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LaSSI is similar to LSA in that it involves the construction of an occurrence matrix from a corpus of items and the application of singular value decomposition to that matrix to derive latent features. What differs is that the occurrence matrix represents the frequency of two- and three-dimensional chemical descriptors (rather than natural language terms) found within a chemical database of chemical structures. This process derives latent chemical structure concepts that can be used to calculate chemical similarities and structure–activity relationships for drug discovery. | 1 | Applied and Interdisciplinary Chemistry |
Specialized UV gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes. Argon and deuterium arc lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride. These are often the emitting sources in UV spectroscopy equipment for chemical analysis.
Other UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), deuterium arc lamps, mercury-xenon arc lamps, and metal-halide arc lamps.
The excimer lamp, a UV source developed in the early 2000s, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet. | 0 | Theoretical and Fundamental Chemistry |
The most notable classes of biological macromolecules used in the fundamental processes of living organisms include:
* Proteins, which are the building blocks from which the structures of living organisms are constructed (this includes almost all enzymes, which catalyse organic chemical reactions).
* Amino acid, make up proteins, included the use in genetic code of life.
* Nucleic acids, which carry genetic information.
* Ribonucleic acid (RNA), production of proteins.
* Deoxyribonucleic acid (DNA), nucleic acid in genetic form.
* Peptide, building block of proteins.
* Lipids, which also store energy, but in a more concentrated form, and which may be stored for extended periods in the bodies of animals.
* Phospholipid used in cell membrane.
* Carbohydrates, which store energy in a form that can be used by living cells.
* Lectin, for binding proteins.
* Monosaccharide, simple sugars, including glucose and fructose.
* Disaccharides, sugar soluble in water, including lactose, maltose, and sucrose.
* Starch, made of amylose and amylopectin, plants energy storage.
* Glycogen, energy in animals.
* Cellulose, a biopolymer, found in the cell walls of plants.
* Fatty acid, two types, saturated fat and unsaturated fat (oil), are stored energy.
* Essential fatty acid, needed but not synthesized by the human body.
* Steroid, hormone, and used in cell membrane.
* Neurotransmitter, are signaling molecules.
* Cholesterol, used in the brain and spinal cord of animals.
* Wax, found in beeswax and lanolin. Plant wax used for protection. | 1 | Applied and Interdisciplinary Chemistry |
Louis Lémery (25 January 1677 – 9 June 1743) was a French botanist and chemist.
The son of scientist Nicolas Lemery, Louis was appointed physician at the Hôtel-Dieu de Paris in 1710, and became demonstrator of chemistry at the Jardin du Roi in 1731. He was the author of a Traité des aliments (1702), and of a Dissertation sur la nature des os (1704), as well as of a number of papers on chemical topics. He also wrote "A Treatise of All Sorts of Foods, Both Animal and Vegetable; also of Drinkables: Giving an Account how to chuse the best Sort of all Kinds", first published in English in 1745. | 1 | Applied and Interdisciplinary Chemistry |
Nickel-63 is a radioisotope of nickel that can be used as an energy source in Radioisotope Piezoelectric Generators. It has a half-life of 100.1 years. It can be created by irradiating nickel-62 with neutrons in a nuclear reactor. | 0 | Theoretical and Fundamental Chemistry |
Many common addition polymers are formed from unsaturated monomers (usually having a C=C double bond). The most prevalent addition polymers are polyolefins, i.e. polymers derived by the conversion of olefins (alkenes) to long-chain alkanes. The stoichiometry is simple:
:n RCH=CH → [RCH-CH]
This conversion can be induced by a variety of catalysts including free radicals, acids, carbanions and metal complexes.
Examples of such polyolefins are polyethenes, polypropylene, PVC, Teflon, Buna rubbers, polyacrylates, polystyrene, and PCTFE. | 0 | Theoretical and Fundamental Chemistry |
The saprobic system is a tool to measure water quality, and specifically it deals with the capacity of a water body to self-regulate and degrade organic matter. The saprobic system derives from so-called saprobes — organisms that thrive through degradation of organic matter, which is called saprotrophic nutrition.
The saprobic system is based on a survey of indicator organisms. For example, the abundance of Lymnaea stagnalis water snails and other organisms is estimated, and using a formula, the listed saprobic and tolerance values of the organisms allow the water quality grade — the saprobic index — to be computed.
Saprobic water quality is expressed in four classes ranging from I to IV; and with three intermediate grades (I-II, II-III and III-IV). Water bodies of class I are the cleanest and of the highest quality. The inherent drawback of the saprobic systems as a water quality measure is that it only regards biodegradable organic material, and so ignores other factors like heavy metal pollution. Though the presence of certain organisms can rule out the presence of toxic substances, the incorporation of such organisms would deviate from the saprobic system's concept. | 1 | Applied and Interdisciplinary Chemistry |
Dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors) are enzyme inhibitors that inhibit the enzyme dipeptidyl peptidase-4 (DPP-4). They are used in the treatment of type 2 diabetes mellitus. Inhibition of the DPP-4 enzyme prolongs and enhances the activity of incretins that play an important role in insulin secretion and blood glucose control regulation.
Type 2 diabetes mellitus is a chronic metabolic disease that results from inability of the β-cells in the pancreas to secrete sufficient amounts of insulin to meet the bodys needs. Insulin resistance and increased hepatic glucose production can also play a role by increasing the bodys demand for insulin. Current treatments, other than insulin supplementation, are sometimes not sufficient to achieve control and may cause undesirable side effects, such as weight gain and hypoglycemia. In recent years, new drugs have been developed, based on continuing research into the mechanism of insulin production and regulation of the metabolism of sugar in the body. The enzyme DPP-4 has been found to play a significant role. | 1 | Applied and Interdisciplinary Chemistry |
Cyclic molecules often exist in much more rigid conformations than their linear counterparts. Even very large macrocycles like erythromycin exist in defined geometries despite having many degrees of freedom. Because of these properties, it is often easier to achieve asymmetric induction with macrocyclic substrates rather than linear ones. Early experiments performed by W. Clark Still and colleagues showed that medium- and large-ring organic molecules can provide striking levels of stereo induction as substrates in reactions such as kinetic enolate alkylation, dimethylcuprate addition, and catalytic hydrogenation. Even a single methyl group is often sufficient to bias the diastereomeric outcome of the reaction. These studies, among others, helped challenge the widely-held scientific belief that large rings are too floppy to provide any kind of stereochemical control.
A number of total syntheses have made use of macrocyclic stereocontrol to achieve desired reaction products. In the synthesis of (−)-cladiella-6,11-dien-3-ol, a strained trisubstituted olefin was dihydroxylated diasetereoselectively with N-methylmorpholine N-oxide (NMO) and osmium tetroxide, in the presence of an unstrained olefin. En route to (±)-periplanone B, chemists achieved a facial selective epoxidation of an enone intermediate using tert-butyl hydroperoxide in the presence of two other alkenes. Sodium borohydride reduction of a 10-membered ring enone intermediate en route to the sesquiterpene eucannabinolide proceeded as predicted by molecular modelling calculations that accounted for the lowest energy macrocycle conformation. Substrate-controlled synthetic schemes have many advantages, since they do not require the use of complex asymmetric reagents to achieve selective transformations. | 0 | Theoretical and Fundamental Chemistry |
Seawater desalination plants have produced potable water for many years. However, until recently desalination had been used only in special circumstances because of the high energy consumption of the process.
Early designs for desalination plants made use of various evaporation technologies. The most advanced are the multi-stage flash distillation seawater evaporation desalinators, which make use of multiple stages and have an energy consumption of over 9 kWh per cubic meter of potable water produced. For this reason large seawater desalinators were initially constructed in locations with low energy costs, such as the Middle East, or next to process plants with available waste heat.
In the 1970s the seawater reverse osmosis (SWRO) process was developed which made potable water from seawater by forcing it under high pressure through a tight membrane thus filtering out salts and impurities. These salts and impurities are discharged from the SWRO device as a concentrated brine solution in a continuous stream, which contains a large amount of high-pressure energy. Most of this energy can be recovered with a suitable device. Many early SWRO plants built in the 1970s and early 1980s had an energy consumption of over 6.0 kWh per cubic meter of potable water produced, due to low membrane performance, pressure drop limitations and the absence of energy recovery devices.
An example where a pressure exchange engine finds application is in the production of potable water using the reverse osmosis membrane process. In this process, a feed saline solution is pumped into a membrane array at high pressure. The input saline solution is then divided by the membrane array into super saline solution (brine) at high pressure and potable water at low pressure. While the high pressure brine is no longer useful in this process as a fluid, the pressure energy that it contains has high value. A pressure exchange engine is employed to recover the pressure energy in the brine and transfer it to feed saline solution. After transfer of the pressure energy in the brine flow, the brine is expelled at low pressure to drain.
Nearly all reverse osmosis plants operated for the desalination of sea water in order to produce drinking water in
industrial scale are equipped with an energy recovery system based on turbines. These are activated by the concentrate (brine) leaving the plant and transfer the energy contained in the high pressure of this concentrate usually mechanically to the high-pressure pump. In the pressure exchanger the energy contained in the brine is transferred hydraulically and with an efficiency of approximately 98% to the feed. This reduces the energy demand for the desalination process significantly and thus the operating costs. Therefrom results an economic energy recovery, amortization times for such systems varying between 2 and 4 years depending on the place of operation.
Reduced energy and capital costs mean that for the first time ever it is possible to produce potable water from seawater at a cost below $1 per cubic meter in many locations worldwide. Although the cost may be a bit higher on islands with high power costs, the PE has the potential to rapidly expand the market for seawater desalination.
By means of the application of a pressure exchange system, which is already used in other domains, a considerably higher efficiency of energy recovery of reverse osmosis systems may be achieved than with the use of reverse running pumps or turbines.
The pressure exchange system is suited, above all, for bigger plants i.e. approx. ≥ 2000 m3/d permeate production. | 1 | Applied and Interdisciplinary Chemistry |
Heat transfer fluids are integral to various industrial applications, enabling precise temperature control in manufacturing processes. In the food industry, they are vital for processing meats and snacks. Chemical processes often rely on them for batch reactors and continuous operations. The plastics, rubber, and composites sectors use heat transfer fluids in molding and extrusion processes. They are also critical in petrochemical synthesis and distillation, oil and gas refining, and for converting materials in presses and laminating operations. | 1 | Applied and Interdisciplinary Chemistry |
A widely used British Standard (BS) for marking equipment is:
* BS 1710:2019 Graphical symbols — Safety colours and safety signs — Registered safety signs
The Standard stipulates the colours to be used. These are as follows:
In addition to the basic colours, certain safety colours are used:
The arrangement of markings is for the safety colour to be between bands of the basic colour.
Firewater service would be:
The pipe contents must be identified adjacent to the banding. This can be done by giving either:
* The full name
* Abbreviation
* Chemical symbol
* Refrigerant number
* Coloured bands (user specified)
The direction of flow should also be identified near the banding.
Examples using this system are as shown. | 1 | Applied and Interdisciplinary Chemistry |
* [http://www.science.uottawa.ca/~eih/ch1/ch1.htm Environmental Isotopes] (University of Ottawa)
* [http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html Fundamentals of Isotope Geochemistry] (C. Kendall & E.A. Caldwell, chap.2 in Isotope Tracers in Catchment Hydrology [edited by C. Kendall & J.J. McDonnell], 1998)
* [http://pubs.usgs.gov/info/seal2/ Stable Isotopes and Mineral Resource Investigations in the United States] (USGS) | 0 | Theoretical and Fundamental Chemistry |
The tailings contain mainly decay products from the decay chain involving Uranium-238. Uranium tailings contain over a dozen radioactive nuclides, which are the primary hazard posed by the tailings. The most important of these are thorium-230, radium-226, radon-222 (radon gas) and the daughter isotopes of radon decay, including polonium-210. All of those are naturally occurring radioactive materials or "NORM". | 0 | Theoretical and Fundamental Chemistry |
Additional, mathematically equivalent forms of the Colebrook equation are:
::where:
:::1.7384... = 2 log (2 × 3.7) = 2 log (7.4)
:::18.574 = 2.51 × 3.7 × 2
and
:or
::where:
:::1.1364... = 1.7384... − 2 log (2) = 2 log (7.4) − 2 log (2) = 2 log (3.7)
:::9.287 = 18.574 / 2 = 2.51 × 3.7.
The additional equivalent forms above assume that the constants 3.7 and 2.51 in the formula at the top of this section are exact. The constants are probably values which were rounded by Colebrook during his curve fitting; but they are effectively treated as exact when comparing (to several decimal places) results from explicit formulae (such as those found elsewhere in this article) to the friction factor computed via Colebrook's implicit equation.
Equations similar to the additional forms above (with the constants rounded to fewer decimal places, or perhaps shifted slightly to minimize overall rounding errors) may be found in various references. It may be helpful to note that they are essentially the same equation. | 1 | Applied and Interdisciplinary Chemistry |
It is possible to create IBIs for use by minimally trained monitoring personnel, however the precision obtainable is lower than that conducted by trained professionals. Safeguards to assure robustness in spite of potential misidentifications or protocol variations require careful testing. Ongoing quality control by established experts is needed to maintain data integrity, and the analysis of IBI results becomes more complex. Use of trained volunteers is being pioneered by government agencies responsible for monitoring large numbers of water bodies with limited resources, such as the Minnesota Pollution Control Agency (MPCA) and local volunteer stream monitoring programs supported by MPCA. EPA has published guidance to assist volunteer programs in formulating IBIs and related findings. While IBIs from such programs are legally admissible in US courts, defending the validity of conclusions based solely on such results is unlikely to be feasible.
Agreement among multiple IBIs from data collected by established professionals can be more conclusive. A case in point is the phenomenon that stream IBI scores indicate significant impairment, or partial ecological collapse where more than 10 to 15 percent of the immediately surrounding watershed is impervious due to urbanization. Identifying reasons for such impairments, and possible exceptions to these trends, are major research challenges for academics studying cumulative watershed effects, and the use of low-impact development techniques to mitigate the impacts of stormwater runoff pollution. | 1 | Applied and Interdisciplinary Chemistry |
F NMR chemical shifts are more difficult to predict than H NMR shifts. Specifically, F NMR shifts are strongly affected by contributions from electronic excited states whereas H NMR shifts are dominated by diamagnetic contributions. | 0 | Theoretical and Fundamental Chemistry |
By the time Loewi began his experiments there was much discussion among scientists whether communication between nerves and muscles was chemical or electrical by nature. Experiments by Luigi Galvani in the 18th century had demonstrated that electrical stimulation of the frog sciatic nerve resulted in twitching of the leg muscles, and from this he developed the concept of bioelectricity. This led to the idea that direct electrical contact between nerves and muscles mediated transmission of excitation. However, work by John Newport Langley had suggested that in the autonomic nervous system communication in the ciliary ganglion was chemical. Loewi's experiments, published in 1921, finally settled the issue, proving that synaptic transmission was chemical.
Loewi performed a very simple yet elegant experiment. Using an isolated frog heart he had previously found that stimulation of the vagus nerve resulted in a slowing of the heart rate, while stimulation of the sympathetic nerve caused the heart rate to speed up (Figure 1). He reasoned that stimulation of either the vagus or sympathetic nerve would cause the nerve terminal to release a substance which would either slow or accelerate the heart rate. To prove this, he took a frog heart, which had been cannulated in order to perfuse the fluid surrounding the heart, and electrically stimulated the vagus nerve until the heart rate slowed. He then collected the fluid surrounding the heart and added it to a second frog heart which had been stripped of its vagal and sympathetic nerves. By adding the fluid surrounding the first heart to the second heart, he caused the heart rate of the second heart to slow down. This proved that stimulation of the vagus nerve caused the release of a substance which acted upon the heart tissue and directly caused the heart rate to slow down. (Figure 2) This substance was called vagusstoff. Vagustoff was later confirmed to be acetylcholine and was found to be the principal neurotransmitter in the parasympathetic nervous system.
In an interesting aside, Loewi apparently had the idea for his experiment in a dream. He wrote it down in the middle of the night but the next morning could not decipher his writing. He eventually had the same dream on another night, and decided to run to the laboratory to perform the experiment in the middle of the night. About this incident, Loewi writes:
:On mature consideration, in the cold light of the morning, I would not have done it. After all, it was an unlikely enough assumption that the vagus should secrete an inhibitory substance; it was still more unlikely that a chemical substance that was supposed to be effective at very close range between nerve terminal and muscle be secreted in such large amounts that it would spill over and, after being diluted by the perfusion fluid, still be able to inhibit another heart. (Loewi 1921)
Loewi was fortunate in his choice of experimental preparation. In the species of frog used (Rana esculenta), the vagus contains both inhibitory and stimulatory fibers. In the winter, inhibitory fibers predominate, so Loewi was also fortunate to have performed his experiments in February or March. Additionally, acetylcholinesterase activity (the enzyme that degrades acetylcholine) is low, particularly in an unheated laboratory, allowing the neurotransmitter to remain long enough to be collected and applied to a second heart. Thanks to this confluence of events, Loewi was able to describe the existence of vagusstoff and prove the existence of chemical synaptic transmission. | 1 | Applied and Interdisciplinary Chemistry |
In the 1780s for the French Academy of Sciences, Lavoisier, Laplace, and Seguin investigated and published relationships between direct calorimetry and respiratory gas exchanges from mammalian subjects. 100 years later in the 19th century for the Connecticut-based Wesleyan University, Professors Atwater and Rosa provided ample evidence of nitrogen, carbon dioxide, and oxygen transport during the metabolism of amino acids, glucose, and fatty acids in human subjects, further establishing the value of indirect calorimetry in determining bioenergetics of free-living humans. The work of Atwater and Rosa also made it possible to calculate the caloric values of foods, which eventually became the criteria adopted by the USDA to create the food calorie library.
In the early 20th century at Oxford University, physiology researcher Claude Gordon Douglas developed an inexpensive and mobile method of collecting exhaled breath (partly in preparation for experiments to be conducted on Pike's Peak, Colorado). In this method, the subject exhales into a nearly impermeable and large volume collection bag over a recorded period of time. The entire volume is measured, the oxygen and carbon dioxide content are analyzed, and the differences from inspired "ambient" air are calculated to determine the rates of oxygen uptake and carbon dioxide output.
To estimate energy expenditure from the exhaled gases, several algorithms were developed. One of the most widely used was developed in 1949 at University of Glasgow by research physiologist J. B. de V. Weir. His abbreviated equation for estimating metabolic rate was written with rates of gas exchange being volume/time, excluded urinary nitrogen, and allowed for the inclusion of a time conversion factor of 1.44 to extrapolate to 24-hour energy expenditure from 'kcal per minute" to "kcal per day." Weir used the Douglas Bag method in his experiments, and in support of neglecting the effect of protein metabolism under normal physiological conditions and eating patterns of ~12.5% protein calories, he wrote:
:"...In fact if the percentage of protein calories [consumed] lies between 10 and 14 the maximum error in using [the equation] is less than 1 in 500." | 1 | Applied and Interdisciplinary Chemistry |
Alchermes (, ; from the , from ) is a type of Italian liqueur (especially in Tuscany, Emilia-Romagna, and Sicily) prepared by infusing neutral spirits with sugar, cinnamon, cloves, nutmeg, and vanilla, and other herbs and flavoring agents. Its most striking characteristic is its scarlet color, obtained by the addition of Kermes, a small scale insect from which the drink derives its name. Several proprietary variants are commercially available, where the coloring agent is a coal tar-derived dye such as E124 or E126, with alcoholic contents ranging from 21 to 32%. Its chief use is in coloring pastry, although a quick dessert is sometimes made by adding it to custard cream and sugar. In the Italian pudding zuppa inglese, sponge cake or ladyfingers soaked in this liqueur are a major ingredient.
Alkermes was a modification of an 8th-century potion confectio alchermes, a tonic composed of raw silk, apple juice, ground pearls, musk, ambergris, gold leaf, rose water, cinnamon, sugar, and honey. In pre-modern medicine, it was ranked among the best tonics for the heart and was frequently used for the palpitation of the heart, or syncope, sometimes for smallpox or measles, and as a general restorative. | 1 | Applied and Interdisciplinary Chemistry |
Many other medical conditions have been targeted with encapsulation therapies, especially those involving a deficiency in some biologically derived protein. One of the most successful approaches is an external device that acts similarly to a dialysis machine, only with a reservoir of pig hepatocytes surrounding the semipermeable portion of the blood-infused tubing. This apparatus can remove toxins from the blood of patients suffering severe liver failure. Other applications that are still in development include cells that produce ciliary-derived neurotrophic factor for the treatment of ALS and Huntingtons disease, glial-derived neurotrophic factor for Parkinsons disease, erythropoietin for anemia, and HGH for dwarfism. In addition, monogenic diseases such as haemophilia, Gaucher's disease and some mucopolysaccharide disorders could also potentially be targeted by encapsulated cells expressing the protein that is otherwise lacking in the patient. | 1 | Applied and Interdisciplinary Chemistry |
In ancient times, cinobufacini, which is extracted from the skin and the parotid venom glands of toad of the bufo genus was used to treat symptoms like swelling and pain. In the present time, cinobufacinin injections are used to achieve satisfactory effect on Hepatocellular carcinoma (HCC) in China. Bufothionine is a major active component of cinobufacini. Bufothionine has been shown to suppress growth of cancerous liver cells in vitro . In vivo, bufothionine has also been showing relieved symptoms and anti inflammatory activities in tumor bearing mice. Experiments were conducted in which cultured cancer cells were shown to have an increase in G2-M damage checkpoint, ensuring that growth of the cell will not continue until the damage to the DNA is corrected while also showing a drop in the G0 and G1 activity, which pertains to phase where there is cell growth and RNA production.
Bufothionine is shown to induce autophagy in hepatocellular carcinomas by inhibiting JAK2/STAT3 pathways, which may present possibilities of anti cancer mechanism in bufothionine through cinobufacini injections. Similarly, bufothionine has also been shown to increase the chances of cell death and decrease cell growth of gastric cancer related cells by inhibiting the PIM3 gene, which, in cancerous cells, increases the resistance of chemotherapeutic treatments. In glioblastoma multiforme (GBM), bufothionine presents anti-tumor activities in the GBM cells lines U87 and U373 by triggering endoplasmic reticulum stress to lead cell death in the U87 and U373 cells. | 1 | Applied and Interdisciplinary Chemistry |
Cancer research has been ongoing for centuries, trying to elucidate the origin of its cause. As cancer research evolves with time, the scientific community tends to pay more attention to cell metabolism and how to target these metabolic needs and changes that cells undergo during carcinogenesis. There is growing evidence that metabolic dependencies in cancer are influenced by tissue environment, being this important to consider the TME for different in vitro and in vivo models to study oncometabolism in different cancer scenarios.
There is extensive research on the modulation of BET proteins in cancer models of breast. These proteins appear to be involved in oncometabolism and targeting and uncoupling BRD4 actions in carcinogenic cells, as well as stopping pro-migratory signals and changing cytokine metabolism, particularly IL-6. The same group has reported on the importance of exosomes in the TME and how these vesicles, shed by adipocytes, can carry a specific molecular cargo that causes metabolic changes in the cell, leading to pro-metastatic changes in the recipient breast cancer cells. | 1 | Applied and Interdisciplinary Chemistry |
In January 2011, the ASTM withdrew standard ASTM D 6002, which had provided plastic manufacturers with the legal credibility to label a plastic as compostable. Its description is as follows:
The ASTM has yet to replace this standard. | 0 | Theoretical and Fundamental Chemistry |
The Lorentz reciprocal theorem states a relationship between two Stokes flows in the same region. Consider fluid filled region bounded by surface . Let the velocity fields and solve the Stokes equations in the domain , each with corresponding stress fields and . Then the following equality holds:
Where is the unit normal on the surface . The Lorentz reciprocal theorem can be used to show that Stokes flow "transmits" unchanged the total force and torque from an inner closed surface to an outer enclosing surface. The Lorentz reciprocal theorem can also be used to relate the swimming speed of a microorganism, such as cyanobacterium, to the surface velocity which is prescribed by deformations of the body shape via cilia or flagella.
The Lorentz reciprocal theorem has also been used in the context of elastohydrodynamic theory to derive the lift force exerted on a solid object moving tangent to the surface of an elastic interface at low Reynolds numbers. | 1 | Applied and Interdisciplinary Chemistry |
Noyori has also demonstrated the kinetic resolution of allylic alcohols by asymmetric hydrogenation of the olefin.
Utilizing the Ru[BINAP] complex, selective hydrogenation can give high ees of the unsaturated alcohol in addition to the hydrogenated alcohol, as shown below. Thus, a second hydrogenation of the enantioenriched allylic alcohol remaining will give enantiomerically pure samples of both enantiomers of the saturated alcohol. Noyori has resolved a number of allylic alcohols with good to excellent yields and good to excellent ees (up to >99%). | 0 | Theoretical and Fundamental Chemistry |
After receiving her masters degree, Brown began work as a research chemist at CIBA Pharmaceutical Company, where she was involved in research programs for drug development targeting tuberculosis and coccidiosis. She moved to Merck in 1969, where she co-authored 15 publications, obtained one patent and contributed to 5 others. Browns work focused on synthesizing novel medicinal compounds. She worked to develop the compound cilastatin sodium. Cilastatin is an inhibitor of renal dehydropeptidase. Since the antibiotic, imipenem, is one such antibiotic that is hydrolyzed by dehydropeptidase, cilastatin is used in combination with imipenem to prevent its metabolism. This combination creates the antibiotic Primaxin (imipenem/cilastatin), which is used to treat severe internal infections, as well as diseases caused by flesh-eating bacteria and some types of pneumonia. In order to succeed in industry, she believed that one needed to be an effective communicator, be able to work on a team, and have a strong scientific education in an ever-changing field. | 1 | Applied and Interdisciplinary Chemistry |
Pittsfield, in western Massachusetts, was home to the General Electric (GE) transformer, capacitor, and electrical generating equipment divisions. The electrical generating division built and repaired equipment that was used to power the electrical utility grid throughout the nation. PCB-contaminated oil routinely migrated from GE's industrial plant located in the very center of the city to the surrounding groundwater, nearby Silver Lake, and to the Housatonic River, which flows through Massachusetts, Connecticut, and down to Long Island Sound. PCB-containing solid material was widely used as fill, including oxbows of the Housatonic River. Fish and waterfowl who live in and around the river contain significant levels of PCBs and are not safe to eat. EPA designated the Pittsfield plant and several miles of the river as a Superfund site in 1997, and ordered GE to remediate the site. EPA and GE began a cleanup of the area in 1999.
New Bedford Harbor, which is a listed Superfund site, contained some of the highest sediment concentrations of PCBs in the marine environment. Cleanup of the area began in 1994 and is mostly complete as of 2020.
Investigations into historic waste dumping in the Bliss Corner neighborhood have revealed the existence of PCBs, among other hazardous materials, buried into soil and waste material. | 1 | Applied and Interdisciplinary Chemistry |
Magnetic resonance imaging uses the resonance of the protons to generate images. Protons are excited by a radio frequency pulse at an appropriate frequency (Larmor frequency) and then the excess energy is released in the form of a minuscule amount of heat to the surroundings as the spins return to their thermal equilibrium. The magnetization of the proton ensemble goes back to its equilibrium value with an exponential curve characterized by a time constant T (see Relaxation (NMR)).
T weighted images can be obtained by setting short repetition time (TR) such as while setting TE values to less than 15 ms.
T is significantly different between grey matter and white matter and is used when undertaking brain scans. A strong T contrast is present between fluid and more solid anatomical structures, making T contrast suitable for morphological assessment of the normal or pathological anatomy, e.g., for musculoskeletal applications. | 0 | Theoretical and Fundamental Chemistry |
Ocean salinity has been constant at about 3.5% for a very long time. Salinity stability in oceanic environments is important as most cells require a rather constant salinity and do not generally tolerate values above 5%. The constant ocean salinity was a long-standing mystery, because no process counterbalancing the salt influx from rivers was known. Recently it was suggested that salinity may also be strongly influenced by seawater circulation through hot basaltic rocks, and emerging as hot water vents on mid-ocean ridges. However, the composition of seawater is far from equilibrium, and it is difficult to explain this fact without the influence of organic processes. One suggested explanation lies in the formation of salt plains throughout Earth's history. It is hypothesized that these are created by bacterial colonies that fix ions and heavy metals during their life processes.
In the biogeochemical processes of Earth, sources and sinks are the movement of elements. The composition of salt ions within our oceans and seas is: sodium (Na), chlorine (Cl), sulfate (SO), magnesium (Mg), calcium (Ca) and potassium (K). The elements that comprise salinity do not readily change and are a conservative property of seawater. There are many mechanisms that change salinity from a particulate form to a dissolved form and back. Considering the metallic composition of iron sources across a multifaceted grid of thermomagnetic design, not only would the movement of elements hypothetically help restructure the movement of ions, electrons, and the like, but would also potentially and inexplicably assist in balancing the magnetic bodies of the Earth's geomagnetic field. The known sources of sodium i.e. salts are when weathering, erosion, and dissolution of rocks are transported into rivers and deposited into the oceans.
The Mediterranean Sea as being Gaia's kidney is found ([http://scimar.icm.csic.es/scimar/index.php/secId/6/IdArt/209/ here]) by Kenneth J. Hsu, a correspondence author in 2001. Hsu suggests the "desiccation" of the Mediterranean is evidence of a functioning Gaia "kidney". In this and earlier suggested cases, it is plate movements and physics, not biology, which performs the regulation. Earlier "kidney functions" were performed during the "deposition of the Cretaceous (South Atlantic), Jurassic (Gulf of Mexico), Permo-Triassic (Europe), Devonian (Canada), and Cambrian/Precambrian (Gondwana) saline giants." | 0 | Theoretical and Fundamental Chemistry |
Conformational analysis of medium rings begins with examination of cyclooctane. Spectroscopic methods have determined that cyclooctane possesses three main conformations: chair-boat, chair-chair, and boat-boat. Cyclooctane prefers to reside in a chair-boat conformation, minimizing the number of eclipsing ethane interactions (shown in blue), as well as torsional strain. The chair-chair conformation is the second most abundant conformation at room temperature, with a ratio of 96:4 chair-boat:chair-chair observed.
Substitution positional preferences in the ground state conformer of methyl cyclooctane can be approximated using parameters similar to those for smaller rings. In general, the substituents exhibit preferences for equatorial placement, except for the lowest energy structure (pseudo A-value of -0.3 kcal/mol in figure below) in which axial substitution is favored. The "pseudo A-value" is best treated as the approximate energy difference between placing the methyl substituent in the equatorial or axial positions. The most energetically unfavorable interaction involves axial substitution at the vertex of the boat portion of the ring (6.1 kcal/mol).
These energetic differences can help rationalize the lowest energy conformations of 8 atom ring structures containing an sp center. In these structures, the chair-boat is the ground state model, with substitution forcing the structure to adopt a conformation such that non-bonded interactions are minimized from the parent structure. From the cyclooctene figure below, it can be observed that one face is more exposed than the other, foreshadowing a discussion of privileged attack angles (see peripheral attack).
X-ray analysis of functionalized cyclooctanes provided proof of conformational preferences in these medium rings. Significantly, calculated models matched the obtained X-ray data, indicating that computational modeling of these systems could in some cases quite accurately predict conformations. The increased sp character of the cyclopropane rings favor them to be placed similarly such that they relieve non-bonded interactions. | 0 | Theoretical and Fundamental Chemistry |
Depending on the type of substrates to which the phytobenthos is attached, they would be considered as epilithic (growing on rocks and other manmade, artificial substances), epipelic (growing on silt), episammic (growing on sand), epiphytic (growing on other plants), or epizoic (growing on animals). Epizoic phytobenthos such as Ostreobium and Symbiodinium have also been found to grow on skeletons or within corals to which they have established symbiotic relationships by exchanging nutrients.
The phytobenthos' habitats can range from freshwater systems such as rivers and lakes to coastal regions. In the marine environment, phytobenthos can be found as far back from the shore as the subtidal zones where they are consistently submerged in water. Their productivity does not extend beyond the outer boundary of the littoral zones, the region to which sunlight can still penetrate to the bottom.
With increasing depth, there is a decline in algal cover due in part to light availability. In addition to depth, turbidity can restrict the extent of light availability, which would also impact the extent of phytobenthic growth. However, phytobenthos such as Ostreobium have demonstrated capability to adapt to low-light conditions as grow in areas as deep as 200 meters. Some diatoms also demonstrated mobility and rise to the surface during the earlier part of the year.
Other physical and chemical conditions that also determine phytobenthos distributions include flow, acidity, nutrient, temperature, and the community's composition. Water flow can determine the types and distributions of phytobenthos, especially in the stream communities where the water is constantly moving. Rivers with more steady flow contribute to the stable environment that can promote the growth of phytobenthos communities. | 0 | Theoretical and Fundamental Chemistry |
For more "light" quark species, flavors in general, the corresponding chiral symmetries are , decomposing into
and exhibiting a very analogous chiral symmetry breaking pattern.
Most usually, is taken, the u, d, and s quarks taken to be light (the eightfold way), so then approximately massless for the symmetry to be meaningful to a lowest order, while the other three quarks are sufficiently heavy to barely have a residual chiral symmetry be visible for practical purposes. | 0 | Theoretical and Fundamental Chemistry |
The PUREX process was invented by Herbert H. Anderson and Larned B. Asprey at the Metallurgical Laboratory at the University of Chicago, as part of the Manhattan Project under Glenn T. Seaborg; their patent "Solvent Extraction Process for Plutonium" filed in 1947, mentions tributyl phosphate as the major reactant which accomplishes the bulk of the chemical extraction. | 0 | Theoretical and Fundamental Chemistry |
*Hydrides such as sodium borohydride, lithium aluminium hydride, diisobutylaluminium hydride (DIBAL) and super hydride, are commonly used as reducing agents in chemical synthesis. The hydride adds to an electrophilic center, typically unsaturated carbon.
*Hydrides such as sodium hydride and potassium hydride are used as strong bases in organic synthesis. The hydride reacts with the weak Bronsted acid releasing H.
*Hydrides such as calcium hydride are used as desiccants, i.e. drying agents, to remove trace water from organic solvents. The hydride reacts with water forming hydrogen and hydroxide salt. The dry solvent can then be distilled or vacuum transferred from the "solvent pot".
*Hydrides are important in storage battery technologies such as nickel-metal hydride battery. Various metal hydrides have been examined for use as a means of hydrogen storage for fuel cell-powered electric cars and other purposed aspects of a hydrogen economy.
* Hydride complexes are catalysts and catalytic intermediates in a variety of homogeneous and heterogeneous catalytic cycles. Important examples include hydrogenation, hydroformylation, hydrosilylation, hydrodesulfurization catalysts. Even certain enzymes, the hydrogenase, operate via hydride intermediates. The energy carrier nicotinamide adenine dinucleotide reacts as a hydride donor or hydride equivalent. | 0 | Theoretical and Fundamental Chemistry |
Multiple studies have found the MPT to be a key factor in the damage to neurons caused by excitotoxicity.
The induction of MPT, which increases mitochondrial membrane permeability, causes mitochondria to become further depolarized, meaning that Δψ is abolished. When Δψ is lost, protons and some molecules are able to flow across the outer mitochondrial membrane uninhibited.
Loss of Δψ interferes with the production of adenosine triphosphate (ATP), the cell's main source of energy, because mitochondria must have an electrochemical gradient to provide the driving force for ATP production.
In cell damage resulting from conditions such as neurodegenerative diseases and head injury, opening of the mitochondrial permeability transition pore can greatly reduce ATP production, and can cause ATP synthase to begin hydrolysing, rather than producing, ATP. This produces an energy deficit in the cell, just when it most needs ATP to fuel activity of ion pumps.
MPT also allows Ca to leave the mitochondrion, which can place further stress on nearby mitochondria, and which can activate harmful calcium-dependent proteases such as calpain.
Reactive oxygen species (ROS) are also produced as a result of opening the MPT pore. MPT can allow antioxidant molecules such as glutathione to exit mitochondria, reducing the organelles ability to neutralize ROS. In addition, the electron transport chain (ETC) may produce more free radicals due to loss of components of the ETC, such as cytochrome c', through the MPTP. Loss of ETC components can lead to escape of electrons from the chain, which can then reduce molecules and form free radicals.
MPT causes mitochondria to become permeable to molecules smaller than 1.5 kDa, which, once inside, draw water in by increasing the organelles osmolar load. This event may lead mitochondria to swell and may cause the outer membrane to rupture, releasing cytochrome c. Cytochrome c can in turn cause the cell to go through apoptosis ("commit suicide") by activating pro-apoptotic factors. Other researchers contend that it is not mitochondrial membrane rupture that leads to cytochrome c' release, but rather another mechanism, such as translocation of the molecule through channels in the outer membrane, which does not involve the MPTP.
Much research has found that the fate of the cell after an insult depends on the extent of MPT. If MPT occurs to only a slight extent, the cell may recover, whereas if it occurs more it may undergo apoptosis. If it occurs to an even larger degree the cell is likely to undergo necrotic cell death. | 1 | Applied and Interdisciplinary Chemistry |
This is an example of a DNA microarray experiment which includes details for a particular case to better explain DNA microarray experiments, while listing modifications for RNA or other alternative experiments.
# The two samples to be compared (pairwise comparison) are grown/acquired. In this example treated sample (case) and untreated sample (control).
# The nucleic acid of interest is purified: this can be RNA for expression profiling, DNA for comparative hybridization, or DNA/RNA bound to a particular protein which is immunoprecipitated (ChIP-on-chip) for epigenetic or regulation studies. In this example total RNA is isolated (both nuclear and cytoplasmic) by Guanidinium thiocyanate-phenol-chloroform extraction (e.g. Trizol) which isolates most RNA (whereas column methods have a cut off of 200 nucleotides) and if done correctly has a better purity.
# The purified RNA is analysed for quality (by capillary electrophoresis) and quantity (for example, by using a NanoDrop or NanoPhotometer spectrometer). If the material is of acceptable quality and sufficient quantity is present (e.g., >1μg, although the required amount varies by microarray platform), the experiment can proceed.
# The labeled product is generated via reverse transcription and followed by an optional PCR amplification. The RNA is reverse transcribed with either polyT primers (which amplify only mRNA) or random primers (which amplify all RNA, most of which is rRNA). miRNA microarrays ligate an oligonucleotide to the purified small RNA (isolated with a fractionator), which is then reverse transcribed and amplified.
#* The label is added either during the reverse transcription step, or following amplification if it is performed. The sense labeling is dependent on the microarray; e.g. if the label is added with the RT mix, the cDNA is antisense and the microarray probe is sense, except in the case of negative controls.
#* The label is typically fluorescent; only one machine uses radiolabels.
#* The labeling can be direct (not used) or indirect (requires a coupling stage). For two-channel arrays, the coupling stage occurs before hybridization, using aminoallyl uridine triphosphate (aminoallyl-UTP, or aaUTP) and NHS amino-reactive dyes (such as cyanine dyes); for single-channel arrays, the coupling stage occurs after hybridization, using biotin and labeled streptavidin. The modified nucleotides (usually in a ratio of 1 aaUTP: 4 TTP (thymidine triphosphate)) are added enzymatically in a low ratio to normal nucleotides, typically resulting in 1 every 60 bases. The aaDNA is then purified with a column (using a phosphate buffer solution, as Tris contains amine groups). The aminoallyl group is an amine group on a long linker attached to the nucleobase, which reacts with a reactive dye.
#** A form of replicate known as a dye flip can be performed to control for dye artifacts in two-channel experiments; for a dye flip, a second slide is used, with the labels swapped (the sample that was labeled with Cy3 in the first slide is labeled with Cy5, and vice versa). In this example, aminoallyl-UTP is present in the reverse-transcribed mixture.
# The labeled samples are then mixed with a proprietary hybridization solution which can consist of SDS, SSC, dextran sulfate, a blocking agent (such as Cot-1 DNA, salmon sperm DNA, calf thymus DNA, PolyA, or PolyT), Denhardt's solution, or formamine.
# The mixture is denatured and added to the pinholes of the microarray. The holes are sealed and the microarray hybridized, either in a hyb oven, where the microarray is mixed by rotation, or in a mixer, where the microarray is mixed by alternating pressure at the pinholes.
# After an overnight hybridization, all nonspecific binding is washed off (SDS and SSC).
# The microarray is dried and scanned by a machine that uses a laser to excite the dye and measures the emission levels with a detector.
# The image is gridded with a template and the intensities of each feature (composed of several pixels) is quantified.
# The raw data is normalized; the simplest normalization method is to subtract background intensity and scale so that the total intensities of the features of the two channels are equal, or to use the intensity of a reference gene to calculate the t-value for all of the intensities. More sophisticated methods include z-ratio, loess and lowess regression and RMA (robust multichip analysis) for Affymetrix chips (single-channel, silicon chip, in situ synthesized short oligonucleotides). | 1 | Applied and Interdisciplinary Chemistry |
Packings where all spheres are constrained by their neighbours to stay in one location are called rigid or jammed. The strictly jammed (mechanically stable even as a finite system) sphere packing with the lowest known density is a diluted ("tunneled") fcc crystal with a density of only . The loosest known jammed packing has a density of approximately 0.0555. | 0 | Theoretical and Fundamental Chemistry |
The stack effect or chimney effect is the movement of air into and out of buildings through unsealed openings, chimneys, flue-gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation, air infiltration, and fires (e.g. the Kaprun tunnel fire, King's Cross underground station fire and the Grenfell Tower fire). | 0 | Theoretical and Fundamental Chemistry |
A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. The polaron concept was proposed by Lev Landau in 1933 and Solomon Pekar in 1946 to describe an electron moving in a dielectric crystal where the atoms displace from their equilibrium positions to effectively screen the charge of an electron, known as a phonon cloud. This lowers the electron mobility and increases the electron's effective mass.
The general concept of a polaron has been extended to describe other interactions between the electrons and ions in metals that result in a bound state, or a lowering of energy compared to the non-interacting system. Major theoretical work has focused on solving Fröhlich and Holstein Hamiltonians. This is still an active field of research to find exact numerical solutions to the case of one or two electrons in a large crystal lattice, and to study the case of many interacting electrons.
Experimentally, polarons are important to the understanding of a wide variety of materials. The electron mobility in semiconductors can be greatly decreased by the formation of polarons. Organic semiconductors are also sensitive to polaronic effects, which is particularly relevant in the design of organic solar cells that effectively transport charge. Polarons are also important for interpreting the optical conductivity of these types of materials.
The polaron, a fermionic quasiparticle, should not be confused with the polariton, a bosonic quasiparticle analogous to a hybridized state between a photon and an optical phonon. | 0 | Theoretical and Fundamental Chemistry |
In the laboratory, it is used to detect the presence of alkaline phosphatase activity by hydrolysis of PNPP. In basic conditions, presence of hydrolytic enzymes will turn reaction vessel yellow.
4-Nitrophenol is a product of the enzymatic cleavage of several synthetic substrates such as 4-nitrophenyl phosphate (used as a substrate for alkaline phosphatase), 4-nitrophenyl acetate (for carbonic anhydrase), 4-nitrophenyl-β--glucopyranoside and other sugar derivatives which are used to assay various glycosidase enzymes. Amounts of 4-nitrophenol produced by a particular enzyme in the presence of its corresponding substrate can be measured with a spectrophotometer at or around 405 nm and used as a proxy measurement for the amount of the enzyme activity in the sample.
Accurate measurement of enzyme activity requires that the 4-nitrophenol product is fully deprotonated, existing as 4-nitrophenolate, given the weak absorbance of 4-nitrophenol at 405 nm. Complete ionization of the alcohol functional group affects the conjugation of the pi bonds on the compound. A lone pair from the oxygen can be delocalized via conjugation to the benzene ring and nitro group. Since the length of conjugated systems affects the color of organic compounds, this ionization change causes the 4-nitrophenol to turn yellow when fully deprotonated and existing as 4-nitrophenolate.
A common mistake in measuring enzyme activity using these substrates is to perform the assays at neutral or acidic pH without considering that only part of the chromophoric product is ionized. The problem can be overcome by stopping the reaction with sodium hydroxide (NaOH) or other strong base, which converts all product into 4-nitrophenoxide; final pH must be > ca. 9.2 to ensure more than 99% of the product is ionised. Alternatively enzyme activity can be measured at 348 nm, the isosbestic point for 4-nitrophenol/4-nitrophenoxide. | 0 | Theoretical and Fundamental Chemistry |
The demand for vanilla flavoring has long exceeded the supply of vanilla beans. , the annual demand for vanillin was 12,000 tons, but only 1,800 tons of natural vanillin were produced. The remainder was produced by chemical synthesis. Vanillin was first synthesized from eugenol (found in oil of clove) in 1874–75, less than 20 years after it was first identified and isolated. Vanillin was commercially produced from eugenol until the 1920s. Later it was synthesized from lignin-containing "brown liquor", a byproduct of the sulfite process for making wood pulp. Counterintuitively, though it uses waste materials, the lignin process is no longer popular because of environmental concerns, and today most vanillin is produced from the petrochemical raw material guaiacol. Several routes exist for synthesizing vanillin from guaiacol.
At present, the most significant of these is the two-step process practiced by Rhodia since the 1970s, in which guaiacol (1) reacts with glyoxylic acid by electrophilic aromatic substitution. The resulting vanillylmandelic acid (2) is then converted by 4-Hydroxy-3-methoxyphenylglyoxylic acid (3) to vanillin (4) by oxidative decarboxylation. | 0 | Theoretical and Fundamental Chemistry |
Type M (82%Ni/18%Mo–99.2%Ni/0.8%Co, by weight) are used in vacuum furnaces for the same reasons as with type C (described below). Upper temperature is limited to 1400 °C. It is less commonly used than other types. | 1 | Applied and Interdisciplinary Chemistry |
Bina Shaheen Siddiqui is a Pakistani chemist and the Director of the H.E.J. Research Institute of Chemistry at the University of Karachi. Siddiqui graduated from the University of Karachi with an MPhil in 1978. In 1980, she graduated from the same university with a PhD in organic chemistry.
She specialises in the chemical components of Pakistan's indigenous plants. She was elected to The World Academy of Sciences in 1989, and was elected a Fellow of the Pakistan Academy of Sciences in 1997. She is also a Fellow of the Chemical Society of Pakistan. | 0 | Theoretical and Fundamental Chemistry |
BMB offers three degrees: Master of Health Science (MHS), Master of Science (ScM), and a Doctoral (PhD) degree. The MHS program is a one-year program in which students only take classes and the ScM program takes about two years to complete and consists of students taking classes their first year and laboratory work their second year. Both require writing a thesis to obtain a degree. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, a flow with periodic variations is known as pulsatile flow, or as Womersley flow. The flow profiles was first derived by John R. Womersley (1907–1958) in his work with blood flow in arteries. The cardiovascular system of chordate animals is a very good example where pulsatile flow is found, but pulsatile flow is also observed in engines and hydraulic systems, as a result of rotating mechanisms pumping the fluid. | 1 | Applied and Interdisciplinary Chemistry |
Gas chromatography (GC) is ideal to separate volatilized VOCs due to their low molecular weight. VOCs are carried by a gas vector (helium) through a chromatographic column (the solid phase) on which they have different affinities, which allows to separate them.
Liquid chromatography may be used for liquid extractions of floral tissue. | 1 | Applied and Interdisciplinary Chemistry |
Although other cells lines, such as African green monkey kidney (COS) and baby hamster kidney (BHK), can be used for recombinant protein production, the most commonly employed host system in transient expression of mammalian cells involves derivatives of the HEK293 cell line, which is based on the human embryonic kidney cell line established in 1977 by Graham et al. The HEK293 cell line was created via transformation with sheared Adenovirus 5 DNA. Advantages of using this cell line include their high rates of transfection and ability to grow in a serum-free medium, which results in reduced cost and lowered risk of contamination with animal-derived material typically found in serum.
Several engineered sublines were later developed by incorporating viral elements derived from mammalian viruses, such as SV40 virus or Epstein–Barr virus (EBV), which are notable for their high retention of plasmid DNA in an episomal state and their capacity to increase transcription and translation via specific viral properties. These later sublines were consequently identified to have two interacting components: the SV40 large T-antigen binding to the SV20 origin of replication (SV40ori) and the EBV-derived nuclear antigen-1 (EBNA-1) protein to its associated origin of replication (oriP).
Typical historical yields of transient expression in HEK293 cells transfected using PEI-25kDa was 20-40 mg/L of recombinant antibody protein. In 2008, Backliwal et. al reported for the first time yields crossing 1 g/L of recombinant antibody protein. | 1 | Applied and Interdisciplinary Chemistry |
Faraday's laws of electrolysis are quantitative relationships based on the electrochemical research published by Michael Faraday in 1833. | 0 | Theoretical and Fundamental Chemistry |
Another extension to the traditional form of Darcy's law is the Brinkman term, which is used to account for transitional flow between boundaries (introduced by Brinkman in 1949),
where is an effective viscosity term. This correction term accounts for flow through medium where the grains of the media are porous themselves, but is difficult to use, and is typically neglected. | 1 | Applied and Interdisciplinary Chemistry |
Instead of the differential symbol , the symbol is used, a convention which originated in the 19th century work of German mathematician Carl Gottfried Neumann, indicating that (heat) and (work) are path-dependent, while (internal energy) is not. | 0 | Theoretical and Fundamental Chemistry |
AMGs play a crucial role in microbial adaptation to environmental changes. In extreme environments, AMGs can encode for alternate energy pathways such as subunits of dissimilatory sulfite reductase. The ability of viruses to confer new metabolic traits to their hosts enhances the resilience of microbial communities facing shifts in temperature, nutrient availability, or other environmental stressors. AMGs can also serve as a genetic pool in shaping the evolution of their hosts. | 1 | Applied and Interdisciplinary Chemistry |
Boiling tea leaves in water extracts the tannins, theobromine, and caffeine out of the leaves and into the water, as an example of a solid-liquid extraction.
Decaffeination of tea and coffee is also an example of an extraction, where the caffeine molecules are removed from the tea leaves or coffee beans, often utilising supercritical fluid extraction with CO or standard solid-liquid extraction techniques. | 0 | Theoretical and Fundamental Chemistry |
Defective Fas-mediated apoptosis may lead to oncogenesis as well as drug resistance in existing tumors. Germline mutation of Fas is associated with autoimmune lymphoproliferative syndrome (ALPS), a childhood disorder of apoptosis.
Increases in Fas-mediated signaling have been implicated in the pathology of low-risk myelodysplastic syndromes (MDS) and glioblastoma.
More recently, FasL-mediated apoptosis of T cells has also been suggested as an immune-evasive mechanism by which tumors can suppress T cell infiltration similar to inhibitory immune checkpoints such as PD-1 and CTLA-4. | 1 | Applied and Interdisciplinary Chemistry |
Janet Jones was once married to Robert Osteryoung, who was also an award-winning chemist. In April 2010, she married Chris Cobb in Washington, D.C. Together, Jones and Cobb established the Comis Foundation, a family philanthropic foundation to benefit children and youth. | 0 | Theoretical and Fundamental Chemistry |
India has a growing population, and large impoverished rural population that relies on monsoon-irrigated agriculture. Weather uncertainties, and potential climate change induced weather volatilities, raise concerns of social stability and impact of floods and droughts on rural poverty. The population of India is expected to grow further at a decelerating pace and stabilize around 1.5 billion by 2050, or another 300 million people – the size of United States – compared to the 2011 census. This will increase demand for reliable sources of food and improved agriculture yields – both of which, claims India's National Council of Applied Economic Research, require significantly improve irrigation network than the current state. The average rainfall in India is about 4,000 billion cubic meters, of which annual surface water flow in India is estimated at 1,869 billion cubic meters. Of this, for topological and other reasons, only about 690 billion cubic meter of the available surface water can be utilised for irrigation, industrial, drinking and ground water replenishment purposes. In other words, about 1,100 billion cubic meter of water is available, on average, every year for irrigation in India. This amount of water is adequate for irrigating 140 million hectares. As of 2007, about 60% of this potential was realized through irrigation network or natural flow of Indian rivers, lakes and adoption of pumps to pull ground water for irrigation.
80% of the water India receives through its annual rains and surface water flow, happens over a 4-month period – June through September. This spatial and time variance in availability of natural water versus year-round demand for irrigation, drinking and industrial water creates a demand-supply gap, that only worsens with Indias rising population. Proponents claim the answers to Indias water problem is to conserve the abundant monsoon water bounty, store it in reservoirs, and use this water in areas which have occasional inadequate rainfall, or are known to be drought-prone or in those times of the year when water supplies become scarce. | 1 | Applied and Interdisciplinary Chemistry |
Theoretical descriptions of contrast formation in X-ray topography are largely based on the dynamical theory of diffraction. This framework is helpful in the description of many aspects of topographic image formation: entrance of an X-ray wavefield into a crystal, propagation of the wavefield inside the crystal, interaction of wavefield with crystal defects, altering of wavefield propagation by local lattice strains, diffraction, multiple scattering, absorption.
The theory is therefore often helpful in the interpretation of topographic images of crystal defects. The exact nature of a defect often cannot be deduced directly from the observed image (i.e., a "backwards calculation" is problematic). Instead, one has to make assumptions about the structure of the defect, deduce a hypothetical image from the assumed structure ("forward calculation", based on theory), and compare with the experimental image. If the match between both is not good enough, the assumptions have to be varied until sufficient correspondence is reached. Theoretical calculations, and in particular numerical simulations by computer based on this theory, are thus a valuable tool for the interpretation of topographic images. | 0 | Theoretical and Fundamental Chemistry |
The thread form follows the British Standard Whitworth standard:
* Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)
* One-sixth of this sharp V is truncated at the top and the bottom
* The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r ≈ 0.1373P
* The theoretical depth of the thread is therefore 0.6403 times the nominal pitch h ≈ 0.6403P | 1 | Applied and Interdisciplinary Chemistry |
An assay (analysis) is never an isolated process, as it must be accompanied with pre- and post-analytic procedures. Both the communication order (the request to perform an assay plus related information) and the handling of the specimen itself (the collecting, documenting, transporting, and processing done before beginning the assay) are pre-analytic steps. Similarly, after the assay is completed the results must be documented, verified and communicated—the post-analytic steps. As with any multi-step information handling and transmission system, the variation and errors in reporting final results entail not only those intrinsic to the assay itself but also those occurring in the pre-analytic and post-analytic procedures.
While the analytic steps of the assay itself get much attention, it is those that get less attention of the chain of users—the pre-analytic and post-analytic procedures—that typically accumulate the most errors; e.g., pre-analytic steps in medical laboratory assays may contribute 32–75% of all lab errors.
Assays can be very diverse, but generally involve the following general steps:
# Sample processing and manipulation in order to selectively present the target in a discernible or measurable form to a discrimination/identification/detection system. It might involve a simple centrifugal separation or washing or filtration or capture by some form of selective binding or it may even involve modifying the target e.g. epitope retrieval in immunological assays or cutting down the target into pieces e.g. in Mass Spectrometry. Generally there are multiple separate steps done before an assay and are called preanalytic processing. But some of the manipulations may be inseparable part of the assay itself and will not thus be considered pre-analytic.
# Target-specific discrimination/identification principle: to discriminate from background (noise) of similar components and specifically identify a particular target component ("analyte") in a biological material by its specific attributes. (e.g. in a PCR assay a specific oligonucleotide primer identifies the target by base pairing based on the specific nucleotide sequence unique to the target).
# Signal (or target) amplification system: The presence and quantity of that analyte is converted into a detectable signal generally involving some method of signal amplification, so that it can be easily discriminated from noise and measured - e.g. in a PCR assay among a mixture of DNA sequences only the specific target is amplified into millions of copies by a DNA polymerase enzyme so that it can be discerned as a more prominent component compared to any other potential components. Sometimes the concentration of the analyte is too large and in that case the assay may involve sample dilution or some sort of signal diminution system which is a negative amplification.
# Signal detection (and interpretation) system: A system of deciphering the amplified signal into an interpretable output that can be quantitative or qualitative. It can be visual or manual very crude methods or can be very sophisticated electronic digital or analog detectors.
#Signal enhancement and noise filtering may be done at any or all of the steps above. Since the more downstream a step/process during an assay, the higher the chance of carrying over noise from the previous process and amplifying it, multiple steps in a sophisticated assay might involve various means of signal-specific sharpening/enhancement arrangements and noise reduction or filtering arrangements. These may simply be in the form of a narrow band-pass optical filter, or a blocking reagent in a binding reaction that prevents nonspecific binding or a quenching reagent in a fluorescence detection system that prevents "autofluorescence" of background objects. | 1 | Applied and Interdisciplinary Chemistry |
Clone Manager is a commercial bioinformatics software work suite of Sci-Ed, that supports molecular biologists with data management and allows them to perform certain in silico preanalysis.
This type of bioinformatics software is used for managing, analyzing and visualizing DNA and protein sequence data essential for molecular biology.
For enzyme read control, sequence processing of identical individuals, cloning simulation, graphic map drawing, primer design and analysis, global and local sequence alignment, similarity search, laboratory scale sequence assembly projects A comprehensive set of tools. | 1 | Applied and Interdisciplinary Chemistry |
Many regular fluid dynamics equations are used in astrophysical fluid dynamics. Some of these equations are:
* Continuity equations
* The Navier–Stokes equations
* Euler's equations
Conservation of mass
The continuity equation is an extension of conservation of mass to fluid flow. Consider a fluid flowing through a fixed volume tank having one inlet and one outlet. If the flow is steady (no accumulation of fluid within the tank), then the rate of fluid flow at entry must be equal to the rate of fluid flow at the exit for mass conservation. If, at an entry (or exit) having a cross-sectional area m, a fluid parcel travels a distance in time , then the volume flow rate ( ms) is given by:
but since is the fluid velocity ( ms) we can write:
The mass flow rate ( kgs) is given by the product of density and volume flow rate
Because of conservation of mass, between two points in a flowing fluid we can write . This is equivalent to:
If the fluid is incompressible, () then:
This result can be applied to many areas in astrophysical fluid dynamics, such as neutron stars. | 1 | Applied and Interdisciplinary Chemistry |
Since the dawn of modern chemistry, humic substances are among the most studied among the natural materials. Despite long study, their molecular structure remains elusive. The traditional view is that humic substances are heteropolycondensates, in varying associations with clay. A more recent view is that relatively small molecules also play a role. Humic substances account for 50 – 90% of cation exchange capacity. Similar to clay, char and colloidal humus hold cation nutrients. | 0 | Theoretical and Fundamental Chemistry |
The bovids (family Bovidae) comprise some 140 species of ruminants in which at least the males bear unbranched, hollow horns covered in a permanent sheath of keratin. Most species of bovids have means of spacing themselves across their habitat; territorial behavior is the most consistent type of spacing behavior.
Caprids (dwarf antelope, such as the sheep, goats, muskox, serows, gorals, and several similar species) use their preorbital glands to establish social rank. For example, when competition arises between two grazing sheep (Ovis aries), they have been observed to nuzzle each other's preorbital glands. By sending and receiving olfactory cues, this behavior appears to be a means of establishing dominance and of avoiding a fight, which would otherwise involve potentially injurious butting or clashing with the forehead.
The antilopine bovids (dwarf antelope, such as the springbok, blackbuck, gazelles, dik-diks, oribi, and several similar species) have well-developed preorbital glands.
Among the cephalophines, members of the Philantomba and Sylvicapra genera are all solitary animals which display territorial behavior and have well developed preorbital glands. Maxwells duiker (Philantomba maxwellii') is a solitary animal which utilizes preorbital gland secretions to mark its territory. This behavior is observed most in adult males, less frequently in females, and less still in subadults of this species. Secretions from the preorbital gland of the common duiker contain at least 33 different chemical compounds. Two thiazole compounds and an epoxy ketone are present in significantly higher concentrations in male than in female secretions, suggesting that they could serve as sex recognition cues.
The alcephine bovids (wildebeests, hartebeests, hirola, bontebok, blesbok, and several similar species) have preorbital glands which secrete complex mixtures of chemical compounds. The preorbital glands of the bontebok (Damaliscus pygargus pygarus) are larger in males than in females. Their secretions contain at least forty different chemical compounds, and are deposited on grass and twigs at the borders of their territory. They then appear to transfer the secretions from the grass to their horns and forehead by waving the head from side to side across the stalk bearing the secretion. Marking of plant stalks with preorbital gland secretions is seen in both sexes. In contrast to the duikers and raphicerids, the klipspringer (Oreotragus oreotragus) is a semi-gregarious species, while the hirola (Beatragus hunteri) is fully gregarious. Nevertheless, these animals display territorial scent marking of grasses with secretions from their preorbital glands.
Differences in the social structure and marking behavior among different species may lead to a different size and position of the preorbital glands on the animals face. For example, Günthers dik-dik (Madoqua guentheri) is a monogamous species of antelope that lives in a permanent territory, the boundaries of which the animals mark several times a day by actively pressing the preorbital glands to grasses and low-lying plants and applying the secretions. In this territorial animal, the preorbital glands remain of considerable size throughout the year. The glands are located in large preorbital pits in the lacrimal bone, and are surrounded by specialized facial muscles that compress them to express the secretions more effectively. In contrast, the saiga antelope (Saiga tatarica) is a polygamous and somewhat nomadic species which does not occupy any permanent territory at any time during the year. For most of the year the preorbital glands remain small, only growing to substantial size during the rut. At that time of year, secretions ooze more or less continuously from the glands. In this nonterritorial animal, the preorbital glands are not as well-developed, lack well-developed surrounding facial muscles, and are positioned in an inconspicuous and shallow depression of the lacrimal bone. | 1 | Applied and Interdisciplinary Chemistry |
Selectfluor reagent also serves as a strong oxidant, a property that is useful in other reactions in organic chemistry. Oxidation of alcohols and phenols. As applied to electrophilic iodination, Selectfluor reagent activates the I–I bond in I molecule. | 0 | Theoretical and Fundamental Chemistry |
π-effects can be broken down into numerous categories, including π-π interactions, cation-π and anion-π interactions, and polar-π interactions. In general, π-effects are associated with the interactions of molecules with the π-systems of conjugated molecules such as benzene. | 0 | Theoretical and Fundamental Chemistry |
Battlefield dynamics require portable power. Conventional diesel generators are too heavy for use in the field. Scalability allows TPVs to be smaller and lighter than conventional generators. Also, TPVs have few emissions and are silent. Multifuel operation is another potential benefit.
Investigations in the 1970s failed due to PV limitations. However, the GaSb photocell led to a renewed effort in the 1990s with improved results. In early 2001, JX Crystals delivered a TPV based battery charger to the US Army that produced 230 W fueled by propane. This prototype utilized an SiC emitter operating at 1250 °C and GaSb photocells and was approximately 0.5 m tall. The power source had an efficiency of 2.5%, calculated as the ratio of the power generated to the thermal energy of the fuel burned. This is too low for practical battlefield use. No portable TPV power sources have reached troop testing. | 0 | Theoretical and Fundamental Chemistry |
In the 16th century, heap leaching became commonly used to extract copper as well as saltpeter, from organic matter. Primarily used in Germany and Spain, pyrite would be brought to the surface and left out in the open. The pyrite would be set outside for months at a time, where rain and air exposure would lead to chemical weathering. A solution containing copper sulfide would be collected in a basin, then precipitated in a process called cementation, resulting in metallic copper. Heap leaching, in this natural chemical-free form, was further developed to obtain different, more economically viable, types of ore. This was done by incorporating chemical lixiviation, which applies more chemical manipulation and technique to heap leaching.
From 1767-1867, the production of potash in Quebec became an important industry to supply France's glass and soap manufacturers. Potash was most frequently made from the ash remains of wood-burning stoves and fireplaces, which were agitated with water and filtered. Once evaporated, the remains would be potash. 400 tons of hardwood would be required to burn to yield one ton of potash.
In 1858, Adolf von Patera, an Austrian metallurgist, utilized lixiviation to separate soluble and insoluble compounds from silver in an aqueous solution.The technique of Patera's lixiviation was further developed by American E. H. Russell around 1884, creating the "Russell Process". In 1887, when the cyanidation process was patented in England, it began to be incorporated into the existing leaching process, creating the more specific cyanide leaching.
In 1887, when the cyanidation process was patented in England, it began to phase out the existing Russell Process. Cyanidation was much more efficient and had a recovery rate of up to 90%.
Leading up to World War I, many new ideas for leaching processes were experimented. This included using ammonia solutions for copper sulfides, and nitric acid for leaching sulfide ores. Most of these ideas were phased out into obscurity due to the high cost of the leaching agents required. | 1 | Applied and Interdisciplinary Chemistry |
Faraday discovered that when the same amount of electric current is passed through different electrolytes connected in series, the masses of the substances deposited or liberated at the electrodes are directly proportional to their respective chemical equivalent/equivalent weight (). This turns out to be the molar mass () divided by the valence () | 0 | Theoretical and Fundamental Chemistry |
Notch signalling is a cell signalling pathway whose role is, among many others, to control the cell differentiation process in equivalent precursor cells. This means it is crucial in embryonic development, to the point that it has been tested on mice that the removal of glycans in Notch proteins can result in embryonic death or malformations of vital organs like the heart.
Some of the specific modulators that control this process are glycosyltransferases located in the endoplasmic reticulum and the Golgi apparatus. The Notch proteins go through these organelles in their maturation process and can be subject to different types of glycosylation: N-linked glycosylation and O-linked glycosylation (more specifically: O-linked glucose and O-linked fucose).
All of the Notch proteins are modified by an O-fucose, because they share a common trait: O-fucosylation consensus sequences. One of the modulators that intervene in this process is the Fringe, a glycosyltransferase that modifies the O-fucose to activate or deactivate parts of the signalling, acting as a positive or negative regulator, respectively. | 0 | Theoretical and Fundamental Chemistry |
For classical silencers, the signaling pathway is relatively simple. Since repression is active, silencer elements target the assembly of GTFs, necessary for transcription of the gene. These silencer elements are mostly located upstream of the gene and can vary between short and long distances. For long-range silencers, it has been observed that the DNA will form a loop in order to bring the silencer closer to the promoter and loop out the interfering DNA. Silencers also target helicase sites in the DNA that are rich in adenine and thymine (AT) and prone to unwinding the DNA, allowing room to initiate transcription. The inhibited helicase activity leads to the inhibition of transcription. This is commonly seen in the human thyrotropin-β gene promoter. NREs can induce a bend in the promoter region to block interactions, as seen when an NRE binds to Yin-Yang 1 (YY1), and flank regulatory signals or promoter regions as well. When the silencer region is located within an intron, there can be two types of repressions. First, there can be a physical blockage of a splice site. Second, there can be a bend in the DNA that will inhibit RNA processing.
When located in the exon or the untranslated region, the silencer will mainly be classical or position-dependent. However, these silencers can carry out their activity prior to transcription. Most silencers are constitutively expressed in organisms, only allowing activation of a gene by either inhibiting the silencer or by activating an enhancer region. The best example of this is the Neuronal-Restrictive Silencer Factor (NRSF) that is produced by the REST gene. The REST gene produces NRSF in order to repress the transcription of neuronal genes that are essential for localization of neuronal tissue. When a silencer represses REST, NRSF is also inhibited, allowing for the transcription of neuronal genes. | 1 | Applied and Interdisciplinary Chemistry |
* This is an irreversible physical immobilization technique which can be considered as a physical restriction of enzyme in a specified area/space. It can be used for raising mechanical stability and can be also used for the reduction of leaching events of enzymes. Since the enzyme in this process does not interact chemically with the polymer/ material of the support fibers/lattice, it remains protected from denaturation with time.
* Basically, the enzyme is trapped in insoluble beads or microspheres, such as calcium alginate beads. However, these insoluble substances hinder the arrival of the substrate, and the exit of products. | 0 | Theoretical and Fundamental Chemistry |
Modern reactive transport modeling has arisen from several separate schools of thought. Hydrologists primarily concerned with the physical nature of mass transport assumed relatively simple reaction formulations, such as linear distribution coefficients or linear decay terms, which could be added to the advection-dispersion equation. By assuming linear, equilibrium sorption, for example, the advection-dispersion equation can be modified by a simple retardation factor and solved analytically. Such analytical solutions are limited to relatively simple flow systems and reactions.
Geochemical models, on the other hand, have been developed to provide thermodynamic descriptions of multicomponent systems without regard to transport. Reaction path models were created, for instance, to describe the sequence of chemical reactions resulting from chemical weathering or hydrothermal alteration in batch systems, in terms of the overall reaction progress. By adopting the reference frame of a packet of fluid and treating reaction progress as travel time (or distance along a flowpath), however, a batch reaction path model could be thought of as describing advective transport through an aquifer.
The most sophisticated multi-component reactive transport models consider both reaction and transport. Early studies developed the theoretical basis of reactive transport models, and the numerical tools necessary to solve them, and applied them to problems of reactive contaminant transport and flow through reacting hydrothermal systems.
Reactive transport models have found increased application in recent years with improvements in the power of personal computers and modeling software. | 0 | Theoretical and Fundamental Chemistry |
Ferredoxin can also be reduced by using NADH (-320 mV) or (-414 mV), but these processes are coupled to the consumption of the membrane potential to power the "boosting" of electrons to the higher energy state. The Rnf complex is a widespread membrane protein in bacteria that reversibly transfers electrons between NADH and ferredoxin while pumping or ions across the membrane. The chemiosmotic potential of the membrane is consumed to power the unfavorable reduction of by NADH. This reaction is an essential source of in many autotrophic organisms. If the cell is growing on substrates that provide excess , the Rnf complex can transfer these electrons to and store the resultant energy in the membrane potential. The energy converting hydrogenases (Ech) are a family of enzymes that reversibly couple the transfer of electrons between and while pumping ions across the membrane to balance the energy difference. | 0 | Theoretical and Fundamental Chemistry |
# Despite scientific advances in making microdialysis probes smaller and more efficient, the invasive nature of this technique still poses some practical and ethical limitations. For example, it has been shown that implantation of a microdialysis probe can alter tissue morphology resulting in disturbed microcirculation, rate of metabolism or integrity of physiological barriers, such as the blood–brain barrier. While acute reactions to probe insertion, such as implantation traumas, require sufficient recovery time, additional factors, such as necrosis, inflammatory responses, or wound healing processes have to be taken into consideration for long-term sampling as they may influence the experimental outcome. From a practical perspective, it has been suggested to perform microdialysis experiments within an optimal time window, usually 24–48 hours after probe insertion.
# Microdialysis has a relatively low temporal and spatial resolution compared to, for example, electrochemical biosensors. While the temporal resolution is determined by the length of the sampling intervals (usually a few minutes), the spatial resolution is determined by the dimensions of the probe. The probe size can vary between different areas of application and covers a range of a few millimeters (intracerebral application) up to a few centimeters (subcutaneous application) in length and a few hundred micrometers in diameter.
# Application of the microdialysis technique is often limited by the determination of the probe’s recovery, especially for in vivo experiments. Determination of the recovery may be time-consuming and may require additional subjects or pilot experiments. The recovery is largely dependent on the flow rate: the lower the flow rate, the higher the recovery. However, in practice the flow rate cannot be decreased too much since either the sample volume obtained for analysis will be insufficient or the temporal resolution of the experiment will be lost. It is therefore important to optimize the relationship between flow rate and the sensitivity of the analytical assay. The situation may be more complex for lipophilic compounds as they can stick to the tubing or other probe components, resulting in a low or no analyte recovery. | 1 | Applied and Interdisciplinary Chemistry |
Nucleotides are the fundamental molecules that combine in series to form RNA. They consist of a nitrogenous base attached to a sugar-phosphate backbone. RNA is made of long stretches of specific nucleotides arranged so that their sequence of bases carries information. The RNA world hypothesis holds that in the primordial soup (or sandwich), there existed free-floating nucleotides. These nucleotides regularly formed bonds with one another, which often broke because the change in energy was so low. However, certain sequences of base pairs have catalytic properties that lower the energy of their chain being created, enabling them to stay together for longer periods of time. As each chain grew longer, it attracted more matching nucleotides faster, causing chains to now form faster than they were breaking down.
These chains have been proposed by some as the first, primitive forms of life. In an RNA world, different sets of RNA strands would have had different replication outputs, which would have increased or decreased their frequency in the population, i.e., natural selection. As the fittest sets of RNA molecules expanded their numbers, novel catalytic properties added by mutation, which benefitted their persistence and expansion, could accumulate in the population. Such an autocatalytic set of ribozymes, capable of self-replication in about an hour, has been identified. It was produced by molecular competition (in vitro evolution) of candidate enzyme mixtures.
Competition between RNA may have favored the emergence of cooperation between different RNA chains, opening the way for the formation of the first protocell. Eventually, RNA chains developed with catalytic properties that help amino acids bind together (a process called peptide-bonding). These amino acids could then assist with RNA synthesis, giving those RNA chains that could serve as ribozymes the selective advantage. The ability to catalyze one step in protein synthesis, aminoacylation of RNA, has been demonstrated in a short (five-nucleotide) segment of RNA.
In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine, and thymine, have been formed in the laboratory under conditions found only in outer space, using starting chemicals, like pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), may have been formed in red giant stars or in interstellar dust and gas clouds, according to the scientists.
In 2018, researchers at Georgia Institute of Technology identified three molecular candidates for the bases that might have formed an earliest version of proto-RNA: barbituric acid, melamine, and 2,4,6-triaminopyrimidine (TAP). These three molecules are simpler versions of the four bases in current RNA, which could have been present in larger amounts and could still be forward-compatible with them but may have been discarded by evolution in exchange for more optimal base pairs. Specifically, TAP can form nucleotides with a large range of sugars. Both TAP and melamine base pair with barbituric acid. All three spontaneously form nucleotides with ribose. | 0 | Theoretical and Fundamental Chemistry |
Schrock carbenes do not have π-accepting ligands on the metal centre, and are typically found with:
* high oxidation state metal center
* early transition metals Ti(IV), Ta(V)
* σ-donor and sometimes π-donor metal ligands
* hydrogen and alkyl substituents on carbenoid carbon.
Examples include and .
Bonding in such complexes can be viewed as the coupling of a triplet state metal and triplet carbene, forming a true double bond. Both the metal and carbon atom donate 2 electrons, one to each bond. Since there is no donation to the carbene atom from adjacent groups, the extent of pi backbonding is much greater, giving a strong double bond. These bonds are weakly polarized towards carbon and therefore the carbene atom is a nucleophile. Furthermore, the major resonance structures of Schrock carbene put the negative charge on the carbon atom, making it nucleophilic. Complexes with the methylidene ligand () are the simplest Schrock-type carbenes. | 0 | Theoretical and Fundamental Chemistry |
While molecular glue compounds hold great potential in various fields, there are challenges to overcome. Ensuring the specificity of these compounds and minimizing off-target effects is essential. Additionally, understanding the long-term consequences of manipulating protein interactions is crucial for their safe and effective application in medicine.
Ongoing research in molecular glue is unlocking new compounds and insights into their mechanisms. With an expanding understanding of protein-protein interactions, molecular glue holds significant promise across biology, medicine, and chemistry, potentially revolutionizing cellular processes and advancing innovative disease treatments. As this field progresses, it may open new therapeutic avenues and deepen our understanding of life's molecular intricacies. | 1 | Applied and Interdisciplinary Chemistry |
The in vivo synthesis of firefly luciferin is not completely understood. Only the final step of the enzymatic pathway has been studied, which is the condensation reaction of -cysteine with 2-cyano-6-hydroxybenzothiazole, and is the same reaction used to produce the compound synthetically. This was confirmed by radiolabeling of atoms in the two compounds and by identification of a luciferin-regenerating enzyme.
In firefly, oxidation of luciferins, which is catalyzed by luciferases, yields a peroxy compound 1,2-dioxetane. The dioxetane is unstable and decays spontaneously to carbon dioxide and excited ketones, which release excess energy by emitting light (bioluminescence).
Firefly luciferin and modified substrates are fatty acid mimics and have been used to localize fatty acid amide hydrolase (FAAH) in vivo. Firefly luciferin is a substrate of the ABCG2 transporter and has been used as part of a bioluminescence imaging high throughput assay to screen for inhibitors of the transporter. | 1 | Applied and Interdisciplinary Chemistry |
This reagent was originally prepared by Conrad Willgerodt by reacting iodobenzene with a mixture of acetic acid and peracetic acid:
PIDA can also be prepared from iodosobenzene and glacial acetic acid:
More recent preparations direct from iodine, acetic acid, and benzene have been reported, using either sodium perborate or potassium peroxydisulfate as the oxidizing agent:
The PIDA molecule is termed hypervalent as its iodine atom (technically a hypervalent iodine) is in its +III oxidation state and has more than typical number of covalent bonds. It adopts a T-shaped molecular geometry, with the phenyl group occupying one of the three equatorial positions of a trigonal bipyramid (lone pairs occupy the other two) and the axial positions occupied by oxygen atoms from the acetate groups. The "T" is distorted in that the phenyl-C to I to acetate-O bond angles are less than 90°. A separate investigation of the crystal structure confirmed that it has orthorhombic crystals in space group Pnn2 and reported unit-cell dimensions in good agreement with the original paper. The bond lengths around the iodine atom were 2.08 Å to the phenyl carbon atom and equal 2.156 Å bonds to the acetate oxygen atoms. This second crystal structure determination explained the distortion in the geometry by noting the presence of two weaker intramolecular iodine–oxygen interactions, resulting in an "overall geometry of each iodine [that] can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds." | 0 | Theoretical and Fundamental Chemistry |
This is the smallest piece, which was moved to Mandu during Dilawar Khan's reign. Its length is according to both Coussen and Roessler. It is mostly of an octagonal cross-section, except one circular part at the end. Roessler estimated its weight at .
This piece was brought back from Mandu to Dhar sometime between 1844 and 1893. In 1893, A. A. Führer of ASI noticed it in the garden of the Dhar Maharaja's guest house. In February 1902, this piece was fixed in a masonry basement at Lal Bagh public gardens near the Anand High School. Henry Cousens of ASI later had it removed from the basement to measure it. The piece was then moved to the Anand High School museum. From there, it was moved to Lat Masjid, similar to the second piece. | 1 | Applied and Interdisciplinary Chemistry |
Oxygen can be consumed by organisms in the sediment. This process is referred to as sediment oxygen demand (SOD). Measurement of SOD can be undertaken by measuring the change of oxygen in a box on the sediment (benthic respirometer).
The change in oxygen deficit due to consumption by sediment is described as
where
* is the depth of the river [m]
* is the SOD
* D is the saturation deficit .
* is the reaeration rate [].
The range of the SOD is typically in the range of 0.1 – 1 for a natural river with low pollution and 5 – 10 for a river with moderate to heavy pollution. | 1 | Applied and Interdisciplinary Chemistry |
Over 90% of the dry weight of hair comprises proteins called keratins, which have a high disulfide content, from the amino acid cysteine. The robustness conferred in part by disulfide linkages is illustrated by the recovery of virtually intact hair from ancient Egyptian tombs. Feathers have similar keratins and are extremely resistant to protein digestive enzymes. The stiffness of hair and feather is determined by the disulfide content. Manipulating disulfide bonds in hair is the basis for the permanent wave in hairstyling. Reagents that affect the making and breaking of S−S bonds are key, e.g., ammonium thioglycolate. The high disulfide content of feathers dictates the high sulfur content of bird eggs. The high sulfur content of hair and feathers contributes to the disagreeable odor that results when they are burned. | 0 | Theoretical and Fundamental Chemistry |
The three cinnamyl alcohol-vicianosides of rhodiola rosea commonly referred to as "rosavins" are rosin and the structurally related disaccharide Rosavin which is the arabinose ester of rosin, and Rosarin, the arabinofuranose ester of rosin. Salidroside, common in rhodiola spp. and occurring in Rhodiola rosea is not a cinnamyl alcohol glycoside, but a glycoside of tyrosol. | 0 | Theoretical and Fundamental Chemistry |
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy, for example, to heat. The absorption of light during wave propagation is often called attenuation. Usually, the absorption of waves does not depend on their intensity (linear absorption), although in certain conditions (usually, in optics), the medium changes its transparency dependently on the intensity of waves going through, and the Saturable absorption (or nonlinear absorption) occurs. | 0 | Theoretical and Fundamental Chemistry |
Epoxides are uncommon in nature. They arise usually via oxygenation of alkenes by the action of cytochrome P450. (but see also the short-lived epoxyeicosatrienoic acids which act as signalling molecules. and similar epoxydocosapentaenoic acids, and epoxyeicosatetraenoic acids.) | 0 | Theoretical and Fundamental Chemistry |
Atomic, Molecular and Optical physics frequently considers atoms and molecules in isolation. Atomic models will consist of a single nucleus that may be surrounded by one or more bound electrons, whilst molecular models are typically concerned with molecular hydrogen and its molecular hydrogen ion. It is concerned with processes such as ionization, above threshold ionization and excitation by photons or collisions with atomic particles.
While modelling atoms in isolation may not seem realistic, if one considers molecules in a gas or plasma then the time-scales for molecule-molecule interactions are huge in comparison to the atomic and molecular processes that we are concerned with. This means that the individual molecules can be treated as if each were in isolation for the vast majority of the time. By this consideration atomic and molecular physics provides the underlying theory in plasma physics and atmospheric physics even though both deal with huge numbers of molecules. | 0 | Theoretical and Fundamental Chemistry |
The reduced Damköhler number is defined as follows
where and . The theory predicted an expression for the reduced Damköhler number at which the flame will extinguish, given by
where . | 1 | Applied and Interdisciplinary Chemistry |
The EPS process produces scale-free steel strip which is interchangeable with acid-pickled steel strip, yet the EPS process entails lower capital and operating (variable) cost than an acid-pickling line of equivalent output. For this reason the EPS process is considered to be a direct replacement of acid pickling.
In addition, the EPS process is considered less damaging to the environment than acid pickling for these reasons:
* Lower energy consumption;
* No hazardous/acidic substances used in the process;
* No potential exposure to acid fumes for people, equipment or buildings;
* No hazardous or polluting outputs or byproducts of the process with disposal or fume stack liabilities. | 1 | Applied and Interdisciplinary Chemistry |
Abnormal grain growth (AGG) is encountered in metallic or ceramic systems exhibiting one or more of several characteristics:
# Systems with secondary phase inclusions, precipitates or impurities above a certain threshold concentration.
# Systems with a highly anisotropic surface energy.
# Systems far from chemical equilibrium.
Abnormal grain growth occurs due to very high local rates of interface migration and is enhanced by the localized formation of liquid at grain boundaries. In 2023, Liss et al.
have shown that the spontaneous activation of a grain boundary opens diffusion pathways, leading to the activation of one grain in an otherwise inactive microstructure and allowing the grain to rotate and coalesce with a neighbor grain. However, due to competition with the surrounding grains, rotation may proceed erratically. Coupled with spontaneous activation, this makes abnormal grain growth a largely erratic process. While the activation of grain boundaries (leading to rotation and growth) can occur at temperatures well below the temperatures required for partial melting of the grain boundaries, the effect is emphasized when melting occurs. | 0 | Theoretical and Fundamental Chemistry |
Although chlororespiration is not as efficient as photosynthesis in producing energy, its significance its attributed to its role as a survival adaptation for plants when placed in conditions lacking light and water or if placed in uncomfortable temperatures (note: optimum temperatures vary across different plant species). Additionally, Cournac and Peltier noticed that chlororespiratory ETCs play a role in balancing electron flow across respiratory and photosynthetic ETCs. This helps maintain water balance and regulate the plant's internal temperature. | 1 | Applied and Interdisciplinary Chemistry |
Somatomedins are a group of proteins produced predominantly by the liver when growth hormones act on target tissue. Somatomedins inhibit the release of growth hormones by acting directly on anterior pituitary and by stimulating the secretion of somatostatin from the hypothalamus.
Somatomedins are a group of proteins that promote cell growth and division in response to stimulation by growth hormone (GH), also known as somatotropin (STH).
Somatomedins have similar biological effects to somatotropin.
In addition to their actions that stimulate growth, somatomedins also stimulate production of somatostatin, which suppresses growth hormone release. Thus, levels of somatomedins are controlled via negative feedback through the intermediates of somatostatin and growth hormone. Somatomedins are produced in many tissues and have autocrine and paracrine actions in addition to their endocrine action. The liver is thought to be the predominant source of circulating somatomedins.
Three forms include:
* Somatomedin A, which is another name for insulin-like growth factor 2 (IGF-2)
* Somatomedin B, which is derived from vitronectin
* Somatomedin C, which is another name for insulin-like growth factor 1 (IGF-1) | 1 | Applied and Interdisciplinary Chemistry |
In the early years of serious research into the locations of stations on the Antonine Itineraries, the location of Ariconium was in doubt, and William Camden (1551–1623) suggested Magnis, the site of modern Kenchester, some northwest of modern Hereford. Later analysis of the Antonine Itineraries, notably by John Horsley (1685–1732), refined previous estimates and ultimately placed Ariconium at Bury Hill, Weston under Penyard, west-northwest of Glevum (at modern Gloucester), and northeast of Blestium (at modern Monmouth). With confidence that the overgrown ruins near Weston under Penyard were actually the site of Ariconium, local people began clearing away the brush, revealing the enormous magnitude of the cinder piles, and further revealing the walls of buildings. Stories emerged of significant Roman-era relics, and there were unverified stories that existing relics having no provenance had actually been found in Ariconium.
Such capable modern research as has been done so far supports the characterisation of a large iron working site with massive refuse piles covering approximately , pottery remnants, and numerous artefacts. Finds have included pre-Roman British coins, including one minted by Cunobelin, and coins from the Roman arrival until 360, after which there are no coins found. | 1 | Applied and Interdisciplinary Chemistry |
HTS is a relatively recent innovation, made feasible largely through modern advances in robotics and high-speed computer technology. It still takes a highly specialized and expensive screening lab to run an HTS operation, so in many cases a small- to moderate-size research institution will use the services of an existing HTS facility rather than set up one for itself.
There is a trend in academia for universities to be their own drug discovery enterprise. These facilities, which normally are found only in industry, are now increasingly found at universities as well. UCLA, for example, features an open access HTS laboratory Molecular Screening Shared Resources (MSSR, UCLA), which can screen more than 100,000 compounds a day on a routine basis. The open access policy ensures that researchers from all over the world can take advantage of this facility without lengthy intellectual property negotiations. With a compound library of over 200,000 small molecules, the MSSR has one of the largest compound deck of all universities on the west coast. Also, the MSSR features full functional genomics capabilities (genome wide siRNA, shRNA, cDNA and CRISPR) which are complementary to small molecule efforts: Functional genomics leverages HTS capabilities to execute genome wide screens which examine the function of each gene in the context of interest by either knocking each gene out or overexpressing it. Parallel access to high-throughput small molecule screen and a genome wide screen enables researchers to perform target identification and validation for given disease or the mode of action determination on a small molecule. The most accurate results can be obtained by use of "arrayed" functional genomics libraries, i.e. each library contains a single construct such as a single siRNA or cDNA. Functional genomics is typically paired with high content screening using e.g. epifluorescent microscopy or laser scanning cytometry.
The University of Illinois also has a facility for HTS, as does the University of Minnesota. The Life Sciences Institute at the University of Michigan houses the HTS facility in the Center for Chemical Genomics. Columbia University has an HTS shared resource facility with ~300,000 diverse small molecules and ~10,000 known bioactive compounds available for biochemical, cell-based and NGS-based screening. The Rockefeller University has an open-access HTS Resource Center HTSRC (The Rockefeller University, HTSRC), which offers a library of over 380,000 compounds. Northwestern University's High Throughput Analysis Laboratory supports target identification, validation, assay development, and compound screening. The non-profit Sanford Burnham Prebys Medical Discovery Institute also has a long-standing HTS facility in the Conrad Prebys Center for Chemical Genomics which was part of the MLPCN. The non-profit Scripps Research Molecular Screening Center (SRMSC) continues to serve academia across institutes post-MLPCN era. The SRMSC uHTS facility maintains one of the largest library collections in academia, presently at well-over 665,000 small molecule entities, and routinely screens the full collection or sub-libraries in support of multi-PI grant initiatives.
In the United States, the National Institutes of Health or NIH has created a nationwide consortium of small-molecule screening centers to produce innovative chemical tools for use in biological research. The Molecular Libraries Probe Production Centers Network, or MLPCN, performs HTS on assays provided by the research community, against a large library of small molecules maintained in a central molecule repository. | 1 | Applied and Interdisciplinary Chemistry |
The structure, properties, and reactivity of a molecule are dependent on straightforward bonding interactions including covalent bonds, ionic bonds, hydrogen bonds, and other forms of bonding. This bonding supplies a basic molecular skeleton that is modified by repulsive forces generally considered steric effects. Basic bonding and steric effects are at times insufficient to explain many structures, properties, and reactivity. Thus, steric effects are often contrasted and complemented by electronic effects, implying the influence of effects such as induction, conjunction, orbital symmetry, electrostatic interactions, and spin state. There are more esoteric electronic effects but these are among the most important when considering chemical structure and reactivity.
Special computational procedure was developed to separate steric and electronic effects of an arbitrary group in the molecule and to reveal their influence on structure and reactivity. | 0 | Theoretical and Fundamental Chemistry |
Notable descaling agents include acetic acid, citric acid, glycolic acid, formic acid, lactic acid, phosphoric acid, sulfamic acid and hydrochloric acid. The calcium salts are soluble and thus washed away during dissolution or solvation. The speed of the descaling action depends on the concentration and acidity or pH of the solution provided. Hydrochloric acid is much stronger than acetic acid, for example, and therefore tends to remove scale faster. Weak acids such as acetic or citric acids may be preferred, however, where damage to the substrate is to be minimised.
Many companies offer inhibited or "buffered" acids that inhibit the corrosive effect of the acids on various materials. Approximately 10% concentrated hydrochloric acid with a corrosion inhibitor and some added penetrating and wetting agents added is typical. This allows for a better cleaning of machinery and especially heat exchangers because often the scale is mixed with silica and other contaminants. These additives reduce the corrosion on the metals and cut through and loosen these other materials mixed with the scale for faster and more thorough cleaning. | 1 | Applied and Interdisciplinary Chemistry |
Releaser pheromones are pheromones that cause an alteration in the behavior of the recipient. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. In general, this type of pheromone elicits a rapid response, but is quickly degraded. In contrast, a primer pheromone has a slower onset and a longer duration. For example, rabbit (mothers) release mammary pheromones that trigger immediate nursing behavior by their babies. | 1 | Applied and Interdisciplinary Chemistry |
Nesfatin-1 is a neuropeptide produced in the hypothalamus of mammals. It participates in the regulation of hunger and fat storage. Increased nesfatin-1 in the hypothalamus contributes to diminished hunger, a sense of fullness, and a potential loss of body fat and weight.
A study of metabolic effects of nesfatin-1 in rats was done in which subjects administered nesfatin-1 ate less, used more stored fat and became more active. Nesfatin-1-induced inhibition of feeding may be mediated through the inhibition of orexigenic neurons. In addition, the protein stimulated insulin secretion from the pancreatic beta cells of both rats and mice. | 1 | Applied and Interdisciplinary Chemistry |
IMAGE cDNA clones are a collection of DNA vectors containing cDNAs from various organisms including human, mouse, rat, non-human primates, zebrafish, pufferfish, Xenopus (frogs), and cow. Together they represent a more or less complete set of expressed genes from these organisms. IMAGE stands for integrated molecular analysis of genomes and their expression. | 1 | Applied and Interdisciplinary Chemistry |
The Vortex lattice method, (VLM), is a numerical method used in computational fluid dynamics, mainly in the early stages of aircraft design and in aerodynamic education at university level. The VLM models the lifting surfaces, such as a wing, of an aircraft as an infinitely thin sheet of discrete vortices to compute lift and induced drag. The influence of the thickness and viscosity is neglected.
VLMs can compute the flow around a wing with rudimentary geometrical definition. For a rectangular wing it is enough to know the span and chord. On the other side of the spectrum, they can describe the flow around a fairly complex aircraft geometry (with multiple lifting surfaces with taper, kinks, twist, camber, trailing edge control surfaces and many other geometric features).
By simulating the flow field, one can extract the pressure distribution or as in the case of the VLM, the force distribution, around the simulated body. This knowledge is then used to compute the aerodynamic coefficients and their derivatives that are important for assessing the aircraft's handling qualities in the conceptual design phase. With an initial estimate of the pressure distribution on the wing, the structural designers can start designing the load-bearing parts of the wings, fin and tailplane and other lifting surfaces. Additionally, while the VLM cannot compute the viscous drag, the induced drag stemming from the production of lift can be estimated. Hence as the drag must be balanced with the thrust in the cruise configuration, the propulsion group can also get important data from the VLM simulation. | 1 | Applied and Interdisciplinary Chemistry |
In graphite-moderated reactors, fissile uranium rods are placed inside graphite blocks. These blocks act as a neutron moderator whose purpose is to slow down fast-moving neutrons so that nuclear chain reactions can occur with thermal neutrons. During their use, some of the non-radioactive carbon-12 and carbon-13 isotopes in graphite get converted into radioactive C by capturing neutrons. When the graphite blocks are removed during station decommissioning, their induced radioactivity qualifies them as low-level waste requiring safe disposal.
Researchers at the University of Bristol demonstrated that a large amount of the radioactive C was concentrated on the inner walls of the graphite blocks. Due to this, they propose that much of it can be effectively removed from the blocks. This can be done by heating them to the sublimation point of which will release the carbon in gaseous form. After this, blocks will be less radioactive and possibly easier to dispose of with most of the radioactive C having been extracted.
Those researchers propose that this C gas could be collected and used to produce man-made diamonds by a process known as chemical vapor deposition using low pressure and elevated temperature, noting that this diamond would be a thin sheet and not of the stereotypical diamond cut. The resulting diamond made of radioactive C would still produce beta radiation which researchers claim would allow it to be used as a betavoltaic source. Researchers also claim this diamond would be sandwiched between non-radioactive man-made diamonds made from C which would block radiation from the source and would also be used for energy conversion as a diamond semiconductor instead of conventional silicon semiconductors. | 0 | Theoretical and Fundamental Chemistry |
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