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Some η-aldehyde complexes insert alkenes to give five-membered metallacycles.
η-Complexes of alpha-beta unsaturated carbonyls exhibit enhanced reactivity toward dienes. This interaction is the basis of Lewis-acid catalyzed Diels-Alder reactions. | 0 | Theoretical and Fundamental Chemistry |
In the light-independent reactions (also known as the Calvin-Benson cycle), two 3-phosphoglycerate molecules are synthesized. RuBP, a 5-carbon sugar, undergoes carbon fixation, catalyzed by the rubisco enzyme, to become an unstable 6-carbon intermediate. This intermediate is then cleaved into two, separate 3-carbon molecules of 3-PGA. One of the resultant 3-PGA molecules continues through the Calvin-Benson cycle to be regenerated into RuBP while the other is reduced to form one molecule of glyceraldehyde 3-phosphate (G3P) in two steps: the phosphorylation of 3-PGA into 1,3-bisphosphoglyceric acid via the enzyme phosphoglycerate kinase (the reverse of the reaction seen in glycolysis) and the subsequent catalysis by glyceraldehyde 3-phosphate dehydrogenase into G3P. G3P eventually reacts to form the sugars such as glucose or fructose or more complex starches. | 0 | Theoretical and Fundamental Chemistry |
If an infinitesimally small amount of heat is supplied to a system in a reversible way then, according to the second law of thermodynamics, the entropy change of the system is given by:
Since
where C is the heat capacity, it follows that:
The heat capacity depends on how the external variables of the system are changed when the heat is supplied. If the only external variable of the system is the volume, then we can write:
From this follows:
Expressing dS in terms of dT and dP similarly as above leads to the expression:
One can find the above expression for by expressing dV in terms of dP and dT in the above expression for dS.
results in
and it follows:
Therefore,
The partial derivative can be rewritten in terms of variables that do not involve the entropy using a suitable Maxwell relation. These relations follow from the fundamental thermodynamic relation:
It follows from this that the differential of the Helmholtz free energy is:
This means that
and
The symmetry of second derivatives of F with respect to T and V then implies
allowing one to write:
The r.h.s. contains a derivative at constant volume, which can be difficult to measure. It can be rewritten as follows. In general,
Since the partial derivative is just the ratio of dP and dT for dV = 0, one can obtain this by putting dV = 0 in the above equation and solving for this ratio:
which yields the expression:
The expression for the ratio of the heat capacities can be obtained as follows:
The partial derivative in the numerator can be expressed as a ratio of partial derivatives of the pressure w.r.t. temperature and entropy. If in the relation
we put and solve for the ratio we obtain . Doing so gives:
One can similarly rewrite the partial derivative by expressing dV in terms of dS and dT, putting dV equal to zero and solving for the ratio . When one substitutes that expression in the heat capacity ratio expressed as the ratio of the partial derivatives of the entropy above, it follows:
Taking together the two derivatives at constant S:
Taking together the two derivatives at constant T:
From this one can write: | 0 | Theoretical and Fundamental Chemistry |
In contrast to receptor uncoupling, endocytosis can occur through multiple pathways. GPCR endocytosis has been shown to be either dependent or independent of arrestin activity, depending on the cell type used in the experiment; however, the former is more common. Furthermore, the same receptor expressed in two distinct cell types can be endocytosed through different mechanisms due to differences in GRK and arrestin expression: either through clathrin-coated vesicles or caveolae. In general, receptor sequestration preferentially affects receptors that are both activated and phosphorylated, but the phosphorylation is not always a necessary component of endocytosis. After being sequestered, the affected receptors can either be degraded by lysosomes or reinserted into the plasma membrane, which is called receptor recycling.
Post-translational modification also affects receptor endocytosis. For example, different glycosylations on the exterior N-terminus of dopamine receptors D and D were associated with specific endocytotic pathways. Additionally, palmitoylation, which primarily mediates receptor localization within the membrane, can also affect endocytosis. It is required for the endocytosis of thyrotropin-releasing hormone and D receptors, and it is inhibitory for leutinizing hormone and vasopressin receptor 1A receptors. It has been shown to have no effect on adrenergic receptors (specifically ß and α). | 1 | Applied and Interdisciplinary Chemistry |
The number of peaks produced by a single element varies from 1 to more than 20. Tables of binding energies that identify the shell and spin-orbit of each peak produced by a given element are included with modern XPS instruments, and can be found in various handbooks and websites. Because these experimentally determined energies are characteristic of specific elements, they can be directly used to identify experimentally measured peaks of a material with unknown elemental composition.
Before beginning the process of peak identification, the analyst must determine if the binding energies of the unprocessed survey spectrum (0-1400 eV) have or have not been shifted due to a positive or negative surface charge. This is most often done by looking for two peaks that are due to the presence of carbon and oxygen. | 0 | Theoretical and Fundamental Chemistry |
If the polymeric system is amorphous, then the anchor points of the crystalline structure are not available and the only way to ensure the stability of the temporary shape is through chain entanglements (physical entanglements and not chemical crosslinking), in addition to the possibility of crosslinking. | 0 | Theoretical and Fundamental Chemistry |
A study was conducted to define the pharmacological response of humans to ractopamine. A single oral dose of 40 mg of ractopamine hydrochloride was given to human volunteers. The drug was rapidly absorbed; the mean blood plasma half-life was around 4 hrs and it was not detected in plasma 24 hrs after dosing. Less than 5% of total ractopamine excreted represented the parent drug, while the urinary metabolites were monoglucuronide and monosulfate conjugates, with ractopamine monosulfate being the major metabolite present.
The metabolic fate of ractopamine hydrochloride is similar in the target species (pigs and cattle), laboratory animals, and humans. Besides the pharmacology effect, ractopamine may cause intoxication effect; therefore, any consumption by humans of a meat and/or byproducts of animals that consumed ractopamine with feed for growth stimulation, may result in such clinical effects as tachycardia and other heart rate increases, tremor, headache, muscle spasm, or high arterial blood pressure. The effect of ractopamine on humans is not entirely known, but consumption of products that contain ractopamine residues is not advisable for persons with cardiovascular diseases. | 0 | Theoretical and Fundamental Chemistry |
Upon blood exiting the body, hemoglobin in blood transits from bright red to dark brown, which is attributed to oxidation of oxy-hemoglobin (HbO) to methemoglobin (met-Hb) and ending up in hemichrome (HC). For forensic purposes, the fractions of HbO, met-Hb and HC in a bloodstain can be used for age determination of bloodstains when measured with Reflectance Spectroscopy [http://plosone.org/article/info:doi/10.1371/journal.pone.0021845]. | 1 | Applied and Interdisciplinary Chemistry |
Poroelasticity is a characteristic of materials related to the migration of solvent through a porous material and the concurrent deformation that occurs. Poroelasticity in hydrated materials such as hydrogels occurs due to friction between the polymer and water as the water moves through the porous matrix upon compression. This causes a decrease in water pressure, which adds additional stress upon compression. Similar to viscoelasticity, this behavior is time dependent, thus poroelasticity is dependent on compression rate: a hydrogel shows softness upon slow compression, but fast compression makes the hydrogel stiffer. This phenomenon is due to the friction between the water and the porous matrix is proportional to the flow of water, which in turn is dependent on compression rate. Thus, a common way to measure poroelasticity is to do compression tests at varying compression rates. Pore size is an important factor in influencing poroelasticity. The Kozeny–Carman equation has been used to predict pore size by relating the pressure drop to the difference in stress between two compression rates.
Poroelasticity is described by several coupled equations, thus there are few mechanical tests that relate directly to the poroelastic behavior of the material, thus more complicated tests such as indentation testing, numerical or computational models are utilized. Numerical or computational methods attempt to simulate the three dimensional permeability of the hydrogel network. | 0 | Theoretical and Fundamental Chemistry |
The ratio of the free-surface amplitudes at second order and first order – according to Stokes's second-order theory – is:
In deep water, for large kh the ratio has the asymptote
For long waves, i.e. small kh, the ratio behaves as
or, in terms of the wave height and wavelength :
with
Here is the Ursell parameter (or Stokes parameter). For long waves () of small height H, i.e. , second-order Stokes theory is applicable. Otherwise, for fairly long waves () of appreciable height H a cnoidal wave description is more appropriate. According to Hedges, fifth-order Stokes theory is applicable for , and otherwise fifth-order cnoidal wave theory is preferable. | 1 | Applied and Interdisciplinary Chemistry |
Some people experience persistent sexual side effects when taking SSRIs or after discontinuing them. Symptoms of medication-induced sexual dysfunction from antidepressants include difficulty with orgasm, erection, or ejaculation. Other symptoms may be genital anesthesia, anhedonia, decreased libido, vaginal lubrication issues, and nipple insensitivity in women. Rates are unknown, and there is no established treatment. | 0 | Theoretical and Fundamental Chemistry |
This acid–base theory was a revival of the oxygen theory of acids and bases proposed by German chemist Hermann Lux in 1939, further improved by Håkon Flood and is still used in modern geochemistry and electrochemistry of molten salts. This definition describes an acid as an oxide ion () acceptor and a base as an oxide ion donor. For example:
This theory is also useful in the systematisation of the reactions of noble gas compounds, especially the xenon oxides, fluorides, and oxofluorides. | 0 | Theoretical and Fundamental Chemistry |
To determine the percent solids (or solids fraction) of a slurry from the density of the slurry, solids and liquid
where
: is the solids fraction of the slurry (state by mass)
: is the solids density
: is the slurry density
: is the liquid density
In aqueous slurries, as is common in mineral processing, the specific gravity of the species is typically used, and since specific gravity of water is taken to be 1, this relation is typically written:
even though specific gravity with units tonnes/m (t/m) is used instead of the SI density unit, kg/m. | 1 | Applied and Interdisciplinary Chemistry |
ANT has long been thought to function as a homodimer, but this concept was challenged by the projection structure of the yeast Aac3p solved by electron crystallography, which showed that the protein was three-fold symmetric and monomeric, with the translocation pathway for the substrate through the centre. The atomic structure of the bovine ANT confirmed this notion, and provided the first structural fold of a mitochondrial carrier. Further work has demonstrated that ANT is a monomer in detergents and functions as a monomer in mitochondrial membranes.
ADP/ATP translocase 1 is the major AAC in human cells and the archetypal protein of this family. It has a mass of approximately 30 kDa, consisting of 297 residues. It forms six transmembrane α-helices that form a barrel that results in a deep cone-shaped depression accessible from the outside where the substrate binds. The binding pocket, conserved throughout most isoforms, mostly consists of basic residues that allow for strong binding to ATP or ADP and has a maximal diameter of 20 Å and a depth of 30 Å. Indeed, arginine residues 96, 204, 252, 253, and 294, as well as lysine 38, have been shown to be essential for transporter activity. | 1 | Applied and Interdisciplinary Chemistry |
The earliest scientific evidence that such reactions can oscillate was met with extreme scepticism. In 1828, G.T. Fechner published a report of oscillations in a chemical system. He described an electrochemical cell that produced an oscillating current. In 1899, W. Ostwald observed that the rate of chromium dissolution in acid periodically increased and decreased. Both of these systems were heterogeneous and it was believed then, and through much of the last century, that homogeneous oscillating systems were nonexistent. While theoretical discussions date back to around 1910, the systematic study of oscillating chemical reactions and of the broader field of non-linear chemical dynamics did not become well established until the mid-1970s. | 1 | Applied and Interdisciplinary Chemistry |
Saturation conditions can be viewed as a special case of pre-equilibrium conditions. At the concentration of substrate examined, formation of the catalyst-substrate complex is rapid and essentially irreversible. The catalyst resting state consists entirely of the bound complex, and [A] is no longer present in the rate law; changing [A] will have no effect on reaction rate because the catalyst is already completely bound and reacting as rapidly as k allows. The simplest case of saturation kinetics is the well-studied Michaelis-Menten model for enzyme kinetics. | 0 | Theoretical and Fundamental Chemistry |
The most efficient subset in TRA presentation and both modes of central tolerance was found to be CD8α thymic-derived DCs (tDCs). This subset was also shown to express XCR1 and to be attracted by mTECs via XCL1 chemokine expression. tDCs rise intrathymically and constitute approximately half of thymic DCs population. | 1 | Applied and Interdisciplinary Chemistry |
Manganese is a component of some enzymes and stimulates the development and activity of other enzymes. Manganese superoxide dismutase (MnSOD) is the principal antioxidant in mitochondria. Several enzymes activated by manganese contribute to the metabolism of carbohydrates, amino acids, and cholesterol.
A deficiency of manganese causes skeletal deformation in animals and inhibits the production of collagen in wound healing. | 1 | Applied and Interdisciplinary Chemistry |
This action has been demonstrated in animals and humans.
The medical use of the NSTX anesthetic effect is supported by three reasons:
#NSTX anesthetic duration:
#* Any current available local anesthetic hardly produces clinical effects 12 hours after a single injection. Then, in cases of severe or prolonged pain, some patients need repeated injections, catheters, pumps and opioids to feel comfortable, with different kinds of side effects, costs and risks.
#* On the other hand, NSTX local infiltration produces long lasting anesthesia, well over all the current available local anesthetics. Some investigations demonstrated anesthetic effect lasting over one week after single injection in rodents, using extended release formulation, without histologic or functional sequelae.
#* Additionally, two human reports demonstrated strong potentiation between NSTX anesthetic effect, bupivacaine and epinephrine.
#NSTX local safety:
#* All available local anesthetic are associated with local damage in different models. This undesired effect could be enhanced by sustained release formulations.
#* On the contrary, several investigations show local safety of saxitoxin-related neurotoxins, including very sensitive models, and there is no reason to presume otherwise for NSTX.
#NSTX systemic safety:
#* In spite of advances of ultrasound guided injections, acute systemic local anesthetic toxicity is still an unsolved clinical problem, and can produce devastating consequences, related to the neurologic and cardiovascular effects of all available local anesthetics.
#* Otherwise, clinical experience and animal models shows the relative safety of accidental and experimental NSTX intoxication (when appropriate support therapy is provided in a timely manner).
#* Recent investigation in sheep shows a safe limit, due to motor block, over 1 µg/kg for intravenous injection of NSTX, with full recovery after a brief course of mechanical ventilation.
#* Regarding systemic safety, saxitoxins diffuse through the blood–brain barrier, but, because of Nav channel specificity, acute toxicity is associated to a very low risk of seizures. This establishes an important difference with current local anesthetic toxicity.
#* As could be predicted from its ion channel selectivity, NSTX intoxication clinical picture is almost devoid of arrhythmias, establishing another difference with available local anesthetic's numerous cardiac effects.
#* And last but not least, some degree of improving in therapeutic index of NSTX can be observed when is mixed with bupivacaine and/or epinephrine.
In conclusion, NSTX is a well defined molecule with a long-lasting and sometimes dangerous relationship with human subjects. Recent investigations suggest a clinical application as a new local anesthetic that sounds "too good to be true", but more investigation is required. | 1 | Applied and Interdisciplinary Chemistry |
The chief medical examiner of Essex County, New Jersey, Harrison Stanford Martland, MD, published a report in 1925 that identified the radioactive material the women had ingested as the cause of their bone disease and aplastic anemia, and ultimately death.
Illness and death resulting from ingestion of radium paint and the subsequent legal action taken by the women forced closure of the company's Orange facility in 1927. The case was settled out of court in 1928, but not before a substantial number of the litigants were seriously ill or had died from bone cancer and other radiation-related illnesses. The company, it was alleged, deliberately delayed settling litigation, leading to further deaths.
In November 1928, Dr. von Sochocky, the inventor of the radium-based paint, died of aplastic anemia resulting from his exposure to the radioactive material, "a victim of his own invention."
The victims were so contaminated that radiation can still be detected at their graves, using a Geiger counter. | 0 | Theoretical and Fundamental Chemistry |
Henry Cavendish showed that water was composed of oxygen and hydrogen in 1781. The first decomposition of water into hydrogen and oxygen, by electrolysis, was done in 1800 by English chemist William Nicholson and Anthony Carlisle. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is composed of two parts hydrogen and one part oxygen.
Gilbert Newton Lewis isolated the first sample of pure heavy water in 1933.
The properties of water have historically been used to define various temperature scales. Notably, the Kelvin, Celsius, Rankine, and Fahrenheit scales were, or currently are, defined by the freezing and boiling points of water. The less common scales of Delisle, Newton, Réaumur, and Rømer were defined similarly. The triple point of water is a more commonly used standard point today. | 1 | Applied and Interdisciplinary Chemistry |
Tropical peatlands extensively occur in Southeast Asia, mainland East Asia, the Caribbean and Central America, South,America,Romania and southern Africa. Often located in lowlands, tropical peatlands are uniquely identified by rapid rates of peat soil formation, under high precipitation and high temperature regimes. In contrast, a high temperature climate accelerates decomposition rates, causing degraded tropical peatlands to contribute more substantially to global green house gas emissions. Although tropical peatlands cover only 587,000 km, they store 119.2 Gigatonnes C at a density per unit area of 203,066 tonnes C km. For decades, these large carbon stores have succumbed to draining in order to cater for humanity's socio-economic needs. Between 1990 and 2015, cultivation (for management including industrial and small-holder agriculture) had increased from 11 to 50% of forested peatlands in Peninsular Malaysia, Sumatra, and Borneo. In Malaysia and Indonesia in the last twenty years, peat swamp forests have retreated from covering 77% of peatlands to 36%, endangering many mammals and birds in the region. In 2010, industrial agriculture covers about 3-3.1 million hectares, with oil palm accounting for 2.15 million hectares of this area. The conversion of natural tropical peatlands into other land uses leads to peat fires and the associated health effects, soil subsidence increasing flood risks, substantial greenhouse gas emissions and loss of biodiversity. Today efforts are being made to restore degraded tropical peatlands through paludiculture. Paludiculture is researched as a sustainable solution to reduce and reverse the degradation of peat swamp forests, and includes traditional local agricultural practices which predate the use of the term. Commercial paludiculture has not been trialled to the extent that it has in northern peatlands. Below are examples of paludiculture practices in tropical peatlands. | 1 | Applied and Interdisciplinary Chemistry |
Light production may first be triggered by nerve impulses which stimulate the photocyte to release the enzyme luciferase into a "reaction chamber" of luciferin substrate. In some species the release occurs continually without the precursor impulse via osmotic diffusion. Molecular oxygen is then actively gated through surrounding tracheal cells which otherwise limit the natural diffusion of oxygen from blood vessels; the resulting reaction with the luciferase and luciferin produces light energy and a by-product (usually carbon dioxide). The reaction occurs in the peroxisome of the cell.
Researchers once postulated that ATP was the source of reaction energy for photocytes, but since ATP only produces a fraction the energy of the luciferase reaction, any resulting light wave-energy would be too small for detection by a human eye. The wavelengths produced by most photocytes fall close to 490 nm; although light as energetic as 250 nm is reportedly possible.
The variations of color seen in different photocytes are usually the result of color filters that alter the wavelength of the light prior to exiting the endoderm, thanks to the other parts of the photophore. The range of colors vary between bioluminescent species.
The exact combinations of luciferase and luciferin types found among photocytes are specific to the species to which they belong. This would seem to be the result of consistent evolutionary divergence. | 1 | Applied and Interdisciplinary Chemistry |
For altering moss genes in a targeted way, the DNA-construct needs to be incubated together with moss protoplasts and with polyethylene glycol (PEG). Because mosses are haploid organisms, the regenerating moss filaments (protonemata) can be directly assayed for gene targeting within six weeks when utilizing PCR methods. | 1 | Applied and Interdisciplinary Chemistry |
In 2006, The Lacassane Company became the parent company of Louisiana Native Seed Company, that provides ecospecies such as Little Bluestem, Brownseed Paspalum, Florida Paspalum, Switchgrass, Partridge Pea, and Eastern Gamagrass and has consultants with experience in Agricultural science and botany. The Louisiana Native Seed Company is listed as a provider for the United States Department of Agriculture's Natural Resources Conservation Service. | 1 | Applied and Interdisciplinary Chemistry |
Rapamycin (Sirolimus) inhibits mTORC1, resulting in the suppression of cellular senescence. This appears to provide most of the beneficial effects of the drug (including life-span extension in animal studies). Suppression of insulin resistance by sirtuins accounts for at least some of this effect. Impaired sirtuin 3 leads to mitochondrial dysfunction.
Rapamycin has a more complex effect on mTORC2, inhibiting it only in certain cell types under prolonged exposure. Disruption of mTORC2 produces the diabetic-like symptoms of decreased glucose tolerance and insensitivity to insulin. | 1 | Applied and Interdisciplinary Chemistry |
Liu et al. synthesized a HILIC/RP stationary phase which could show RPLC or HILIC retention by adjusting the organic phase in mobile phase. | 0 | Theoretical and Fundamental Chemistry |
The Geochemical Society has nearly 4,000 members from more than 70 countries. Most members are students, researchers and faculty of geochemistry related fields, although anyone with an interest in geochemistry may join. Membership is calendar year and dues are US$35 for a Professional, US$15 for Student, and $20 for Seniors. Membership includes a subscription to Elements Magazine and also offers discounts on Geochemical Society publications, Mineralogical Society of America publications and conference registration discounts at the Goldschmidt Conference, Fall AGU, and the annual GSA conference. | 0 | Theoretical and Fundamental Chemistry |
Archaeological evidence indicates that the earliest metal objects in China were made in the late fourth millennium BCE. Copper was generally the earliest metal to be used by humanity, and was used in China since at least 3000 BCE.
Early metal-using communities have been found at the Qijia and Siba sites in Gansu. The metal knives and axes recovered in Qijia apparently point to some interactions with Siberian and Central Asian cultures, in particular with the Seima-Turbino complex, or the Afanasievo culture. Archeological evidence points to plausible early contact between the Qijia culture and Central Asia. Similar sites have been found in Xinjiang in the west and Shandong, Liaoning and Inner Mongolia in the east and north. The Central Plain sites associated with the Erlitou culture also contain early metalworks.
Copper manufacturing, more complex than jade working, gradually appeared in the Yangshao period (5000–3000 BCE). Jiangzhai is the only place where copper artifacts were found in the Banpo culture. Archaeologists have found remains of copper metallurgy in various cultures from the late fourth to the early third millennia BCE. These include the copper-smelting remains and copper artifacts of the Hongshan culture (4700–2900) and copper slag at the Yuanwozhen site. This indicates that inhabitants of the Yellow River valley had already learned how to make copper artifacts by the later Yangshao period.
The Qijia culture (c. 2500–1900) of Qinghai, Gansu, and western Shaanxi produced copper and bronze utilitarian items and gold, copper, and bronze ornaments. The earliest metalworks in this region are found at a Majiayao site at Linjia, Dongxiang, Gansu. "Their dates range from 2900 to 1600 BCE. These metal objects represent the Majiayao 馬家窯 type of the Majiayao culture (c. 3100–2700 BCE), Zongri 宗日 Culture (c. 3600–2050 BCE), Machang 馬廠 Type (c. 2300–2000 BCE), Qijia 齊家 Culture (c. 2050–1915 BCE), and Siba 四壩 Culture (c. 2000–1600 BCE)."
At Dengjiawan, in the Shijiahe site complex in Hubei, some pieces of copper were discovered; they are the earliest copper objects discovered in southern China. The Linjia site (林家遺址, Línjiā yízhǐ) has the earliest evidence for bronze in China, dating to c. 3000 BCE. | 1 | Applied and Interdisciplinary Chemistry |
The aqueous homogeneous reactors (AHRs) use a solution of uranyl sulfate or other uranium salt in water. Historically, AHRs have all been small research reactors, not large power reactors. An AHR known as the Medical Isotope Production System is being considered for production of medical isotopes. | 0 | Theoretical and Fundamental Chemistry |
Because fibrin fulfills the mechanical aspects of neuronal growth without initiation of glial proliferation, it can be potentially used in neuronal wound healing even with no need of growth factors or such constituents. Neurons and astrocytes, two major cell type of central nervous system, can show various responses to differences in matrix stiffness. Neuronal development of precursor cells is maintained by gels with low elastic modulus. When stiffness of the matrix is more than that of a normal brain, extension of spinal cord and cortical brain neurons is inhibited since neurite extension and branch forming take place on soft materials (, salmon fibrin promotes the neurite growth best and it is more proteolysis resistant than mammalian fibrins. Because down to 0 °C, salmon fibrinogen can clot whereas polymerization of human fibrinogen occurs slowly below 37 °C, this can be taken as an advantage in surgical settings that are cooler. Therefore, for treatment of central nervous system damages, salmon fibrin can be a useful biomaterial.
For sciatic nerve regeneration, fibrin scaffold is used with glial derived neurotrophic factor (GDNF) in a recent study. Survival of both sensory and motor neurons is promoted by glial-derived neurotrophic factor and its delivery to peripheral nervous system improves regeneration after an injury. GDNF and nerve growth factor (NGF) is sequestered in the gel via a bi-domain peptide. This peptide is composed of heparin binding domain and transglutaminase substrate domain which can be cross-linked into the fibrin matrix by polymerization via transglutaminase activity of factor XIIIa. Many neurotrophic factors can bind to heparin through its sulfated domains. This is the affinity-based delivery system in which growth factors are released by cell-based degradation control. After a 13 mm rat sciatic nerve defect is made, the fibrin matrix delivery system is applied to the gap as a nerve guiding channel. Results show that such a delivery system is efficient to enhance maturity and promote organized architecture of nerve regenerating in presence of GDNF, in addition to expressing the promising treatment variations for peripheral nerve injuries. | 1 | Applied and Interdisciplinary Chemistry |
Since the carbon cycle is tightly connected to the issue of ocean acidification, the most effective method for minimizing the effects of ocean acidification is to slow climate change. Anthropogenic inputs of CO can be reduced through methods such as limiting the use of fossil fuels and employing renewable energies. This will ultimately lower the amount of CO in the atmosphere and reduce the amount dissolved into the oceans. More intrusive methods to mitigate acidification involve a technique called enhanced weathering where powdered minerals like silicate are applied to the land or ocean surface. The powdered minerals enable accelerated dissolution, releasing cations, converting CO to bicarbonate and increasing the pH of the oceans. Other mitigation methods, like ocean iron fertilization, still need more experimentation and evaluation in order to be deemed effective. Ocean iron fertilization in particular has been shown to increase acidification in the deep ocean while only slightly reducing acidification at the surface. | 0 | Theoretical and Fundamental Chemistry |
Capillary comes from the Latin word capillaris, meaning "of or resembling hair". The meaning stems from the tiny, hairlike diameter of a capillary. | 0 | Theoretical and Fundamental Chemistry |
The Streeter–Phelps equation determines the relation between the dissolved oxygen concentration and the biological oxygen demand over time and is a solution to the linear first order differential equation
This differential equation states that the total change in oxygen deficit (D) is equal to the difference between the two rates of deoxygenation and reaeration at any time.
The Streeter–Phelps equation, assuming a plug-flow stream at steady state is then
where
* is the saturation deficit, which can be derived from the dissolved oxygen concentration at saturation minus the actual dissolved oxygen concentration (). has the dimensions .
* is the deoxygenation rate, usually in .
* is the reaeration rate, usually in .
* is the initial oxygen demand of organic matter in the water, also called the ultimate BOD (BOD at time t=infinity). The unit of is .
* is the oxygen demand remaining at time t, .
* is the initial oxygen deficit .
* is the elapsed time, usually .
<br>
lies typically within the range 0.05-0.5 and lies typically within the range 0.4-1.5 .
<br>
The Streeter–Phelps equation is also known as the DO sag equation. This is due to the shape of the graph of the DO over time. | 1 | Applied and Interdisciplinary Chemistry |
In soldering metals, flux serves a threefold purpose: it removes any oxidized metal from the surfaces to be soldered, seals out air thus preventing further oxidation, and improves the wetting characteristics of the liquid solder. Some fluxes are corrosive, so the parts have to be cleaned with a damp sponge or other absorbent material after soldering to prevent damage. Several types of flux are used in electronics.
A number of standards exist to define the various flux types. The principal standard is J-STD-004.
Various tests, including the ROSE test, may be used after soldering to check for the presence of ionic or other contaminants that could cause short circuits or other problems. | 1 | Applied and Interdisciplinary Chemistry |
The body of living organisms are composed of many enantiopure chiral substances. For example, amino acids that make up the proteins in the body have the same configuration, L-absolute configuration. Because of this specificity, vital processes such as constructing proteins, rely on stereoselectivity to ensure that out of all the potential enantiomers available, the body is utilizing the correct enantiopure compound.
Selectivity is a very important part of organic synthesis. In scientific papers regarding synthesis, selectivity is often listed in data tables alongside percent yield and other reaction conditions. While selectivity is deemed important in scientific literature, it has been challenging to effectively implement selectivity in drug development and production. A major issue with selectivity in pharmaceuticals is that a large percentage of drug syntheses by nature are not selective reactions, racemic mixtures are formed as the products. Separating racemic mixtures into their respective enantiomers takes extra time, money, and energy. One way to separate enantiomers is to chemically convert them into species that can be separated: diastereomers. Diastereomers, unlike enantiomers, have entirely different physical properties—boiling points, melting points, NMR shifts, solubilities—and they can be separated by conventional means such as chromatography or recrystallization. This is a whole extra step in the synthesis process and not desirable from a manufacturing standpoint. As a result, a number of pharmaceuticals are synthesized and marketed as a racemic mixture of enantiomers in cases where the less-effective enantiomer is benign. However, by identifying and specifically purifying the enantiomer which effectively binds to its respective binding site in the body, less of the drug would be needed to achieve the desired effect. With the improvement of chiral technology, a rich repertoire of enantioselective chromatographic methods have become available for the separation of drug enantiomers on the analytical, preparative, and industrial scales. | 0 | Theoretical and Fundamental Chemistry |
Fluciclovine is a [F]-tagged synthetic analog of the amino acid L-leucine. FACBC uptake by the tumor is related to functional activity of two amino acid transporters, specifically sodium-dependent system ASC, with a lesser contribution by sodium-independent system L. Although it is handled by the amino acid transporter system, it does not undergo terminally incorporative metabolism within the body. The distribution of the tracer in the body differs from choline and FDG, as kidney uptake of FACBC is negligible, and no activity is found in the urinary tract. There is low native brain uptake compared to FDG, which may enhance detection of brain metastases or primary brain tumors. The more intense native liver and pancreatic uptake seen with this agent would be expected to limit disease detection in those organs. FACBC has a short synthesis time and a long half-life, which eliminate the need for an onsite cyclotron. | 1 | Applied and Interdisciplinary Chemistry |
The efficiency of a heat engine is ultimately dependent on the temperature difference between heat source and sink (Carnot cycle). To improve efficiency of power stations the operating temperature must be raised. Using water as the working fluid, this takes it into supercritical conditions. Efficiencies can be raised from about 39% for subcritical operation to about 45% using current technology. Supercritical water reactors (SCWRs) are promising advanced nuclear systems that offer similar thermal efficiency gains. Carbon dioxide can also be used in supercritical cycle nuclear power plants, with similar efficiency gains. Many coal-fired supercritical steam generators are operational all over the world, and have enhanced the efficiency of traditional steam-power plants. Supercritical carbon dioxide is also proposed as a working fluid, which would have the advantage of lower critical pressure than water, but issues with corrosion are not yet fully solved. One proposed application is the Allam cycle. Both carbon dioxide and water are neutron moderators, but they have a lower density as supercritical fluids than liquid water does. This allows nuclear reactors with those supercritical fluids as a primary coolant to run in a reduced moderation mode ("semi-fast" or "epithermal") but not usually as a fast neutron reactor. On the other hand, some extra moderation would have to be provided for a fully thermal neutron spectrum. | 0 | Theoretical and Fundamental Chemistry |
Prothrombin fragment 1+2 (F1+2), also written as prothrombin fragment 1.2 (F1.2), is a polypeptide fragment of prothrombin (factor II) generated by the in vivo cleavage of prothrombin into thrombin (factor IIa) by the enzyme prothrombinase (a complex of factor Xa and factor Va). It is released from the N-terminus of prothrombin. F1+2 is a marker of thrombin generation and hence of coagulation activation. It is considered the best marker of in vivo thrombin generation.
F1+2 levels can be quantified with blood tests and is used in the diagnosis of hyper- and hypocoagulable states and in the monitoring of anticoagulant therapy. It was initially determined with a radioimmunoassay, but is now measured with several enzyme-linked immunosorbent assays.
The molecular weight of F1+2 is around 41 to 43 kDa. Its biological half-life is 90 minutes and it persists in blood for a few hours after formation. The half-life of F1+2 is relatively long, which makes it more reliable for measuring ongoing coagulation than other markers like thrombin–antithrombin complexes and fibrinopeptide A. Concentrations of F1+2 in healthy individuals range from 0.44 to 1.11 nM.
F1+2 levels increase with age. Levels of F1+2 have been reported to be elevated in venous thromboembolism, protein C deficiency, protein S deficiency, atrial fibrillation, unstable angina, acute myocardial infarction, acute stroke, atherosclerosis, peripheral arterial disease, and in smokers. Anticoagulants have been found to reduce F1+2 levels. F1+2 levels are increased with pregnancy and by ethinylestradiol-containing birth control pills. Conversely, they do not appear to be increased with estetrol- or estradiol-containing birth control pills. However, F1+2 levels have been reported to be increased with oral estrogen-based menopausal hormone therapy, whereas transdermal estradiol-based menpausal hormone therapy appears to result in less or no consistent increase. | 1 | Applied and Interdisciplinary Chemistry |
Macle is a term used in crystallography. It is a crystalline form, twin-crystal or double crystal (such as chiastolite). It is crystallographic twin according to the spinel twin law and is seen in octahedral crystals or minerals such as diamond and spinel. The twin law name comes from the fact that is commonly observed in the mineral spinel.
Macle is an old French word, a heraldic term for a voided lozenge (one diamond shape within another). Etymologically the word is derived from the Latin macula meaning spot, mesh, or hole. | 0 | Theoretical and Fundamental Chemistry |
Dr. Raymond U. Lemieux was born in Lac La Biche, Alberta, Canada. His family moved to Edmonton, Alberta in 1926. He studied chemistry at the University of Alberta and received a BSc with Honours in Chemistry in 1943. He went on to study at McGill University, where he received his PhD in Organic Chemistry in 1946. He won a post-doctoral scholarship at Ohio State University, where Bristol Laboratories Inc. sponsored his research on the structure of streptomycin. He met his future wife, a doctoral student, at Ohio State and they were married in 1948.
In following years, he returned to Canada where he spent two years as an assistant professor at the University of Saskatchewan. Next he served as Senior Research Officer at the National Research Council's Prairie Regional Laboratory in Saskatoon. In 1953 he and a fellow researcher, George Huber, were the first scientists to successfully synthesize sucrose. In 1954, he accepted the position of Dean in the Faculty of Pure and Applied Sciences at the University of Ottawa, where he established their Department of Chemistry. In 1961 he returned to the University of Alberta as a professor in the Chemistry Department and to serve as the chairman of the Organic Chemistry Division. He developed a method to make synthetic versions of oligosaccharides, which led to improved treatments for leukemia and hemophilia and the development of new antibiotics, blood reagents, and organ anti-rejection drugs.
While at the University of Alberta, he established a number of biochemical companies, including R&L Molecular Research Ltd. in 1962, Raylo Chemicals Ltd. in 1966 (which purchased R&L) and Chembiomed in 1977 (which has since been taken over by Synsorb Biotech of Calgary, Alberta.) Prof. Lemieux published an autobiography, entitled "Explorations with Sugars: How Sweet It Was," in 1990.
Dr. Raymond Lemieux died of an aneurysm in 2000.
In 1999, the University of Alberta Faculty of Science and Strathcona County established the Strathcona County/R.U. Lemieux Chair in Carbohydrate Chemistry. In 2001, the University of Alberta renamed the building(s) housing the Department of Chemistry to the Gunning/Lemieux Chemistry Centre to acknowledge the contributions of Profs. Raymond Lemieux and Harry Gunning. | 0 | Theoretical and Fundamental Chemistry |
A molecular switch is a molecule that can be reversibly shifted between two or more stable states. The molecules may be shifted between the states in response to environmental stimuli, such as changes in pH, light, temperature, an electric current, microenvironment, or in the presence of ions and other ligands. In some cases, a combination of stimuli is required. The oldest forms of synthetic molecular switches are pH indicators, which display distinct colors as a function of pH. Currently synthetic molecular switches are of interest in the field of nanotechnology for application in molecular computers or responsive drug delivery systems. Molecular switches are also important in biology because many biological functions are based on it, for instance allosteric regulation and vision. They are also one of the simplest examples of molecular machines. | 0 | Theoretical and Fundamental Chemistry |
Pig iron contains much free carbon and is brittle. Before it can be used, and before it can be worked by a blacksmith, it must be converted to a more malleable form as bar iron, the early stage of wrought iron.
Abraham Darbys successful use of coke for his blast furnace at Coalbrookdale in 1709 reduced the price of iron, but this coke-fuelled pig iron was not initially accepted as it could not be converted to bar iron by the existing methods. Sulfur impurities from the coke made it red short', or brittle when heated, and so the finery process was unworkable for it. It was not until around 1750, when steam powered blowing increased furnace temperatures enough to allow sufficient lime to be added to remove the sulfur, that coke pig iron began to be adopted. Also, better processes were developed to refine it. | 1 | Applied and Interdisciplinary Chemistry |
Triethyl orthoacetate is the organic compound with the formula CHC(OCH). It is the ethyl orthoester of acetic acid. It is a colorless oily liquid.
Triethyl orthoacetate is used in organic synthesis for acetylation.
It is also used in the Johnson-Claisen rearrangement. | 0 | Theoretical and Fundamental Chemistry |
The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, which can deposit to form sediments or the exoskeletons of organisms. Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function. The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes. Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing atmospheric carbon dioxide due to ocean acidification.
Biogenic calcium carbonate is formed when marine organisms, such as coccolithophores, corals, pteropods, and other mollusks transform calcium ions and bicarbonate into shells and exoskeletons of calcite or aragonite, both forms of calcium carbonate. This is the dominant sink for dissolved calcium in the ocean. Dead organisms sink to the bottom of the ocean, depositing layers of shell which over time cement to form limestone. This is the origin of both marine and terrestrial limestone.
Calcium precipitates into calcium carbonate according to the following equation:
Ca + 2HCO → CO+ HO + CaCO
The relationship between dissolved calcium and calcium carbonate is affected greatly by the levels of carbon dioxide (CO) in the atmosphere.
Increased carbon dioxide leads to more bicarbonate in the ocean according to the following equation:
CO + CO + HO → 2HCO
With its close relation to the carbon cycle and the effects of greenhouse gasses, both calcium and carbon cycles are predicted to change in the coming years. Tracking calcium isotopes enables the prediction of environmental changes, with many sources suggesting increasing temperatures in both the atmosphere and marine environment. As a result, this will drastically alter the breakdown of rock, the pH of oceans and waterways and thus calcium sedimentation, hosting an array of implications on the calcium cycle.
Due to the complex interactions of calcium with many facets of life, the effects of altered environmental conditions are unlikely to be known until they occur. Predictions can however be tentatively made, based upon evidence-based research. Increasing carbon dioxide levels and decreasing ocean pH will alter calcium solubility, preventing corals and shelled organisms from developing their calcium-based exoskeletons, thus making them vulnerable or unable to survive.
Most biological production of biogenic silica in the ocean is driven by diatoms, with further contributions from radiolarians. These microorganisms extract dissolved silicic acid from surface waters during growth, and return this by recycling throughout the water column after they die. Inputs of silicon to the ocean from above arrive via rivers and aeolian dust, while those from below include seafloor sediment recycling, weathering, and hydrothermal activity. | 0 | Theoretical and Fundamental Chemistry |
* Novosil is a stimulant of plant immunity and growth. It is also used in the fight against plant viruses. The product was developed by the Institute together with the Institute of Cytology and Genetics in 1992. It is used in various regions of Russia, as well as in Kazakhstan, Belarus, Ukraine and Georgia.
* Acrylate-siloxane hybrid monomer is a material with the addition of silicon. It can be used to create microcircuits. | 0 | Theoretical and Fundamental Chemistry |
Contaminant trace metals such as zinc, lead, and copper are found in stormwater runoff from impervious surfaces (e.g. roadways and sidewalks). Treatment systems such as rain gardens and stormwater planters utilize a bioretention layer to remove heavy metals in stormwater runoff. Dissolved forms of heavy metals may bind to sediment particles in the roadway that are then captured by the bioretention system. Additionally, heavy metals may adsorb to soil particles in the bioretention media as the runoff filters through. In laboratory experiments, bioretention cells removed 94%, 88%, 95%, and >95% of zinc, copper, lead, and cadmium, respectively from water with metal concentrations typical of stormwater runoff. While this is a great benefit for water quality improvement, bioretention systems have a finite capacity for heavy metal removal. This will ultimately control the lifetime of bioretention systems, especially in areas with high heavy metal loads.
Metal removal by bioretention cells in cold climates was similar or slightly lower than that in warmer environments. Plants are less active in colder seasons, suggesting that most of the heavy metals remain in the bioretention media rather than being taken up by plant roots. Therefore, removal and replacement of the bioretention layer will become necessary in areas with heavy metal pollutants in stormwater runoff to extend the life of the treatment system. | 1 | Applied and Interdisciplinary Chemistry |
Drugs derived from natural sources are usually produced by isolation from the natural source or, as described here, by semisynthesis from such an isolated agent. From the viewpoint of chemical synthesis, living organisms are remarkable chemical factories that can easily produce structurally-complex chemical compounds by biosynthesis. In contrast, engineered chemical synthesis is necessarily simpler, with a lower chemical diversity in each reaction, than the incredibly-diverse biosynthesis pathways that are crucial to life.
As a result, certain functional groups are much easier to prepare by engineered synthesis than others, such as acetylation, in which certain biosynthetic pathways can generate groups and structures with minimal economic input that would be prohibitive via total synthesis.
Plants, animals, fungi, and bacteria are all used as sources for those tricky precursor molecules, including the use of bioreactors at the meeting point between engineered and biological chemical synthesis.
Semisynthesis, when it is used in drug discovery, aims to retain the sought-after medicinal activity while other molecule characteristics are altered, such as those that affect its adverse events or its oral bioavailability in a few chemical steps. In that regard, semisynthesis stands in contrast with the approach of total synthesis, whose aim is to arrive at a target molecule from low-molecular-weight, inexpensive starting materials, often petrochemicals or minerals. While there is no hard-and-fast division between total synthesis and semisynthesis, which rather differ in the degree of engineered synthesis that is used, many commodity precursor molecules with complex or fragile functional groups are much cheaper in practice to extract from an organism than to prepare from simple precursors only. Hence, methods of semisynthesis are applied when a needed precursor molecule is too structurally complex, too costly, or too difficult to produce by total synthesis.
Examples of practical application of the use of semisynthesis include in the groundbreaking historic case of the isolation of the antibiotic chlortetracycline and the semisyntheses of the further novel antibiotics tetracycline, doxycycline, and tigecycline.
Further examples of semisynthesis include the early commercial production of the anti-cancer agent paclitaxel from 10-deacetylbaccatin isolated from the needles of Taxus baccata (European yew), the preparation of LSD from ergotamine isolated from fungal cultures of ergot, and the semisynthesis of the antimalarial drug artemether from naturally-occurring artemisinin. As the field of synthetic chemistry advances, certain transformations become cheaper or easier, and the economics of a semisynthetic route may become less favorable. | 1 | Applied and Interdisciplinary Chemistry |
The optical properties of semiconductors are directly related to the dielectric constant of the material. This dielectric constant gives the ratio between the electric permeability of a material in relation to the permeability of a vacuum. The imaginary refractive index of a material is given by the square root of the dielectric constant. The reflectance of a material can be calculated using the Fresnel equations. A present electric field alters the dielectric constant and therefore alters the optical properties of the material, like the reflectance. | 0 | Theoretical and Fundamental Chemistry |
In clinical trials SPINA-GT was significantly elevated in patients with Graves disease and toxic adenoma compared to normal subjects. It is also elevated in diffuse and nodular goiters, and reduced in untreated autoimmune thyroiditis. In patients with toxic adenoma it has higher specificity and positive likelihood ratio for diagnosis of thyrotoxicosis than serum concentrations of thyrotropin, free T4 or free T3. GTs specificity is also high in thyroid disorders of secondary or tertiary origin.
Calculating SPINA-GT has proved to be useful in challenging clinical situations, e.g. for differential diagnosis of subclinical hypothyroidism and elevated TSH concentration due to type 2 allostatic load (as it is typical for obesity and certain psychiatric diseases). For this purpose, its usage has been recommended in sociomedical assessment. | 1 | Applied and Interdisciplinary Chemistry |
Check dams have traditionally been implemented in two environments: across channel bottoms and on hilly slopes. Check dams are used primarily to control water velocity, conserve soil, and improve land. They are used when other flow-control practices, such as lining the channel or creating bioswales, are impractical. Accordingly, they are commonly used in degrading temporary channels, in which permanent stabilization is impractical and infeasible in terms of resource allocation and funding due to the short life period. They are also used when construction delays and weather conditions prevent timely installation of other erosion control practices. This is typically seen during the construction process of large-scale permanent dams or erosion control. As such, check dams serve as temporary grade-control mechanisms along waterways until resolute stabilization is established or along permanent swales that need protection prior to installation of a non-erodible lining. | 1 | Applied and Interdisciplinary Chemistry |
Isotope analysis has many applications in archaeology, from dating sites and artefacts, determination of past diets and migration patterns and for environmental reconstruction.
Information is determined by assessing the ratio of different isotopes of a particular element in a sample. The most widely studied and used isotopes in archaeology are carbon, oxygen, nitrogen, strontium and calcium.
An isotope is an atom of an element with an abnormal number of neutrons, changing their atomic mass. Isotopes can be subdivided into stable and unstable or radioactive. Unstable isotopes decay at a predictable rate over time. The first stable isotope was discovered in 1913, and most were identified by the 1930s. Archaeology was relatively slow to adopt the study of isotopes. Whereas chemistry, biology and physics, saw a rapid uptake in applications of isotope analysis in the 1950s and 1960s, following the commercialisation of the mass spectrometer. It wasn't until the 1970s, with the publication of works by Vogel and Van Der Merwe (1977) and DeNiro and Epstein (1978; 1981) that isotopic analysis became a mainstay of archaeological study. | 0 | Theoretical and Fundamental Chemistry |
Merrilactone A was found to exhibit a significant neurotrophic activity, such as greatly promoting neurite outgrowth in the primary cultures of fetal rat cortical neurons at concentrations from 10 to 0.1 μmol/L. It was also found that this compound had a property of neuroprotection at same concentration. | 0 | Theoretical and Fundamental Chemistry |
The first mitogen-activated protein kinase to be discovered was ERK1 (MAPK3) in mammals. Since ERK1 and its close relative ERK2 (MAPK1) are both involved in growth factor signaling, the family was termed "mitogen-activated". With the discovery of other members, even from distant organisms (e.g. plants), it has become increasingly clear that the name is a misnomer, since most MAPKs are actually involved in the response to potentially harmful, abiotic stress stimuli (hyperosmosis, oxidative stress, DNA damage, low osmolarity, infection, etc.). Because plants cannot "flee" from stress, terrestrial plants have the highest number of MAPK genes per organism ever found. Thus the role of mammalian ERK1/2 kinases as regulators of cell proliferation is not a generic, but a highly specialized function. | 1 | Applied and Interdisciplinary Chemistry |
The classic click reaction is the copper-catalyzed reaction of an azide with an alkyne to form a 5-membered heteroatom ring: a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The first triazole synthesis, from diethyl acetylenedicarboxylate and phenyl azide, was reported by Arthur Michael in 1893. Later, in the middle of the 20th century, this family of 1,3-dipolar cycloadditions took on Rolf Huisgen's name after his studies of their reaction kinetics and conditions.
The copper(I)-catalysis of the Huisgen 1,3-dipolar cycloaddition was discovered concurrently and independently by the groups of Valery V. Fokin and K. Barry Sharpless at the Scripps Research Institute in California and Morten Meldal in the Carlsberg Laboratory, Denmark. The copper-catalyzed version of this reaction gives only the 1,4-isomer, whereas Huisgen's non-catalyzed 1,3-dipolar cycloaddition gives both the 1,4- and 1,5-isomers, is slow, and requires a temperature of 100 degrees Celsius.
Moreover, this copper-catalyzed "click" does not require ligands on the metal, although accelerating ligands such as tris(triazolyl)methyl amine ligands with various substituents have been reported and used with success in aqueous solution. Other ligands such as PPh3 and TBIA can also be used, even though PPh is liable to Staudinger ligation with the azide substituent. CuO in water at room temperature was found also to catalyze the same reaction in 15 minutes with 91% yield.
The first reaction mechanism proposed included one catalytic copper atom; but isotope, kinetic, and other studies have suggested a dicopper mechanism may be more relevant. Even though this reaction proceeds effectively at biological conditions, copper in this range of dosage is cytotoxic. Solutions to this problem have been presented, such as using water-soluble ligands on the copper to enhance cell penetration of the catalyst and thereby reduce the dosage needed, or to use chelating ligands to further increase the effective concentration of Cu(I) and thereby decreasing the actual dosage.
Although the Cu(I)-catalyzed variant was first reported by Meldal and co-workers for the synthesis of peptidotriazoles on solid support, their conditions were far from the true spirit of click chemistry and were overtaken by the publicly more recognized Sharpless. Meldal and co-workers also chose not to label this reaction type "click chemistry" which allegedly caused their discovery to be largely overlooked by the mainstream chemical society. Fokin and Sharpless independently described it as a reliable catalytic process offering "an unprecedented level of selectivity, reliability, and scope for those organic synthesis endeavors which depend on the creation of covalent links between diverse building blocks".
An analogous RuAAC reaction catalyzed by ruthenium, instead of copper, was reported by the Jia and Fokin groups in 2005, and allows for the selective production of 1,5-isomers. | 0 | Theoretical and Fundamental Chemistry |
El-Shall started his academic career in 1986 as a research associate at the University of California at Los Angeles (UCLA) while working with Howard Reiss on vapor phase nucleation and with Robert L. Whetten on molecular clusters and cluster ions. Since 1989, he has been on the faculty of the Chemistry Department, and has served as the Chair of the Chemistry Department at Virginia Commonwealth University (VCU) from 2015 to 2021. He is the Mary Eugenia Kapp Endowed Chair in Chemistry and Commonwealth Professor at Virginia Commonwealth University (VCU).
El-Shall served as a Senior Science Advisor in the Bureau for the Middle East, Middle East Regional Cooperation (MERC) Program of the USAID. He focused on enhancing and expanding joint Arab-Israeli research activities through MERC projects, and has also conducted site project reviews in Israel, Jordan and Egypt to improve collaborative research opportunities across borders and enhance implementation of research results. He also worked on creating new initiatives for young investigators in order to catalyze the next generation of Arab-Israeli research cooperation, and to create long-term sustainable collaborations between Arab and Israeli scientists. | 0 | Theoretical and Fundamental Chemistry |
An example of desirable work hardening is that which occurs in metalworking processes that intentionally induce plastic deformation to exact a shape change. These processes are known as cold working or cold forming processes. They are characterized by shaping the workpiece at a temperature below its recrystallization temperature, usually at ambient temperature. Cold forming techniques are usually classified into four major groups: squeezing, bending, drawing, and shearing. Applications include the heading of bolts and cap screws and the finishing of cold rolled steel. In cold forming, metal is formed at high speed and high pressure using tool steel or carbide dies. The cold working of the metal increases the hardness, yield strength, and tensile strength. | 1 | Applied and Interdisciplinary Chemistry |
DIOS has been shown to be an ultra-sensitive means of generating and detecting molecules at the yoctomole level, both for DIOS nanostructured surfaces modified with fluorocarbons, and a subsequent related technology known as nanostructure-initiator mass spectrometry or nanostructure imaging mass spectrometry (NIMS).
DIOS has been shown to detect peptides, natural products, small organic molecules, and polymers with little fragmentation.
DIOS can be used for proteomics. It has been reported as a useful method protein identification. Because it is matrix free, it can be used to identify smaller biomolecules than MALDI. In addition, it can be used to monitor reactions on a single surface through repeated MS analyses. Reaction monitoring can be used to screen enzyme inhibitors.
Atmospheric pressure DIOS was shown to be an effective tool for quantitative analysis of drugs with high proton affinity.
The use of DIOS to image small molecules has been demonstrated. Lin He and coworkers imaged small molecules on mouse liver cells. They also used marker molecules to image HEK 293 cancer cells. | 0 | Theoretical and Fundamental Chemistry |
Reference materials are compounds which are carefully calibrated against the primary reference or a calibration material. These compounds allow for isotopic analysis of materials differing in chemical or isotopic composition from the compounds defining the isotopic scales on which measurements are reported. In general these are the materials most researchers mean when they say "reference materials". An example of a reference material is USGS-34, a KNO salt with a δN of -1.8‰ vs. AIR. In this case the reference material has a mutually agreed upon value of δN when measured relative to the primary reference of atmospheric N (Böhlke et al., 2003). USGS-34 is useful because it allows researchers to directly measure the N/N of NO in natural samples against the standard and report observations relative to N without having to first convert the sample to N gas. | 0 | Theoretical and Fundamental Chemistry |
The "come up" phase can be defined as the period between the first noticeable changes in perception and the point of highest subjective intensity. This is colloquially known as "coming up." | 1 | Applied and Interdisciplinary Chemistry |
Selective ligands have a tendency to bind to very limited kinds of receptor, whereas non-selective ligands bind to several types of receptors. This plays an important role in pharmacology, where drugs that are non-selective tend to have more adverse effects, because they bind to several other receptors in addition to the one generating the desired effect. | 1 | Applied and Interdisciplinary Chemistry |
Thermodynamic operations appear in the statements of the laws of thermodynamics. For the zeroth law, one considers operations of thermally connecting and disconnecting systems. For the second law, some statements contemplate an operation of connecting two initially unconnected systems. For the third law, one statement is that no finite sequence of thermodynamic operations can bring a system to absolute zero temperature. | 0 | Theoretical and Fundamental Chemistry |
Bachrach earned a Bachelor of Science degree from the University of Illinois Urbana-Champaign and a PhD from the University of California, Berkeley. | 0 | Theoretical and Fundamental Chemistry |
Alkali metals also dissolve in some small primary amines, such as methylamine and ethylamine and hexamethylphosphoramide, forming blue solutions. THF dissolves alkali metal, but a Birch reduction (see ) analogue does not proceed without a diamine ligand. Solvated electron solutions of the alkaline earth metals magnesium, calcium, strontium and barium in ethylenediamine have been used to intercalate graphite with these metals. | 0 | Theoretical and Fundamental Chemistry |
Klaproth was born in Wernigerode. He was the son of a tailor, and attended the Latin school at Wernigerode for four years.
For much of his life he followed the profession of apothecary. In 1759, when he was 16 years old, he apprenticed at Quedlinburg. In 1764, he became a journeyman. He trained in pharmacies at Quedlinburg (1759–1766); Hanover (1766–1768, with August Hermann Brande); Berlin (1768); and Danzig (1770).
In 1771, Klaproth returned to Berlin to work for Valentin Rose the Elder as manager of his business. Following Roses death, Klaproth passed the required examinations to become senior manager. Following his marriage in 1780, he was able to buy his own establishment, the Apotheke zum Baren. Between 1782 and 1800, Klaproth published 84 papers based on researches carried out in the Apothekes laboratory. His shop was the most productive site of artisanal chemistry investigations in Europe at that time.
Beginning in 1782, he was the assessor of pharmacy for the examining board of the Ober-Collegium Medicum. In 1787 Klaproth was appointed lecturer in chemistry to the Prussian Royal Artillery.
In 1788, Klaproth became an unsalaried member of the Berlin Academy of Sciences. In 1800, he became the salaried director of the Berlin Academy of Sciences. He sold the apothecary and moved to the academy, where he convinced the university to build a new laboratory. Upon completion in 1802, Klaproth moved the equipment from his apothecary laboratory into the new building.
When the University of Berlin was founded in 1810 he was selected to be the professor of chemistry.
He died in Berlin on New Year's Day in 1817. | 1 | Applied and Interdisciplinary Chemistry |
The acidic triad member forms a hydrogen bond with the basic residue. This aligns the basic residue by restricting its side-chain rotation, and polarises it by stabilising its positive charge. Two amino acids have acidic side chains at physiological pH (aspartate or glutamate) and so are the most commonly used for this triad member. Cytomegalovirus protease uses a pair of histidines, one as the base, as usual, and one as the acid. The second histidine is not as effective an acid as the more common aspartate or glutamate, leading to a lower catalytic efficiency. In some enzymes, the acid member of the triad is less necessary and some act only as a dyad. For example, papain uses asparagine as its third triad member which orients the histidine base but does not act as an acid. Similarly, hepatitis A virus protease contains an ordered water in the position where an acid residue should be. | 1 | Applied and Interdisciplinary Chemistry |
Most applications of hydrothermal liquefaction operate at temperatures between 250-550 °C and high pressures of 5-25 MPa as well as catalysts for 20–60 minutes, although higher or lower temperatures can be used to optimize gas or liquid yields, respectively. At these temperatures and pressures, the water present in the biomass becomes either subcritical or supercritical, depending on the conditions, and acts as a solvent, reactant, and catalyst to facilitate the reaction of biomass to bio-oil.
The exact conversion of biomass to bio-oil is dependent on several variables:
* Feedstock composition
* Temperature and heating rate
* Pressure
* Solvent
* Residence time
* Catalysts | 0 | Theoretical and Fundamental Chemistry |
The adsorption/bio-oxidation process is used for treatment of industrial wastewater with high COD, including wastewater from:
* Pulp and paper industry
* Textile industry
* Food industry, including dairy industry
* Pharmaceutical industry
* Leather tanning industry
The C/N and C/P ratios of industrial wastewater is often too high for complete aerobic biodegradation of the influent organic matter, even after the adsorption stage. Addition of nutrients prior to bio-oxidation stage is required in these cases. | 1 | Applied and Interdisciplinary Chemistry |
Dimethyl methylphosphonate is an organophosphorus compound with the chemical formula CHPO(OCH). It is a colourless liquid, which is primarily used as a flame retardant. | 1 | Applied and Interdisciplinary Chemistry |
Some samples of water contain high levels of oxidizable inorganic materials which may interfere with the determination of COD. Because of its high concentration in most wastewater, chloride is often the most serious source of interference. Its reaction with potassium dichromate follows the equation:
Prior to the addition of other reagents, mercuric sulfate can be added to the sample to eliminate chloride interference.
The following table lists a number of other inorganic substances that may cause interference. The table also lists chemicals that may be used to eliminate such interference, and the compounds formed when the inorganic molecule is eliminated. | 0 | Theoretical and Fundamental Chemistry |
Classically, it converts carboxylic acids to acyl chlorides:
The reaction mechanism has been investigated: | 0 | Theoretical and Fundamental Chemistry |
Four different gas collection and measurement techniques can be used to perform this test:
*Douglas Bag: Expired respiratory gases are collected on an inflatable airtight bag. After completion of any test using Douglas Bags, gas collected must be analysed for volume and composition.
*Canopy (dilution): The dilution technique is considered the gold standard technology for Resting Energy Expenditure measurement in clinical nutrition. The test lasts just few minutes and consists of making a patient lie down relaxed on a bed or on a comfortable couch, with the head under a transparent hood connected to a pump, which applies an adjustable ventilation through it. Exhaled gas dilutes with the fresh air ventilated under the hood and a sample of this mixture is conveyed to the analysers, through a capillary tube and analysed. Ambient and diluted fractions of O and CO are measured for a known ventilation rate, and O consumption and CO production are determined and converted into Resting Energy Expenditure.
*Face mask (breath by breath): Indirect calorimetry tests are also often performed with a face mask, which is used to convey exhaled and inhaled gas through a turbine flowmeter able to measure the patient's breath by breath minute ventilation, at the same time a sample of gas is conveyed to the analyser and VO and VCO are measured and converted in energy expenditure.
*Interface with a Ventilator (Intensive Care settings): In case the patient is mechanically ventilated, an indirect calorimeter can still measure breath by breath inhaled/exhaled O and CO if interfaced with the ventilator through the endotracheal tube. | 1 | Applied and Interdisciplinary Chemistry |
Tailorability is one of the biggest advantages of these materials. The matrix material can be selected from almost any metal, polymer, or ceramic. Microballoons are available in a variety of sizes and materials, including glass microspheres, cenospheres, carbon, and polymers. The most widely used and studied foams are glass microspheres (in epoxy or polymers), and cenospheres or ceramics (in aluminium). One can change the volume fraction of microballoons or use microballoons of different effective density, the latter depending on the average ratio between the inner and outer radii of the microballoons.
A manufacturing method for low density syntactic foams is based on the principle of buoyancy. | 0 | Theoretical and Fundamental Chemistry |
Pulsed Pressure Cavitation Technique (PPCT) is a method to simulate cavitation damage using repetitive pressure pulses. It is developed at Oak Ridge National Laboratory.
The major components of PPCT include a repetitive pulse source and a testing chamber. For examples, a pulsed laser source can be used to generate large shock waves in a confined space. The shock waves then can induce cavitating bubbles. | 1 | Applied and Interdisciplinary Chemistry |
* Thionyl chloride will transform sulfinic acids into sulfinyl chlorides
* Sulfonic acids react with thionyl chloride to produce sulfonyl chlorides. Sulfonyl chlorides have also been prepared from the direct reaction of the corresponding diazonium salt with thionyl chloride.
* Thionyl chloride can be used in variations of the Pummerer rearrangement. | 0 | Theoretical and Fundamental Chemistry |
Ribosomal RNA (rRNA) is essential to the makeup of ribosomes and peptide transfer during translation processes. Ribosomal RNA modifications are made throughout ribosome synthesis, and often occur during and/or after translation. Modifications primarily play a role in the structure of the rRNA in order to protect translational efficiency. Chemical modification in rRNA consists of methylation of ribose sugars, isomerization of uridines, and methylation and acetylation of individual bases. | 1 | Applied and Interdisciplinary Chemistry |
With the development of native chemical ligation in 1994, total chemical synthesis of pairs of D-protein and L-protein enantiomers became feasible. In the first practical application to solving an unknown structure, racemic and quasi-racemic X-ray crystallography were used to determine the structure of snow flea anti-freeze protein. In the course of that work it was observed that racemic and even quasi-racemic protein mixtures dramatically facilitated the formation of diffraction quality, centrosymmetric crystals. Quasi-racemates are formed by mirror image protein molecules that are not true enantiomers but which are sufficiently similar mirror image objects to form ordered pseudo-centrosymmetric arrays.
Subsequently, pairs of racemic and quasi-racemic protein molecules prepared by total chemical synthesis have been shown to dramatically increase the rate of success in forming diffraction-quality crystals from a wide range of globular protein molecules.
Rv1738, a protein of Mycobacterium tuberculosis is the most up-regulated gene product when M. tb enters persistent dormancy. Preparations of recombinantly expressed Rv1738 L-protein resisted extensive attempts to form crystals. A racemic mixture of the chemically synthesized D-protein and L-protein forms of Rv1738 gave crystals in the centrosymmetric space group C2/c. The structure, containing L-protein and D-protein dimers in a centrosymmetric space group, revealed structural similarity to hibernation-promoting factors that can bind to ribosomes and suppress translation.
Crystallization of ubiquitin protein was successfully done using racemic crystallography. Crystallization of either D-ubiquitin or L-ubiquitin alone is difficult, whereas a racemic mixture of D-ubiquitin and L-ubiquitin was readily crystallized and diffraction quality crystals were obtained overnight in almost half the conditions tested in a standard commercial crystallization screen.
Crystallization of racemates of disulfide-containing microprotein molecules was used to determine the structure of trypsin inhibitor SFTI-1 (14 amino acids,1 disulfide), conotoxin cVc1.1 (22 amino acids, 2 disul-fides) and cyclotide kB1 (29 amino acids, 3 disulfides). Using X-ray diffraction, it was found that the racemates crystallized in the centrosymmetric spacegroups P3(bar), Pbca and P1(bar).
Interestingly, achiral "peptoid" chains were found to fold as racemic pairs and crystallize in highly preferred centrosymmetric space groups.
A high-resolution crystal structure of the racemate of a heterochiral D-protein complex with vascular endothelial growth factor A (VEGF-A). The mirror image D-protein form of VEGF-A was used in phage display to identify a 56 residue L-protein binder with nanomolar affinity; the chemically synthesized D-protein binder had the same affinity for the L-protein form of VEGF-A. A mixture of chemically synthesized proteins consisting of D-VEGF-A, L-VEGF-A, and two equivalents each of the D-protein binder and L-protein binder, gave racemic crystals in the centrosymmetric space group P21/n. The structure of this 71kDa heterochiral protein complex was solved at a resolution of 1.6 Å | 0 | Theoretical and Fundamental Chemistry |
HFB machines measure the strength of particle interactions using liquid flow to separate the particles. This method is used to find depletion force strength by adhering to a static plate one particle in a dispersion particle doublet and applying shear force through fluid flow. The drag created by the dispersion particles resists the depletion force between them, pulling the free particle away from the adhered particle. A force balance of the particles at separation can be used to determine the depletion force between the particles. | 0 | Theoretical and Fundamental Chemistry |
A ChemFET is a chemically-sensitive field-effect transistor, that is a field-effect transistor used as a sensor for measuring chemical concentrations in solution. When the target analyte concentration changes, the current through the transistor will change accordingly. Here, the analyte solution separates the source and gate electrodes. A concentration gradient between the solution and the gate electrode arises due to a semi-permeable membrane on the FET surface containing receptor moieties that preferentially bind the target analyte. This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET. | 0 | Theoretical and Fundamental Chemistry |
The liquid-drop model was first proposed by George Gamow and further developed by Niels Bohr, John Archibald Wheeler and Lise Meitner
. It treats the nucleus as a drop of incompressible fluid of very high density, held together by the nuclear force (a residual effect of the strong force), there is a similarity to the structure of a spherical liquid drop. While a crude model, the liquid-drop model accounts for the spherical shape of most nuclei and makes a rough prediction of binding energy.
The corresponding mass formula is defined purely in terms of the numbers of protons and neutrons it contains. The original Weizsäcker formula defines five terms:
* Volume energy, when an assembly of nucleons of the same size is packed together into the smallest volume, each interior nucleon has a certain number of other nucleons in contact with it. So, this nuclear energy is proportional to the volume.
* Surface energy corrects for the previous assumption made that every nucleon interacts with the same number of other nucleons. This term is negative and proportional to the surface area, and is therefore roughly equivalent to liquid surface tension.
* Coulomb energy, the potential energy from each pair of protons. As this is a repelling force, the binding energy is reduced.
* Asymmetry energy (also called Pauli energy), which accounts for the Pauli exclusion principle. Unequal numbers of neutrons and protons imply filling higher energy levels for one type of particle, while leaving lower energy levels vacant for the other type.
* Pairing energy, which accounts for the tendency of proton pairs and neutron pairs to occur. An even number of particles is more stable than an odd number due to spin coupling. | 0 | Theoretical and Fundamental Chemistry |
Humans, like all animals, produce heat as a result of metabolism. In warm conditions, this heat exceeds a level required for homeostasis in warm-blooded animals, and is disposed of by various thermoregulation methods such as sweating and panting. Fiala et al. modelled human thermoregulation. | 0 | Theoretical and Fundamental Chemistry |
Yu is the recipient of numerous awards and honors for his work in organic chemistry reaction development, including a MacArthur Fellowship (also known as a "Genius Grant") in 2016. He was elected a member of the American Academy of Arts and Sciences in 2019, a fellow of the American Association for the Advancement of Science and the Royal Society of Chemistry in 2012. In 2013, he received the Raymond and Beverly Sackler Prize in the Physical Sciences.
Yu received the Pedler Award from the Royal Society of Chemistry in 2016, and the Elias J. Corey Award for Outstanding Original Contribution in Organic Synthesis by a Young Investigator from the American Chemical Society. In 2012, he was awarded the Mukaiyama Award from the Japanese Society of Organic Synthesis, the ACS Cope Scholar Award, and the Bristol-Myers Squibb Award. His honors also include the Novartis Early Career Award in Organic Chemistry (2011), Eli Lilly Grantee Award (2008), Amgen Young Investigator's Award (2008), and Sloan Research Fellowship (2008). | 0 | Theoretical and Fundamental Chemistry |
Carbon chauvinism is a neologism meant to disparage the assumption that the chemical processes of hypothetical extraterrestrial life must be constructed primarily from carbon (organic compounds) because as far as is known, carbon's chemical and thermodynamic properties render it far superior to all other elements at forming molecules used in living organisms.
The expression "carbon chauvinism" is also used to criticize the idea that artificial intelligence cant in theory be sentient or truly intelligent because the underlying matter isnt biological. | 1 | Applied and Interdisciplinary Chemistry |
After his PhD, Wüthrich continued postdoctoral research with Fallab for a short time before leaving to work at the University of California, Berkeley for two years from 1965 with Robert E. Connick. That was followed by a stint working with Robert G. Shulman at the Bell Telephone Laboratories in Murray Hill, New Jersey from 1967 to 1969.
Wüthrich returned to Switzerland, to Zürich, in 1969, where he began his career there at the ETH Zürich, rising to Professor of Biophysics by 1980. He currently maintains a laboratory at the ETH Zürich, at The Scripps Research Institute, in La Jolla, California and at the of ShanghaiTech University. He has also been a visiting professor at the University of Edinburgh (1997–2000), the Chinese University of Hong Kong (where he was an Honorary Professor) and Yonsei University.
During his graduate studies Wüthrich started out working with electron paramagnetic resonance spectroscopy, and the subject of his PhD thesis was "the catalytic activity of copper compounds in autoxidation reactions". During his time as a postdoc in Berkeley he began working with the newly developed and related technique of nuclear magnetic resonance spectroscopy to study the hydration of metal complexes. When Wüthrich joined the Bell Labs, he was put in charge of one of the first superconducting NMR spectrometers, and started studying the structure and dynamics of proteins. He has pursued this line of research ever since.
After returning to Switzerland, Wüthrich collaborated with, among others, Nobel laureate Richard R. Ernst on developing the first two-dimensional NMR experiments, and established the nuclear Overhauser effect as a convenient way of measuring distances within proteins. This research later led to the complete assignment of resonances for among others the bovine pancreatic trypsin inhibitor and glucagon.
In October 2010, Wüthrich participated in the USA Science and Engineering Festivals Lunch with a Laureate program where middle and high school students will get to engage in an informal conversation with a Nobel Prize–winning scientist over a brown-bag lunch. Wüthrich is also a member on the USA Science and Engineering Festivals Advisory Board and a supporter of the Campaign for the Establishment of a United Nations Parliamentary Assembly, an organisation which campaigns for democratic reform in the United Nations. | 0 | Theoretical and Fundamental Chemistry |
Consider, for one, the familiar example of a marble on the edge of a bowl. If we consider the marble and bowl to be an isolated system, then when the marble drops, the potential energy will be converted to the kinetic energy of motion of the marble. Frictional forces will convert this kinetic energy to heat, and at equilibrium, the marble will be at rest at the bottom of the bowl, and the marble and the bowl will be at a slightly higher temperature. The total energy of the marble-bowl system will be unchanged. What was previously the potential energy of the marble, will now reside in the increased heat energy of the marble-bowl system. This will be an application of the maximum entropy principle as set forth in the principle of minimum potential energy, since due to the heating effects, the entropy has increased to the maximum value possible given the fixed energy of the system.
If, on the other hand, the marble is lowered very slowly to the bottom of the bowl, so slowly that no heating effects occur (i.e. reversibly), then the entropy of the marble and bowl will remain constant, and the potential energy of the marble will be transferred as energy to the surroundings. The surroundings will maximize its entropy given its newly acquired energy, which is equivalent to the energy having been transferred as heat. Since the potential energy of the system is now at a minimum with no increase in the energy due to heat of either the marble or the bowl, the total energy of the system is at a minimum. This is an application of the minimum energy principle.
Alternatively, suppose we have a cylinder containing an ideal gas, with cross sectional area A and a variable height x. Suppose that a weight of mass m has been placed on top of the cylinder. It presses down on the top of the cylinder with a force of mg where g is the acceleration due to gravity.
Suppose that x is smaller than its equilibrium value. The upward force of the gas is greater than the downward force of the weight, and if allowed to freely move, the gas in the cylinder would push the weight upward rapidly, and there would be frictional forces that would convert the energy to heat. If we specify that an external agent presses down on the weight so as to very slowly (reversibly) allow the weight to move upward to its equilibrium position, then there will be no heat generated and the entropy of the system will remain constant while energy is transferred as work to the external agent. The total energy of the system at any value of x is given by the internal energy of the gas plus the potential energy of the weight:
where T is temperature, S is entropy, P is pressure, μ is the chemical potential, N is the number of particles in the gas, and the volume has been written as V=Ax. Since the system is closed, the particle number N is constant and a small change in the energy of the system would be given by:
Since the entropy is constant, we may say that dS=0 at equilibrium and by the principle of minimum energy, we may say that dU=0 at equilibrium, yielding the equilibrium condition:
which simply states that the upward gas pressure force (PA) on the upper face of the cylinder is equal to the downward force of the mass due to gravitation (mg). | 0 | Theoretical and Fundamental Chemistry |
When in 1981 Rob Aalberse from the University of Amsterdam noticed the enormous cross-reactivity of some patients´ sera against virtually any plant and even insects, notably, insect venoms, it took ten years to arrive at a possible structural explanation of this phenomenon. 1991, Japanese researchers determined the structure of the epitope common to horseradish peroxidase and Drosophila neurons as being an asparagine-linked oligosaccharide (N-glycan) containing a xylose and a core-linked α1,3-linked fucose residue. These structural features are not present in humans and animals. Core α1,3-fucose was then found to be relevant for the binding of patients´ IgE to honeybee venom allergens, which contain N-glycans with structural similarities to plant N-glycans. Ever since then, core α1,3-fucose emerged as the structural element most relevant as a CCD in plants and insect allergens. Much later, both xylose and core α1,3-fucose were revealed as heart pieces of two independent glycan epitopes for rabbit IgG. The occurrence of human anti-xylose IgE, however, has not been verified so far. Still, because of the two possible epitopes and the different carrier structures, the plural CCDs is in frequent use even though core α1,3-fucose appears to be the single culprit. | 0 | Theoretical and Fundamental Chemistry |
Glide planes are noted in the Hermann–Mauguin notation by a, b or c, depending on which axis the glide is along. (The orientation of the plane is determined by the position of the symbol in the Hermann–Mauguin designation.) If the axis is not defined, then the glide plane may be noted by g. When the glide plane is parallel to the screen, these planes may be indicated by a bent arrow in which the arrowhead indicates the direction of the glide. When the glide plane is perpendicular to the screen, these planes can be represented either by dashed lines when the glide is parallel to the plane of the screen or dotted lines when the glide is perpendicular to the plane of the screen. Additionally, a centered lattice can cause a glide plane to exist in two directions at the same time. This type of glide plane may be indicated by a bent arrow with an arrowhead on both sides when the glide plan is parallel to the plane of the screen or a dashed and double-dotted line when the glide plane is perpendicular to the plane of the screen. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, which is along a fourth of either a face or space diagonal of the unit cell . The latter is often called the diamond glide plane as it features in the diamond structure. The n glide plane may be indicated by diagonal arrow when it is parallel to the plane of the screen or a dashed-dotted line when the glide plane is perpendicular to the plane of the screen. A d glide plane may be indicated by a diagonal half-arrow if the glide plane is parallel to the plane of the screen or a dashed-dotted line with arrows if the glide plane is perpendicular to the plane of the screen. If a d glide plane is present in a crystal system, then that crystal must have a centered lattice.
In todays version of Hermann–Mauguin notation, the symbol e is used in cases where there are two possible ways of designating the glide direction because both are true. For example if a crystal has a base-centered Bravais lattice centered on the C face, then a glide of half a cell unit in the a direction gives the same result as a glide of half a cell unit in the b' direction.
The isometry group generated by just a glide reflection is an infinite cyclic group. Combining two equal glide plane operations gives a pure translation with a translation vector that is twice that of the glide reflection, so the even powers of the glide reflection form a translation group.
In the case of glide-reflection symmetry, the symmetry group of an object contains a glide reflection and the group generated by it. For any symmetry group containing a glide reflection, the glide vector is one half of an element of the translation group. If the translation vector of a glide plane operation is itself an element of the translation group, then the corresponding glide plane symmetry reduces to a combination of reflection symmetry and translational symmetry. | 0 | Theoretical and Fundamental Chemistry |
Whole genome shotgun sequencing for small (4000- to 7000-base-pair) genomes was first suggested in 1979. The first genome sequenced by shotgun sequencing was that of cauliflower mosaic virus, published in 1981. | 1 | Applied and Interdisciplinary Chemistry |
Semi-solid metal (SSM) casting is a modified die casting process that reduces or eliminates the residual porosity present in most die castings. Rather than using liquid metal as the feed material, SSM casting uses a higher viscosity feed material that is partially solid and partially liquid. A modified die casting machine is used to inject the semi-solid slurry into reusable hardened steel dies. The high viscosity of the semi-solid metal, along with the use of controlled die filling conditions, ensures that the semi-solid metal fills the die in a non-turbulent manner so that harmful porosity can be essentially eliminated.
Used commercially mainly for aluminium and magnesium alloys, SSM castings can be heat treated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates (from using uncoated steel dies) and minimal porosity provides excellent combinations of strength and ductility. Other advantages of SSM casting include the ability to produce complex shaped parts net shape, pressure tightness, tight dimensional tolerances and the ability to cast thin walls. | 1 | Applied and Interdisciplinary Chemistry |
Even though ideally the flowmeter should be unaffected by its environment, in practice this is unlikely to be the case. Often measurement errors originate from incorrect installation or other environment dependent factors. In situ methods are used when flowmeter is calibrated in the correct flow conditions. The result of a flowmeter calibration will result in two related statistics: a performance indicator metric and a flow rate metric. | 1 | Applied and Interdisciplinary Chemistry |
A screening machine consist of a drive that induces vibration, a screen media that causes particle separation, and a deck which holds the screen media and the drive and is the mode of transport for the vibration.
There are physical factors that makes screening practical. For example, vibration, g force, bed density, and material shape all facilitate the rate or cut. Electrostatic forces can also hinder screening efficiency in way of water attraction causing sticking or plugging, or very dry material generate a charge that causes it to attract to the screen itself.
As with any industrial process there is a group of terms that identify and define what screening is. Terms like blinding, contamination, frequency, amplitude, and others describe the basic characteristics of screening, and those characteristics in turn shape the overall method of dry or wet screening.
In addition, the way a deck is vibrated differentiates screens. Different types of motion have their advantages and disadvantages. In addition media types also have their different properties that lead to advantages and disadvantages.
Finally, there are issues and problems associated with screening. Screen tearing, contamination, blinding, and dampening all affect screening efficiency. | 1 | Applied and Interdisciplinary Chemistry |
A finery forge was used to refine wrought iron at least by the 3rd century BC in ancient China, based on the earliest archaeological specimens of cast and pig iron fined into wrought iron and steel found at the early Han Dynasty (202 BC – 220 AD) site at Tieshengguo. Pigott speculates that the finery forge existed in the previous Warring States period (403–221 BC), because of the wrought iron items from China dating to that period and there was no documented evidence of the bloomery ever being used in China. Wagner writes that in addition to the Han Dynasty hearths believed to be fining hearths, there is also pictorial evidence of the fining hearth from a Shandong tomb mural dated 1st to 2nd century AD, as well as a hint of written evidence in the 4th century AD Daoist text Taiping Jing.
In Europe, the concept of the finery forge may have been evident as early as the 13th century. However, it was perhaps not capable of being used to fashion plate armor until the 15th century, as described in conjunction with the waterwheel-powered blast furnace by the Florentine Italian engineer Antonio Averlino (c. 1400 - 1469). The finery forge process began to be replaced in Europe from the late 18th century by others, of which puddling was the most successful, though some continued in use through the mid-19th century. The new methods used mineral fuel (coal or coke), and freed the iron industry from its dependence on wood to make charcoal. | 1 | Applied and Interdisciplinary Chemistry |
The Craig plot, named after Paul N. Craig, is a plot of two substituent parameters (e.g. Hansch-Fujita π constant and sigma constant) used in rational drug design.
Two most used forms of a Craig plot are
* plotting the sigma constants of the Hammett equation versus hydrophobicity
* plotting the steric terms of the Taft equation against hydrophobicity | 1 | Applied and Interdisciplinary Chemistry |
Hyperspectral data is often used to determine what materials are present in a scene. Materials of interest could include roadways, vegetation, and specific targets (i.e. pollutants, hazardous materials, etc.). Trivially, each pixel of a hyperspectral image could be compared to a material database to determine the type of material making up the pixel. However, many hyperspectral imaging platforms have low resolution (>5m per pixel) causing each pixel to be a mixture of several materials. The process of unmixing one of these mixed pixels is called hyperspectral image unmixing or simply hyperspectral unmixing.
A solution to hyperspectral unmixing is to reverse the mixing process. Generally, two models of mixing are assumed: linear and nonlinear.
Linear mixing models the ground as being flat and incident sunlight on the ground causes the materials to radiate some amount of the incident energy back to the sensor. Each pixel then, is modeled as a linear sum of all the radiated energy curves of materials making up the pixel. Therefore, each material contributes to the sensor's observation in a positive linear fashion. Additionally, a conservation of energy constraint is often observed thereby forcing the weights of the linear mixture to sum to one in addition to being positive. The model can be described mathematically as follows:
where represents a pixel observed by the sensor, is a matrix of material reflectance signatures (each signature is a column of the matrix), and is the proportion of material present in the observed pixel. This type of model is also referred to as a simplex.
With satisfying the two constraints:
1. Abundance Nonnegativity Constraint (ANC) - each element of x is positive.
2. Abundance Sum-to-one Constraint (ASC) - the elements of x must sum to one.
Non-linear mixing results from multiple scattering often due to non-flat surface such as buildings and vegetation.
There are many algorithms to unmix hyperspectral data each with their own strengths and weaknesses. Many algorithms assume that pure pixels (pixels which contain only one materials) are present in a scene.
Some algorithms to perform unmixing are listed below:
* Pixel Purity Index Works by projecting each pixel onto one vector from a set of random vectors spanning the reflectance space. A pixel receives a score when it represent an extremum of all the projections. Pixels with the highest scores are deemed to be spectrally pure.
* N-FINDR
* Gift Wrapping Algorithm
* Independent Component Analysis Endmember Extraction Algorithm - works by assuming that pure pixels occur independently than mixed pixels. Assumes pure pixels are present.
* Vertex Component Analysis - works on the fact that the affine transformation of a simplex is another simplex which helps to find hidden (folded) vertices of the simplex. Assumes pure pixels are present.
* Principal component analysis - could also be used to determine endmembers, projection on principal axes could permit endmember selection [Smith, Johnson et Adams (1985), Bateson et Curtiss (1996)]
* Multi endmembers spatial mixture analysis based on the SMA algorithm
* Spectral phasor analysis based on Fourier transformation of spectra and plotting them on a 2D plot.
Non-linear unmixing algorithms also exist: support vector machines or analytical neural network.
Probabilistic methods have also been attempted to unmix pixel through Monte Carlo unmixing algorithm.
Once the fundamental materials of a scene are determined, it is often useful to construct an abundance map of each material which displays the fractional amount of material present at each pixel. Often linear programming is done to observed ANC and ASC. | 0 | Theoretical and Fundamental Chemistry |
In July 2010, the UN General Assembly declared that access to clean water and sanitation is a human right. The assembly did not specify whether a public authority or the private sector would be best capable of providing this right. | 1 | Applied and Interdisciplinary Chemistry |
:These are used for high-temperature FT synthesis (nearly 340 °C) to produce low-molecular-weight unsaturated hydrocarbons on alkalized fused iron catalysts. The fluid-bed technology (as adapted from the catalytic cracking of heavy petroleum distillates) was introduced by Hydrocarbon Research in 1946–50 and named the Hydrocol process. A large scale Fischer–Tropsch Hydrocol plant (350,000 tons per annum) operated during 1951–57 in Brownsville, Texas. Due to technical problems, and impractical economics due to increasing petroleum availability, this development was discontinued. Fluid-bed FT synthesis has been reinvestigated by Sasol. One reactor with a capacity of 500,000 tons per annum is in operation. The process has been used for C and C alkene production. A high-temperature process with a circulating iron catalyst (circulating fluid bed, riser reactor, entrained catalyst process) was introduced by the Kellogg Company and a respective plant built at Sasol in 1956. It was improved by Sasol for successful operation. At Secunda, South Africa, Sasol operated 16 advanced reactors of this type with a capacity of approximately 330,000 tons per annum each. The circulating catalyst process can be replaced by fluid-bed technology. Early experiments with cobalt catalyst particles suspended in oil have been performed by Fischer. The bubble column reactor with a powdered iron slurry catalyst and a CO-rich syngas was particularly developed to pilot plant scale by Kölbel at the Rheinpreuben Company in 1953. Since 1990, low-temperature FT slurry processes are under investigation for the use of iron and cobalt catalysts, particularly for the production of a hydrocarbon wax, or to be hydrocracked and isomerized to produce diesel fuel, by Exxon and Sasol. Slurry-phase (bubble column) low-temperature FT synthesis is efficient. This technology is also under development by the Statoil Company (Norway) for use on a vessel to convert associated gas at offshore oil fields into a hydrocarbon liquid. | 0 | Theoretical and Fundamental Chemistry |
Only precious metal watch cases must be hallmarked in Switzerland. Swiss hallmarking for other articles such as jewelry and cutlery is optional. In addition to the Swiss hallmark, all precious metal goods may be stamped with the Common Control Mark of the Vienna Convention. Switzerland recognizes platinum, gold, silver and palladium as precious metals which may be hallmarked and thus are subject to assay. | 0 | Theoretical and Fundamental Chemistry |
The term was originally coined by the Bakelite Company, in 1955, for their lightweight composites made of hollow phenolic microspheres bonded to a matrix of phenolic, epoxy, or polyester.
These materials were developed in early 1960s as improved buoyancy materials for marine applications. Other characteristics led these materials to aerospace and ground transportation vehicle applications.
Research on syntactic foams has recently been advanced by Nikhil Gupta. | 0 | Theoretical and Fundamental Chemistry |
The Institution of Metallurgists was a British professional association for metallurgists, largely involved in the iron and steel industry. | 1 | Applied and Interdisciplinary Chemistry |
The key concepts of physical chemistry are the ways in which pure physics is applied to chemical problems.
One of the key concepts in classical chemistry is that all chemical compounds can be described as groups of atoms bonded together and chemical reactions can be described as the making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they bond is one of the major goals of physical chemistry. To describe the atoms and bonds precisely, it is necessary to know both where the nuclei of the atoms are, and how electrons are distributed around them. | 0 | Theoretical and Fundamental Chemistry |
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