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Unsaturated esters may be epoxidized using either electrophilic or nucleophilic methods. Lanthanide-mediated epoxidation has been successfully applied to cinnamates and β-heteroaryl unsaturated esters. Amides are also epoxidized under lanthanide-mediated conditions.
Epoxidations of other electron-deficient double bonds (substituted by electron-withdrawing groups other than carbonyls) are limited in scope, although a few examples have been reported. The ability of the carbonyl group to coordinate Lewis acidic functionality is critical for most existing methods. | 0 | Organic Chemistry |
The Büchner–Curtius–Schlotterbeck reaction can be used to facilitate one carbon ring expansions when the substrate ketone is cyclic. For instance, the reaction of cyclopentanone with diazomethane forms cyclohexanone (shown below). The Büchner ring expansion reactions utilizing diazoalkanes have proven to be synthetically useful as they can not only be used to form 5- and 6-membered rings, but also more unstable 7- and 8-membered rings.
An acyl-diazomethane can react with an aldehyde to form a β-diketone in the presence of a transition metal catalyst (SnCl in the example shown below). β-Diketones are common biological products, and as such, their synthesis is relevant to biochemical research. Furthermore, the acidic β-hydrogens of β-diketones are useful for broader synthetic purposes, as they can be removed by common bases.
Acyl-diazomethane can also add to esters to form β-keto esters, which are important for fatty acid synthesis. As mentioned above, the acidic β-hydrogens also have productive functionality.
The Büchner–Curtius–Schlotterbeck reaction can also be used to insert a methylene bridge between a carbonyl carbon and a halogen of an acyl halide. This reaction allows conservation of the carbonyl and halide functionalities.
It is possible to isolate nitrogen-containing compounds using the Büchner–Curtius–Schlotterbeck reaction. For example, an acyl-diazomethane can react with an aldehyde in the presence of a DBU catalyst to form isolable α-diazo-β-hydroxy esters (shown below). | 0 | Organic Chemistry |
In chemistry, a hydrogen bond (or H-bond) is primarily an electrostatic force of attraction between a hydrogen (H) atom which is covalently bonded to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted , where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the period 2 elements nitrogen (N), oxygen (O), and fluorine (F).
Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule). The energy of a hydrogen bond depends on the geometry, the environment, and the nature of the specific donor and acceptor atoms and can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. Hydrogen bonds are responsible for holding materials such as paper and felted wool together, and for causing separate sheets of paper to stick together after becoming wet and subsequently drying.
The hydrogen bond is also responsible for many of the physical and chemical properties of compounds of N, O, and F that seem unusual compared with other similar structures. In particular, intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C) compared to the other group-16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structures of proteins and nucleic acids. | 6 | Supramolecular Chemistry |
A dispersed medium consists of two media that do not mix. More specifically, it contains discrete elements of one medium which are dispersed in a continuous second medium. The two media can be of very different nature. In particular, they can be a gas, a liquid or a solid.
Many materials which we encounter during the day are dispersed media. For example, milk consists of oil drops dispersed in water, fog contains tiny water drops dispersed in air, shaving cream contains bubbles dispersed in a liquid, sand consists of solid grains in air and a kitchen sponge of bubbles dispersed in a solid.
Dispersed media are commonly classified according to the nature of the two media and the volume fraction of the dispersed medium. At very low volume fraction the dispersed objects are not in contact with each other. At intermediate volume fraction they start to be in contact (they jam). And at even higher volume fraction, the dispersed objects deform in a tight packing.
Another classification takes into account the typical size of the dispersed objects. When the objects are very small (typically < 1 micrometer), for example, one speaks of colloids.
The following table provides an overview of the main types of dispersed media.
| style="text-align:center" | GASEOUS SUSPENSION<br />
| Liquid
| style="text-align:center" | AERATED LIQUID<br />
| style="text-align:center" | EMULSION<br />
| style="text-align:center" | LIQUID SUSPENSION<br />
| Solid
| style="text-align:center" | AERATED SOLIDS<br />
| style="text-align:center" | GEL<br />
| style="text-align:center" | IMPURE SUBSTANCE<br />
See also: Dispersion | 7 | Physical Chemistry |
The Randle cycle is a biochemical mechanism involving the competition between glucose and fatty acids for their oxidation and uptake in muscle and adipose tissue. The cycle controls fuel selection and adapts the substrate supply and demand in normal tissues. This cycle adds a nutrient-mediated fine tuning on top of the more coarse hormonal control on fuel metabolism. This adaptation to nutrient availability applies to the interaction between adipose tissue and muscle. Hormones that control adipose tissue lipolysis affect circulating concentrations of fatty acids, these in turn control the fuel selection in muscle. Mechanisms involved in the Randle Cycle include allosteric control, reversible phosphorylation and the expression of key enzymes. The energy balance from meals composed of differing macronutrient composition is identical, but the glucose and fat balances that contribute to the overall energy balance change reciprocally with meal composition. | 1 | Biochemistry |
When an herbivore starts eating a plant, the plant may respond by increasing its production of volatiles or changing its volatile profile. This plasticity is controlled by either the jasmonic acid pathway or the salicylic acid pathway, depending largely on the herbivore; these substances are often called herbivore-induced plant volatiles (HIPVs). The plant hormone jasmonic acid increases in concentration when plants are damaged and is responsible for inducing the transcription of enzymes that synthesize secondary metabolites. This hormone also aids in the production of defensive proteins such as α-amylase inhibitors, as well as lectins. Since α-amylase breaks down starch, α-amylase inhibitors prevent insects from deriving nutrition from starch. Lectins likewise interfere with insect nutrient absorption as they bind to carbohydrates.
Though volatiles of any kind have an attractive effect on natural enemies, this effect is stronger for damaged plants than for undamaged plants, perhaps because induced volatiles signal definitive and recent herbivore activity. The inducibility gives rise to the idea that plants are sending out a "distress call" to the third trophic level in times of herbivore attack.
Natural enemies can distinguish between mechanical tissue damage, which might occur during events other than herbivory, and damage that is the direct result of insect feeding behavior. The presence of herbivore saliva or regurgitant mediates this differentiation, and the resulting chemical pathway leads to a stronger natural enemy response than mechanical damage could. The reliability of HIPVs in broadcasting the location of prey means that, for many foraging enemies, induced plant volatiles are more attractive than even the odors emitted by the prey insect itself.
Plants are able to determine what types of herbivore species are present, and will react differently given the herbivore's traits. If certain defense mechanisms are not effective, plants may turn to attracting natural enemies of herbivore populations. For example, wild tobacco plants use nicotine, a neurotoxin, to defend against herbivores. However, when faced with nicotine-tolerant herbivores, they will attract natural enemies. | 1 | Biochemistry |
Gas lasers, laser diodes, and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6 nm in wavelength. Another type of high-power gas lasers are excimer lasers. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride excimer lasers operating at 193 nm are routinely used in integrated circuit production by photolithography. The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar* excimer laser.
Direct UV-emitting laser diodes are available at 375 nm. UV diode-pumped solid state lasers have been demonstrated using cerium-doped lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at Lawrence Livermore National Laboratory. Wavelengths shorter than 325 nm are commercially generated in diode-pumped solid-state lasers. Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers.
Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology, and keratectomy), chemistry (MALDI), free-air secure communications, computing (optical storage), and manufacture of integrated circuits. | 5 | Photochemistry |
In 1822, Baron Charles Cagniard de la Tour discovered the critical point of a substance in his famous cannon barrel experiments. Listening to discontinuities in the sound of a rolling flint ball in a sealed cannon filled with fluids at various temperatures, he observed the critical temperature. Above this temperature, the densities of the liquid and gas phases become equal and the distinction between them disappears, resulting in a single supercritical fluid phase.
In recent years, a significant effort has been devoted to investigation of various properties of supercritical fluids. Supercritical fluids have found application in a variety of fields, ranging from the extraction of floral fragrance from flowers to applications in food science such as creating decaffeinated coffee, functional food ingredients, pharmaceuticals, cosmetics, polymers, powders, bio- and functional materials, nano-systems, natural products, biotechnology, fossil and bio-fuels, microelectronics, energy and environment. Much of the excitement and interest of the past decade is due to the enormous progress made in increasing the power of relevant experimental tools. The development of new experimental methods and improvement of existing ones continues to play an important role in this field, with recent research focusing on dynamic properties of fluids. | 7 | Physical Chemistry |
A quinone dimethide (or "xylylene") is a compound with the formula CH(=CH). Thus they are related to quinone monomethides (the topic of this article) by replacing the keto group with methylidene. A well studied example is tetracyanoquinodimethane. | 0 | Organic Chemistry |
p75NTR serves as a regulator for actin assembly. Ras homolog family member A (RhoA) causes the actin cytoskeleton to become rigid which limits growth cone mobility and inhibits neuronal elongation in the developing nervous system. p75NTR without a ligand bound activates RhoA and limits actin assembly, but neurotrophin binding to p75NTR can inactivate RhoA and promote actin assembly. p75NTR associates with the Rho GDP dissociation inhibitor (RhoGDI), and RhoGDI associates with RhoA. Interactions with Nogo can strengthen the association between p75NTR and RhoGDI. Neurotrophin binding to p75NTR inhibits the association of RhoGDI and p75NTR, thereby suppressing RhoA release and promoting growth cone elongation (inhibiting RhoA actin suppression). | 1 | Biochemistry |
Normal energy requirement, and therefore normal energy intake, depends mainly on age, sex and physical activity level (PAL). The Food and Agriculture Organization (FAO) of the United Nations has compiled a detailed report on human energy requirements. An older but commonly used and fairly accurate method is the Harris-Benedict equation.
Yet, there are currently ongoing studies to show if calorie restriction to below normal values have beneficial effects, and even though they are showing positive indications in nonhuman primates it is still not certain if calorie restriction has a positive effect on longevity for humans and other primates. Calorie restriction may be viewed as attaining energy balance at a lower intake and expenditure, and is, in this sense, not generally an energy imbalance, except for an initial imbalance where decreased expenditure hasn't yet matched the decreased intake. | 1 | Biochemistry |
In the early history of the Solar System, radioactive isotopes having a half-life on the order of a few million years (such as aluminium-26 and iron-60) were sufficiently abundant to produce enough heat to cause internal melting of some moons and even some asteroids, such as Vesta noted above. After these radioactive isotopes had decayed to insignificant levels, the heat generated by longer-lived radioactive isotopes (such as potassium-40, thorium-232, and uranium-235 and uranium-238) was insufficient to keep these bodies molten unless they had an alternative source of internal heating, such as tidal heating. Thus, Earth's Moon, which has no alternative source of internal heating is now geologically dead, whereas a moon as small as Enceladus that has sufficient tidal heating (or at least had it recently) and some remaining radioactive heating, is able to maintain an active and directly detectable cryovolcanism. | 7 | Physical Chemistry |
The prognosis is good for paracetamol overdoses if treatment is initiated up to 8 hours after the drug has been taken. Most hospitals stock the antidote (acetylcysteine), which replenishes the liver's supply of glutathione, allowing the NAPQI to be metabolized safely. Without early administration of the antidote, fulminant liver failure follows, often in combination with kidney failure, and death generally occurs within several days. | 1 | Biochemistry |
William Christopher Zeise was born 15 October 1789 in Slagelse, the son of an apothecary, Frederick Zeise (1754–1836), who was an old friend of physicist Hans Christian Ørsteds father. Zeise attended Slagelse Latin school until he went to Copenhagen in 1805 to take up an apprenticeship under Gottfried Becker as a pharmacy assistant (Apoteksmedhjælper') at the Royal Court Pharmacy. Gottfried Becker, was an accomplished chemist who was employed as extraordinary Professor of Chemistry at the University. However Zeise felt dissatisfied there and returned home complaining of his health after having been there only a few months.
Around this time his interest in science (Natural Philosophy) began to develop. He familiarised himself with the new quantitative chemical theory of Antoine Lavosier; and read widely, including - Nicolai Tychsens "Apothekerkunst" (Theoretical and practical instructions for Pharmacists, 1804), Grens Chemistry, Adam Hauchs Principles of Natural Philosophy and Ørsteds papers in Scandinavian Literature and Letters (whose treatise on spontaneous combustion made an especially strong impression on him). At the same time he experimented with a home-made voltaic pile. At 17 years old, he rearranged his father's pharmacy in accordance with the new pharmacopoeia of 1805, which had imposed the antiphlogistic nomenclature. About the same time (summer of 1806) he mentioned in his diary "a most remarkable awakening within me for something higher, for scientific creative work in general, but for Science, chiefly Chemistry, deeply and in particular". How strong an impression this inner experience had made on him, can be established by the fact that he now wanted to return to Copenhagen, not to return to the Court apothecary, but to pursue a path studying chemistry. | 0 | Organic Chemistry |
The lost-wax casting tradition was developed by the peoples of Nicaragua, Costa Rica, Panama, Colombia, northwest Venezuela, Andean America, and the western portion of South America. Lost-wax casting produced some of the regions typical gold wire and delicate wire ornament, such as fine ear ornaments. The process was employed in prehispanic times in Colombias Muisca and Sinú cultural areas. Two lost-wax moulds, one complete and one partially broken, were found in a shaft and chamber tomb in the vereda of Pueblo Tapado in the municipio of Montenegro (Department of Quindío), dated roughly to the pre-Columbian period. The lost-wax method did not appear in Mexico until the 10th century, and was thereafter used in western Mexico to make a wide range of bell forms. | 8 | Metallurgy |
Phenolphthalein's pH sensitivity is exploited in other applications: concrete has naturally high pH due to the calcium hydroxide formed when Portland cement reacts with water. As the concrete reacts with carbon dioxide in the atmosphere, pH decreases to 8.5–9. When a 1% phenolphthalein solution is applied to normal concrete, it turns bright pink. However, if it remains colorless, it shows that the concrete has undergone carbonation. In a similar application, some spackling used to repair holes in drywall contains phenolphthalein. When applied, the basic spackling material retains a pink color; when the spackling has cured by reaction with atmospheric carbon dioxide, the pink color fades. | 3 | Analytical Chemistry |
The Planet Simulator, also known as a Planetary Simulator, is a climate-controlled simulation chamber designed to study the origin of life. The device was announced by researchers at McMaster University on behalf of the Origins Institute on 4 October 2018. The simulator project begun in 2012 and was funded with $1 million from the Canada Foundation for Innovation, the Ontario government, and McMaster University. It was built and manufactured by [https://angstromengineering.com/ Angstrom Engineering Inc] of Kitchener, Ontario.
The device was designed and developed by biophysicist Maikel Rheinstadter and co-principal investigators biochemist Yingfu Li and astrophysicist Ralph Pudritz for researchers to study a theory that suggests life on early Earth began in "warm little ponds" rather than in deep ocean vents nearly four billion years ago. The device can recreate conditions of the primitive Earth to see whether cellular life can be created, and then later, evolve.
In an 2018 news release, Maikel Rheinstadter stated: "We want to understand how the first living cell was formed - how the Earth moved from a chemical world to a biological world."
The Planet Simulator can mimic the environmental conditions consistent on the early Earth and other astronomical bodies, including other planets and exoplanets by controlling temperature, humidity, pressure, atmosphere and radiation levels within the simulation chamber. | 9 | Geochemistry |
Levorphanol is listed under the Single Convention On Narcotic Drugs 1961 and is regulated like morphine in most countries. In the U.S., it is a Schedule II Narcotic controlled substance with a DEA ACSCN of 9220 and 2013 annual aggregate manufacturing quota of 4.5 kilograms. The salts in use are the tartrate (free base conversion ratio 0.58) and hydrobromide (0.76). | 4 | Stereochemistry |
The Strecker degradation is a chemical reaction which converts an α-amino acid into an aldehyde containing the side chain, by way of an imine intermediate. It is named after Adolph Strecker, a German chemist.
The original observation by Strecker involved the use of alloxan as the oxidant in the first step, followed by hydrolysis:
The reaction can take place using a variety of organic and inorganic reagents. | 0 | Organic Chemistry |
With the excellent nature in biodegradation and biocompatibility, supramolecular polymers show great potential in the development of drug delivery, gene transfection and other biomedical applications.
: Multiple cellular stimuli could induce responses in supramolecular polymers. The dynamic molecular skeletons of supramolecular polymers can be depolymerized when exposing to the external stimuli like pH in vivo. On the basis of this property, supramolecular polymers are capable of being a drug carrier. Making use of hydrogen bonding between nucleobases to induce self-assemble into pH-sensitive spherical micelles.
: Effective and low-toxic nonviral cationic vectors are highly desired in the field of gene therapy. On account of the dynamic and stimuli-responsive properties, supramolecular polymers offer a cogent platform to construct vectors for gene transfection. By combining ferrocene dimer with β-cyclodextrin dimer, a redox-control supramolecular polymers system has been proposed as a vector. In COS-7 cells, this supramolecular polymersic vector can release enclosed DNA upon exposing to hydrogen peroxide and achieve gene transfection. | 6 | Supramolecular Chemistry |
There are four main factors influencing photosynthesis and several corollary factors. The four main are:
* Light irradiance and wavelength
* Water absorption
* Carbon dioxide concentration
* Temperature.
Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), the rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis. | 5 | Photochemistry |
Most genes considered master regulators code for transcription factor proteins, which in turn alter the expression of downstream genes in the pathway. Canonical examples of master regulators include Oct-4 (also called POU5F1), SOX2, and NANOG, all transcription factors involved in maintaining pluripotency in stem cells. Master regulators involved in development and morphogenesis can also appear as oncogenes relevant to tumorigenesis and metastasis, as with the Twist transcription factor.
Other genes reported as master regulators code for SR proteins, which function as splicing factors, and some noncoding RNAs. | 1 | Biochemistry |
When monomers with two types of functional groups A and B undergo step growth polymerisation by virtue of a reaction between A and B groups, a similar analytical results are known. See the table on the right for several examples. In this case, is the fraction of initial monomers with groups A and groups B. Suppose that A is the group that is depleted first. Random graph theory states that gelation takes place when , where the gelation conversion is and . Molecular size distribution, the molecular weight averages, and the distribution of gyration radii have known formal analytical expressions. When degree distribution , giving the fraction of monomers in the network with neighbours connected via A group and connected via B group at time is solved numerically, the gel state is detected when , where and . | 7 | Physical Chemistry |
Isoaspartyl formation reactions have been conjectured to be one of the factors that limit the useful lifetime of proteins.
Isoaspartyl formation proceeds much more quickly if the asparagine is followed by a small, flexible residue (such as Gly) that leaves the peptide group open for attack. These reactions also proceed much more quickly at elevated pH (>10) and temperatures. | 1 | Biochemistry |
Base-catalyzed transesterification reacts lipids (fats and oils) with alcohol (typically methanol or ethanol) to produce biodiesel and an impure coproduct, glycerol. If the feedstock oil is used or has a high acid content, acid-catalyzed esterification can be used to react fatty acids with alcohol to produce biodiesel. Other methods, such as fixed-bed reactors, supercritical reactors, and ultrasonic reactors, forgo or decrease the use of chemical reaction that reduces the quality of substance in chemistry. | 0 | Organic Chemistry |
Rotational–vibrational spectroscopy is a branch of molecular spectroscopy that is concerned with infrared and Raman spectra of molecules in the gas phase. Transitions involving changes in both vibrational and rotational states can be abbreviated as rovibrational (or ro-vibrational) transitions. When such transitions emit or absorb photons (electromagnetic radiation), the frequency is proportional to the difference in energy levels and can be detected by certain kinds of spectroscopy. Since changes in rotational energy levels are typically much smaller than changes in vibrational energy levels, changes in rotational state are said to give fine structure to the vibrational spectrum. For a given vibrational transition, the same theoretical treatment as for pure rotational spectroscopy gives the rotational quantum numbers, energy levels, and selection rules. In linear and spherical top molecules, rotational lines are found as simple progressions at both higher and lower frequencies relative to the pure vibration frequency. In symmetric top molecules the transitions are classified as parallel when the dipole moment change is parallel to the principal axis of rotation, and perpendicular when the change is perpendicular to that axis. The ro-vibrational spectrum of the asymmetric rotor water is important because of the presence of water vapor in the atmosphere. | 7 | Physical Chemistry |
Mitochondria (or related structures) are found in all eukaryotes (except the Oxymonad Monocercomonoides). Although commonly depicted as bean-like structures they form a highly dynamic network in the majority of cells where they constantly undergo fission and fusion. The population of all the mitochondria of a given cell constitutes the chondriome. Mitochondria vary in number and location according to cell type. A single mitochondrion is often found in unicellular organisms, while human liver cells have about 1000–2000 mitochondria per cell, making up 1/5 of the cell volume. The mitochondrial content of otherwise similar cells can vary substantially in size and membrane potential, with differences arising from sources including uneven partitioning at cell division, leading to extrinsic differences in ATP levels and downstream cellular processes. The mitochondria can be found nestled between myofibrils of muscle or wrapped around the sperm flagellum. Often, they form a complex 3D branching network inside the cell with the cytoskeleton. The association with the cytoskeleton determines mitochondrial shape, which can affect the function as well: different structures of the mitochondrial network may afford the population a variety of physical, chemical, and signalling advantages or disadvantages. Mitochondria in cells are always distributed along microtubules and the distribution of these organelles is also correlated with the endoplasmic reticulum. Recent evidence suggests that vimentin, one of the components of the cytoskeleton, is also critical to the association with the cytoskeleton. | 1 | Biochemistry |
With the restoration of democracy in 1974, Zervas was able to contribute once more to research and educational policy. As previously, refusing to take a salary for these positions, he served a second time as the President of the Greek Atomic Energy Commission (1974–1975) and then as the President of the National Hellenic Research Foundation (1975–1979).
Zervas had suffered from periodic issues with respiratory health throughout his adult life, but in his final years the situation deteriorated. The extended use of phosgene in his research has been implicated as the cause of this chronic pulmonary disease. He showed perseverance and a pleasant attitude despite his health issues, continuing to attend meetings of the Academy of Athens until the very end of his life. This came in the summer of 1980 after an acute pulmonary episode, which lasted three weeks before he died at the age of 78. | 0 | Organic Chemistry |
Heterotopic groups are those that when substituted are structurally different. They are neither diastereotopic or enantiotopic nor homotopic. | 4 | Stereochemistry |
Water has a very high specific heat capacity of 4184 J/(kg·K) at 20 °C (4182 J/(kg·K) at 25 °C) —the second-highest among all the heteroatomic species (after ammonia), as well as a high heat of vaporization (40.65 kJ/mol or 2257 kJ/kg at the normal boiling point), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature. Most of the additional energy stored in the climate system since 1970 has accumulated in the oceans.
The specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher. This property confers resistance to melting on the ice of glaciers and drift ice. Before and since the advent of mechanical refrigeration, ice was and still is in common use for retarding food spoilage.
The specific heat capacity of ice at −10 °C is 2030 J/(kg·K) and the heat capacity of steam at 100 °C is 2080 J/(kg·K). | 2 | Environmental Chemistry |
Globo H (globohexaosylceramide) is a globo-series glycosphingolipid antigen that is present on the outer membrane of some cancer cells. Globo H is not expressed in normal tissue cells, but is expressed in a number of types of cancers, including cancers of the breast, prostate, and pancreas. Globo H's exclusivity for cancer cells makes it a target of interest for cancer therapies. | 1 | Biochemistry |
Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom (i.e. nitrogen, sulfur, or oxygen) as part of the ring. Their names originate from the Hantzsch–Widman nomenclature. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs (azolines and azolidines) with fewer. One, and only one, lone pair of electrons from each heteroatom in the ring is part of the aromatic bonding in an azole. Names of azoles maintain the prefix upon reduction (e.g., pyrazoline, pyrazolidine). The numbering of ring atoms in azoles starts with the heteroatom that is not part of a double bond, and then proceeds towards the other heteroatom.
Imidazole and other five-membered aromatic heterocyclic systems with two nitrogens are extremely common in nature and form the core of many biomolecules, such as histidine. | 0 | Organic Chemistry |
Huang et al. investigated the feasibility of using gold nanorods for both cancer cell imaging as well as photothermal therapy. The authors conjugated antibodies (anti-EGFR monoclonal antibodies) to the surface of gold nanorods, allowing the gold nanorods to bind specifically to certain malignant cancer cells (HSC and HOC malignant cells). After incubating the cells with the gold nanorods, an 800 nm Ti:sapphire laser was used to irradiate the cells at varying powers. The authors reported successful destruction of the malignant cancer cells, while nonmalignant cells were unharmed.
When AuNRs are exposed to NIR light, the oscillating electromagnetic field of the light causes the free electrons of the AuNR to collectively coherently oscillate. Changing the size and shape of AuNRs changes the wavelength that gets absorbed. A desired wavelength would be between 700-1000 nm because biological tissue is optically transparent at these wavelengths. While all AuNP are sensitive to change in their shape and size, Au nanorods properties are extremely sensitive to any change in any of their dimensions regarding their length and width or their aspect ratio. When light is shone on a metal NP, the NP forms a dipole oscillation along the direction of the electric field. When the oscillation reaches its maximum, this frequency is called the surface plasmon resonance (SPR). AuNR have two SPR spectrum bands: one in the NIR region caused by its longitudinal oscillation which tends to be stronger with a longer wavelength and one in the visible region caused by the transverse electronic oscillation which tends to be weaker with a shorter wavelength. The SPR characteristics account for the increase in light absorption for the particle. As the AuNR aspect ratio increases, the absorption wavelength is redshifted and light scattering efficiency is increased. The electrons excited by the NIR lose energy quickly after absorption via electron-electron collisions, and as these electrons relax back down, the energy is released as a phonon that then heats the environment of the AuNP which in cancer treatments would be the cancerous cells. This process is observed when a laser has a continuous wave onto the AuNP. Pulsed laser light beams generally results in the AuNP melting or ablation of the particle. Continuous wave lasers take minutes rather than a single pulse time for a pulsed laser, continues wave lasers are able to heat larger areas at once. | 5 | Photochemistry |
Genome-wide knockdown studies are an example of the reverse genetics made possible by the acquisition of whole genome sequences, and the advent of genomics and gene-silencing technologies, mainly siRNA and deletion mapping. Genome-wide knockdown studies involve systematic knockdown or deletion of genes or segments of the genome. This is generally done in prokaryotes or in a tissue culture environment due to the massive number of knockdowns that must be performed. After the systematic knockout is completed (and possibly confirmed by mRNA expression analysis), the phenotypic results of the knockdown/knockout can be observed. Observation parameters can be selected to target a highly specific phenotype. The resulting dataset is then queried for samples which exhibit phenotypes matching the disease in question – the gene(s) knocked down/out in said samples can then be considered candidate disease genes for the individual in question. | 1 | Biochemistry |
Pyridine is readily degraded by bacteria to ammonia and carbon dioxide. The unsubstituted pyridine ring degrades more rapidly than picoline, lutidine, chloropyridine, or aminopyridines, and a number of pyridine degraders have been shown to overproduce riboflavin in the presence of pyridine. Ionizable N-heterocyclic compounds, including pyridine, interact with environmental surfaces (such as soils and sediments) via multiple pH-dependent mechanisms, including partitioning to soil organic matter, cation exchange, and surface complexation. Such adsorption to surfaces reduces bioavailability of pyridines for microbial degraders and other organisms, thus slowing degradation rates and reducing ecotoxicity. | 0 | Organic Chemistry |
Metals can be coated with paint or other less conductive metals (passivation). This prevents the metal surface from being exposed to electrolytes. Scratches exposing the metal substrate will result in corrosion. The region under the coating adjacent to the scratch acts as the anode of the reaction. | 7 | Physical Chemistry |
In cooperativity, the initial ligand binding affects the host's affinity for subsequent ligands. In positive cooperativity, the first binding event enhances the affinity of the host for another ligand. Examples of positive and negative cooperativity are hemoglobin and aspartate receptor, respectively.
The thermodynamic properties of cooperativity have been studied in order to define mathematical parameters that distinguish positive or negative cooperativity. The traditional Gibbs free energy equation states: . However, to quantify cooperativity in a host–guest system, the binding energy needs to be considered. The schematic on the right shows the binding of A, binding of B, positive cooperative binding of A–B, and lastly, negative cooperative binding of A–B. Therefore, an alternate form of the Gibbs free energy equation would be
where:
: = free energy of binding A
: = free energy of binding B
: = free energy of binding for A and B tethered
: = sum of the free energies of binding
It is considered that if more than the sum of and , it is positively cooperative. If is less, then it is negatively cooperative.
Host–guest chemistry is not limited to receptor-lingand interactions. It is also demonstrated in ion-pairing systems. Such interactions are studied in an aqueous media utilizing synthetic organometallic hosts and organic guest molecules. For example, a poly-cationic receptor containing copper (the host) is coordinated with molecules such as tetracarboxylates, tricarballate, aspartate, and acetate (the guests). This study illustrates that entropy rather than enthalpy determines the binding energy of the system leading to negative cooperativity. The large change in entropy originates from the displacement of solvent molecules surrounding the ligand and the receptor. When multiple acetates bind to the receptor, it releases more water molecules to the environment than a tetracarboxylate. This led to a decrease in free energy implying that the system is cooperating negatively. In a similar study, utilizing guanidinium and Cu(II) and polycarboxylate guests, it is demonstrated that positive cooperatively is largely determined by enthalpy. In addition to thermodynamic studies, host–guest chemistry also has biological applications. | 6 | Supramolecular Chemistry |
Neurochemistry International is a peer-reviewed scientific journal covering research in neurochemistry, including molecular and cellular neurochemistry, neuropharmacology and genetic aspects of central nervous system function, neuroimmunology, metabolism as well as the neurochemistry of neurological and psychiatric disorders of the CNS. It is published by Elsevier and the editor-in-chief is Michael Robinson (Childrens Hospital of Philadelphia). According to the Journal Citation Reports', the journal has a 2021 impact factor of 4.297. | 1 | Biochemistry |
Carotenoids are located primarily outside the cell nucleus in different cytoplasm organelles, lipid droplets, cytosomes and granules. They have been visualised and quantified by raman spectroscopy in an algal cell.
With the development of monoclonal antibodies to trans-lycopene it was possible to localise this carotenoid in different animal and human cells. | 5 | Photochemistry |
Most of the time, artificial tissue is grown from the patients own cells. However, when the damage is so extreme that it is impossible to use the patients own cells, artificial tissue cells are grown. The difficulty is in finding a scaffold that the cells can grow and organize on. The characteristics of the scaffold must be that it is biocompatible, cells can adhere to the scaffold, mechanically strong and biodegradable. One successful scaffold is a copolymer of lactic acid and glycolic acid. | 1 | Biochemistry |
The free-living bioluminescent marine bacterium, Vibrio harveyi, uses another signaling molecule in addition to an acylated homoserine lactone. This molecule, termed Autoinducer-2 (or AI-2), is a furanosyl borate diester. AI-2, which is also produced and used by a number of Gram-negative and Gram-positive bacteria, is believed to be an evolutionary link between the two major types of quorum sensing circuits. | 1 | Biochemistry |
Yulia Sister was born in 1936 in Chișinău (Russian: Kishinev), at the time in the Kingdom of Romania, a city which later became the capital of the Moldavian SSR and since 1991 is the capital of Moldova. Her parents and paternal grandparents were also born in this city. The grandparents were there and survived the pogrom of 1903.
David Iosifovich, Yulias father, was a doctor educated in Prague at Charles University. He used to tell his daughter about his student years, the Bessarabian association of fellow-countrymen in Prague and his meetings with famous people. Yulias mother Yevgenia (Bathsheba) Moiseevna copied for her by hand children's verses and Yulia learned to read quite early. Among the first poems was "What Is Good and What Is Bad" by Mayakovsky.
Yulia's grandparents stuck to traditions and spoke Yiddish, and grandfather Yosef (Iosif) even wrote Yiddish poetry. But Yulia could hardly remember them. Her grandfather Moshe (Moisei) died before she was born; her parental grandparents lost their lives in the Kishinev Ghetto in the Holocaust and her grandmother Sarah died during the World War II in evacuation.
During the 2nd World War Bessarabia was reclaimed and then occupied by the Soviet Union in June 1940. A year later in July 1941 it was reconquered by Germany and Romania, and in August 1944 reoccupied by the Soviet Union. In her memoirs Yulia recalled the day when the Red Army entered Kishinev. She also remembered the German bombing of the city and the air raids on the roads, by which her family escaped to the East from the Nazis.
At the beginning of the war David Sister and his family was evacuated to the left bank of the Volga River where he was appointed chief physician at the district hospital and a consultant of the nearby military hospital. The hospital was located in the open steppe between two villages and on the other side of Volga there was Stalingrad. The family lived there a few years. There were no other children in the neighborhood and Yulia had no friends to play with. But she was fascinated by the local nature and made observations of plants and animals. The inhabitants of the hospital could hear the cannonade from the other bank, and during the battle of Stalingrad it became particularly strong.
In 1944 Yulias family moved to Kirovograd where she, after a years delay, was enrolled in the first grade of primary education. A year later the family came back to the native city of Kishinev. Despite severe post-war shortages and difficulties, the Sister's family succeeded to restore their home, which included a huge library. Among the family friends and guests were writers, actors, musicians and scientists, and Yulia grew up in an atmosphere of thirst for knowledge.
Between the years of 1945 and 1954 Yulia Sister studied at the School for Girls Number 2 in Kishinev. Chemistry was taught very passionately by a teacher that loved the subject and was able to convey her enthusiasm to the students. On the advice of her teacher Sister participated in the chemistry enrichment program for school children that was carried out by Professor at the University of Kishinev. | 3 | Analytical Chemistry |
PaNie is a 25 kDa protein produced by the root rot disease-causing pathogen Pythium aphanidermatum. It stands for Pythium aphanidermatum Necrosis inducing elicitor. PaNie (aka NLP) belongs to a family of elicitors named the Nep1-like proteins (NLPs), which cause necrosis when injected into the leaves of dicotyledonous plants. | 1 | Biochemistry |
Ertl is one of the editors of the Handbook of Heterogeneous Catalysis. ()
Ertl is the co-editor of Engineering Of Chemical Complexity. 2013, World Scientific Publishing. () | 7 | Physical Chemistry |
The perchlorate ion is monovalent, in other words, it has valence 1.<br />
Valences may also be different from absolute values of oxidation states due to different polarity of bonds. For example, in dichloromethane, , carbon has valence 4 but oxidation state 0.<br />
Iron oxides appear in a crystal structure, so no typical molecule can be identified. In ferrous oxide, Fe has oxidation state +2; in ferric oxide, oxidation state +3. | 3 | Analytical Chemistry |
Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed messenger RNA (mRNA) produced from that gene. This means the exons are joined in different combinations, leading to different (alternative) mRNA strands. Consequently, the proteins translated from alternatively spliced mRNAs usually contain differences in their amino acid sequence and, often, in their biological functions (see Figure).
Biologically relevant alternative splicing occurs as a normal phenomenon in eukaryotes, where it increases the number of proteins that can be encoded by the genome. In humans, it is widely believed that ~95% of multi-exonic genes are alternatively spliced to produce functional alternative products from the same gene but many scientists believe that most of the observed splice variants are due to splicing errors and the actual number of biologically relevant alternatively spliced genes is much lower.
Alternative splicing enables the regulated generation of multiple mRNA and protein products from a single gene.
There are numerous modes of alternative splicing observed, of which the most common is exon skipping. In this mode, a particular exon may be included in mRNAs under some conditions or in particular tissues, and omitted from the mRNA in others.
The production of alternatively spliced mRNAs is regulated by a system of trans-acting proteins that bind to cis-acting sites on the primary transcript itself. Such proteins include splicing activators that promote the usage of a particular splice site, and splicing repressors that reduce the usage of a particular site. Mechanisms of alternative splicing are highly variable, and new examples are constantly being found, particularly through the use of high-throughput techniques. Researchers hope to fully elucidate the regulatory systems involved in splicing, so that alternative splicing products from a given gene under particular conditions ("splicing variants") could be predicted by a "splicing code".
Abnormal variations in splicing are also implicated in disease; a large proportion of human genetic disorders result from splicing variants. Abnormal splicing variants are also thought to contribute to the development of cancer, and splicing factor genes are frequently mutated in different types of cancer. | 1 | Biochemistry |
In 2007 a quantum model was proposed by Graham Fleming and his co-workers which includes the possibility that photosynthetic energy transfer might involve quantum oscillations, explaining its unusually high efficiency.
According to Fleming there is direct evidence that remarkably long-lived wavelike electronic quantum coherence plays an important part in energy transfer processes during photosynthesis, which can explain the extreme efficiency of the energy transfer because it enables the system to sample all the potential energy pathways, with low loss, and choose the most efficient one. This claim has, however, since been proven wrong in several publications.
This approach has been further investigated by Gregory Scholes and his team at the University of Toronto, which in early 2010 published research results that indicate that some marine algae make use of quantum-coherent electronic energy transfer (EET) to enhance the efficiency of their energy harnessing. | 5 | Photochemistry |
An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium (high Mg/Ca ratio) for an aragonite sea to form. This is in contrast to a calcite sea in which seawater low in magnesium content relative to calcium (low Mg/Ca ratio) favors the formation of low-magnesium calcite as the primary inorganic marine calcium carbonate precipitate.
The Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic (including today) are characterized by aragonite seas.
Aragonite seas occur due to several factors, the most obvious of these is a high seawater Mg/Ca ratio (Mg/Ca > 2), which occurs during intervals of slow seafloor spreading. However, the sea level, temperature, and calcium carbonate saturation state of the surrounding system also determine which polymorph of calcium carbonate (aragonite, low-magnesium calcite, high-magnesium calcite) will form.
Likewise, the occurrence of calcite seas is controlled by the same suite of factors controlling aragonite seas, with the most obvious being a low seawater Mg/Ca ratio (Mg/Ca < 2), which occurs during intervals of rapid seafloor spreading. | 9 | Geochemistry |
Transacetylation uses vinyl acetate as an acetyl donor and lipase as a catalyst. This methodology allows the preparation of enantio-enriched alcohols and acetates. | 0 | Organic Chemistry |
Levoketoconazole, sold under the brand name Recorlev, is a steroidogenesis inhibitor that is used for the treatment of Cushing's syndrome. Levoketoconazole was approved for medical use in the United States in December 2021.
Levoketoconazole is the levorotatory or (2S,4R) enantiomer of ketoconazole, and it is an inhibitor of the enzymes CYP11B1 (11β-hydroxylase), CYP17A1 (17α-hydroxylase/17,20-lyase), and CYP21A2 (21-hydroxylase). It inhibits glucocorticoid biosynthesis and hence circulating levels of glucocorticoids, thereby treating Cushing's syndrome. In addition to its increased potency, the drug is 12-fold less potent than racemic ketoconazole in inhibiting CYP7A1 (cholesterol 7α-hydroxylase), theoretically resulting in further reduced interference with bile acid production and metabolite elimination and therefore less risk of hepatotoxicity. Levoketoconazole has also been found to inhibit CYP11A1 (cholesterol side-chain cleavage enzyme) and CYP51A1 (lanosterol-14α-demethylase), similarly but more potently relative to ketoconazole. | 4 | Stereochemistry |
Wood-tar creosote is to some extent used for wood preservation, but it is generally mixed with coal-tar creosote, since the former is not as effective. Commercially available preparations of "liquid smoke", marketed to add a smoked flavour to meat and aid as a preservative, consist primarily of creosote and other constituents of smoke. Creosote is the ingredient that gives liquid smoke its function; guaicol lends to the taste and the creosote oils help act as the preservative. Creosote can be destroyed by treatment with chlorine, either sodium hypochlorite, or calcium hypochlorite solutions. The phenol ring is essentially opened, and the molecule is then subject to normal digestion and normal respiration. | 7 | Physical Chemistry |
Contraindications to its use include volume-depleted patients, a history of angioedema while on an ACE inhibitor, pregnancy and hypotension.
People should not take ramipril (or any ACE inhibitors) if they have hyperkalemia. It is also recommended to avoid using salt-substitutes as this can further increase potassium levels in the blood.
Ramipril can be considered in patients with bilateral or unilateral significant renal artery stenosis (RAS). An early rise in serum creatinine above baseline is expected after initiation of therapy with Ramipril, however, monitoring serum biochemistry and renal function after initiation is crucial. Treatment with Ramipril in some patients with significant narrowing in both kidneys can increase serum creatinine concentration (measured in the blood test), which returns to baseline upon therapy cessation. | 4 | Stereochemistry |
Diethylaminosulfur trifluoride (DAST) is the organosulfur compound with the formula EtNSF. This liquid is a fluorinating reagent used for the synthesis of organofluorine compounds. The compound is colourless; older samples assume an orange colour. | 0 | Organic Chemistry |
Crystallographic image processing (CIP) is traditionally understood as being a set of key steps in the determination of the atomic structure of crystalline matter from high-resolution electron microscopy (HREM) images obtained in a transmission electron microscope (TEM) that is run in the parallel illumination mode. The term was created in the research group of [http://www.fos.su.se/~svenh/index.html Sven Hovmöller] at Stockholm University during the early 1980s and became rapidly a label for the "3D crystal structure from 2D transmission/projection images" approach. Since the late 1990s, analogous and complementary image processing techniques that are directed towards the achieving of goals with are either complementary or entirely beyond the scope of the original inception of CIP have been developed independently by members of the computational symmetry/geometry, scanning transmission electron microscopy, scanning probe microscopy communities, and applied crystallography communities. | 3 | Analytical Chemistry |
Alcohols react with acyl chlorides and acid anhydrides to give esters:
The reactions are irreversible simplifying work-up. Since acyl chlorides and acid anhydrides also react with water, anhydrous conditions are preferred. The analogous acylations of amines to give amides are less sensitive because amines are stronger nucleophiles and react more rapidly than does water. This method is employed only for laboratory-scale procedures, as it is expensive. | 0 | Organic Chemistry |
Levonorgestrel has been studied in combination with androgens such as testosterone and dihydrotestosterone as a hormonal contraceptive for men. | 4 | Stereochemistry |
The recent discovery of the reversibility of many reactions catalyzed by inverting glycosyltransferases served as a paradigm shift in the field and raises questions regarding the designation of sugar nucleotides as activated donors. | 0 | Organic Chemistry |
The discovery of the internucleosomal fragmentation of genomic DNA to regular repeating oligonucleosomal fragments generated by Ca/Mg-dependent endonuclease is accepted as one of the best-characterized biochemical markers of apoptosis (programmed cell death).
In 1970, described that cytoplasmic DNA isolated from mouse liver cells after culture was characterized by DNA fragments with a molecular weight consisting of multiples of 135 kDa. This finding was consistent with the hypothesis that these DNA fragments were a specific degradation product of nuclear DNA. In 1972, , , and coined the term apoptosis and distinguished this type of cell death from necrosis based on morphological features. In 1973, and , during the study of subchromatin structure, found that chromatin is accessible to the Ca/Mg endonuclease, resulting in the formation of a digestion product with a regular series of molecular weight similar to the one previously described by Williamson (1970). In 1974, , , and , using cells exposed to widely differing types of trauma, found that during cell death, degraded DNA in "every case had a modal value of between 10(x6) and 10(x7) Dalton and cellular metabolism is required to produce degradation of DNA". However, this observation was without indication of "whether the incision attack on the DNA molecule was a random or rather at a particular site, that have structural or functional meaning". In 1976, , , and described internucleosomal fragmentation of irradiated lymphoid chromatin DNA in vivo.
Six years passed from 1972 to 1978/1980 until the discovery and evaluation of internucleosomal fragmentation of DNA during apoptotic cell death as a hallmark of apoptosis. Since 1972 (, , and ), it is accepted that glucocorticoid-induced death of lymphocytes is a form of apoptosis. In 1978, and presented a paper revealing that glucocorticoid-induced DNA degradation in rat lymphoid tissue, thymus, and spleen occurred in a specific pattern producing fragments of DNA that were electrophoretically similar to those observed after treatment of chromatin with microccoccal nuclease, which indicated internucleosomal cleavage pattern of DNA degradation occurred during apoptosis. Thus, the first link between programmed cell death/apoptosis and internucleosomal fragmentation of chromatin DNA was discovered and soon became as a specific feature of apoptosis.
In 1980, reported additional evidence for an internucleosomal DNA cleavage pattern as a specific feature of glucocorticoid-treated thymocytes undergoing apoptosis. The internucleosomal DNA cleavage pattern was observed as a specific feature of apoptosis in 1978/1980 and has become a recognised hallmark of programmed cell death since then. In 1992 Gorczyca et al. and Gavrieli et al. independently described the DNA fragmentation assay based on the use of the terminal deoxynucleotidyl transferase (TUNEL) which become one of the standard methods to detect and identify apoptotic cells. | 1 | Biochemistry |
Sometimes the term point mutation is used to describe insertions or deletions of a single base pair (which has more of an adverse effect on the synthesized protein due to the nucleotides' still being read in triplets, but in different frames: a mutation called a frameshift mutation). | 1 | Biochemistry |
Source:
* 2024: Kelly Nguyen
* 2023: Stephen Wallace
* 2022: Tanmay A. M. Bharat
* 2021: Giulia Zanetti
* 2020: Stephan Uphoff
* 2019: Melina Schuh
* 2018: Matthew Johnson
* 2017: Markus Ralser
* 2016: David Grainger
* 2015: Helen Walden
* 2014: M. Madan Babu
* 2012: Akhilesh Reddy
* 2011: Sarah Teichmann
* 2007: Frank Sargent
* 2006: Simon J. Boulton
* 2004: James H. Naismith
* 2000: Dario Alessi
* 1999: Nigel Scrutton
* 1998: David Barford
* 1997: Stephen P. Jackson
* 1996: Sheena Radford
* 1995: Jonathon Pines
* 1993: Nicholas Tonks
* 1991: Michael A. J. Ferguson
* 1988: Hugh Pelham
* 1987: C. Peter Downes
* 1986: Greg Winter
* 1985: Alec Jeffreys
* 1981: Terence H. Rabbitts
* 1980: Richard A. Flavell
* 1979: Ronald Laskey
* 1977: Philip Cohen
* 1976: George Brownlee
* 1972: John M. Ashworth
* 1970: Dai Rees
* 1969: George Radda
* 1966: Mark Henry Richmond
* 1964: Jamshed R. Tata
* 1963: Hans Kornberg | 1 | Biochemistry |
For a monodisperse aerosol, a single number—the particle diameter—suffices to describe the size of the particles. However, more complicated particle-size distributions describe the sizes of the particles in a polydisperse aerosol. This distribution defines the relative amounts of particles, sorted according to size. One approach to defining the particle size distribution uses a list of the sizes of every particle in a sample. However, this approach proves tedious to ascertain in aerosols with millions of particles and awkward to use. Another approach splits the size range into intervals and finds the number (or proportion) of particles in each interval. These data can be presented in a histogram with the area of each bar representing the proportion of particles in that size bin, usually normalised by dividing the number of particles in a bin by the width of the interval so that the area of each bar is proportionate to the number of particles in the size range that it represents. If the width of the bins tends to zero, the frequency function is:
where
:is the diameter of the particles
: is the fraction of particles having diameters between and +
: is the frequency function
Therefore, the area under the frequency curve between two sizes a and b represents the total fraction of the particles in that size range:
It can also be formulated in terms of the total number density N:
Assuming spherical aerosol particles, the aerosol surface area per unit volume (S) is given by the second moment:
And the third moment gives the total volume concentration (V) of the particles:
The particle size distribution can be approximated. The normal distribution usually does not suitably describe particle size distributions in aerosols because of the skewness associated with a long tail of larger particles. Also for a quantity that varies over a large range, as many aerosol sizes do, the width of the distribution implies negative particles sizes, which is not physically realistic. However, the normal distribution can be suitable for some aerosols, such as test aerosols, certain pollen grains and spores.
A more widely chosen log-normal distribution gives the number frequency as:
where:
: is the standard deviation of the size distribution and
: is the arithmetic mean diameter.
The log-normal distribution has no negative values, can cover a wide range of values, and fits many observed size distributions reasonably well.
Other distributions sometimes used to characterise particle size include: the Rosin-Rammler distribution, applied to coarsely dispersed dusts and sprays; the Nukiyama–Tanasawa distribution, for sprays of extremely broad size ranges; the power function distribution, occasionally applied to atmospheric aerosols; the exponential distribution, applied to powdered materials; and for cloud droplets, the Khrgian–Mazin distribution. | 7 | Physical Chemistry |
GPC is a type of chromatography in which analytes are separated, based on their size or hydrodynamic volume (radius of gyration). This differs from other chromatographic techniques, which depend upon chemical or physical interactions between the mobile and stationary phases to separate analytes. Separation occurs via the use of porous gel beads packed inside a column (see stationary phase (chemistry)). The principle of separation relies on the differential exclusion or inclusion of the macromolecules by the porous gel stationary phase. Larger molecules are excluded from entering the pores and elute earlier, while smaller molecules can enter the pores, thus staying longer inside the column. The entire process takes place without any interaction of the analytes with the surface of the stationary phase. The smaller analytes relative to the pore sizes can permeate these pores and spend more time inside the gel particles, increasing their retention time. Conversely, larger analytes relative to the pores sizes spend little if any time inside the column, hence they elute sooner. Each type of column has a range of molecular weights that can be separated, according to their pores sizes. If an analyte is too large relative to the column's pores, it will not be retained at all and will be totally excluded; conversely, if the analyte is small relative to the pores sizes, it will be totally permeating. Analytes that are totally excluded, elute with the free volume outside around the particles (V), the total exclusion limit, while analytes that are completely delayed, elute with the solvent, marking the total permeation volume of the column, including also the solvent held inside the pores (V). The total volume can be considered by the following equation, where V is the volume of the polymer gel and V is the total volume:
As can be inferred, there is a limited range of molecular weights that can be separated by each column, therefore the size of the pores for the packing should be chosen according to the range of molecular weight of analytes to be separated. For polymer separations the pore sizes should be on the order of the polymers being analyzed. If a sample has a broad molecular weight range it may be necessary to use several GPC columns with varying pores volumes in tandem to resolve the sample fully. | 3 | Analytical Chemistry |
The Krupp-Renn process is suitable for producing pre-reduced iron ore from highly siliceous and acidic ores (CaO/SiO2 basicity index of 0.1 to 0.4), which begin generating a pasty slag at 1,200 °C. Additionally, due to the slag's acidity, it becomes vitreous, facilitating separation from the iron through easy crushing. Furthermore, this process is also ideal for treating ores with high concentrations of titanium dioxide. Due to its ability to cause slag to become especially infusible and viscous, ores that contain this oxide cannot be used with blast furnaces as they must remove all their production in liquid form. For this reason, the preferred ores for this technique are those that would become uneconomical if they had to be modified with basic additives, usually those with a low iron content (between 35 and 51%), and whose gangue needs to be neutralized.
Integrated into a steelmaking complex, the Krupp-Renn process provides an alternative to sinter plants or beneficiation processes, effectively eliminating waste rock and undesired elements like zinc, lead, and tin. Integrated into a steelmaking complex, the Krupp-Renn process provides an alternative to sinter plants or beneficiation processes, effectively eliminating waste rock and undesired elements like zinc, lead, and tin. In a blast furnace, these elements undergo vaporization-condensation cycles which progressively saturates the furnace. However, with the Krupp-Renn process, the high temperature of the fumes prevents condensation within the furnace, before they are retrieved by the dust-removal system. The process recovers by-products or extracts specific metals. The Luppen is subsequently remelted in either the blast furnace or the cupola furnace, or the Martin-Siemens furnace, because it involves melting a pre-reduced, iron-rich charge.
The process has been effective in treating ores abundant in nickel(II) oxide, vanadium, and other metals. Additionally, the process is applicable in the production of ferronickel. In this instance, saprolitic ores with a high magnesium content are as infusible as highly acidic ores, distinguishing their relevance to the process.
Direct reduction methods such as this one offer the flexibility of using any solid fuel and in this case, 240 to 300 kg of hard coal is needed to process one metric ton of iron ore that contains 30 to 40% iron. Assuming a consumption of 300 kg/ton of ore at 30%, the hard coal consumption is 800 kg per ton of iron. Additionally, 300 kg of coke is consumed during the smelting of Luppen in the blast furnace. When this ore is smelted entirely in the blast furnace, total fuel consumption remains the same. However, it only uses coke, which is a much more expensive fuel than hard coal.
However, using slags with over 60% silica content, making them acidic, contradicts metal desulfurization that demands highly basic slags. Consequently, 30% of the fuel's sulfur settles in the iron, entailing expensive after-treatments to eliminate it. | 8 | Metallurgy |
Paterson and his co-workers at the University of Cambridge have developed a strategy which utilizes novel chelation-controlled and reagent-controlled aldol reactions with high selectivity for subunit connections. Another feature of this synthesis was the induction of C(8)-C(9) olefin with cis geometry via Still-Gennari Horner-Wadsworth-Emmons reaction. The Paterson first-generation synthesis of (+)-discodermolide has an overall yield of 10.3% with a longest linear sequence of 23 steps and 42 total steps. | 0 | Organic Chemistry |
Let's assume that we understand mechanics well enough to understand and measure volume, area, mass, and force. These may be combined to understand the concept of pressure, which is force per unit area and density, which is mass per unit volume. It has been experimentally determined that, at low enough pressures and densities, all gases behave as ideal gases. The behavior of an ideal gas is given by the ideal gas law:
where P is pressure, V is volume, N is the number of particles (total mass divided by mass per particle), k is Boltzmanns constant, and T is temperature. In fact, this equation is more than a phenomenological equation, it gives an operational, or experimental, definition of temperature. A thermometer is a tool that measures temperature - a primitive thermometer would simply be a small container of an ideal gas, that was allowed to expand against atmospheric pressure. If we bring it into thermal contact with the system whose temperature we wish to measure, wait until it equilibrates, and then measure the volume of the thermometer, we will be able to calculate the temperature of the system in question via T=PV/Nk'. Hopefully, the thermometer will be small enough that it does not appreciably alter the temperature of the system it is measuring, and also that the atmospheric pressure is not affected by the expansion of the thermometer.
The ideal gas thermometer can be defined more precisely by saying it is a system containing an ideal gas, which is thermally connected to the system it is measuring, while being dynamically and materially insulated from it. It is simultaneously dynamically connected to an external pressure reservoir, from which it is materially and thermally insulated. Other thermometers (e.g. mercury thermometers, which display the volume of mercury to the observer), may now be constructed, and calibrated against the ideal gas thermometer. | 7 | Physical Chemistry |
Popular growth models include:
* KPZ equation
* Dimer model
* Eden growth model
* SOS model
*Self-avoiding walk
*Abelian sandpile model
*Kuramoto–Sivashinsky equation (or the flame equation, for studying the surface of a flame front)
They are studied for their fractal properties, scaling behavior, critical exponents, universality classes, and relations to chaos theory, dynamical system, non-equilibrium / disordered / complex systems.
Popular tools include statistical mechanics, renormalization group, rough path theory, etc. | 7 | Physical Chemistry |
Similarly to Rosetta@home, Foldit is a means to discover native protein structures faster through distributed computing. However, Foldit has a greater emphasis on community collaboration through its forums, where users can collaborate on certain folds. Furthermore, Foldits crowdsourced approach places a greater emphasis on the user. Foldits virtual interaction and gamification create a unique and innovative environment with the potential to greatly advance protein folding research. | 1 | Biochemistry |
Two vertices (or edges) of a periodic graph are symmetric if they are in the same orbit of the symmetry group of the graph; in other words, two vertices (or edges) are symmetric if there is a symmetry of the net that moves one onto the other. In chemistry, there is a tendency to refer to orbits of vertices or edges as “kinds” of vertices or edges, with the recognition that from any two vertices or any two edges (similarly oriented) of the same orbit, the geometric graph “looks the same”. Finite colorings of vertices and edges (where symmetries are to preserve colorings) may be employed.
The symmetry group of a crystal net will be a (group of restrictions of a) crystallographic space group, and many of the most common crystals are of very high symmetry, i.e. very few orbits. A crystal net is uninodal if it has one orbit of vertex (if the vertices were colored and the symmetries preserve colorings, this would require that a corresponding crystal have atoms of one element or molecular building blocks of one compound – but not vice versa, for it is possible to have a crystal of one element but with several orbits of vertices). Crystals with uninodal crystal nets include cubic diamond and some representations of quartz crystals. Uninodality corresponds with isogonality in geometry and vertex-transitivity in graph theory, and produces examples objective structures. A crystal net is binodal if it has two orbits of vertex; crystals with binodal crystal nets include boracite and anatase. It is edge-transitive or isotoxal if it has one orbit of edges; crystals with edge-transitive crystal nets include boracite but not anatase – which has two orbits of edges. | 3 | Analytical Chemistry |
*DNA sequencing
*Polymerase chain reaction
*Northern blotting
*Southern blotting
*Fusion proteins
*DNA microarray
*Bioinformatics
*Flow cytometry | 1 | Biochemistry |
There are at least ten methods of naming space groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names.
; Number: The International Union of Crystallography publishes tables of all space group types, and assigns each a unique number from 1 to 230. The numbering is arbitrary, except that groups with the same crystal system or point group are given consecutive numbers.
; Hall notation
: Space group notation with an explicit origin. Rotation, translation and axis-direction symbols are clearly separated and inversion centers are explicitly defined. The construction and format of the notation make it particularly suited to computer generation of symmetry information. For example, group number 3 has three Hall symbols: P 2y (P 1 2 1), P 2 (P 1 1 2), P 2x (P 2 1 1).
; Schönflies notation: The space groups with given point group are numbered by 1, 2, 3, ... (in the same order as their international number) and this number is added as a superscript to the Schönflies symbol for the point group. For example, groups numbers 3 to 5 whose point group is C have Schönflies symbols C, C, C.
; Coxeter notation: Spatial and point symmetry groups, represented as modifications of the pure reflectional Coxeter groups.
; Geometric notation
: A geometric algebra notation. | 4 | Stereochemistry |
Hydrazones are susceptible to hydrolysis:
Alkyl hydrazones are 10- to 10-fold more sensitive to hydrolysis than analogous oximes.
When derived from hydrazine itself, hydrazones condense with a second equivalent of a carbonyl to give azines:
Hydrazones are intermediates in the Wolff–Kishner reduction.
Hydrazones are reactants in hydrazone iodination, the Shapiro reaction, and the Bamford-Stevens reaction to vinyl compounds. Hydrazones can also be synthesized by the Japp–Klingemann reaction via β-keto acids or β-keto-esters and aryl diazonium salts. Hydrazones are converted to azines when used in the preparation of 3,5-disubstituted 1H-pyrazoles, a reaction also well known using hydrazine hydrate. With a transition metal catalyst, hydrazones can serve as organometallic reagent surrogates to react with various electrophiles. | 0 | Organic Chemistry |
Sometimes, special circuits are built for the purpose of sensing and controlling the temperature or voltage status. Devices such as thermistors, voltage-dependent resistors, thermostats and sensors such as infrared thermometers are used to modify the current upon different conditions such as circuit-temperature and input voltage. | 7 | Physical Chemistry |
Immunoglobulin-like receptors are members of the immunoglobulin superfamily and have one or more 70-110 residue immunoglobulin domains (Ig) in their extracellular region, typically multiple such domains in tandem. Many of the genes encoding these proteins occur in the leukocyte receptor complex (LRC), a large gene cluster on human chromosome 19. Members of this group found in the human genome include:
* The killer-cell immunoglobulin-like receptor (KIR) family contains proteins with 2-3 extracellular Ig domains and long (inhibitory) or short (activating) cytoplasmic regions. Typically expressed in NK and some T cells, they interact with MHC class I. This gene family located in the LRC is highly polymorphic and there is individual variation in both alleles and copy number, as well as in alternative splicing. This family has undergone significant diversification in primate lineages.
* The leukocyte immunoglobulin-like receptors (LILR) family contains 13 genes, including two pseudogenes. They have 2-4 Ig domains. One member, LILRA3, lacks a transmembrane region and is a soluble protein; others may be expressed in soluble form through alternative splicing. Like the similar KIR family, LILR genes are found in the LRC and are polymorphic, though less so than KIR. LILR proteins are broadly expressed in immune cells and have very diverse ligands.
* The paired type 2 immunoglobulin like receptor (PILR) family contains two genes, PILRA (inhibiting) and PILRB (activating). They have a single extracellular Ig domain with a siglec-like structure.
* The signal regulatory protein (SIRP) family contains three genes, SIRPA (inhibiting), SIRPB1 (activating), and SIRPG (non-signaling), with the more distantly related SIRPD and SIRPB2 not yet well characterized. SIRPA interacts with CD47, a regulator of phagocytosis. This family also interacts with surfactant protein D.
* The carcinoembryonic antigen-related cell adhesion (CEACAM) family contains 12 genes with one or more Ig domains. They are expressed broadly, especially in endothelium and epithelium and have roles in cell-cell recognition. They have been extensively studied for their role in cancer and have been used as cancer biomarkers.
* The siglec family contains 15 genes divided into two evolutionarily related groups. This family has three members with activating motifs, Siglec-14, Siglec-15, and Siglec-16. These proteins bind sialic acids, and are often targeted by pathogens.
* TIGIT (T cell immunoreceptor with Ig and ITIM domains) is an inhibitory receptor that forms a nonhomologous but functional pair with DNAM1 (CD226). | 1 | Biochemistry |
The Sommerfeld–Kossel displacement law states that the first spark (singly ionized) spectrum of an element is similar in all details to the arc (neutral) spectrum of the element preceding it in the periodic table. Likewise, the second (doubly ionized) spark spectrum of an element is similar in all details to the first (singly ionized) spark spectrum of the element preceding it, or to the arc (neutral) spectrum of the element with atomic number two less, and so forth.
Hence, the spectra of C I (neutral carbon), N II (singly ionized nitrogen), and O III (doubly ionized oxygen) atoms are similar, apart from shifts of the spectra to shorter wavelengths. C I, N II, and O III all have the same number of electrons, six, and the same ground-state electron configuration:
The law was discovered by and named after Arnold Sommerfeld and Walther Kossel, who set it forth in a paper submitted to Verhandungen der Deutschen Physikalischen Gesellschaft in early 1919. | 7 | Physical Chemistry |
Nickel–cadmium batteries (Ni-Cd) use nickel oxide hydroxide and metallic cadmium electrodes with an electrolyte of potassium hydroxide. Sealed Ni-Cd batteries were widely used in photography equipment, handheld power tools, and radio-controlled toys from the early 1940s until the early 1990s, when nickel–metal hydride batteries supplanted them (like how alkaline batteries replaced zinc–carbon batteries). In personal computers, Ni-Cd batteries first saw use in the mid-1980s as a cheaper alternative to lithium batteries for powering real-time clocks and preserving BIOS settings. Nickel–cadmium batteries were also briefly used in laptop battery packs, until the advent of commercially viable nickel–metal hydride batteries in the early 1990s. Ni-Cd batteries are still used in some uninterruptible power supplies and emergency lighting setups.
Except in aeronautical or other high-risk applications, Ni-Cd batteries are intentionally not hermetically sealed and include pressure vents for safety if the batteries are charged improperly. With age and sufficient thermal cycles the seal will degrade and allow electrolyte to leak through. The leakage usually travels down the positive and/or negative terminals onto any surrounding circuitry (see the top image).
Like with alkaline battery leakage, Ni-Cd leakage can be effectively neutralized with lemon juice or distilled white vinegar. | 8 | Metallurgy |
Along with several other NSAIDs, chronic ibuprofen use has been found correlated with risk of progression to hypertension in women, though less than for paracetamol (acetaminophen), and myocardial infarction (heart attack), particularly among those chronically using higher doses. On 9 July 2015, the US FDA toughened warnings of increased heart attack and stroke risk associated with ibuprofen and related NSAIDs; the NSAID aspirin is not included in this warning. The European Medicines Agency (EMA) issued similar warnings in 2015. | 4 | Stereochemistry |
siRNAs act in the nucleus and the cytoplasm and are involved in RNAi as well as CDGS. siRNAs come from long dsRNA precursors derived from a variety of single-stranded RNA (ssRNA) precursors, such as sense and antisense RNAs. siRNAs also come from hairpin RNAs derived from transcription of inverted repeat regions. siRNAs may also arise enzymatically from non-coding RNA precursors. The volume of literature on siRNA within the framework of RNAi is extensive. One of the potent applications of siRNAs is the ability to distinguish the target versus non-target sequence with a single-nucleotide difference. This approach has been considered as therapeutically crucial for the silencing dominant gain-of-function (GOF) disorders,where mutant allele causing disease is differed from wt-allele by a single nucleotide (nt). This type of siRNAs with capability to distinguish a single-nt difference are termed as allele-specific siRNAs. | 1 | Biochemistry |
Due to its ease of operation and its usefulness in polishing irregularly-shaped objects, electropolishing has become a common process in the production of semiconductors.
As electropolishing can also be used to sterilize workpieces, the process plays an essential role in the food, medical, and pharmaceutical industries.
It is commonly used in the post-production of large metal pieces such as those used in drums of washing machines, bodies of ocean vessels and aircraft, and automobiles.
While nearly any metal may be electropolished, the most-commonly polished metals are 300- and 400-series stainless steel, aluminum, copper, titanium, and nickel- and copper-alloys.
Ultra-high vacuum (UHV) components are typically electropolished in order to have a smoother surface for improved vacuum pressures, out-gassing rates, and pumping speed.
Electropolishing is commonly used to prepare thin metal samples for transmission electron microscopy and atom probe tomography because the process does not mechanically deform surface layers like mechanical polishing does. | 8 | Metallurgy |
The Ripper Method is commonly used in wine making applications as SO is often added to wine to maintain its freshness and the concentration needs to be determined. The technique is not precise and is prone to systematic error as well. This limits its use, despite being a fast and inexpensive test. | 3 | Analytical Chemistry |
Carbohydrates have four major functions within the body:
# Energy supply, particularly for the brain in the form of glucose
# Avoiding the breakdown of amino acids for energy
# Avoiding ketosis from the breakdown of fatty acids
# Cellular and protein recognition | 0 | Organic Chemistry |
The dihydroxyacetone (DHA) pathway, also known as the xylulose monophosphate (XuMP) pathway, is found exclusively in yeast. This pathway assimilates three molecules of formaldehyde into 1 molecule of DHAP using 3 molecules of xylulose 5-phosphate as the key intermediate.
DHA synthase acts as a transferase (transketolase) to transfer part of xylulose 5-phosphate to DHA. Then these 3 molecules of DHA are phosphorylated to DHAP by triokinase. Like the other cycles, 3 molecules are produced with 1 molecule being directed for use as cell material. The other 2 molecules are used to regenerate xylulose 5-phosphate. | 0 | Organic Chemistry |
Despite, or possibly because of, its long-known toxicity, arsenic-containing potions and drugs have a history in medicine and quackery that continues into the 21st century. Starting in the early 19th century and continuing into the 20th century, Fowler's solution, a toxic concoction of sodium arsenite, was sold. The organoarsenic compound Salvarsan was the first synthetic chemotherapeutic agent, discovered by Paul Ehrlich. The treatment, however, led to many problems causing long lasting health complications. Around 1943 it was finally superseded by penicillin.
The related drug Melarsoprol is still in use against late-state African trypanosomiasis (sleeping sickness), despite its high toxicity and possibly fatal side effects.
Arsenic trioxide (AsO) inhibits cell growth and induces apoptosis (programmed cell death) in certain types of cancer cells, which are normally immortal and can multiply without limit. In combination with all-trans retinoic acid, it is FDA-approved as first-line treatment for promyelocytic leukemia. | 1 | Biochemistry |
ISO 7027:1999 is an ISO standard for water quality that enables the determination of turbidity. The ISO 7027 technique is used to determine the concentration of suspended particles in a sample of water by measuring the incident light scattered at right angles from the sample. The scattered light is captured by a photodiode, which produces an electronic signal that is converted to a turbidity. | 3 | Analytical Chemistry |
In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (E) of a reaction is measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). Activation energy can be thought of as the magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy. The term "activation energy" was introduced in 1889 by the Swedish scientist Svante Arrhenius. | 7 | Physical Chemistry |
IRsweep is a Swiss company offering optical spectroscopy solutions and multipass absorption cells.
The spectroscopy is based on semiconductor quantum cascade laser frequency combs
in the mid-infrared wavelength range. The company is based in Zurich, Switzerland and was founded in 2014 and acquired by Sensirion Holding in May 2021.
The technology is used for high speed absorption measurements of different molecules and is robust against cross-sensitivities. Such sensor systems are in high demand for process analytics as well as research applications, as the mid-infrared range hosts the strongest absorption features of many molecules. | 7 | Physical Chemistry |
The analogy applies to other shapes besides tetrahedral and octahedral geometries. The derivations used in octahedral geometry are valid for most other geometries. The exception is square-planar because square-planar complexes typically abide by the 16-electron rule. Assuming ligands act as two-electron donors the metal center in square-planar molecules is d. To relate an octahedral fragment, ML, where M has a d electron configuration to a square planar analogous fragment, the formula ML where M has a d electron configuration should be followed.
Further examples of the isolobal analogy in various shapes and forms are shown in figure 8. | 0 | Organic Chemistry |
The TRH test involves administration of a small amount of TRH intravenously, following which levels of TSH will be measured at several subsequent time points using samples of blood taken from a peripheral vein.
The test is used in the differential diagnosis of secondary and tertiary hypothyroidism. First, blood is drawn and a baseline TSH level is measured. Then, TRH is administered via a vein. After 30 minutes blood is drawn again and the levels of TSH are measured and compared to the baseline. Some authors recommend additional blood sampling at 15 minutes. In children, late blood sampling at 60 to 120 minutes is necessary.
An increase in the serum TSH level following TRH administration means that the cause of the hypothyroidism is in the hypothalamus (tertiary hypothyroidism), i.e. the hypothalamus is not producing TRH. Therefore, when TRH is given exogenously, TSH levels increase. If the increase in serum TSH level following TRH administration is absent or very slight, then the cause of the hypothyroidism is in the anterior pituitary gland, i.e. the pituitary is not secreting TSH. Therefore, even when TRH is given exogenously, TSH levels do not rise as the pituitary is diseased. | 1 | Biochemistry |
The growth (starting materials, flux, and crucible) are heated to form a complete liquid solution. The growth is cooled to a temperature where the solution is fully saturated. Further cooling causes crystals to precipitate from the solution, lowering the concentration of starting materials in solution, and lowering the temperature where the solution is fully saturated. The process is repeated, decreasing temperature and precipitating more crystals. The process is then stopped at a desired temperature, and the growth is removed from the furnace. Practically, the flux method is done by placing the growth into a programmable furnace:
# Ramp - The furnace is heated from an initial temperature to a maximum temperature, where the growth forms a complete liquid solution.
# Dwell - The furnace is maintained at the maximum temperature to homogenize the solution.
# Cool - The furnace is cooled to a desired temperature over a specified rate or time.
# Removal - The growth is removed from the furnace. The growth can be quenched, centrifuged, or simply removed if already at room temperature.
Additional steps may be added to this basic temperature profile, such as additional dwells or different cooling rates over different points of the cool. Crystallization can occur through spontaneous nucleation, encouragement with a seed, or through mechanical stress. | 3 | Analytical Chemistry |
Mitochondrial respirometry is used to study mitochondrial functionality in
mitochondrial diseases or diseases with a (suspected) strong link to mitochondria, e.g. diabetes mellitus type 2, obesity and cancer. Other fields of application are e.g. sports science and the connection between mitochondrial function and aging. | 1 | Biochemistry |
The General Meeting of the Association is the ultimate authority in the Association. A delegate of each ECCA member company is appointed to participate in and vote at the General Meeting of the Association.
The Executive Committee comprises the President, the immediate Past-President, the Vice-President, the Marketing Committee, the Technical Committee, the Environment and Sustainability Committee chairs and the Managing Director of the Association.
The Board of Directors includes the members of the Executive Committee plus some other members elected by the General Meeting. In 2013, there are 16 Board members.
The Head office is responsible for the day-to-day management of the Association. 4 staff members are working on a full-time basis (in 2013).
ECCA is also nationally represented in France, Germany, the UK, Italy, the Netherlands, and Nordic Countries. | 8 | Metallurgy |
In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure. Anil refers to a common subset of Schiff bases: imines derived from anilines. The term can be synonymous with azomethine which refers specifically to secondary aldimines (i.e. where R' ≠ H). | 0 | Organic Chemistry |
ATSDR works closely with communities to evaluate the public health effects related to redevelopment of brownfields properties. These are sites that were formerly used for industrial purposes and may still be contaminated with hazardous substances. ATSDR has worked at more than 400 brownfield or land reuse sites to assess health effects of potential exposure to hazardous substances. The agency has created resources to provide guidance to communities when planning redevelopment projects, including tools to evaluate the potential threat of chemicals at development sites. In addition to evaluating the health effects of contamination at specific brownfield sites, ATSDR encourages communities to monitor community health. One of the agency's brownfields projects was the Menomonee Valley in Milwaukee, Wisconsin, where the agency evaluated potential health effects of contamination at the site and worked closely with developers and the city. | 1 | Biochemistry |
In this section of the Holton Taxol synthesis (Scheme 4), the oxetane D ring was completed and ring B was functionalized with the correct substituents. Allylic alcohol 34, obtained from deprotection of silyl enol ether 33 with hydrofluoric acid, was oxidized with osmium tetroxide in pyridine to give triol 35. After protection of the primary hydroxyl group, the secondary hydroxyl group in 36 was converted to a good leaving group using p-toluenesulfonyl chloride. Subsequent deprotection of the trimethylsilyl ether 37 gave tosylate 38, which underwent cyclization to give oxetane 39 by nucleophilic displacement of the tosylate that occurred with inversion of configuration. The remaining unprotected tertiary alcohol was acylated, and the triethylsilyl group was removed to give allylic alcohol 41. The carbonate ester was cleaved by reaction with phenyllithium in tetrahydrofuran at -78 °C to give alcohol 42. The unprotected secondary alcohol was oxidized to ketone 43 using tetrapropylammonium perruthenate (TPAP) and N-methylmorpholine N-oxide (NMO). This ketone was deprotonated with potassium tert-butoxide in tetrahydrofuran at low temperature and further oxidized by reaction with benzeneseleninic anhydride to give α-hydroxyketone 44. Further treatment of 44 with potassium tert-butoxide furnished α-hydroxyketone 45 through a Lobry-de Bruyn-van Ekenstein Rearrangement. Substrate 45 was subsequently acylated to give α-acetoxyketone 46. | 0 | Organic Chemistry |
In addition to the method of proton extrusion discussed above, it is believed that the general method of cellular respiration is different in obligate alkaliphiles as compared to neutrophiles. Generally, ATP production operates by establishing a proton gradient (greater H+ concentration outside the membrane) and a transmembrane electrical potential (with a positive charge outside the membrane). However, since alkaliphiles have a reversed pH gradient, it would seem that ATP production—which is based on a strong proton-motive force – would be severely reduced. However, the opposite is true. It has been proposed that while the pH gradient has been reversed, the transmembrane electrical potential is greatly increased. This increase in charge causes the production of greater amounts of ATP by each translocated proton when driven through an ATPase. Research in this area is ongoing. | 1 | Biochemistry |
pHydrion is the trademarked name for a popular line of chemical test products, marketed by Micro Essential Laboratory, Inc., the original manufacturer of Hydrion and pHydrion products. The trademarked pHydrion product line comprises chemical test papers, chemical indicators, chemical test kits, chemical indicator kits, pH indicator pencils, chemical buffers, buffer salts, buffer preservatives, dispensers, color charts, and testing products, for use in testing, detecting, identifying, measuring, and indicating levels of pH, of sanitizers, and of other substances. | 3 | Analytical Chemistry |
Adrenal androgen stimulating hormone (AASH), also known as cortical androgen stimulating hormone (CASH), is a hypothetical hormone which has been proposed to stimulate the adrenal glands to produce adrenal androgens such as dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and androstenedione (A4). It is hypothesized to be involved in adrenarche and adrenopause. The existence of this hormone is controversial and disputed and it has not been identified to date. A number of other mechanisms and/or hormones may instead play the functional role of the so-called AASH. | 1 | Biochemistry |
The simplest forge, known as the Corsican, was used prior to the advent of Christianity. Examples of improved bloomeries are the Stuckofen, sometimes called wolf-furnace,) which remained until the beginning of the 19th century. Instead of using natural draught, air was pumped in by a trompe, resulting in better quality iron and an increased capacity. This pumping of air in with bellows is known as cold blast, and it increases the fuel efficiency of the bloomery and improves yield. They can also be built bigger than natural draught bloomeries. | 8 | Metallurgy |
In chemistry, binding selectivity is defined with respect to the binding of ligands to a substrate forming a complex. Binding selectivity describes how a ligand may bind more preferentially to one receptor than another. A selectivity coefficient is the equilibrium constant for the reaction of displacement by one ligand of another ligand in a complex with the substrate. Binding selectivity is of major importance in biochemistry and in chemical separation processes. | 7 | Physical Chemistry |
The vast majority of genetically modified animals are at the research stage with the number close to entering the market remaining small. As of 2018 only three genetically modified animals have been approved, all in the USA. A goat and a chicken have been engineered to produce medicines and a salmon has increased its own growth. Despite the differences and difficulties in modifying them, the end aims are much the same as for plants. GM animals are created for research purposes, production of industrial or therapeutic products, agricultural uses, or improving their health. There is also a market for creating genetically modified pets. | 1 | Biochemistry |
Greek prefixes in alphabetical order indicate ring size.
This ring-size nomenclature stems from the fact that hydrolysis of an α-lactam gives an α-amino acid and that of a β-Lactam gives a β-amino acid, and so on. | 0 | Organic Chemistry |
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