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Hydrogen and deuterium nuclei are grossly different in their magnetic properties. Thus it is possible to distinguish between them by NMR spectroscopy. Deuterons will not be observed in a H NMR spectrum and conversely, protons will not be observed in a H NMR spectrum. Where small signals are observed in a H NMR spectrum of a highly deuterated sample, these are referred to as residual signals. They can be used to calculate the level of deuteration in a molecule. Analogous signals are not observed in H NMR spectra because of the low sensitivity of this technique compared to the H analysis. Deuterons typically exhibit very similar chemical shifts to their analogous protons. Analysis via C NMR spectroscopy is also possible: the different spin values of hydrogen (/) and deuterium (1) gives rise to different splitting multiplicities. NMR spectroscopy can be used to determine site-specific deuteration of molecules.
Another method uses HSQC spectra. Typically HSQC spectra are recorded at a series of timepoints while the hydrogen is exchanging with the deuterium. Since the HSQC experiment is specific for hydrogen, the signal will decay exponentially as the hydrogen exchanges. It is then possible to fit an exponential function to the data, and obtain the exchange constant. This method gives residue-specific information for all the residues in the protein simultaneously The major drawback is that it requires a prior assignment of the spectrum for the protein in question. This can be very labor-intensive, and usually limits the method to proteins smaller than 25 kDa. Because it takes minutes to hours to record a HSQC spectrum, amides that exchange quickly must be measured using other pulse sequences. | 7 | Physical Chemistry |
The Hiyama coupling is a palladium-catalyzed cross-coupling reaction of organosilanes with organic halides used in organic chemistry to form carbon–carbon bonds (C-C bonds). This reaction was discovered in 1988 by Tamejiro Hiyama and Yasuo Hatanaka as a method to form carbon-carbon bonds synthetically with chemo- and regioselectivity. The Hiyama coupling has been applied to the synthesis of various natural products.
:* : aryl, alkenyl or alkynyl
:* : aryl, alkenyl, alkynyl or alkyl
:* : Cl, F or alkyl
:* : Cl, Br, I or OTf | 0 | Organic Chemistry |
After synthesising the potassium salt of the phosphaethynolate anion in 2013, Goicoechea et al. began to look into the potential of PCO towards cycloadditions. They found that the anion could react in a [2+2] fashion with a diphenyl ketene to produce the first isolatable example of a four-membered monoanionic phosphorus containing heterocycle. They employed the same method to test other unsaturated substrates such as carbodiimides and found that the likelihood of cyclisation heavily relies on the nature of the substituents on the unsaturated substrate.
Cycloaddition reactions involving the phosphaethynolate anion have also been shown by Grutzmacher and co-workers to be a viable synthetic route to other heterocycles. One simple example is the reaction between the NaPCO and an α-pyrone. This reaction yields the sodium phosphinin-2-olate salt which is stable to both air and moisture. | 7 | Physical Chemistry |
Metallurgical failure analysis is the process to determine the mechanism that has caused a metal component to fail. It can identify the cause of failure, providing insight into the root cause and potential solutions to prevent similar failures in the future, as well as culpability, which is important in legal cases. Resolving the source of metallurgical failures can be of financial interest to companies. The annual cost of corrosion (a common cause of metallurgical failures) in the United States was estimated by NACE International in 2012 to be $450 billion a year, a 67% increase compared to estimates for 2001. These failures can be analyzed to determine their root cause, which if corrected, would save reduce the cost of failures to companies.
Failure can be broadly divided into functional failure and expected performance failure. Functional failure occurs when a component or process fails and its entire parent system stops functioning entirely. This category includes the common idea of a component fracturing rapidly. Expected performance failures are when a component causes the system to perform below a certain performance criterion, such as life expectancy, operating limits, or shape and color. Some performance criteria are documented by the supplier, such as maximum load allowed on a tractor, while others are implied or expected by the customer, such gas consumption (miles per gallon for automobiles).
Often a combination of both environmental conditions and stress will cause failure. Metal components are designed to withstand the environment and stresses that they will be subjected to. The design of a metal component involves not only a specific elemental composition but also specific manufacturing process such as heat treatments, machining processes, etc. The huge arrays of different metals that result all have unique physical properties. Specific properties are designed into metal components to make them more robust to various environmental conditions. These differences in physical properties will exhibit unique failure modes. A metallurgical failure analysis takes into account as much of this information as possible during analysis. The ultimate goal of failure analysis is to provide a determination of the root cause and a solution to any underlying problems to prevent future failures. | 8 | Metallurgy |
In isochromat mode, the incident electron energy is ramped and the emitted photons are detected at a fixed energy that is determined by the photon detector. Typically, an I gas filled Geiger-Müller tube with an entrance window of either SrF or CaF is used as the photon detector. The combination of window and filling gas determines the detected photon energy, and for I gas and either a SrF or CaF window, the photons energies are ~ 9.5 eV and ~ 9.7 eV, respectively. | 7 | Physical Chemistry |
The first metal carbonyl clusters, Fe(CO), Ir(CO), and Rh(CO), were reported starting in the 1930s, often by Walter Hieber. The structures were subsequently established by X-ray crystallography.
Paolo Chini (1928–1980) was a pioneer for the synthesis and characterization of high-nuclearity metal carbonyl clusters. His first studies started in 1958, in the attempt to repeat a patent that claimed an improved selectivity in hydroformylation. From a mixture of iron and cobalt carbonyls the first bimetallic carbonyl cluster HFeCo(CO) was obtained. | 7 | Physical Chemistry |
Another type of cellular glycan is the glycosaminoglycans (GAGs). These comprise 2-aminosugars linked in an alternating fashion with uronic acids, and include polymers such as heparin, heparan sulfate, chondroitin, keratan and dermatan. Some glycosaminoglycans, such as heparan sulfate, are found attached to the cell surface, where they are linked through a tetrasacharide linker via a xylosyl residue to a protein (forming a glycoprotein or proteoglycan). | 0 | Organic Chemistry |
Nitrates are used as fertilizers in agriculture because of their high solubility and biodegradability. The main nitrate fertilizers are ammonium, sodium, potassium, calcium, and magnesium salts. Several billion kilograms are produced annually for this purpose. | 0 | Organic Chemistry |
His first post was with the Atomic Energy Research Establishment (AERE) near the village of Harwell where he lived, working at the Wantage Research Laboratory, then in Berkshire. His early work started an interest in radioisotopes and trace elements that he maintained throughout his working life. While at AERE, he spent several months in 1956 attending the British nuclear tests at Maralinga in Australia to study the environmental effects of radiation.
Bowen realized that the calibration of different instruments intended to measure trace elements was an important issue that needed addressing. His solution was to produce a good supply of a material which later become known as Bowens Kale'. This was a dried, crushed chomogenate of the plant kale, that was stable and consistent enough to be distributed as a research calibration standard - probably the first successful example of such a standard.
In 1964, he was appointed as a lecturer in the chemistry department at the University of Reading. Later he was promoted to Reader in analytical chemistry in 1974. At Reading, Bowen undertook consultancy for Dunlop, investigating potential uses for their products. When the Torrey Canyon oil disaster occurred in 1967, he realized that it might be possible to use foam booms to block the oil from spreading in the English Channel. His original experiments were conducted in a small bucket in his laboratory. Although not entirely successful in reality at the time due to the rough seas, this lateral thinking combined his interest in chemistry with his love of nature and has since been effectively deployed to protect ports and harbours against encroaching oil slicks. Bowen wrote a number of professional books in the field of chemistry, including two editions of Trace elements in Biochemistry (1966 and 1976).
In 1968, Bowen noted that the paint used for yellow line road markings can contain chromate pigment, which may cause urban pollution as it deteriorates. He pointed out that hexavalent chromium in dust can cause dermatitis ulceration on the skin, inflammation of the nasal mucosa and larynx, and lung cancer.
From 1951 onwards, Bowen was a long-serving member of the Botanical Society of the British Isles (BSBI). He was meetings secretary for a period and the official recorder of plants for the counties of Berkshire and Dorset, producing Floras for both counties. He retired to Winterborne Kingston in Dorset at the end of his life. He was also one of the leading contributors of botanical data for the Flora of Oxfordshire. He acted as an expert botanical guide on tours around Europe, especially Greece and Turkey.
Humphry Bowen donated a large collection of lichens from Berkshire and Oxfordshire to the Museum of Reading in the 1970s. He established the Bowen Cup at the University of Reading in 1988, an annual prize for the student in the Department of Chemistry at the University who achieves the top marks in Part II Analytical Chemistry. | 3 | Analytical Chemistry |
The exact mechanism of the action of general anaesthetics has not been delineated. Sevoflurane acts as a positive allosteric modulator of the GABA receptor in electrophysiology studies of neurons and recombinant receptors. However, it also acts as an NMDA receptor antagonist, potentiates glycine receptor currents, and inhibits nAChR and 5-HT receptor currents. | 2 | Environmental Chemistry |
Purple bacteria contain a single photosystem that is structurally related to PSII in cyanobacteria and chloroplasts:
: P870 → P870 → ubiquinone → cyt bc → cyt c → P870
This is a cyclic process in which electrons are removed from an excited chlorophyll molecule (bacteriochlorophyll; P870), passed through an electron transport chain to a proton pump (cytochrome bc complex; similar to the chloroplastic one), and then returned to the chlorophyll molecule. The result is a proton gradient that is used to make ATP via ATP synthase. As in cyanobacteria and chloroplasts, this is a solid-state process that depends on the precise orientation of various functional groups within a complex transmembrane macromolecular structure.
To make NADPH, purple bacteria use an external electron donor (hydrogen, hydrogen sulfide, sulfur, sulfite, or organic molecules such as succinate and lactate) to feed electrons into a reverse electron transport chain. | 5 | Photochemistry |
A nested gene is a gene whose entire coding sequence lies within the bounds (between the start codon and the stop codon) of a larger external gene. The coding sequence for a nested gene differs greatly from the coding sequence for its external host gene. Typically, nested genes and their host genes encode functionally unrelated proteins, and have different expression patterns in an organism.
There are two categories of nested genes:
* genes nested within an intron of a larger gene
* genes which lie opposite the coding sequence of a larger gene | 1 | Biochemistry |
HFCs were developed in the 1990s to substitute for substances such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). As these substances were found to deplete the ozone layer, the Montreal Protocol began to lay down provisions for them to be phased-out globally after the agreement was ratified in 1987.
PFCs and SF were already in use prior to the Montreal Protocol.
NF use has grown since the 1990s along with the rapid expansion of the microelectronics fabrication industry. | 2 | Environmental Chemistry |
In ambient conditions, most samples develop a liquid meniscus layer. Because of this, keeping the probe tip close enough to the sample for short-range forces to become detectable while preventing the tip from sticking to the surface presents a major problem for contact mode in ambient conditions. Dynamic contact mode (also called intermittent contact, AC mode or tapping mode) was developed to bypass this problem. Nowadays, tapping mode is the most frequently used AFM mode when operating in ambient conditions or in liquids.
In tapping mode, the cantilever is driven to oscillate up and down at or near its resonance frequency. This oscillation is commonly achieved with a small piezo element in the cantilever holder, but other possibilities include an AC magnetic field (with magnetic cantilevers), piezoelectric cantilevers, or periodic heating with a modulated laser beam. The amplitude of this oscillation usually varies from several nm to 200 nm. In tapping mode, the frequency and amplitude of the driving signal are kept constant, leading to a constant amplitude of the cantilever oscillation as long as there is no drift or interaction with the surface. The interaction of forces acting on the cantilever when the tip comes close to the surface, van der Waals forces, dipole–dipole interactions, electrostatic forces, etc. cause the amplitude of the cantilevers oscillation to change (usually decrease) as the tip gets closer to the sample. This amplitude is used as the parameter that goes into the electronic servo that controls the height of the cantilever above the sample. The servo adjusts the height to maintain a set cantilever oscillation amplitude as the cantilever is scanned over the sample. A tapping AFM' image is therefore produced by imaging the force of the intermittent contacts of the tip with the sample surface.
Although the peak forces applied during the contacting part of the oscillation can be much higher than typically used in contact mode, tapping mode generally lessens the damage done to the surface and the tip compared to the amount done in contact mode. This can be explained by the short duration of the applied force, and because the lateral forces between tip and sample are significantly lower in tapping mode over contact mode.
Tapping mode imaging is gentle enough even for the visualization of supported lipid bilayers or adsorbed single polymer molecules (for instance, 0.4 nm thick chains of synthetic polyelectrolytes) under liquid medium. With proper scanning parameters, the conformation of single molecules can remain unchanged for hours, and even single molecular motors can be imaged while moving.
When operating in tapping mode, the phase of the cantilevers oscillation with respect to the driving signal can be recorded as well. This signal channel contains information about the energy dissipated by the cantilever in each oscillation cycle. Samples that contain regions of varying stiffness or with different adhesion properties can give a contrast in this channel that is not visible in the topographic image. Extracting the samples material properties in a quantitative manner from phase images, however, is often not feasible. | 6 | Supramolecular Chemistry |
Fluorescent proteins have had a substantial impact on bioimaging, which is why biliproteins have made suitable candidates for the application, due to their properties of fluorescence, light-harvesting, light-sensitivity and photoswitching (the latter occurring only in phytochromes). Phycobiliproteins, which are highly fluorescent, have been used in external applications of bioimaging since the early 1980s. That application requires the bilin chromophore to be synthesised from haem, after which a lyase is needed to covalently bond the bilin to its corresponding apoprotein. An alternative method of uses phytochromes instead; some phytochromes only require one enzyme, haem oxygenase, for synthesising chromophores. Another benefit of using phytochromes is that they bind to their bilins autocatalytically. While there are photochromic pigments with poor fluorescence, this problem has been alleviated by engineering protein variants that reduce photochemistry and enhance fluorescence. | 1 | Biochemistry |
In species of algae that contain a single chloroplast, regulation of chloroplast division is extremely important to ensure that each daughter cell receives a chloroplast—chloroplasts can't be made from scratch. In organisms like plants, whose cells contain multiple chloroplasts, coordination is looser and less important. It is likely that chloroplast and cell division are somewhat synchronized, though the mechanisms for it are mostly unknown.
Light has been shown to be a requirement for chloroplast division. Chloroplasts can grow and progress through some of the constriction stages under poor quality green light, but are slow to complete division—they require exposure to bright white light to complete division. Spinach leaves grown under green light have been observed to contain many large dumbbell-shaped chloroplasts. Exposure to white light can stimulate these chloroplasts to divide and reduce the population of dumbbell-shaped chloroplasts. | 5 | Photochemistry |
Glycosylation-dependent cell adhesion molecule-1 (GLYCAM1) is a proteoglycan ligand expressed on cells of the high endothelial venules in lymphoid tissues. It is the ligand for the receptor L-selectin allowing for naive lymphocytes to exit the bloodstream into lymphoid tissues.
GLYCAM1 binds to L-selectin by presenting one or more O-linked carbohydrates to the lectin domain of the leukocyte cell surface selectin.
Data suggests that GLYCAM1 is a hormone-regulated milk protein that is part of the milk mucin complex.
GlyCAM-1 is expressed exclusively on high endothelial venules. It is unclear how GlyCAM-1 is attached to the membrane as it lacks a transmembrane region. | 1 | Biochemistry |
Another method involves the use of oxalyl chloride:
The reaction is catalysed by dimethylformamide (DMF), which reacts with oxalyl chloride to give the Vilsmeier reagent, an iminium intermediate that which reacts with the carboxylic acid to form a mixed imino-anhydride. This structure undergoes an acyl substitution with the liberated chloride, forming the acid anhydride and releasing regenerated molecule of DMF. Relative to thionyl chloride, oxalyl chloride is more expensive but also a milder reagent and therefore more selective. | 0 | Organic Chemistry |
Geological deposits of arsenic may be released into rivers where deep ground-waters are exploited as in parts of Pakistan. Many metalloid ores such as lead, gold and copper contain traces of arsenic and poorly stored tailings may result in arsenic entering the hydrological cycle. | 2 | Environmental Chemistry |
UPt forms crystals of hexagonal symmetry (some studies hypothesize a trigonal structure instead), space group P6/mmc, cell parameters a = 0.5766 nm and c = 0.4898 nm (c should be understood as distance from planes), with a structure similar to nisnite (NiSn) and MgCd.
The compound congruently melts at 1700 °C. The enthalpy of formation of the compound is -111 kJ/mol.
At temperatures below 1 K it becomes superconducting, thought to be due to the presence of heavy fermions (the uranium atoms). | 8 | Metallurgy |
Trimethylenemethane cycloaddition is the formal (3+2) annulation of trimethylenemethane (TMM) derivatives to two-atom pi systems. Although TMM itself is too reactive and unstable to be stored, reagents which can generate TMM or TMM synthons in situ can be used to effect cycloaddition reactions with appropriate electron acceptors. Generally, electron-deficient pi bonds undergo cyclization with TMMs more easily than electron-rich pi bonds. | 0 | Organic Chemistry |
The terms megaphyll, macrophyll, mesophyll, notophyll, microphyll, nanophyll and leptophyll are used to describe leaf sizes (in descending order), in a classification devised in 1934 by Christen C. Raunkiær and since modified by others. | 5 | Photochemistry |
The Goldich dissolution series can be applied to Lithosequences, which are a way characterizing of a soil profile based on its parent material. Lithosequences include soils that have undergone relatively similar weathering conditions, so variations in composition are based on the relative weathering rates of parent minerals. Therefore, the weathering rates of these soils and their compositions are primarily influenced by the relative proportion of minerals in the Goldich dissolution series. | 9 | Geochemistry |
In chromatography, internal standards are used to determine the concentration of other analytes by calculating response factor. The selected internal standard should have a similar retention time and derivatization. It must be stable and not interfere with the sample components. This mitigates the uncertainty that can occur in preparatory steps such as sample injection.
In gas chromatography-mass spectrometry (GC-MS), deuterated compounds with similar structures to the analyte commonly act as effective internal standards. However, there are non-deuterated internal standards such as norleucine, which is popular in the analysis of amino acids because it can be separated from accompanying peaks.
Selecting an internal standard for liquid chromatography-mass spectrometry (LC-MS) depends on the employed ionization method. The internal standard needs a comparable ionization response and fragmentation pattern to the analyte. LC-MS internal standards are often isotopically analogous to the structure of the analyte, using isotopes such as deuterium (H), C, N and O. | 3 | Analytical Chemistry |
Organotantalum compounds are of academic interest, but few or no commercial applications have been described. | 0 | Organic Chemistry |
The mode of action through which chromium aided in the regulation of blood glucose levels is poorly understood. Recently, it has been suggested that chromium interacts with the low-molecular weight chromium (LMWCr) binding substance to potentiate the action of insulin. LMWCr has a molecular weight of 1500, and is composed solely of the four amino acid residues of glycine, cysteine, aspartic acid and glutamate. It is a naturally occurring oligopeptide that has been purified from many sources: rabbit liver, porcine kidney and kidney powder, bovine liver, colostrum, dog, rat and mouse liver. Widely distributed in mammals, LMWCr is capable of tightly binding four chromic ions. The binding constant of this oligopeptide for chromium ions is very large, (K ≈ 10 M), suggesting it is strong and tightly binding. LMWCr exists in its inactive or apo form within the cytosol and nucleus of insulin-sensitive cells.
When insulin concentrations within the blood rise, insulin binds to the external subunit of the insulin-receptor proteins, and induces a conformational change. This change results in the autophosphorylation of the tyrosine residue located on the internal ß-subunit of the receptor, thereby activating the receptor's kinase activity. An increase in insulin levels also signals for the movement of transferrin receptors from the vesicles of insulin-sensitive cells to the plasma membrane. Transferrin, the protein responsible for the movement of chromium through the body, binds to these receptors, and becomes internalized via the process of endocytosis. The pH of these vesicles containing the transferrin molecules is then decreased (resulting in increased acidity) by the action of ATP-driven proton pumps, and as a consequence, chromium is released from the transferrin. The free chromium within the cell is then sequestered by LMWCr. The binding of LMWCr to chromium converts it into its holo or active form, and once activated, LMWCr binds to the insulin receptors and aids in maintaining and amplifying the tyrosine kinase activity of the insulin receptors. In one experiment that was performed on bovine liver LMWCr, it was determined that LMWCr could amplify the activity of protein kinase receptors by up to seven-fold in the presence of insulin. Furthermore, evidence suggests that the action of LMWCr is most effective when it is bound to four chromic ions.
When the insulin signaling pathway is turned off, the insulin receptors on the plasma membrane relax and become inactivated. The holo-LMWCr is expelled from the cell and ultimately excreted from the body via urine. LMWCr cannot be converted back into its inactive from due to the high binding affinity of this oligopeptide for its chromium ions. As of currently, the mechanism through which apo-LMWCr is replaced within the body is unknown. | 1 | Biochemistry |
Radiocarbon dating is a radiometric dating method that uses () to determine the age of carbonaceous materials up to about 60,000 years old. The technique was developed by Willard Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago. Libby estimated that the radioactivity of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram of pure carbon, and this is still used as the activity of the modern radiocarbon standard. In 1960, Libby was awarded the Nobel Prize in chemistry for this work.
One of the frequent uses of the technique is to date organic remains from archaeological sites. Plants fix atmospheric carbon during photosynthesis, so the level of in plants and animals when they die approximately equals the level of in the atmosphere at that time. However, it decreases thereafter from radioactive decay, allowing the date of death or fixation to be estimated. The initial level for the calculation can either be estimated, or else directly compared with known year-by-year data from tree-ring data (dendrochronology) up to 10,000 years ago (using overlapping data from live and dead trees in a given area), or else from cave deposits (speleothems), back to about 45,000 years before the present. A calculation or (more accurately) a direct comparison of carbon-14 levels in a sample, with tree ring or cave-deposit carbon-14 levels of a known age, then gives the wood or animal sample age-since-formation. Radiocarbon is also used to detect disturbance in natural ecosystems; for example, in peatland landscapes, radiocarbon can indicate that carbon which was previously stored in organic soils is being released due to land clearance or climate change.
Cosmogenic nuclides are also used as proxy data to characterize cosmic particle and solar activity of the distant past. | 9 | Geochemistry |
The popularity of the Karl Fischer titration (henceforth referred to as KF) is due in large part to several practical advantages that it holds over other methods of moisture determination, such as accuracy, speed and selectivity.
KF is selective for water, because the titration reaction itself consumes water. In contrast, measurement of mass loss on drying will detect the loss of any volatile substance. However, the strong redox chemistry () means that redox-active sample constituents may react with the reagents. For this reason, KF is unsuitable for solutions containing e.g. dimethyl sulfoxide.
KF has a high accuracy and precision, typically within 1% of available water, e.g. 3.00% appears as 2.97–3.03%. Although KF is a destructive analysis, the sample quantity is small and is typically limited by the accuracy of weighing. For example, in order to obtain an accuracy of 1% using a scale with the typical accuracy of 0.2 mg, the sample must contain 20 mg water, which is e.g. 200 mg for a sample with 10% water. For coulometers, the measuring range is from 1–5 ppm to about 5%. Volumetric KF readily measures samples up to 100%, but requires impractically large amounts of sample for analytes with less than 0.05% water. The KF response is linear. Therefore, single-point calibration using a calibrated 1% water standard is sufficient and no calibration curves are necessary.
Little sample preparation is needed: a liquid sample can usually be directly injected using a syringe. The analysis is typically complete within a minute. However, KF suffers from an error called drift, which is an apparent water input that can confuse the measurement. The glass walls of the vessel adsorb water, and if any water leaks into the cell, the slow release of water into the titration solution can continue for a long time. Therefore, before measurement, it is necessary to carefully dry the vessel and run a 10–30-minute "dry run" in order to calculate the rate of drift. The drift is then subtracted from the result.
KF is suitable for measuring liquids and, with special equipment, gases. The major disadvantage with solids is that the water has to be accessible and easily brought into methanol solution. Many common substances, especially foods such as chocolate, release water slowly and with difficulty, requiring additional efforts to reliably bring the total water content into contact with the Karl Fischer reagents. For example, a high-shear mixer may be installed to the cell in order to break the sample. KF has problems with compounds with strong binding to water, as in water of hydration, for example with lithium chloride, so KF is unsuitable for the special solvent LiCl/DMAc.
KF is suitable for automation. Generally, KF is conducted using a separate KF titrator, or for volumetric titration, a KF titration cell installed into a general-purpose titrator. There are also oven attachments that can be used for materials that have problems being analyzed normally in the cell. The important aspect about the oven attachment is that the material doesn't decompose into water when heated to release the water. The oven attachment also supports automation of samples.
Using volumetric titration with visual detection of a titration endpoint is also possible with coloured samples by UV/VIS spectrophotometric detection. | 3 | Analytical Chemistry |
Scientists are capable of retrieving genetic information from hair, skin, blood, sperm, tissue, and saliva as long as the sample contains intact DNA. Nucleotide sequences between humans differ by only 0.1%. Even so, this 0.1% includes approximately three million bases. DNA can be analyzed through restriction fragment length polymorphism (RFLP) and Polymerase chain reactions (PCR). The RFLP process was introduced in 1988. Restriction enzymes digest portions of the DNA, leaving short fragments. These fragments are sorted through gel electrophoresis. The gel demonstrates the length of the fragments allowing specialists to determine whether the fragments came from the same person. PCR is more commonly used today because it more efficient and requires smaller samples of genetic samples. | 1 | Biochemistry |
The main theory that describes the rates of outer sphere electron transfer was developed by Rudolph A. Marcus in the 1950s. A major aspect of Marcus theory is the dependence of the electron transfer rate on the thermodynamic driving force (difference in the redox potentials of the electron-exchanging sites). For most reactions, the rates increase with increased driving force. A second aspect is that the rate of outer sphere electron-transfer depends inversely on the "reorganizational energy." Reorganization energy describes the changes in bond lengths and angles that are required for the oxidant and reductant to switch their oxidation states. This energy is assessed by measurements of the self-exchange rates (see below).
Outer sphere electron transfer is the most common type of electron transfer, especially in biochemistry, where redox centers are separated by several (up to about 11) angstroms by intervening protein. In biochemistry, there are two main types of outer sphere ET: ET between two biological molecules or fixed distance electron transfer, in which the electron transfers within a single biomolecule (e.g., intraprotein). | 7 | Physical Chemistry |
In astrophysics, photodissociation is one of the major processes through which molecules are broken down (but new molecules are being formed). Because of the vacuum of the interstellar medium, molecules and free radicals can exist for a long time. Photodissociation is the main path by which molecules are broken down. Photodissociation rates are important in the study of the composition of interstellar clouds in which stars are formed.
Examples of photodissociation in the interstellar medium are ( is the energy of a single photon of frequency ): | 5 | Photochemistry |
* 2015 elected board member, European Academy of Microbiology (EAM)
* 2013 elected member, European Academy of Microbiology (EAM)
* 2012 iGEM Team Groningen: European and World Champion 2012 (Kuipers was supervisor/coach/coordinator of the iGEM team Groningen from 2008-2015)
* 2011 elected member, Royal Netherlands Academy of Arts and Sciences (KNAW)
* 2011 Simon Stevin Meester Award (Science and Technology Award of STW, NWO, the Netherlands) €500,000 | 0 | Organic Chemistry |
A hexagonal structure that is often described as chicken wire-like can also be found in other types of chemical compounds such as:
* Non-aromatic polycyclic hydrocarbons, e.g. steroids like cholesterol
* Flat hexagonal hydrogen bonded trimesic acid (benzene-1,3,5-tricarboxylic acid), boric acid, or melamine-cyanuric acid complexes
* Interwoven molecule chains in the inorganic polymer NaAuS
* Complexes of the protein clathrin | 4 | Stereochemistry |
The first use of epitope tagging was described by Munro and Pelham in 1984. The FLAG-tag was the second example of a fully functional, improved epitope tag, published in the scientific literature. and was the only epitope tag to be patented. It has since become one of the most commonly used protein tags in laboratories worldwide. Unlike some other tags (e.g. myc, HA), where a monoclonal antibody was first isolated against an existing protein, then the epitope was characterized and used as a tag, the FLAG epitope was an idealized, artificial design, to which monoclonal antibodies were raised. The FLAG-tag's sequence was optimized for compatibility with proteins it is attached to, in that FLAG-tag is more hydrophilic than other common epitope tags and therefore less likely to reduce the activity of proteins to which FLAG-tag is appended. In addition, N-terminal FLAG tags can be removed readily from proteins once they have been isolated, by treatment with the specific protease, enterokinase (enteropeptidase).
The third report of epitope tagging, (HA-tag), appeared about one year after the Flag system had been first shipped. | 1 | Biochemistry |
The pheromone is synthesized in the same region as venom, or other primary hormonal departments within the organism. Often, trail pheromone synthesis occurs in the ventral venom gland, poison gland, Dufour's gland, sternal gland, or hindgut. When secreted, the pheromone is dropped in a blotch-like fashion from the foraging organism onto the surface leading to the food source. As the organism proceeds to the food source, the trail pheromone creates a narrow and precise pathway between the food source and the nesting location, which another organism of the same species, and often the same nest, follows precisely. Commonly, an organism, when initially laying down the trail may renew the trail a number of times to demonstrate the value of the food source while running in tandem. Once the trail is laid, other members of the species will recognize the chemical signal and follow the trail, and each individually renew the trail on the way back to the home source. While this pheromone is constantly deposited by its members, the chemicals diffuse up into the environment propagating its message. Once the food source runs out the organisms will simply skip the task of renewing the trail on the way back, thus resulting in the diffusion and weakening of the pheromone. Studies have shown that with quality of food, distance from nest, and amounts of food, the strength of the trail pheromone may vary. Often the foraging individual may synthesize the trail pheromone as a mixture of chemicals produced by different glands which allows such specificity. While members of the same species who discovered the food constantly renew this trail pathway, as the chemical is secreted into the environment as a signal for food in their umwelt, the very same chemical can often be interpreted as a territorial mark for outside species. | 1 | Biochemistry |
The authors Buchdahl, Callen, and Haase make no mention of the passage of radiation, thermal or coherent, across their adiabatic walls. Carathéodory explicitly discusses problems with respect to thermal radiation, which is incoherent, and he was probably unaware of the practical possibility of laser light, which is coherent. Carathéodory in 1909 says that he leaves such questions unanswered.
For the thermodynamic stream of thinking, the notion of empirical temperature is coordinately presupposed in the notion of heat transfer for the definition of an adiabatic wall.
For the mechanical stream of thinking, the exact way in which the adiabatic wall is defined is important.
In the presentation of Carathéodory, it is essential that the definition of the adiabatic wall should in no way depend upon the notions of heat or temperature. This is achieved by careful wording and reference to transfer of energy only as work. Buchdahl is careful in the same way. Nevertheless, Carathéodory explicitly postulates the existence of walls that are permeable only to heat, that is to say impermeable to work and to matter, but still permeable to energy in some unspecified way. One might be forgiven for inferring from this that heat is energy in transfer across walls permeable only to heat, and that such exist as undefined postulated primitives.
In the widely cited presentation of Callen, the notion of an adiabatic wall is introduced as a limit of a wall that is poorly conductive of heat. Although Callen does not here explicitly mention temperature, he considers the case of an experiment with melting ice, done on a summer's day, when, the reader may speculate, the temperature of the surrounds would be higher. Nevertheless, when it comes to a hard core definition, Callen does not use this introductory account. He eventually defines an adiabatic enclosure as does Carathéodory, that it passes energy only as work, and does not pass matter. Accordingly, he defines heat, therefore, as energy that is transferred across the boundary of a closed system other than by work.
As suggested for example by Carathéodory and used for example by Callen, the favoured instance of an adiabatic wall is that of a Dewar flask. A Dewar flask has rigid walls. Nevertheless, Carathéodory requires that his adiabatic walls shall be imagined to be flexible, and that the pressures on these flexible walls be adjusted and controlled externally so that the walls are not deformed, unless a process is undertaken in which work is transferred across the walls. The work considered by Carathéodory is pressure-volume work. Another text considers asbestos and fiberglass as good examples of materials that constitute a practicable adiabatic wall.
The mechanical stream of thinking thus regards the adiabatic enclosure's property of not allowing the transfer of heat across itself as a deduction from the Carathéodory axioms of thermodynamics. | 7 | Physical Chemistry |
The Standard Model of physics, in particular the work of Murray Gell-Mann in the 1960s, had been successful in uniting much of the previously disparate concepts in particle physics into one, relatively straightforward, scheme. In essence, there were three types of particles:
* The leptons, which were low-mass particles such as electrons, neutrinos and their antiparticles. They have integer electric charge.
* The gauge bosons, which were particles that exchange forces. These ranged from the massless, easy-to-detect photon (the carrier of the electro-magnetic force) to the exotic (though still massless) gluons that carry the strong nuclear force.
*The quarks, which were massive particles that carried fractional electric charges. They are the "building blocks" of the hadrons. They are also the only particles to be affected by the strong interaction.
The leptons had been detected since 1897, when J. J. Thomson had shown that electric current is a flow of electrons. Some bosons were being routinely detected, although the W, W and Z particles of the electroweak force were only categorically seen in the early 1980s, and gluons were only firmly pinned down at DESY in Hamburg at about the same time. Quarks, however, were still elusive.
Drawing on Rutherford's groundbreaking experiments in the early years of the 20th century, ideas for detecting quarks were formulated. Rutherford had proven that atoms had a small, massive, charged nucleus at their centre by firing alpha particles at atoms of gold. Most had gone through with little or no deviation, but a few were deflected through large angles or came right back. This suggested that atoms had internal structure and a lot of empty space.
In order to probe the interiors of baryons, a small, penetrating and easily produced particle needed to be used. Electrons were ideal for the role, as they are abundant and easily accelerated to high energies due to their electric charge. In 1968, at the Stanford Linear Accelerator Center (SLAC), electrons were fired at protons and neutrons in atomic nuclei. Later experiments were conducted with muons and neutrinos, but the same principles apply.
The collision absorbs some kinetic energy, and as such it is inelastic. This is a contrast to Rutherford scattering, which is elastic: no loss of kinetic energy. The electron emerges from the nucleus, and its trajectory and velocity can be detected. Analysis of the results led to the conclusion that hadrons do indeed have internal structure. The experiments were important because not only did they confirm the physical reality of quarks, but also proved again that the Standard Model was the correct avenue of research for particle physicists to pursue. | 7 | Physical Chemistry |
The prefix "S" indicates that the NO group is attached to sulfur. The angle is near 114°, reflecting the influence of the lone pair of electrons on nitrogen.
S-Nitrosothiols may arise from condensation from nitrous acid and a thiol:
Other methods for their synthesis. They can be synthesized from and tert-butyl nitrite (tBuONO) are commonly used.
Once formed, these deeply colored compounds are often thermally unstable with respect to formation of the disulfide and nitric oxide:
S-Nitrosothiols release nitrosonium ions () upon treatment with acids:
and they can transfer nitroso groups to other thiols: | 0 | Organic Chemistry |
Given the advantages of , a group of scientists from institutions around the world are working on the Rice Project to produce a strain of rice, naturally a plant, that uses the pathway by studying the plants maize and Brachypodium. As rice is the world's most important human food—it is the staple food for more than half the planet—having rice that is more efficient at converting sunlight into grain could have significant global benefits towards improving food security. The team claims rice could produce up to 50% more grain—and be able to do it with less water and nutrients.
The researchers have already identified genes needed for photosynthesis in rice and are now looking towards developing a prototype rice plant. In 2012, the Government of the United Kingdom along with the Bill & Melinda Gates Foundation provided US$14 million over three years towards the Rice Project at the International Rice Research Institute. In 2019, the Bill & Melinda Gates Foundation granted another US$15 million to the Oxford-University-led C4 Rice Project. The goal of the 5-year project is to have experimental field plots up and running in Taiwan by 2024.
C photosynthesis, an intermediate step between and Kranz , may be preferred over for rice conversion. The simpler system is less optimized for high light and high temperature conditions than , but has the advantage of requiring fewer steps of genetic engineering and performing better than under all temperatures and light levels. In 2021, the UK Government provided £1.2 million on studying C engineering. | 5 | Photochemistry |
All enzyme assays measure either the consumption of substrate or production of product over time. A large number of different methods of measuring the concentrations of substrates and products exist and many enzymes can be assayed in several different ways. Biochemists usually study enzyme-catalysed reactions using four types of experiments:
* Initial rate experiments. When an enzyme is mixed with a large excess of the substrate, the enzyme-substrate intermediate builds up in a fast initial transient. Then the reaction achieves a steady-state kinetics in which enzyme substrate intermediates remains approximately constant over time and the reaction rate changes relatively slowly. Rates are measured for a short period after the attainment of the quasi-steady state, typically by monitoring the accumulation of product with time. Because the measurements are carried out for a very short period and because of the large excess of substrate, the approximation that the amount of free substrate is approximately equal to the amount of the initial substrate can be made. The initial rate experiment is the simplest to perform and analyze, being relatively free from complications such as back-reaction and enzyme degradation. It is therefore by far the most commonly used type of experiment in enzyme kinetics.
* Progress curve experiments. In these experiments, the kinetic parameters are determined from expressions for the species concentrations as a function of time. The concentration of the substrate or product is recorded in time after the initial fast transient and for a sufficiently long period to allow the reaction to approach equilibrium. Progress curve experiments were widely used in the early period of enzyme kinetics, but are less common now.
* Transient kinetics experiments. In these experiments, reaction behaviour is tracked during the initial fast transient as the intermediate reaches the steady-state kinetics period. These experiments are more difficult to perform than either of the above two classes because they require specialist techniques (such as flash photolysis of caged compounds) or rapid mixing (such as stopped-flow, quenched flow or continuous flow).
* Relaxation experiments. In these experiments, an equilibrium mixture of enzyme, substrate and product is perturbed, for instance by a temperature, pressure or pH jump, and the return to equilibrium is monitored. The analysis of these experiments requires consideration of the fully reversible reaction. Moreover, relaxation experiments are relatively insensitive to mechanistic details and are thus not typically used for mechanism identification, although they can be under appropriate conditions.
Enzyme assays can be split into two groups according to their sampling method: continuous assays, where the assay gives a continuous reading of activity, and discontinuous assays, where samples are taken, the reaction stopped and then the concentration of substrates/products determined. | 1 | Biochemistry |
ePaint is a less-toxic alternative to conventional antifouling marine paints that generates hydrogen peroxide.
Photocatalysis of organic reactions by polypyridyl complexes, porphyrins, or other dyes can produce materials inaccessible by classical approaches. Most photocatalytic dye degradation studies have employed . The anatase form of has higher photon absorption characteristics. | 5 | Photochemistry |
Allyl- and vinylsilanes react with a variety of electrophiles under conditions of nucleophilic catalysis or Lewis acid promotion (often stoichiometric). The primary advantage of using Lewis acids versus fluoride catalysis is site selectivity—fluoride activation tends to generate allyl anions, which can then react at either the α or γ position. Use of Lewis-acid-activated electrophiles leads to reaction at only the γ position of allylsilanes. | 0 | Organic Chemistry |
Compilation of data into secure and readily searchable databases ensures ease of use and is fundamental to the success of the programme. The [http://www.bodc.ac.uk/geotraces/ GEOTRACES Data Assembly Centre] (GDAC) is responsible for the compilation, quality control and secure archiving of data received from national data centers and from core international GEOTRACES cruises. It has as its main aims the integration of core GEOTRACES data into global data sets, and making this data accessible to participating scientist and the larger science community according to the GEOTRACES data policy. The GDAC is hosted at the British Oceanographic Data Centre and a dedicated committee with international representation oversees it. | 9 | Geochemistry |
In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (). The terms enol and alkenol are portmanteaus deriving from "-ene"/"alkene" and the "-ol" suffix indicating the hydroxyl group of alcohols, dropping the terminal "-e" of the first term. Generation of enols often involves deprotonation at the α position to the carbonyl group—i.e., removal of the hydrogen atom there as a proton . When this proton is not returned at the end of the stepwise process, the result is an anion termed an enolate (see images at right). The enolate structures shown are schematic; a more modern representation considers the molecular orbitals that are formed and occupied by electrons in the enolate. Similarly, generation of the enol often is accompanied by "trapping" or masking of the hydroxy group as an ether, such as a silyl enol ether.
Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other. | 0 | Organic Chemistry |
The scattered intensity can be plotted as a function of the angle to give information on the R which can simply be calculated using the Guinier approximation as follows:
where ln(ΔR(θ)) = lnP(θ) also known as the form factor with q = 4πnsin(θ/2)/λ. Hence a plot of the corrected Rayleigh ratio, ΔR(θ) vs sin(θ/2) or q will yield a slope R/3. However, this approximation is only true for qR < 1. Note that for a Guinier plot, the value of dn/dc and the concentration is not needed. | 7 | Physical Chemistry |
Expanded out, the grand potential is:
All thermodynamic properties can be computed from this potential. The following table lists various thermodynamic quantities calculated in the limit of low temperature and high temperature, and in the limit of infinite particle number. An equal sign (=) indicates an exact result, while an approximation symbol indicates that only the first few terms of a series in is shown.
It is seen that all quantities approach the values for a classical ideal gas in
the limit of large temperature. The above values can be used to calculate other
thermodynamic quantities. For example, the relationship between internal energy and
the product of pressure and volume is the same as that for a classical ideal gas over
all temperatures:
A similar situation holds for the specific heat at constant volume
The entropy is given by:
Note that in the limit of high temperature, we have
which, for α=3/2 is simply a restatement of the Sackur–Tetrode equation. In one dimension bosons with delta interaction behave as fermions, they obey Pauli exclusion principle. In one dimension Bose gas with delta interaction can be solved exactly by Bethe ansatz. The bulk free energy and thermodynamic potentials were calculated by Chen-Ning Yang. In one dimensional case correlation functions also were evaluated. In one dimension Bose gas is equivalent to quantum non-linear Schrödinger equation. | 7 | Physical Chemistry |
Reactions of organocopper reagents involve species containing copper-carbon bonds acting as nucleophiles in the presence of organic electrophiles. Organocopper reagents are now commonly used in organic synthesis as mild, selective nucleophiles for substitution and conjugate addition reactions.
Since the discovery that copper(I) halides catalyze the conjugate addition of Grignard reagents in 1941, organocopper reagents have emerged as weakly basic, nucleophilic reagents for substitution and addition reactions. The constitution of organocopper compounds depends on their method of preparation and the various kinds of organocopper reagents exhibit different reactivity profiles. As a result, the scope of reactions involving organocopper reagents is extremely broad.
* Organocopper complexes (RCu) are produced when a copper(I) halide and organolithium are combined. In conjunction with Lewis acidic additives such as boron trifluoride etherate, these reagents are used for conjugate addition reactions.
* Lower-order cuprates (RCuLi, also known as Gilman reagents) result when organocopper complexes are treated with an equivalent of organolithium. Alternatively, they may be formed by the treatment of a copper(I) halide with two equivalents of organolithium. They undergo substitution, conjugate addition, and carbocupration reactions in the presence of the appropriate organic substrates. Mixed Gilman reagents consist of two different R groups, one of which is typically a non-transferable "dummy" group.
* Lower-order cyanocuprates (RCu(CN)Li) are similarly derived from an organolithium compound and copper(I) cyanide; however, intermediate organocopper complexes do not form during this reaction and thus only a single equivalent of organolithium reagent is necessary. Cyanocuprates undergo S2' substitution in the presence of allyl electrophiles and conjugate addition reactions in the presence of enones.
* Higher-order cyanocuprates (RCu(CN)Li) are formed upon the reaction of two equivalents of organolithium with copper(I) cyanide. These reagents are more reactive towards substitution than the corresponding lower-order cyanocuprates. | 0 | Organic Chemistry |
The rust resistance of EPS-processed steel strip is superior to that of acid pickled steel strip primarily because acid pickling imposes a corrosion "penalty" on the steel which EPS processing does not. This penalty is a result of chemical reactions that occur after acid pickling and serve as a catalyst for oxidation. The primary pickling agent is hydrochloric acid (HCl). Although the steel strip is thoroughly rinsed with clean water after immersion in the HCl bath, some residual amount of chlorine (Cl) remains on the surface of the strip. Chlorine reacts very readily with oxygen to form chlorides, so the free Cl acts as something of a "magnet" for oxygen. This mechanism makes acid-pickled steel more prone to picking up oxygen, whereas there is no comparable mechanism at work with EPS mechanical pickling.
In addition to the free Cl, compounds known as "chloride salts" remain on the surface of acid pickled steel in trace amounts, even after rinsing. Chloride salts react rapidly with moisture and accelerate oxidation of iron on the steel's surface. To prevent oxidation of the iron in the acid pickled strip, a thin film of oil is applied to the surface to serve as a barrier between the free Cl, chloride salts and oxygen. No such protective barrier is needed for EPS-processed steel, as no free Cl or chloride salts are present.
However, an additive is used in the EPS slurry blast carrier liquid to reduce the "smut" that would otherwise remain on the surface and dull the appearance of EPS-processed strip. This additive contains a rust inhibitor, a residual amount of which remains on the surface even after rinsing. It is believed that the presence of the rust inhibitor adds to the overall EPS-processed strip's ability to resist rusting. The additive has been demonstrated to have no impact on paint performance. | 8 | Metallurgy |
* Dr. Abdus Salam Prize in Chemistry (1986)
* Nishan-e-Azmat-e-Ilm Plaque, Karachi University (1989)
* Nishan-e-Azmat-e-Danish Plaque, Karachi University (1993)
* Nishane- Danish Plaque, Karachi University (1998)
* First Prize of the National Book Foundation (1997)
* Star Woman of the Year Award and gold medal by Star Girls and Women's Foundation (1997)
* Tamgha-i-Imtiaz, Government of Pakistan (2000)
* Khwarizmi Award by the President of Islamic Republic of Iran (2001)
* Sitara-i-Imtiaz by the Govt. of Pakistan (2004)
*Distinguished National Professor (HEC) | 0 | Organic Chemistry |
Brunauer–Emmett–Teller (BET) theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of materials. The observations are very often referred to as physical adsorption or physisorption. In 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller presented their theory in the Journal of the American Chemical Society. BET theory applies to systems of multilayer adsorption that usually utilizes a probing gas (called the adsorbate) that does not react chemically with the adsorptive (the material upon which the gas attaches to) to quantify specific surface area. Nitrogen is the most commonly employed gaseous adsorbate for probing surface(s). For this reason, standard BET analysis is most often conducted at the boiling temperature of N (77 K). Other probing adsorbates are also utilized, albeit less often, allowing the measurement of surface area at different temperatures and measurement scales. These include argon, carbon dioxide, and water. Specific surface area is a scale-dependent property, with no single true value of specific surface area definable, and thus quantities of specific surface area determined through BET theory may depend on the adsorbate molecule utilized and its adsorption cross section. | 7 | Physical Chemistry |
All chain-growth polymerization reactions must include chain initiation and chain propagation. Chain transfer and chain termination steps also occur in many but not all chain-growth polymerizations. | 7 | Physical Chemistry |
Abdulrahman Obaid Al-Youbi (born 1958) was the president of King Abdulaziz University from June 2016 to October 2022. | 7 | Physical Chemistry |
*[http://nptel.ac.in/courses/105104102/solids%202.htm National Programme on Technology Enhanced Learning]
*[http://www.ebsbiowizard.com/2011/01/total-suspended-solids-tss-volatile-suspended-solids-vss-2/ Environmental Business Specialists] | 3 | Analytical Chemistry |
Each duplex sequencing read contains a fixed 5-nucleotide sequence (shown in figures in black) located upstream of the 12-nucleotide tag sequence. The reads are filtered if they do not have the expected 5-nucleotide sequence or have more than nine identical or ambiguous bases within each tag. The two 12-nucleotide tags at each end of the reads are combined and moved to the read header. Two families of reads are formed that originate from the two strands of DNA. One family contains reads with αβ header originating from strand 1 and the second contains reads with βα header originating from strand 2 (Figure 2). The reads are then trimmed by removing the fixed 5-base pair sequence and 4 error-prone nucleotides located at the sites of ligation and end repair. The remaining reads are assembled to consensus sequences using SSCS and DCS assemblies. | 1 | Biochemistry |
There are several quality control techniques used to ensure the quality of extracted DNA, including:
* Spectrophotometry: This is a widely used method for measuring the concentration and purity of a DNA sample. Spectrophotometry measures the absorbance of a sample at different wavelengths, typically at 260 nm and 280 nm. The ratio of absorbance at 260 nm and 280 nm is used to determine the purity of the DNA sample.
* Gel electrophoresis: This technique is used to visualize and compare the size and integrity of DNA samples. The DNA is loaded onto an agarose gel and then subjected to an electric field, which causes the DNA to migrate through the gel. The migration of the DNA can be visualized using ethidium bromide, which intercalates into the DNA and fluoresces under UV light.
* Fluorometry: Fluorometry is a method to determine the concentration of nucleic acids by measuring the fluorescence of the sample when excited by a specific wavelength of light. Fluorometry uses dyes that specifically bind to nucleic acids and have a high fluorescence intensity.
* PCR: Polymerase Chain Reaction (PCR) is a technique that amplifies a specific region of DNA, it is also used as a QC method by amplifying a small fragment of the DNA, if the amplification is successful, it means the extracted DNA is of good quality and it's not degraded.
* Qubit Fluorometer: The Qubit Fluorometer is an instrument that uses fluorescent dyes to measure the concentration of DNA and RNA in a sample. It is a quick and sensitive method that can be used to determine the concentration of DNA samples.
* Bioanalyzer: The bioanalyzer is an instrument that uses electrophoresis to separate and analyze DNA, RNA, and protein samples. It can provide detailed information about the size, integrity, and purity of a DNA sample. | 1 | Biochemistry |
Spectroscopy is a branch of science concerned with the spectra of electromagnetic radiation as a function of its wavelength or frequency measured by spectrographic equipment, and other techniques, in order to obtain information concerning the structure and properties of matter. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers. Most spectroscopic analysis in the laboratory starts with a sample to be analyzed, then a light source is chosen from any desired range of the light spectrum, then the light goes through the sample to a dispersion array (diffraction grating instrument) and captured by a photodiode. For astronomical purposes, the telescope must be equipped with the light dispersion device. There are various versions of this basic setup that may be employed.
Spectroscopy began with Isaac Newton splitting light with a prism; a key moment in the development of modern optics. Therefore, it was originally the study of visible light which we call color that later under the studies of James Clerk Maxwell came to include the entire electromagnetic spectrum. Although color is involved in spectroscopy, it is not equated with the color of elements or objects which involve the absorption and reflection of certain electromagnetic waves to give objects a sense of color to our eyes. Rather spectroscopy involves the splitting of light by a prism, diffraction grating, or similar instrument, to give off a particular discrete line pattern called a "spectrum" unique to each different type of element. Most elements are first put into a gaseous phase to allow the spectra to be examined although today other methods can be used on different phases. Each element that is diffracted by a prism-like instrument displays either an absorption spectrum or an emission spectrum depending upon whether the element is being cooled or heated.
Until recently all spectroscopy involved the study of line spectra and most spectroscopy still does. Vibrational spectroscopy is the branch of spectroscopy that studies the spectra. However, the latest developments in spectroscopy can sometimes dispense with the dispersion technique. In biochemical spectroscopy, information can be gathered about biological tissue by absorption and light scattering techniques. Light scattering spectroscopy is a type of reflectance spectroscopy that determines tissue structures by examining elastic scattering. In such a case, it is the tissue that acts as a diffraction or dispersion mechanism.
Spectroscopic studies were central to the development of quantum mechanics, because the first useful atomic models described the spectra of hydrogen which models include the Bohr model, the Schrödinger equation, and Matrix mechanics which all can produce the spectral lines of hydrogen, therefore providing the basis for discrete quantum jumps to match the discrete hydrogen spectrum. Also, Max Planck's explanation of blackbody radiation involved spectroscopy because he was comparing the wavelength of light using a photometer to the temperature of a Black Body. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature, density of elements in a star, velocity, black holes and more). An important use for spectroscopy is in biochemistry. Molecular samples may be analyzed for species identification and energy content. | 7 | Physical Chemistry |
Plants are under horticulture care, but the environment is managed to near natural conditions. This occurs with either restored or semi-natural environments. This technique is primarily used for taxa that are rare or in areas where habitat has been severely degraded. | 1 | Biochemistry |
EPSs are mostly composed of polysaccharides (exopolysaccharides) and proteins, but include other macromolecules such as DNA, lipids and humic substances. EPSs are the construction material of bacterial settlements and either remain attached to the cells outer surface, or are secreted into its growth medium. These compounds are important in biofilm formation and cells attachment to surfaces. EPSs constitute 50% to 90% of a biofilm's total organic matter.
Exopolysaccharides (also sometimes abbreviated EPSs; EPS sugars thereafter) are the sugar-based parts of EPS. Microorganisms synthesize a wide spectrum of multifunctional polysaccharides including intracellular polysaccharides, structural polysaccharides and extracellular polysaccharides or exopolysaccharides. Exopolysaccharides generally consist of monosaccharides and some non-carbohydrate substituents (such as acetate, pyruvate, succinate, and phosphate). Owing to the wide diversity in composition, exopolysaccharides have found diverse applications in various food and pharmaceutical industries. Many microbial EPS sugars provide properties that are almost identical to the gums currently in use. With innovative approaches, efforts are underway to supersede the traditionally used plant and algal gums by their microbial counterparts. Moreover, considerable progress has been made in discovering and developing new microbial EPS sugars that possess novel industrial applications. Levan produced by Pantoea agglomerans ZMR7 was reported to decrease the viability of rhabdomyosarcoma (RD) and breast cancer (MDA) cells compared with untreated cancer cells. In addition, it has high antiparasitic activity against the promastigote of Leishmania tropica. In the1960s and 1970s, the presence of exopolysaccharides in the matrix of plaques associated with tooth decay was investigated. In the field of paleomicrobiology, dental biofilms and their EPS components provide scientists with information about the composition of ancient microbial and host biomolecules as well as the diet of the host.
The minerals, results of biomineralization processes regulated by the environment or bacteria, are also essential components of the EPS. They provide structural integrity to biofilm matrix and act as a scaffold to protect bacterial cells from shear forces and antimicrobial chemicals. The minerals in EPS were found to contribute to morphogenesis of bacteria and the structural integrity of the matrix. For example, in Bacillus subtilis, Mycobacterium smegmatis, and Pseudomonas aeruginosa biofilms, calcite () contributes to the integrity of the matrix. The minerals also associate with medical conditions. In the biofilms of Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri, the minerals calcium and magnesium cause catheter encrustation. | 1 | Biochemistry |
Many peripheral membrane proteins bind to the membrane primarily through interactions with integral membrane proteins. But there is a diverse group of proteins which interact directly with the surface of the lipid bilayer. Some, such as myelin basic protein, and spectrin have mainly structural roles. A number of water-soluble proteins can bind to the bilayer surface transiently or under specific conditions.
Misfolding processes, typically exposing hydrophobic regions of proteins, often are associated with binding to lipid membranes and subsequent aggregation, for example, during neurodegenerative disorders, neuronal stress and apoptosis. | 1 | Biochemistry |
Indium gallium arsenide (InGaAs) is a compound III-V semiconductor. It can be applied in two ways for use in TPVs. When lattice-matched to an InP substrate, InGaAs has a bandgap of 0.74 eV, no better than GaSb. Devices of this configuration have been produced with a fill factor of 69% and an efficiency of 15%. However, to absorb higher wavelength photons, the bandgap may be engineered by changing the ratio of In to Ga. The range of bandgaps for this system is from about 0.4 to 1.4 eV. However, these different structures cause strain with the InP substrate. This can be controlled with graded layers of InGaAs with different compositions. This was done to develop of device with a quantum efficiency of 68% and a fill factor of 68%, grown by MBE. This device had a bandgap of 0.55 eV, achieved in the compound InGaAs. It is a well-developed material. InGaAs can be made to lattice match perfectly with Ge resulting in low defect densities. Ge as a substrate is a significant advantage over more expensive or harder-to-produce substrates. | 7 | Physical Chemistry |
Fine particles dispersed in the atmosphere can serve as cloud condensation nuclei and thereby cause marine cloud brightening
Eventually all FeCl particles are washed out of the air and fall on land or water, where they dissolve into iron compounds and salt.
Iron salt aerosols may also therefore contribute to iron fertilization. | 2 | Environmental Chemistry |
Thiosulfines, also called thiocarbonyl S-sulfides, are compounds with the formula RCSS. Although superficially appearing to be cumulenes, with the linkage RC=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions. Thiosulfines are proposed to exist in equilibrium with dithiiranes, three-membered CS rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4-trithiolane (PhC)S, which arises via the cycloaddition of PhCSS to its parent PhCS. | 0 | Organic Chemistry |
Failure of thermal barrier coating usually manifests as delamination, which arises from the temperature gradient during thermal cycling between ambient temperature and working conditions coupled with the difference in thermal expansion coefficient of substrate and coating. It is rare for the coating to fail completely – some pieces remain intact, and significant scatter is observed in the time to failure if testing is repeated under identical conditions. Various degradation mechanisms affect thermal barrier coating, and some or all of these must operate before failure finally occurs:
* Oxidation at the interface of thermal barrier coating and underlying bond coat;
* Depletion of aluminum in bond coat due to oxidation and diffusion with substrate;
* Thermal stresses from mismatch in thermal expansion coefficient and growth stress due to the formation of thermally grown oxide layer;
* Imperfections near thermally grown oxide layer;
* Various other complicating factors during engine operation.
Additionally, TBC life is sensitive to the combination of materials (substrate, bond coat, ceramic) and processes (EB-PVD, plasma spraying) used. | 8 | Metallurgy |
Vitrification (, via French ) is the full or partial transformation of a substance into a glass, that is to say, a non-crystalline amorphous solid. Glasses differ from liquids structurally and glasses possess a higher degree of connectivity with the same Hausdorff dimensionality of bonds as crystals: dim = 3. In the production of ceramics, vitrification is responsible for their impermeability to water.
Vitrification is usually achieved by heating materials until they liquidize, then cooling the liquid, often rapidly, so that it passes through the glass transition to form a glassy solid. Certain chemical reactions also result in glasses.
In terms of chemistry, vitrification is characteristic for amorphous materials or disordered systems and occurs when bonding between elementary particles (atoms, molecules, forming blocks) becomes higher than a certain threshold value. Thermal fluctuations break the bonds; therefore, the lower the temperature, the higher the degree of connectivity. Because of that, amorphous materials have a characteristic threshold temperature termed glass transition temperature (T): below T amorphous materials are glassy whereas above T they are molten.
The most common applications are in the making of pottery, glass, and some types of food, but there are many others, such as the vitrification of an antifreeze-like liquid in cryopreservation.
In a different sense of the word, the embedding of material inside a glassy matrix is also called vitrification. An important application is the vitrification of radioactive waste to obtain a substance that is thought to be safer and more stable for disposal.
One study suggests during the eruption of Mount Vesuvius in 79 AD, a victim's brain was vitrified by the extreme heat of the volcanic ash; however, this has been strenuously disputed. | 1 | Biochemistry |
*UVR8: UV-B light reception
*Cryptochrome: blue and UV-A light reception
*Phototropin: blue and UV-A light perception (to mediate phototropism and chloroplast movement)
*Zeitlupe: blue light entrainment of the circadian clock
*Phytochrome: red and far-red light reception
All the photoreceptors listed above allow plants to sense light with wavelengths range from 280 nm (UV-B) to 750 nm (far-red light). Plants use light of different wavelengths as environmental cues to both alter their position and to trigger important developmental transitions. The most prominent wavelength responsible for plant mechanisms is blue light, which can trigger cell elongation, plant orientation, and flowering. One of the most important processes regulated by photoreceptors is known as photomorphogenesis. When a seed germinates underground in the absence of light, its stem rapidly elongates upwards. When it breaks through the surface of the soil, photoreceptors perceive light. The activated photoreceptors cause a change in developmental program; the plant starts producing chlorophyll and switches to photosynthetic growth. | 1 | Biochemistry |
There are a few old studies indicating efficacy of lithium for acute depression with lithium having the same efficacy as tricyclic antidepressants. A recent study concluded that lithium works best on chronic and recurrent depression when compared to modern antidepressant (i.e. citalopram) but not for patients with no history of depression. | 1 | Biochemistry |
The magnetism of the early full-Heusler compound CuMnAl varies considerably with heat treatment and composition. It has a room-temperature saturation induction of around 8,000 gauss, which exceeds that of the element nickel (around 6100 gauss) but is smaller than that of iron (around 21500 gauss). For early studies see. In 1934, Bradley and Rogers showed that the room-temperature ferromagnetic phase was a fully ordered structure of the L2 Strukturbericht type. This has a primitive cubic lattice of copper atoms with alternate cells body-centered by manganese and aluminium. The lattice parameter is 5.95 Å. The molten alloy has a solidus temperature of about 910 °C. As it is cooled below this temperature, it transforms into disordered, solid, body-centered cubic beta-phase. Below 750 °C, a B2 ordered lattice forms with a primitive cubic copper lattice, which is body-centered by a disordered manganese-aluminium sublattice. Cooling below 610 °C causes further ordering of the manganese and aluminium sub-lattice to the L2 form. In non-stoichiometric alloys, the temperatures of ordering decrease, and the range of anealing temperatures, where the alloy does not form microprecipitates, becomes smaller than for the stoichiometric material.
Oxley found a value of 357 °C for the Curie temperature, below which the compound becomes ferromagnetic. Neutron diffraction and other techniques have shown that a magnetic moment of around 3.7 Bohr magnetons resides almost solely on the manganese atoms. As these atoms are 4.2 Å apart, the exchange interaction, which aligns the spins, is likely indirect and is mediated through conduction electrons or the aluminium and copper atoms.
Electron microscopy studies demonstrated that thermal antiphase boundaries (APBs) form during cooling through the ordering temperatures, as ordered domains nucleate at different centers within the crystal lattice and are often out of step with each other where they meet. The anti-phase domains grow as the alloy is annealed. There are two types of APBs corresponding to the B2 and L2 types of ordering. APBs also form between dislocations if the alloy is deformed. At the APB the manganese atoms will be closer than in the bulk of the alloy and, for non-stoichiometric alloys with an excess of copper (e.g. CuMnAl), an antiferromagnetic layer forms on every thermal APB. These antiferromagnetic layers completely supersede the normal magnetic domain structure and stay with the APBs if they are grown by annealing the alloy. This significantly modifies the magnetic properties of the non-stoichiometric alloy relative to the stoichiometric alloy which has a normal domain structure. Presumably this phenomenon is related to the fact that pure manganese is an antiferromagnet although it is not clear why the effect is not observed in the stoichiometric alloy. Similar effects occur at APBs in the ferromagnetic alloy MnAl at its stoichiometric composition.
Some Heusler compounds also exhibit properties of materials known as ferromagnetic shape-memory alloys. These are generally composed of nickel, manganese and gallium and can change their length by up to 10% in a magnetic field. | 8 | Metallurgy |
Supramolecular polymers with specific, directional, tunable and reversible non-covalent interactions should be advantageous for biomaterials as well as biomedical applications. For instance, the reversible nature of supramolecular polymers can produce biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signaling. On the basis of their formation mechanisms, supramolecular biomaterials can be broadly classified as: (1) materials prepared from one-dimensional assemblies of molecular stacking motifs as in the case of peptide amphiphiles introduced by Samuel I. Stupp, and (2) materials prepared through chain extension of oligomers or through crosslinking of polymeric precursors by specific supramolecular recognition motifs.
Rationally designed supramolecular polymers-based polymers can simultaneously meet the requirements of aqueous compatibility, bio-degradability, biocompatibility, stimuli-responsiveness and other strict criterion. Consequently, supramolecular polymers can be applied to the biomedical field as a robust system. Other than applications mentioned above, other important and fascinating biomedical applications, like protein delivery, bio-imaging and diagnosis and tissue engineering, are also well developed. | 6 | Supramolecular Chemistry |
This method, also called Free energy perturbation (or FEP), involves sampling from state A only. It requires that all the high probability configurations of super state B are contained in high probability configurations of super state A, which is a much more stringent requirement than the overlap condition stated above. | 7 | Physical Chemistry |
Thomsen–Friedenreich antigen (Galβ1-3GalNAcα1-Ser/Thr) is a disaccharide that serves as a core 1 structure in O-linked glycosylation. First described by Thomsen as a red blood cell's antigen, later research have determined it to be an oncofetal antigen. it is present in the body as a part of membrane transport proteins where it is normally masked from the immune system. It is commonly demasked in cancer cells, with it being expressed in up to 90% of carcinomas, making it a potential target for immunotherapy. | 1 | Biochemistry |
RNA polymerase II holoenzyme stability determines the number of base pairs that can be transcribed before the holoenzyme loses its ability to transcribe. The length of the CTD is essential for RNA polymerase II stability. RNA polymerase II stability has been shown to be regulated by post-translation proline hydroxylation. The von Hippel–Lindau tumor suppressor protein (pVHL, human GeneID: 7428) complex binds the hyperphosphorylated large subunit of the RNA polymerase II complex, in a proline hydroxylation- and CTD phosphorylation-dependent manner, targeting it for ubiquitination. | 1 | Biochemistry |
It currently has around 7000 members, two-thirds in the UK. It is affiliated with the European body, Federation of European Biochemical Societies (FEBS). The Societys current President (2016) is Sir David Baulcombe. The Societys headquarters are in London. | 1 | Biochemistry |
A system is enclosed by walls that bound it and connect it to its surroundings. Often a wall restricts passage across it by some form of matter or energy, making the connection indirect. Sometimes a wall is no more than an imaginary two-dimensional closed surface through which the connection to the surroundings is direct.
A wall can be fixed (e.g. a constant volume reactor) or moveable (e.g. a piston). For example, in a reciprocating engine, a fixed wall means the piston is locked at its position; then, a constant volume process may occur. In that same engine, a piston may be unlocked and allowed to move in and out. Ideally, a wall may be declared adiabatic, diathermal, impermeable, permeable, or semi-permeable. Actual physical materials that provide walls with such idealized properties are not always readily available.
The system is delimited by walls or boundaries, either actual or notional, across which conserved (such as matter and energy) or unconserved (such as entropy) quantities can pass into and out of the system. The space outside the thermodynamic system is known as the surroundings, a reservoir, or the environment. The properties of the walls determine what transfers can occur. A wall that allows transfer of a quantity is said to be permeable to it, and a thermodynamic system is classified by the permeabilities of its several walls. A transfer between system and surroundings can arise by contact, such as conduction of heat, or by long-range forces such as an electric field in the surroundings.
A system with walls that prevent all transfers is said to be isolated. This is an idealized conception, because in practice some transfer is always possible, for example by gravitational forces. It is an axiom of thermodynamics that an isolated system eventually reaches internal thermodynamic equilibrium, when its state no longer changes with time.
The walls of a closed system allow transfer of energy as heat and as work, but not of matter, between it and its surroundings. The walls of an open system allow transfer both of matter and of energy. This scheme of definition of terms is not uniformly used, though it is convenient for some purposes. In particular, some writers use closed system where isolated system is here used.
Anything that passes across the boundary and effects a change in the contents of the system must be accounted for in an appropriate balance equation. The volume can be the region surrounding a single atom resonating energy, such as Max Planck defined in 1900; it can be a body of steam or air in a steam engine, such as Sadi Carnot defined in 1824. It could also be just one nuclide (i.e. a system of quarks) as hypothesized in quantum thermodynamics. | 7 | Physical Chemistry |
The smelting process was often carried out away from the rest of the community. Ironworkers engaged in rituals designed to encourage good production and to ward off bad spirits, including song and prayers, plus the giving of medicines and sacrifices. The latter were usually put in the furnace itself or buried under the base of the furnace. Examples of these date back as far as the early Iron Age in Tanzania and Rwanda (Schmidt 1997 in Childs et al., 2005 p. 293).
Some cultures associated sexual symbolism with iron production. Smelting was integrated with the fertility of their society, The production of the bloom was compared to human conception and birth. There were sexual taboos surrounding the process. The smelting process was carried out entirely by men and often away from the village. For women to touch any of the materials or be present could jeopardise the success of the production. The furnaces were also often adorned to resemble a woman, the mother of the bloom. | 8 | Metallurgy |
Archaeological evidence has not revealed metal smelting or alloying of metals by pre-Columbian native peoples north of the Rio Grande; however, they did use native copper extensively. | 8 | Metallurgy |
Despite the different stoichiometry in these mixtures which varies the concentration of the reagent, they all follow the same idea of adding HgO to distilled water and concentrated sulfuric acid. The Denigés' reagent is ultimately mercury(II) sulfate in an aqueous solution.
*5 grams of mercury(II) oxide (HgO) is dissolved in 40 mL of distilled water. The mixture is slowly stirred, while 20 mL of concentrated sulfuric acid is added. After adding another 40 mL of distilled water, the solution is stirred until the HgO is completely dissolved.
* The Denigés' reagent can also be prepared by dissolving 5 grams of HgO in 20 mL of concentrated sulfuric acid and 100 mL of distilled water.
*The Denigés' reagent can be modified by using nitric acid in place of sulfuric acid | 3 | Analytical Chemistry |
When it was discovered that the self-cleaning qualities of ultrahydrophobic surfaces come from physical-chemical properties at the microscopic to nanoscopic scale rather than from the specific chemical properties of the leaf surface, the possibility arose of using this effect in manmade surfaces, by mimicking nature in a general way rather than a specific one.
Some nanotechnologists have developed treatments, coatings, paints, roof tiles, fabrics and other surfaces that can stay dry and clean themselves by replicating in a technical manner the self-cleaning properties of plants, such as the lotus plant. This can usually be achieved using special fluorochemical or silicone treatments on structured surfaces or with compositions containing micro-scale particulates.
In addition to chemical surface treatments, which can be removed over time, metals have been sculpted with femtosecond pulse lasers to produce the lotus effect. The materials are uniformly black at any angle, which combined with the self-cleaning properties might produce very low maintenance solar thermal energy collectors, while the high durability of the metals could be used for self-cleaning latrines to reduce disease transmission.
Further applications have been marketed, such as self-cleaning glasses installed in the sensors of traffic control units on German autobahns developed by a cooperation partner (Ferro GmbH).
The Swiss companies HeiQ and [http://www.schoeller-textiles.com/en.html Schoeller Textil] have developed stain-resistant textiles under the brand names "[https://web.archive.org/web/20160812113734/http://heiq.com/products/eco-dry/ HeiQ Eco Dry]" and "[http://www.schoeller-textiles.com/en/technologies/nanosphere.html nanosphere]" respectively. In October 2005, tests of the Hohenstein Research Institute showed that clothes treated with NanoSphere technology allowed tomato sauce, coffee and red wine to be easily washed away even after a few washes. Another possible application is thus with self-cleaning awnings, tarpaulins and sails, which otherwise quickly become dirty and difficult to clean.
Superhydrophobic coatings applied to microwave antennas can significantly reduce rain fade and the buildup of ice and snow. "Easy to clean" products in ads are often mistaken in the name of the self-cleaning properties of hydrophobic or ultrahydrophobic surfaces. Patterned ultrahydrophobic surfaces also show promise for "lab-on-a-chip" microfluidic devices and can greatly improve surface-based bioanalysis.
Superhydrophobic or hydrophobic properties have been used in dew harvesting, or the funneling of water to a basin for use in irrigation. The Groasis Waterboxx has a lid with a microscopic pyramidal structure based on the ultrahydrophobic properties that funnel condensation and rainwater into a basin for release to a growing plant's roots. | 7 | Physical Chemistry |
A relatively non-toxic metal to humans and the second most abundant, the body has 2-3 grams of zinc. It can enter the body through inhalation, skin absorption, and ingestion, with the latter of the bunch being the most common. The mucosal cells of the digestive tract contain metallothionein proteins that store the zinc ions.
Nearly 90% of zinc is found in the bones, muscles, and vesicles in the brain. Zinc is a cofactor in hundreds of enzyme reactions and a major component of zinc finger proteins. | 9 | Geochemistry |
carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.
fixation is an addition to the ancestral and more common carbon fixation. The main carboxylating enzyme in photosynthesis is called RuBisCO, which catalyses two distinct reactions using either (carboxylation) or oxygen (oxygenation) as a substrate. RuBisCO oxygenation gives rise to phosphoglycolate, which is toxic and requires the expenditure of energy to recycle through photorespiration. photosynthesis reduces photorespiration by concentrating around RuBisCO.
To enable RuBisCO to work in an environment where there is a lot of carbon dioxide and very little oxygen, leaves generally contain two partially isolated compartments called mesophyll cells and bundle-sheath cells. is initially fixed in the mesophyll cells in a reaction catalysed by the enzyme PEP carboxylase in which the three-carbon phosphoenolpyruvate (PEP) reacts with to form the four-carbon oxaloacetic acid (OAA). OAA can then be reduced to malate or transaminated to aspartate. These intermediates diffuse to the bundle sheath cells, where they are decarboxylated, creating a -rich environment around RuBisCO and thereby suppressing photorespiration. The resulting pyruvate (PYR), together with about half of the phosphoglycerate (PGA) produced by RuBisCO, diffuses back to the mesophyll. PGA is then chemically reduced and diffuses back to the bundle sheath to complete the reductive pentose phosphate cycle (RPP). This exchange of metabolites is essential for photosynthesis to work.
Additional biochemical steps require more energy in the form of ATP to regenerate PEP, but concentrating allows high rates of photosynthesis at higher temperatures. Higher CO concentration overcomes the reduction of gas solubility with temperature (Henry's law). The concentrating mechanism also maintains high gradients of concentration across the stomatal pores. This means that plants have generally lower stomatal conductance, reduced water losses and have generally higher water-use efficiency. plants are also more efficient in using nitrogen, since PEP carboxylase is cheaper to make than RuBisCO. However, since the pathway does not require extra energy for the regeneration of PEP, it is more efficient in conditions where photorespiration is limited, typically at low temperatures and in the shade. | 5 | Photochemistry |
Many lichens produce secondary compounds, including pigments that reduce harmful amounts of sunlight and powerful toxins that deter herbivores or kill bacteria. These compounds are very useful for lichen identification, and have had economic importance as dyes such as cudbear or primitive antibiotics.
A pH indicator (which can indicate acidic or basic substances) called litmus is a dye extracted from the lichen Roccella tinctoria ("dyer's weed") by boiling. It gives its name to the well-known litmus test.
Traditional dyes of the Scottish Highlands for Harris tweed and other traditional cloths were made from lichens, including the orange Xanthoria parietina ("common orange lichen") and the grey foliaceous Parmelia saxatilis common on rocks and known colloquially as "crottle".
There are reports dating almost 2,000 years old of lichens being used to make purple and red dyes. Of great historical and commercial significance are lichens belonging to the family Roccellaceae, commonly called orchella weed or orchil. Orcein and other lichen dyes have largely been replaced by synthetic versions. | 2 | Environmental Chemistry |
In a SRAS measurement, as in most laser ultrasound techniques, two lasers are used, one for the generation of acoustic waves and one for the subsequent detection of these waves. Considering first the generation of acoustic waves, an optical amplitude grating, illuminated by the a short pulse pump laser (typically ~1ns), is imaged onto the sample surface. The incident light is thermoelastically absorbed, creating surface acoustic waves, such as Rayleigh waves. As the laser pulse contains a broad range of frequencies, only the frequencies which match the grating spacing and acoustic velocity of that sample point will be generated. Using a second, continuous wave, laser these surface acoustic waves can then be measured through a number of interferometry techniques. Detection is usually achieved by optical beam deflection.
As Rayleigh waves are non-dispersive the phase velocity of the acoustic wave can be found by
where is the distance between the grating fringes imaged onto the sample surface and is the dominant frequency of the wave packet, found by fast Fourier transform.
As the measurement probes the frequency of the wave packet, which does not change along the propagation length, the measured SAW velocity is determined by only the properties of the specimen at the area where the grating pattern is imaged, unlike more traditional time of flight measurements that are influenced by the sample properties along the propagation length. This makes SRAS robust and immune to the aberrating and scattering effects of the microstructure. | 7 | Physical Chemistry |
A key concept that might be used for applications is the (numerical) derivative of the solid fraction fs with temperature. A numerical example using a copper zinc alloy at composition Zn 30% in weight is proposed as an example here using the opposite sign for using both temperature and its derivative in the same graph.
Kozlov and Schmid-Fetzer have calculated numerically the derivative of the Scheil curve in an open paper https://iopscience.iop.org/article/10.1088/1757-899X/27/1/012001 and applied it to the growth restriction factor Q in Al-Si-Mg-Cu alloys. | 8 | Metallurgy |
β-Hydroxybutyric acid, also known as 3-hydroxybutyric acid or BHB, is an organic compound and a beta hydroxy acid with the chemical formula CHCH(OH)CHCOH; its conjugate base is β-hydroxybutyrate, also known as 3-hydroxybutyrate. β-Hydroxybutyric acid is a chiral compound with two enantiomers: -β-hydroxybutyric acid and -β-hydroxybutyric acid. Its oxidized and polymeric derivatives occur widely in nature. In humans, -β-hydroxybutyric acid is one of two primary endogenous agonists of hydroxycarboxylic acid receptor 2 (HCA), a G protein-coupled receptor (GPCR). | 1 | Biochemistry |
The source of ADP-ribose for most enzymes that perform this modification is the redox cofactor NAD. In this transfer reaction, the N-glycosidic bond of NAD that bridges the ADP-ribose molecule and the nicotinamide group is cleaved, followed by nucleophilic attack by the target amino acid side chain. (ADP-ribosyl)transferases can perform two types of modifications: mono(ADP-ribosyl)ation and poly(ADP-ribosyl)ation. | 1 | Biochemistry |
Proton transfer reaction mass spectrometry has traditionally used drift tubes as ion traps. However, radio frequency ion funnels offer an attractive alternative, as they improve compound specific sensitivity significantly. This is due to increasing the effective reaction time and focusing the ions. The same pressure ranges are required for ion funnels and drift tubes, so the technology is not difficult to implement. Ion funnels have been shown to favor transmission of ions with high m/z. | 7 | Physical Chemistry |
The moving-belt interface (MBI) was developed by McFadden et al. in 1977 and commercialized by Finnigan. This interface consisted of an endless moving belt onto which the LC column effluent was deposited in a band. On the belt, the solvent was evaporated by gently heating and efficiently exhausting the solvent vapours under reduced pressure in two vacuum chambers. After the liquid phase was removed, the belt passed over a heater which flash desorbed the analytes into the MS ion source. One of the significant advantages of the MBI was its compatibility with a wide range of chromatographic conditions. MBI was successfully used for LC–MS applications between 1978 and 1990 because it allowed coupling of LC to MS devices using EI, CI, and fast-atom bombardment (FAB) ion sources. The most common MS systems connected by MBI interfaces to LC columns were magnetic sector and quadrupole instruments. MBI interfaces for LC–MS allowed MS to be widely applied in the analysis of drugs, pesticides, steroids, alkaloids, and polycyclic aromatic hydrocarbons. This interface is no longer used because of its mechanical complexity and the difficulties associated with belt renewal (or cleaning) as well as its inability to handle very labile biomolecules. | 3 | Analytical Chemistry |
Lead and silver in river waters are commonly found together and associated with lead mining. Impacts from very old mines can be very long-lived. In the River Ystwyth in Wales for example, the effects of silver and lead mining in the 17th and 18th centuries in the headwaters still causes unacceptably high levels of Zinc and Lead in the river water right down to its confluence with the sea.
Silver is very toxic even at very low concentrations but leaves no visible evidence of its contamination.
Lead is also highly toxic to freshwater organisms and to humans if the water is used as drinking water. As with Silver, Lead pollution is not visible to the naked eye. The River Rheidol in west Wales had a major series of lead mines in its headwaters until the end of the 19th century and its mine discharges and waste tips remain to this day. In 1919 - 1921 only 14 species of invertebrates were found in the lower Rheidol when Lead concentrations were between 0.2ppm and 0.5ppm. By 1932 the lead concentration had reduced to 0.02ppm to 0.1ppm because of the abandonment of mining and, at those concentrations, the bottom fauna had stabilized to 103 species including three leeches.
Coal mining is also a very significant source of metals, especially Iron, Zinc and Nickel particularly where the coal is rich if pyrites which oxidises on contact with the air producing a very acidic leachate which is able to dissolve metals from the coal.
Significant levels of copper are unusual in rivers and where it does it occur the source is most likely to be mining activities, coal stocking, or pig farming. Rarely elevated levels may be of geological origin. Copper is acutely toxic to many freshwater organisms, especially algae, at very low concentrations and significant concentration in river water may have serious adverse effects on the local ecology. | 2 | Environmental Chemistry |
Acid digestion is the most common dissolution method used for many types of samples. Unfortunately, acid digestion involves numerous manipulations of concentrated acids. Some types of samples even require the use of perchloric acid (HClO) that is explosive when it comes into contact with any organic materials. It can be readily combined with hydrofluoric acid (HF) and brought to a fumic state to drive off this volatile acid that is extremely dangerous to human health, not to mention it will dissolve the walls of any glass container it is being processed within. Moreover, it is often difficult to get full dissolution of the sample, even when using these hazardous chemicals. | 3 | Analytical Chemistry |
Cytochemical research aims to study individual cells that may contain several cell types within a tissue. It takes a nondestructive approach to study the localization of the cell. By remaining the cell components intact, researcher are able to study the intact cell activity rather than studying an isolated biochemical activity which the result may be influenced by the distorted cell membrane and spatial difference. | 1 | Biochemistry |
In population ecology, a regulating factor, also known as a limiting factor, is something that keeps a population at equilibrium (neither increasing nor decreasing in size over time). Common limiting factor resources are environmental features that limit the growth, abundance, or distribution of an organism or a population of organisms in an ecosystem. The concept of limiting factors is based on Liebigs Law of the Minimum, which states that growth is controlled not by the total amount of resources available, but by the scarcest resource. In other words, a factor is limiting if a change in the factor produces increased growth, abundance, or distribution of an organism when other factors necessary to the organisms life do not. Limiting factors may be physical or biological.
Limiting factors are not limited to the condition of the species. Some factors may be increased or reduced based on circumstances. An example of a limiting factor is sunlight in the rain forest, where growth is limited to all plants on the forest floor unless more light becomes available. This decreases the number of potential factors that could influence a biological process, but only one is in effect at any one place and time. This recognition that there is always a single limiting factor is vital in ecology, and the concept has parallels in numerous other processes. The limiting factor also causes competition between individuals of a species population. For example, space is a limiting factor. Many predators and prey need a certain amount of space for survival: food, water, and other biological needs. If the population of a species is too high, they start competing for those needs. Thus the limiting factors hold down population in an area by causing some individuals to seek better prospects elsewhere and others to stay and starve. Some other limiting factors in biology include temperature and other weather related factors. Species can also be limited by the availability of macro- and micronutrients. There has even been evidence of co-limitation in prairie ecosystems. A study published in 2017 showed that sodium (a micronutrient) had no effect on its own, but when in combination with nitrogen and phosphorus (macronutrients), it did show positive effects, which is evidence of serial co-limitation. | 7 | Physical Chemistry |
Bacteria related to the nitrogen fixing Rhizobia are an interesting case of inter-kingdom conjugation. For example, the tumor-inducing (Ti) plasmid of Agrobacterium and the root-tumor inducing (Ri) plasmid of A. rhizogenes contain genes that are capable of transferring to plant cells. The expression of these genes effectively transforms the plant cells into opine-producing factories. Opines are used by the bacteria as sources of nitrogen and energy. Infected cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.
The Ti and Ri plasmids can also be transferred between bacteria using a system (the tra, or transfer, operon) that is different and independent of the system used for inter-kingdom transfer (the vir, or virulence, operon). Such transfers create virulent strains from previously avirulent strains. | 1 | Biochemistry |
Site-specific recombination, also known as conservative site-specific recombination, is a type of genetic recombination in which DNA strand exchange takes place between segments possessing at least a certain degree of sequence homology. Enzymes known as site-specific recombinases (SSRs) perform rearrangements of DNA segments by recognizing and binding to short, specific DNA sequences (sites), at which they cleave the DNA backbone, exchange the two DNA helices involved, and rejoin the DNA strands. In some cases the presence of a recombinase enzyme and the recombination sites is sufficient for the reaction to proceed; in other systems a number of accessory proteins and/or accessory sites are required. Many different genome modification strategies, among these recombinase-mediated cassette exchange (RMCE), an advanced approach for the targeted introduction of transcription units into predetermined genomic loci, rely on SSRs.
Site-specific recombination systems are highly specific, fast, and efficient, even when faced with complex eukaryotic genomes. They are employed naturally in a variety of cellular processes, including bacterial genome replication, differentiation and pathogenesis, and movement of mobile genetic elements. For the same reasons, they present a potential basis for the development of genetic engineering tools.
Recombination sites are typically between 30 and 200 nucleotides in length and consist of two motifs with a partial inverted-repeat symmetry, to which the recombinase binds, and which flank a central crossover sequence at which the recombination takes place. The pairs of sites between which the recombination occurs are usually identical, but there are exceptions (e.g. attP and attB of λ integrase). | 1 | Biochemistry |
On June 17, 2004, a children's playground "City of Smiles" was opened in the park area of the plant. In the "City of Smiles" a sports area and playground, a railway for children, as well as a zoo were arranged, which contained a mouflon, a Bactrian camel, a pony, a donkey, a collared peccary, a raccoon, a red-headed duck, a chubataya duck, a mandarin duck, a wood duck, a pechanka, a Muscovy duck, a common pochard, a coypu, a rhea ostrich, a bush wallabi, a macaque monkey, a rhesus monkey, a Romanian pheasant, a trogopan pheasant, chickens, a golden pheasant, a royal pheasant, a common peacock, a guinea fowl, gray nymphs, rose-ringed parakeets, a demoiselle crane, kings, strassers, pigeons, pectoral sandpiper, trumpeters, a porcupine, a Cameroon goat, a llama, a spotted deer, a European fallow deer, a Barbary sheep, a savannah zebra, and an American bison. | 8 | Metallurgy |
Point mutations in multiple tumor suppressor proteins cause cancer. For instance, point mutations in Adenomatous Polyposis Coli promote tumorigenesis. A novel assay, Fast parallel proteolysis (FASTpp), might help swift screening of specific stability defects in individual cancer patients. | 1 | Biochemistry |
Results will vary depending on sample adulteration, quantity, temperature, lighting, exposure to air, storage, as well as reagent quality and degradation. Colorimetric techniques have been developed.
If more than one bottle are open at the same time and the cap are put on the wrong reagent bottle, this may cross-contaminate the reagents and ruin them.
According to a 2003 research published in Pharmacotherapy, neither the Marquis, Mecke, nor Simon's reagents should be used by the public for harm reduction purposes. These agents do not help identify pure MDMA tablets. The research team suggests using gas chromatography-mass spectrometry as the most sensitive and specific testing method for identifying MDMA and its contaminants but this is out of reach for users in most countries and reagent tests remain popular, often distributed by harm-reduction organisations due to their low cost and high utility when multiple test reagents are used. | 3 | Analytical Chemistry |
The organizational structure of the NADP follows the State Agricultural Experiment Station Guidelines for Multi-State Research Activities (SAESD, 2006). This framework allows any individual or institution to participate in any segment of NADP, whether it be the monitoring or the research aspect of atmospheric deposition. NADP is managed by two groups. The first being Program Management, which is largely a volunteer group made up of site sponsors and supervisors, policy experts from several agencies (at the federal, state, and local levels), scientists and research specialists, and anyone with an interest in atmospheric deposition. Program management is organized through an Executive Committee, Technical Subcommittees, several advisory subcommittees, science subcommittees, and ad hoc groups. The second group is Program Operations, which is managed by a professional staff housed at the Wisconsin State Laboratory of Hygiene at the University of Wisconsin-Madison. The Program Office oversees day to day tasks, including coordinating with the Executive Committee, the individual monitoring networks, the analytical laboratories, the External Quality Assurance Program, and the Network Equipment Depot. | 2 | Environmental Chemistry |
Coordination isomerism is a form of structural isomerism in which the composition of the coordination complex ion varies. In a coordination isomer the total ratio of ligand to metal remains the same, but the ligands attached to a specific metal ion change. Examples of a complete series of coordination isomers require at least two metal ions and sometimes more.
For example, a solution containing ([Co(NH)] and [Cr(CN)]) is a coordination isomer with a solution containing [Cr(NH)] and [Co(CN)]. | 4 | Stereochemistry |
The pH of a solution containing a buffering agent can only vary within a narrow range, regardless of what else may be present in the solution. In biological systems this is an essential condition for enzymes to function correctly. For example, in human blood a mixture of carbonic acid (HCO) and bicarbonate (HCO) is present in the plasma fraction; this constitutes the major mechanism for maintaining the pH of blood between 7.35 and 7.45. Outside this narrow range (7.40 ± 0.05 pH unit), acidosis and alkalosis metabolic conditions rapidly develop, ultimately leading to death if the correct buffering capacity is not rapidly restored.
If the pH value of a solution rises or falls too much, the effectiveness of an enzyme decreases in a process, known as denaturation, which is usually irreversible. The majority of biological samples that are used in research are kept in a buffer solution, often phosphate buffered saline (PBS) at pH 7.4.
In industry, buffering agents are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters. | 7 | Physical Chemistry |
The Bradford assay is linear over a short range, typically from 0 µg/mL to 2000 µg/mL, often making dilutions of a sample necessary before analysis. In making these dilutions, error in one dilution is compounded in further dilutions resulting in a linear relationship that may not always be accurate.
Basic conditions and detergents, such as SDS, can interfere with the dye's ability to bind to the protein through its side chains.
The reagents in this method tend to stain the test tubes. Same test tubes cannot be used since the stain would affect the absorbance reading. This method is also time sensitive. When more than one solution is tested, it is important to make sure every sample is incubated for the same amount of time for accurate comparison.
It is also inhibited by the presence of detergents, although this problem can be alleviated by the addition of cyclodextrins to the assay mixture.
Much of the non-linearity stems from the equilibrium between two different forms of the dye which is perturbed by adding the protein. The Bradford assay linearizes by measuring the ratio of the absorbances, 595 over 450 nm. This modified Bradford assay is approximately 10 times more sensitive than the conventional one.
The Coomassie Blue G250 dye used to bind to the proteins in the original Bradford method readily binds to arginine and lysine groups of proteins. This is a disadvantage because the preference of the dye to bind to these amino acids can result in a varied response of the assay between different proteins. Changes to the original method, such as increasing the pH by adding NaOH or adding more dye have been made to correct this variation. Although these modifications result in a less sensitive assay, a modified method becomes sensitive to detergents that can interfere with sample. | 3 | Analytical Chemistry |
While the biosynthesis has not been conclusively elucidated, brevianamide A and B are constructed from tryptophan, proline, and an isoprene unit. | 0 | Organic Chemistry |
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