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*phenylalanine racemase
*phenylalanine racemase (adenosine triphosphate-hydrolysing)
*gramicidin S synthetase I | 1 | Biochemistry |
The International Union of Pure and Applied Chemistry (IUPAC) recommends definitions for several classes of chain-growth polymerization. | 7 | Physical Chemistry |
A Guinier–Preston zone, or GP-zone, is a fine-scale metallurgical phenomenon, involving early stage precipitation.
GP-zones are associated with the phenomenon of age hardening, whereby room-temperature reactions continue to occur within a material through time, resulting in changing physical properties. In particular, this occurs in several aluminium series, such as the 6000 and 7000 series alloys.
Physically, GP zones are extremely fine-scaled (on the order of 3–10 nm in size) solute enriched regions of the material, which offer physical obstructions to the motion of dislocations, above that of the solid solution strengthening of the solute components. In 7075 aluminium for example, Zn–Mg clusters precede the formation of equilibrium MgZn precipitates.
The zone is named after André Guinier and George Dawson Preston who independently identified the zones in 1938. | 7 | Physical Chemistry |
Cannon has conducted research in the field of mammalian thermogenesis. Her research portfolio includes 185 original articles, as well as 125 invited review articles and book chapters. Notably, she authored a fundamental review on brown adipose tissue function in Physiological Reviews and a paradigm-changing review article for the American Journal of Physiology where she presented findings from radiology literature suggesting the existence of brown adipose tissue in adult humans. | 1 | Biochemistry |
The NPIS operates a 24-hour telephone advice service and internet database TOXBASE ([http://www.toxbase.org www.toxbase.org] for registered healthcare departments only). TOXBASE is free for UK NHS departments, and available by subscription to departments outside the UK NHS. The TOXBASE app is also available for Apple and Android devices. The app is free for individual NHS users.
The TOXBASE database contains information on approximately 17,000 products, together with generic advice on the management of poisoning. In excess of 1.5 million product accesses are made to the database each year. Most of the accesses are made by A&E staff.
NHS 111, NHS 24 and NHS Direct all use the TOXBASE database. In the UK poisons information can also be found in the British National Formulary. | 1 | Biochemistry |
A structurally complete leaf of an angiosperm consists of a petiole (leaf stalk), a lamina (leaf blade), stipules (small structures located to either side of the base of the petiole) and a sheath. Not every species produces leaves with all of these structural components. The proximal stalk or petiole is called a stipe in ferns. The lamina is the expanded, flat component of the leaf which contains the chloroplasts. The sheath is a structure, typically at the base that fully or partially clasps the stem above the node, where the leaf is attached. Leaf sheathes typically occur in Poaceae (grasses) and Apiaceae (umbellifers). Between the sheath and the lamina, there may be a pseudopetiole, a petiole like structure. Pseudopetioles occur in some monocotyledons including bananas, palms and bamboos. Stipules may be conspicuous (e.g. beans and roses), soon falling or otherwise not obvious as in Moraceae or absent altogether as in the Magnoliaceae. A petiole may be absent (apetiolate), or the blade may not be laminar (flattened). The petiole mechanically links the leaf to the plant and provides the route for transfer of water and sugars to and from the leaf. The lamina is typically the location of the majority of photosynthesis. The upper (adaxial) angle between a leaf and a stem is known as the axil of the leaf. It is often the location of a bud. Structures located there are called "axillary".
External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules and glands, are frequently important for identifying plants to family, genus or species levels, and botanists have developed a rich terminology for describing leaf characteristics. Leaves almost always have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and will usually continue to grow as long as they have the resources to do so.
The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or polymorphic). The longest leaves are those of the Raffia palm, R. regalis which may be up to long and wide. The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks.
Where leaves are basal, and lie on the ground, they are referred to as prostrate. | 5 | Photochemistry |
It has recently been found that Acinetobacter sp. also show quorum sensing activity. This bacterium, an emerging pathogen, produces AHLs. Acinetobacter sp. shows both quorum sensing and quorum quenching activity. It produces AHLs and can also degrade the AHL molecules. | 1 | Biochemistry |
The G1 algorithm produces a numerical derivative that has the shape of a bell curve, this derivative obeys to certain laws, for example the G1 derivative of a cyclic voltammogram is mirrored at the abscissa as long as the electrochemical reaction is diffusion controlled, the planar diffusion approximation can be applied to the electrode geometry and ohmic drop distortion is minimal. The FWHM of the curve is approximately 100 mV for a system that behaves in the described manner. The maximum is found at the value of the formal potential, this is equivalent to the 1.5th order semiderivative hitting the abscissa at this potential. Moreover the semiderivative scales linearly with the scanrate, while the current scales linearly with the square root of the scanrate (Randles–Sevcik equation). Plotting the semiderivatives produced at different scanrates gives a family of curves that are linearly related by the scanrate quotient in an ideal system. | 3 | Analytical Chemistry |
Imprelis is a selective herbicide created by DuPont. The active ingredient is aminocyclopyrachlor, a synthetic auxin.
Imprelis was registered with the United States Environmental Protection Agency for sale in October 2010. Sale of Imprelis was voluntarily suspended a week before the EPA required sales stopped. DuPont acknowledged it was killing or damaging evergreen trees, including white pine and Norway spruce. DuPont allegedly knew Imprelis would damage evergreens before seeking EPA approval.
DuPont offered to compensate customers whose trees were affected. They asked that a claim be submitted, and said that they would send a claim resolution agreement, which would specify the amount DuPont would pay to settle the claim. By late May 2012, the end of the planting season, many tree owners had not heard from DuPont. Other tree owners who accepted payment agreements with DuPont had not been paid.
Several hundred tree owners have filed lawsuits with DuPont. , they are seeking class action status. | 2 | Environmental Chemistry |
Superose is a trade name for a collection of FPLC columns which are used in the automated separation of biological molecules. The different columns provided can separate a variety of macromolecules, ranging from small peptides and polysaccharides to DNA strands and entire viruses. The material inside the column is agarose based, meaning that it consists of sugars that are crosslinked to form a gel-like mass. The pores in this material have different sizes, and if a molecule is too big, it does not fit into the pores, meaning that it follows a shorter way to the end of the column.
The columns are placed in a holder, and a computerized pumping system pumps a watery solution, often a buffer through the column. A special injection loop allows the injection of the desired sample. | 1 | Biochemistry |
Melt inclusions have been imaged in three dimensions using X-ray microtomography. This method can be used to determine the dimensions of different phases present in melt inclusions more precisely than by using visible light microscopy. | 9 | Geochemistry |
In formal mathematical presentations of T-symmetry, three different kinds of notation for T need to be carefully distinguished: the T that is an involution, capturing the actual reversal of the time coordinate, the T that is an ordinary finite dimensional matrix, acting on spinors and vectors, and the T that is an operator on an infinite-dimensional Hilbert space.
For a real (not complex) classical (unquantized) scalar field , the time reversal involution can simply be written as
as time reversal leaves the scalar value at a fixed spacetime point unchanged, up to an overall sign . A slightly more formal way to write this is
which has the advantage of emphasizing that is a map, and thus the "mapsto" notation whereas is a factual statement relating the old and new fields to one-another.
Unlike scalar fields, spinor and vector fields might have a non-trivial behavior under time reversal. In this case, one has to write
where is just an ordinary matrix. For complex fields, complex conjugation may be required, for which the mapping can be thought of as a 2x2 matrix. For a Dirac spinor, cannot be written as a 4x4 matrix, because, in fact, complex conjugation is indeed required; however, it can be written as an 8x8 matrix, acting on the 8 real components of a Dirac spinor.
In the general setting, there is no ab initio value to be given for ; its actual form depends on the specific equation or equations which are being examined. In general, one simply states that the equations must be time-reversal invariant, and then solves for the explicit value of that achieves this goal. In some cases, generic arguments can be made. Thus, for example, for spinors in three-dimensional Euclidean space, or four-dimensional Minkowski space, an explicit transformation can be given. It is conventionally given as
where is the y-component of the angular momentum operator and is complex conjugation, as before. This form follows whenever the spinor can be described with a linear differential equation that is first-order in the time derivative, which is generally the case in order for something to be validly called "a spinor".
The formal notation now makes it clear how to extend time-reversal to an arbitrary tensor field In this case,
Covariant tensor indexes will transform as and so on. For quantum fields, there is also a third T, written as which is actually an infinite dimensional operator acting on a Hilbert space. It acts on quantized fields as
This can be thought of as a special case of a tensor with one covariant, and one contravariant index, and thus two 's are required.
All three of these symbols capture the idea of time-reversal; they differ with respect to the specific space that is being acted on: functions, vectors/spinors, or infinite-dimensional operators. The remainder of this article is not cautious to distinguish these three; the T that appears below is meant to be either or or depending on context, left for the reader to infer. | 7 | Physical Chemistry |
Introns are the parts of a gene that are transcribed into the precursor RNA sequence, but ultimately removed by RNA splicing during the processing to mature RNA. Introns are found in both types of genes: protein-coding genes and noncoding genes. They are present in prokaryotes but they are much more common in eukaryotic genomes.
Group I and group II introns take up only a small percentage of the genome when they are present. Spliceosomal introns (see Figure) are only found in eukaryotes and they can represent a substantial proportion of the genome. In humans, for example, introns in protein-coding genes cover 37% of the genome. Combining that with about 1% coding sequences means that protein-coding genes occupy about 38% of the human genome. The calculations for noncoding genes are more complicated because there is considerable dispute over the total number of noncoding genes but taking only the well-defined examples means that noncoding genes occupy at least 6% of the genome. | 1 | Biochemistry |
Recent algae blooms in Lake Erie have been fed primarily by agricultural runoff and have led to warnings for some people in Canada and Ohio not to drink their water. The International Joint Commission has called on United States and Canada to drastically reduce phosphorus loads into Lake Erie to address the threat. | 3 | Analytical Chemistry |
*"Theory of thermal unimolecular reactions in the fall-off range. II. Weak collision rate constants". RG Gilbert, K Luther, J Troe, Ber Bunsenges Phys Chem, 87, 169–77 (1982)
::(How the pressure dependence of a major class of chemical reactions can be fitted and extrapolated; widely used in atmospheric and combustion modelling.)
*Theory of unimolecular and recombination reactions. RG Gilbert, SC Smith. Oxford: Blackwell Scientific Publications (1990), 364 pp
::(Set out a major process in chemical kinetics, including many of his discoveries.)
*"Critically evaluated rate coefficients for free-radical polymerization. 1. Propagation rate coefficients for styrene". M Buback, RG Gilbert, RA Hutchinson, B Klumperman, F-D Kuchta, BG Manders, KF O’Driscoll, GT Russell, J Schweer. Macromol. Chem. Phys., 196, 3267–80 (1995) (authors in alphabetical order)
::(One of a series of papers from an IUPAC Working Party that Gilbert created and led, which established reliability criteria for what is now a widely used technique for measuring the propagation rate coefficient that controls the speed of polymer growth.)
*"The entry of free radicals into latex particles in emulsion polymerization". IA Maxwell, BR Morrison, DH Napper, RG Gilbert, Macromolecules, 24, 1629–40 (1991)
::(Discovery of the mechanism of an important process in this major industrial process.)
*Emulsion polymerization: a mechanistic approach. RG Gilbert. London: Academic Press (1995), 362pp
::(Basic mechanisms in this major industrial process, including many of his discoveries.)
*"Molecular weight distributions in free-radical polymerizations. Understanding the effects of chain-length-dependent termination". PA Clay, RG Gilbert. Macromolecules, 28, 552–69 (1995)
::(How microscopic events govern a major determinant of properties in this widely used process.)
*"A priori prediction of propagation rate coefficients in free radical polymerizations: propagation of ethylene". JPA Heuts, RG Gilbert, L Radom. Macromolecules, 28, 8771–81 (1995)
::(How the sizes of rate coefficients for polymer growth can be understood in terms of basic quantum mechanics.)
*"Pulsed-laser polymerization measurements of the propagation rate coefficient for butyl acrylate". RA Lyons, J Hutovic, MC Piton, DI Christie, PA Clay, BG Manders, SH Kable, RG Gilbert. Macromolecules, 29, 1918–27 (1996)
::(The first measure of the propagation rate coefficient for a widely used monomer, showing that it is 100 times faster than previously assumed; now used for the improved design of certain manufacturing processes.)
*"Effective ab initio emulsion polymerization under RAFT control". CJ Ferguson, RJ Hughes, BTT Pham, BS Hawkett, RG Gilbert, AK Serelis, CH Such. Macromolecules, 35, 9243–45 (2002)
::(How a new technique of making polymers can be implemented in the commonest industrial manufacturing process; the basis of a new generation of paints soon to be on the market.)
*"Mechanistic information from analysis of molecular weight distributions of starch". JV Castro, C Dumas, H Chiou, MA Fitzgerald, RG Gilbert, Biomacromolecules, 6, 2248–59 (2005)
::(How molecular weight data on starch can be plotted to reveal biosynthetic pathways and structure–property relations.) | 0 | Organic Chemistry |
The Dahms pathway starts as the Weimberg pathway but the 2-keto-3 deoxy-xylonate is split by an aldolase to pyruvate and glycolaldehyde. | 1 | Biochemistry |
An ironmaster is the manager, and usually owner, of a forge or blast furnace for the processing of iron. It is a term mainly associated with the period of the Industrial Revolution, especially in Great Britain.
The ironmaster was usually a large-scale entrepreneur and thus an important member of a community. He would have a large country house or mansion as his residence. The organization of operations surrounding the smelting, refining and casting of iron was labour-intensive, and so there would be numerous workers reliant on the furnace works.
There were ironmasters (possibly not called such) from the 17th century onwards, but they became more prominent with the great expansion in the British iron industry during the Industrial Revolution. | 8 | Metallurgy |
Sedimentation field flow fractionation (SFFF) is a non-destructive separation technique which can be used for both separation, and collecting fractions. Some applications of SFFF include characterization of particle size of latex materials for adhesives, coatings and paints, colloidal silica for binders, coatings and compounding agents, titanium oxide pigments for paints, paper and textiles, emulsion for soft drinks, and biological materials like viruses and liposomes.
Some main aspects of SFFF include: it provides high-resolution possibilities for size distribution measurements with high precision, the resolution is dependent on experimental conditions, the typical analysis time is 1 to 2 hours, and it is a non-destructive technique which offers the possibility of collecting fraction. | 7 | Physical Chemistry |
Triplet fluorenylidene reacts with olefins in a stepwise fashion to produce a racemic mixture, provided that the rate of spin inversion (intersystem crossing) is not significantly faster than rates of intermediate bond rotation. | 0 | Organic Chemistry |
The curve is usually best described by a sigmoid plot, using a formula of the kind:
A hemoglobin molecule can bind up to four oxygen molecules in a reversible method.
The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second, third and fourth, this is due to the induced conformational change in the structure of the hemoglobin molecule induced by the binding of an oxygen molecule.
In its simplest form, the oxyhemoglobin dissociation curve describes the relation between the partial pressure of oxygen (x axis) and the oxygen saturation (y axis). Hemoglobin's affinity for oxygen increases as successive molecules of oxygen bind. More molecules bind as the oxygen partial pressure increases until the maximum amount that can be bound is reached. As this limit is approached, very little additional binding occurs and the curve levels out as the hemoglobin becomes saturated with oxygen. Hence the curve has a sigmoidal or S-shape. At pressures above about 60 mmHg, the standard dissociation curve is relatively flat, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure. To get more oxygen to the tissue would require blood transfusions to increase the hemoglobin count (and hence the oxygen-carrying capacity), or supplemental oxygen that would increase the oxygen dissolved in plasma.
Although binding of oxygen to hemoglobin continues to some extent for pressures about 50 mmHg, as oxygen partial pressures decrease in this steep area of the curve, the oxygen is unloaded to peripheral tissue readily as the hemoglobin's affinity diminishes.
The partial pressure of oxygen in the blood at which the hemoglobin is 50% saturated, typically about 26.6 mmHg (3.5 kPa) for a healthy person, is known as the P. The P is a conventional measure of hemoglobin affinity for oxygen. In the presence of disease or other conditions that change the hemoglobin oxygen affinity and, consequently, shift the curve to the right or left, the P changes accordingly. An increased P indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P indicates a leftward shift and a higher affinity.
The plateau portion of the oxyhemoglobin dissociation curve is the range that exists at the pulmonary capillaries (minimal reduction of oxygen transported until the p(O) falls 50 mmHg).
The steep portion of the oxyhemoglobin dissociation curve is the range that exists at the systemic capillaries (a small drop in systemic capillary p(O) can result in the release of large amounts of oxygen for the metabolically active cells).
To see the relative affinities of each successive oxygen as you remove/add oxygen from/to the hemoglobin from the curve compare the relative increase/decrease in p(O) needed for the corresponding increase/decrease in s(O). | 1 | Biochemistry |
A monovalent ion requires 1 electron for discharge, a divalent ion requires 2 electrons for discharge and so on. Thus, if electrons flow, atoms are discharged.
Thus, the mass discharged is
where
* is the Avogadro constant;
* is the total charge, equal to the number of electrons () times the elementary charge ;
* is the Faraday constant. | 7 | Physical Chemistry |
The melting temperature of the amplicon at which the two DNA strands come apart is entirely predictable. It is dependent on the sequence of the DNA bases. If you are comparing two samples from two different people, they should give exactly the same shaped melt curve. However, if one person has a mutation in the DNA region you have amplified, then this will alter the temperature at which the DNA strands melt apart. So now the two melt curves appear different. The difference may only be tiny, perhaps a fraction of a degree, but because the HRM machine has the ability to monitor this process in "high resolution", it is possible to accurately document these changes and therefore identify if a mutation is present or not. | 1 | Biochemistry |
Polypeptides have an N-terminus and a C-terminus, which refer to the ends of the polymer in a way that reflects the direction in which the polymer was synthesized. The chronological sequence of each amino acid sub-unit is the basis for directionality notation in polypeptides; a given protein can be represented as its set of unique amino acid abbreviations within an N-terminus and a C-terminus. | 1 | Biochemistry |
There are two classes of receptors for neurotrophins: p75 and the "Trk" family of Tyrosine kinases receptors. | 1 | Biochemistry |
A tetrasaccharide is a carbohydrate which gives upon hydrolysis four molecules of the same or different monosaccharides. For example, stachyose upon hydrolysis gives one molecule each of glucose and fructose and two molecules of galactose. The general formula of a tetrasaccharide is typically CHO. | 0 | Organic Chemistry |
Gold(III) bromide is a dark-red to black crystalline solid. It has the empirical formula , but exists primarily as a dimer with the molecular formula in which two gold atoms are bridged by two bromine atoms. It is commonly referred to as gold(III) bromide, gold tribromide, and rarely but traditionally auric bromide, and sometimes as digold hexabromide. As is similar with the other gold halides, this compound is unique for being a coordination complex of a group 11 transition metal that is stable in an oxidation state of +3 whereas copper or silver complexes persist in oxidation states of +1 or +2. | 3 | Analytical Chemistry |
A macromonomer is a macromolecule with one end-group that enables it to act as a monomer. Macromonomers will contribute a single monomeric unit to a chain of the completed macromolecule.
Several macromonomers have been successfully synthesized utilizing various methods such as controlled radical polymerization (CRP) and copper-catalyzed "click" coupling.
Due to the larger size of macromonomers (as opposed to the size of regular monomers), synthetic challenges are brought about, giving reason for the analysis of polymerization mechanisms. Recent studies have shown that macromonomer polymerization kinetics and mechanisms can be significantly affected by the topological effect. | 7 | Physical Chemistry |
Sonoporation, or cellular sonication, is the use of sound in the ultrasonic range for increasing the permeability of the cell plasma membrane. This technique is usually used in molecular biology and non-viral gene therapy in order to allow uptake of large molecules such as DNA into the cell, in a cell disruption process called transfection or transformation. Sonoporation employs the acoustic cavitation of microbubbles to enhance delivery of these large molecules. The exact mechanism of sonoporation-mediated membrane translocation remains unclear, with a few different hypotheses currently being explored.
Sonoporation is under active study for the introduction of foreign genes in tissue culture cells, especially mammalian cells. Sonoporation is also being studied for use in targeted Gene therapy in vivo, in a medical treatment scenario whereby a patient is given modified DNA, and an ultrasonic transducer might target this modified DNA into specific regions of the patient's body. The bioactivity of this technique is similar to, and in some cases found superior to, electroporation. Extended exposure to low-frequency (<MHz) ultrasound has been demonstrated to result in complete cellular death (rupturing), thus cellular viability must also be accounted for when employing this technique. | 1 | Biochemistry |
The data is presented to the user with a strong emphasis on the relation to curated background information and underlying evidence that led to the observation of a terminus, its modification or proteolytic cleavage. In brief the protein information, its domain structure, protein termini, terminus modifications and proteolytic processing of and by other proteins is listed. All information is accompanied by metadata like its original source, method of identification, confidence measurement or related publication. A positional cross correlation evaluation matches termini and cleavage sites with protein features (such as amino acid variants) and domains to highlight potential effects and dependencies in a unique way. Also, a network view of all proteins showing their functional dependency as protease, substrate or protease inhibitor tied in with protein interactions is provided for the easy evaluation of network wide effects. A powerful yet user friendly filtering mechanism allows the presented data to be filtered based on parameters like methodology used, in vivo relevance, confidence or data source (e.g. limited to a single laboratory or publication). This provides means to assess physiological relevant data and to deduce functional information and hypotheses relevant to the bench scientist. In a later release analysis tools for the evaluation of proteolytic pathways in experimental data have been added. | 1 | Biochemistry |
Metabolic imprinting refers to the long-term physiological and metabolic effects that an offsprings prenatal and postnatal environments have on them. Perinatal nutrition has been identified as a significant factor in determining an offsprings likelihood of it being predisposed to developing cardiovascular disease, obesity, and type 2 diabetes amongst other conditions.
During pregnancy, maternal glucose can cross the blood-placental barrier meaning maternal hyperglycaemia is associated with foetal hyperglycaemia. Despite maternal glucose being able to cross the blood-placental barrier, maternal insulin is not able and the foetus has to make its own. As a result, if a mother is hyperglycaemic the foetus is likely to be hyperinsulinaemic which leads to it having increased levels of growth and adiposity. | 1 | Biochemistry |
RNA is notoriously unstable and vulnerable to ribonucleases, which has thus been an obstacle to the production and analysis of the cellular transcriptome. First referenced by Berger et al., the substance was used to prevent the digestion of RNA during isolation from white blood cells, and was rapidly adopted for such purposes as the acquisition of RNA from green beans. | 1 | Biochemistry |
It can be prepared by reacting carbon tetrachloride with hydrogen fluoride in the presence of a catalytic amount of antimony pentachloride:
:CCl + 2HF CClF + 2HCl
This reaction can also produce trichlorofluoromethane (CClF), chlorotrifluoromethane (CClF) and tetrafluoromethane (CF). | 2 | Environmental Chemistry |
Prior to the availability of sensitive TSH assays, thyrotropin releasing hormone or TRH stimulation tests were relied upon for confirming and assessing the degree of suppression
in suspected hyperthyroidism. Typically, this stimulation test involves determining basal
TSH levels and levels 15 to 30 minutes after an intravenous bolus of TRH. Normally,
TSH would rise into the concentration range measurable with less sensitive TSH assays.
Third generation TSH assays do not have this
limitation and thus TRH stimulation is generally not required when third generation TSH
assays are used to assess degree of suppression. | 1 | Biochemistry |
A molecular logic gate is a molecule that performs a logical operation based on one or more physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations (i.e. moleculators and memory storage algorithms). Molecular logic gates work with input signals based on chemical processes and with output signals based on spectroscopic phenomena.
Logic gates are the fundamental building blocks of electrical circuits. They can be used to construct digital architectures with varying degrees of complexity by a cascade of a few to several million logic gates. Logic gates are essentially physical devices that produce a singular binary output after performing logical operations based on Boolean functions on one or more binary inputs. The concept of molecular logic gates, extending the applicability of logic gates to molecules, aims to convert chemical systems into computational units. Over the past three decades, the field has evolved to realize several practical applications in molecular electronics, biosensing, DNA computing, nanorobotics, and cell imaging, among others. | 6 | Supramolecular Chemistry |
G protein can refer to two distinct families of proteins. Heterotrimeric G proteins, sometimes referred to as the "large" G proteins, are activated by G protein-coupled receptors and are made up of alpha (α), beta (β), and gamma (γ) subunits. "Small" G proteins (20-25kDa) belong to the Ras superfamily of small GTPases. These proteins are homologous to the alpha (α) subunit found in heterotrimers, but are in fact monomeric, consisting of only a single unit. However, like their larger relatives, they also bind GTP and GDP and are involved in signal transduction. | 1 | Biochemistry |
Solutions of methanesulfonic acid are used for the electroplating of tin and tin-lead solders. It is displacing the use of fluoroboric acid, which releases corrosive and volatile hydrogen fluoride.
Methanesulfonic acid is also a primary ingredient in rust and scale removers. It is used to clean off surface rust from ceramic, tiles and porcelain which are usually susceptible to acid attack. | 0 | Organic Chemistry |
Bis(trimethylsilyl)mercury (CH)Si-Hg-Si(CH) reacts with chloro-iminium and chloro-amidinium salts to give a metal-free carbene and elemental mercury. For example:
:(CH)Si−Hg−Si(CH) + RN=C(Cl)−Cl → RN−C−NR + Hg + 2(CH)SiCl | 0 | Organic Chemistry |
From the formation of the Roman Empire, Rome was an almost completely closed economy, not reliant on imports although exotic goods from India and China (such as gems, silk and spices) were highly prized (Shepard 1993). Through the recovery of Roman coins and ingots throughout the ancient world (Hughes 1980), metallurgy has supplied the archaeologist with material culture through which to see the expanse of the Roman world. | 8 | Metallurgy |
Receptor proteins on the cell surface have the ability to bind specific signaling molecules secreted by other cells. Cell signaling allows cells to communicate with adjacent cells, nearby cells (paracrine) and even distant cells (endocrine). This binding induces a conformational change in the receptor which, in turn, elicits a response in the corresponding cell. These responses include changes in gene expression and alterations in cytoskeleton structure. The extracellular face of the plasma membrane has a variety of proteins, carbohydrates, and lipids which project outward and act as signals. Direct contact between cells allows the receptors on one cell to bind the small molecules attached to the plasma membrane of different cell. In eukaryotes, many of the cells during early development communicate through direct contact.
Synaptic signaling, an integral part of nervous system activity, occurs between neurons and target cells. These target cells can also be neurons or other cell types (i.e. muscle or gland cells). Protocadherins, a member of the cadherin family, mediate the adhesion of neurons to their target cells at synapses otherwise known as synaptic junctions. In order to for communication to occur between a neuron and its target cell, a wave of depolarization travels the length of the neuron and causes neurotransmitters to be released into the synaptic junction. These neurotransmitters bind and activate receptors on the post-synaptic neuron thereby transmitting the signal to the target cell. Thus, a post-synaptic membrane belongs to the membrane receiving the signal, while a pre-synaptic membrane is the source of the neurotransmitter. In a neuromuscular junction, a synapse is formed between a motor neuron and muscle fibers. In vertebrates, acetylcholine released from the motor neuron acts as a neurotransmitter which depolarizes the muscle fiber and causes muscle contraction. A neuron’s ability to receive and integrate simultaneous signals from the environment and other neurons allows for complex animal behavior. | 1 | Biochemistry |
Interpolymer complexes can be prepared either by mixing complementary polymers in solutions or by matrix (template) polymerisation. It is also possible to prepare IPCs at liquid-liquid interfaces or at solid or soft surfaces. Usually the structure of IPCs formed will depend on many factors, including the nature of interacting polymers, concentrations of their solutions, nature of solvent and presence of inorganic ions or organic molecules in solutions. Mixing of dilute polymer solutions usually leads to formation of IPCs as a colloidal dispersion, whereas more concentrated polymer solutions form IPCs in the form of a gel. | 7 | Physical Chemistry |
A number of forams have been cited to have different coiling directions in response to surface temperature. Globierina pachyderma, for example, exhibits dominant population of right coiling direction in cold water vs. left in warm water, and the ratio of these two forms have been utilized to estimate paleotemperature. A similar dependency of coiling directions on temperatures has been reported for Muricohebergella delrioensis in Cretaceous sediments.
Globigerina bulloides, a benthic foram, has been documented for its coiling directions related to seawater temperatures in surface sediments of the southern Indian Ocean.
A similar relationship has been documented for another benthic foram Bulinina marginata. | 9 | Geochemistry |
To effect dual activation by a single metal, the same metal species that activates the enolate also interacts with the alkyne. Though the precise mechanisms are poorly understood and likely vary from case to case, metals such as In, Zn, Fe, and Cu are proposed to operate via this mode. One reaction system thought to proceed via one-metal dual activation is that developed by Shaw et al. in 2014. Using a catalytic Fe(III)-(Salen) complex, Shaw and coworkers were able to access chiral cyclopentanes from an array of alkynyl-tethered β-ketoesters and analogs thereof. The reaction tolerated a wide range of ketones (phenyl, homoallyl, cyclopropyl, 2-furyl, etc.), esters (ethyl, tert-butyl, etc.), and ester analogs (nitro, , cyano, sulfonyl, etc.). | 0 | Organic Chemistry |
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with the first one. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. There are two types of wetting: non-reactive wetting and reactive wetting.
Wetting is important in the bonding or adherence of two materials. Wetting and the surface forces that control wetting are also responsible for other related effects, including capillary effects. Surfactants can be used to increase the wetting power of a liquid like water.
Wetting is a focus of research attention in nanotechnology and nanoscience studies due to the advent of many nanomaterials in the past two decades (e.g. graphene, carbon nanotube, boron nitride nanomesh). | 7 | Physical Chemistry |
In the Conception Bay in Newfoundland, Southeastern coast of Canada, a series of Pre-Cambrian to Cambrian-linked volcanic rocks were silicified. The rocks mainly consist of rhyolitic and basaltic flows, with crystal tuffs and breccia interbedded. Regional silicification was taken place as a preliminary alteration process before other geochemical processes occurred. The source of silica near the area was from hot siliceous fluids from rhyolitic flow under a static condition. A significant portion of silica appeared in the form of white chalcedonic quartz, quartz veins as well as granular quartz crystal. Due to the difference in rock structures, silica replaces different materials in rocks of close locations. The following table shows the replacement of silica at different localities: | 9 | Geochemistry |
The bacteria R-M system has been proposed as a model for devising human anti-viral gene or genomic vaccines and therapies since the RM system serves an innate defense-role in bacteria by restricting tropism of bacteriophages. Research is on REases and ZFN that can cleave the DNA of various human viruses, including HSV-2, high-risk HPVs and HIV-1, with the ultimate goal of inducing target mutagenesis and aberrations of human-infecting viruses. The human genome already contains remnants of retroviral genomes that have been inactivated and harnessed for self-gain. Indeed, the mechanisms for silencing active L1 genomic retroelements by the three prime repair exonuclease 1 (TREX1) and excision repair cross complementing 1 (ERCC) appear to mimic the action of RM-systems in bacteria, and the non-homologous end-joining (NHEJ) that follows the use of ZFN without a repair template.
A major advance is the creation of artificial restriction enzymes created by linking the FokI DNA cleavage domain with an array of DNA binding proteins or zinc finger arrays, denoted now as zinc finger nucleases (ZFN). ZFNs are a powerful tool for host genome editing due to their enhanced sequence specificity. ZFN work in pairs, their dimerization being mediated in-situ through the FoKI domain. Each zinc finger array (ZFA) is capable of recognizing 9–12 base-pairs, making for 18–24 for the pair. A 5–7 bp spacer between the cleavage sites further enhances the specificity of ZFN, making them a safe and more precise tool that can be applied in humans. A recent Phase I clinical trial of ZFN for the targeted abolition of the CCR5 co-receptor for HIV-1 has been undertaken. | 1 | Biochemistry |
A number of techniques exist to quantitatively analyze metallographic specimens. These techniques are valuable in the research and production of all metals and alloys and non-metallic or composite materials.
Microstructural quantification is performed on a prepared, two-dimensional plane through the three-dimensional part or component. Measurements may involve simple metrology techniques, e.g., the measurement of the thickness of a surface coating, or the apparent diameter of a discrete second-phase particle, (for example, spheroidal graphite in ductile iron). Measurement may also require application of stereology to assess matrix and second-phase structures. Stereology is the field of taking 0-, 1- or 2-dimensional measurements on the two-dimensional sectioning plane and estimating the amount, size, shape or distribution of the microstructure in three dimensions. These measurements may be made using manual procedures with the aid of templates overlaying the microstructure, or with automated image analyzers. In all cases, adequate sampling must be made to obtain a proper statistical basis for the measurement. Efforts to eliminate bias are required.
Some of the most basic measurements include determination of the volume fraction of a phase or constituent, measurement of the grain size in polycrystalline metals and alloys, measurement of the size and size distribution of particles, assessment of the shape of particles, and spacing between particles.
Standards organizations, including ASTM International's Committee E-4 on Metallography and some other national and international organizations, have developed standard test methods describing how to characterize microstructures quantitatively.
For example, the amount of a phase or constituent, that is, its volume fraction, is defined in ASTM E 562; manual grain size measurements are described in ASTM E 112 (equiaxed grain structures with a single size distribution) and E 1182 (specimens with a bi-modal grain size distribution); while ASTM E 1382 describes how any grain size type or condition can be measured using image analysis methods. Characterization of nonmetallic inclusions using standard charts is described in ASTM E 45 (historically, E 45 covered only manual chart methods and an image analysis method for making such chart measurements was described in ASTM E 1122. The image analysis methods are currently being incorporated into E 45). A stereological method for characterizing discrete second-phase particles, such as nonmetallic inclusions, carbides, graphite, etc., is presented in ASTM E 1245. | 8 | Metallurgy |
The invariance of a Hamiltonian of an isolated system under time translation implies its energy does not change with the passage of time. Conservation of energy implies, according to the Heisenberg equations of motion, that .
or:
Where is the time-translation operator which implies invariance of the Hamiltonian under the time-translation operation and leads to the conservation of energy. | 7 | Physical Chemistry |
The diagram shows a ceramic crucible with a steel cylinder suspended within. Both cathode (C) and anode (A) are made of iron or nickel. The temperature is cooler at the bottom and hotter at the top so that the sodium hydroxide is solid in the neck (B) and liquid in the body of the vessel. Sodium metal forms at the cathode but is less dense than the fused sodium hydroxide electrolyte. Wire gauze (G) confines the sodium metal to accumulating at the top of the collection device (P). The cathode reaction is
:2 Na + 2 e → 2Na
The anode reaction is
:4 OH → O + 2 HO + 4 e
Despite the elevated temperature, some of the water produced remains dissolved in the electrolyte. This water diffuses throughout the electrolyte and results in the reverse reaction taking place on the electrolyzed sodium metal:
:2 Na + 2 HO → H + 2 Na + 2 OH
with the hydrogen gas also accumulating at (P). This, of course, reduces the efficiency of the process. | 8 | Metallurgy |
The ISASMELT process began with the invention in 1973 of the Sirosmelt lance by Drs Bill Denholm and John Floyd at the CSIRO. The lance was developed as a result of investigations into improved tin-smelting processes, in which it was found that the use of a top-entry submerged lance would result in greater heat transfer and mass transfer efficiencies.
The idea of top-entry submerged lances goes back to at least 1902, when such a system was attempted in Clichy, France. However, early attempts failed because of the short lives of the lances on submersion in the bath. The Mitsubishi copper smelting process is one alternative approach, wherein lances are used in a furnace, but they are not submerged into the bath. Instead, they blow oxygen-enriched air onto the surface of the slag (top jetting). Similarly, a water-cooled, top-jetting lance was the basis of the LD (Linz-Donawitz) steelmaking process. This does not produce the same intensity of mixing in the bath as a submerged lance.
The CSIRO scientists first tried developing a submerged lance system using a water-cooled lance, but moved to an air-cooled system because "scale up of the water-cooled lance would have been problematic". Introducing any water to a system involving molten metals and slags can result in catastrophic explosions, such as that in the Scunthorpe Steelworks in November 1975 in which 11 men lost their lives.
The inclusion of the swirlers in the Sirosmelt lance and forming a splash coating of slag on the lance were the major innovations that led to the successful development of submerged lance smelting.
From 1973, the CSIRO scientists began a series of trials using the Sirosmelt lance to recover metals from industrial slags in Australia, including lead softener slag at the Broken Hill Associated Smelters in Port Pirie (1973), tin slag from Associated Tin Smelters in Sydney (1974), copper converter slag at the Electrolytic Refining and Smelting ("ER&S") Port Kembla plant (1975) and copper anode furnace slag at Copper Refineries Limited (another subsidiary of MIM Holdings) in Townsville (1976) and of copper converter slag in Mount Isa (1977). The work then proceeded to smelting tin concentrates (1975) and then sulfidic tin concentrates (1977).
MIM and ER&S jointly funded the 1975 Port Kembla converter slag treatment trials and MIM's involvement continued with the slag treatment work in Townsville and Mount Isa.
In parallel with the copper slag treatment work, the CSIRO was continuing to work in tin smelting. Projects included a five tonne ("t") plant for recovering tin from slag being installed at Associated Tin Smelters in 1978, and the first sulfidic smelting test work being done in collaboration with Aberfoyle Limited, in which tin was fumed from pyritic tin ore and from mixed tin and copper concentrates. Aberfoyle was investigating the possibility of using the Sirosmelt lance approach to improve the recovery of tin from complex ores, such as its mine at Cleveland, Tasmania, and the Queen Hill ore zone near Zeehan in Tasmania.
The Aberfoyle work led to the construction and operation in late 1980 of a four t/h tin matte fuming pilot plant at the Western Mining Corporation's Kalgoorlie Nickel Smelter, located to the south of Kalgoorlie, Western Australia. | 8 | Metallurgy |
Bounded by impoundments (an impoundment is a dam), these dams typically use "local materials" including the tailings themselves, and may be considered embankment dams. Traditionally, the only option for tailings storage was to contain the tailings slurry with locally available earthen materials. This slurry is a dilute stream of the tailings solids within water that was sent to the tailings storage area. The modern tailings designer has a range of tailings products to choose from depending upon how much water is removed from the slurry prior to discharge. It is increasingly common for tailings storage facilities to require special barriers like Bituminous Geomembranes (BGMs) to contain liquid tailings slurries and prevent impact to the surrounding environment. The removal of water not only can create a better storage system in some cases (e.g. dry stacking, see below) but can also assist in water recovery which is a major issue as many mines are in arid regions. In a 1994 description of tailings impoundments, however, the U.S. EPA stated that dewatering methods may be prohibitively expensive except in special circumstances. Subaqueous storage of tailings has also been used.
Tailing ponds are areas of refused mining tailings where the waterborne refuse material is pumped into a pond to allow the sedimentation (meaning separation) of solids from the water. The pond is generally impounded with a dam, and known as tailings impoundments or tailings dams. It was estimated in 2000 that there were about 3,500 active tailings impoundments in the world. The ponded water is of some benefit as it minimizes fine tailings from being transported by wind into populated areas where the toxic chemicals could be potentially hazardous to human health; however, it is also harmful to the environment. Tailing ponds are often somewhat dangerous because they attract wildlife such as waterfowl or caribou as they appear to be a natural pond, but they can be highly toxic and harmful to the health of these animals. Tailings ponds are used to store the waste made from separating minerals from rocks, or the slurry produced from tar sands mining. Tailings are sometimes mixed with other materials such as bentonite to form a thicker slurry that slows the release of impacted water to the environment.
There are many different subsets of this method, including valley impoundments, ring dikes, in-pit impoundments, and specially dug pits. The most common is the valley pond, which takes advantage of the natural topographical depression in the ground. Large earthen dams may be constructed and then filled with the tailings. Exhausted open pit mines may be refilled with tailings. In all instances, due consideration must be made to contamination of the underlying water table, amongst other issues. Dewatering is an important part of pond storage, as the tailings are added to the storage facility the water is removed – usually by draining into decant tower structures. The water removed can thus be reused in the processing cycle. Once a storage facility is filled and completed, the surface can be covered with topsoil and revegetation commenced. However, unless a non-permeable capping method is used, water that infiltrates into the storage facility will have to be continually pumped out into the future. | 8 | Metallurgy |
For more details on this topic, see flow cytometry
Since the optical identity of each microsphere is known, the quantification of target samples hybridized to the microspheres can be achieved by comparing the relative intensity of target markers in one set of microspheres to target markers in another set of microspheres using flow cytometry. Microspheres can be sorted based using both their unique optical properties and level of hybridization to the target sequence. | 1 | Biochemistry |
The use of N-terminal Fmoc protection allows for a milder deprotection scheme than used for Boc/Bzl SPPS, and this protection scheme is truly orthogonal under SPPS conditions. Fmoc deprotection utilizes a base, typically 20–50% piperidine in DMF. The exposed amine is therefore neutral, and consequently no neutralization of the peptide-resin is required, as in the case of the Boc/Bzl approach. The lack of electrostatic repulsion between the peptide chains can lead to increased risk of aggregation with Fmoc/tBu SPPS however. Because the liberated fluorenyl group is a chromophore, Fmoc deprotection can be monitored by UV absorbance of the reaction mixture, a strategy which is employed in automated peptide synthesizers.
The ability of the Fmoc group to be cleaved under relatively mild basic conditions while being stable to acid allows the use of side chain protecting groups such as Boc and tBu that can be removed in milder acidic final cleavage conditions (TFA) than those used for final cleavage in Boc/Bzl SPPS (HF). Scavengers such as water and triisopropylsilane (TIPS) are most commonly added during the final cleavage in order to prevent side reactions with reactive cationic species released as a result of side chain deprotection. Nevertheless, many other scavenger compounds could be used as well. The resulting crude peptide is obtained as a TFA salt, which is potentially more difficult to solubilize than the fluoride salts generated in Boc SPPS.
Fmoc/tBu SPPS is less atom-economical, as the fluorenyl group is much larger than the Boc group. Accordingly, prices for Fmoc amino acids were high until the large-scale piloting of one of the first synthesized peptide drugs, enfuvirtide, began in the 1990s, when market demand adjusted the relative prices of Fmoc- vs Boc- amino acids. | 1 | Biochemistry |
Some of the most notable contributors to the Corrosion Engineering discipline include among others:
* Michael Faraday (1791–1867)
* Marcel Pourbaix (1904–1998)
* Herbert H. Uhlig (1907–1993)
* Ulick Richardson Evans (1889–1980)
* Mars Guy Fontana (1910–1988)
* Melvin Romanoff ( -1970) | 8 | Metallurgy |
Ground-state depletion occurs when the pump beam sends the electron into an excited state. However, unlike in ESA, the probe beam cannot send an electron into a secondary excited state. Instead, it sends remaining electrons from the ground state to the first excited state. However, since the pump beam has decreased the number of electrons in the ground state, fewer probe photons are absorbed, and the probe signal increases at the detector site. | 7 | Physical Chemistry |
Rosenkranz was a world-class bridge player and one of the most successful in Mexico. He won 12 NABC-level events at thrice-annual North American Bridge Championships meets, including all four major titles: the Grand Nationals, Reisinger, Spingold and Vanderbilt. In world championship teams competition, he represented Mexico in the quadrennial World Team Olympiad three times from 1972 to 1996 and the United States in the 1983 Bermuda Bowl. In addition, he has made significant contributions to bidding theory. He created the Romex bidding system, an extension of Standard American with many gadgets. He invented the Rosenkranz double and Rosenkranz redouble, and wrote more than a dozen books on bridge. | 0 | Organic Chemistry |
Yoon's research lab at the University of Wisconsin-Madison focuses on developing new reaction methods for organic synthesis, especially those involving transition metal photochemistry, stereocontrolling, and dual catalysis.
Overview
In particular, Yoons group aims to leverage the ability of visible light–absorbing transition metal complexes to catalyze synthetic reactions. They investigate various mechanisms of photocatalytic activation, which differ from complex to complex depending on reactivity patterns of intermediates and their ability to be activated by sources of white light, including sunlight. Traditionally, chemists have used high-energy UV light to activate simple organic molecules, but Yoons group focuses instead on expanding the application of visible light sources to synthesize increasingly complex target molecules. By providing strategies for activation of organic substrates that do not require specialized high-pressure UV photolysis apparatuses, these procedures are rendered more environmentally-friendly and widely available to synthetic and organic chemists.
Significant Developments
One notable process explored by Yoon's research is the generation of photoreductants by irradiation of [Ru(bpy)] that can initiate desired cycloaddition. The group proved [Ru(bpy)]Cl to be an efficient photocatalyst for the formal [2+2] cycloaddition of enones and yields potential for development of new reaction protocols with reduced environmental impact.
Yoon's group has also researched into crossed intermolecular [2+2] heterodimerizations, proving the possibility of using two dissimilar enone substrates to successfully produce these dimers. This method bypasses some synthetic limitations of cycloadditions conducted under standard UV photolysis conditions.
Yoon reviews the ways how cocatalyst strategies can be applied to synthesis, ranging from developments in organic photochemistry and the precedents that brought interest in photocatalytic synthesis. The interaction between an excited photocatalyst and organic molecule can show a diverse sample of reactive intermediates that can be manipulated to form a synthetic bond construction. This impacts the photocatalyst and the photoactivation steps such as the interaction with the excited state of the photocatalyst or controlling the rate and selectivity of the photoactivation steps.
Additionally, Yoon takes a dual approach to the asymmetric of enantioselective [2+2] photocycloadditions by using visible light that can absorb transition metal and a Lewis acid cocatalyst. Yoon was able to see that each catalyst can be enabled to be independent resulting in a broader scope and greater flexibility and efficiency in enantioselective photochemical cycloadditions. Along with the metal photocatalyst being compatible with several types of Lewis acid catalyst.
Yoon developed the first highly enantioselective intermolecular reaction of α-amino radicals by using the dual-catalyst protocol to combine the transition metal photoredox catalysis with the chiral Lewis acid catalysis. The combination of these catalysts provided an approach to control the stereochemistry of a wide variety of photoinitiated organic reactions.
Furthermore, Yoon was able to perform quantum yield measurements to showcase that three distinct photoredox processes and involvement in the formation of chain reactions. In the combination of doing quantum yield and luminescence quenching experiments, it displays a method to estimate the length of these chains, to determine a lower limit for these chains and to diagnose inefficient initiation steps in photoredox reactions. Yoon demonstrated that the chain processes dominated the product formation of the three photoredox transformations. | 0 | Organic Chemistry |
For its main use as a fertilizer urea is mostly marketed in solid form, either as prills or granules. Prills are solidified droplets, whose production predates satisfactory urea granulation processes. Prills can be produced more cheaply than granules, but the limited size of prills (up to about 2.1 mm in diameter), their low crushing strength, and the caking or crushing of prills during bulk storage and handling make them inferior to granules. Granules are produced by acretion onto urea seed particles by spraying liquid urea in a succession of layers. Formaldehyde is added during the production of both prills and granules in order to increase crushing strength and suppress caking. Other shaping techniques such as pastillization (depositing uniform-sized liquid droplets onto a cooling conveyor belt) are also used. | 0 | Organic Chemistry |
Transposable elements (transposons, TEs, jumping genes) are short strands of repetitive DNA that can self-replicate and translocate within the eukaryotic genome, and are generally perceived as parasitic in nature. Their transcription can lead to the production of dsRNAs (double-stranded RNAs), which resemble retroviruses transcripts. While most host cellular RNA has a singular, unpaired sense strand, dsRNA possesses sense and anti-sense transcripts paired together, and this difference in structure allows an host organism to detect dsRNA production, and thereby the presence of transposons. Plants lack distinct divisions between somatic cells and reproductive cells, and also have, generally, larger genomes than animals, making them an intriguing case-study kingdom to be used in attempting to better understand the epigenetics function of transposable elements. | 1 | Biochemistry |
One proposed mechanism for Müllerian mimicry is the "two step hypothesis". This states that a large mutational leap initially establishes an approximate resemblance of the mimic to the model, both species already being aposematic. In a second step, smaller changes establish a closer resemblance. This is only likely to work, however, when a trait is governed by a single gene, and many coloration patterns are certainly controlled by multiple genes. | 1 | Biochemistry |
In October 2006, Taiwan banned ractopamine along with other beta-adrenergic agonists. In a 2012 climb-down, its legislature passed amendments to its Act Governing Food Sanitation, authorising government agencies to set safety standards for ractopamine. The Taiwanese Department of Health ultimately established an MRL of 10 ppb for ractopamine in beef on 31 July 2012.
The American Institute in Taiwan, which represents US interests in Taiwan, states that these "and many other countries have determined that meat from animals fed ractopamine is safe for human consumption"; this is in the context of an ongoing trade dispute between Taiwan and the US on this subject, which threatened to prevent Taiwan's entry to the Trans-Pacific Partnership trade pact.
In 2020, restrictions on imports of US pork with ractopamine were relaxed, leading to protests. A referendum took place on December 18, 2021 , deciding whether to ban the import of pork with ractopamine, and the ban was rejected. | 4 | Stereochemistry |
Atmospheric Methane Removal is a category of potential approaches being researched to accelerate the breakdown of methane once in the atmosphere to mitigate some of the impacts of climate change.
Different methods to remove methane from the atmosphere include thermal-catalytic oxidation, photocatalytic oxidation, biological methanotrophic methane removal, concentration with zeolites or other porous solids, and separation by membranes. | 2 | Environmental Chemistry |
A broad range of enzymes including DNA ligase, DNA polymerase and nucleases have been employed to generate high-fidelity SNP genotyping methods. | 1 | Biochemistry |
According to the Poisson summation formula:
is a reciprocal lattice vector of the periodic potential and is the volume of its unit cell. By comparison of (3) and (4), we find that the Laue equation must be satisfied for scattering to occur:
(5) is a statement of the conservation of crystal momentum. Particles scattered in a crystal experience a change in wave vector equal to a reciprocal lattice vector of the crystal. When they do, the contribution to the matrix element is simply a finite constant. Thus, we find an important link between scattered particles and the scattering crystal. The Laue condition, which states that crystal momentum must be conserved, is equivalent to the Bragg condition , which demands constructive interference for scattered particles. Now that we see how the first factor of (3) determines whether or not incident particles are scattered, we consider how the second factor influences scattering. | 7 | Physical Chemistry |
Amoxicillin was one of several semisynthetic derivatives of 6-aminopenicillanic acid (6-APA) developed by the Beecham Group in the 1960s. It was invented by Anthony Alfred Walter Long and John Herbert Charles Nayler, two British scientists. It became available in 1972 and was the second aminopenicillin to reach the market (after ampicillin in 1961). Co-amoxiclav became available in 1981. | 4 | Stereochemistry |
Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein. The first chitin receptor was cloned in 2006. When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systemic defenses. Commensal fungi have ways to interact with the host immune response that, , were not well understood.
Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors. Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops. | 1 | Biochemistry |
Transcription begins with the RNA polymerase and one or more general transcription factors binding to a DNA promoter sequence to form an RNA polymerase-promoter closed complex. In the closed complex, the promoter DNA is still fully double-stranded.
RNA polymerase, assisted by one or more general transcription factors, then unwinds approximately 14 base pairs of DNA to form an RNA polymerase-promoter open complex. In the open complex, the promoter DNA is partly unwound and single-stranded. The exposed, single-stranded DNA is referred to as the "transcription bubble".
RNA polymerase, assisted by one or more general transcription factors, then selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP (or a short RNA primer and an extending NTP) complementary to the transcription start site sequence, and catalyzes bond formation to yield an initial RNA product.
In bacteria, RNA polymerase holoenzyme consists of five subunits: 2 α subunits, 1 β subunit, 1 β' subunit, and 1 ω subunit. In bacteria, there is one general RNA transcription factor known as a sigma factor. RNA polymerase core enzyme binds to the bacterial general transcription (sigma) factor to form RNA polymerase holoenzyme and then binds to a promoter.
(RNA polymerase is called a holoenzyme when sigma subunit is attached to the core enzyme which is consist of 2 α subunits, 1 β subunit, 1 β' subunit only). Unlike eukaryotes, the initiating nucleotide of nascent bacterial mRNA is not capped with a modified guanine nucleotide. The initiating nucleotide of bacterial transcripts bears a 5′ triphosphate (5′-PPP), which can be used for genome-wide mapping of transcription initiation sites.
In archaea and eukaryotes, RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and also contains additional subunits. In archaea and eukaryotes, the functions of the bacterial general transcription factor sigma are performed by multiple general transcription factors that work together. In archaea, there are three general transcription factors: TBP, TFB, and TFE. In eukaryotes, in RNA polymerase II-dependent transcription, there are six general transcription factors: TFIIA, TFIIB (an ortholog of archaeal TFB), TFIID (a multisubunit factor in which the key subunit, TBP, is an ortholog of archaeal TBP), TFIIE (an ortholog of archaeal TFE), TFIIF, and TFIIH. The TFIID is the first component to bind to DNA due to binding of TBP, while TFIIH is the last component to be recruited. In archaea and eukaryotes, the RNA polymerase-promoter closed complex is usually referred to as the "preinitiation complex".
Transcription initiation is regulated by additional proteins, known as activators and repressors, and, in some cases, associated coactivators or corepressors, which modulate formation and function of the transcription initiation complex. | 1 | Biochemistry |
François Stanislas Cloez (24 June 1817 – 12 October 1883) was a French chemist, who authored both as "F. S. Cloez" and "S. Cloez", and is known for his pioneering role in analytical chemistry during the 19th century. He was a founder and later president of the Chemistry Society of France.
In 1851, Cloez and Italian chemist Stanislao Cannizzaro, working on collaborative research, prepared cyanamide by the action of ammonia on cyanogen chloride in ethereal solution.
In the 1870s, he commenced the identification of the constituents of individual essential oils and their classification into groups according to their suitability for medicinal, industrial and perfumery purposes. He identified the major constituent of eucalyptus oil, which he called "eucalyptol" (now generally known as cineole). In honour of his work on eucalyptus oil Eucalyptus cloeziana (Gympie messmate) is named after him.
Cloez also played a role in developing a theory on the origin of life elsewhere in the Solar System.
In 1864, Cloez was the first scientist to examine a carbonaceous chondrite, the Orgueil meteorite, after it had fallen in France. Cloez said that its content "would seem to indicate the existence of organized substances in celestial bodies."
The Orgueil meteorite was subject to a hoax, when a sample of the meteorite was contaminated with a rush seed. The hoax was discovered in the 1960s when the meteorite was being examined for evidence of extraterrestrial biological material. There is no suggestion in literature that Cloez was party to this hoax. | 0 | Organic Chemistry |
The configuration index consists of two digits which are the priority numbers of the ligands on the threefold rotation axis. The lowest numerical value is cited first. | 4 | Stereochemistry |
In a solution that decreases in acidity, methyl orange moves from the color red to orange and finally to yellow with the opposite occurring for a solution increasing in acidity. This color change from yellow to red occurs because the protons in the acidic solution react with the N=N bond of the molecule, protonating one of them and changing the visible light absorption of the molecule to reflect more red light than orange/yellow.
In an acid, it is reddish and in alkali, it is yellow. Methyl orange has a pK of 3.47 in water at . | 3 | Analytical Chemistry |
Gel extraction kits are available from several major biotech manufacturers for a final cost of approximately 1–2 US$ per sample.
Protocols included in these kits generally call for the dissolution of the gel-slice in 3 volumes of chaotropic agent at 50 °C, followed by application of the solution to a spin-column (the DNA remains in the column), a 70% ethanol wash (the DNA remains in the column, salt and impurities are washed out), and elution of the DNA in a small volume (30 µL) of water or buffer. | 1 | Biochemistry |
As opposed to DNA gene editing techniques (e.g., using CRISPR-Cas proteins to make modifications directly to a defective gene), LEAPER targets editing messenger RNA (mRNA) for the same gene which is transcribed into a protein. Post-transcriptional RNA modification typically involves the strategy of converting adenosine-to-inosine (A-to-I) since inosine (I) demonstrably mimics guanosine (G) during translation into a protein. A-to-I editing is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes, whose substrates are double-stranded RNAs. Three human ADAR genes have been identified with ADAR1 (official symbol ADAR) and ADAR2 (ADARB1) proteins developed activity profiles. LEAPER achieves this targeted RNA editing through the use of short engineered ADAR-recruiting RNAs (). consist of endogenous ADAR1 proteins with several RNA binding domains (RBDs) fused with a peptide, CRISPR-Cas13b protein, and a guide RNA (gRNA) between 100 and 150 nt in length for high editing efficiency designed to recruit the chimeric ADAR protein to a target site.
This results in a change in which protein is synthesized during translation. | 1 | Biochemistry |
The applications of DCP are comparable to inductively coupled plasma (ICP). Some applications include, but are not limited to:
* identification of boron in tissues and cells
* analysis of trace metals in cows
* synthesis of carbon nanofibers
Figure 2 shows DCP being used to grow carbon nanofibers. | 3 | Analytical Chemistry |
Coexpression networks are data-derived representations of genes behaving in a similar way across tissues and experimental conditions. Their main purpose lies in hypothesis generation and guilt-by-association approaches for inferring functions of previously unknown genes. RNA-Seq data has been used to infer genes involved in specific pathways based on Pearson correlation, both in plants and mammals. The main advantage of RNA-Seq data in this kind of analysis over the microarray platforms is the capability to cover the entire transcriptome, therefore allowing the possibility to unravel more complete representations of the gene regulatory networks. Differential regulation of the splice isoforms of the same gene can be detected and used to predict their biological functions.
Weighted gene co-expression network analysis has been successfully used to identify co-expression modules and intramodular hub genes based on RNA seq data. Co-expression modules may correspond to cell types or pathways. Highly connected intramodular hubs can be interpreted as representatives of their respective module. An eigengene is a weighted sum of expression of all genes in a module. Eigengenes are useful biomarkers (features) for diagnosis and prognosis. Variance-Stabilizing Transformation approaches for estimating correlation coefficients based on RNA seq data have been proposed. | 1 | Biochemistry |
Another example is [Co(HO)]. Note that the ligand is the same as the last example. Here the cobalt ion has the oxidation state of +2, and it is a d ion. From the high-spin (left) side of the d Tanabe–Sugano diagram, the ground state is T(F), and the spin multiplicity is a quartet. The diagram shows that there are three quartet excited states: T, A, and T(P). From the diagram one can predict that there are three spin-allowed transitions. However, the spectrum of [Co(HO)] does not show three distinct peaks that correspond to the three predicted excited states. Instead, the spectrum has a broad peak (spectrum shown below). Based on the T–S diagram, the lowest energy transition is T to T, which is seen in the near IR and is not observed in the visible spectrum. The main peak is the energy transition T(F) to T(P), and the slightly higher energy transition (the shoulder) is predicted to be T to A. The small energy difference leads to the overlap of the two peaks, which explains the broad peak observed in the visible spectrum. | 7 | Physical Chemistry |
In iron ore smelting, haematite gets reduced at the top of the furnace, where temperature is in the range 600 – 700 °C. The Ellingham diagram indicates that in this range carbon monoxide acts as a stronger reducing agent than carbon since the process
:2 CO + → 2
has a more-negative free energy change than the process:
:2 C + → 2 CO.
In the upper part of the blast furnace, haematite is reduced by CO (produced by oxidation of coke lower down at the bottom of blast furnace, at higher temperature) even in the presence of carbon – though this is mainly because the kinetics for gaseous CO reacting with the ore are better. | 8 | Metallurgy |
Sigma hole interactions exhibit a strong preference for linearity. Theoretical studies have shown that the interaction is most stabilizing when the negative site is colinear with the bond that gives rise to the sigma hole. As the angle between this bond and the sigma hole interaction is decreased, the strength of the interaction is generally found to decrease rapidly. This finding is consistent with the hypothesis that the sigma hole arises from electronic anisotropy. There are cases in which the angle of interaction does differ somewhat from 180° - in these cases, the influence of additional intermolecular interactions are implicated in determining the overall geometry. | 6 | Supramolecular Chemistry |
In chemistry, ion association is a chemical reaction whereby ions of opposite electric charge come together in solution to form a distinct chemical entity. Ion associates are classified, according to the number of ions that associate with each other, as ion pairs, ion triplets, etc. Ion pairs are also classified according to the nature of the interaction as contact, solvent-shared or solvent-separated. The most important factor to determine the extent of ion association is the dielectric constant of the solvent. Ion associates have been characterized by means of vibrational spectroscopy, as introduced by Niels Bjerrum, and dielectric-loss spectroscopy. | 7 | Physical Chemistry |
BTO draws upon the comprehensive enzyme specific data of the BRENDA enzyme information system. Presently (October 2019) 112,200 enzyme-organism-tissue specific data from more than 11,000 proteins are stored in BRENDA. These entries were manually annotated from more than 150,000 different literature references. All terms in BTO are evaluated and classified according to the OBO-format, and are connected by specific relationships. Each term is a distinct entry within the ontology and is automatically assigned to a unique BTO-identifier (BTO-ID). The BTO-IDs serve as stable accession numbers in order to create cross-references to further external biochemical databases. Further tissue und cell-type specific terms from external databases (i.e. UniProt) are integrated into BTO.
The terms are classified in 4 main categories (subgraphs):
* animal
* plant
* fungus
* other sources
Further levels are defined below the main categories (=nodes), classifying the “parent”, “child”, and “grandchild” all connected via specific relationships (=edges)
* is_a (e.g. skeletal muscle fibre is_a muscle fibre)
* part_of (e.g. muscle fibre part_of muscle)
* develops/derives_from (e.g.myoma cell develops/derives_from muscle fibre)
* related_to (description of more general relationships between terms which are not covered by the other ones)
Most of the terms are clearly associated with specific organisms, organs, tissues, or cell types. There are several identical designations for tissues both in plants and animals, e.g. “epidermis”. To distinguish between those tissue terms and to classify them correctly into BTO for plant tissues the prefix “plant” is placed before the term, e.g. “plant epidermis”.
More than 80% of the tissue terms have definitions that describe the meaning and context. These definitions are obtained from i.e. medical dictionaries and cell line databases (Webster's Dictionary, DSMZ). | 1 | Biochemistry |
The ideal gas law follows from the van der Waals equation whenever is sufficiently large (or correspondingly whenever the molar density, , is sufficiently small), Specifically
* when , then is numerically indistinguishable from ,
* and when , then is numerically indistinguishable from .
Putting these two approximations into the van der Waals equation when is large enough that both inequalities are satisfied reduces it to
which is the ideal gas law. This is not surprising since the van der Waals equation was constructed from the ideal gas equation in order to obtain an equation valid beyond the limit of ideal gas behavior.
What is truly remarkable is the extent to which van der Waals succeeded. Indeed, Epstein in his classic thermodynamics textbook began his discussion of the van der Waals equation by writing: "In spite of its simplicity, it comprehends both the gaseous and the liquid state and brings out, in a most remarkable way, all the phenomena pertaining to the continuity of these two states". Also in Volume 5 of his Lectures on Theoretical Physics Sommerfeld, in addition to noting that "Boltzmann described van der Waals as the Newton of real gases", also wrote "It is very remarkable that the theory due to van der Waals is in a position to predict, at least qualitatively, the unstable [referring to superheated liquid, and subcooled vapor now called metastable] states" that are associated with the phase change process. | 7 | Physical Chemistry |
Alkylation reactions of chiral (S)-1-amino-2-methoxymethylpyrrolidine (SAMP) and (R)-1-amino-2-methoxymethylpyrrolidine (RAMP) hydrazones were developed by Dieter Enders and E.J. Corey. | 4 | Stereochemistry |
Dicumyl peroxide is relatively stable compound owing to the steric protection provided by the several substituents adjacent to the peroxide group. Upon heating, it breaks down by homolysis of the relatively weak O-O bond. | 0 | Organic Chemistry |
According to Agnes Arber's partial-shoot theory of the leaf, leaves are partial shoots, being derived from leaf primordia of the shoot apex. Early in development they are dorsiventrally flattened with both dorsal and ventral surfaces. Compound leaves are closer to shoots than simple leaves. Developmental studies have shown that compound leaves, like shoots, may branch in three dimensions. On the basis of molecular genetics, Eckardt and Baum (2010) concluded that "it is now generally accepted that compound leaves express both leaf and shoot properties." | 5 | Photochemistry |
Ultraviolet-sensitive beads (UV beads) are beads that are colorful in the presence of ultraviolet radiation. Ultraviolet rays are present in sunlight and light from various artificial sources and can cause sunburn or skin cancer. The color change in the beads alerts the wearer to the presence of the radiation.
When changing colour they undergo photochromism.
When the beads are not exposed to ultraviolet rays, they are colorless and either translucent or opaque. However, when sunlight falls onto the beads, they instantly turn into red, orange, yellow, blue, purple, or pink. | 5 | Photochemistry |
The Woodward–Hoffmann rules (or the pericyclic selection rules) are a set of rules devised by Robert Burns Woodward and Roald Hoffmann to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions, an important class of reactions in organic chemistry. The rules originate in certain symmetries of the molecule's orbital structure that any molecular Hamiltonian conserves. Consequently, any symmetry-violating reaction must couple extensively to the environment; this imposes an energy barrier on its occurrence, and such reactions are called symmetry-forbidden. Their opposites are symmetry-allowed.
Although the symmetry-imposed barrier is often formidable (up to ca. 5 eV or 480 kJ/mol in the case of a forbidden [2+2] cycloaddition), the prohibition is not absolute, and symmetry-forbidden reactions can still take place if other factors (e.g. strain release) favor the reaction. Likewise, a symmetry-allowed reaction may be preempted by an insurmountable energetic barrier resulting from factors unrelated to orbital symmetry. All known cases only violate the rules superficially; instead, different parts of the mechanism become asynchronous, and each step conforms to the rules. | 7 | Physical Chemistry |
The Chen-Kao test is performed by creating an acidic solution of the compound to be tested and adding dilute Copper (II) Sulfate and Sodium hydroxide solutions.<br />The procedure is as follows:
#Place small amount of material to be tested on a spot plate.
#Add 2 drops of reagent A
#Add 2 drops of reagent B
#Add 2 drops of reagent C
#A violet color indicates presence of ephedrine or pseudoephedrine
*Reagent A - 1% (vol/vol) aqueous acetic acid solution
*Reagent B - dissolve 1g Copper(II) sulfate in 100ml water
*Reagent C - dissolve 8g of NaOH in 100ml of water (that is 2N NaOH solution)
Further, the coordination complex might be extracted with organic solvent like diethyl Ether or n-butanol (see Table II), as proposed in the literature, which provides additional confirmation of the original results, but no further differentiation. This modification is not included in the UN Precursor Test Kit and other spot tests alike. In order to further differentiate between ephedrine enantiomers - ephedrine, pseudoephedrine and other ephedrine-related compounds, Simon’s test (with acetaldehyde) and Simon’s test (with acetone) are used. (see Table III) | 3 | Analytical Chemistry |
Lovelock has suggested that global biological feedback mechanisms could evolve by natural selection, stating that organisms that improve their environment for their survival do better than those that damage their environment. However, in the early 1980s, W. Ford Doolittle and Richard Dawkins separately argued against this aspect of Gaia. Doolittle argued that nothing in the genome of individual organisms could provide the feedback mechanisms proposed by Lovelock, and therefore the Gaia hypothesis proposed no plausible mechanism and was unscientific. Dawkins meanwhile stated that for organisms to act in concert would require foresight and planning, which is contrary to the current scientific understanding of evolution. Like Doolittle, he also rejected the possibility that feedback loops could stabilize the system.
Margulis argued in 1999 that "Darwins grand vision was not wrong, only incomplete. In accentuating the direct competition between individuals for resources as the primary selection mechanism, Darwin (and especially his followers) created the impression that the environment was simply a static arena". She wrote that the composition of the Earths atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time.
Evolutionary biologist W. D. Hamilton called the concept of Gaia Copernican, adding that it would take another Newton to explain how Gaian self-regulation takes place through Darwinian natural selection. More recently Ford Doolittle building on his and Inkpens ITSNTS (Its The Song Not The Singer) proposal proposed that differential persistence can play a similar role to differential reproduction in evolution by natural selections, thereby providing a possible reconciliation between the theory of natural selection and the Gaia hypothesis. | 9 | Geochemistry |
With the proliferation of PDRC development, many proposed radiative cooling materials are not biodegradable. As per Park et al., "sustainable materials for radiative cooling have not been sufficiently investigated."
* Park et al. (2022), eco-friendly porous polymer structure via thermally induced phase separation, solar reflectance 91%, heat emittance 92%, daytime temperature reduction up to 9 °C, sufficient durability for use on buildings and highest cooling effect reported "among all organic-based passive radiation cooling emitters." | 7 | Physical Chemistry |
Spiro structures contain chiral molecules with no say asymmetric center. The rings of a spiro structure lie at right angles to each other. It's important to note that the mirror images of spiro structures are non-superimposable and are enantiomers. | 4 | Stereochemistry |
Ammonia volatilization reduces the economic efficiency of agricultural cropping systems. Either yield will be reduced or additional costs will be incurred from additional nitrogen fertilizer. The amount of ammonia volatilization depends on several environmental factors, including temperature, pH, and the soil water content. Additionally, the amount of surface residue and time between urea application and precipitation are also critical. Generally speaking, volatilization will be lower when urea is applied during the wetter and cooler conditions that generally occur in early spring (March and April). However, drying surface soil and rising temperatures as spring progresses increases the probability of ammonia volatilization. Ideally, a manager should attempt to apply nitrogen immediately before a moderate rain event (0.1 inch), allowing urea to dissolve and move into the soil. However, this is not always possible. The soil's pH also has a strong effect on the amount of volatilization. Specifically, highly alkaline soils (pH~8.2 or higher) have proven to increase urea hydrolysis. One study has shown complete hydrolysis of urea within two days of application on such soils. In acidic soils (pH 5.2) the urea took twice as long to hydrolyze. Surface residues, such as thatch and plant stubble exhibit increased urease activity. Soils that have high organic matter content also tend to have higher urease concentrations. More urease results in greater hydrolysis of urea and ammonia volatilization, particularly if urea fails to move into the soil. | 9 | Geochemistry |
Dispersants can be delivered in aerosolized form by an aircraft or boat. Sufficient dispersant with droplets in the proper size are necessary; this can be achieved with an appropriate pumping rate. Droplets larger than 1,000 µm are preferred, to ensure they are not blown away by the wind. The ratio of dispersant to oil is typically 1:20. | 2 | Environmental Chemistry |
The electron distribution around an atom or molecule undergoes fluctuations in time. These fluctuations create instantaneous electric fields which are felt by other nearby atoms and molecules, which in turn adjust the spatial distribution of their own electrons. The net effect is that the fluctuations in electron positions in one atom induce a corresponding redistribution of electrons in other atoms, such that the electron motions become correlated. While the detailed theory requires a quantum-mechanical explanation (see quantum mechanical theory of dispersion forces), the effect is frequently described as the formation of instantaneous dipoles that (when separated by vacuum) attract each other. The magnitude of the London dispersion force is frequently described in terms of a single parameter called the Hamaker constant, typically symbolized . For atoms that are located closer together than the wavelength of light, the interaction is essentially instantaneous and is described in terms of a "non-retarded" Hamaker constant. For entities that are farther apart, the finite time required for the fluctuation at one atom to be felt at a second atom ("retardation") requires use of a "retarded" Hamaker constant.
While the London dispersion force between individual atoms and molecules is quite weak and decreases quickly with separation like , in condensed matter (liquids and solids), the effect is cumulative over the volume of materials, or within and between organic molecules, such that London dispersion forces can be quite strong in bulk solid and liquids and decay much more slowly with distance. For example, the total force per unit area between two bulk solids decreases by where is the separation between them. The effects of London dispersion forces are most obvious in systems that are very non-polar (e.g., that lack ionic bonds), such as hydrocarbons and highly symmetric molecules like bromine (Bra liquid at room temperature) or iodine (I a solid at room temperature). In hydrocarbons and waxes, the dispersion forces are sufficient to cause condensation from the gas phase into the liquid or solid phase. Sublimation heats of e.g. hydrocarbon crystals reflect the dispersion interaction. Liquification of oxygen and nitrogen gases into liquid phases is also dominated by attractive London dispersion forces.
When atoms/molecules are separated by a third medium (rather than vacuum), the situation becomes more complex. In aqueous solutions, the effects of dispersion forces between atoms or molecules are frequently less pronounced due to competition with polarizable solvent molecules. That is, the instantaneous fluctuations in one atom or molecule are felt both by the solvent (water) and by other molecules.
Larger and heavier atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones. This is due to the increased polarizability of molecules with larger, more dispersed electron clouds. The polarizability is a measure of how easily electrons can be redistributed; a large polarizability implies that the electrons are more easily redistributed. This trend is exemplified by the halogens (from smallest to largest: F, Cl, Br, I). The same increase of dispersive attraction occurs within and between organic molecules in the order RF, RCl, RBr, RI (from smallest to largest) or with other more polarizable heteroatoms. Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. The London forces are thought to arise from the motion of electrons. | 6 | Supramolecular Chemistry |
A common method of quantitative nitrite detection is the Griess test, which relies on the reaction of nitrite with the two components of a Griess reagent to form a red azo dye. This allows the concentration of nitrite to be determined by UV-vis spectroscopy. | 3 | Analytical Chemistry |
Positive and negative controls should be run after preparation of each lot of medium.
Positive control: Klebsiella
Negative control: Escherichia coli | 3 | Analytical Chemistry |
Non-stop decay (NSD) is a cellular mechanism of mRNA surveillance to detect mRNA molecules lacking a stop codon and prevent these mRNAs from translation. The non-stop decay pathway releases ribosomes that have reached the far 3' end of an mRNA and guides the mRNA to the exosome complex, or to RNase R in bacteria for selective degradation. In contrast to nonsense-mediated decay (NMD), polypeptides do not release from the ribosome, and thus, NSD seems to involve mRNA decay factors distinct from NMD. | 1 | Biochemistry |
NANOG is highly expressed in cancer stem cells and may thus function as an oncogene to promote carcinogenesis. High expression of NANOG correlates with poor survival in cancer patients.
Recent research has shown that the localization of NANOG and other transcription factors have potential consequences on cellular function. Experimental evidence has shown that the level of NANOG p8 expression is elevated specially in cancer cells, which mean that NANOG p8 gene is a critical member in (CSCs) Cancer stem cells, so knocking it down could reduce the cancer malignancy. | 1 | Biochemistry |
There are drugs, called depolarization blocking agents, that cause prolonged depolarization by opening channels responsible for depolarization and not allowing them to close, preventing repolarization. Examples include the nicotinic agonists, suxamethonium and decamethonium. | 7 | Physical Chemistry |
As illustrated to the right, tholins are thought to form in nature through a chain of chemical reactions known as pyrolysis and radiolysis. This begins with the dissociation and ionization of molecular nitrogen () and methane () by energetic particles and solar radiation. This is followed by the formation of ethylene, ethane, acetylene, hydrogen cyanide, and other small simple molecules and small positive ions. Further reactions form benzene and other organic molecules, and their polymerization leads to the formation of an aerosol of heavier molecules, which then condense and precipitate on the planetary surface below.
Tholins formed at low pressure tend to contain nitrogen atoms in the interior of their molecules, while tholins formed at high pressure are more likely to have nitrogen atoms located in terminal positions.
Tholins may be a major constituent of the interstellar medium. On Titan, their chemistry is initiated at high altitudes and participates in the formation of solid organic particles.
These atmospherically-derived substances are distinct from ice tholin II, which are formed instead by irradiation (radiolysis) of clathrates of water and organic compounds such as methane () or ethane (). The radiation-induced synthesis on ice are non-dependant on temperature.
Models show that even when far from UV radiation of a star, cosmic ray doses may be fully sufficient to convert carbon-containing ice grains entirely to complex organics in less than the lifetime of the typical interstellar cloud. | 9 | Geochemistry |
Gene knock-in originated as a slight modification of the original knockout technique developed by Martin Evans, Oliver Smithies, and Mario Capecchi. Traditionally, knock-in techniques have relied on homologous recombination to drive targeted gene replacement, although other methods using a transposon-mediated system to insert the target gene have been developed. The use of loxP flanking sites that become excised upon expression of Cre recombinase with gene vectors is an example of this. Embryonic stem cells with the modification of interest are then implanted into a viable blastocyst, which will grow into a mature chimeric mouse with some cells having the original blastocyst cell genetic information and other cells having the modifications introduced to the embryonic stem cells. Subsequent offspring of the chimeric mouse will then have the gene knock-in.
Gene knock-in has allowed, for the first time, hypothesis-driven studies on gene modifications and resultant phenotypes. Mutations in the human p53 gene, for example, can be induced by exposure to benzo(a)pyrene (BaP) and the mutated copy of the p53 gene can be inserted into mouse genomes. Lung tumors observed in the knock-in mice offer support for the hypothesis of BaP’s carcinogenicity. More recent developments in knock-in technique have allowed for pigs to have a gene for green fluorescent protein inserted with a CRISPR/Cas9 system, which allows for much more accurate and successful gene insertions. The speed of CRISPR/Cas9-mediated gene knock-in also allows for biallelic modifications to some genes to be generated and the phenotype in mice observed in a single generation, an unprecedented timeframe. | 1 | Biochemistry |
In this example, the following sequence is a region of the human mitochondrial genome with the two overlapping genes MT-ATP8 and MT-ATP6.
When read from the beginning, these codons make sense to a ribosome and can be translated into amino acids (AA) under the vertebrate mitochondrial code:
|Start|AAC GAA AAT CTG TTC GCT TCA ...
|Start|123 123 123 123 123 123 123 ...
| AA | N E N L F A S ...
However, let's change the reading frame by starting one nucleotide downstream (effectively a "+1 frameshift" when considering the 0 position to be the initial position of A):
A|Start|ACG AAA ATC TGT TCG CTT CA...
-|Start|123 123 123 123 123 123 12...
| AA | T K I C S L ...
Because of this +1 frameshifting, the DNA sequence is read differently. The different codon reading frame therefore yields different amino acids. | 1 | Biochemistry |
This test calls for a sample of the material in question to be placed in an airtight container with three coupons of different metals—silver, lead, and copper—that are not touching each other or the sample of the material. The container is sealed with a small amount of de-ionized water to maintain a high humidity, then heated at 60 degrees Celsius for 28 days. An identical container with three metal coupons acts as a control. If the metal coupons show no signs of corrosion, then the material is deemed suitable to be placed in and around art objects. The Oddy test is not a contact test, but is for testing off-gassing.
Each metal detects a different set of corrosive agents. The silver is for detecting reduced sulfur compounds and carbonyl sulfides. The lead is for detecting organic acids, aldehyde, and acidic gases. The copper is for detecting chloride, oxide, and sulfur compounds.
There are many types of materials testing for other purposes, including chemical testing and physical testing. | 1 | Biochemistry |
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