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Vitamin A deficiency (VAD) has been linked to compromised resistance to infectious diseases. In countries where early childhood VAD is common, vitamin A supplementation public health programs initiated in the 1980s were shown to reduce the incidence of diarrhea and measles, and all-cause mortality. VAD also increases the risk of immune system over-reaction, leading to chronic inflammation in the intestinal system, stronger allergic reactions and autoimmune diseases.
Lymphocytes and monocytes are types of white blood cells of the immune system. Lymphocytes include natural killer cells, which function in innate immunity, T cells for adaptive cellular immunity and B cells for antibody-driven adaptive humoral immunity. Monocytes differentiate into macrophages and dendritic cells. Some lymphocytes migrate to the thymus where they differentiate into several types of T cells, in some instances referred to as "killer" or "helper" T cells and further differentiate after leaving the thymus. Each subtype has functions driven by the types of cytokines secreted and organs to which the cells preferentially migrate, also described as trafficking or homing.
Reviews based on in vitro and animal research describe the role that retinoic acid (RA) has in the immune system. RA triggers receptors in bone marrow, resulting in generation of new white blood cells. RA regulates proliferation and differentiation of white blood cells, the directed movement of T cells to the intestinal system, and to the up- and down-regulation of lymphocyte function. If RA is adequate, T helper cell subtype Th1 is suppressed and subtypes Th2, Th17 and iTreg (for regulatory) are induced. Dendritic cells located in intestinal tissue have enzymes that convert retinal to all-trans-retinoic acid, to be taken up by retinoic acid receptors on lymphocytes. The process triggers gene expression that leads to T cell types Th2, Th17 and iTreg moving to and taking up residence in mesenteric lymph nodes and Peyer's patches, respectively outside and on the inner wall of the small intestine. The net effect is a down-regulation of immune activity, seen as tolerance of food allergens, and tolerance of resident bacteria and other organisms in the microbiome of the large intestine. In a vitamin A deficient state, innate immunity is compromised and pro-inflammatory Th1 cells predominate. | 1 | Applied and Interdisciplinary Chemistry |
Chiral switch, a re-engineering approach, has enabled in the remarketing of a number of racemic drugs as chiral specific enantiomer products. Chiral switching strategy is the way most blockbuster drugs have entered the market as enantiopure drugs. A more appropriate term may be unichiral. But the alternate route is de novo (anew) synthesis of chiral specific drugs. The chiral switches may have the same, very similar, therapeutic indications as the original racemic drug. But, there are instances where new indications for the old drug have been reported. The table below gives a brief list of launched chiral switches. | 0 | Theoretical and Fundamental Chemistry |
The anthocyanins, anthocyanidins with sugar group(s), are mostly 3-glucosides of the anthocyanidins. The anthocyanins are subdivided into the sugar-free anthocyanidin aglycones and the anthocyanin glycosides. As of 2003, more than 400 anthocyanins had been reported, while later literature in early 2006, puts the number at more than 550 different anthocyanins. The difference in chemical structure that occurs in response to changes in pH, is the reason why anthocyanins often are used as pH indicators, as they change from red in acids to blue in bases through a process called halochromism. | 0 | Theoretical and Fundamental Chemistry |
The Magnetometer Navigation (MAGNAV) algorithm was initially running as a flight experiment in 2004. Later on, diamond magnetometers were developed by the United States Air Force Research Laboratory (AFRL) as a better method of navigation which cannot be jammed by the enemy. | 0 | Theoretical and Fundamental Chemistry |
Polymerization-induced phase separation (PIPS) is the occurrence of phase separation in a multicomponent mixture induced by the polymerization of one or more components. The increase in molecular weight of the reactive component renders one or more components to be mutually immiscible in one another, resulting in spontaneous phase segregation. | 0 | Theoretical and Fundamental Chemistry |
This method is able to detect as low as 25 μg/ml and up to 2000 μg/ml of protein in a 65 ul sample, using standard protocol.
This method may be preferred for samples containing detergents or other reducing agents.
This method has a fast detection speed and low protein-to-protein variability in comparison to the BCA or Coomassie (Bradford) Assays.
This method has a stable end point. | 1 | Applied and Interdisciplinary Chemistry |
The similarity of many PDE5 inhibitors to the structure of many of the analogs of caffeine that are also adenosine antagonists suggests that in the future, it may be possible to design an PDE5 inhibitor that, like caffeine, is also an adenosine antagonist. | 1 | Applied and Interdisciplinary Chemistry |
In plasma physics, a burning plasma is one in which most of the heating comes from fusion reactions involving thermal plasma ions. The Sun and similar stars are a burning plasma, and in 2020 the National Ignition Facility achieved burning plasma. A closely related concept is that of an ignited plasma, in which all of the heating comes from fusion reactions. | 0 | Theoretical and Fundamental Chemistry |
The above equations are limited in many regards. For example, the geometry of the separator is not considered, the particles are assumed to achieve a steady state and the effect of the vortex inversion at the base of the cyclone is also ignored, all behaviours which are unlikely to be achieved in a cyclone at real operating conditions.
More complete models exist, as many authors have studied the behaviour of cyclone separators., simplified models allowing a quick calculation of the cyclone, with some limitations, have been developed for common applications in process industries. Numerical modelling using computational fluid dynamics has also been used extensively in the study of cyclonic behaviour. A major limitation of any fluid mechanics model for cyclone separators is the inability to predict the agglomeration of fine particles with larger particles, which has a great impact on cyclone collection efficiency. | 1 | Applied and Interdisciplinary Chemistry |
T-DNA contains two types of genes: the oncogenic genes, encoding for enzymes involved in the synthesis of auxins and cytokinins and responsible for tumor formation, and the genes encoding for the synthesis of opines. These compounds, produced by the condensation between amino acids and sugars, are synthesized and excreted by the crown gall cells, and they are consumed by A. tumefaciens as carbon and nitrogen sources.
The genes involved in opine catabolism, T-DNA transfer from the bacterium to the plant cell and bacterium-bacterium plasmid conjugative transfer are located outside the T-DNA. The T-DNA fragment is flanked by 25-bp direct repeats, which act as a cis-element signal for the transfer apparatus. The process of T-DNA transfer is mediated by the cooperative action of proteins encoded by genes determined in the Ti plasmid virulence region (vir genes) and in the bacterial chromosome. The Ti plasmid also contains the genes for opine catabolism produced by the crown gall cells and regions for conjugative transfer and for its own integrity and stability. The 30 kb virulence (vir) region is a regulon organized in six operons essential for the T-DNA transfer (virA, virB, virD, and virG) or for the increasing of transfer efficiency (virC and virE). Several chromosomal-determined genetic elements have shown their functional role in the attachment of A. tumefaciens to the plant cell and bacterial colonization. The loci chvA and chvB are involved in the synthesis and excretion of the b -1,2 glucan, the required for the sugar enhancement of vir genes induction and bacterial chemotaxis. The cell locus is responsible for the synthesis of cellulose fibrils. The locus is involved in the synthesis of both cyclic glucan and acid succinoglycan. The att locus is involved in the cell surface proteins. | 1 | Applied and Interdisciplinary Chemistry |
Organic Geochemistry is a monthly peer-reviewed scientific journal published by Elsevier covering research on all aspects of organic geochemistry. It is an official journal of the European Association of Organic Geochemists. The editors-in-chief are Steven Rowland (University of Plymouth), John Volkman (CSIRO Oceans and Atmosphere), and Cliff Walters (University of Texas at Austin). | 0 | Theoretical and Fundamental Chemistry |
Precipitation in grasslands is equal to or less than evapotranspiration and causes soil development to operate in relative drought. Leaching and migration of weathering products is therefore decreased. Large amounts of evaporation causes buildup of calcium (Ca) and other large cations flocculate clay minerals and fulvic acids in the upper soil profile. Low amounts of precipitation and high levels of evapotranspiration limit the downward percolation of water and organic acids, reducing chemical weathering and soil development. The depth to the maximum concentration of clay increases in areas of increased precipitation and leaching. When leaching is decreased, the calcium precipitates as calcite (CaCO) in the lower soil levels, a layer known as caliche.
Deserts behave similarly to grasslands but operate in constant drought as precipitation is less than evapotranspiration. Chemical weathering proceeds more slowly than in grasslands and beneath the caliche layer may be a layer of gypsum and halite. To study soils in deserts, pedologists have used the concept of chronosequences to relate timing and development of the soil layers. It has been shown that phosphorus is leached very quickly from the system and therefore decreases with increasing age. Furthermore, carbon buildup in the soils is decreased due to slower decomposition rates. As a result, the rates of carbon circulation in the biogeochemical cycle is decreased. | 0 | Theoretical and Fundamental Chemistry |
Relaxase nomenclature is varied. In conjugative bacterial plasmids, Mob-class relaxases go by names such as TraI (in plasmid RP4), VirD2 (pTi), TrwC (R388), TraI (F-plasmid), MobB (CloDF13), or TrsK (pGO1). | 1 | Applied and Interdisciplinary Chemistry |
The Bluebelt is a large scale system of stormwater best management practices (BMPs) in New York City. The program originated on Staten Island in the early 1990s, but has also been implemented in Queens and the Bronx. The Bluebelt includes structural and nonstructural stormwater management control measures taken to mitigate changes to both quantity and quality of runoff caused through changes to land use. | 1 | Applied and Interdisciplinary Chemistry |
Gross heating value accounts for water in the exhaust leaving as vapor, as does LHV, but gross heating value also includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning. | 0 | Theoretical and Fundamental Chemistry |
This form was developed in the 2000s and introduced commercially around 2009. Also called cast-mono, this design uses polycrystalline casting chambers with small "seeds" of mono material. The result is a bulk mono-like material that is polycrystalline around the outsides. When sliced for processing, the inner sections are high-efficiency mono-like cells (but square instead of "clipped"), while the outer edges are sold as conventional poly. This production method results in mono-like cells at poly-like prices. | 0 | Theoretical and Fundamental Chemistry |
Peptide PHI, also known as peptide histidine isoleucine, is a peptide which functions as a hormone. This peptide contains a composition of 27 amino acids with histidine on the N-terminus and isoleucine on the C-terminus. It was originally isolated from the mammalian small intestine amongst mammalian neurons called intramural neurons which function in the motor activity of the intestinal walls. An example of this was revealed in a study that demonstrated that this peptide regulates water and electrolyte transportation in the human jejunum; similar to its inhibitory effects on fluid absorption in the small intestine of pigs and rats.
Peptide histidine isoleucine (PHI) is part of family that plays a vital role in the cell growth rate such as in the intestine as well as in brain. It was derived from glucagon family called the pituitary adenylate cyclase-activating polypeptide (PACAP) and it has an amino acid sequence homology to vasoactive intestinal peptide, secretin, glucagon, and other growth hormone releasing factor. Human studies have shown that the release of PHI into the stomach regulates the neuroendocrine cell processes that affect gastrointestinal physiology. This peptide is present within the central nervous system that help regulate food consumption behavior, while at peripheral nervous system this peptide accumulates in the stomach which controls the digestion of food.
It also plays a role in the regulation of prolactin in humans. It functions specifically function in the G protein signaling pathway through G protein, which is a transmembrane protein that causes the cascade phosphorylation. It is located throughout the entire length of intestine while PHI is mostly concentrated in the colon region. | 1 | Applied and Interdisciplinary Chemistry |
Follicle-stimulating hormone (FSH) is an agonist of the FSHR.
Small-molecule positive allosteric modulators of the FSHR have been developed. | 1 | Applied and Interdisciplinary Chemistry |
A hot shower will produce steam that condenses on the shower side of the curtain, lowering the pressure there. In a steady state the steam will be replaced by new steam delivered by the shower but in reality the water temperature will fluctuate and lead to times when the net steam production is negative. | 1 | Applied and Interdisciplinary Chemistry |
Hydrolysis constants (log values) in critical compilations at infinite dilution, I = 0.1 M and T = 298.15 K: | 0 | Theoretical and Fundamental Chemistry |
CFC-113 was one of the most heavily produced CFCs. In 1989, an estimated 250,000 tons were produced. It has been used as a cleaning agent for electrical and electronic components. CFC-113’s low flammability and low toxicity made it ideal for use as a cleaner for delicate electrical equipment, fabrics, and metals. It would not harm the product it was cleaning, ignite with a spark or react with other chemicals. It was used as a dry-cleaning solvent, introduced by Du Pont in March 1961 as "Valclene" and was also marketed as the "solvent of the future" by Imperial Chemical Industries in the 1970s under the tradename Arklone. Others from this series were Perklone (Tetrachloroethylene), Triklone (Trichloroethylene), Methoklone (Dichloromethane) and Genklene (1,1,1-Trichloroethane).
CFC-113 is one of the three most popular CFCs, along with CFC-11 and CFC-12.
CFC-113 in laboratory analytics has been replaced by other solvents.
Reduction of CFC-113 with zinc gives chlorotrifluoroethylene: | 1 | Applied and Interdisciplinary Chemistry |
For a single salt solute with molal activity (), the osmotic coefficient can be written as where is the stochiometric number of salt and the activity of the solvent. can be calculated from the salt activity coefficient via:
Moreover, the activity coefficient of the salt can be calculated from:
According to Debye–Hückel theory, which is accurate only at low concentrations, is asymptotic to , where I is ionic strength and A is the Debye–Hückel constant (equal to about 1.17 for water at 25 °C).
This means that, at least at low concentrations, the vapor pressure of the solvent will be greater than that predicted by Raoults law. For instance, for solutions of magnesium chloride, the vapor pressure is slightly greater than that predicted by Raoults law up to a concentration of 0.7 mol/kg, after which the vapor pressure is lower than Raoult's law predicts. For aqueous solutions, the osmotic coefficients can be calculated theoretically by Pitzer equations or TCPC model. | 0 | Theoretical and Fundamental Chemistry |
The selectivity in the reaction is due to the stronger electron withdrawing power of the esters compared to the ethers. A stronger electron withdrawing substituent leads to a greater destabilization of the oxocarbenium ion. This slows this reaction pathway, and allows for disaccharide formation to occur with the benzylated sugar. Other effective electron withdrawing groups that have shown selectivity are halogens and azido groups, while deoxygenation has been proven an effective tool in “arming” sugars. | 0 | Theoretical and Fundamental Chemistry |
When the force becomes large, the semi-angle of the jet becomes small, in which case,
and the solution inside and outside of the jet become
The jet in this limiting case is called the Schlichting jet. On the other extreme, when the force is small,
the semi-angle approaches 90 degree (no inside and outside region, the whole domain is considered as single region), the solution itself goes to | 1 | Applied and Interdisciplinary Chemistry |
In a typical spectrum analyzer there are options to set the start, stop, and center frequency. The frequency halfway between the stop and start frequencies on a spectrum analyzer display is known as the center frequency. This is the frequency that is in the middle of the display's frequency axis. Span specifies the range between the start and stop frequencies. These two parameters allow for adjustment of the display within the frequency range of the instrument to enhance visibility of the spectrum measured. | 0 | Theoretical and Fundamental Chemistry |
The average untrained healthy male has a V̇O max of approximately 35–40 mL/(kg·min). The average untrained healthy female has a V̇O max of approximately 27–31 mL/(kg·min). These scores can improve with training and decrease with age, though the degree of trainability also varies widely. | 1 | Applied and Interdisciplinary Chemistry |
The use of the amino acid glutamine as an energy source is facilitated by the multistep catabolism of glutamine called glutaminolysis. This energy pathway is upregulated in cancer, which may represent a therapeutic target as cancer cells are thought to be more dependent on glutamine than healthy cells. This especially holds true for specific tumor types that are metabolically dysregulated, such as malignant brain tumors (i.e. glioblastoma) that carry mutations in the IDH1 gene. These tumors use glutamine or the structurally related amino acid glutamate as an energy source and a chemotactic sensor in the brain, which increases their malignancy and may explain why these tumors grow so invasive.[9][10] | 1 | Applied and Interdisciplinary Chemistry |
The original Bürgi-Dunitz measurements were of a series of intramolecular amine-ketone carbonyl interactions, in crystals of compounds bearing both functionalities—e.g., methadone and protopine. These gave a narrow range of BD angle values (105 ± 5°); corresponding computations—molecular orbital calculations of the SCF-LCAO-type—describing the approach of the s-orbital of a hydride anion (H) to the pi-system of the simplest aldehyde, formaldehyde (HC=O), gave a BD angle value of 107°.
Hence, Bürgi, Dunitz, and thereafter many others noted that the crystallographic measurements of the aminoketones and the computational estimate for the simplest nucleophile-electrophile system were quite close to a theoretical ideal, the tetrahedral angle (internal angles of a tetrahedron, 109.5°), and so consistent with a geometry understood to be important to developing transition states in nucleophilic attacks at trigonal centers.
In the structure of -methadone (above, left), note the tertiary amine projecting to the lower right, and the carbonyl (CO) group at the center, which engage in an intramolecular interaction in the crystal structure (after rotation around the single bonds connecting them, during the crystallization process).
Similarly, in the structure of protopine (above, center), note the tertiary amine at the center of the molecule, part of a ten-membered ring, and the CO group opposite it on the ring; these engage in an intramolecular interaction allowed by changes in the torsion angles of the atoms of the ring. | 0 | Theoretical and Fundamental Chemistry |
A typical thermodynamic operation is externally imposed change of position of a piston, so as to alter the volume of the system of interest. Another thermodynamic operation is a removal of an initially separating wall, a manipulation that unites two systems into one undivided system. A typical thermodynamic process consists of a redistribution that spreads a conserved quantity between a system and its surroundings across a previously impermeable but newly semi-permeable wall between them.
More generally, a process can be considered as a transfer of some quantity that is defined by a change of an extensive state variable of the system, corresponding to a conserved quantity, so that a transfer balance equation can be written. According to Uffink, "... thermodynamic processes only take place after an external intervention on the system (such as: removing a partition, establishing thermal contact with a heat bath, pushing a piston, etc.). They do not correspond to the autonomous behaviour of a free system." For example, for a closed system of interest, a change of internal energy (an extensive state variable of the system) can be occasioned by transfer of energy as heat. In thermodynamics, heat is not an extensive state variable of the system. The quantity of heat transferred, is however, defined by the amount of adiabatic work that would produce the same change of the internal energy as the heat transfer; energy transferred as heat is the conserved quantity.
As a matter of history, the distinction, between a thermodynamic operation and a thermodynamic process, is not found in these terms in nineteenth century accounts. For example, Kelvin spoke of a "thermodynamic operation" when he meant what present-day terminology calls a thermodynamic operation followed by a thermodynamic process. Again, Planck usually spoke of a "process" when our present-day terminology would speak of a thermodynamic operation followed by a thermodynamic process. | 0 | Theoretical and Fundamental Chemistry |
Particle size and surface area influence the release of a drug from a dosage form that is administered orally, rectally, parenterally, and topically. Higher surface area brings about intimate contact of the drug with the dissolution fluids in vivo and increases the drug solubility and dissolution. | 0 | Theoretical and Fundamental Chemistry |
In radiation protection, radiation is often separated into two categories, ionizing and non-ionizing, to denote the level of danger posed to humans. Ionization is the process of removing electrons from atoms, leaving two electrically charged particles (an electron and a positively charged ion) behind. The negatively charged electrons and positively charged ions created by ionizing radiation may cause damage in living tissue. Basically, a particle is ionizing if its energy is higher than the ionization energy of a typical substance, i.e., a few eV, and interacts with electrons significantly.
According to the International Commission on Non-Ionizing Radiation Protection, electromagnetic radiations from ultraviolet to infrared, to radiofrequency (including microwave) radiation, static and time-varying electric and magnetic fields, and ultrasound belong to the non-ionizing radiations.
The charged particles mentioned above all belong to the ionizing radiations. When passing through matter, they ionize and thus lose energy in many small steps. The distance to the point where the charged particle has lost all its energy is called the range of the particle. The range depends upon the type of particle, its initial energy, and the material it traverses. Similarly, the energy loss per unit path length, the stopping power, depends on the type and energy of the charged particle and upon the material. The stopping power and hence, the density of ionization, usually increases toward the end of range and reaches a maximum, the Bragg Peak, shortly before the energy drops to zero. | 0 | Theoretical and Fundamental Chemistry |
4-nitro phenol is a slightly yellow, crystalline material, moderately toxic.
It shows two polymorphs in the crystalline state. The alpha-form is colorless pillars, unstable at room temperature, and stable toward sunlight. The beta-form is yellow pillars, stable at room temperature, and gradually turns red upon irradiation of sunlight. Usually 4-nitrophenol exists as a mixture of these two forms.
In solution, 4-nitrophenol has a dissociation constant (pK) of 7.15 at 25 °C. | 0 | Theoretical and Fundamental Chemistry |
The Planet Simulator, also known as a Planetary Simulator, is a climate-controlled simulation chamber designed to study the origin of life. The device was announced by researchers at McMaster University on behalf of the Origins Institute on 4 October 2018. The simulator project begun in 2012 and was funded with $1 million from the Canada Foundation for Innovation, the Ontario government, and McMaster University. It was built and manufactured by [https://angstromengineering.com/ Angstrom Engineering Inc] of Kitchener, Ontario.
The device was designed and developed by biophysicist Maikel Rheinstadter and co-principal investigators biochemist Yingfu Li and astrophysicist Ralph Pudritz for researchers to study a theory that suggests life on early Earth began in "warm little ponds" rather than in deep ocean vents nearly four billion years ago. The device can recreate conditions of the primitive Earth to see whether cellular life can be created, and then later, evolve.
In an 2018 news release, Maikel Rheinstadter stated: "We want to understand how the first living cell was formed - how the Earth moved from a chemical world to a biological world."
The Planet Simulator can mimic the environmental conditions consistent on the early Earth and other astronomical bodies, including other planets and exoplanets by controlling temperature, humidity, pressure, atmosphere and radiation levels within the simulation chamber. | 0 | Theoretical and Fundamental Chemistry |
An osmometer is a device for measuring the osmotic strength of a solution, colloid, or compound.
There are several different techniques employed in osmometry:
* Freezing point depression osmometers may also be used to determine the osmotic strength of a solution, as osmotically active compounds depress the freezing point of a solution. This is the most common method in clinical laboratories because it is the most accurate and simple method.
* Vapor pressure osmometers determine the concentration of osmotically active particles that reduce the vapor pressure of a solution.
* Membrane osmometers measure the osmotic pressure of a solution separated from pure solvent by a semipermeable membrane.
Osmometers are useful for determining the total concentration of dissolved salts and sugars in blood or urine samples. Osmometry is also useful in determining the molecular weight of unknown compounds and polymers.
Osmometry is the measurement of the osmotic strength of a substance. This is often used by chemists for the determination of average molecular weight.
Osmometry is also useful for estimating the drought tolerance of plant leaves. | 0 | Theoretical and Fundamental Chemistry |
Optogenetics and chemogenetics are the more recent and popular methods used to study this relationship. Both of these methods target specific brain circuits and cell population to influence cell activity. However, they use different procedures to accomplish this task. Optogenetics uses light-sensitive channels and pumps that are virally introduced into neurons. Cells' activity, having these channels, can then be manipulated by light. Chemogenetics, on the other hand, uses chemically engineered receptors and exogenous molecules specific for those receptors, to affect the activity of those cells. The engineered macromolecules used to design these receptors include nucleic acid hybrids, kinases, variety of metabolic enzymes, and G-protein coupled receptors such as DREADDs.
DREADDs are the most common G protein–coupled receptors used in chemogenetics. These receptors solely get activated by the drug of interest (inert molecule) and influence physiological and neural processes that take place within and outside of the central nervous system.
Chemogenetics has recently been favored over optogenetics, and it avoids some of the challenges of optogenetics. Chemogenetics does not require the expensive light equipment, and therefore, is more accessible. The resolution in optogenetics declines due to light scattering and illuminance declined levels as the distance between the subject and the light source increases. These factors, therefore, don’t allow for all cells to be affected by light and lead to a lower spatial resolution. Chemogenetics, however, does not require light usage and therefore can achieve a higher spatial resolution. | 1 | Applied and Interdisciplinary Chemistry |
Her awards and honours include;
* 2012 European Research Council Starting Grant
* 2012 University of Twente De Winter Prize
* 2014 Elected to the Royal Netherlands Academy of Arts and Sciences Young Academy
* 2016 Netherlands Organisation for Scientific Research Athena Award
* 2016 Elected a member of the Global Young Academy
* 2016 Elected to the Council for Physics and Chemistry
* 2017 Royal Netherlands Chemical Society Gold Medal
* 2018 European Research Council Consolidator Grant | 0 | Theoretical and Fundamental Chemistry |
Synthesis of vitamin D in nature is dependent on the presence of UV radiation and subsequent activation in the liver and in the kidneys. Many animals synthesize vitamin D from 7-dehydrocholesterol, and many fungi synthesize vitamin D from ergosterol. | 1 | Applied and Interdisciplinary Chemistry |
There are two main types of transmetalation, redox-transmetalation (RT) and redox-transmetalation/ligand-exchange (RTLE). Below, M is usually a 4d or 5d transition metal and M is usually a main group or 3d transition metal. By looking at the electronegativities of the metals and ligands, one can predict whether the RT or RTLE reaction will proceed and what products the reaction will yield. For example, one can predict that the addition of 3 HgPh to 2 Al will yield 3 Hg and 2 AlPh because Hg is a more electronegative element than Al. | 0 | Theoretical and Fundamental Chemistry |
Electrowinning is the oldest industrial electrolytic process. The English chemist Humphry Davy obtained sodium metal in elemental form for the first time in 1807 by the electrolysis of molten sodium hydroxide.
Electrorefining of copper was first demonstrated experimentally by Maximilian, Duke of Leuchtenberg in 1847.
James Elkington patented the commercial process in 1865 and opened the first successful plant in Pembrey, Wales in 1870. The first commercial plant in the United States was the Balbach and Sons Refining and Smelting Company in Newark, New Jersey in 1883. | 1 | Applied and Interdisciplinary Chemistry |
In biochemical signaling, diacylglycerol functions as a second messenger signaling lipid, and is a product of the hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP) by the enzyme phospholipase C (PLC) (a membrane-bound enzyme) that, through the same reaction, produces inositol trisphosphate (IP). Although inositol trisphosphate diffuses into the cytosol, diacylglycerol remains within the plasma membrane, due to its hydrophobic properties. IP stimulates the release of calcium ions from the smooth endoplasmic reticulum, whereas DAG is a physiological activator of protein kinase C (PKC). The production of DAG in the membrane facilitates translocation of PKC from the cytosol to the plasma membrane. | 1 | Applied and Interdisciplinary Chemistry |
An extremely thin cantilever portion moves like a flexible door due to the pressure variations in the surrounding gas. The displacement of the cantilever is measured with an accurate interferometric readout system. This way the "breathing effect" can be avoided. The so-called breathing effect occurs in capacitive measurement principle where the other electrode damps the movement of the sensor and restricts the dynamic range. | 0 | Theoretical and Fundamental Chemistry |
The diagram shows a ceramic crucible with a steel cylinder suspended within. Both cathode (C) and anode (A) are made of iron or nickel. The temperature is cooler at the bottom and hotter at the top so that the sodium hydroxide is solid in the neck (B) and liquid in the body of the vessel. Sodium metal forms at the cathode but is less dense than the fused sodium hydroxide electrolyte. Wire gauze (G) confines the sodium metal to accumulating at the top of the collection device (P). The cathode reaction is
:2 Na + 2 e → 2Na
The anode reaction is
:4 OH → O + 2 HO + 4 e
Despite the elevated temperature, some of the water produced remains dissolved in the electrolyte. This water diffuses throughout the electrolyte and results in the reverse reaction taking place on the electrolyzed sodium metal:
:2 Na + 2 HO → H + 2 Na + 2 OH
with the hydrogen gas also accumulating at (P). This, of course, reduces the efficiency of the process. | 1 | Applied and Interdisciplinary Chemistry |
Evergreening refers to the various strategies whereby owners (innovators/sponsors) of pharmaceutical products use patent laws and minor drug modifications to extend their monopoly privileges on the drug. An enantiomer patent is another form of evergreening based on a chiral switch strategy. Single-enantiomer drugs represent more than 50% of the top-selling 100 drugs worldwide. There are some studies which go to suggest that drug companies employ chiral switching for life-cycle management/patent protection of the parent racemic drug and also as a marketing strategy. Pharmaceutical companies support evergreening practices. Some chiral switches are performed to re-start the patent clock for a medication without reducing side effects or improving efficacy. A high price can then continue to be charged for a medication. Examples include citalopram and escitalopram, and omeprazole and esomeprazole. In both these medications, proposed theoretical benefits were used to market the enantiopure drugs, without any clinical trials being conducted to provide evidence that the racemic drugs improved patient centered outcomes. | 0 | Theoretical and Fundamental Chemistry |
The effect of the bulbous bow can be explained using the concept of destructive interference of waves:
A conventionally shaped bow causes a bow wave. A bulb alone forces the water to flow up and over it forming a trough. Thus, if a bulb is added to a conventional bow at the proper position, the bulb trough coincides with the crest of the bow wave, and the two cancel out, reducing the vessel's wake. While inducing another wave stream saps energy from the ship, cancelling out the second wave stream at the bow changes the pressure distribution along the hull, thereby reducing wave resistance. The effect that pressure distribution has on a surface is known as the form effect.
A sharp bow on a conventional hull form would produce waves and low drag like a bulbous bow, but waves coming from the side would strike it harder. The blunt bulbous bow also produces higher pressure in a large region in front, making the bow wave start earlier.
The addition of a bulb to a ships hull increases its overall wetted area. As wetted area increases, so does drag. At greater speeds and in larger vessels it is the bow wave that is the greatest force impeding the vessels forward motion through the water. For a vessel that is small or spends a great deal of its time at a slow speed, the increase in drag will not be offset by the benefit in damping bow wave generation. As the wave counter effects are only significant at the vessel's higher range of speed, bulbous bows are not energy efficient when the vessel cruises outside of these ranges, specifically at lower speeds.
Bulbous bows may be configured differently, according to the designed interaction between the bow wave and the countering wave from the bulb. Design parameters include:
* a) upward curvature (a "ram" bulb) versus straight forward (a "faired-in" bulb),
* b) bulb position with respect to the waterline, and
* c) bulb volume.
Bulbous bows also decrease a ships pitching motion, when they are ballasted, by increasing the mass at a distance removed from the ships longitudinal centre of gravity. | 1 | Applied and Interdisciplinary Chemistry |
The pipecolate region of rapamycin structure seems necessary for rapamycin-binding to FKBP12. This step is required for further binding of rapamycin to the mTOR kinase, which is the key enzyme in many biological actions of rapamycin.
The high affinity of rapamycin binding to FKBP12 is explained by number of hydrogen bonds through two different hydrophobic binding pockets, and this has been revealed by X-ray crystal structure of the compound bound to the protein. The structural characteristics common to temsirolimus and sirolimus; the pipecolic acid, tricarbonyl region from C13-C15, and lactone functionalities play the key role in binding groups with the FKBP12.
The most important hydrogen bonds are the lactone carbonyl oxygen at C-21 to the backbone NH of Ile56, amide carbonyl at C-15 to the phenolic group on the sidechain of Tyr82, and the hydroxyl proton at the hemiketal carbon, C-13, to the sidechain of Asp37.
Structural changes to the rapamycin structure can affect binding to mTOR. This could include both direct and indirect binding as a part of binding to FKBP12. Interaction of the FKBP12-rapamycin complex with mTOR corresponds with conformational flexibility of the effector domain of rapamycin. This domain consists of molecular regions that make hydrophobic interactions with the FKB domain and triene region from C-1-C-6, methoxy group at C-7, and methyl groups at C-33, C-27 and C-25. All changes of the macrolide ring can have unpredictable effects on binding and therefore, make determination of SAR for rapalogs problematic.
Rapamycin contains no functional groups that ionize in the pH range 1-10 and therefore, are rather insoluble in water. Despite its effectiveness in preclinic cancer models, its poor solubility in water, stability, and the long half-life elimination made its parenteral use difficult, but the development of soluble rapamycin analogs vanquished various barriers.
Nonetheless, the rapamycin analogs that have been approved for human use are modified at C-43 hydroxyl group and show improvement in pharmacokinetic parameters as well as drug properties, for example, solubility.
Rapamycin and temsirolimus have similar chemical structures and bind to FKBP12, though their mechanism of action differs.
Temsirolimus is a dihydroxymethyl propionic acid ester of rapamycin, and its first derivative. Therefore, it is more water-soluble, and due to its water solubility it can be given by intravenous formulation.
Everolimus has O-2 hydroxyethyl chain substitution and deforolimus has a phosphine oxide substitution at position C-43 in the lactone ring of rapamycin.
Deforolimus (Ridaforolimus ) has C43 secondary alcohol moiety of the cyclohexyl group of Rapamycin that was substituted with phosphonate and phosphinate groups, preventing the high-affinity binding to mTOR and FKBP. Computational modelling studies helped the synthesise of the compound. | 1 | Applied and Interdisciplinary Chemistry |
Cyanidin can be synthesized in berry plants through the shikimate pathway and polyketide synthase (PKS) III. The shikimate pathway is a biosynthetic pathways that uses the starting materials Phosphoenolpyruvic acid (PEP) and Erythrose 4-phosphate to form shikimic acid, which then further reacts to form specific aromatic amino acids. L-phenylalanine, which is necessary in the production of cyanidin, is synthesized through the shikimate pathway.
In the synthesis of L-phenylalanine, chorismate undergoes a Claisen rearrangement by a Chorismate mutase enzyme to form prephenate. Prephenate undergoes dehydration, decarboxylation, and transamination with Pyridoxal phosphate (PLP) and alpha-Ketoglutaric acid to form L-phenylalanine (figure 1).
L-phenylalanine then undergoes an elimination of the primary amine with Phenylalanine ammonia-lyase (PAL) to form cinnamate. Through an oxidation with molecular oxygen and NADPH, a hydroxyl group is added to the para position of the aromatic ring. The compound then reacts with Coenzyme A (CoA), CoA ligase, and ATP to attach CoA to the carboxylic acid group. The compound reacts with naringenin-chalcone synthase and three malonyl CoA molecules to add six carbon atoms and three more keto groups ring through PKS III. Aureusidin synthase catalyses the aromatization and cyclization of the newly added carbonyl groups and facilitates the release of CoA. The compound then spontaneously cyclizes to form naringenin (figure 2).
Naringenin is then converted to cyanidin through several oxidizing and reducing steps. First naringenin is reacted with two equivalents of oxygen, alpha-Ketogluteratic acid, and flavanone 3-hydroxylase to form dihydrokaempferol. The compound then reacts with NADPH and dihydroflavonol 4-reductase to form leucopelargonidin, which is further oxidized with oxygen, alpha-Ketogluteratic acid, and anthocyanidin synthase. This compound spontaneously loses a water molecule and a hydroxide ion to form cyanidin (figure 3). | 0 | Theoretical and Fundamental Chemistry |
Igor V. Komarov graduated with distinction from Taras Shevchenko National University of Kyiv, and started to work at the same university in 1986 first as an engineer. He obtained his Candidate of Sciences degree in 1991 in organic chemistry at Taras Shevchenko National University of Kyiv under supervision of Mikhail Yu. Kornilov; the candidate thesis was devoted to the use of lanthanide shift reagents in NMR spectroscopy. Afterwards, he was a postdoctoral fellow at the University Chemical Laboratory in Cambridge (1996–1997, United Kingdom) and at the [https://www.catalysis.de/home/ Institut für Organische Katalyseforschung] in Rostock (2000–2001, Germany). He holds the Supramolecular Chemistry Chair of Institute of High Technologies at Taras Shevchenko National University. Komarov earned his Doctor of Sciences degree in 2003; the title of his thesis is "Design and synthesis of model compounds: study of stereoelectronic, steric effects, reactive intermediates, catalytic enantioselective hydrogenation and dynamic protection of functional groups" He is also a scientific advisor for Enamine Ltd. and Lumobiotics GmbH. Igor V. Komarov was awarded the title of Professor in 2007. | 0 | Theoretical and Fundamental Chemistry |
The cpFOCE uses replicate experimental flumes to enclose sections of a coral reef and dose them with CO-enriched seawater using peristaltic pumps with computer controlled feedback loop to maintain a specified pH offset from ambient conditions. A cpFOCE chamber has forward and rear flow conditioners on either end to accommodate bidirectional ocean currents. The openings are placed parallel to the dominant axis of tidal currents over the reef flat, and the chamber is anchored with sand stakes. The flow conditioners are attached to maximize turbulence and provide passive mixing of the CO enriched seawater. Four of the tubes in the flow conditioners furthest from the chamber have small holes along their length through which low pH water is pumped to dispense it evenly along the entire width and height of the conditioner. The flow conditioners are also painted white to minimize heating and algal growth. The cpFOCE system was deployed at Heron Island (Great Barrier Reef) to investigate the response of coral communities to ocean acidification. | 0 | Theoretical and Fundamental Chemistry |
The photo-oxidation of polymers can be investigated by either natural or accelerated weather testing. Such testing is important in determining the expected service-life of plastic items as well as the fate of waste plastic.
In natural weather testing, polymer samples are directly exposed to open weather for a continuous period of time, while accelerated weather testing uses a specialized test chamber which simulates weathering by sending a controlled amount of UV light and water at a sample. A test chamber may be advantageous in that the exact weathering conditions can be controlled, and the UV or moisture conditions can be made more intense than in natural weathering. Thus, degradation is accelerated and the test is less time-consuming.
Through weather testing, the impact of photooxidative processes on the mechanical properties and lifetimes of polymer samples can be determined. For example, the tensile behavior can be elucidated through measuring the stress–strain curve for a specimen. This stress–strain curve is created by applying a tensile stress (which is measured as the force per area applied to a sample face) and measuring the corresponding strain (the fractional change in length). Stress is usually applied until the material fractures, and from this stress–strain curve, mechanical properties such as the Young’s modulus can be determined. Overall, weathering weakens the sample, and as it becomes more brittle, it fractures more easily. This is observed as a decrease in the yield strain, fracture strain, and toughness, as well as an increase in the Young’s modulus and break stress (the stress at which the material fractures).
Aside from measuring the impact of degradation on mechanical properties, the degradation rate of plastic samples can also be quantified by measuring the change in mass of a sample over time, as microplastic fragments can break off from the bulk material as degradation progresses and the material becomes more brittle through chain-scission. Thus, the percentage change in mass is often measured in experiments to quantify degradation.
Mathematical models can also be created to predict the change in mass of a polymer sample over the weathering process. Because mass loss occurs at the surface of the polymer sample, the degradation rate is dependent on surface area. Thus, a model for the dependence of degradation on surface area can be made by assuming that the rate of change in mass resulting from degradation is directly proportional to the surface area SA of the specimen:
Here, is the density and k is known as the specific surface degradation rate (SSDR), which changes depending on the polymer sample’s chemical composition and weathering environment. Furthermore, for a microplastic sample, SA is often approximated as the surface area of a cylinder or sphere. Such an equation can be solved to determine the mass of a polymer sample as a function of time. | 0 | Theoretical and Fundamental Chemistry |
As a more complex example, the ionic strength of a mixed solution 0.050 M in NaSO and 0.020 M in KCl is: | 0 | Theoretical and Fundamental Chemistry |
* Lewis, Peter Rhys, Reynolds, K and Gagg, C, Forensic Materials Engineering: Case studies, CRC Press (2004)
* Ezrin, Meyer, Plastics Failure Guide: Cause and Prevention, Hanser-SPE (1996).
* Wright, David C., Environmental Stress Cracking of Plastics RAPRA (2001).
* Lewis, Peter Rhys, and Gagg, C, Forensic Polymer Engineering: Why polymer products fail in service, Woodhead/CRC Press (2010). | 0 | Theoretical and Fundamental Chemistry |
Thioglycosides were first reported in 1909 by Fischer and since then have been explored constantly allowing for the development of numerous protocols for their preparation.
The advantage of using thioglycosides is their stability under a wide range of reaction conditions allowing for protecting group manipulations. Additionally thioglycosides act as temporary protecting groups at the anomeric position allowing for thioglycosides to be useful as both glycosyl donors as well as glycosyl acceptors.
Thioglycosides are usually prepared by reacting per-acetylated sugars with and the appropriate thiol.
Thioglycosides used in glycosylation reactions as donors can be activated under a wide range of conditions, most notably using NIS/AgOTf. | 0 | Theoretical and Fundamental Chemistry |
The major difference between atomic force microscopy and competing technologies such as optical microscopy and electron microscopy is that AFM does not use lenses or beam irradiation. Therefore, it does not suffer from a limitation in spatial resolution due to diffraction and aberration, and preparing a space for guiding the beam (by creating a vacuum) and staining the sample are not necessary.
There are several types of scanning microscopy including scanning probe microscopy (which includes AFM, scanning tunneling microscopy (STM) and near-field scanning optical microscope (SNOM/NSOM), STED microscopy (STED), and scanning electron microscopy and electrochemical AFM, EC-AFM). Although SNOM and STED use visible, infrared or even terahertz light to illuminate the sample, their resolution is not constrained by the diffraction limit. | 0 | Theoretical and Fundamental Chemistry |
* 2000 - Janos Hajdu, Richard Neutze, and colleagues calculated that they could use Sayre’s ideas from the 1950s, to implement a ‘diffraction before destruction’ concept, using an X-ray free-electron laser (XFEL).
* 2001 - Harry F. Noller’s group published the 5.5-Å structure of the complete Thermus thermophilus 70S ribosome. This structure revealed that the major functional regions of the ribosome were based on RNA, establishing the primordial role of RNA in translation.
* 2001 - Roger Kornberg’s group published the 2.8-Å structure of Saccharomyces cerevisiae RNA polymerase. The structure allowed both transcription initiation and elongation mechanisms to be deduced. Simultaneously, this group reported the structure of free RNA polymerase II, which contributed towards the eventual visualisation of the interaction between DNA, RNA, and the ribosome.
* 2007 - Two X-ray crystal structures of a GPCR, the human β2 adrenergic receptor, were published. Because many drugs elicit their biological effect(s) by binding to a GPCR, the structures of these and other GPCRs may be used to develop efficacious drugs with few side effects.
* 2009 - Venkatraman Ramakrishnan, Thomas A. Steitz and Ada E. Yonath shared the Nobel Prize in Chemistry "for studies of the structure and function of the ribosome."
* 2009 - Judith Howard and her collaborators created the Olex2 crystallographic software package.
* 2011 - Gustaaf Van Tendeloo led a team including Sandra Van Aert, Kees Joost Batenburg et. al. determined the 3D atomic positions of a silver nanoparticle using electron tomography.
* 2011 - Dan Shechtman received the Nobel Prize in chemistry "for the discovery of quasicrystals."
* 2011 - Henry N. Chapman, John C. H. Spence and 86 co-workers used femtosecond pulses from a Free-electron laser (XFEL) to examine the structure of nanocrystals of Photosystem I. By using very brief x-ray pulses, most radiation damage is mitigated using the technique called serial femtosecond crystallography.
* 2012 - Jianwei Miao and his co-workers applied the coherent diffraction imaging (CDI) method to pioneer Atomic Electron Tomography (AET), enabling the first determination of 3D atomic structures without assuming crystallinity or averaging.
* 2013 - Tamir Gonen and his co-workers demonstrated microcrystal electron diffraction (microED) for lysozyme microcrystals at the Janelia Farm Research Campus.
* 2014 - The International Union of Crystallography named 2014 the International Year of Crystallography to commemorate the century of discovery since the invention of X-ray diffraction.
* 2017 - Lukas Palatinus and co-workers used dynamical structure refinement to resolve hydrogen atom positions in nanocrystals using electron diffraction.
* 2017 - Jacques Dubochet, Joachim Frank and Richard Henderson shared the Nobel Prize in chemistry "for developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution."
* 2019 - The Cambridge Structural Database reached the milestone of one million structures.
* 2021 - Kenneth G. Libbrecht published the book Snow Crystals: A Case Study in Spontaneous Structure Formation, summarizing his decade-spanning work on the subject for engineering conditions for designer ice crystals. | 1 | Applied and Interdisciplinary Chemistry |
Their mechanism of action is not entirely clear, but it is known that they inhibit the production of tumour necrosis factor, interleukin 6 and immunoglobulin G and VEGF (which leads to its anti-angiogenic effects), co-stimulates T cells and NK cells and increases interferon gamma and interleukin 2 production. Their teratogenic effects appear to be mediated by binding to cereblon.
Thalidomide and its analogs, lenalidomide and pomalidomide, are believed to act in a similar fashion even though their exact mechanism of action is not yet fully understood. It is believed that they work through different mechanisms in various diseases. The net effect is probably due to different mechanisms combined. Mechanism of action will be explained in light of today's knowledge. | 1 | Applied and Interdisciplinary Chemistry |
Ellen Gleditsch (29 December 1879 – 5 June 1968) was a Norwegian radiochemist and Norways second female professor. Starting her career as an assistant to Marie Curie, she became a pioneer in radiochemistry, establishing the half-life of radium and helping demonstrate the existence of isotopes. She was Vice President of the Norwegian Association for Womens Rights 1937–1939. | 0 | Theoretical and Fundamental Chemistry |
In bioinorganic chemistry and bioorganometallic chemistry, coordination complexes serve either structural or catalytic functions. An estimated 30% of proteins contain metal ions. Examples include the intensely colored vitamin B, the heme group in hemoglobin, the cytochromes, the chlorin group in chlorophyll, and carboxypeptidase, a hydrolytic enzyme important in digestion. Another complex ion enzyme is catalase, which decomposes the cell's waste hydrogen peroxide. Synthetic coordination compounds are also used to bind to proteins and especially nucleic acids (e.g. anticancer drug cisplatin). | 0 | Theoretical and Fundamental Chemistry |
Metastable metallic hydrogen may have potential as a highly efficient rocket propellant, with a theoretical specific impulse of up to 1700 seconds (for reference, the current most efficient chemical rocket propellants have an less than 500 s), although a metastable form suitable for mass-production and conventional high-volume storage may not exist. Another significant issue is the heat of the reaction, which at over 6000 K is too high for any known engine materials to be used. This would necessitate diluting the metallic hydrogen with water or liquid hydrogen, a mixture that would still provide a significant performance boost from current propellants. | 0 | Theoretical and Fundamental Chemistry |
Side effects include irregular heartbeat, respiratory depression, and hepatotoxicity. It appears to be safe in porphyria. It is unclear whether use during pregnancy is harmful to the baby, and it is not generally recommended for use during a C-section.
In rare cases, repeated exposure to halothane in adults was noted to result in severe liver injury. This occurred in about one in 10,000 exposures. The resulting syndrome was referred to as halothane hepatitis, immunoallergic in origin, and is thought to result from the metabolism of halothane to trifluoroacetic acid via oxidative reactions in the liver. About 20% of inhaled halothane is metabolized by the liver and these products are excreted in the urine. The hepatitis syndrome had a mortality rate of 30% to 70%. Concern for hepatitis resulted in a dramatic reduction in the use of halothane for adults and it was replaced in the 1980s by enflurane and isoflurane. By 2005, the most common volatile anesthetics used were isoflurane, sevoflurane, and desflurane. Since the risk of halothane hepatitis in children was substantially lower than in adults, halothane continued to be used in pediatrics in the 1990s as it was especially useful for inhalation induction of anesthesia. However, by 2000, sevoflurane, excellent for inhalation induction, had largely replaced the use of halothane in children.
Halothane sensitises the heart to catecholamines, so it is liable to cause cardiac arrhythmia, occasionally fatal, particularly if hypercapnia has been allowed to develop. This seems to be especially problematic in dental anesthesia.
Like all the potent inhalational anaesthetic agents, it is a potent trigger for malignant hyperthermia. Similarly, in common with the other potent inhalational agents, it relaxes uterine smooth muscle and this may increase blood loss during delivery or termination of pregnancy. | 0 | Theoretical and Fundamental Chemistry |
Heat engines are not the most efficient ones, and with the use of bimetallic strips the efficiency of the heat engine is even lower as there is no chamber to contain the heat. Moreover, the bimetallic strips cannot produce strength in its moves, the reason why is that in order to achieve reasonables bendings (movements) both metallic strips have to be thin to make the difference between the expansion noticeable. So the uses for metallic strips in heat engines are mostly in simple toys that have been built to demonstrate how the principle can be used to drive a heat engine. | 1 | Applied and Interdisciplinary Chemistry |
The electron that is captured is one of the atom's own electrons, and not a new, incoming electron, as might be suggested by the way the reactions are written below. A few examples of electron capture are:
Radioactive isotopes that decay by pure electron capture can be inhibited from radioactive decay if they are fully ionized ("stripped" is sometimes used to describe such ions). It is hypothesized that such elements, if formed by the r-process in exploding supernovae, are ejected fully ionized and so do not undergo radioactive decay as long as they do not encounter electrons in outer space. Anomalies in elemental distributions are thought to be partly a result of this effect on electron capture. Inverse decays can also be induced by full ionisation; for instance, decays into by electron capture; however, a fully ionised decays into a bound state of by the process of bound-state β decay.
Chemical bonds can also affect the rate of electron capture to a small degree (in general, less than 1%) depending on the proximity of electrons to the nucleus. For example, in Be, a difference of 0.9% has been observed between half-lives in metallic and insulating environments. This relatively large effect is due to the fact that beryllium is a small atom that employs valence electrons that are close to the nucleus, and also in orbitals with no orbital angular momentum. Electrons in s orbitals (regardless of shell or primary quantum number), have a probability antinode at the nucleus, and are thus far more subject to electron capture than p or d electrons, which have a probability node at the nucleus.
Around the elements in the middle of the periodic table, isotopes that are lighter than stable isotopes of the same element tend to decay through electron capture, while isotopes heavier than the stable ones decay by electron emission. Electron capture happens most often in the heavier neutron-deficient elements where the mass change is smallest and positron emission is not always possible. When the loss of mass in a nuclear reaction is greater than zero but less than the process cannot occur by positron emission, but occurs spontaneously for electron capture. | 0 | Theoretical and Fundamental Chemistry |
Dextromethorphan (DXM) is a cough suppressant used in many cough and cold medicines. It affects serotonin, norepinephrine, NMDA, and sigma-1 receptors in the brain, all of which have been implicated in the pathophysiology of depression. In 2022, the FDA approved the combination dextromethorphan/bupropion to serve as a rapid acting antidepressant in patients with major depressive disorder.
It is in the morphinan class of medications with sedative, dissociative, and stimulant properties (at lower doses). Dextromethorphan does not have a significant affinity for the mu-opioid receptor activity typical of morphinan compounds and exerts its therapeutic effects through several other receptors. In its pure form, dextromethorphan occurs as a white powder.
When exceeding approved dosages, dextromethorphan acts as a dissociative hallucinogen. It has multiple mechanisms of action, including actions as a nonselective serotonin reuptake inhibitor and a sigma-1 receptor agonist. Dextromethorphan and its major metabolite, dextrorphan, also block the NMDA receptor at high doses, which produces effects similar to other dissociative anesthetics such as ketamine, nitrous oxide, and phencyclidine.
It was patented in 1949 and approved for medical use in 1953. | 0 | Theoretical and Fundamental Chemistry |
In 2002, J. Macdonald, D. Stefanović and M. Stojanović created a DNA computer able to play tic-tac-toe against a human player. The calculator consists of nine bins corresponding to the nine squares of the game. Each bin contains a substrate and various combinations of DNA enzymes. The substrate itself is composed of a DNA strand onto which was grafted a fluorescent chemical group at one end, and the other end, a repressor group. Fluorescence is only active if the molecules of the substrate are cut in half. The DNA enzymes simulate logical functions. For example, such a DNA will unfold if two specific types of DNA strand are introduced to reproduce the logic function AND.
By default, the computer is considered to have played first in the central square. The human player starts with eight different types of DNA strands corresponding to the eight remaining boxes that may be played. To play box number i, the human player pours into all bins the strands corresponding to input #i. These strands bind to certain DNA enzymes present in the bins, resulting, in one of these bins, in the deformation of the DNA enzymes which binds to the substrate and cuts it. The corresponding bin becomes fluorescent, indicating which box is being played by the DNA computer. The DNA enzymes are divided among the bins in such a way as to ensure that the best the human player can achieve is a draw, as in real tic-tac-toe. | 1 | Applied and Interdisciplinary Chemistry |
Locascio attended James Madison University from 1979 to 1983 where she earned her B.Sc. in chemistry with a minor in biochemistry. In 1982, Locascio was a research assistant in the department of chemistry at West Virginia University. She attended the University of Utah from 1983 to 1986 while working as a research assistant in the department of bioengineering. Locascio completed her M.Sc. in bioengineering in 1986.
From 1986 to 1999, Locascio was a research biomedical engineer in the molecular spectroscopy and microfluidic methods group in the analytical chemistry division of the National Institute of Standards and Technology (NIST). She received a certificate of recognition from the United States Department of Commerce in 1987, 1989, and 1990. Locascio was awarded the Department of Commerce Bronze Medal in 1991. While working at NIST, she was encouraged by her manager Willie E. May and mentor Richard Durst to pursue a doctoral degree. From 1995 to 1999, Locascio completed a Ph.D. in toxicology at the University of Maryland School of Medicine. At the University of Maryland, Katherine S. Squibb and Bruce O. Fowler, the director of the toxicology program, supported Locascios efforts to attend graduate school while also working at NIST. Her dissertation was titled Miniaturization of bioassays for analytical toxicology'. Cheng S. Lee was her doctoral advisor and Mohyee E. Eldefrawi served on her advisory committee. | 0 | Theoretical and Fundamental Chemistry |
A stable configuration is desirable not only in sailing, but in aircraft design as well. Aircraft design therefore borrowed the term center of pressure. And like a sail, a rigid non-symmetrical airfoil not only produces lift, but a moment.
The center of pressure of an aircraft is the point where all of the aerodynamic pressure field may be represented by a single force vector with no moment. A similar idea is the aerodynamic center which is the point on an airfoil where the pitching moment produced by the aerodynamic forces is constant with angle of attack.
The aerodynamic center plays an important role in analysis of the longitudinal static stability of all flying machines. It is desirable that when the pitch angle and angle of attack of an aircraft are disturbed (by, for example wind shear/vertical gust) that the aircraft returns to its original trimmed pitch angle and angle of attack without a pilot or autopilot changing the control surface deflection. For an aircraft to return towards its trimmed attitude, without input from a pilot or autopilot, it must have positive longitudinal static stability. | 1 | Applied and Interdisciplinary Chemistry |
In the radiopharmaceutical industry, fluorine-18 is made using either a cyclotron or linear particle accelerator to bombard a target, usually of natural or enriched [O]water with high energy protons (typically ~18 MeV). The fluorine produced is in the form of a water solution of [F]fluoride, which is then used in a rapid chemical synthesis of various radio pharmaceuticals. The organic oxygen-18 pharmaceutical molecule is not made before the production of the radiopharmaceutical, as high energy protons destroy such molecules (radiolysis). Radiopharmaceuticals using fluorine must therefore be synthesized after the fluorine-18 has been produced. | 1 | Applied and Interdisciplinary Chemistry |
Enzymes can use cofactors as ‘helper molecules’. Coenzymes are referred to those non-protein molecules that bind with enzymes to help them fulfill their jobs. Mostly they are connected to the active site by non-covalent bonds such as hydrogen bond or hydrophobic interaction. But sometimes a covalent bond can also form between them. For example, the heme in cytochrome C is bound to the protein through thioester bond. In some occasions, coenzymes can leave enzymes after the reaction is finished. Otherwise, they permanently bind to the enzyme. Coenzyme is a broad concept which includes metal ions, various vitamins and ATP. If an enzyme needs coenzyme to work itself, it is called an apoenzyme. In fact, it alone cannot catalyze reactions properly. Only when its cofactor comes in and binds to the active site to form holoenzyme does it work properly.
One example of the coenzyme is Flavin. It contains a distinct conjugated isoalloxazine ring system. Flavin has multiple redox states and can be used in processes that involve the transfer of one or two electrons. It can act as an electron acceptor in reaction, like the oxidation of NAD to NADH, to accept two electrons and form 1,5-dihydroflavin. On the other hand, it can form semiquinone(free radical) by accepting one electron, and then converts to fully reduced form by the addition of an extra electron. This property allows it to be used in one electron oxidation process. | 1 | Applied and Interdisciplinary Chemistry |
Evapoporometry is a method used to determine pore-size in synthetic membranes. Based on the Kelvin equation, this technique is most accurate for detection of pore diameters between 4 nm to 150 nm. | 0 | Theoretical and Fundamental Chemistry |
The toxicity of palytoxin is due to its binding to external part of Na/K-ATPase (the sodium–potassium pump), where it interacts with the natural binding site of ouabain with very high affinity. Na/K-ATPase is a transmembrane protein, which is found on the surface of every vertebrate cell. The sodium–potassium pump is necessary for viability of all cells, and this explains the fact that palytoxin affects all cells. Through this channel, which it forms within the sodium–potassium pump, monovalent positive ions such as sodium and potassium can diffuse freely, thereby destroying the ion gradient of the cell. Once palytoxin is bound to the pump, it flips constantly between open and normal conformations. The open conformation is more likely (over 90% probability). If palytoxin detaches, the pump will return to closed conformation. In open conformation, millions of ions diffuse through the pump per second, whereas only about one hundred ions per second are transported through a normally functioning transporter.
Loss of ion gradient leads to death and hemolysis of red blood cells, for example, and also to violent contractions of heart and other muscle cells.
First evidence of the mechanism described above was obtained in 1981 and the proposed mechanism was published in 1982. Because the mechanism of action of palytoxin was so unlike any other, it was initially not widely accepted. This was primarily because it was not expected that a pump which provides active transport, could become an ion channel by binding of a compound such as palytoxin. Therefore, there were some alternative hypotheses, which were reviewed by Frelin and van Renterghem in 1995. The breakthrough research which is seen as proof for the sodium–potassium pump mechanism was performed in yeast cells (Saccharomyces cerevisiae). These cells do not have the sodium–potassium pump, and hence palytoxin does not affect them. But once they were given the DNA to encode for complete sheep Na/K-ATPase, they were killed by palytoxin. | 0 | Theoretical and Fundamental Chemistry |
* Alcan Lynemouth Aluminium Smelter, powered by the coal-fired Lynemouth Power Station in North East England, ceased production in 2012, demolished in 2018.
* Anglesey Aluminium, powered by Wylfa nuclear power station in north-west Wales, closed in 2013, with redevelopment of the site announced in 2022.
* The Valco aluminium smelter in Ghana, powered by the Akosombo Hydroelectric Project
* Fjarðaál in Iceland, powered by the Kárahnjúkar Hydropower Plant
* Jharsuguda in Orissa, India, to be powered by its own coal-fired power station.
* Aluminerie Alouette in Sept-Îles, Québec, powered by the Churchill Falls Hydro Electric project.
* Alba Smelter in Bahrain, powered by its own four power stations with a total generating capacity of . | 1 | Applied and Interdisciplinary Chemistry |
Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which burns and produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas made them a serious hazard. The presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition. Carbide lamps were still used extensively in slate, copper, and tin mines where methane is not a serious hazard. Most miners' lamps have now been replaced by electric lamps.
Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are also still used by some cavers exploring caves and other underground areas, although they are increasingly being replaced in this use by LED lights.
Carbide lamps were also used extensively as headlamps in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps. | 1 | Applied and Interdisciplinary Chemistry |
In Swedish Uppland north of Stockholm and certain adjacent provinces, another kind known as the Walloon forge was used, mainly for the production of a particularly pure kind of iron known as oregrounds iron, which was exported to England to make blister steel. Its purity depended on the use of ore from the Dannemora mine. The Walloon forge was virtually the only kind used in Great Britain.
The forge had two kinds of hearths, the finery to finish the product and the chafery to reheat the bloom that was the raw material of the process. | 1 | Applied and Interdisciplinary Chemistry |
The overall pressure loss caused by an orifice plate is less than the differential pressure measured across tappings near the plate. For sharp-edged plates such as corner, flange or D and D/2 tappings, it can be approximated by the equation
or<br /> | 1 | Applied and Interdisciplinary Chemistry |
Terpenoids facilitate communication between plants and insects, mammals, fungi, microorganisms, and other plants. Terpenoids may act as both attractants and repellants for various insects. For example, pine shoot beetles (Tomicus piniperda) are attracted to certain monoterpenes ( (+/-)-a-pinene, (+)-3-carene and terpinolene) produced by Scots pines (Pinus sylvestris), while being repelled by others (such as verbenone).
Terpenoids are a large family of biological molecules with over 22,000 compounds. Terpenoids are similar to terpenes in their carbon skeleton but unlike terpenes contain functional groups. The structure of terpenoids is described by the biogenetic isoprene rule which states that terpenoids can be thought of being made of isoprenoid subunits, arranged either regularly or irregularly. The biosynthesis of terpenoids occurs via the methylerythritol phosphate (MEP) and mevalonic acid(MVA) pathways both of which include isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) as key components. The MEP pathway produces hemiterpenes, monoterpenes, diterpenes, and volatile carotenoid derivatives while the MVA pathway produces sesquiterpenes. | 1 | Applied and Interdisciplinary Chemistry |
Plastic crystals behave like true plastic metals under mechanical stress.
For example, closer to melting, plastic crystals show high ductility and/or malleability. Plastic crystals can flow through a hole under pressure. For example, aminoborane plastic crystals bend, twist and stretch with characteristic necking, under appropriate stress. These crystals can be literally shaped into any possible way, like copper or silver metals.
This way, they are very unique compared to other molecular crystals, which are generally brittle and fragile. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (−OH) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.
Phenols are both synthesized industrially and produced by plants and microorganisms. | 0 | Theoretical and Fundamental Chemistry |
Tetramethylazodicarboxamide (also known as TMAD and diamide) is a reagent used in biochemistry for oxidation of thiols in proteins to disulfides. It has also been used as a reagent in the Mitsunobu reaction in place of diethyl azodicarboxylate. | 0 | Theoretical and Fundamental Chemistry |
The situation on rough surfaces is much more complicated. The main characteristic of the wetting properties of rough surfaces is the so-called apparent contact angle (APCA). It is well known that the APCA usually measured are different from those predicted by the Young equation. Two main hypotheses were proposed in order to explain this discrepancy, namely the Wenzel and Cassie wetting models. According to the traditional Cassie model, air can remain trapped below the drop, forming "air pockets". Thus, the hydrophobicity of the surface is strengthened because the drop sits partially on air. On the other hand, according to the Wenzel model the roughness increases the area of a solid surface, which also geometrically modifies the wetting properties of this surface. Transition from Cassie to Wenzel regime is also called wetting transition. Under certain external stimuli, such as pressure or vibration, the Cassie air trapping wetting state could be converted into the Wenzel state. Apart from external stimuli, intrinsic contact angle of the liquid (below or above 90 degree), liquid volatility, structure of cavities (reentrant or non-reentrant, connected or unconnected) are known to be important factors determining the rate of wetting transition. It is well accepted that the Cassie air trapping wetting regime corresponds to a higher energetic state, and the Cassie–Wenzel transition is irreversible. However, the mechanism of the transition remains unclear. It was suggested that the Cassie–Wenzel transition occurs via a nucleation mechanism starting from the drop center. On the other hand, recent experiments showed that the Cassie–Wenzel transition is more likely to be due to the displacement of a triple line under an external stimulus. The existence of so-called impregnating Cassie wetting state also has to be considered. Understanding wetting transitions is of a primary importance for design of superhydrophobic surfaces. | 0 | Theoretical and Fundamental Chemistry |
During assaying, the value of copper and the value of gold in the ore is determined and a monetary value per tonne is placed on the material. When this value exceeds a particular threshold, workers start processing the material.
Subsequently, the material is processed through a mill where the minerals get floated. In particular, the copper and gold minerals both float and are then concentrated. This process, called upgrading, creates a concentrated material that is approximately 23% copper. Gold is also captured in the concentrate. | 1 | Applied and Interdisciplinary Chemistry |
Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also often used as a dehydrating or oxidizing agent in industrial reactions, such as the dehydration of various sugars to form solid carbon. | 0 | Theoretical and Fundamental Chemistry |
There are numerous wastewater treatment technologies. A wastewater treatment train can consist of a primary clarifier system to remove solid and floating materials, a secondary treatment system consisting of an aeration basin followed by flocculation and sedimentation or an activated sludge system and a secondary clarifier, a tertiary biological nitrogen removal system, and a final disinfection process. The aeration basin/activated sludge system removes organic material by growing bacteria (activated sludge). The secondary clarifier removes the activated sludge from the water. The tertiary system, although not always included due to costs, is becoming more prevalent to remove nitrogen and phosphorus and to disinfect the water before discharge to a surface water stream or ocean outfall. | 1 | Applied and Interdisciplinary Chemistry |
Three proteinaceous iron–sulfur reaction centers are found in PSI. Labeled F, F, and F, they serve as electron relays. F and F are bound to protein subunits of the PSI complex and F is tied to the PSI complex. Various experiments have shown some disparity between theories of iron–sulfur cofactor orientation and operation order. In one model, F passes an electron to F, which passes it on to F to reach the ferredoxin. | 0 | Theoretical and Fundamental Chemistry |
Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity. It is used to understand how different parts of the brain respond to external stimuli or passive activity in a resting state, and has applications in behavioral and cognitive research, and in planning neurosurgery of eloquent brain areas. Researchers use statistical methods to construct a 3-D parametric map of the brain indicating the regions of the cortex that demonstrate a significant change in activity in response to the task. Compared to anatomical T1W imaging, the brain is scanned at lower spatial resolution but at a higher temporal resolution (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via T changes; this mechanism is referred to as the BOLD (blood-oxygen-level dependent) effect. Increased neural activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated hemoglobin relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.
While BOLD signal analysis is the most common method employed for neuroscience studies in human subjects, the flexible nature of MR imaging provides means to sensitize the signal to other aspects of the blood supply. Alternative techniques employ arterial spin labeling (ASL) or weighting the MRI signal by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method requires injection of a class of MRI contrast agents that are now in human clinical trials. Because this method has been shown to be far more sensitive than the BOLD technique in preclinical studies, it may potentially expand the role of fMRI in clinical applications. The CBF method provides more quantitative information than the BOLD signal, albeit at a significant loss of detection sensitivity. | 0 | Theoretical and Fundamental Chemistry |
Good operation and maintenance (O&M) is essential for the long-term sustainability of any sewerage system, but particularly for simplified sewerage, since the small diameter of pipes and low gradients make the system highly vulnerable to clogging. Solids can readily block the small diameter piping and the shallow grade of pipe alignment prevents sewage flow from reaching scouring velocity, meaning that solids fall out of suspension and depositing within the low gradient pipe before reaching the downstream receiving body.
The original concept of householders being responsible for O&M of in-block condominial sewers has not worked well in the long term. A study of simplified sewerage systems in Brazil has shown that effective maintenance of sewers by utilities has often been the result of community pressure by neighborhood associations. Without such pressure maintenance by utilities has often been inadequate, and community maintenance has not come about either.
Few situation exist where simplified sewers are appropriate sanitation solutions to install. Therefore, alternative management systems had to be developed to mitigate the high issues of simplified sewers, and a few examples are provided below:
* In rural Ceará a villager is employed by the Residents’ Association to maintain the sewers and the wastewater treatment plant (typically, a single facultative waste stabilization pond). He is also responsible for the water supply.
* In parts of Recife in northeast Brazil the state water and sewerage company employs local contracting firms for O&M. Usually this is done by a small team comprising a technician engineer and two laborers who work in a low-income area served by simplified sewerage and to whom residents report any problems.
* In Brasília the water and sewerage company, which has over 1,200 km of condominial sewers, uses van-mounted water jet units to clear any blockages.
Concerning maintenance costs, available information indicates similar costs and requirements for the simplified and the conventional system under the same conditions. Simplified systems typically require more interventions, but the cost per intervention is lower. Comparative analytical studies are not yet available, however. | 1 | Applied and Interdisciplinary Chemistry |
He is the Director of Center for Chemistry at the Space-Time Limit, a National Science Foundation Center for Chemical Innovation. He graduated from University of Southern California with B.S. degrees in Chemistry followed by Ph.D. degree in chemistry from Northwestern University. Following a postdoctoral fellowship at Cornell University, he joined the University of California as Chemistry faculty in 1983. He served as the Chair of the Chemistry Department (2004-2007) at UC Irvine.
He is a Foreign Member of the National Academy of Sciences of Armenia, and a Fellow of American Physical Society, American Association for the Advancement of Sciences. His teaching and research has been recognized with awards including the Humboldt Prize (1996), USC Distinguished Alumnus (2007), Charles Bennett Service Through Chemistry Award of ACS (2008) ACS Award in Experimental Physical Chemistry (2014), Honorary Doctorate from the University of Jyväskylä, Finland (2016).
His recent scientific contributions include creating a single-molecule sensor and developing tools to confine the light to atomic dimensions. His team visualized the internal structure of single molecules and imaging the normal vibrational modes of single molecules. | 0 | Theoretical and Fundamental Chemistry |
* 1.H.1 The Claudin Tight Junction (Claudin1) Family
* 1.H.2 The Invertebrate PMP22-Claudin (Claudin2) Family | 1 | Applied and Interdisciplinary Chemistry |
NAPPA uses DNA template that has already been immobilized onto the same protein capture surface. The DNA template is biotinylated and is bound to avidin that is pre-coated onto the protein capture surface. Newly synthesized proteins which are tagged with GST are then immobilized next to the template DNA by binding to the adjacent polyclonal anti-GST capture antibody that is also pre-coated onto the capture surface. The main drawback of this method is the extra and tedious preparation steps at the beginning of the process: (1) the cloning of cDNAs in an expression-ready vector; and (2) the need to biotinylate the plasmid DNA but not to interfere with transcription. Moreover, the resulting protein array is not ‘pure’ because the proteins are co-localized with their DNA templates and capture antibodies. | 1 | Applied and Interdisciplinary Chemistry |
The relative static permittivity of a solvent is a relative measure of its chemical polarity. For example, water is very polar, and has a relative static permittivity of 80.10 at 20 °C while n-hexane is non-polar, and has a relative static permittivity of 1.89 at 20 °C. This information is important when designing separation, sample preparation and chromatography techniques in analytical chemistry.
The correlation should, however, be treated with caution. For instance, dichloromethane has a value of ε of 9.08 (20 °C) and is rather poorly soluble in water (13g/L or 9.8mL/L at 20 °C); at the same time, tetrahydrofuran has its ε = 7.52 at 22 °C, but it is completely miscible with water. In the case of tetrahydrofuran, the oxygen atom can act as a hydrogen bond acceptor; whereas dichloromethane cannot form hydrogen bonds with water.
This is even more remarkable when comparing the ε values of acetic acid (6.2528) and that of iodoethane (7.6177). The large numerical value of ε is not surprising in the second case, as the iodine atom is easily polarizable; nevertheless, this does not imply that it is polar, too (electronic polarizability prevails over the orientational one in this case). | 0 | Theoretical and Fundamental Chemistry |
A histone fold is a structurally conserved motif found near the C-terminus in every core histone sequence in a histone octamer responsible for the binding of histones into heterodimers.
The histone fold averages about 70 amino acids and consists of three alpha helices connected by two short, unstructured loops. When not in the presence of DNA, the core histones assemble into head-to-tail intermediates (H3 and H4 first assemble into heterodimers then fuse two heterodimers to form a tetramer, while H2A and H2B form heterodimers) via extensive hydrophobic interactions between each histone fold domain in a "handshake motif". Also the histone fold was first found in TATA box-binding protein-associated factors, which is a main component in transcription.
The histone fold's evolution can be found by different combinations of ancestral sets of peptides that make up helix-strand-helix motif that come from the three folds from the ancestral fragments. These peptide chains can be found in the archaeal histones, which could have come from eukaryotic H3-H4 tetramer. The archaeal single-chain histones are also found in the bacterium Aquifex aeolicus. Which helps the diverse bacteria phylogeny coming from the ancestry of eukaryotes and archaea with lateral gene transfers to get to the bacteria. These lead into the octamer articulated protein endoskeleton for DNA compaction. From this endoskeleton it has a central segment that folds for the histone dimerization. This then leads into the end segments of the fold to make properties of dimer-dimer contacts that also cap the protein super helix at the octamer.
One species that looked at is Drosophila, and in the subunits of the Drosophila transcription initiation factor has specific amino acid sequences that have different characteristics of the histone folds that make up the two proteins make up the subunits. When just looking at the histone fold motif in the Drosophila the protein-protein and the protein DNA interaction of the core histone proteins can be found by looking at the non-histone proteins. This can then be used in “Structural studies on the TAFII42/TAFII62 complex from Drosophila and HMfB from Methanococcus fervidus, proteins identified as containing the histone fold in the aforementioned searches, confirmed that a histone-like substructure exists in these proteins, with the individual proteins folding into the canonical histone fold motif”. The evolutionary structure and range of the histone protein-protein and DNA-protein interactions of the histone fold proteins has a very wide range of evolutionary traits that form the structures and other proteins.
Histone folds play a role in the nucleosomal core particle by conserving histone interactions when looking at interface surfaces. These contain more than one histone fold. The structure of the nucleosome core particle has two modes that have the largest interaction surfaces with are in groups H3-H4 and H2A-H2B heterotypic dimer interactions. When looking at the H2A-H2A structure it has a modification of the loop at the interface that excludes it from clustering with the same interface of other structures. Which makes it have a different function in the transcriptional activation. Also the two modes are distinct due to having the longest helix chains. These use the handshake interactions between the two histone folds, while they also use it to make themselves unique comparted to the rest of the modes. Similarly modes 5 and 7 of the core nucleosome particle use two types of histone fold dimers which show that all histone domains share a similar structural motif to be able to be able to interact with one another and to interact in different ways. Showing how flexible and adaptive the structure of histones are.
H4 and H2A can form an internucleosomal contacts that can be acetylated to be able to perform ionic interactions between two peptides, which in turn could change the surrounding internucleosomal contacts that can make a way to opening the chromatin. | 1 | Applied and Interdisciplinary Chemistry |
Phosphatases act in opposition to kinases/phosphorylases, which add phosphate groups to proteins. The addition of a phosphate group may activate or de-activate an enzyme (e.g., kinase signalling pathways) or enable a protein-protein interaction to occur (e.g., SH2 domains ); therefore phosphatases are integral to many signal transduction pathways. Phosphate addition and removal do not necessarily correspond to enzyme activation or inhibition, and that several enzymes have separate phosphorylation sites for activating or inhibiting functional regulation. CDK, for example, can be either activated or deactivated depending on the specific amino acid residue being phosphorylated. Phosphates are important in signal transduction because they regulate the proteins to which they are attached. To reverse the regulatory effect, the phosphate is removed. This occurs on its own by hydrolysis, or is mediated by protein phosphatases.
Protein phosphorylation plays a crucial role in biological functions and controls nearly every cellular process, including metabolism, gene transcription and translation, cell-cycle progression, cytoskeletal rearrangement, protein-protein interactions, protein stability, cell movement, and apoptosis. These processes depend on the highly regulated and opposing actions of PKs and PPs, through changes in the phosphorylation of key proteins. Histone phosphorylation, along with methylation, ubiquitination, sumoylation and acetylation, also regulates access to DNA through chromatin reorganisation.
One of the major switches for neuronal activity is the activation of PKs and PPs by elevated intracellular calcium. The degree of activation of the various isoforms of PKs and PPs is controlled by their individual sensitivities to calcium. Furthermore, a wide range of specific inhibitors and targeting partners such as scaffolding, anchoring, and adaptor proteins also contribute to the control of PKs and PPs and recruit them into signalling complexes in neuronal cells. Such signalling complexes typically act to bring PKs and PPs in close proximity with target substrates and signalling molecules as well as enhance their selectivity by restricting accessibility to these substrate proteins. Phosphorylation events, therefore, are controlled not only by the balanced activity of PKs and PPs but also by their restricted localisation. Regulatory subunits and domains serve to restrict specific proteins to particular subcellular compartments and to modulate protein specificity. These regulators are essential for maintaining the coordinated action of signalling cascades, which in neuronal cells include short-term (synaptic) and long-term (nuclear) signalling. These functions are, in part, controlled by allosteric modification by secondary messengers and reversible protein phosphorylation.
It is thought that around 30% of known PPs are present in all tissues, with the rest showing some level of tissue restriction. While protein phosphorylation is a cell-wide regulatory mechanism, recent quantitative proteomics studies have shown that phosphorylation preferentially targets nuclear proteins. Many PPs that regulate nuclear events, are often enriched or exclusively present in the nucleus. In neuronal cells, PPs are present in multiple cellular compartments and play a critical role at both pre- and post-synapses, in the cytoplasm and in the nucleus where they regulate gene expression.
Phosphoprotein phosphatase is activated by the hormone insulin, which indicates that there is a high concentration of glucose in the blood. The enzyme then acts to dephosphorylate other enzymes, such as phosphorylase kinase, glycogen phosphorylase, and glycogen synthase. This leads to phosphorylase kinase and glycogen phosphorylase's becoming inactive, while glycogen synthase is activated. As a result, glycogen synthesis is increased and glycogenolysis is decreased, and the net effect is for energy to enter and be stored inside the cell. | 1 | Applied and Interdisciplinary Chemistry |
Shotgun lipidomics was developed by Richard W. Gross and Xianlin Han, by employing ESI intrasource separation techniques. Individual molecular species of most major and many minor lipid classes can be fingerprinted and quantitated directly from biological lipid extracts without the need for chromatographic purification. | 1 | Applied and Interdisciplinary Chemistry |
With 800,000 years of Azolla bloom episodes and a basin to cover, even by very conservative estimates more than enough carbon could be sequestered by plant burial to account for the observed 80% drop in CO by this one phenomenon alone. Other factors almost certainly played a role. This drop initiated the switch from a greenhouse to the current icehouse Earth; the Arctic cooled from an average sea-surface temperature of 13 °C to todays −9 °C, and the rest of the globe underwent a similar change. For perhaps the first time in its history, the planet had ice caps at both of its poles. A geologically rapid decrease in temperature between 49 and , around the Azolla' event, is evident; dropstones (which are taken as evidence for the presence of glaciers) are common in Arctic sediments thereafter. This is set against a backdrop of gradual, long-term cooling; it is not until that evidence for widespread northern polar freezing is common. | 1 | Applied and Interdisciplinary Chemistry |
A post-metallocene catalyst is a kind of catalyst for the polymerization of olefins, i.e., the industrial production of some of the most common plastics. "Post-metallocene" refers to a class of homogeneous catalysts that are not metallocenes. This area has attracted much attention because the market for polyethylene, polypropylene, and related copolymers is large. There is a corresponding intense market for new processes as indicated by the fact that, in the US alone, 50,000 patents were issued between 1991-2007 on polyethylene and polypropylene.
Many methods exist to polymerize alkenes, including the traditional routes using Philips catalyst and traditional heterogeneous Ziegler-Natta catalysts, which still are used to produce the bulk of polyethylene. | 0 | Theoretical and Fundamental Chemistry |
In 1856, Rudolf Clausius, referring to closed systems, in which transfers of matter do not occur, defined the second fundamental theorem (the second law of thermodynamics) in the mechanical theory of heat (thermodynamics): "if two transformations which, without necessitating any other permanent change, can mutually replace one another, be called equivalent, then the generations of the quantity of heat Q from work at the temperature T, has the equivalence-value:"
In 1865, he came to define the entropy symbolized by S, such that, due to the supply of the amount of heat Q at temperature T the entropy of the system is increased by
In a transfer of energy as heat without work being done, there are changes of entropy in both the surroundings which lose heat and the system which gains it. The increase, , of entropy in the system may be considered to consist of two parts, an increment, that matches, or compensates, the change, , of entropy in the surroundings, and a further increment, that may be considered to be generated or produced in the system, and is said therefore to be uncompensated. Thus
This may also be written
The total change of entropy in the system and surroundings is thus
This may also be written
It is then said that an amount of entropy has been transferred from the surroundings to the system. Because entropy is not a conserved quantity, this is an exception to the general way of speaking, in which an amount transferred is of a conserved quantity.
From the second law of thermodynamics it follows that in a spontaneous transfer of heat, in which the temperature of the system is different from that of the surroundings:
For purposes of mathematical analysis of transfers, one thinks of fictive processes that are called reversible, with the temperature of the system being hardly less than that of the surroundings, and the transfer taking place at an imperceptibly slow rate.
Following the definition above in formula (), for such a fictive reversible process, a quantity of transferred heat (an inexact differential) is analyzed as a quantity , with (an exact differential):
This equality is only valid for a fictive transfer in which there is no production of entropy, that is to say, in which there is no uncompensated entropy.
If, in contrast, the process is natural, and can really occur, with irreversibility, then there is entropy production, with . The quantity was termed by Clausius the "uncompensated heat", though that does not accord with present-day terminology. Then one has
This leads to the statement
which is the second law of thermodynamics for closed systems.
In non-equilibrium thermodynamics that makes the approximation of assuming the hypothesis of local thermodynamic equilibrium, there is a special notation for this. The transfer of energy as heat is assumed to take place across an infinitesimal temperature difference, so that the system element and its surroundings have near enough the same temperature . Then one writes
where by definition
The second law for a natural process asserts that | 0 | Theoretical and Fundamental Chemistry |
Oxycholesterol or 5,6-epoxycholesterol is a form of oxidized cholesterol implicated in atherosclerosis. It is commonly formed from the reaction of fats and oxygen during high temperature cooking such as frying.
In a study about the effects of oxycholesterol in rabbits with induced hypercholesterolemia, it was shown that compared feeding rabbits cholesterol and unoxidized cholesterol, feeding rabbits oxycholesterol resulted in their developing much higher levels of total cholesterol and low-density lipoprotein cholesterol. It is also shown to increase the amount of homocysteine and asymmetric dimethylarginine levels in the rabbits. An abundance of homocysteine leads to an organism with greater chances of endothelial cell injury which can then lead to coronary artery disease. Asymmetric dimethylarginine is shown to cause adverse effects on humans in the form of cardiovascular and metabolic diseases. Therefore it was concluded that adding oxycholesterol into diets of animals with hypercholesterolemia increases endothelial dysfunction and inflammatory response. | 1 | Applied and Interdisciplinary Chemistry |
The method is based on the generated loops and the equations are simply mathematical representation of Kirchhoff's second law which states that the sum of the pressure-drops around any loop should be zero. Before using loops method the fundamental set of loops need to be found. Basically the fundamental set of loops can be found by constructing spanning tree for the network. The standard methods for producing spanning tree is based on a breadth-first search or on a depth-first search which are not so efficient for large networks, because the computing time of these methods is proportional to n, where n is the number of pipes in the network. More efficient method for large networks is the forest method and its computational time is proportional to n*logn.
The loops that are produced from the spanning tree are not the best set that could be produced. There is often significant overlap between loops with some pipes shared between several loops. This usually slows convergence, therefore the loops' reduction algorithm needs to be applied to minimize the loops overlapping. This is usually performed by replacing the loops in the original fundamental set by smaller loops produced by linear combination of the original set. | 1 | Applied and Interdisciplinary Chemistry |
The hydroxyl HO radicals is one of the main chemical species controlling the oxidizing capacity of the global Earth atmosphere. This oxidizing reactive species has a major impact on the concentrations and distribution of greenhouse gases and pollutants in the Earth atmosphere. It is the most widespread oxidizer in the troposphere, the lowest part of the atmosphere. Understanding HO variability is important to evaluating human impacts on the atmosphere and climate. The HO species has a lifetime in the Earth atmosphere of less than one second. Understanding the role of HO in the oxidation process of methane (CH) present in the atmosphere to first carbon monoxide (CO) and then carbon dioxide (CO) is important for assessing the residence time of this greenhouse gas, the overall carbon budget of the troposphere, and its influence on the process of global warming. The lifetime of HO radicals in the Earth atmosphere is very short, therefore HO concentrations in the air are very low and very sensitive techniques are required for its direct detection. Global average hydroxyl radical concentrations have been measured indirectly by analyzing methyl chloroform (CHCCl) present in the air. The results obtained by Montzka et al. (2011) shows that the interannual variability in HO estimated from CHCCl measurements is small, indicating that global HO is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases primarily oxidized by HO, as well as global photochemical model calculations. | 1 | Applied and Interdisciplinary Chemistry |
Faradaic losses are experienced by both electrolytic and galvanic cells when electrons or ions participate in unwanted side reactions. These losses appear as heat and/or chemical byproducts.
An example can be found in the oxidation of water to oxygen at the positive electrode in electrolysis. Some electrons are diverted to the production of hydrogen peroxide. The fraction of electrons so diverted represent a faradaic loss and vary in different apparatuses.
Even when the proper electrolysis products are produced, losses can still occur if the products are permitted to recombine. During water electrolysis, the desired products (H and O), could recombine to form water. This could realistically happen in the presence of catalytic materials such as platinum or palladium commonly used as electrodes. Failure to account for this Faraday-efficiency effect has been identified as the cause of the misidentification of positive results in cold fusion experiments.
Proton exchange membrane fuel cells provide another example of faradaic losses when some of the electrons separated from hydrogen at the anode leak through the membrane and reach the cathode directly instead of passing through the load and performing useful work. Ideally the electrolyte membrane would be a perfect insulator and prevent this from happening.
An especially familiar example of faradaic loss is the self-discharge that limits battery shelf-life. | 0 | Theoretical and Fundamental Chemistry |
A universal indicator is usually composed of water, 1-propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, sodium bisulfite, and thymol blue. The colours that indicate the pH of a solution, after adding a universal indicator, are:
The colors from yellow to red indicate an acidic solution, colours blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral.
Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased. | 0 | Theoretical and Fundamental Chemistry |
Selegiline belongs to the phenethylamine and amphetamine chemical families. It is also known as -deprenyl, as well as (R)-(–)-N,α-dimethyl-N-(2-propynyl)phenethylamine or (R)-(–)-N-methyl-N-2-propynylamphetamine. The compound is a derivative of levomethamphetamine (-methamphetamine) with a propargyl group attached to the nitrogen atom. This detail is borrowed from pargyline, an older MAO-B inhibitor of the phenylalkylamine group. Selegiline is the levorotatory enantiomer of the racemic mixture deprenyl.
Selegiline is synthesized by the alkylation of (–)-methamphetamine using propargyl bromide.
Another clinically used MAOI of the amphetamine class is tranylcypromine. | 0 | Theoretical and Fundamental Chemistry |
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