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Transitions made by the free valence electrons of the molecules are responsible for the production of scintillation light in organic crystals. These electrons are associated with the whole molecule rather than any particular atom and occupy the so-called -molecular orbitals. The ground state S is a singlet state above which are the excited singlet states (S, the lowest triplet state (T), and its excited levels (T, A fine structure corresponding to molecular vibrational modes is associated with each of those electron levels. The energy spacing between electron levels is ≈1 eV; the spacing between the vibrational levels is about 1/10 of that for electron levels.
An incoming particle can excite either an electron level or a vibrational level. The singlet excitations immediately decay ( state without the emission of radiation (internal degradation). The S state then decays to the ground state S (typically to one of the vibrational levels above S) by emitting a scintillation photon. This is the prompt component or fluorescence. The transparency of the scintillator to the emitted photon is due to the fact that the energy of the photon is less than that required for an S → S transition (the transition is usually being to a vibrational level above S).
When one of the triplet states gets excited, it immediately decays to the T state with no emission of radiation (internal degradation). Since the T → S transition is very improbable, the T state instead decays by interacting with another T molecule:
and leaves one of the molecules in the S state, which then decays to S with the release of a scintillation photon. Since the T-T interaction takes time, the scintillation light is delayed: this is the slow or delayed component (corresponding to delayed fluorescence). Sometimes, a direct T → S transition occurs (also delayed), and corresponds to the phenomenon of phosphorescence. Note that the observational difference between delayed-fluorescence and phosphorescence is the difference in the wavelengths of the emitted optical photon in an S → S transition versus a T → S transition.
Organic scintillators can be dissolved in an organic solvent to form either a liquid or plastic scintillator. The scintillation process is the same as described for organic crystals (above); what differs is the mechanism of energy absorption: energy is first absorbed by the solvent, then passed onto the scintillation solute (the details of the transfer are not clearly understood). | 5 | Photochemistry |
One might believe that sodium or potassium hydride would be the ideal base for deprotonating these precursor salts. The hydride should react irreversibly with the loss of hydrogen to give the desired carbene, with the inorganic by-products and excess hydride being removed by filtration. In practice this reaction is often too slow, requiring the addition of DMSO or t-BuOH. These reagents generate soluble catalysts, which increase the rate of reaction of this heterogeneous system, via the generation of tert-butoxide or dimsyl anion. However, these catalysts have proved ineffective for the preparation of non-imidazolium adducts as they tend to act as nucleophiles towards the precursor salts and in so doing are destroyed. The presence of hydroxide ions as an impurity in the metal hydride could also destroy non-aromatic salts.
Deprotonation with sodium or potassium hydride in a mixture of liquid ammonia/THF at −40 °C has been reported for imidazole-based carbenes. Arduengo and coworkers managed to prepare a dihydroimidazol-2-ylidene using NaH. However, this method has not been applied to the preparation of diaminocarbenes. In some cases, potassium tert-butoxide can be employed without the addition of a metal hydride. | 0 | Organic Chemistry |
Mycosporine-like amino acids are small secondary metabolites produced by organisms that live in environments with high volumes of sunlight, usually marine environments. | 1 | Biochemistry |
Statistical mechanics suggests that can be expressed by a power series called a virial expansion,
The functions are the virial coefficients; the th term represents a particle interaction.
If we note in the expression for that for , the term can be expanded in an absolutely convergent series; this yields
This is the virial expansion for the van der Waals fluid. The first virial coefficient is the slope of at . Notice that it can be positive or negative depending on whether or not , which agrees with the result found previously by differentiation. | 7 | Physical Chemistry |
The first synthesis of tropinone was by Richard Willstätter in 1901. It started from the seemingly related cycloheptanone, but required many steps to introduce the nitrogen bridge; the overall yield for the synthesis path is only 0.75%. Willstätter had previously synthesized cocaine from tropinone, in what was the first synthesis and elucidation of the structure of cocaine. | 0 | Organic Chemistry |
People who are taking meperidine, tramadol, methadone, propoxyphene, dextromethorphan, St. John’s wort, cyclobenzaprine, or another MAO inhibitor should not take rasagiline.
The FDA drug label carries a warning of the risk of serotonin syndrome when rasagiline is used with antidepressants or with meperidine. However the risk appears to be low, based on a multicenter retrospective study in 1504 people, which looked for serotonin syndrome in people with PD who were treated with rasagiline plus antidepressants, rasagiline without antidepressants, or antidepressants plus Parkinson's drugs other than either rasagiline or selegiline; no cases were identified.
There is a risk of psychosis or bizarre behavior if rasagiline is used with dextromethorphan and there is a risk of non-selective MAO inhibition and hypertensive crisis if rasagiline is used with other MAO inhibitors. | 4 | Stereochemistry |
In 1993, Richard J. Roberts and Phillip Allen Sharp received the Nobel Prize in Physiology or Medicine for their discovery of "split genes". Using the model adenovirus in their research, they were able to discover splicing—the fact that pre-mRNA is processed into mRNA once introns were removed from the RNA segment. These two scientists discovered the existence of splice sites, thereby changing the face of genomics research. They also discovered that the splicing of the messenger RNA can occur in different ways, opening up the possibility for a mutation to occur. | 1 | Biochemistry |
Potassium humate is used in agriculture as a fertilizer additive to increase the efficiency of fertilizers especially nitrogen- and phosphorus-based fertilizer inputs. Other salts of humic acid are manufactured, mainly sodium humate, which is used in animal health supplements. It also can be used in aquaculture. | 9 | Geochemistry |
Ristocetin is a glycopeptide antibiotic, obtained from Amycolatopsis lurida, previously used to treat staphylococcal infections. It is no longer used clinically because it caused thrombocytopenia and platelet agglutination. It is now used solely to assay those functions in vitro in the diagnosis of conditions such as von Willebrand disease (vWD) and Bernard–Soulier syndrome. Platelet agglutination caused by ristocetin can occur only in the presence of von Willebrand factor multimers, so if ristocetin is added to blood lacking the factor (or its receptor—see below), the platelets will not clump.
Through an unknown mechanism, the antibiotic ristocetin causes von Willebrand factor to bind the platelet receptor glycoprotein Ib (GpIb), so when ristocetin is added to normal blood, it causes agglutination.
In some types of vWD (types 2B and platelet-type), even very small amounts of ristocetin cause platelet aggregation when the patients platelet-rich plasma is used. This paradox is explained by these types having gain-of-function mutations which cause the vWD high molecular-weight multimers to bind more tightly to their receptors on platelets (the alpha chains of glycoprotein Ib (GPIb) receptors). In the case of type 2B vWD, the gain-of-function mutation involves von Willebrands factor (VWF gene), and in platelet-type vWD, the receptor is the object of the mutation (GPIb). This increased binding causes vWD because the high-molecular weight multimers are removed from circulation in plasma since they remain attached to the patients platelets. Thus, if the patients platelet-poor plasma is used, the ristocetin cofactor assay will not agglutinate standardized platelets (i.e., pooled platelets from normal donors that are fixed in formalin), similar to the other types of vWD.
In all forms of the ristocetin assay, the platelets are fixed in formalin prior to the assay to prevent von Willebrand's factor stored in platelet granules from being released and participating in platelet aggregation. Thus, the ristocetin cofactor activity depends only upon high-molecular multimers of the factor present in circulating plasma. | 1 | Biochemistry |
Precipitation in hydrometallurgy involves the chemical precipitation from aqueous solutions, either of metals and their compounds or of the contaminants. Precipitation will proceed when, through reagent addition, evaporation, pH change or temperature manipulation, the amount of a species present in the solution exceeds the maximum determined by its solubility. | 8 | Metallurgy |
Hawkins et al.. demonstrated the toxic effects of CYN by mouse bioassay, using an extract of the original Palm Island strain. Acutely poisoned mice displayed anorexia, diarrhoea and gasping respiration. Autopsy results revealed haemorrhages in the lungs, livers, kidneys, small intestines and adrenal glands. Histopathology revealed dose-related necrosis of hepatocytes, lipid accumulation, and fibrin thrombi formation in blood vessels of the liver and lungs, along with varying epithelial cell necrosis in areas of the kidneys.
A more recent mouse bioassay of the effects of cylindrospermopsin revealed an increase in liver weight, with both lethal and non-lethal doses; in addition the livers appeared dark-coloured. Extensive necrosis of hepatocytes was visible in mice administered a lethal dose, and some localised damage was also observed in mice administered a non-lethal dose. | 0 | Organic Chemistry |
*The reaction has been attempted in the microwave, improving yields with the α-glucopyranoside to 88% and reducing the reaction time significantly to 14 minutes.
*The original paper by Tipson and Cohen also used acyclic sugars to illustrate the utility of the reaction. Thus the reaction is not limited to cyclic carbohydrate derivatives.
*Sulphonoxy groups such as methanesulfonyl and toluenesulfonyl were both used, however it was found that substrates with toluenesulfonyl groups gave higher yields and lower reaction times. | 0 | Organic Chemistry |
Type III restriction enzymes (e.g., EcoP15) recognize two separate non-palindromic sequences that are inversely oriented. They cut DNA about 20–30 base pairs after the recognition site. These enzymes contain more than one subunit and require AdoMet and ATP cofactors for their roles in DNA methylation and restriction digestion, respectively. They are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. Type III enzymes are hetero-oligomeric, multifunctional proteins composed of two subunits, Res () and Mod (). The Mod subunit recognises the DNA sequence specific for the system and is a modification methyltransferase; as such, it is functionally equivalent to the M and S subunits of type I restriction endonuclease. Res is required for restriction digestion, although it has no enzymatic activity on its own. Type III enzymes recognise short 5–6 bp-long asymmetric DNA sequences and cleave 25–27 bp downstream to leave short, single-stranded 5' protrusions. They require the presence of two inversely oriented unmethylated recognition sites for restriction digestion to occur. These enzymes methylate only one strand of the DNA, at the N-6 position of adenine residues, so newly replicated DNA will have only one strand methylated, which is sufficient to protect against restriction digestion. Type III enzymes belong to the beta-subfamily of N6 adenine methyltransferases, containing the nine motifs that characterise this family, including motif I, the AdoMet binding pocket (FXGXG), and motif IV, the catalytic region (S/D/N (PP) Y/F). | 1 | Biochemistry |
Electron wake is the disturbance left after a high-energy charged particle passes through condensed matter or plasma. Ions passing through can introduce periodic oscillations in the crystal lattice or plasma wave with the characteristic frequency of the crystal or plasma frequency. Interactions of the field created by these oscillations with the charged particle field alternate from constructive interference to destructive interference, producing alternating waves of electric field and displacement. The frequency of the wake field is determined by the nature of the penetrated matter, and the period of the wake field is directly proportional to the speed of the incoming charged particle. The amplitude of the first wake wave is the most important, as it produces a braking force on the charged particle, eventually slowing it down. Wake fields also can capture and guide lightweight ions or positrons in the direction perpendicular to the wake. The larger the speed of the original charged particle, the larger the angle between the initial particles velocity and the captured ions velocity. | 7 | Physical Chemistry |
Sulfur concrete was developed and promoted as a building material to get rid of large amounts of stored sulfur produced by hydrodesulfurization of gas and oil (Claus process). As of 2011, sulfur concrete has only been used in small quantities when fast curing or acid resistance is necessary.The material has been suggested by researchers as a potential building material on Mars, where water and limestone are not easily available, but sulfur is. | 8 | Metallurgy |
Thermal spraying is a line of sight process and the bond mechanism is primarily mechanical. Thermal spray application is not compatible with the substrate if the area to which it is applied is complex or blocked by other bodies. | 8 | Metallurgy |
In the 1920s, Otto Heinrich Warburg discovered an intriguing bioenergetic phenotype shared by most tumor cells: a higher-than-normal reliance on lactic acid fermentation for energy generation. He is known as the "Father of Oncometabolism". Although the roots of this research field trace back to the 1920s, it was only recently recognized Over the last decade, research on cancer progression has focused on the role of shifting metabolic pathways for both the cancer and immune cells, leading to an increase interest in characterizing the metabolic alterations that cells undergo in the TME. | 1 | Biochemistry |
Pulse radiolysis is a recent method of initiating fast reactions to study reactions occurring on a timescale faster than approximately one hundred microseconds, when simple mixing of reagents is too slow and other methods of initiating reactions have to be used.
The technique involves exposing a sample of material to a beam of highly accelerated electrons, where the beam is generated by a linac. It has many applications. It was developed in the late 1950s and early 1960s by John Keene in Manchester and Jack W. Boag in London. | 5 | Photochemistry |
The mechanism for chloroplast DNA (cpDNA) replication has not been conclusively determined, but two main models have been proposed. Scientists have attempted to observe chloroplast replication via electron microscopy since the 1970s. The results of the microscopy experiments led to the idea that chloroplast DNA replicates using a double displacement loop (D-loop). As the D-loop moves through the circular DNA, it adopts a theta intermediary form, also known as a Cairns replication intermediate, and completes replication with a rolling circle mechanism. Replication starts at specific points of origin. Multiple replication forks open up, allowing replication machinery to replicate the DNA. As replication continues, the forks grow and eventually converge. The new cpDNA structures separate, creating daughter cpDNA chromosomes.
In addition to the early microscopy experiments, this model is also supported by the amounts of deamination seen in cpDNA. Deamination occurs when an amino group is lost and is a mutation that often results in base changes. When adenine is deaminated, it becomes hypoxanthine (H). Hypoxanthine can bind to cytosine, and when the HC base pair is replicated, it becomes a GC (thus, an A → G base change).
In cpDNA, there are several A → G deamination gradients. DNA becomes susceptible to deamination events when it is single stranded. When replication forks form, the strand not being copied is single stranded, and thus at risk for A → G deamination. Therefore, gradients in deamination indicate that replication forks were most likely present and the direction that they initially opened (the highest gradient is most likely nearest the start site because it was single stranded for the longest amount of time). This mechanism is still the leading theory today; however, a second theory suggests that most cpDNA is actually linear and replicates through homologous recombination. It further contends that only a minority of the genetic material is kept in circular chromosomes while the rest is in branched, linear, or other complex structures. | 5 | Photochemistry |
Lead and LBE coolant are more corrosive to steel than sodium, and this puts an upper limit on the velocity of coolant flow through the reactor due to safety considerations. Furthermore, the higher melting points of lead and LBE (327 °C and 123.5 °C respectively) may mean that solidification of the coolant may be a greater problem when the reactor is operated at lower temperatures.
Finally, upon neutron radiation bismuth-209, the main isotope of bismuth present in LBE coolant, undergoes neutron capture and subsequent beta decay, forming polonium-210, a potent alpha emitter. The presence of radioactive polonium in the coolant would require special precautions to control alpha contamination during refueling of the reactor and handling components in contact with LBE. | 8 | Metallurgy |
Peptide-based self-healing hydrogels may be selectively grown onto nanofiber material which can then incorporated into the desired reconstructive tissue target. The hydrogel framework is then chemically modified to promote cell adhesion to the nanofiber peptide scaffold. Because the growth of the extracellular matrix scaffold is pH dependent, the materials selected must be factored for pH response when selecting the scaffolding material. | 7 | Physical Chemistry |
The most critical aspect in biomass fermentation processes is related to its productivity. The ABE fermentation via Clostridium beijerinckii or Clostridium acetobutylicum for instance is characterized by product inhibition. This means that there is a product concentration threshold that cannot be overcome, resulting in a product stream highly diluted in water.
For this reason, in order to have a comparable productivity and profitability with respect to the petrochemical processes, cost and energy effective solutions for the product purification sections are required to provide a significant product recovery at the desired purity.
The main solutions adopted during the last decades have been as follows:
* The employment of less expensive raw materials, and in particular lignocellulosic waste or algae;
* The microorganisms modifications or the research of new strains less sensitive to the butanol concentration poisoning to increase productivity and selectivity towards the butanol species;
* The fermentation reactor optimization aimed at increasing the productivity;
* The reduction of the energy costs of the separation and purification downstream processing and, in particular, to carry out the separation in-situ in the reactor;
* The use of side products such as hydrogen and carbon dioxide, solid wastes and discharged microorganisms and carry out less expensive process wastewater treatments.
In the second half of the 20th century, these technologies allowed an increase in the final product concentration in the broth from 15 to 30 g/L, an increase in the final productivity from 0.46 to 4.6 g/(L*h) and an increase in the yield from 15 to 42%.
From a compound purification perspective, the main criticalities in the ABE/W product recovery are due to the water–alcohol mixture's non-ideal interactions leading to homogeneous and heterogeneous azeotropic species, as shown by the ternary equilibrium diagram.
This causes the separation by standard distillation to be particularly impractical but, on the other hand, allows the exploitation of the liquid–liquid demixing region both for analogous and alternative separation processes.
Therefore, in order to enhance the ABE fermentation yield, mainly in situ product recovery systems have been developed. These include gas stripping, pervaporation, liquid–liquid extraction, distillation via Dividing Wall Column, membrane distillation, membrane separation, adsorption, and reverse osmosis. Green Biologics Ltd. implemented many of these technologies at an industrial scale.
Moreover, differently from crude oil feedstocks, biomasses nature fluctuates over the years seasons and according to the geographical location. For this reasons, biorefinery operations need not only to be effective but also to be flexible and to be able to switch between two operating conditions rather quickly.[citation needed'] | 1 | Biochemistry |
The cholinergic system consists of projection neurons from the pedunculopontine nucleus, laterodorsal tegmental nucleus, and basal forebrain and interneurons from the striatum and nucleus accumbens. It is not yet clear whether acetylcholine as a neuromodulator acts through volume transmission or classical synaptic transmission, as there is evidence to support both theories. Acetylcholine binds to both metabotropic muscarinic receptors (mAChR) and the ionotropic nicotinic receptors (nAChR). The cholinergic system has been found to be involved in responding to cues related to the reward pathway, enhancing signal detection and sensory attention, regulating homeostasis, mediating the stress response, and encoding the formation of memories. | 1 | Biochemistry |
In 2005 a two hybrid system in plants was developed. Using protoplasts of A. thaliana protein-protein interactions can be studied in plants. This way the interactions can be studied in their native context. In this system the GAL4 AD and BD are under the control of the strong 35S promoter. Interaction is measured using a GUS reporter. In order to enable a high-throughput screening the vectors were made gateway compatible.
The system is known as the protoplast two hybrid (P2H) system. | 1 | Biochemistry |
The designations were established by the journal Zeitschrift für Kristallographie – Crystalline Materials, which published its first round of supplemental reviews under the name Strukturbericht from 1913-1928. These reports were collected into a book published in 1931 by Paul Peter Ewald and Carl Hermann which became Volume 1 of Strukturbericht. While the series was continued after the war under the name Structure reports, which was published through 1990, the series stopped generating new symbols. Instead, some new additional designations were given in books by Smithels, and Pearson.
For the first volume, the designation consisted of a capital letter (A,B,C,D,E,F,G,H,L,M,O) specifying a broad category of compounds, and then a number to specify a particular crystal structure. In the second volume, subscript numbers were added, some early symbols were modified (e.g. what was initially D1 became D0, noted in the tables below as "D1 → D0"), and the categories were modified (types I,K,S were added). In the third volume, the class I was renamed J. Later designations began to use a lower case letter in subscripts as well. | 3 | Analytical Chemistry |
In theoretical chemistry, Specific ion Interaction Theory (SIT theory) is a theory used to estimate single-ion activity coefficients in electrolyte solutions at relatively high concentrations. It does so by taking into consideration interaction coefficients between the various ions present in solution. Interaction coefficients are determined from equilibrium constant values obtained with solutions at various ionic strengths. The determination of SIT interaction coefficients also yields the value of the equilibrium constant at infinite dilution. | 7 | Physical Chemistry |
The Yukawa–Tsuno equation allows for treatment of both para- and meta- substituents, and it also better correlates data from reactions with high electron demand than the original Hammett equation. However, this equation does not take into account the effects of various solvents on organic reactions. Also, Yukawa and Tsuno note that, even within a group of similar reactions, -values for more electron-withdrawing substituents tend to be higher than predicted—seen as a slight increase in slope on a Yukawa–Tsuno plot—and thus, are not as strongly correlated with the remainder of the data. | 7 | Physical Chemistry |
Most chloroplasts in a photosynthetic cell do not develop directly from proplastids or etioplasts. In fact, a typical shoot meristematic plant cell contains only 7–20 proplastids. These proplastids differentiate into chloroplasts, which divide to create the 30–70 chloroplasts found in a mature photosynthetic plant cell. If the cell divides, chloroplast division provides the additional chloroplasts to partition between the two daughter cells.
In single-celled algae, chloroplast division is the only way new chloroplasts are formed. There is no proplastid differentiation—when an algal cell divides, its chloroplast divides along with it, and each daughter cell receives a mature chloroplast.
Almost all chloroplasts in a cell divide, rather than a small group of rapidly dividing chloroplasts. Chloroplasts have no definite S-phase—their DNA replication is not synchronized or limited to that of their host cells.
Much of what we know about chloroplast division comes from studying organisms like Arabidopsis and the red alga Cyanidioschyzon merolæ.
The division process starts when the proteins FtsZ1 and FtsZ2 assemble into filaments, and with the help of a protein ARC6, form a structure called a Z-ring within the chloroplast's stroma. The Min system manages the placement of the Z-ring, ensuring that the chloroplast is cleaved more or less evenly. The protein MinD prevents FtsZ from linking up and forming filaments. Another protein ARC3 may also be involved, but it is not very well understood. These proteins are active at the poles of the chloroplast, preventing Z-ring formation there, but near the center of the chloroplast, MinE inhibits them, allowing the Z-ring to form.
Next, the two plastid-dividing rings, or PD rings form. The inner plastid-dividing ring is located in the inner side of the chloroplasts inner membrane, and is formed first. The outer plastid-dividing ring is found wrapped around the outer chloroplast membrane. It consists of filaments about 5 nanometers across, arranged in rows 6.4 nanometers apart, and shrinks to squeeze the chloroplast. This is when chloroplast constriction begins. <br />In a few species like Cyanidioschyzon merolæ, chloroplasts have a third plastid-dividing ring located in the chloroplasts intermembrane space.
Late into the constriction phase, dynamin proteins assemble around the outer plastid-dividing ring, helping provide force to squeeze the chloroplast. Meanwhile, the Z-ring and the inner plastid-dividing ring break down. During this stage, the many chloroplast DNA plasmids floating around in the stroma are partitioned and distributed to the two forming daughter chloroplasts.
Later, the dynamins migrate under the outer plastid dividing ring, into direct contact with the chloroplast's outer membrane, to cleave the chloroplast in two daughter chloroplasts.
A remnant of the outer plastid dividing ring remains floating between the two daughter chloroplasts, and a remnant of the dynamin ring remains attached to one of the daughter chloroplasts.
Of the five or six rings involved in chloroplast division, only the outer plastid-dividing ring is present for the entire constriction and division phase—while the Z-ring forms first, constriction does not begin until the outer plastid-dividing ring forms. | 5 | Photochemistry |
The mechanism by which natural siRNA causes gene silencing through repression of translation occurs as follows:
# Long dsRNA (which can come from hairpin, complementary RNAs, and RNA-dependent RNA polymerases) is cleaved by an endo-ribonuclease called Dicer. Dicer cuts the long dsRNA to form short interfering RNA or siRNA; this is what enables the molecules to form the RNA-Induced Silencing Complex (RISC).
# Once siRNA enters the cell it gets incorporated into other proteins to form the RISC.
# Once the siRNA is part of the RISC complex, the siRNA is unwound to form single stranded siRNA.
# The strand that is thermodynamically less stable due to its base pairing at the 5´end is chosen to remain part of the RISC-complex
# The single stranded siRNA which is part of the RISC complex now can scan and find a complementary mRNA
# Once the single stranded siRNA (part of the RISC complex) binds to its target mRNA, it induces mRNA cleavage.
# The mRNA is now cut and recognized as abnormal by the cell. This causes degradation of the mRNA and in turn no translation of the mRNA into amino acids and then proteins. Thus silencing the gene that encodes that mRNA.
siRNA is also similar to miRNA, however, miRNAs are derived from shorter stemloop RNA products. miRNAs typically silence genes by repression of translation and have broader specificity of action, while siRNAs typically work with higher specificity by cleaving the mRNA before translation, with 100% complementarity. | 1 | Biochemistry |
Micronutrients are essential dietary elements required in varying quantities throughout life to serve metabolic and physiological functions.
* Dietary minerals, such as copper and iron, are elements native to Earth, and cannot be synthesized. They are required in the diet in microgram or milligram amounts. As plants obtain minerals from the soil, dietary minerals derive directly from plants consumed or indirectly from edible animal sources.
* Vitamins are organic compounds required in microgram or milligram amounts. The importance of each dietary vitamin was first established when it was determined that a disease would develop if that vitamin was absent from the diet. | 9 | Geochemistry |
The reaction of carbon dioxide with epoxides is a general route to the preparation of cyclic 5-membered carbonates. Annual production of cyclic carbonates was estimated at 100,000 tonnes per year in 2010. Industrially, ethylene and propylene oxides readily react with carbon dioxide to give ethylene and propylene carbonates (with an appropriate catalyst). For example:
: CHO + CO → CHOCO | 0 | Organic Chemistry |
Eukaryotic Rad51 and its related family members are homologous to the archaeal RadA and bacterial RecA recombinases. Rad51 is highly conserved from yeast to humans. It has a key function in the recombinational repair of DNA damages, particularly double-strand damages such as double-strand breaks. In humans, over- or under-expression of Rad51 occurs in a wide variety of cancers.
During meiosis Rad51 interacts with another recombinase, Dmc1, to form a presynaptic filament that is an intermediate in homologous recombination. Dmc1 function appears to be limited to meiotic recombination. Like Rad51, Dmc1 is homologous to bacterial RecA. | 1 | Biochemistry |
Increases in carbon capture and sequestration have been observed in both mangrove and seagrass ecosystems which have been subjected to high nutrient loads, either intentionally or due to waste from human activities.
Research done on mangrove soils from the Red Sea have shown that increases in nutrient loads to these soils do not increase carbon mineralization and subsequent CO release. This neutral effect of fertilization was not found to be true in all mangrove forest types. Carbon capture rates also increased in these forests due to increased growth rates of the mangroves. In forests with increases in respiration there were also increases in mangrove growth of up to six times the normal rate. | 9 | Geochemistry |
Levan is synthesized in archaea, fungi, bacteria, and a limited number of plant species. Fructans such as levan are synthesized from sucrose, a disaccharide containing glucose and fructose. In plants, the vacuole is where fructan production occurs. Sucrose:sucrose/fructan 6-fructosyltransferase is the fructosyltransferase in the vacuole which creates the beta 2,6 linkages to form the linear form of levan. Bacteria also use a fructosyltransferase known as levansucrase to form levan. These enzymes in bacteria form the 2,1 linkages in the linear basal chains of levan to allow for branching points to occur. Many bacteria produce levan in the cell exterior. This production can be sensitive to temperature, oxygen concentration, pH, and other factors. Levan production in bacteria is typically a sign of growth in population. There are also possible ways to produce by fracturing soybean mucilage.
Levans are produced by microbes during colonization of a food substrate. Erwinia amylovora exudes levan and amylovoran as part of its biofilm. Together they contribute to its pathogenicity. In 2016, Ua-Arak et al. developed a sourdough method with high levan output (among other exopolysaccharides). | 1 | Biochemistry |
There are three common naming conventions for specifying one of the two enantiomers (the absolute configuration) of a given chiral molecule: the R/S system is based on the geometry of the molecule; the (+)- and (−)- system (also written using the obsolete equivalents d- and l-) is based on its optical rotation properties; and the / system is based on the molecule's relationship to enantiomers of glyceraldehyde.
The R/S system is based on the molecule's geometry with respect to a chiral center. The R/S system is assigned to a molecule based on the priority rules assigned by Cahn–Ingold–Prelog priority rules, in which the group or atom with the largest atomic number is assigned the highest priority and the group or atom with the smallest atomic number is assigned the lowest priority.
The (+)- and (−)- is used to specify a molecule's optical rotation — the direction that the molecule rotates in polarized light. When a molecule is denoted dextrorotatory it is rotating the plane of polarized light clockwise and can also be denoted as (+). When it is denoted as levorotatory it is rotating the plane of polarized light counterclockwise and can also be denoted as (−).
The Latin words for left are laevus and sinister, and the word for right is dexter (or rectus in the sense of correct or virtuous). The English word right is a cognate of rectus. This is the origin of the D/L and R/S notations, and the employment of prefixes levo- and dextro- in common names.
The prefix ar-, from the Latin recto (right), is applied to the right-handed version; es-, from the Latin sinister (left), to the left-handed molecule. Example: ketamine, arketamine, esketamine. | 4 | Stereochemistry |
Magmatic water, also known as juvenile water, is an aqueous phase in equilibrium with minerals that have been dissolved by magma deep within the Earth's crust and is released to the atmosphere during a volcanic eruption. It plays a key role in assessing the crystallization of igneous rocks, particularly silicates, as well as the rheology and evolution of magma chambers. Magma is composed of minerals, crystals and volatiles in varying relative natural abundance. Magmatic differentiation varies significantly based on various factors, most notably the presence of water. An abundance of volatiles within magma chambers decreases viscosity and leads to the formation of minerals bearing halogens, including chloride and hydroxide groups. In addition, the relative abundance of volatiles varies within basaltic, andesitic, and rhyolitic magma chambers, leading to some volcanoes being exceedingly more explosive than others. Magmatic water is practically insoluble in silicate melts but has demonstrated the highest solubility within rhyolitic melts. An abundance of magmatic water has been shown to lead to high-grade deformation, altering the amount of δO and δH within host rocks. | 9 | Geochemistry |
Type E (chromel–constantan) has a high output (68 μV/°C), which makes it well suited to cryogenic use. Additionally, it is non-magnetic.
Wide range is −270 °C to +740 °C
and narrow range is −110 °C to +140 °C. | 8 | Metallurgy |
Peptidoglycan recognition is an evolutionarily conserved process. The overall structure is similar between bacterial species, but various modifications can increase the diversity. These include modifications of the length of sugar polymers, modifications in the sugar structures, variations in cross-linking or substitutions of amino acids (primarily at the third position). The aim of these modifications is to alter the properties of the cell wall, which plays a vital role in pathogenesis.
Peptidoglycans can be degraded by several enzymes (lysozyme, glucosaminidase, endopeptidase...), producing immunostimulatory fragments (sometimes called muropeptides) that are critical for mediating host-pathogen interactions. These include MDP (muramyl dipeptide), NAG (N-acetylglucosamine) or iE-DAP (γ-d-glutamyl-meso-diaminopimelic acid).
Peptidoglycan from intestinal bacteria (both pathogens and commensals) crosses the intestinal barrier even under physiological conditions. Mechanisms through which peptidoglycan or its fragments enter the host cells can be direct (carrier-independent) or indirect (carrier-dependent), and they are either bacteria-mediated (secretion systems, membrane vesicles) or host cell-mediated (receptor-mediated, peptide transporters). Bacterial secretion systems are protein complexes used for the delivery of virulence factors across the bacterial cell envelope to the exterior environment. Intracellular bacterial pathogens invade eukaryotic cells (which may lead to the formation of phagolysosomes and/or autophagy activation), or bacteria may be engulfed by phagocytes (macrophages, monocytes, neutrophils...). The bacteria-containing phagosome may then fuse with endosomes and lysosomes, leading to degradation of bacteria and generation of polymeric peptidoglycan fragments and muropeptides. | 1 | Biochemistry |
Using vibrational perturbation theory, effects such as tunnelling and variational effects can be accounted for within the SCTST formalism. | 7 | Physical Chemistry |
Before the Industrial Revolution, the ocean was a source of CO to the atmosphere balancing the impact of rock weathering and terrestrial particulate organic carbon; now it has become a sink for the excess atmospheric CO. Carbon dioxide is absorbed from the atmosphere at the ocean's surface at an exchange rate which varies locally but on average, the oceans have a net absorption of CO 2.2 Pg C per year. Because the solubility of carbon dioxide increases when temperature decreases, cold areas can contain more CO and still be in equilibrium with the atmosphere; In contrast, rising sea surface temperatures decrease the capacity of the oceans to take in carbon dioxide. The North Atlantic and Nordic oceans have the highest carbon uptake per unit area in the world, and in the North Atlantic deep convection transports approximately 197 Tg per year of non-refractory carbon to depth.
A 2020 study found significantly higher net flux of carbon into the oceans compared to previous studies. The new study used satellite data to account for small temperature differences between the surface of the ocean and the depth of a few meters where the measurements are made. | 9 | Geochemistry |
An alternating magnetic field is applied at the atomizer (graphite furnace) to split the absorption line into three components, the π component, which remains at the same position as the original absorption line, and two σ components, which are moved to higher and lower wavelengths, respectively. Total absorption is measured without magnetic field and background absorption with the magnetic field on. The π component has to be removed in this case, e.g. using a polarizer, and the σ components do not overlap with the emission profile of the lamp, so that only the background absorption is measured. The advantages of this technique are that total and background absorption are measured with the same emission profile of the same lamp, so that any kind of background, including background with fine structure can be corrected accurately, unless the molecule responsible for the background is also affected by the magnetic field and using a chopper as a polariser reduces the signal to noise ratio. While the disadvantages are the increased complexity of the spectrometer and power supply needed for running the powerful magnet needed to split the absorption line. | 3 | Analytical Chemistry |
The most widely used numerical laser diffraction results are:
* The median volume-weighted diameter, or D. Derived from the cumulative curve, it represents the particle diameter separating the upper 50 % of the data from the lower 50 %.
* The D and D values, also derived from the cumulative curve.
* The mean volume-weighted diameter, also termed D[4,3] or De Brouckere mean diameter.
* The span, which gives a measure of the width of the particle size distribution, and is calculated as span = [D – D]/D. | 7 | Physical Chemistry |
A cDNA library is a combination of cloned cDNA (complementary DNA) fragments inserted into a collection of host cells, which constitute some portion of the transcriptome of the organism and are stored as a "library". cDNA is produced from fully transcribed mRNA found in the nucleus and therefore contains only the expressed genes of an organism. Similarly, tissue-specific cDNA libraries can be produced. In eukaryotic cells the mature mRNA is already spliced, hence the cDNA produced lacks introns and can be readily expressed in a bacterial cell. While information in cDNA libraries is a powerful and useful tool since gene products are easily identified, the libraries lack information about enhancers, introns, and other regulatory elements found in a genomic DNA library. | 1 | Biochemistry |
The FRET efficiency () is the quantum yield of the energy-transfer transition, i.e. the probability of energy-transfer event occurring per donor excitation event:
where the radiative decay rate of the donor, is the rate of energy transfer, and the rates of any other de-excitation pathways excluding energy transfers to other acceptors.
The FRET efficiency depends on many physical parameters that can be grouped as: 1) the distance between the donor and the acceptor (typically in the range of 1–10 nm), 2) the spectral overlap of the donor emission spectrum and the acceptor absorption spectrum, and 3) the relative orientation of the donor emission dipole moment and the acceptor absorption dipole moment.
depends on the donor-to-acceptor separation distance with an inverse 6th-power law due to the dipole–dipole coupling mechanism:
with being the Förster distance of this pair of donor and acceptor, i.e. the distance at which the energy transfer efficiency is 50%.
The Förster distance depends on the overlap integral of the donor emission spectrum with the acceptor absorption spectrum and their mutual molecular orientation as expressed by the following equation all in SI units:
where is the fluorescence quantum yield of the donor in the absence of the acceptor, is the dipole orientation factor, is the refractive index of the medium, is the Avogadro constant, and is the spectral overlap integral calculated as
where is the donor emission spectrum, is the donor emission spectrum normalized to an area of 1, and is the acceptor molar extinction coefficient, normally obtained from an absorption spectrum.
The orientation factor is given by
where denotes the normalized transition dipole moment of the respective fluorophore, and denotes the normalized inter-fluorophore displacement.
= 2/3 is often assumed. This value is obtained when both dyes are freely rotating and can be considered to be isotropically oriented during the excited-state lifetime. If either dye is fixed or not free to rotate, then = 2/3 will not be a valid assumption. In most cases, however, even modest reorientation of the dyes results in enough orientational averaging that = 2/3 does not result in a large error in the estimated energy-transfer distance due to the sixth-power dependence of on . Even when is quite different from 2/3, the error can be associated with a shift in , and thus determinations of changes in relative distance for a particular system are still valid. Fluorescent proteins do not reorient on a timescale that is faster than their fluorescence lifetime. In this case 0 ≤ ≤ 4.
The units of the data are usually not in SI units. Using the original units to calculate the Förster distance is often more convenient. For example, the wavelength is often in unit nm and the extinction coefficient is often in unit , where is concentration . obtained from these units will have unit . To use unit Å () for the , the equation is adjusted to
: (Å)
For time-dependent analyses of FRET, the rate of energy transfer () can be used directly instead:
where is the donor's fluorescence lifetime in the absence of the acceptor.
The FRET efficiency relates to the quantum yield and the fluorescence lifetime of the donor molecule as follows:
where and are the donor fluorescence lifetimes in the presence and absence of an acceptor respectively, or as
where and are the donor fluorescence intensities with and without an acceptor respectively. | 1 | Biochemistry |
The Hildebrand solubility parameter (δ) provides a numerical estimate of the degree of interaction between materials and can be a good indication of solubility, particularly for nonpolar materials such as many polymers. Materials with similar values of δ are likely to be miscible. | 7 | Physical Chemistry |
The thermodynamics of metal ion complex formation provides much significant information. In particular it is useful in distinguishing between enthalpic and entropic effects. Enthalpic effects depend on bond strengths and entropic effects have to do with changes in the order/disorder of the solution as a whole. The chelate effect, below, is best explained in terms of thermodynamics.
An equilibrium constant is related to the standard Gibbs free energy change for the reaction
R is the gas constant and T is the absolute temperature. At 25 °C, . Free energy is made up of an enthalpy term and an entropy term.
The standard enthalpy change can be determined by calorimetry or by using the Van 't Hoff equation, though the calorimetric method is preferable. When both the standard enthalpy change and stability constant have been determined, the standard entropy change is easily calculated from the equation above.
The fact that stepwise formation constants of complexes of the type ML decrease in magnitude as n increases may be partly explained in terms of the entropy factor. Take the case of the formation of octahedral complexes.
For the first step m = 6, n = 1 and the ligand can go into one of 6 sites. For the second step m = 5 and the second ligand can go into one of only 5 sites. This means that there is more randomness in the first step than the second one; ΔS is more positive, so ΔG is more negative and . The ratio of the stepwise stability constants can be calculated on this basis, but experimental ratios are not exactly the same because ΔH is not necessarily the same for each step. Exceptions to this rule are discussed below, in #chelate effect and #Geometrical factors. | 7 | Physical Chemistry |
Extensive studies have been performed on the formation of enolates. It is possible to generate, in most cases, the desired enolate geometry:
For ketones, most enolization conditions give Z enolates. For esters, most enolization conditions give E enolates. The addition of HMPA is known to reverse the stereoselectivity of deprotonation.
The stereoselective formation of enolates has been rationalized with the Ireland model, although its validity is somewhat questionable. In most cases, it is not known which, if any, intermediates are monomeric or oligomeric in nature; nonetheless, the Ireland model remains a useful tool for understanding enolates.
In the Ireland model, the deprotonation is assumed to proceed by a six-membered or cyclic monomeric transition state. The larger of the two substituents on the electrophile (in the case above, methyl is larger than proton) adopts an equatorial disposition in the favored transition state, leading to a preference for E enolates. The model clearly fails in many cases; for example, if the solvent mixture is changed from THF to 23% HMPA-THF (as seen above), the enolate geometry is reversed, which is inconsistent with this model and its cyclic transition state. | 0 | Organic Chemistry |
The thermal conductivity of common solders ranges from 30 to 400 W/(m·K), and the density from 9.25 to 15.00 g/cm. | 8 | Metallurgy |
The relation between the change in Gibbs reaction energy and Gibbs energy can be defined as the slope of the Gibbs energy plotted against the extent of reaction at constant pressure and temperature.
This formula leads to the Nernst equation when applied to the oxidation-reduction reaction which generates the voltage of a voltaic cell. Analogously, the relation between the change in reaction enthalpy and enthalpy can be defined. For example, | 7 | Physical Chemistry |
A program package MatchMiner was used to scan HUGO names for cloned genes of interest are scanned, then are input into GoMiner, which leveraged the GO to identify the biological processes, functions and components represented in the gene profile. Also, Database for Annotation, Visualization, and Integrated Discovery (DAVID) and KEGG database can be used for the analysis of microarray expression data and the analysis of each GO biological process (P), cellular component (C), and molecular function (F) ontology. In addition, DAVID tools can be used to analyze the roles of genes in metabolic pathways and show the biological relationships between genes or gene-products and may represent metabolic pathways. These two databases also provide bioinformatics tools online to combine specific biochemical information on a certain organism and facilitate the interpretation of biological meanings for experimental data. By using a combined approach of Microarray-Bioinformatic technologies, a potential metabolic mechanism contributing to colorectal cancer (CRC) has been demonstrated Several environmental factors may be involved in a series of points along the genetic pathway to CRC. These include genes associated with bile acid metabolism, glycolysis metabolism and fatty acid metabolism pathways, supporting a hypothesis that some metabolic alternations observed in colon carcinoma may occur in the development of CRC. | 7 | Physical Chemistry |
The practical uses of an instrument that uses a single probe are that it allows for the developing of a high throughput device. A high throughput surface tension device can be used for formulation in real time for understanding the penetration of drugs in the blood–brain barrier (BBB), understanding the solubility of drugs, development of a screen to test a drugs toxicity, determining the physicochemical properties of oxidized phospholipids, and development of new surfactant/polymers. | 7 | Physical Chemistry |
Pore formation following ultrasound application was first reported in 1999 in a study that observed cell membrane craters following ultrasound application at 255 kHz. Later, sonoporation mediated microinjection of dextran molecules showed that membrane permeability mechanisms differ depending on the size of dextran molecules. Microinjection of dextran molecules from 3 to 70 kDa was reported to have crossed the cellular membrane via transient pores. In contrast, dextran molecules of 155 and 500 kDa were predominantly found in vesicle-like structures, likely indicating the mechanism of endocytosis. This variability in membrane behavior has led to other studies investigating membrane rupture and resealing characteristics depending on ultrasound amplitude and duration. | 1 | Biochemistry |
During the Middle Ages, between the 5th and 16th century AD, Western Europe saw a period of growth in the mining industry. The first important mines were those at Goslar in the Harz mountains, taken into commission in the 10th century. Another notable mining town is Falun in Sweden where copper has been mined since at least the 10th century and possibly even earlier. (Olsson 2010)
The rise of the Western European mining industry depended on the increasing influence of Western Europe on the world stage. Advances in medieval mining and metallurgy enabled the flourishing of Western European civilization. Accessible ores and improved extraction techniques supported economic growth and trade. Innovations like water-powered machinery and better smelting methods increased the productivity and quality of metals.
Metallurgical activities were also encouraged by the central political powers, regional authorities, monastic orders, and ecclesiastical overlords. These powers attempted to claim royal rights over the mines and a share in the output, both on private lands and regions belonging to The Crown. They were particularly interested in the extraction of the precious metal ores, and for this reason, the mines in their territories were open to all miners (Nef 1987, 706–715). | 8 | Metallurgy |
A number of blocking agents maybe employed but a common one is Methylethyl ketone oxime (MEKO). Caprolactam is also used.
When blocked, there is no isocyanate (NCO) functionality, so it is much easier to disperse the species in water if the desire is to produce waterborne resins. One of the key reasons different blocking agents are used apart from chemical properties is that they unblock at different temperatures. MEKO has a fairly low unblocking temperature and is thus in fairly common usage. A mixture of blocking agents maybe used to optimize properties. | 0 | Organic Chemistry |
The specific weight, also known as the unit weight (symbol , the Greek letter gamma), is a volume-specific quantity defined as the weight per unit volume of a material.
A commonly used value is the specific weight of water on Earth at , which is . | 7 | Physical Chemistry |
Caution should be exercised in people who have narcolepsy in comorbidity with postural orthostatic tachycardia syndrome (POTS). Modafinil, like other centrally acting stimulants prescribed for people with narcolepsy, increases POTS-related autonomic dysfunction and results in tachycardia/arrhythmia side effects in people with cardiovascular risk factors. Sodium oxybate, a metabolite of GABA, is a CNS depressant which makes it an alternative drug for stimulant-intolerant people with POTS. | 4 | Stereochemistry |
Vukić Mićović (Serbian: Вукић Мићовић; Bare Kraljske, near Andrijevica, Montenegro, 1 January 1896 – Belgrade, Serbia, Yugoslavia, 19 January 1981) was a Serbian chemist, professor and dean of the Faculty of Natural Sciences and Mathematics in Belgrade, rector of the University of Belgrade and academician of SANU. | 0 | Organic Chemistry |
Recent trends in high-density interconnects have led to the use of copper pillar solder bumps (CPB) for CPU and GPU packaging. CPBs are an attractive replacement for traditional solder bumps because they provide a fixed stand-off independent of pitch. This is extremely important as most of the high-end products are underfilled and a smaller standoff may create difficulties in getting the underfill adhesive to flow under the die.
Figure 2 shows an example of a CPB fabricated by Intel and incorporated into their Presler line of microprocessors among others. The cross section shows copper and a copper pillar (approximately 60 um high) electrically connected through an opening (or via) in the chip passivation layer at the top of the picture. At the bottom is another copper trace on the package substrate with solder between the two copper layers. | 7 | Physical Chemistry |
Disjoining pressure can be expressed as:
where (in SI units):
* - disjoining pressure (N/m)
* - the surface area of the interacting surfaces (m)
* - total Gibbs energy of the interaction of the two surfaces (J)
* - distance (m)
* indices and signify that the temperature, volume, and the surface area remain constant in the derivative.
Using the concept of the disjoining pressure, the pressure in a film can be viewed as:
where:
* - pressure in a film (Pa)
* - pressure in the bulk of the same phase as that of the film (Pa)
Disjoining pressure is interpreted as a sum of several interactions: dispersion forces, electrostatic forces between charged surfaces, interactions due to layers of neutral molecules adsorbed on the two surfaces, and the structural effects of the solvent.
Classic theory predicts that the disjoining pressure of a thin liquid film on a flat surface as follows,
where:
* - Hamaker constant (J)
* - liquid film thickness (m)
For a solid-liquid-vapor system where the solid surface is structured, the disjoining pressure is affected by the solid surface profile, , and the meniscus shape,
where:
* - solid-liquid potential (J/m)
The meniscus shape can be by minimization of total system free energy as follows
where:
* - total system free energy including surface excess energy and free energy due to solid-liquid interactions (J/m)
* - meniscus shape (m)
* - slope of meniscus shape (1)
In the theory of liquid drops and films, the disjoining pressure can be shown to be related to the equilibrium liquid-solid contact angle through the relation
where is the liquid-vapor surface tension and is the precursor film thickness. | 7 | Physical Chemistry |
Red mud is the waste product that is produced in the digestion of bauxite with sodium hydroxide. It has high calcium and sodium hydroxide content with a complex chemical composition, and accordingly is very caustic and a potential source of pollution. The amount of red mud produced is considerable, and this has led scientists and refiners to seek uses for it. It has received attention as a possible source of vanadium. Due to the low extraction yield much of the gallium ends up in the aluminium oxide as an impurity and in the red mud.
One use of red mud is in ceramic production. Red mud dries into a fine powder that contains iron, aluminium, calcium and sodium. It becomes a health risk when some plants use the waste to produce aluminium oxides.
In the United States, the waste is disposed in large impoundments, a sort of reservoir created by a dam. The impoundments are typically lined with clay or synthetic liners. The US does not approve of the use of the waste due to the danger it poses to the environment. The EPA identified high levels of arsenic and chromium in some red mud samples. | 8 | Metallurgy |
Although oxygen levels inside processing equipment are usually low, it cannot be fully excluded and thermal-oxidation will usually take place more readily than degradation that is exclusively thermal (i.e. without air). Reactions follow the general autoxidation mechanism, leading to the formation of organic peroxides and carbonyls. The addition of antioxidants may inhibit such processes. | 7 | Physical Chemistry |
Autacoids or autocoids are biological factors (molecules) which act like local hormones, have a brief duration, and act near their site of biosynthesis. The word autacoid comes from the Greek words "autos" (self) and "acos" (relief; i.e., drug). The effects of autacoids are primarily local, though large quantities can be produced and moved into circulation. Autacoids may thus have systemic effects by being transported via the circulation. These regulating molecules are also metabolized locally. In sum, these compounds typically are produced locally, act locally and are metabolized locally. Autacoids can have a variety of different biological actions, including modulating the activities of smooth muscles, glands, nerves, platelets and other tissues.
Some autacoids are chiefly characterized by the effect they have on specific tissues, such as smooth muscle. With respect to vascular smooth muscle, there exist both vasoconstrictor and vasodilator autacoids. Vasodilator autacoids are released during periods of exercise. Their main effect is seen in the skin, where they facilitate heat loss.
These are local hormones; they therefore have a paracrine effect. Some notable autacoids are: eicosanoids, angiotensin, neurotensin, NO (nitric oxide), kinins, histamine, serotonin, endothelins and palmitoylethanolamide.
In 2015, a more precise definition of autacoids was proposed: "An autacoid is a locally produced modulating factor, influencing locally the function of cells and/or tissues, which is produced on demand and which subsequently is metabolized in the same cells and/or tissues". | 1 | Biochemistry |
The seas name stems from Caspi, the ancient people who lived to the southwest of the sea in Transcaucasia. Strabo (died circa AD 24) wrote that "to the country of the Albanians (Caucasian Albania, not to be confused with the country of Albania) belongs also the territory called Caspiane, which was named after the Caspian tribe, as was also the sea; but the tribe has now disappeared". Moreover, the Caspian Gates, part of Irans Tehran province, may evince such people migrated to the south. The Iranian city of Qazvin shares the root of its name with this common name for the sea. The traditional and medieval Arabic name for the sea was Baḥr (sea) Khazar, but in recent centuries the common and standard name in Arabic language has become بحر قزوين Baḥr Qazvin, the Arabized form of Caspian. In modern Russian language, it is known as , Kaspiyskoye more.
Some Turkic ethnic groups refer to it with the Caspi(an) descriptor; in Kazakh it is called , Kaspiy teñizi, , . Others refer to it as the Khazar sea: ; , . In all these the first word refers to the historical Khazar Khaganate, a large empire based to the north of the Caspian Sea between the 7th and 10th centuries.
In Iran, the lake is referred to as the Mazandaran Sea (), after the historic Mazandaran Province at its southern shores.
Old Russian sources use the Khvalyn or Khvalis Sea () after the name of Khwarezmia.
Among Greeks and Persians in classical antiquity it was the Hyrcanian ocean.
Renaissance European maps labelled it as the Abbacuch Sea (Oronce Fines 1531 world map), Mar de Bachu (Ortellius 1570 map), or Mar de Sala (the Mercator 1569 world map).
It was also sometimes called the Kumyk Sea and Tarki Sea (derived from the name of the Kumyks and their historical capital Tarki). | 2 | Environmental Chemistry |
Advantages include minimal overlap in metal signals meaning the instrument is theoretically capable of detecting 100 parameters per cell, entire cell signaling networks can be inferred organically without reliance on prior knowledge, and one well-constructed experiment produces large amounts of data.
Disadvantages, in the case of CyTOF, include the practical flow rate is around 500 cells per second versus several thousand in flow cytometry and current reagents available limit cytometer use to around 50 parameters per cell. Additionally, mass cytometry is a destructive method and cells cannot be sorted for further analysis. In the case of IMC, the resolution of the data is relatively low (1μm2/pixel), the technique is as well destructive, acquiring of the data is also very slow, and it requires specialized expensive equipment and expertise. | 3 | Analytical Chemistry |
The asialoglycoprotein receptors (ASGPR) are lectins which bind asialoglycoprotein and glycoproteins from which a sialic acid has been removed to expose galactose residues. The receptors, which are integral membrane proteins and are located on mammalian hepatocytes (liver cells), remove target glycoproteins from circulation. The asialoglycoprotein receptor has been demonstrated to have high expression on the surface of hepatocytes and several human carcinoma cell lines It is also weakly expressed by glandular cells of the gallbladder and the stomach. Lactobionic acid has been used as a targeting moiety for drug delivery to cells expressing asialoglycoprotein receptors.
The asialoglycoprotein receptor contains two subunits, asialoglycoprotein receptor 1 (ASGR1) and asialoglycoprotein receptor 2 (ASGR2). These subunits may form different quaternary forms such as dimers, trimers, tetramers to allow for specific substrate binding or endocytosis. ASGR 1 is the major subunit and has 8 exons and is roughly 6 kb in length. ASGR 2 is the minor subunit and has 9 exons and is about 13.5 kb long. | 1 | Biochemistry |
During starvation, less than half of the energy used by the brain comes from metabolized glucose. Because the human brain can use ketone bodies as major fuel sources, the body is not forced to break down skeletal muscles at a high rate, thereby maintaining both cognitive function and mobility for up to several weeks. This response is extremely important in human evolution and allowed for humans to continue to find food effectively even in the face of prolonged starvation.
Initially, the level of insulin in circulation drops and the levels of glucagon, epinephrine and norepinephrine rise. At this time, there is an up-regulation of glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis. The body's glycogen stores are consumed in about 24 hours. In a normal 70 kg adult, only about 8,000 kilojoules of glycogen are stored in the body (mostly in the striated muscles). The body also engages in gluconeogenesis to convert glycerol and glucogenic amino acids into glucose for metabolism. Another adaptation is the Cori cycle, which involves shuttling lipid-derived energy in glucose to peripheral glycolytic tissues, which in turn send the lactate back to the liver for resynthesis to glucose. Because of these processes, blood glucose levels remain relatively stable during prolonged starvation.
However, the main source of energy during prolonged starvation is derived from triglycerides. Compared to the 8,000 kilojoules of stored glycogen, lipid fuels are much richer in energy content, and a 70 kg adult stores over 400,000 kilojoules of triglycerides (mostly in adipose tissue). Triglycerides are broken down to fatty acids via lipolysis. Epinephrine precipitates lipolysis by activating protein kinase A, which phosphorylates hormone sensitive lipase (HSL) and perilipin. These enzymes, along with CGI-58 and adipose triglyceride lipase (ATGL), complex at the surface of lipid droplets. The concerted action of ATGL and HSL liberates the first two fatty acids. Cellular monoacylglycerol lipase (MGL), liberates the final fatty acid. The remaining glycerol enters gluconeogenesis.
Fatty acids cannot be used as a direct fuel source. They must first undergo beta oxidation in the mitochondria (mostly of skeletal muscle, cardiac muscle, and liver cells). Fatty acids are transported into the mitochondria as an acyl-carnitine via the action of the enzyme CAT-1. This step controls the metabolic flux of beta oxidation. The resulting acetyl-CoA enters the TCA cycle and undergoes oxidative phosphorylation to produce ATP. The body invests some of this ATP in gluconeogenesis to produce more glucose.
Triglycerides and long-chain fatty acids are too hydrophobic to cross into brain cells, so the liver must convert them into short-chain fatty acids and ketone bodies through ketogenesis. The resulting ketone bodies, acetoacetate and β-hydroxybutyrate, are amphipathic and can be transported into the brain (and muscles) and broken down into acetyl-CoA for use in the TCA cycle. Acetoacetate breaks down spontaneously into acetone, and the acetone is released through the urine and lungs to produce the “acetone breath” that accompanies prolonged fasting. The brain also uses glucose during starvation, but most of the body's glucose is allocated to the skeletal muscles and red blood cells. The cost of the brain using too much glucose is muscle loss. If the brain and muscles relied entirely on glucose, the body would lose 50% of its nitrogen content in 8–10 days.
After prolonged fasting, the body begins to degrade its own skeletal muscle. To keep the brain functioning, gluconeogenesis continues to generate glucose, but glucogenic amino acids—primarily alanine—are required. These come from the skeletal muscle. Late in starvation, when blood ketone levels reach 5-7 mM, ketone use in the brain rises, while ketone use in muscles drops.
Autophagy then occurs at an accelerated rate. In autophagy, cells cannibalize critical molecules to produce amino acids for gluconeogenesis. This process distorts the structure of the cells, and a common cause of death in starvation is due to diaphragm failure from prolonged autophagy. | 1 | Biochemistry |
Methylacetylene-propadiene (MPS) gas is a type of fuel gas used in oxy-fuel welding and cutting torches, comprising a mixture of several gases. | 0 | Organic Chemistry |
After being scattered by the sample, the profile of the diffracted beam needs to be detected by a two-dimensionally resolving X-ray detector. The classical "detector" is X-ray sensitive film, with nuclear plates as a traditional alternative. The first step beyond these "offline" detectors were the so-called image plates, although limited in readout speed and spatial resolution. Since about the mid-1990s, CCD cameras have emerged as a practical alternative, offering many advantages such as fast online readout and the possibility to record entire image series in place. X-ray sensitive CCD cameras, especially those with spatial resolution in the micrometer range, are now well established as electronic detectors for topography. A promising further option for the future may be pixel detectors, although their limited spatial resolution may restrict their usefulness for topography.
General criteria for judging the practical usefulness of detectors for topography applications include spatial resolution, sensitivity, dynamic range ("color depth", in black-white mode), readout speed, weight (important for mounting on diffractometer arms), and price. | 3 | Analytical Chemistry |
The iodolactonization reaction includes a number of nuances that affect product formation including regioselectivity, ring size preference, and thermodynamic and kinetic control. In terms of regioselectivity, iodolactonization preferentially occurs at the most hindered carbon atom adjacent to the iodonium cation. This is due to the fact that the more substituted carbon is better able to maintain a partial positive charge and is thus more electrophilic and susceptible to nucleophilic attack. When multiple double bonds in a molecule are equally reactive, conformational preferences dominate. However, when one double bond is more reactive, that reactivity always dominates regardless of conformational preference.
Both five- and six-membered rings could be formed in the iodolactonization shown below, but the five-membered ring is formed preferentially as predicted by Baldwin's rules for ring closure.
According to the rules, 5-exo-tet ring closures are favored while 6-endo-tet ring closures are disfavored. The regioselectivity of each iodolactonization can be predicted and explained using Baldwin's rules.
Stereoselective iodolactonizations have been seen in literature and can be very useful in synthesizing large molecules such as the aforementioned vernopelin and vernomenin because the lactone can be formed while maintaining other stereocenters. The ring closure can even be driven by stereocenters adjacent to the carbon-carbon multiple bond as shown below.
Even in systems without existing stereocenters, Bartlett and coworkers found that stereoselectivity was achievable. They were able to synthesize the cis and trans five membered lactones by adjusting reactions conditions such as temperature and reaction time. The trans product was formed under thermodynamic conditions (e.g. a long reaction time) while the cis product was formed under kinetic conditions (e.g. a relatively shorter reaction time). | 0 | Organic Chemistry |
The Kfar Monash Hoard is a hoard of metal objects dated to the Early Bronze Age (the third millennium BCE) found in the spring of 1962 by the agriculturalist Zvi Yizhar in Kfar Monash, Israel. Kfar Monash is located 3.3 km south-east of Tel Hefer (Tell Ishbar) in the Plain of Sharon or in modern terms 9 km/6 mi northeast of Netanya, which is roughly located along the Israeli coast between Netanya and Haifa.
The Monash Hoard consists of:
The Crescentic Axehead was found about 5 years later at about 200m distance.
As of June 2006, the Kfar Monash Hoard was on display in the Israel Museum. | 8 | Metallurgy |
Supermicelle is a hierarchical micelle structure (supramolecular assembly) where individual components are also micelles. Supermicelles are formed via bottom-up chemical approaches, such as self-assembly of long cylindrical micelles into radial cross-, star- or dandelion-like patterns in a specially selected solvent; solid nanoparticles may be added to the solution to act as nucleation centers and form the central core of the supermicelle. The stems of the primary cylindrical micelles are composed of various block copolymers connected by strong covalent bonds; within the supermicelle structure they are loosely held together by hydrogen bonds, electrostatic or solvophobic interactions. | 6 | Supramolecular Chemistry |
Methods that screen protein–protein interactions in the living cells.
Bimolecular fluorescence complementation (BiFC) is a technique for observing the interactions of proteins. Combining it with other new techniques, dual expression recombinase based (DERB) methods can enable the screening of protein–protein interactions and their modulators.
The yeast two-hybrid screen investigates the interaction between artificial fusion proteins inside the nucleus of yeast. This approach can identify the binding partners of a protein without bias. However, the method has a notoriously high false-positive rate, which makes it necessary to verify the identified interactions by co-immunoprecipitation. | 1 | Biochemistry |
It is still not clear on how to find the linear range of the BET plot for microporous materials in a way that reduces any subjectivity in the assessment of the monolayer capacity. A crowd-sourced study involving 61 research groups has shown that reproducibility of BET area determination from identical isotherms is, in some cases, problematic. Rouquerol et al. suggested a procedure that is based on two criteria:
* C must be positive implying that any negative intercept on the BET plot indicates that one is outside the valid range of the BET equation.
* Application of the BET equation must be limited to the range where the term V(1-P/P) continuously increases with P/P.
These corrections are an attempt to salvage the BET theory, which is restricted to type II isotherms. Even while using this type, use of the data itself is restricted to 0.05 to 0.35 of , routinely discarding 70% of the data. This restriction must be modified depending upon conditions. | 7 | Physical Chemistry |
Glycoside hydrolases are classified into EC 3.2.1 as enzymes catalyzing the hydrolysis of O- or S-glycosides. Glycoside hydrolases can also be classified according to the stereochemical outcome of the hydrolysis reaction: thus they can be classified as either retaining or inverting enzymes. Glycoside hydrolases can also be classified as exo or endo acting, dependent upon whether they act at the (usually non-reducing) end or in the middle, respectively, of an oligo/polysaccharide chain. Glycoside hydrolases may also be classified by sequence or structure-based methods. | 0 | Organic Chemistry |
Brass was used in Lothal and Atranjikhera in the 3rd and 2nd millennium BCE. Brass and probably zinc was also found at Taxila in 4th to 3rd century BCE contexts. | 8 | Metallurgy |
The case of an ideal chain whose two ends are attached to fixed points will be considered in this sub-section. The vector joining these two points characterizes the macroscopic state (or macro-state) of the ideal chain. Each macro-state corresponds a certain number of micro-states, that we will call (micro-states are defined in the introduction to this section). Since the ideal chain's energy is constant, each of these micro-states is equally likely to occur. The entropy associated to a macro-state is thus equal to:
where is Boltzmann's constant
The above expression gives the absolute (quantum) entropy of the system. A precise determination of would require a quantum model for the ideal chain, which is beyond the scope of this article. However, we have already calculated the probability density associated with the end-to-end vector of the unconstrained ideal chain, above. Since all micro-states of the ideal chain are equally likely to occur, is proportional to . This leads to the following expression for the classical (relative) entropy of the ideal chain:
where is a fixed constant. Let us call the force exerted by the chain on the point to which its end is attached. From the above expression of the entropy, we can deduce an expression of this force. Suppose that, instead of being fixed, the positions of the two ends of the ideal chain are now controlled by an operator. The operator controls the evolution of the end to end vector . If the operator changes by a tiny amount , then the variation of internal energy of the chain is zero, since the energy of the chain is constant. This condition can be written as:
is defined as the elementary amount of mechanical work transferred by the operator to the ideal chain, and is defined as the elementary amount of heat transferred by the solvent to the ideal chain. Now, if we assume that the transformation imposed by the operator on the system is quasistatic (i.e., infinitely slow), then the system's transformation will be time-reversible, and we can assume that during its passage from macro-state to macro-state , the system passes through a series of thermodynamic equilibrium macro-states. This has two consequences:
# first, the amount of heat received by the system during the transformation can be tied to the variation of its entropy: where is the temperature of the chain.
# second, in order for the transformation to remain infinitely slow, the mean force exerted by the operator on the end points of the chain must balance the mean force exerted by the chain on its end points. Calling the force exerted by the operator and the force exerted by the chain, we have:
We are thus led to:
The above equation is the equation of state of the ideal chain. Since the expression depends on the central limit theorem, it is only exact in the limit of polymers containing a large number of monomers (that is, the thermodynamic limit). It is also only valid for small end-to-end distances, relative to the overall polymer contour length, where the behavior is like a hookean spring. Behavior over larger force ranges can be modeled using a canonical ensemble treatment identical to magnetization of paramagnetic spins. For the arbitrary forces the extension-force dependence will be given by Langevin function :
where the extension is .
For the arbitrary extensions the force-extension dependence can be approximated by:
where is the inverse Langevin function, is the number of bonds in the molecule (therefore if the molecule has bonds it has monomers making up the molecule.).
Finally, the model can be extended to even larger force ranges by inclusion of a stretch modulus along the polymer contour length. That is, by allowing the length of each unit of the chain to respond elastically to the applied force. | 7 | Physical Chemistry |
The Rosetta stone approach is a computational method for de-novo protein function prediction. It is based on the hypothesis that some proteins involved in a given physiological process may exist as two separate genes in one organism and as a single gene in another. Genomes are scanned for sequences that are independent in one organism and in a single open reading frame in another. If two genes have fused, it is predicted that they have similar biological functions that make such co-regulation advantageous. | 1 | Biochemistry |
Stereoelectronic effects can have a significant influence in pharmaceutical research. Generally, the substitution of hydrogen by fluorine could be regarded as a way to tune both the hydrophobicity and the metabolic stability of a drug candidate. Moreover, it can have a profound influence on conformations, often due to stereoelectronic effects, in addition to normal steric effects resulting from the larger size of the fluorine atom. For instance, the ground state geometries of anisole (methoxybenzene) and (trifluoromethoxy)benzene differ dramatically. In anisole, the methyl group prefers to be coplanar with the phenyl group, while (trifluoromethoxy)benzene favors a geometry in which the [C(aryl)–C(aryl)–O–C(F)] dihedral angle is around 90°. In other words, the O–CF bond is perpendicular to the plane of the phenyl group.
Further studies illustrate that even for only one or two hydrogen atoms in a methyl group being replaced by a fluorine atom, the distortion in the structure can also be significant, with the [C(aryl)–C(aryl)–O–C(HF)] dihedral angle in the energy minimized structure being around 24° and the [C(aryl)–C(aryl)–O–C(HF)] dihedral angle 33°. | 4 | Stereochemistry |
Adverse effects are similar to those for other β-lactam antibiotics, including nausea, vomiting, rashes, and antibiotic-associated colitis. Loose bowel movements (diarrhea) may also occur. Rarer adverse effects include mental changes, lightheadedness, insomnia, confusion, anxiety, sensitivity to lights and sounds, and unclear thinking. Immediate medical care is required upon the first signs of these adverse effects.
The onset of an allergic reaction to amoxicillin can be very sudden and intense; emergency medical attention must be sought as quickly as possible. The initial phase of such a reaction often starts with a change in mental state, skin rash with intense itching (often beginning in fingertips and around groin area and rapidly spreading), and sensations of fever, nausea, and vomiting. Any other symptoms that seem even remotely suspicious must be taken very seriously. However, more mild allergy symptoms, such as a rash, can occur at any time during treatment, even up to a week after treatment has ceased. For some people allergic to amoxicillin, the adverse effects can be fatal due to anaphylaxis.
Use of the amoxicillin/clavulanic acid combination for more than one week has caused a drug-induced immunoallergic-type hepatitis in some patients. Young children having ingested acute overdoses of amoxicillin manifested lethargy, vomiting, and renal dysfunction.
There is poor reporting of adverse effects of amoxicillin from clinical trials. For this reason, the severity and frequency of adverse effects from amoxicillin is probably higher than reported from clinical trials. | 4 | Stereochemistry |
The established method for the production of synthetic peptides in the lab is known as solid phase peptide synthesis (SPPS). Pioneered by Robert Bruce Merrifield, SPPS allows the rapid assembly of a peptide chain through successive reactions of amino acid derivatives on a macroscopically insoluble solvent-swollen beaded resin support.
The solid support consists of small, polymeric resin beads functionalized with reactive groups (such as amine or hydroxyl groups) that link to the nascent peptide chain. Since the peptide remains covalently attached to the support throughout the synthesis, excess reagents and side products can be removed by washing and filtration. This approach circumvents the comparatively time-consuming isolation of the product peptide from solution after each reaction step, which would be required when using conventional solution-phase synthesis.
Each amino acid to be coupled to the peptide chain N-terminus must be protected on its N-terminus and side chain using appropriate protecting groups such as Boc (acid-labile) or Fmoc (base-labile), depending on the side chain and the protection strategy used (see below).
The general SPPS procedure is one of repeated cycles of alternate N-terminal deprotection and coupling reactions. The resin can be washed between each steps. First an amino acid is coupled to the resin. Subsequently, the amine is deprotected, and then coupled with the activated carboxyl group of the next amino acid to be added. This cycle is repeated until the desired sequence has been synthesized. SPPS cycles may also include capping steps which block the ends of unreacted amino acids from reacting. At the end of the synthesis, the crude peptide is cleaved from the solid support while simultaneously removing all protecting groups using a reagent such as trifluoroacetic acid. The crude peptide can be precipitated from a non-polar solvent like diethyl ether in order to remove organic soluble byproducts. The crude peptide can be purified using reversed-phase HPLC. The purification process, especially of longer peptides can be challenging, because cumulative amounts of numerous minor byproducts, which have properties similar to the desired peptide product, have to be removed. For this reason so-called continuous chromatography processes such as MCSGP are increasingly being used in commercial settings to maximize the yield without sacrificing purity.
SPPS is limited by reaction yields due to the exponential accumulation of by-products, and typically peptides and proteins in the range of 70 amino acids are pushing the limits of synthetic accessibility. Synthetic difficulty also is sequence dependent; typically aggregation-prone sequences such as amyloids are difficult to make. Longer lengths can be accessed by using ligation approaches such as native chemical ligation, where two shorter fully deprotected synthetic peptides can be joined in solution. | 1 | Biochemistry |
Crystal field excitation is the electronic transition of an electron between two orbitals of an atom that is situated in a crystal field environment. They are often observed in coordination complexes of transition metals. Some examples of crystal field excitations are dd-transitions on a copper atom that is surrounded by an octahedron of oxygen atoms, or ff-transitions on the uranium atom in uranium antimonide. | 3 | Analytical Chemistry |
The HITRAN compilation also provides collision-induced absorption (CIA) that was first introduced into HITRAN in the 2012 edition. CIA refers to absorption by transient electric dipoles induced by the interaction between colliding molecules. Instructions for accessing the CIA data files can be found on [https://hitran.org/cia/ HITRAN/CIA]. | 7 | Physical Chemistry |
Asbestiform is a crystal habit. It describes a mineral that grows in a fibrous aggregate of high tensile strength, flexible, long, and thin crystals that readily separate. The most common asbestiform mineral is chrysotile, commonly called "white asbestos", a magnesium phyllosilicate part of the serpentine group. Other asbestiform minerals include riebeckite, an amphibole whose fibrous form is known as crocidolite or "blue asbestos", and brown asbestos, a cummingtonite-grunerite solid solution series.
The United States Environmental Protection Agency explains that, "In general, exposure may occur only when the asbestos-containing material is disturbed or damaged in some way to release particles and fibers into the air."
"Mountain leather" is an old-fashioned term for flexible, sheet-like natural formations of asbestiform minerals which resemble leather. Asbestos-containing minerals known to form mountain leather include: actinolite, palygorskite, saponite, sepiolite, tremolite, and zeolite. | 3 | Analytical Chemistry |
While relative entropy is a statistical distance, it is not a metric on the space of probability distributions, but instead it is a divergence. While metrics are symmetric and generalize linear distance, satisfying the triangle inequality, divergences are asymmetric in general and generalize squared distance, in some cases satisfying a generalized Pythagorean theorem. In general does not equal , and while this can be symmetrized (see ), the asymmetry is an important part of the geometry.
It generates a topology on the space of probability distributions. More concretely, if is a sequence of distributions such that
then it is said that
Pinsker's inequality entails that
where the latter stands for the usual convergence in total variation. | 7 | Physical Chemistry |
In non-scanning, a single 2-D sensor output contains all spatial (x, y) and spectral (λ) data. HSI devices for non-scanning yield the full datacube at once, without any scanning. Figuratively speaking, a single snapshot represents a perspective projection of the datacube, from which its three-dimensional structure can be reconstructed. The most prominent benefits of these snapshot hyperspectral imaging systems are the snapshot advantage (higher light throughput) and shorter acquisition time. A number of systems have been designed, including computed tomographic imaging spectrometry (CTIS), fiber-reformatting imaging spectrometry (FRIS), integral field spectroscopy with lenslet arrays (IFS-L), multi-aperture integral field spectrometer (Hyperpixel Array), integral field spectroscopy with image slicing mirrors (IFS-S), image-replicating imaging spectrometry (IRIS), filter stack spectral decomposition (FSSD), coded aperture snapshot spectral imaging (CASSI), image mapping spectrometry (IMS), and multispectral Sagnac interferometry (MSI). However, computational effort and manufacturing costs are high. In an effort to reduce the computational demands and potentially the high cost of non-scanning hyperspectral instrumentation, prototype devices based on Multivariate Optical Computing have been demonstrated. These devices have been based on the Multivariate Optical Element spectral calculation engine or the Spatial Light Modulator spectral calculation engine. In these platforms, chemical information is calculated in the optical domain prior to imaging such that the chemical image relies on conventional camera systems with no further computing. As a disadvantage of these systems, no spectral information is ever acquired, i.e. only the chemical information, such that post processing or reanalysis is not possible. | 7 | Physical Chemistry |
The synthesis of metal carbonyls is a widely studied subject of organometallic research. Since the work of Mond and then Hieber, many procedures have been developed for the preparation of mononuclear metal carbonyls as well as homo- and heterometallic carbonyl clusters. | 0 | Organic Chemistry |
Penicillamine is a trifunctional organic compound, consisting of a thiol, an amine, and a carboxylic acid. It is an amino acid structurally similar to cysteine, but with geminal dimethyl substituents α to the thiol. Like most amino acids, it is a colorless solid that exists in the zwitterionic form at physiological pH.
Penicillamine is a chiral drug with one stereogenic center and exist as a pair of enantiomers. Refer the image for the structure of penicillamine enantiomers. The (S)-enantiomer, the eutomer, is antiarthritic while the distomer (R)-penicillamine is extremely toxic. Of its two enantiomers, -penicillamine (having R absolute configuration) is toxic because it inhibits the action of pyridoxine (also known as vitamin B). That enantiomer is a metabolite of penicillin but has no antibiotic properties itself. A variety of penicillamine–copper complex structures are known. | 4 | Stereochemistry |
Perfluorotributylamine (PFTBA), also referred to as FC43, is an organic compound with the chemical formula . It is a colorless liquid. A molecule of this chemical compound consists of three butyl groups connected to one nitrogen atom, in which all of the hydrogen atoms are replaced with fluorine atoms. The compound is produced for the electronics industry, along with other perfluoroalkylamines. The high degree of fluorination significantly reduces the basicity of the central amine due to electron-withdrawing effects. | 2 | Environmental Chemistry |
In contrast to materials with a single ferroic order, domains in multiferroics have additional properties and functionalities. For instance, they are characterized by an assembly of at least two order parameters. The order parameters may be independent (typical yet not mandatory for a Type-I multiferroic) or coupled (mandatory for a Type-II multiferroic).
Many outstanding properties that distinguish domains in multiferroics from those in materials with a single ferroic order are consequences of the coupling between the order parameters.
*The coupling can lead to patterns with a distribution and/or topology of domains that is exclusive to multiferroics.
*The order-parameter coupling is usually homogeneous across a domain, i.e., gradient effects are negligible.
*In some cases the averaged net value of the order parameter for a domain pattern is more relevant for the coupling than the value of the order parameter of an individual domain.
These issues lead to novel functionalities which explain the current interest in these materials. | 7 | Physical Chemistry |
Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine palladium) is the chemical compound [Pd(P(CH))], often abbreviated Pd(PPh), or rarely PdP. It is a bright yellow crystalline solid that becomes brown upon decomposition in air. | 0 | Organic Chemistry |
Al-Si-Cu-Mg alloys form Al5FeSi- plate like intermetallic phases like -Al8Fe2Si, Al2Cu, etc. The size and morphology of these intermetallic phases in these alloys control the mechanical properties of these alloys, especially strength and ductility. The size of these phases depends on the secondary dendrite arm spacing, as well as the Si content of the alloy, of the primary phase in the micro structure. | 8 | Metallurgy |
Protein interference is the process where in some signaling protein interacts, either with the promoter or with some stage of the partially constructed complex, to prevent further construction of the polymerase complex, so preventing initiation. In general, this is a very rapid response and is used for fine level, individual gene control and for cascade processes for a group of genes useful under a specific conditions (for example, DNA repair genes or heat shock genes).
Chromatin structure inhibition is the process wherein the promoter is hidden by chromatin structure. Chromatin structure is controlled by post-translational modification of the histones involved and leads to gross levels of high or low transcription levels. See: chromatin, histone, and nucleosome.
These methods of control can be combined in a modular method, allowing very high specificity in transcription initiation control. | 1 | Biochemistry |
Carbene insertion use a different strategy for the functionalization of methane. A strategy using metallocarbenes has been shown with several linear and branched alkanes with rhodium, silver, copper, and gold-based catalysts. With a carbene ligand attached to a metal center, it can be transferred from the coordination sphere and inserted into an activated C-H bond. In this case, there is no interaction between the metal center and the alkane in question, which separates this method from the other methods mentioned above. The general mechanism for this cycle begins with the reaction of an electron-poor metal center with a diazocompound to form a metallo-carbene intermediate. In order for this reaction to occur, the diazocompound must be very electrophilic, since the C-H bond is such a poor nucleophile as well as being an unactivated alkane. The reaction then proceeds in a concerted manner, where the C-H bond of the incoming molecule coordinates with the carbene carbon of the metallocarbene complex. The hydrocarbon then dissociates from the metal center to regenerate the catalyst and free the newly formed carbon-carbon bond ().
This route is very successful for higher order alkanes due to the fact that there is no formation of strong metal-carbon or metal-hydrogen bonds that could prevent any intermediates from reacting further. The reactions also take place in room temperature under mild conditions. However, when applying this method to methane specifically, the gaseous nature of methane requires an appropriate solvent. Reactions with other alkanes usually have the alkane in question be the solvent itself; however, any C-H bond with a lower BDE or higher polarity than methane will react first and prevent methane functionalization. Therefore, Pérez, Asensio, Etienne, et al. developed a solution to use supercritical carbon dioxide as the solvent, which is formed under the critical pressure of 73 bar and a temperature of 31 °C. In these conditions, scCO behaves as a liquid, and since fluorinated compounds can dissolve easily in scCO, highly fluorinated silver-based catalysts were developed and tested with methane and ethyl diazoacetate. However, under the reaction conditions, only 19% yield of ethyl propionate was able to be achieved. The reaction depends on a delicate balance between methane pressure and catalyst concentration, and consequently more work is being done to further improve yields. | 0 | Organic Chemistry |
Although gas handling and processing are far more economical than converting coal into coke (not to mention the associated constraints, such as bulk handling, high sensitivity of coking plants to production fluctuations, environmental impact, etc.), replacing coke with natural gas only makes direct reduction attractive to steelmakers with cheap gas resources. This point is essential, as European steelmakers pointed out in 1998:This explains the development of certain reduction-melting processes which, because of the high temperatures involved, have a surplus of reducing gas. Reduction-melting processes such as the COREX, capable of feeding an ancillary Midrex direct reduction unit, or the Tecnored, are justified by their ability to produce CO-rich gas despite their higher investment cost. In addition, coke oven gas is an essential co-product in the energy strategy of a steel complex: the absence of a coke oven must therefore be compensated for by higher natural gas consumption for downstream tools, notably hot rolling and annealing furnaces.
The worldwide distribution of direct reduction plants is therefore directly correlated with the availability of natural gas and ore. In 2007, the breakdown was as follows:
* natural gas processes are concentrated in Latin America (where many have already been developed) and the Middle East;
* coal-fired processes are remarkably successful in India, maintaining the proportion of steel produced by direct reduction despite the strong development of the Chinese steel industry.
China, a country with gigantic needs and a deficit of scrap metal, and Europe, lacking competitive ore and fuels, have never invested massively in these processes, remaining faithful to the blast furnace route. The United States, meanwhile, has always had a few units, but since 2012, the exploitation of shale gas has given a new impetus to natural gas processes.
However, because direct reduction uses much more hydrogen as a reducing agent than blast furnaces (which is very clear for natural gas processes), it produces much less CO, a greenhouse gas. This advantage has motivated the development of ULCOS processes in developed countries, such as HISARNA, ULCORED, and others. The emergence of mature gas treatment technologies, such as pressure swing adsorption or amine gas treating, has also rekindled the interest of researchers. In addition to reducing CO emissions, pure hydrogen processes such as Hybrit are being actively studied with a view to decarbonizing the steel industry. | 8 | Metallurgy |
Screw operations are given the symbol R , where R and i are numbers greater than or equal to 1. Examples of symbols for screw operations are 2 or 4 (pronounced “two sub one” and “four sub three,” respectively). The operation involves choosing a vector→U and acts by a rotation of θ = 360/R degrees about an axis parallel to →U, together with a translation by i/R times →U; the translation direction relative to the rotation follows the right-hand rule. This rather complicated definition is, however, simple to visualize: it describes movement along a “spiral” (actually, helical!) staircase. | 7 | Physical Chemistry |
The probability of a transition taking place is the most important factor influencing the intensity of an observed rotational line. This probability is proportional to the population of the initial state involved in the transition. The population of a rotational state depends on two factors. The number of molecules in an excited state with quantum number J, relative to the number of molecules in the ground state, N/N is given by the Boltzmann distribution as
where k is the Boltzmann constant and T the absolute temperature. This factor decreases as J increases. The second factor is the degeneracy of the rotational state, which is equal to . This factor increases as J increases. Combining the two factors
The maximum relative intensity occurs at
The diagram at the right shows an intensity pattern roughly corresponding to the spectrum above it. | 7 | Physical Chemistry |
Using Kickstarter, the project's founders raised $484,000 on June 8, 2013. This was significantly more than the initial target of $65,000.
Seeds were initially scheduled to be delivered in April 2014, and subsequently scheduled for the fall of 2014. In March 2016, delivery of seeds was forecast for 2016 on the Glowing Plant website. The company encountered difficulty in producing plants that emit significant amounts of light, resulting in a transition to producing moss that emits a patchouli scent. They later announced via email December 2017 that the company was permanently ceasing operations. | 1 | Biochemistry |
Polythiophene (PTh) and its derivatives-based polymers are also one kind of conjugated polymers for PTT. Polythiophene-based polymers usually exhibit excellent photostability, large light-harvesting ability, easy synthesis, and facile functionalization with different substituents.
Conjugated copolymer (C3) with promising photothermal properties can be prepared by linking 2-N,N′-bis(2-(ethyl)hexyl)-perylene-3,4,9,10-tetra-carboxylic acid bis-imide to a thienylvinylene oligomer. C3 was coprecipitated with PEG-PCL and indocyanine green (ICG) to obtain PEG-PCL-C3-ICG nanoparticles for fluorescence-guided photothermal/photodynamic therapy against oral squamous cell carcinoma (OSCC). A biodegradable PLGA-PEGylated DPPV (poly{2,2′-[(2,5-bis(2-hexyldecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]-pyrrole-1,4-diyl)-dithiophene]-5,5′-diyl-alt-vinylene) conjugated polymer for PA-guided PTT with PCE 71% (@ 808 nm, 0.3 W cm−2). The vinylene bonds in the main chain improves the biodegradability, biocompatibility and photothermal conversion efficiency of CPs. | 5 | Photochemistry |
Zinc is an essential trace element for humans and other animals, for plants and for microorganisms. Zinc is required for the function of over 300 enzymes and 1000 transcription factors, and is stored and transferred in metallothioneins. It is the second most abundant trace metal in humans after iron and it is the only metal which appears in all enzyme classes.
In proteins, zinc ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult.
Roughly grams of zinc are distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, a key factor in prostate gland function and reproductive organ growth.
Zinc homeostasis of the body is mainly controlled by the intestine. Here, ZIP4 and especially TRPM7 were linked to intestinal zinc uptake essential for postnatal survival.
In humans, the biological roles of zinc are ubiquitous. It interacts with "a wide range of organic ligands", and has roles in the metabolism of RNA and DNA, signal transduction, and gene expression. It also regulates apoptosis. A review from 2015 indicated that about 10% of human proteins (~3000) bind zinc, in addition to hundreds more that transport and traffic zinc; a similar in silico study in the plant Arabidopsis thaliana found 2367 zinc-related proteins.
In the brain, zinc is stored in specific synaptic vesicles by glutamatergic neurons and can modulate neuronal excitability. It plays a key role in synaptic plasticity and so in learning. Zinc homeostasis also plays a critical role in the functional regulation of the central nervous system. Dysregulation of zinc homeostasis in the central nervous system that results in excessive synaptic zinc concentrations is believed to induce neurotoxicity through mitochondrial oxidative stress (e.g., by disrupting certain enzymes involved in the electron transport chain, including complex I, complex III, and α-ketoglutarate dehydrogenase), the dysregulation of calcium homeostasis, glutamatergic neuronal excitotoxicity, and interference with intraneuronal signal transduction. L- and D-histidine facilitate brain zinc uptake. SLC30A3 is the primary zinc transporter involved in cerebral zinc homeostasis. | 1 | Biochemistry |
While characterizing the compound resulting from deprotonation of cyclooctatriene by H NMR spectroscopy, the group observed that the resonance corresponding to two protons bonded to the same methylene bridge carbon exhibited an astonishing degree of separation in chemical shift.
From this observation, Pettit, et al. concluded that the classical structure of the cyclooctatrienyl cation must be incorrect. Instead, the group proposed the structure of the bicyclo[5.1.0]octadienyl compound, theorizing that the cyclopropane bond located on the interior of the eight-membered ring must be subject to considerable delocalization, thus explaining the dramatic difference in observed chemical shift. Upon further consideration, Pettit was inclined to represent the compound as the "homotropylium ion," which shows the "internal cyclopropane" bond totally replaced by electron delocalization. This structure shows how delocalization is cyclic and involves 6 π electrons, consistent with Huckel's rule for aromaticity. The magnetic field of the NMR could thus induce a ring current in the ion, responsible for the significant differences in resonance between the exo and endo protons of this methylene bridge. Pettit, et al. thus emphasized the remarkable similarity between this compound and the aromatic tropylium ion, describing a new "homo-counterpart" to an aromatic species already known, precisely as predicted by Winstein.
Subsequent NMR studies undertaken by Winstein and others sought to evaluate the properties of metal carbonyl complexes with the homotropylium ion. Comparison between a molybdenum-complex and an iron-complex proved particularly fruitful. Molybdenum tricarbonyl was expected to coordinate to the homotropylium cation by accepting 6 π electrons, thereby preserving the homoaromatic features of the complex. By contrast, iron tricarbonyl was expected to coordinate to the cation by accepting only 4 π electrons from the homotropylium ion, creating a complex in which the electrons of the cation are localized. Studies of these complexes by H NMR spectroscopy showed a large difference in chemical shift values for methylene protons of the Mo-complex, consistent with a homoaromatic structure, but detected virtually no comparable difference in resonance for the same protons in the Fe-complex. | 7 | Physical Chemistry |
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