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By the end of the war in 1944, post war recovery started: Alain Bertons work on the application of absorption and emission spectroscopy in the ultraviolet and infrared, and within the frame of concerns about labor force protection, the specific dosage of atmospheric pollutants became of vital interest in factories to effectively detect and remedy industrial pollution. Thus, in the 1950s, based on the method of gas chromatography analysis by low temperature followed by pyrolysis, he managed to isolate chlorinated substances and acid vapors components in the air. He was able to individualize traces of gas and vapors by using ultra-sensitive galvanic batteries and galvanic microcell detectors. He presented his research in the preamble to the convention of the Analytical Chemistry Group in 1958. Alain Berton named his invention "the Osmopile," later nicknamed "the sniffing cells" by the scientific journal Atomes'. The first "artificial nose" was thus born. His invention was adopted and developed in the US and went around the world with a report from the Associated Press dated December 8, 1958.
Berton’s Osmopile was marketed by Jouan, a laboratory equipment manufacturer founded in the 1940s by a researcher from the Pasteur Institute and acquired in 2003 by Thermo Electron. The Osmopile device was modernized over time and used in the fight against industrial pollution.
Through his invention, Alain Berton proved to be an ecology pioneer. | 3 | Analytical Chemistry |
The dehydration of boronic acids gives boroxines, the trimeric anhydrides of phenylboronic acid. The dehydration reaction is driven thermally, sometimes with a dehydration agent.
Phenylboronic acid participates in numerous cross coupling reactions where it serves as a source of a phenyl group. One example is the Suzuki reaction where, in the presence of a Pd(0) catalyst and base, phenylboronic acid and vinyl halides are coupled to produce phenyl alkenes. This method was generalized to a route producing biaryls by coupling phenylboronic acid with aryl halides.
C-C bond forming processes commonly use phenylboronic acid as a reagent. Alpha-amino acids can be generated using the uncatalyzed reaction between alpha-ketoacids, amines, and phenylboronic acid. Heck-type cross coupling of phenylboronic acid and alkenes and alkynes has been demonstrated.
Aryl azides and nitroaromatics can also be generated from phenylboronic acid. Phenylboronic acid can also be regioselectively halodeboronated using aqueous bromine, chlorine, or iodine:
:PhB(OH) + Br + HO → PhBr + B(OH) + HBr
Boronic esters result from the condensation of boronic acids with alcohols. This transformation is simply the replacement of the hydroxyl group by alkoxy or aryloxy groups. This reversible reaction is commonly driven to product by the use of Dean-Stark apparatus or a dehydration agent to remove water.
:PhB(OH) + 2 ROH PhB(OR) + 2 HO
As an extension of this reactivity, PhB(OH) can be used as a protecting group for diols and diamines. This reactivity is the basis of the use of phenylboronic acid's use as a receptor and sensor for carbohydrates, antimicrobial agents, and enzyme inhibitors, neutron capture therapy for cancer, transmembrane transport, and bioconjugation and labeling of proteins and cell surface. | 0 | Organic Chemistry |
The metals of antiquity generally have low melting points, with iron being the exception.
* Mercury melts at −38.829 °C (−37.89 °F) (being liquid at room temperature).
* Tin melts at 231 °C (449 °F)
* Lead melts at 327 °C (621 °F)
* Silver at 961 °C (1763 °F)
* Gold at 1064 °C (1947 °F)
* Copper at 1084 °C (1984 °F)
* Iron is the outlier at 1538 °C (2800 °F), making it far more difficult to melt in antiquity. Cultures developed ironworking proficiency at different rates; however, evidence from the Near East suggests that smelting was possible but impractical circa 1500 BC, and relatively commonplace across most of Eurasia by 500 BC. However, until this period, generally known as the Iron Age, ironwork would have been impossible.
The other metals discovered before the Scientific Revolution largely fit the pattern, except for high-melting platinum:
* Bismuth melts at 272 °C (521 °F)
* Zinc melts at 420 °C (787 °F), but importantly boils at 907 °C (1665 °F), a temperature below the melting point of silver. Consequently, at the temperatures needed to reduce zinc oxide to the metal, the metal is already gaseous.
* Arsenic sublimes at 615 °C (1137 °F), passing directly from the solid state to the gaseous state.
* Antimony melts at 631 °C (1167 °F)
* Platinum melts at 1768 °C (3215 °F), even higher than iron. Native South Americans worked with it instead by sintering: they combined gold and platinum powders, until the alloy became soft enough to shape with tools. | 8 | Metallurgy |
The Isa Process was originally developed for the CRL copper electrorefinery in Townsville. It was subsequently licensed to the Copper Range Company for its White Pine copper refinery.
The next licence issued was for an electrowinning application at the Broken Hill Associated Smelters (“BHAS”) lead smelter at Port Pirie, in South Australia. BHAS commissioned in 1985 a solvent extraction and electrowinning (“SX–EW”) to recover copper from copper–lead matte produced as a by-product of the lead smelting operations. The process used involves leaching the copper from the material using an acidic chloride–sulfate solution, followed by solvent extraction to concentrate the leached copper and electrowinning.
Electrowinning copper differs from electrorefining in that electrorefining uses a copper anode that is dissolved and redeposited on the cathode, while in electrowinning the copper is already in solution and is extracted from the solution by passing a current through the solution using an inert lead-alloy anode, and a cathode.
The chloride in the leach solution at Port Pirie proved to be a problem for the stainless steel cathodes of the Isa Process. A small amount of the chloride ions in the leach solution passed through the solvent into the electrolyte, leading to a reported chloride concentration of 80 milligrams per liter (“mg/L”) in the electrolyte. The presence of the chloride in the electrolyte caused pitting corrosion of the stainless steel cathode plates. After trying other types of stainless steel, BHAS switched to using titanium cathode plates.
Other electrowinning operations followed, including Gibraltar Mines’ McLeese Lake operation and Magma Copper’s San Manuel copper mine in 1986, the Mexicana de Cananea operation in Mexico in 1989, and the Gunpowder Copper Limited operation at Gunpowder in north-west Queensland 1990. These operations did not suffer the chloride corrosion problems experienced by BHAS. | 8 | Metallurgy |
García Mancheño is head of a research group at the University of Münster that focuses on developing new catalysts to accomplish organic chemical transformations. She has authored several review articles in peer-reviewed journals on topics in organocatalytic chemistry, and is the editor of a textbook on anion-binding catalysts. | 0 | Organic Chemistry |
Percoll is a tool for efficient density separation in Cell biology that was first formulated by Pertoft and colleagues. It is used for the isolation of cells, organelles, and/or viruses by density centrifugation. Percoll consists of colloidal silica particles of 15–30 nm diameter (23% w/w in water) which have been coated with polyvinylpyrrolidone (PVP).
Percoll is well suited for density gradient experiments because it possesses a low viscosity compared to alternatives, a low osmolarity, and no toxicity towards cells and their constituents.
Percoll is a registered trademark of GE Healthcare. | 1 | Biochemistry |
The creation of a mirror human is the basis of 1950 Arthur C. Clarke's story "Technical Error", from The Collected Stories. In this story, a physical accident transforms a person into his mirror image, speculatively explained by travel through a fourth physical dimension.
In the 1970 Star Trek novel Spock Must Die! by James Blish, the science officer of the USS Enterprise is replicated in mirror form by a transporter mishap. He locks himself in the sick bay where he is able to synthesize mirror forms of basic nutrients needed for his survival.
An alien machine that reverses chirality, and a blood-symbiote that functions properly only when in one chirality, were central to Roger Zelaznys 1976 novel Doorways in the Sand'.
On the titular planet of Sheri S. Tepper’s 1989 novel Grass, some lifeforms have evolved to use the right-handed isomer of alanine.
In the Mass Effect series, chirality of amino acids in foodstuffs is discussed often in both dialogue and encyclopedia files.
In the 2014 science fiction novel Cibola Burn by James S. A. Corey, the planet Ilus has indigenous life with partially-mirrored chirality. This renders human colonists unable to digest native flora and fauna, and greatly complicates conventional farming. Consequently, the colonists have to rely upon hydroponic farming and food importation.
In the 2017 Daniel Suarez novel Change Agent, an antagonist, Otto, nicknamed the "Mirror Man", is revealed to be a genetically-engineered mirror human. He views other humans with disdain and causes them to feel an inexplicable repulsion by his very presence.
The concept is used during Ryan North's 2023 run on Fantastic Four as an existential threat towards the human population. | 4 | Stereochemistry |
The quantity is commonly referred to as the "generalized Rabi frequency." For cases in which , Rabi flopping actually occurs at this frequency, where is the detuning, a measure of how far the light is off-resonance relative to the transition. For instance, examining the above animation at an offset frequency of ±1.73, one can see that during the 1/2 Rabi cycle (at resonance) shown during the animation, the oscillation instead undergoes one full cycle, thus at twice the (normal) Rabi frequency , just as predicted by this equation. Also note that as the incident light frequency shifts further from the transition frequency, the amplitude of the Rabi oscillation decreases, as is illustrated by the dashed envelope in the above plot. | 7 | Physical Chemistry |
In chemistry, recrystallization is a procedure for purifying compounds. The most typical situation is that a desired "compound A" is contaminated by a small amount of "impurity B". There are various methods of purification that may be attempted (see Separation process), recrystallization being one of them. There are also different recrystallization techniques that can be used such as: | 3 | Analytical Chemistry |
Problems in the digestion of phenylalanine (phe) to tyrosine (tyr) lead to the buildup of both phe and phenylpyruvate, in a disease called Phenylketonuria (PKU). These two compounds build up in the blood stream and cerebral spinal fluid, which can lead to mental retardation if left untreated. Treatment consists of a restricted diet of foods that contain phe or compounds that can breakdown into phe. Children in the US are routinely tested for this at birth. For more information see the Phenylketonuria page or the link below. | 1 | Biochemistry |
Nerve growth factor (NGF), the prototypical growth factor, is a protein secreted by a neurons target cell. NGF is critical for the survival and maintenance of sympathetic and sensory neurons. NGF is released from the target cells, binds to and activates its high affinity receptor TrkA on the neuron, and is internalized into the responsive neuron. The NGF/TrkA complex is subsequently trafficked back to the neurons cell body. This movement of NGF from axon tip to soma is thought to be involved in the long-distance signaling of neurons. | 1 | Biochemistry |
The cross-over temperature from the normal hadronic to the QGP phase is about . This "crossover" may actually not be only a qualitative feature, but instead one may have to do with a true (second order) phase transition, e.g. of the universality class of the three-dimensional Ising model. The phenomena involved correspond to an energy density of a little less than . For relativistic matter, pressure and temperature are not independent variables, so the equation of state is a relation between the energy density and the pressure. This has been found through lattice computations, and compared to both perturbation theory and string theory. This is still a matter of active research. Response functions such as the specific heat and various quark number susceptibilities are currently being computed. | 7 | Physical Chemistry |
Wide varieties of aromatic compounds are enzymatically reduced to form free radicals that contain one more electron than their parent compounds. In general, the electron donor is any of a wide variety of flavoenzymes and their coenzymes. Once formed, these anion free radicals reduce molecular oxygen to superoxide and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as a futile cycle or redox cycling. | 9 | Geochemistry |
In the US, the EPA issued a health advisory in 2015. A ten day Health Advisory was calculated for different ages which is considered protective of non-carcinogenic adverse health effects over a ten-day exposure to microcystins in drinking water: 0.3 μg/L for bottle-fed infants and young children of pre-school age and 1.6 μg/L for children of school age through adults. | 2 | Environmental Chemistry |
Solomon has been the recipient of numerous prestigious awards throughout his career. A selected list is outlined below.
* 2016 Companion of the Order of Australia.
* 2011 Prime Minister's Prize for Science, awarded jointly with Dr Ezio Rizzardo.
* 2006 Victoria Prize.
* 2001 Centenary Medal.
* 1994 Clunies Ross National Science and Technology Award.
* 1990 Member of the Order of Australia.
* 1989 Ian William Wark Medal and Lecture. | 7 | Physical Chemistry |
It is used in organic synthesis. One example is in the Perkin synthesis: the formation of unsaturated cinnamic-type acids by the condensation of aromatic aldehydes with fatty acids. Replacement of the commonly used sodium acetate with caesium acetate has been shown to improve yields by up to 10 times.
It is often used to invert secondary alcohols, first by direct S2 substitution of the hydroxyl group with acetate, which is then converted back to a hydroxyl group.
Caesium acetate is occasionally used instead of caesium formate in petroleum drilling fluids. | 0 | Organic Chemistry |
The non-specific DNA cleavage domain from the end of the FokI endonuclease can be used to construct hybrid nucleases that are active in a yeast assay. These reagents are also active in plant cells and in animal cells. Initial TALEN studies used the wild-type FokI cleavage domain, but some subsequent TALEN studies also used FokI cleavage domain variants with mutations designed to improve cleavage specificity and cleavage activity. The FokI domain functions as a dimer, requiring two constructs with unique DNA binding domains for sites in the target genome with proper orientation and spacing. Both the number of amino acid residues between the TALE DNA binding domain and the FokI cleavage domain and the number of bases between the two individual TALEN binding sites appear to be important parameters for achieving high levels of activity. | 1 | Biochemistry |
Cold solutions (−10 to −20 °C) are stable for days. Decomposition is accelerated by light and heavy metals. | 0 | Organic Chemistry |
In its pill form, selegiline is used to treat symptoms of Parkinson's disease. It is most often used as an adjunct to drugs such as levodopa (-DOPA), although it has been used off-label as a monotherapy. The rationale for adding selegiline to levodopa is to decrease the required dose of levodopa and thus reduce the motor complications of levodopa therapy. Selegiline delays the point when levodopa treatment becomes necessary from about 11 months to about 18 months after diagnosis. There is some evidence that selegiline acts as a neuroprotectant and reduces the rate of disease progression, though this is disputed.
Selegiline has also been used off-label as a palliative treatment for dementia in Alzheimer's disease. | 4 | Stereochemistry |
David Auerbach has described an effect that he observed in samples in glass beakers placed into a liquid cooling bath. In all cases the water supercooled, reaching a temperature of typically before spontaneously freezing. Considerable random variation was observed in the time required for spontaneous freezing to start and in some cases this resulted in the water which started off hotter (partially) freezing first.
In 2016, Burridge and Linden defined the criterion as the time to reach , carried out experiments, and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers: "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect."
In controlled experiments, the effect can entirely be explained by undercooling and the time of freezing was determined by what container was used. Experimental results confirming the Mpemba effect have been criticized for being flawed, not accounting for dissolved solids and gasses, and other confounding factors.
Philip Ball, a reviewer for Physics World wrote: "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." Ball wrote that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.
New Scientist recommends starting the experiment with containers at , respectively, to maximize the effect. In a related study, it was found that freezer temperature also affects the probability of observing the Mpemba phenomenon as well as container temperature does. | 7 | Physical Chemistry |
It is possible that specific molecules are dissolved in lyotropic mesophases, where they can be located mainly inside, outside, or at the surface of the aggregates.
Some of such molecules act as dopants, inducing specific properties to the whole phase, other ones can be considered simple guests with limited effect on the surrounding environment but possibly strong consequences on their physico-chemical properties, and some of them are used as probe to detect molecular-level properties of the whole mesophase in specific analytical techniques. | 7 | Physical Chemistry |
* Water temperature
* Specific conductance or electrical conductance (EC) or conductivity
* Total suspended solids (TSS)
* Transparency or turbidity
* Water clarity
* Total dissolved solids (TDS)
* Odour of water
* Color of water (such as Forel-Ule scale or Pt/Co scale)
* Taste of water | 3 | Analytical Chemistry |
We can use the above equations to derive some differential definitions of some thermodynamic parameters. If we define to stand for any of the thermodynamic potentials, then the above equations are of the form:
where and are conjugate pairs, and the are the natural variables of the potential . From the chain rule it follows that:
where is the set of all natural variables of except that are held as constants. This yields expressions for various thermodynamic parameters in terms of the derivatives of the potentials with respect to their natural variables. These equations are known as equations of state since they specify parameters of the thermodynamic state. If we restrict ourselves to the potentials (Internal energy), (Helmholtz energy), (Enthalpy) and (Gibbs energy), then we have the following equations of state (subscripts showing natural variables that are held as constants):
where, in the last equation, is any of the thermodynamic potentials (, , , or ), and are the set of natural variables for that potential, excluding . If we use all thermodynamic potentials, then we will have more equations of state such as
and so on. In all, if the thermodynamic space is dimensions, then there will be equations for each potential, resulting in a total of equations of state because thermodynamic potentials exist. If the equations of state for a particular potential are known, then the fundamental equation for that potential (i.e., the exact differential of the thermodynamic potential) can be determined. This means that all thermodynamic information about the system will be known because the fundamental equations for any other potential can be found via the Legendre transforms and the corresponding equations of state for each potential as partial derivatives of the potential can also be found. | 7 | Physical Chemistry |
Yeasts naturally harbour various plasmids. Notable among them are 2 μm plasmids—small circular plasmids often used for genetic engineering of yeast—and linear pGKL plasmids from Kluyveromyces lactis, that are responsible for killer phenotypes.
Other types of plasmids are often related to yeast cloning vectors that include:
* Yeast integrative plasmid (YIp), yeast vectors that rely on integration into the host chromosome for survival and replication, and are usually used when studying the functionality of a solo gene or when the gene is toxic. Also connected with the gene URA3, that codes an enzyme related to the biosynthesis of pyrimidine nucleotides (T, C);
* Yeast Replicative Plasmid (YRp), which transport a sequence of chromosomal DNA that includes an origin of replication. These plasmids are less stable, as they can be lost during budding. | 1 | Biochemistry |
The simplest method of lipid separation is the use of thin layer chromatography (TLC). Although not as sensitive as other methods of lipid detection, it offers a rapid and comprehensive screening tool prior to more sensitive and sophisticated techniques.
Solid-phase extraction (SPE) chromatography is useful for rapid, preparative separation of crude lipid mixtures into different lipid classes. This involves the use of prepacked columns containing silica or other stationary phases to separate glycerophospholipids, fatty acids, cholesteryl esters, glycerolipids, and sterols from crude lipid mixtures.
High-performance liquid chromatography (HPLC or LC) is extensively used in lipidomic analysis to separate lipids prior to mass analysis. Separation can be achieved by either normal-phase (NP) HPLC or reverse-phase (RP) HPLC. For example, NP-HPLC effectively separates glycerophospholipids on the basis of headgroup polarity, whereas RP-HPLC
effectively separates fatty acids such as eicosanoids on the basis of chain length, degree of unsaturation and substitution. For global, untargeted lipidomic studies it is common to use both RP and NP or Hydrophilic Interaction Liquid Chromatrography (HILC) columns for increased lipidome coverage. The application of nano-flow liquid chromatography (nLC) proved thereby to be most efficient to enhance both general measurement sensitivity and lipidome coverage for a global lipidomics approach. Chromatographic (HPLC/UHPLC) separation of lipids may either be performed offline or online where the eluate is integrated with the ionization source of a mass spectrometer. | 1 | Biochemistry |
A major mechanism of resistance against piperacillin-tazobactam is Gram-negative bacteria producing β-lactamases. Other currently known mechanisms include mutations in the active site of penicillin-binding proteins, changes in membrane efflux, or bacteria permeability. Some enzymes, such as extended-spectrum β-lactamase (ESBL) have evolved from narrow-spectrum β-lactamases due to genetic mutations, increasing their capabilities to hydrolyze much broader spectrum penicillin. Due to prior conflicting reports on the drug's affinity with ESBL-producing bacteria, piperacillin-tazobactam treatment for such is not recommended. Antibiotic resistance occurs sporadically, conferred by the continuous use of piperacillin-tazobactam in situations where it may prove to be ineffective, leading to cases where plasmid-mediated β-lactamases are being produced in bacteria that do not naturally produce it.
Some Gram-positive bacteria penicillin-binding proteins such as Enterococcus faecium (PBP-5) or Staphylococcus aureus (PBP-2a) are intrinsically antibiotic resistant, consisting of relatively low affinity with piperacillin and therefore high resistance to piperacillin-tazobactam. Furthermore, mutations in penicillin-binding proteins cause fluctuations in piperacillin affinity, whereas Streptococcus pneumoniae (PBP-2b) autolytic response is significantly reduced due to decreased affinity with piperacillin. Although membrane permeability changes are less common as a mechanism of resistance, studies investigating Klebsiella pneumoniae have reported a correlation between decreased permeability of piperacillin and increased SHV-1 β-lactamase production. | 4 | Stereochemistry |
The zero-phonon line is an optical analogy to the Mössbauer lines, which originate in the recoil-free emission or absorption of gamma rays from the nuclei of atoms bound in a solid matrix. In the case of the optical zero-phonon line, the position of the chromophore is the physical parameter that may be perturbed, whereas in the gamma transition, the momenta of the atoms may be changed. More technically, the key to the analogy is the symmetry between position and momentum in the Hamiltonian of the quantum harmonic oscillator. Both position and momentum contribute in the same way (quadratically) to the total energy. | 7 | Physical Chemistry |
In the absence of an external field, the director of a liquid crystal is free to point in any direction. It is possible, however, to force the director to point in a specific direction by introducing an outside agent to the system. For example, when a thin polymer coating (usually a polyimide) is spread on a glass substrate and rubbed in a single direction with a cloth, it is observed that liquid crystal molecules in contact with that surface align with the rubbing direction. The currently accepted mechanism for this is believed to be an epitaxial growth of the liquid crystal layers on the partially aligned polymer chains in the near surface layers of the polyimide.
Several liquid crystal chemicals also align to a command surface which is in turn aligned by electric field of polarized light. This process is called photoalignment. | 7 | Physical Chemistry |
The liver is the main site of transferrin synthesis but other tissues and organs, including the brain, also produce transferrin. A major source of transferrin secretion in the brain is the choroid plexus in the ventricular system. The main role of transferrin is to deliver iron from absorption centers in the duodenum and white blood cell macrophages to all tissues. Transferrin plays a key role in areas where erythropoiesis and active cell division occur. The receptor helps maintain iron homeostasis in the cells by controlling iron concentrations.
The gene coding for transferrin in humans is located in chromosome band 3q21.
Medical professionals may check serum transferrin level in iron deficiency and in iron overload disorders such as hemochromatosis. | 1 | Biochemistry |
Molecules containing an N-glycosidic bond are known as glycosylamines. Many authors in biochemistry call these compounds N-glycosides and group them with the glycosides; this is considered a misnomer and is discouraged by the International Union of Pure and Applied Chemistry. Glycosylamines and glycosides are grouped together as glycoconjugates; other glycoconjugates include glycoproteins, glycopeptides, peptidoglycans, glycolipids, and lipopolysaccharides. | 0 | Organic Chemistry |
Levofloxacin, sold under the brand name Levaquin among others, is an antibiotic medication. It is used to treat a number of bacterial infections including acute bacterial sinusitis, pneumonia, H. pylori (in combination with other medications), urinary tract infections, chronic prostatitis, and some types of gastroenteritis. Along with other antibiotics it may be used to treat tuberculosis, meningitis, or pelvic inflammatory disease. Use is generally recommended only when other options are not available. It is available by mouth, intravenously, and in eye drop form.
Common side effects include nausea, diarrhea, and trouble sleeping. Serious side effects may include tendon rupture, tendon inflammation, seizures, psychosis, and potentially permanent peripheral nerve damage. Tendon damage may appear months after treatment is completed. People may also sunburn more easily. In people with myasthenia gravis, muscle weakness and breathing problems may worsen. While use during pregnancy is not recommended, risk appears to be low. The use of other medications in this class appear to be safe while breastfeeding; however, the safety of levofloxacin is unclear. Levofloxacin is a broad-spectrum antibiotic of the fluoroquinolone drug class. It usually results in death of the bacteria. It is the left-handed isomer of the medication ofloxacin.
Levofloxacin was patented in 1985 and approved for medical use in the United States in 1996. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2021, it was the 223rd most commonly prescribed medication in the United States, with more than 1million prescriptions. | 4 | Stereochemistry |
There is no space group restriction for the crystallization of racemic compound crystallizing either in centrosymmetric or in non-centrosymmetric space group (SG). The frequency of organic racemic compounds in the Cambridge Structural Database is summarized in the following table:
Kryptoracemic compounds are thus very rare and represent circa 1% of the racemic compounds. The frequency of kryptoracemic compounds in the whole organic Cambridge Structural Database was estimated to circa 0.4% to 0.8%.
A review covering organometallic compounds with a stereogenic metal atom sorted a list of 26 possible kryptoracemic compounds. | 4 | Stereochemistry |
When choosing between inducing transient or stable expression in cells, time frame and experimental goal must be taken into consideration. Transiently transfected cells are often used to study the effects of short-term gene expression, perform RNA interference (RNAi)‑mediated gene silencing, or quickly generate small-scale recombinant proteins. This rapid generation small quantities of recombinant proteins can be applied towards evaluating their potential as drug candidates or examining their integrity of constructs during stages of vector development. Additionally, transient expression can be a useful tool when aiming to optimize selected parameters before undergoing the time-consuming process of scale-up in stably transfected cells. Typically, the cells are harvested within 1-4 days after successful transfection. For even quicker results, replacing DNA with mRNA can result in transient expression within minutes after successful transfection in some systems; this process bypasses translocation to the nucleus and transcription.
If stable, long-term gene expression is desired, stable transfection of cells is more useful. However, since successful integration of a DNA vector into the chromosome is a rare occurrence, this process is more difficult and time-consuming, and is reserved for large-scale protein production, gene therapies, and long-term pharmacology studies. | 1 | Biochemistry |
Salen refers to a tetradentate C-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff bases. Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states. For this reason salen-type compounds are used as metal deactivators. Metal salen complexes also find use as catalysts. | 0 | Organic Chemistry |
The compressor flow and pressure range is shown with a carpet plot of engine constant rpm and constant torque lines superimposed on the map. OpenCourseWare material shows a carpet plot of engine speed and load for the airflow requirements of 4-stroke truck engine. Shahed shows lines of constant engine speed and engine BMEP for a heavy-duty diesel engine. Woollenweber shows engine airflow requirements at different engine speeds and load/fuelling/torque. Hiereth et al. show operating lines for various applications such as a full-load operating line for a passenger car engine, the effect of an uncontrolled turbocharger on a truck diesel engine and wastegate control on passenger diesel and gasoline engines, and the effect of altitude on a compressor operating line. | 7 | Physical Chemistry |
The reaction mechanism consists of two nucleophilic substitutions: the amine is the first nucleophile displacing the bromine atom which then acts as the second nucleophile. In following the mechanism is described using trimethylamine as example:
First, the trimethylamine reacts with the cyanogen bromide to form a quaternary ammonium salt, which in the next step reacts by splitting off bromomethane to give the dimethylcyanamide. This is a second-order nucleophilic substitution (S2). | 0 | Organic Chemistry |
Traditionally, ultrasound B-Mode imaging has been designed for allowing a visual evaluation of human organs and their features by clinicians; however, this implies that the huge quantity of information carried by ultrasound signals is processed and significantly reduced for visualization purposes. REMS technology instead analyses the raw, unfiltered ultrasound signals by comparing their spectral representation with the spectral models stored in a proprietary database which has been previously obtained from healthy and osteoporotic patients; these models are specific and vary with sex, age, BMI and skeletal site. The comparison allows the BMD estimation of the patient as well as a both fast and reliable diagnostic classification, compliant to the recommendations and diagnostic criteria defined by the World Health Organization. | 7 | Physical Chemistry |
Some molecules, such as XeF or , have a lone pair that distorts the symmetry of the molecule from O to C. The specific geometry is known as a monocapped octahedron, since it is derived from the octahedron by placing the lone pair over the centre of one triangular face of the octahedron as a "cap" (and shifting the positions of the other six atoms to accommodate it). These both represent a divergence from the geometry predicted by VSEPR, which for AXE predicts a pentagonal pyramidal shape. | 4 | Stereochemistry |
Inversions and translocations are relatively easy to detect by an invalid pair of sequenced-end. For instance, a translocation can be detected if the paired-ends are mapped onto different chromosomes on the reference genome. Inversion can be detected by divergent orientation of the reads, where the insert will have two plus-end or two minus-end. | 1 | Biochemistry |
The elementary example operates under quasi equilibrium conditions. Its main quantum feature is the discrete energy level structure.
More realistic devices operate out of equilibrium possessing friction heat leaks and finite heat flow.
Quantum thermodynamics supplies a dynamical theory required for systems out of equilibrium such as heat engines, thus,
inserting dynamics into thermodynamics.
The theory of open quantum systems constitutes the basic theory. For heat engines a reduced description of the dynamics
of the working substance is sought, tracing out the hot and cold baths.
The starting point is the general Hamiltonian of the combined systems:
and the system Hamiltonian is time dependent.
A reduced description leads to the equation of motion of the system:
where is the density operator describing the state of the working medium and is the generator of dissipative dynamics
which includes the heat transport terms from the baths.
Using this construction, the total change in energy of the sub-system becomes:
leading to the dynamical version of the first law of thermodynamics:
* The power
* Heat currents and .
The rate of entropy production becomes:
The global structure of quantum mechanics is reflected in the derivation of the reduced description.
A derivation which is consistent with the laws of thermodynamics is based on
the weak coupling limit.
A thermodynamical idealization assumes that the system and the baths are uncorrelated, meaning that the total state
of the combined system becomes a tensor product at all times:
Under these conditions the dynamical equations of motion become:
where is the Liouville superoperator described in terms of the system's Hilbert space,
where the reservoirs are described implicitly.
Within the formalism of quantum open system, can take the form of the
Gorini-Kossakowski-Sudarshan-Lindblad (GKS-L) Markovian generator or also known just as Lindblad equation
. Theories beyond the weak coupling regime have been proposed. | 7 | Physical Chemistry |
Secreted frizzled-related protein 1 (SFRP1) is a member of the SFRP family that contains a cysteine-rich domain homologous to the putative Wnt-binding site of Frizzled proteins. SFRPs act as soluble modulators of Wnt signaling. SFRP1 and SFRP5 may be involved in determining the polarity of photoreceptor cells in the retina. SFRP1 is expressed in several human tissues, with the highest levels in the heart.
The Secreted frizzled-related protein (SFRP) family consists of five secreted glycoproteins in humans (SFRP1, SFRP2, SFRP3, SFRP4, SFRP5) that act as extracellular signaling ligands. Each SFRP is ~300 amino acids in length and contains a cysteine-rich domain (CRD) that shares 30-50% sequence homology with the CRD of Frizzled (Fz) receptors. SFRPs are able to bind Wnt proteins and Fz receptors in the extracellular compartment. The interaction between SFRPs and Wnt proteins prevents the latter from binding the Fz receptors. SFRPs are also able to downregulate Wnt signaling by the formation of an inhibitory complex with the Frizzled receptors. The Wnt pathway plays a key role in embryonic development, cell differentiation and cell proliferation. It has been shown that the deregulation of this critical developmental pathway occurs in several human tumor entities.
SFRP1 is a 35 kDa prototypical member of the SFRP family. It acts as a biphasic modulator of Wnt signaling, counteracting Wnt-induced effects at high concentrations and promoting them at lower concentrations. It is located in a chromosomal region (8p12-p11.1) that is frequently deleted in breast cancer and is thought to harbour a tumor suppressor gene. | 1 | Biochemistry |
Another major use of plasmids is to make large amounts of proteins. In this case, researchers grow bacteria containing a plasmid harboring the gene of interest. Just as the bacterium produces proteins to confer its antibiotic resistance, it can also be induced to produce large amounts of proteins from the inserted gene. This is a cheap and easy way of mass-producing the protein the gene codes for, for example, insulin. | 1 | Biochemistry |
Nanofiber Seeding is a process to control the bulk morphology of chemically synthesized conducting polymers.
Typically, catalytic amount of nanofiber seeds are added in prior to onset of nanofiber seeding polymerization (reaction), where seeds are served as the morphology directing agent rather than conventional templates (see hard or soft templating methods). | 7 | Physical Chemistry |
Below 912 °C (1,674 °F), iron has a body-centered cubic (bcc) crystal structure and is known as α-iron or ferrite. It is thermodynamically stable and a fairly soft metal. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-Fe discussed below.
Magnetically, α-iron is paramagnetic at high temperatures. However, below its Curie temperature (T or A) of 771 °C (1044K or 1420 °F), it becomes ferromagnetic. In the past, the paramagnetic form of α-iron was known as beta iron (β-Fe). Even though the slight tetragonal distortion in the ferromagnetic state does constitute a true phase transition, the continuous nature of this transition results in only minor importance in steel heat treating. The A line forms the boundary between the beta iron and alpha fields in the phase diagram in Figure 1.
Similarly, the A boundary is of only minor importance compared to the A (eutectoid), A and A critical temperatures. The A, where austenite is in equilibrium with cementite + γ-Fe, is beyond the right edge in Fig. 1. The α + γ phase field is, technically, the β + γ field above the A. The beta designation maintains continuity of the Greek-letter progression of phases in iron and steel: α-Fe, β-Fe, austenite (γ-Fe), high-temperature δ-Fe, and high-pressure hexaferrum (ε-Fe).
The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic α-Fe. It has a hardness of approximately 80 Brinell. The maximum solubility of carbon is about 0.02 wt% at and 0.001% at . When it dissolves in iron, carbon atoms occupy interstitial "holes". Being about twice the diameter of the tetrahedral hole, the carbon introduces a strong local strain field.
Mild steel (carbon steel with up to about 0.2 wt% C) consists mostly of α-Fe and increasing amounts of cementite (FeC, an iron carbide). The mixture adopts a lamellar structure called pearlite. Since bainite and pearlite each contain α-Fe as a component, any iron-carbon alloy will contain some amount of α-Fe if it is allowed to reach equilibrium at room temperature. The amount of α-Fe depends on the cooling process. | 8 | Metallurgy |
The pH dependence is given by the factor −0.059m/n per pH unit, where m relates to the number of protons in the equation, and n the number of electrons exchanged. Electrons are always exchanged in electrochemistry, but not necessarily protons. If there is no proton exchange in the reaction equilibrium, the reaction is said to be pH-independent. This means that the values for the electrochemical potential rendered in a redox half-reaction, whereby the elements in question change oxidation states are the same whatever the pH conditions under which the procedure is carried out.
The Frost diagram is also a useful tool for comparing the trends of standard potentials (slope) of acidic and basic solutions. The pure, neutral element transitions to different compounds depending whether the species is in acidic and basic pHs. Though the value and amount of oxidation states remain unchanged, the free energies can vary greatly. The Frost diagram allows the superimposition of acidic and basic graphs for easy and convenient comparison. | 7 | Physical Chemistry |
Modern classification of meteorites and micrometeorites is complex; the 2007 review paper of Krot et al. summarizes modern meteorite taxonomy. Linking individual micrometeorites to meteorite classification groups requires a comparison of their elemental, isotopic and textural characteristics. | 9 | Geochemistry |
The STRENDA project is driven by 15 scientists from all over the world forming the STRENDA Commission and supporting the work with expertises in biochemistry, [https://www.qmul.ac.uk/sbcs/iubmb/enzyme/ enzyme nomenclature], bioinformatics, systems biology, modelling, mechanistic enzymology and theoretical biology. | 1 | Biochemistry |
Fatty acid synthase (FAS) is an enzyme that in humans is encoded by the FASN gene.
Fatty acid synthase is a multi-enzyme protein that catalyzes fatty acid synthesis. It is not a single enzyme but a whole enzymatic system composed of two identical 272 kDa multifunctional polypeptides, in which substrates are handed from one functional domain to the next.
Its main function is to catalyze the synthesis of palmitate (C16:0, a long-chain saturated fatty acid) from acetyl-CoA and malonyl-CoA, in the presence of NADPH.
The fatty acids are synthesized by a series of decarboxylative Claisen condensation reactions from acetyl-CoA and malonyl-CoA. Following each round of elongation the beta keto group is reduced to the fully saturated carbon chain by the sequential action of a ketoreductase (KR), dehydratase (DH), and enoyl reductase (ER). The growing fatty acid chain is carried between these active sites while attached covalently to the phosphopantetheine prosthetic group of an acyl carrier protein (ACP), and is released by the action of a thioesterase (TE) upon reaching a carbon chain length of 16 (palmitic acid). | 1 | Biochemistry |
Eating fish or shellfish from lakes with a bloom nearby is not recommended. Potent toxins are accumulated in shellfish that feed on the algae. If the shellfish are consumed, various types of poisoning may result. These include amnesic shellfish poisoning (ASP), diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and paralytic shellfish poisoning. A 2002 study has shown that algal toxins may be the cause for as many as 60,000 intoxication cases in the world each year.
In 1987 a new illness emerged: amnesic shellfish poisoning (ASP). People who had eaten mussels from Prince Edward Island were found to have ASP. The illness was caused by domoic acid, produced by a diatom found in the area where the mussels were cultivated. A 2013 study found that toxic paralytic shellfish poisoning in the Philippines during HABs has caused at least 120 deaths over a few decades. After a 2014 HAB incident in Monterey Bay, California, health officials warned people not to eat certain parts of anchovy, sardines, or crab caught in the bay. In 2015 most shellfish fisheries in Washington, Oregon and California were shut down because of high concentrations of toxic domoic acid in shellfish. People have been warned that inhaling vapors from waves or wind during a HAB event may cause asthma attacks or lead to other respiratory ailments.
In 2018 agricultural officials in Utah worried that even crops could become contaminated if irrigated with toxic water, although they admit that they can't measure contamination accurately because of so many variables in farming. They issued warnings to residents, however, out of caution. | 3 | Analytical Chemistry |
Bursting may result from the stochastic nature of biochemical events superimposed upon a two step fluctuation. In its simplest form, the gene is proposed to exist in two states, one where activity is negligible and one where there is a certain probability of activation. Only in the second state does transcription readily occur. It seems likely that some rudimentary eukaryotes have genes which do not show bursting. The genes are always in the permissive state, with a simple probability describing the numbers of RNAs generated.
More recent data indicate the two state model can be an oversimplification. Transcription of the c-Fos gene in response to serum stimulation can, for the most part, be summarised by two states, although at certain times after stimulation, a third state better explains the variance in the data. Another model suggests a two state model can apply, but with each cell having a different transcription rate in the active state. Other analyses indicate a spectrum or continuum of activity states. The nuclear and signaling landscapes of complex eukaryotic nuclei may favour more than two simple states- for example, there are over several dozen post-translational modifications of nucleosomes and perhaps a hundred different proteins involved in the average eukaryotic transcription reaction.
What do the repressive and permissive states represent? An attractive idea is that the repressed state is a closed chromatin conformation whilst the permissive states are more open. Another hypothesis is that the fluctuations between states reflect reversible transitions in the binding and dissociation of pre-initiation complexes. Bursts may also result from bursty signalling, cell cycle effects or movement of chromatin to and from transcription factories. Bursting dynamics have been demonstrated to be influenced by cell size and the frequency of extracellular signalling. Recent data suggest different degrees of supercoiling distinguish the permissive and inactive states.
The bursting phenomenon, as opposed to simple probabilistic models of transcription, can account for the high variability (see transcriptional noise) in gene expression occurring between cells in isogenic populations. This variability in turn can have tremendous consequences on cell behaviour, and must be mitigated or integrated. Suggested mechanisms by which noise can be dampened include strong extracellular signalling, diffusion of RNA and protein in cell syncitia, promoter proximal pausing, and nuclear retention of transcripts. In certain contexts, such as the survival of microbes in rapidly changing stressful environments, the expression variability may be essential. Variability also impacts upon the effectiveness of clinical treatment, with resistance of bacteria to antibiotics demonstrably caused by non-genetic differences. Similar phenomena may contribute to the resistance of sub-populations of cancer cells to chemotherapy. Spontaneous variability in gene expression is also proposed to act as a source of cell fate diversity in self-organizing differentiation processes, and may act as a barrier to effective cellular reprogramming strategies. | 1 | Biochemistry |
Tear gas, also known as a lachrymatory agent or lachrymator (), sometimes colloquially known as "mace" after the early commercial self-defense spray, is a chemical weapon that stimulates the nerves of the lacrimal gland in the eye to produce tears. In addition, it can cause severe eye and respiratory pain, skin irritation, bleeding, and blindness. Common lachrymators both currently and formerly used as tear gas include pepper spray (OC gas), PAVA spray (nonivamide), CS gas, CR gas, CN gas (phenacyl chloride), bromoacetone, xylyl bromide and Mace (a branded mixture).
While lachrymatory agents are commonly deployed for riot control by law enforcement and military personnel, its use in warfare is prohibited by various international treaties. During World War I, increasingly toxic and deadly lachrymatory agents were used.
The short and long-term effects of tear gas are not well studied. The published peer-reviewed literature consists of lower quality evidence that does not establish causality. More rigorous research is needed. Exposure to tear gas agents may produce numerous short-term and long-term health effects, including development of respiratory illnesses, severe eye injuries and diseases (such as traumatic optic neuropathy, keratitis, glaucoma, and cataracts), dermatitis, damage of cardiovascular and gastrointestinal systems, and death, especially in cases with exposure to high concentrations of tear gas or application of the tear gases in enclosed spaces. | 1 | Biochemistry |
One current goal of the Joint Center for Structural Genomics (JCSG), a part of the Protein Structure Initiative (PSI) is to solve the structures for all the proteins in Thermotoga maritima, a thermophillic bacterium. T. maritima was selected as a structural genomics target based on its relatively small genome consisting of 1,877 genes and the hypothesis that the proteins expressed by a thermophilic bacterium would be easier to crystallize.
Lesley et al used Escherichia coli to express all the open-reading frames (ORFs) of T. martima. These proteins were then crystallized and structures were determined for successfully crystallized proteins using X-ray crystallography. Among other structures, this structural genomics approach allowed for the determination of the structure of the TM0449 protein, which was found to exhibit a novel fold as it did not share structural homology with any known protein. | 1 | Biochemistry |
Glycopolymer is synthetic polymer with pendant carbohydrates. Glycopolymers play an important role in many biological recognition events such as cell–cell adhesion, development of new tissues and infectious behavior of virus and bacteria. They have high potential in targeted drug delivery, tissue engineering and synthesis of bio-compatible materials.
The first glycopolymer was synthesized in 1978 by free-radical polymerization. Subsequent efforts have been devoted to synthesizing glycopolymers with various structures and sizes, and the synthesis techniques have widened to controlled/living radical polymerisation, ring-opening polymerization, ring-opening metathesis polymerization and post-functionalization. | 0 | Organic Chemistry |
Human genetic enhancement or human genetic engineering refers to human enhancement by means of a genetic modification. This could be done in order to cure diseases (gene therapy), prevent the possibility of getting a particular disease (similarly to vaccines), to improve athlete performance in sporting events (gene doping), or to change physical appearance, metabolism, and even improve physical capabilities and mental faculties such as memory and intelligence.
These genetic enhancements may or may not be done in such a way that the change is heritable (which has raised concerns within the scientific community). | 1 | Biochemistry |
One way that enzymatic catalysis proceeds is by stabilizing the transition state through electrostatics. By lowering the energy of the transition state, it allows a greater population of the starting material to attain the energy needed to overcome the transition energy and proceed to product. | 7 | Physical Chemistry |
In chemistry, reaction progress kinetic analysis (RPKA) is a subset of a broad range of kinetic techniques utilized to determine the rate laws of chemical reactions and to aid in elucidation of reaction mechanisms. While the concepts guiding reaction progress kinetic analysis are not new, the process was formalized by Professor Donna Blackmond (currently at Scripps Research Institute) in the late 1990s and has since seen increasingly widespread use. Unlike more common pseudo-first-order analysis, in which an overwhelming excess of one or more reagents is used relative to a species of interest, RPKA probes reactions at synthetically relevant conditions (i.e. with concentrations and reagent ratios resembling those used in the reaction when not exploring the rate law.) Generally, this analysis involves a system in which the concentrations of multiple reactants are changing measurably over the course of the reaction. As the mechanism can vary depending on the relative and absolute concentrations of the species involved, this approach obtains results that are much more representative of reaction behavior under commonly utilized conditions than do traditional tactics. Furthermore, information obtained by observation of the reaction over time may provide insight regarding unexpected behavior such as induction periods, catalyst deactivation, or changes in mechanism. | 7 | Physical Chemistry |
Transcriptional gene regulation process depends on many spatial and temporal factors in the nucleus such as global or local chromatin states, nucleosome positioning, TF binding, enhancer/promoter activities. Variant that alter the function of any of these biological processes may alter the gene regulation and cause phenotypic abnormality. Genetic variants that located in distal regulatory region can affect the binding motif of TFs, chromatin regulators and other distal transcriptional factors, which disturb the interaction between enhancer/silencer and its target gene. | 1 | Biochemistry |
Secondary metabolites are often characterized as either qualitative or quantitative. Qualitative metabolites are defined as toxins that interfere with a herbivore's metabolism, often by blocking specific biochemical reactions. Qualitative chemicals are present in plants in relatively low concentrations (often less than 2% dry weight), and are not dosage dependent. They are usually small, water-soluble molecules, and therefore can be rapidly synthesized, transported and stored with relatively little energy cost to the plant. Qualitative allelochemicals are usually effective against non-adapted generalist herbivores.
Quantitative chemicals are those that are present in high concentration in plants (5 – 40% dry weight) and are equally effective against all specialists and generalist herbivores. Most quantitative metabolites are digestibility reducers that make plant cell walls indigestible to animals. The effects of quantitative metabolites are dosage dependent and the higher these chemicals proportion in the herbivores diet, the less nutrition the herbivore can gain from ingesting plant tissues. Because they are typically large molecules, these defenses are energetically expensive to produce and maintain, and often take longer to synthesize and transport.
The geranium, for example, produces the amino acid, quisqualic acid in its petals to defend itself from Japanese beetles. Within 30 minutes of ingestion the chemical paralyzes the herbivore. While the chemical usually wears off within a few hours, during this time the beetle is often consumed by its own predators. | 1 | Biochemistry |
The Macromolecular Interpenetration theory, also known as the diffusion theory, states that the mucoadhesive molecules and mucus glycoproteins mutually interact by means of interpenetration of their chains and the forming of secondary semi-permanent adhesive bonds. It is necessary that the mucoadhesive device has features or properties that favor both chemical and mechanical interactions for the macromolecular interpenetration theory to take place. Molecules that can present mucoadhesive properties are molecules with hydrogen bond building groups, high molecular weight, flexible chains, and surface active properties.
It is perceived that increase in adhesion force is associated with the degree of penetration of polymer chains. Literature states that the degree of penetration required for efficient bioadhesive bonds lies in the range of 0.2-0.5μm. The following equation can be used to estimate the degree of penetration of polymer and mucus chains:
with as contact time and as the diffusion coefficient of the mucoadhesive material in the mucus. Maximum adhesion strength is reached when penetration depth is approximately equal to polymer chain size. Properties of mutual solubility and structural similarity will improve the mucoadhesive bond. | 1 | Biochemistry |
He appears as a character in the Russian film Prediction by Eldar Ryazanov and has a tiny cameo mention in The Eighth Life, the prize-winning epic novel by Nino Haratischwili. | 1 | Biochemistry |
Bromine is used in flame retardants, pesticides, lighter fuel, antiknocking agents, and for water purification. The organic form of this element is used as flame retardants commercially and in pesticides. These chemicals have led to an increase in the depletion of the stratospheric ozone layer. Some countries use bromine to treat drinking water, similar to chlorination. Bromine is also present as impurities emitted from cooling towers. | 9 | Geochemistry |
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Diamond and graphite are a familiar example; they are isomers of carbon. Isomerism refers to the existence or possibility of isomers.
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism or (spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ.
Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest.
The English word "isomer" () is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish ; which in turn was coined from Greek ἰσόμερoς , with roots = "equal", = "part". | 4 | Stereochemistry |
The contact graph of an arbitrary finite packing of unit balls is the graph whose vertices correspond to the packing elements and whose two vertices are connected by an edge if the corresponding two packing elements touch each other. The cardinality of the edge set of the contact graph gives the number of touching pairs, the number of 3-cycles in the contact graph gives the number of touching triplets, and the number of tetrahedrons in the contact graph gives the number of touching quadruples (in general for a contact graph associated with a sphere packing in n dimensions that the cardinality of the set of n-simplices in the contact graph gives the number of touching (n + 1)-tuples in the sphere packing). In the case of 3-dimensional Euclidean space, non-trivial upper bounds on the number of touching pairs, triplets, and quadruples were proved by Karoly Bezdek and Samuel Reid at the University of Calgary.
The problem of finding the arrangement of n identical spheres that maximizes the number of contact points between the spheres is known as the "sticky-sphere problem". The maximum is known for n ≤ 11, and only conjectural values are known for larger n. | 3 | Analytical Chemistry |
The Goldschmidt classification,
developed by Victor Goldschmidt (1888–1947), is a geochemical classification which groups the chemical elements within the Earth according to their preferred host phases into lithophile (rock-loving), siderophile (iron-loving), chalcophile (sulfide ore-loving or chalcogen-loving), and atmophile (gas-loving) or volatile (the element, or a compound in which it occurs, is liquid or gaseous at ambient surface conditions).
Some elements have affinities to more than one phase. The main affinity is given in the table below and a discussion of each group follows that table. | 9 | Geochemistry |
In the 17th century Guillaume Amontons discovered a regular relationship between the pressure and temperature of a gas at constant volume. Some introductory physics textbooks still define the pressure-temperature relationship as Gay-Lussac's law. Gay-Lussac primarily investigated the relationship between volume and temperature and published it in 1802, but his work did cover some comparison between pressure and temperature. Given the relative technology available to both men, Amontons could only work with air as a gas, whereas Gay-Lussac was able to experiment with multiple types of common gases, such as oxygen, nitrogen, and hydrogen. | 7 | Physical Chemistry |
Canada has the worlds largest deposit of natural bitumen in the Athabasca oil sands, and Canadian First Nations along the Athabasca River had long used it to waterproof their canoes. In 1719, a Cree named Wa-Pa-Su brought a sample for trade to Henry Kelsey of the Hudsons Bay Company, who was the first recorded European to see it. However, it wasn't until 1787 that fur trader and explorer Alexander MacKenzie saw the Athabasca oil sands and said, "At about 24 miles from the fork (of the Athabasca and Clearwater Rivers) are some bituminous fountains into which a pole of 20 feet long may be inserted without the least resistance."
The value of the deposit was obvious from the start, but the means of extracting the bitumen was not. The nearest town, Fort McMurray, Alberta, was a small fur trading post, other markets were far away, and transportation costs were too high to ship the raw bituminous sand for paving. In 1915, Sidney Ells of the Federal Mines Branch experimented with separation techniques and used the product to pave 600 feet of road in Edmonton, Alberta. Other roads in Alberta were paved with material extracted from oil sands, but it was generally not economic. During the 1920s Dr. Karl A. Clark of the Alberta Research Council patented a hot water oil separation process and entrepreneur Robert C. Fitzsimmons built the Bitumount oil separation plant, which between 1925 and 1958 produced up to per day of bitumen using Dr. Clark's method. Most of the bitumen was used for waterproofing roofs, but other uses included fuels, lubrication oils, printers ink, medicines, rust- and acid-proof paints, fireproof roofing, street paving, patent leather, and fence post preservatives. Eventually Fitzsimmons ran out of money and the plant was taken over by the Alberta government. Today the Bitumount plant is a Provincial Historic Site. | 7 | Physical Chemistry |
Most studies to date have focused on the development of synthetic methodologies with the aim of maximizing pore size and surface area for gas storage. That means the functions of COFs have not yet been well explored, but COFs can be used as catalysts, or for gas separation, etc. | 6 | Supramolecular Chemistry |
Gerhard Ertl is known for determining the detailed molecular mechanisms of the catalytic synthesis of ammonia over iron (Haber Bosch process) and the catalytic oxidation of carbon monoxide over platinum (catalytic converter). During his research he discovered the important phenomenon of oscillatory reactions on platinum surfaces and, using photoelectron microscopy, was able to image for the first time, the oscillating changes in surface structure and coverage that occur during reaction.
He always used new observation techniques like low-energy electron diffraction (LEED) at the beginning of his career, later ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscope (STM) yielding ground breaking results.
He won the Wolf Prize in Chemistry in 1998 along with Gabor A. Somorjai of the University of California, Berkeley for "their outstanding contributions to the field of the surface science in general and for their elucidation of fundamental mechanisms of heterogeneous catalytic reactions at single crystal surface in particular."
Gerhard Ertl was awarded the 2007 Nobel Prize in Chemistry for his studies of chemical processes on solid surfaces. The award, worth SEK 10 million (US$1.7 million, £1.15 million), was announced on Ertl's 71st birthday. "I am speechless", Ertl told Associated Press from his office in Berlin. "I was not counting on this."
, Ertl has an h-index of 124 according to Scopus. | 7 | Physical Chemistry |
Typically the reaction to form Grignard reagents involves the use of magnesium ribbon. All magnesium is coated with a passivating layer of magnesium oxide, which inhibits reactions with the organic halide. Many methods have been developed to weaken this passivating layer, thereby exposing highly reactive magnesium to the organic halide. Mechanical methods include crushing of the Mg pieces in situ, rapid stirring, and sonication. Iodine, methyl iodide, and 1,2-dibromoethane are common activating agents. The use of 1,2-dibromoethane is advantageous as its action can be monitored by the observation of bubbles of ethylene. Furthermore, the side-products are innocuous:
The amount of Mg consumed by these activating agents is usually insignificant. A small amount of mercuric chloride will amalgamate the surface of the metal, enhancing its reactivity. Addition of preformed Grignard reagent is often used as the initiator.
Specially activated magnesium, such as Rieke magnesium, circumvents this problem.The oxide layer can also be broken up using ultrasound, using a stirring rod to scratch the oxidized layer off, or by adding a few drops of iodine or 1,2-Diiodoethane. Another option is to use sublimed magnesium or magnesium anthracene.
"Rieke magnesium" is prepared by a reduction of an anhydrous magnesium chloride with an potassium: | 0 | Organic Chemistry |
The metallurgical production of the Republic of Azerbaijan is considered high due to the large deposits of alunite, polymetallic ores, deposits of iron ore, etc. The metallurgy industry of Azerbaijan encompasses both ferrous and non-ferrous branches. | 8 | Metallurgy |
The mechanism for the conversion of an alcohol to the N-substituted thiocarbamate is shown below. The reaction proceeds under acidic conditions. The alcohol accepts a hydrogen ion from sulfuric acid to form a water, which then leaves, creating a carbocation. The mesomeric form of the cyanogroup reacts with the carbocation. The carbocation is attacked by a water, which then loses an hydrogen to form the product. The product then undergoes hydrolysis to form the N-substituted thiocarbamate.
The reaction requires the formation of a carbocation and does not work for primary alcohols. Only secondary and tertiary alcohols undergo the Riemschneider reaction. | 0 | Organic Chemistry |
Magnesium oil (also referred to as transdermal magnesium, magnesium hexahydrate) is a compound of magnesium chloride dissolved in six molecules of water, with magnesium as the alkaline earth metal and chlorine as the nonmetal, it is a concentrated magnesium chloride solution. In reality, it is not a oil, as it is not composed of one or more hydrocarbons. Magnesium oil is supposed to be applied to the skin as an alternative to taking a magnesium supplement by mouth, although it is ineffective and scientifically unsupported due to lack of any convincing data that magnesium is absorbed in significant amounts through the skin. | 1 | Biochemistry |
Alkylated diphenylamines function as antioxidants in lubricants, approved for use in machines, in which contact with food is not ruled out. Alkylated diphenylamines and other derivatives are used as anti-ozonants in the manufacture of rubber products, reflecting the antioxidant nature of aniline derivatives. | 3 | Analytical Chemistry |
Chemical mimicry (or molecular mimicry) is a type of biological mimicry involving the use of chemicals to dupe an operator.
A chemical mimic dupes an operator (e.g. a predator) by showing an adaptive chemical resemblance to an object of its environment and as a consequence receives selective advantage. In all cases of chemical mimicry it has been found that the mimicking species is the only species to benefit from the reaction with either costs or no effect on the duped species.
This is by adapting to produce chemicals (ex: allomones, pheromones, odours, etc.) that will cause a desirable behavioural reaction in the species being deceived and a selective advantage to the mimic, as in ant mimicry. Chemical mimicry exists within many of the different forms of mimicry such as aggressive, protective, Batesian, and Müllerian mimicry and can involve a number of different senses.
Mimicking semiochemicals make up some of the most widely used forms of chemical mimicry, but is less apparent than more visual forms. As a result, this topic has been relatively neglected in research and literature.
Two examples of organisms displaying chemical mimicry are the mimicking of Noctuid pheromones by bolas spiders to lure prey and the duping of insects within their own nests by mimicking their odours in order to enter and hide within the nest undetected. | 1 | Biochemistry |
In the time-independent formalism of quantum scattering, the initial wave function (before scattering) is taken to be a plane wave with definite momentum :
where and are the relative coordinates between the projectile and the target. The arrow indicates that this only describes the asymptotic behavior of the wave function when the projectile and target are too far apart for the interaction to have any effect.
After scattering takes place it is expected that the wave function takes on the following asymptotic form:
where is some function of the angular coordinates known as the scattering amplitude. This general form is valid for any short-ranged, energy-conserving interaction. It is not true for long-ranged interactions, so there are additional complications when dealing with electromagnetic interactions.
The full wave function of the system behaves asymptotically as the sum
The differential cross section is related to the scattering amplitude:
This has the simple interpretation as the probability density for finding the scattered projectile at a given angle.
A cross section is therefore a measure of the effective surface area seen by the impinging particles, and as such is expressed in units of area. The cross section of two particles (i.e. observed when the two particles are colliding with each other) is a measure of the interaction event between the two particles. The cross section is proportional to the probability that an interaction will occur; for example in a simple scattering experiment the number of particles scattered per unit of time (current of scattered particles ) depends only on the number of incident particles per unit of time (current of incident particles ), the characteristics of target (for example the number of particles per unit of surface ), and the type of interaction. For we have | 7 | Physical Chemistry |
Pyridines are highly variable substrates for asymmetric reduction (even compared to other heteroaromatics), in that five carbon centers are available for differential substitution on the initial ring. As of October 2012 no method seems to exist that can control all five, although at least one reasonably general method exists.
The most-general method of asymmetric pyridine hydrogenation is actually a heterogeneous method, where asymmetry is generated from a chiral oxazolidinone bound to the C2 position of the pyridine. Hydrogenating such functionalized pyridines over a number of different heterogeneous metal catalysts gave the corresponding piperidine with the substituents at C3, C4, and C5 positions in an all-cis geometry, in high yield and excellent enantioselectivity. The oxazolidinone auxiliary is also conveniently cleaved under the hydrogenation conditions.
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Methods designed specifically for 2-substituted pyridine hydrogenation can involve asymmetric systems developed for related substrates like 2-substituted quinolines and quinoxalines. For example, an iridium(I)\chiral phosphine\I system is effective in the asymmetric hydrogenation of activated (alkylated) 2-pyridiniums or certain cyclohexanone-fused pyridines. Similarly, chiral Brønsted acid catalysis with a Hantzsh ester as a hydride source is effective for some 2-alkyl pyridines with additional activating substitution. | 0 | Organic Chemistry |
The structure of binary oxides can be predicted on the basis of the relative sizes of the metal and oxide ions and the filling of holes in a close packed oxide lattice. However, the predictions of structure are more difficult for ternary oxides. The combination of two or more metals in an oxide creates a lot of structural possibilities. Also, the stoichiometry of ternary oxide may be changed by varying the proportions of the two components and their oxidation states. For example, at least twenty ternary oxide phases are formed between strontium and vanadium including SrVO, SrVO, SrVO and SrVO. The structural chemistry of ternary and more complex oxides is an extensive subject, but there are a few structures that are widely adopted by ternary oxides, such as the perovskite structure. | 7 | Physical Chemistry |
Blood types are an example of how glycolipids on cell membranes mediate cell interactions with the surrounding environment. The four main human blood types (A, B, AB, O) are determined by the oligosaccharide attached to a specific glycolipid on the surface of red blood cells, which acts as an antigen. The unmodified antigen, called the H antigen, is the characteristic of type O, and is present on red blood cells of all blood types. Blood type A has an N-acetylgalactosamine added as the main determining structure, type B has a galactose, and type AB has all three of these antigens. Antigens which are not present in an individual's blood will cause antibodies to be produced, which will bind to the foreign glycolipids. For this reason, people with blood type AB can receive transfusions from all blood types (the universal acceptor), and people with blood type O can act as donors to all blood types (the universal donor). | 0 | Organic Chemistry |
Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula FeC. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy. While cementite is present in most steels and cast irons, it is produced as a raw material in the iron carbide process, which belongs to the family of alternative ironmaking technologies. The name cementite originated from the theory of Floris Osmond and J. Werth, in which the structure of solidified steel consists of a kind of cellular tissue, with ferrite as the nucleus and FeC the envelope of the cells. The carbide therefore cemented the iron. | 8 | Metallurgy |
A key characteristic of ATM is the orientation of the polarized electric field of THz light at the sample. In particular, unlike other microspectroscopy techniques like scattering scanning near-field optical microscopy (s-SNOM), the electric field of the interrogating THz field is parallel to the surface of the sample. In s-SNOM, the shape of the oscillating metallic probe tip directs the THz polarization into a direction predominantly perpendicular to the sample surface. | 7 | Physical Chemistry |
Bulkier than IMes is the NHC ligand IPr (CAS 244187-81-3). IPr features diisopropylphenyl in place of the mesityl substituents.
Some variants of IMes and IPr have saturated backbones, two such ligands are SIMes and SIPr. They are prepared by alkylation of substituted anilines with dibromoethane followed by ring closure and dehydrohalogenation of the dihydroimidazolium salt. | 0 | Organic Chemistry |
Aldehydes characteristically form "addition compounds" with bisulfites:
This reaction is used as a test for aldehydes and is useful for separation or purification of aldehydes. | 0 | Organic Chemistry |
In the United States, Brownfield regulation and development is largely governed by state environmental agencies in cooperation with the Environmental Protection Agency (EPA). In 1995, the EPA launched the Brownfields Program, which was expanded in 2002 with the Brownfields Law.
The EPA, together with local and national government, can provide technical help and some funding for assessment and cleanup. From 2002 through 2013, the EPA awarded nearly 1,000 grants for clean up, for a total of almost $190 million. It can also provide tax incentives for cleanup that is not paid for outright; specifically, cleanup costs are fully tax-deductible in the year they are incurred. Many of the most important provisions on liability relief are contained in state codes that can differ significantly from state to state. | 2 | Environmental Chemistry |
* Contamination by phenol, which is commonly used in nucleic acid purification, can significantly throw off quantification estimates. Phenol absorbs with a peak at 270 nm and a A of 1.2. Nucleic acid preparations uncontaminated by phenol should have a A of around 2. Contamination by phenol can significantly contribute to overestimation of DNA concentration.
* Absorption at 230 nm can be caused by contamination by phenolate ion, thiocyanates, and other organic compounds. For a pure RNA sample, the A should be around 1:2:1, and for a pure DNA sample, the A should be around 1:1.8:1.
* Absorption at 330 nm and higher indicates particulates contaminating the solution, causing scattering of light in the visible range. The value in a pure nucleic acid sample should be zero.
* Negative values could result if an incorrect solution was used as blank. Alternatively, these values could arise due to fluorescence of a dye in the solution. | 7 | Physical Chemistry |
Bacteria themselves do not have noticeable effect on concrete. However, sulfate-reducing bacteria (SRB) in untreated sewage water tend to produce hydrogen sulfide (HS), which is then oxidized in sulfuric acid (HSO) by atmospheric oxygen (abiotic reaction) and by aerobic bacteria present in biofilm (biotic reaction) on the concrete surface above the water level. The sulfuric acid dissolves the carbonates in the hardened cement paste (HCP), and also calcium hydroxide (portlandite: Ca(OH)) and calcium silicate hydrate (CaO·SiO·nHO), and causes strength loss, as well as producing sulfates which are harmful to concrete.
:HSO + Ca(OH) → CaSO + 2 HO
:HSO + CaO·SiO·n HO → CaSO + HSiO + n HO
In each case the soft expansive and water-soluble corrosion product of gypsum (CaSO) is formed. Gypsum is easily washed away in wastewater causing a loss of concrete aggregate and exposing fresh material to acid attack.
Concrete floors lying on ground that contains pyrite (iron(II) disulfide) are also at risk.
As a preventive measure sewage may be pretreated to increase pH or oxidize or precipitate the sulfides in order to minimize the activity of sulfide-reducing bacteria.
As bacteria often prefer to adhere to the surfaces of solids than to remain into suspension in water (planktonic bacteria), the biofilms formed by sessile (i.e., fixed) bacteria are often the place where they are the most active. Biofilms made of multiple layers (like an onion) of dead and living bacteria protect the living ones from the harsh conditions often prevailing in water outside biofilm. Biofilms developing on the already exposed surface of metallic elements encased in concrete can also contribute to accelerate their corrosion (differential aeration and formation of anodic zones at the surface of the metal). Sulfides produced by the SRB bacteria can also induce stress corrosion cracking in steel and other metals. | 8 | Metallurgy |
Two older prefixes still commonly used to distinguish diastereomers are threo and erythro. In the case of saccharides, when drawn in the Fischer projection the erythro isomer has two identical substituents on the same side and the threo isomer has them on opposite sides. When drawn as a zig-zag chain, the erythro isomer has two identical substituents on different sides of the plane (anti). The names are derived from the diastereomeric four-carbon aldoses erythrose and threose. These prefixes are not recommended for use outside of the realm of saccharides because their definitions can lead to conflicting interpretations.
Another threo compound is threonine, one of the essential amino acids. The erythro diastereomer of it is allothreonine. | 4 | Stereochemistry |
Paytan was born and raised in Israel. As an undergraduate, Paytan encountered geochemistry which she likens to a big complex puzzle. Paytan obtained undergraduate degrees in geology and biology (1985) and an M.S. in Earth Sciences Oceanography (1989) from Hebrew University of Jerusalem. Paytan's Ph.D. is from Scripps Institution of Oceanography (1996) where she worked with Miriam Kastner on using barite as a recorder of ocean chemistry. After postdoctoral work at University of California, San Diego she moved to the Department of Geological and Environmental Sciences at Stanford, and then onto a position at University of California, Santa Cruz. | 9 | Geochemistry |
Mohamed Mohamed Atalla was born in Port Said, Kingdom of Egypt. He studied at Cairo University in Egypt, where he received his Bachelor of Science degree. He later moved to the United States to study mechanical engineering at Purdue University. There, he received his master's degree (MSc) in 1947 and his doctorate (PhD) in 1949, both in mechanical engineering. His MSc thesis was titled "High Speed Flow in Square Diffusers" and his PhD thesis was titled "High Speed Compressible Flow in Square Diffusers". | 7 | Physical Chemistry |
Pyridine supports a series of radical reactions, which is used in its dimerization to bipyridines. Radical dimerization of pyridine with elemental sodium or Raney nickel selectively yields 4,4-bipyridine, or 2,2-bipyridine, which are important precursor reagents in the chemical industry. One of the name reactions involving free radicals is the Minisci reaction. It can produce 2-tert-butylpyridine upon reacting pyridine with pivalic acid, silver nitrate and ammonium in sulfuric acid with a yield of 97%. | 0 | Organic Chemistry |
Agrominerals (also known as stone bread or petrol fertilizer) are minerals of importance to agriculture and horticulture industries for they can provide essential plant nutrients. Some agrominerals occur naturally or can be processed to be used as alternative fertilizers or soil amendments. The term agromineral was created in the 19th century and is now one of the leading research topics for sustainable agriculture. These geomaterials are used to replenish the nutrients and amend soils. Agrominerals started with small uses most often seen in hobbyist gardening but are moving to a much larger scale such as commercial farming operations that take up 100's acres of land. In this transition the focus changed to be more on ground nutrients, mainly on the three major plant nutrients nitrogen (N), phosphorus (P), and potassium (K). Two of the three elements are only being harvested from a geomaterial called potash. Alternative sources are being researched, due to potash finite supply and cost.
The process of using agrominerals starts with crushing rocks into a "rock powder," than using the powder to replenish soil nutrients. The process of replenishing mineral levels in a soil is called soil remineralization. While studying alternative ways to replenish ground nutrients, it has been found that agrominerals can also help mitigate other issues such climate change, water preservation and soil management. | 9 | Geochemistry |
To fabricate synthetic self-cleaning surfaces, there are a variety of methods used to obtain the desired nanotopography and then characterize surface nanostructure and wettability. | 7 | Physical Chemistry |
The and pH of a solution are related by the Nernst equation as commonly represented by a Pourbaix diagram . For a half cell equation, conventionally written as a reduction reaction (i.e., electrons accepted by an oxidant on the left side):
The half-cell standard reduction potential is given by
where is the standard Gibbs free energy change, is the number of electrons involved, and is Faraday's constant. The Nernst equation relates pH and :
where curly braces { } indicate activities, and exponents are shown in the conventional manner. as a function of pH with a slope of volt (pH has no units).
This equation predicts lower at higher pH values. This is observed for the reduction of O into HO, or OH, and for reduction of H into H. | 1 | Biochemistry |
Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine. The word "synapse" was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Fosters Textbook of Physiology. Sherrington struggled to find a good term that emphasized a union between two separate elements, and the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall, a friend of Foster. The word was derived from the Greek synapsis (), meaning "conjunction", which in turn derives from synaptein (), from syn () "together" and haptein' () "to fasten".
However, while the synaptic gap remained a theoretical construct, and was sometimes reported as a discontinuity between contiguous axonal terminations and dendrites or cell bodies, histological methods using the best light microscopes of the day could not visually resolve their separation which is now known to be about 20 nm. It needed the electron microscope in the 1950s to show the finer structure of the synapse with its separate, parallel pre- and postsynaptic membranes and processes, and the cleft between the two. | 1 | Biochemistry |
Disaccharides consist of two monosaccharides and may be either reducing or nonreducing. Even a reducing disaccharide will only have one reducing end, as disaccharides are held together by glycosidic bonds, which consist of at least one anomeric carbon. With one anomeric carbon unable to convert to the open-chain form, only the free anomeric carbon is available to reduce another compound, and it is called the reducing end of the disaccharide.
A nonreducing disaccharide is that which has both anomeric carbons tied up in the glycosidic bond.
Similarly, most polysaccharides have only one reducing end. | 0 | Organic Chemistry |
In metallurgy, solid solution strengthening is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal), forming a solid solution. The local nonuniformity in the lattice due to the alloying element makes plastic deformation more difficult by impeding dislocation motion through stress fields. In contrast, alloying beyond the solubility limit can form a second phase, leading to strengthening via other mechanisms (e.g. the precipitation of intermetallic compounds). | 8 | Metallurgy |
Suppose that the reactions between carbon dioxide, hydrogen ions, bicarbonate and carbonate ions, all dissolved in water, are as follows:
Note that reaction is actually the combination of two elementary reactions:
: + H +
Assuming the mass action law applies to these two reactions, that water is abundant, and that the different chemical species are always well-mixed, their rate equations are
where denotes concentration, t is time, and K and k are appropriate proportionality constants for reaction , called respectively the forwards and reverse rate constants for this reaction. (Similarly K and k for reaction .)
, the concentrations are unchanging, hence the left hand sides of these equations are zero. Then, from the first of these four equations, the ratio of reaction s rate constants equals the ratio of its equilibrium concentrations, and this ratio, called K', is called the equilibrium constant for reaction , i.e.
where the subscript eq denotes that these are equilibrium concentrations.
Similarly, from the fourth equation for the equilibrium constant K for reaction ,
Rearranging gives
and rearranging , then substituting in , gives
The total concentration of dissolved inorganic carbon in the system is given by substituting in and :
Re-arranging this gives the equation for :
The equations for and are obtained by substituting this into and . | 7 | Physical Chemistry |
There are several software packages in different programming languages that allow easy use of Blosum matrices.
Examples are the [https://pypi.org/project/blosum/ blosum] module for Python, or the BioJava library for Java. | 1 | Biochemistry |
Inhomogeneous broadening is a general term for broadening because some emitting particles are in a different local environment from others, and therefore emit at a different frequency. This term is used especially for solids, where surfaces, grain boundaries, and stoichiometry variations can create a variety of local environments for a given atom to occupy. In liquids, the effects of inhomogeneous broadening is sometimes reduced by a process called motional narrowing. | 7 | Physical Chemistry |
Lysine is synthesized from aspartate via the diaminopimelate (DAP) pathway. The initial two stages of the DAP pathway are catalyzed by aspartokinase and aspartate semialdehyde dehydrogenase. These enzymes play a key role in the biosynthesis of lysine, threonine, and methionine. There are two bifunctional aspartokinase/homoserine dehydrogenases, ThrA and MetL, in addition to a monofunctional aspartokinase, LysC. Transcription of aspartokinase genes is regulated by concentrations of the subsequently produced amino acids, lysine, threonine, and methionine. The higher these amino acids concentrations, the less the gene is transcribed. ThrA and LysC are also feed-back inhibited by threonine and lysine. Finally, DAP decarboxylase LysA mediates the last step of the lysine synthesis and is common for all studied bacterial species. The formation of aspartate kinase (AK), which catalyzes the phosphorylation of aspartate and initiates its conversion into other amino acids, is also inhibited by both lysine and threonine, which prevents the formation of the amino acids derived from aspartate. Additionally, high lysine concentrations inhibit the activity of dihydrodipicolinate synthase (DHPS). So, in addition to inhibiting the first enzyme of the aspartate families biosynthetic pathway, lysine also inhibits the activity of the first enzyme after the branch point, i.e. the enzyme that is specific for lysine's own synthesis. | 1 | Biochemistry |
In the processing of dairy milk, for example during cheese making, syneresis is the formation of the curd due to the sudden removal of the hydrophilic macropeptides, which causes an imbalance in intermolecular forces. Bonds between hydrophobic sites start to develop and are enforced by calcium bonds, which form as the water molecules in the micelles start to leave the structure. This process is usually referred to as the phase of coagulation and syneresis. The splitting of the bond between residues 105 and 106 in the κ-casein molecule is often called the primary phase of the rennet action, while the phase of coagulation and syneresis is referred to as the secondary phase.
In cooking, syneresis is the sudden release of moisture contained within protein molecules, usually caused by excessive heat, which over-hardens the protective shell. Moisture inside expands upon heating. The hard protein shell pops, expelling the moisture.
This process is responsible for transforming juicy rare steak into dry steak when cooked thoroughly. It creates weeping in scrambled eggs, with dry protein curd swimming in the released moisture. It also causes emulsified sauces, such as hollandaise, to "break" ("split"). Additionally, it creates unsightly moisture pockets within baked custard dishes, such as flan or crème brûlée.
In dentistry, syneresis is the expulsion of water or other liquid molecules from dental impression materials (for instance, alginate) after an impression has been taken. Due to this process, the impression shrinks a little and therefore its size is no longer accurate. For this reason, many dental impression companies strongly recommend to pour the dental cast as soon as possible to prevent distortion of the dimension of the teeth and objects in the impression.
Gels formed from agarose are prone to syneresis, and the degree of syneresis is inversely proportional to the concentration of the agarose in the gels.
The opposite process of syneresis is imbibition, which is the process of a material absorbing water molecules from the surroundings. Alginate is also an example of imbibition because it will absorb water if soaked in it. | 7 | Physical Chemistry |
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