Spot or feature: a small area on an array slide that contains picomoles of specific DNA samples.
* For other relevant terms see:
** Glossary of gene expression terms
** Protocol (natural sciences) | 1 | Biochemistry |
Thermal rearrangements of aromatic hydrocarbons have been shown to be important in areas of chemical research and industry including fullerene synthesis, materials applications, and the formation of soot in combustion. Thermal rearrangements of aceanthrylene and acephenanthrylene can yield fluoranthene, an important species in syntheses of corannulene and fullerenes that proceed through additional internal rearrangements.
Many of the polycyclic aromatic hydrocarbons known to be tumorigenic or mutagenic are found in atmospheric aerosols, which is connected to the thermal rearrangement of polycyclic aromatic hydrocarbons in fast soot formation during combustion. | 5 | Photochemistry |
Photoacoustic spectroscopy is the measurement of the effect of absorbed electromagnetic energy (particularly of light) on matter by means of acoustic detection. The discovery of the photoacoustic effect dates to 1880 when Alexander Graham Bell showed that thin discs emitted sound when exposed to a beam of sunlight that was rapidly interrupted with a rotating slotted disk. The absorbed energy from the light causes local heating, generating a thermal expansion which creates a pressure wave or sound. Later Bell showed that materials exposed to the non-visible portions of the solar spectrum (i.e., the infrared and the ultraviolet) can also produce sounds.
A photoacoustic spectrum of a sample can be recorded by measuring the sound at different wavelengths of the light. This spectrum can be used to identify the absorbing components of the sample. The photoacoustic effect can be used to study solids, liquids and gases. | 7 | Physical Chemistry |
The grand potential or Landau potential or Landau free energy is a quantity used in statistical mechanics, especially for irreversible processes in open systems.
The grand potential is the characteristic state function for the grand canonical ensemble. | 7 | Physical Chemistry |
He has been involved in many editorial boards of scientific journals. He was member of the editorial board of the Journal of Applied Electrochemistry (1988-2010), [http://www.scielo.cl/scielo.php?script=sci_serial&pid=0717-9707&lng=es&nrm=iso Journal of the Chilean Chemical Society] (1984-2007) and Electrocatalysis (2010-2015) and is presently member of the Editorial Board of several international publications: [https://link.springer.com/journal/10008 Journal of Solid State Electrochemistry] (Springer), [http://www.hindawi.com/journals/ijelc/ International Journal of Electrochemistry] (Hindawi), [http://www.journals.elsevier.com/electrochemistry-communications/ Electrochemistry Communications] (Elsevier), [https://web.archive.org/web/20141003071519/http://www.shd.org.rs/JSCS/ Journal of the Serbian Chemical Society], [http://www.degruyter.com/view/j/eetech Electrochemical Energy Technology] (De Goutyer) and [http://www.scielo.br/revistas/qn/iedboard.htm Chimica Nova] and Frontiers in Chemistry. He has been a Guest Editor for the Journal of Applied Electrochemistry, Current Opinion in Electrochemistry and for the International Journal of Electrochemistry. | 7 | Physical Chemistry |
An introduction to Landau theory can be found here.
Based on Ginzburg–Landau theory, the free energy of a ferroelectric material, in the absence of an electric field and applied stress may be written as a Taylor expansion in terms of the order parameter, P. If a sixth order expansion is used (i.e. 8th order and higher terms truncated), the free energy is given by:
where P, P, and P are the components of the polarization vector in the x, y, and z directions respectively, and the coefficients, must be consistent with the crystal symmetry. To investigate domain formation and other phenomena in ferroelectrics, these equations are often used in the context of a phase field model. Typically, this involves adding a gradient term, an electrostatic term and an elastic term to the free energy. The equations are then discretized onto a grid using the finite difference method or finite element method and solved subject to the constraints of Gauss's law and Linear elasticity.
In all known ferroelectrics, and . These coefficients may be obtained experimentally or from ab-initio simulations. For ferroelectrics with a first order phase transition, , whereas for a second order phase transition.
The spontaneous polarization, P of a ferroelectric for a cubic to tetragonal phase transition may be obtained by considering the 1D expression of the free energy which is:
This free energy has the shape of a double well potential with two free energy minima at , the spontaneous polarization. We find the derivative of the free energy, and set it equal to zero in order to solve for :
Since the P = 0 solution of this equation rather corresponds to a free energy maxima in the ferroelectric phase, the desired solutions for P correspond to setting the remaining factor to zero:
whose solution is:
and eliminating solutions which take the square root of a negative number (for either the first or second order phase transitions) gives:
If , the solution for the spontaneous polarization reduces to:
The hysteresis loop (P versus E) may be obtained from the free energy expansion by including the term -E P corresponding to the energy due to an external electric field E interacting with the polarization P, as follows:
We find the stable polarization values of P under the influence of the external field, now denoted as P, again by setting the derivative of the energy with respect to P to zero:
Plotting E (on the X axis) as a function of P (but on the Y axis) gives an S-shaped curve which is multi-valued in P for some values of E. The central part of the S corresponds to a free energy local maximum (since ). Elimination of this region, and connection of the top and bottom portions of the S curve by vertical lines at the discontinuities gives the hysteresis loop of internal polarization due to an external electric field. | 7 | Physical Chemistry |
Nearly all cell membranes in animals, plants and fungi maintain a voltage difference between the exterior and interior of the cell, called the membrane potential. A typical voltage across an animal cell membrane is −70 mV. This means that the interior of the cell has a negative voltage relative to the exterior. In most types of cells, the membrane potential usually stays fairly constant. Some types of cells, however, are electrically active in the sense that their voltages fluctuate over time. In some types of electrically active cells, including neurons and muscle cells, the voltage fluctuations frequently take the form of a rapid upward (positive) spike followed by a rapid fall. These up-and-down cycles are known as action potentials. In some types of neurons, the entire up-and-down cycle takes place in a few thousandths of a second. In muscle cells, a typical action potential lasts about a fifth of a second. In plant cells, an action potential may last three seconds or more.
The electrical properties of a cell are determined by the structure of its membrane. A cell membrane consists of a lipid bilayer of molecules in which larger protein molecules are embedded. The lipid bilayer is highly resistant to movement of electrically charged ions, so it functions as an insulator. The large membrane-embedded proteins, in contrast, provide channels through which ions can pass across the membrane. Action potentials are driven by channel proteins whose configuration switches between closed and open states as a function of the voltage difference between the interior and exterior of the cell. These voltage-sensitive proteins are known as voltage-gated ion channels. | 7 | Physical Chemistry |
PELP1 functions as a coactivator of several NRs and regulates genes involved in proliferation and cancer progression. PELP1 enhances transcription functions of ESR1, ESR2, AR, GR, E2F and STAT3. PELP1 participates in activation of ESR1 extra-nuclear actions by coupling ESR1 with Src kinase PI3K STAT3 ILK1 and mTOR PELP1 participates in E2-mediated cell proliferation and is a substrate of CDK4/cyclin D1, CDK2/cyclin E and CDK2/cyclin A complexes. Studies using TG mice model suggested the existence of an autocrine loop involving the CDK–cyclin D1–PELP1 axis in promoting mammary tumorigenesis
PELP1 has a histone binding domain; functions as a reader of histone modifications, interacts with epigenetic modifiers such as HDAC2, KDM1, PRMT6, CARM1; and facilitates activation of genes involved in proliferation and cancer progression. PELP1 modulates the expression of miRs, PELP1-mediated epigenetic changes play important role in the regulation miR expression and many of PELP1 mediated miRS are involved in promoting metastasis. PELP1 is needed for optimal DNA damage response, is phosphorylated by DDR kinases and is important for p53 coactivation function. PELP1 also interacts with MTp53, regulates its recruitment, and alters MTp53 target gene expression. PELP1 depletion contributes to increased stability of E2F1. PELP1 binds RNA, and participates in RNA splicing. The PELP1-regulated genome includes several uniquely spliced isoforms. Mechanistic studies showed that PELP1 interaction with the arginine methyltransferase PRMT6 plays a role in RNA splicing.
PELP1 plays critical roles in 60S ribosomal subunit synthesis and ribosomal RNA transcription. The SENP3-associated complex comprising PELP1, TEX10 and WDR18 is involved in maturation and nucleolar release of the large ribosomal subunit. SUMO conjugation/deconjugation of PELP1 controls its dynamic association with the AAA ATPase MDN1, a key factor of pre-60S remodeling. Modification of PELP1 promotes the recruitment of MDN1 to pre-60S particles, while deSUMOylation is needed to release both MDN1 and PELP1 from pre-ribosomes.
PELP1 is widely expressed in many regions of brain, including the hippocampus, hypothalamus, and cerebral cortex. PELP1 interacts with ESR1, Src, PI3K and GSK3β in the brain. It is essential for E2-mediated extra-nuclear signaling following global cerebral ischemic. PELP1 plays an essential role in E2-mediated rapid extranuclear signaling, neuroprotection, and cognitive function in the brain. Ability of E2 to exert anti-inflammatory effects was lost in PELP1 forebrain-specific knockout mice, indicating a key role for PELP1 in E2 anti-inflammatory signaling.
PELP1 is a proto-oncogene that provides cancer cells with a distinct growth and survival advantage. PELP1 interacts with various enzymes that modulate the cytoskeleton, cell
migration, and metastasis. PELP1 deregulation in vivo promotes development of mammary gland hyperplasia and carcinoma PELP1 is implicated in progression of breast, endometrial, ovarian, salivary prostate, lung, pancreas, and colon neoplasms.
PELP1 signaling contributes to hormonal therapy resistance. Altered localization of PLP1 contributes to tamoxifen resistance via excessive activation of the AKT pathway and cytoplasmic PELP1 induces signaling pathways that converge on ERRγ to promote cell survival in the presence of tamoxifen. AR, PELP1 and Src form constitutive complexes in prostate neoplasms model cells that exhibit androgen independence. Cytoplasmic localization of PELP1 upregulates pro-tumorigenic IKKε and secrete inflammatory signals, which through paracrine macrophage activation, regulate the migratory phenotype associated with breast cancer initiation. | 1 | Biochemistry |
This book is a description of the various types of veins that can be found. There are 30 illustrations of different forms of these veins, forming the majority of Book III. Agricola also describes a compass to determine the direction of veins and mentions that some writers claim that veins lying in certain directions are richer, although he provides counter-examples. He also mentions the theory that the sun draws the metals in veins to the surface, although he himself doubts this. Finally he explains that gold is not generated in the beds of streams and rivers and east-west streams are not more productive than others inherently. Gold occurs in streams because it is torn from veins by the water. | 8 | Metallurgy |
A nitrate test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble salts, e.g. halides precipitate with silver, and sulfate precipitate with barium.
The nitrate anion is an oxidizer, and many tests for the nitrate anion are based on this property. However, other oxidants present in the analyte may interfere and give erroneous results.
Nitrate can also be detected by first reducing it to the more reactive nitrite ion and using one of many nitrite tests. | 3 | Analytical Chemistry |
In 2000, with the help of plant breeders and the Organic Research Centre, the scientist Martin Wolfe crossed 20 varieties of wheat (selected for quality and yield) and crossed them to obtain 190 new crosses. These seeds were not further selected and planted, grown, harvested and reseeded together as a population.
Martin Wolfe called it YQ, for "yield" and "quality". Wolfe lobbied in Brussels and Westminster to receive an exception to the EU regulations that would allow YQ to be sold. In 2014, it was accepted and since 2017 the YQ seed, officially called the "ORC Wakelyns Population" was the first population wheat to go on sale in Europe. | 1 | Biochemistry |
A DID is an ion detector which uses a high-voltage electric discharge to produce ions. The detector uses an electrical discharge in helium to
generate high energy UV photons and metastable helium which ionizes all compounds except helium. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current. | 3 | Analytical Chemistry |
Attosecond pump-probe experiments with simple atoms is a fundamental tool to measure the time duration of an attosecond pulse and to explore several quantum proprieties of matter.
This kind of experiments can be easily described within strong field approximation by exploiting the results of Eq. , as discussed below.
As a simple model, consider the interaction between a single active electron in a single-level atom and two fields: an intense femtosecond infrared (IR) pulse (,
and a weak attosecond pulse (centered in the extreme ultraviolet (XUV) region) .
Then, by substituting these fields to it results
with
At this point, we can divide Eq. in two contributions: direct ionization and strong field ionization (multiphoton regime), respectively.
Typically, these two terms are relevant in different energetic regions of the continuum.
Consequently, for typical experimental condition, the latter process is disregarded, and only direct ionization from the attosecond pulse is considered.
Then, since the attosecond pulse is weaker than the infrared one, it holds . Thus, is typically neglected in Eq. .
In addition to that, we can re-write the attosecond pulse as a delayed function with respect to the IR field, .
Therefore, the probability distribution, , of finding an electron ionized in the continuum with momentum , after the interaction has occurred (at ), in a pump-probe experiments,
with an intense IR pulse and a delayed-attosecond XUV pulse, is given by:
with
Equation describes the photoionization phenomenon of two-color interaction (XUV-IR) with a single-level atom and single active electron.
This peculiar result can be regarded as a quantum interference process between all the possible ionization paths, started by a delayed XUV attosecond pulse, with a following motion in the continuum states driven by a strong IR field.
The resulting 2D photo-electron (momentum, or equivalently energy, vs delay) distribution is called streaking trace. | 7 | Physical Chemistry |
To measure the IMFP, one well known method is elastic-peak electron spectroscopy (EPES). This method measures the intensity of elastically backscattered electrons with a certain energy from a sample material in a certain direction. Applying a similar technique to materials whose IMFP is known, the measurements are compared with the results from the Monte Carlo simulations under the same conditions. Thus, one obtains the IMFP of a certain material in a certain energy spectrum. EPES measurements show a root-mean-square (RMS) difference between 12% and 17% from the theoretical expected values. Calculated and experimental results show higher agreement for higher energies.
For electron energies in the range 30 keV – 1 MeV, IMFP can be directly measured by electron energy loss spectroscopy inside a transmission electron microscope, provided the sample thickness is known. Such measurements reveal that IMFP in elemental solids is not a smooth, but an oscillatory function of the atomic number.
For energies below 100 eV, IMFP can be evaluated in high-energy secondary electron yield (SEY) experiments. Therefore, the SEY for an arbitrary incident energy between 0.1 keV-10 keV is analyzed. According to these experiments, a Monte Carlo model can be used to simulate the SEYs and determine the IMFP below 100 eV. | 7 | Physical Chemistry |
*1972 Paul W. Gast
*1973 Robert M. Garrels
*1974 Hans E. Suess
*1975 Harold C. Urey
*1976 Hans P. Eugster
*1977 Samuel Epstein
*1978 Gerald J. Wasserburg
*1979 Harmon Craig
*1980 Clair C. Patterson
*1981 Robert N. Clayton
*1982 Konrad B. Krauskopf
*1983 Samuel S. Goldich
*1984 Alfred Nier
*1985 James B. Thompson Jr.
*1986 Claude Allègre
*1987 Wallace S. Broecker
*1988 Harold C. Helgeson
*1989 Karl K. Turekian
*1990 Edward Anders
*1991 Alfred Edward Ringwood
*1992 Stanley R. Hart
*1993 S. Ross Taylor
*1994 Heinrich D. Holland
*1995 Robert A. Berner
*1996 Albrecht W. Hofmann
*1997 Devendra Lal
*1998 Werner Stumm
*2000 Geoffrey Eglinton
*2001 Ikuo Kushiro
*2002 John M. Hayes
*2003 Bernard J. Wood
*2004 James R. O'Neil
*2005 E. Bruce Watson
*2006 Susan Solomon
*2007 Guenter Lugmair
*2008 Francis Albarède
*2009 Mark H. Thiemens
*2010 Minoru Ozima
*2011 Frank Millero
*2012 Edward M. Stolper
*2013 Henry "Harry" Elderfield
*2014 Timothy Grove
*2015 Miriam Kastner
*2016 Alexandra Navrotsky
*2017 Jill Banfield
*2018 Michael A. Arthur
*2019 Donald DePaolo
*2020 Richard Carlson
*2021 Bernard Marty | 9 | Geochemistry |
Until 2007, in the United States, Lugol's solution was unregulated and available over the counter as a general reagent, an antiseptic, a preservative, or as a medicament for human or veterinary application.
Since 1 August 2007, the DEA regulates all iodine solutions containing greater than 2.2% elemental iodine as a List I precursor because they may potentially be used in the illicit production of methamphetamine. Transactions of up to one fluid ounce (30 ml) of Lugol's solution are exempt from this regulation. | 3 | Analytical Chemistry |
A deficiency associated with lysosomal acid lipase deficiency, Wolman disease, and cholesteryl ester storage disease.
Chlorpromazine is an inhibitor of lysosomal lipase.
A genome wide survey suggests that lysosomal lipase A (located at chromosome 10q23.31) is associated with coronary artery disease in humans. | 1 | Biochemistry |
The Fenna–Matthews–Olson (FMO) complex is a water-soluble complex and was the first pigment-protein complex (PPC) to be structure analyzed by x-ray spectroscopy. It appears in green sulfur bacteria and mediates the excitation energy transfer from light-harvesting chlorosomes to the membrane-embedded bacterial reaction center (bRC). Its structure is trimeric (C3-symmetry). Each of the three monomers contains eight bacteriochlorophyll a (BChl a) molecules. They are bound to the protein scaffold via chelation of their central magnesium atom either to amino acids of the protein (mostly histidine) or water-bridged oxygen atoms (only one BChl a of each monomer).
Since the structure is available, calculating structure-based optical spectra is possible for comparison with experimental optical spectra. In the simplest case only the excitonic coupling of the BChls is taken into account. More realistic theories consider pigment-protein coupling. An important property is the local transition energy (site energy) of the BChls, different for each, due to their individual local protein environment. The site energies of the BChls determine the direction of the energy flow.
Some structural information on the FMO-RC super complex is available, which was obtained by electron microscopy and linear dichroism spectra measured on FMO trimers and FMO-RC complexes. From these measurements, two orientations of the FMO complex relative to the RC are possible. The orientation with BChl 3 and 4 close to the RC and BChl 1 and 6 (following Fenna and Matthews' original numbering) oriented towards the chlorosomes is useful for efficient energy transfer. | 5 | Photochemistry |
Lowering photorespiration may not result in increased growth rates for plants. Photorespiration may be necessary for the assimilation of nitrate from soil. Thus, a lowering in photorespiration by genetic engineering or because of increasing atmospheric carbon dioxide may not benefit plants as has been proposed. Several physiological processes may be responsible for linking photorespiration and nitrogen assimilation. Photorespiration increases availability of NADH, which is required for the conversion of nitrate to nitrite. Certain nitrite transporters also transport bicarbonate, and elevated has been shown to suppress nitrite transport into chloroplasts. However, in an agricultural setting, replacing the native photorespiration pathway with an engineered synthetic pathway to metabolize glycolate in the chloroplast resulted in a 40 percent increase in crop growth.
Although photorespiration is much lower in C species, it is still an essential pathwaymutants without functioning 2-phosphoglycolate metabolism cannot grow in normal conditions. One mutant was shown to rapidly accumulate glycolate.
Although the functions of photorespiration remain controversial, it is widely accepted that this pathway influences a wide range of processes from bioenergetics, photosystem II function, and carbon metabolism to nitrogen assimilation and respiration. The oxygenase reaction of RuBisCO may prevent depletion near its active sites and contributes to the regulation of CO concentration in the atmosphere The photorespiratory pathway is a major source of hydrogen peroxide () in photosynthetic cells. Through production and pyrimidine nucleotide interactions, photorespiration makes a key contribution to cellular redox homeostasis. In so doing, it influences multiple signalling pathways, in particular, those that govern plant hormonal responses controlling growth, environmental and defense responses, and programmed cell death.
It has been postulated that photorespiration may function as a "safety valve", preventing the excess of reductive potential coming from an overreduced NADPH-pool from reacting with oxygen and producing free radicals (oxidants), as these can damage the metabolic functions of the cell by subsequent oxidation of membrane lipids, proteins or nucleotides. The mutants deficient in photorespiratory enzymes are characterized by a high redox level in the cell, impaired stomatal regulation, and accumulation of formate. | 5 | Photochemistry |
Microcystins covalently bond to and inhibit protein phosphatases PP1 and PP2A and can thus cause pansteatitis. The ADDA residue is key to this functionality: greatly simplified synthetic analogues consisting of ADDA and one additional amino acid can show the same inhibiting function. | 2 | Environmental Chemistry |
The adapters that annealed successfully are extended and synthesized by a DNA polymerase to complete a double-stranded adapter containing complementary tags (Figure 1). | 1 | Biochemistry |
Electrodeionization (EDI) is a water treatment technology that utilizes DC power, ion exchange membranes, and ion exchange resin to deionize water. EDI is typically employed as a polishing treatment following reverse osmosis (RO), and is used in the production of ultrapure water. It differs from other RO polishing methods, like chemically regenerated mixed beds, by operating continuously without chemical regeneration.
Electrodeionization can be used to produce high purity water, reaching electrical resistivity values as high as 18.2 MΩ/cm.
Electrodeionization (EDI) integrates three distinct processes:
# Electrolysis: A continuous DC current directs positive and negative ions toward electrodes with opposing electrical charges. The electrical potential draws anions and cations from diluting chambers, through cation or anion exchange membranes, into concentrating chambers.
# Ion exchange: An ion exchange resin fills the diluting chambers. As water flows through the resin bed, cations and anions become affixed to resin sites.
# Electrochemical regeneration: Unlike chemically regenerated mixed beds, EDI accomplishes regeneration through water splitting induced by the continuous electric current. Water splits from H and OH to effectively regenerate the resin without the need for external chemical additives.
EDI is sometimes labeled "continuous electrodeionization" (CEDI) because the electric current continually regenerates the ion exchange resin mass. | 7 | Physical Chemistry |
Hypothermia therapy for neonatal encephalopathy has been proven to improve outcomes for newborn infants affected by perinatal hypoxia-ischemia, hypoxic ischemic encephalopathy or birth asphyxia. A 2013 Cochrane review found that it is useful in full term babies with encephalopathy. Whole body or selective head cooling to , begun within six hours of birth and continued for 72 hours, reduces mortality and reduces cerebral palsy and neurological deficits in survivors. | 1 | Biochemistry |
Carbomethoxymethylenetriphenylphosphorane can be made via a multistep reaction using bromoacetic acid, dicyclohexylcarbodiimide, and triphenylphosphine. This makes a phosphonium salt, which is converted to the final product by sodium carbonate in water. | 0 | Organic Chemistry |
Imperfect inverted repeats can lead to mutations through intrastrand and interstrand switching. The antithrombin III gene's coding region is an example of an imperfect inverted repeat as shown in the figure on the right.
The stem-loop structure forms with a bump at the bottom because the G and T do not pair up. A strand switch event could result in the G (in the bump) being replaced by an A which removes the "imperfection" in the inverted repeat and provides a stronger stem-loop structure. However, the replacement also creates a point mutation converting the GCA codon to ACA. If the strand switch event is followed by a second round of DNA replication, the mutation may become fixed in the genome and lead to disease. Specifically, the missense mutation would lead to a defective gene and a deficiency in antithrombin which could result in the development of venous thromboembolism (blood clots within a vein). | 1 | Biochemistry |
The radial spoke is a multi-unit protein structure found in the axonemes of eukaryotic cilia and flagella. Although experiments have determined the importance of the radial spoke in the proper function of these organelles, its structure and mode of action remain poorly understood. | 1 | Biochemistry |
Rivers and submarine hydrothermal emanations supply 6.1 × 10 g SiO yr to the marine environment. Approximately two-thirds of this silica input is stored in continental margin and deep-sea deposits. Siliceous deep-sea sediments located beneath the Antarctic Convergence (convergence zone) host some 25% of the silica supplied to the oceans (i.e. 1.6 × 10 g SiO yr) and consequently form one of Earth's major silica sinks. The highest biogenic silica accumulation rates in this area are observed in the South Atlantic, with values as large as 53 cm.kyr during the last 18,000 yr. Further, extensive biogenic silica accumulation has been recorded in the deep-sea sediments of the Bering Sea, Sea of Okhotsk, and Subarctic North Pacific. Total biogenic silica accumulation rates in these regions amounts nearly 0.6 × 10 g SiO yr, which is equivalent to 10% of the dissolved silica input to the oceans.
Continental margin upwelling areas, such as the Gulf of California, the Peru and Chile coast, are characteristic for some of the highest biogenic silica accumulation rates in the world. For example, biogenic silica accumulation rates of 69 g SiO/cm/kyr have been reported for the Gulf of California. Due to the laterally confined character of these rapid biogenic silica accumulation zones, upwelling areas solely account for approximately 5% of the dissolved silica supplied to the oceans. At last, extremely low biogenic silica accumulation rates have been observed in the extensive deep-sea deposits of the Atlantic, Indian and Pacific Oceans, rendering these oceans insignificant for the global marine silica budget. | 1 | Biochemistry |
Vapor diffusion is the most commonly employed method of protein crystallization. In this method, droplets containing purified protein, buffer, and precipitant are allowed to equilibrate with a larger reservoir containing similar buffers and precipitants in higher concentrations. Initially, the droplet of protein solution contains comparatively low precipitant and protein concentrations, but as the drop and reservoir equilibrate, the precipitant and protein concentrations increase in the drop. If the appropriate crystallization solutions are used for a given protein, crystal growth occurs in the drop. This method is used because it allows for gentle and gradual changes in concentration of protein and precipitant concentration, which aid in the growth of large and well-ordered crystals.
Vapor diffusion can be performed in either hanging-drop or sitting-drop format. Hanging-drop apparatus involve a drop of protein solution placed on an inverted cover slip, which is then suspended above the reservoir. Sitting-drop crystallization apparatus place the drop on a pedestal that is separated from the reservoir. Both of these methods require sealing of the environment so that equilibration between the drop and reservoir can occur. | 3 | Analytical Chemistry |
Bi-metallic coins and medals have been issued for a long time. The Roman Empire issued special-occasion, large medallions with a center of bronze or copper and an outer ring of orichalcum, starting with the reign of Hadrian. Meanwhile, circulating bi-metallic coins are known from the 17th century. English farthings from 1684 through 1693 were made of tin with a central plug of copper for value. The silver-center cent pattern produced by the United States in 1792 is another example.
In the 1830s and 1840s, British medalist Joseph Moore produced large numbers of bi-metallic "penny model" and less common "halfpenny model" tokens, as a proposal to replace the relatively large penny and halfpenny coins. Though not legal tender, Moore's tokens were circulated widely and accepted at face value by many merchants. Despite their popularity, the Royal Mint rejected the proposal, and did not reduce the size of the penny and halfpenny until decimalization.
The first modern circulating bi-metallic coin was the Italian 500 lire, first issued in 1982. Based on the minting process of the lire coin, the following issued bi-metallic coins for circulation were issued:
* Morocco, with its 5-dirhams coin in 1987;
* France, with a 10-francs coin in 1988;
* Monaco, with a 10 francs;
* Thailand, with a 10 baht, in 1988;
* Czech Republic, with a 50 Kč coin in 1993;
* Hong Kong, with a $10 coin, in 1993;
* Indonesia, with a Rp1,000 coin, in 1993;
* Israel, with a ₪10 coin in 1995;
* Canada, with a $2 coin (nicknamed "toonie") in 1996;
* Hungary, with a 100-forint coin in 1996 and a 200 forint coin in 2009;
* Brazil with the 1 real coin, in 1998;
* The United Kingdom has issued a bi-metallic £2 coin since 1997, and a bi-metallic £1 coin since March 2017;
* The Philippines has minted a bi-metallic 10-peso coin from 2000 to 2017 and a 20-peso coin since 2019.
* The Eurozone circulated the €1 and €2 coins on 1 January 2002;
* India has issued a bi-metallic ₹10 coin since 2009 and a bi-metallic ₹20 coin since 2019;
* Singapore has issued a bi-metallic 1-dollar coin since 2013.
* Japan has issued a bi-metallic 500 yen coin since 2021.
* Costa Rica announced a bi-metallic 500-colones coin that will start to circulate in November 2021.
The first ever tri-metallic circulating coins were 20-francs coins introduced in France and Monaco in 1992. These were similar to the corresponding bi-metallic 10-francs coins, but had two rings instead of one. | 8 | Metallurgy |
Bacteria become highly tolerant to antibiotics when nutrients are limited. Starvation contributes to antibiotic tolerance during infection, as nutrients become limited when they are sequestered by host defenses and consumed by proliferating bacteria. One of the most important causes of starvation induced tolerance in vivo is biofilm growth, which occurs in many chronic infections. Starvation in biofilms is due to nutrient consumption by cells located on the periphery of biofilm clusters and by reduced diffusion of substrates through the biofilm. Biofilm bacteria shows extreme tolerance to almost all antibiotic classes, and supplying limiting substrates can restore sensitivity. | 1 | Biochemistry |
In classical Lewis structures, molecular oxygen, O, is depicted as having a double bond between the two oxygen atoms. However, the molecular orbitals of O are actually more complex than Lewis structures seem to suggest. The highest occupied molecular orbital (HOMO) of O is a pair of degenerate antibonding π orbitals, π* and π*, which are both singly occupied by spin unpaired electrons. These electrons are the cause of O being a triplet diradical in the ground state (indicated as O).
While many stable molecules’ HOMOs consist of bonding molecular orbitals and therefore require a moderate energy jump from bonding to antibonding to reach their first excited state, the antibonding nature of molecular oxygen’s HOMO allows for a lower energy gap between its ground state and first excited state. This makes excitation of O a less energetically restrictive process. In the first excited state of O, a 22 kcal/mol energy increase from the ground state, both electrons in the antibonding orbitals occupy a degenerate π* orbital, and oxygen is now in a singlet state (indicated as O). O is very reactive with a lifetime between 10-100µs. | 5 | Photochemistry |
In human digestion, proteins in food are broken down into smaller peptide chains by digestive enzymes such as pepsin, trypsin, chymotrypsin, and elastase, and into amino acids by various enzymes such as carboxypeptidase, aminopeptidase, and dipeptidase. It is necessary to break down proteins into small peptides (tripeptides and dipeptides) and amino acids so they can be absorbed by the intestines, and the absorbed tripeptides and dipeptides are also further broken into amino acids intracellularly before they enter the bloodstream. Different enzymes have different specificity for their substrate; trypsin, for example, cleaves the peptide bond after a positively charged residue (arginine and lysine); chymotrypsin cleaves the bond after an aromatic residue (phenylalanine, tyrosine, and tryptophan); elastase cleaves the bond after a small non-polar residue such as alanine or glycine.
In order to prevent inappropriate or premature activation of the digestive enzymes (they may, for example, trigger pancreatic self-digestion causing pancreatitis), these enzymes are secreted as inactive zymogen. The precursor of pepsin, pepsinogen, is secreted by the stomach, and is activated only in the acidic environment found in stomach. The pancreas secretes the precursors of a number of proteases such as trypsin and chymotrypsin. The zymogen of trypsin is trypsinogen, which is activated by a very specific protease, enterokinase, secreted by the mucosa of the duodenum. The trypsin, once activated, can also cleave other trypsinogens as well as the precursors of other proteases such as chymotrypsin and carboxypeptidase to activate them.
In bacteria, a similar strategy of employing an inactive zymogen or prezymogen is used. Subtilisin, which is produced by Bacillus subtilis, is produced as preprosubtilisin, and is released only if the signal peptide is cleaved and autocatalytic proteolytic activation has occurred. | 1 | Biochemistry |
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