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In Twin Roll Melt Spinning two rollers or drums are used instead of one. The rollers are placed side by side, and rotated such that the one to the left spins clockwise, and the one on the right spins counter-clockwise. This configuration results in material passing between the rollers being pulled down. The melt is jetted between the rollers where it is cooled and ejected as a ribbon. The advantage of twin-roll melt spinning is that it gives a high degree of control over the thickness of the resulting ribbon. With a single roller, controlling ribbon thickness is complicated involving close control over the flow rate of the melt, rotational speed of the wheel, and temperature of the melt. With the twin roller setup, a particular and consistent thickness can be achieved by simply changing the distance between the rollers.
To date, twin roll melt spinning is still limited almost exclusively to laboratory scales. | 8 | Metallurgy |
There are two methods of smelting zinc: the pyrometallurgical process and the electrolysis process. Both methods are still used. Both of these processes share the same first step: roasting. | 8 | Metallurgy |
Solar energy conversion can impact not only just individual customers but whole communities. In a growing number of neighborhoods across America, the conventional model of independent, non-connected rooftop installations is being replaced by community-sized solar microgrids. The idea of “community solar” first became popular because of issues regarding energy storage. Because as of 2018 the wide-scale production of lithium-ion battery and other storage technologies lags the progress of rooftop PV installations, a main issue preventing a nationwide shift to rooftop solar energy generation is the lack of a reliable, single-home storage system that would provide contingencies for night-time energy use, cloud cover, curtailments and blackouts. Additionally, financing solar installations for single homes may be more difficult to secure given a smaller project scope and lack of access to funds. A viable alternative is to connect blocks of homes together in a community microgrid, using more proven large storage installations, thus lowering barriers to solar adoption. In some cases, a microgrid “web” is made by connecting each independent rooftop PV house to a greater storage facility. Other designs, primarily where rooftop installations are not possible, feature a large combined solar array + storage facility located on an adjacent field. As an added social impact, this form of installation makes solar energy economically viable for multi-family homes and historically low income neighborhoods. | 7 | Physical Chemistry |
An organism is suitable for a GUS assay if it lacks naturally occurring β-glucuronidase activity or if the activity is very low (background activity). For this reason, the assay is not useful in most vertebrates and many molluscs. Since there is no detectable GUS activity in higher plants, mosses, algae, ferns, fungi and most bacteria, the assay is ideally suited for gene expression studies in these organisms, and considered the reporter gene of choice for in plant science. | 1 | Biochemistry |
The principle can also be used in renal physiology to calculate renal blood flow.
In this context, it is not oxygen which is measured, but a marker such as para-aminohippurate. However, the principles are essentially the same. | 1 | Biochemistry |
Molecules, by definition, are most often held together with covalent bonds involving single, double, and/or triple bonds, where a "bond" is a shared pair of electrons (the other method of bonding between atoms is called ionic bonding and involves a positive cation and a negative anion).
Molecular geometries can be specified in terms of bond lengths, bond angles and torsional angles. The bond length is defined to be the average distance between the nuclei of two atoms bonded together in any given molecule. A bond angle is the angle formed between three atoms across at least two bonds. For four atoms bonded together in a chain, the torsional angle is the angle between the plane formed by the first three atoms and the plane formed by the last three atoms.
There exists a mathematical relationship among the bond angles for one central atom and four peripheral atoms (labeled 1 through 4) expressed by the following determinant. This constraint removes one degree of freedom from the choices of (originally) six free bond angles to leave only five choices of bond angles. (The angles θ, θ, θ, and θ are always zero and that this relationship can be modified for a different number of peripheral atoms by expanding/contracting the square matrix.)
Molecular geometry is determined by the quantum mechanical behavior of the electrons. Using the valence bond approximation this can be understood by the type of bonds between the atoms that make up the molecule. When atoms interact to form a chemical bond, the atomic orbitals of each atom are said to combine in a process called orbital hybridisation. The two most common types of bonds are sigma bonds (usually formed by hybrid orbitals) and pi bonds (formed by unhybridized p orbitals for atoms of main group elements). The geometry can also be understood by molecular orbital theory where the electrons are delocalised.
An understanding of the wavelike behavior of electrons in atoms and molecules is the subject of quantum chemistry. | 4 | Stereochemistry |
Surface plasmon resonance (SPR) has been widely used for measuring protein adsorption with high sensitivity. This technique is based on the excitation of surface plasmons, longitudinal electromagnetic waves originated at the interface between metals and dielectrics. The deposition on the conducting surface of molecules and thin layers within 200 nm modifies the dielectric properties of the system and thus the SPR response, signaling the presence of molecules on a metal surface. | 1 | Biochemistry |
In optics, absorbance or decadic absorbance is the common logarithm of the ratio of incident to radiant power through a material, and spectral absorbance or spectral decadic absorbance is the common logarithm of the ratio of incident to spectral radiant power through a material. Absorbance is dimensionless, and in particular is not a length, though it is a monotonically increasing function of path length, and approaches zero as the path length approaches zero. | 7 | Physical Chemistry |
The absorbance of a material that has only one absorbing species also depends on the pathlength and the concentration of the species, according to the Beer–Lambert law
where
* is the molar absorption coefficient of that material;
* is the molar concentration of those species;
* is the path length.
Different disciplines have different conventions as to whether absorbance is decadic (10-based) or Napierian (e-based), i.e., defined with respect to the transmission via common logarithm (log) or a natural logarithm (ln). The molar absorption coefficient is usually decadic. When ambiguity exists, it is important to indicate which one applies.
When there are N absorbing species in a solution, the overall absorbance is the sum of the absorbances for each individual species i:
The composition of a mixture of N absorbing species can be found by measuring the absorbance at N wavelengths (the values of the molar absorption coefficient for each species at these wavelengths must also be known). The wavelengths chosen are usually the wavelengths of maximum absorption (absorbance maxima) for the individual species. None of the wavelengths may be an isosbestic point for a pair of species. The set of the following simultaneous equations can be solved to find the concentrations of each absorbing species:
The molar absorption coefficient (in units of cm) is directly related to the attenuation cross section via the Avogadro constant N: | 3 | Analytical Chemistry |
*2009 – Our Women, Our State (Queensland Government) – Highly Commended
*2011 – Leighton Medal of the Royal Australian Chemical Institute, in recognition of her contributions and leadership to the chemistry community, within Australia and overseas.
*2013 – Distinguished Woman in Chemistry or Chemical Engineering award of the International Union of Pure and Applied Chemistry
*2014 – named as one of "175 Faces of Chemistry" by the Royal Society of Chemistry, UK
*2017 – inaugural Margaret Sheil Women in Chemistry Leadership award of the Royal Australian Chemical Institute
*2018 - Royal Society of Chemistry, Australasian lecturer (by invitation)
*2019 – Member of the Order of Australia (AM) in the Australia Day Honours for "significant service to education, particularly to organic chemistry, and as an advocate for women in science".
*2023 - named as a Distinguished Fellow of the Royal Australian Chemical Institute
A species of marine flatworm, discovered at Heron Island, is named for her Maritigrella marygarsonae. | 0 | Organic Chemistry |
Born in Accrington, Lancashire, England, on 9 March 1941, Halton was the only child of John Henry Halton and Mary (May) Halton (née Robinson). He contracted bovine tuberculosis as a young child and consequently missed two years of his early education. Later he attended St Josephs College, Blackpool, and St Josephs Academy, Blackheath. After winning a state scholarship, Halton studied chemistry at the University of Southampton, graduating BSc(Hons) in 1963. He went on to complete a PhD supervised by Richard Cookson at the same institution in 1966. His two-part thesis was titled Part I: Addition reactions of a methyleneaziridine. Part II: Conformational aspects of cyclotriveratrylene derivatives.
Halton moved to Wellington, New Zealand, in 1968, and married Margaret Leach in 1970. The couple went on to have two children. In 1980, Halton became a naturalised New Zealander. | 0 | Organic Chemistry |
Neurochemical Research is a monthly peer-reviewed scientific journal covering neurochemistry. It was established in 1976 and is published by Springer Science+Business Media. The editor-in-chief is Arne Schousboe (University of Copenhagen). | 1 | Biochemistry |
The Folin–Ciocâlteu reagent (FCR) or Folins phenol reagent or Folin–Denis reagent, is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric in vitro' assay of phenolic and polyphenolic antioxidants, also called the gallic acid equivalence method (GAE). It is named after Otto Folin, Vintilă Ciocâlteu, and Willey Glover Denis. The Folin-Denis reagent is prepared by mixing sodium tungstate and phosphomolybdic acid in phosphoric acid. The Folin–Ciocalteu reagent is just a modification of the Folin-Denis reagent. The modification consisted of the addition of lithium sulfate and bromine to the phosphotungstic-phosphomolybdic reagent.
The reagent does not measure only phenols, but will react with any reducing substance. It therefore measures the total reducing capacity of a sample, not just phenolic compounds. This reagent is part of the Lowry protein assay, and will also react with some nitrogen-containing compounds such as hydroxylamine and guanidine. The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base guanine, the trioses glyceraldehyde and dihydroxyacetone, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent.
This reagent is distinct from Folin's reagent, which is used to detect amines and sulfur-containing compounds.
A 1951 paper entitled "Protein measurement with the Folin phenol reagent" was the most cited paper in the 1945–1988 Science Citation Index, with 187,652 citations. | 3 | Analytical Chemistry |
Merrilactone A is one of the four sesquiterpenes that were newly discovered from the fruit of Illicium merrillianum in 2000. Members of the genus Illicium include Chinese star anise, widely used as a spice for flavouring food and beverages, and also poisonous plants such as Japanese star anise. Chemical studies of Illicium have developed rapidly over the last 20 years, and merrilactone A has been shown to have neurotrophic activity in fetal rat cortical neuron cultures. This has led researchers to believe that Merrilactone A may hold therapeutic potential in the treatment of neuro-degenerative diseases such as Alzheimers disease and Parkinsons disease. | 0 | Organic Chemistry |
Mond gas could be produced and used more efficiently than other gases in the late 19th and early 20th century. The gas was used as fuel for street lighting and basic residential uses that required gas such as ovens, kilns, furnaces, and boilers. | 7 | Physical Chemistry |
The heat deflection temperature or heat distortion temperature (HDT, HDTUL, or DTUL) is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in many aspects of product design, engineering and manufacture of products using thermoplastic components. | 7 | Physical Chemistry |
On the periodic table, homologous elements share many electrochemical properties and appear in the same group (column) of the table. For example, all noble gases are colorless, monatomic gases with very low reactivity. These similarities are due to similar structure in their outer shells of valence electrons. Mendeleev used the prefix eka- for an unknown element below a known one in the same group. | 0 | Organic Chemistry |
Let the unperturbed atom or molecule be in a g-fold degenerate state with orthonormal zeroth-order state functions . (Non-degeneracy is the special case g = 1). According to perturbation theory the first-order energies are the eigenvalues of the g × g matrix with general element
If g = 1 (as is often the case for electronic states of molecules) the first-order energy becomes proportional to the expectation (average) value of the dipole operator ,
Because the electric dipole moment is a vector (tensor of the first rank), the diagonal elements of the perturbation matrix V vanish between states with a certain parity. Atoms and molecules possessing inversion symmetry do not have a (permanent) dipole moment and hence do not show a linear Stark effect.
In order to obtain a non-zero matrix V for systems with an inversion center it is necessary that some of the unperturbed functions have opposite parity (obtain plus and minus under inversion), because only functions of opposite parity give non-vanishing matrix elements. Degenerate zeroth-order states of opposite parity occur for excited hydrogen-like (one-electron) atoms or Rydberg states. Neglecting fine-structure effects, such a state with the principal quantum number n is n-fold degenerate and
where is the azimuthal (angular momentum) quantum number. For instance, the excited n = 4 state contains the following states,
The one-electron states with even are even under parity, while those with odd are odd under parity. Hence hydrogen-like atoms with n>1 show first-order Stark effect.
The first-order Stark effect occurs in rotational transitions of symmetric top molecules (but not for linear and asymmetric molecules). In first approximation a molecule may be seen as a rigid rotor. A symmetric top rigid rotor has the unperturbed eigenstates
with 2(2J+1)-fold degenerate energy for |K| > 0 and (2J+1)-fold degenerate energy for K=0.
Here D is an element of the Wigner D-matrix. The first-order perturbation matrix on basis of the unperturbed rigid rotor function is non-zero and can be diagonalized. This gives shifts and splittings
in the rotational spectrum. Quantitative analysis of these Stark shift yields the permanent electric dipole moment of the symmetric top molecule. | 7 | Physical Chemistry |
DNA molecules contain 5-membered carbon rings called riboses that are directly attached to two phosphate groups and a nucleobase that contains amino groups. The nitrogen atoms from the amino group in the nucleotides are covalently linked to the anomeric carbon of the ribose sugar structure through an N-glycosidic bond. Occasionally, the nucleobases attached to the ribose undergo deamination, alkylation, or oxidation which results in cytotoxic lesions along the DNA backbone. These modifications severely threaten the cohesiveness of the DNA molecule, leading to the development of diseases such as cancer. DNA glycosylases are enzymes that catalyze the hydrolysis the N-glycosidic bond to free the damaged or modified nucleobase from the DNA, by cleaving the carbon-nitrogen glycosidic bond at the 2' carbon, subsequently initiating the base excision repair (BER) pathway.
Monofunctional glycosylases catalyze the hydrolysis of the N-glycosidic bond via either a stepwise, S1 like mechanism, or a concerted, S2 like mechanism. The stepwise function, the nucleobase acts as a leaving group before the anomeric carbon gets attacked by the water molecule, producing a short-lived unstable oxacarbenium ion intermediate. This intermediate rapidly reacts with the nearby water molecule to substitute the N-glycosidic bond of the ribose and the nucleobase with an O-glycosidic bond with a hydroxy group. The concerted mechanism, the water acts as a nucleophile and attacks at the anomeric carbon before the nucelobase gets to act like a leaving group. The intermediate produced is a similar oxacarbenium ion where both the hydroxy groups and the nucleobase are still attached to the anomeric carbon. Both mechanisms theoretically yield the same product. Most ribonucleotides are hydrolyzed via the concerted S2 like mechanism, while most deoxyribonucleotides proceed through the stepwise like mechanism.
These reactions are practically irreversible. Due to the fact that the cleavage of the N-glycosidic bond from the DNA backbone can lead to detrimental mutagenic and cytotoxic responses in an organism, have the ability to also catalyze the synthesis of N-glycosidic bonds by way of an abasic DNA site and a specific nucleobase. | 0 | Organic Chemistry |
Argentation chromatography is chromatography using a stationary phase that contains silver salts. Silver-containing stationary phases are well suited for separating organic compounds on the basis of the number and type of alkene groups. The technique is employed for gas chromatography and various types of liquid chromatography, including thin layer chromatography. Analytes containing alkene groups elute more slowly than the analogous compounds lacking alkenes. Separations are also sensitive to the type of alkene. The technique is especially useful in the analysis of fats and fatty acids, which are well known to exist in both saturated and unsaturated (alkene-containing) forms. For example, trans fats, undesirable contaminants in ultra-processed foods, are quantified by argentation chromatography. | 3 | Analytical Chemistry |
Faraday's laws can be summarized by
where is the molar mass of the substance (usually given in SI units of grams per mole) and is the valency of the ions .
For Faraday's first law, are constants; thus, the larger the value of , the larger will be.
For Faraday's second law, are constants; thus, the larger the value of (equivalent weight), the larger will be.
In the simple case of constant-current electrolysis, , leading to
and then to
where:
* is the amount of substance ("number of moles") liberated:
* is the total time the constant current was applied.
For the case of an alloy whose constituents have different valencies, we have
where represents the mass fraction of the -th element.
In the more complicated case of a variable electric current, the total charge is the electric current integrated over time :
Here is the total electrolysis time. | 7 | Physical Chemistry |
In 1772, the chemist Joseph Priestley carried out a series of experiments relating to the gases involved in respiration and combustion. In his first experiment, he lit a candle and placed it under an upturned jar. After a short period of time, the candle burned out. He carried out a similar experiment with a mouse in the confined space of the burning candle. He found that the mouse died a short time after the candle had been extinguished. However, he could revivify the foul air by placing green plants in the area and exposing them to light. Priestley's observations were some of the first experiments that demonstrated the activity of a photosynthetic reaction center.
In 1779, Jan Ingenhousz carried out more than 500 experiments spread out over 4 months in an attempt to understand what was really going on. He wrote up his discoveries in a book entitled Experiments upon Vegetables. Ingenhousz took green plants and immersed them in water inside a transparent tank. He observed many bubbles rising from the surface of the leaves whenever the plants were exposed to light. Ingenhousz collected the gas that was given off by the plants and performed several different tests in attempt to determine what the gas was. The test that finally revealed the identity of the gas was placing a smouldering taper into the gas sample and having it relight. This test proved it was oxygen, or, as Joseph Priestley had called it, de-phlogisticated air.
In 1932, Robert Emerson and his student, William Arnold, used a repetitive flash technique to precisely measure small quantities of oxygen evolved by chlorophyll in the algae Chlorella. Their experiment proved the existence of a photosynthetic unit. Gaffron and Wohl later interpreted the experiment and realized that the light absorbed by the photosynthetic unit was transferred. This reaction occurs at the reaction center of Photosystem II and takes place in cyanobacteria, algae and green plants. | 5 | Photochemistry |
Ellipsometry is an optical technique for investigating the dielectric properties (complex refractive index or dielectric function) of thin films. Ellipsometry measures the change of polarization upon reflection or transmission and compares it to a model.
It can be used to characterize composition, roughness, thickness (depth), crystalline nature, doping concentration, electrical conductivity and other material properties. It is very sensitive to the change in the optical response of incident radiation that interacts with the material being investigated.
A spectroscopic ellipsometer can be found in most thin film analytical labs. Ellipsometry is also becoming more interesting to researchers in other disciplines such as biology and medicine. These areas pose new challenges to the technique, such as measurements on unstable liquid surfaces and microscopic imaging. | 7 | Physical Chemistry |
Vanadium nitrogenases are found in members of the bacterial genus Azotobacter as well as the species Rhodopseudomonas palustris and Anabaena variabilis. Most of the functions of vanadium nitrogenase match those of the more common molybdenum nitrogenases and serve as an alternative pathway for nitrogen fixation in molybdenum deficient conditions. Like molybdenum nitrogenase, dihydrogen functions as a competitive inhibitor and carbon monoxide functions as a non-competitive inhibitor of nitrogen fixation. Vanadium nitrogenase has an αβΎ subunit structure while molybdenum nitrogenase has an αβ structure. Though the structural genes encoding vanadium nitrogenase show only about 15% conservation with molybdenum nitrogenases, the two nitrogenases share the same type of iron-sulphur redox centers. At room temperature, vanadium nitrogenase is less efficient at fixing nitrogen than molybdenum nitrogenases because it converts more H to H as a side reaction. However, at low temperatures vanadium nitrogenases have been found to be more active than the molybdenum type, and at temperatures as low as 5 °C its nitrogen-fixing activity is 10 times higher than that of molybdenum nitrogenase. Like molybdenum nitrogenase, vanadium nitrogenase is easily oxidized and is thus only active under anaerobic conditions. Various bacteria employ complex protection mechanisms to avoid oxygen.
The overall stoichiometry of nitrogen fixation catalyzed by vanadium nitrogenase can be summarized as follows:
:N + 12e + 14H + 24MgATP → 2NH + 3H + 24MgADP + 24HPO
The crystal structure of A. vinelandii vanadium nitrogenase was resolved in 2017 (). Compared to Mo nitrogenase, V nitrogenase replaces one sulfide in the active site with a bridging ligand. | 0 | Organic Chemistry |
If an abnormality is found, i.e. the B12 in the urine is only present in low levels, the test is repeated, this time with additional oral intrinsic factor.
* If this second urine collection is normal, this shows a lack of intrinsic factor production. This is by definition pernicious anemia.
* A low result on the second test implies abnormal intestinal absorption (malabsorption), which could be caused by coeliac disease, biliary disease, Whipple's disease, small bowel bacterial overgrowth syndrome, fish tapeworm infestation (Diphyllobothrium latum), or liver disease. Malabsorption of B can be caused by intestinal dysfunction from a low vitamin level in-and-of-itself (see below), causing test result confusion if repletion has not been done for some days previously. | 1 | Biochemistry |
This category groups pages related to Internal ribosome entry sites (IRESs) of RNA. IRESs are a nucleotide sequence that directs translation initiation in the middle of a messenger RNA (mRNA) as opposed to the usual process where initiation occurs at the five-prime end. | 1 | Biochemistry |
Vitamin D (cholecalciferol) is produced industrially by exposing 7-dehydrocholesterol to UVB and UVC light, followed by purification. The 7-dehydrocholesterol is a natural substance in fish organs, especially the liver, in wool grease (lanolin) from sheep and in some plants, like lichen (Cladonia rangiferina). Vitamin D (ergocalciferol) is produced in a similar way using ergosterol from yeast or mushrooms as a starting material. | 1 | Biochemistry |
This book consists of the arguments used against the art and Agricolas counter arguments. He explains that mining and prospecting are not just a matter of luck and hard work; there is specialized knowledge that must be learned. A miner should have knowledge of philosophy, medicine, astronomy, surveying, arithmetic, architecture, drawing and law, though few are masters of the whole craft and most are specialists. This section is full of classical references and shows Agricolas classical education to its fullest. The arguments range from philosophical objections to gold and silver as being intrinsically worthless, to the danger of mining to its workers and its destruction of the areas in which it is carried out. He argues that without metals, no other activity such as architecture or agriculture are possible. The dangers to miners are dismissed, noting that most deaths and injuries are caused by carelessness, and other occupations are hazardous too. Clearing forests for timber is advantageous as the land can be farmed. Mines tend to be in mountains and gloomy valleys with little economic value. The loss of food from the forests destroyed can be replaced by purchase from profits, and metals have been placed underground by God and man is right to extract and use them. Finally, Agricola argues that mining is an honorable and profitable occupation. | 8 | Metallurgy |
There are three groups of methods for correlating and predicting LCSTs. The first group proposes models that are based on a solid theoretical background using liquid–liquid or vapor–liquid experimental data. These methods require experimental data to adjust the unknown parameters, resulting in limited predictive ability . Another approach uses empirical equations that correlate θ (LCST) with physicochemical properties such as density, critical properties etc., but suffers from the disadvantage that these properties are not always available. A new approach proposed by Liu and Zhong develops linear models for the prediction of θ(LCST) using molecular connectivity indices, which depends only on the solvent and polymer structures. The latter approach has proven to be a very useful technique in quantitative structure–activity/property relationships (QSAR/QSPR) research for polymers and polymer solutions. QSAR/QSPR studies constitute an attempt to reduce the trial-and-error element in the design of compounds with desired activity/properties by establishing mathematical relationships between the activity/property of interest and measurable or computable parameters, such as topological, physicochemical, stereochemistry, or electronic indices. More recently QSPR models for the prediction of the θ (LCST) using molecular (electronic, physicochemical etc.) descriptors have been published. Using validated robust QSPR models, experimental time and effort can be reduced significantly as reliable estimates of θ (LCST) for polymer solutions can be obtained before they are actually synthesized in the laboratory. | 7 | Physical Chemistry |
One solution to the problem of oxidation is to replace the hydrogens ortho to the carbon-carbon double bond by groups that can not be removed during the oxidation. Following the Woodward–Hoffmann rules, the photochemical 6π cyclization takes place in a conrotatory fashion, leading to products with an anti configuration of the methyl substituents. As both methyl groups are attached to a stereogenic center, two enantiomers (R,R and S,S) are formed, normally as a racemic mixture. This approach also has the advantage that the thermal (disrotatory) ring closure can not take place because of steric hindrance between the substitution groups. | 5 | Photochemistry |
In chemistry, a cavitand is a container-shaped molecule. The cavity of the cavitand allows it to engage in host–guest chemistry with guest molecules of a complementary shape and size. The original definition proposed by Cram includes many classes of molecules: cyclodextrins, calixarenes, pillararenes and cucurbiturils. However, modern usage in the field of supramolecular chemistry specifically refers to cavitands formed on a resorcinarene scaffold by bridging adjacent phenolic units. The simplest bridging unit is methylene (), although dimethylene (), trimethylene (), benzal, xylyl, pyridyl, 2,3-disubstituted-quinoxaline, o-dinitrobenzyl, dialkylsilylene, and phosphonates are known. Cavitands that have an extended aromatic bridging unit, or an extended cavity containing 3 rows of aromatic rings are referred to as deep-cavity cavitands and have broad applications in host-guest chemistry. These types of cavitands were extensively investigated by Rebek, and Gibb, among others. | 6 | Supramolecular Chemistry |
The saprobic system has a long history in German-language countries. The idea of saprobes to estimate water quality has been foreshadowed by the works of Arthur Hill Hassall (1850) and Ferdinand Julius Cohn (1853). In a series of publications, the Germans botanists Richard Kolkwitz and Maximilian Marsson (1902, 1908, 1909) have developed the saprobic system to judge water quality. They compiled a list of about 300 plant and 500 animal species (excluding fish), and estimated saprobic values for them.
In 1955, H. Knöpp introduced abundance classes, and the calculation of a water quality index was established during the 1950s and 1960s (Pantle & Buck, 1955; Zelinka & Marvan, 1961; Marvan, 1969).
In 2000, the Pantle & Buck technique has been criticized because it requires the surveyed organisms to be identified by genus, something that freshwater ecologists are rarely trained for. Furthermore, it focuses on aquatic organisms that are prevalent in Western Europe, something that hampers water quality assays in Eastern Europe and Asia.
The procedure used in Germany to estimate the saprobic index has been standardized in DIN 38410. | 2 | Environmental Chemistry |
Respiration in cyanobacteria can occur in the thylakoid membrane alongside photosynthesis, with their photosynthetic electron transport sharing the same compartment as the components of respiratory electron transport. While the goal of photosynthesis is to store energy by building carbohydrates from CO, respiration is the reverse of this, with carbohydrates turned back into CO accompanying energy release.
Cyanobacteria appear to separate these two processes with their plasma membrane containing only components of the respiratory chain, while the thylakoid membrane hosts an interlinked respiratory and photosynthetic electron transport chain. Cyanobacteria use electrons from succinate dehydrogenase rather than from NADPH for respiration.
Cyanobacteria only respire during the night (or in the dark) because the facilities used for electron transport are used in reverse for photosynthesis while in the light. | 5 | Photochemistry |
The H function can be approximated up to an order as
where are the zeros of Legendre polynomials and are the positive, non vanishing roots of the associated characteristic equation
where are the quadrature weights given by | 7 | Physical Chemistry |
Biotin carboxyl carrier protein (BCCP) refers to proteins containing a biotin attachment domain that carry biotin and carboxybiotin throughout the ATP-dependent carboxylation by biotin-dependent carboxylases. The biotin carboxyl carrier protein is an Acetyl CoA subunit that allows for Acetyl CoA to be catalyzed and converted to malonyl-CoA. More specifically, BCCP catalyzes the carboxylation of the carrier protein to form an intermediate. Then the carboxyl group is transferred by the transcacrboxylase to form the malonyl-CoA. This conversion is an essential step in the biosynthesis of fatty acids. In the case of E. coli Acetyl-CoA carboxylase, the BCCP is a separate protein known as accB (). On the other hand, in Haloferax mediterranei, propionyl-CoA carboxylase, the BCCP pccA () is fused with biotin carboxylase.
The biosynthesis of fatty acids in plants, such as triacylglycerol, is vital to the plant's overall health because it allows for accumulation of seed oil. The biosynthesis that is catalyzed by BCCP usually takes place in the chloroplast of plant cells. The biosynthesis performed by the BCCP protein allows for the transfer of CO within active sites of the cell.
The biotin carboxyl carrier protein carries approximately 1 mol of biotin per 22,000 g of protein.
There is not much research on BCCPs at the moment. However, a recent studyon plant genomics found that Brassica BCCPs might play a key role in abiotic and biotic stress responses. Meaning that these proteins may be relaying messages to the rest of the plant body after it has been exposed to extreme conditions that disrupt the plant's homeostasis. | 1 | Biochemistry |
Multistep tandem reactions (or cascade reactions) are a sequence of chemical transformations (usually more than two steps) that happens consecutively to convert a starting material to a complex product. This kind of organic reactions are designed to construct difficult structures encountered in natural product total synthesis.
In the total synthesis of spiroketal ionophore antibiotic routiennocin 1 (Fig. 1), the central spiroketal skeleton was constructed by a multistep tandem reaction (Fig. 2). Fragment A and fragment B were coupled in a single step to form the key intermediate G that could be further elaborated to afford the final product routiennocin.
Four chemical transformations happened in this tandem reaction. First, treating fragment A with n-butyllithium formed carbon anion that attacked the alkyliodide part of fragment B to generate intermediate C (step 1). Then a 3, 4-dihydropyran derivative D was formed through base-mediated elimination reaction on intermediate C (step 2). The protecting group on 1, 3-diol moiety in intermediate D was removed by acid treatment to give the diol product E (step 3). The spiroketal product G was generated via intramolecular ketal formation reaction. This multistep tandem reaction greatly simplified the construction of this complex spiroketal structure and eased the path towards the total synthesis of routiennocin. | 0 | Organic Chemistry |
The precursor to nylon, adipic acid, is produced on a large scale by oxidation of "KA oil"—a mixture of cyclohexanone and cyclohexanol—with nitric acid. | 3 | Analytical Chemistry |
A large number of examples of vicinal difunctionalization of unsaturated carbonyl compounds exist in the literature. In one example, the difunctionalization of unsaturated lactone 1 was employed en route to isostegane. This transformation was accomplished in one pot.
Because the reaction creates two new bonds with a moderately high degree of stereocontrol, it represents a highly convergent synthetic method. | 0 | Organic Chemistry |
There are several counterparts of pepper spray developed and legal to possess in some countries.
* In the United Kingdom, desmethyldihydrocapsaicin (known also as PAVA spray) is used by police officers. As a Section 5 weapon, it is not generally permitted to the public.
* Pelargonic acid morpholide (MPK) is widely used as a self-defense chemical agent spray in Russia, though its effectiveness compared to natural pepper spray is unclear.
* In China, Ministry of Public Security police units and security guards use tear gas ejectors with OC, CS or CN gases. These are defined as a "restricted" weapon that only police officers, as well as approved security, can use. | 1 | Biochemistry |
In eutactic macromolecules, substituents may occupy any specific (but potentially complex) sequence of positions along the chain. Isotactic and syndiotactic polymers are instances of the more general class of eutactic polymers, which also includes heterogeneous macromolecules in which the sequence consists of substituents of different kinds (for example, the side-chains in proteins and the bases in nucleic acids). | 4 | Stereochemistry |
A direct fluorescent antibody (DFA or dFA), also known as "direct immunofluorescence", is an antibody that has been tagged in a direct fluorescent antibody test. Its name derives from the fact that it directly tests the presence of an antigen with the tagged antibody, unlike western blotting, which uses an indirect method of detection, where the primary antibody binds the target antigen, with a secondary antibody directed against the primary, and a tag attached to the secondary antibody.
Commercial DFA testing kits are available, which contain fluorescently labelled antibodies, designed to specifically target unique antigens present in the bacteria or virus, but not present in mammals (Eukaryotes). This technique can be used to quickly determine if a subject has a specific viral or bacterial infection.
In the case of respiratory viruses, many of which have similar broad symptoms, detection can be carried out using nasal wash samples from the subject with the suspected infection. Although shedding cells in the respiratory tract can be obtained, it is often in low numbers, and so an alternative method can be adopted where compatible cell culture can be exposed to infected nasal wash samples, so if the virus is present it can be grown up to a larger quantity, which can then give a clearer positive or negative reading.
As with all types of fluorescence microscopy, the correct absorption wavelength needs to be determined in order to excite the fluorophore tag attached to the antibody, and detect the fluorescence given off, which indicates which cells are positive for the presence of the virus or bacteria being detected.
Direct immunofluorescence can be used to detect deposits of immunoglobulins and complement proteins in biopsies of skin, kidney and other organs. Their presence is indicative of an autoimmune disease. When skin not exposed to the sun is tested, a positive direct IF (the so-called Lupus band test) is an evidence of systemic lupus erythematosus. Direct fluorescent antibody can also be used to detect parasitic infections, as was pioneered by Sadun, et al. (1960). | 1 | Biochemistry |
Besides education, CrysTBox is mainly used in research with fields of application spanning from nuclear research to archaeology and paleontology. Among others, the suite was employed in development of additive manufacturing (including 3D printed biodegradable alloys, metallic glass or high-entropy alloys), resistant coatings, laser shock peening, water cleaning technologies or characterization of 50 million years old flint.
Institutions whose research was supported by CrysTBox include educational facilities such as ETH Zurich, University of California, Uppsala University, Oxford University, University of Waterloo, Indian Institute of Technology, Nanyang Technological University or University of Tokyo as well as research institutes like Max Planck Institutes, Chinese Academy of Sciences, Fraunhofer Institutes or US national laboratories (NL) such as Oak Ridge NL, Lawrence Berkeley NL, Idaho NL and Lawrence Livermoore NL. | 3 | Analytical Chemistry |
Methylphenidate is a catecholamine reuptake inhibitor that indirectly increases catecholaminergic neurotransmission by inhibiting the dopamine transporter (DAT) and norepinephrine transporter (NET), which are responsible for clearing catecholamines from the synapse, particularly in the striatum and meso-limbic system. Moreover, it is thought to "increase the release of these monoamines into the extraneuronal space."
Although four stereoisomers of methylphenidate (MPH) are possible, only the threo diastereoisomers are used in modern practice. There is a high eudysmic ratio between the SS and RR enantiomers of MPH. Dexmethylphenidate (d-threo-methylphenidate) is a preparation of the RR enantiomer of methylphenidate. In theory, D-TMP (d-threo-methylphenidate) can be anticipated to be twice the strength of the racemic product. | 4 | Stereochemistry |
Ultraviolet radiation is invisible to the human eye, but illuminating certain materials with UV radiation causes the emission of visible light, causing these substances to glow with various colors. This is called fluorescence, and has many practical uses. Black lights are required to observe fluorescence, since other types of ultraviolet lamps emit visible light which drowns out the dim fluorescent glow. | 5 | Photochemistry |
The various liquid-crystal phases (called mesophases together with plastic crystal phases) can be characterized by the type of ordering. One can distinguish positional order (whether molecules are arranged in any sort of ordered lattice) and orientational order (whether molecules are mostly pointing in the same direction). Liquid crystals are characterized by orientational order, but only partial or completely absent positional order. In contrast, materials with positional order but no orientational order are known as plastic crystals. Most thermotropic LCs will have an isotropic phase at high temperature: heating will eventually drive them into a conventional liquid phase characterized by random and isotropic molecular ordering and fluid-like flow behavior. Under other conditions (for instance, lower temperature), a LC might inhabit one or more phases with significant anisotropic orientational structure and short-range orientational order while still having an ability to flow.
The ordering of liquid crystals extends up to the entire domain size, which may be on the order of micrometers, but usually not to the macroscopic scale as often occurs in classical crystalline solids. However some techniques, such as the use of boundaries or an applied electric field, can be used to enforce a single ordered domain in a macroscopic liquid crystal sample. The orientational ordering in a liquid crystal might extend along only one dimension, with the material being essentially disordered in the other two directions. | 7 | Physical Chemistry |
In polymer chemistry and materials science, the term "polymer" refers to large molecules whose structure is composed of multiple repeating units. Supramolecular polymers are a new category of polymers that can potentially be used for material applications beyond the limits of conventional polymers. By definition, supramolecular polymers are polymeric arrays of monomeric units that are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. The direction and strength of the interactions are precisely tuned so that the array of molecules behaves as a polymer (that is, it behaves in a way that can be described by the theories of polymer physics) in dilute and concentrated solution, as well as in the bulk.
In conventional polymers, monomeric units are linked by strong covalent bonds and have excellent properties as materials; however, high temperatures and pressures are typically required for processing due to polymer entanglement in the highly viscous melt. Supramolecular polymers combine good material properties with low-viscosity melts that are easy to handle. Additionally, some supramolecular polymers have unique characteristics, such as the ability to self-heal fractures. Although covalent polymers can be recycled, their strong covalent bonds never disintegrate, and go on to negatively affect the environment as plastic wastes. Thus, supramolecular polymers are increasingly getting attention because of their potential for the design of responsive, adaptive, self-healing, and environmentally friendly materials. | 6 | Supramolecular Chemistry |
Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound (silyl halide), with the formula , often abbreviated or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. It is widely used in organic chemistry. | 0 | Organic Chemistry |
A Rydberg molecule is an electronically excited chemical species. Electronically excited molecular states are generally quite different in character from electronically excited atomic states. However, particularly for highly electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula, named after the Swedish physicist Johannes Rydberg, and they are called Rydberg states of molecules. Rydberg series are associated with partially removing an electron from the ionic core.
Each Rydberg series of energies converges on an ionization energy threshold associated with a particular ionic core configuration. These quantized Rydberg energy levels can be associated with the quasiclassical Bohr atomic picture. The closer you get to the ionization threshold energy, the higher the principal quantum number, and the smaller the energy difference between near threshold Rydberg states. As the electron is promoted to higher energy levels in a Rydberg series, the spatial excursion of the electron from the ionic core increases and the system is more like the Bohr quasiclassical picture.
The Rydberg states of molecules with low principal quantum numbers can interact with the other excited electronic states of the molecule. This can cause shifts in energy. The assignment of molecular Rydberg states often involves following a Rydberg series from intermediate to high principal quantum numbers. The energy of Rydberg states can be refined by including a correction called the quantum defect in the Rydberg formula. The quantum defect correction can be associated with the presence of a distributed ionic core.
The experimental study of molecular Rydberg states has been conducted with traditional methods for generations. However, the development of laser-based techniques such as Resonance Ionization Spectroscopy has allowed relatively easy access to these Rydberg molecules as intermediates. This is particularly true for Resonance Enhanced Multiphoton Ionization (REMPI) spectroscopy, since multiphoton processes involve different selection rules from single photon processes. The study of high principal quantum number Rydberg states has spawned a number of spectroscopic techniques. These "near threshold Rydberg states" can have long lifetimes, particularly for the higher orbital angular momentum states that do not interact strongly with the ionic core.
Rydberg molecules can condense to form clusters of Rydberg matter which has an extended lifetime against de-excitation.
Dihelium (He) was the first known Rydberg molecule. | 7 | Physical Chemistry |
In organosulfur chemistry, a sulfonyl group can refer either to a functional group found primarily in sulfones, or to a substituent obtained from a sulfonic acid by the removal of the hydroxyl group, similarly to acyl groups. Sulfonyl groups can be written as having the general formula , where there are two double bonds between the sulfur and oxygen.
Sulfonyl groups can be reduced to the sulfide with DIBALH. Lithium aluminium hydride () reduces some but not all sulfones to sulfides.
In inorganic chemistry, when the group is not connected to any carbon atoms, it is referred to as sulfuryl. | 0 | Organic Chemistry |
Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale). They are generated from percentage transformation-vs time measurements, and are useful for understanding the transformations of an alloy steel at elevated temperatures.
An isothermal transformation diagram is only valid for one specific composition of material, and only if the temperature is held constant during the transformation, and strictly with rapid cooling to that temperature. Though usually used to represent transformation kinetics for steels, they also can be used to describe the kinetics of crystallization in ceramic or other materials. Time-temperature-precipitation diagrams and time-temperature-embrittlement diagrams have also been used to represent kinetic changes in steels.
Isothermal transformation (IT) diagram or the C-curve is associated with mechanical properties, microconstituents/microstructures, and heat treatments in carbon steels. Diffusional transformations like austenite transforming to a cementite and ferrite mixture can be explained using the sigmoidal curve; for example the beginning of pearlitic transformation is represented by the pearlite start (P) curve. This transformation is complete at P curve. Nucleation requires an incubation time. The rate of nucleation increases and the rate of microconstituent growth decreases as the temperature decreases from the liquidus temperature reaching a maximum at the bay or nose of the curve. Thereafter, the decrease in diffusion rate due to low temperature offsets the effect of increased driving force due to greater difference in free energy. As a result of the transformation, the microconstituents, pearlite and bainite, form; pearlite forms at higher temperatures and bainite at lower.
Austenite is slightly undercooled when quenched below Eutectoid temperature. When given more time, stable microconstituents can form: ferrite and cementite. Coarse pearlite is produced when atoms diffuse rapidly after phases that form pearlite nucleate. This transformation is complete at the pearlite finish time (P).
However, greater undercooling by rapid quenching results in formation of martensite or bainite instead of pearlite. This is possible provided the cooling rate is such that the cooling curve intersects the martensite start temperature or the bainite start curve before intersecting the Pcurve. The martensite transformation being a diffusionless shear transformation is represented by a straight line to signify the martensite start temperature. | 8 | Metallurgy |
Malonyl-CoA provides 2-carbon units to fatty acids and commits them to fatty acid chain synthesis.
Malonyl-CoA is formed by carboxylating acetyl-CoA using the enzyme acetyl-CoA carboxylase. One molecule of acetyl-CoA joins with a molecule of bicarbonate, requiring energy rendered from ATP.
Malonyl-CoA is utilised in fatty acid biosynthesis by the enzyme malonyl coenzyme A:acyl carrier protein transacylase (MCAT). MCAT serves to transfer malonate from malonyl-CoA to the terminal thiol of holo-acyl carrier protein (ACP). | 1 | Biochemistry |
The early 19th century witnessed a sharp increase in the demand for natural ice during the summer months, particularly among breweries producing lager. Thanks to the advent of railways and steam ships, natural ice came onto the market. In order to meet demand, suppliers began looking for alternative ways of producing ice artificially.
Thus, entrepreneurs begin research on the means of producing ice.
Although Oliver Evans was the first to document the cycle, it was Jacob Perkins, an American working in England, who first patented a machine based on the vapour-compression cycle in 1835.
In 1855, the first compression machines that proved to be successful on an industrial scale were developed by James Harrison. Ferdinand Carré invented the absorption device in 1859, then came the model of vapor compression refrigerator.
This absorption machine was later replaced by a much simpler vapour-compression refrigerator, invented by French engineer Charles Tellier in 1885, that is still used today.
In order to support the development of refrigeration technologies and in view of the economic development potential they represented, the IIR was created in several stages:
* October 5–10, 1908 - The rapidly growing, global industry and scientific quest for absolute zero lead to the 1st International Congress of Refrigeration held in Paris, France, at the Paris-Sorbonne University, which welcomed over 5,000 participants.
* January 25, 1909 - From this first Congress, the International Association of Refrigeration was born, formed by delegates from 35 countries.
* June 21, 1920 - The association was reorganised and officially titled as the International Institute of Refrigeration – IIR (Institut International du Froid – IIF, in French).
The IIR status as an international organisation were defined by an International Agreement signed on December 1, 1954, and General Regulations for the Application of the International Agreements signed on November 20, 1956.
Since then, the IIR has been operating at its headquarters based in Paris and is now an international organisation for expertise on refrigeration. The institute has continued to run the [https://iifiir.org/en/iir-conferences-series International Congress of Refrigeration] every four years since its inauguration and has now expanded its event portfolio to ten conference series covering a vast variety of refrigeration topics. Working alongside governments, today the IIR remains committed to promoting knowledge on refrigeration for sustainable development, and continues to provide key services to disseminate information on associated technologies to all stakeholders (companies, universities, professionals...). | 7 | Physical Chemistry |
The values for the octanol-water system in the following table are from the Dortmund Data Bank. They are sorted by the partition coefficient, smallest to largest (acetamide being hydrophilic, and 2,2,4,4,5-pentachlorobiphenyl lipophilic), and are presented with the temperature at which they were measured (which impacts the values).
Values for other compounds may be found in a variety of available reviews and monographs. Critical discussions of the challenges of measurement of log P and related computation of its estimated values (see below) appear in several reviews. | 7 | Physical Chemistry |
Luminol's use in a crime scene investigation is somewhat hampered by the fact that it reacts to iron- and copper-containing compounds, bleaches, horseradish, fecal matter, or cigarette smoke residue. Application of luminol to a piece of evidence may prevent other tests from being performed on it; however DNA has been successfully extracted from samples exposed to luminol. | 3 | Analytical Chemistry |
The International Institute of Welding Technology IIW published the Guideline "Recommendations for the HFMI Treatment" in October 2016. An overview of higher frequency hammers (HFMI) is presented, and recommendations for the correct application of the method and quantitative measurements for quality assurance the guideline provides the basis for measurements of HFMI improved welded joints on the basis of all known stress calculation concepts.
In numerous experiments at various institutes and universities an 80 to 100 percent increase of fatigue strength and a 5 – to 15-fold increase in weld-life could be demonstrated. The most extensive research project was from 2006 to 2009 "REFRESH – life extension of existing and new welded steel structures (P702). In this research project, the HiFIT device was developed and made ready for production. This report is available in book form at the FOSTA (Forschungsvereinigung Stahlanwendung e.V.) and can be ordered under the number . The book contains detailed scientific verifications and validations. | 8 | Metallurgy |
In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts an organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals (Li, Na, Mg) and organochlorides, bromides, and iodides. Particularly well-developed is the use of metal–halogen exchange for the preparation of organolithium compounds. | 0 | Organic Chemistry |
Carbon dioxide, a greenhouse gas, traps heat in the atmosphere, the bionic leaf can potentially be used to reduce the carbon dioxide within the atmosphere. While the bionic leaf is running mimics photosynthesis by converting the carbon dioxide in air into fuels. The bionic leaf can eliminate 180 grams of carbon dioxide out of 230,000 liters of air for each kilowatt hour of energy it consumes. While removing large amounts of carbon dioxide from the atmosphere not possible yet on a large scale, this technology is useful in areas where carbon dioxide is produced such as power plants. It can also be implemented within urban areas, providing clean air to the area. The technology may also be used on a smaller scale, helping communities produce, harness, and consume the require energy they need. | 5 | Photochemistry |
An inhibitor of alpha-amylase, called phaseolamin, has been tested as a potential diet aid.
When used as a food additive, amylase has E number E1100, and may be derived from pig pancreas or mold fungi.
Bacilliary amylase is also used in clothing and dishwasher detergents to dissolve starches from fabrics and dishes.
Factory workers who work with amylase for any of the above uses are at increased risk of occupational asthma. Five to nine percent of bakers have a positive skin test, and a fourth to a third of bakers with breathing problems are hypersensitive to amylase. | 1 | Biochemistry |
Various aromatic alkynes can be employed to yield desired disubstituted products with satisfactory yields. Aliphatic alkynes are generally less reactive. | 0 | Organic Chemistry |
In the biological sciences, accidental introduction of "foreign" material can seriously distort the results of experiments where small samples are used. In cases where the contaminant is a living microorganism, it can often multiply to dominate the sample and render it useless, as in contaminated cell culture lines. A similar affect can be seen in geology, geochemistry, and archaeology, where even a few grains of a material can distort results of sophisticated experiments. | 9 | Geochemistry |
Hydroamination reactions are atom-efficient processes that generally use readily available and cheap starting materials, therefore a general catalytic strategy is highly desirable. Also, direct catalytic hydroamination strategies have in principle significant benefits over more classical methods to prepare amine containing compounds, including the reduction in the number of synthetic steps required.
However, hydroamination reactions pose some tough challenges for catalysis: Strong electron repulsion of the nitrogen atom lone pair and the electron rich carbon-carbon multiple bond, coupled with hydroamination reactions being entropically disfavoured (particularly the intermolecular version), results in a large reaction barrier. Regioselectivity issues also hamper the synthetic utility of the resulting products, with Markovnikov addition of the amine being the most common outcome over the less favoured anti-Markovnikov addition (see figure). As a result, there are now numerous catalysts that can be utilised in the hydroamination of alkene, allene and alkyne substrates, including various metal based heterogeneous catalysts, early-transition metal complexes (e.g. titanium and zirconium), late-transition metal complexes (e.g. ruthenium and palladium), lanthanide and actinide complexes (e.g. samarium and lanthanum), as well as Brønsted acids and bases. | 0 | Organic Chemistry |
TTM has been studied in several use scenarios where it has not usually been found to be helpful, or is still under investigation, despite theoretical grounds for its usefulness. | 1 | Biochemistry |
As 2-chlorobenzalmalononitrile is a solid at room temperature, not a gas, a variety of techniques have been used to make this solid usable as an aerosol:
* Melted and sprayed in the molten form.
* Dissolved in organic solvent.
* CS2 dry powder (CS2 is a siliconized, micro-pulverized form of CS).
* CS from thermal grenades by generation of hot gases.
In the Waco Siege in the United States, CS was dissolved in the organic solvent dichloromethane (also known as methylene chloride). The solution was dispersed as an aerosol via explosive force and when the highly volatile dichloromethane evaporated, CS crystals precipitated and formed a fine dispersion in the air. | 1 | Biochemistry |
The Iron & Steel Museum of Alabama, also known as the Tannehill Museum, is an industrial museum that demonstrates iron production in the nineteenth-century Alabama located at Tannehill Ironworks Historical State Park in McCalla, Tuscaloosa County, Alabama. Opened in 1981, it covers .
The museum is an interpretive center focusing on 19th-century iron-making technology. It features an extensive collection of machinery and other iron industry artifacts spanning from the time of the American Civil War until the 1960s, including belt-driven machines, a reconstruction of an 1870s machine shop, and four steam engines. The collection also houses over ten thousand artifacts and other items sourced from archaeological digs at various iron-making sites in Alabama such as the Roupes Valley Ironworks, and from the Alabama Department of Archives and History, the Henry Ford Museum, and the Washington Navy Yard. The collection includes rare steam engines, forge cams and war materials manufactured at the CS Naval Gun Works at Selma, Alabama.
In the museum, the collections and displays feature both belt-driven machines and the nineteenth century iron-making tools and products. The museum preserves more than 10,000 historical relics, including collections from the Washington Navy Yard and the Henry Ford Museum, as well as rare iron-making machinery from the Tredegar Ironworks from Virginia. The displayed ironworks show how iron making developed during the period from the Civil war to the 1960s. By visiting the museum, visitors can understand how iron making in this area grows into the later Birmingham District. This site preserves and demonstrates thousands of artefacts from archaeological digs in this area, showing the previous human activities in Alabama from the end of the Civil war to the middle of the 20 centuries. On top of that, 16 slave cabins have also been unearthed on the site in more recent excavations. The museum is connected with the best preserved furnaces at Tannehill Ironworks by the Tram Track Hiking Trail. Various interactive displays are available in the museum, which can enable the visitors to go back into the historical environments in the nineteenth-century Alabama. Visitors can follow the timeline of industrial growth to trace how iron trade developed from the ancient Egypt to modern Fairfield Works in Birmingham. The Tannehill Learning Centre currently offers educational programmes and tours to school children in this region. Museum visitors are provided with field trips during the spring and fall.
The museum underwent a major renovation of its exhibits in 2004–05. The site also has a 30-seat theatre which plays a short video on the park's history. | 8 | Metallurgy |
It is an intermediate in the catabolism of aromatic amino acids such as phenylalanine and tyrosine.
4-Hydroxyphenylpyruvate (produced by transamination of tyrosine) is acted upon by the enzyme 4-hydroxyphenylpyruvate dioxygenase to yield homogentisate. If active and present, the enzyme homogentisate 1,2-dioxygenase further degrades homogentisic acid to yield 4-maleylacetoacetic acid. | 1 | Biochemistry |
Single-strand breaks (SSBs) occur when one strand of the DNA double helix experiences breakage of a single nucleotide accompanied by damaged 5’- and/or 3’-termini at this point. One common source of SSBs is due to oxidative attack by physiological reactive oxygen species (ROS) such as hydrogen peroxide. HO causes SSBs three times more frequently than double-strand breaks (DSBs). Alternative methods of SSB acquisition include direct disintegration of the oxidized sugar or through DNA base-excision repair (BER) of damaged bases. Additionally, cellular enzymes may perform erroneous activity leading to SSBs or DSBs by a variety of mechanisms. One such example would be when the cleavage complex formed by DNA topoisomerase 1 (TOP1) relaxes DNA during transcription and replication through the transient formation of a nick. While TOP1 normally reseals this nick shortly after, these cleavage complexes may collide with RNA or DNA polymerases or be proximal to other lesions, leading to TOP1-linked SSBs or TOP1-linked DSBs. | 1 | Biochemistry |
Oligosaccharides and polysaccharides are an important class of polymeric carbohydrates found in virtually all living entities. Their structural features make their nomenclature challenging and their roles in living systems make their nomenclature important. | 0 | Organic Chemistry |
Capillary penetration in porous media shares its dynamic mechanism with flow in hollow tubes, as both processes are resisted by viscous forces. Consequently, a common apparatus used to demonstrate the phenomenon is the capillary tube. When the lower end of a glass tube is placed in a liquid, such as water, a concave meniscus forms. Adhesion occurs between the fluid and the solid inner wall pulling the liquid column along until there is a sufficient mass of liquid for gravitational forces to overcome these intermolecular forces. The contact length (around the edge) between the top of the liquid column and the tube is proportional to the radius of the tube, while the weight of the liquid column is proportional to the square of the tube's radius. So, a narrow tube will draw a liquid column along further than a wider tube will, given that the inner water molecules cohere sufficiently to the outer ones. | 7 | Physical Chemistry |
DksA is a 17-kDa protein, its structure is similar to GreA and GreB, which are well-characterized transcriptional elongation factors. GreA and GreB bind directly to RNAP rather than DNA and act by inserting their N-terminal coiled-coil finger domain through the RNAP secondary channel. Two conserved acidic residues at the tip of the finger domain are necessary to induce RNAP's intrinsic ability to cleave backtracked RNA. DksA also possesses two acidic residues at its finger tip, but it does not induce nucleolytic cleavage activity. Instead, these residues are proposed to stabilize ppGpp binding to RNAP by mutual coordination of an Mg2+ ion that is crucial for polymerization. | 1 | Biochemistry |
Two effects which are closely related to pyroelectricity are ferroelectricity and piezoelectricity. Normally materials are very nearly electrically neutral on the macroscopic level. However, the positive and negative charges which make up the material are not necessarily distributed in a symmetric manner. If the sum of charge times distance for all elements of the basic cell does not equal zero the cell will have an electric dipole moment (a vector quantity). The dipole moment per unit volume is defined as the dielectric polarization. If this dipole moment changes with the effect of applied temperature changes, applied electric field, or applied pressure, the material is pyroelectric, ferroelectric, or piezoelectric, respectively.
The ferroelectric effect is exhibited by materials which possess an electric polarization in the absence of an externally applied electric field such that the polarization can be reversed if the electric field is reversed. Since all ferroelectric materials exhibit a spontaneous polarization, all ferroelectric materials are also pyroelectric (but not all pyroelectric materials are ferroelectric).
The piezoelectric effect is exhibited by crystals (such as quartz or ceramic) for which an electric voltage across the material appears when pressure is applied. Similar to pyroelectric effect, the phenomenon is due to the asymmetric structure of the crystals that allows ions to move more easily along one axis than the others. As pressure is applied, each side of the crystal takes on an opposite charge, resulting in a voltage drop across the crystal.
Pyroelectricity should not be confused with thermoelectricity: In a typical demonstration of pyroelectricity, the whole crystal is changed from one temperature to another, and the result is a temporary voltage across the crystal. In a typical demonstration of thermoelectricity, one part of the device is kept at one temperature and the other part at a different temperature, and the result is a permanent voltage across the device as long as there is a temperature difference. Both effects convert temperature change to electrical potential, but the pyroelectric effect converts temperature change over time into electrical potential, while the thermoelectric effect converts temperature change with position into electrical potential. | 7 | Physical Chemistry |
CIDNP (chemically induced dynamic nuclear polarization), often pronounced like "kidnip", is a nuclear magnetic resonance (NMR) technique that is used to study chemical reactions that involve radicals. It detects the non-Boltzmann (non-thermal) nuclear spin state distribution produced in these reactions as enhanced absorption or emission signals.
CIDNP was discovered in 1967 by Bargon and Fischer, and, independently, by Ward and Lawler. Early theories were based on dynamic nuclear polarisation (hence the name) using the Overhauser Effect. The subsequent experiments, however, have found that in many cases DNP fails to explain CIDNP polarization phase. In 1969 an alternative explanation which relies on the nuclear spins affecting the probability of a radical pair recombining or separating.
It is related to chemically induced dynamic electron polarization (CIDEP) insofar as the radical-pair mechanism explains both phenomena. | 7 | Physical Chemistry |
Phosphorus compounds are usually found as relatively insoluble phosphates in river water and, except in some exceptional circumstances, their origin is agriculture or human sewage. Phosphorus can encourage excessive growths of plants and algae and contribute to eutrophication. If a river discharges into a lake or reservoir phosphate can be mobilised year after year by natural processes. In the summer time, lakes stratify so that warm oxygen rich water floats on top of cold oxygen poor water. In the warm upper layers - the epilimnion- plants consume the available phosphate. As the plants die in the late summer they fall into the cool water layers underneath - the hypolimnion - and decompose. During winter turn-over, when a lake becomes fully mixed through the action of winds on a cooling body of water - the phosphates are spread throughout the lake again to feed a new generation of plants. This process is one of the principal causes of persistent algal blooms at some lakes. | 2 | Environmental Chemistry |
The ideal IR source should be monochromatic and tunable within a wide range of wavelength. According to T ∝d/λ, where T is the transmission coefficient, d the aperture diameter and λ is wavelength, the aperture-based NSOM/FTIR transmission is even more limited due to the long infrared wavelength; therefore, an intense IR source is needed to offset the low transmission through the optical fiber. The common bright IR light sources are the free-electron laser (FEL), color-center lasers, CO lasers and laser diodes. FEL is an excellent IR source, with 2–20 μm spectral range, short pulses (picosecond) and high average power (0.1-1 W). Alternately, a tabletop picosecond optical parametric oscillator (OPO) can be used which is less expensive, but has a limited tunability and a lower power-output. | 7 | Physical Chemistry |
For any given atom, there are quantum numbers that can specify the wavefunction of that atom. Using the hydrogen atom as an example, four quantum numbers are required to fully describe the state of the system. Quantum numbers that are eigenvalues of the operators that commute with the wavefunction to describe physical aspects of the system, and are called “good” numbers because of this. Once good quantum numbers have been found for a given atomic transition, the selection rules determine what changes in quantum numbers are allowed.
The electric dipole (E1) transition of a hydrogen atom can be described with the quantum numbers l (orbital angular momentum quantum number), m (magnetic quantum number), m (electron spin quantum number), and n (principal quantum number). When evaluating the effect of the electric dipole moment operator μ on the wavefunction of the system, we see that all values of the eigenvalue are 0, except for when the changes in the quantum numbers follow a specific pattern.
For example in the E1 transition, unless Δ l = ± 1, Δ m = 0 or ± 1, Δ m = 0, and Δ n = any integer, the equation above will yield a value equal to zero and the transition would be known as a “forbidden transition”. For example, this would occur for certain cases like when Δ l = 2. In this case, the transition would not be allowed and therefore would be much weaker than an allowed transition. These specific values for the changes in quantum numbers are known as the selection rules for the allowed transitions and are shown for common transitions in the table below: | 7 | Physical Chemistry |
In chemical kinetics, isosbestic points are used as reference points in the study of reaction rates, as the absorbance at those wavelengths remains constant throughout the whole reaction.
Isosbestic points are used in medicine in a laboratory technique called oximetry to determine hemoglobin concentration, regardless of its saturation. Oxyhaemoglobin and deoxyhaemoglobin have (not exclusively) isosbestic points at 586 nm and near 808 nm.
Isosbestic points are also used in clinical chemistry, as a quality assurance method, to verify the accuracy in the wavelength of a spectrophotometer. This is done by measuring the spectra of a standard solution at two different pH conditions (above and below the pK of the substance). The standards used include potassium dichromate (isosbestic points at 339 and 445 nm), bromothymol blue (325 and 498 nm) and congo red (541 nm). The wavelength of the isosbestic point determined does not depend on the concentration of the substance used, and so it becomes a very reliable reference.
One example of the use of isosbestic points in organic synthesis is seen in the photochemical A/D-corrin cycloisomerization ring closure reaction, which was the key step in the Eschenmoser / ETH Zürich vitamin B total synthesis. The isosbestic points provide proof for a direct conversion of the seco-corrin complex to the metal-free corrin ligand without intermediary or side products (within the detection limits of UV/VIS spectroscopy). | 7 | Physical Chemistry |
The rate of change of temperature with respect to pressure in a Joule–Thomson process (that is, at constant enthalpy ) is the Joule–Thomson (Kelvin) coefficient . This coefficient can be expressed in terms of the gas's specific volume , its heat capacity at constant pressure , and its coefficient of thermal expansion as:
See the below for the proof of this relation. The value of is typically expressed in °C/bar (SI units: K/Pa) and depends on the type of gas and on the temperature and pressure of the gas before expansion. Its pressure dependence is usually only a few percent for pressures up to 100 bar.
All real gases have an inversion point at which the value of changes sign. The temperature of this point, the Joule–Thomson inversion temperature, depends on the pressure of the gas before expansion.
In a gas expansion the pressure decreases, so the sign of is negative by definition. With that in mind, the following table explains when the Joule–Thomson effect cools or warms a real gas:
Helium and hydrogen are two gases whose Joule–Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 40 K, −233 °C for helium). Thus, helium and hydrogen warm when expanded at constant enthalpy at typical room temperatures. On the other hand, nitrogen and oxygen, the two most abundant gases in air, have inversion temperatures of 621 K (348 °C) and 764 K (491 °C) respectively: these gases can be cooled from room temperature by the Joule–Thomson effect.
For an ideal gas, is always equal to zero: ideal gases neither warm nor cool upon being expanded at constant enthalpy. | 7 | Physical Chemistry |
Stereospecific cis-hydroalumination is possible through the use of dialkylalanes. The most common reagent used for this purpose is di(isobutyl)aluminium hydride (DIBAL-H). Analogous to hydroboration reactions with RBH, hydroalumination with RAlH leads to the attachment of aluminium at the carbon less able to stabilize developing positive charge (anti-Markovnikov selectivity). Metalation of terminal alkynes is a significant side reaction that occurs under these conditions. If metalation is desired, tertiary amine complexes of DIBAL-H are useful.
The use of silyl acetylenes avoids the problem of competitive metalation of terminal alkenes. The stereoselectivity of hydroalumination can be altered through a change in solvent: tertiary amine solvents provide the cis alkenylalane and hydrocarbon solvents provide the trans isomer.
Lithium aluminium hydride hydroaluminates alkynes to afford trans alkenylalanes. In equation (7) hydride adds to the terminal carbon, which places the developing negative charge next to the stabilizing phenyl substituent. | 0 | Organic Chemistry |
The presence of VOCs in the air and in groundwater has prompted more studies. Several studies have been performed to measure the effects of dermal absorption of specific VOCs. Dermal exposure to VOCs like formaldehyde and toluene downregulate antimicrobial peptides on the skin like cathelicidin LL-37, human β-defensin 2 and 3. Xylene and formaldehyde worsen allergic inflammation in animal models. Toluene also increases the dysregulation of filaggrin: a key protein in dermal regulation. this was confirmed by immunofluorescence to confirm protein loss and western blotting to confirm mRNA loss. These experiments were done on human skin samples. Toluene exposure also decreased the water in the trans-epidermal layer allowing for vulnerability in the skin's layers. | 0 | Organic Chemistry |
A partially coherent interphase boundary is an intermediate type of IPB that lies between the completely coherent and non-coherent IPBs. In this type of boundary, there is a partial match between the atomic arrangements of the particle and the matrix, but not a perfect match. As a result, coherency strains are partially relieved, but not completely eliminated. The periodic introduction of dislocations along the boundary plays a key role in partially relieving the coherency strains. These dislocations act as periodic defects that accommodate the lattice mismatch between the particle and the matrix. The dislocations can be introduced during the precipitation process or during subsequent annealing treatments. | 8 | Metallurgy |
Pseudin is a peptide derived from Pseudis paradoxa. Pseudins have some antimicrobial function.
There are several different forms:
* pseudin-1
* pseudin-2 -- has been proposed as a treatment for type 2 diabetes.
* pseudin-4 | 1 | Biochemistry |
Like other straight-line forms of the Michaelis–Menten equation, the Eadie–Hofstee plot was used historically for rapid evaluation of the parameters and , but has been largely superseded by nonlinear regression methods that are significantly more accurate when properly weighted and no longer computationally inaccessible. | 1 | Biochemistry |
* 1988 Alexander von Humboldt fellowship of Germany: Research with Jürgen Martens at the University of Oldenburg and Hans Brückner University of Giessen.
* 1992 European Economic Community Fellowship: Research with Peter Shewry University of Bristol
* 1993 Fellow of the Royal Society of Chemistry
* 2001 Fellow of the National Academy of Sciences India | 3 | Analytical Chemistry |
By symmetry of second derivatives, for any "well-behaved" (non-pathological) function , we have
Hence, in a simply-connected region R of the xy-plane, where are independent, a differential form
is an exact differential if and only if the equation
holds. If it is an exact differential so and , then is a differentiable (smoothly continuous) function along and , so . If holds, then and are differentiable (again, smoothly continuous) functions along and respectively, and is only the case.
For three dimensions, in a simply-connected region R of the xyz-coordinate system, by a similar reason, a differential
is an exact differential if and only if between the functions A, B and C there exist the relations
These conditions are equivalent to the following sentence: If G is the graph of this vector valued function then for all tangent vectors X,Y of the surface G then s(X, Y) = 0 with s the symplectic form.
These conditions, which are easy to generalize, arise from the independence of the order of differentiations in the calculation of the second derivatives. So, in order for a differential dQ, that is a function of four variables, to be an exact differential, there are six conditions (the combination ) to satisfy. | 7 | Physical Chemistry |
If the spin–orbit interaction dominates over the effect of the external magnetic field, and are not separately conserved, only the total angular momentum is. The spin and orbital angular momentum vectors can be thought of as precessing about the (fixed) total angular momentum vector . The (time-)"averaged" spin vector is then the projection of the spin onto the direction of :
and for the (time-)"averaged" orbital vector:
Thus,
Using and squaring both sides, we get
and:
using and squaring both sides, we get
Combining everything and taking , we obtain the magnetic potential energy of the atom in the applied external magnetic field,
where the quantity in square brackets is the Landé g-factor g of the atom ( and ) and is the z-component of the total angular momentum.
For a single electron above filled shells and , the Landé g-factor can be simplified into:
Taking to be the perturbation, the Zeeman correction to the energy is | 7 | Physical Chemistry |
The exact mechanism for the reduction is unknown, although there are two hypothesized pathways. The first pathway is the transferral of electrons from one electron reduced ETF one at a time to the lower potential FAD center. One electron is transferred from the reduced FAD to the iron cluster, resulting in a two electron reduced state with one electron each on the FAD and cluster domains. Then, the bound ubiquinone is reduced to ubiquinol, at least transiently forming the singly reduced semiubiquinone. The second pathway involves the donation of electrons from ETF to the iron cluster, followed by internal transitions between the two electron centers. After equilibration, the rest of the pathway follows as above. | 1 | Biochemistry |
Stephen C. Harrison is professor of biological chemistry and molecular pharmacology, professor of pediatrics, and director of the Center for Molecular and Cellular Dynamics of Harvard Medical School, head of the Laboratory of Molecular Medicine at Boston Children's Hospital, and investigator of the Howard Hughes Medical Institute. | 1 | Biochemistry |
Morpholinos are synthetic molecules that are the product of a redesign of natural nucleic acid structure. Usually 25 bases in length, they bind to complementary sequences of RNA or single-stranded DNA by standard nucleic acid base-pairing. In terms of structure, the difference between Morpholinos and DNA is that, while Morpholinos have standard nucleic acid bases, those bases are bound to methylenemorpholine rings linked through phosphorodiamidate groups instead of phosphates. The figure compares the structures of the two strands depicted there, one of RNA and the other of a Morpholino. Replacement of anionic phosphates with the uncharged phosphorodiamidate groups eliminates ionization in the usual physiological pH range, so Morpholinos in organisms or cells are uncharged molecules. The entire backbone of a Morpholino is made from these modified subunits. | 1 | Biochemistry |
Highly favourable binding of a substrate at a non-reactive site will force the reactive site of the substrate to be more reactive by putting it in a very unfavourable position. This effect was observed in orotidine 5‘-phosphate decarboxylase. This can occur by positioning a charged amino acid group next to the charged substrate thus destabilizing it, thus making the reaction occur faster. Furthermore, the substrate is put into an optimal position by the enzyme for the reaction to occur, thus decreasing the entropy greatly.
A corollary of the effect is to explain the existence of one-way enzymes that are much more effective catalysts for one direction of reaction than the other. For example, the limiting rate in the forward direction of the reaction catalyzed by methionine adenosyltransferase is about 2 × 10 times higher than it is for the reverse reaction. This concept is frequently misunderstood: it does not imply any violation of thermodynamic principles. It is a kinetic effect, not a thermodynamic one, and the reaction always proceeds toward equilibrium, regardless of where the process starts. And when it is at equilibrium the rate is always zero. | 1 | Biochemistry |
The noble metals are siderophiles (iron-lovers). They tend to sink into the Earth's core because they dissolve readily in iron either as solid solutions or in the molten state. Most siderophile elements have practically no affinity whatsoever for oxygen: indeed, oxides of gold are thermodynamically unstable with respect to the elements.
Copper, silver, gold, and the six platinum group metals are the only native metals that occur naturally in relatively large amounts. | 8 | Metallurgy |
Organic Syntheses is a peer-reviewed scientific journal that was established in 1921. It publishes detailed and checked procedures for the synthesis of organic compounds. A unique feature of the review process is that all of the data and experiments reported in an article must be successfully repeated in the laboratory of a member of the editorial board as a check for reproducibility prior to publication. The journal is published by Organic Syntheses, Inc., a non-profit corporation. An annual print version is published by John Wiley & Sons on behalf of Organic Syntheses, Inc. | 0 | Organic Chemistry |
Consider the two equilibria, in aqueous solution, between the copper(II) ion, Cu and ethylenediamine (en) on the one hand and methylamine, MeNH on the other.
In the first reaction the bidentate ligand ethylene diamine forms a chelate complex with the copper ion. Chelation results in the formation of a five-membered ring. In the second reaction the bidentate ligand is replaced by two monodentate methylamine ligands of approximately the same donor power, meaning that the enthalpy of formation of Cu–N bonds is approximately the same in the two reactions. Under conditions of equal copper concentrations and when the concentration of methylamine is twice the concentration of ethylenediamine, the concentration of the bidentate complex will be greater than the concentration of the complex with 2 monodentate ligands. The effect increases with the number of chelate rings so the concentration of the EDTA complex, which has six chelate rings, is much higher than a corresponding complex with two monodentate nitrogen donor ligands and four monodentate carboxylate ligands. Thus, the phenomenon of the chelate effect is a firmly established empirical fact: under comparable conditions, the concentration of a chelate complex will be higher than the concentration of an analogous complex with monodentate ligands.
The thermodynamic approach to explaining the chelate effect considers the equilibrium constant for the reaction: the larger the equilibrium constant, the higher the concentration of the complex.
When the analytical concentration of methylamine is twice that of ethylenediamine and the concentration of copper is the same in both reactions, the concentration [Cu(en)] is much higher than the concentration [Cu(MeNH)] because
The difference between the two stability constants is mainly due to the difference in the standard entropy change, ΔS. In the reaction with the chelating ligand there are two particles on the left and one on the right, whereas in equation with the monodentate ligand there are three particles on the left and one on the right. This means that less entropy of disorder is lost when the chelate complex is formed than when the complex with monodentate ligands is formed. This is one of the factors contributing to the entropy difference. Other factors include solvation changes and ring formation. Some experimental data to illustrate the effect are shown in the following table.
These data show that the standard enthalpy changes are indeed approximately equal for the two reactions and that the main reason why the chelate complex is so much more stable is that the standard entropy term is much less unfavourable, indeed, it is favourable in this instance. In general it is difficult to account precisely for thermodynamic values in terms of changes in solution at the molecular level, but it is clear that the chelate effect is predominantly an effect of entropy. Other explanations, including that of Schwarzenbach, are discussed in Greenwood and Earnshaw.
The chelate effect increases as the number of chelate rings increases. For example, the complex [Ni(dien))] is more stable than the complex [Ni(en))]; both complexes are octahedral with six nitrogen atoms around the nickel ion, but dien (diethylenetriamine, 1,4,7-triazaheptane) is a tridentate ligand and en is bidentate. The number of chelate rings is one less than the number of donor atoms in the ligand. EDTA (ethylenediaminetetracetic acid) has six donor atoms so it forms very strong complexes with five chelate rings. Ligands such as DTPA, which have eight donor atoms are used to form complexes with large metal ions such as lanthanide or actinide ions which usually form 8- or 9-coordinate complexes.
5-membered and 6-membered chelate rings give the most stable complexes. 4-membered rings are subject to internal strain because of the small inter-bond angle is the ring. The chelate effect is also reduced with 7- and 8- membered rings, because the larger rings are less rigid, so less entropy is lost in forming them. | 7 | Physical Chemistry |
* There is a monument of Zelinsky in Elektrostal city. It was opened in July 2013 in front of the entrance of the Elektrostal Chemical and Mechanical Plant OJSC. | 0 | Organic Chemistry |
One of the classic structures of resorcinarenes and pyrogallolarenes is shown below. Because of the phenol group, some hydrogen bonds are foromed among the molecules. Sometimes, the binding ratio of the host and guest could reach 2 : 1. | 6 | Supramolecular Chemistry |
In protein folding, a native contact is a contact between the side chains of two amino acids that are not neighboring in the amino acid sequence (i.e., they are more than four residues apart in the primary sequence in order to remove trivial i to i+4 contacts along alpha helices) but are spatially close in the protein's native state tertiary structure. The fraction of native contacts reproduced in a particular structure is often used as a reaction coordinate for measuring the deviation from the native state of structures produced during molecular dynamics simulations or in benchmarks of protein structure prediction methods.
The contact order is a measure of the locality of a protein's native contacts; that is, the sequence distance between amino acids that form contacts. Proteins with low contact order are thought to fold faster and some may be candidates for downhill folding. | 1 | Biochemistry |
In structural biology, a heterologous association is a binding mode between the protomers of a protein structure. In a heterologous association, each protomer contributes a different set of residues to the binding interface. In contrast, two protomers form an isologous association when they contribute the same set of residues to the protomer-protomer interface. | 1 | Biochemistry |
In 2021, a study proposed that L1 elements may be responsible for potential endogenisation of the SARS-CoV-2 genome in Huh7 mutant cancer cells, which would possibly explain why some patients test PCR positive for SARS-CoV-2 even after clearance of the virus. These results however have been criticized as not reproducible, misleading and infrequent or artefactual. | 1 | Biochemistry |
FISH can be used to study the evolution of chromosomes. Species that are related have similar chromosomes. This homology can be detected by gene or genome sequencing but also by FISH. For instance, human and chimpanzee chromosomes are very similar and FISH can demonstrate that two chimpanzee chromosomes fused to result in one human chromosome. Similarly, species that are more distantly related, have similar chromosomes but with increasing distance chromosomes tend to break and fuse and thus result in mosaic chromosomes. This can be impressively demonstrated by FISH (see figure). | 1 | Biochemistry |
In 1941, Tisza immigrated to the United States and joined the faculty at the Massachusetts Institute of Technology. His research areas included theoretical physics and the history and philosophy of science, specifically on the foundation of thermodynamics and quantum mechanics. He taught at MIT until 1973. | 7 | Physical Chemistry |
Pectins are a family of complex polysaccharides that contain 1,4-linked α--galactosyl uronic acid residues. They are present in most primary cell walls and in the nonwoody parts of terrestrial plants. | 0 | Organic Chemistry |
The size of materials being processed in an operation is very important. Having oversize material being conveyed will cause damage to equipment and slow down production. Particle-size analysis also helps the effectiveness of SAG Mills when crushing material.
In the building industry, the particle size can directly affect the strength of the final material, as it observed for cement. Two of the most used techniques used for the particle size characterization of minerals are sieving and laser diffraction. These techniques are faster and cheaper compared to image-based techniques. | 3 | Analytical Chemistry |
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