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Alcohols () take the suffix "-ol" with a numerical suffix indicating the bonding position: is propan-1-ol. The suffixes , , , etc., are used for multiple groups: Ethylene glycol is ethane-1,2-diol.
If higher precedence functional groups are present (see order of precedence, below), the prefix "hydroxy" is used with the bonding position: is 2-hydroxypropanoic acid. | 0 | Organic Chemistry |
Bottromycins contain a C-terminal decarboxylated thiazole in addition to a macrocyclic amidine.
There are currently six known bottromycin compounds, which differ in the extent of side chain methylation, an additional characteristic of the bottromycin class. The total synthesis of bottromycin A2 was required to definitively determine the structure of the first bottromycin.
Thus far, gene clusters predicted to produce bottromycins have been identified in the genus Streptomyces. Bottromycins differ from other RiPPs in that there is no N-terminal leader peptide. Rather, the precursor peptide has a C-terminal extension of 35-37 amino acids, hypothesized to act as a recognition sequence for posttranslational machinery. | 1 | Biochemistry |
A common 1,4-dithiol is dithiothreitol (DTT), HSCHCH(OH)CH(OH)CHSH, sometimes called Cleland's reagent, for to reduce protein disulfide bonds. Oxidation of DTT results a stable six-membered heterocyclic ring with an internal disulfide bond. | 0 | Organic Chemistry |
The punkah (fan) was used in India about 500 BCE. It was a handheld fan made from bamboo strips or other plant fiber, that could be rotated or fanned to move air. During British rule, the word came to be used by Anglo-Indians to mean a large swinging flat fan, fixed to the ceiling and pulled by a servant called the punkawallah.
For purposes of air conditioning, the Han dynasty craftsman and engineer Ding Huan (fl. 180 CE) invented a manually operated rotary fan with seven wheels that measured 3 m (10 ft) in diameter; in the 8th century, during the Tang dynasty (618–907), the Chinese applied hydraulic power to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the Song dynasty (960–1279).
During the Heian period (794-1185) in Japan, fans adapted the role of symbolizing social class as well as a mechanical role. The tessen, a Japanese fan used in Feudal times, was a dangerous weapon hidden in plain sight in the shape of a regular fan, a weapon used by samurais when katanas were not ideal.
In the 17th century, the experiments of scientists including Otto von Guericke, Robert Hooke and Robert Boyle, established the basic principles of vacuum and airflow. The English architect Sir Christopher Wren applied an early ventilation system in the Houses of Parliament that used bellows to circulate air. Wren's design was the catalyst for much later improvement and innovation. The first rotary fan used in Europe was for mine ventilation during the 16th century, as illustrated by Georg Agricola (1494–1555).
John Theophilus Desaguliers, a British engineer, demonstrated the successful use of a fan system to draw out stagnant air from coal mines in 1727—ventilation was particularly important in coal mines to prevent asphyxiation—and soon afterwards he installed a similar apparatus in Parliament. The civil engineer John Smeaton, and later John Buddle installed reciprocating air pumps in the mines in the North of England, though the machinery was liable to breaking down. | 7 | Physical Chemistry |
Fibrous proteins, such as proteins involved in Alzheimer's disease and prion proteins fulfil the requirements for UV LD in that they are a class of long, thin molecules. In addition, cytoskeletal proteins can also be measured using LD. | 7 | Physical Chemistry |
Chemical messengers bind to metabotropic receptors to initiate a diversity of effects caused by biochemical signaling cascades. G protein-coupled receptors are all metabotropic receptors. When a ligand binds to a G protein-coupled receptor, a guanine nucleotide-binding protein, or G protein, activates a second messenger cascade which can alter gene transcription, regulate other proteins in the cell, release intracellular Ca, or directly affect ion channels on the membrane. These receptors can remain open from seconds to minutes and are associated with long-lasting effects, such as modifying synaptic strength and modulating short- and long-term synaptic plasticity.
Metabotropic receptors have a diversity of ligands, including but not limited to: small molecule transmitters, monoamines, peptides, hormones, and even gases. In comparison to fast-acting neurotransmitters, these ligands are not taken up again or degraded quickly. They can also enter the circulatory system to globalize a signal. Most metabotropic ligands have unique receptors. Some examples include: metabotropic glutamate receptors, muscarinic acetylcholine receptors, GABA receptors. | 1 | Biochemistry |
The word hydrolysis is applied to chemical reactions in which a substance reacts with water. In organic chemistry, the products of the reaction are usually molecular, being formed by combination with H and OH groups (e.g., hydrolysis of an ester to an alcohol and a carboxylic acid). In inorganic chemistry, the word most often applies to cations forming soluble hydroxide or oxide complexes with, in some cases, the formation of hydroxide and oxide precipitates. | 7 | Physical Chemistry |
Mycoestrogens and their metabolites are largely excreted in urine in humans and in feces in other animal systems. | 1 | Biochemistry |
The first computational model of dendritic solidification was published by Kobayashi, who used a phase-field model to solve two coupled partial differential equations describing the evolution of the phase-field, (with in the liquid phase and in the solid phase), and the temperature field, , for a pure material in two dimensions:
which is an Allen-Cahn equation with an anisotropic gradient energy coefficient:
where is an average value of , is the angle between the interface normal and the x-axis, and and are constants representing the strength and mode of anisotropy, respectively.
The parameter describes the thermodynamic driving force for solidification, which Kobayashi defines for a supercooled melt as:
where is a constant between 0 and 1, is a positive constant, and is the dimensionless equilibrium temperature. The temperature has been non-dimensionalized such that the equilibrium temperature is and the initial temperature of the undercooled melt is .
The evolution equation for the temperature field is given by
and is simply the heat equation with a source term due to the evolution of latent heat upon solidification, where is a constant representing the latent heat normalized by the strength of the cooling.
When this system is numerically evolved, random noise representing thermal fluctuations is introduced to the interface via the term, where is the magnitude of the noise and is a random number distributed uniformly on . | 8 | Metallurgy |
Inverting enzymes utilize two enzymic residues, typically carboxylate residues, that act as acid and base respectively, as shown below for a β-glucosidase.
The product of the reaction has an axial position on C1, but some spontaneous changes of conformation can appear. | 0 | Organic Chemistry |
Hazards posed by titanium tetrachloride generally arise from its reaction with water that releases hydrochloric acid, which is severely corrosive itself and whose vapors are also extremely irritating. is a strong Lewis acid, which exothermically forms adducts with even weak bases such as THF and water. | 0 | Organic Chemistry |
Electro sinter forging is an electric current assisted sintering (ECAS) technology originated from capacitor discharge sintering. It is used for the production of diamond metal matrix composites and is under evaluation for the production of hard metals, nitinol and other metals and intermetallics. It is characterized by a very low sintering time, allowing machines to sinter at the same speed as a compaction press. | 8 | Metallurgy |
Supercritical carbon dioxide is also emerging as a useful high-temperature refrigerant, being used in new, CFC/HFC-free domestic heat pumps making use of the transcritical cycle. These systems are undergoing continuous development with supercritical carbon dioxide heat pumps already being successfully marketed in Asia. The EcoCute systems from Japan are some of the first commercially successful high-temperature domestic water heat pumps. | 7 | Physical Chemistry |
The seasonal harvesting of snow and ice is an ancient practice estimated to have begun earlier than 1000 BC. A Chinese collection of lyrics from this time period known as the Sleaping, describes religious ceremonies for filling and emptying ice cellars. However, little is known about the construction of these ice cellars or the purpose of the ice. The next ancient society to record the harvesting of ice may have been the Jews in the book of Proverbs, which reads, "As the cold of snow in the time of harvest, so is a faithful messenger to them who sent him." Historians have interpreted this to mean that the Jews used ice to cool beverages rather than to preserve food. Other ancient cultures such as the Greeks and the Romans dug large snow pits insulated with grass, chaff, or branches of trees as cold storage. Like the Jews, the Greeks and Romans did not use ice and snow to preserve food, but primarily as a means to cool beverages. Egyptians cooled water by evaporation in shallow earthen jars on the roofs of their houses at night. The ancient people of India used this same concept to produce ice. The Persians stored ice in a pit called a Yakhchal and may have been the first group of people to use cold storage to preserve food. In the Australian outback before a reliable electricity supply was available many farmers used a Coolgardie safe, consisting of a room with hessian (burlap) curtains hanging from the ceiling soaked in water. The water would evaporate and thereby cool the room, allowing many perishables such as fruit, butter, and cured meats to be kept. | 7 | Physical Chemistry |
Other oxygenates are available as additives for gasoline including ethanol and other ethers such as ETBE.
Ethanol has been advertised as a safe alternative by agricultural and other interest groups in the U.S. and Europe. In 2003, California was the first U.S. state to start replacing MTBE with ethanol.
An alternative to ethanol is ETBE, which is manufactured from ethanol and isobutene. Its performance as an additive is similar to MTBE, but due to the higher price of ethanol compared to methanol, it is more expensive.
Higher quality gasoline is also an alternative, so that additives such as MTBE are unnecessary. Iso-octane itself is used. MTBE plants can be retrofitted to produce iso-octane from isobutylene. | 2 | Environmental Chemistry |
For a d-dimensional system, the ideal gas pressure is:
where is the volume of the d-dimensional domain in which the gas exists. The dimensions of the pressure changes with dimensionality. | 7 | Physical Chemistry |
Small impurity interstitial atoms are usually on true interstitial sites between the lattice atoms. Large impurity interstitials can also be in split interstitial configurations together with a lattice atom, similar to those of the self-interstitial atom. | 8 | Metallurgy |
Ferrouranium, also called ferro-uranium, is a ferroalloy, an alloy of iron and uranium, after World War II usually depleted uranium. | 8 | Metallurgy |
Cells are the foundation of all organisms and are the fundamental units of life. The growth and development of cells are essential for the maintenance of the host and survival of the organism. For this process, the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, and cell death.
The cell cycle is divided into four distinct phases: G1, S, G2, and M. The G phase – which is the cell growth phase – makes up approximately 95% of the cycle. The proliferation of cells is instigated by progenitors. All cells start out in an identical form and can essentially become any type of cells. Cell signaling such as induction can influence nearby cells to determinate the type of cell it will become. Moreover, this allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems. The G1, G2, and S phase (DNA replication, damage and repair) are considered to be the interphase portion of the cycle, while the M phase (mitosis) is the cell division portion of the cycle. Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively. The ultimate result of mitosis is the formation of two identical daughter cells.
The cell cycle is regulated in cell cycle checkpoints, by a series of signaling factors and complexes such as cyclins, cyclin-dependent kinase, and p53. When the cell has completed its growth process and if it is found to be damaged or altered, it undergoes cell death, either by apoptosis or necrosis, to eliminate the threat it can cause to the organism's survival. | 1 | Biochemistry |
In recent research that builds on his work in polymerisation, Gilbert has developed a new way of understanding the biochemistry of the enzymatic processes involved in starch biosynthesis, in collaboration with Dr Melissa Fitzgerald, International Rice Research Institute, Manilla. In this new field, he applied the methods he had developed for understanding molecular-weight distributions in synthetic polymers to understanding those of natural ones. He has thus created a powerful new technique for probing the enzymatic processes in starch biosynthesis in grains, again, creating a methodology to obtain reliable mechanistic knowledge by isolating steps in highly complex systems. Each enzymatic step that creates individual chains—analysed by debranching the starch—can now be associated with particular regions in the molecular-weight distribution of a starch. This supported the applicability of one of two rival mechanistic postulates made by starch biochemists. | 0 | Organic Chemistry |
Fluorine is the thirteenth most common element in Earth's crust, comprising between 600 and 700 ppm of the crust by mass. Because of its reactivity, it is essentially only found in compounds. | 9 | Geochemistry |
Quartz crystal microbalance (QCM) is an acoustic sensor built around a disk shaped quartz crystal. It makes use of the converse piezoelectric effect. QCM, and extended versions such as QCM-D, has been widely used for protein adsorption studies, especially, real time monitoring of label-free protein adsorption. In addition to the adsorption studies, QCM-D also provides information regarding elastic moduli, viscosity, and conformational changes | 1 | Biochemistry |
Anaplerotic reactions, a term coined by Hans Kornberg and originating from the Greek [http://en.wiktionary.org/wiki/%E1%BC%80%CE%BD%CE%AC#Ancient_Greek ἀνά]= up and [http://en.wiktionary.org/wiki/%CF%80%CE%BB%CE%B7%CF%81%CF%8C%CF%89 πληρόω]= to fill, are chemical reactions that form intermediates of a metabolic pathway. Examples of such are found in the citric acid cycle (TCA cycle). In normal function of this cycle for respiration, concentrations of TCA intermediates remain constant; however, many biosynthetic reactions also use these molecules as a substrate. Anaplerosis is the act of replenishing TCA cycle intermediates that have been extracted for biosynthesis (in what are called anaplerotic reactions).
The TCA cycle is a hub of metabolism, with central importance in both energy production and biosynthesis. Therefore, it is crucial for the cell to regulate concentrations of TCA cycle metabolites in the mitochondria. Anaplerotic flux must balance cataplerotic flux in order to retain homeostasis of cellular metabolism. | 1 | Biochemistry |
In the 1930s, USSR geochemist Alexander Fersman defined the relative abundance of chemical elements in geological objects, denoted in percents, as . This was in honor to the American geochemist Frank Wigglesworth Clarke, who pioneered in estimating the chemical composition of Earths crust, based on Clarke and colleagues extensive chemical analysis of numerous rock samples, throughout 1889 to 1924().
Examples based on Fersman's definition:
* : When the whole mass of a planet X is , and the mass of oxygen there is , then the weight clarke of oxygen in planet X is (dimensionless)
* : When the whole count of atoms in a rock Y is , and the atom count of silicon there is , then silicon's clarke of atom count in rock Y is (dimensionless)
* Fersmans "clarke of Earths crust" is the Earth's surface including 16 km-thick lithosphere, hydrosphere and atmosphere. | 9 | Geochemistry |
In general, igneous, metamorphic and sedimentary processes do not appear to strongly fractionate Cu isotopes, while δCu values of Cu minerals vary widely. The average Cu isotopic composition of bulk silicate Earth has been measured as 0.06 ± 0.20‰ based on 132 different terrestrial samples. MORBs and oceanic island basalts (OIBs) generally have homogenous Cu isotopic compositions that fall around 0‰, while arc and continental basalts have more heterogeneous Cu isotope compositions that range from -0.19 to +0.47‰. These Cu isotope ratios of basalts suggest that mantle partial melting imparts negligible Cu isotopic fractionation, while recycling of crustal materials leads to widely variable δCu values. The Cu isotope compositions of copper-containing minerals vary over a wide range, likely due to alteration of the primary high-temperature deposits. In one study that investigated Cu isotopic compositions of various minerals from hydrothermal fields along the mid-Atlantic ridge, chalcopyrite from mafic igneous rocks had δCu values of -0.1 to -0.2‰, while Cu minerals in black smokers (chalcopyrite, bornite, covellite and atacamite) exhibited a wider range of δCu values from -1.0 to +4.0‰. Additionally, atacamite lining the outer rims of black smokers can be up to 2.5‰ heavier than chalcopyrite contained within the black smoker. δCu values of Cu minerals (including chrysocolle, azurite, malachite, cuprite and native copper) in low-temperature deposits have been observed to vary widely over a range of -3.0 to +5.6‰. | 9 | Geochemistry |
Combining the well-known formula for the Gibbs free energy of reaction
where is the entropy of the system, with the Gibbs free energy isotherm equation:
we obtain
Differentiation of this expression with respect to the variable while assuming that both and are independent of yields the Van 't Hoff equation. These assumptions are expected to break down somewhat for large temperature variations.
Provided that and are constant, the preceding equation gives as a linear function of and hence is known as the linear form of the Van 't Hoff equation. Therefore, when the range in temperature is small enough that the standard reaction enthalpy and reaction entropy are essentially constant, a plot of the natural logarithm of the equilibrium constant versus the reciprocal temperature gives a straight line. The slope of the line may be multiplied by the gas constant to obtain the standard enthalpy change of the reaction, and the intercept may be multiplied by to obtain the standard entropy change. | 7 | Physical Chemistry |
The specific weight, , of a material is defined as the product of its density, , and the standard gravity, :
The density of the material is defined as mass per unit volume, typically measured in kg/m. The standard gravity is acceleration due to gravity, usually given in m/s, and on Earth usually taken as .
Unlike density, specific weight is not a fixed property of a material. It depends on the value of the gravitational acceleration, which varies with location. Pressure may also affect values, depending upon the bulk modulus of the material, but generally, at moderate pressures, has a less significant effect than the other factors. | 7 | Physical Chemistry |
The Edmond–Ogston model is a thermodynamic model proposed by Elizabeth Edmond and Alexander George Ogston in 1968 to describe phase separation of two-component polymer mixtures in a common solvent. At the core of the model is an expression for the Helmholtz free energy
that takes into account terms in the concentration of the polymers up to second order, and needs three virial coefficients and as input. Here is the molar concentration of polymer , is the universal gas constant, is the absolute temperature, is the system volume. It is possible to obtain explicit solutions for the coordinates of the critical point
where represents the slope of the binodal and spinodal in the critical point. Its value can be obtained by solving a third order polynomial in ,
which can be done analytically using Cardano's method and choosing the solution for which both and are positive.
The spinodal can be expressed analytically too, and the Lambert W function has a central role to express the coordinates of binodal and tie-lines.
The model is closely related to the Flory–Huggins model. | 7 | Physical Chemistry |
Anomers are diastereoisomers of glycosides, hemiacetals or related cyclic forms of sugars, or related molecules differing in configuration only at C-1. When the stereochemistry of the first carbon matches the stereochemistry of the last stereogenic center the sugar is the α-anomer when they are opposite the sugar is the β-anomer. | 0 | Organic Chemistry |
It typically has a strong maximum at the minimal number of photons to ionize the system, with successive peaks (known as ATI peaks) separated by the photon energy and thus corresponding to higher numbers of photons being absorbed.
In the non-perturbative regime the bound states are dressed with the electric field, shifting the ionization energy. If the ponderomotive energy of the field is greater than the photon energy , then the first peak disappears. | 7 | Physical Chemistry |
Terminal epoxides suffer from the limitation that competitive nucleophilic addition of the base to the unsubstituted epoxide carbon may take place. Non-nucleophilic, sterically hindered bases have been used to isomerize terminal epoxides successfully, however.
Acyclic disubstituted epoxides undergo deprotonation at the least substituted site (unless a conjugated double bond can be formed; see equation (9) below) with high selectivity for trans double bonds.
Five- and six-membered rings containing epoxides afford allylic alcohols upon treatment with amide bases; however, reactions of medium-ring epoxides may be complicated by competitive transannular C–H insertion or ketone formation.
Trisubstituted epoxides do not easily undergo metalation in the ring. As a result, allylic alcohols are formed from these substrates without competitive carbenoid transformations. The use of bulky aluminum amide bases facilitates elimination at the substituent cis to hydrogen, which occurs from the less sterically hindered epoxide-base complex.
Suitably substituted unsaturated epoxides may undergo vinylogous elimination, which leads to conjugated allylic alcohols. Substituted vinyl epoxides undergo 1,4-elimination in some but not all cases; however, epoxides with β unsaturation eliminate cleanly to give conjugated allylic alcohols. | 0 | Organic Chemistry |
The microscope setup is based on an inverted microscope design. An automated stage is used to record larger areas by mosaicing a series of single adjacent frames. The LED light is focused using a ball lens with a short focal length onto the sample surface in an oblique-angle cis-illumination scheme since standard microscopy optics do not transmit UV light efficiently. No dichroic mirror or filter is required as microscope objectives are opaque to UV excitation light. The emitted fluorescence light is collected using a long-working-distance objective and focused via a tube lens onto a CCD camera.
Specimens are submerged in exogenous dye for 10 seconds and then briefly washed in water or phosphate-buffered saline (PBS). The resulting stained specimens generate bright enough signals for direct and interpretable visualization through microscope eyepiece. | 5 | Photochemistry |
The properties of ferromanganese vary considerably with the precise type and composition of the alloy. The melting point is generally between and . The density of the alloy depend slightly on the types of impurities present, but is generally around . | 8 | Metallurgy |
The administration of a nucleoside-modified messenger RNA sequence can cause a cell to make a protein, which in turn could directly treat a disease or could function as a vaccine; more indirectly the protein could drive an endogenous stem cell to differentiate in a desired way.
The primary challenges of RNA therapy center on delivering the RNA to the appropriate cells. Challenges include the fact that naked RNA sequences naturally degrade after preparation; they may trigger the bodys immune system to attack them as an invader; and they are impermeable to the cell membrane. Once within the cell, they must then leave the cells transport mechanism to take action within the cytoplasm, which houses the necessary ribosomes.
Overcoming these challenges, mRNA as a therapeutic was first put forward in 1989 "after the development of a broadly applicable in vitro transfection technique." In the 1990s, mRNA vaccines for personalized cancer have been developed, relying on non-nucleoside modified mRNA. mRNA based therapies continue to be investigated as a method of treatment or therapy for both cancer as well as auto-immune, metabolic, and respiratory inflammatory diseases. Gene editing therapies such as CRISPR may also benefit from using mRNA to induce cells to make the desired Cas protein.
Since the 2010s, RNA vaccines and other RNA therapeutics have been considered to be "a new class of drugs". The first mRNA-based vaccines received restricted authorization and were rolled out across the world during the COVID-19 pandemic by Pfizer–BioNTech COVID-19 vaccine and Moderna, for example.
The 2023 Nobel Prize in Physiology or Medicine was awarded to Katalin Karikó and Drew Weissman for the development of effective mRNA vaccines against COVID-19. | 1 | Biochemistry |
In 2022, Malaysia was the third-largest PV module producer, with a production capacity of 10.8 GW, accounting for 2.8% of global production. This placed it behind China, which dominated with 77.8%, and Vietnam, which contributed 6.4%. | 7 | Physical Chemistry |
Within mathematics, inexact differentials are usually just referred more generally to as differential forms which are often written just as . | 7 | Physical Chemistry |
Lead-Bismuth Eutectic or LBE is a eutectic alloy of lead (44.5 at%) and bismuth (55.5 at%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative.
It has a melting point of 123.5 °C/254.3 °F (pure lead melts at 327 °C/621 °F, pure bismuth at 271 °C/520 °F) and a boiling point of 1,670 °C/3,038 °F.
Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C/392 °F.
Alloys with between 48% and 63% bismuth have melting points below 150 °C/302 °F.
While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting. | 8 | Metallurgy |
Matrai is known for her work on marine aerosols, especially those that contain sulfur. She has examined the production of sulfur compounds by coccolithophores, a type of phytoplankton. She has also examined the amount of organic sulfur inside phytoplankton cells and during phytoplankton blooms. Matrai has worked on the impact of declines in sea ice and how primary production is measured in the Arctic. In 2001 she went to the North Pole on an icebreaker where she studied aerosols produced by phytoplankton. She also does work on outreach and mentoring children to introduce them to science | 9 | Geochemistry |
Selegiline, also known as -deprenyl and sold under the brand names Eldepryl, Emsam, Selgin, among other names, is a medication which is used in the treatment of Parkinsons disease and major depressive disorder. It is provided in the form of a capsule or tablet taken by mouth or orally disintegrating tablets taken on the tongue for Parkinsons disease and as a patch applied to skin for depression.
Selegiline acts as a monoamine oxidase inhibitor, and increases levels of monoamine neurotransmitters in the brain. At typical clinical doses used for Parkinson's disease, selegiline is a selective and irreversible inhibitor of monoamine oxidase B (MAO-B), increasing levels of dopamine in the brain. In larger doses (more than 20 mg/day), it loses its specificity for MAO-B and also inhibits MAO-A, which increases serotonin and norepinephrine levels in the brain. | 4 | Stereochemistry |
As required for all separation techniques, ionic liquids exhibit selectivity towards one or more of the phases of a mixture. 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF) is a room-temperature ionic liquid that was identified early on as a viable substitute for volatile organic solvents in liquid-liquid separations. Other [PF]- and [BF]- containing ionic liquids have been studied for their CO absorption properties, as well as 1-ethyl-3-methylimidazolium (EMIM) and unconventional cations like trihexyl(tetradecyl) phosphonium ([P]). Selection of different anion and cation combinations in ionic liquids affects their selectivity and physical properties. Additionally, the organic cations in ionic liquids can be "tuned" by changing chain lengths or by substituting radicals. Finally, ionic liquids can be mixed with other ionic liquids, water, or amines to achieve different properties in terms of absorption capacity and heat of absorption. This tunability has led some to call ionic liquids "designer solvents." 1-butyl-3-propylamineimidazolium tetrafluoroborate was specifically developed for CO capture; it is designed to employ chemisorption to absorb CO and maintain efficiency under repeated absorption/regeneration cycles. Other ionic liquids have been simulated or experimentally tested for potential use as CO absorbents. | 7 | Physical Chemistry |
Members of the family include blood serotransferrin (or siderophilin, usually simply called transferrin); lactotransferrin (lactoferrin); milk transferrin; egg white ovotransferrin (conalbumin); and membrane-associated melanotransferrin. | 1 | Biochemistry |
A depsipeptide is a peptide in which one or more of its amide, -C(O)NHR-, groups are replaced by the corresponding ester, -C(O)OR-. Many depsipeptides have both peptide and ester linkages. Elimination of the N–H group in a peptide structure results in a decrease of H-bonding capability, which is responsible for secondary structure and folding patterns of peptides, thus inducing structural deformation of the helix and β-sheet structures. Because of decreased resonance delocalization in esters relative to amides, depsipeptides have lower rotational barriers for cis-trans isomerization and therefore they have more flexible structures than their native analogs. They are mainly found in marine and microbial natural products. | 1 | Biochemistry |
Several plants are allelopathic, producing chemicals which inhibit the growth of other species. For example, rye is useful as a cereal crop, and can be used as a cover crop to suppress weeds in companion plantings, or mown and used as a weed-suppressing mulch. Rye produces two phytotoxic substances, [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)]. These inhibit germination and seedling growth of both grasses and dicotyledonous plants. | 1 | Biochemistry |
ASBMB gives out an array of annual awards in different categories.
* Lemberg Medal - after 5 years' membership for significant contribution
* Shimadzu Research Medal - within 15 years post-PhD graduation
* Eppendorf Edman ECR Award - within 7 years post-PhD
* SDR Scientific Education Award - education (especially innovation and creativity)
* Boomerang Award - for expatriate Australians to return to present at the ASBMB conference and seminars at universities/institutes.
The society also awards fellowships to researchers within 2 years post-PhD. | 1 | Biochemistry |
Sample thickness can be estimated using twoBeamGUI from a convergent beam electron diffraction pattern (CBED) in two beam approximation. The procedure is based on an automated extraction of the intensity profile across the diffracted disk in the following steps:
# diffraction disk radius is determined using multi-scale Hough transform,
# the transmitted and diffracted disks are localized and the reflection is indexed,
# the disks are horizontally aligned, cropped out and profiles are measured across the disks,
# the profile across the diffracted disk is matched with a series of profiles automatically simulated for given material, reflection and specified thickness range.
Once the procedure is completed, the measured profile and the most similar simulated profile are displayed with the diffracted disk on the background. This allows the user to verify correctness of the automated estimate and easily check the similarity of other intensity profiles within the specified thickness range. | 3 | Analytical Chemistry |
Applications of AFM-IR have include the characterisation of protein, polymers composites, bacteria, cells, biominerals, pharmaceutical sciences, photonics/nanoantennas, fuel cells, fibers, skin, hair, metal organic frameworks, microdroplets, self-assembled monolayers, nanocrystals, and semiconductors. | 3 | Analytical Chemistry |
There are four major methods used to quantify the metabolome of single cells, they are: fluorescence–based detection, fluorescence biosensors, FRET biosensors, and mass spectroscopy. The first three methods listed use fluorescence microscopy to detect molecules in a cell. Usually these assays use small fluorescent tags attached to molecules of interest, however this has been shown be too invasive for single cell metabolomics, and alters the activity of the metabolites. The current solution to this problem is to use fluorescent proteins which will act as metabolite detectors, fluorescing when ever they bind to a metabolite of interest.
Mass spectroscopy is becoming the most frequently used method for single cell metabolomics. Its advantages are that there is no need to develop fluorescent proteins for all molecules of interest, and is capable of detecting metabolites in the femtomole range. Similar to the methods discussed in proteomics, there has also been success in combining mass spectroscopy with separation techniques such as capillary electrophoresis to quantify metabolites. This method is also capable of detecting metabolites present in femtomole concentrations. Another method utilizing capillary microsampling combined with mass spectrometry with ion mobility separation has been demonstrated to enhance the molecular coverage and ion separation for single cell metabolomics. Researchers are trying to develop a technique that can fulfil what current techniques are lacking: high throughput, higher sensitivity for metabolites that have a lower abundance or that have low ionization efficiencies, good replicability and that allow quantification of metabolites. | 1 | Biochemistry |
Preparing TNP-ATP is a one-step synthesis that is relatively safe and easy. Adenosine’s ribose moiety can be trinitrophenylated by 2,4,6-trinitrobenzene-1-sulfonate (TNBS). The resulting compound assumes a bright orange color and has visible absorption characteristics, as is characteristic of a Meiseinheimer spiro complex compound linking.
To see the exact method of preparion, please refer to T. Hiratsukas and K. Uchidas paper "Preparation and Properties of 2(r 3)-O(2,4,6-trinitrophenyl) Adenosine 5-triphosphate, an Analog of Adenosine Triphosphate,"' found in the reference section.
To revert TNP-ATP back to its constituent parts, or in other words to hydrolyze TNP-ATP to give equilmolar amounts of picric acid (TNP) and ATP, TNP-ATP should be treated with 1 M HCl at 100 degrees Celsius for 1.5 hours. This is because if TNP-ATP is acidified under mild conditions, it results in the opening of the dioxolane ring attached to the 2’-oxygen, leaving a 3’O-TNP derivative as the only product. | 7 | Physical Chemistry |
Atomic energy-level and Grotrian diagrams by Stanley Bashkin and John O. Stoner, Jr.
* [https://www.osti.gov/etdeweb/biblio/7245253 Volume I: Hydrogen - Phosphorus]
* [https://www.osti.gov/etdeweb/biblio/5726087 Volume I: Hydrogen - Phosphorus (Addenda)]
* [https://www.osti.gov/etdeweb/biblio/5286863 Volume III]
* [https://www.osti.gov/etdeweb/biblio/7095470 Volume IV] | 7 | Physical Chemistry |
Only a few lists of information will be output from a calculation, in general. For the ions, the position, velocity and net force on each ion are recorded at each step. For electrons, the guess as to the electronic state function may be recorded as well. Finally, the total energy of the system is recorded. From these three types of information, we may deduce a number of properties. | 3 | Analytical Chemistry |
Hydrogen embrittlement can be prevented through several methods, all of which are centered on minimizing contact between the metal and hydrogen, particularly during fabrication and the electrolysis of water. Embrittling procedures such as acid pickling should be avoided, as should increased contact with elements such as sulfur and phosphate.
If the metal has not yet started to crack, hydrogen embrittlement can be reversed by removing the hydrogen source and causing the hydrogen within the metal to diffuse out through heat treatment. This de-embrittlement process, known as low hydrogen annealing or "baking", is used to overcome the weaknesses of methods such as electroplating which introduce hydrogen to the metal, but is not always entirely effective because a sufficient time and temperature must be reached. Tests such as ASTM F1624 can be used to rapidly identify the minimum baking time (by testing using design of experiments, a relatively low number of samples can be used to pinpoint this value). Then the same test can be used as a quality control check to evaluate if baking was sufficient on a per-batch basis.
In the case of welding, often pre-heating and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage. This is specifically done with high-strength steels and low alloy steels such as the chromium/molybdenum/vanadium alloys. Due to the time needed to re-combine hydrogen atoms into the hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed.
Another way of preventing this problem is through materials selection. This will build an inherent resistance to this process and reduce the need of post processing or constant monitoring for failure. Certain metals or alloys are highly susceptible to this issue, so choosing a material that is minimally affected while retaining the desired properties would also provide an optimal solution. Much research has been done to catalog the compatibility of certain metals with hydrogen.
Tests such as ASTM F1624 can also be used to rank alloys and coatings during materials selection to ensure (for instance) that the threshold of cracking is below the threshold for hydrogen-assisted stress corrosion cracking. Similar tests can also be used during quality control to more effectively qualify materials being produced in a rapid and comparable manner. | 7 | Physical Chemistry |
Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions, whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in the case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states (i.e., semi-crystalline and amorphous). Crystallization occurs above the glass-transition temperature (T) and below the melting temperature (T). | 7 | Physical Chemistry |
A Bjerrum plot (named after Niels Bjerrum), sometimes also known as a Sillén diagram (after Lars Gunnar Sillén), or a Hägg diagram (after Gunnar Hägg) is a graph of the concentrations of the different species of a polyprotic acid in a solution, as a function of pH, when the solution is at equilibrium. Due to the many orders of magnitude spanned by the concentrations, they are commonly plotted on a logarithmic scale. Sometimes the ratios of the concentrations are plotted rather than the actual concentrations. Occasionally H and OH are also plotted.
Most often, the carbonate system is plotted, where the polyprotic acid is carbonic acid (a diprotic acid), and the different species are dissolved carbon dioxide, carbonic acid, bicarbonate, and carbonate. In acidic conditions, the dominant form is ; in basic (alkaline) conditions, the dominant form is ; and in between, the dominant form is . At every pH, the concentration of carbonic acid is assumed to be negligible compared to the concentration of dissolved , and so is often omitted from Bjerrum plots. These plots are very helpful in solution chemistry and natural water chemistry. In the example given here, it illustrates the response of seawater pH and carbonate speciation due to the input of man-made emission by the fossil fuel combustion.
The Bjerrum plots for other polyprotic acids, including silicic, boric, sulfuric and phosphoric acids, are other commonly used examples. | 7 | Physical Chemistry |
The nucleus-independent chemical shift (NICS) is a computational method that calculates the absolute magnetic shielding at the center of a ring. The values are reported with a reversed sign to make them compatible with the chemical shift conventions of NMR spectroscopy. In this method, negative NICS values indicate aromaticity, and positive values indicate antiaromaticity. There are a variety of methods to calculate NICS values, however, the most robust method for calculating NICS values involves scanning the molecule in a NICSzz scan. In this process, the NICS value is calculated above the rings, and this allows for evaluating the aromatics of each ring, which is especially useful for polycyclic compounds. | 7 | Physical Chemistry |
Edman degradation, developed by Pehr Edman, is a method of sequencing amino acids in a peptide. In this method, the amino-terminal residue is labeled and cleaved from the peptide without disrupting the peptide bonds between other amino acid residues. | 0 | Organic Chemistry |
An early example of this bonding mode was provided by prepared from diazomethane:
Another example of this family of compounds is Tebbe's reagent. It features a methylene bridge joining titanium and aluminum. | 0 | Organic Chemistry |
These newly cooked strange quarks find their way into a multitude of different final particles that emerge as the hot quark–gluon plasma fireball breaks up, see the scheme of different processes in figure. Given the ready supply of antiquarks in the "fireball", one also finds a multitude of antimatter particles containing more than one strange quark. On the other hand, in a system involving a cascade of nucleon–nucleon collisions, multi-strange antimatter are produced less frequently considering that several relatively improbable events must occur in the same collision process. For this reason one expects that the yield of multi-strange antimatter particles produced in the presence of quark matter is enhanced compared to conventional series of reactions. Strange quarks also bind with the heavier charm and bottom quarks which also like to bind with each other. Thus, in the presence of a large number of these quarks, quite unusually abundant exotic particles can be produced; some of which have never been observed before. This should be the case in the forthcoming exploration at the new Large Hadron Collider at CERN of the particles that have charm and strange quarks, and even bottom quarks, as components. | 7 | Physical Chemistry |
On 6 July 2012, the international reference standard Codex Alimentarius Commission narrowly approved the adoption of a maximum residue limit (MRL) of 10 parts per billion (ppb) for muscle cuts of beef and pork. Setting any limit was a controversial move. Countries with major meat export markets had been lobbying for the establishment of such a standard for several years to use it as leverage to erode individual national-level bans in World Trade Organization disputes. Consumers International, a world federation of consumer groups that represents 220 consumer organizations in 115 countries, strongly opposed the move.
Ractopamine use in food animals is banned in over 160 countries. | 4 | Stereochemistry |
The International Molecular Exchange Consortium (IMEx) is a group of the major public providers of molecular interaction data to provide a single, non-redundant set of molecular interactions. Data is captured using a detailed curation model and made available in the PSI-MI standard formats. Participating databases include DIP, IntAct, the Molecular Interaction Database (MINT), MatrixDB, InnateDB, IID, HPIDB, UCL Cardiovascular Gene Annotation, MBInfo, Molecular Connections and UniProt. The group collates the interaction data and prevents duplicate entries in the various databases. The IMEx consortium also supports and contributes to the development of the HUPO-PSI-MI XML format, which is now widely implemented. | 1 | Biochemistry |
Howard E. Zimmerman (July 5, 1926 – February 12, 2012) was a professor of chemistry at the University of Wisconsin–Madison. He was elected to the National Academy of Sciences in 1980 and the recipient of the 1986 American Institute of Chemists Chemical Pioneer Award. | 5 | Photochemistry |
The hydrogen bond can be compared with the closely related dihydrogen bond, which is also an intermolecular bonding interaction involving hydrogen atoms. These structures have been known for some time, and well characterized by crystallography; however, an understanding of their relationship to the conventional hydrogen bond, ionic bond, and covalent bond remains unclear. Generally, the hydrogen bond is characterized by a proton acceptor that is a lone pair of electrons in nonmetallic atoms (most notably in the nitrogen, and chalcogen groups). In some cases, these proton acceptors may be pi-bonds or metal complexes. In the dihydrogen bond, however, a metal hydride serves as a proton acceptor, thus forming a hydrogen-hydrogen interaction. Neutron diffraction has shown that the molecular geometry of these complexes is similar to hydrogen bonds, in that the bond length is very adaptable to the metal complex/hydrogen donor system. | 6 | Supramolecular Chemistry |
Phytobenthos () (from Greek (phyton, meaning "plants") and (benthos, meaning "depths") are autotrophic organisms found attached to bottom surfaces aquatic environments, such as rocks, sediments, or even other organisms. This photosynthetic community includes single-celled or filamentous cyanobacteria, microalgae, and macrophytes. Phytobenthos are highly diverse, and can be found in freshwater and marine environments, as well as transitional water systems. However, their distribution and availability still depend on the factors and stressors that exist in the environment. Because phytobenthos are autotrophs, they need to be able to subsist where it is still possible to perform photosynthesis. Similar to phytoplankton, phytobenthos contribute to the aquatic food web for grazers and heterotrophic bacteria, and researchers have also been studying their health as an indicator for water quality and environmental integrity of aquatic ecosystems. | 5 | Photochemistry |
Nipah virus is a causative agent of outbreaks of encephalitis with pneumonia and has a high case fatality rate. The first outbreak occurred in Malaysia-Singapore, related to contact with pigs in slaughterhouses and an outbreak in Philippines related to slaughter of horses, most other outbreaks have affected India and Bangladesh. in Bangladesh outbreaks are often associated with consumption of raw date palm sap contaminated by saliva and urine of fruit bats. In a study published in the Scientific Reports, Syrian hamster model for Nipah virus infection was used, which closely mirrors most aspects of human disease, such as widespread vasculitis, pneumonia, and encephalitis. The hamsters were infected with a lethal dose of 10 PFU NiV-M via the intraperitoneal (i.p.) route similar to previous studies and treatment was initiated immediately after infection. Favipiravir was administered twice daily via the peroral (p.o.) route for 14 days. The treated hamsters displayed 100% survival and no obvious morbidity after lethal NiV challenge, whereas all the control cases died of severe disease. | 4 | Stereochemistry |
This compound may be prepared by reacting the corresponding sulfonic acid with excess phosphorus oxychloride (POCl) at room temperature. | 0 | Organic Chemistry |
Chymosin (EC 3.4.23.4) is an aspartic protease that specifically hydrolyzes the peptide bond in Phe105-Met106 of κ- casein and is considered to be the most efficient protease for the cheesemaking industry. However, there are milk-clotting proteases able to cleave other peptide bonds in the κ-casein chain, such as the endothiapepsin produced by Endothia parasitica. There are also several milk-clotting proteases that, being able to cleave the Phe105-Met106 bond in the κ-casein molecule, also cleave other peptide bonds in other caseins, such as those produced by Cynara cardunculus or even bovine chymosin. This allows the manufacture of different cheeses with a variety of rheological and organoleptic properties.
The milk-clotting process consists of three main phases:
# Enzymatic degradation of κ-casein.
# Micellar flocculation.
# Gel formation.
Each step follows a different kinetic pattern, the limiting step in milk-clotting being the degradation rate of κ-casein. The kinetic pattern of the second step of the milk-clotting process is influenced by the cooperative nature of micellar flocculation, whereas the rheological properties of the gel formed depend on the type of action of the proteases, the type of milk, and the patterns of casein proteolysis. The overall process is influenced by several different factors, such as pH or temperature.
The conventional way of quantifying a given milk-clotting enzyme employs milk as the substrate and determines the time elapsed before the appearance of milk clots. However, milk clotting may take place without the participation of enzymes because of variations in physicochemical factors, such as low pH or high temperature. Consequently, this may lead to confusing and irreproducible results, particularly when the enzymes have low activity. At the same time, the classical method is not specific enough, in terms of setting the precise onset of milk gelation, such that the determination of the enzymatic units involved becomes difficult and unclear. Furthermore, although it has been reported that κ-casein hydrolysis follows typical Michaelis–Menten kinetics, it is difficult to determine with the classic milk-clotting assay.
To overcome this, several alternative methods have been proposed, such as the determination of halo diameter in agar-gelified milk, colorimetric measurement, or determination of the rate of degradation of casein previously labeled with either a radioactive tracer or a fluorochrome compound. All these methods use casein as the substrate to quantify proteolytic or milk-clotting activities. | 1 | Biochemistry |
Thermotropic phases are those that occur in a certain temperature range. If the temperature rise is too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase. At too low temperature, most LC materials will form a conventional crystal. Many thermotropic LCs exhibit a variety of phases as temperature is changed. For instance, a particular type of LC molecule (called a mesogen) may exhibit various smectic phases followed by the nematic phase and finally the isotropic phase as temperature is increased. An example of a compound displaying thermotropic LC behavior is para-azoxyanisole. | 7 | Physical Chemistry |
The six criteria air pollutants were the first set of pollutants recognized by the United States Environmental Protection Agency as needing standards on a national level. The Clean Air Act requires the EPA to set US National Ambient Air Quality Standards (NAAQS) for the six CAPs. The NAAQS are health based and the EPA sets two types of standards: primary and secondary. The primary standards are designed to protect the health of sensitive populations such as asthmatics, children, and the elderly. The secondary standards are concerned with protecting the environment. They are designed to address visibility, damage to crops, vegetation, buildings, and animals.
The EPA established the NAAQS according to Sections 108 and 109 of the U.S. Clean Air Act, which was last amended in 1990. These sections require the EPA "(1) to list widespread air pollutants that reasonably may be expected to endanger public health or welfare; (2) to issue air quality criteria for them that assess the latest available scientific information on nature and effects of ambient exposure to them; (3) to set primary NAAQS to protect human health with adequate margin of safety and to set secondary NAAQS to protect against welfare effects (e.g., effects on vegetation, ecosystems, visibility, climate, manmade materials, etc); and (5) to periodically review and revise, as appropriate, the criteria and NAAQS for a given listed pollutant or class of pollutants." | 2 | Environmental Chemistry |
Commercially available siliconates include potassium methyl siliconate (CAS 31795-24-1, CHKOSi) and sodium methyl siliconate (CAS 16589-43-8, CHNaOSi). These are supplied as a concentrate in water with an active content of between 30 and 40% by weight. This solution is further diluted in water prior to their application by spraying, dipping or rolling to a mineral building material, such as brickwork, to make the surface water repellent. The dilution is clear, stable with a high pH of 13 to 14. When applied to a surface the siliconate reacts with carbon dioxide in the air to form an insoluble water resistant treatment within 24 hours.
:CHKOSi + silanol functional substrate OHSi → CHOSi + KOH
The methyl group has now attached itself to the substrata.
:2KOH + CO → KCO + HO
The salts formed by this reaction are often the cause of white efflorescence when too much of the solution is applied to the surface. | 6 | Supramolecular Chemistry |
A dilute solution of a certain polymer has a unique feature: all polymers are considered independent from each other, so that interactions between polymers may be neglected. By illuminating such a solution with a ray of considerable width, a macroscopic number of chain conformations are being sampled simultaneously. In this situation the accessible observables are all ensemble averages, i.e. averages over all possible configurations and deformations of the polymer.
In such a solution, where the polymer density is low (dilute) enough, homogenous and isotropic (on average), intermolecular contributions to the structure factor are averaged out, and only the single-molecule/polymer structure factor is preserved:
with representing the ensemble average. This reduces to the following for an isotropic system (which is typically the case):
where two more definitions were made: and . | 7 | Physical Chemistry |
HDAC1 & HDAC2 are in the first class of HDACs are most closely related to one another. By analyzing the overall sequences of both HDACs, their similarity was found to be approximately 82% homologous. These enzymes have been found to be inactive when isolated which led to the conclusion that they must be incorporated with cofactors in order to activate their deacetylase abilities. There are three major protein complexes that HDAC 1 & 2 may incorporate themselves into. These complexes include Sin3 (named after its characteristic protein mSin3A), Nucleosome Remodelling and Deacetylating complex (NuRD), and Co-REST. The Sin3 complex and the NuRD complex both contain HDACs 1 and 2, the Rb-associated protein 48 (RbAp48) and RbAp46 which make up the core of each complex. Other complexes may be needed though in order to initiate the maximum amount of available activity possible. HDACs 1 and 2 can also bind directly to DNA binding proteins such as Yin and Yang 1 (YY1), Rb binding protein 1 and Sp1. HDACs 1 and 2 have been found to express regulatory roles in key cell cycle genes including p21.
Activity of these HDACs can be affected by phosphorylation. An increased amount of phosphorylation (hyperphosphorylation) leads to increased deacetylase activity, but degrades complex formation between HDACs 1 and 2 and between HDAC1 and mSin3A/YY1. A lower than normal amount of phosphorylation (hypophosphorylation) leads to a decrease in the amount of deacetylase activity, but increases the amount of complex formation. Mutation studies found that major phosphorylation happens at residues Ser and Ser. Indeed, when these residues were mutated, a drastic reduction was seen in the amount of deacetylation activity. This difference in the state of phosphorylation is a way of keeping an optimal level of phosphorylation to ensure there is no over or under expression of deacetylation. HDACs 1 and 2 have been found only exclusively in the nucleus. In HDAC1 knockout (KO) mice, mice were found to die during embryogenesis and showed a drastic reduction in the production but increased expression of Cyclin-Dependent Kinase Inhibitors (CDKIs) p21 and p27. Not even upregulation of the other Class I HDACs could compensate for the loss of HDAC1. This inability to recover from HDAC1 KO leads researchers to believe that there are both functional uniqueness to each HDAC as well as regulatory cross-talk between factors. | 0 | Organic Chemistry |
Disease gene identification techniques often follow the same overall procedure. DNA is first collected from several patients who are believed to have the same genetic disease. Then, their DNA samples are analyzed and screened to determine probable regions where the mutation could potentially reside. These techniques are mentioned below. These probable regions are then lined-up with one another and the overlapping region should contain the mutant gene. If enough of the genome sequence is known, that region is searched for candidate genes. Coding regions of these genes are then sequenced until a mutation is discovered or another patient is discovered, in which case the analysis can be repeated, potentially narrowing down the region of interest.
The differences between most disease gene identification procedures are in the second step (where DNA samples are analyzed and screened to determine regions in which the mutation could reside). | 1 | Biochemistry |
Disarming sugars can also be accomplished by adding 1,3-dioxane and 1,3-dioxolane protecting groups onto sugars. These protecting groups “lock” the sugars into a rigid chair conformation. When the sugar forms the necessary oxocarbenium ion, it flattens at the anomeric position. This change in configuration is a high-energy transformation when cyclic protecting groups are present, and leads to the sugar being “disarmed”. These groups can be easily removed following glycosylation, effectively “arming” the sugar, and allowing for control of the glycosylation.
Further work has shown that the effect of 1,3-dioxanes and 1,3-dioxolanes on disarming sugars can be attributed to the electronics of the systems as well as torsional strain. When a 1,3-dioxane is formed between O-4 and O-6, the oxygens adapt an anti-periplanar geometry with O-5. This orientation allows for hyperconjugation of O-5 to O-4 and O-6, removing electron density from O-5. The loss of electron density at O-5 results in a destabilization of the oxocarbenium ion, slowing its formation, and “disarming” the sugar. Experiments were conducted by altering the configuration of the O-6 and examining the rate of hydrolysis of these compounds. The gauche-gauche orientation seen in the second example has a higher rate of hydrolysis due to its longer bond length. The hydrogen at C-5 is able to hyperconjugate with O-6, effectively lengthening the bond. This increase in bond length decreases the inductive electron withdrawing ability of O-6, causing a higher rate of hydrolysis than the other two conformations. The effect of anti-periplanar orientation is also visible in comparing glucopyranose and galactopyranose hydrolysis. Glucopyranose has an anti-perplanar orientation between O-4 and O-5, while galactopyranose does not and shows the appropriate increase in reactivity. | 0 | Organic Chemistry |
Electrophilic amination reactions can be classified as either additions or substitutions. Although the resulting product is not always an amine, these reactions are unified by the formation of a carbon–nitrogen bond and the use of an electrophilic aminating agent. A wide variety of electrophiles have been used; for substitutions, these are most commonly amines substituted with electron-withdrawing groups: chloramines, hydroxylamines, hydrazines, and oxaziridines, for instance. Addition reactions have employed imines, oximes, azides, azo compounds, and others. | 0 | Organic Chemistry |
Many materials are able to be sprayed as coatings using the D-gun. These materials used for the feedstock are powders of metals, alloys and cermets; as well as their oxides. However, mainly high-tech coatings are used, these include ceramics, and complex composites. Characteristics such as strength, hardness, shrink, corrosion resistance and wearing quality of possible spraying materials are factored into the decision of selecting a coating material.
Some examples include:
* Al2O3
* Cu–Al
* Cu–SiC
* Al–Al2O3
* Cu–Al2O3
* Al–SiC
* Al–Ti
* TiMo(CN)–36NiCo
* Fe–A | 8 | Metallurgy |
A loading control is a protein used as a control in a Western blotting experiment. Typically, loading controls are proteins with high and ubiquitous expression, such as beta-actin or GADPH. They are used to make sure that the protein has been loaded equally across all wells. | 1 | Biochemistry |
In chemical equations, radicals are frequently denoted by a dot placed immediately to the right of the atomic symbol or molecular formula as follows:
Radical reaction mechanisms use single-headed arrows to depict the movement of single electrons:
The homolytic cleavage of the breaking bond is drawn with a "fish-hook" arrow to distinguish from the usual movement of two electrons depicted by a standard curly arrow. The second electron of the breaking bond also moves to pair up with the attacking radical electron.
Radicals also take part in radical addition and radical substitution as reactive intermediates. Chain reactions involving radicals can usually be divided into three distinct processes. These are initiation, propagation, and termination.
*Initiation reactions are those that result in a net increase in the number of radicals. They may involve the formation of radicals from stable species as in Reaction 1 above or they may involve reactions of radicals with stable species to form more radicals.
*Propagation reactions are those reactions involving radicals in which the total number of radicals remains the same.
*Termination reactions are those reactions resulting in a net decrease in the number of radicals. Typically two radicals combine to form a more stable species, for example:
*:2 Cl → Cl | 2 | Environmental Chemistry |
Microbial growth in alkaline conditions presents several complications to normal biochemical activity and reproduction, as high pH is detrimental to normal cellular processes. For example, alkalinity can lead to denaturation of DNA, instability of the plasma membrane and inactivation of cytosolic enzymes, as well as other unfavorable physiological changes. Thus, to adequately circumvent these obstacles, alkaliphiles must either possess specific cellular machinery that works best in the alkaline range, or they must have methods of acidifying the cytosol in relation to the extracellular environment. To determine which of the above possibilities an alkaliphile uses, experimentation has demonstrated that alkaliphilic enzymes possess relatively normal pH optimums. The determination that these enzymes function most efficiently near physiologically neutral pH ranges (about 7.5–8.5) was one of the primary steps in elucidating how alkaliphiles survive intensely basic environments. Since the cytosolic pH must remain nearly neutral, alkaliphiles must have one or more mechanisms of acidifying the cytosol when in the presence of a highly alkaline environment. | 1 | Biochemistry |
Enterics that subsequently metabolize pyruvic acid to other acids lower the pH of the medium to 4.2. At this pH, methyl red turns red, a positive test. Enterics that subsequently metabolize pyruvic acid to neutral end products lower the pH of the medium to only 6.0. At this pH, methyl red is yellow, a negative test. | 3 | Analytical Chemistry |
Like β-hydride elimination, β-carbon elimination requires the metal to have an open coordination site cis to the alkyl group for this reaction to occur. β-carbon elimination is usually less favored than hydride elimination because the metal–hydride bond is stronger than the metal–carbon bond for most metals in catalytic reactions. The principles governing β-alkyl elimination are not well-established experimentally. One reason for this is that breaking C−C bonds in the presence of other reactive C−H bonds is a rare event, and systems designed to interrogate the reaction are more difficult to devise. | 0 | Organic Chemistry |
Lipophosphoglycan (LPG) is a class of molecules found on the surface of some eukaryotes, in particular protozoa. Each is made up of two parts, lipid and polysaccharide (also called glycan). They are bonded by a phosphodiester, hence the name lipo-phospho-glycan.
One species with extensive lipophosphoglycan coating is Leishmania, a group of single-celled protozoan parasite which cause leishmaniasis in many mammals, including humans. Their coats help modulate their hosts' immunological responses. | 1 | Biochemistry |
An advanced spatio-spectral scanning system, proposed in June 2014, consists of a dispersive element before a spatial scanning system. (This allows for easy switching between spatial and spatio-spectral scanning). The imaging process is based on spectral analysis of a strip of a dispersed image of the scene. The field of view in the wavelength-coded spatial dimension equals the dispersion angle of the dispersive element. As in the more basic system, scanning is achieved by transverse movement of the slit or by moving the system relative to the scene. | 7 | Physical Chemistry |
The system size expansion, also known as van Kampen's expansion or the Ω-expansion, is a technique pioneered by Nico van Kampen used in the analysis of stochastic processes. Specifically, it allows one to find an approximation to the solution of a master equation with nonlinear transition rates. The leading order term of the expansion is given by the linear noise approximation, in which the master equation is approximated by a Fokker–Planck equation with linear coefficients determined by the transition rates and stoichiometry of the system.
Less formally, it is normally straightforward to write down a mathematical description of a system where processes happen randomly (for example, radioactive atoms randomly decay in a physical system, or genes that are expressed stochastically in a cell). However, these mathematical descriptions are often too difficult to solve for the study of the systems statistics (for example, the mean and variance of the number of atoms or proteins as a function of time). The system size expansion allows one to obtain an approximate statistical description that can be solved much more easily than the master equation. | 7 | Physical Chemistry |
As some carotenoids can be converted into vitamin A, attempts have been made to determine how much of them in the diet is equivalent to a particular amount of retinol, so that comparisons can be made of the benefit of different foods. The situation can be confusing because the accepted equivalences have changed over time.
For many years, a system of equivalencies in which an international unit (IU) was equal to 0.3 μg of retinol (~1 nmol), 0.6 μg of β-carotene, or 1.2 μg of other provitamin-A carotenoids was used. This relationship was alternatively expressed by the retinol equivalent (RE): one RE corresponded to 1 μg retinol, to 2 μg β-carotene dissolved in oil, to 6 μg β-carotene in foods, and to 12 μg of either α-carotene, γ-carotene, or β-cryptoxanthin in food.
Newer research has shown that the absorption of provitamin-A carotenoids is only half as much as previously thought. As a result, in 2001 the US Institute of Medicine recommended a new unit, the retinol activity equivalent (RAE). Each μg RAE corresponds to 1 μg retinol, 2 μg of β-carotene in oil, 12 μg of "dietary" beta-carotene, or 24 μg of the three other dietary provitamin-A carotenoids.
Animal models have shown that at the enterocyte cell wall, β-carotene is taken up by the membrane transporter protein scavenger receptor class B, type 1 (SCARB1). Absorbed β-carotene is converted to retinal and then retinol. The first step of the conversion process consists of one molecule of β-carotene cleaved by the enzyme
β-carotene-15, 15'-monooxygenase, which in humans and other mammalian species is encoded by the BCM01 gene, into two molecules of retinal. When plasma retinol is in the normal range, gene expression for SCARB1 and BC01 are suppressed, creating a feedback loop that suppresses β-carotene absorption and conversion. Absorption suppression is not complete, as receptor 36 is not downregulated. | 1 | Biochemistry |
Another aspect is the similarity of arsenic effects to the heat shock response. Short-term arsenic exposure has effects on signal transduction inducing heat shock proteins with masses of 27, 60, 70, 72, 90, and 110 kDa as well as metallothionein, ubiquitin, mitogen-activated [MAP] kinases, extracellular regulated kinase [ERK], c-jun terminal kinases [JNK] and p38.
Via JNK and p38 it activates c-fos, c-jun and egr-1 which are usually activated by growth factors and cytokines. The effects are largely dependent on the dosing regime and may be as well inversed.
As shown by some experiments reviewed by Del Razo (2001), reactive oxygen species induced by low levels of inorganic arsenic increase the transcription and the activity of the activator protein 1 (AP-1) and the nuclear factor-κB (NF-κB) (maybe enhanced by elevated MAPK levels), which results in c-fos/c-jun activation, over-secretion of pro-inflammatory and growth promoting cytokines stimulating cell proliferation. Germolec et al. (1996) found an increased cytokine expression and cell proliferation in skin biopsies from individuals chronically exposed to arsenic-contaminated drinking water.
Increased AP-1 and NF-κB obviously also result in an up-regulation of mdm2 protein, which decreases p53 protein levels. Thus, taking into account p53's function, a lack of it could cause a faster accumulation of mutations contributing to carcinogenesis. However, high levels of inorganic arsenic inhibit NF-κB activation and cell proliferation. An experiment of Hu et al. (2002) demonstrated increased binding activity of AP-1 and NF-κB after acute (24 h) exposure to +3 sodium arsenite, whereas long-term exposure (10–12 weeks) yielded the opposite result. The authors conclude that the former may be interpreted as a defense response while the latter could lead to carcinogenesis. As the contradicting findings and connected mechanistic hypotheses indicate, there is a difference in acute and chronic effects of arsenic on signal transduction which is not clearly understood yet. | 1 | Biochemistry |
Pauline Rudd is a British biochemist and Professor at the Microbiome Institute, University College Cork. She is a founder of Wessex Biochemicals, a Fellow of the Royal Society of Medicine and was awarded the James Gregory Medal in 2010. | 1 | Biochemistry |
Some other lattice packings are often found in physical systems. These include the cubic lattice with a density of , the hexagonal lattice with a density of and the tetrahedral lattice with a density of . | 3 | Analytical Chemistry |
Eshelby was clear and amusing as a lecturer, and prepared his lectures with great care, but was not keen on doing experimental work. He was well versed in Sanskrit (among other classical languages) and was an avid second-hand book buyer.
Eshelby died on 10 December 1981. | 8 | Metallurgy |
All equilibrium constants vary with temperature according to the Van 't Hoff equation
Alternatively
R is the gas constant and T is the thermodynamic temperature. Thus, for exothermic reactions, where the standard enthalpy change, ΔH, is negative, K decreases with temperature, but for endothermic reactions, where ΔH is positive, K increases with temperature. | 7 | Physical Chemistry |
Phillips' research on heme proteins and ligand affinity has provided insights into engineering strategies for physiological functions. He explored the impact of His64 in sperm whale myoglobin on ligand affinity, shedding light on structural changes induced by ligand binding and mechanisms of ligand discrimination in myoglobin. By measuring CO binding properties in various mutants and comparing them to mutant myoglobins, he elucidated how mutations influence CO affinity. In his 1994 study, he delved into how heme proteins like myoglobin and hemoglobin differentiate between oxygen (O2) and carbon monoxide (CO) binding at the atomic level. He investigated the role of nitric oxide in physiological functions by examining the kinetics of NO-induced oxidation in myoglobins and hemoglobins revealing insights into protein engineering strategies aimed at mitigating hypertensive events. | 1 | Biochemistry |
Nanofuidic triode is a three-terminal double junction nanofluidic device composed of positive-charged alumina and negative-charged silica nanochannels. The device is essentially a three-terminal bipolar junction transistor. By controlling the voltage across emitter and collector terminals, one can regulate the ion current from base terminal to one of the other two terminals, functioning as an ionic single-pole, double-throw switch. | 7 | Physical Chemistry |
Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes. It was discovered in 1990 in the lab of Roger D. Kornberg, recipient of the 2006 Nobel Prize in Chemistry. Mediator complexes interact with transcription factors and RNA polymerase II. The main function of mediator complexes is to transmit signals from the transcription factors to the polymerase.
Mediator complexes are variable at the evolutionary, compositional and conformational levels. The first image shows only one "snapshot" of what a particular mediator complex might be composed of, but it certainly does not accurately depict the conformation of the complex in vivo. During evolution, mediator has become more complex. The yeast Saccharomyces cerevisiae (a simple eukaryote) is thought to have up to 21 subunits in the core mediator (exclusive of the CDK module), while mammals have up to 26.
Individual subunits can be absent or replaced by other subunits under different conditions. Also, there are many intrinsically disordered regions in mediator proteins, which may contribute to the conformational flexibility seen both with and without other bound proteins or protein complexes. A more realistic model of a mediator complex without the CDK module is shown in the second figure.
The mediator complex is required for the successful transcription by RNA polymerase II. Mediator has been shown to make contacts with the polymerase in the transcription preinitiation complex. A recent model showing the association of the polymerase with mediator in the absence of DNA is shown in the figure to the left. In addition to RNA polymerase II, mediator must also associate with transcription factors and DNA. A model of such interactions is shown in the figure to the right. Note that the different morphologies of mediator do not necessarily mean that one of the models is correct; rather those differences may reflect the flexibility of mediator as it interacts with other molecules. For example, after binding the enhancer and core promoter, the mediator complex undergoes a compositional change in which the kinase module dissociates from the complex to allow association with RNA polymerase II and transcriptional activation.
The Mediator complex is located within the cell nucleus. It is required for the successful transcription of nearly all class II gene promoters in yeast. It works in the same manner in mammals. The mediator functions as a coactivator and binds to the C-terminal domain of RNA polymerase II holoenzyme, acting as a bridge between this enzyme and transcription factors. | 1 | Biochemistry |
Many protein-coding genes have more than one polyadenylation site, so a gene can code for several mRNAs that differ in their 3′ end. The 3’ region of a transcript contains many polyadenylation signals (PAS). When more proximal (closer towards 5’ end) PAS sites are utilized, this shortens the length of the 3’ untranslated region (3 UTR) of a transcript. Studies in both humans and flies have shown tissue specific APA. With neuronal tissues preferring distal PAS usage, leading to longer 3’ UTRs and testis tissues preferring proximal PAS leading to shorter 3’ UTRs. Studies have shown there is a correlation between a genes conservation level and its tendency to do alternative polyadenylation, with highly conserved genes exhibiting more APA. Similarly, highly expressed genes follow this same pattern. Ribo-sequencing data (sequencing of only mRNAs inside ribosomes) has shown that mRNA isoforms with shorter 3’ UTRs are more likely to be translated.
Since alternative polyadenylation changes the length of the 3' UTR, it can also change which binding sites are available for microRNAs in the 3′ UTR. MicroRNAs tend to repress translation and promote degradation of the mRNAs they bind to, although there are examples of microRNAs that stabilise transcripts. Alternative polyadenylation can also shorten the coding region, thus making the mRNA code for a different protein, but this is much less common than just shortening the 3′ untranslated region.
The choice of poly(A) site can be influenced by extracellular stimuli and depends on the expression of the proteins that take part in polyadenylation. For example, the expression of CstF-64, a subunit of cleavage stimulatory factor (CstF), increases in macrophages in response to lipopolysaccharides (a group of bacterial compounds that trigger an immune response). This results in the selection of weak poly(A) sites and thus shorter transcripts. This removes regulatory elements in the 3′ untranslated regions of mRNAs for defense-related products like lysozyme and TNF-α. These mRNAs then have longer half-lives and produce more of these proteins. RNA-binding proteins other than those in the polyadenylation machinery can also affect whether a polyadenylation site is used, as can DNA methylation near the polyadenylation signal. In addition, numerous other components involved in transcription, splicing or other mechanisms regulating RNA biology can affect APA. | 1 | Biochemistry |
Single-nucleotide polymorphisms may fall within coding sequences of genes, non-coding regions of genes, or in the intergenic regions (regions between genes). SNPs within a coding sequence do not necessarily change the amino acid sequence of the protein that is produced, due to degeneracy of the genetic code.
SNPs in the coding region are of two types: synonymous SNPs and nonsynonymous SNPs. Synonymous SNPs do not affect the protein sequence, while nonsynonymous SNPs change the amino acid sequence of protein.
* SNPs in non-coding regions can manifest in a higher risk of cancer, and may affect mRNA structure and disease susceptibility. Non-coding SNPs can also alter the level of expression of a gene, as an eQTL (expression quantitative trait locus).
* SNPs in coding regions:
** synonymous substitutions by definition do not result in a change of amino acid in the protein, but still can affect its function in other ways. An example would be a seemingly silent mutation in the multidrug resistance gene 1 (MDR1), which codes for a cellular membrane pump that expels drugs from the cell, can slow down translation and allow the peptide chain to fold into an unusual conformation, causing the mutant pump to be less functional (in MDR1 protein e.g. C1236T polymorphism changes a GGC codon to GGT at amino acid position 412 of the polypeptide (both encode glycine) and the C3435T polymorphism changes ATC to ATT at position 1145 (both encode isoleucine)).
** nonsynonymous substitutions:
*** missense – single change in the base results in change in amino acid of protein and its malfunction which leads to disease (e.g. c.1580G>T SNP in LMNA gene – position 1580 (nt) in the DNA sequence (CGT codon) causing the guanine to be replaced with the thymine, yielding CTT codon in the DNA sequence, results at the protein level in the replacement of the arginine by the leucine in the position 527, at the phenotype level this manifests in overlapping mandibuloacral dysplasia and progeria syndrome)
*** nonsense – point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product (e.g. Cystic fibrosis caused by the G542X mutation in the cystic fibrosis transmembrane conductance regulator gene).
SNPs that are not in protein-coding regions may still affect gene splicing, transcription factor binding, messenger RNA degradation, or the sequence of noncoding RNA. Gene expression affected by this type of SNP is referred to as an eSNP (expression SNP) and may be upstream or downstream from the gene. | 1 | Biochemistry |
In catalytic reforming, a mixture of hydrocarbons with boiling points between 60 and 200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps.
In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics. | 2 | Environmental Chemistry |
Bacterial and mammalian SCSs are made up of α and β subunits. In E. coli two αβ heterodimers link together to form an αβ heterotetrameric structure. However, mammalian mitochondrial SCSs are active as αβ dimers and do not form a heterotetramer.
The E. coli SCS heterotetramer has been crystallized and characterized in great detail. As can be seen in Image 2, the two α subunits (pink and green) reside on opposite sides of the structure and the two β subunits (yellow and blue) interact in the middle region of the protein. The two α subunits only interact with a single β unit, whereas the β units interact with a single α unit (to form the αβ dimer) and the β subunit of the other αβ dimer. A short amino acid chain links the two β subunits which gives rise to the tetrameric structure.
The crystal structure of Succinyl-CoA synthetase alpha subunit (succinyl-CoA-binding isoform) was determined by Joyce et al. to a resolution of 2.10 A, with PDB code 1CQJ. [http://www.rcsb.org/pdb/explore.do?structureId=1CQJ]. | 1 | Biochemistry |
Trandolapril is a prodrug that is deesterified to trandolaprilat. It is believed to exert its antihypertensive effect through the renin–angiotensin–aldosterone system. Trandolapril has a half-life of about six hours, while trandolaprilat has a half life of about ten hours. Trandolaprilat has about eight times the activity of its parent drug. About one-third of trandolapril and its metabolites are excreted in the urine, and about two-thirds of trandolapril and its metabolites are excreted in the feces. Serum protein binding of trandolapril is about 80%. | 4 | Stereochemistry |
The famous controversy between Pasteur and Liebig over the nature of alcoholic fermentation was uncovered by Eduard Büchner, a German chemist and zymologist. Influenced by his brother Hans, who became the famous bacteriologist, Büchner developed an interest in the fermentation process in which yeast breaks down sugar into alcohol and carbon dioxide. He published his first paper in 1885 which revealed that fermentation could occur in the presence of oxygen, a conclusion contrary to the view held by Louis Pasteur.
By 1893, Büchner was fully involved in seeking the active agent of fermentation. He obtained pure samples of the inner fluid of yeast cells by pulverizing yeast within a mixture of sand and diatomaceous earth, then squeezing the mixture through a canvas filter. This process avoided using solvents and high temperatures which had foiled previous investigations. He assumed that the collected fluid was incapable of producing fermentation because the yeast cells were dead. However, when he attempted to preserve the fluid in concentrated sugar, he was startled to observe carbon dioxide being released, a sign that fermentation was taking place. Büchner hypothesized that the fermentation was caused by an enzyme which he named zymase. His findings that fermentation was the result of chemical process both inside and outside cells, were published in 1897. | 1 | Biochemistry |
Many physical processes over ocean surface can generate sea salt aerosols. One common cause is the bursting of air bubbles, which are entrained by the wind stress during the whitecap formation. Another is tearing of drops from wave tops. Wind speed is the key factor to determine the production rate in both mechanisms. Sea salt particle number concentration can reach 50 cm or more with high winds (>10 m s), compared to ~10 cm or less under moderate wind regimes. Due to the dependence on wind speed, it could be expected that sea-salt particle production and its impacts on climate may vary with climate change. | 9 | Geochemistry |
The Falcon Continuous (C) centrifugal concentrator is primarily used for the separation of heavy minerals which occur in ore concentrations above 0.1% by weight, such as cassiterite, tantalum and scheelite. It is also used for coal cleaning and pre-concentration of gold bearing ores. The machine generates forces up to 300 times the force of gravity (300 G's) and operates by using a smooth-walled, rotating bowl to stratify the material into heavier and lighter fractions then uses pneumatic valves to control the amount of heavy material that reports to the concentrate collection stream. It does not use any fluidization water and relies entirely on centrifugal force for separation. The Falcon C concentrator is used in various process plants around the world, such as the Tanco mine in Canada, the Sekisovskoye mine in Kazakhstan and the Renison tin mine in Tasmania. | 8 | Metallurgy |
Copper goes through a natural oxidation process that forms a unique protective patina on the metal. The surface of the metal undergoes a series of color changes: from iridescent/salmon pinks to oranges and reds interspersed with brassy yellows, blues, greens and purples. As the oxide thickens, these colors are replaced by russet and chocolate browns, dull slate grays or blacks, and finally to a light-green or blue-green.
Copper's patination process is complex. It starts immediately on exposure to the environment with the initial formation of copper oxide conversion films that are noticeable within six months. Weathering may be uneven at first but the film becomes even after about nine months. Within the first few years, cuprous and cupric sulfide conversion films darken the surface to browns and then dull slate gray or dull black. Continued weathering transforms the sulfide films to sulfates, which are the notable blue-green or gray-green patinas.
The rate of patination conversion is dependent upon copper's exposure to moisture, salt, and acidity from acid-forming pollutants. In marine climates, the entire patination process can take seven to nine years. In industrial environments, patina formation reaches its final stage in about fifteen to twenty-five years. In clean rural atmospheres with low concentrations of airborne sulfur dioxide, the final stage may take ten to thirty years to develop. In arid environments, a patina may not form at all if the moisture is insufficient. Where patination does take place in arid environments, it may mature to an ebony or nut brown. In all environments except the coastal areas, patination takes longer for vertical surfaces due to more rapid water runoff.
The copper patinas are very thin: just in thickness. Yet, they are highly adherent to the underlying copper metal. The initial and intermediate oxide and sulfide patina films are not particularly corrosion resistant. The final sulfate patina is a particularly durable layer that is highly resistant to all forms of atmospheric corrosion and protects the underlying metal against further weathering. As patination progresses and the durable sulfate layer forms, the rate of corrosion decreases, averaging between per year. For a sheet, this equates to less than 5% corrosion over a period of 100 years. Further information is available on copper patination. | 8 | Metallurgy |
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