text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The International Institute of Refrigeration (IIR) (also known, in French, as the Institut International du Froid (IIF)), is an independent intergovernmental science and technology-based organization which promotes knowledge of refrigeration and associated technologies and applications on a global scale that improve quality of life in a cost-effective and environmentally sustainable manner, including:
* Food quality and safety from farm to consumer
* Comfort in homes and commercial buildings
* Health products and services
* Low temperature technology and liquefied gas technology
* Energy efficiency
* Use of non-ozone-depleting and low global warming refrigerants in a safe manner.
Its scientific and technical activities are coordinated by ten commissions which are divided into five distinct sections. | 7 | Physical Chemistry |
Perfluorocarbon tracers (PFTs) are a range of perfluorocarbons used in flow tracers and other tracing applications. They are used by releasing the PFT at a certain point, and determining the concentration of that PFT at another set of points, allowing the flow from the source to the points to be determined. | 2 | Environmental Chemistry |
Tropinone is an alkaloid, famously synthesised in 1917 by Robert Robinson as a synthetic precursor to atropine, a scarce commodity during World War I. Tropinone and the alkaloids cocaine and atropine all share the same tropane core structure. Its corresponding conjugate acid at pH 7.3 major species is known as tropiniumone. | 0 | Organic Chemistry |
Sialic acid is synthesized by glucosamine 6 phosphate and acetyl-CoA through a transferase, resulting in N-acetylglucosamine-6-P. This becomes N-acetylmannosamine-6-P through epimerization, which reacts with phosphoenolpyruvate producing N-acetylneuraminic-9-P (sialic acid). For it to become active to enter in the oligosaccharide biosynthesis process of the cell, a monophosphate nucleoside is added, which comes from a cytidine triphosphate, turning sialic acid into cytidine monophosphate-sialic acid (CMP-sialic acid). This compound is synthesized in the nucleus of the animal cell.
In bacterial systems, sialic acids can be also biosynthesized by an aldolase. This enzyme uses for example a mannose derivative as a substrate, inserting three carbons from pyruvate into the resulting sialic acid structure. These enzymes can be used for chemoenzymatic synthesis of sialic acid derivatives. | 0 | Organic Chemistry |
During calibration with the no-net-flux-method, the microdialysis probe is perfused with at least four different concentrations of the analyte of interest (C) and steady-state concentrations of the analyte leaving the probe are measured in the dialysate (C). The recovery for this method can be determined by plotting C−C over C and computing the slope of the regression line. If analyte concentrations in the perfusate are equal to concentrations at the sampling site, no-net flux occurs. Respective concentrations at the no-net-flux point are represented by the x-intercept of the regression line. The strength of this method is that, at steady-state, no assumptions about the behaviour of the compound in the vicinity of the probe have to be made, since equilibrium exists at a specific time and place. However, under transient conditions (e.g. after drug challenge), the probe recovery may be altered resulting in biased estimates of the concentrations at the sampling site. To overcome this limitation, several approaches have been developed that are also applicable under non-steady-state conditions. One of these approaches is the dynamic no-net-flux method. | 1 | Biochemistry |
Before being taken to the ingenio (amalgamation refinery), excess material would be broken off of the silver ore. At the refiner, it was ground to a fine sand (harina) by an arrastra or stamp mill, which consisted of a rotating shaft fitted with heavy iron stamps that crushed the ore against a mortar block. The harina was then placed in heaps of 2,000 lbs or more, to which was added salt, water, magistral (essentially an impure form of copper sulfate, CuSO), and mercury. This was then mixed by bare-legged Indian laborers or by horses or mules and spread in a 1-to-2-foot-thick (0.30 to 0.61 m) layer in a patio (a shallow-walled, open enclosure). After six to eight weeks of mixing and soaking in the sun, a complex reaction converted the silver to native metal, which formed an amalgam with the mercury. The mixture was then washed and strained through a canvas bag before being placed into a hooded oven. Heating this amalgam vaporized the mercury, leaving the silver. The mercury vapor would then condense on the cooled hood, where it could be collected and reused. The amount of salt and copper sulfate varied from one-quarter to ten pounds of one or the other, or both, per ton of ore treated. The decision of how much of each ingredient to add, how much mixing was needed, and when to halt the process depended on the skill of an (English: quicksilver man). The loss of mercury in amalgamation processes is generally one to two times the weight of silver recovered.
The patio process was the first form of amalgamation. However, it is unclear whether this process or a similar process—in which amalgamation occurred in heated vats rather than open patios—was the predominant form of amalgamation in New Spain, as the earliest known illustration of the patio process dates from 1761. There is substantial evidence that both processes were used from an early date in New Spain, while open patios were never adopted in Peru. Instead, Andean refiners placed milled ore in stone tanks vaulted over a fire, which helped accelerate amalgamation by mitigating the bitterly cold temperatures at the high elevation of the Andean mines. Both processes required that ore be crushed and refiners quickly established mills to process ore once amalgamation was introduced. Water mills were common in the Andes, powered by man-made dams, while in New Spain, where water was relatively scarce, mills were often powered by horses or other draft animals.
Due to amalgamation's reliance upon mercury, an expansion of mercury production was central to the expansion of silver production. A key source of mercury was at Huancavelica, Peru, where vast deposits were discovered in 1563. Additional mercury was sourced from Almadén, Spain, and Idrija in present-day Slovenia. From shortly after the invention of mercury amalgamation to the end of the colonial period, the Spanish crown maintained a monopoly on mercury production and distribution, ensuring a steady supply of royal income. Fluctuations in mercury prices generally resulted in corresponding increases and decreases in silver production. Crown control over these prices could be used to intentionally depress or stimulate silver production in Spanish colonies. | 8 | Metallurgy |
When energy transfer ceases from a system, this condition is referred to as thermodynamic equilibrium. Usually, this condition implies the system and surroundings are at the same temperature so that heat no longer transfers between them. It also implies that external forces are balanced (volume does not change), and all chemical reactions within the system are complete. The timeline varies for these events depending on the system in question. A container of ice allowed to melt at room temperature takes hours, while in semiconductors the heat transfer that occurs in the device transition from an on to off state could be on the order of a few nanoseconds. | 7 | Physical Chemistry |
π-effects can be broken down into numerous categories, including π-π interactions, cation-π and anion-π interactions, and polar-π interactions. In general, π-effects are associated with the interactions of molecules with the π-systems of conjugated molecules such as benzene. | 6 | Supramolecular Chemistry |
Some examples of glow-in-the-dark materials do not glow by phosphorescence. For example, glow sticks glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemiluminescence, an excited state is created via a chemical reaction. The light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will then transfer to a dye molecule, also known as a sensitizer or fluorophor, and subsequently fluoresce back to the ground state. | 7 | Physical Chemistry |
In chemistry the polyhedral skeletal electron pair theory (PSEPT) provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade, and were further developed by others including Michael Mingos; they are sometimes known as Wades rules or the Wade–Mingos rules. The rules are based on a molecular orbital treatment of the bonding. These rules have been extended and unified in the form of the Jemmis mno' rules. | 7 | Physical Chemistry |
The structural components of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. Humans and many animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Certain animals, such as termites can digest cellulose, because bacteria possessing the enzyme are present in their gut. Cellulose is insoluble in water. It does not change color when mixed with iodine. On hydrolysis, it yields glucose. It is the most abundant carbohydrate in nature. | 0 | Organic Chemistry |
It is also used to illuminate pictures painted with fluorescent colors, particularly on black velvet, which intensifies the illusion of self-illumination. The use of such materials, often in the form of tiles viewed in a sensory room under UV light, is common in the United Kingdom for the education of students with profound and multiple learning difficulties. Such fluorescence from certain textile fibers, especially those bearing optical brightener residues, can also be used for recreational effect, as seen, for example, in the opening credits of the James Bond film A View to a Kill. Black light puppetry is also performed in a black light theater. | 5 | Photochemistry |
Resistance to mefloquine is common around the west border in Cambodia and other parts of Southeast Asia. The mechanism of resistance is by increase in Pfmdr1 copy number. | 4 | Stereochemistry |
Nervana is an investigational V construct that knocks down the expression of protein kinase C gamma (PKCγ) known to be associated with neuropathic pain and morphine tolerance.
Two conserved PKCγ sequences across all key model species and humans have been identified, and both single and double DNA cassettes are designed. In vitro, the expression of PKCγ was silenced by 80%. When similar DDRNAI constructs were delivered intrathecally using a lentiviral vector, pain relief in a neuropathic-rat model was demonstrated. | 1 | Biochemistry |
In mammals, UPR has mostly been studied using transfection with a truncated, dysfunctional mitochondrial enzyme (OTCΔ) that does not fold correctly after translocation into the mitochondrial matrix. Using this approach, several components of the mammalian UPR have been identified including the mitochondrial chaperone heat shock protein 60 (Hsp60), the mitochondrial caseinolytic peptidase ClpP, the transcription factor Chop and the kinases c-Jun N-terminal kinase (JNK) and the interferon-induced, double-stranded RNA-activated protein kinase (Pkr).
The appropriately named activating transcription factor associated with stress (ATFS-1) is one of the primary transcription factors required for UPR activation in worms. ATFS-1 has a nuclear localization sequence that allows it to be imported into the nucleus as well as an N-terminal mitochondrial targeting sequence (MTS) that allows for import into the mitochondria. In healthy cells, ATFS-1 is preferentially targeted to the mitochondrial matrix where it is degraded by the Lon protease. The MTS on ATFS-1 is predicted by Mitofates to be substantially weaker than most MTSs which would allow it to be sensitive to subtle mitochondrial dysfunction. Following mitochondrial stress, ATFS-1 mitochondrial import efficiency is decreased resulting in a cytoplasmic accumulation of ATFS-1. Subsequently, ATFS-1 will enter the nucleus via its nuclear transport signal. In the nucleus, ATFS-1 has a broad transcriptional regulation as it will: attenuate OXPHOS gene expression in both the nucleus and mitochondria, upregulate chaperones and proteases to re-establish mitochondrial proteostasis, increase ROS detoxification, and increase mitochondrial import machinery. | 1 | Biochemistry |
The Great Calcite Belt (GCB) refers to a region of the ocean where there are high concentrations of calcite, a mineral form of calcium carbonate. The belt extends over a large area of the Southern Ocean surrounding Antarctica. The calcite in the Great Calcite Belt is formed by tiny marine organisms called coccolithophores, which build their shells out of calcium carbonate. When these organisms die, their shells sink to the bottom of the ocean, and over time, they accumulate to form a thick layer of calcite sediment.
The Great Calcite Belt occurs in areas of the Southern ocean where the calcite compensation depth (CCD) is relatively shallow, meaning that calcite minerals from the shells of marine organisms dissolve at a shallower depth in the water column. This results in a higher concentration of calcium carbonate sediments in the ocean floor, which can be observed in the form of white chalky sediments.
The Great Calcite Belt plays a significant role regulating the global carbon cycle. Calcite is a form of carbon that is removed from the atmosphere and stored in the ocean, which helps to reduce the amount of carbon dioxide in the atmosphere and mitigate the effects of climate change. Recent studies suggest the belt sequesters something between 15 and 30 million tonnes of carbon per year.
Scientists have further interest in the calcite sediments in the belt, which contain valuable information about past climate, ocean currents, ocean chemistry, and marine ecosystems. For example, variations in the CCD depth over time can indicate changes in the amount of carbon dioxide in the atmosphere and the ocean's ability to absorb it. The belt is also home to a diverse range of contemporary marine life, including deep-sea corals and fish that are adapted to the unique conditions found in this part of the ocean. The Great Calcite Belt is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. | 9 | Geochemistry |
Surface energy is conventionally defined as the work that is required to build an area of a particular surface. Another way to view the surface energy is to relate it to the work required to cleave a bulk sample, creating two surfaces. If the new surfaces are identical, the surface energy γ of each surface is equal to half the work of cleavage, W: γ = (1/2)W.
If the surfaces are unequal, the Young-Dupré equation applies:
W = γ + γ – γ, where γ and γ are the surface energies of the two new surfaces, and γ is the interfacial energy.
This methodology can also be used to discuss cleavage that happens in another medium: γ = (1/2)W = (1/2)W. These two energy quantities refer to the energy that is needed to cleave one species into two pieces while it is contained in a medium of the other species. Likewise for a three species system: γ + γ – γ = W + W – W – W = W, where W is the energy of cleaving species 1 from species 2 in a medium of species 3.
A basic understanding of the terminology of cleavage energy, surface energy, and surface tension is very helpful for understanding the physical state and the events that happen at a given surface, but as discussed below, the theory of these variables also yields some interesting effects that concern the practicality of adhesive surfaces in relation to their surroundings. | 6 | Supramolecular Chemistry |
Arner et al. identified 65,423 transcribed enhancers (producing eRNA) among 33 different cell types under different conditions and different timings of stimulation. The transcription of enhancers generally preceded transcription of transcription factors which, in turn, generally preceded messenger RNA(mRNA) transcription of genes.
Carullo et al. examined one particular cell type, neurons (from primary neuron cultures). They exhibited 28,492 putative enhancers generating eRNAs. These eRNAs were often transcribed from both strands of the enhancer DNA in opposite directions. Carullo et al. used these cultured neurons to examine the timing of specific enhancer eRNAs compared to the mRNAs of their target genes. The cultured neurons were activated and RNA was isolated from those neurons at 0, 3.75, 5, 7.5, 15, 30, and 60 minutes after activation. In these experimental conditions, they found that 2 of the 5 enhancers of the immediate early gene (IEG) FOS, that is FOS enhancer 1 and FOS enhancer 3, became activated and initiated transcription of their eRNAs (eRNA1 and eRNA3). FOS eRNA1 and eRNA3 were significantly up-regulated within 7.5 minutes, whereas FOS mRNA was only upregulated 15 minutes after stimulation. Similar patterns occurred at IEGs FOSb and NR4A1, indicating that for many IEGs, eRNA induction precedes mRNA induction in response to neuronal activation.
While some enhancers can activate their target promoters at their target genes without transcribing eRNA, most active enhancers do transcribe eRNA during activation of their target promoters. | 1 | Biochemistry |
A photooxygenation is a light-induced oxidation reaction in which molecular oxygen is incorporated into the product(s). Initial research interest in photooxygenation reactions arose from Oscar Raab's observations in 1900 that the combination of light, oxygen and photosensitizers is highly toxic to cells. Early studies of photooxygenation focused on oxidative damage to DNA and amino acids, but recent research has led to the application of photooxygenation in organic synthesis and photodynamic therapy.
Photooxygenation reactions are initiated by a photosensitizer, which is a molecule that enters an excited state when exposed to light of a specific wavelength (e.g. dyes and pigments). The excited sensitizer then reacts with either a substrate or ground state molecular oxygen, starting a cascade of energy transfers that ultimately result in an oxygenated molecule. Consequently, photooxygenation reactions are categorized by the type and order of these intermediates (as type I, type II, or type III reactions). | 5 | Photochemistry |
is a Japanese chemist. In 1974 he earned his doctorate in chemistry, in the group of Shun’ichi Yamada. He did a post doc with Elias J. Corey at Harvard. He returned to Japan and became a professor in 1977 at Teikyō University and moved to Hokkaidō University 1986. 1983–1986 Shibasaki was a research group leader at the Sagami chemical research center. From 1991 until 2010 he served as professor at Tokyo University. Since 2010 he is representative director of Microbial Chemistry Research Foundation (Chemistry), Tokyo. He is perhaps best known for developing a range of binol based heterobimetallic catalysts, which now bear his name. | 0 | Organic Chemistry |
Hérisson and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis. The direct [2+2] cycloaddition of two alkenes is formally symmetry forbidden and thus has a high activation energy. The Chauvin mechanism involves the [2+2] cycloaddition of an alkene double bond to a transition metal alkylidene to form a metallacyclobutane intermediate. The metallacyclobutane produced can then cycloeliminate to give either the original species or a new alkene and alkylidene. Interaction with the d-orbitals on the metal catalyst lowers the activation energy enough that the reaction can proceed rapidly at modest temperatures.
Olefin metathesis involves little change in enthalpy for unstrained alkenes. Product distributions are determined instead by le Chatelier's Principle, i.e. entropy.
Cross metathesis and ring-closing metathesis are driven by the entropically favored evolution of ethylene or propylene, which can be removed from the system because they are gases. Because of this CM and RCM reactions often use alpha-olefins. The reverse reaction of CM of two alpha-olefins, ethenolysis, can be favored but requires high pressures of ethylene to increase ethylene concentration in solution. The reverse reaction of RCM, ring-opening metathesis, can likewise be favored by a large excess of an alpha-olefin, often styrene. Ring-opening metathesis usually involves a strained alkene (often a norbornene) and the release of ring strain drives the reaction. Ring-closing metathesis, conversely, usually involves the formation of a five- or six-membered ring, which is enthalpically favorable; although these reactions tend to also evolve ethylene, as previously discussed. RCM has been used to close larger macrocycles, in which case the reaction may be kinetically controlled by running the reaction at high dilutions. The same substrates that undergo RCM can undergo acyclic diene metathesis, with ADMET favored at high concentrations. The Thorpe–Ingold effect may also be exploited to improve both reaction rates and product selectivity.
Cross-metathesis is synthetically equivalent to (and has replaced) a procedure of ozonolysis of an alkene to two ketone fragments followed by the reaction of one of them with a Wittig reagent. | 0 | Organic Chemistry |
* A nuclease frees the nucleotide
** A nucleotidase creates adenosine, then adenosine deaminase creates inosine
** Alternatively, AMP deaminase creates inosinic acid, then a nucleotidase creates inosine
* Purine nucleoside phosphorylase acts upon inosine to create hypoxanthine
* Xanthine oxidase catalyzes the biotransformation of hypoxanthine to xanthine
* Xanthine oxidase acts upon xanthine to create uric acid | 1 | Biochemistry |
Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit. The benefit to Müllerian mimics is that predators only need one unpleasant encounter with one member of a set of Müllerian mimics, and thereafter avoid all similar coloration, whether or not it belongs to the same species as the initial encounter. It is named after the German naturalist Fritz Müller, who first proposed the concept in 1878, supporting his theory with the first mathematical model of frequency-dependent selection, one of the first such models anywhere in biology.
Müllerian mimicry was first identified in tropical butterflies that shared colourful wing patterns, but it is found in many groups of insects such as bumblebees, and other animals such as poison frogs and coral snakes. The mimicry need not be visual; for example, many snakes share auditory warning signals. Similarly, the defences involved are not limited to toxicity; anything that tends to deter predators, such as foul taste, sharp spines, or defensive behaviour can make a species unprofitable enough to predators to allow Müllerian mimicry to develop.
Once a pair of Müllerian mimics has formed, other mimics may join them by advergent evolution (one species changing to conform to the appearance of the pair, rather than mutual convergence), forming mimicry rings. Large rings are found for example in velvet ants. Since the frequency of mimics is positively correlated with survivability, rarer mimics are likely to adapt to resemble commoner models, favouring both advergence and larger Müllerian mimicry rings. Where mimics are not strongly protected by venom or other defences, honest Müllerian mimicry becomes, by degrees, the better-known bluffing of Batesian mimicry. | 1 | Biochemistry |
Water's Lewis base character makes it a common ligand in transition metal complexes, examples of which include metal aquo complexes such as to perrhenic acid, which contains two water molecules coordinated to a rhenium center. In solid hydrates, water can be either a ligand or simply lodged in the framework, or both. Thus, consists of [Fe(HO)] centers and one "lattice water". Water is typically a monodentate ligand, i.e., it forms only one bond with the central atom. | 2 | Environmental Chemistry |
Charles Sibley and Jon Ahlquist, pioneers of the technique, used DNA–DNA hybridization to examine the phylogenetic relationships of avians (the Sibley–Ahlquist taxonomy) and primates. | 1 | Biochemistry |
* Molecular mass of the crosslinked polymer.
* Molecular weight of the crystallizable polymer.
* Degree of crosslinking.
* Phase separation.
* Moduli of the original polymers and proportion in the copolymer.
* Moisture (in polymers susceptible to moisture degradation).
* Cooling speed. | 7 | Physical Chemistry |
Casting processes simulation uses numerical methods to calculate cast component quality considering mold filling, solidification and cooling, and provides a quantitative prediction of casting mechanical properties, thermal stresses and distortion. Simulation accurately describes a cast component's quality up-front before production starts. The casting rigging can be designed with respect to the required component properties. This has benefits beyond a reduction in pre-production sampling, as the precise layout of the complete casting system also leads to energy, material, and tooling savings.
The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment, and finishing. This saves costs along the entire casting manufacturing route.
Casting process simulation was initially developed at universities starting from the early 70s, mainly in Europe and in the U.S., and is regarded as the most important innovation in casting technology over the last 50 years. Since the late 80s, commercial programs are available which make it possible for foundries to gain new insight into what is happening inside the mold or die during the casting process. | 8 | Metallurgy |
11β-hydroxylase has strong catalytic activity during conversion of 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone, by catalyzing the hydroxylation of carbon hydrogen bond at 11-beta position. Note the extra "–OH" added at the 11 position (near the center, on ring "C"): | 1 | Biochemistry |
The molecular mechanisms of CB-mediated changes to the membrane voltage have also been studied in detail. Cannabinoids reduce calcium influx by blocking the activity of voltage-dependent N-, P/Q- and L-type calcium channels. In addition to acting on calcium channels, activation of Gi/o and Gs, the two most commonly coupled G-proteins to cannabinoid receptors, has been shown to modulate potassium channel activity. Recent studies have found that CB activation specifically facilitates potassium ion flux through GIRKs, a family of potassium channels. Immunohistochemistry experiments demonstrated that CB is co-localized with GIRK and Kv1.4 potassium channels, suggesting that these two may interact in physiological contexts.
In the central nervous system, CB receptors influence neuronal excitability, reducing the incoming synaptic input.
This mechanism, known as presynaptic inhibition, occurs when a postsynaptic neuron releases endocannabinoids in retrograde transmission, which then bind to cannabinoid receptors on the presynaptic terminal. CB receptors then reduce the amount of neurotransmitter released, so that subsequent excitation in the presynaptic neuron results in diminished effects on the postsynaptic neuron. It is likely that presynaptic inhibition uses many of the same ion channel mechanisms listed above, although recent evidence has shown that CB receptors can also regulate neurotransmitter release by a non-ion channel mechanism, i.e., through Gi/o-mediated inhibition of adenylyl cyclase and protein kinase A.
Direct effects of CB receptors on membrane excitability have been reported, and strongly impact the firing of cortical neurons.
A series of behavioral experiments demonstrated that NMDAR, an ionotropic glutamate receptor, and the metabotropic glutamate receptors (mGluRs) work in concert with CB to induce analgesia in mice, although the mechanism underlying this effect is unclear. | 1 | Biochemistry |
Morpholinos do not trigger the degradation of their target RNA molecules, unlike many antisense structural types (e.g., phosphorothioates, siRNA). Instead, Morpholinos act by "steric blocking", binding to a target sequence within an RNA, inhibiting molecules that might otherwise interact with the RNA. Morpholino oligos are often used to investigate the role of a specific mRNA transcript in an embryo. Developmental biologists inject Morpholino oligos into eggs or embryos of zebrafish, African clawed frog (Xenopus), sea urchin and killifish (F. heteroclitus) producing morphant embryos, or electroporate Morpholinos into chick embryos at later development stages. With appropriate cytosolic delivery systems, Morpholinos are effective in cell culture. Vivo-Morpholinos, in which the oligo is covalently linked to a delivery dendrimer, enter cells when administered systemically in adult animals or in tissue cultures. | 1 | Biochemistry |
The output of Saltmod is given for each season of any year during any number of years, as specified with the input data. The output data comprise hydrological and salinity aspects.
The data are filed in the form of tables that can be inspected directly or further analyzed with spreadsheet programs.
As the soil salinity is very variable from place to place (figure left) SaltMod includes frequency distributions in the output. The figure was made with the CumFreq program [http://www.waterlog.info/cumfreq.htm] .
The program offers the possibility to develop a multitude of relations between varied input data, resulting outputs and time.<br>
However, as it is not possible to foresee all different uses that may be made, the program offers only a limited number of standard graphics.
The program is designed to make use of spreadsheet programs for the detailed output analysis, in which the relations between various input and output variables can be established according to the scenario developed by the user.
Although the computations need many iterations, all the end results can be checked by hand using the equations presented in the manual. | 9 | Geochemistry |
Non-exercise activity thermogenesis (), also known as non-exercise physical activity (NEPA), is energy expenditure during activities that are not part of a structured exercise program. NEAT includes physical activity at the workplace, hobbies, standing instead of sitting, walking around, climbing stairs, doing chores, and fidgeting. Besides differences in body composition, it represents most of the variation in energy expenditure across individuals and populations, accounting from 6-10 percent to as much as 50 percent of energy expenditure in highly active individuals. | 1 | Biochemistry |
Adsorption Method for Sampling of Dioxins and Furans (AMESA) is an automatic system for continuous monitoring of emissions of dioxins and furans from industrial processes which require official approval in compliance with environmental regulations. Applications include refuse incinerators and hazardous material incinerators. | 3 | Analytical Chemistry |
NRA can also be used non-resonantly (of course, RBS is non-resonant). For example, deuterium can easily be profiled with a He beam without changing the incident energy by using the
:He + D = α + p + 18.353 MeV
reaction, usually written H(He,p)α. The energy of the fast proton detected depends on the depth of the deuterium atom in the sample. | 7 | Physical Chemistry |
Sub-Doppler cooling is a class of laser cooling techniques that reduce the temperature of atoms and molecules below the Doppler cooling limit. Doppler cooling processes have a cooling limit that is characterized by the momentum recoil from the emission of a photon from the particle.
Some methods of sub-Doppler cooling include optical molasses, Sisyphus cooling, evaporative cooling, free space Raman cooling, Raman side-band cooling, resolved sideband cooling, polarization gradient cooling, and the use of a dark magneto-optical trap.
For example, an optical molasses time-of-flight technique was used to cool sodium (Doppler limit ) to .
Some possible motivations for sub-doppler cooling include cooling to the motional ground state, a requirement for maintaining fidelity during many quantum computation operations. | 7 | Physical Chemistry |
Captive populations are subject to problems such as inbreeding depression, loss of genetic diversity and adaptations to captivity. It is important to manage captive populations in a way that minimizes these issues so that the individuals to be introduced will resemble the original founders as closely as possible, which will increase the chances of successful reintroductions. During the initial growth phase, the population size is rapidly expanded until a target population size is reached. The target population size is the number of individuals that are required to maintain appropriate levels of genetic diversity, which is generally considered to be 90% of the current genetic diversity after 100 years. The number of individuals required to meet this goal varies based on potential growth rate, effective size, current genetic diversity, and generation time. Once the target population size is reached, the focus shifts to maintaining the population and avoiding genetic issues within the captive population. | 1 | Biochemistry |
Many cell assays have been developed to assess specific parameters or response of cells (biomarkers, cell physiology). Techniques used to study cells include :
*reporter assays using i.e. Luciferase, calcium signaling assays using Coelenterazine, CFSE or Calcein
*Immunostaining of cells on slides by Microscopy (ImmunoHistoChemistry or Fluorescence), on microplates by photometry including the ELISpot (and its variant FluoroSpot) to enumerate B-Cells or antigen-specific cells, in solution by Flow cytometry
*Molecular biology techniques such as DNA microarrays, in situ hybridization, combined to PCR, Computational genomics, and Transfection; Cell fractionation or Immunoprecipitation
*Migration assays, Chemotaxis assay
*Secretion assays
*Apoptosis assays such as the DNA laddering assay, the Nicoletti assay, caspase activity assays, and Annexin V staining
*Chemosensitivity assay measures the number of tumor cells that are killed by a cancer drug
*Tetramer assay detect the presence of antigen specific T-cells
*Gentamicin protection assay or survival assay or invasion assay to assess ability of pathogens (bacteria) to invade eukaryotic cells
Metastasis Assay | 1 | Biochemistry |
An ecologically significant aspect of bacterial organohalide respiration is the reduction of tetrachloroethene (PCE) and Trichloroethene (TCE); anthropogenic pollutants with high neuro and hepatotoxicity. Their presence as environmental pollutants arose from their common industrial use as metal-degreasing agents from the 1920s - 1970. These xenobiotic compounds tend to form partially insoluble layers called dense non-aqueous phase liquids (DNAPLs) at the bottom of groundwater aquifers, which solubilize in a slow, reservoir-like manner, making TCE and PCE among the most common groundwater pollutants.
A commonly used strategy for the removal of TCE and PCE from groundwater is the use of bioremediation via enhanced reductive dechlorination (ERD). ERD involves in-situ injections of dehalorespiring bacteria, among fermentable organic substrates serving as electron donors, while the two pollutants, TCE and PCE, act as the electron acceptors. This facilitates the sequential dechlorination of PCE and TCE into noxious cis-dichloroethene (DCE) and Vinyl chloride (VC), which then suit as electron acceptors for the full dechlorination into innocuous ethene.
A wide array of bacteria across different genera have the capacity to partially dechlorinate PCE and TCE into cis-DCE and VC. One such example of this is the Magnetospirillum bacterium, strain MS-1, which can reduce PCE into cis-DCE under aerobic conditions. However, these daughter substrates have higher toxicity profiles than their parent compounds. As such, effective dechlorination of cis-DCE and VC into innocuous ethene is crucial for bioremediation of PCE and TCE-contaminated aquifers. Currently, bacteria of the Dehalococcoides genera are the only known organisms that can fully dechlorinate PCE into ethene. This is due to their specific transmembrane reductive dehalogenases (RDases) that metabolize the chlorine atoms on the xenobiotic pollutants for cellular energy. In particular, Dehalococcoides isolates VS and BAV1 encode Vinyl Chloride RDases, which metabolize VC into innocuous ethene, making them required species in ERD systems used in bioremediation of PCE and TCE. | 7 | Physical Chemistry |
The process was discovered by the German chemist Otto Roelen in 1938 in the course of investigations of the Fischer–Tropsch process. Aldehydes and diethylketone were obtained when ethylene was added to an F-T reactor. Through these studies, Roelen discovered the utility of cobalt catalysts. HCo(CO), which had been isolated only a few years prior to Roelen's work, was shown to be an excellent catalyst. The term oxo synthesis was coined by the Ruhrchemie patent department, who expected the process to be applicable to the preparation of both aldehydes and ketones. Subsequent work demonstrated that the ligand tributylphosphine (PBu) improved the selectivity of the cobalt-catalysed process. The mechanism of Co-catalyzed hydroformylation was elucidated by Richard F. Heck and David Breslow in the 1960s.
In 1968, highly active rhodium-based catalysts were reported. Since the 1970s, most hydroformylation relies on catalysts based on rhodium. Water-soluble catalysts have been developed. They facilitate the separation of the products from the catalyst. | 0 | Organic Chemistry |
Hybrid dysgenesis refers to the high rate of mutation in germ line cells of Drosophila strains resulting from a cross of males with autonomous P elements (P Strain/P cytotype) and females that lack P elements (M Strain/M cytotype). The hybrid dysgenesis syndrome is marked by temperature-dependent sterility, elevated mutation rates, and increased chromosomal rearrangement and recombination.
The hybrid dysgenesis phenotype is affected by the transposition of P elements within the germ-line cells of offspring of P strain males with M strain females. Transposition only occurs in germ-line cells, because a splicing event needed to make transposase mRNA does not occur in somatic cells.
Hybrid dysgenesis manifests when crossing P strain males with M strain females and not when crossing P strain females (females with autonomous P elements) with M strain males. The eggs of P strain females contain high amounts of a repressor protein that prevents transcription of the transposase gene. The eggs of M strain mothers, which do not contain the repressor protein, allow for transposition of P elements from the sperm of fathers. In P strain females, the repressors are found in the cytoplasm. Hence, when P strain males fertilize M strain females (whose cytoplasm contain no repressor), the male contributes its genome with the P element but not the male cytoplasm leading to P strain progeny.
This effect contributes to piRNAs being inherited only in the maternal line, which provides a defense mechanism against P elements. | 1 | Biochemistry |
The use of metal hydrides (tin, silicon and mercury hydrides) is common in radical cyclization reactions; the primary limitation of this method is the possibility of reduction of the initially formed radical by H-M. Fragmentation methods avoid this problem by incorporating the chain-transfer reagent into the substrate itself—the active chain-carrying radical is not released until after cyclization has taken place. The products of fragmentation methods retain a double bond as a result, and extra synthetic steps are usually required to incorporate the chain-carrying group.
Atom-transfer methods rely on the movement of an atom from the acyclic starting material to the cyclic radical to generate the product. These methods use catalytic amounts of weak reagents, preventing problems associated with the presence of strong reducing agents (such as tin hydride). Hydrogen- and halogen-transfer processes are known; the latter tend to be more synthetically useful.
Oxidative and reductive cyclization methods also exist. These procedures require fairly electrophilic and nucleophilic radicals, respectively, to proceed effectively. Cyclic radicals are either oxidized or reduced and quenched with either external or internal nucleophiles or electrophiles, respectively. | 0 | Organic Chemistry |
The dominant technology used for the production of transgenic plants for transient expression is Agrobacterium-mediated genetic transformation, or "agroinfiltration," and virus expression machinery. Agrobacterium tumefaciens and related Agrobacterium species are well-known plant pathogens that have been engineered to efficiently transfer specific pieces of DNA (called transfer DNA, or T-DNA) into the plant nucleus using binary vector systems, which consists of a T-DNA binary vector and a vir helper plasmid. This binary vector separates T-DNA from trans-acting virulence proteins that help mediate the transfer. Advantages of this method include modularity of broad host-range plasmids of small size through standard molecular biology techniques. Furthermore, since the parent tumor-inducing plasmid in Agrobacterium strains have been disarmed and only non-reproductive cells have been modified (as opposed to germ-line modifications), the process is considered environmentally harmless.
Applications of this process has resulted in advancements made in the use of plants to synthetic biology. Plant-derived bioproducts show promise of high competitiveness towards traditional mammalian cell expression systems. | 1 | Biochemistry |
The blood cells (erythrocytes, leukocytes and platelets) are produced by hematopoiesis.
The erythrocytes have as main function the O delivery to the tissues, and this transfer occurs by diffusion and is determined by the O tension (PO). The erythrocyte is able to feel the tissue need for O and cause a change in vascular caliber, through the pathway of ATP release, which requires an increase in cAMP, and are regulated by the phosphodiesterase (PDE). This pathway can be triggered via two mechanisms: physiological stimulus (like reduced O2 tension) and activation of the prostacyclin receptor (IPR). This pathway includes heterotrimeric G proteins, adenylyl cyclase (AC), protein kinase A (PKA), cystic fibrosis transmembrane conductance regulator (CFTR), and a final conduit that transport ATP to vascular lumen (pannexin 1 or voltage-dependent anion channel (VDAC)). The released ATP acts on purinergic receptors on endothelial cells, triggering the synthesis and release of several vasodilators, like nitric oxide (NO) and prostacyclin (PGI).
The current model of leukocyte adhesion cascade includes many steps mentioned in Table 1. The integrin-mediated adhesion of leukocytes to endothelial cells is related with morphological changes in both leukocytes and endothelial cells, which together support leukocyte migration through the venular walls. Rho and Ras small GTPases are involved in the principal leukocyte signaling pathways underlying chemokine-stimulated integrin-dependent adhesion, and have important roles in regulating cell shape, adhesion and motility.
After a vascular injury occurs, platelets are activated by locally exposed collagen (glycoprotein (GP) VI receptor), locally generated thrombin (PAR1 and PAR4 receptors), platelet-derived thromboxane A2 (TxA2) (TP receptor) and ADP (P2Y1 and P2Y12 receptors) that is either released from damaged cells or secreted from platelet dense granules. The von Willebrand factor (VWF) serves as an essential accessory molecule. In general terms, platelet activation initiated by agonist takes to a signaling cascade that leads to an increase of the cytosolic calcium concentration. Consequently, the integrin αβ is activated and the binding to fibrinogen allows the aggregation of platelets to each other. The increase of cytosolic calcium also leads to shape change and TxA2 synthesis, leading to signal amplification. | 7 | Physical Chemistry |
Rasaratna Samuccaya ( Devanagari: रसरत्न समुच्चय) is an Indian Sanskrit treatise on alchemy. The text is dated between 13th to 16th century CE.
The text contains detailed descriptions of various complex metallurgical processes, as well as descriptions of how to set up and equip a laboratory and other topics concerning Indian alchemy. It is a work that synthesises the writings and opinions of several earlier authors and presents a coherent account of medieval Indian alchemy. | 8 | Metallurgy |
The primary debate concerning the mechanism of the rearrangement centers on whether it is a concerted (sigmatropic) or stepwise (diradical) process. Mechanistic experiments have shown that trans-divinylcyclopropanes epimerize to the corresponding cis isomers and undergo the rearrangement via what is most likely a concerted pathway. A boat-like transition state has been proposed and helps explain the observed stereospecificity of the process. Whether the initial epimerization of trans substrates occurs via a one- or two-center process is unclear in most cases.
Transition-metal-catalyzed versions of the rearrangement are known, and mechanisms vary. In one example employing rhodium bis(ethylene) hexafluoroacetylacetonate, coordination and formation of a bis-π-allyl complex precede electrocyclic ring closure and catalyst release. | 0 | Organic Chemistry |
A Type V-K system was originally characterized from a cyanobacteria, Scytonema hofmanni, and contains a single Cas effector, Cas12k, that functions with a tracrRNA. This system functions similarly to Tn7 but does not have a TnsA protein which can result in off-targeting and chimera formation during over-expression. The Cas12k and tracrRNA complex bind to the target site and TnsC is polymerized directly adjacent prior to TniQ attachment and TnsB recognition and integration. While these systems use traditional tracrRNA characteristic of Type II CRISPR systems, they can also target with short crRNA located adjacent to the transposon end. Type V-K spacers preferentially target locations near tRNA genes, but other sites have been observed in these short crRNA guides which have been acquired by non-traditional means. | 1 | Biochemistry |
Gas is one of the four fundamental states of matter. The others are solid, liquid, and plasma. A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes gases from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer.
The gaseous state of matter occurs between the liquid and plasma states, the latter of which provides the upper-temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention.
High-density atomic gases super-cooled to very low temperatures are classified by their statistical behavior as either Bose gases or Fermi gases. For a comprehensive listing of these exotic states of matter, see list of states of matter. | 7 | Physical Chemistry |
In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds. Because of this symmetric geometry, CCl is non-polar. Methane gas has the same structure, making carbon tetrachloride a halomethane. As a solvent, it is well suited to dissolving other non-polar compounds such as fats and oils. It can also dissolve iodine. It is volatile, giving off vapors with an odor characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene odor reminiscent of dry cleaners' shops.
Solid tetrachloromethane has two polymorphs: crystalline II below −47.5 °C (225.6 K) and crystalline I above −47.5 °C. At −47.3 °C it has monoclinic crystal structure with space group C2/c and lattice constants a = 20.3, b = 11.6, c = 19.9 (.10 nm), β = 111°.
With a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilt in the environment. | 2 | Environmental Chemistry |
Calorimetry is the measurement of the heat released or absorbed by chemical reactions. These assays are very general, since many reactions involve some change in heat and with use of a microcalorimeter, not much enzyme or substrate is required. These assays can be used to measure reactions that are impossible to assay in any other way. | 1 | Biochemistry |
Abouna showed that ammonia was released into the perfusate during 3 day kidney storage, and suggested that this might be toxic to the kidney cells unless removed by frequent replacement of the perfusate. Some support for the use of perfusate exchange during long perfusions was provided by Liu who used perfusate exchange in his successful 7 day storage experiments. Grundmann also found that 96-hour preservation quality was improved by the use of a double volume of perfusate or by perfusate exchange. However, Grundmann's conclusions were based on comparisons with a control group of only 3 dogs. Cohen was unable to demonstrate any production of ammonia during 8 days of perfusion and no benefit from perfusate exchange; the progressive alkalinity that occurred during perfusion was shown to be due to bicarbonate production. | 1 | Biochemistry |
In welding, equivalent carbon content (C.E) is used to understand how the different alloying elements affect hardness of the steel being welded. This is then directly related to hydrogen-induced cold cracking, which is the most common weld defect for steel, thus it is most commonly used to determine weldability. Higher concentrations of carbon and other alloying elements such as manganese, chromium, silicon, molybdenum, vanadium, copper, and nickel tend to increase hardness and decrease weldability. Each of these elements tends to influence the hardness and weldability of the steel to different magnitudes, however, making a method of comparison necessary to judge the difference in hardness between two alloys made of different alloying elements. There are two commonly used formulas for calculating the equivalent carbon content. One is from the American Welding Society (AWS) and recommended for structural steels and the other is the formula based on the International Institute of Welding (IIW).
The AWS states that for an equivalent carbon content above 0.40% there is a potential for cracking in the heat-affected zone (HAZ) on flame cut edges and welds. However, structural engineering standards rarely use CE, but rather limit the maximum percentage of certain alloying elements. This practice started before the CE concept existed, so just continues to be used. This has led to issues because certain high strength steels are now being used that have a CE higher than 0.50% that have brittle failures.
The other and most popular formula is the Dearden and O'Neill formula, which was adopted by IIW in 1967. This formula has been found suitable for predicting hardenability in a large range of commonly used plain carbon and carbon-manganese steels, but not to microalloyed high-strength low-alloy steels or low-alloy Cr-Mo steels. The formula is defined as follows:
For this equation the weldability based on a range of CE values can be defined as follows:
The Japanese Welding Engineering Society adopted the critical metal parameter (Pcm) for weld cracking, which was based on the work from Ito and Bessyo, is:
If some of the values are not available, the following formula is sometimes used:
The carbon equivalent is a measure of the tendency of the weld to form martensite on cooling and to suffer brittle fracture. When the carbon equivalent is between 0.40 and 0.60 weld preheat may be necessary. When the carbon equivalent is above 0.60, preheat is necessary, postheat may be necessary.
The following carbon equivalent formula is used to determine if a spot weld will fail in high-strength low-alloy steel due to excessive hardenability:
Where UTS is the ultimate tensile strength in ksi and h is the strip thickness in inches. A CE value of 0.3 or less is considered safe.
A special carbon equivalent was developed by Yurioka, which could determine the critical time in seconds Δt for the formation of martensitic in the Heat Affected Zone (HAZ) in low-carbon alloy steels. The equation is given as:
where:
Then the critical time length in seconds Δt can be determined as follows: | 8 | Metallurgy |
Another use for affinity chromatography is the purification of specific proteins using a gel matrix that is unique to a specific protein. For example, the purification of E. coli β-galactosidase is accomplished by affinity chromatography using p-aminobenyl-1-thio-β-D-galactopyranosyl agarose as the affinity matrix. p-aminobenyl-1-thio-β-D-galactopyranosyl agarose is used as the affinity matrix because it contains a galactopyranosyl group, which serves as a good substrate analog for E. coli β-Galactosidase. This property allows the enzyme to bind to the stationary phase of the affinity matrix and β-Galactosidase is eluted by adding increasing concentrations of salt to the column. | 3 | Analytical Chemistry |
Careful and well informed writers about thermodynamics, in their accounts of thermodynamic equilibrium, often enough make provisos or reservations to their statements. Some writers leave such reservations merely implied or more or less unstated.
For example, one widely cited writer, H. B. Callen writes in this context: "In actuality, few systems are in absolute and true equilibrium." He refers to radioactive processes and remarks that they may take "cosmic times to complete, [and] generally can be ignored". He adds "In practice, the criterion for equilibrium is circular. Operationally, a system is in an equilibrium state if its properties are consistently described by thermodynamic theory!"
J.A. Beattie and I. Oppenheim write: "Insistence on a strict interpretation of the definition of equilibrium would rule out the application of thermodynamics to practically all states of real systems."
Another author, cited by Callen as giving a "scholarly and rigorous treatment", and cited by Adkins as having written a "classic text", A.B. Pippard writes in that text: "Given long enough a supercooled vapour will eventually condense, ... . The time involved may be so enormous, however, perhaps 10 years or more, ... . For most purposes, provided the rapid change is not artificially stimulated, the systems may be regarded as being in equilibrium."
Another author, A. Münster, writes in this context. He observes that thermonuclear processes often occur so slowly that they can be ignored in thermodynamics. He comments: "The concept absolute equilibrium or equilibrium with respect to all imaginable processes, has therefore, no physical significance." He therefore states that: "... we can consider an equilibrium only with respect to specified processes and defined experimental conditions."
According to L. Tisza: "... in the discussion of phenomena near absolute zero. The absolute predictions of the classical theory become particularly vague because the occurrence of frozen-in nonequilibrium states is very common." | 7 | Physical Chemistry |
An evanescent field is a residue optical field that "leaks" during total internal reflection. This "leaking" of light fades off at an exponential rate. The evanescent field has found a number of applications in nanometer resolution imaging (microscopy); optical micromanipulation (optical tweezers) are becoming ever more relevant in research.
In optical tweezers, a continuous evanescent field can be created when light is propagating through an optical waveguide (multiple total internal reflection). The resulting evanescent field has a directional sense and will propel microparticles along its propagating path. This work was first pioneered by S. Kawata and T. Sugiura, in 1992, who showed that the field can be coupled to the particles in proximity on the order of 100 nanometers. This direct coupling of the field is treated as a type of photon tunnelling across the gap from prism to microparticles. The result is a directional optical propelling force.
A recent updated version of the evanescent field optical tweezers makes use of extended optical landscape patterns to simultaneously guide a large number of particles into a preferred direction without using a waveguide. It is termed as Lensless Optical Trapping ("LOT"). The orderly movement of the particles is aided by the introduction of Ronchi Ruling that creates well-defined optical potential wells (replacing the waveguide). This means that particles are propelled by the evanescent field while being trapped by the linear bright fringes. At the moment, there are scientists working on focused evanescent fields as well.
In recent studies, the evanescent field generated by mid-infrared laser has been used to sort particles by molecular vibrational resonance selectively. Mid-infrared light is commonly used to identify molecular structures of materials because the vibrational modes exist in the mid-infrared region. A study by Statsenko et al. described optical force enhancement by molecular vibrational resonance by exciting the stretching mode of Si-O-Si bond at 9.3 μm. It is shown that silica microspheres containing significant Si-O-Si bond move up to ten times faster than polystyrene microspheres due to molecular vibrational resonance. Moreover, this same group also investigated the possibility of optical force chromatography based on molecular vibrational resonance.
Another approach that has been recently proposed makes use of surface plasmons, which is an enhanced evanescent wave localized at a metal/dielectric interface. The enhanced force field experienced by colloidal particles exposed to surface plasmons
at a flat metal/dielectric interface has been for the first time measured using a photonic force microscope, the total force magnitude being found 40 times stronger compared to a normal evanescent wave. By patterning the surface with gold microscopic islands it is possible to have selective and parallel trapping in these islands. The forces of the latter optical tweezers lie in the femtonewton range.
The evanescent field can also be used to trap cold atoms and molecules near the surface of an optical waveguide or optical nanofiber. | 1 | Biochemistry |
Two kinds of complexes of molecules exist: the collisional complexes discussed
above, which are short lived. Besides, bound (i.e. relatively stable) complexes
of two or more molecules exist, the so-called van der Waals molecules. These
exist usually for much longer times than the collisional complexes and, under
carefully chosen experimental conditions (low temperature, moderate gas density),
their rotovibrational band spectra show "sharp" (or resolvable) lines (Heisenberg
uncertainty principle), much like ordinary molecules. If the parent molecules
are nonpolar, the same induced dipole mechanisms, which are discussed above,
are responsible for the observable spectra of van der Waals molecules.
Figure 1 (to be included) | 7 | Physical Chemistry |
Tool compounds are an important class of reagent in biology. They are small molecules or biochemicals like siRNA or antibodies that are known to affect a given biomolecule—for example a drug target—but are unlikely to be useful as drugs themselves, and are often starting points in the drug discovery process.
However, many natural substances are hits in almost any assay in which they are tested, and therefore not useful as tool compounds. Medicinal chemists class them instead as pan-assay interference compounds. One example is curcumin. | 0 | Organic Chemistry |
The RNA world hypothesis, if true, has important implications for the definition of life and the origin of life. For most of the time that followed Franklin, Watson and Crick's elucidation of DNA structure in 1953, life was largely defined in terms of DNA and proteins: DNA and proteins seemed the dominant macromolecules in the living cell, with RNA only aiding in creating proteins from the DNA blueprint.
The RNA world hypothesis places RNA at center-stage when life originated. The RNA world hypothesis is supported by the observations that ribosomes are ribozymes: the catalytic site is composed of RNA, and proteins hold no major structural role and are of peripheral functional importance. This was confirmed with the deciphering of the 3-dimensional structure of the ribosome in 2001. Specifically, peptide bond formation, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA.
RNAs are known to play roles in other cellular catalytic processes, specifically in the targeting of enzymes to specific RNA sequences. In eukaryotes, the processing of pre-mRNA and RNA editing take place at sites determined by the base pairing between the target RNA and RNA constituents of small nuclear ribonucleoproteins (snRNPs). Such enzyme targeting is also responsible for gene down regulation through RNA interference (RNAi), where an enzyme-associated guide RNA targets specific mRNA for selective destruction. Likewise, in eukaryotes the maintenance of telomeres involves copying of an RNA template that is a constituent part of the telomerase ribonucleoprotein enzyme. Another cellular organelle, the vault, includes a ribonucleoprotein component, although the function of this organelle remains to be elucidated. | 9 | Geochemistry |
NaK containing 40% to 90% potassium by mass is liquid at room temperature. The eutectic mixture consists of 77% potassium and 23% sodium by mass (NaK-77), and it is a liquid from , and has a density of 0.866 g/cm at and 0.855 g/cm at , making it less dense than water. It is highly reactive with water and is stored usually under hexane or other hydrocarbons, or under an inert gas (usually dry nitrogen or argon) if high purity and low levels of oxidation are required.
A solid compound, , exists at low temperatures, containing 46 percent potassium by mass.
NaK has a very high surface tension, which makes large amounts of it pull into a bun-like shape. Its specific heat capacity is 982 J/(kg⋅K), which is roughly one quarter of that for water, but heat transfer is higher over a temperature gradient due to higher thermal conductivity. | 8 | Metallurgy |
SMIE is less common that LMIE and much less common that other failure mechanisms such as hydrogen embrittlement, fatigue, and stress-corrosion cracking. Still, embrittlement mechanisms can be introduced during fabrication, coatings, testing or during service of the material components. Susceptibility for SMIE increases with the following material characteristics:
* Increase in strength of high-strength material
* Increasing grain size
* Materials with more planar-slip than wavy-slip | 8 | Metallurgy |
In the sugarcane industry, the organic waste is usually burned in the power cogeneration process. When contaminated by chloride, this waste burns, releasing methyl chloride in the atmosphere. | 2 | Environmental Chemistry |
The Italian company Caffaro, located in Brescia, specialized in producing PCBs from 1938 to 1984, following the acquisition of the exclusive rights to use the patent in Italy from Monsanto. The pollution resulting from this factory and the case of Anniston, in the US, are the largest known cases in the world of PCB contamination in water and soil, in terms of the amount of toxic substance dispersed, size of the area contaminated, number of people involved and duration of production.
The values reported by the local health authority (ASL) of Brescia since 1999 are 5,000 times above the limits set by Ministerial Decree 471/1999 (levels for residential areas, 0.001 mg/kg). As a result of this and other investigations, in June 2001, a complaint of an environmental disaster was presented to the Public Prosecutors Office of Brescia. Research on the adult population of Brescia showed that residents of some urban areas, former workers of the plant, and consumers of contaminated food, have PCB levels in their bodies that are in many cases 10–20 times higher than reference values in comparable general populations. PCBs entered the human food supply by animals grazing on contaminated pastures near the factory, especially in local veal mostly eaten by farmers families. The exposed population showed an elevated risk of Non-Hodgkin lymphoma, but not for other specific cancers. | 2 | Environmental Chemistry |
The grand potential is related to the number of particles at finite temperature in the following way
where the derivative is taken at fixed temperature and volume, and it appears
also known as the Fermi–Dirac distribution.
Similarly, the total internal energy is | 7 | Physical Chemistry |
The advantages of the method include:
* uniquely wide field of view (because translation complexes of any type, including scanning small ribosomal subunits, are captured for the first time);
* potentially more natural representation of complex dynamics (because all, and not only selected, translation processes are arrested by formaldehyde fixation);
* possibly more faithful and/or sensitive detection of translation complexes locations (as covalent fixation prevents detachment of the fragments from the ribosomes or their subunits).
The disadvantages include:
* higher overall complexity of the experimental procedure (due to requirement of the initial isolation of translated mRNA and preparative sedimentation to separate ribosomes and ribosomal subunits);
* higher contamination of the useful sequencing read depth with the undesired fragments of the ribosomal RNA (inherited from the wide size selection window used for protected RNA fragments);
* a pre-requirement for optimization of the formaldehyde fixation procedure for each new cell or sample type (as optimal formaldehyde fixation timings strongly depend on sample morphology and both over- and under-fixation will compromise the results). | 1 | Biochemistry |
In order for a molecule (or crystal) to exhibit circular birefringence and circular dichroism, it must be distinguishable from its mirror image. An object that cannot be superimposed on its mirror image is said to be chiral, and optical rotatory dispersion and circular dichroism are known as chiroptical properties.
Most biological molecules have one or more chiral centers and undergo enzyme-catalyzed transformations that either maintain or invert the chirality at one or more of these centers. Still other enzymes produce new chiral centers, always with a high specificity. These properties account for the fact that optical rotatory dispersion and circular dichroism are widely used in organic and inorganic chemistry and in biochemistry.
In the absence of magnetic fields, only chiral substances exhibit optical rotatory dispersion and circular dichroism. In a magnetic field, even substances that lack chirality rotate the plane of polarized light, as shown by Michael Faraday. Magnetic optical rotation is known as the Faraday effect, and its wavelength dependence is known as magnetic optical rotatory dispersion. In regions of absorption, magnetic circular dichroism is observable. | 4 | Stereochemistry |
In cellulose, glycosyl groups link together 1,4-β-D-glucosyl units to form chains of (1,4-β-D-glucosyl).
Other examples include ribityl in 6,7-Dimethyl-8-ribityllumazine, and glycosylamines. | 0 | Organic Chemistry |
The most-substantiated role for APP is in synaptic formation and repair; its expression is upregulated during neuronal differentiation and after neural injury. Roles in cell signaling, long-term potentiation, and cell adhesion have been proposed and supported by as-yet limited research. In particular, similarities in post-translational processing have invited comparisons to the signaling role of the surface receptor protein Notch.
APP knockout mice are viable and have relatively minor phenotypic effects including impaired long-term potentiation and memory loss without general neuron loss. On the other hand, transgenic mice with upregulated APP expression have also been reported to show impaired long-term potentiation.
The logical inference is that because Aβ accumulates excessively in Alzheimers disease its precursor, APP, would be elevated as well. However, neuronal cell bodies contain less APP as a function of their proximity to amyloid plaques. The data indicate that this deficit in APP results from a decline in production rather than an increase in catalysis. Loss of a neurons APP may affect physiological deficits that contribute to dementia. | 1 | Biochemistry |
Acid chlorides are useful for the preparation of amides, esters, anhydrides. These reactions generate chloride, which can be undesirable. Acyl chlorides hydrolyze, yielding the carboxylic acid:
This hydrolysis is usually a nuisance rather than intentional. Acyl chlorides are used to prepare acid anhydrides, amides and esters, by reacting acid chlorides with: a salt of a carboxylic acid, an amine, or an alcohol, respectively. | 0 | Organic Chemistry |
Photochromic units have been employed extensively in supramolecular chemistry. Their ability to give a light-controlled reversible shape change means that they can be used to make or break molecular recognition motifs, or to cause a consequent shape change in their surroundings. Thus, photochromic units have been demonstrated as components of molecular switches. The coupling of photochromic units to enzymes or enzyme cofactors even provides the ability to reversibly turn enzymes "on" and "off", by altering their shape or orientation in such a way that their functions are either "working" or "broken". | 5 | Photochemistry |
Cannon completed her B.Sc in Biochemistry from London University in 1967. In 1971, she obtained a Ph.D. in Physiology from Stockholm University. | 1 | Biochemistry |
Whole genome shotgun sequencing for small (4000- to 7000-base-pair) genomes was first suggested in 1979. The first genome sequenced by shotgun sequencing was that of cauliflower mosaic virus, published in 1981. | 1 | Biochemistry |
Protein misfolding cyclic amplification (PMCA) is an amplification technique (conceptually like polymerase chain reaction (PCR) but not involving nucleotides) to multiply misfolded prions originally developed by Soto and colleagues. It is a test for spongiform encephalopathies like chronic wasting disease (CWD) or bovine spongiform encephalopathy (BSE). | 1 | Biochemistry |
Several analytical methods are used for qualitative and quantitative determination of peroxides. A simple qualitative detection of peroxides is carried out with the iodine-starch reaction. Here peroxides, hydroperoxides or peracids oxidize the added potassium iodide into iodine, which reacts with starch producing a deep-blue color. Commercial paper indicators using this reaction are available. This method is also suitable for quantitative evaluation, but it can not distinguish between different types of peroxide compounds. Discoloration of various indigo dyes in presence of peroxides is used instead for this purpose. For example, the loss of blue color in leuco-methylene blue is selective for hydrogen peroxide.
Quantitative analysis of hydroperoxides can be performed using potentiometric titration with lithium aluminium hydride. Another way to evaluate the content of peracids and peroxides is the volumetric titration with alkoxides such as sodium ethoxide. | 0 | Organic Chemistry |
The database user interface is web-based and can be queried using text or accession numbers/identifiers. Since its integration with the other components of BOND, sequences have been added to interactions, molecular complexes and pathways in the results. Records include information on: BIND ID, description of the interaction/complex/pathway, publications, update records, organism, OntoGlyphs, ProteoGlyphs, and links to other databases where additional information can be found. BIND records include various viewing formats (e.g. HTML, ASN.1, XML, FASTA), various formats for exporting results (e.g. ASN.1, XML, GI list, PDF), and visualizations (e.g. Cytoscape). The exact viewing and exporting options vary depending on what type of data has been retrieved. | 1 | Biochemistry |
Unfortunately, the probabilities and cannot be measured directly. Instead, we assay the relative population of folded molecules using various structural probes, e.g., absorbance at 287 nm (which reports on the solvent exposure of tryptophan and tyrosine), far-ultraviolet circular dichroism (180-250 nm, which reports on the secondary structure of the protein backbone), dual polarisation interferometry (which reports the molecular size and fold density) and near-ultraviolet fluorescence (which reports on changes in the environment of tryptophan and tyrosine). However, nearly any probe of folded structure will work; since the measurement is taken at equilibrium, there is no need for high time resolution. Thus, measurements can be made of NMR chemical shifts, intrinsic viscosity, solvent exposure (chemical reactivity) of side chains such as cysteine, backbone exposure to proteases, and various hydrodynamic measurements.
To convert these observations into the probabilities and , one generally assumes that the observable adopts one of two values, or , corresponding to the native or unfolded state, respectively. Hence, the observed value equals the linear sum
By fitting the observations of under various solution conditions to this functional form, one can estimate and , as well as the parameters of . The fitting variables and are sometimes allowed to vary linearly with the solution conditions, e.g., temperature or denaturant concentration, when the asymptotes of are observed to vary linearly under strongly folding or strongly unfolding conditions. | 7 | Physical Chemistry |
Some basic conventions, such as (1) that animal/human homolog (ortholog) pairs differ in letter case (title case and all caps, respectively) and (2) that the symbol is italicized when referring to the gene but nonitalic when referring to the protein, are often not followed by contributors to medical journals. Many journals have the copyeditors restyle the casing and formatting to the extent feasible, although in complex genetics discussions only subject-matter experts (SMEs) can effortlessly parse them all. One example that illustrates the potential for ambiguity among non-SMEs is that some official gene names have the word "protein" within them, so the phrase "brain protein I3 (BRI3)" (referring to the gene) and "brain protein I3 (BRI3)" (referring to the protein) are both valid. The AMA Manual gives another example: both "the TH gene" and "the TH gene" can validly be parsed as correct ("the gene for tyrosine hydroxylase"), because the first mentions the alias (description) and the latter mentions the symbol. This seems confusing on the surface, although it is easier to understand when explained as follows: in this genes case, as in many others, the alias (description) "happens to use the same letter string" that the symbol uses. (The matching of the letters is of course acronymic in origin and thus the phrase "happens to" implies more coincidence than is actually present; but phrasing it that way helps to make the explanation clearer.) There is no way for a non-SME to know this is the case for any particular letter string without looking up every gene from the manuscript in a database such as NCBI Gene, reviewing its symbol, name, and alias list, and doing some mental cross-referencing and double-checking (plus it helps to have biochemical knowledge). Most medical journals do not (in some cases cannot) pay for that level of fact-checking as part of their copyediting service level; therefore, it remains the authors responsibility. However, as pointed out earlier, many authors make little attempt to follow the letter case or italic guidelines; and regarding protein symbols, they often will not use the official symbol at all. For example, although the guidelines would call p53 protein "TP53" in humans or "Trp53" in mice, most authors call it "p53" in both (and even refuse to call it "TP53" if edits or queries try to), not least because of the biologic principle that many proteins are essentially or exactly the same molecules regardless of mammalian species. Regarding the gene, authors are usually willing to call it by its human-specific symbol and capitalization, TP53, and may even do so without being prompted by a query. But the end result of all these factors is that the published literature often does not follow the nomenclature guidelines completely. | 1 | Biochemistry |
An autoluminograph is a photograph produced by placing a light emitting object directly on a piece of film. A famous example is an autoluminograph published in Science magazine in 1986 of a glowing transgenic tobacco plant bearing the luciferase gene of fireflies placed on Kodak Ektachrome 200 film. | 1 | Biochemistry |
Without loss of generality, we can consider only centered profiles, which peak at zero. The Voigt profile is then
where x is the shift from the line center, is the centered Gaussian profile:
and is the centered Lorentzian profile:
The defining integral can be evaluated as:
where Re[w(z)] is the real part of the Faddeeva function evaluated for
In the limiting cases of and then simplifies to and , respectively. | 7 | Physical Chemistry |
The Young–Dupré equation (Thomas Young 1805, Lewis Dupré 1855) dictates that neither γ nor γ can be larger than the sum of the other two surface energies. The consequence of this restriction is the prediction of complete wetting when γ > γ + γ and zero wetting when γ > γ + γ. The lack of a solution to the Young–Dupré equation is an indicator that there is no equilibrium configuration with a contact angle between 0 and 180° for those situations.
A useful parameter for gauging wetting is the spreading parameter S,
When S > 0, the liquid wets the surface completely (complete wetting).
When S < 0, partial wetting occurs.
Combining the spreading parameter definition with the Young relation yields the Young–Dupré equation:
which only has physical solutions for θ when S < 0. | 7 | Physical Chemistry |
: MARS include identification and selection of several genomic regions (up to 20 or even more) for complex traits within a single population. | 1 | Biochemistry |
Early European bloomeries were relatively small, primarily due to the mechanical limits of human-powered bellows and the amount of force possible to apply with hand-driven sledge hammers. Those known archaeologically from the pre-Roman Iron Age tend to be in the 2 kg range, produced in low shaft furnaces. Roman-era production often used furnaces tall enough to create a natural draft effect (into the range of 200 cm tall), and increasing bloom sizes into the range of 10–15 kg. Contemporary experimenters had routinely made blooms using Northern European-derived "short-shaft" furnaces with blown air supplies in the 5–10 kg range The use of waterwheels, spreading around the turn of the first millennium and used to power more massive bellows, allowed the bloomery to become larger and hotter, with associated trip hammers allowing the consolidation forging of the larger blooms created. Progressively larger bloomeries were constructed in the late 14th century, with a capacity of about 15 kg on average, though exceptions did exist. European average bloom sizes quickly rose to 300 kg, where they levelled off until the demise of the bloomery.
As a bloomerys size is increased, the iron ore is exposed to burning charcoal for a longer time. When combined with the strong air blast required to penetrate the large ore and charcoal stack, this may cause part of the iron to melt and become saturated with carbon in the process, producing unforgeable pig iron, which requires oxidation to be reduced into cast iron, steel, and iron. This pig iron was considered a waste product detracting from the largest bloomeries yield, and early blast furnaces, identical in construction, but dedicated to the production of molten iron, were not built until the 14th century.
Bloomery type furnaces typically produced a range of iron products from very low-carbon iron to steel containing around 0.2–1.5% carbon. The master smith had to select pieces of low-carbon iron, carburize them, and pattern-weld them together to make steel sheets. Even when applied to a noncarburized bloom, this pound, fold, and weld process resulted in a more homogeneous product and removed much of the slag. The process had to be repeated up to 15 times when high-quality steel was needed, as for a sword. The alternative was to carburize the surface of a finished product. Each welding's heat oxidises some carbon, so the master smith had to make sure enough carbon was in the starting mixture.
In England and Wales, despite the arrival of the blast furnace in the Weald in about 1491, bloomery forges, probably using waterpower for the hammer and the bellows, were operating in the West Midlands region beyond 1580. In Furness and Cumberland, they operated into the early 17th century and the last one in England (near Garstang) did not close until about 1770.
One of the oldest-known blast furnaces in Europe has been found in Lapphyttan in Sweden, carbon-14 dated to be from the 12th century. The oldest bloomery in Sweden, also found in the same area, has been carbon-14 dated to 700 BCE.
Bloomeries survived in Spain and southern France as Catalan forges into the mid-19th century, and in Austria as the to 1775. | 8 | Metallurgy |
Many catabolic biochemical processes, such as glycolysis, the citric acid cycle, and beta oxidation, produce the reduced coenzyme NADH. This coenzyme contains electrons that have a high transfer potential; in other words, they will release a large amount of energy upon oxidation. However, the cell does not release this energy all at once, as this would be an uncontrollable reaction. Instead, the electrons are removed from NADH and passed to oxygen through a series of enzymes that each release a small amount of the energy. This set of enzymes, consisting of complexes I through IV, is called the electron transport chain and is found in the inner membrane of the mitochondrion. Succinate is also oxidized by the electron transport chain, but feeds into the pathway at a different point.
In eukaryotes, the enzymes in this electron transport system use the energy released from O by NADH to pump protons across the inner membrane of the mitochondrion. This causes protons to build up in the intermembrane space, and generates an electrochemical gradient across the membrane. The energy stored in this potential is then used by ATP synthase to produce ATP. Oxidative phosphorylation in the eukaryotic mitochondrion is the best-understood example of this process. The mitochondrion is present in almost all eukaryotes, with the exception of anaerobic protozoa such as Trichomonas vaginalis that instead reduce protons to hydrogen in a remnant mitochondrion called a hydrogenosome. | 1 | Biochemistry |
The oxidative release of natural glycans technique was developed at the center. This process involves household bleach treatment of tissues to release glycans for glycomics. The eventual aim of this approach is to make glycomics accessible by a larger community of scientists by the development of tools which are easily available. | 0 | Organic Chemistry |
Inside a magnet the wires are subjected to high Lorentz forces as well as thermal stresses during cooling. Any strain in the niobium tin causes a decrease in the superconducting performance of the material, and can cause the brittle material to fracture. Because of this, the wires need to be as stiff as possible. The Young's modulus of niobium tin is around 140 GPa at room temperature. However, the stiffness drops down to as low as 50 GPa when the material is cooled below . Engineers must therefore find ways of improving the strength of the material. Strengthening fibers are often incorporated in the composite niobium tin wires to increase their stiffness. Common strengthening materials include Inconel, stainless steel, molybdenum, and tantalum because of their high stiffness at cryogenic temperatures. Since the thermal expansion coefficients of the matrix, fiber, and niobium tin are all different, significant amounts of strain can be generated after the wire is annealed and cooled all the way down to operating temperatures. This strain is referred to as the pre-strain in the wire. Since any strain in the niobium tin generally decreases the superconducting performance of the material, a proper combination of materials must be used to minimize this value. The pre-strain in a composite wire can be calculated by the formula
where ε is the pre-strain, ΔL/L and ΔL/L are changes in length due to thermal expansion of the niobium tin conduit and strengthening fiber respectively; V, V, V, and V are the volume fractions of conduit, fiber, copper, and bronze; σ, and σ are the yield stresses of copper and bronze; and E, and E are the Young's modulus of the conduit and the fiber. Since the copper and bronze matrix deforms plastically during cooldown, they apply a constant stress equal to their yield stress. The conduit and fiber, however, deform elastically by design. Commercial superconductors manufactured by the bronze process generally have a pre-strain value around 0.2% to 0.4%. The so-called strain effect causes a reduction in the superconducting properties of many materials including niobium tin. The critical strain, the maximum allowable strain over which superconductivity is lost, is given by the formula
where ε is the critical strain, ε is a material dependent parameter equal to 1.5% in tension (−1.8% in compression) for niobium tin, B is the applied magnetic field, and B is the maximum upper critical field of the material. Strain in the niobium tin causes tetragonal distortions in the crystal lattice, which changes the electron-phonon interaction spectrum. This is equivalent to an increase in disorder in the A15 crystal structure. At high enough strain, around 1%, the niobium tin conduit will develop fractures and the current carrying capability of the wire will be irreversibly damaged. In most circumstances, except for high field conditions, the niobium tin conduit will fracture before the critical strain is reached. | 8 | Metallurgy |
Large-scale industrial/municipal systems recover typically 75% to 80% of the feed water, or as high as 90%, because they can generate the required higher pressure. | 3 | Analytical Chemistry |
With a pK near 3.4, thioacetic acid is about 15 times more acidic than acetic acid. The conjugate base is thioacetate:
In neutral water, thioacetic acid is fully ionized. | 0 | Organic Chemistry |
For uniaxial extension in the -direction, the principal stretches are . From incompressibility . Hence .
Therefore,
The left Cauchy–Green deformation tensor can then be expressed as
If the directions of the principal stretches are oriented with the coordinate basis vectors, we have
If , we have
Therefore,
The engineering strain is . The engineering stress is | 7 | Physical Chemistry |
* Cathodic reduction of carbon dioxide and anodic oxidation of acetonitrile afford cyanoacetic acid.
* An electrosynthesis employing alternating current prepares phenol at both the cathode and the anode. | 7 | Physical Chemistry |
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, or any other element to be added to obtain a desired alloying effect;
* the specified minimum for copper does not exceed 0.40%;
* or the specified maximum for any of the following elements does not exceed the percentages noted: manganese 1.65%; silicon 0.60%; copper 0.60%.
The term carbon steel may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels. High carbon steel has many different uses such as milling machines, cutting tools (such as chisels) and high strength wires. These applications require a much finer microstructure, which improves the toughness.
As the carbon content percentage rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point. | 8 | Metallurgy |
The consequence of an electron transfer is the rearrangement of charges, and this greatly influences the solvent environment. For the dipolar solvent molecules rearrange in the direction of the field of the charges (this is called orientation polarisation), and also the atoms and electrons in the solvent molecules are slightly displaced (atomic and electron polarization, respectively). It is this solvent polarization which determines the free energy of activation and thus the reaction rate.
Substitution, elimination and isomerization reactions differ from the outer sphere redox reaction not only in the structural changes outlined above, but also in the fact that the movements of the nuclei and the shift of charges (charge transfer, CT) on the reactions path take place in a continuous and concerted way: nuclear configurations and charge distribution are always "in equilibrium". This is illustrated by the S2 substitution of the saponification of an alkyl halide where the rear side attack of the OH ion pushes out a halide ion and where a transition state with a five-coordinated carbon atom must be visualized. The system of the reactants becomes coupled so tightly during the reaction that they form the activated complex as an integral entity. The solvent here has a minor effect.
By contrast, in outer sphere redox reactions the displacement of nuclei in the reactants are small, here the solvent has the dominant role. Donor-acceptor coupling is weak, both keep their identity during the reaction. Therefore, the electron, being an elementary particle, can only "jump" as a whole (electron transfer, ET). If the electron jumps, the transfer is much faster than the movement of the large solvent molecules, with the consequence that the nuclear positions of the reaction partners and the solvent molecules are the same before and after the electron jump (Franck–Condon principle). The jump of the electron is governed by quantum mechanical rules, it is only possible if also the energy of the ET system does not change "during" the jump.
The arrangement of solvent molecules depends on the charge distribution on the reactants. If the solvent configuration must be the same before and after the jump and the energy may not change, then the solvent cannot be in the solvation state of the precursor nor in that of the successor complex as they are different, it has to be somewhere in between. For the self-exchange reaction for symmetry reasons an arrangement of the solvent molecules exactly in the middle of those of precursor and successor complex would meet the conditions. This means that the solvent arrangement with half of the electron on both donor and acceptor would be the correct environment for jumping. Also, in this state the energy of precursor and successor in their solvent environment would be the same.
However, the electron as an elementary particle cannot be divided, it resides either on the donor or the acceptor and arranges the solvent molecules accordingly in an equilibrium. The "transition state", on the other hand, requires a solvent configuration which would result from the transfer of half an electron, which is impossible. This means that real charge distribution and required solvent polarization are not in an "equilibrium". Yet it is possible that the solvent takes a configuration corresponding to the "transition state", even if the electron sits on the donor or acceptor. This, however, requires energy. This energy may be provided by the thermal energy of the solvent and thermal fluctuations can produce the correct polarization state. Once this has been reached the electron can jump. The creation of the correct solvent arrangement and the electron jump are decoupled and do not happen in a synchronous process. Thus the energy of the transition state is mostly polarization energy of the solvent. | 7 | Physical Chemistry |
The Arruda–Boyce model is based on the statistical mechanics of polymer chains. In this approach, each macromolecule is described as a chain of segments, each of length . If we assume that the initial configuration of a chain can be described by a random walk, then the initial chain length is
If we assume that one end of the chain is at the origin, then the probability that a block of size around the origin will contain the other end of the chain, , assuming a Gaussian probability density function, is
The configurational entropy of a single chain from Boltzmann statistical mechanics is
where is a constant. The total entropy in a network of chains is therefore
where an affine deformation has been assumed. Therefore the strain energy of the deformed network is
where is the temperature. | 7 | Physical Chemistry |
The binding of proteins to the SELDI surface acts as a solid-phase chromatographic separation step, and as a result, the proteins attached to the surface are easier to analyze. The surface is composed primarily of materials with a variety of physico-chemical characteristics, metal ions, or anion or cation exchangers. Common surfaces include CM10 (weak cation exchange), H50 (hydrophobic surface, similar to C-C reverse phase chromatography), IMAC30 (metal-binding surface), and Q10 (strong anion exchange). SELDI surfaces can also be modified to study DNA-protein binding, antibody-antigen assays, and receptor-ligand interactions. | 1 | Biochemistry |
Several commodity chemicals are produced by alkylation. Included are several fundamental benzene-based feedstocks such as ethylbenzene (precursor to styrene), cumene (precursor to phenol and acetone), linear alkylbenzene sulfonates (for detergents). | 0 | Organic Chemistry |
While liquids do not exhibit long-range ordering as in a crystalline lattice, they do possess short-range order, which persists over a few molecular diameters.
In all liquids, excluded volume interactions induce short-range order in molecular positions (center-of-mass coordinates). Classical monatomic liquids like argon and krypton are the simplest examples. Such liquids can be modeled as disordered "heaps" of closely packed spheres, and the short-range order corresponds to the fact that nearest and next-nearest neighbors in a packing of spheres tend to be separated by integer multiples of the diameter.
In most liquids, molecules are not spheres, and intermolecular forces possess a directionality, i.e., they depend on the relative orientation of molecules. As a result, there is short-ranged orientational order in addition to the positional order mentioned above. Orientational order is especially important in hydrogen-bonded liquids like water. The strength and directional nature of hydrogen bonds drives the formation of local "networks" or "clusters" of molecules. Due to the relative importance of thermal fluctuations in liquids (compared with solids), these structures are highly dynamic, continuously deforming, breaking, and reforming. | 7 | Physical Chemistry |
Yeast ATP synthase is one of the best-studied eukaryotic ATP synthases; and five F, eight F subunits, and seven associated proteins have been identified. Most of these proteins have homologues in other eukaryotes. | 5 | Photochemistry |
The execution of the Chen-Kao reaction is simple, needs little practice and limited skills.
Also, the violet color obtained in the reaction is easy to define.
For a correct execution, it is important to note that the typical colors develop relatively slowly, and that a good color intensity requires a sample of a few milligrams of the substances tested (i.e., more than what would typically be required for most other tests included in the UN test kits).
Of all ephedrine-related compounds, only ephedrine and pseudoephedrine produce the typical, stable violet color. Other ephedrine-related compounds produce a blue to greenish-blue precipitate. This precipitate could be seen as characteristic for the members of the ephedrine group other than pseudoephedrine and ephedrine itself, hence, the Chen-Kao test appears to show a significant specificity within the ephedrine group. However, it is known from previously published cross-testing work that various pharmaceuticals not related to the ephedrine group may produce similar blue copper complexes.
The two keto-amines, cathinone and methcathinone, initially also produce blue-colored complexes with the Chen-Kao reagent. However, a slow transition of the initial color into yellow, followed by an orange-brown color can be observed with both compounds, thus indicating the instability of the complexes initially formed, and an obvious decomposition of the two compounds under the alkaline conditions of this color reaction.
The results of the solvent extractions, summarized in Table II appear to add little novelty to the results of the original Chen-Kao reactions. However, in cases of doubts, they may serve as confirmatory steps. | 3 | Analytical Chemistry |
The formation of a complex between a metal ion, M, and a ligand, L, is in fact usually a substitution reaction. For example, In aqueous solutions, metal ions will be present as aquo ions, so the reaction for the formation of the first complex could be written as
:[M(HO)] + L [M(HO)L] + HO
However, since water is in vast excess, the concentration of water is usually assumed to be constant and is omitted from equilibrium constant expressions. Often, the metal and the ligand are in competition for protons. For the equilibrium
:p M + q L + r H MLH
a stability constant can be defined as follows:
The definition can easily be extended to include any number of reagents. It includes hydroxide complexes because the concentration of the hydroxide ions is related to the concentration of hydrogen ions by the self-ionization of water
Stability constants defined in this way, are association constants. This can lead to some confusion as pK values are dissociation constants. In general purpose computer programs it is customary to define all constants as association constants. The relationship between the two types of constant is given in association and dissociation constants.
In biochemistry, an oxygen molecule can bind to an iron(II) atom in a heme prosthetic group in hemoglobin. The equilibrium is usually written, denoting hemoglobin by Hb, as
: Hb + O HbO
but this representation is incomplete as the Bohr effect shows that the equilibrium concentrations are pH-dependent. A better representation would be
: [HbH] + O HbO + H
as this shows that when hydrogen ion concentration increases the equilibrium is shifted to the left in accordance with Le Châtelier's principle. Hydrogen ion concentration can be increased by the presence of carbon dioxide, which behaves as a weak acid.
:HO + CO + H
The iron atom can also bind to other molecules such as carbon monoxide. Cigarette smoke contains some carbon monoxide so the equilibrium
:HbO + CO + O
is established in the blood of cigarette smokers.
Chelation therapy is based on the principle of using chelating ligands with a high binding selectivity for a particular metal to remove that metal from the human body.
Complexes with polyamino carboxylic acids find a wide range of applications. EDTA in particular is used extensively. | 7 | Physical Chemistry |
At small (but still positive) values of and , the pulsation decays slowly, and this decay can be described analytically. In the first approximation, the parameters and give additive contributions to the decay; the decay rate, as well as the amplitude and phase of the nonlinear oscillation, can be approximated with elementary functions in a manner similar to the period above. In describing the behavior of the idealized Toda oscillator, the error of such approximations is smaller than the differences between the ideal and its experimental realization as a self-pulsing laser at the optical bench. However, a self-pulsing laser shows qualitatively very similar behavior. | 7 | Physical Chemistry |
Since alkenes are mainly produced as mixtures with alkanes, the separation of alkanes and alkenes is of commercial interest. Separation technologies often rely on facilitated transport membranes containing Ag or Cu salts that reversibly bind alkenes.
In argentation chromatography, stationary phases that contain silver salts are used to analyze organic compounds on the basis of the number and type of alkene (olefin) groups. This methodology is commonly employed for the analysis of the unsaturated content in fats and fatty acids. | 0 | Organic Chemistry |
In 2010, when Craig Venter unveiled the first fully functioning, reproducing cell controlled by synthetic DNA he described how his team used frequent stop codons to create watermarks in RNA and DNA to help confirm the results were indeed synthetic (and not contaminated or otherwise), using it to encode authors' names and website addresses. | 1 | Biochemistry |
It can be prepared by the reaction of allyl magnesium bromide with anhydrous nickel chloride. It was first prepared similarly by Gunther Wilke et al. The same group reported that the complex react with carbon monoxide to give nickel tetracarbonyl and 1,5-hexadiene. It catalyzes the trimerization of butadiene. With tertiary phosphines, the complex gives the tetrakis derivative. Such reactions to proceed via the intermediacy of the 18-electron adduct. | 0 | Organic Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.