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Potassium thioacetate, which is commercially available, can be prepared by combining acetyl chloride and potassium hydrogen sulfide:
It arises also by the neutralization of thioacetic acid with potassium hydroxide. | 0 | Organic Chemistry |
The first intelectin was discovered in Xenopus laevis oocyte and is named XL35 or XCGL-1. X. laevis oocyte also contains a closely related XCGL-2. In addition, X. laevis embryos secrete Xenopus embryonic epidermal lectin into the environmental water, presumably to bind microbes. XSL-1 and XSL-2 are also expressed in X. laevis serum when stimulated with lipopolysaccharide. Two additional intestinal intelectins are discovered in X. laevis
Human has two intelectins: hIntL-1 (omentin) and hIntL-2. Mouse also has two intelectins: mIntL-1 and mIntL-2. | 1 | Biochemistry |
The use of RNA-dependent RNA polymerase plays a major role in RNA interference in eukaryotes, a process used to silence gene expression via small interfering RNAs (siRNAs) binding to mRNA rendering them inactive. Eukaryotic RdRp becomes active in the presence of dsRNA, and is a less widely distributed compared to other RNAi components as it lost in some animals, though still found in C. elegans and P. tetraurelia and plants. This presence of dsRNA triggers the activation of RdRp and RNAi processes by priming the initiation of RNA transcription through the introduction of siRNAs into the system. In C. elegans, siRNAs are integrated into the RNA-induced silencing complex, RISC, which works alongside mRNAs targeted for interference to recruit more RdRps to synthesize more secondary siRNAs and repress gene expression. | 1 | Biochemistry |
Oscillating binding energies of all surface chemical species introduces periodic instances of transient behavior to the catalytic surface. For slow oscillation frequencies, the transient period is only a small quantity of the oscillation time scale, and the surface reaction achieves a new steady state. However, as the oscillation frequency increases, the surface transient period approaches the timescale of the oscillation and the catalytic surface remains in a constant transient condition. A plot of the averaged turnover frequency of a reaction with respect to applied oscillation frequency identifies the resonant frequency range for which the transient conditions of the catalyst surface match the applied frequencies. The resonance band exists above the Sabatier volcano plot maximum of a static system with average reaction rates as high as five orders of magnitude faster than that achievable by conventional catalysis.
Surface binding energy oscillation also occurs to different extent with the various chemical surface species as defined by the γ parameter. For any non-unity γ system, the asymmetry in the surface energy profile results in conducting work to bias the reaction to a steady state away from equilibrium. Similar to the controlled directionality of molecular machines, the resulting ratchet (device) energy mechanism selectively moves molecules through a catalytic reaction against a free energy gradient.
Application of dynamic binding energy to a surface with multiple catalytic reactions exhibits complex behavior derived from the differences in the natural frequencies of each chemistry; these frequencies are identified by the inverse of the adsorption, desorption, and surface kinetic rate parameters. Considering a system of two parallel elementary reactions of A-to-B and A-to-C that only occur on a surface, the performance of the catalyst under dynamic conditions will result in varying capability for selecting either reaction product (B or C). For the depicted system, both reactions have the same overall thermodynamics and will produce B and C in equal amounts (50% selectivity) at chemical equilibrium. Under normal static catalyst operation, only product B can be produced at selectivities greater than 50% and product C is never favored. However, as shown, the application of surface binding dynamics in the form of a square wave at varying frequency and fixed oscillation amplitude but varying endpoints exhibits the full range of possible reactant selectivity. In the range of 1-10 Hertz, there exists a small island of parameters for which product C is highly selective; this condition is only accessible via dynamics. | 7 | Physical Chemistry |
A large research effort involves approaches to know whether proteins have binding sites which are specific for particular lipids and whether the protein–lipid complexes can be considered to be long-lived, on the order of the time required for the turnover a typical enzyme, that is 10 sec. This is now known through the use of H-NMR, ESR, and fluorescent methods.
There are two approaches used to measure the relative affinity of lipids binding to specific membrane proteins. These involve the use of lipid analogues in reconstituted phospholipid vesicles containing the protein of interest:
1) Spin-labeled phospholipids are motionally restricted when they are adjacent to membrane proteins. The result is a component in the ESR spectrum which is broadened. The experimental spectrum can be analyzed as the sum of the two components, a rapidly tumbling species in the "bulk" lipid phase with a sharp spectrum, and a motionally restricted component adjacent to the protein. Membrane protein denaturation causes further broadening of ESR spin label spectrum and throws more light on membrane lipid-proteins interactions
2) Spin-labeled and brominated lipid derivatives are able to quench the intrinsic tryptophan fluorescence from membrane proteins. The efficiency of quenching depends on the distance between the lipid derivative and the fluorescent tryptophans. | 1 | Biochemistry |
Neutral red (toluylene red, Basic Red 5, or C.I. 50040) is a eurhodin dye used for staining in histology. It stains lysosomes red. It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital staining of blood. Can be used for staining Golgi apparatus in cells and Nissl granules in neurons.
In microbiology, it is used in the MacConkey agar to differentiate bacteria for lactose fermentation.
[https://medium.com/@GSPChem/neutral-red-8d9c51584fa Neutral red] can be used as a vital stain. The Neutral Red Cytotoxicity Assay was first developed by Ellen Borenfreund in 1984. In the Neutral Red Assay live cells incorporate neutral red into their lysosomes. As cells begin to die, their ability to incorporate neutral red diminishes. Thus, loss of neutral red uptake corresponds to loss of cell viability. The neutral red is also used to stain cell cultures for plate titration of viruses.
Neutral red is added to some growth media for bacterial and cell cultures. It usually is available as a chloride salt.
Neutral red acts as a pH indicator, changing from red to yellow between pH 6.8 and 8.0. | 3 | Analytical Chemistry |
Protein catabolism produces amino acids that are used to form other proteins or oxidized to meet the energy needs of the cell. The amino acids that are produced by protein catabolism can then be further catabolized in amino acid catabolism. Among the several degradative processes for amino acids are Deamination (removal of an amino group), transamination (transfer of amino group), decarboxylation (removal of carboxyl group), and dehydrogenation (removal of hydrogen). Degradation of amino acids can function as part of a salvage pathway, whereby parts of degraded amino acids are used to create new amino acids, or as part of a metabolic pathway whereby the amino acid is broken down to release or recapture chemical energy. For example, the chemical energy that is released by oxidization in a dehydrogenation reaction can be used to reduce NAD to NADH, which can then be fed directly into the Krebs/Citric Acid (TCA) Cycle. | 1 | Biochemistry |
Pregnancy-specific biological substances, which include the placenta, umbilical cord, amniotic fluid, and amniotic membrane are being studied for a number of health uses. For example, Placental-derived stem cells are being studied so they can serve as a potential treatment method for cell therapy. Hepatocyte-like cells (HLC) are generated from differentiated human amniotic epithelial cells (hAEC) that are abundant in the placenta. HLC may replace hepatocytes for hepatocyte transplantation to treat acute or chronic liver damage.
Recent research has shown that the placenta and placenta derivatives are being regenerative cell therapies and also includes immunological features. Placenta structures consist of unique physiognomies. Placenta's structure not only regulates its function but also gives the probability of efficient use in clinics and in biotechnology.
According to a research study by Bhattacharya N., Anemia caused by Diabetes mellitus in patients with albuminuria can be treated with cord blood transfusion. The research showed increased in albumin per gram of creatinine that assessed for albuminuria for patients that received cord blood transfusions. | 1 | Biochemistry |
Absinthin is a naturally produced triterpene lactone from the plant Artemisia absinthium (Wormwood). It constitutes one of the most bitter chemical agents responsible for absinthes distinct taste. The compound shows biological activity and has shown promise as an anti-inflammatory agent, and should not be confused with thujone, a neurotoxin also found in Artemisia absinthium'. | 0 | Organic Chemistry |
Pulsatile insulin secretion from individual beta cells is driven by oscillation of the calcium concentration in the cells. In beta cells lacking contact (i.e. outside islet of Lagerhans), the periodicity of these oscillations is rather variable (2-10 min). However, within an islet of Langerhans, the oscillations become synchronized by electrical coupling between closely located beta cells that are connected by gap junctions, and the periodicity is more uniform (3-6 min). In addition to gap junctions, pulse coordination is managed by ATP signaling. α and δ cells in the pancreas also share secrete factors in a similar pulsatile manner. | 1 | Biochemistry |
Le Chatelier's principle refers to states of thermodynamic equilibrium. The latter are stable against perturbations that satisfy certain criteria; this is essential to the definition of thermodynamic equilibrium.
OR
It states that changes in the temperature, pressure, volume, or concentration of a system will result in predictable and opposing changes in the system in order to achieve a new equilibrium state.
For this, a state of thermodynamic equilibrium is most conveniently described through a fundamental relation that specifies a cardinal function of state, of the energy kind, or of the entropy kind, as a function of state variables chosen to fit the thermodynamic operations through which a perturbation is to be applied.
In theory and, nearly, in some practical scenarios, a body can be in a stationary state with zero macroscopic flows and rates of chemical reaction (for example, when no suitable catalyst is present), yet not in thermodynamic equilibrium, because it is metastable or unstable; then Le Chatelier's principle does not necessarily apply. | 7 | Physical Chemistry |
As it is known that survivin is over-expressed in most cancers, which may be contributing to the cancer cells' resistance to apoptotic stimuli from the environment. The use of antisense survivin therapy hopes to render cancer cells susceptible to apoptosis by eliminating survivin expression in the cancer cells.
Olie et al. developed different 20-mer phosphorothioate antisense oligonucleotides that target different regions in the mRNA of the survivin gene. The antisense function of the oligonucleotides allows binding to surviving mRNA and, depending on the region on which it binds, might inhibit surviving mRNA from being translated into a functional protein. Real-time PCR was used to assess the levels of mRNA present in a lung adenocarcinoma cell line A549 that overexpresses survivin. The best antisense oligonucleotide was identified that effectively down-regulated survivin mRNA levels and resulted in apoptosis of the cells. Survivin's role in cancer development in the context of a signaling pathway is its ability to inhibit activation of downstream caspase-3 and -7 from apoptosis inducing stimuli. The overexpression of survivin in tumors may serve to increase the tumors resistance to apoptosis and, thus, contribute to cell immortality even in the presence of death stimuli. In this experiment, the oligonucleotide 4003 that targets nucleotides 232-251 of survivin mRNA was found to be the most effective at down-regulating the levels of survivin mRNA in the A549 tumour line. The 4003 oligonucleotides were introduced into the tumour cells by transfection. Further experiments were then conducted on 4003. One of the additional experiments involved determining the dose-dependent effect of 4003 on the down-regulation of survivin mRNA levels. It was found that a concentration of 400 nM resulted in a maximum down-regulation of 70% of the initial survivin mRNA present. Another experiment on 4003 involved assessing any biological or cytotoxic effect 4003 down-regulation of survivin mRNA has on A549 cells using the MTT assay. The numbers of A549 cells transfected with 4003 significantly decreased with increasing concentration of 4003 compared to cells transfected either with a mismatch form of the 4003 or lipofectin control. Many physical observations that confirmed the induction of apoptosis by 4003 were made. For example, lysates of the 4003-treated cells showed increased levels of caspase-3-like protease activity; nuclei were observed to be condensed and chromatin was fragmented. | 1 | Biochemistry |
β-Hydroxy β-methylglutaryl-CoA (HMG-CoA), also known as 3-hydroxy-3-methylglutaryl coenzyme A, is an intermediate in the mevalonate and ketogenesis pathways. It is formed from acetyl CoA and acetoacetyl CoA by HMG-CoA synthase. The research of Minor J. Coon and Bimal Kumar Bachhawat in the 1950s at University of Illinois led to its discovery.
HMG-CoA is a metabolic intermediate in the metabolism of the branched-chain amino acids, which include leucine, isoleucine, and valine. Its immediate precursors are β-methylglutaconyl-CoA (MG-CoA) and β-hydroxy β-methylbutyryl-CoA (HMB-CoA).
HMG-CoA reductase catalyzes the conversion of HMG-CoA to mevalonic acid, a necessary step in the biosynthesis of cholesterol. | 1 | Biochemistry |
Hoveyda and Schrock have developed a catalyst for ring-closing metathesis kinetic resolution of dienyl allylic alcohols. The molybdenum alkylidene catalyst selectively catalyzes one enantiomer to perform ring closing metathesis, resulting in an enantiopure alcohol, and an enantiopure closed ring, as shown below. The catalyst is most effective at resolving 1,6-dienes. However, slight structural changes in the substrate, such as increasing the inter-alkene distance to 1,7, can sometimes necessitate the use of a different catalyst, reducing the efficacy of this method. | 4 | Stereochemistry |
The unique metabolism of acetogens has significant applications in biotechnology. In carbohydrate fermentations, the decarboxylation reactions end up in the conversion of organic carbon into carbon dioxide, the main greenhouse gas. This release is no longer compatible with the need to minimize the world CO emissions. It is not only an environmental concern but also not economically profitable in the frame of the biofuel competition with fossil fuels. Acetogens can ferment glucose without CO emission and convert one glucose molecule into three molecules of acetic acid, increasing the production yield of this latter by 50%. Acetogenesis does not replace glycolysis with a different pathway, but rather captures the CO from glycolysis and uses it for acetogenesis. Although three molecules of acetic acid can be produced in this way, the production of three molecules of ethanol would require an additional reducing agent such as hydrogen gas. | 1 | Biochemistry |
CRTC2, initially called TORC2, is a transcriptional coactivator for the transcription factor CREB and a central regulator of
gluconeogenic gene expression in response to cAMP. CRTC2 is thought to drive tumorigenesis in STK11(LKB1)-null non-small cell lung cancers (NSCLC). | 1 | Biochemistry |
Gentian violet has antibacterial, antifungal, antihelminthic, antitrypanosomal, antiangiogenic, and antitumor properties. It is used medically for these properties, in particular for dentistry, and is also known as "pyoctanin" (or "pyoctanine"). It is commonly used for:
* Marking the skin for surgery preparation and allergy testing;
* Treating Candida albicans and related fungal infections, such as thrush, yeast infections, various types of tinea (ringworm, athlete's foot, jock itch);
* Treating impetigo; it was used primarily before the advent of antibiotics, but still useful to persons who may be allergic to penicillin.
In resource-limited settings, gentian violet is used to manage burn wounds, inflammation of the umbilical cord stump (omphalitis) in the neonatal period, oral candidiasis in HIV-infected patients and mouth ulcers in children with measles. | 3 | Analytical Chemistry |
Thiourea reduces peroxides to the corresponding diols. The intermediate of the reaction is an unstable endoperoxide.
Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds. Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (boiling point ) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity). | 0 | Organic Chemistry |
In the presence of an anionic initiator (M X), the reagent reacts with aldehydes and ketones to give a trimethylsilyl ether, the net product of insertion of the carbonyl into the Si-CF bond. Hydrolysis gives trifluoromethyl methanols. The reagent also converts esters to trifluoromethyl ketones. A typical initiator is a soluble fluoride-containing species such as tetrabutylammonium fluoride; however, simple alkoxides such as KOtBu are also effective. The mechanism begins by generation of Si(CH)X and a highly reactive [CF] (trifluoromethide) intermediate. The [CF] attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus [CF], thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering [CF] in a reversibly-generated -ate complex [(CF)Si(CH)]. This -ate complex is unable to react directly with the carbonyl, resulting in powerful inhibition of the chain reaction by the reagent. This inhibitory process is common to all anion-initiated reactions of the reagent, with the identity of the counter-cation (M) playing a major role in controlling the overall rate.
The reagent has largely supplanted trifluoromethyllithium, which is not isolable and rapidly decomposes to yield lithium fluoride and difluorocarbene. | 0 | Organic Chemistry |
Avogadros law, Avogadros hypothesis, Avogadros principle or Avogadro-Ampères hypothesis is an experimental gas law which was hypothesized by Amedeo Avogadro in 1811. It related the volume of a gas to the amount of substance of gas present. | 7 | Physical Chemistry |
A multiple hearth furnace also known as a vertical calciner, is used for continuous preparation and calcining of materials. | 8 | Metallurgy |
Amplicons in general are direct repeat (head-to-tail) or inverted repeat (head-to-head or tail-to-tail) genetic sequences, and can be either linear or circular in structure. Circular amplicons consist of imperfect inverted duplications annealed into a circle and are thought to arise from precursor linear amplicons.
During artificial amplification, amplicon length is dictated by the experimental goals. | 1 | Biochemistry |
Limited proteolysis of a polypeptide during or after translation in protein synthesis often occurs for many proteins. This may involve removal of the N-terminal methionine, signal peptide, and/or the conversion of an inactive or non-functional protein to an active one. The precursor to the final functional form of protein is termed proprotein, and these proproteins may be first synthesized as preproprotein. For example, albumin is first synthesized as preproalbumin and contains an uncleaved signal peptide. This forms the proalbumin after the signal peptide is cleaved, and a further processing to remove the N-terminal 6-residue propeptide yields the mature form of the protein. | 1 | Biochemistry |
Although some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 19th century.
Jan van Helmont began the research of the process in the mid-17th century when he carefully measured the mass of the soil a plant was using and the mass of the plant as it grew. After noticing that the soil mass changed very little, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate – much of the gained mass comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's biomass comes from the inputs of photosynthesis, not the soil itself.
Joseph Priestley, a chemist and minister, discovered that when he isolated a volume of air under an inverted jar and burned a candle in it (which gave off CO), the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that a plant could restore the air the candle and the mouse had "injured."
In 1779, Jan Ingenhousz repeated Priestley's experiments. He discovered that it was the influence of sunlight on the plant that could cause it to revive a mouse in a matter of hours.
In 1796, Jean Senebier, a Swiss pastor, botanist, and naturalist, demonstrated that green plants consume carbon dioxide and release oxygen under the influence of light. Soon afterward, Nicolas-Théodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO but also to the incorporation of water. Thus, the basic reaction by which organisms use photosynthesis to produce food (such as glucose) was outlined. | 5 | Photochemistry |
The Brønsted–Lowry definition, formulated in 1923, independently by Johannes Nicolaus Brønsted in Denmark and Martin Lowry in England, is based upon the idea of protonation of bases through the deprotonation of acids – that is, the ability of acids to "donate" hydrogen ions () otherwise known as protons to bases, which "accept" them.
An acid–base reaction is, thus, the removal of a hydrogen ion from the acid and its addition to the base. The removal of a hydrogen ion from an acid produces its conjugate base, which is the acid with a hydrogen ion removed. The reception of a proton by a base produces its conjugate acid, which is the base with a hydrogen ion added.
Unlike the previous definitions, the Brønsted–Lowry definition does not refer to the formation of salt and solvent, but instead to the formation of conjugate acids and conjugate bases, produced by the transfer of a proton from the acid to the base. In this approach, acids and bases are fundamentally different in behavior from salts, which are seen as electrolytes, subject to the theories of Debye, Onsager, and others. An acid and a base react not to produce a salt and a solvent, but to form a new acid and a new base. The concept of neutralization is thus absent. Brønsted–Lowry acid–base behavior is formally independent of any solvent, making it more all-encompassing than the Arrhenius model. The calculation of pH under the Arrhenius model depended on alkalis (bases) dissolving in water (aqueous solution). The Brønsted–Lowry model expanded what could be pH tested using insoluble and soluble solutions (gas, liquid, solid).
The general formula for acid–base reactions according to the Brønsted–Lowry definition is:
where HA represents the acid, B represents the base, represents the conjugate acid of B, and represents the conjugate base of HA.
For example, a Brønsted–Lowry model for the dissociation of hydrochloric acid (HCl) in aqueous solution would be the following:
The removal of from the produces the chloride ion, , the conjugate base of the acid. The addition of to the (acting as a base) forms the hydronium ion, , the conjugate acid of the base.
Water is amphoteric that is, it can act as both an acid and a base. The Brønsted–Lowry model explains this, showing the dissociation of water into low concentrations of hydronium and hydroxide ions:
This equation is demonstrated in the image below:
Here, one molecule of water acts as an acid, donating an and forming the conjugate base, , and a second molecule of water acts as a base, accepting the ion and forming the conjugate acid, .
As an example of water acting as an acid, consider an aqueous solution of pyridine, .
In this example, a water molecule is split into a hydrogen ion, which is donated to a pyridine molecule, and a hydroxide ion.
In the Brønsted–Lowry model, the solvent does not necessarily have to be water, as is required by the Arrhenius Acid–Base model. For example, consider what happens when acetic acid, , dissolves in liquid ammonia.
An ion is removed from acetic acid, forming its conjugate base, the acetate ion, . The addition of an ion to an ammonia molecule of the solvent creates its conjugate acid, the ammonium ion, .
The Brønsted–Lowry model calls hydrogen-containing substances (like ) acids. Thus, some substances, which many chemists considered to be acids, such as or , are excluded from this classification due to lack of hydrogen. Gilbert N. Lewis wrote in 1938, "To restrict the group of acids to those substances that contain hydrogen interferes as seriously with the systematic understanding of chemistry as would the restriction of the term oxidizing agent to substances containing oxygen." Furthermore, and are not considered Brønsted bases, but rather salts containing the bases and . | 7 | Physical Chemistry |
A huge variety of ionization techniques can be used to analyze single cells. The choice of ionization method is crucial for analyte detection. It can be decisive which type of compounds are ionizable and in which state they appear, e.g., charge and possible fragmentation of the ions. A few examples of ionization are mentioned in the paragraphs below. | 1 | Biochemistry |
The units used for rotational constants depend on the type of measurement. With infrared spectra in the wavenumber scale (), the unit is usually the inverse centimeter, written as cm, which is literally the number of waves in one centimeter, or the reciprocal of the wavelength in centimeters (). On the other hand, for microwave spectra in the frequency scale (), the unit is usually the gigahertz. The relationship between these two units is derived from the expression
where ν is a frequency, λ is a wavelength and c is the velocity of light. It follows that
As 1 GHz = 10 Hz, the numerical conversion can be expressed as | 7 | Physical Chemistry |
DNA sequencing is the process of determining the nucleotide sequence of a given DNA fragment. The sequence of the DNA of a living thing encodes the necessary information for that living thing to survive and reproduce. Therefore, determining the sequence is useful in fundamental research into why and how organisms live, as well as in applied subjects. Because of the importance of DNA to living things, knowledge of a DNA sequence may be useful in practically any biological research. For example, in medicine it can be used to identify, diagnose and potentially develop treatments for genetic diseases. Similarly, research into pathogens may lead to treatments for contagious diseases. Biotechnology is a burgeoning discipline, with the potential for many useful products and services.
RNA is not sequenced directly. Instead, it is copied to a DNA by reverse transcriptase, and this DNA is then sequenced.
Current sequencing methods rely on the discriminatory ability of DNA polymerases, and therefore can only distinguish four bases. An inosine (created from adenosine during RNA editing) is read as a G, and 5-methyl-cytosine (created from cytosine by DNA methylation) is read as a C. With current technology, it is difficult to sequence small amounts of DNA, as the signal is too weak to measure. This is overcome by polymerase chain reaction (PCR) amplification. | 1 | Biochemistry |
Elemental fluorine is highly toxic. Above a concentration of 25 ppm, it causes significant irritation while attacking the eyes, airways and lungs and affecting the liver and kidneys. At a concentration of 100 ppm, human eyes and noses are seriously damaged. People can be exposed to fluorine in the workplace by breathing it in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for fluorine exposure in the workplace as 0.1 ppm (0.2 mg/m) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 ppm (0.2 mg/m) over an 8-hour workday. At levels of 25 ppm, fluorine is immediately dangerous to life and health. | 1 | Biochemistry |
Tetramethylguanidine is an organic compound with the formula HNC(N(CH)). This colourless liquid is a strong base, as judged by the high pK of it conjugate acid.
It was originally prepared from tetramethylthiourea via S-methylation and amination, but alternative methods start from cyanogen iodide. | 0 | Organic Chemistry |
Calcium is the most abundant metal in the eukaryotes and by extension humans. The body is made up of approximate 1.5% calcium and this abundance is reflected in its lack of redox toxicity and its participation in the structure stability of membranes and other biomolecules. Calcium plays a part in fertilization of an egg, controls several developmental process and may regulate cellular processes like metabolism or learning. Calcium also plays a part in bone structure as the rigidity of vertebrae bone matrices are akin to the nature of the calcium hydroxyapatite. Calcium usually binds with other proteins and molecules in order to perform other functions in the body. The calcium bound proteins usually play an important role in cell-cell adhesion, hydrolytic processes (such as hydrolytic enzymes like glycosidases and sulfatases) and protein folding and sorting. These processes play into the larger part of cell structure and metabolism. | 1 | Biochemistry |
* Preplant: Preplant herbicides are nonselective herbicides applied to the soil before planting. Some preplant herbicides may be mechanically incorporated into the soil. The objective for incorporation is to prevent dissipation through photodecomposition and/or volatility. The herbicides kill weeds as they grow through the herbicide-treated zone. Volatile herbicides have to be incorporated into the soil before planting the pasture. Crops grown in soil treated with a preplant herbicide include tomatoes, corn, soybeans, and strawberries. Soil fumigants like metam-sodium and dazomet are in use as preplant herbicides.
* Preemergence: Preemergence herbicides are applied before the weed seedlings emerge through the soil surface. Herbicides do not prevent weeds from germinating but they kill weeds as they grow through the herbicide-treated zone by affecting the cell division in the emerging seedling. Dithiopyr and pendimethalin are preemergence herbicides. Weeds that have already emerged before application or activation are not affected by pre-herbicides as their primary growing point escapes the treatment.
* Postemergence: These herbicides are applied after weed seedlings have emerged through the soil surface. They can be foliar or root absorbed, selective or nonselective, and contact or systemic. Application of these herbicides is avoided during rain since being washed off the soil makes it ineffective. 2,4-D is a selective, systemic, foliar-absorbed postemergence herbicide. | 2 | Environmental Chemistry |
This element describes the impedance of a finite-length diffusion with transmissive boundary. It is described by the following equation: | 7 | Physical Chemistry |
Extensive studies involving the phosphaethynolate anion have shown that it can react in a variety of ways. It has documented use in cycloadditions, as a phosphorus transfer agent, a synthetic building block and as pseudo halide ligands (as described above). | 7 | Physical Chemistry |
Under certain conditions, protons can re-enter the mitochondrial matrix without contributing to ATP synthesis. This process is known as proton leak or mitochondrial uncoupling and is due to the facilitated diffusion of protons into the matrix. The process results in the unharnessed potential energy of the proton electrochemical gradient being released as heat. The process is mediated by a proton channel called thermogenin, or UCP1. Thermogenin is primarily found in brown adipose tissue, or brown fat, and is responsible for non-shivering thermogenesis. Brown adipose tissue is found in mammals, and is at its highest levels in early life and in hibernating animals. In humans, brown adipose tissue is present at birth and decreases with age. | 1 | Biochemistry |
Pyruvate kinase catalyzes the last step within glycolysis, the dephosphorylation of phosphoenolpyruvate to pyruvate, and is responsible for net ATP production within the glycolytic sequence. In contrast to mitochondrial respiration, energy regeneration by pyruvate kinase is independent from oxygen supply and allows survival of the organs under hypoxic conditions often found in solid tumors.
The involvement of this enzyme in a variety of pathways, protein–protein interactions, and nuclear transport suggests its potential to perform multiple nonglycolytic functions with diverse implications, although multidimensional role of this protein is as yet not fully explored. However, a functional role in angiogenesis the so-called process of blood vessel formation by interaction and regulation of Jmjd8 has been shown. | 1 | Biochemistry |
Like other fuel cells, biological photovoltaic systems are divided into anodic and cathodic half-cells.
Oxygenic photosynthetic biological material, such as purified photosystems or whole algal or cyanobacterial cells, are employed in the anodic half-cell. These organisms are able to use light energy to drive the oxidation of water, and a fraction of the electrons produced by this reaction are transferred to the extracellular environment, where they can be used to reduce an anode. No heterotrophic organisms are included in the anodic chamber - electrode reduction is performed directly by the photosynthetic material.
The higher electrode potential of the cathodic reaction relative to the reduction of the anode drives current through an external circuit. In the illustration, oxygen is being reduced to water at the cathode, though other electron acceptors can be used. If water is regenerated there is a closed loop in terms of electron flow (similar to a conventional photovoltaic system), i.e. light energy is the only net input required for production of electrical power. Alternatively, electrons can be used at the cathode for electrosynthetic reactions that produce useful compounds, such as the reduction of protons to hydrogen gas. | 7 | Physical Chemistry |
The most common anodizing processes, for example, sulphuric acid on aluminium, produce a porous surface which can accept dyes easily. The number of dye colours is almost endless; however, the colours produced tend to vary according to the base alloy. The most common colours in the industry, due to them being relatively cheap, are yellow, green, blue, black, orange, purple and red. Though some may prefer lighter colours, in practice they may be difficult to produce on certain alloys such as high-silicon casting grades and 2000-series aluminium-copper alloys. Another concern is the "lightfastness" of organic dyestuffs—some colours (reds and blues) are particularly prone to fading. Black dyes and gold produced by inorganic means (ferric ammonium oxalate) are more lightfast. Dyed anodizing is usually sealed to reduce or eliminate dye bleed out. White color cannot be applied due to the larger molecule size than the pore size of the oxide layer.
Alternatively, metal (usually tin) can be electrolytically deposited in the pores of the anodic coating to provide more lightfast colours. Metal dye colors range from pale champagne to black. Bronze shades are commonly used for architectural metals. Alternatively, the colour may be produced integral to the film. This is done during the anodizing process using organic acids mixed with the sulfuric electrolyte and a pulsed current.
Splash effects are created by dying the unsealed porous surface in lighter colours and then splashing darker colour dyes onto the surface. Aqueous and solvent-based dye mixtures may also be alternately applied since the coloured dyes will resist each other and leave spotted effects.
Another interesting coloring method is anodizing interference coloring. The thin oil film resting on the waters surface displays a rainbow hue due to the interference between light reflected from the water-oil interface and the oil films surface. Because the oil films thickness isnt regulated, the resulting rainbow color appears random.
In the anodizing coloring of aluminum, desired colors are achieved by depositing a controllably thick metal layer (typically tin) at the base of the porous structure. This involves reflections on the aluminum substrate and the upper metal surface. The color resulting from interference shifts from blue, green, and yellow to red as the deposited metal layer thickens. Beyond a specific thickness, the optical interference vanishes, and the color turns bronze. Interference-colored anodized aluminum parts exhibit a distinctive quality: their color varies when viewed from different angles. The interference coloring involves a 3-step process: sulfuric acid anodizing, electrochemical modification of the anodic pore, and metal (tin) deposition. | 8 | Metallurgy |
Trans-regulatory elements work through an intermolecular interaction between two different molecules and so are said to be "acting in trans". For example (1) a transcribed and translated transcription factor protein derived from the trans-regulatory element; and a (2) DNA regulatory element that is adjacent to the regulated gene. This is in contrast to cis-regulatory elements that work through an intramolecular interaction between different parts of the same molecule: (1) a gene; and (2) an adjacent regulatory element for that gene in the same DNA molecule. Additionally, each trans-regulatory element affects a large number of genes on both alleles, while cis-regulatory element is allele specific and only controls genes nearby.
Exonic and promoter sequences of the genes are significantly more conserved than the genes in cis- and trans- regulatory elements. Hence, they have higher resistance to genetic divergence, yet retains its susceptibility to mutations in upstream regulators. This accentuates the significance of genetic divergence within species due to cis- and trans-regulatory variants.
Trans- and cis-regulatory elements co-evolved rapidly in large-scale to maintain gene expression. They often act in opposite directions, one up-regulates while another down-regulates, to compensate for their effects on the exonic and promoter sequences they act on. Other evolutionary models, such as the independent evolution of trans- or cis-regulatory elements, were deemed incompatible in regulatory systems. Co-evolution of the two regulatory elements was suggested to arise from the same lineage.
TRE is more evolutionary constraint than cis-regulatory element, suggesting a hypothesis that TRE mutations are corrected by CRE mutations to maintain stability in gene expression. This makes biological sense, due to TREs effect on a broad range of genes and CREs compensatory effect on specific genes. Following a TRE mutation, accumulation of CRE mutations act to fine-tune the mutative effect. | 1 | Biochemistry |
* Beautyberry (Callicarpa) leaves
* Birch tree bark is traditionally made into tar. Combined with another oil (e.g., fish oil) at 1/2 dilution, it is then applied to the skin for repelling mosquitos
* Bog myrtle (Myrica gale)
* Catnip oil whose active compound is Nepetalactone
* Citronella oil (citronella candles are not effective)
* Essential oil of the lemon eucalyptus (Corymbia citriodora) and its active compound p-menthane-3,8-diol (PMD)
* Lemongrass
* Neem oil
* Tea tree oil from the leaves of Melaleuca alternifolia
* Tobacco | 1 | Biochemistry |
Adverse effects can include hypersensitivity reactions including urticaria, fever, joint pains, rashes, angioedema, anaphylaxis, serum sickness-like reaction. Rarely central nervous system toxicity including convulsions (especially with high doses or in severe renal impairment), interstitial nephritis, haemolytic anaemia, leucopenia, thrombocytopenia, and coagulation disorders. Also reported diarrhoea (including antibiotic-associated colitis). Benzylpenicillin has relatively low toxicity, except for in the nervous system, in which it is one of the most active drugs among β-lactam agents. In addition, benzylpenicillin is an irritant, a health hazard, and an environmental hazard.
Benzylpenicillin serum concentrations can be monitored either by traditional microbiological assay or by more modern chromatographic techniques. Such measurements can be useful to avoid central nervous system toxicity in any person receiving large doses of the drug on a chronic basis, but they are especially relevant to patients with kidney failure, who may accumulate the drug due to reduced urinary excretion rates. | 4 | Stereochemistry |
It is possible to build a computer simulation of a linear biochemical pathway. This can be done by building a simple model that describes each intermediate through a differential equation. The differential equations can be written by invoking mass conservation. For example, for the linear pathway:
where and are fixed boundary species, the non-fixed intermediate can be described using the differential equation:
The rate of change of the non-fixed intermediates and can be written in the same way:
To run a simulation the rates, need to be defined. If mass-action kinetics are assumed for the reaction rates, then the differential equation can be written as:
If values are assigned to the rate constants, , and the fixed species and the differential equations can be solved. | 1 | Biochemistry |
TaqMan probes are hydrolysis probes that are designed to increase the specificity of quantitative PCR. The method was first reported in 1991 by researcher Kary Mullis at Cetus Corporation, and the technology was subsequently developed by Hoffmann-La Roche for diagnostic assays and by Applied Biosystems (now part of Thermo Fisher Scientific) for research applications.
The TaqMan probe principle relies on the 5´–3´ exonuclease activity of Taq polymerase to cleave a dual-labeled probe during hybridization to the complementary target sequence and fluorophore-based detection. As in other quantitative PCR methods, the resulting fluorescence signal permits quantitative measurements of the accumulation of the product during the exponential stages of the PCR; however, the TaqMan probe significantly increases the specificity of the detection. TaqMan probes were named after the videogame Pac-Man (Taq Polymerase + PacMan = TaqMan) as its mechanism is based on the Pac-Man principle. | 1 | Biochemistry |
Tight junctions are multi-protein complexes that hold cells of a same tissue together and prevent movement of water and water-soluble molecules between cells. In epithelial cells, they function also to separate the extracellular fluid surrounding their apical and basolateral membranes. These junctions exist as a continuous band located just below the apical surface between the membranes of neighboring epithelial cells. The tight junctions on adjacent cells line up so as to produce a seal between different tissues and body cavities. For example, the apical surface of gastrointestinal epithelial cells serve as a selective permeable barrier that separates the external environment from the body. The permeability of these junctions is dependent on a variety of factors including protein makeup of that junction, tissue type and signaling from the cells.
Tight junctions are made up of many different proteins. The four main transmembrane proteins are occludin, claudin, junctional adhesion molecules (JAMs) and tricellulins. The extracellular domains of these proteins form the tight junction barrier by making homophilic (between proteins of the same kind) and heterophilic interactions (between different types of proteins) with the protein domains on adjacent cells. Their cytoplasmic domains interact with the cell cytoskeleton to anchor them. | 1 | Biochemistry |
Substituted phenethylamines are a chemical class of organic compounds based upon the phenethylamine structure; the class is composed of all the derivative compounds of phenethylamine which can be formed by replacing, or substituting, one or more hydrogen atoms in the phenethylamine core structure with substituents.
Many substituted phenethylamines are psychoactive drugs, which belong to a variety of different drug classes, including central nervous system stimulants (e.g., amphetamine), hallucinogens (e.g., 2,5-dimethoxy-4-methylamphetamine), entactogens (e.g., 3,4-methylenedioxyamphetamine), appetite suppressants (e.g. phentermine), nasal decongestants and bronchodilators (e.g., pseudoephedrine), antidepressants (e.g. bupropion), antiparkinson agents (e.g., selegiline), and vasopressors (e.g., ephedrine), among others. Many of these psychoactive compounds exert their pharmacological effects primarily by modulating monoamine neurotransmitter systems; however, there is no mechanism of action or biological target that is common to all members of this subclass.
Numerous endogenous compounds – including hormones, monoamine neurotransmitters, and many trace amines (e.g., dopamine, norepinephrine, adrenaline, tyramine, and others) – are substituted phenethylamines. Dopamine
is simply phenethylamine with a hydroxyl group attached to the 3 and 4 position of the benzene ring. Several notable recreational drugs, such as MDMA (ecstasy), methamphetamine, and cathinones, are also members of the class. All of the substituted amphetamines are phenethylamines, as well.
Pharmaceutical drugs that are substituted phenethylamines include phenelzine, phenformin, and fanetizole, among many others. | 1 | Biochemistry |
Interleukin 34 (IL-34) is a protein belonging to a group of cytokines called interleukins. It was originally identified in humans, by large scale screening of secreted proteins; chimpanzee, murine, rat and chicken interleukin 34 orthologs have also been found. The protein is composed of 241 amino acids, 39 kilodaltons in mass, and forms homodimers. IL-34 increases growth or survival of immune cells known as monocytes; it elicits its activity by binding the Colony stimulating factor 1 receptor.
Messenger RNA (mRNA) expression of human IL-34 is most abundant in spleen but occurs in several other tissues: thymus, liver, small intestine, colon, prostate gland, lung, heart, brain, kidney, testes, and ovary. The discovery of IL-34 protein in the red pulp of the spleen suggests involvement in growth and development of myeloid cells, consistent with its activity on monocytes. | 1 | Biochemistry |
The Gibbsian ensemble idealizes the notion of repeating an experiment again and again on different systems, not again and again on the same system. So long-term time averages and the ergodic hypothesis, despite the intense interest in them in the first part of the twentieth century, strictly speaking are not relevant to the probability assignment for the state one might find the system in.
However, this changes if there is additional knowledge that the system is being prepared in a particular way some time before the measurement. One must then consider whether this gives further information which is still relevant at the time of measurement. The question of how rapidly mixing different properties of the system are then becomes very much of interest. Information about some degrees of freedom of the combined system may become unusable very quickly; information about other properties of the system may go on being relevant for a considerable time.
If nothing else, the medium and long-run time correlation properties of the system are interesting subjects for experimentation in themselves. Failure to accurately predict them is a good indicator that relevant macroscopically determinable physics may be missing from the model. | 7 | Physical Chemistry |
Paul J. Gemperline (born 1955) is an American analytical chemist and chemometrician. He is a Distinguished Professor of Chemistry at East Carolina University (ECU) located in Greenville, North Carolina and has been the recipient of several scientific awards, including the 2003 Eastern Analytical Symposium Award in Chemometrics. He is author of more than 60 publications in the field of chemometrics. Dr. Gemperline served as Dean of the Graduate School at ECU from 2008 to 2022. He retired from ECU June 30, 2022 and is now professor emeritus. | 3 | Analytical Chemistry |
A cannulated cow or fistulated cow refers to a cow that has been surgically fitted with a cannula. A cannula acts as a porthole-like device that allows access to the rumen of a cow, to perform research and analysis of the digestive system and to allow veterinarians to transplant rumen contents from one cow to another.
The practice of rumen cannulation was first documented in 1928 by Arthur Frederick Schalk and R.S. Amadon of North Dakota Agricultural College. | 1 | Biochemistry |
Besides pzc, iep, and cip, there are also numerous other terms used in the literature, usually expressed as initialisms, with identical or (confusingly) near-identical meaning: zero point of charge (zpc), point of zero net charge (pznc), point of zero net proton charge (pznpc), pristine point of zero charge (ppzc), point of zero salt effect (pzse), zero point of titration (zpt) of colloidal dispersion, and isoelectric point of the solid (ieps) and point of zero surface tension (pzst or pzs). | 7 | Physical Chemistry |
In electrochemistry, the electrochemical potential (ECP), , is a thermodynamic measure of chemical potential that does not omit the energy contribution of electrostatics. Electrochemical potential is expressed in the unit of J/mol. | 7 | Physical Chemistry |
Metabolic wastes or excrements are substances left over from metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus or toxic), and must therefore be excreted. This includes nitrogen compounds, water, CO, phosphates, sulphates, etc. Animals treat these compounds as excretes. Plants have metabolic pathways which transforms some of them (primarily the oxygen compounds) into useful substances.
All the metabolic wastes are excreted in a form of water solutes through the excretory organs (nephridia, Malpighian tubules, kidneys), with the exception of CO, which is excreted together with the water vapor throughout the lungs. The elimination of these compounds enables the chemical homeostasis of the organism. | 1 | Biochemistry |
Many industries such as food, beverages, cosmetics, and even medicine utilize levan in their products. One of the reasons levan is able to be used in such a versatile way is that it fulfills all safety guidelines. Levan does not cause any form of skin or eye irritation, has not shown any allergenic effects, and poses no threat of cytotoxicity. | 1 | Biochemistry |
There are other ways by which messages can be degraded, including non-stop decay and silencing by Piwi-interacting RNA (piRNA), among others. | 1 | Biochemistry |
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation reaction) while an unknown but potentially vast area becomes cathodic (reduction reaction), leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with a limited diffusion of ions.
Another term arises, pitting factor, which is defined as the ratio of the depth of the deepest pit (resulting due to corrosion) to the average penetration, which can be calculated based on the weight loss. | 8 | Metallurgy |
Wagner's gene network model is a computational model of artificial gene networks, which explicitly modeled the developmental and evolutionary process of genetic regulatory networks. A population with multiple organisms can be created and evolved from generation to generation. It was first developed by Andreas Wagner in 1996 and has been investigated by other groups to study the evolution of gene networks, gene expression, robustness, plasticity and epistasis. | 1 | Biochemistry |
The solid sample is taken in a Petri dish and melted by heating it on a standard hot plate. The bubble free liquefied sample is poured from the Petri dish and cast into the ring. The brass shouldered rings in this apparatus have 6.4 mm depth. The cast sample in the ring is kept undisturbed for one hour to solidify. Excess material is removed with a hot knife. The ring is set with the ball on top with ball guides on the grooved plate within the heating bath. As the temperature rises, the balls begin to sink through the rings carrying a portion of the softened sample with it. The temperature at which the steel balls touch the bottom plate determines the softening point in degrees Celsius. | 7 | Physical Chemistry |
The use of thermal mass is the most challenging in this environment where night temperatures remain elevated. Its use is primarily as a temporary heat sink. However, it needs to be strategically located to prevent overheating. It should be placed in an area that is not directly exposed to solar gain and also allows adequate ventilation at night to carry away stored energy without increasing internal temperatures any further. If to be used at all it should be used in judicious amounts and again not in large thicknesses. | 7 | Physical Chemistry |
Separating molecules in a solution by dialysis is a relatively straightforward process. Other than the sample and dialysate buffer, all that is typically needed is:
* Dialysis membrane in an appropriate format (e.g., tubing, cassette, etc.) and molecular weight cut-off (MWCO)
* A container to hold the dialysate buffer
* The ability to stir the solutions and control the temperature | 1 | Biochemistry |
Polymerase III terminates transcription at small polyUs stretch (5-6). In eukaryotes, a hairpin loop is not required, but may enhance termination efficiency in humans. In Saccharomyces cerevisiae, it was found that termination of transcription occurred in the sequence T7GT6 and was progressive. The presence of transcripts with five, six, and seven U residues and the slow readthrough of the T7 stretch suggest that the incorporation of a single G into the RNA chain served to reset elongation rates either entirely or substantially. | 1 | Biochemistry |
Food physical chemistry is considered to be a branch of Food chemistry concerned with the study of both physical and chemical interactions in foods in terms of physical and chemical principles applied to food systems, as well as the applications of physical/chemical techniques and instrumentation for the study of foods. This field encompasses the "physiochemical principles of the reactions and conversions that occur during the manufacture, handling, and storage of foods."
Food physical chemistry concepts are often drawn from rheology, theories of transport phenomena, physical and chemical thermodynamics, chemical bonds and interaction forces, quantum mechanics and reaction kinetics, biopolymer science, colloidal interactions, nucleation, glass transitions, and freezing, disordered/noncrystalline solids.
Techniques utilized range widely from dynamic rheometry, optical microscopy, electron microscopy, AFM, light scattering, X-ray diffraction/neutron diffraction, to MRI, spectroscopy (NMR, FT-NIR/IR, NIRS, ESR and EPR, CD/VCD, Fluorescence, FCS, HPLC, GC-MS, and other related analytical techniques.
Understanding food processes and the properties of foods requires a knowledge of physical chemistry and how it applies to specific foods and food processes. Food physical chemistry is essential for improving the quality of foods, their stability, and food product development. Because food science is a multi-disciplinary field, food physical chemistry is being developed through interactions with other areas of food chemistry and food science, such as food analytical chemistry, food process engineering/food processing, food and bioprocess technology, food extrusion, food quality control, food packaging, food biotechnology, and food microbiology. | 7 | Physical Chemistry |
In polymer chemistry, the equivalent weight of a reactive polymer is the mass of polymer which has one equivalent of reactivity (often, the mass of polymer which corresponds to one mole of reactive side-chain groups). It is widely used to indicate the reactivity of polyol, isocyanate, or epoxy thermoset resins which would undergo crosslinking reactions through those functional groups.
It is particularly important for ion-exchange polymers (also called ion-exchange resins): one equivalent of an ion-exchange polymer will exchange one mole of singly charged ions, but only half a mole of doubly charged ions.
Nevertheless, given the decline in use of the term "equivalent weight" in the rest of chemistry, it has become more usual to express the reactivity of a polymer as the inverse of the equivalent weight, that is in units of mmol/g or meq/g. | 7 | Physical Chemistry |
Agarose gel electrophoresis is a method of gel electrophoresis used in biochemistry, molecular biology, genetics, and clinical chemistry to separate a mixed population of macromolecules such as DNA or proteins in a matrix of agarose, one of the two main components of agar. The proteins may be separated by charge and/or size (isoelectric focusing agarose electrophoresis is essentially size independent), and the DNA and RNA fragments by length. Biomolecules are separated by applying an electric field to move the charged molecules through an agarose matrix, and the biomolecules are separated by size in the agarose gel matrix.
Agarose gel is easy to cast, has relatively fewer charged groups, and is particularly suitable for separating DNA of size range most often encountered in laboratories, which accounts for the popularity of its use. The separated DNA may be viewed with stain, most commonly under UV light, and the DNA fragments can be extracted from the gel with relative ease. Most agarose gels used are between 0.7–2% dissolved in a suitable electrophoresis buffer. | 1 | Biochemistry |
Phenethylamine, being similar to amphetamine in its action at their common biomolecular targets, releases norepinephrine and dopamine. Phenethylamine also appears to induce acetylcholine release via a glutamate-mediated mechanism.
Phenethylamine has been shown to bind to human trace amine-associated receptor 1 (hTAAR1) as an agonist. β-PEA is also an odorant binding TAAR4 in mice thought to mediate predator avoidance. | 1 | Biochemistry |
Ionic strength determines the Debye length that correlates with the damping distance of the electric potential of a fixed charge in an electrolyte. So, higher the ionic strength the shorter are electrostatic interactions between charged entities. As a result, the adsorption of charged proteins to oppositely charged substrates is hindered whereas the adsorption to like charged substrates is enhanced, thereby influencing adsorption kinetics. Also, high ionic strength increases the tendency of proteins to aggregate. | 1 | Biochemistry |
Secondary production is the generation of biomass of heterotrophic (consumer) organisms in a system. This is driven by the transfer of organic material between trophic levels, and represents the quantity of new tissue created through the use of assimilated food. Secondary production is sometimes defined to only include consumption of primary producers by herbivorous consumers (with tertiary production referring to carnivorous consumers), but is more commonly defined to include all biomass generation by heterotrophs.
Organisms responsible for secondary production include animals, protists, fungi and many bacteria.
Secondary production can be estimated through a number of different methods including increment summation, removal summation, the instantaneous growth method and the Allen curve method. The choice between these methods will depend on the assumptions of each and the ecosystem under study. For instance, whether cohorts should be distinguished, whether linear mortality can be assumed and whether population growth is exponential.
Net ecosystem production is defined as the difference between gross primary production (GPP) and ecosystem respiration. The formula to calculate net ecosystem production is NEP = GPP - respiration (by autotrophs) - respiration (by heterotrophs). The key difference between NPP and NEP is that NPP focuses primarily on autotrophic production, whereas NEP incorporates the contributions of other aspects of the ecosystem to the total carbon budget. | 9 | Geochemistry |
One of the most basic tasks in spectroscopy is to characterize the spectrum of a light source: how much light is emitted at each different wavelength. The most straightforward way to measure a spectrum is to pass the light through a monochromator, an instrument that blocks all of the light except the light at a certain wavelength (the un-blocked wavelength is set by a knob on the monochromator). Then the intensity of this remaining (single-wavelength) light is measured. The measured intensity directly indicates how much light is emitted at that wavelength. By varying the monochromators wavelength setting, the full spectrum can be measured. This simple scheme in fact describes how some' spectrometers work.
Fourier-transform spectroscopy is a less intuitive way to get the same information. Rather than allowing only one wavelength at a time to pass through to the detector, this technique lets through a beam containing many different wavelengths of light at once, and measures the total beam intensity. Next, the beam is modified to contain a different combination of wavelengths, giving a second data point. This process is repeated many times. Afterwards, a computer takes all this data and works backwards to infer how much light there is at each wavelength.
To be more specific, between the light source and the detector, there is a certain configuration of mirrors that allows some wavelengths to pass through but blocks others (due to wave interference). The beam is modified for each new data point by moving one of the mirrors; this changes the set of wavelengths that can pass through.
As mentioned, computer processing is required to turn the raw data (light intensity for each mirror position) into the desired result (light intensity for each wavelength). The processing required turns out to be a common algorithm called the Fourier transform (hence the name, "Fourier-transform spectroscopy"). The raw data is sometimes called an "interferogram". Because of the existing computer equipment requirements, and the ability of light to analyze very small amounts of substance, it is often beneficial to automate many aspects of the sample preparation. The sample can be better preserved and the results are much easier to replicate. Both of these benefits are important, for instance, in testing situations that may later involve legal action, such as those involving drug specimens. | 7 | Physical Chemistry |
Edwin "Ed" Vedejs was born in Riga, Latvia to Velta (nee Robežnieks) and Nikolajs Vedējs. Not long after his birth, the German occupation of Latvia during World War II occurred followed by the Soviet re-occupation of Latvia in 1944. These events forced his family to settle in the Fischbach Displaced Persons camp in Germany for six years. In 1950, they emigrated to the United States and first settled in Fort Atkinson, WI. They eventually moved to Grand Rapids, MI.
He attended Grand Rapids Junior College for a few years before transferring to the University of Michigan where he received a BS degree in 1962. He moved to the University of Wisconsin and joined the group of Professor for his Ph.D. studies (Progress toward the total synthesis of terramycin), which he completed in 1966. From 1966–67, he did post-doctoral research on the total synthesis of prostaglandins at Harvard University in the laboratory of Nobel Laureate Professor E. J. Corey. | 0 | Organic Chemistry |
The key terms involved in redox can be confusing. For example, a reagent that is oxidized loses electrons; however, that reagent is referred to as the reducing agent. Likewise, a reagent that is reduced gains electrons and is referred to as the oxidizing agent. These mnemonics are commonly used by students to help memorise the terminology:
* "OIL RIG" — oxidation is loss of electrons, reduction is gain of electrons
* "LEO the lion says GER [grr]" — loss of electrons is oxidation, gain of electrons is reduction
* "LEORA says GEROA" — the loss of electrons is called oxidation (reducing agent); the gain of electrons is called reduction (oxidizing agent).
* "RED CAT" and "AN OX", or "AnOx RedCat" ("an ox-red cat") — reduction occurs at the cathode and the anode is for oxidation
* "RED CAT gains what AN OX loses" – reduction at the cathode gains (electrons) what anode oxidation loses (electrons)
* "PANIC" – Positive Anode and Negative is Cathode. This applies to electrolytic cells which release stored electricity, and can be recharged with electricity. PANIC does not apply to cells that can be recharged with redox materials. These galvanic or voltaic cells, such as fuel cells, produce electricity from internal redox reactions. Here, the positive electrode is the cathode and the negative is the anode. | 9 | Geochemistry |
A primary function of floral scent is to attract pollinators and ensure the reproduction of animal-pollinated plants.
Some families of VOCs presented in floral scents have likely evolved as herbivore repellents. However, these plant defenses are also used by herbivores themselves to locate a plant resource, similar to pollinators attracted by the floral scent. Therefore, flower traits can be subject to antagonistic selection pressures (positive selection by pollinators and negative selection by herbivores). | 1 | Biochemistry |
Crime scene investigators use luminol to find traces of blood, even if someone has cleaned or removed it. The investigator sprays a solution of luminol and the oxidant. The iron in blood catalyses the luminescence. The amount of catalyst necessary to cause the reaction is very small relative to the amount of luminol, allowing detection of even trace amounts of blood. The blue glow lasts for about 30 seconds per application. Detecting the glow requires a fairly dark room. Any glow detected may be documented by a long-exposure photograph. | 3 | Analytical Chemistry |
Magma contains dissolved volatile components, as described above. The solubilities of the different volatile constituents are dependent on pressure, temperature and the composition of the magma. As magma ascends towards the surface, the ambient pressure decreases, which decreases the solubility of the dissolved volatiles. Once the solubility decreases below the volatile concentration, the volatiles will tend to come out of solution within the magma (exsolve) and form a separate gas phase (the magma is super-saturated in volatiles).
The gas will initially be distributed throughout the magma as small bubbles, that cannot rise quickly through the magma. As the magma ascends the bubbles grow through a combination of expansion through decompression and growth as the solubility of volatiles in the magma decreases further causing more gas to exsolve. Depending on the viscosity of the magma, the bubbles may start to rise through the magma and coalesce, or they remain relatively fixed in place until they begin to connect and form a continuously connected network. In the former case, the bubbles may rise through the magma and accumulate at a vertical surface, e.g. the roof of a magma chamber. In volcanoes with an open path to the surface, e.g. Stromboli in Italy, the bubbles may reach the surface and as they pop small explosions occur. In the latter case, the gas can flow rapidly through the continuous permeable network towards the surface. This mechanism has been used to explain activity at Santiaguito, Santa Maria volcano, Guatemala and Soufrière Hills Volcano, Montserrat. If the gas cannot escape fast enough from the magma, it will fragment the magma into small particles of ash. The fluidised ash has a much lower resistance to motion than the viscous magma, so accelerates, causing further expansion of the gases and acceleration of the mixture. This sequence of events drives explosive volcanism. Whether gas can escape gently (passive eruptions) or not (explosive eruptions) is determined by the total volatile contents of the initial magma and the viscosity of the magma, which is controlled by its composition.
The term closed system degassing refers to the case where gas and its parent magma ascend together and in equilibrium with each other. The composition of the emitted gas is in equilibrium with the composition of the magma at the pressure, temperature where the gas leaves the system. In open system degassing, the gas leaves its parent magma and rises up through the overlying magma without remaining in equilibrium with that magma. The gas released at the surface has a composition that is a mass-flow average of the magma exsolved at various depths and is not representative of the magma conditions at any one depth.
Molten rock (either magma or lava) near the atmosphere releases high-temperature volcanic gas (>400 °C).
In explosive volcanic eruptions, the sudden release of gases from magma may cause rapid movements of the molten rock. When the magma encounters water, seawater, lake water or groundwater, it can be rapidly fragmented. The rapid expansion of gases is the driving mechanism of most explosive volcanic eruptions. However, a significant portion of volcanic gas release occurs during quasi-continuous quiescent phases of active volcanism. | 2 | Environmental Chemistry |
Electron phenomenological spectroscopy (EPS) is based on the correlations between integral optical characteristics and properties of substance as a single whole quantum continuum: spectrum-properties and color-properties. According to these laws the physicochemical properties of substance solutions in ultraviolet (UV), visible light and near infrared (IR) regions of the electromagnetic spectrum are in proportion to the quantity of radiation absorbed. Such aspects of electron spectroscopy have been shown in the works of Mikhail Yu Dolomatov and has been named electron phenomenological spectroscopy because the integral characteristics of the system are studied. Qualitatively, new laws appear on the integral level.
Unlike conventional spectroscopic methods, the EPS studies substances as a comprehensive quantum continuum without separating the spectrum of the substance into characteristic spectral bands on certain frequencies or wavelengths of individual functional groups or components.
New physical phenomena appear in consideration of the integral systems which absorb radiation. For example, EPS is based on the regularities of the correlation of physico-chemical properties and integral spectral characteristics for UV or (and) visible regions of the electromagnetic spectrum (so-called law spectrum-properties). Color is also an integral characteristic of a visible spectrum. Therefore, the consequence of this is so-called law color-properties. All this allow the use of EPS methods for studying individual and complex multicomponent substances.
Methods of EPS were developed after 1988 by the group of Mikhail Yu Dolomatov.
The EPS methods belong to number of new effective techniques of monitoring and control and can be used in petroleum and petrochemical industries, environmental monitoring, electronics, biophysics, medicine, criminalistics, space exploration and other fields. | 7 | Physical Chemistry |
Cyclooxygenase (COX) catalyzes the conversion of the free essential fatty acids to prostanoids by a two-step process.
In the first step, two molecules of O are added as two peroxide linkages and a 5-member carbon ring is forged near the middle of the fatty acid chain. This forms the short-lived, unstable intermediate Prostaglandin G (PGG).
One of the peroxide linkages sheds a single oxygen, forming PGH. (See diagrams and more detail at Cyclooxygenase).
All other prostanoids originate from PGH (as PGH, PGH, or PGH).
The image at right shows how PGH (derived from Arachidonic acid) is converted:
* By PGE synthetase into PGE2 (which in turn is converted into PGF2)
* By PGD synthetase into PGD2
* By Prostacyclin synthase into prostacyclin (PGI2)
* By Thromboxane synthase into thromboxanes TXA
Arachidonic acid is made up of a 20-Carbon unnatural poly unsaturated Omega-fatty acid. Arachidonic acid presents within the phospholipid bi-layer as well as in the plasma membrane of a cell. With Arachidonic acid prostaglandins are formed through synthesis and oxygenation of enzymes. Active lipids in the oxylipin family derive from the synthesis of Cyclooxygenase or Prostaglandins.
The three classes of prostanoids have distinctive rings in the center of the molecule. They differ in their structures and do not share common structure as Thromboxane. The PGH compounds (parents to all the rest) have a 5-carbon ring, bridged by two oxygens (a peroxide.) The derived prostaglandins contain a single, unsaturated 5-carbon ring. In prostacyclins, this ring is conjoined to another oxygen-containing ring. In thromboxanes the ring becomes a 6-member ring with one oxygen.
Production of PGE in bacterial and viral infections appear to be stimulated by certain cytokines, e.g., interleukin-1. | 1 | Biochemistry |
ODS steels creep properties are dependent on the characteristics of the oxide particles in the metal matrix, specifically their ability to prevent dislocation motion as well as the size and distribution of the particles. Hoelzer and coworkers showed that an alloy containing a homogeneous dispersion of 1-5 nm YTiO nanoclusters has superior creep properties to an alloy with a heterogeneous dispersion of 5-20 nm nanoclusters of the same composition.
ODS steels are commonly produced through ball-milling an oxide of interest (e.g. YO, AlO) with pre-alloyed metal powders followed by compression and sintering. It is believed that the oxides enter into solid solution with the metal during ball-milling and subsequently precipitate during the thermal treatment. This process seems simple but many parameters need to be carefully controlled to produce a successful alloy. Leseigneur and coworkers carefully controlled some of these parameters and achieved more consistent and better microstructures. In this two step method the oxide is ball-milled for longer periods to ensure a homogeneous solid solution of the oxide. The powder is annealed at higher temperatures to begin a controlled nucleation of the oxide clusters. Finally the powder is again compressed and sintered to yield the final material. | 8 | Metallurgy |
Dda is a molecular motor, specifically a helicase that moves in the 5 end to 3 direction along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands, using the free energy released by the hydrolysis of adenosine triphosphate. The National Center for Biotechnology Information (NCBI) Reference Sequence accession number is NP_049632. | 1 | Biochemistry |
In some groups of mixotrophic protists, like some dinoflagellates (e.g. Dinophysis), chloroplasts are separated from a captured alga and used temporarily. These klepto chloroplasts may only have a lifetime of a few days and are then replaced. | 5 | Photochemistry |
In organic chemistry, dehalogenation is a set of chemical reactions that involve the cleavage of carbon-halogen bonds; as such, it is the inverse reaction of halogenation. Dehalogenations come in many varieties, including defluorination (removal of fluorine), dechlorination (removal of chlorine), debromination (removal of bromine), and deiodination (removal of iodine). Incentives to investigate dehalogenations include both constructive and destructive goals. Complicated organic compounds such as pharmaceutical drugs are occasionally generated by dehalogenation. Many organohalides are hazardous, so their dehalogenation is one route for their detoxification. | 0 | Organic Chemistry |
Some ion channels are classified by the duration of their response to stimuli:
*Transient receptor potential channels: This group of channels, normally referred to simply as TRP channels, is named after their role in Drosophila visual phototransduction. This family, containing at least 28 members, is diverse in its mechanisms of activation. Some TRP channels remain constitutively open, while others are gated by voltage, intracellular Ca, pH, redox state, osmolarity, and mechanical stretch. These channels also vary according to the ion(s) they pass, some being selective for Ca while others are less selective cation channels. This family is subdivided into 6 subfamilies based on homology: canonical TRP (TRPC), vanilloid receptors (TRPV), melastatin (TRPM), polycystins (TRPP), mucolipins (TRPML), and ankyrin transmembrane protein 1 (TRPA). | 1 | Biochemistry |
Many types of substances are known to interact with amphetamine, resulting in altered drug action or metabolism of amphetamine, the interacting substance, or both. Inhibitors of the enzymes that metabolize amphetamine (e.g., CYP2D6 and FMO3) will prolong its elimination half-life, meaning that its effects will last longer. Amphetamine also interacts with , particularly monoamine oxidase A inhibitors, since both MAOIs and amphetamine increase plasma catecholamines (i.e., norepinephrine and dopamine); therefore, concurrent use of both is dangerous. Amphetamine modulates the activity of most psychoactive drugs. In particular, amphetamine may decrease the effects of sedatives and depressants and increase the effects of stimulants and antidepressants. Amphetamine may also decrease the effects of antihypertensives and antipsychotics due to its effects on blood pressure and dopamine respectively. Zinc supplementation may reduce the minimum effective dose of amphetamine when it is used for the treatment of ADHD. | 4 | Stereochemistry |
In a conventional n-type DSSC, sunlight enters the cell through the transparent SnO:F top contact, striking the dye on the surface of the TiO. Photons striking the dye with enough energy to be absorbed create an excited state of the dye, from which an electron can be "injected" directly into the conduction band of the TiO. From there it moves by diffusion (as a result of an electron concentration gradient) to the clear anode on top.
Meanwhile, the dye molecule has lost an electron and the molecule will decompose if another electron is not provided. The dye strips one from iodide in electrolyte below the TiO, oxidizing it into triiodide. This reaction occurs quite quickly compared to the time that it takes for the injected electron to recombine with the oxidized dye molecule, preventing this recombination reaction that would effectively short-circuit the solar cell.
The triiodide then recovers its missing electron by mechanically diffusing to the bottom of the cell, where the counter electrode re-introduces the electrons after flowing through the external circuit. | 5 | Photochemistry |
As is standard for resonance diagrams, a double-headed arrow is used to indicate that the two structures are not distinct entities, but merely hypothetical possibilities. Neither is an accurate representation of the actual compound, which is best represented by a hybrid (average) of these structures, which can be seen at right. A C=C bond is shorter than a C−C bond, but benzene is perfectly hexagonal—all six carbon-carbon bonds have the same length, intermediate between that of a single and that of a double bond.
A better representation is that of the circular π bond (Armstrongs inner cycle'), in which the electron density is evenly distributed through a π-bond above and below the ring. This model more correctly represents the location of electron density within the aromatic ring.
The single bonds are formed with electrons in line between the carbon nuclei — these are called σ-bonds. Double bonds consist of a σ-bond and a π-bond. The π-bonds are formed from overlap of atomic p-orbitals above and below the plane of the ring. The following diagram shows the positions of these p-orbitals:
Since they are out of the plane of the atoms, these orbitals can interact with each other freely, and become delocalized. This means that, instead of being tied to one atom of carbon, each electron is shared by all six in the ring. Thus, there are not enough electrons to form double bonds on all the carbon atoms, but the "extra" electrons strengthen all of the bonds on the ring equally. The resulting molecular orbital has π symmetry. | 7 | Physical Chemistry |
The hepatitis B virus (HBV) genome encodes its own DNA polymerase for replication. Biomics Biotechnologies has evaluated around 5000 siRNA sequences of this gene for effective knockdown; five sequences were chosen for further investigation and shown to have potent silencing activity when converted into shRNA expression cassettes. A multi-cassette construct, Hepbarna, is under preclinical development for delivery by an adeno-associated virus 8 (AAV-8) liver-targeting vector. | 1 | Biochemistry |
The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pK value is directly proportional to the standard Gibbs free energy change for the reaction. The value of the pK changes with temperature and can be understood qualitatively based on Le Châteliers principle: when the reaction is endothermic, K increases and pK' decreases with increasing temperature; the opposite is true for exothermic reactions.
The value of pK also depends on molecular structure of the acid in many ways. For example, Pauling proposed two rules: one for successive pK of polyprotic acids (see Polyprotic acids below), and one to estimate the pK of oxyacids based on the number of =O and −OH groups (see Factors that affect pK values below). Other structural factors that influence the magnitude of the acid dissociation constant include inductive effects, mesomeric effects, and hydrogen bonding. Hammett type equations have frequently been applied to the estimation of pK.
The quantitative behaviour of acids and bases in solution can be understood only if their pK values are known. In particular, the pH of a solution can be predicted when the analytical concentration and pK values of all acids and bases are known; conversely, it is possible to calculate the equilibrium concentration of the acids and bases in solution when the pH is known. These calculations find application in many different areas of chemistry, biology, medicine, and geology. For example, many compounds used for medication are weak acids or bases, and a knowledge of the pK values, together with the octanol-water partition coefficient, can be used for estimating the extent to which the compound enters the blood stream. Acid dissociation constants are also essential in aquatic chemistry and chemical oceanography, where the acidity of water plays a fundamental role. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the pK values of the many acids and bases present in the cell and in the body. In chemistry, a knowledge of pK values is necessary for the preparation of buffer solutions and is also a prerequisite for a quantitative understanding of the interaction between acids or bases and metal ions to form complexes. Experimentally, pK values can be determined by potentiometric (pH) titration, but for values of pK less than about 2 or more than about 11, spectrophotometric or NMR measurements may be required due to practical difficulties with pH measurements. | 7 | Physical Chemistry |
At the high temperatures for Earth, no volatiles would be in the solid state, and the dust would be made up of silicate and metal.
The continental crust and lower mantle have average K/U values of about 12,000. mid-ocean ridge basalt (MORB) or upper mantle have more volatiles and have a K/U ratio of about 19,000.
Volatile depletion explains why Earth's sodium (volatile) content is about 10% of its calcium (refractory) content, despite the similar abundance in chondrites. | 9 | Geochemistry |
Alkylation of beryllium halide is another common method to react to make an organoberyllium compound such as this:
M is not limited to any main group and/or transition metal. is not limited to phenyl, methyl, methyl oxide, carbene etc. can be any halide such as fluoride, bromide, iodide, or chloride.
An example of such reaction is the synthesis of bis(cyclopentadienyl)beryllium () or beryllocene from and potassium cyclopentadienide: | 0 | Organic Chemistry |
The Long Harbour Nickel Processing Plant is a Canadian nickel concentrate processing facility located in Long Harbour, Newfoundland and Labrador.
Operated by Vale Limited, construction on the plant started in April 2009 and operations began in 2014. Construction costs were in excess of CAD $4.25 billion. Construction involved over 3,200 workers generating approximately 3,000 person-years of employment. Operation of the plant will require approximately 475 workers.
Production began in July 2014, reported in November 2014. Vales nickel processing plant in Long Harbour received its first major shipment from its Labrador mine in Voiseys Bay in May 2015. As of that date, a small proportion of the plants raw materials came from Voiseys Bay but the majority were imported from Indonesia. A spokesman for Vale said 100 per cent of the Long Harbour facilitys production materials will come from Voiseys Bay by early 2016.
Using the metal processing technology of hydrometallurgy, the plant is designed to produce per year of finished nickel product, together with associated cobalt and copper products. The hydrometallurgy technology was piloted at a demonstration plant that opened in Argentia, Newfoundland and Labrador in 2004. This demonstration plant operated until 2008 and was instrumental in helping Vale decide to use the hydrometallurgy process for the Long Harbour processing plant.
A processing plant on Newfoundland was one of the requirements established by the Government of Newfoundland and Labrador in order to exploit the nickel deposit at the Voiseys Bay Mine in Labrador. The bulk carrier MV Umiak I was one of several ice-strengthened bulk carriers built to transport nickel concentrate from Voiseys Bay to the Long Harbour Nickel Processing Plant.
The Long Harbour Nickel Processing Plant was built on a partially brownfield site near the port of Long Harbour. The facility consists of a wharf for offloading nickel ore concentrate from bulk carriers, crushing and grinding facilities, a main processing plant approximately south of the port, a pipeline to supply process water, an effluent discharge pipe and diffuser, and a residue pipeline to a nearby disposal area. The hydrometallurgical process in the plant will pressure-leach the nickel ore concentrate in acidic solutions to separate iron, sulfur and other impurities from nickel, copper and cobalt.
On June 11, 2018, Premier Dwight Ball announced Vale is moving forward with its underground mine at Voiseys Bay. Ball stated that the move will extend the mines operating life by at least 15 years. First ore is expected by April 2021 with processing to take place in Long Harbour. | 8 | Metallurgy |
Carbon can be produced in stars at least as massive as the Sun by fusion of three helium-4 nuclei: He + He + He --> C. This is the triple alpha process.
In stars as massive as the Sun, carbon 12 is also converted to carbon 13 and then onto nitrogen 14 by fusion with protons. C + H --> C + e. C + H --> N. In more massive stars, two carbon nuclei can fuse to magnesium, or a carbon and an oxygen to sulfur. | 9 | Geochemistry |
Another typical example is that of the particles in a nucleus of an atom. The radius of the nucleus is roughly:
where A is the number of nucleons.
The number density of nucleons in a nucleus is therefore:
This density must be divided by two, because the Fermi energy only applies to fermions of the same type. The presence of neutrons does not affect the Fermi energy of the protons in the nucleus, and vice versa.
The Fermi energy of a nucleus is approximately:
where m is the proton mass.
The radius of the nucleus admits deviations around the value mentioned above, so a typical value for the Fermi energy is usually given as 38 MeV. | 7 | Physical Chemistry |
To name conformations of pyranose, first the conformer is determined. The common conformers are similar to those found in cyclohexane, and these form the basis of the name. Common conformations are chair (C), boat (B), skew (S), half-chair (H) or envelope (E). The ring atoms are then numbered; the anomeric, or hemiacetal, carbon is always 1. Oxygen atoms in the structure are, in general, referred to by the carbon atom they are attached to in the acyclic form, and designated O. Then:
*Position the ring so that, if looking at the top face, the atoms are numbered clockwise.
*In the chair and skew conformations, the reference plane should be selected. In the chair conformation, the reference plane is chosen such that the lowest-numbered atom (usually C-1) is exoplanar. In the skew conformation, the plane contains three adjacent atoms and one other with the atom with the lowest possible number exoplanar.
*Atoms above the plane are written before the conformer label, as a superscript
*Atoms below the plane are written following the conformer label, as a subscript | 0 | Organic Chemistry |
The White catalyst can effect both branched and linear regioselective allylic C-H aminations. In order to promote nucleophilic attack at the internal terminus of the π-allyl to generate branched product, a tethered N-sulfonyl carbamate nucleophile is used. This strategy has been applied to the synthesis of 1,2 and 1,3-amino alcohols. The amination proceeds with high yields and good diastereoselectivity, and the products may be readily elaborated to amino acids and other synthetic intermediates and natural products. Key to the development of the reaction was identification of a very acidic nitrogen nucleophile with a pKa close to acetic acid, as more basic nucleophiles divert reactivity to aminopalladation. The intermolecular version of the allylic C-H amination is also known. Using methyl N-tosyl carbamate nucleophile, the linear E-allylic amine products are obtained from α-olefin substrates. It has been shown that functionalization of the π-allyl intermediate may be promoted by chromium(III) salen chloride activation of the electrophile, or Hunig's base activation of the nucleophile. | 0 | Organic Chemistry |
Many substances can form gels when a suitable thickener or gelling agent is added to their formula. This approach is common in manufacture of wide range of products, from foods to paints and adhesives.
In fiber optic communications, a soft gel resembling hair gel in viscosity is used to fill the plastic tubes containing the fibers. The main purpose of the gel is to prevent water intrusion if the buffer tube is breached, but the gel also buffers the fibers against mechanical damage when the tube is bent around corners during installation, or flexed. Additionally, the gel acts as a processing aid when the cable is being constructed, keeping the fibers central whilst the tube material is extruded around it. | 7 | Physical Chemistry |
Brownian motors are nanoscale or molecular machines that use chemical reactions to generate directed motion in space. The theory behind Brownian motors relies on the phenomenon of Brownian motion, random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid.
On the nanoscale (1-100 nm), viscosity dominates inertia, and the extremely high degree of thermal noise in the environment makes conventional directed motion all but impossible, because the forces impelling these motors in the desired direction are minuscule when compared to the random forces exerted by the environment. Brownian motors operate specifically to utilise this high level of random noise to achieve directed motion, and as such are only viable on the nanoscale.
The concept of Brownian motors is a recent one, having only been coined in 1995 by Peter Hänggi, but the existence of such motors in nature may have existed for a very long time and help to explain crucial cellular processes that require movement at the nanoscale, such as protein synthesis and muscular contraction. If this is the case, Brownian motors may have implications for the foundations of life itself.
In more recent times, humans have attempted to apply this knowledge of natural Brownian motors to solve human problems. The applications of Brownian motors are most obvious in nanorobotics due to its inherent reliance on directed motion. | 7 | Physical Chemistry |
Dexrazoxane has been used to protect the heart against the cardiotoxic side effects of chemotherapeutic drugs such as anthracyclines, such as daunorubicin or doxorubicin or other chemotherapeutic agents. However, in July 2011 the European Medicines Agency (EMA) released a statement restricting use only in adult patients with cancer who have received > 300 mg/m doxorubicin or > 540 mg/m epirubicin and general approval for use for cardioprotection. That showed a possibly higher rate of secondary malignancies and acute myelogenous leukemia in pediatric patients treated for different cancers with both dexrazoxane and other chemotherapeutic agents that are associated with secondary malignancies. On July 19, 2017, based on evaluation of the currently available data the European Commission issued an EU-wide legally binding decision to implement the recommendations of the Committee for Medicinal Products for Human Use (CHMP) on dexrazoxane and lifted its 2011-contraindication for primary prevention of anthracycline-induced cardiotoxicity with dexrazoxane in children and adolescents where high doses (≥ 300 mg/m) of anthracyclines are anticipated.
Dexrazoxane was designated by the US FDA as an orphan drug for "prevention of cardiomyopathy for children and adults 0 through 16 years of age treated with anthracyclines". This decision allows virtually all children to receive dexrazoxane starting with the first dose of anthracycline at the discretion of the treating provider. The label change by the agency announcing dexrazoxane as an approved cardio-oncology protectant has been followed by a review by the agency. Currently, the only FDA and EMA approved cardioprotective treatment for anthracycline cardioprotection is dexrazoxane, which provides effective primary cardioprotection against anthracycline-induced cardiotoxicity without reducing anthracycline activity and without enhancing secondary malignancies.
The United States Food and Drug Administration has also approved a dexrazoxane for use as a treatment of extravasation resulting from IV anthracycline chemotherapy. Extravasation is an adverse event in which chemotherapies containing anthracylines leak out of the blood vessel and necrotize the surrounding tissue. | 4 | Stereochemistry |
Two types of convective heat transfer may be distinguished:
* Free or natural convection: when fluid motion is caused by buoyancy forces that result from the density variations due to variations of thermal ±temperature in the fluid. In the absence of an internal source, when the fluid is in contact with a hot surface, its molecules separate and scatter, causing the fluid to be less dense. As a consequence, the fluid is displaced while the cooler fluid gets denser and the fluid sinks. Thus, the hotter volume transfers heat towards the cooler volume of that fluid. Familiar examples are the upward flow of air due to a fire or hot object and the circulation of water in a pot that is heated from below.
* Forced convection: when a fluid is forced to flow over the surface by an internal source such as fans, by stirring, and pumps, creating an artificially induced convection current.
In many real-life applications (e.g. heat losses at solar central receivers or cooling of photovoltaic panels), natural and forced convection occur at the same time (mixed convection).
Internal and external flow can also classify convection. Internal flow occurs when a fluid is enclosed by a solid boundary such as when flowing through a pipe. An external flow occurs when a fluid extends indefinitely without encountering a solid surface. Both of these types of convection, either natural or forced, can be internal or external because they are independent of each other. The bulk temperature, or the average fluid temperature, is a convenient reference point for evaluating properties related to convective heat transfer, particularly in applications related to flow in pipes and ducts.
Further classification can be made depending on the smoothness and undulations of the solid surfaces. Not all surfaces are smooth, though a bulk of the available information deals with smooth surfaces. Wavy irregular surfaces are commonly encountered in heat transfer devices which include solar collectors, regenerative heat exchangers, and underground energy storage systems. They have a significant role to play in the heat transfer processes in these applications. Since they bring in an added complexity due to the undulations in the surfaces, they need to be tackled with mathematical finesse through elegant simplification techniques. Also, they do affect the flow and heat transfer characteristics, thereby behaving differently from straight smooth surfaces.
For a visual experience of natural convection, a glass filled with hot water and some red food dye may be placed inside a fish tank with cold, clear water. The convection currents of the red liquid may be seen to rise and fall in different regions, then eventually settle, illustrating the process as heat gradients are dissipated. | 7 | Physical Chemistry |
Green rust compounds can be synthesized at ordinary ambient temperature and pressure, from solutions containing iron(II) cations, hydroxide anions, and the appropriate intercalatory anions, such as chloride, sulfate, or carbonate.
The result is a suspension of ferrous hydroxide () in a solution of the third anion. This suspension is oxidized by stirring in air, or bubbling air through it. Since the product is very prone to oxidation, it is necessary to monitor the process and exclude oxygen once the desired ratio of and is achieved.
One method first combines an iron(II) salt with sodium hydroxide to form the ferrous hydroxide suspension. Then the sodium salt of the third anion is added, and the suspension is oxidized by stirring in air.
For example, carbonate green rust can be prepared by mixing solutions of iron(II) sulfate and sodium hydroxide; then adding sufficient amount of sodium carbonate solution, followed by the air oxidation step.
Sulfate green rust can be obtained by mixing solutions of ·4 and to precipitate () then immediately adding sodium sulfate and proceeding to the air oxidation step.
A more direct method combines a solution of iron(II) sulfate with , and proceeding to the oxidizing step. The suspension must have a slight excess of (in the ratio of 0.5833 for each ) for the green rust to form; however, too much of it will produce instead an insoluble basic iron sulfate, iron(II) sulfate hydroxide ()·n. The production of green rust is reduced as temperature increases. | 8 | Metallurgy |
Alpha-oxidation of phytanic acid is believed to take place entirely within peroxisomes.
#Phytanic acid is first attached to CoA to form phytanoyl-CoA.
#Phytanoyl-CoA is oxidized by phytanoyl-CoA dioxygenase, in a process using Fe and O, to yield 2-hydroxyphytanoyl-CoA.
#2-hydroxyphytanoyl-CoA is cleaved by 2-hydroxyphytanoyl-CoA lyase in a TPP-dependent reaction to form pristanal and formyl-CoA (in turn later broken down into formate and eventually CO).
#Pristanal is oxidized by aldehyde dehydrogenase to form pristanic acid (which can then undergo beta-oxidation).
(Propionyl-CoA is released as a result of beta oxidation when the beta carbon is substituted) | 1 | Biochemistry |
The term "autoinduction" was first coined in 1970, when it was observed that the bioluminescent marine bacterium Vibrio fischeri produced a luminescent enzyme (luciferase) only when cultures had reached a threshold population density. At low cell concentrations, V. fischeri did not express the luciferase gene. However, once the cultures had reached exponential growth phase, the luciferase gene was rapidly activated. This phenomenon was termed “autoinduction” because it involved a molecule (autoinducer) that accumulated in a growth medium and induced the synthesis of components of the luminescence system. Subsequent research revealed that the actual autoinducer used by V. fischeri is an acylated homoserine lactone (AHL) signaling molecule. | 1 | Biochemistry |
Urea (46-0-0) accounts for more than fifty percent of the world's nitrogenous fertilizers. It is found in granular or prill form, which allows urea to be easily stored, transported and applied in agricultural settings. It is also the cheapest form of granular nitrogen fertilizer. Since urea is not an oxidizer at standard temperature and pressure, it is safer to handle and less of a security risk than other common nitrogen fertilizers, such as ammonium nitrate. However, if urea is applied to the soil surface, a meaningful fraction of applied fertilizer nitrogen may be lost to the atmosphere as ammonia gas; this only occurs under certain conditions. | 9 | Geochemistry |
A push-pull olefin is a type of olefin characterized by an electron-withdrawing substituent on one side of the double bond and an electron-donating substituent on the other side. This makes the pi bond very polarized. The rotational barrier for a push-pull olefin is lower than that of an ordinary olefin and this makes it an interesting candidate for a molecular switch, for instance azobenzenes. A push-pull configuration also helps to stabilize the double bond because the carbon-carbon bond has considerably less double bond character. For instance, cyclobutadiene is a very unstable molecule but with both olefinic bonds in push-pull configuration (two ester substituents and two tertiary amine substituents) the molecule is stable indeed. | 0 | Organic Chemistry |
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