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In the kinetic proofreading schema, a time delay (equivalently, an irreversible intermediate stage) is introduced during the formation of the correct or incorrect complexes. This time delay reduces the production rates of both complexes but enhances the fidelity beyond the equilibrium limit. The irreversibility of the scheme requires an energy source. The time delay in kinetic proofreading is analogous to the spatial difference in conformational proofreading. However, the conformational proofreading can be an equilibrium scheme that does not consume energy. | 1 | Biochemistry |
The Earth-atmosphere system is radiatively cooled, emitting long-wave (infrared) radiation which balances the absorption of short-wave (visible light) energy from the sun.
Convective transport of heat, and evaporative transport of latent heat are both important in removing heat from the surface and distributing it in the atmosphere. Pure radiative transport is more important higher up in the atmosphere. Diurnal and geographical variation further complicate the picture.
The large-scale circulation of the Earth's atmosphere is driven by the difference in absorbed solar radiation per square meter, as the sun heats the Earth more in the Tropics, mostly because of geometrical factors. The atmospheric and oceanic circulation redistributes some of this energy as sensible heat and latent heat partly via the mean flow and partly via eddies, known as cyclones in the atmosphere. Thus the tropics radiate less to space than they would if there were no circulation, and the poles radiate more; however in absolute terms the tropics radiate more energy to space. | 7 | Physical Chemistry |
The waste discharge can be used as land stabilizer as dry bio-solids that can be distributed to the market. The land stabilizer is used in reclaiming marginal land such as mining waste land. This process will help to restore the land to its initial appearance. | 3 | Analytical Chemistry |
WikiPathways is a community resource for contributing and maintaining content dedicated to biological pathways. Any registered WikiPathways user can contribute, and anybody can become a registered user. Contributions are monitored by a group of admins, but the bulk of peer review, editorial curation, and maintenance is the responsibility of the user community. WikiPathways is originally built using MediaWiki software, a custom graphical pathway editing tool (PathVisio) and integrated BridgeDb databases covering major gene, protein, and metabolite systems. WikiPathways was founded in 2008 by Thomas Kelder, Alex Pico, Martijn Van Iersel, Kristina Hanspers, Bruce Conklin and Chris Evelo. Current architects are Alex Pico and Martina Summer-Kutmon. | 1 | Biochemistry |
Cyclopropanation of olefins with diazocarbonyl compounds is commonly accomplished using rhodium carboxylate complexes, although copper was originally used. The scope of the olefin is generally quite broad—electron-rich, neutral, and electron-poor olefins have all been cyclopropanated efficiently using rhodium-based catalyst systems. This section describes the various classes of diazocarbonyl compounds that react with olefins under rhodium catalysis to afford cyclopropanes.
Diazoacetates that possess a single carbonyl substituent attached to the diazo carbon, have been used for the cyclopropanation of a wide array of olefins. Diastereoselectivity for the (E) cyclopropane increases as the size of the ester group increases. In addition, adding electron density to the catalyst (for instance by replacing acetate ligands with acetamide, acam) increases the diastereoselectivity of the reaction.
Diazocarbonyl compounds substituted with two electron-withdrawing groups, such as diazomalonates, are prone to experience side reactions under cyclopropanation conditions. [3+2] Cycloaddition and C-H insertion side products have been observed.
Diazoacetates substituted with a vinyl or aryl group on the diazo carbon are unreactive towards trans-alkenes. This result has been explained by invoking the transition state model in Eq. (2). Reactions of these substrates are highly selective for the (E) cyclopropane isomer.
Vinyl diazoacetates react with dienes to afford divinyl cyclopropanes, which undergo Cope rearrangement to afford cycloheptadienes. The more substituted double bond of the diene reacts preferentially.
Furans react similarly with vinyl diazoacetates, although the intermediate cyclopropane may transform either into the Cope rearrangement product or an opened unsaturated carbonyl compound. The distribution of these products is highly dependent on the substitution pattern of the furan.
Pyrroles react with vinyl diazoacetates to form nitrogen-bridged cycloheptadienes. The use of methyl lactate as a chiral auxiliary on the vinyl diazoacetate led to moderate diastereoselectivity in the tandem cyclopropanation/Cope rearrangement of Boc-protected pyrrole.
The enantioselectivity of asymmetric cyclopropanations may depend profoundly on the solvent. | 0 | Organic Chemistry |
As a 1,2-dithiol, this compound is widely used in organic chemistry because it reacts with aldehydes and ketones to give 1,3-dithiolanes, which are useful intermediates.
::CH(SH) + RRCO → CHSCRR + HO
Other 1,2- and 1,3-dithiols undergo this reaction to give related 1,3-dithiolanes and 1,3-dithianes (six-membered rings). Diols such as ethylene glycol undergo analogous reactions to 1,3-dioxolanes and 1,3-dioxanes. One distinguishing feature of the dithiolanes and dithianes derived from aldehydes is that the methyne group can be deprotonated and the resulting carbanion alkylated.
1,2-Ethanedithiol is commonly used as a scavenger in peptide cleavage synthesis. | 0 | Organic Chemistry |
Below is a table of the handbooks published by ASM International as of April 2023. These handbooks are recognized as a standard reference in the field of materials science. | 8 | Metallurgy |
ELPs modified with certain functional groups have the capacity to be conjugated with drugs, including chemotherapeutic agents. Together, the ELP-drug complex can be taken up by tumor cells to a greater extent, promoting the cytotoxic activity of the drug. The reason that the complexes preferentially target the tumor cells is that these cells tend to be associated with more permeable blood vessels and also possess a weaker lymphatic presence. This essentially means that the drugs can cross over from the vessels to the tumor cells more frequently and can remain in the vessels for a longer period of time, without being filtered out. The phase transition associated with ELPs can also be used to promote tumor cell uptake of the drug. By locally heating tumor cell regions, the ELP-drug complex will aggregate into spherical clumps. If this ELP-drug complex is engineered to expose functional domains in the spherical clump shape that are recognized by tumor cell surfaces, then this cell surface interaction would promote uptake of the drug as the tumor cell would mistake the ELP-drug complex as being a harmless substance. | 7 | Physical Chemistry |
Bioluminescent bacteria are most abundant in marine environments during spring blooms when there are high nutrient concentrations. These light-emitting organisms are found mainly in coastal waters near the outflow of rivers, such as the northern Adriatic Sea, Gulf of Trieste, northwestern part of the Caspian Sea, coast of Africa and many more. These are known as milky seas. Bioluminescent bacteria are also found in freshwater and terrestrial environments but are less wide spread than in seawater environments. They are found globally, as free-living, symbiotic or parasitic forms and possibly as opportunistic pathogens. Factors that affect the distribution of bioluminescent bacteria include temperature, salinity, nutrient concentration, pH level and solar radiation. For example, Aliivibrio fischeri grows favourably in environments that have temperatures between 5 and 30 °C and a pH that is less than 6.8; whereas, Photobacterium phosphoreum thrives in conditions that have temperatures between 5 and 25 °C and a pH that is less than 7.0. | 1 | Biochemistry |
Julian Voss-Andreae, a German-born artist specializing in "protein sculptures," created sculptures based on the structure of GFP, including the 1.70 m (56") tall "Green Fluorescent Protein" (2004) and the 1.40 m (47") tall "Steel Jellyfish" (2006). The latter sculpture is located at the place of GFPs discovery by Shimomura in 1962, the University of Washingtons Friday Harbor Laboratories. | 1 | Biochemistry |
A number of computational tools have been developed for the prediction of the location of binding sites on proteins. These can be broadly classified into sequence based or structure based. Sequence based methods rely on the assumption that the sequences of functionally conserved portions of proteins such as binding site are conserved. Structure based methods require the 3D structure of the protein. These methods in turn can be subdivided into template and pocket based methods. Template based methods search for 3D similarities between the target protein and proteins with known binding sites. The pocket based methods search for concave surfaces or buried pockets in the target protein that possess features such as hydrophobicity and hydrogen bonding capacity that would allow them to bind ligands with high affinity. Even though the term pocket is used here, similar methods can be used to predict binding sites used in protein-protein interactions that are usually more planar, not in pockets. | 1 | Biochemistry |
Tropospheric ozone depletion events are phenomena that reduce the concentration of ozone in the earth's troposphere. Ozone (O3) is a trace gas which has been of concern because of its unique dual role in different layers of the lower atmosphere. Apart from absorbing UV-B radiation and converting solar energy into heat in the stratosphere, ozone in the troposphere provides greenhouse effect and controls the oxidation capacity of the atmosphere. | 2 | Environmental Chemistry |
A breakthrough has been brought about in the last decades by the development of large scale synchrotron radiation facilities. Here, bunches of relativistic electrons kept in orbit inside a storage ring are accelerated through bending magnets or insertion devices like wigglers and undulators to produce a high brilliance and high flux photon beam. The beam is orders of magnitude more intense and better collimated than typically produced by anode-based sources. Synchrotron radiation is also tunable over a wide wavelength range, and can be made polarized in several distinct ways. This way, photon can be selected yielding optimum photoionization cross-sections for probing a particular core level. The high photon flux, in addition, makes it possible to perform XPS experiments also from low density atomic species, such as molecular and atomic adsorbates.
One of the synchrotron facilities that allows XPS measurement is Max IV synchrotron in Lund, Sweden. The Hippie beam line of this facility also allows to perform in operando Ambient Pressure X-Ray Photoelectron Spectroscopy (AP-XPS9. This latter technique allows to measure samples in ambient conditions, rather than in vacuum. | 7 | Physical Chemistry |
An emulsifier is a substance that stabilizes an emulsion by reducing the oil-water interface tension. Emulsifiers are a part of a broader group of compounds known as surfactants, or "surface-active agents". Surfactants are compounds that are typically amphiphilic, meaning they have a polar or hydrophilic (i.e., water-soluble) part and a non-polar (i.e., hydrophobic or lipophilic) part. Emulsifiers that are more soluble in water (and, conversely, less soluble in oil) will generally form oil-in-water emulsions, while emulsifiers that are more soluble in oil will form water-in-oil emulsions.
Examples of food emulsifiers are:
* Egg yolk – in which the main emulsifying and thickening agent is lecithin.
* Mustard – where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers
* Soy lecithin is another emulsifier and thickener
* Pickering stabilization – uses particles under certain circumstances
* Mono- and diglycerides – a common emulsifier found in many food products (coffee creamers, ice creams, spreads, breads, cakes)
* Sodium stearoyl lactylate
* DATEM (diacetyl tartaric acid esters of mono- and diglycerides) – an emulsifier used primarily in baking
* Proteins – those with both hydrophilic and hydrophobic regions, e.g. sodium caseinate, as in meltable cheese product
In food emulsions, the type of emulsifier greatly affects how emulsions are structured in the stomach and how accessible the oil is for gastric lipases, thereby influencing how fast emulsions are digested and trigger a satiety inducing hormone response.
Detergents are another class of surfactant, and will interact physically with both oil and water, thus stabilizing the interface between the oil and water droplets in suspension. This principle is exploited in soap, to remove grease for the purpose of cleaning. Many different emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions. Common examples include emulsifying wax, polysorbate 20, and ceteareth 20.
Sometimes the inner phase itself can act as an emulsifier, and the result is a nanoemulsion, where the inner state disperses into "nano-size" droplets within the outer phase. A well-known example of this phenomenon, the "ouzo effect", happens when water is poured into a strong alcoholic anise-based beverage, such as ouzo, pastis, absinthe, arak, or raki. The anisolic compounds, which are soluble in ethanol, then form nano-size droplets and emulsify within the water. The resulting color of the drink is opaque and milky white. | 7 | Physical Chemistry |
Ben Feringa has served as an editorial board member for several journals published by the Royal Society of Chemistry, including Chemical Communications (until 2012), the Faraday Transactions of the Royal Society, and as Chair of the Editorial Board of Chemistry World. He is the founding Scientific Editor (2002–2006) of the Royal Society of Chemistry journal Organic & Biomolecular Chemistry. In addition, he is an editorial (advisory) board member for the journals Advanced Synthesis and Catalysis, Adv. Phys. Org. Chem., Topics in Stereochemistry, Chemistry: An Asian Journal published by Wiley, and advisory board member for the Journal of Organic Chemistry, Journal of the American Chemical Society published by the American Chemical Society.
On 26 November 2017, Feringa, on a visit to South China Normal University in Guangzhou was appointed honorary Professor of South China Normal University. From December 2017, he holds a "green card" in China, and will lead a team researching “self-healing materials” at Shanghai’s East China University of Science and Technology.
Feringa is a co-founder of the contract research company Selact (now a part of Kiadis), which was originally established to provide services in the area of organic synthesis but later developed high throughput screening methods. | 4 | Stereochemistry |
Precession electron diffraction is typically conducted using accelerating voltages between 100-400 kV. Patterns can be formed under parallel or convergent beam conditions. Most modern TEMs can achieve a tilt angle, φ, ranging from 0-3°. Precession frequencies can be varied from Hz to kHz, but in standard cases 60 Hz has been used. In choosing a precession rate, it is important to ensure that many revolutions of the beam occur over the relevant exposure time used to record the diffraction pattern. This ensures adequate averaging over the excitation error of each reflection. Beam sensitive samples may dictate shorter exposure times and thus, motivate the use of higher precession frequencies.
One of the most significant parameters affecting the diffraction pattern obtained is the precession angle, φ. In general, larger precession angles result in more kinematical diffraction patterns, but both the capabilities of the beam tilt coils in the microscope and the requirements on the probe size limit how large this angle can become in practice. Because PED takes the beam off of the optic axis by design, it accentuates the effect of the spherical aberrations within the probe forming lens. For a given spherical aberration, C, the probe diameter, d, varies with convergence angle, α, and precession angle, φ, as
Thus, if the specimen of interest is quite small, the maximum precession angle will be restrained. This is most significant for conditions of convergent beam illumination. 50 nm is a general lower limit on probe size for standard TEMs operating at high precession angles (>30 mrad), but can be surpassed in C corrected instruments. In principle the minimum precessed probe can reach approximately the full-width-half-max (FWHM) of the converged un-precessed probe in any instrument, however in practice the effective precessed probe is typically ~10-50x larger due to uncontrolled aberrations present at high angles of tilt. For example, a 2 nm precessed probe with >40 mrad precession angle was demonstrated in an aberration-corrected Nion UltraSTEM with native sub-Å probe (aberrations corrected to ~35 mrad half-angle).
If the precession angle is made too large, further complications due to the overlap of the ZOLZ and HOLZ reflections in the projected pattern can occur. This complicates the indexing of the diffraction pattern and can corrupt the measured intensities of reflections near the overlap region, thereby reducing the effectiveness of the collected pattern for direct methods calculations. | 3 | Analytical Chemistry |
Azomethine ylides are nitrogen-based 1,3-dipoles, consisting of an iminium ion next to a carbanion. They are used in 1,3-dipolar cycloaddition reactions to form five-membered heterocycles, including pyrrolidines and pyrrolines. These reactions are highly stereo- and regioselective, and have the potential to form four new contiguous stereocenters. Azomethine ylides thus have high utility in total synthesis, and formation of chiral ligands and pharmaceuticals. Azomethine ylides can be generated from many sources, including aziridines, imines, and iminiums. They are often generated in situ, and immediately reacted with dipolarophiles. | 0 | Organic Chemistry |
The study of dynamics in multiferroic systems is concerned with understanding the time evolution of the coupling between various ferroic orders, in particular under external applied fields. Current research in this field is motivated both by the promise of new types of application reliant on the coupled nature of the dynamics, and the search for new physics lying at the heart of the fundamental understanding of the elementary MF excitations. An increasing number of studies of MF dynamics are concerned with the coupling between electric and magnetic order parameters in the magnetoelectric multiferroics. In this class of materials, the leading research is exploring, both theoretically and experimentally, the fundamental limits (e.g. intrinsic coupling velocity, coupling strength, materials synthesis) of the dynamical magnetoelectric coupling and how these may be both reached and exploited for the development of new technologies.
At the heart of the proposed technologies based on magnetoelectric coupling are switching processes, which describe the manipulation of the material's macroscopic magnetic properties with electric field and vice versa. Much of the physics of these processes is described by the dynamics of domains and domain walls. An important goal of current research is the minimization of the switching time, from fractions of a second ("quasi"-static regime), towards the nanosecond range and faster, the latter being the typical time scale needed for modern electronics, such as next generation memory devices.
Ultrafast processes operating at picosecond, femtosecond, and even attosecond scale are both driven by, and studied using, optical methods that are at the front line of modern science. The physics underpinning the observations at these short time scales is governed by non-equilibrium dynamics, and usually makes use of resonant processes. One demonstration of ultrafast processes is the switching from collinear antiferromagnetic state to spiral antiferromagnetic state in CuO under excitation by 40 fs 800 nm laser pulse. A second example shows the possibility for the direct control of spin waves with THz radiation on antiferromagnetic NiO. These are promising demonstrations of how the switching of electric and magnetic properties in multiferroics, mediated by the mixed character of the magnetoelectric dynamics, may lead to ultrafast data processing, communication and quantum computing devices.
Current research into MF dynamics aims to address various open questions; the practical realisation and demonstration of ultra-high speed domain switching, the development of further new applications based on tunable dynamics, e.g. frequency dependence of dielectric properties, the fundamental understanding of the mixed character of the excitations (e.g. in the ME case, mixed phonon-magnon modes – electromagnons), and the potential discovery of new physics associated with the MF coupling. | 7 | Physical Chemistry |
Oxycholesterol or 5,6-epoxycholesterol is a form of oxidized cholesterol implicated in atherosclerosis. It is commonly formed from the reaction of fats and oxygen during high temperature cooking such as frying.
In a study about the effects of oxycholesterol in rabbits with induced hypercholesterolemia, it was shown that compared feeding rabbits cholesterol and unoxidized cholesterol, feeding rabbits oxycholesterol resulted in their developing much higher levels of total cholesterol and low-density lipoprotein cholesterol. It is also shown to increase the amount of homocysteine and asymmetric dimethylarginine levels in the rabbits. An abundance of homocysteine leads to an organism with greater chances of endothelial cell injury which can then lead to coronary artery disease. Asymmetric dimethylarginine is shown to cause adverse effects on humans in the form of cardiovascular and metabolic diseases. Therefore it was concluded that adding oxycholesterol into diets of animals with hypercholesterolemia increases endothelial dysfunction and inflammatory response. | 1 | Biochemistry |
Compounds with double bonds between carbon and sulfur are relatively uncommon, but include the important compounds carbon disulfide, carbonyl sulfide, and thiophosgene. Thioketones (RC(=S)R′) are uncommon with alkyl substituents, but one example is thiobenzophenone. Thioaldehydes are rarer still, reflecting their lack of steric protection ("thioformaldehyde" exists as a cyclic trimer). Thioamides, with the formula RC(=S)N(R)R are more common. They are typically prepared by the reaction of amides with Lawesson's reagent. Isothiocyanates, with formula R−N=C=S, are found naturally. Vegetable foods with characteristic flavors due to isothiocyanates include wasabi, horseradish, mustard, radish, Brussels sprouts, watercress, nasturtiums, and capers. | 9 | Geochemistry |
Pasteur responded to Liebigs works, often through his own writings, and using results from his own experiments to support his theories. For example, in 1858, Pasteur wrote a paper trying to disprove Liebigs theory that fermentation cannot be caused by the growth of the yeast when it takes place when yeast is added to pure sugar-water. Pasteur thought that in pure sugar-water, yeast was both growing and disintegrating, and developed experiments to support his theories. Liebig, however, was not convinced, and claimed that Pasteur was not solving the questions he had about the decomposition in fermentation.
In 1869, Liebig responded to Pasteurs challenge, which he had made public ten years before. Liebig still held this ground, and mentioned that some of Pasteurs experiments were difficult to replicate and use effectively. Pasteur was furious, and suggested the Royal Academy hire a third scientist who would replicate his experiments and verify his results in order to support his theories. Neither Liebig nor the Academy responded.
Later, Pasteur demanded a meeting with Liebig, but Liebig did not him receive cordially, and refused to discuss the topic of fermentation. | 1 | Biochemistry |
Translation complex profile sequencing (TCP-seq) is a molecular biology method for obtaining snapshots of momentary distribution of protein synthesis complexes along messenger RNA (mRNA) chains. | 1 | Biochemistry |
In some cells certain amino acids can be depleted and thus affect translation efficiency. For instance, activated T cells secrete interferon-γ which triggers intracellular tryptophan shortage by upregulating the indoleamine 2,3-dioxygenase 1 (IDO1) enzyme. Surprisingly, despite tryptophan depletion, in-frame protein synthesis continues across tryptophan codons. This is achieved by incorporation of phenylalanine instead of tryptophan. The resulting peptides are called W>F "substitutants". Such W>F substitutants are abundant in certain cancer types and have been associated with increased IDO1 expression. Functionally, W>F substitutants can impair protein activity. | 1 | Biochemistry |
Scientists Francisco Gasulla, Leonardo Casano and Alfredo Guéra, observed the lichen's metabolic response when placed in dark conditions. The light harvesting complex (LHC) inside the chloroplasts of Lichen is activated when subjected to darkness. Gasulla, Casano and Guéra, noticed that this increase in LHC activity caused PS II and the PQ pool within lichen to decrease, indicating the initiation of chlororespiration.
Immunodetection analysis was used to determine the amount of LHC molecules inside lichen in a dark environment, and a luminous environment. By determining the amount of LHC within the chloroplast, scientists were able to notice the reduction in PS II activity. This reduction was caused by a loss in excitation energy in the PS II ETC, which then stimulated an incline in chlororespiratory pathways. Gasulla, Casano and Guéra, gathered this result, when both light-adapted and dark-adapted lichen were placed in darkness. They found that the level of LHC molecules in dark-adapted lichen had doubled compared to light adapted lichen. It was also noted that the chlororespiratory ETCs were triggered at a much earlier time in dark-adapted lichen, than compared to light-adapted lichen. This resulted in a faster metabolic rate and chemical synthesis response in dark-adapted lichen due to chlororespiration. | 1 | Biochemistry |
The focus of Hieberts research was the history and philosophy of chemistry and physical sciences in the 2nd half of 19th century and 1st half of the 20th century. During his lifetime he completed three books and his fourth book (which deals with acoustics) was nearly complete at the time of his death. His book 1961 book The Impact of Atomic Energy examined the Manhattan Project, the atomic bombs dropped on Hiroshima and Nagasaki, and WW IIs consequences related to atomic energy from an ethical and religious perspective. He wrote numerous papers on the history of science, the relations between science and religion, and the philosophy of science as viewed by outstanding scientists of the modern era, especially among those scientists from 1850 to 1930 in Germany and Austria. His 1962 book Historical Roots of the Principle of Conservation of Energy is a notable achievement in writing the history of thermodynamics. He wrote papers about the science and philosophy of Max Planck, Ernst Mach, Walther Nernst, Ludwig Boltzmann, Hermann von Helmholtz, and Wilhelm Ostwald. Hiebert
had a strong conviction that historians of science should have a good, scientific grounding in the particular science that they study and write about. | 7 | Physical Chemistry |
The space groups with given point group are numbered by 1, 2, 3, ... (in the same order as their international number) and this number is added as a superscript to the Schönflies symbol for the corresponding point group. For example, groups numbers 3 to 5 whose point group is C have Schönflies symbols C, C, C.
While in case of point groups, Schönflies symbol defines the symmetry elements of group unambiguously, the additional superscript for space group doesn't have any information about translational symmetry of space group (lattice centering, translational components of axes and planes), hence one needs to refer to special tables, containing information about correspondence between Schönflies and Hermann–Mauguin notation. Such table is given in List of space groups page. | 7 | Physical Chemistry |
Overheating is a phenomenon of rising temperatures in an electrical circuit. Overheating causes damage to the circuit components and can cause fire, explosion, and injury. Damage caused by overheating is usually irreversible; the only way to repair it is to replace some components. | 7 | Physical Chemistry |
The three TET genes are expressed as different isoforms, including at least two isoforms of TET1, three of TET2 and three of TET3. Different isoforms of the TET genes are expressed in different cells and tissues. The full-length canonical TET1 isoform appears virtually restricted to early embryos, embryonic stem cells and primordial germ cells (PGCs). The dominant TET1 isoform in most somatic tissues, at least in the mouse, arises from alternative promoter usage which gives rise to a short transcript and a truncated protein designated TET1s. The three isoforms of TET2 arise from different promoters. They are expressed and active in embryogenesis and differentiation of hematopoietic cells. The isoforms of TET3 are the full length form TET3FL, a short form splice variant TET3s, and a form that occurs in oocytes designated TET3o. TET3o is created by alternative promoter use and contains an additional first N-terminal exon coding for 11 amino acids. TET3o only occurs in oocytes and the one cell stage of the zygote and is not expressed in embryonic stem cells or in any other cell type or adult mouse tissue tested. Whereas TET1 expression can barely be detected in oocytes and zygotes, and TET2 is only moderately expressed, the TET3 variant TET3o shows extremely high levels of expression in oocytes and zygotes, but is nearly absent at the 2-cell stage. It appears that TET3o, high in oocytes and zygotes at the one cell stage, is the major TET enzyme utilized when almost 100% rapid demethylation occurs in the paternal genome just after fertilization and before DNA replication begins (see DNA demethylation). | 1 | Biochemistry |
Endogenous retroviruses (ERVs) are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. They are abundant in the genomes of jawed vertebrates, and they comprise up to 5–8% of the human genome (lower estimates of ~1%).
ERVs are a vertically inherited proviral sequence and a subclass of a type of gene called a transposon, which can normally be packaged and moved within the genome to serve a vital role in gene expression and in regulation. ERVs however lack most transposon functions, are typically not infectious and are often defective genomic remnants of the retroviral replication cycle. They are distinguished as germline provirus retroelements due to their integration and reverse-transcription into the nuclear genome of the host cell.
Researchers have suggested that retroviruses evolved from a type of transposon called a retrotransposon, a Class I element; these genes can mutate and instead of moving to another location in the genome they can become exogenous or pathogenic. This means that not all ERVs may have originated as an insertion by a retrovirus but that some may have been the source for the genetic information in the retroviruses they resemble. When integration of viral DNA occurs in the germ-line, it can give rise to an ERV, which can later become fixed in the gene pool of the host population. | 1 | Biochemistry |
A major importance of macromolecular crowding to biological systems stems from its effect on protein folding. The underlying physical mechanism by which macromolecular crowding helps to stabilize proteins in their folded state is often explained in terms of excluded volume - the volume inaccessible to the proteins due to their interaction with macromolecular crowders. This notion goes back to Asakura and Oosawa, who have described depletion forces induced by steric, hard-core, interactions. A hallmark of the mechanism inferred from the above is that the effect is completely a-thermal, and thus completely entropic. These ideas were also proposed to explain why small cosolutes, namely protective osmolytes, which are preferentially excluded from proteins, also shift the protein folding equilibrium towards the folded state. However, it has been shown by various methods, both experimental and theoretical, that depletion forces are not always entropic in nature. | 7 | Physical Chemistry |
Non-specific acting modes of toxic action result in narcosis; therefore, narcosis is a mode of toxic action. Narcosis is defined as a generalized depression in biological activity due to the presence of toxicant molecules in the organism. The target site and mechanism of toxic action through which narcosis affects organisms are still unclear, but there are hypotheses that support that it occurs through alterations in the cell membranes at specific sites of the membranes, such as the lipid layers or the proteins bound to the membranes. Even though continuous exposure to a narcotic toxicant can produce death, if the exposure to the toxicant is stopped, narcosis can be reversible. | 1 | Biochemistry |
In 1919, he was elected a Fellow of the Royal Society of Edinburgh. His proposers were Alexander Gray, George Alexander Gibson, John Glaister, Diarmid Noel Paton, Ralph Stockman, Thomas Hastie Bryce, Robert Muir, Frederick Orpen Bower and Robert Alexander Houston. He resigned from the Society in 1931.
He retired in 1942 and died in 1949. | 0 | Organic Chemistry |
Kapustinskii originally proposed the following simpler form, which he faulted as "associated with antiquated concepts of the character of repulsion forces".
Here, K. This form of the Kapustinskii equation may be derived as an approximation of the Born–Landé equation, below.
Kapustinskii replaced r, the measured distance between ions, with the sum of the corresponding ionic radii. In addition, the Born exponent, n, was assumed to have a mean value of 9. Finally, Kapustinskii noted that the Madelung constant, M, was approximately 0.88 times the number of ions in the empirical formula. The derivation of the later form of the Kapustinskii equation followed similar logic, starting from the quantum chemical treatment in which the final term is where d is as defined above. Replacing r as before yields the full Kapustinskii equation. | 3 | Analytical Chemistry |
Various polymers such as poloxamers exhibit in situ gelling properties. Because of these properties they can be administered as liquid formulations forming stable gels once having reached their site of application. An unintended rapid elimination or outflow of the formulation from mucosal membranes such as the ocular, nasal or vaginal mucosa can therefore be avoided. Thiolated polymers are capable of providing a comparatively more pronounced increase in viscosity after application, as an extensive crosslinking process by the formation of disulfide bonds between the polymer chains due to oxidation takes place. This effect was first described in 1999 by Bernkop-Schnürch et al. for polymeric excipients. In case of thiolated chitosan, for instance, a more than 10,000-fold increase in viscosity within a few minutes was shown. These high in situ gelling properties can also be used for numerous further reasons such as for parenteral formulations, as coating material or for food additives | 7 | Physical Chemistry |
Diphenylamine was discovered by A. W. Hofmann in 1864 amongst the products of dry distillation of aniline dyes; it was first purposefully synthesized through deamination of a mix of aniline and its salts by a group of French chemists two years later.
In 1872, diphenylamine was suggested as a means to detect nitrous acid in sulfuric acid due to its blue coloration in the presence of oxidizing agents. By 1875, it was also being used to detect nitrites and nitrates in drinking water. | 3 | Analytical Chemistry |
In particle physics, the acoplanarity of a scattering experiment is the degree to which the paths of the scattered particles deviate from being coplanar. Measurements of acoplanarity provide a test of perturbative quantum chromodynamics, because QCD predicts that the emission of gluons can lead to acoplanar scattering events. | 7 | Physical Chemistry |
Relies on the operation of either a lever arm, tightening screws, or pneumatic or hydraulic pressure applied to a membrane. In all cases the force is uniaxial and is applied to the tables (bases) of the two anvils. | 7 | Physical Chemistry |
A class II gene is a type of gene that codes for a protein. Class II genes are transcribed by RNAP II .
Class II genes have a promoter that may contain a TATA box.
Basal transcription of class II genes requires the formation of a preinitiation complex.
They are transcribed by RNA polymerase II, include both intron and exon, and code for polypeptide.
Major histocompatibility complex (MHC) class II genes are important in the immune response.
Major histocompatibility complex (MHC) II is found on antigen-presenting cells (APCs) and functions to present exogenous proteins to CD4+ T cells. MHC II thus plays an important role in activating the immune system in response to extracellular pathogens via activation of CD4+ T cells. MHC class II molecules are differentially expressed across multiple cell-types. For example, MHC II molecules are constitutively expressed in thymic epithelial cells and antigen-presenting cells (APC's), whereas they undergo interferon-γ-mediated expression in other cell types. Central to the regulation of the complex gene-expression profile exhibited by MHC class II molecules is a single master regulatory factor known as the class II transactivator (CIITA). CIITA is a non-DNA-binding co-activator whose expression is tightly controlled by a regulatory region containing three independent promoters (pI, pIII and pIV). | 1 | Biochemistry |
The Cleveland open-cup method is one of three main methods in chemistry for determining the flash point of a petroleum product using a Cleveland open-cup apparatus, also known as a Cleveland open-cup tester. First, the test cup of the apparatus (usually brass) is filled to a certain level with a portion of the product. Then, the temperature of this chemical is increased rapidly and then at a slow, constant rate as it approaches the theoretical flash point. The increase in temperature will cause the chemical to begin to produce flammable vapor in increasing quantities and density. The lowest temperature at which a small test flame passing over the surface of the liquid causes the vapor to ignite is considered the chemicals flash point. This apparatus may also be used to determine the chemicals fire point which is considered to have been reached when the application of the test flame produces at least five continuous seconds of ignition. Temperature range of this apparatus is 120 to 250 degree c
The other principal methods of establishing chemical flash points are the Pensky–Martens closed-cup test and the Tagliabue cup method (often called simply the "Tag method"). | 3 | Analytical Chemistry |
The time-of-flight principle can be applied for mass spectrometry. Ions are accelerated by an electric field of known strength. This acceleration results in an ion having the same kinetic energy as any other ion that has the same charge. The velocity of the ion depends on the mass-to-charge ratio. The time that it subsequently takes for the particle to reach a detector at a known distance is measured. This time will depend on the mass-to-charge ratio of the particle (heavier particles reach lower speeds). From this time and the known experimental parameters one can find the mass-to-charge ratio of the ion. The elapsed time from the instant a particle leaves a source to the instant it reaches a detector. | 7 | Physical Chemistry |
Rust can be avoided by controlling the moisture in the atmosphere. An example of this is the use of silica gel packets to control humidity in equipment shipped by sea. | 8 | Metallurgy |
Early studies of the bioluminescence of Aequorea by E. Newton Harvey had noted that the bioluminescence appears as a ring around the bell, and occurs even in the absence of air. This was remarkable because most bioluminescence reactions require oxygen, and led to the idea that the animals somehow store oxygen. It was later discovered that the apoprotein can stably bind coelenterazine-2-hydroperoxide, and oxygen is required for the regeneration to this active form of aequorin. However, in the presence of calcium ions, the protein undergoes a conformational change and converts its prosthetic group, coelenterazine-2-hydroperoxide, into excited coelenteramide and CO. As the excited coelenteramide relaxes to the ground state, blue light (wavelength of 465 nm) is emitted. Before coelenteramide is exchanged out, the entire protein is still fluorescent blue. because of the connection between bioluminescence and fluorescence, this property was ultimately important in the discovery of the luciferin coelenterazine. | 1 | Biochemistry |
Case hardening processes harden only the exterior of the steel part, creating a hard, wear-resistant skin (the "case") but preserving a tough and ductile interior. Carbon steels are not very hardenable meaning they can not be hardened throughout thick sections. Alloy steels have a better hardenability, so they can be through-hardened and do not require case hardening. This property of carbon steel can be beneficial, because it gives the surface good wear characteristics but leaves the core flexible and shock-absorbing. | 8 | Metallurgy |
Pyridine has historically been added to foods to give them a bitter flavour, although this practise is now banned in the U.S. It may still be added to ethanol to make it unsuitable for drinking. | 0 | Organic Chemistry |
Groups that are attached to the side of the backbone are held by bonds which are weaker than the bonds connecting the chain. When the polymer is heated, the side groups are stripped off from the chain before it is broken into smaller pieces.
For example, the PVC eliminates HCl, under 100–120 °C.
CH(Cl)CHCHCH(Cl)→CH=CH-CH=CH+2HCl
Side group elimination can also proceed in a radical manner. For instance, methyl groups in polypropylene are susceptible to homolysis at high temperatures, leaving radicals on the polymer backbone. | 7 | Physical Chemistry |
This gene contains a single nucleotide polymorphism that causes an amino acid substitution within the 11 of 12 ankyrin repeats of ANKK1 (Glu713Lys of 765 residues). This polymorphism, which is commonly referred to Taq1A, was previously believed to be located in the promoter region of the DRD2 gene, since the polymorphism is proximal to the DRD2 gene and can influence DRD2 receptor expression. It is now known to be located in the coding region of the ANKK1 gene which controls the synthesis of dopamine in the brain. The A1 allele is associated with increased activity of striatal L-amino acid decarboxylase. | 1 | Biochemistry |
22-Dihydroergocalciferol is a form of vitamin D, also known as vitamin D. It has the systematic name (5Z,7E)-(3S)-9,10-seco-5,7,10(19)-ergostatrien-3-ol.
Vitamin D is found in certain mushrooms, being produced from ergosta-5,7-dienol (22,23-dihydroergosterol) instead of ergosterol. | 1 | Biochemistry |
In common with recovery and recrystallisation, growth phenomena can be separated into continuous and discontinuous mechanisms. In the former the microstructure evolves from state A to B (in this case the grains get larger) in a uniform manner. In the latter, the changes occur heterogeneously and specific transformed and untransformed regions may be identified. Abnormal or discontinuous grain growth is characterised by a subset of grains growing at a high rate and at the expense of their neighbours and tends to result in a microstructure dominated by a few very large grains. In order for this to occur the subset of grains must possess some advantage over their competitors such as a high grain boundary energy, locally high grain boundary mobility, favourable texture or lower local second-phase particle density. | 8 | Metallurgy |
Originally the process was confined to optical equipment such as prisms—the earliest examples being made around 1900. Later the range of use was expanded to microelectronics and other miniaturised devices. | 6 | Supramolecular Chemistry |
Isomerization of epoxides to allylic alcohols under strongly basic conditions proceeds by a β-elimination process. A model has been advanced that invokes an initial complex between the lithium amide base and epoxide. Concerted C–O bond cleavage and deprotonation proceeds via a syn transition state to give an allylic alkoxide, which is protonated upon workup. Deprotonation typically occurs at the exist in the transition state for cis double bond formation.
Other processes may take place competitively under basic conditions, particularly when β-elimination is slow or not possible. These pathways likely begin with lithiation of a carbon in the epoxide ring, followed by α-elimination to afford a carbene intermediate. 1,2-hydrogen migration leads to ketones, while intramolecular C–H insertion affords cyclic alcohols with the formation of a new carbon-carbon bond.
In many cases when hexamethylphosphoramide (HMPA) is used as an additive with lithium amide bases, selectivity for the formation of allylic alcohols increases. These reactions are believed to proceed through E2 elimination. | 0 | Organic Chemistry |
Despite their many advantages, the use of PPGs in total syntheses are relatively rare. Nevertheless, PPGs’ "orthogonality" to common synthetic reagents, as well as the possibility of conducting a "traceless reagent process", has proven useful in natural product synthesis. Two examples include the syntheses of ent-Fumiquinazoline and (-)-diazonamide A. The syntheses required irradiation at 254 and 300 nm, respectively. | 5 | Photochemistry |
The sigma-2 receptor is located in the lipid raft. The sigma-2 receptor is found in several areas of the brain, including high densities in the cerebellum, motor cortex, hippocampus, and substantia nigra. It is also highly expressed in the lungs, liver, and kidneys. | 1 | Biochemistry |
FeTAML(=O), TAML = tetra-amido macrocyclic ligand, is formed by the reaction of [Fe(TAML)(HO)](PPh) with 2-5 equivalents of meta-chloroperbenzoic acid at -60 ˚C in n-butyronitrile. This deep green compound (two λ at 445 and 630 nm respectively) is stable at 77 K. The stabilization of Fe(V) is attributed to the strong π–donor capacity of deprotonated amide nitrogens. | 7 | Physical Chemistry |
The Woodward–Hoffmann rules can also explain bimolecular cycloaddition reactions through correlation diagrams. A [p + q] cycloaddition brings together two components, one with p π-electrons, and the other with q π-electrons. Cycloaddition reactions are further characterized as suprafacial (s) or antarafacial (a) with respect to each of the π components. (See below "General formulation" for a detailed description of the generalization of WH notation to all pericyclic processes.) | 7 | Physical Chemistry |
Laminin–111 (also "laminin–1") is a protein of the type known as laminin isoforms. It was among the first of the laminin isoforms to be discovered. The "111" identifies the isoform's chain composition of α1β1γ1. This protein plays an important role in embryonic development. Injections of this substance are used in treatment for Duchenne muscular dystrophy, and its cellular action may potentially become a focus of study in cancer research. | 0 | Organic Chemistry |
Russian biochemist Aleksander Oparin and British biologist J.B.S. Haldane independently hypothesized in the 1920s that the first cells in early Earths oceans could be, in essence, coacervate droplets. Haldane used the term primordial soup to refer to the dilute mixture of organic molecules that could have built up as a result of reactions between inorganic building blocks such as ammonia, carbon dioxide and water, in presence of UV light as an energy source. Oparin proposed that simple building blocks with increasing complexity could organize locally, or self-assemble, to form protocells with living properties. He performed experiments based on Bungenberg de Jongs colloidal aggregates (coacervates) to encapsulate proteinoids and enzymes within protocells. Further work by chemists Sidney Fox, Kaoru Harada, Stanley Miller and Harold Urey further strengthened the theory that inorganic building blocks could increase in complexity and give rise to cell-like structures.
The Oparin-Haldane hypothesis established the foundations of research on the chemistry of abiogenesis, but the lipid-world and RNA-world scenarios have gained more attention since the 1980s with the work of Morowitz, Luisi and Szostak. However, recently, there has been a rising interest in coacervates as protocells, resonating with current findings that reactions too slow or unlikely in aqueous solutions can be significantly favored in such membraneless compartments. | 7 | Physical Chemistry |
Type P (55%Pd/31%Pt/14%Au–65%Au/35%Pd, by weight) thermocouples give a thermoelectric voltage that mimics the type K over the range 500 °C to 1400 °C, however they are constructed purely of noble metals and so shows enhanced corrosion resistance. This combination is also known as Platinel II. | 8 | Metallurgy |
A coating or paint is usually a fluid applied covering applied to a surface in contact with a corrosive situation such as the atmosphere. The surface is usually called the substrate. In corrosion prevention applications the purpose of applying the coating is mainly functional rather than decorative. Paints and lacquers are coatings that have dual uses of protecting the substrate and being decorative, but paint on large industrial pipes as well as preventing corrosion is also used for identification e.g. red for fire-fighting control etc. Functional coatings may be applied to change the surface properties of the substrate, such as adhesion, wettability, corrosion resistance, or wear resistance. In the automotive industry, coatings are used to control corrosion but also for aesthetic reasons. Coatings are also extensively used in marine environments to control corrosion in an oceanic environment. Corrosion will eventually breakthrough a coating and so have a design life before maintenance. | 8 | Metallurgy |
Between 1950 and 2020, the average pH value of the ocean surface is estimated to have decreased from approximately 8.15 to 8.05. This represents an increase of around 26% in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH unit is equivalent to a tenfold change in hydrogen ion concentration). For example, in the 15-year period 1995–2010 alone, acidity has increased 6 percent in the upper 100 meters of the Pacific Ocean from Hawaii to Alaska.
The IPCC Sixth Assessment Report in 2021 stated that "present-day surface pH values are unprecedented for at least 26,000 years and current rates of pH change are unprecedented since at least that time. The pH value of the ocean interior has declined over the last 20–30 years everywhere in the global ocean. The report also found that "pH in open ocean surface water has declined by about 0.017 to 0.027 pH units per decade since the late 1980s".
The rate of decline differs by region. This is due to complex interactions between different types of forcing mechanisms: "In the tropical Pacific, its central and eastern upwelling zones exhibited a faster pH decline of minus 0.022 to minus 0.026 pH unit per decade." This is thought to be "due to increased upwelling of -rich sub-surface waters in addition to anthropogenic uptake." Some regions exhibited a slower acidification rate: a pH decline of minus 0.010 to minus 0.013 pH unit per decade has been observed in warm pools in the western tropical Pacific.
The rate at which ocean acidification will occur may be influenced by the rate of surface ocean warming, because warm waters will not absorb as much . Therefore, greater seawater warming could limit CO absorption and lead to a smaller change in pH for a given increase in CO. The difference in changes in temperature between basins is one of the main reasons for the differences in acidification rates in different localities.
Current rates of ocean acidification have been likened to the greenhouse event at the Paleocene–Eocene boundary (about 56 million years ago), when surface ocean temperatures rose by 5–6 degrees Celsius. In that event, surface ecosystems experienced a variety of impacts, but bottom-dwelling organisms in the deep ocean actually experienced a major extinction. Currently, the rate of carbon addition to the atmosphere-ocean system is about ten times the rate that occurred at the Paleocene–Eocene boundary.
Extensive observational systems are now in place or being built for monitoring seawater chemistry and acidification for both the global open ocean and some coastal systems. | 9 | Geochemistry |
Source:
A solution of the olefinic acid (0.499 g, 2.25 mmol) dissolved in benzene (20 ml, freshly distilled from calcium hydride) was stirred at 0 °C (ice bath) under nitrogen while oxalyl chloride (1.35 ml, 2.0 g, 15.75 mmol) was added dropwise. The ice bath
was removed and the solution was stirred at room temperature for 2 hr. The solvent and excess reagent were removed in vacuo. The resulting orange oil was dissolved in benzene (2 x 5.0 mi, freshly distilled from calcium hydride) under nitrogen.
This solution was added dropwise at 0 °C (ice bath) to an anhydrous ethereal solution of diazomethane (50 ml, −20 mmol, predried over sodium metal) with vigorous stirring under nitrogen. The resulting solution was stirred at 0 °C for 1 hr and then at room temperature for 1.5 hr. The solvents and excess reagent were removed in vacuo.
Tetrahydrofuran (40 ml, freshly distilled from lithium aluminum hydride) and finely divided metallic copper powder (0.67 g) were added to the crude diazo ketone, sequentially. This suspension was vigorously stirred at reflux under nitrogen for 2 hr. The resulting suspension was allowed to stir at room temperature for an additional 14 hr. The solution was filtered into water (100 ml). The mixture was shaken vigorously for 5 min and then extracted with ether (3 x 50 ml). The combined ethereal extracts were washed with saturated sodium bicarbonate solution (4 X 40 ml), water (40 ml), and saturated sodium chloride solution (40 ml), dried (NaSO), and concentrated in vacuo to give 0.673 g of a crude brown oil. This crude oil was chromatographed on silica gel (67 g) in a 2-cm diameter column using 10% ether-90% petroleum ether to develop the column, taking 37-ml sized fractions. Fractions 11–16 gave 0.164 g (33%) of pure ketone product: mp 64-64.5° (from pentane); IR (CCl) 3095 (cyclopropyl CH)
and 1755 cm (CO); NMR (CCl) δ 1.18 (s, 3H, CH) 1.03 (9, 3H, CH),
0.97 (s, 3H, CH), and 0.90 ppm (s, 3H, CH). Anal. Calcd for CHO: C, 82.52; H, 10.16. Found: C, 82.61; H, 10.01. | 0 | Organic Chemistry |
Secondary antibodies can be conjugated to enzymes such as horseradish peroxidase (HRP) or alkaline phosphatase (AP); or fluorescent dyes such as fluorescein isothiocyanate (FITC), rhodamine derivatives, Alexa Fluor dyes; or other molecules to be used in various applications. Secondary antibodies are used in many biochemical assays including:
* ELISA, including many HIV tests
* Western blot
* Immunostaining
* Immunohistochemistry
* Immunocytochemistry | 1 | Biochemistry |
Riboswitches have been found to act as regulators of gene expression, particularly in bacteria, but also in plants and archaea. Riboswitches alter their secondary structure in response to the binding of a metabolite. Riboswitch classes have highly conserved aptamer domains, even among diverse organisms. When a target metabolite is bound to this aptamer, conformational changes occur, modulating the expression of genes carried by mRNA. These changes occur in an expression platform, located downstream from the aptamer. This change in structure can result in the formation or disruption of a terminator, truncating or permitting transcription respectively. Alternatively, riboswitches may bind or occlude the Shine–Dalgarno sequence, affecting translation. It has been suggested that these originated in an RNA-based world. In addition, RNA thermometers regulate gene expression in response to temperature changes. | 9 | Geochemistry |
Another major responsibility of ATSDR is producing [https://www.atsdr.cdc.gov/toxprofiledocs/index.html toxicological profiles] for the most common substances that are found at Superfund sites. The toxicological profiles summarize important studies on the substances’ health effects. ATSDR also publishes [https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsLanding.aspx ToxFAQs], [https://wwwn.cdc.gov/TSP/ToxGuides/ToxGuidesLanding.aspx ToxGuides], and [https://web.archive.org/web/20091225113852/http://www.atsdr.cdc.gov/phs/index.asp public health statements], which summarize the health information in toxicological profiles for use by the general public and health professionals. The agency maintains a [https://wwwn.cdc.gov/TSP/index.aspx Toxic Substances Portal] that compiles all of the agency’s toxicology information and allows users to search by chemical. ATSDR has published toxicological profiles for more than 250 hazardous substances.
ATSDR has a computational toxicology laboratory that conducts research and modeling on the effects of toxic substances on human health. The agency's toxicology work involves pharmacokinetic/pharmacodynamic modeling, quantitative structure–activity relationship methods, and benchmark dose modeling, as well as establishing minimal risk levels for human exposure to hazardous substances. One model developed by the toxicology laboratory showed that children were much more susceptible than adults to chemical exposure from inhalation and oral exposure. In the aftermath of chemical spills and emergencies, the laboratory also conducts research for state and local health departments on the health effects of the chemicals involved. | 1 | Biochemistry |
Neutrons undergo many types of scattering, including both elastic and inelastic scattering. Whether elastic or inelastic scatter occurs is dependent on the speed of the neutron, whether fast or thermal, or somewhere in between. It is also dependent on the nucleus it strikes and its neutron cross section. In inelastic scattering, the neutron interacts with the nucleus and the kinetic energy of the system is changed. This often activates the nucleus, putting it into an excited, unstable, short-lived energy state which causes it to quickly emit some kind of radiation to bring it back down to a stable or ground state. Alpha, beta, gamma, and protons may be emitted. Particles scattered in this type of nuclear reaction may cause the nucleus to recoil in the other direction. | 7 | Physical Chemistry |
It is common to describe where electrons reside as electron bands in bulk materials and electron orbitals in molecules. For the sake of expedience the following description will be described in molecular terms. When a photon excites a molecule, an electron in a ground state orbital can be excited to a higher energy orbital. This excited state leaves a vacancy in a ground state orbital that can be filled by an electron donor. It produces an electron in a high energy orbital which can be donated to an electron acceptor. In these respects a photoexcited molecule can act as a good oxidizing agent or a good reducing agent.
:Photoinduced oxidation
:[ML] + hν → [ML]*
:[ML]* + donor → [ML] + donor
:Photoinduced reduction
:[ML] + hν → [ML]*
:[ML]* + acceptor → [ML] + acceptor
The end result of both reactions is that an electron is delivered to an orbital that is higher in energy than where it previously resided. This is often described as a charge separated electron-hole pair when working with semiconductors.
In the absence of a proper electron donor or acceptor it is possible for such molecules to undergo ordinary fluorescence emission. The electron transfer is one form of photoquenching. | 5 | Photochemistry |
Stresses higher than anticipated can also accelerate rolling contact fatigue, which is a known precursor to WECs. WECs commence at subsurface during the initial phases of their formation, particularly at non-metallic inclusions. As the sliding contact period extended, these cracks extended from the subsurface region to the contact surface, ultimately leading to flaking. Furthermore, there was an observable rise in the extent of microstructural modifications near the cracks, suggesting that the presence of the crack is a precursor to these alterations.
The direction of sliding on the bearing surface played a significant role in WEC formation. When the traction force opposed the direction of over-rolling (referred to as negative sliding), it consistently led to the development of WECs. Conversely, when the traction force aligned with the over-rolling direction (positive sliding), WECs did not manifest. The magnitude of sliding exerted a dominant influence on WEC formation. Tests conducted at a sliding-to-rolling ratio (SRR) of -30% consistently resulted in the generation of WECs, while no WECs were observed in tests at -5% SRR. Furthermore, the number of WECs appeared to correlate with variations in contact severity, including changes in surface roughness, rolling speed, and lubricant temperature. | 8 | Metallurgy |
Although the free-water method likely contains some benthic metabolic signal, isolating the benthic contribution to whole-lake metabolism requires benthic-specific methods. Analogous to the light and dark bottle methods described above, lake sediment cores can be collected and changes in dissolved oxygen or carbon fixation can be used to estimate rates of primary productivity and respiration. Relatively new methods describe isolating the sediment-water interface with transparent domes and measure changes in dissolved oxygen in-situ, which is a hybrid between the free-water method and light-dark bottle method. These in-situ benthic chamber methods allow for relatively easy multi-day estimate of benthic metabolism, which helps the researcher determine how benthic metabolism changes with varying weather patterns and lake characteristics. | 1 | Biochemistry |
Milos Vratislav Novotny (born 19 April 1942) is an American chemist, currently the Distinguished Professor Emeritus and Director of the Novotny Glycoscience Laboratory and the Institute for Pheromone Research at Indiana University, and also a published author. Milos Novotny received his Bachelor of Science from the University of Brno, Czechoslovakia in 1962. In 1965, Novotny received his Ph.D. at the University of Brno. Novotny also holds honorary doctorates from Uppsala University, Masaryk University and Charles University, and he has been a major figure in analytical separation methods. Novotny was recognized for the development of PAGE Polyacrylamide Gel-filled Capillaries for Capillary Electrophoresis in 1993. In his years of work dedicated to analytical chemistry he has earned a reputation for being especially innovative in the field and has contributed a great deal to several analytical separation methods. Most notably, Milos has worked a great deal with microcolumn separation techniques of liquid chromatography, supercritical fluid chromatography, and capillary electrophoresis. Additionally, he is highly acclaimed for his research in proteomics and glycoanalysis and for identifying the first mammalian pheromones. | 3 | Analytical Chemistry |
Unlike viruses, bacteria are not as susceptible to silencing by siRNA. This is largely due to how bacteria replicate. Bacteria replicate outside of the host cell and do not contain the necessary machinery for RNAi to function. However, bacterial infections can still be suppressed by siRNA by targeting the host genes that are involved in the immune response caused by the infection or by targeting the host genes involved in mediating the entry of bacteria into cells. For instance, siRNA was used to reduce the amount of pro-inflammatory cytokines expressed in the cells of mice treated with lipopolysaccharide (LPS). The reduced expression of the inflammatory cytokine, tumor necrosis factor α (TNFα), in turn, caused a reduction in the septic shock felt by the LPS-treated mice. In addition, siRNA was used to prevent the bacteria, Psueomonas aeruginosa, from invading murine lung epithelial cells by knocking down the caveolin-2 (CAV2) gene. Thus, though bacteria cannot be directly targeted by siRNA mechanisms, they can still be affected by siRNA when the components involved in the bacterial infection are targeted. | 1 | Biochemistry |
In organoboron chemistry, the Brellochs reaction provides a way to generate the monocarboranes. The use of acetylenes to insert two carbons into boron hydrides is well established. The Brellochs method uses formaldehyde to insert single carbon atoms into boron hydrides.
Illustrative is the synthesis of CBH from commercially available decaborane.
:BH + CHO + 2 OH + HO → CBH + B(OH) + H
Oxidation of the arachno anion gives nido-6-CBH. Base degradation of the latter gives arachno-4-CBH. | 7 | Physical Chemistry |
In organic chemistry, nitrosamines (or more formally N-nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are carcinogenic in nonhuman animals. A 2006 systematic review supports a "positive association between nitrite and nitrosamine intake and gastric cancer, between meat and processed meat intake and gastric cancer and oesophageal cancer, and between preserved fish, vegetable and smoked food intake and gastric cancer, but is not conclusive". | 0 | Organic Chemistry |
He is a founding scientist and current director of 908 Devices incorporated, a company which focuses on building handheld mass spectrometry devices for applications in laboratory analysis, safety and security, as well as for use in the life sciences. In 2017 908 Devices Inc. received the Federal Laboratory Consortium Excellence in Technology Transfer Award. The company is known for several products, including the zipchip ™ separations platform for quick and high quality separation and mass spectrometry analysis of biological samples and the M908 ™ handheld High Pressure Mass Spectrometry tool for analysis of chemical warfare agents. Dr. Ramsey is also a founding scientist and former scientific advisory board member of Caliper Technologies incorporated, later renamed Caliper Life Sciences, a company that commercializes microfluidics and lab-on-a-chip technologies. Caliper Life Sciences was acquired by PerkinElmer in 2011 for $650M.
Between 1979 and 2004, Ramsey worked as a Eugene P. Wigner Fellow, research associate, and eventually a group leader for Oak Ridge National Laboratory. | 3 | Analytical Chemistry |
The ruling in the Corby toxic waste case, delivered in July 2009, found Corby Borough Council liable in negligence, public nuisance and a breach of statutory duty for its reclamation of a steel works and the resulting atmospheric contamination. The case against the council cited: "The Defendants urban land reclamation programme and the presence of poisonous waste presented a significant risk to health. The poisonous waste was ultra hazardous and various sites contained substantial quantities of contaminated waste and toxic materials that were likely to cause personal injuries to persons in the surrounding area in the event of their escape." While recognising that there was insufficient epidemiological data to establish whether the victims injuries arose from a "common cause", or from airborne contamination or from the reclamation works, the judge ruled that there was a "statistically significant cluster" of birth defects in Corby which needed "explanation other than chance": it was not the courts purpose to establish whether the victims were individually exposed to contaminants from the reclamation, rather to determine whether any relevant breach of duty had the ability to cause injuries of the type complained of. The judge also ruled that it was "reasonably foreseeable that the local population might be exposed to hazardous or contaminated substances" as a result of the councils clean-up programme.
Matt Townsend, head of the environmental practice at Allen & Overy, says: "One of the important lessons from the case is that because of the rapidly evolving nature of environmental science and advancing knowledge and techniques, it will no longer be possible for developers to hide behind the science. To claim that you didn’t know is now unacceptable.". Stephen Matthew, a partner in the project group at corporate law firm Nabarro, advises: "Councils and regeneration bodies still need to be very open and clear about how they intend to deal with material on brownfield sites. Councils need to take professional advice... Don't leave a gaping hole for any future class actions."
Following the Corby ruling, Jason Addy stated: "The Corby ruling could have huge implications for the actions and responsibilities of Rochdale Council for the Spodden Valley site. Environmental pollution has been a problem at the Rochdale factory with acknowledged cases of asbestos-related cancer caused by environmental exposure." Laurie Kazan Allen, Editor of the British Asbestos Newsletter, said: "This landmark decision has ramifications for Rochdale Council regarding the Spodden Valley asbestos factory site. There is now a clear legal principle that local authorities hold a duty of care to protect communities from the hazardous effects of disturbing contaminated land. Since at least the 1960s there has been clear evidence that the inhalation of asbestos fibres, even in low quantities, can cause terminal cancer decades after initial exposure. Rochdale Council must take heed of this historic decision and act to protect local people."
Hilda Palmer of the Greater Manchester Hazards Centre said: "This has serious implications for Rochdale MBC in its management and control of the ex T&N site. The site is known to be extensively contaminated with the known carcinogen asbestos, which may be released into the air whenever the site is disturbed, and the invisible microscopic fibres spread in the air across the area to be inhaled by people, including children who are especially at risk of developing asbestos related terminal cancers such as mesothelioma years later. These facts are not in dispute and though the owner of the site is the responsible duty holder, the court judgment on Corby Council confirms the duty of care of a council as the planning authority and environmental health authority in terms of managing and controlling the risks to long term health presented by the airborne asbestos fibres from this site." | 2 | Environmental Chemistry |
For the majority of eukaryotic messenger RNAs (mRNAs), translation initiates from a methionine-encoding AUG start codon following the molecular processes of cap-binding and scanning by ribosomal pre-initiation complexes (PICs). In rare exceptions, such as translation by viral IRES-containing mRNAs, cap-binding and/or scanning are not required for initiation, although AUG is still typically used as the first codon. RAN translation is an exception to the canonical rules as it uses variable start site selection and initiates from a non-AUG codon, but may still depend on cap-binding and scanning. | 1 | Biochemistry |
Materials can now be analysed through photoanalysis procedures. Unlike sieve analyses which can be time-consuming and inaccurate, taking a photo of a sample of the materials to be measured and using software to analyze the photo can result in rapid, accurate measurements. Another advantage is that the material can be analyzed without being handled. This is beneficial in the agricultural industry, as handling of food products can lead to contamination. Photoanalysis equipment and software is currently being used in mining, forestry and agricultural industries worldwide. | 7 | Physical Chemistry |
*[http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.htm Animated diagrams illustrating oxidative phosphorylation] Wiley and Co Concepts in Biochemistry
*[http://www.life.uiuc.edu/crofts/bioph354/ On-line biophysics lectures] Antony Crofts, University of Illinois at Urbana–Champaign
*[https://www.youtube.com/watch?v=PjdPTY1wHdQ ATP Synthase] Graham Johnson | 1 | Biochemistry |
Tectin is an organic substance secreted by certain ciliates. Tectin may form an adhesive stalk, disc or other sticky secretion. Tectin may also form a gelatinous envelope or membrane enclosing some ciliates as a protective capsule or lorica. Tectin is also called pseudochitin. Granules or rods (called protrichocysts) in the pellicle of some ciliates are also thought to be involved in tectin secretion. | 1 | Biochemistry |
In order to generate a molecular tool to discriminate between Interleukin-6 classic signaling and Interleukin-6 trans-signaling, a cDNA coding for human Interleukin-6 and a cDNA coding for the human soluble Interleukin-6 receptor were connected by a cDNA coding for a 13 amino acids long linker, which was long enough to bridge the 40 Å distance between the COOH terminus of the soluble Interleukin-6 receptor and the NH2 terminus of human Interleukin-6. The generated cDNA was expressed in yeast cells and in mammalian cells and it was shown that. | 1 | Biochemistry |
There are several PREN formulas. They commonly range from:
: PREN = %Cr + 3.3 × %Mo + 16 × %N
to:
: PREN = %Cr + 3.3 × %Mo + 30 × %N.
There are a few stainless steels which add tungsten (W), for those the following formula is used:
: PREN = %Cr + 3.3 × (%Mo + 0.5 × %W ) + 16 × %N
All % values of elements must be expressed by mass, or weight (wt. %), and not by volume. Tolerance on element measurements could be ignored as the PREN value is indicative only. | 8 | Metallurgy |
Electrogravimetry is a method used to separate and quantify ions of a substance, usually a metal. In this process, the analyte solution is electrolyzed. Electrochemical reduction causes the analyte to be deposited on the cathode. The mass of the cathode is determined before and after the experiment, and the difference is used to calculate the mass of analyte in the original solution.
Controlling the potential of the electrode is important to ensure that only the metal being analyzed will be deposited on the electrode.
The process is similar to electroplating.
The phenomenon of polarization exerts a back EMF in electrolysis, which reduces the actual EMF of the cell. Thus electrolysis of an electrolyte is possible only when this back EMF is overcome.
If two separated platinum electrodes are placed in a dilute solution of copper sulfate and if a source of potential is applied, no appreciable current will flow through the system, until some minimum potential is applied after which the current will increase as the applied potential increases. The applied voltage which is just sufficient to overcome the back EMF due to polarization and also to bring about the electrolysis of an electrolyte without any hindrance is known as decomposition potential.
The decomposition potential Ed is composed of various potentials and is given by:
:Ea (min)= Ed= Eb+ Es+ Ev
where:
*Ea = applied potential
*Ed = decomposition potential
*Eb = theoretical counter or back potential
*Ev = overvoltage.
The origins of electrogravimetry date back to the 19th century, when Oliver Wilcott Gibbs, an American chemist, studied the electrolytic precipitation of copper and nickel. This procedure was the first of its kind until Carl Luckow did similar research on electric metal analysis. Today, these two are credited with the invention of the electrogravimetry, known at the time as “electrochemical analysis,” “electroanalysis,” or “electrolytic analysis”.
All methods of electrogravimetry involve a traditional quartz crystal microbalance (QCM) system in which a sensor is used from an AT cut quartz crystal. The groundwork of the QCM is built upon the notion that any mass delivered on the quartz electrode's interfacial region can be detected through the resonating frequency of the vibrating quartz crystal. While most vibrational modes occurring in the AT cut quartz are negligible, the vibration mode is known as thickness shear mode. These vibrations are extremely sensitive, which permits accurate detection of atomic interactions near the sensor, allowing these techniques to be used in analytical chemistry .
Through combining the techniques of QCM with classic electrochemical techniques, the electrochemical quartz crystal microbalance (EQCM) was created. EQCM is a new device used to perform the process of electrogravimetry. This device employs a high frequency acoustic wave generated by a piezoelectric resonator to store and dissipate energy infused into the device's interfacial region.
Electrogravimetry has been useful in polymer studies, copper electrodeposition, gold oxidation in an acidic medium, and passivity of iron in a sulfuric medium, as well as Ionic insertion in WO3. | 3 | Analytical Chemistry |
Different methods to determine the endpoint include:
*Indicator: A substance that changes color in response to a chemical change. An acid–base indicator (e.g., phenolphthalein) changes color depending on the pH. Redox indicators are also used. A drop of indicator solution is added to the titration at the beginning; the endpoint has been reached when the color changes.
*Potentiometer: An instrument that measures the electrode potential of the solution. These are used for redox titrations; the potential of the working electrode will suddenly change as the endpoint is reached.
*pH meter: A potentiometer with an electrode whose potential depends on the amount of H ion present in the solution. (This is an example of an ion-selective electrode.) The pH of the solution is measured throughout the titration, more accurately than with an indicator; at the endpoint there will be a sudden change in the measured pH.
*Conductivity: A measurement of ions in a solution. Ion concentration can change significantly in a titration, which changes the conductivity. (For instance, during an acid–base titration, the H and OH ions react to form neutral HO.) As total conductance depends on all ions present in the solution and not all ions contribute equally (due to mobility and ionic strength), predicting the change in conductivity is more difficult than measuring it.
*Color change: In some reactions, the solution changes color without any added indicator. This is often seen in redox titrations when the different oxidation states of the product and reactant produce different colors.
*Precipitation: If a reaction produces a solid, a precipitate will form during the titration. A classic example is the reaction between Ag and Cl to form the insoluble salt AgCl. Cloudy precipitates usually make it difficult to determine the endpoint precisely. To compensate, precipitation titrations often have to be done as "back" titrations (see below).
*Isothermal titration calorimeter: An instrument that measures the heat produced or consumed by the reaction to determine the endpoint. Used in biochemical titrations, such as the determination of how substrates bind to enzymes.
*Thermometric titrimetry: Differentiated from calorimetric titrimetry because the heat of the reaction (as indicated by temperature rise or fall) is not used to determine the amount of analyte in the sample solution. Instead, the endpoint is determined by the rate of temperature change.
*Spectroscopy: Used to measure the absorption of light by the solution during titration if the spectrum of the reactant, titrant or product is known. The concentration of the material can be determined by Beer's Law.
*Amperometry: Measures the current produced by the titration reaction as a result of the oxidation or reduction of the analyte. The endpoint is detected as a change in the current. This method is most useful when the excess titrant can be reduced, as in the titration of halides with Ag. | 3 | Analytical Chemistry |
Alizarine Yellow R is produced by azo coupling of salicylic acid and diazonium derivative of 4-Nitroaniline | 3 | Analytical Chemistry |
* Nematoda: Ascaris, Caenorhabditis ;
* Mollusca: Bivalvia); Polyplacophora;
* Arthropoda/Crustacea: Artemia;
* Arthropoda/Insecta: Drosophila [<nowiki />Locusta migratoria (migratory locust), Apis mellifera (honeybee)]. | 1 | Biochemistry |
Evapoporometry is a method used to determine pore-size in synthetic membranes. Based on the Kelvin equation, this technique is most accurate for detection of pore diameters between 4 nm to 150 nm. | 7 | Physical Chemistry |
From 1942 to 1945, Cram worked in chemical research at Merck & Co laboratories, doing penicillin research with mentor Max Tishler. Postdoctoral work was as an American Chemical Society postdoctoral fellow at the Massachusetts Institute of Technology, with John D. Roberts. Cram was the originator of Cram's rule, which provides a model for predicting the outcome of nucleophilic attack of carbonyl compounds. He published over 350 research papers and eight books on organic chemistry, and taught graduate and post-doctoral students from 21 different countries. | 4 | Stereochemistry |
In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. different K values), or are regulated differently. They permit the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage.
In many cases, isozymes are encoded by homologous genes that have diverged over time. Strictly speaking, enzymes with different amino acid sequences that catalyse the same reaction are isozymes if encoded by different genes, or allozymes if encoded by different alleles of the same gene; the two terms are often used interchangeably. | 1 | Biochemistry |
Many different nucleophiles have been reported to be effective for this reaction. Some of the most common nucleophiles include malonates, enolates, primary alkoxides, carboxylates, phenoxides, amines, azide, sulfonamides, imides, and sulfones. | 0 | Organic Chemistry |
Sulfoxide undergo thermal elimination via an E mechanism to yield vinyl alkenes and sulfenic acids.
:CHS(O)CHCHR → CHSOH + CH=CHR
The acids are powerful antioxidants, but lack long-term stability. Some parent sulfoxides are therefore marketed as antioxidant polymer stabilisers. Structures based on thiodipropionate esters are popular. The reverse reaction is possible. | 0 | Organic Chemistry |
pH neutral AORFBs are operated at pH7 conditions, typically using NaCl as a supporting electrolyte. At pH neutral conditions, organic and organometallic molecules are more stable than at corrosive acidic and alkaline conditions. For example, K4[Fe(CN)], a common catholyte used in AORFBs, is not stable in alkaline solutions but is at pH neutral conditions.
AORFBs used methyl viologen as an anolyte and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl as a catholyte at pH neutral conditions, plus NaCL and a low-cost anion exchange membrane. This MV/TEMPO system has the highest cell voltage, 1.25V, and, possibly, lowest capital cost ($180/kWh) reported for AORFBs. The aqueous liquid electrolytes were designed as a drop-in replacement for current systems without replacing existing infrastructure. A 600-milliwatt test battery was stable for 100 cycles with nearly 100 percent efficiency at current densities ranging from 20 to 100 mA/cm, with optimal performance rated at 40–50mA, at which about 70% of the batterys original voltage was retained. Neutral AORFBs can be more environmentally friendly than acid or alkaline AORFBs while showing electrochemical performance comparable to corrosive RFBs. The MV/TEMPO AORFB has an energy density of 8.4Wh/L with the limitation on the TEMPO side. Viologen-based flow batteries have been mainly developed by Lius group at Utah State University. In 2019, the group reported an ultralight sulfonate–viologen/ferrocyanide AORFB stable for 1000 cycles at an energy density of 10 Wh/L, so far the most stable, energy dense AORFB. | 7 | Physical Chemistry |
An atom interferometer creates coherent atomic beams, where the coherence is with respect to the phase of the atom's de Broglie wave. | 7 | Physical Chemistry |
Each of the functional regions of TFIIB interacts with different parts of RNA polymerase II. The amino terminal B ribbon is located on dock domain of RNA polymerase II and extends in to the cleft towards the active site. Extending the B ribbon is the B reader that extends via the RNA exit tunnel to the binding site of the DNA-RNA hybrid and towards the active site. The B linker is the region between the B reader and the B core that is found in the cleft of RNA polymerase II and continues by the rudder and the clamp coiled-coil until it reaches the C terminal B core that is found above the wall of RNA polymerase II.
The B reader and the B linker consist of highly conserved residues that are positioned through the RNA polymerase II tunnel towards the active site and ensure tight binding, without these key residues dissociation would occur. These two domains are also thought to adjust the position of some of the more flexible areas of RNA polymerase II to allow for the precise positioning of the DNA and allowing the addition of the new NTPs onto the nascent RNA chain.
Upon binding RNA polymerase II, the B reader and B linker cause slight repositioning of the protrusion domain of RNA polymerase II which allows an essential second magnesium ion to bind in the active site. It forms a beta sheet and an ordered loop that helps with the stability of the structure when transcription is initiated. | 1 | Biochemistry |
The discovery of introns and the split gene architecture of the eukaryotic genes started a new era of eukaryotic biology. The question of why eukaryotic genes had fragmented genes prompted speculation and discussion almost immediately.
Ford Doolittle published a paper in 1978 in which he stated that most molecular biologists assumed that the eukaryotic genome arose from a ‘simpler’ and more ‘primitive’ prokaryotic genome rather like that of Escherichia coli. However, this type of evolution would require that introns be introduced into the coding sequences of bacterial genes. Regarding this requirement, Doolittle said, “It is extraordinarily difficult to imagine how informationally irrelevant sequences could be introduced into pre-existing structural genes without deleterious effects.” He stated “I would like to argue that the eukaryotic genome, at least in that aspect of its structure manifested as ‘genes in pieces’ is in fact the primitive original form.”
James Darnell expressed similar views in 1978. He stated, “The differences in the biochemistry of messenger RNA formation in eukaryotes compared to prokaryotes are so profound as to suggest that sequential prokaryotic to eukaryotic cell evolution seems unlikely. The recently discovered non-contiguous sequences in eukaryotic DNA that encode messenger RNA may reflect an ancient, rather than a new, distribution of information in DNA and that eukaryotes evolved independently of prokaryotes.”
However, in an apparent attempt to reconcile with the idea that RNA preceded DNA in evolution, and with the concept of the three evolutionary lineages of archea, bacteria and eukarya, both Doolittle and Darnell deviated from their original speculation in a joint paper in 1985. They suggested that the ancestor of all three groups of organisms, the ‘progenote,’ had a genes-in-pieces structure, from which all three lineages evolved. They speculated that the precellular stage had primitive RNA genes which had introns, which were reverse transcribed into DNA and formed the progenote. Bacteria and archea evolved from the progenote by losing introns, and ‘urkaryote’ evolved from it by retaining introns. Later, the eukaryote evolved from the urkaryote by evolving a nucleus and absorbing mitochondria from bacteria. Multicellular organisms then evolved from the eukaryote.
These authors predicted that the distinctions between the prokaryote and the eukaryote were so profound that the prokaryote to eukaryote evolution was not tenable, and had different origins. However, other than the speculations that the precellular RNA genes must have had introns, they did not address the key questions of intron origin. No explanations described why exons were short and introns were long, how the splice junctions originated, what the structure and sequence of the splice junctions meant, and why eukaryote genomes were large.
Around the same time that Doolittle and Darnell suggested that introns in eukaryotic genes could be ancient, Colin Blake and Walter Gilbert published their views on intron origins independently. In their view, introns originated as spacer sequences that enabled convenient recombination and shuffling of exons that encoded distinct functional domains in order to evolve new genes. Thus, new genes were assembled from exon modules that coded for functional domains, folding regions, or structural elements from preexisting genes in the genome of an ancestral organism, thereby evolving genes with new functions. They did not specify how exons or introns originated. In addition, even after many years, extensive analysis of thousands of proteins and genes showed that only extremely rarely do genes exhibit the supposed exon shuffling phenomenon. Furthermore, molecular biologists questioned the exon shuffling proposal, from a purely evolutionary view for both methodological and conceptual reasons, and, in the long run, this theory did not survive. | 1 | Biochemistry |
Cucurbiturils have also been explored as supramolecular catalysts. Larger cucurbiturils, such as cucurbit[8]uril can bind multiple guest molecules. CB[8] forms a complex 2:1 (guest:host) with (E)-diaminostilbene dihydrochloride which is accommodated by CB[8]'s larger internal diameter of 8.8 angstrom and height 9.1 angstrom. The close proximity and optimal orientation of the guest molecules within the cavity enhances the rate of the photochemical cyclization to give cyclobutane dimer with a 19:1 stereoselectivity for the syn configuration when bound to CB[8]. In the absence of CB[8] the cyclization reaction does not occur, but only the isomerization of the trans isomer to the cis isomer is observed. | 6 | Supramolecular Chemistry |
By far, the most prevalent bulk material for solar cells is crystalline silicon (c-Si), also known as "solar grade silicon". Bulk silicon is separated into multiple categories according to crystallinity and crystal size in the resulting ingot, ribbon or wafer. These cells are entirely based around the concept of a p–n junction. Solar cells made of c-Si are made from wafers between 160 and 240 micrometers thick. | 7 | Physical Chemistry |
The Electrochemical Society is a learned society (professional association) based in the United States that supports scientific inquiry in the field of electrochemistry solid-state science and related technology. The Society membership comprises more than 8,000 scientists and engineers in over 85 countries at all degree levels and in all fields of electrochemistry, solid-state science and related technologies. Additional support is provided by institutional members including corporations and laboratories.
ECS is a 501(c)(3) non-profit organization.
The Society publishes numerous journals including the Journal of The Electrochemical Society (the oldest peer-reviewed journal in its field), the Journal of Solid State Science and Technology, ECS Meeting Abstracts, ECS Transactions, and ECS Interface. The Society sponsors the ECS Monographs Series. These distinguished monographs, published by John Wiley & Sons, are the leading textbooks in their fields.
The ECS Digital Library on IOPscience encompasses over 160,000 journal and magazine articles and meeting abstracts. The Society supports open access through the Society’s initiative to make research freely available to world readers and free for authors to publish.
The Society has thirteen topic interest area divisions as well as regional sections in Asia, Europe, Latin America, the Middle East, North America, and Southern Asia; over 100 ECS student chapters are located in major universities in all of these regions as well as Eastern Europe and South Africa. Student members benefit from exposure to experts in their fields, sharing research, volunteer activities, and career development.
ECS administers numerous international awards and supports STEM educational and outreach efforts. | 7 | Physical Chemistry |
Oil analysis (OA) is the laboratory analysis of a lubricants properties, suspended contaminants, and wear debris. OA' is performed during routine predictive maintenance to provide meaningful and accurate information on lubricant and machine condition. By tracking oil analysis sample results over the life of a particular machine, trends can be established which can help eliminate costly repairs. The study of wear in machinery is called tribology. Tribologists often perform or interpret oil analysis data.
OA can be divided into three categories:
# analysis of oil properties including those of the base oil and its additives,
# analysis of contaminants,
# analysis of wear debris from machinery, | 3 | Analytical Chemistry |
Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. Examples of these include cytidine (C), uridine (U), adenosine (A), guanosine (G), and thymidine (T).
Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides.
Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, and T, while RNA uses the ribonucleotides (which have an extra hydroxyl(OH) group on the pentose ring) C, G, A, and U. Modified bases are fairly common (such as with methyl groups on the base ring), as found in ribosomal RNA or transfer RNAs or for discriminating the new from old strands of DNA after replication.
Each nucleotide is made of an acyclic nitrogenous base, a pentose and one to three phosphate groups. They contain carbon, nitrogen, oxygen, hydrogen and phosphorus. They serve as sources of chemical energy (adenosine triphosphate and guanosine triphosphate), participate in cellular signaling (cyclic guanosine monophosphate and cyclic adenosine monophosphate), and are incorporated into important cofactors of enzymatic reactions (coenzyme A, flavin adenine dinucleotide, flavin mononucleotide, and nicotinamide adenine dinucleotide phosphate). | 0 | Organic Chemistry |
Vitamin D can be synthesized only by a photochemical process. Its production from sterols would have started very early in the evolution of life around the origin of photosynthesis, possibly helping to prevent DNA damage by absorbing UVB, making vitamin D an inactive end product. The familiar vitamin D endocrine machinery containing vitamin D receptor (VDR), various CYP450 enzymes for activation and inactivation, and a vitamin D binding protein (DBP) is found in vertebrates only. Primitive marine vertebrates are thought to absorb calcium from the ocean into their skeletons and eat plankton rich in vitamin D, although the function in those without a calcified cartilage is unclear. Phytoplankton in the ocean (such as coccolithophore and Emiliania huxleyi) have been photosynthesizing vitamin D for more than 500million years.
Land vertebrates required another source of vitamin D other than plants for their calcified skeletons. They had to either ingest it or be exposed to sunlight to photosynthesize it in their skin. Land vertebrates have been photosynthesizing vitamin D for more than 350million years.
In birds and fur-bearing mammals, fur or feathers block UV rays from reaching the skin. Instead, vitamin D is created from oily secretions of the skin deposited onto the feathers or fur, and is obtained orally during grooming. However, some animals, such as the naked mole-rat, are naturally cholecalciferol-deficient, as serum 25-OH vitamin D levels are undetectable. Dogs and cats are practically incapable of vitamin D synthesis due to high activity of 7-dehydrocholesterol reductase, but get vitamin D from prey animals. | 1 | Biochemistry |
MCP-RHEED is a system in which an electron beam is amplified by a micro-channel plate (MCP). This system consists of an electron gun and an MCP equipped with a fluorescent screen opposite to the electron gun. Because of the amplification, the intensity of the electron beam can be decreased by several orders of magnitude and the damage to the samples is diminished. This method is used to observe the growth of insulator crystals such as organic films and alkali halide films, which are easily damaged by electron beams. | 3 | Analytical Chemistry |
The main components of a UV curing solution includes resins, monomers, and photoinitiators. Resin is an oligomer that imparts specific properties to the final polymer. A monomer is used as a cross-linking agent and regulates the viscosity of the mixture to suit the application. The photoinitiator is responsible for absorbing the light and kickstarting the reaction, which helps control the cure rate and depth of cure. Each of these elements has a role to play in the crosslinking process and is linked to the composition of the final polymer. | 5 | Photochemistry |
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