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The mean daily BSi rate strongly depends on the region:
* Coastal upwelling: 46 mmol.m.d
* Sub-arctic Pacific: 18 mmol.m.d
* Southern Ocean: 3–38 mmol.m.d
* mid-ocean gyres: 0.2–1.6 mmol.m.d
Likewise, the integrated annual BSi production strongly depends on the region:
* Coastal upwelling: 3 × 10 mol.yr
* Subarctic Pacific: 8 × 10 mol.yr
* Southern Ocean: 17–37 × 10 mol.yr
* mid-ocean gyres: 26 × 10 mol.yr
BSi production is controlled by:
* Dissolved silica availability, however, half saturation constant Kμ for silicon-limited growth is lower than Ks for silicon uptake.
* Light availability: There is no direct light requirement; silicon uptake at 2x depth of photosynthesis; silicon uptake continues at night but cells must be actively growing.
* Micronutrient availability. | 1 | Biochemistry |
Additional forces beyond the DLVO construct have been reported to also play a major role in determining colloid stability.
DLVO theory is not effective in describing ordering processes such as the evolution of colloidal crystals in dilute dispersions with low salt concentrations. It also cannot explain the relation between the formation of colloidal crystals and salt concentrations. | 7 | Physical Chemistry |
Methanesulfonic acid (MsOH) or methanesulphonic acid (in British English) is an organosulfuric, colorless liquid with the molecular formula and structure . It is the simplest of the alkylsulfonic acids (). Salts and esters of methanesulfonic acid are known as mesylates (or methanesulfonates, as in ethyl methanesulfonate). It is hygroscopic in its concentrated form. Methanesulfonic acid can dissolve a wide range of metal salts, many of them in significantly higher concentrations than in hydrochloric acid (HCl) or sulfuric acid (). | 0 | Organic Chemistry |
Plasma () is one of four fundamental states of matter (the other three being solid, liquid, and gas) characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including the Sun), but also dominating the rarefied intracluster medium and intergalactic medium.
Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field.
The presence of charged particles makes plasma electrically conductive, with the dynamics of individual particles and macroscopic plasma motion governed by collective electromagnetic fields and very sensitive to externally applied fields. The response of plasma to electromagnetic fields is used in many modern devices and technologies, such as plasma televisions or plasma etching.
Depending on temperature and density, a certain number of neutral particles may also be present, in which case plasma is called partially ionized. Neon signs and lightning are examples of partially ionized plasmas.
Unlike the phase transitions between the other three states of matter, the transition to plasma is not well defined and is a matter of interpretation and context. Whether a given degree of ionization suffices to call a substance "plasma" depends on the specific phenomenon being considered. | 7 | Physical Chemistry |
In molecular biology, biochips are engineered substrates ("miniaturized laboratories") that can host large numbers of simultaneous biochemical reactions. One of the goals of biochip technology is to efficiently screen large numbers of biological analytes, with potential applications ranging from disease diagnosis to detection of bioterrorism agents. For example, digital microfluidic biochips are under investigation for applications in biomedical fields. In a digital microfluidic biochip, a group of (adjacent) cells in the microfluidic array can be configured to work as storage, functional operations, as well as for transporting fluid droplets dynamically. | 1 | Biochemistry |
Transition metal hydrides include compounds that can be classified as covalent hydrides. Some are even classified as interstitial hydrides and other bridging hydrides. Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., and . The anions potassium nonahydridorhenate and are examples from the growing collection of known molecular homoleptic metal hydrides. As pseudohalides, hydride ligands are capable of bonding with positively polarized hydrogen centres. This interaction, called dihydrogen bonding, is similar to hydrogen bonding, which exists between positively polarized protons and electronegative atoms with open lone pairs. | 0 | Organic Chemistry |
CataCXium F sulf is a water-soluble organophosphorus compound derived from fluorene. The palladium complexes of the respective phosphine show an excellent activity in various palladium-catalyzed coupling reactions, including Suzuki reactions, Sonogashira couplings and Buchwald–Hartwig reactions. | 0 | Organic Chemistry |
An example of photochlorination at low temperatures and under ambient pressure is the chlorination of chloromethane to dichloromethane. The liquefied chloromethane (boiling point -24 °C) is mixed with chlorine in the dark and then irradiated with a mercury-vapor lamp. The resulting dichloromethane has a boiling point of 41 °C and is later separated by distillation from methyl chloride.
The photochlorination of methane has a lower quantum yield than the chlorination of dichloromethane. Due to the high light intensity required, the intermediate products are directly chlorinated, so that mainly tetrachloromethane is formed. | 5 | Photochemistry |
Tramadol, sold under the brand name Ultram among others, is an opioid pain medication and a serotonin–norepinephrine reuptake inhibitor (SNRI) used to treat moderately severe pain. When taken by mouth in an immediate-release formulation, the onset of pain relief usually begins within an hour. It is also available by injection. It is available in combination with paracetamol (acetaminophen).
As is typical of opioids, common side effects include constipation, itchiness, and nausea. Serious side effects may include hallucinations, seizures, increased risk of serotonin syndrome, decreased alertness, and drug addiction. A change in dosage may be recommended in those with kidney or liver problems. It is not recommended in those who are at risk of suicide or in those who are pregnant. While not recommended in women who are breastfeeding, those who take a single dose should not generally have to stop breastfeeding. Tramadol is converted in the liver to O-desmethyltramadol (desmetramadol), an opioid with a stronger affinity for the μ-opioid receptor.
Tramadol was patented in 1972 and launched under the name "Tramal" in 1977 by the West German pharmaceutical company Grünenthal GmbH. In the mid-1990s, it was approved in the United Kingdom and the United States. It is available as a generic medication and marketed under many brand names worldwide. In 2021, it was the 41st most commonly prescribed medication in the United States, with more than 15million prescriptions. | 4 | Stereochemistry |
Silicon carbide fibers are used to measure gas temperatures in an optical technique called thin-filament pyrometry. It involves the placement of a thin filament in a hot gas stream. Radiative emissions from the filament can be correlated with filament temperature. Filaments are SiC fibers with a diameter of 15 micrometers, about one fifth that of a human hair. Because the fibers are so thin, they do little to disturb the flame and their temperature remains close to that of the local gas. Temperatures of about 800–2500 K can be measured. | 8 | Metallurgy |
Froth flotation efficiency is determined by a series of probabilities: those of particle–bubble contact, particle–bubble attachment, transport between the pulp and the froth, and froth collection into the product launder. In a conventional mechanically-agitated cell, the void fraction (i.e. volume occupied by air bubbles) is low (5 to 10 percent) and the bubble size is usually greater than 1 mm. This results in a relatively low interfacial area and a low probability of particle–bubble contact. Consequently, several cells in series are required to increase the particle residence time, thus increasing the probability of particle–bubble contact. | 8 | Metallurgy |
The bond angle for a symmetric tetrahedral molecule such as CH may be calculated using the dot product of two vectors. As shown in the diagram, the molecule can be inscribed in a cube with the tetravalent atom (e.g. carbon) at the cube centre which is the origin of coordinates, O. The four monovalent atoms (e.g. hydrogens) are at four corners of the cube (A, B, C, D) chosen so that no two atoms are at adjacent corners linked by only one cube edge.
If the edge length of the cube is chosen as 2 units, then the two bonds OA and OB correspond to the vectors a = (1, –1, 1) and b = (1, 1, –1), and the bond angle θ is the angle between these two vectors. This angle may be calculated from the dot product of the two vectors, defined as a • b = ||a|| ||b|| cos θ where ||a|| denotes the length of vector a. As shown in the diagram, the dot product here is –1 and the length of each vector is √3, so that cos θ = –1/3 and the tetrahedral bond angle θ = arccos(–1/3) ≃ 109.47°. | 4 | Stereochemistry |
There are some common types of spectrophotometers include:
UV-vis spectrophotometer: Measures light absorption in UV and visible ranges (200-800 nm). Used for quantification of many inorganic and organic compounds.
1. Infrared spectrophotometer: Measures infrared light absorption, allowing identification of chemical bonds and functional groups.
2. Atomic absorption spectrophotometer (AAS): Uses absorption of light by vaporized analyte atoms to determine concentrations of metals and metalloids.
3. Fluorescence spectrophotometer: Measures intensity of fluorescent light emitted from samples after excitation. Allows highly sensitive analysis of samples with native or induced fluorescence.
4. Colorimeter: Simple spectrophotometers used to measure light absorption for colorimetric assays and tests. | 7 | Physical Chemistry |
Calcineurin along with NFAT, may improve the function of diabetics' pancreatic beta cells. Thus tacrolimus contributes to the frequent development of new diabetes following renal transplantation.
Calcineurin/NFAT signaling is required for perinatal lung maturation and function. | 1 | Biochemistry |
Hydrologic transport models are used to mathematically analyze movement of TDS within river systems. The most common models address surface runoff, allowing variation in land use type, topography, soil type, vegetative cover, precipitation, and land management practice (e.g. the application rate of a fertilizer). Runoff models have evolved to a good degree of accuracy and permit the evaluation of alternative land management practices upon impacts to stream water quality.
Basin models are used to more comprehensively evaluate total dissolved solids within a catchment basin and dynamically along various stream reaches. The DSSAM model was developed by the U.S. Environmental Protection Agency (EPA). This hydrology transport model is actually based upon the pollutant-loading metric called "Total Maximum Daily Load" (TMDL), which addresses TDS and other specific chemical pollutants. The success of this model contributed to the Agency's broadened commitment to the use of the underlying TMDL protocol in its national policy for management of many river systems in the United States. | 2 | Environmental Chemistry |
Unlike in plants, animals do not have a pathway for the direct assimilation of inorganic sulfate into organic compounds. In animals, the primary source of sulfur is dietary methionine, an essential amino acid that contains a sulfur atom. Methionine is first converted to S-adenosylmethionine (SAM), a compound that is involved in many important biological processes, including DNA methylation and neurotransmitter synthesis.
SAM can then be used to synthesize other important sulfur-containing compounds such as cysteine, taurine, and glutathione. Cysteine is a precursor for the synthesis of several important proteins and peptides, as well as glutathione, a powerful antioxidant that protects cells from oxidative stress. Taurine is involved in a variety of physiological processes, including osmoregulation, modulation of calcium signaling, and regulation of mitochondrial function. | 1 | Biochemistry |
Hybridization is the process of complementary base pairs binding to form a double helix. Melting is the process by which the interactions between the strands of the double helix are broken, separating the two nucleic acid strands. These bonds are weak, easily separated by gentle heating, enzymes, or physical force. Melting occurs preferentially at certain points in the nucleic acid. T and A rich sequences are more easily melted than C and G rich regions. Particular base steps are also susceptible to DNA melting, particularly T A and T G base steps. These mechanical features are reflected by the use of sequences such as TATAA at the start of many genes to assist RNA polymerase in melting the DNA for transcription.
Strand separation by gentle heating, as used in PCR, is simple providing the molecules have fewer than about 10,000 base pairs (10 kilobase pairs, or 10 kbp). The intertwining of the DNA strands makes long segments difficult to separate. The cell avoids this problem by allowing its DNA-melting enzymes (helicases) to work concurrently with topoisomerases, which can chemically cleave the phosphate backbone of one of the strands so that it can swivel around the other. Helicases unwind the strands to facilitate the advance of sequence-reading enzymes such as DNA polymerase. | 4 | Stereochemistry |
In clearance, or the rate at which a substance is removed or cleared from the body, it has been found that the cellular proteolysis of AGEs—the breakdown of proteins—produces AGE peptides and "AGE free adducts" (AGE adducts bound to single amino acids). These latter, after being released into the plasma, can be excreted in the urine.
Nevertheless, the resistance of extracellular matrix proteins to proteolysis renders their advanced glycation end products less conducive to being eliminated. While the AGE free adducts are released directly into the urine, AGE peptides are endocytosed by the epithelial cells of the proximal tubule and then degraded by the endolysosomal system to produce AGE amino acids. It is thought that these acids are then returned to the kidney's inside space, or lumen, for excretion.
AGE free adducts are the major form through which AGEs are excreted in urine, with AGE-peptides occurring to a lesser extent but accumulating in the plasma of patients with chronic kidney failure.
Larger, extracellularly derived AGE proteins cannot pass through the basement membrane of the renal corpuscle and must first be degraded into AGE peptides and AGE free adducts. Peripheral macrophage as well as liver sinusoidal endothelial cells and Kupffer cells
have been implicated in this process, although the real-life involvement of the liver has been disputed.
Large AGE proteins unable to enter the Bowman's capsule are capable of binding to receptors on endothelial and mesangial cells and to the mesangial matrix. Activation of RAGE induces production of a variety of cytokines, including TNFβ, which mediates an inhibition of metalloproteinase and increases production of mesangial matrix, leading to glomerulosclerosis and decreasing kidney function in patients with unusually high AGE levels.
Although the only form suitable for urinary excretion, the breakdown products of AGE—that is, peptides and free adducts—are more aggressive than the AGE proteins from which they are derived, and they can perpetuate related pathology in diabetic patients, even after hyperglycemia has been brought under control.
Some AGEs have an innate catalytic oxidative capacity, while activation of NAD(P)H oxidase through activation of RAGE and damage to mitochondrial proteins leading to mitochondrial dysfunction can also induce oxidative stress. A 2007 study found that AGEs could significantly increase expression of TGF-β1, CTGF, Fn mRNA in NRK-49F cells through enhancement of oxidative stress, and suggested that inhibition of oxidative stress might underlie the effect of ginkgo biloba extract in diabetic nephropathy. The authors suggested that antioxidant therapy might help prevent the accumulation of AGEs and induced damage. In the end, effective clearance is necessary, and those suffering AGE increases because of kidney dysfunction might require a kidney transplant.
In diabetics who have an increased production of an AGE, kidney damage reduces the subsequent urinary removal of AGEs, forming a positive feedback loop that increases the rate of damage. In a 1997 study, diabetic and healthy subjects were given a single meal of egg white (56 g protein), cooked with or without 100 g of fructose; there was a greater than 200-fold increase in AGE immunoreactivity from the meal with fructose. | 1 | Biochemistry |
As dissimilatory nitrate reduction to ammonium is an anaerobic respiration process, marine microorganisms capable of performing DNRA are most commonly found in environments low in O, such as oxygen minimum zones (OMZs) in the water column, or sediments with steep O gradients.
DNRA has been documented in prokaryotes inhabiting the upper layer of marine sediments. For example, benthic sulfur bacteria in genera such as Beggiatoa and Thioploca inhabit anoxic sediments on continental shelves and obtain energy by oxidizing sulfide via DNRA. These bacteria are able to carry out DNRA using intracellular nitrate stored in vacuoles. The direct reduction of nitrate to ammonium via dissimilatory nitrate reduction, coupled with the direct conversion of ammonium to dinitrogen via Anammox, has been attributed to significant nitrogen loss in certain parts of the ocean; this DNRA-Anammox coupling by DNRA and Anammox bacteria can account for nitrate loss in areas with no detectable denitrification, such as in OMZs off the coast of Chile, Peru, and Namibia, as well as OMZs over the Omani Shelf in the Arabian Sea. While denitrification is more energetically favourable than DNRA, there is evidence that bacteria using DNRA conserve more energy than denitrifiers, allowing them to grow faster. Thus, via DNRA-Anammox coupling, bacteria using DNRA and Anammox may be stronger competitors for substrates than denitrifiers.
While dissimilatory nitrate reduction to ammonium is more commonly associated with prokaryotes, recent research has found increasing evidence of DNRA in various eukaryotic microorganisms. Of the known DNRA-capable fungal species, one is found in marine ecosystems; an isolate of ascomycete Aspergillus terreus from an OMZ of the Arabian Sea has been found to be capable of performing DNRA under anoxic conditions. Evidence of DNRA has also been found in marine foraminifers.
More recently, it has been discovered that using intracellular nitrate stores, diatoms can carry out dissimilatory nitrate reduction to ammonium, likely for short-term survival or for entering resting stages, thereby allowing them to persist in dark and anoxic conditions. However, their metabolism is probably not sustained by DNRA for long-term survival during resting stages, as these resting stages often can be much longer than their intracellular nitrate supply would last. The use of DNRA by diatoms is a possible explanation for how they can survive buried in dark, anoxic sediment layers on the ocean floor, without being able to carry out photosynthesis or aerobic respiration. Currently, DNRA is known to be carried out by the benthic diatom Amphora coffeaeformis, as well as the pelagic diatom Thalassiosira weissflogii. As diatoms are a significant source of oceanic primary production, the ability for diatoms to perform DNRA has major implications on their ecological role, as well as their role in the marine nitrogen cycle. | 1 | Biochemistry |
Another identification mechanism is through immunoassay. Abbott Laboratories AxSYM is an immunoassay device utilizing Fluorescence Polarization Immunoassay (FPIA) technology that can determine the presence and quantify salicylates. The introduction of a salicylate specific antigen labeled with fluorescein into the sample will mark the sample. Upon irradiation with 490nm light, some of that light will be reflected back to a detector at 520nm. Polarization allows the machine to detect the difference between antibody bound, and unbound fluorescein. It is therefore possible to quantify the serum salicylate level through the signal strength—the amount of reflected light received. | 3 | Analytical Chemistry |
Water is miscible with many liquids, including ethanol in all proportions. Water and most oils are immiscible, usually forming layers according to increasing density from the top. This can be predicted by comparing the polarity. Water being a relatively polar compound will tend to be miscible with liquids of high polarity such as ethanol and acetone, whereas compounds with low polarity will tend to be immiscible and poorly soluble such as with hydrocarbons.
As a gas, water vapor is completely miscible with air. On the other hand, the maximum water vapor pressure that is thermodynamically stable with the liquid (or solid) at a given temperature is relatively low compared with total atmospheric pressure. For example, if the vapor's partial pressure is 2% of atmospheric pressure and the air is cooled from 25 °C, starting at about 22 °C, water will start to condense, defining the dew point, and creating fog or dew. The reverse process accounts for the fog burning off in the morning. If the humidity is increased at room temperature, for example, by running a hot shower or a bath, and the temperature stays about the same, the vapor soon reaches the pressure for phase change and then condenses out as minute water droplets, commonly referred to as steam.
A saturated gas or one with 100% relative humidity is when the vapor pressure of water in the air is at equilibrium with vapor pressure due to (liquid) water; water (or ice, if cool enough) will fail to lose mass through evaporation when exposed to saturated air. Because the amount of water vapor in the air is small, relative humidity, the ratio of the partial pressure due to the water vapor to the saturated partial vapor pressure, is much more useful. Vapor pressure above 100% relative humidity is called supersaturated and can occur if the air is rapidly cooled, for example, by rising suddenly in an updraft. | 2 | Environmental Chemistry |
Present day global emissions of volcanic gases to the atmosphere can be classified as eruptive or non-eruptive. Although all volcanic gas species are emitted to the atmosphere, the emissions of CO (a greenhouse gas) and SO have received the most study.
It has long been recognized that eruptions contribute much lower total SO emissions than passive degassing does. Fischer et al (2019) estimated that, from 2005 to 2015, SO emissions during eruptions were 2.6 teragrams (Tg or 10g or 0.907 gigatons Gt) per year and during non-eruptive periods of passive degassing were 23.2 ± 2Tg per year. During the same time interval, CO emissions from volcanoes during eruptions were estimated to be 1.8 ± 0.9 Tg per year and during non-eruptive activity were 51.3 ± 5.7 Tg per year. Therefore, CO emissions during volcanic eruptions are less than 10% of CO emissions released during non-eruptive volcanic activity.
The 15 June 1991 eruption of Mount Pinatubo (VEI 6) in the Philippines released a total of 18 ± 4 Tg of SO. Such large VEI 6 eruptions are rare and only occur once every 50 – 100 years. The 2010 eruptions of Eyjafjallajökull (VEI 4) in Iceland emitted a total of 5.1 Tg CO. VEI 4 eruptions occur about once per year.
For comparison, Le Quéré, C. et al estimates that human burning of fossil fuels and production of cement processed 9.3 Gt carbon per year from 2006 through 2015, creating up to 34.1 Gt CO2 annually.
Some recent volcanic CO emission estimates are higher than Fischer et al (2019). The estimates of Burton et al. (2013) of 540 Tg CO/year and of Werner et al. (2019) of 220 - 300 Tg CO/year take into account diffuse CO emissions from volcanic regions. | 2 | Environmental Chemistry |
During capping, a 7-methylguanosine residue is attached to the 5-terminal end of the primary transcripts.This is otherwise known as the GTP or 5 cap. The 5 cap is used to increase mRNA stability. Further, the 5 cap is used as an attachment point for ribosomes. Beyond this, the 5' cap has also been shown to have a role in exporting the mature mRNA from the nucleus and into the cytoplasm. | 1 | Biochemistry |
The field of Cu isotope biogeochemistry is still in a relatively early stage, so the Cu isotope compositions of materials in the environment are not well-documented. However, based on a compilation of measurements already made, it appears that Cu isotope ratios vary somewhat widely within and between environmental materials (e.g., plants, minerals, seawater, etc.), though as a whole, these ratios do not vary by more than ±10‰. | 9 | Geochemistry |
Radioligands are administered through four main routes: intravenously, subcutaneous injection, intraperitoneally, and orally. While intravenous application is the most used route of injection, the route is dependent on the mechanism of action and overall aim of the binding. Before application of the ligand, clinicians will perform imaging, generally via Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) for baseline comparison after radioligand administration. Once the radioligand is administered, the radioligand will travel to the target tissue and selectively bind. The structure of the compound allows clinicians to easily identify the path traveled and the destination via repeated imaging and the signal put out by the radiotracer attached to the ligand.
Direct radiotherapy performed via ionizing radiation can cause tissue damage and hypoxia to tissues other than the target. While this effect is lessened in a target radiotracer therapy utilizing radioligands, there is still an impact on the surrounding tissue described as Radiation Induced Bystander Effect (RIBE). Surrounding cells altered by the radioligand and displaying RIBE can show signs of stress, chromosomal abnormalities, or even experience cell death. However, the type of radiation used, whether 𝜶, β, or both can have a dramatically different effect on both the target binding site and surrounding tissue. Changes in nearby tissue is not the only possible impact of ligand therapy, there may be immunologic responses from the target tissue that cause changes remotely. This has been deemed, "abscopal effect". While this mechanism is not well understood, it explains the impact of other tissue, both benign and malignant, after targeted radiotherapy. | 1 | Biochemistry |
The magnitude of the constant may be higher than the value of the molar extinction coefficient, ε, for a species. When this is so, the detection limit for that species will be lower. At high solute concentrations, fluorescence intensity becomes non-linear with respect to concentration due to self-absorption of the scattered radiation. | 7 | Physical Chemistry |
Gene symbols are italicised and all letters are in lowercase (shh). Protein designations are the same as the gene symbol, but are not italicised; the first letter is in uppercase and the remaining letters are in lowercase (Shh). | 1 | Biochemistry |
Glycomics is the comprehensive study of glycomes (the entire complement of sugars, whether free or present in more complex molecules of an organism), including genetic, physiologic, pathologic, and other aspects. Glycomics "is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology. The term glycomics is derived from the chemical prefix for sweetness or a sugar, "glyco-", and was formed to follow the omics naming convention established by genomics (which deals with genes) and proteomics (which deals with proteins). | 0 | Organic Chemistry |
The optimal defense hypothesis attempts to explain how the kinds of defenses a particular plant might use reflect the threats each individual plant faces. This model considers three main factors, namely: risk of attack, value of the plant part, and the cost of defense.
The first factor determining optimal defense is risk: how likely is it that a plant or certain plant parts will be attacked? This is also related to the plant apparency hypothesis, which states that a plant will invest heavily in broadly effective defenses when the plant is easily found by herbivores. Examples of apparent plants that produce generalized protections include long-living trees, shrubs, and perennial grasses. Unapparent plants, such as short-lived plants of early successional stages, on the other hand, preferentially invest in small amounts of qualitative toxins that are effective against all but the most specialized herbivores.
The second factor is the value of protection: would the plant be less able to survive and reproduce after removal of part of its structure by a herbivore? Not all plant parts are of equal evolutionary value, thus valuable parts contain more defenses. A plant's stage of development at the time of feeding also affects the resulting change in fitness. Experimentally, the fitness value of a plant structure is determined by removing that part of the plant and observing the effect. In general, reproductive parts are not as easily replaced as vegetative parts, terminal leaves have greater value than basal leaves, and the loss of plant parts mid-season has a greater negative effect on fitness than removal at the beginning or end of the season. Seeds in particular tend to be very well protected. For example, the seeds of many edible fruits and nuts contain cyanogenic glycosides such as amygdalin. This results from the need to balance the effort needed to make the fruit attractive to animal dispersers while ensuring that the seeds are not destroyed by the animal.
The final consideration is cost: how much will a particular defensive strategy cost a plant in energy and materials? This is particularly important, as energy spent on defense cannot be used for other functions, such as reproduction and growth. The optimal defense hypothesis predicts that plants will allocate more energy towards defense when the benefits of protection outweigh the costs, specifically in situations where there is high herbivore pressure. | 1 | Biochemistry |
In 1914, Polanyi wrote his first paper proposed on adsorption where he proposed a model for the adsorption of gas onto a solid surface. Afterwards, he published a fully developed paper in 1916, which included experimental verification by his students and other authors.
During his research in the University of Budapest, his mentor, Professor Georg Bredig, sent his research findings to Albert Einstein. Einstein wrote back to Bredig stating:
Polanyi later described this event by saying:
Polanyi and Einstein continued to write to each other on and off for the next 20 years. | 7 | Physical Chemistry |
A phagemid or phasmid is a DNA-based cloning vector, which has both bacteriophage and plasmid properties. These vectors carry, in addition to the origin of plasmid replication, an origin of replication derived from bacteriophage. Unlike commonly used plasmids, phagemid vectors differ by having the ability to be packaged into the capsid of a bacteriophage, due to their having a genetic sequence that signals for packaging. Phagemids are used in a variety of biotechnology applications; for example, they can be used in a molecular biology technique called "Phage Display".
The term (and new word) "phagemid" or "phagemids" was offered to the world science community by a group of Soviet scientists, who discovered them, named them, and published the article in April 1984 in Gene magazine. After that, the world community started using this term. | 1 | Biochemistry |
Tens of oligonucleotide probes are designed to be complementary to the RNA of interest. These oligos are labeled with biotin. Cells are cross-linked by UV or formalin and nuclei are isolated from these treated cells. The isolated nuclei were lysed and the released chromatin was fragmented by sonication to produce approximately 100-500 bp sized fragments. These chromatin fragments were hybridized to the biotinylated probe set. Complexes containing biotin-probe + RNA of interest + DNA fragment are captured by magnetic beads labeled with streptavidin.
DNA is isolated from an aliquot of the bound complex by treatment with RNAse (or proteinase followed by RNAse) to digest associated protein and RNA. RNA may also be isolated from an additional aliquot of the bound complex to detect other RNA molecules associated with the RNA of interest. The purified DNA is then used to prepare a sequencing library and the library is sequenced on a next generation DNA sequencing system. The sequencing reads are then mapped to the genome. A pile-up of reads at specific locations on the genome indicates that the RNA of interest had bound to that region of the genome. This helps delineate specific genomic regions that interact with RNA. For example, genomic targets of enhancer RNA which act at a distance from their site of synthesis can be easily evaluated by ChiRP-Seq. | 1 | Biochemistry |
An upstream open reading frame (uORF) is an open reading frame (ORF) within the 5 untranslated region (5UTR) of an mRNA. uORFs can regulate eukaryotic gene expression. Translation of the uORF typically inhibits downstream expression of the primary ORF. However, in some genes such as yeast GCN4, translation of specific uORFs may increase translation of the main ORF. In bacteria, uORFs are called leader peptides and were originally discovered on the basis of their impact on the regulation of genes involved in the synthesis or transport of amino acids.
Approximately 50% of human genes contain uORFs in their 5'UTR, and when present, these cause reductions in protein expression. Human peptides derived from translated uORFs can be detected from cellular material with a mass spectrometer. | 1 | Biochemistry |
Related to the Carothers equation are the following equations (for the simplest case of linear polymers formed from two monomers in equimolar quantities):
where:
:*X is the weight average degree of polymerization,
:*M is the number average molecular weight,
:*M is the weight average molecular weight,
:*M is the molecular weight of the repeating monomer unit,
:*Đ is the dispersity index. (formerly known as polydispersity index, symbol PDI)
The last equation shows that the maximum value of the Đ is 2, which occurs at a monomer conversion of 100% (or p = 1). This is true for step-growth polymerization of linear polymers. For chain-growth polymerization or for branched polymers, the Đ can be much higher.
In practice the average length of the polymer chain is limited by such things as the purity of the reactants, the absence of any side reactions (i.e. high yield), and the viscosity of the medium. | 7 | Physical Chemistry |
Fatal infantile lactic acidosis: Defective SCS has been implicated as a cause of fatal infantile lactic acidosis, which is a disease in infants that is characterized by the build-up of toxic levels of lactic acid. The condition (when it is most severe) results in death usually within 2–4 days after birth. It has been determined that patients with the condition display a two base pair deletion within the gene known as SUCLG1 that encodes the α subunit of SCS. As a result, functional SCS is absent in metabolism causing a major imbalance in flux between glycolysis and the citric acid cycle. Since the cells do not have a functional citric acid cycle, acidosis results because cells are forced to choose lactic acid production as the primary means of producing ATP. | 1 | Biochemistry |
LEIS systems consist of the following:
# Ion Gun, used to direct a beam of ions at a target sample. An electron ionization ion source is typically used to ionize noble gas atoms such as He, Ne or Ar, while heating of wafers containing alkali atoms is used to create an alkali ion beam. The ions thus created hold a positive charge, typically +1, due to the ejection of electrons from the atoms. The range of energies used most often in LEIS is 500 eV to 20 keV. In order to attain good experimental resolution it is important to have a narrow energy spread (ΔE/E < 1%) in the outgoing ion beam.
# Ion beam manipulator, includes the electrostatic lenses of the ion gun for focusing and beam-chopping. Lenses consist of a series of either plate or cylinder geometries and serve to collimate the beam as well as to selectively filter the beam based on mass and velocity. Beam chopping is performed using a pulsed-wave generator when time-of-flight (TOF) experiments are performed. Ions only pass through the chopper when there is no applied voltage.
# Sample manipulator, allows an operator to change the position and/or angle of the target in order to perform experiments with varying geometries. Using directional controls, azimuthal (rotational) and incident angle adjustments may be made.
# Drift tube/drift region, used in TOF setup. TOF measurements are used when analysis of particle velocity is required. By pulsing ions towards the sample with a regular frequency, and observing the time to travel a certain distance after surface impact to a detector, it is possible to calculate the velocity of ions and neutrals coming from the surface. An accelerator may also be used in this setup, prior to the drift tube, in order to achieve separation of ions from neutrals when desired.
# Detector/electrostatic analyzer, used to detect the velocities and/or energies of scattered particles including ions and, in some cases, neutral species. As opposed to TOF analyzers, electrostatic analyzers achieve ion energy resolution using electrostatic deflectors to direct only ions of a particular energy range into a collector, while all other ions are redirected. This type of analyzer can give good energy resolution (and thus, selectivity) but typically suffers from poor sensitivity due to the fact that it only detects ions of a certain energy range and ignores neutral species altogether. Two types of detectors are used: channel electron multiplier (CEM) and microchannel plate (MCP) detectors. CEMs operate in a similar manner to photomultipliers, displaying a cascade of secondary electron emission processes initiated by ion or fast neutral (energy > 1 keV) impact to give a gain in signal current. In this way it is possible to efficiently detect even small ion or neutral particle fluxes. MCP detectors are essentially 2-dimensional arrays of CEMs, and they allow additional information about particle position to be obtained at the cost of sensitivity at any given position.
# Vacuum pumps; Studies are performed in ultra-high vacuum (UHV) conditions ( torr) in order to prevent unwanted interference with the ion beam and/or sample. Common UHV pumps include turbomolecular and ion pumps, with roughing pumping typically performed using a rotary vane pump. Due to the extreme surface (i.e. first-layer) sensitivity of LEIS, samples also need to be rigorously cleaned prior to analysis. Some common processes used to clean samples include sputtering and annealing. Appropriate equipment for cleaning must be contained within the vacuum chamber.
# Other analysis tools; in many cases it is desirable to perform multiple types of analysis on a sample within the same UHV system, or even at the same time. Some additional tools may include Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). Use of these tools typically requires the presence of additional detectors as well as electron and/or x-ray sources where applicable. | 7 | Physical Chemistry |
Vancomycin must be given intravenously (IV) for systemic therapy, since it is poorly absorbed from the intestine. It is a large hydrophilic molecule that partitions poorly across the gastrointestinal mucosa. Due to short half-life, it is often injected twice daily. | 0 | Organic Chemistry |
The advantage in atom economy of using NCAs for peptide formation is that there is no need for a protecting group on the functional group reacted with the amino acid. For example, the Merrifield synthesis depends on the use of Boc and Bzl protecting groups, which need be removed after the reaction. In the case of Bailey peptide synthesis, the free peptide is directly obtained after the reaction. However, unwanted and difficult to remove by-products may be formed. An N-substitution of the NCA (for example, by an o-nitrophenylsulfenyl group) can simplify the subsequent purification process, but on the other hand deteriorates the atom economy of the reaction. The synthesis of NCAs can be carried out by the Leuchs reaction or by the reaction of N-(benzyloxycarbonyl)-amino acids with oxalyl chloride. In the latter case, again the procedure is less efficient in the sense of atom economy. | 1 | Biochemistry |
In geometry, the mirror image of an object or two-dimensional figure is the virtual image formed by reflection in a plane mirror; it is of the same size as the original object, yet different, unless the object or figure has reflection symmetry (also known as a P-symmetry).
Two-dimensional mirror images can be seen in the reflections of mirrors or other reflecting surfaces, or on a printed surface seen inside-out. If we first look at an object that is effectively two-dimensional (such as the writing on a card) and then turn the card to face a mirror, the object turns through an angle of 180° and we see a left-right reversal in the mirror. In this example, it is the change in orientation rather than the mirror itself that causes the observed reversal. Another example is when we stand with our backs to the mirror and face an object that is in front of the mirror. Then we compare the object with its reflection by turning ourselves 180°, towards the mirror. Again we perceive a left-right reversal due to a change in our orientation. So, in these examples the mirror does not actually cause the observed reversals. | 4 | Stereochemistry |
Cerebrospinal fluid is found in the brain and spinal cord. It is a clear fluid that provides a barrier to absorb shock and prevent injury to the brain. It is useful for diagnosing neuro-degenerative diseases such as Alzheimers. There are various substances in the cerebrospinal fluid that can be measured including urea, glucose, potassium, chloride, sodium, protein, creatinine, calcium, alkaline phosphatase, and cortisol. Different things can be learned about the person or how the died by looking at the concentrations of some of these substances. For example, high levels of urea can indicate kidney damage. High levels of cortisol, the hormone released under stress, could indicate a violent death. Creatinine is stable post-mortem, so the concentration at death is preserved. This is also helpful to determine the kidney function of an individual. Sodium and Potassium can also be measured in the cerebrospinal fluid to predict the time since death, but it is not as accurate as it would be if the vitreous humor was used, since it has a lower correlation. | 1 | Biochemistry |
The insertion of carbon monoxide into a metal-carbon bond to form an acyl group is the basis of carbonylation reactions, which provides many commercially useful products. | 0 | Organic Chemistry |
Side effects of gestonorone caproate have been reported to include worsened glucose tolerance, decreased libido in men, and local injection site reactions such as irritation. | 4 | Stereochemistry |
Phosphoric monoester hydrolases (or phosphomonoesterases) are enzymes that catalyse the hydrolysis of O-P bonds by nucleophilic attack of phosphorus by cysteine residues or coordinated metal ions.
They are categorized with the EC number 3.1.3.
Examples include:
* acid phosphatase
* alkaline phosphatase
* fructose-bisphosphatase
* glucose-6-phosphatase
* phosphofructokinase-2
* phosphoprotein phosphatase
* calcineurin
* 6-phytase | 1 | Biochemistry |
To facilitate further preparation, the sawed specimen is usually embedded (or mounted or encapsulated) in a plastic disc, 25, 32 or 38 mm in diameter. A thermosetting solid resin, activated by heat and compression, e.g. mineral-filled epoxy, is best for most applications. A castable (liquid) resin such as unfilled epoxy, acrylic or polyester may be used for porous refractory ceramics or microelectronic devices. The castable resins are also available with fluorescent dyes that aid in fluorescence microscopy. The left and right specimens in Fig. 3 were embedded in mineral-filled epoxy. The center refractory in Fig. 3 was embedded in castable, transparent acrylic. | 8 | Metallurgy |
Some manufacturers primarily produce left-hand drive vehicles, due to the larger or nearer market for such vehicles. For such models supplied to left-hand traffic markets, in the right-hand drive configuration, the manufacturer may reuse the same dashboard configuration as is used in the left-hand drive models, with the steering column and pedals moved to the right-hand side. Oft-used controls (such as audio volume and climate controls) that were placed near the left-hand driver for ease of access, are now situated on the far side of the center console for the right-hand driver. This may make them more difficult to reach quickly or without looking away from the road ahead.
In some cases, the manufacturer's dashboard design incorporates blanks and modular components, which permits the controls and underlying electronics to be rearranged to suit the right-hand drive model. This may be done in the factory, after import, or as an after-market modification. | 4 | Stereochemistry |
Thermally enclosed spaces, including automobiles and greenhouses, are particularly susceptible to harmful temperature increases, especially during extreme weather. This is because of the heavy presence of windows, which are act as "transparent" to incoming solar radiation yet "opaque" to outgoing long-wave thermal radiation, which causes them to heat rapidly. The temperature of an automobile in direct sunlight can rise to 60–82ᵒC when ambient temperatures is only 21ᵒC. This accumulation of heat "can cause heat stroke and hyperthermia in the occupants, especially children", which can be alleviated with passive radiative cooling. | 7 | Physical Chemistry |
The main factor affecting the formal (or apparent) reduction potentials in biochemical or biological processes is the pH. To determine approximate values of formal reduction potentials, neglecting in a first approach changes in activity coefficients due to ionic strength, the Nernst equation has to be applied taking care to first express the relationship as a function of pH. The second factor to be considered are the values of the concentrations taken into account in the Nernst equation. To define a formal reduction potential for a biochemical reaction, the pH value, the concentrations values and the hypotheses made on the activity coefficients must always be clearly indicated. When using, or comparing, several formal (or apparent) reduction potentials they must also be internally consistent.
Problems may occur when mixing different sources of data using different conventions or approximations (i.e., with different underlying hypotheses). When working at the frontier between inorganic and biological processes (e.g., when comparing abiotic and biotic processes in geochemistry when microbial activity could also be at work in the system), care must be taken not to inadvertently directly mix standard reduction potentials ( versus SHE, pH = 0) with formal (or apparent) reduction potentials ( at pH = 7). Definitions must be clearly expressed and carefully controlled, especially if the sources of data are different and arise from different fields (e.g., picking and directly mixing data from classical electrochemistry textbooks ( versus SHE, pH = 0) and microbiology textbooks ( at pH = 7) without paying attention to the conventions on which they are based). | 1 | Biochemistry |
Inverse polymerase chain reaction (Inverse PCR) is a variant of the polymerase chain reaction that is used to amplify DNA with only one known sequence. One limitation of conventional PCR is that it requires primers complementary to both termini of the target DNA, but this method allows PCR to be carried out even if only one sequence is available from which primers may be designed.
Inverse PCR is especially useful for the determination of insert locations. For example, various retroviruses and transposons randomly integrate into genomic DNA. To identify the sites where they have entered, the known, "internal" viral or transposon sequences can be used to design primers that will amplify a small portion of the flanking, "external" genomic DNA. The amplified product can then be sequenced and compared with DNA databases to locate the sequence which has been disrupted.
The inverse PCR method involves a series of restriction digests and ligation, resulting in a looped fragment that can be primed for PCR from a single section of known sequence. Then, like other polymerase chain reaction processes, the DNA is amplified by the thermostable DNA polymerase:
# A target region with an internal section of known sequence and unknown flanking regions is identified
# Genomic DNA is digested into fragments of a few kilobases by a usually low-moderate frequency (6-8 base) cutting restriction enzyme.
# Under low DNA concentrations or quick ligation conditions, self-ligation is induced to give a circular DNA product.
# PCR is carried out as usual with the circular template, with primers complementary to sections of the known internal sequence pointing outwards.
Finally the sequence of the sequenced PCR product is compared against sequence databases.
It is used in case of chromosome crawling. | 1 | Biochemistry |
A major function of the peroxisome is the breakdown of very long chain fatty acids through beta oxidation. In animal cells, the long fatty acids are converted to medium chain fatty acids, which are subsequently shuttled to mitochondria where they eventually are broken down to carbon dioxide and water. In yeast and plant cells, this process is carried out exclusively in peroxisomes.
The first reactions in the formation of plasmalogen in animal cells also occur in peroxisomes. Plasmalogen is the most abundant phospholipid in myelin. Deficiency of plasmalogens causes profound abnormalities in the myelination of nerve cells, which is one reason why many peroxisomal disorders affect the nervous system. Peroxisomes also play a role in the production of bile acids important for the absorption of fats and fat-soluble vitamins, such as vitamins A and K. Skin disorders are features of genetic disorders affecting peroxisome function as a result.
The specific metabolic pathways that occur exclusively in mammalian peroxisomes are:
* α-oxidation of phytanic acid
* β-oxidation of very-long-chain and polyunsaturated fatty acids
* biosynthesis of plasmalogens
* conjugation of cholic acid as part of bile acid synthesis
Peroxisomes contain oxidative enzymes, such as D-amino acid oxidase and uric acid oxidase. However the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid. Certain enzymes within the peroxisome, by using molecular oxygen, remove hydrogen atoms from specific organic substrates (labeled as R), in an oxidative reaction, producing hydrogen peroxide (HO, itself toxic):
Catalase, another peroxisomal enzyme, uses this HO to oxidize other substrates, including phenols, formic acid, formaldehyde, and alcohol, by means of the peroxidation reaction:
:, thus eliminating the poisonous hydrogen peroxide in the process.
This reaction is important in liver and kidney cells, where the peroxisomes detoxify various toxic substances that enter the blood. About 25% of the ethanol that humans consume by drinking alcoholic beverages is oxidized to acetaldehyde in this way. In addition, when excess HO accumulates in the cell, catalase converts it to HO through this reaction:
In higher plants, peroxisomes contain also a complex battery of antioxidative enzymes such as superoxide dismutase, the components of the ascorbate-glutathione cycle, and the NADP-dehydrogenases of the pentose-phosphate pathway. It has been demonstrated that peroxisomes generate superoxide (O) and nitric oxide (NO) radicals.
There is evidence now that those reactive oxygen species including peroxisomal HO are also important signalling molecules in plants and animals and contribute to healthy ageing and age-related disorders in humans.
The peroxisome of plant cells is polarised when fighting fungal penetration. Infection causes a glucosinolate molecule to play an antifungal role to be made and delivered to the outside of the cell through the action of the peroxisomal proteins (PEN2 and PEN3).
Peroxisomes in mammals and humans also contribute to anti-viral defense. and the combat of pathogens | 1 | Biochemistry |
If an inducer, a molecule that initiates the gene expression, is present, then it can interact with the repressor protein and detach it from the operator. RNA polymerase then can transcribe the message (expressing the gene). A co-repressor is a molecule that can bind to the repressor and make it bind to the operator tightly, which decreases transcription.
A repressor that binds with a co-repressor is termed an aporepressor or inactive repressor. One type of aporepressor is the trp repressor, an important metabolic protein in bacteria. The above mechanism of repression is a type of a feedback mechanism because it only allows transcription to occur if a certain condition is present: the presence of specific inducer(s). In contrast, an active repressor binds directly to an operator to repress gene expression.
While repressors are more commonly found in prokaryotes, they are rare in eukaryotes. Furthermore, most known eukaryotic repressors are found in simple organisms (e.g., yeast), and act by interacting directly with activators. This contrasts prokaryotic repressors which can also alter DNA or RNA structure.
Within the eukaryotic genome are regions of DNA known as silencers. These are DNA sequences that bind to repressors to partially or fully repress a gene. Silencers can be located several bases upstream or downstream from the actual promoter of the gene. Repressors can also have two binding sites: one for the silencer region and one for the promoter. This causes chromosome looping, allowing the promoter region and the silencer region to come in proximity of each other. | 1 | Biochemistry |
This technique has found applications in many different fields, from semiconductor physics to microelectronics and biology, from basic research to industrial applications. Ellipsometry is a very sensitive measurement technique and provides unequaled capabilities for thin film metrology. As an optical technique, spectroscopic ellipsometry is non-destructive and contactless. Because the incident radiation can be focused, small sample sizes can be imaged and desired characteristics can be mapped over a larger area (m). | 7 | Physical Chemistry |
Within the Earth's atmosphere and surface, the liquid phase is the most common and is the form that is generally denoted by the word "water". The solid phase of water is known as ice and commonly takes the structure of hard, amalgamated crystals, such as ice cubes, or loosely accumulated granular crystals, like snow. Aside from common hexagonal crystalline ice, other crystalline and amorphous phases of ice are known. The gaseous phase of water is known as water vapor (or steam). Visible steam and clouds are formed from minute droplets of water suspended in the air.
Water also forms a supercritical fluid. The critical temperature is 647 K and the critical pressure is 22.064 MPa. In nature, this only rarely occurs in extremely hostile conditions. A likely example of naturally occurring supercritical water is in the hottest parts of deep water hydrothermal vents, in which water is heated to the critical temperature by volcanic plumes and the critical pressure is caused by the weight of the ocean at the extreme depths where the vents are located. This pressure is reached at a depth of about 2200 meters: much less than the mean depth of the ocean (3800 meters). | 2 | Environmental Chemistry |
*ATF1 NM_005171
*ATF2 NM_001880
*ATF4 Activating transcription factor 4 NM_001675
*ATF6 NM_007348
*ATF7 NM_001206682
*ATF7IP NM_018179
*BTF3 NM_001207 Homo sapiens basic transcription factor 3
*E2F4 Homo sapiens E2F transcription factor 4, p107/p130-binding (E2F4), mRNA
*ERH (gene) Enhancer of rudimentary homolog of drosophila (which in turn is the first enzymatic step in pyrimidine synthesis. Regulated by MITF)
*HMGB1 High mobility group box binds DNA
*ILF2 Homo sapiens interleukin enhancer binding factor 2, 45kDa (ILF2), mRNA
*IER2 formerly ETR101 Immediate Early Protein?
*JUND Homo sapiens jun D proto-oncogene (JUND), mRNA
*TCEB2 Elongin Matheo er rar | 1 | Biochemistry |
The Redlich–Kwong equation is formulated as:
where:
*p is the gas pressure
*R is the gas constant,
*T is temperature,
*V is the molar volume (V/n),
*a is a constant that corrects for attractive potential of molecules, and
*b is a constant that corrects for volume.
The constants are different depending on which gas is being analyzed. The constants can be calculated from the critical point data of the gas:
where:
*T is the temperature at the critical point, and
*P is the pressure at the critical point.
The Redlich–Kwong equation can also be represented as an equation for the compressibility factor of gas, as a function of temperature and pressure:
where:
Or more simply:
This equation only implicitly gives Z as a function of pressure and temperature, but is easily solved numerically, originally by graphical interpolation, and now more easily by computer. Moreover, analytic solutions to cubic functions have been known for centuries and are even faster for computers. The Redlich-Kwong equation of state may also be expressed as a cubic function of the molar volume.
For all Redlich–Kwong gases:
where:
*Z is the compressibility factor at the critical point
Using the equation of state can be written in the reduced form:
And since it follows: with
From the Redlich–Kwong equation, the fugacity coefficient of a gas can be estimated: | 7 | Physical Chemistry |
Electronic components that require clear transparency for light to exit or enter (photovoltaic panels and sensors) can be potted using acrylic resins that are cured using UV energy. The advantages are low VOC emissions and rapid curing.
Certain inks, coatings, and adhesives are formulated with photoinitiators and resins. When exposed to UV light, polymerization occurs, and so the adhesives harden or cure, usually within a few seconds. Applications include glass and plastic bonding, optical fiber coatings, the coating of flooring, UV coating and paper finishes in offset printing, dental fillings, and decorative fingernail "gels".
UV sources for UV curing applications include UV lamps, UV LEDs, and excimer flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are used, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs can be used for static applications. Small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.
The impact of UV on polymers is used for modification of the (roughness and hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet.
UV radiation is useful in preparing low-surface-energy polymers for adhesives. Polymers exposed to UV will oxidize, thus raising the surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger. | 5 | Photochemistry |
The toxicity of palytoxin is due to its binding to external part of Na/K-ATPase (the sodium–potassium pump), where it interacts with the natural binding site of ouabain with very high affinity. Na/K-ATPase is a transmembrane protein, which is found on the surface of every vertebrate cell. The sodium–potassium pump is necessary for viability of all cells, and this explains the fact that palytoxin affects all cells. Through this channel, which it forms within the sodium–potassium pump, monovalent positive ions such as sodium and potassium can diffuse freely, thereby destroying the ion gradient of the cell. Once palytoxin is bound to the pump, it flips constantly between open and normal conformations. The open conformation is more likely (over 90% probability). If palytoxin detaches, the pump will return to closed conformation. In open conformation, millions of ions diffuse through the pump per second, whereas only about one hundred ions per second are transported through a normally functioning transporter.
Loss of ion gradient leads to death and hemolysis of red blood cells, for example, and also to violent contractions of heart and other muscle cells.
First evidence of the mechanism described above was obtained in 1981 and the proposed mechanism was published in 1982. Because the mechanism of action of palytoxin was so unlike any other, it was initially not widely accepted. This was primarily because it was not expected that a pump which provides active transport, could become an ion channel by binding of a compound such as palytoxin. Therefore, there were some alternative hypotheses, which were reviewed by Frelin and van Renterghem in 1995. The breakthrough research which is seen as proof for the sodium–potassium pump mechanism was performed in yeast cells (Saccharomyces cerevisiae). These cells do not have the sodium–potassium pump, and hence palytoxin does not affect them. But once they were given the DNA to encode for complete sheep Na/K-ATPase, they were killed by palytoxin. | 0 | Organic Chemistry |
In meteorology, mixing ratio usually refers to the mass ratio of water , which is defined as the mass of water divided by the mass of dry air () in a given air parcel:
The unit is typically given in . The definition is similar to that of specific humidity. | 3 | Analytical Chemistry |
By the late 1860s, Wislicenus devoted his research to organic chemistry. His work on the isomeric lactic acids from 1868 to 1872 resulted in the discovery of two substances with different physical properties but with an identical chemical structure. He called this difference "geometrical isomerism". He would later promote J. H. vant Hoffs theory of the tetrahedral carbon atom, believing that it, together with the supposition that there are "specially directed forces, the affinity-energies", which determine the relative position of atoms in the molecule, afforded a method by which the spatial arrangement of atoms in particular cases may be ascertained by experiment. While at Würzburg, Wislicenus developed the use of ethyl aceto acetate in organic synthesis. However, he was also active in inorganic chemistry, finding a reaction for the production of sodium azide. He was the first to prepare cyclopentane in 1893 | 4 | Stereochemistry |
Electrokinetic phenomena are a family of several different effects that occur in heterogeneous fluids, or in porous bodies filled with fluid, or in a fast flow over a flat surface. The term heterogeneous here means a fluid containing particles. Particles can be solid, liquid or gas bubbles with sizes on the scale of a micrometer or nanometer. There is a common source of all these effects—the so-called interfacial double layer of charges. Influence of an external force on the diffuse layer generates tangential motion of a fluid with respect to an adjacent charged surface. This force might be electric, pressure gradient, concentration gradient, or gravity. In addition, the moving phase might be either continuous fluid or dispersed phase. | 7 | Physical Chemistry |
The condition on linearly independent translations means that there exist linearly independent vectors v and w (in R) such that the group contains both T and T.
The purpose of this condition is to distinguish wallpaper groups from frieze groups, which possess a translation but not two linearly independent ones, and from two-dimensional discrete point groups, which have no translations at all. In other words, wallpaper groups represent patterns that repeat themselves in two distinct directions, in contrast to frieze groups, which only repeat along a single axis.
(It is possible to generalise this situation. One could for example study discrete groups of isometries of R with m linearly independent translations, where m is any integer in the range 0 ≤ m ≤ n.) | 3 | Analytical Chemistry |
There are generally accepted rules and conventions used for naming genes in bacteria. Standards were proposed in 1966 by Demerec et al. | 1 | Biochemistry |
Photoacoustic spectroscopy has become a powerful technique to study concentrations of gases at the part per billion or even part per trillion levels. Modern photoacoustic detectors still rely on the same principles as Bell's apparatus; however, to increase the sensitivity, several modifications have been made.
Instead of sunlight, intense lasers are used to illuminate the sample since the intensity of the generated sound is proportional to the light intensity; this technique is referred to as laser photoacoustic spectroscopy (LPAS). The ear has been replaced by sensitive microphones. The microphone signals are further amplified and detected using lock-in amplifiers. By enclosing the gaseous sample in a cylindrical chamber, the sound signal is amplified by tuning the modulation frequency to an acoustic resonance of the sample cell.
By using cantilever enhanced photoacoustic spectroscopy sensitivity can still be further improved enabling reliable monitoring of gases on ppb-level. | 7 | Physical Chemistry |
The first law of thermodynamics states: In a process without transfer of matter, the change in internal energy, , of a thermodynamic system is equal to the energy gained as heat, , less the thermodynamic work, , done by the system on its surroundings.
where denotes the change in the internal energy of a closed system (for which heat or work through the system boundary are possible, but matter transfer is not possible), denotes the quantity of energy supplied to the system as heat, and denotes the amount of thermodynamic work done by the system on its surroundings. An equivalent statement is that perpetual motion machines of the first kind are impossible; work done by a system on its surrounding requires that the system's internal energy decrease or be consumed, so that the amount of internal energy lost by that work must be resupplied as heat by an external energy source or as work by an external machine acting on the system (so that is recovered) to make the system work continuously.
For processes that include transfer of matter, a further statement is needed: With due account of the respective fiducial reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of the wall, then
where denotes the internal energy of the combined system, and and denote the internal energies of the respective separated systems.
Adapted for thermodynamics, this law is an expression of the principle of conservation of energy, which states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.
Internal energy is a principal property of the thermodynamic state, while heat and work are modes of energy transfer by which a process may change this state. A change of internal energy of a system may be achieved by any combination of heat added or removed and work performed on or by the system. As a function of state, the internal energy does not depend on the manner, or on the path through intermediate steps, by which the system arrived at its state. | 7 | Physical Chemistry |
While the original Y2H system used a reconstituted transcription factor, other systems create enzymatic activities to detect PPIs. For instance, the KInase Substrate Sensor ("KISS"), is a mammalian two-hybrid approach has been designed to map intracellular PPIs. Here, a bait protein is fused to a kinase-containing portion of TYK2 and a prey is coupled to a gp130 cytokine receptor fragment. When bait and prey interact, TYK2 phosphorylates STAT3 docking sites on the prey chimera, which ultimately leads to activation of a reporter gene. | 1 | Biochemistry |
*Monocytes / macrophages: the key chemokines that attract these cells to the site of inflammation include: CCL2, CCL3, CCL5, CCL7, CCL8, CCL13, CCL17 and CCL22.
*T-lymphocytes: the four key chemokines that are involved in the recruitment of T lymphocytes to the site of inflammation are: CCL2, CCL1, CCL22 and CCL17. Furthermore, CXCR3 expression by T-cells is induced following T-cell activation and activated T-cells are attracted to sites of inflammation where the IFN-y inducible chemokines CXCL9, CXCL10 and CXCL11 are secreted.
*Mast cells: on their surface express several receptors for chemokines: CCR1, CCR2, CCR3, CCR4, CCR5, CXCR2, and CXCR4. Ligands of these receptors CCL2 and CCL5 play an important role in mast cell recruitment and activation in the lung. There is also evidence that CXCL8 might be inhibitory of mast cells.
*Eosinophils: the migration of eosinophils into various tissues involved several chemokines of CC family: CCL11, CCL24, CCL26, CCL5, CCL7, CCL13, and CCL3. Chemokines CCL11 (eotaxin) and CCL5 (RANTES) acts through a specific receptor CCR3 on the surface of eosinophils, and eotaxin plays an essential role in the initial recruitment of eosinophils into the lesion.
*Neutrophils: are regulated primarily by CXC chemokines. An example CXCL8 (IL-8) is chemoattractant for neutrophils and also activating their metabolic and degranulation. | 1 | Biochemistry |
The material was first described in 1908. The catalyst was developed in North America by Homer Burton Adkins and Wilbur Arthur Lazier, partly based on interrogation of German chemists after World War II in relation to the Fischer–Tropsch process. For this reason it is sometimes referred to as the Adkins catalyst or the Lazier catalyst. | 0 | Organic Chemistry |
The notion of isomer also appears in other fields such as chemistry and meteorology. Therefore, in the first publications devoted to this effect the name nuclear isomeric shift on spectral lines was used. Before the discovery of the Mössbauer effect, the isomeric shift referred exclusively to atomic spectra; this explains the absence of the word atomic in the initial definition of the effect. Subsequently, the isomeric shift was also observed in gamma spectroscopy through the Mössbauer effect and was called Mössbauer isomeric shift. For further details on the history of the isomeric shift and the terminology used, see. | 7 | Physical Chemistry |
Geometric Dynamic Recrystallization (GDR) is a recrystallization mechanism that has been proposed to occur in several alloys, particularly aluminium, at high temperatures and low strain rates. It is a variant of dynamic recrystallization.
The basic mechanism is that during deformation the grains will be increasingly flattened until the boundaries on each side are separated by only a small distance. The deformation is accompanied by the serration of the grain boundaries due to surface tension effects where they are in contact with low-angle grain boundaries belonging to sub-grains.
Eventually the points of the serrations will come into contact. Since the contacting boundaries are defects of opposite sign they are able to annihilate and so reduce the total energy in the system. In effect the grain will pinch in two new grains.
The grain size is known to decrease as the applied stress is increased. However, high stresses require a high strain rate and at some point statically recrystallized grains will begin to nucleate and consume the GDRX microstructure.
There are features that are unique to GDRX:
* The recrystallisation spreads throughout the specimen over a strain range (0.5-1 in Al-Mg-Mn alloys) without any change in flow stress. This is in contrast to discontinuous mechanisms where the flow stress normally decreases by ~25% as the recrystallized grains form.
* GDRX results in grains that are around 3 times the sub-grain size. Statically recrystallized grains are normally 20-30 times the sub-grain size. | 8 | Metallurgy |
The relative reducing and oxidizing natures of these photocatalysts can be understood by considering the ligands electronegativity and the catalyst complexs metal center. More electronegative metals and ligands can stabilize electrons better than their less electronegative counterparts. Therefore, complexes with more electronegative ligands are more oxidizing than less electronegative ligand complexes. For example, the ligands 2,2-bipyridine and 2,2-phenylpyridine are isoelectronic structures, containing the same number and arrangement of electrons. Phenylpyridine replaces one of the nitrogen atoms in bipyridine with a carbon atom. Carbon is less electronegative than nitrogen is, so it holds electrons less tightly. Since the remainder of the ligand molecule is identical and phenylpyridine holds electrons less tightly than bipyridine, it is more strongly electron-donating and less electronegative as a ligand. Hence, complexes with phenylpyridine ligands are more strongly reducing and less strongly oxidizing than equivalent complexes with bipyridine ligands.
Similarly, a fluorinated phenylpyridine ligand is more electronegative than phenylpyridine so complexes with fluorine-containing ligands are more strongly oxidizing and less strongly reducing than equivalent unsubstituted phenylpyridine complexes. The metal center's electronic influence on the complex is more complex than the ligand effect. According to the Pauling scale of electronegativity, both ruthenium and iridium have an electronegativity of 2.2. If this was the sole factor relevant to redox potentials, then complexes of ruthenium and iridium with the same ligands should be equally powerful photoredox catalysts. However, considering the Rehm-Weller equation, the spectroscopic properties of the metal play a role in determining the redox properties of the excited state. In particular, the parameter E is related to the emission wavelength of the complex and therefore, to the size of the Stokes shift - the difference in energy between the maximum absorption and emission of a molecule. Typically, ruthenium complexes have large Stokes shifts and hence, low energy emission wavelengths and small zero-zero excitation energies when compared to iridium complexes. In effect, while ground-state ruthenium complexes can be potent reductants, the excited-state complex is a far less potent reductant or oxidant than its equivalent iridium complex. This makes iridium preferred for the development of general organic transformations because the stronger redox potentials of the excited catalyst allows the use of weaker stoichiometric reductants and oxidants or the use of less reactive substrates.
It is often the case that these photocatalysts are balanced with a counter-ion, as is the case with the example complex tris-(2,2’-bipyridyl)ruthenium which is accompanied by two anions to balance the overall charge of the ion pair to zero. However, there are transition metal photoredox catalysts that exist without a counter-ion such as tris(2-phenylpyridine)iridium (often abbreviated Ir(ppy)). The significance of these counter-ions are dependent on the ion association between the photoredox catalyst and its counter-ion(s) and is dependent on the solvent used for the reaction. Although photophysical properties such as redox potential, excitation energy, and ligand electronegative have often been considered key parameters for the use and reactivity of these complexes, counter-ion identity has been shown to play a significant role in low-polarity solvents. Particularly, it has been shown that having a tightly associated counter-ion increases the rate of electron-transfer when reducing a substrate but significantly reduces the rate of electron-transfer when oxidizing a substrate. This is believed to occur because the counter-ion essentially "blocks" the electron-transfer into the photoredox complex by shielding the more positively charged region of the complex; whereas, having the tight counter-ion association pushes the electron density further from the photoredox catalyst's metal-center, making it easier to be transferred from the catalyst (of course this only applies to the case where the photoredox catalyst is a cation and the counter-ion is an anion). Counter-ion identity thus is an additional parameter to consider when developing new photoredox reactions. | 5 | Photochemistry |
All cloning vectors have features that allow a gene to be conveniently inserted into the vector or removed from it. This may be a multiple cloning site (MCS) or polylinker, which contains many unique restriction sites. The restriction sites in the MCS are first cleaved by restriction enzymes, then a PCR-amplified target gene also digested with the same enzymes is ligated into the vectors using DNA ligase. The target DNA sequence can be inserted into the vector in a specific direction if so desired. The restriction sites may be further used for sub-cloning into another vector if necessary.
Other cloning vectors may use topoisomerase instead of ligase and cloning may be done more rapidly without the need for restriction digest of the vector or insert. In this TOPO cloning method a linearized vector is activated by attaching topoisomerase I to its ends, and this "TOPO-activated" vector may then accept a PCR product by ligating both the 5' ends of the PCR product, releasing the topoisomerase and forming a circular vector in the process. Another method of cloning without the use of DNA digest and ligase is by DNA recombination, for example as used in the Gateway cloning system. The gene, once cloned into the cloning vector (called entry clone in this method), may be conveniently introduced into a variety of expression vectors by recombination. | 1 | Biochemistry |
Currently, CO capture uses mostly amine-based absorption technologies, which are energy intensive and solvent intensive. Volatile organic compounds alone in chemical processes represent a multibillion-dollar industry. Therefore, ionic liquids offer an alternative that prove attractive should their other deficiencies be addressed.
During the capture process, the anion and cation play a crucial role in the dissolution of CO. Spectroscopic results suggest a favorable interaction between the anion and CO, wherein CO molecules preferentially attach to the anion. Furthermore, intermolecular forces, such as hydrogen bonds, van der Waals bonds, and electrostatic attraction, contributes to the solubility of CO in ionic liquids. This makes ionic liquids promising candidates for CO capture because the solubility of CO can be modeled accurately by the regular solubility theory (RST), which reduces operational costs in developing more sophisticated model to monitor the capture process. | 7 | Physical Chemistry |
Pioneer factors can also affect transcription and differentiation through the control of DNA methylation. Pioneer factors that bind to CpG islands and cytosine residues block access to methyltransferases. Many eukaryotic cells have CpG islands in their promoters that can be modified by methylation having adverse effects on their ability to control transcription. This phenomenon is also present in promoters without CpG islands where single cytosine residues are protected from methylation until further cell differentiation. An example is FoxD3 preventing methylation of a cytosine residue in Alb1 enhancer, acting as a place holder for FoxA1 later in hepatic as well as in CpG islands of genes in chronic lymphocytic leukemia. For stable control of methylation state the cytosine residues are covered during mitosis, unlike most other transcription factors, to prevent methylation. Studies have shown that during mitosis 15% of all interphase FoxA1 binding sites were bound. The protection of cytosine methylation can be quickly removed allowing for rapid induction when a signal is present. | 1 | Biochemistry |
Kowalski was the founding editor of the Journal of Chemometics, the first issue of which came out in January 1987. The editorial of the first issue, written by Kowalski, Steven Brown and Bernard Vandeginst, explains that after 10 years of the founding of the field of chemometrics and 20 years of researchers actually doing chemometrics and having their publications "widely distributed through the literature," it was time for a journal "to bring together papers on how chemists use mathematics and statistics in their work in novel ways and also on potentially new tools that chemists may find useful in the future." After his death the journal published a special issue in his honor in May 2014. It also established the annual Kowalski Prize for the best theoretical and applied papers published in the journal in the two preceding years. | 3 | Analytical Chemistry |
Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae, and sometimes also in certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is to make the process of light accumulation required for photosynthesis more efficient; while in insects they play a role in growth and development. Some of their properties: including light-receptivity, light-harvesting and fluorescence have made them suitable for applications in bioimaging and as indicators; while other properties such as anti-oxidation, anti-aging and anti-inflammation in phycobiliproteins have given them potential for use in medicine, cosmetics and food technology. While research on biliproteins dates back as far as 1950, it was hindered due to issues regarding biliprotein structure, lack of methods available for isolating individual biliprotein components, as well as limited information on lyase reactions (which are needed to join proteins with their chromophores). Research on biliproteins has also been primarily focused on phycobiliproteins; but advances in technology and methodology, along with the discovery of different types of lyases, has renewed interest in biliprotein research, allowing new opportunities for investigating biliprotein processes such as assembly/disassembly and protein folding. | 1 | Biochemistry |
One of the most commonly used practices to quantitate DNA or RNA is the use of spectrophotometric analysis using a spectrophotometer. A spectrophotometer is able to determine the average concentrations of the nucleic acids DNA or RNA present in a mixture, as well as their purity.
Spectrophotometric analysis is based on the principles that nucleic acids absorb ultraviolet light in a specific pattern. In the case of DNA and RNA, a sample is exposed to ultraviolet light at a wavelength of 260 nanometres (nm) and a photo-detector measures the light that passes through the sample. Some of the ultraviolet light will pass through and some will be absorbed by the DNA / RNA. The more light absorbed by the sample, the higher the nucleic acid concentration in the sample. The resulting effect is that less light will strike the photodetector and this will produce a higher optical density (OD)
Using the Beer–Lambert law it is possible to relate the amount of light absorbed to the concentration of the absorbing molecule. At a wavelength of 260 nm, the average extinction coefficient for double-stranded DNA is 0.020 (μg/ml) cm, for single-stranded DNA it is 0.027 (μg/ml) cm, for single-stranded RNA it is 0.025 (μg/ml) cm and for short single-stranded oligonucleotides it is dependent on the length and base composition. Thus, an Absorbance (A) of 1 corresponds to a concentration of 50 μg/ml for double-stranded DNA. This method of calculation is valid for up to an A of at least 2. A more accurate extinction coefficient may be needed for oligonucleotides; these can be predicted using the nearest-neighbor model. | 7 | Physical Chemistry |
In genetics, DNase I hypersensitive sites (DHSs) are regions of chromatin that are sensitive to cleavage by the DNase I enzyme. In these specific regions of the genome, chromatin has lost its condensed structure, exposing the DNA and making it accessible. This raises the availability of DNA to degradation by enzymes, such as DNase I. These accessible chromatin zones are functionally related to transcriptional activity, since this remodeled state is necessary for the binding of proteins such as transcription factors.
Since the discovery of DHSs 30 years ago, they have been used as markers of regulatory DNA regions. These regions have been shown to map many types of cis-regulatory elements including promoters, enhancers, insulators, silencers and locus control regions. A high-throughput measure of these regions is available through DNase-Seq. | 1 | Biochemistry |
Antitranspirants are compounds applied to the leaves of plants to reduce transpiration. They are used on Christmas trees, on cut flowers, on newly transplanted shrubs, and in other applications to preserve and protect plants from drying out too quickly. They have also been used to protect leaves from salt burn and fungal diseases .
They block the active excretion of hydrogen cation from the guard cells. Due to presence of carbon dioxide, a rapid acidification of cytoplasm takes place leading to stomatal closure. Milbarrow (1974) has described the formation of these chemicals in the chloroplast. It moves to the stomata, where it is responsible for checking the intake of Potassium ion or induces loss of potassium ion from the guard cells.
Antitranspirants are of two types: metabolic inhibitors and film-forming antitranspirants.
Metabolic inhibitors reduce the stomatal opening and increase the leaf resistance to water vapour diffusion without affecting carbon dioxide uptake. Examples include phenylmercury acetate, abscisic acid (ABA), and aspirin.
Film-forming antitranspirants form a colorless film on the leaf surface that allows diffusion of gases but not of water vapour. Examples include silicone oil, waxes. | 0 | Organic Chemistry |
Telomeres are regions of repetitive DNA at the end of a chromosome, which provide protection from chromosomal deterioration during DNA replication. Recent studies have shown that telomeres function to aid in its own stability. Telomeric repeat-containing RNA (TERRA) are transcripts derived from telomeres. TERRA has been shown to maintain telomerase activity and lengthen the ends of chromosomes. | 1 | Biochemistry |
A viruss host range determines which host it can acquire AMGs from. Additionally, the abundance of a host surrounding a virus will affect its likelihood to acquire genes from the host. Virus populations increasingly occupy lytic lifestyles as bacterial production increases. The strong evolutionary connection between viruses and their hosts makes AMG acquisition mirror the hosts own adaptation to its environment over time.
Synechococcus and Prochlorococcus are the most abundant picocyanobacteria, accounting for up to 50% of primary production in the marine environment. As such, many AMGs characterized have been discovered in phages of these host systems. | 1 | Biochemistry |
Before considering the propagation of action potentials along axons and their termination at the synaptic knobs, it is helpful to consider the methods by which action potentials can be initiated at the axon hillock. The basic requirement is that the membrane voltage at the hillock be raised above the threshold for firing. There are several ways in which this depolarization can occur. | 7 | Physical Chemistry |
* Azafullerenes are a class of heterofullerenes in which the element substituting for carbon is nitrogen. Examples include (biazafullerenyl), (diaza[60]fullerene), (triaza[60]fullerene) and . | 0 | Organic Chemistry |
The Eigen-Wilkins mechanism, named after chemists Manfred Eigen and R. G. Wilkins, is a mechanism and rate law in coordination chemistry governing associative substitution reactions of octahedral complexes. It was discovered for substitution by ammonia of a chromium-(III) hexaaqua complex. The key feature of the mechanism is an initial rate-determining pre-equilibrium to form an encounter complex ML-Y from reactant ML and incoming ligand Y. This equilibrium is represented by the constant K:
:ML + Y ML-Y
The subsequent dissociation to form product is governed by a rate constant k:
:ML-Y → MLY + L
A simple derivation of the Eigen-Wilkins rate law follows:
:[ML-Y] = K[ML][Y]
:[ML-Y] = [M] - [ML]
:rate = k[ML-Y]
:rate = kK[Y][ML]
Leading to the final form of the rate law, using the steady-state approximation (d[ML-Y] / dt = 0),
:rate = kK[Y][M] / (1 + K[Y]) | 0 | Organic Chemistry |
3-Hydroxypropionaldehyde is formed by the condensation of acetaldehyde and formaldehyde. This reaction, when conducted in the gas-phase, was the basis for a now obsolete industrial route acrolein:
:CHCHO + CHO → HOCHCHCHO
:HOCHCHCHO → CH=CHCHO + HO
Presently 3-hydroxypropionaldehyde is an intermediate in the production of pentaerythritol. Hydrogenation of reuterin gives 1,3-propanediol. | 1 | Biochemistry |
Alkoxides can be produced by several routes starting from an alcohol. Highly reducing metals react directly with alcohols to give the corresponding metal alkoxide. The alcohol serves as an acid, and hydrogen is produced as a by-product. A classic case is sodium methoxide produced by the addition of sodium metal to methanol:
Other alkali metals can be used in place of sodium, and most alcohols can be used in place of methanol. Generally, the alcohol is used in excess and left to be used as a solvent in the reaction. Thus, an alcoholic solution of the alkali alkoxide is used. Another similar reaction occurs when an alcohol is reacted with a metal hydride such as NaH. The metal hydride removes the hydrogen atom from the hydroxyl group and forms a negatively charged alkoxide ion. | 0 | Organic Chemistry |
*National Academy of Medicine of Mexico
*New York Academy of Science
*University of Tel Aviv boardmember
*Weizmann Institute of Science in Rehovot, Israel, board member | 0 | Organic Chemistry |
The strip mill was a major innovation, with the first being erected at Ashland, Kentucky in 1923. This provided a continuous process, eliminating the need to pass the plates over the rolls and to double them. At the end the strip was cut with a guillotine shear or rolled into a coil. Early (hot rolling) strip mills did not produce strip suitable for tinplate, but in 1929 cold rolling began to be used to reduce the gauge further. The first strip mill in Great Britain was opened at Ebbw Vale in 1938 with an annual output of 200,000 tons.
The strip mill had several advantages over pack mills:
* It was cheaper due to having all parts of the process, starting with blast furnaces, on the same site.
* Softer steel could be used.
* Larger sheets could be produced at lower cost; this reduced cost and enabled tinplate and steel sheet to be used for more purposes.
* It was capital-intensive, rather than labour-intensive. | 8 | Metallurgy |
Materials can be tested for the degree of flammability and combustibility in accordance with the German [http://www.din.de/ DIN] 4102. DIN 4102, as well as its British cousin [http://www.bsi-global.com/ BS] 476 include for testing of passive fire protection systems, as well as some of its constituent materials.
The following are the categories in order of degree of combustibility and flammability:
A more recent industrial standard is the European EN 13501-1 - Fire classification of construction products and building elements—which roughly replaces A2 with A2/B, B1 with C, B2 with D/E and B3 with F.
B3 or F rated materials may not be used in building unless combined with another material that reduces the flammability of those materials. | 7 | Physical Chemistry |
Amino acids are designated either L or D depending on relative group arrangements around the stereogenic carbon center. L/D designations are not related to S/R absolute configurations. Only L configured amino acids are found in biological organisms. All amino acids except for L-cysteine have an S configuration and glycine is non-chiral.
In general, all L designated amino acids are enantiomers of their D counterparts except for isoleucine and threonine which contain two carbon stereocenters, making them diastereomers. | 4 | Stereochemistry |
Boiling systems are those in which liquid coolant absorbs energy from a heated solid surface and undergoes a change in phase. In flow boiling systems, the saturated fluid progresses through a series of flow regimes as vapor quality is increased. In systems that utilize boiling, the heat transfer rate is significantly higher than if the fluid were a single phase (i.e. all liquid or all vapor). The more efficient heat transfer from the heated surface is due to heat of vaporization and sensible heat. Therefore, boiling heat transfer has played an important role in industrial heat transfer processes such as macroscopic heat transfer exchangers in nuclear and fossil power plants, and in microscopic heat transfer devices such as heat pipes and microchannels for cooling electronic chips.
The use of boiling as a means of heat removal is limited by a condition called critical heat flux (CHF). The most serious problem that can occur around CHF is that the temperature of the heated surface may increase dramatically due to significant reduction in heat transfer. In industrial applications such as electronics cooling or instrumentation in space, the sudden increase in temperature may possibly compromise the integrity of the device. | 7 | Physical Chemistry |
The yeast interactome, i.e. all protein–protein interactions among proteins of Saccharomyces cerevisiae, has been estimated to contain between 10,000 and 30,000 interactions. A reasonable estimate may be on the order of 20,000 interactions. Larger estimates often include indirect or predicted interactions, often from affinity purification/mass spectrometry (AP/MS) studies. | 1 | Biochemistry |
In organometallic chemistry, a transition metal alkyne complex is a coordination compound containing one or more alkyne ligands. Such compounds are intermediates in many catalytic reactions that convert alkynes to other organic products, e.g. hydrogenation and trimerization. | 0 | Organic Chemistry |
Lower alkyl tin compounds are often highly toxic and have penetrating odors. Tributyltin azide causes skin rashes, itching or blisters. | 0 | Organic Chemistry |
Factors affecting the rate of olefin insertions include the formation of the cyclic, planar, four-center transition state involving incipient formation of a bond between the metal and an olefin carbon. From this transition state, it can be seen that a partial positive charge forms on the β-carbon with a partial negative charge formed on the carbon initially bonded to the metal. This polarization explains the subsequently observed formation of the bond between the negatively charged carbon/hydrogen and the positively charged β-carbon as well as the simultaneous formation of the metal-α-carbon bond. This transition state also highlights the two factors that most strongly contribute to the rate of olefin insertion reactions: (i) orbital overlap of the alkyl group initially attached to the metal and (ii) the strength of the metal-alkyl bond. With greater orbital overlap between the partially positive β-carbon and the partially negative hydrogen/alkyl group carbon, the formation of the new C-C bond is facilitated. With increasing strength of the metal-alkyl bond, the breaking of the bond between the metal and the hydrogen/alkyl carbon bond to form the two new bonds with the α-carbon and β-carbon (respectively) is slower, thus decreasing the rate of the insertion reaction. | 0 | Organic Chemistry |
The zilch is often described in terms of the zilch tensor, . The latter can be expressed using the dual electromagnetic tensor as
The zilch tensor is symmetric under the exchange of its first two indices, and , while it is also traceless with respect to any two indices, as well as divergence-free with respect to any index.
The conservation law means that the following ten quantities are time-independent:
:These are the ten zilches (or just the zilch) discovered by Lipkin. In fact, only nine zilches are independent.
:The time-independent quantity is known as the 00-zilch and is equal to the aforementioned optical chirality
:In general, the time-independent quantity is known as the -zilch (the indices run from 0 to 3) and it is clear that there are ten such quantities (nine independent).
It was later demonstrated that Lipkin's zilch is part of an infinite number of zilch-like conserved quantities, a general property of free fields. | 4 | Stereochemistry |
The mechanism for transition metal-catalyzed olefin metathesis has been widely researched over the past forty years. RCM undergoes a similar mechanistic pathway as other olefin metathesis reactions, such as cross metathesis (CM), ring-opening metathesis polymerization (ROMP), and acyclic diene metathesis (ADMET). Since all steps in the catalytic cycle are considered reversible, it is possible for some of these other pathways to intersect with RCM depending on the reaction conditions and substrates. In 1971, Chauvin proposed the formation of a metallacyclobutane intermediate through a [2+2] cycloaddition which then cycloeliminates to either yield the same alkene and catalytic species (a nonproductive pathway), or produce a new catalytic species and an alkylidene (a productive pathway). This mechanism has become widely accepted among chemists and serves as the model for the RCM mechanism.
Initiation occurs through substitution of the catalyst’s alkene ligand with substrate. This process occurs via formation of a new alkylidene through one round of [2+2] cycloaddition and cycloelimination. Association and dissociation of a phosphine ligand also occurs in the case of Grubbs catalysts. In an RCM reaction, the alkylidene undergoes an intramolecular [2+2] cycloaddition with the second reactive terminal alkene on the same molecule, rather than an intermolecular addition of a second molecule of starting material, a common competing side reaction which may lead to polymerization Cycloelimination of the metallacyclobutane intermediate forms the desired RCM product along with a [M]=CH, or alkylidene, species which reenters the catalytic cycle. While the loss of volatile ethylene is a driving force for RCM, it is also generated by competing metathesis reactions and therefore cannot be considered the only driving force of the reaction. | 0 | Organic Chemistry |
Porous crystalline solids consist of secondary building units (SBUs) which assemble to form a periodic and porous framework. An almost infinite number of frameworks can be formed through various SBU combinations leading to unique material properties for applications in separations, storage, and heterogeneous catalysis.
Types of porous crystalline solids include zeolites, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. MOFs are a class of porous polymeric material, consisting of metal ions linked together by organic bridging ligands and are a new development on the interface between molecular coordination chemistry and materials science.
COFs are another class of porous polymeric materials, consisting of porous, crystalline, covalent bonds that usually have rigid structures, exceptional thermal stabilities (to temperatures up to 600 °C), are stable in water and low densities. They exhibit permanent porosity with specific surface areas surpassing those of well-known zeolites and porous silicates. | 6 | Supramolecular Chemistry |
Dextromethorphan is the dextrorotatory enantiomer of levomethorphan, which is the methyl ether of levorphanol, both opioid analgesics. It is named according to IUPAC rules as (+)-3-methoxy-17-methyl-9α,13α,14α-morphinan. As its pure form, dextromethorphan occurs as an odorless, opalescent white powder. It is freely soluble in chloroform and insoluble in water; the hydrobromide salt is water-soluble up to 1.5 g/100 mL at 25 °C. Dextromethorphan is commonly available as the monohydrated hydrobromide salt, and is also available in extended-release formulations (sold as dextromethorphan polistirex) contain dextromethorphan bound to an ion-exchange resin based on polystyrene sulfonic acid. Dextromethorphan's specific rotation in water is +27.6° (20 °C, Sodium D-line). | 4 | Stereochemistry |
Dicloxacillin is insensitive to beta-lactamase (also known as penicillinase) enzymes secreted by many penicillin-resistant bacteria. The presence of the isoxazolyl group on the side chain of the penicillin nucleus facilitates the β-lactamase resistance, since they are relatively intolerant of side-chain steric hindrance. Thus, it is able to bind to penicillin-binding proteins (PBPs) and inhibit peptidoglycan crosslinking, but is not bound by or inactivated by β-lactamase | 4 | Stereochemistry |
A common synthesis for porphyrins is the Rothemund reaction, first reported in 1936, which is also the basis for more recent methods described by Adler and Longo. The general scheme is a condensation and oxidation process starting with pyrrole and an aldehyde. | 1 | Biochemistry |
Dry water was first patented in 1968 and quickly found use in the cosmetic industry. In 2006, new work with dry water from the University of Hull increased interest in its potential use in other fields.
Dry water can be made by blending a mixture of silicon dioxide dust with water. | 7 | Physical Chemistry |
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