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As discussed by Jin and Roberston in their review, silencing of a DNA repair gene by hypermethylation may be a very early step in progression to cancer. Such silencing is proposed to act similarly to a germ-line mutation in a DNA repair gene, and predisposes the cell and its descendants to progression to cancer. Another review also indicated an early role for hypermethylation of DNA repair genes in cancer. If a gene necessary for DNA repair is hypermethylated, resulting in deficient DNA repair, DNA damages will accumulate. Increased DNA damage tends to cause increased errors during DNA synthesis, leading to mutations that can give rise to cancer.
If hypermethylation of a DNA repair gene is an early step in carcinogenesis, then it may also occur in the normal-appearing tissues surrounding the cancer from which the cancer arose (the field defect). See the table below.
While DNA damages may give rise to mutations through error prone translesion synthesis, DNA damages can also give rise to epigenetic alterations during faulty DNA repair processes. The DNA damages that accumulate due to hypermethylation of the promoters of DNA repair genes can be a source of the increased epigenetic alterations found in many genes in cancers.
In an early study, looking at a limited set of transcriptional promoters, Fernandez et al. examined the DNA methylation profiles of 855 primary tumors. Comparing each tumor type with its corresponding normal tissue, 729 CpG island sites (55% of the 1322 CpG island sites evaluated) showed differential DNA methylation. Of these sites, 496 were hypermethylated (repressed) and 233 were hypomethylated (activated). Thus, there is a high level of promoter methylation alterations in tumors. Some of these alterations may contribute to cancer progression. | 1 | Biochemistry |
Most countries require continuous monitoring of emissions produced by coal and oil-fired power plants, municipal and hazardous waste incinerators, cement plants, as well as many other types of industrial sources. This monitoring is usually performed using extractive sampling systems coupled with infrared spectroscopy techniques. Some recent standoff measurements performed allowed the evaluation of the air quality but not many remote independent methods allow for low uncertainty measurements. | 7 | Physical Chemistry |
In organic chemistry, the Conia-ene reaction is an intramolecular cyclization reaction between an enolizable carbonyl such as an ester or ketone and an alkyne or alkene, giving a cyclic product with a new carbon-carbon bond. As initially reported by J. M. Conia and P. Le Perchec, the Conia-ene reaction is a heteroatom analog of the ene reaction that uses an enol as the ene component. Like other pericyclic reactions, the original Conia-ene reaction required high temperatures to proceed, limiting its wider application. However, subsequent improvements, particularly in metal catalysis, have led to significant expansion of reaction scope. Consequently, various forms of the Conia-ene reaction have been employed in the synthesis of complex molecules and natural products. | 0 | Organic Chemistry |
Strongly alkaline soils are sodic and dispersive, with slow infiltration, low hydraulic conductivity and poor available water capacity. Plant growth is severely restricted because aeration is poor when the soil is wet; while in dry conditions, plant-available water is rapidly depleted and the soils become hard and cloddy (high soil strength). The higher the pH in the soil, the less water available to be distributed to the plants and organisms that depend on it. With a decreased pH, this does not allow for plants to uptake water like they normally would. This causes them to not be able to photosynthesize.
Many strongly acidic soils, on the other hand, have strong aggregation, good internal drainage, and good water-holding characteristics. However, for many plant species, aluminium toxicity severely limits root growth, and moisture stress can occur even when the soil is relatively moist. | 9 | Geochemistry |
Diphenylchlorarsine is known to cause sneezing, coughing, headache, salivation, and vomiting. China and Japan are negotiating remediation of stocks of a variety of organoarsenic weapons, including chlorodiphenylarsine, dumped in northeastern China after Japan's numerous invasions of China. | 1 | Biochemistry |
In women, progesterone levels are relatively low during the preovulatory phase of the menstrual cycle, rise after ovulation, and are elevated during the luteal phase, as shown in the diagram above. Progesterone levels tend to be less than 2 ng/mL prior to ovulation and greater than 5 ng/mL after ovulation. If pregnancy occurs, human chorionic gonadotropin is released, maintaining the corpus luteum and allowing it to maintain levels of progesterone. Between 7 and 9 weeks, the placenta begins to produce progesterone in place of the corpus luteum in a process called the luteal-placental shift.
After the luteal-placental shift, progesterone levels start to rise further and may reach 100 to 200 ng/mL at term. Whether a decrease in progesterone levels is critical for the initiation of labor has been argued and may be species-specific. After delivery of the placenta and during lactation, progesterone levels are very low.
Progesterone levels are low in children and postmenopausal women. Adult males have levels similar to those in women during the follicular phase of the menstrual cycle. | 0 | Organic Chemistry |
5β-Coprostanol (5β-cholestan-3β-ol) is a 27-carbon stanol formed from the net reductive metabolism of cholesterol (cholest-5en-3β-ol) in the gut of most higher animals and birds. This compound has frequently been used as a biomarker for the presence of human faecal matter in the environment. 5β-coprostanol is thought to be exclusively bacterial in origin. | 2 | Environmental Chemistry |
Many new monomeric versions of EosFP have been developed that offer advantages over wild type EosFP. Developed by a team at the Janelia Farm Research Campus at Howard Hughes Medical Institute, mEos4 has higher photostability and longer imaging abilities than EosFP. It is also highly resistant to chemical fixatives such as PFA, gluteraldehyde and OsO4 which are used to preserve samples. mEos4 is effective at higher temperatures than EosFP, phot-converts at an increased rate and has a higher emission amplitude in both green and red fluorescent states. Applications for the mEos4 protein include photoactivation localization microscopy (PALM), correlative light/ electron microscopy (CLEM), protein activity indication and activity integration (post-hoc imaging for protein activity over time). | 1 | Biochemistry |
Many different proteins bind to particular TET enzymes and recruit the TETs to specific genomic locations. In some studies, further analysis is needed to determine whether the interaction per se mediates the recruitment or instead the interacting partner helps to establish a favourable chromatin environment for TET binding. TET1‑depleted and TET2‑depleted cells revealed distinct target preferences of these two enzymes, with TET1‑preferring promoters and TET2‑preferring gene bodies of highly expressed genes and enhancers.
The three mammalian DNA methyltransferases (DNMTs) show a strong preference for adding a methyl group to the 5 carbon of a cytosine where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5 → 3 direction (at CpG sites). This forms a 5mCpG site. More than 98% of DNA methylation occurs at CpG sites in mammalian somatic cells. Thus TET enzymes largely initiate demethylation at 5mCpG sites.
Oxoguanine glycosylase (OGG1) is one example of a protein that recruits a TET enzyme. TET1 is able to act on 5mCpG if an ROS has first acted on the guanine to form 8-hydroxy-2'-deoxyguanosine (8-OHdG or its tautomer 8-oxo-dG), resulting in a 5mCp-8-OHdG dinucleotide (see Figure). After formation of 5mCp-8-OHdG, the base excision repair enzyme OGG1 binds to the 8-OHdG lesion without immediate excision (see Figure). Adherence of OGG1 to the 5mCp-8-OHdG site recruits TET1, allowing TET1 to oxidize the 5mC adjacent to 8-OHdG. This initiates the demethylation pathway.
EGR1 is another example of a protein that recruits a TET enzyme. EGR1 has an important role in learning and memory. When a new event such as fear conditioning causes a memory to be formed, EGR1 messenger RNA is rapidly and selectively up-regulated in subsets of neurons in specific brain regions associated with learning and memory formation. TET1s is the predominant isoform of TET1 that is expressed in neurons. When EGR1 proteins are expressed, they appear to bring TET1s to about 600 sites in the neuron genome. Then EGR1 and TET1 appear to cooperate in demethylating and thereby activating the expression of genes downstream of the EGR1 binding sites in DNA. | 1 | Biochemistry |
Like any mechanical and physical entity there are scientific, industrial, and layman terminology. The following is a partial list of terms that are associated with mechanical screening.
*Amplitude - This is a measurement of the screen cloth as it vertically peaks to its tallest height and troughs to its lowest point. Measured in multiples of the acceleration constant g (g-force).
*Acceleration - Applied Acceleration to the screen mesh in order to overcome the van der waal forces
*Blinding - When material plugs into the open slots of the screen cloth and inhibits overflowing material from falling through.
*Brushing - This procedure is performed by an operator who uses a brush to brush over the screen cloth to dislodged blinded opening.
*Contamination - This is unwanted material in a given grade. This occurs when there is oversize or fine size material relative to the cut or grade. Another type of contamination is foreign body contamination.
**Oversize contamination occurs when there is a hole in the screen such that the hole is larger than the mesh size of the screen. Other instances where oversize occurs is material overflow falling into the grade from overhead, or there is the wrong mesh size screen in place.
**Fines contamination is when large sections of the screen cloth is blinded over, and material flowing over the screen does not fall through. The fines are then retained in the grade.
**Foreign body contamination is unwanted material that differs from the virgin material going over and through the screen. It can be anything ranging from tree twigs, grass, metal slag to other mineral types and composition. This contamination occurs when there is a hole in the scalping screen or a foreign material's mineralogy or chemical composition differs from the virgin material.
*Deck - a deck is frame or apparatus that holds the screen cloth in place. It also contains the screening drive. It can contain multiple sections as the material travels from the feed end to the discharge end. Multiple decks are screen decks placed in a configuration where there are a series of decks attached vertically and lean at the same angle as it preceding and exceeding decks. Multiple decks are often referred to as single deck, double deck, triple deck, etc.
*Frequency - Measured in hertz (Hz) or revolutions per minute (RPM). Frequency is the number of times the screen cloth sinusoidally peaks and troughs within a second. As for a gyratory screening motion it is the number of revolutions the screens or screen deck takes in a time interval, such as revolution per minute (RPM).
*Gradation, grading - Also called "cut" or "cutting." Given a feed material in an initial state, the material can be defined to have a particle size distribution. Grading is removing the maximum size material and minimum size material by way of mesh selection.
*Screen Media (Screen cloth) - it is the material defined by mesh size, which can be made of any type of material such steel, stainless steel, rubber compounds, polyurethane, brass, etc.
*Shaker - the whole assembly of any type mechanical screening machine.
*Stratification - This phenomenon occurs as vibration is passed through a bed of material. This causes coarse (larger) material to rise and finer (smaller) material to descend within the bed. The material in contact with screen cloth either falls through a slot or blinds the slot or contacts the cloth material and is thrown from the cloth to fall to the next lower level.
*Mesh - The number of open slots per linear inch. Mesh is arranged in multiple configuration. Mesh can be a square pattern, long-slotted rectangular pattern, circular pattern, or diamond pattern.
*Scalp, scalping - this is the very first cut of the incoming material with the sum of all its grades. Scalping is removing the largest size particles. This includes enormously large particles relative to the other particle's sizes. Scalping also cleans the incoming material from foreign body contamination such as twigs, trash, glass, or other unwanted oversize material. | 8 | Metallurgy |
Fluid inclusions can provide useful data in mineral exploration, as their characteristics depend on the mineralization process. The methods of using fluid inclusions to identify mineral deposits include assessing the abundance of a specific inclusion type, looking into variations in the inclusions' temperatures of phase changes during heating and cooling, and variations in other properties such as decrepitation behavior, and inclusions chemistry. Observation and point-counting of thin-sections of samples is used to identify the occurrence of specific inclusion types. If an abundance of similar fluid inclusions are found in close geographic proximity, one can conclude that the surrounding rock types are similar if not the same. Microthermometric properties (changes in temperature during phase changes) are used to characterize and categorize areas that witnessed thermal activity during mineral formation.
Fluid inclusions have been used to identify deposits of oil and gas. Drilling cuts, cores, and/or outcrop materials are preserved for their pore-fluids, and the chemistry of the fluid is analyzed with Fluid Inclusion Stratigraphy (FIS). FIS analysis takes the spectrometric reading of a fluid inclusion's volatile species; these are indicative of a natural gas or oil deposit nearby. The abundance of similar fluid inclusions could, however, be attributed to hydrocarbon migration and accumulation, so other techniques are used to confirm the presence of the oil deposit after initial detection of fluid inclusions. | 9 | Geochemistry |
Impregnation is, in essence, the converse of extraction. A substance is dissolved in the supercritical fluid, the solution flowed past a solid substrate, and is deposited on or dissolves in the substrate. Dyeing, which is readily carried out on polymer fibres such as polyester using disperse (non-ionic) dyes, is a special case of this. Carbon dioxide also dissolves in many polymers, considerably swelling and plasticising them and further accelerating the diffusion process. | 7 | Physical Chemistry |
Calcium in a blood sample should be estimated when required medically. Calcium should be precipitated out of 0.1 mL of the blood sample serum as calcium oxalate. After that, the decomposition of the calcium oxalate should occur by heat. Then, the sample should be estimated colorimetrically by o-cresolphthalein complexone. The required liquid complexone is made by dissolving 10 mg o-cresolphthalein complexone in 50 mL alkaline borate, and then 50 mL of 0.05 N HCl are added to make the solution's pH 8.5. This method for calcium determination is efficient and effective, requiring a minimal amount of blood serum sample and a reasonable amount of time. | 3 | Analytical Chemistry |
The concentrations of carbon dioxide in the atmosphere are expressed as parts per million by volume (abbreviated as ppmv or just ppm). To convert from the usual ppmv units to ppm mass, multiply by the ratio of the molar weight of CO to that of air, i.e. times 1.52 (44.01 divided by 28.96).
The first reproducibly accurate measurements of atmospheric CO were from flask sample measurements made by Dave Keeling at Caltech in the 1950s. Measurements at Mauna Loa have been ongoing since 1958. Additionally, measurements are also made at many other sites around the world. Many measurement sites are part of larger global networks. Global network data are often made publicly available. | 2 | Environmental Chemistry |
The equilibrium of two molecular conformations is determined by the difference in Gibbs free energy of the two conformations. From this energy difference, the equilibrium constant for the two conformations can be determined.
If there is a decrease in Gibbs free energy from one state to another, this transformation is spontaneous and the lower energy state is more stable. A highly strained, higher energy molecular conformation will spontaneously convert to the lower energy molecular conformation.
Enthalpy and entropy are related to Gibbs free energy through the equation (at a constant temperature):
Enthalpy is typically the more important thermodynamic function for determining a more stable molecular conformation. While there are different types of strain, the strain energy associated with all of them is due to the weakening of bonds within the molecule. Since enthalpy is usually more important, entropy can often be ignored. This isn't always the case; if the difference in enthalpy is small, entropy can have a larger effect on the equilibrium. For example, n-butane has two possible conformations, anti and gauche. The anti conformation is more stable by 0.9 kcal mol. We would expect that butane is roughly 82% anti and 18% gauche at room temperature. However, there are two possible gauche conformations and only one anti conformation. Therefore, entropy makes a contribution of 0.4 kcal in favor of the gauche conformation. We find that the actual conformational distribution of butane is 70% anti and 30% gauche at room temperature. | 4 | Stereochemistry |
A major function of the thylakoid membrane and its integral photosystems is the establishment of chemiosmotic potential. The carriers in the electron transport chain use some of the electron's energy to actively transport protons from the stroma to the lumen. During photosynthesis, the lumen becomes acidic, as low as pH 4, compared to pH 8 in the stroma. This represents a 10,000 fold concentration gradient for protons across the thylakoid membrane. | 5 | Photochemistry |
Radioisotopic labeling is a technique for tracking the passage of a sample of substance through a system. The substance is "labeled" by including radionuclides in its chemical composition. When these decay, their presence can be determined by detecting the radiation emitted by them. Radioisotopic labeling is a special case of isotopic labeling.
For these purposes, a particularly useful type of radioactive decay is positron emission. When a positron collides with an electron, it releases two high-energy photons traveling in diametrically opposite directions. If the positron is produced within a solid object, it is likely to do this before traveling more than a millimeter. If both of these photons can be detected, the location of the decay event can be determined very precisely.
Strictly speaking, radioisotopic labeling includes only cases where radioactivity is artificially introduced by experimenters, but some natural phenomena allow similar analysis to be performed. In particular, radiometric dating uses a closely related principle. | 7 | Physical Chemistry |
Swiss-Prot lists 137 types of neuraminidase from various species as of October 18, 2006. Nine subtypes of influenza neuraminidase are known; many occur only in various species of duck and chicken. Subtypes N1 and N2 have been positively linked to epidemics in humans, and strains with N3 or N7 subtypes have been identified in a number of isolated deaths.
CAZy defines a total of 85 glycosyl hydrolase families, of which families GH34 (viral), GH33 (cellular organisms), GH58 (viral and bacterial), GH83 (viral) are major families that contain this enzyme. GH58 is the only endo-acting family.
The following is a list of major classes of neuraminidase enzymes:
* Viral neuraminidase
* Bacterial neuraminidase
* Mammalian neuraminidases: | 0 | Organic Chemistry |
Cryptands and crown ethers typically do not form inclusion complexes since the guest is bound by forces stronger than van der Waals bonding. If the guest is enclosed on all sides so that it is trapped, the compound is known as a clathrate, not an inclusion complex. In molecular encapsulation, a guest molecule is trapped inside another molecule. | 6 | Supramolecular Chemistry |
Besides the above-mentioned two most commonly used family of techniques, a wide range of protocols were developed to measure chemotactic activity. Some of them are only qualitative, like aggregation tests, where small pieces of agar or filters are placed onto a slide and accumulation of cells around is measured.
In another semiquantitative technique, cells are overlaid the test substance and changes in opalescence of the originally cell-free compartment is recorded during the incubation time.
The third frequently used qualitative technique is the T-maze and its adaptations for microplates. In the original version, a container drilled in a peg is filled with cells. Then the peg is twisted and the cells get contact with two other containers filled with different substances. The incubation is stopped by resetting the peg and the cell number is counted from the containers.
Also, lately, microfluidic devices have been used more and more frequently to test quantitatively, and precisely, for chemotaxis. | 1 | Biochemistry |
Even though Pourbaix diagrams are useful for a metal corrosion potential estimation they have, however, some important limitations:
# Equilibrium is always assumed, though in practice it may differ.
# The diagram does not provide information on actual corrosion rates.
# Does not apply to alloys.
# Does not indicate whether passivation (in the form of oxides or hydroxides) is protective or not. Diffusion of oxygen ions through thin oxide layers are possible.
# Excludes corrosion by chloride ions (, etc.).
# Usually applicable only to temperature of , which is assumed by default. The Pourbaix diagrams for higher temperatures exist. | 7 | Physical Chemistry |
Naturally, it is produced in the human placenta by the syncytiotrophoblast.
Like any other gonadotropins, it can be extracted from the urine of pregnant women or produced from cultures of genetically modified cells using recombinant DNA technology.
In Pubergen, Pregnyl, Follutein, Profasi, Choragon and Novarel, it is extracted from the urine of pregnant women. In Ovidrel, it is produced with recombinant DNA technology. | 1 | Biochemistry |
Anisotropic terahertz microspectroscopy (ATM) is a spectroscopic technique in which molecular vibrations in an anisotropic material are probed with short pulses of terahertz radiation whose electric field is linearly polarized parallel to the surface of the material. The technique has been demonstrated in studies involving single crystal sucrose, fructose, oxalic acid, and molecular protein crystals in which the spatial orientation of molecular vibrations are of interest. | 7 | Physical Chemistry |
Siddiqui died on 14 April 1994 due to cardiac arrest after a brief illness in Karachi. He was buried in the Karachi University Graveyard. Despite his death, the academic and research institutes that he founded during more than 65 years of his research career are still contributing to the international level research in natural products chemistry.
As a person of multiple talents, Siddiqui was also a refined poet, musician, and a painter. In August 1924, he held his first international exhibition of paintings in Frankfurt. Later in 1927, his works of art were exhibited at the Uzielli Gallery, Frankfurt. During his stay in Germany, he also translated Rainer Maria Rilkes poetry into Urdu, which was published in the journal of Jamia Millia Islamia. Though, his passion for arts was superseded by the enthusiasm in scientific research, he continued to patronise arts and culture. In 1966, he was at the forefront for setting up the Central Institute of Arts and Crafts in Karachi. He also compiled a selection of poetry of Mir Taqi Mir into Intekhab-e-Meer'. In 1983, he published a portfolio collection of charcoal drawings from 1920 to 1950s.
On 14 April 1999, the Pakistan Post, as part of its Scientists of Pakistan series, issued a commemorative stamp to honour the contributions and services of Siddiqui. In the same year, the street leading to PCSIR Laboratories Complex in Karachi was named as Shahrah-e-Dr. Salim-uz-Zaman Siddiqui. Siddiqui was also remembered by his students and colleagues, many of whom continued to dedicate their international research and publications to his memory. In 2002, a research article was published in the journal Tetrahedron in which, authors Faizi and Naz dedicated their break-through research to the memory of Siddiqui, their mentor. | 0 | Organic Chemistry |
In the next phase (Scheme 2), starting from ketal 12, the cyclohexane ring was cleaved to provide two anchoring points for fusion with the A ring. Alcohol 12 was protected by a benzyl group. The acetonide protecting group was removed from the ketone. Ketone 14 was converted to silyl enol ether 15 by reaction with trimethylsilyl triflate, and a modified Rubottom oxidation using 3,3-dimethyldioxirane followed by a treatment with camphorsulfonic acid introduced a hydroxyl group alpha to the ketone. Ring opening by oxidative cleavage with lead tetraacetate in methanol gave compound 17. In the next step, the aldehyde was protected as a dimethyl acetal, and the ester was reduced to give primary alcohol 18. The hydroxyl group was converted in a Grieco elimination to the selenide (19), which on oxidation with hydrogen peroxide gave alkene 20. Ozonolysis with ozone and triphenylphosphine provided aldehyde 21. | 0 | Organic Chemistry |
A common sulfinamide is tert-butanesulfinamide (Ellmans sulfinamide), p-toluenesulfinamide (Davis sulfinamide), and 2,4,6-trimethylbenzenesulfinamide.
Sulfinamides arise in nature by the addition of nitroxyl (HNO) to thiols:
:RSH + HNO → RS(O)NH | 0 | Organic Chemistry |
Multiple studies have found the MPT to be a key factor in the damage to neurons caused by excitotoxicity.
The induction of MPT, which increases mitochondrial membrane permeability, causes mitochondria to become further depolarized, meaning that Δψ is abolished. When Δψ is lost, protons and some molecules are able to flow across the outer mitochondrial membrane uninhibited.
Loss of Δψ interferes with the production of adenosine triphosphate (ATP), the cell's main source of energy, because mitochondria must have an electrochemical gradient to provide the driving force for ATP production.
In cell damage resulting from conditions such as neurodegenerative diseases and head injury, opening of the mitochondrial permeability transition pore can greatly reduce ATP production, and can cause ATP synthase to begin hydrolysing, rather than producing, ATP. This produces an energy deficit in the cell, just when it most needs ATP to fuel activity of ion pumps.
MPT also allows Ca to leave the mitochondrion, which can place further stress on nearby mitochondria, and which can activate harmful calcium-dependent proteases such as calpain.
Reactive oxygen species (ROS) are also produced as a result of opening the MPT pore. MPT can allow antioxidant molecules such as glutathione to exit mitochondria, reducing the organelles ability to neutralize ROS. In addition, the electron transport chain (ETC) may produce more free radicals due to loss of components of the ETC, such as cytochrome c', through the MPTP. Loss of ETC components can lead to escape of electrons from the chain, which can then reduce molecules and form free radicals.
MPT causes mitochondria to become permeable to molecules smaller than 1.5 kDa, which, once inside, draw water in by increasing the organelles osmolar load. This event may lead mitochondria to swell and may cause the outer membrane to rupture, releasing cytochrome c. Cytochrome c can in turn cause the cell to go through apoptosis ("commit suicide") by activating pro-apoptotic factors. Other researchers contend that it is not mitochondrial membrane rupture that leads to cytochrome c' release, but rather another mechanism, such as translocation of the molecule through channels in the outer membrane, which does not involve the MPTP.
Much research has found that the fate of the cell after an insult depends on the extent of MPT. If MPT occurs to only a slight extent, the cell may recover, whereas if it occurs more it may undergo apoptosis. If it occurs to an even larger degree the cell is likely to undergo necrotic cell death. | 1 | Biochemistry |
According to the National Geographic, the Chesapeake Bay was one of the first hypoxic zones to be identified in the 1970s. The Chesapeake Bay experiences seasonal hypoxia due to high nitrogen levels. These nitrogen levels are caused by urbanization, there are multiple factories that pollute the atmosphere with nitrogen, and agriculture, the opposite side of the bay is used for poultry farming, which produces a lot of manure that ends up running off into the Chesapeake Bay.
From 1985 - 2019, there were efforts from the caretakers of Chesapeake Bay to reduce the annual hypoxic volumes. There was significant improvement in 2016-2017 that gave assurance to the caretakers that the efforts were successful, however recent data has shown that further efforts are needed to continuously curb the effects of global warming. | 9 | Geochemistry |
SIR3 is principally involved in heterochromatin spreading, the silencing activity of the SIR protein complex. When overexpressed, SIR3 leads to spreading beyond the normal nucleation site. SIR3 can continue to operate at very low levels of SIR2 and SIR4, but not without them. It preferentially binds to unmodified nucleosomes (no acetylation at H4K16 or methylation at H3K79), and relies on SIR2's deacetylation of H4K16 to enhance silencing. H3K79 methylation by DOT1 methyltransferase inhibits SIR3, resulting in an unsilenced chromatin region. SIR3 is recruited to target sequence by the transcription factors RAP1 or ABF1. | 1 | Biochemistry |
The name Akkermansia (Ak.ker.mansi.a.) derives from: Neo-Latin feminine gender noun Akkermansia, named after Anton Dirk Louis Akkermans (28 October 1940 – 21 August 2006), a Dutch microbiologist recognized for his contribution to microbial ecology. Neo-Latin neuter gender noun mucinum, mucin; Neo-Latin adjective philus from Greek adjective philos (φίλος) meaning friend, loving; Neo-Latin feminine gender adjective muciniphila', mucin-loving). | 1 | Biochemistry |
Aluminum based nanogalvanic alloys are characterized by the size of their galvanic microstructure and consist of particles with a mesh size of -325, which is equivalent to a diameter of around 50 microns. Since the grain size of the powders is in the nanometer scale and the particle size is tens of microns similar to conventional powders, no additional health hazards are associated with the handling of the nanogalvanic powders. The by-products of the powder reaction with water is non-toxic and occurs naturally. The aluminum based nanogalvanic alloys were also demonstrated to produce 1000 ml. of hydrogen gas per gram of aluminum in less than 1 minute and 1340 ml—100% of the theoretical yield at 295 K and 1 atm.—in 3 minutes without the need for hazardous or costly materials, or additional processes. These nanogalvanic structured powders can be manufactured by means of high energy ball milling at room temperature or at lower temperatures. The powders may be compacted in the form of tablets for ease of transportation, which would reduce reliance on high-pressure or liquid hydrogen cylinders traditionally used for shipment. Additionally, they are stable in the atmosphere at standard temperature, pressure, and humidity levels, allowing for convenient storage. | 2 | Environmental Chemistry |
Huntingtin protein co-localizes with ATM repair protein at sites of DNA damage. Huntingtin is a scaffolding protein in the ATM oxidative DNA damage response complex. Huntingtons disease patients with aberrant huntingtin protein are deficient in repair of oxidative DNA damage. Oxidative DNA damage appears to underlie Huntingtons disease pathogenesis. Huntington's disease is likely caused by the dysfunction of mutant huntingtin scaffold protein in DNA repair leading to increased oxidative DNA damage in metabolically active cells. | 1 | Biochemistry |
As an example, in a typical pump-probe experimental apparatus, an attosecond (XUV-SXR) pulse and an intense ( W/cm) low-frequency infrared pulse with a time duration of few to tens femtoseconds are collinearly focused on the studied sample.
At this point, by varying the delay of the attosecond pulse, which could be pump/probe depending on the experiment, with respect to the IR pulse (probe/pump), the desired physical observable is recorded.
The subsequent challenge is to interpret the collected data and retrieve fundamental information on the hidden dynamics and quantum processes occurring in the sample. This can be achieved with advanced theoretical tools and numerical calculations.
By exploiting this experimental scheme, several kinds of dynamics can be explored in atoms, molecules and solids; typically light-induced dynamics and out-of-equilibrium excited states within attosecond time-resolution. | 7 | Physical Chemistry |
The standard preparation for n-BuLi is reaction of 1-bromobutane or 1-chlorobutane with Li metal:
: 2 Li + CHX → CHLi + LiX (X = Cl, Br)
If the lithium used for this reaction contains 1–3% sodium, the reaction proceeds more quickly than if pure lithium is used. Solvents used for this preparation include benzene, cyclohexane, and diethyl ether. When BuBr is the precursor, the product is a homogeneous solution, consisting of a mixed cluster containing both LiBr and BuLi, together with a small amount of octane. BuLi forms a weaker complex with LiCl, so that the reaction of BuCl with Li produces a precipitate of LiCl.
Solutions of butyllithium, which are susceptible to degradation by air, are standardized by titration. A popular weak acid is biphenyl-4-methanol, which gives a deeply colored dilithio derivative at the end point. | 0 | Organic Chemistry |
A phylloquinone, sometimes called vitamin K, is the next early electron acceptor in PSI. It oxidizes A in order to receive the electron and in turn is re-oxidized by F, from which the electron is passed to F and F. The reduction of F appears to be the rate-limiting step. | 5 | Photochemistry |
A low pressure ratio fan (such as that used on a high bypass ratio turbofan) has a range of working lines. At high flight speeds, the ram pressure ratio factors up the cold nozzle pressure ratio, causing the nozzle to choke. Above the choking condition, the working lines tend to coalesce into a unique steep straight line. When the nozzle unchokes, the working line starts to become more curved, reflecting the curvature of the nozzle characteristic. With falling flight Mach number, the cold nozzle pressure ratio decreases. Initially this has no effect upon the position of the working line, apart from the curved (unchoked) tail, which becomes longer. Eventually, the cold nozzle will become unchoked at lower flight Mach numbers, even at full throttle. The working lines will now become curved, gradually migrating towards surge as flight Mach number decreases. The lowest surge margin working line occurs at static conditions.
Owing to the nature of the constraints involved, the fan working lines of a mixed turbofan are somewhat steeper than those of the equivalent unmixed engine.
A fan may have two maps, one for the bypass (i.e. outer) section and one for the inner section which typically has longer, flatter, speed lines.
Military turbofans tend to have a much higher design fan pressure ratio than civil engines. Consequently, the final (mixed) nozzle is choked at all flight speeds, over most of the throttle range. However, at low throttle settings the nozzle will unchoke, causing the lower end of the working lines to have a short curved tail, particularly at low flight speeds.
However, ultra-high bypass ratio turbofans have a very low design fan pressure ratio (e.g. 1.2, on the bypass section). Consequently, even at cruise flight speeds, the cold (or mixed final) propelling nozzle may only be choked at high throttle settings. The fan working lines become more curved and migrate quickly towards surge as flight Mach number decreases. As a result, the static working line can be well into surge, particularly at low throttle settings.
One solution is to have a variable area cold (or mixed) nozzle. Increasing the nozzle area at low flight speeds brings the fan working line away from surge.
An alternative solution is to fit a variable pitch fan. Scheduling the pitch of the fan blades has no impact upon the position of the fan working lines, but can be used to move the surge line upwards, to improve fan surge margin. | 7 | Physical Chemistry |
Flash joule heating (transient high-temperature electrothermal heating) has been used to synthesize allotropes of carbon, including graphene and diamond. Heating various solid carbon feedstocks (carbon black, coal, coffee grounds, etc.) to temperatures of ~3000 K for 10-150 milliseconds produces turbostratic graphene flakes. FJH has also been used to recover rare-earth elements used in modern electronics from industrial wastes. Beginning from a fluorinated carbon source, fluorinated activated carbon, fluorinated nanodiamond, concentric carbon (carbon shell around a nanodiamond core), and fluorinated flash graphene can be synthesized. | 7 | Physical Chemistry |
Rhodoquinone (RQ) is a modified ubiquinone-like molecule that is an important cofactor used in anaerobic energy metabolism by many organisms. Recently, it has gained attention as a potential anthelmintic drug target due to the fact that parasitic hosts do not synthesize or use this cofactor. Because this cofactor is used in low oxygen environments, many helminth-like organisms have adapted to survive host environments such as the areas within the gastrointestinal tracks. | 1 | Biochemistry |
Thymidine diphosphate (TDP) or deoxythymidine diphosphate (dTDP) (also thymidine pyrophosphate, dTPP) is a nucleotide diphosphate. It is an ester of pyrophosphoric acid with the nucleoside thymidine. dTDP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase thymine. Unlike the other deoxyribonucleotides, thymidine diphosphate does not always contain the "deoxy" prefix in its name. | 1 | Biochemistry |
During his lifetime Woodward authored or coauthored almost 200 publications, of which 85 are full papers, the remainder comprising preliminary communications, the text of lectures, and reviews. The pace of his scientific activity soon outstripped his capacity to publish all experimental details, and much of the work in which he participated was not published until a few years after his death. Woodward trained more than two hundred Ph.D. students and postdoctoral workers, many of whom later went on to distinguished careers.
Some of his best-known students include [https://web.archive.org/web/20100718223149/http://rwindigo1.chm.colostate.edu/ Robert M. Williams] (Colorado State), Harry Wasserman (Yale), Yoshito Kishi (Harvard), Stuart Schreiber (Harvard), William R. Roush (Scripps-Florida), Steven A. Benner (UF), James D. Wuest (Montreal), Christopher S. Foote (UCLA), Kendall Houk (UCLA), porphyrin chemist Kevin M. Smith (LSU), Thomas R. Hoye (University of Minnesota), Ronald Breslow (Columbia University) and David Dolphin (UBC).
Woodward had an encyclopaedic knowledge of chemistry, and an extraordinary memory for detail. Probably the quality that most set him apart from his peers was his remarkable ability to tie together disparate threads of knowledge from the chemical literature and bring them to bear on a chemical problem. | 4 | Stereochemistry |
A relaxase is a single-strand DNA transesterase enzyme produced by some prokaryotes and viruses. Relaxases are responsible for site- and strand-specific nicks in unwound double-stranded DNA . Known relaxases belong to the rolling circle replication (RCR) initiator superfamily of enzymes and fall into two broad classes: replicative (Rep) and mobilization (Mob). The nicks produced by Rep relaxases initiate plasmid or virus RCR. Mob relaxases nick at origin of transfer (oriT) to initiate the process of DNA mobilization and transfer known as bacterial conjugation. Relaxases are so named because the single-stranded DNA nick that they catalyze lead to relaxation of helical tension. | 1 | Biochemistry |
The ketyl radicals derived from the reaction of sodium and benzophenone is a common laboratory desiccant. Ketyls react quickly with the water, peroxides, and with oxygen. Thus, the deep purple coloration qualitatively indicates dry, peroxide-free, and oxygen-free conditions. The method for drying is still popular in many laboratories due to its ability to produce such pure solvent quickly. An alternative option for chemists interested only in water-free solvent is the use of molecular sieves. This is a much safer method than using an alkali metal still, produces solvent as dry as sodium-ketyl (though not as dry as potassium, or potassium-sodium alloy) but takes longer. | 0 | Organic Chemistry |
There are a huge number of industries and applications which benefit from induction shrink fitting or removal using solid state RF and MF heaters. In practice, the methodology employed can vary from a simple manual approach where an operator assembles or disassembles the parts to fully automatic pneumatic and hydraulic press arrangements.
* Automotive starter rings onto flywheels
* Timing gears to crankshafts
* Motor stators into motor bodies
* Motor shafts into stators
* Removal and re-fitting of a gas turbine impeller
* Removal and re-fitting of hollow bolts in electrical generators
* Assembly of high precision roller bearings
* Shrink fitting of 2-stroke crankshafts for ship engines | 8 | Metallurgy |
The indenyl analogues of ferrocene, which is orange, and cobaltocenium cation were first reported by Pauson and Wilkinson. The cobalt derivative is a poorer reductant than cobaltocene.
The indenyl effect was discovered by Hart-Davis and Mawby in 1969 through studies on the conversion of (η-CH)Mo(CO)CH to the phosphine-substituted acetyl complex, which follows bimolecular kinetics. This rate law was attributed to the haptotropic rearrangement of the indenyl ligand from η to η. The corresponding reaction of tributylphosphine with (η-CH)Mo(CO)CH was 10 x slower. The term indenyl effect was coined by Fred Basolo.
Subsequent work by Hart-Davis, Mawby, and White compared CO substitution by phosphines in Mo(η-CH)(CO)X and Mo(η-CH)(CO)X (X = Cl, Br, I) and found the cyclopentadienyl compounds to substitute by an S1 pathway and the indenyl compounds to substitute by both S1 and S2 pathways. Mawby and Jones later studied the rate of CO substitution with P(OEt) with Fe(η-CH)(CO)I and Fe(η-CH)(CO)I and found that both occur by an S1 pathway with the indenyl substitution occurring about 575 times faster. Hydrogenation of the arene ring in the indenyl ligand resulted in CO substitution at about half the rate of the cyclopentadienyl compound.
Work in the early 1980s by Basolo found the S2 replacement of CO in Rh(η-CH)(CO) to be 10 times faster than in Rh(η-CH)(CO). Shortly afterwards, Basolo tested the effect of the indene ligand on Mn(η-CH)(CO), the cyclopentadienyl analogue of which having been shown to be inert to CO substitution. Mn(η-CH)(CO) did undergo CO loss and was found to substitute via an S2 mechanism. | 0 | Organic Chemistry |
By the early 1970s the climate for R&D was again changing.
Government R&D budgets continued to tighten.
The earlier pattern of Fulmer sponsorship, with a large proportion of contracts from UK ministries and government agencies, no longer applied. In 1955 this proportion had been 70% but by 1970 it had fallen to 45%. By 1985 it was to become less than 5%.
Meanwhile, contract R&D was becoming a familiar concept in the UK.
Following Fulmer, many other contract R&D companies had been formed, important examples being Huntingdon Life Sciences(1957) and Cambridge Consultants(1960).
This gave Fulmer opportunities for collaboration but also increased competition.
Fulmer promoted contract R&D by publishing Register of Consulting Scientists and Contract Research Organizations.
In 1971 Lord Rothschild published his report on Government R&D in which a major recommendation was that "applied R&D ... must be done on a customer-contractor basis. The customer says what he wants; the contractor does it (if he can); and the customer pays".
Despite Rothschild's recommendations, government procurement was slow to change. By 1975, leading independent research companies felt that they were not getting a fair share of government R&D contracts and needed a stronger voice. Fulmer joined with six other companies in setting up the Association of Independent Contract Research Organizations (AICRO).
The journal New Scientist published a special supplement on Contract Research in 1974
There were two major developments that intensified competition in Fulmer's market.
Firstly, organizations such as Harwell, which had been fully government funded, were seeking contracts from industry to make good their declining government income.
Secondly by 1969, following the Robbins Report(1963) on higher education, nine completely new universities had been founded and the ten existing Colleges of Advanced Technology had been converted into full universities.
Robbins found that in the existing universities, teachers spent a third of their time on teaching and rather less than a third on research.
He recommended that "The balance between teaching and research in the universities should in general be maintained."
The net effect was a huge expansion of R&D facilities in universities, funded by their block grants, and they were naturally keen to supplement their incomes with contracts using these facilities. | 8 | Metallurgy |
In an ideal system, the emitter is surrounded by converters so no light is lost. Realistically, geometries must accommodate the input energy (fuel injection or input light) used to heat the emitter. Additionally, costs have prohibited surrounding the filter with converters. When the emitter reemits light, anything that does not travel to the converters is lost. Mirrors can be used to redirect some of this light back to the emitter; however, the mirrors may have their own losses. | 7 | Physical Chemistry |
Crosstalk can even be observed across membranes. Membrane interactions with the extracellular matrix (ECM) and with neighboring cells can trigger a variety of responses within the cell. However, the topography and mechanical properties of the ECM also come to play an important role in powerful, complex crosstalk with the cells growing on or inside the matrix. For example, integrin-mediated cytoskeleton assembly and even cell motility are affected by the physical state of the ECM. Binding of the α5β1 integrin to its ligand (fibronectin) activates the formation of fibrillar adhesions and actin filaments. Yet, if the ECM is immobilized, matrix reorganization of this kind and formation of fibrillar adhesions is inhibited. In turn, binding of the same integrin (α5β1) to an immobilized fibronectin ligand is seen to form highly phosphorylated focal contacts/focal adhesion (cells involved in matrix adhesion) within the membrane and reduces cell migration rates In another example of crosstalk, this change in the composition of focal contacts in the cytoskeleton can be inhibited by members of yet another pathway: inhibitors of myosin light-chain kinases or Rho kinases, H-7 or ML-7, which reduce cell contractility and consequently motility. (see figure 2). | 1 | Biochemistry |
Photografting is a technique used in the study of polymers and more in specific polymeric biomaterials. Technically speaking it is the covalent incorporation of functional additives to a polymer matrix or polymer surface using a light-induced mechanism. It is an important technique for the modification of biomaterial surfaces. For example, by graft with polar monomers, the inert polymer surface can become more biocompatible. | 7 | Physical Chemistry |
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, but may also occur by intra-molecular digestion.
Proteolysis in organisms serves many purposes; for example, digestive enzymes break down proteins in food to provide amino acids for the organism, while proteolytic processing of a polypeptide chain after its synthesis may be necessary for the production of an active protein. It is also important in the regulation of some physiological and cellular processes including apoptosis, as well as preventing the accumulation of unwanted or misfolded proteins in cells. Consequently, abnormality in the regulation of proteolysis can cause disease.
Proteolysis can also be used as an analytical tool for studying proteins in the laboratory, and it may also be used in industry, for example in food processing and stain removal. | 1 | Biochemistry |
Most tanning beds are horizontal enclosures with a bench and canopy (lid) that house long, low-pressure fluorescent bulbs (100–200 watt) under an acrylic surface. The tanner is surrounded by bulbs when the canopy is closed. Modern tanning beds emit mostly UVA (the sun emits around 95% UVA and 5% UVB). One review of studies found that the UVB irradiance of beds was on average lower than the summer sun at latitudes 37°S to 35°N, but that UVA irradiance was on average much higher.
The user sets a timer (or it is set remotely by the salon operator), lies on the bed and pulls down the canopy. The maximum exposure time for most low-pressure beds is 15–20 minutes. In the US, maximum times are set by the manufacturer according to how long it takes to produce four "minimal erythema doses" (MEDs), an upper limit laid down by the FDA. An MED is the amount of UV radiation that will produce erythema (redness of the skin) within a few hours of exposure.
High-pressure beds use smaller, higher-wattage quartz bulbs and emit a higher percentage of UVA. They may emit 10–15 times more UVA than the midday sun, and have a shorter maximum exposure time (typically 10–12 minutes). UVA gives an immediate, short-term tan by bronzing melanin in the skin, but no new melanin is formed. UVB has no immediate bronzing effect, but with a delay of 72 hours makes the skin produce new melanin, leading to tans of longer duration. UVA is less likely to cause burning or dry skin than UVB, but is associated with wrinkling and loss of elasticity because it penetrates deeper.
Commercial tanning beds cost $6,000 to $30,000 as of 2006, with high-pressure beds at the high end. One Manhattan chain was charging $10 to $35 per session in 2016, depending on the number, strength, and type of bulbs. This is known as level 1–6 tanning; level 1 involves a basic low-pressure bed with 36 x 100-watt bulbs. Depending on the quality of the bed, it may contain a separate facial tanner, shoulder tanners, a choice of tanning levels and UVA/UVB combinations, sound system, MP3 connection, aromatherapy, air conditioning, a misting option and voice guide. There are also open-air beds, in which the tanner is not entirely enclosed. | 5 | Photochemistry |
Nonribosomal peptides (NRP) are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms. While there exist a wide range of peptides that are not synthesized by ribosomes, the term nonribosomal peptide typically refers to a very specific set of these as discussed in this article.
Nonribosomal peptides are synthesized by nonribosomal peptide synthetases, which, unlike the ribosomes, are independent of messenger RNA. Each nonribosomal peptide synthetase can synthesize only one type of peptide. Nonribosomal peptides often have cyclic and/or branched structures, can contain non-proteinogenic amino acids including -amino acids, carry modifications like N-methyl and N-formyl groups, or are glycosylated, acylated, halogenated, or hydroxylated. Cyclization of amino acids against the peptide "backbone" is often performed, resulting in oxazolines and thiazolines; these can be further oxidized or reduced. On occasion, dehydration is performed on serines, resulting in dehydroalanine. This is just a sampling of the various manipulations and variations that nonribosomal peptides can perform. Nonribosomal peptides are often dimers or trimers of identical sequences chained together or cyclized, or even branched.
Nonribosomal peptides are a very diverse family of natural products with an extremely broad range of biological activities and pharmacological properties. They are often toxins, siderophores, or pigments. Nonribosomal peptide antibiotics, cytostatics, and immunosuppressants are in commercial use. | 1 | Biochemistry |
Gates' total synthesis of morphine provided a proof of the structure of morphine proposed by Robinson in 1925. This synthesis of morphine features one of the first examples of the Diels-Alder reaction in the context of total synthesis. | 0 | Organic Chemistry |
Aerobic respiration requires oxygen (O) in order to create ATP. Although carbohydrates, fats and proteins are consumed as reactants, aerobic respiration is the preferred method of pyruvate production in glycolysis, and requires pyruvate to the mitochondria in order to be fully oxidized by the citric acid cycle. The products of this process are carbon dioxide and water, and the energy transferred is used to make bonds between ADP and a third phosphate group to form ATP (adenosine triphosphate), by substrate-level phosphorylation, NADH and FADH.
The negative ΔG indicates that the reaction is exothermic (exergonic) and can occur spontaneously.
The potential of NADH and FADH is converted to more ATP through an electron transport chain with oxygen and protons (hydrogen) as the "terminal electron acceptors". Most of the ATP produced by aerobic cellular respiration is made by oxidative phosphorylation. The energy released is used to create a chemiosmotic potential by pumping protons across a membrane. This potential is then used to drive ATP synthase and produce ATP from ADP and a phosphate group. Biology textbooks often state that 38 ATP molecules can be made per oxidized glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle, and about 34 from the electron transport system). However, this maximum yield is never quite reached because of losses due to leaky membranes as well as the cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose.
Aerobic metabolism is up to 15 times more efficient than anaerobic metabolism (which yields 2 molecules of ATP per 1 molecule of glucose). However, some anaerobic organisms, such as methanogens are able to continue with anaerobic respiration, yielding more ATP by using inorganic molecules other than oxygen as final electron acceptors in the electron transport chain. They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post-glycolytic reactions take place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells.
Although plants are net consumers of carbon dioxide and producers of oxygen via photosynthesis, plant respiration accounts for about half of the CO generated annually by terrestrial ecosystems. | 1 | Biochemistry |
Macrostructure refers to the overall geometric properties that will influence the force at failure, stiffness, bending, stress distribution, and the weight of the material. It requires little to no magnification to reveal the macrostructure of a material. Observing the macrostructure reveals properties such as cavities, porosity, gas bubbles, stratification, and fissures. The material's strength and elastic modulus are both independent of the macrostructure. | 1 | Biochemistry |
Petite mutants show extranuclear inheritance.The inheritance pattern varying with the type of petite involved.
Segregational petites (pet–): mutants are created by nuclear mutations and exhibit Mendelian 1:1 segregation.
Neutral petites (rho–N): Neutral petite when crossed to wild-type, all offspring are wild-type. It has inherited normal mitochondrial DNA from wild-type parent, which is replicated in the offspring.
Suppressive petites (rho–S): crosses between petite and wild-type, all offspring are petite, showing "dominant" behavior to suppress wild-type mitochondrial function.
Most petite mutants of S. cerevisiae are of a suppressive type, and they differ from neutral petite by affecting the wild-type, although both are a mutation in mitochondrial DNA. Mitochondrial genome of yeast will be the first eukaryotic genome to be understood in terms of both structure and function and this should smooth the way to understand the evolution of organelle genomes and its relationship with nuclear genomes.It is evident that Ephrussi's work not only opened the field of extrachromosomal genetics, but also provide a fantastic incentive for the investigations which followed up to this day.
Though S. cerevisiae has been extensively studied in this and other areas, it is difficult to say if the molecular mechanisms of this process in the mitochondrial DNA are conserved across other yeast species. Other yeast species, such as Kluyveromyces lactis, Saccharomyces castellii, and Candida albicans have all shown to produce petite negative mutants. Potentially, these yeasts have a different inheritance system in place for their mitochondrial genome than S. cerevisiae does.
The frequency at which S. castellii spontaneously produces petites is similar to that of S. cerevisiae, with the mitochondrial DNA of those petites being highly altered via deletion and rearrangement. Suppressive petites of S. cerevisiae are the most commonly observed spontaneously created mutants, whereas in S. castellii, the most commonly observed spontaneous mutant is the neutral petite, further leading to speculation that the transference of this mutation differs between species. | 1 | Biochemistry |
The λ (lambda) universality class is a group in condensed matter physics. It regroups several systems possessing strong analogies, namely, superfluids, superconductors and smectics (liquid crystals). All these systems are expected to belong to the same universality class for the thermodynamic critical properties of the phase transition. While these systems are quite different at the first glance, they all are described by similar formalisms and their typical phase diagrams are identical. | 7 | Physical Chemistry |
Though many genes have simple structures, as with much of biology, others can be quite complex or represent unusual edge-cases. Eukaryotic genes often have introns are often much larger than their exons, and those introns can even have other genes nested inside them. Associated enhancers may be many kilobase away, or even on entirely different chromosomes operating via physical contact between two chromosomes. A single gene can encode multiple different functional products by alternative splicing, and conversely gene may be split across chromosomes but those transcripts are concatenated back together into a functional sequence by trans-splicing. It is also possible for overlapping genes to share some of their DNA sequence, either on opposite strands or the same strand (in a different reading frame, or even the same reading frame). | 1 | Biochemistry |
After comparing the metabolic responses between oat plants under an average light intensity to that of oat plants under extreme light intensity, Quiles noted that the amount of PS II produced was of a lower amount in the leaves that underwent chlororespiration in extreme light. Whereas higher levels of PS II were yielded by those leaves that underwent average light intensity. A higher of PS II is more efficient for chemical energy synthesis and thus for a plant's survival. Quiles indicates that although the chlororespiratory pathway is less efficient, it still serves as a back-up response for energy production in plants. Ultimately, Quiles concluded that the intense light on oat plants had caused PS II levels to reduce and thus, initiate an influx of gate-way (NAD(P)H) proteins to start the process of chlororespiration. | 1 | Biochemistry |
Chirality is another property that a DNAzyme can exploit. DNA occurs in nature as a right-handed double helix and in asymmetric synthesis a chiral catalyst is a valuable tool in the synthesis of chiral molecules from an achiral source. In one application an artificial DNA catalyst was prepared by attaching a copper ion to it through a spacer. The copper - DNA complex catalysed a Diels-Alder reaction in water between cyclopentadiene and an aza chalcone. The reaction products (endo and exo) were found to be present in an enantiomeric excess of 50%. Later it was found that an enantiomeric excess of 99% could be induced, and that both the rate and the enantioselectivity were related to the DNA sequence. | 7 | Physical Chemistry |
There is no agreement about the definition of depth resolution. For example, it can be defined as the depth where ~92% of the signal is generated, or defined by pattern quality, or can be as ambiguous as "where useful information is obtained". Even for a given definition, depth resolution increases with electron energy and decreases with the average atomic mass of the elements making up the studied material: for example, it was estimated as 40 nm for Si and 10 nm for Ni at 20 kV energy. Unusually small values were reported for materials whose structure and composition vary along the thickness. For example, coating monocrystalline silicon with a few nm of amorphous chromium reduces the depth resolution to a few nm at 15 kV energy. In contrast, Isabell and David concluded that depth resolution in homogeneous crystals could also extend up to 1 µm due to inelastic scattering (including tangential smearing and channelling effect).
A recent comparison between reports on EBSD depth resolution, Koko et al indicated that most publications do not present a rationale for the definition of depth resolution, while not including information on the beam size, tilt angle, beam-to-sample and sample-to-detector distances. These are critical parameters for determining or simulating the depth resolution. The beam current is generally not considered to affect the depth resolution in experiments or simulations. However, it affects the beam spot size and signal-to-noise ratio, and hence, indirectly, the details of the pattern and its depth information.
Monte Carlo simulations provide an alternative approach to quantifying the depth resolution for EBSPs formation, which can be estimated using the Bloch wave theory, where backscattered primary electrons – after interacting with the crystal lattice – exit the surface, carrying information about the crystallinity of the volume interacting with the electrons. The backscattered electrons (BSE) energy distribution depends on the material's characteristics and the beam conditions. This BSE wave field is also affected by the thermal diffuse scattering process that causes incoherent and inelastic (energy loss) scattering – after the elastic diffraction events – which does not, yet, have a complete physical description that can be related to mechanisms that constitute EBSP depth resolution.
Both the EBSD experiment and simulations typically make two assumptions: that the surface is pristine and has a homogeneous depth resolution; however, neither of them is valid for a deformed sample. | 7 | Physical Chemistry |
French chemists Jean-Baptiste Dumas and Eugene Peligot, after determining methanols chemical structure, introduced "methylene" from the Greek methy "wine" and hȳlē' "wood, patch of trees" with the intention of highlighting its origins, "alcohol made from wood (substance)". The term "methyl" was derived in about 1840 by back-formation from "methylene", and was then applied to describe "methyl alcohol" (which since 1892 is called "methanol").
Methyl is the IUPAC nomenclature of organic chemistry term for an alkane (or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon. | 0 | Organic Chemistry |
In the field of biology, the biotechnology revolution in the 1980s grew from the development of reagents that could be used to identify and manipulate the chemical matter in and on cells. These reagents included antibodies (polyclonal and monoclonal), oligomers, all sorts of model organisms and immortalised cell lines, reagents and methods for molecular cloning and DNA replication, and many others. | 0 | Organic Chemistry |
The plant immune system carries two interconnected tiers of receptors, one most frequently sensing molecules outside the cell and the other most frequently sensing molecules inside the cell. Both systems sense the intruder and respond by activating antimicrobial defenses in the infected cell and neighboring cells. In some cases, defense-activating signals spread to the rest of the plant or even to neighboring plants. The two systems detect different types of pathogen molecules and classes of plant receptor proteins.
The first tier is primarily governed by pattern recognition receptors that are activated by recognition of evolutionarily conserved pathogen or microbial–associated molecular patterns (PAMPs or MAMPs). Activation of PRRs leads to intracellular signaling, transcriptional reprogramming, and biosynthesis of a complex output response that limits colonization. The system is known as PAMP-triggered immunity or as pattern-triggered immunity (PTI).
The second tier, primarily governed by R gene products, is often termed effector-triggered immunity (ETI). ETI is typically activated by the presence of specific pathogen "effectors" and then triggers strong antimicrobial responses (see R gene section below).
In addition to PTI and ETI, plant defenses can be activated by the sensing of damage-associated compounds (DAMP), such as portions of the plant cell wall released during pathogenic infection.
Responses activated by PTI and ETI receptors include ion channel gating, oxidative burst, cellular redox changes, or protein kinase cascades that directly activate cellular changes (such as cell wall reinforcement or antimicrobial production), or activate changes in gene expression that then elevate other defensive responses.
Plant immune systems show some mechanistic similarities with the immune systems of insects and mammals, but also exhibit many plant-specific characteristics. The two above-described tiers are central to plant immunity but do not fully describe plant immune systems. In addition, many specific examples of apparent PTI or ETI violate common PTI/ETI definitions, suggesting a need for broadened definitions and/or paradigms.
The term quantitative resistance (discussed below) refers to plant disease resistance that is controlled by multiple genes and multiple molecular mechanisms that each have small effects on the overall resistance trait. Quantitative resistance is often contrasted to ETI resistance mediated by single major-effect R genes. | 1 | Biochemistry |
The heterometallic copper-aluminum superatom is a Mackay‐Type Cluster with formula [CuAl](Cp*). It is an open‐shell 67‐electron superatom.
At the time of its synthesis, it was the largest superatom to be synthesized. Its two distinct features are its large electron count compared to other heterometallic superatoms and its unprecedented electron structure of an open-shell configuration.
This is the very first example of a ligated heterometallic Mackay-type cluster, which is an extremely complex crystal structure whose surface is composed of two-shell 20 equilateral triangles composed of 55 copper and aluminum atoms. This shape is also called an icosahedron. The 43 copper and 12 aluminum atoms form a superatom by the metals forming a shared electron shell that resembles a single metal atom. Through magnetic data and analysis at the DFT level it shows that this superatom has a very unique electronic structure of the cluster which is a 67-electron open jellium shell [CuAl] core, protected by twelve Cp* ligands. These crystals have the chemical properties of individual copper atoms. They are attracted by a magnetic field, or paramagnetic due to three valence electrons in the outermost shell whose spin align themselves in a magnetic field. Another property of this compound is that it is pyrophoric, or can ignite spontaneously when exposed to air, so it is highly sensitive to the air and moisture. Also, this compound cannot be re-dissolved in any solvent without decomposition, which means extensive characterization of the compound cannot be obtained with high-resolution mass spectrometry or solution NMR spectroscopy. Thus X-ray diffraction structural analysis of the data obtained does not meet the accepted high-quality requirements, due to the compound forming relatively small, weakly diffracting cubes when using single crystals. | 7 | Physical Chemistry |
The signal that starts the MAPK/ERK pathway is the binding of extracellular mitogen to a cell surface receptor. This allows a Ras protein (a Small GTPase) to swap a GDP molecule for a GTP molecule, flipping the "on/off switch" of the pathway. The Ras protein can then activate MAP3K (e.g., Raf), which activates MAP2K, which activates MAPK. Finally, MAPK can activate a transcription factor, such as Myc. This process is described in more detail below. | 1 | Biochemistry |
The enhancers comprising super-enhancers share the functions of enhancers, including binding transcription factor proteins, looping to target genes, and activating transcription. Three notable traits of enhancers comprising super-enhancers are their clustering in genomic proximity, their exceptional signal of transcription-regulating proteins, and their high frequency of physical interaction with each other. Perturbing the DNA of enhancers comprising super-enhancers showed a range of effects on the expression of cell identity genes, suggesting a complex relationship between the constituent enhancers. Super-enhancers separated by tens of megabases cluster in three-dimensions inside the nucleus of mouse embryonic stem cells.
High levels of many transcription factors and co-factors are seen at super-enhancers (e.g., CDK7, BRD4, and Mediator).
This high concentration of transcription-regulating proteins suggests why their target genes tend to be more highly expressed than other classes of genes. However, housekeeping genes tend to be more highly expressed than super-enhancer—associated genes.
Super-enhancers may have evolved at key cell identity genes to render the transcription of these genes responsive to an array of external cues. The enhancers comprising a super-enhancer can each be responsive to different signals, which allows the transcription of a single gene to be regulated by multiple signaling pathways. Pathways seen to regulate their target genes using super-enhancers include Wnt, TGFb, LIF, BDNF, and NOTCH. The constituent enhancers of super-enhancers physically interact with each other and their target genes over a long range sequence-wise.
Super-enhancers that control the expression of major cell surface receptors with a crucial role in the function of a given cell lineage have also been defined. This is notably the case for B-lymphocytes, the survival, the activation and the differentiation of which rely on the expression of membrane-form immunoglobulins (Ig). The Ig heavy chain locus super-enhancer is a very large (25kb) cis-regulatory region, including multiple enhancers and controlling several major modifications of the locus (notably somatic hypermutation, class-switch recombination and locus suicide recombination). | 1 | Biochemistry |
Although "ppt" usually means "parts per trillion", it occasionally means "parts per thousand". Unless the meaning of "ppt" is defined explicitly, it has to be determined from the context. | 2 | Environmental Chemistry |
John Joseph Jolly Kyle FRSA (2 February 1838 – 23 February 1922) was a pioneering Argentine chemist. Born and educated in Scotland, he emigrated to Argentina in 1862, and on the outbreak of the Paraguayan War served as a pharmacist in the Argentine Army medical corps. He became an Argentine citizen in 1873. At the time Kyle was active specialisation was not an option in Latin American chemistry and it was necessary for a chemist to be a sort of polymath or jack-of-all-trades. Kyle was appointed professor of chemistry at the Colegio Nacional de Buenos Aires in 1871, and chief chemist to the Casa de Moneda de la República Argentina (the Argentine Mint) in 1881. He was appointed professor of organic chemistry at the University of Buenos Aires (1889); Chemist to the Inspectorate-General of Sanitary Works (1890); professor of industrial chemistry at the Colegio Nacional (1892); and professor of inorganic chemistry at Buenos Aires University (1896). He was director of the first chemistry doctoral thesis in Argentina (1901).
The , awarded quinquennially by the Argentine Chemical Association for the best contribution to any branch of chemistry, and its most prestigious prize, is named in his honour. | 9 | Geochemistry |
C-alkylation is a process for the formation of carbon-carbon bonds. The largest example of this takes place in the alkylation units of petrochemical plants, which convert low-molecular-weight alkenes into high octane gasoline components. Electron-rich species such as phenols are also commonly alkylated to produce a variety of products; examples include linear alkylbenzenes used in the production of surfactants like LAS, or butylated phenols like BHT, which are used as antioxidants. This can be achieved using either acid catalysts like Amberlyst, or Lewis acids like aluminium. On a laboratory scale the Friedel–Crafts reaction uses alkyl halides, as these are often easier to handle than their corresponding alkenes, which tend to be gasses. The reaction is catalysed by aluminium trichloride. This approach is rarely used industrially as alkyl halides are more expensive than alkenes. | 0 | Organic Chemistry |
PBr is prepared by treating red phosphorus with bromine. An excess of phosphorus is used in order to prevent formation of PBr:
:P + 6 Br → 4 PBr
Because the reaction is highly exothermic, it is often conducted in the presence of a diluent such as PBr. Phosphorus tribromide is also generated in situ from red phosphorus and bromine. | 0 | Organic Chemistry |
Silver bromate can be used as an oxidant for the transformation of tetrahydropyranyl ethers to carbonyl compounds. | 0 | Organic Chemistry |
In chemistry, a metallaborane is a compound that contains one or more metal atoms and one or more boron hydride. These compounds are related conceptually and often synthetically to the boron-hydride clusters by replacement of BH units with metal-containing fragments. Often these metal fragments are derived from metal carbonyls or cyclopentadienyl complexes. Their structures can often be rationalized by polyhedral skeletal electron pair theory. The inventory of these compounds is large, and their structures can be quite complex. | 7 | Physical Chemistry |
An excimer (originally short for excited dimer) is a short-lived polyatomic molecule formed from two species that do not form a stable molecule in the ground state. In this case, formation of molecules is possible only if such atom is in an electronic excited state. Heteronuclear molecules and molecules that have more than two species are also called exciplex molecules (originally short for excited complex). Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is very short, on the order of nanoseconds. | 5 | Photochemistry |
A highly efficient gold and palladium combined methodology for the Sonogashira coupling of a wide array of electronically and structurally diverse aryl and heteroaryl halides has been reported.
The orthogonal reactivity of the two metals shows high selectivity and extreme functional group tolerance in Sonogashira coupling. A brief mechanistic study reveals that the gold-acetylide intermediate enters into palladium catalytic cycle at the transmetalation step. | 0 | Organic Chemistry |
where = number of electrons produced, = number of photons absorbed.
Assuming each photon absorbed in the depletion layer produces a viable electron-hole pair, and all other photons do not,
where t is the measurement time (in seconds),
= incident optical power in watts,
= optical power absorbed in depletion layer, also in watts. | 7 | Physical Chemistry |
Redox reactions can occur slowly, as in the formation of rust, or rapidly, as in the case of burning fuel. Electron transfer reactions are generally fast, occurring within the time of mixing.
The mechanisms of atom-transfer reactions are highly variable because many kinds of atoms can be transferred. Such reactions can also be quite complex, involving many steps. The mechanisms of electron-transfer reactions occur by two distinct pathways, inner sphere electron transfer and outer sphere electron transfer.
Analysis of bond energies and ionization energies in water allow calculation of the thermodynamic aspects of redox reactions. | 9 | Geochemistry |
Mechanically, NbSn is extremely brittle and thus cannot be easily drawn into a wire, which is necessary for winding superconducting magnets. To overcome this, wire manufacturers typically draw down composite wires containing ductile precursors. The "internal tin" process includes separate alloys of Nb, Cu and Sn. The "bronze" process contains Nb in a copper–tin bronze matrix. With both processes the strand is typically drawn to final size and coiled into a solenoid or cable before heat treatment. It is only during heat treatment that the Sn reacts with the Nb to form the brittle, superconducting niobium–tin compound. The powder-in-tube process is also used.
The high field section of modern NMR magnets are composed of niobium–tin wire. | 8 | Metallurgy |
Replica plating is a microbiological technique in which one or more secondary Petri plates containing different solid (agar-based) selective growth media (lacking nutrients or containing chemical growth inhibitors such as antibiotics) are inoculated with the same colonies of microorganisms from a primary plate (or master dish), reproducing the original spatial pattern of colonies. The technique involves pressing a velveteen-covered disk, and then imprinting secondary plates with cells in colonies removed from the original plate by the material. Generally, large numbers of colonies (roughly 30-300) are replica plated due to the difficulty in streaking each out individually onto a separate plate.
The purpose of replica plating is to be able to compare the master plate and any secondary plates, typically to screen for a desired phenotype. For example, when a colony that was present on the primary plate (or master dish), fails to appear on a secondary plate, it shows that the colony was sensitive to a substance on that particular secondary plate. Common screenable phenotypes include auxotrophy and antibiotic resistance.
Replica plating is especially useful for "negative selection". However, it is more correct to refer to "negative screening" instead of using the term selection. For example, if one wanted to select colonies that were sensitive to ampicillin, the primary plate could be replica plated on a secondary Amp agar plate. The sensitive colonies on the secondary plate would die but the colonies could still be deduced from the primary plate since the two have the same spatial patterns from ampicillin resistant colonies. The sensitive colonies could then be picked off from the primary plate. Frequently the last plate will be non-selective. In the figure, a nonselective plate will be replica plated after the Amp+ plate to confirm that the absence of growth on the selective plate is due to the selection itself and not a problem with transferring cells. If one sees growth on the third (nonselective) plate but not the second one, the selective agent is responsible for the lack of growth. If the non-selective plate shows no growth, one cannot say whether viable cells were transferred at all, and no conclusions can be made about the presence or absence of growth on selective media. This is particularly useful if there are questions about the age or viability of the cells on the original plate.
By increasing the variety of secondary plates with different selective growth media, it is possible to rapidly screen a large number of individual isolated colonies for as many phenotypes as there are secondary plates.
The development of replica plating required two steps. The first step was to define the problem: a method of identifiably duplicating colonies. The second step was to devise a means to reliably implement the first step. Replica plating was first described by Esther Lederberg and Joshua Lederberg in 1952.One of the nutrient agar plate will have antibiotic ressistance. Lederberg sought to use a fabric that was able to be sterilized, and had a vertical fabric pile, akin to a 2D analog "wire brush" of that had been classically used to transfer colonies. Paper was unsatisfactory as "its lateral capillarity and its compression of the colonies distorted and broke up the original growth pattern.", and nylon velvet was too expensive and its stiffer fibers caused problems, leading to the choice and eventual standardization on cotton velveteen. While first demonstrated with bacteria, velveteen based replica plating has also become a standard technique in the microbiology of eukaryotes, such as yeast. | 1 | Biochemistry |
Bryoamaride is a chemical compound isolated from certain plants, notably Bryonia dioica. It can be seen as a derivative of the triterpene hydrocarbon cucurbitane (), more specifically from cucurbitacin L or 23,24-dihydrocucurbitacin I.
The derivative 25-O-acetylbryoamaride is found in Trichosanthes tricuspidata. | 1 | Biochemistry |
With one more valence electron than diamagnetic TiCl, VCl is a paramagnetic liquid. It is one of only a few paramagnetic compounds that is liquid at room temperature.
VCl is prepared by chlorination of vanadium metal. VCl does not form in this reaction; Cl lacks the oxidizing power to attack VCl. VCl can however be prepared indirectly from VF at −78 °C. | 0 | Organic Chemistry |
Many synthetic steroidic compounds like some sexual hormones frequently appear in municipal and industrial wastewaters, acting as environmental pollutants with strong metabolic activities negatively affecting the ecosystems. Since these compounds are common carbon sources for many different microorganisms their aerobic and anaerobic mineralization has been extensively studied. The interest of these studies lies on the biotechnological applications of sterol transforming enzymes for the industrial synthesis of sexual hormones and corticoids. Very recently, the catabolism of cholesterol has acquired a high relevance because it is involved in the infectivity of the pathogen Mycobacterium tuberculosis (Mtb). Mtb causes tuberculosis disease, and it has been demonstrated that novel enzyme architectures have evolved to bind and modify steroid compounds like cholesterol in this organism and other steroid-utilizing bacteria as well. These new enzymes might be of interest for their potential in the chemical modification of steroid substrates. | 2 | Environmental Chemistry |
Given the advantages provided by the working mechanism of thermogalvanic cells, their main application is electricity production under conditions where there is an excess of heat available. In particular thermogalvanic cells are being used to produce electricity in the following areas. | 7 | Physical Chemistry |
In April 2024 the SBTi Board of Trustees released a statement setting out an intention to permit the use of environmental attribute certificates (EACs) for abatement purposes against Scope 3 emissions reduction targets. SBTi did not previously permit the use of EACs due to the difficulties faced in tracing, measuring and validating their impact.
The statement led to a response letter signed by various teams within the SBTi and media speculation about the policy change. | 2 | Environmental Chemistry |
In their first paper, Guldberg and Waage suggested that in a reaction such as
the "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as had previously been supposed, but also depended on the amount of each reactant in a reaction mixture. Thus the law of mass action was first stated as follows:
:When two reactants, A and B, react together at a given temperature in a "substitution reaction," the affinity, or chemical force between them, is proportional to the active masses, [A] and [B], each raised to a particular power
In this context a substitution reaction was one such as . Active mass was defined in the 1879 paper as "the amount of substance in the sphere of action". For species in solution active mass is equal to concentration. For solids, active mass is taken as a constant. , a and b were regarded as empirical constants, to be determined by experiment.
At equilibrium, the chemical force driving the forward reaction must be equal to the chemical force driving the reverse reaction. Writing the initial active masses of A,B, A and B as p, q, p and q and the dissociated active mass at equilibrium as , this equality is represented by
represents the amount of reagents A and B that has been converted into A and B. Calculations based on this equation are reported in the second paper. | 7 | Physical Chemistry |
Protein synthesis within chloroplasts relies on an RNA polymerase coded by the chloroplasts own genome, which is related to RNA polymerases found in bacteria. Chloroplasts also contain a mysterious second RNA polymerase that is encoded by the plants nuclear genome. The two RNA polymerases may recognize and bind to different kinds of promoters within the chloroplast genome. The ribosomes in chloroplasts are similar to bacterial ribosomes. | 5 | Photochemistry |
The work of Henri Braconnot in 1777 and the work of Christian Schönbein in 1846 led to the discovery of nitrocellulose, which, when treated with camphor, produced celluloid. Dissolved in ether or acetone, it becomes collodion, which has been used as a wound dressing since the U.S. Civil War. Cellulose acetate was first prepared in 1865. In years 1834-1844 the properties of rubber (polyisoprene) were found to be greatly improved by heating with sulfur, thus founding the vulcanization process.
In 1884 Hilaire de Chardonnet started the first artificial fiber plant based on regenerated cellulose, or viscose rayon, as a substitute for silk, but it was very flammable. In 1907 Leo Baekeland invented the first polymer made independent of the products of organisms, a thermosetting phenol-formaldehyde resin called Bakelite. Around the same time, Hermann Leuchs reported the synthesis of amino acid N-carboxyanhydrides and their high molecular weight products upon reaction with nucleophiles, but stopped short of referring to these as polymers, possibly due to the strong views espoused by Emil Fischer, his direct supervisor, denying the possibility of any covalent molecule exceeding 6,000 daltons. Cellophane was invented in 1908 by Jocques Brandenberger who treated sheets of viscose rayon with acid.
The chemist Hermann Staudinger first proposed that polymers consisted of long chains of atoms held together by covalent bonds, which he called macromolecules. His work expanded the chemical understanding of polymers and was followed by an expansion of the field of polymer chemistry during which such polymeric materials as neoprene, nylon and polyester were invented. Before Staudinger, polymers were thought to be clusters of small molecules (colloids), without definite molecular weights, held together by an unknown force. Staudinger received the Nobel Prize in Chemistry in 1953. Wallace Carothers invented the first synthetic rubber called neoprene in 1931, the first polyester, and went on to invent nylon, a true silk replacement, in 1935. Paul Flory was awarded the Nobel Prize in Chemistry in 1974 for his work on polymer random coil configurations in solution in the 1950s. Stephanie Kwolek developed an aramid, or aromatic nylon named Kevlar, patented in 1966. Karl Ziegler and Giulio Natta received a Nobel Prize for their discovery of catalysts for the polymerization of alkenes. Alan J. Heeger, Alan MacDiarmid, and Hideki Shirakawa were awarded the 2000 Nobel Prize in Chemistry for the development of polyacetylene and related conductive polymers. Polyacetylene itself did not find practical applications, but organic light-emitting diodes (OLEDs) emerged as one application of conducting polymers.
Teaching and research programs in polymer chemistry were introduced in the 1940s. An Institute for Macromolecular Chemistry was founded in 1940 in Freiburg, Germany under the direction of Staudinger. In America, a Polymer Research Institute (PRI) was established in 1941 by Herman Mark at the Polytechnic Institute of Brooklyn (now Polytechnic Institute of NYU). | 7 | Physical Chemistry |
One important class of condensation polymers are polyamides. They arise from the reaction of carboxylic acid and an amine. Examples include nylons and proteins. When prepared from amino-carboxylic acids, e.g. amino acids, the stoichiometry of the polymerization includes co-formation of water:
:n HN-X-COH → [HN-X-C(O)] + (n-1) HO
When prepared from diamines and dicarboxylic acids, e.g. the production of nylon 66, the polymerization produces two molecules of water per repeat unit:
:n HN-X-NH + n HOC-Y-COH → [HN-X-NHC(O)-Y-C(O)] + (2n-1) HO | 7 | Physical Chemistry |
There is direct evidence that the Romans mechanised at least part of the extraction processes. They used water power from water wheels for grinding grains and sawing timber or stone, for example. A set of sixteen such overshot wheels is still visible at Barbegal near Arles and dates from the 1st century AD or possibly earlier, the water being supplied by the main aqueduct to Arles. It is likely that the mills supplied flour for Arles and other towns locally. Multiple grain mills also existed on the Janiculum hill in Rome.
Ausonius attests the use of a water mill for sawing stone in his poem Mosella from the 4th century AD. They could easily have adapted the technology to crush ore using tilt hammers, and just such is mentioned by Pliny the Elder in his Naturalis Historia dating to about 75 AD, and there is evidence for the method from Dolaucothi in South Wales. The Roman gold mines developed from c. 75 AD. The methods survived into the medieval period, as described and illustrated by Georgius Agricola in his De re metallica.
They also used reverse overshot water-wheels for draining mines, the parts being prefabricated and numbered for ease of assembly. Multiple set of such wheels have been found in Spain at the Rio Tinto copper mines and a fragment of a wheel at Dolaucothi. An incomplete wheel from Spain is now on public show in the British Museum. | 8 | Metallurgy |
The hydrolysis of nitriles RCN proceeds in the distinct steps under acid or base treatment to first give carboxamides and then carboxylic acids RCOOH. The hydrolysis of nitriles to carboxylic acids is efficient. In acid or base, the balanced equations are as follows:
Strictly speaking, these reactions are mediated (as opposed to catalyzed) by acid or base, since one equivalent of the acid or base is consumed to form the ammonium or carboxylate salt, respectively.
Kinetic studies show that the second-order rate constant for hydroxide-ion catalyzed hydrolysis of acetonitrile to acetamide is 1.6 M s, which is slower than the hydrolysis of the amide to the carboxylate (7.4 M s). Thus, the base hydrolysis route will afford the carboxylate (or the amide contaminated with the carboxylate). On the other hand, the acid catalyzed reactions requires a careful control of the temperature and of the ratio of reagents in order to avoid the formation of polymers, which is promoted by the exothermic character of the hydrolysis. The classical procedure to convert a nitrile to the corresponding primary amide calls for adding the nitrile to cold concentrated sulfuric acid. The further conversion to the carboxylic acid is disfavored by the low temperature and low concentration of water.
Two families of enzymes catalyze the hydrolysis of nitriles. Nitrilases hydrolyze nitriles to carboxylic acids:
Nitrile hydratases are metalloenzymes that hydrolyze nitriles to amides.
These enzymes are used commercially to produce acrylamide.
The "anhydrous hydration" of nitriles to amides has been demonstrated using an oxime as water source: | 0 | Organic Chemistry |
For a molecule with atoms, the positions of all nuclei depend on a total of 3 coordinates, so that the molecule has 3 degrees of freedom including translation, rotation and vibration. Translation corresponds to movement of the center of mass whose position can be described by 3 cartesian coordinates.
A nonlinear molecule can rotate about any of three mutually perpendicular axes and therefore has 3 rotational degrees of freedom. For a linear molecule, rotation about the molecular axis does not involve movement of any atomic nucleus, so there are only 2 rotational degrees of freedom which can vary the atomic coordinates.
An equivalent argument is that the rotation of a linear molecule changes the direction of the molecular axis in space, which can be described by 2 coordinates corresponding to latitude and longitude. For a nonlinear molecule, the direction of one axis is described by these two coordinates, and the orientation of the molecule about this axis provides a third rotational coordinate.
The number of vibrational modes is therefore 3 minus the number of translational and rotational degrees of freedom, or 3–5 for linear and 3–6 for nonlinear molecules. | 7 | Physical Chemistry |
Esomeprazole is available as delayed-release capsules in the United States or as delayed-release tablets in Australia, the United Kingdom, and Canada (containing esomeprazole magnesium) in strengths of 20 and 40mg, as delayed-release capsules in the United States (containing esomeprazole strontium) in a 49.3mg strength (delivering the equivalent of 40mg of esomeprazole, and as esomeprazole sodium for intravenous injection/infusion. Oral esomeprazole preparations are enteric-coated, due to the rapid degradation of the drug in the acidic conditions of the stomach. This is achieved by formulating capsules using the multiple-unit pellet system.
The combination naproxen/esomeprazole magnesium (brand name Vimovo) is used for the prevention of gastric ulcers associated with chronic NSAID therapy. Vimovo is available in two dosage strengths: 500/20mg and 375/20mg. Clinical trials of naproxen/esomeprazole demonstrated an incidence of GI ulcer in 24% of patients on naproxen (alone) versus 7% on naproxen/esomeprazole. The FDA has added warnings to the label for Vimovo concerning acute interstitial nephritis and risk of kidney problems in some patients. | 4 | Stereochemistry |
# To make plain crude kilju, the must weight must be zero: A fermentation lock should indicate less than a bubble per minute. Then the sugar reserve is measured with a must weight refractometer/hygrometer. If there's sugar left, then more yeast should be added to consume it, and this measurement process should be repeated. A solution with sugar is not fermented water, but fermented syrup.
# Clarification: The solution is clarified, typically with a fining agent like bentonite.
# Alcohol by volume: Only when the must weight is zero, and when the solution has been clarified, an alcoholic hydrometer, or an ethanol-type refractometer, will display accurate alcohol volume. A leftover sugar reserve will give false values. | 1 | Biochemistry |
Just as absolute entropy serves as theoretical background for data compression, relative entropy serves as theoretical background for data differencing – the absolute entropy of a set of data in this sense being the data required to reconstruct it (minimum compressed size), while the relative entropy of a target set of data, given a source set of data, is the data required to reconstruct the target given the source (minimum size of a patch). | 7 | Physical Chemistry |
*ISO.15730:2000 Metallic and other Inorganic Coatings - Electropolishing as a Means of Smoothing and Passivating Stainless Steel
*ASME BPE Standards for Electropolishing Bioprocessing Equipment
*SEMI F19, Electropolishing Specifications for Semiconductor Applications
*ASTM B 912-02 (2008), Passivation of Stainless Steels Using Electropolishing
*ASTM E1558, Standard Guide for Electrolytic Polishing of Metallographic Specimens | 8 | Metallurgy |
Mutations in the untranslated region (UTR) affect many post-transcriptional regulation. Distinctive structural features are required for many RNA molecules and cis-acting regulatory elements to execute effective functions during gene regulation. SNVs can alter the secondary structure of RNA molecules and then disrupt the proper folding of RNAs, such as tRNA/mRNA/lncRNA folding and miRNA binding recognition regions. | 1 | Biochemistry |
Relevant to the inner sphere mechanism are the two modes by which imines can coordinate, as a π or as a σ-donor ligand. The pi-imines are also susceptible to conversion to iminium ligands upon N-protonation. The binding mode for the imine is unclear, both η (σ-type) and η (π-type). The final step in the mechanism is release of the amine. In some iridium-catalyzed hydrogenations, the mechanism is believed to proceed via a monohydride species. The oxidation state of iridium is always +3.
Examples: | 0 | Organic Chemistry |
This integral may be evaluated by defining the wave function over the complex E plane and closing the E contour using a semicircle on which the wavefunctions vanish. The integral over the closed contour may then be evaluated, using the Cauchy integral theorem, as a sum of the residues at the various poles. We will now argue that the residues of approach those of at time and so the corresponding wavepackets are equal at temporal infinity.
In fact, for very positive times t the factor in a Schrödinger picture state forces one to close the contour on the lower half-plane. The pole in the from the Lippmann–Schwinger equation reflects the time-uncertainty of the interaction, while that in the wavepackets weight function reflects the duration of the interaction. Both of these varieties of poles occur at finite imaginary energies and so are suppressed at very large times. The pole in the energy difference in the denominator is on the upper half-plane in the case of , and so does not lie inside the integral contour and does not contribute to the integral. The remainder is equal to the wavepacket. Thus, at very late times , identifying as the asymptotic noninteracting out state.
Similarly one may integrate the wavepacket corresponding to at very negative times. In this case the contour needs to be closed over the upper half-plane, which therefore misses the energy pole of , which is in the lower half-plane. One then finds that the and wavepackets are equal in the asymptotic past, identifying as the asymptotic noninteracting in state. | 7 | Physical Chemistry |
Adenosine is very relevant in bone metabolism, as it plays a role in formation and activation of both osteoclasts and osteoblasts. Adenosine acts by binding to purinergic receptors and influencing adenylyl cyclase activity and the formation of cAMP and PKA 54. Adenosine may have opposite effects on bone metabolism, because while certain purinergic receptors stimulate adenylyl cyclase activity, others have the opposite effect. Under certain circumstances adenosine stimulates bone destruction and in other situations it promotes bone formation, depending on the purinergic receptor that is being activated. | 7 | Physical Chemistry |
Cationic polymerization is used in the curing of epoxy resins in the presence of UV in the industry. Light energy from UV breaks apart photoinitiaters, forming an acidic which then donates a proton to the polymer. The monomers then attach themselves to the polymer, forming longer and longer chains leading to a cross-linked network. | 5 | Photochemistry |
* [http://www.eawag.ch/en/department/surf/projects/chemeql/ ChemEQL] Free software for calculation of chemical equilibria from Eawag.
* [http://www.factsage.com/ FactSage] Commercial thermodynamic databank software, also available in a free [http://www.crct.polymtl.ca/ephweb.php?lang= web application].
* [http://www.gwb.com/pourbaix.php The Geochemist's Workbench] Commercial geochemical modeling software from Aqueous Solutions LLC.
* [http://community.gwb.com/pourbaix.php GWB Community Edition] Free download of the popular geochemical modeling software package.
* [http://www.kth.se/che/medusa/ HYDRA/MEDUSA] Free software for creating chemical equilibrium diagrams from the KTH Department of Chemistry.
* [http://www.outotec.com/products/digital-solutions/hsc-chemistry/hsc-eph--eh-ph-diagrams-module HSC Chemistry] Commercial thermochemical calculation software from Outotec Oy.
* [http://www.phreeplot.org/ PhreePlot] Free program for making geochemical plots using the USGS code [http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/ PHREEQC].
* [https://web.archive.org/web/20140424142253/http://www.thermocalc.com/solutions/application/corrosion/ Thermo-Calc Windows] Commercial software for thermodynamic calculations from Thermo-Calc Software.
* [https://materialsproject.org/ Materials Project] Public website that can generate Pourbaix diagrams from a large database of computed material properties, hosted at NERSC. | 7 | Physical Chemistry |
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