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*Nucleobase analogues
**Thiopurines such as thioguanine are used to treat acute leukemias and remissions in acute granulocytic leukemias.
***Azathioprine is the main immunosuppressive cytotoxic substance. A prodrug, it is widely used in transplantation to control rejection reactions. It is nonenzymatically cleaved to mercaptopurine, a purine analogue that inhibits DNA synthesis. By preventing the clonal expansion of lymphocytes in the induction phase of the immune response, it affects both cell immunity and humoral immunity. It also successfully suppresses autoimmunity.
***Mercaptopurine
***Thioguanine
*Nucleoside analogues
**Clofarabine
**Pentostatin and cladribine are adenosine analogs that are used primarily to treat hairy cell leukemia.
*Nucleotide analogues
**Fludarabine inhibits multiple DNA polymerases, DNA primase, and DNA ligase I, and is S phase-specific (since these enzymes are highly active during DNA replication). | 1 | Biochemistry |
Nuclease protection assay is a laboratory technique used in biochemistry and genetics to identify individual RNA molecules in a heterogeneous RNA sample extracted from cells. The technique can identify one or more RNA molecules of known sequence even at low total concentration. The extracted RNA is first mixed with antisense RNA or DNA probes that are complementary to the sequence or sequences of interest and the complementary strands are hybridized to form double-stranded RNA (or a DNA-RNA hybrid). The mixture is then exposed to ribonucleases that specifically cleave only single-stranded RNA but have no activity against double-stranded RNA. When the reaction runs to completion, susceptible RNA regions are degraded to very short oligomers or to individual nucleotides; the surviving RNA fragments are those that were complementary to the added antisense strand and thus contained the sequence of interest. | 1 | Biochemistry |
Aldol reactions are commonly used in organic chemistry to form carbon-to-carbon bonds. The aldehyde-alcohol motif common to the reaction product is ubiquitous to synthetic chemistry and natural products. The reaction utilizes two carbonyl compounds to generate a β-hydroxy carbonyl. Catalysis is always necessary because the barrier of activation between kinetic products and starting materials makes the dynamic reversible process too slow. Catalysts that have been successfully employed include enzymatic aldolase and AlO based systems. | 6 | Supramolecular Chemistry |
Fluorine is estimated to be the 13th-most abundant element in Earth's crust and is widely dispersed in nature, entirely in the form of fluorides. The vast majority is held in mineral deposits, the most commercially important of which is fluorite (CaF). Natural weathering of some kinds of rocks, as well as human activities, releases fluorides into the biosphere through what is sometimes called the fluorine cycle. | 1 | Biochemistry |
The mechanism of nucleophilic epoxidation begins with conjugate addition of the peroxide (or other O-nucleophilic species) to the enone. Metal ions or conjugate acids present in solution coordinate both the peroxide oxygen and the enolate oxygen. Attack of the enolate on the peroxide oxygen generates the epoxide product and releases a leaving group.
Because the process is stepwise, the configuration of the carbon-carbon double bond is not necessarily preserved. Both cis and trans enones form trans epoxides under nearly all nucleophilic epoxidation conditions (methods employing lanthanide-BINOL systems are the exception). | 0 | Organic Chemistry |
The components of a capillary electrochromatograph are a sample vial, source and destination vials, a packed capillary, electrodes, a high voltage power supply, a detector, and a data output and handling device. The source vial, destination vial and capillary are filled with an electrolyte such as an aqueous buffer solution. The capillary is packed with stationary phase. To introduce the sample, the capillary inlet is placed into a vial containing the sample and then returned to the source vial (sample is introduced into the capillary via capillary action, pressure, or siphoning). The migration of the analytes is then initiated by an electric field that is applied between the source and destination vials and is supplied to the electrodes by the high-voltage power supply. The analytes separate as they migrate due to their electrophoretic mobility, and are detected near the outlet end of the capillary. The output of the detector is sent to a data output and handling device such as an integrator or computer. The data is then displayed as an electropherogram, which reports detector response as a function of time. Separated chemical compounds appear as peaks with different migration times in an electropherogram. | 1 | Biochemistry |
The hallmark of linear azol(in)e-containing peptide (LAP) biosynthesis is the formation of azol(in)e heterocycles from the nucleophilic amino acids serine, threonine, or cysteine. This is accomplished by three enzymes referred to as the B, C, and D proteins; the precursor peptide is referred to as the A protein, as in other classes.
The C protein is mainly involved in leader peptide recognition and binding and is sometimes called a scaffolding protein. The D protein is an ATP-dependent cyclodehydratase that catalyzes the cyclodehydration reaction, resulting in formation of an azoline ring. This occurs by direct activation of the amide backbone carbonyl with ATP, resulting in stoichiometric ATP consumption. The C and D proteins are occasionally present as a single, fused protein, as is the case for trunkamide biosynthesis. The B protein is a flavin mononucleotide (FMN)-dependent dehydrogenase which oxidizes certain azoline rings into azoles.
The B protein is typically referred to as the dehydrogenase; the C and D proteins together form the cyclodehydratase, although the D protein alone performs the cyclodehydration reaction. Early work on microcin B17 adopted a different nomenclature for these proteins, but a recent consensus has been adopted by the field as described above. | 1 | Biochemistry |
For effective range see Buffer capacity, above. Also see Good's buffers for the historic design principles and favourable properties of these buffer substances in biochemical applications. | 7 | Physical Chemistry |
An antichlor is a substance used to decompose residual hypochlorite or chlorine after chlorine-based bleaching, in order to prevent ongoing reactions with, and therefore damage to, the material that has been bleached. Sodium bisulfite is an example of an antichlor. Historically, sodium bisulfite has been used in the textile industry, cosmetic industry, food industry, and more.
Antichlors are very useful in the textile industry because bleaching of compounds using chlorine is a standard practice. However, the use of sodium bisulfite in the decomposition of excess hypochlorite can lead to harmful byproducts when it comes into contact with water at the concentrations present for industrial use. Contact with these dangerous byproducts or even strong concentrations of sodium bisulfite can be harmful to the environment and contact with the skin. Strong concentrations of these compounds can contaminate ecosystems, harm animals, and cause contact dermatitis with industrial workers. The concentrations that could result in these outcomes are much stronger than the concentrations discussed in the cosmetic and food industry. | 0 | Organic Chemistry |
An activated complex with high symmetry can decrease the accuracy of rate expressions. Error can arise from introducing symmetry numbers into the rotational partition functions for the reactants and activated complexes. To reduce errors, symmetry numbers can by omitted by multiplying the rate expression by a statistical factor:where the statistical factor is the number of equivalent activated complexes that can be formed, and the Q are the partition functions from the symmetry numbers that have been omitted.
The activated complex is a collection of molecules that forms and then explodes along a particular internal normal coordinate. Ordinary molecules have three translational degrees of freedom, and their properties are similar to activated complexes. However, activated complexed have an extra degree of translation associated with their approach to the energy barrier, crossing it, and then dissociating. | 7 | Physical Chemistry |
There is enormous amount of catalytic processes involving β-alkyl elimination that are synthetically useful. β-alkyl elimination in this case, however, is often considered as an alternative way of C–C bond cleavage while oxidative addition is the direct way. One of the examples is β-alkyl elimination of tert-alcoholates which can generate from either addition of an organometallic reagent or ligand exchange. The consequent organometallic species can undergo various downstream reactivities (reductive elimination, carbonyl insertion, etc.) to generate useful building blocks.
In addition to ring strain, aromaticity-driven β-Me elimination can be effectively employed to dealkylate steroid derivatives and some other cyclohexyl compounds. | 0 | Organic Chemistry |
Yoon Nung-min (윤능민 尹能民, November 21, 1927 – April 1, 2009) is a South Korean chemist, known for his research in organic chemistry, specializing in metal hydrides.
He received his B.A. at Seoul National University in chemistry in 1951 and went on to complete his Ph.D. at Purdue University, under Herbert Charles Brown. He was a postdoc at Purdue, then a researcher for the Ministry of National Defence. He then became an associate professor at the Catholic University of Korea. He later took up full professorship at Sogang University, a position he would hold until his retirement. He served as the president of the Korean Chemical Society in 1989, and was elected a member of the National Academy of Sciences of the Republic of Korea in 2005. He was Professor Emeritus at Sogang University until his death in 2009.
He was a proficient researcher; he published 110 papers and developed reagents which became widely used in both organic and inorganic chemistry. He also discovered new methods of generating free radicals and found new applications. He surprised the Korean chemistry community by publishing a substantial portion of his research as the sole author shortly before his retirement.
He has also been active as an educator. He taught 14 doctorate students, and 56 masters students.
He was awarded the Order of Civil Merit (Mogryeon Medal) in 1983, Korea National Academy of Sciences Award in 1990 and the Korea Science Prize (Science) in 1993. | 0 | Organic Chemistry |
Homoserine is produced from aspartate via aspartate-4-semialdehyde, which is produced from β-phosphoaspartate. By the action of homoserine dehydrogenases, the semialdehyde is converted to homoserine.
-Homoserine is substrate for homoserine kinase, yielding phosphohomoserine (homoserine-phosphate), which is converted to by threonine synthase to yield -threonine.
Homoserine is converted to O-succinyl homoserine by homoserine O-succinyltransferase, a precursor to -methionine.
Homoserine allosterically inhibits aspartate kinase and glutamate dehydrogenase. Glutamate dehydrogenase reversibly converts glutamate to α-ketoglutarate and α-ketoglutarate coverts to oxaloacetate through the citric cycle. Threonine acts as another allosteric inhibitor of aspartate kinase and homoserine dehydrogenase, but it is a competitive inhibitor of homoserine kinase. | 1 | Biochemistry |
Contrary to bacteria and fungi, most plant metabolic pathways are not grouped into biosynthetic gene clusters, but instead are scattered as individual genes. Some exceptions have been discovered: steroidal glycoalkaloids in Solanum, polyketides in Pooideae, benzoxazinoids in Zea mays, triterpenes in Avena sativa, Cucurbitaceae, Arabidopsis, and momilactone diterpenes in Oryza sativa. | 1 | Biochemistry |
In an endothermic reaction or system, energy is taken from the surroundings in the course of the reaction, usually driven by a favorable entropy increase in the system. An example of an endothermic reaction is a first aid cold pack, in which the reaction of two chemicals, or dissolving of one in another, requires calories from the surroundings, and the reaction cools the pouch and surroundings by absorbing heat from them.
Photosynthesis, the process that allows plants to convert carbon dioxide and water to sugar and oxygen, is an endothermic process: plants absorb radiant energy from the sun and use it in an endothermic, otherwise non-spontaneous process. The chemical energy stored can be freed by the inverse (spontaneous) process: combustion of sugar, which gives carbon dioxide, water and heat (radiant energy). | 7 | Physical Chemistry |
According to the location of the rotaxanes units, polyrotaxanes can be mainly divided into two types: main chain polyrotaxanes, in which the rotaxane units locate on the main chain (axis), and side chain polyrotaxanes, in which the rotaxane units are located on the side chain. Corresponding polypseudorotaxanes can also be divided based on the same principle: main chain polypseudorotaxnes or side chain polypseudorotaxanes, in which there is no stopper at the ends.
In both main chain polyrotaxanes or side chain polyrotaxanes, the unique feature from other polymers is the potential for different motion of the ring unit relative to the string units. Because the shape and location of the assembly are capable of showing different responses to changes in temperature, pH or other environment conditions, polyrotaxanes have many distinctive properties. | 6 | Supramolecular Chemistry |
In addition to M–M single bonds, metal pairs can be linked by double, triple, quadruple, and in a few cases, quintuple bonds. Isolable complexes with multiple bonds are most common among the transition metals in the middle of the d-block, such as rhenium, tungsten, technetium, molybdenum and chromium. Typical the coligands are π-donors, not π-acceptors. Well studied examples are the tetraacetates, such as dimolybdenum tetraacetate (quadruple bond) and dirhodium tetraacetate (single bond). Mixed-valence druthenium tetraacetates have fractional M–M bond orders, i.e., 2.5 for [Ru(OAc)(HO)].
The complexes NbX(SR) adopt a face-sharing bioctahedral structures (X = Cl, Br; SR = thioether). As dimers of Nb(III), they feature double metal–metal bonds, the maximum possible for a pair of metals with d configuration.
Hexa(tert-butoxy)ditungsten(III) is a well studied example of a complex with a metal–metal triple bond. | 7 | Physical Chemistry |
The identity of the repeat units (monomer residues, also known as "mers") comprising a polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. A polymer which contains only a single type of repeat unit is known as a homopolymer, while a polymer containing two or more types of repeat units is known as a copolymer. A terpolymer is a copolymer which contains three types of repeat units.
Polystyrene is composed only of styrene-based repeat units, and is classified as a homopolymer. Polyethylene terephthalate, even though produced from two different monomers (ethylene glycol and terephthalic acid), is usually regarded as a homopolymer because only one type of repeat unit is formed. Ethylene-vinyl acetate contains more than one variety of repeat unit and is a copolymer. Some biological polymers are composed of a variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of four types of nucleotide subunits.
A polymer containing ionizable subunits (e.g., pendant carboxylic groups) is known as a polyelectrolyte or ionomer, when the fraction of ionizable units is large or small respectively. | 7 | Physical Chemistry |
The bioactive structures (native or 3D conformation or shape) of the isolated protein molecules do not undergo any significant conformational changes. Thus, active metal cofactor-containing proteins can be isolated reproducibly in the same fractions after a PAGE run. A shifting peak in the respective electropherogram indicates that the standardized time of gel polymerization (69 hr, RT) is not implemented in a PAGE experiment. A lower deviation of the standardized polymerization time (< 69 hr) stands for incomplete polymerization, and thus, for inherent instability due to gel softening during the cross-linking of polymers as the material reaches swelling equilibrium, whereas exceeding this time limit (> 69 hr) is an indicator of gel aging (cf. fig. Electropherogram). The phenomenon of gel aging is closely connected to long-term viscosity decrease of aqueous polyacrylamide solutions and increased swelling of hydrogels.
Under standard conditions, metalloproteins with different molecular mass ranges and isoelectric points have been recovered in biologically active form at a quantitative yield of more than 95%. By preparative SDS-PAGE standard proteins (cytochrome c, aldolase, ovalbumin and bovine serum albumin) with molecular masses of 14–66 ku can be recovered with an average yield of about 73.6%. Preparative isotachophoresis (ITP) is applied for isolating palladium-containing proteins with molecular masses of 362 ku (recovery: 67%) and 158 ku (recovery: 97%). | 3 | Analytical Chemistry |
Plasma level monitoring of vancomycin is necessary due to the drug's biexponential distribution, intermediate hydrophilicity, and potential for ototoxicity and nephrotoxicity, especially in populations with poor renal function and/or increased propensity to bacterial infection. Vancomycin activity is considered to be time-dependent; that is, antimicrobial activity depends on the duration that the serum drug concentration exceeds the minimum inhibitory concentration of the target organism. Thus, peak serum levels have not been shown to correlate with efficacy or toxicity; indeed, concentration monitoring is unnecessary in most cases. Circumstances in which therapeutic drug monitoring is warranted include: patients receiving concomitant aminoglycoside therapy, patients with (potentially) altered pharmacokinetic parameters, patients on haemodialysis, patients administered high-dose or prolonged treatment, and patients with impaired renal function. In such cases, trough concentrations are measured.
Therapeutic drug monitoring is also used for dose optimization of vancomycin in treating children.
Target ranges for serum vancomycin concentrations have changed over the years. Early authors suggested peak levels of 30 to 40 mg/L and trough levels of 5 to 10 mg/L,
but current recommendations are that peak levels need not be measured and that trough levels of 10 to 15 mg/L or 15 to 20 mg/L, depending on the nature of the infection and the specific needs of the patient, may be appropriate. Using measured vancomycin concentrations to calculate doses optimizes therapy in patients with augmented renal clearance. | 0 | Organic Chemistry |
Some metal alkyls feature agostic interactions between a C-H bond on the alkyl group and the metal. Such interactions are especially common for complexes of early transition metals in their highest oxidation states.
One determinant of the kinetic stability of metal-alkyl complexes is the presence of hydrogen at the position beta to the metal. If such hydrogens are present and if the metal center is coordinatively unsaturated, then the complex can undergo beta-hydride elimination to form a metal-alkene complex:
These conversions are assumed to proceed via the intermediacy of agostic interactions. | 0 | Organic Chemistry |
Inductively coupled plasma atomic emission spectroscopy (ICP-AES) uses an inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element.
Advantages of ICP-AES are the excellent limit of detection and linear dynamic range, multi-element capability, low chemical interference and a stable and reproducible signal. Disadvantages are spectral interferences (many emission lines), cost and operating expense and the fact that samples typically must be in a liquid solution.
Inductively coupled plasma (ICP) source of the emission consists of an induction coil and plasma. An induction coil is a coil of wire that has an alternating current flowing through it. This current induces a magnetic field inside the coil, coupling a great deal of energy to plasma contained in a quartz tube inside the coil. Plasma is a collection of charged particles (cations and electrons) capable, by virtue of their charge, of interacting with a magnetic field. The plasmas used in atomic emissions are formed by ionizing a flowing stream of argon gas. Plasma's high-temperature results from resistive heating as the charged particles move through the gas. Because plasmas operate at much higher temperatures than flames, they provide better atomization and a higher population of excited states.
The predominant form of sample matrix in ICP-AES today is a liquid sample: acidified water or solids digested into aqueous forms. Liquid samples are pumped into the nebulizer and sample chamber via a peristaltic pump. Then the samples pass through a nebulizer that creates a fine mist of liquid particles. Larger water droplets condense on the sides of the spray chamber and are removed via the drain, while finer water droplets move with the argon flow and enter the plasma. With plasma emission, it is possible to analyze solid samples directly. These procedures include incorporating electrothermal vaporization, laser and spark ablation, and glow-discharge vaporization. | 3 | Analytical Chemistry |
In organic chemistry, umpolung () or polarity inversion is the chemical modification of a functional group with the aim of the reversal of polarity of that group. This modification allows secondary reactions of this functional group that would otherwise not be possible. The concept was introduced by D. Seebach (hence the German word for reversed polarity) and E.J. Corey. Polarity analysis during retrosynthetic analysis tells a chemist when umpolung tactics are required to synthesize a target molecule. | 0 | Organic Chemistry |
For example, the skeletal formula of hexane (top) is shown below. The carbon atom labeled C appears to have only one bond, so there must also be three hydrogens bonded to it, in order to make its total number of bonds four. The carbon atom labelled C has two bonds to other carbons and is therefore bonded to two hydrogen atoms as well. A Lewis structure (middle) and ball-and-stick model (bottom) of the actual molecular structure of hexane, as determined by X-ray crystallography, are shown for comparison.
It does not matter which end of the chain one starts numbering from, as long as consistency is maintained when drawing diagrams. The condensed formula or the IUPAC name will confirm the orientation. Some molecules will become familiar regardless of the orientation. | 0 | Organic Chemistry |
β-catenin has also been implicated in regulation of cell fates through asymmetric cell division in the model organism C. elegans. Similarly to the Xenopus oocytes, this is essentially the result of non-equal distribution of Dsh, Frizzled, axin and APC in the cytoplasm of the mother cell. | 1 | Biochemistry |
;closo-
:The boron atoms lie on each vertex of the octahedron and are sp hybridized. One sp-hybrid radiates away from the structure forming the bond with the hydrogen atom. The other sp-hybrid radiates into the center of the structure forming a large bonding molecular orbital at the center of the cluster. The remaining two unhybridized orbitals lie along the tangent of the sphere like structure creating more bonding and antibonding orbitals between the boron vertices. The orbital diagram breaks down as follows:
::The 18 framework molecular orbitals, (MOs), derived from the 18 boron atomic orbitals are:
::*1 bonding MO at the center of the cluster and 5 antibonding MOs from the 6 sp-radial hybrid orbitals
::*6 bonding MOs and 6 antibonding MOs from the 12 tangential p-orbitals.
:The total skeletal bonding orbitals is therefore 7, i.e. . | 7 | Physical Chemistry |
Unsaponifiables are components of a fatty substance (oil, fat, wax) that fail to form soaps when treated with alkali and remain insoluble in water but soluble in organic solvents. For instance, typical soybean oil contains, by weight, 1.5 – 2.5% of unsaponifiable matter. Unsaponifiables include nonvolatile components : alkanes, sterols, triterpenes, fatty alcohols, tocopherols and carotenoids as well as those that mainly result from the saponification of fatty esters (sterols esters, wax esters, tocopherols esters, ...). This fraction may also contain environmental contaminants and residues of plasticizers, pesticides, mineral oil hydrocarbons and aromatics.
Unsaponifiable constituents are an important consideration when selecting oil mixtures for the manufacture of soaps. Unsaponifiables can be beneficial to a soap formula because they may have properties such as moisturization, conditioning, antioxidant, texturing etc. On the other hand, when proportion of unsaponifiables is too high (> 3%), or the specific unsaponifiables present do not provide significant benefits, a defective or inferior soap product can result. For example, shark oil is not suitable for soap making as it may contain more than 10% of unsaponifiable matter.
For edible oils, the tolerated limit of unsaponifiable matter is 1.5% (olive, refined soybean), while inferior quality crude or pomace oil could reach 3%.
Determination of unsaponifiables involves a saponification step of the sample followed by extraction of the unsaponifiable using an organic solvent (i.e. diethyl ether). Official methods for animal and vegetable fats and oils are described by ASTM D1065 - 18, ISO 3596: 2000 or 18609: 2000, AOCS method Ca 6a-40. | 3 | Analytical Chemistry |
Electron diffraction in a TEM exploits controlled electron beams using electron optics. Different types of diffraction experiments, for instance Figure 9, provide information such as lattice constants, symmetries, and sometimes to solve an unknown crystal structure.
It is common to combine it with other methods, for instance images using selected diffraction beams, high-resolution images showing the atomic structure, chemical analysis through energy-dispersive x-ray spectroscopy, investigations of electronic structure and bonding through electron energy loss spectroscopy, and studies of the electrostatic potential through electron holography; this list is not exhaustive. Compared to x-ray crystallography, TEM analysis is significantly more localized and can be used to obtain information from tens of thousands of atoms to just a few or even single atoms. | 7 | Physical Chemistry |
The empirical laws that led to the derivation of the ideal gas law were discovered with experiments that changed only 2 state variables of the gas and kept every other one constant.
All the possible gas laws that could have been discovered with this kind of setup are:
* Boyle's law ()
* Charles's law ()
* Avogadro's law ()
* Gay-Lussac's law ()
where P stands for pressure, V for volume, N for number of particles in the gas and T for temperature; where are constants in this context because of each equation requiring only the parameters explicitly noted in them changing.
To derive the ideal gas law one does not need to know all 6 formulas, one can just know 3 and with those derive the rest or just one more to be able to get the ideal gas law, which needs 4.
Since each formula only holds when only the state variables involved in said formula change while the others (which are a property of the gas but are not explicitly noted in said formula) remain constant, we cannot simply use algebra and directly combine them all. This is why: Boyle did his experiments while keeping N and T constant and this must be taken into account (in this same way, every experiment kept some parameter as constant and this must be taken into account for the derivation).
Keeping this in mind, to carry the derivation on correctly, one must imagine the gas being altered by one process at a time (as it was done in the experiments). The derivation using 4 formulas can look like this:
at first the gas has parameters
Say, starting to change only pressure and volume, according to Boyle's law (), then:
After this process, the gas has parameters
Using then equation () to change the number of particles in the gas and the temperature,
After this process, the gas has parameters
Using then equation () to change the pressure and the number of particles,
After this process, the gas has parameters
Using then Charles's law (equation 2) to change the volume and temperature of the gas,
After this process, the gas has parameters
Using simple algebra on equations (), (), () and () yields the result:
or where stands for the Boltzmann constant.
Another equivalent result, using the fact that , where n is the number of moles in the gas and R is the universal gas constant, is:
which is known as the ideal gas law.
If three of the six equations are known, it may be possible to derive the remaining three using the same method. However, because each formula has two variables, this is possible only for certain groups of three. For example, if you were to have equations (), () and () you would not be able to get any more because combining any two of them will only give you the third. However, if you had equations (), () and () you would be able to get all six equations because combining () and () will yield (), then () and () will yield (), then () and () will yield (), as well as would the combination of () and () as is explained in the following visual relation:
where the numbers represent the gas laws numbered above.
If you were to use the same method used above on 2 of the 3 laws on the vertices of one triangle that has a "O" inside it, you would get the third.
For example:
Change only pressure and volume first:
then only volume and temperature:
then as we can choose any value for , if we set , equation () becomes:
combining equations () and () yields , which is equation (), of which we had no prior knowledge until this derivation. | 7 | Physical Chemistry |
Moisture makes the cortex become more transparent. This way, the algae can conduct photosynthesis when moisture is available, and is protected at other times. When the cortex is more transparent, the algae show more clearly and the lichen looks greener. | 2 | Environmental Chemistry |
In Cartesian coordinates the 3 basis vectors are represented by a cell tensor :
The volume of the unit cell, , is given by the determinant of the cell tensor:
For the special case of a cubic, tetragonal, or orthorhombic cell, the matrix is diagonal, and we have that: | 3 | Analytical Chemistry |
Molten sucrose is used instead of solvent. The reaction involves molten sucrose and fatty acid ester (methyl ester or triglyceride) with a basic catalyst, potassium carbonate or potassium soap. The high temperature (170-190 °C) is required for this process. Since the process is carried out at a high temperature, sucrose can be degraded.
Later, a new synthesis pathway was introduced. First, sucrose and fatty acid soap are dissolved in water. Then, fatty acid ester and a basic catalyst are added to the solution. The solution must be heated and the pressure should be reduced to remove water and form a molten mixture. The transesterification is carried in the temperature range of 110-175 °C. | 0 | Organic Chemistry |
Spark or arc atomic emission spectroscopy is used for the analysis of metallic elements in solid samples. For non-conductive materials, the sample is ground with graphite powder to make it conductive. In traditional arc spectroscopy methods, a sample of the solid was commonly ground up and destroyed during analysis. An electric arc or spark is passed through the sample, heating it to a high temperature to excite the atoms within it. The excited analyte atoms emit light at characteristic wavelengths that can be dispersed with a monochromator and detected. In the past, the spark or arc conditions were typically not well controlled, the analysis for the elements in the sample were qualitative. However, modern spark sources with controlled discharges can be considered quantitative. Both qualitative and quantitative spark analysis are widely used for production quality control in foundry and metal casting facilities. | 3 | Analytical Chemistry |
Square antiprisms can be capped on both square faces, giving bicapped square antiprismatic molecular geometry. The bicapped square antiprismatic atoms surrounding a central atom define the vertices of a gyroelongated square bipyramid. The symmetry group of this object is D.
Examples:
*BH, defined by the B framework
*[AsRh(CO)] and [SRh(CO)], defined by the Rh framework, which encapsulates the main group atoms As and S
*[TlSn], a zintl ion | 4 | Stereochemistry |
The precise physiological role of uteroglobin is not yet known. Putative functions are:
# Immunomodulation
# Progesterone binding: weak in some animals, especially weak in humans. (Note: UGB is itself progesterone induced gene in the endometrium in Lagomorphs)
# Inhibits phospholipase A2 in vitro
# Binds phosphatidylcholine, phosphatidylinositol
# Binds to fibronectin: The uteroglobulin knockout mice on the inbred C57Bl6 strain develop Goodpasture's syndrome like glomerulopathy due to fibronectin binding of IgA which might potentially be prevented by uteroglobin replacement. However contrary to the animal model claims, human genetic data might suggest that the effect may be indirect
# Uteroglobin knockout mice on the inbred 129 strain appear to have healthy phenotype (no glomerulopathy development), but show physiological differences in their responses to respiratory challenges. The phenotype exhibited by these mice are; decreased bioaccumulation of biphenyls, susceptibility and increased IL-13, and IL-6 following hyperoxic challenge, and changes in the club cell morphology.
# Target of polychlorinated biphenyl (pcb) binding | 1 | Biochemistry |
*1982 – Arnold O. Beckman Research Award, University of Illinois
*1983 – Established Investigator Award, American Heart Association
*2003 – Vilas Associate Award, UW-Madison | 1 | Biochemistry |
Asemota was born in Nigeria. She earned a Bachelor of Science from the University of Benin, a Master of Science from Ahmadu Bello University, and a Doctor of Philosophy from the University of Benin/Frankfurt University. | 1 | Biochemistry |
The third and last stop codon in the standard genetic code was discovered soon after, and corresponds to the nucleotide triplet "UGA".
To continue matching with the theme of colored minerals, the third nonsense codon came to be known as "opal", which is a type of silica showing a variety of colors. Nonsense mutations that created this premature stop codon were later called opal mutations or umber mutations. | 1 | Biochemistry |
Lichens can show intense antioxidant activity. Secondary metabolites are often deposited as crystals in the apoplast. Secondary metabolites are thought to play a role in preference for some substrates over others. | 2 | Environmental Chemistry |
Surface chemistry of implantable electrodes proves to be more of a design concern for chronically implanted electrodes as compared to those with only acute implantation times. For acute implantations, the main concerns are laceration damage and degradation of particles left behind after electrode removal. For chronically implanted electrodes the cellular response and tissue encapsulation of the foreign body, regardless of degradation – even for materials that are highly biocompatible – are the primary concerns. Degradation, however, is still undesirable because particles can be toxic to tissue, can spread throughout the body, and even trigger an allergic response. Surface chemistry is an area of science applicable to biological implants. Bulk material properties are important when considering applications, however, it is the materials' surface (top several layers of molecules) that determines the biological response and is therefore the key to implant success. Implants within the central nervous system are unique in their manor of cellular response; there is little room for error. Prosthesis in these areas are typically electrodes or electrode arrays. | 7 | Physical Chemistry |
Mill scale is sought after by select abstract expressionist artists as its effect on steel can cause unpredicted and seemingly random abstract organic visual effects. Although the majority of mill scale is removed from steel during its passage through scale breaker rolls during manufacturing, smaller structurally inconsequential residue can be visible. Leveraging this processing vestige by accelerating its corrosive effects through the metallurgical use of phosphoric acid or in conjunction with selenium dioxide can create a high contrast visual substrate onto which other compositional elements can be added. | 8 | Metallurgy |
Old high-precision frequency standards, i.e. hyperfine structure transition-based atomic clocks, may require periodic fine-tuning due to exposure to magnetic fields. This is carried out by measuring the Zeeman effect on specific hyperfine structure transition levels of the source element (cesium) and applying a uniformly precise, low-strength magnetic field to said source, in a process known as degaussing.
The Zeeman effect may also be utilized to improve accuracy in atomic absorption spectroscopy. | 7 | Physical Chemistry |
The following scheme describes the interconversion between an aldose and a ketose, where R is any organic residue.
The equilibrium or the reactant to product ratio depends on concentration, solvent, pH and temperature. At equilibrium the aldose and ketose form a mixture which in the case of the glyceraldehyde and dihydroxyacetone is also called glycerose.
A related reaction is the alpha-ketol rearrangement. | 0 | Organic Chemistry |
Also in the area of nanoparticles, surface stress can play a significant role in the stabilization of decahedral nanoparticle and icosahedral twins. In both cases an arrangement of internal twin boundaries leads to lower energy surface energy facets. Balancing this there are nominal angular gaps (disclinations) which are removed by an elastic deformation. While the main energy contributions are the external surface energy and the strain energy, the surface stress couples the two and can have an important role in the overall stability. | 7 | Physical Chemistry |
Upon blood exiting the body, hemoglobin in blood transits from bright red to dark brown, which is attributed to oxidation of oxy-hemoglobin (HbO) to methemoglobin (met-Hb) and ending up in hemichrome (HC). For forensic purposes, the fractions of HbO, met-Hb and HC in a bloodstain can be used for age determination of bloodstains when measured with Reflectance Spectroscopy [http://plosone.org/article/info:doi/10.1371/journal.pone.0021845]. | 1 | Biochemistry |
Absolute electrode potential, in electrochemistry, according to an IUPAC definition, is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface). | 7 | Physical Chemistry |
The ENCODE (Encyclopedia of DNA elements) project is an in-depth analysis of the human genome whose goal is to identify all the functional elements of genomic DNA, in both coding and non-coding regions. Important results include evidence from genomic tiling arrays that most nucleotides are transcribed as coding transcripts, non-coding RNAs, or random transcripts, the discovery of additional transcriptional regulatory sites, further elucidation of chromatin-modifying mechanisms. | 1 | Biochemistry |
The cost of sequencing has dropped dramatically while the cost of construction of jumping libraries has not. Therefore, as new sequencing technologies and bioinformatic tools are developed, jumping libraries may become redundant. | 1 | Biochemistry |
Neuromelanin-containing neurons in the substantia nigra degenerate during Parkinsons disease. Motor symptoms of Parkinsons disease are caused by cell death in the substantia nigra, which may be partly due to oxidative stress. This oxidation may be relieved by neuromelanin. Patients with Parkinsons disease had 50% the amount of neuromelanin in the substantia nigra as compared to similar patients of their same age, but without Parkinsons. The death of neuromelanin-containing neurons in the substantia nigra, pars compacta, and locus coeruleus have been linked to Parkinsons disease and also have been visualized in vivo' with neuromelanin imaging.
Neuromelanin has been shown to bind neurotoxic and toxic metals that could promote neurodegeneration. | 1 | Biochemistry |
In 16th-century Europe, medical practitioners in army and university settings began to gather information on the cause and manner of death. Ambroise Paré, a French army surgeon, systematically studied the effects of violent death on internal organs. Two Italian surgeons, Fortunato Fidelis and Paolo Zacchia, laid the foundation of modern pathology by studying changes that occurred in the structure of the body as the result of disease. In the late 18th century, writings on these topics began to appear. These included A Treatise on Forensic Medicine and Public Health by the French physician Francois Immanuele Fodéré and The Complete System of Police Medicine by the German medical expert Johann Peter Frank.
As the rational values of the Enlightenment era increasingly permeated society in the 18th century, criminal investigation became a more evidence-based, rational procedure − the use of torture to force confessions was curtailed, and belief in witchcraft and other powers of the occult largely ceased to influence the courts decisions. Two examples of English forensic science in individual legal proceedings demonstrate the increasing use of logic and procedure in criminal investigations at the time. In 1784, in Lancaster, John Toms was tried and convicted for murdering Edward Culshaw with a pistol. When the dead body of Culshaw was examined, a pistol wad (crushed paper used to secure powder and balls in the muzzle) found in his head wound matched perfectly with a torn newspaper found in Tomss pocket, leading to the conviction.
In Warwick 1816, a farm laborer was tried and convicted of the murder of a young maidservant. She had been drowned in a shallow pool and bore the marks of violent assault. The police found footprints and an impression from corduroy cloth with a sewn patch in the damp earth near the pool. There were also scattered grains of wheat and chaff. The breeches of a farm labourer who had been threshing wheat nearby were examined and corresponded exactly to the impression in the earth near the pool.
An article appearing in Scientific American in 1885 describes the use of microscopy to distinguish between the blood of two persons in a criminal case in Chicago. | 3 | Analytical Chemistry |
Supercritical fluids can be used to deposit functional nanostructured films and nanometer-size particles of metals onto surfaces. The high diffusivities and concentrations of precursor in the fluid as compared to the vacuum systems used in chemical vapour deposition allow deposition to occur in a surface reaction rate limited regime, providing stable and uniform interfacial growth. This is crucial in developing more powerful electronic components, and metal particles deposited in this way are also powerful catalysts for chemical synthesis and electrochemical reactions. Additionally, due to the high rates of precursor transport in solution, it is possible to coat high surface area particles which under chemical vapour deposition would exhibit depletion near the outlet of the system and also be likely to result in unstable interfacial growth features such as dendrites. The result is very thin and uniform films deposited at rates much faster than atomic layer deposition, the best other tool for particle coating at this size scale. | 7 | Physical Chemistry |
Mirror life (also called mirror-image life) is a hypothetical form of life with mirror-reflected molecular building blocks. The possibility of mirror life was first discussed by Louis Pasteur. Although this alternative life form has not been discovered in nature, efforts to build a mirror-image version of biology's molecular machinery are already underway. | 4 | Stereochemistry |
Common side effects associated with oral vancomycin administration (used to treat intestinal infections) include:
* gastrointestinal adverse effects (such as abdominal pain and nausea);
* dysgeusia (distorted sense of taste), in case of administration of vancomycin oral solution, but not in case of vancomycin capsules. | 0 | Organic Chemistry |
Liquid ammonia will dissolve all of the alkali metals and other electropositive metals such as Ca, Sr, Ba, Eu, and Yb (also Mg using an electrolytic process), giving characteristic blue solutions. For alkali metals in liquid ammonia, the solution is blue when dilute and copper-colored when more concentrated (> 3 molar). These solutions conduct electricity. The blue colour of the solution is due to ammoniated electrons, which absorb energy in the visible region of light. The diffusivity of the solvated electron in liquid ammonia can be determined using potential-step chronoamperometry.
Solvated electrons in ammonia are the anions of salts called electrides.
:Na + 6 NH → [Na(NH)] + e
The reaction is reversible: evaporation of the ammonia solution produces a film of metallic sodium. | 0 | Organic Chemistry |
Type II rearrangements often involve double hydrogen migration in a carbon skeleton. This reaction type can be found in certain transfer hydrogenations. An example is hydrogen transfer in syn-sesquinorbornene
disulfones. | 0 | Organic Chemistry |
Convection in a large magma chamber is subject to the interplay of forces generated by thermal convection and the resistance offered by friction, viscosity and drag on the magma offered by the walls of the magma chamber. Often near the margins of a magma chamber which is convecting, cooler and more viscous layers form concentrically from the outside in, defined by breaks in viscosity and temperature. This forms laminar flow, which separates several domains of the magma chamber which can begin to differentiate separately.
Flow banding is the result of a process of fractional crystallization which occurs by convection, if the crystals which are caught in the flow-banded margins are removed from the melt. The friction and viscosity of the magma causes phenocrysts and xenoliths within the magma or lava to slow down near the interface and become trapped in a viscous layer. This can change the composition of the melt in large intrusions, leading to differentiation. | 9 | Geochemistry |
This book describes the miner and the finding of veins. Agricola assumes that his audience is the mine owner, or an investor in mines. He advises owners to live at the mine and to appoint good deputies. It is recommended to buy shares in mines that have not started to produce as well as existing mines to balance the risks. The next section of this book recommends areas where miners should search. These are generally mountains with wood available for fuel and a good supply of water. A navigable river can be used to bring fuel, but only gold or gemstones can be mined if no fuel is available. The roads must be good and the area healthy. Agricola describes searching streams for metals and gems that have been washed from the veins. He also suggests looking for exposed veins and also describes the effects of metals on the overlying vegetation. He recommends trenching to investigate veins beneath the surface. He then describes dowsing with a forked twig although he rejects the method himself. The passage is the first written description of how dowsing is done. Finally he comments on the practice of naming veins or shafts. | 8 | Metallurgy |
The compressor has to run with the same speed (or fixed gear ratio) as its driving turbine and have equal power and pass the same flow as its driving turbine. This constitutes a gas generator which produces gas power. The compressor also has to pass the same flow as whatever uses the gas power, ie additional turbine stages for a single shaft engine or separate power turbines or a jet nozzle. This equal-flow requirement is alongside an equal pressure-ratio requirement, between overall compression and expansion ratios, and together they position the running line for steady state operation.
Single-shaft engines which drive an electric generator or helicopter rotor/aircraft propeller run with the compressor at no-load while accelerating to operating speed. No-load refers to a minimum fuelling as necessary to run the generator with no electrical load or rotor/propeller pitch at a minimum and occurs close to choke. Cohen et al. show electrical generators run up to required speed at no load. An increase in electrical load is obtained by increasing fuel flow. Barkey et al. give a detailed description of the sequence of events which bring the generator turbine to design speed, or grid frequency, with no load before increasing fuel as the load comes on. Grandcoing shows the Turbomeca Artouste helicopter engine constant speed operation from no-load idle to maximum power. No-load is minimum rotor pitch and idle fuel flow. The increase in fuel flow is shown on a compressor map as lines of constant engine temperature ratio, Turbine inlet temperature/Compressor inlet temperature. Grandcoing also shows the effect of a rapid load increase where the speed droops before regaining its required setting. | 7 | Physical Chemistry |
The liver contains metabolic active tissues as it is responsible for detoxification, protein and carbohydrate metabolism. Therefore, It needs a lot of energy to function and contains abundant mitochondria. Any abnormalities in mitochondria would affect liver metabolism. If the liver does not work properly, it may produce excess metabolites, leading to accumulation; in contrast, it may also fail to produce certain chemicals. As a result, the imbalance of metabolites may lead to liver cancer development, i.e. hepatocarcinogenesis. | 1 | Biochemistry |
A defoliant is any herbicidal chemical sprayed or dusted on plants to cause their leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the development of other herbicides and pesticides, allowed for the Green Revolution, an increase in agricultural production in mid-20th century. Defoliants have also been used in warfare as a means to deprive an enemy of food crops and/or hiding cover, most notably by the United Kingdom during the Malayan Emergency and the United States in the Vietnam War. Defoliants were also used by Indonesian forces in various internal security operations. | 2 | Environmental Chemistry |
Methanesulfonyl chloride is highly toxic by inhalation, corrosive, and acts as a lachrymator. It reacts with nucleophilic reagents (including water) in a strongly exothermic manner. When heated to decomposition point, it emits toxic vapors of sulfur oxides and hydrogen chloride. | 0 | Organic Chemistry |
Anthocyanins are found in the cell vacuole, mostly in flowers and fruits, but also in leaves, stems, and roots. In these parts, they are found predominantly in outer cell layers such as the epidermis and peripheral mesophyll cells.
Most frequently occurring in nature are the glycosides of cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin. Roughly 2% of all hydrocarbons fixed in photosynthesis are converted into flavonoids and their derivatives, such as the anthocyanins. Not all land plants contain anthocyanin; in the Caryophyllales (including cactus, beets, and amaranth), they are replaced by betalains. Anthocyanins and betalains have never been found in the same plant.
Sometimes bred purposely for high anthocyanin content, ornamental plants such as sweet peppers may have unusual culinary and aesthetic appeal. | 3 | Analytical Chemistry |
In statistical copolymers the sequence of monomer residues follows a statistical rule. If the probability of finding a given type monomer residue at a particular point in the chain is equal to the mole fraction of that monomer residue in the chain, then the polymer may be referred to as a truly random copolymer (structure 3).
Statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as "random" in the polymer literature. As with other types of copolymers, random copolymers can have interesting and commercially desirable properties that blend those of the individual homopolymers. Examples of commercially relevant random copolymers include rubbers made from styrene-butadiene copolymers and resins from styrene-acrylic or methacrylic acid derivatives. Copolymerization is particularly useful in tuning the glass transition temperature, which is important in the operating conditions of polymers; it is assumed that each monomer occupies the same amount of free volume whether it is in a copolymer or homopolymer, so the glass transition temperature (T) falls between the values for each homopolymer and is dictated by the mole or mass fraction of each component.
A number of parameters are relevant in the composition of the polymer product; namely, one must consider the reactivity ratio of each component. Reactivity ratios describe whether the monomer reacts preferentially with a segment of the same type or of the other type. For example, a reactivity ratio that is less than one for component 1 indicates that this component reacts with the other type of monomer more readily. Given this information, which is available for a multitude of monomer combinations in the "Wiley Database of Polymer Properties", the Mayo-Lewis equation can be used to predict the composition of the polymer product for all initial mole fractions of monomer. This equation is derived using the Markov model, which only considers the last segment added as affecting the kinetics of the next addition; the Penultimate Model considers the second-to-last segment as well, but is more complicated than is required for most systems. When both reactivity ratios are less than one, there is an azeotropic point in the Mayo-Lewis plot. At this point, the mole fraction of monomer equals the composition of the component in the polymer.
There are several ways to synthesize random copolymers. The most common synthesis method is free radical polymerization; this is especially useful when the desired properties rely on the composition of the copolymer rather than the molecular weight, since free radical polymerization produces relatively disperse polymer chains. Free radical polymerization is less expensive than other methods, and produces high-molecular weight polymer quickly. Several methods offer better control over dispersity. Anionic polymerization can be used to create random copolymers, but with several caveats: if carbanions of the two components do not have the same stability, only one of the species will add to the other. Additionally, anionic polymerization is expensive and requires very clean reaction conditions, and is therefore difficult to implement on a large scale. Less disperse random copolymers are also synthesized by ″living″ controlled radical polymerization methods, such as atom-transfer radical-polymerization (ATRP), nitroxide mediated radical polymerization (NMP), or reversible addition−fragmentation chain-transfer polymerization (RAFT). These methods are favored over anionic polymerization because they can be performed in conditions similar to free radical polymerization. The reactions require longer experimentation periods than free radical polymerization, but still achieve reasonable reaction rates. | 7 | Physical Chemistry |
The RNA integrity number (RIN) is an algorithm for assigning integrity values to RNA measurements.
The integrity of RNA is a major concern for gene expression studies and traditionally has been evaluated using the 28S to 18S rRNA ratio, a method that has been shown to be inconsistent. This inconsistency arises because subjective, human interpretation is necessary to compare the 28S and 18S gel images. The RIN algorithm was devised to overcome this issue. The RIN algorithm is applied to electrophoretic RNA measurements, typically obtained using capillary gel electrophoresis, and based on a combination of different features that contribute information about the RNA integrity to provide a more universal measure. RIN has been demonstrated to be robust and reproducible in studies comparing it to other RNA integrity calculation algorithms, cementing its position as a preferred method of determining the quality of RNA to be analyzed.
A major criticism to RIN is when using with plants or in studies of eukaryotic-prokaryotic cells interactions. The RIN algorithm is unable to differentiate eukaryotic/prokaryotic/chloroplastic ribosomal RNA, creating serious quality index underestimation in such situations. | 1 | Biochemistry |
Specifically it is used as mefloquine hydrochloride.
Mefloquine is a chiral molecule with two asymmetric carbon centres, which means it has four different stereoisomers. The drug is currently manufactured and sold as a racemate of the (R,S)- and (S,R)-enantiomers by Hoffmann-La Roche, a Swiss pharmaceutical company. Essentially, it is two drugs in one. Plasma concentrations of the (–)-enantiomer are significantly higher than those for the (+)-enantiomer, and the pharmacokinetics between the two enantiomers are significantly different. The (+)-enantiomer has a shorter half-life than the (–)-enantiomer. | 4 | Stereochemistry |
The first event appears to be the accumulation of cell adhesion molecules such as NF186 or NrCAM. The intra-cellular regions of these cell-adhesion molecules interact with ankyrin G, which serves as an anchor for sodium channels. At the same time, the periaxonal extension of the glial cell wraps around the axon, giving rise to the paranodal regions. This movement along the axon contributes significantly to the overall formation of the nodes of Ranvier by permitting heminodes formed at the edges of neighboring glial cells to fuse into complete nodes.
Septate-like junctions form at the paranodes with the enrichment of NF155 in glial paranodal loops. Immediately following the early differentiation of the nodal and paranodal regions, potassium channels, Caspr2 and TAG1 accumulate in the juxta-paranodal regions. This accumulation coincides directly with the formation of compact myelin. In mature nodal regions, interactions with the intracellular proteins appear vital for the stability of all nodal regions. In the CNS, oligodendrocytes do not possess microvilli, but appear capable to initiate the clustering of some axonal proteins through secreted factors. The combined effects of such factors with the subsequent movements generated by the wrapping of oligodendrocyte periaxonal extension could account for the organization of CNS nodes of Ranvier. | 1 | Biochemistry |
Born in Ararat, Victoria, Sarfati moved with his family to New Zealand as a child, where he became a dual Australian and New Zealand citizen. He attended Wellington College in New Zealand, later graduating from Victoria University of Wellington with a BSc (Hons.) in chemistry, and a PhD in the same subject for a thesis entitled "A Spectroscopic Study of some Chalcogenide Ring and Cage Molecules". He co-authored a paper on high-temperature superconductors that was published in Nature in 1987 ("Letters to Nature"), and from 1988 to 1995, had five papers on spectroscopy of condensed matter samples published in other peer-reviewed scientific journals. In 1996, he returned to Brisbane, Australia to work for the Creation Science Foundation, then Answers in Genesis, then its current name Creation Ministries International. In 2010, he moved to the American office of that ministry. | 7 | Physical Chemistry |
Hydrogen–deuterium exchange mass spectrometry (HX-MS or HDX-MS) can determine the overall deuterium content of molecules which have undergone H/D exchange. Because of the sample preparation required, it is typically considered to provide an accurate measurement of non-exchangeable hydrogen atoms only. It can also involve H/D exchange in the gas phase or solution phase exchange prior to ionization. It has several advantages in NMR spectroscopy with respect to analysis of H–D exchange reactions: much less material is needed, the concentration of sample can be very low (as low as 0.1 uM), the size limit is much greater, and data can usually be collected and interpreted much more quickly.
The deuterium nucleus is twice as heavy as the hydrogen nucleus because it contains a neutron as well as a proton. Thus a molecule that contains some deuterium will be heavier than one that contains all hydrogen. As a protein is increasingly deuterated, the molecular mass increases correspondingly. Detecting the change in the mass of a protein upon deuteration was made possible by modern protein mass spectrometry, first reported in 1991 by Katta and Chait.
Determining site specific deuteration via mass spectrometry is more complicated than using NMR spectroscopy. For example, the location and relative amount of deuterium exchange along the peptide backbone can be determined roughly by subjecting the protein to proteolysis after the exchange reaction has been quenched. Individual peptides are then analyzed for overall deuteration of each peptide fragment. Using this technique the resolution of deuterium exchange is determined by the size of the peptides produced during digestion. Pepsin, an acid protease, is commonly used for proteolysis, as the quench pH must be maintained during the proteolytic reaction. To minimize the back-exchange, proteolysis and subsequent mass spectrometry analysis must be done as quickly as possible. HPLC separation of the peptic digest is often carried out at low temperature just prior to electrospray mass spectrometry to minimize back-exchange. More recently, UPLC has been used due to its superior separation capabilities.
It was proposed in 1999 that it might be possible to achieve single-residue resolution by using collision-induced dissociation (CID) fragmentation of deuterated peptides in conjunction with tandem mass spectrometry. It was soon discovered that CID causes "scrambling" of the deuterium position within the peptides. However, fragmentation produced by MALDI in-source decay (ISD), electron capture dissociation (ECD), and electron transfer dissociation (ETD) proceed with little or no scrambling under the correct experimental conditions. Scrambling of the isotopic labeling is caused by collisional heating prior to dissociation of the ion and while CID do cause scrambling, collisional heating can also occur during ionization and ion transport. However, by careful optimization of instrument parameters which cause ion heating, hydrogen scrambling can be minimized to a degree which preserves the solution phase isotopic labeling until fragmentation can be performed using a technique where scrambling does not occur. More recently, ultraviolet photodissociation (UVPD) has also been investigated as a possible fragmentation technique to localize deuterium within peptides and proteins. In this regard, the conclusions have been mixed, while it is possible to obtain UVPD fragments which has not undergone scrambling under certain conditions, others have shown that scrambling can occur for both peptides and proteins during the UVPD fragmentation step itself. The theory consolidating these apparent contradictions has to do with the dual fragmentation pathway that may arise from UV irradiation of peptides and proteins, i.e. direct and statistical dissociation. That is, if experimental conditions favor direct dissociation and the precursor ion is kept at low internal energies before and during fragmentation the deuterium level of the resulting fragments will correspond to the non-scrambled precursor. However, experimental conditions may favor statistical dissociation during UV irradiation, especially at long irradiation times and low gas pressure, leading to internal conversion of the electronic excitation energy contributed by the UV photons. The result is vibrational excitation of the irradiated molecule which in turn undergo scrambling. | 7 | Physical Chemistry |
Measuring the quantity of water vapor in a medium can be done directly or remotely with varying degrees of accuracy. Remote methods such electromagnetic absorption are possible from satellites above planetary atmospheres. Direct methods may use electronic transducers, moistened thermometers or hygroscopic materials measuring changes in physical properties or dimensions. | 2 | Environmental Chemistry |
All HMOs derive from lactose, which can be decorated by four monosaccharides (N-acetyl-D-glucosamine, D-galactose, sialic acid and/or L-fucose) to form an oligosaccharide. The HMO variability in human mothers depend on two specific enzymes, the α1-2-fucosyltransferase (FUT2) and the α1-3/4-fucosyltransferase (FUT3). The milk of mothers with inactivated FUT2 enzyme do not contain α1-2-fucosylated HMOs, and likewise with inactivated FUT3 enzyme there can be almost no α1-4-fucasylated HMOs found. Typically 20% of the global population of mothers do not have active FUT2 enzyme, but still have an active FUT3 enzyme, whereas 1% of mothers express neither FUT2 nor FUT3 enzymes. | 0 | Organic Chemistry |
Because of the full or partial positive charge on the element directly attached to the ring for each of these groups, they all have a moderate to strong electron-withdrawing inductive effect (known as the -I effect). They also exhibit electron-withdrawing resonance effects, (known as the -M effect):
Thus, these groups make the aromatic ring very electron-poor (δ+) relative to benzene and, therefore, they strongly deactivate the ring (i.e. reactions proceed much slower in rings bearing these groups compared to those reactions in benzene.) | 0 | Organic Chemistry |
The relationship between fractional and Cartesian coordinates can be described by the matrix transformation :
Similarly, the Cartesian coordinates can be converted back to fractional coordinates using the matrix transformation : | 3 | Analytical Chemistry |
The concentration of tracer in a step experiment at the reactor inlet changes abruptly from 0 to . The concentration of tracer at the outlet is measured and normalized to the concentration to obtain the non-dimensional curve which goes from 0 to 1:
The step- and pulse-responses of a reactor are related by the following:
A step experiment is often easier to perform than a pulse experiment, but it tends to smooth over some of the details that a pulse response could show. It is easy to numerically integrate an experimental pulse response to obtain a very high-quality estimate of the step response, but the reverse is not the case because any noise in the concentration measurement will be amplified by numeric differentiation. | 9 | Geochemistry |
In the case of the original Grätzel and O'Regan design, the cell has 3 primary parts. On top is a transparent anode made of fluoride-doped tin dioxide (SnO:F) deposited on the back of a (typically glass) plate. On the back of this conductive plate is a thin layer of titanium dioxide (TiO), which forms into a highly porous structure with an extremely high surface area. The (TiO) is chemically bound by a process called sintering. TiO only absorbs a small fraction of the solar photons (those in the UV). The plate is then immersed in a mixture of a photosensitive ruthenium-polypyridyl dye (also called molecular sensitizers) and a solvent. After soaking the film in the dye solution, a thin layer of the dye is left covalently bonded to the surface of the TiO. The bond is either an ester, chelating, or bidentate bridging linkage.
A separate plate is then made with a thin layer of the iodide electrolyte spread over a conductive sheet, typically platinum metal. The two plates are then joined and sealed together to prevent the electrolyte from leaking. The construction is simple enough that there are hobby kits available to hand-construct them. Although they use a number of "advanced" materials, these are inexpensive compared to the silicon needed for normal cells because they require no expensive manufacturing steps. TiO, for instance, is already widely used as a paint base.
One of the efficient DSSCs devices uses ruthenium-based molecular dye, e.g. [Ru(4,4-dicarboxy-2,2-bipyridine)(NCS)] (N3), that is bound to a photoanode via carboxylate moieties. The photoanode consists of 12 μm thick film of transparent 10–20 nm diameter TiO nanoparticles covered with a 4 μm thick film of much larger (400 nm diameter) particles that scatter photons back into the transparent film. The excited dye rapidly injects an electron into the TiO after light absorption. The injected electron diffuses through the sintered particle network to be collected at the front side transparent conducting oxide (TCO) electrode, while the dye is regenerated via reduction by a redox shuttle, I/I, dissolved in a solution. Diffusion of the oxidized form of the shuttle to the counter electrode completes the circuit. | 5 | Photochemistry |
The hydrogen ions displace metal from the salt so that metal, instead of hydrogen, is deposited on the positive plate. Examples:
* Silver oxide, used in the Silver-oxide battery
* Copper sulphate, used in the Daniell cell
* Mercurous sulphate, used in the Weston and Clark standard cells | 7 | Physical Chemistry |
Donnan potential is the difference in the Galvani potentials which appears as a result of Donnan equilibrium, named after Frederick G. Donnan, which refers to the distribution of ion species between two ionic solutions separated by a semipermeable membrane or boundary. The boundary layer maintains an unequal distribution of ionic solute concentration by acting as a selective barrier to ionic diffusion. Some species of ions may pass through the barrier while others may not. The solutions may be gels or colloids as well as ionic liquids, and as such the phase boundary between gels or a gel and a liquid can also act as a selective barrier. Electric potential arises between two solutions is called Donnan potential.
Donnan equilibrium is prominent in the triphasic model for articular cartilage proposed by Mow and Ratcliffe, as well as in electrochemical fuel cells and dialysis.
The Donnan effect is extra osmotic pressure attributable to cations (Na and K) attached to dissolved plasma proteins. | 7 | Physical Chemistry |
A phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes. In humans, Entamoeba histolytica can phagocytose red blood cells. | 1 | Biochemistry |
Nitrogen entering the euphotic zone is referred to as new nitrogen because it is newly arrived from outside the productive layer. The new nitrogen can come from below the euphotic zone or from outside sources. Outside sources are upwelling from deep water and nitrogen fixation. If the organic matter is eaten, respired, delivered to the water as ammonia, and re-incorporated into organic matter by phytoplankton it is considered recycled/regenerated production.
New production is an important component of the marine environment. One reason is that only continual input of new nitrogen can determine the total capacity of the ocean to produce a sustainable fish harvest. Harvesting fish from regenerated nitrogen areas will lead to a decrease in nitrogen and therefore a decrease in primary production. This will have a negative effect on the system. However, if fish are harvested from areas of new nitrogen the nitrogen will be replenished. | 1 | Biochemistry |
Morpholinos have been used to block miRNA activity and maturation. Fluorescein-tagged Morpholinos combined with fluorescein-specific antibodies can be used as probes for in-situ hybridization to miRNAs. Morpholinos can block ribozyme activity. U2 and U12 snRNP functions have been inhibited by Morpholinos. Morpholinos targeted to "slippery" mRNA sequences within protein coding regions can induce translational frameshifts. Morpholinos can block RNA editing, poly-A tailing and translocation sequences. Morpholino activities against this variety of targets suggest that Morpholinos can be used as a general-purpose tool for blocking interactions of proteins or nucleic acids with mRNA. | 1 | Biochemistry |
Iodosobenzene or iodosylbenzene is an organoiodine compound with the empirical formula . This colourless solid compound is used as an oxo transfer reagent in research laboratories examining organic and coordination chemistry. | 0 | Organic Chemistry |
Experimental study of any supramolecular structures in bulk water is difficult because of their short lifetime: the hydrogen bonds are continually breaking and reforming at timescales faster than 200 femtoseconds.
Nevertheless, water clusters have been observed in the gas phase and in dilute mixtures of water and non-polar solvents like benzene and liquid helium. The experimental detection and characterization of the clusters has been achieved with the following methods: far-infrared spectroscopy|far-infrared (FIR), vibration-rotation-tunneling spectroscopy|vibration-rotation-tunneling (VRT), Н-NMR, and neutron diffraction. The hexamer is found to have planar geometry in liquid helium, a chair conformation in organic solvents, and a cage structure in the gas phase. Experiments combining IR spectroscopy with mass spectrometry reveal cubic configurations for clusters in the range n=(8-10).
When the water is part of a crystal structure as in a hydrate, x-ray diffraction can be used. Conformation of a water heptamer was determined (cyclic twisted nonplanar) using this method. Further, multi-layered water clusters with formulae (HO) trapped inside cavities of several polyoxometalate clusters were also reported by Mueller et al. | 7 | Physical Chemistry |
Overshot titrations are a common phenomenon, and refer to a situation where the volume of titrant added during a chemical titration exceeds the amount required to reach the equivalence point. This excess titrant leads to an outcome where the solution becomes slightly more alkaline or over-acidified.
Overshooting the equivalence point can occur due to various factors, such as errors in burette readings, imperfect reaction stoichiometry, or issues with endpoint detection. The consequences of overshot titrations can affect the accuracy of the analytical results, particularly in quantitative analysis.
Researchers and analysts often employ corrective measures, such as back-titration and using more precise titration techniques, to mitigate the impact of overshooting and obtain reliable and precise measurements. Understanding the causes, consequences, and solutions related to overshot titrations is crucial in achieving accurate and reproducible results in the field of chemistry. | 3 | Analytical Chemistry |
S. S. Goldich derived this series in 1938 after studying soil profiles and their parent rocks. Based on sample analysis from a series of weathered localities, Goldich determined that the weathering rate of minerals is controlled at least in part by the order in which they crystallize from a melt. This order meant that the minerals that crystallized first from the melt were the least stable under earth surface conditions, while the minerals that crystallized last were the most stable. This is not the only control on weathering rate; this rate is dependent on both intrinsic (qualities specific to the minerals) and extrinsic (qualities specific to the environment) variables. Climate is a key extrinsic variable, controlling the water to rock ratio, pH, and alkalinity, all of which impact the rate of weathering. The Goldich dissolution series concerns intrinsic mineral qualities, which were proven both by Goldich as well as preceding scientists to also be important for constraining weathering rates.
Earlier work by Steidtmann demonstrated that the order of ionic loss of a rock as it weathers is: CO, Mg, Na, K, SiO, Fe, and finally Al. Goldich furthered this analysis by noting the relative mineral stability order, which is related to the relative resistance of these ions to leaching. Goldich notes that overall, mafic (rich in iron and magnesium) minerals are less stable than felsic (rich in silica) minerals. The order of stability in the series echoes Bowen's reaction series very well, leading Goldich to suggest that the relative stability at the surface is controlled by crystallization order.
While Goldich’s original order of mineral weathering potential was qualitative, later work by Michal Kowalski and J. Donald Rimstidt placed in the series in quantitative terms. Kowalski and Rimstidt performed an analysis of mechanical and chemical grain weathering, and demonstrated that the average lifetime of chemically weathered detrital grains quantitatively fit the Goldich sequence extremely well. This helped to supplement the real-world applicability of the dissolution series. The difference in chemical weathering time can span millions of years. For example, quickest to weather of the common igneous minerals is apatite, which reaches complete weathering in an average of 10 years, and slowest to weather is quartz, which weathers fully in 10 years. | 9 | Geochemistry |
Zhao has published over 200 papers in international journals and obtained 20 Chinese invention patents. Zhao won many awards:
2010 Japanese Photochemistry Association Lectureship Award for Asian and OceanianPhotochemist.
2005 The Second Grade National Prize of Natural Science of China (the first contributor).
2002 The Award of Excellent Young Scientists of Chinese Academy of Sciences- Bayer (Germany).
2002 The Fiste Grade Prize of Science and Technology in Beijing (Natural Science).
2002 The Second Grade Prize Military Science and Technique Progress Prize.
1999 Be selected into the first and second levels of "the National Hundred, Thousand and Ten Thousand Talent Project".
1998 The Special Contribution Award from the State Council of China.
1997 Distinguished Young Scientists of NSFC.
1999, 2002, 2006 The Award of Excellent Advisor of Graduates of CAS. | 2 | Environmental Chemistry |
Polysubstituted benzenes were originally synthesized by substitution reactions on aromatic precursors. However, these reactions can have low regioselectivity and are prone to over substitution. Directed ortho metalation requires precursors that are often unstable to metallating reagents. Both these synthetic routes pose issues in total synthesis. In 1984 a new synthetic strategy was developed by Rick Danheiser to address these shortcomings. | 0 | Organic Chemistry |
The first recorded experimental work in copper was conducted by Cushing in 1894 in order to demonstrate that copper plate found in Hopewell mounds in Ohio could have been produced by the Hopewell people and not come from European trade. In his experiments, Cushing used antler and stone tools to cut out sheets of copper and puncture round holes in them through a method of pressure and grinding. In addition to the copper sheet experiments, Cushing also conducted smelting experiments reconstructed from finding at Salado Valley, Arizona pueblo excavations to reproduce copper artifacts. | 8 | Metallurgy |
In 1924 Ingold moved to the University of Leeds where he spent six years as Professor of Organic Chemistry working alongside his wife, Dr. Dr. Edith Hilda Ingold (Usherwood) . He returned to London in 1930, and served for 24 years as head of the chemistry department at University College London, from 1937 until his retirement in 1961.
During his study of alkyl halides, Ingold found evidence for two possible reaction mechanisms for nucleophilic substitution reactions. He found that tertiary alkyl halides underwent a two-step mechanism (S1) while primary and secondary alkyl halides underwent a one-step mechanism (S2). This conclusion was based on the finding that reactions of tertiary alkyl halides with nucleophiles were dependent on the concentration of the alkyl halide only. Meanwhile, he discovered that primary and secondary alkyl halides, when reacting with nucleophiles, depend on both the concentration of the alkyl halide and the concentration of the nucleophile.
Starting around 1926, Ingold and Robert Robinson carried out a heated debate on the electronic theoretical approaches to organic reaction mechanisms. See, for example, the summary by Saltzman.
Ingold authored and co-authored 443 papers. Notable students include Peter de la Mare, Ronald Gillespie and Ronald Nyholm. | 4 | Stereochemistry |
In 1998 Kubista founded LightUp Technologies AB after his research finding of lightUp probes, a company that specializes in the development of real-time PCR tests for human infectious diseases. Three years later In 2001, Kubista's research led to the establishments of MultiD Analyses AB, which develops GenEx software for gene expression data analysis and TATAA Biocenter for qPCR and gene expression analysis. The company became known for its qPCR training services globally and its provision of qPCR services, particularly in Europe. TATAA Biocenter was the first laboratory in Europe to obtain flexible ISO 17025 accreditation and also was the first to provide COVID tests at the onset of the pandemic. In 2014 Kubista implementated non-invasive prenatal testing (NIPT) in Sweden and subsequently founded Life Genomics AB. In 2020, Kubista co-founded SimSen Diagnostics, a company focused on developing technology for liquid biopsy analyses. | 1 | Biochemistry |
Dibutylboron trifluoromethanesulfonate (also called dibutylboron triflate or DBBT) is a reagent in organic chemistry. Its chemical formula is CHBFOS. It is used in asymmetric synthesis for example in the formation of boron enolates in the aldol reaction. | 0 | Organic Chemistry |
Primary energy sources should not be confused with the energy system components (or conversion processes) through which they are converted into energy carriers. | 7 | Physical Chemistry |
cAMP is a second messenger, used for intracellular signal transduction, such as transferring into cells the effects of hormones like glucagon and adrenaline, which cannot pass through the plasma membrane. It is also involved in the activation of protein kinases. In addition, cAMP binds to and regulates the function of ion channels such as the HCN channels and a few other cyclic nucleotide-binding proteins such as Epac1 and RAPGEF2. | 1 | Biochemistry |
Alkane conformers arise from rotation around sp hybridised carbon–carbon sigma bonds. The smallest alkane with such a chemical bond, ethane, exists as an infinite number of conformations with respect to rotation around the C–C bond. Two of these are recognised as energy minimum (staggered conformation) and energy maximum (eclipsed conformation) forms. The existence of specific conformations is due to hindered rotation around sigma bonds, although a role for hyperconjugation is proposed by a competing theory.
The importance of energy minima and energy maxima is seen by extension of these concepts to more complex molecules for which stable conformations may be predicted as minimum-energy forms. The determination of stable conformations has also played a large role in the establishment of the concept of asymmetric induction and the ability to predict the stereochemistry of reactions controlled by steric effects.
In the example of staggered ethane in Newman projection, a hydrogen atom on one carbon atom has a 60° torsional angle or torsion angle with respect to the nearest hydrogen atom on the other carbon so that steric hindrance is minimised. The staggered conformation is more stable by 12.5 kJ/mol than the eclipsed conformation, which is the energy maximum for ethane. In the eclipsed conformation the torsional angle is minimised.
In butane, the two staggered conformations are no longer equivalent and represent two distinct conformers:the anti-conformation (left-most, below) and the gauche conformation (right-most, below).
Both conformations are free of torsional strain, but, in the gauche conformation, the two methyl groups are in closer proximity than the sum of their van der Waals radii. The interaction between the two methyl groups is repulsive (van der Waals strain), and an energy barrier results.
A measure of the potential energy stored in butane conformers with greater steric hindrance than the anti-conformer ground state is given by these values:
* Gauche, conformer – 3.8 kJ/mol
* Eclipsed H and CH – 16 kJ/mol
* Eclipsed CH and CH – 19 kJ/mol.
The eclipsed methyl groups exert a greater steric strain because of their greater electron density compared to lone hydrogen atoms.
The textbook explanation for the existence of the energy maximum for an eclipsed conformation in ethane is steric hindrance, but, with a C-C bond length of 154 pm and a Van der Waals radius for hydrogen of 120 pm, the hydrogen atoms in ethane are never in each other's way. The question of whether steric hindrance is responsible for the eclipsed energy maximum is a topic of debate to this day. One alternative to the steric hindrance explanation is based on hyperconjugation as analyzed within the Natural Bond Orbital framework. In the staggered conformation, one C-H sigma bonding orbital donates electron density to the antibonding orbital of the other C-H bond. The energetic stabilization of this effect is maximized when the two orbitals have maximal overlap, occurring in the staggered conformation. There is no overlap in the eclipsed conformation, leading to a disfavored energy maximum. On the other hand, an analysis within quantitative molecular orbital theory shows that 2-orbital-4-electron (steric) repulsions are dominant over hyperconjugation. A valence bond theory study also emphasizes the importance of steric effects. | 4 | Stereochemistry |
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the respiratory chains of many organisms from bacteria to humans. It catalyzes the transfer of electrons from NADH to coenzyme Q10 (CoQ10) and translocates protons across the inner mitochondrial membrane in eukaryotes or the plasma membrane of bacteria.
This enzyme is essential for the normal functioning of cells, and mutations in its subunits lead to a wide range of inherited neuromuscular and metabolic disorders. Defects in this enzyme are responsible for the development of several pathological processes such as ischemia/reperfusion damage (stroke and cardiac infarction), Parkinson's disease and others. | 1 | Biochemistry |
In transhydrocyanation, an equivalent of HCN is transferred from a cyanohydrin, e.g. acetone cyanohydrin, to another HCN acceptor. The transfer is an equilibrium process, initiated by base. The reaction can be driven by trapping reactions or by the use of a superior HCN acceptor, such as an aldehyde. | 0 | Organic Chemistry |
As the ordinate scale spans the entire range of theoretically possible vales, from to one can see at a glance at an Eadie–Hofstee plot how well the experimental design fills the theoretical design space, and the plot makes it impossible to hide poor design. By contrast, the other well known straight-line plots make it easy to choose scales that suggest that the design is better than it is. Faulty design, as shown in the right-hand diagram, is common with experiments with a substrate that is not soluble enough or too expensive to use concentrations above , and in this case cannot be estimated satisfactorily. The opposite case, with values concentrated above (left-hand diagram) is less common but not unknown, as for example in a study of nitrate reductase. | 1 | Biochemistry |
* Several in-vitro experiments suggest that ISWI remodelers organize nucleosome into proper bundle form and create equal spacing between nucleosomes, whereas SWI/SNF remodelers disorder nucleosomes.
* The ISWI-family remodelers have been shown to play central roles in chromatin assembly after DNA replication and maintenance of higher-order chromatin structures.
* INO80 and SWI/SNF-family remodelers participate in DNA double-strand break (DSB) repair and nucleotide-excision repair (NER) and thereby plays crucial role in TP53 mediated DNA-damage response.
* NuRD/Mi-2/CHD remodeling complexes primarily mediate transcriptional repression in the nucleus and are required for the maintenance of pluripotency of embryonic stem cells. | 1 | Biochemistry |
In biochemistry, receptor–ligand kinetics is a branch of chemical kinetics in which the kinetic species are defined by different non-covalent bindings and/or conformations of the molecules involved, which are denoted as receptor(s) and ligand(s). Receptor–ligand binding kinetics also involves the on- and off-rates of binding.
A main goal of receptor–ligand kinetics is to determine the concentrations of the various kinetic species (i.e., the states of the receptor and ligand) at all times, from a given set of initial concentrations and a given set of rate constants. In a few cases, an analytical solution of the rate equations may be determined, but this is relatively rare. However, most rate equations can be integrated numerically, or approximately, using the steady-state approximation. A less ambitious goal is to determine the final equilibrium concentrations of the kinetic species, which is adequate for the interpretation of equilibrium binding data.
A converse goal of receptor–ligand kinetics is to estimate the rate constants and/or dissociation constants of the receptors and ligands from experimental kinetic or equilibrium data. The total concentrations of receptor and ligands are sometimes varied systematically to estimate these constants. | 7 | Physical Chemistry |
When only the static magnetic field (B) is turned on, the spin will precess around it with Larmor frequency ν and the corresponding angular frequency is ω.
According to mechanics, the equation of motion of the spin J is:
where μ is the magnetic moment.
g is g-factor, which is dimensionless and reflecting the environmental effect on the spin.
Solving gives the angular frequency (Larmor frequency) with the magnetic field pointing on z-axis:
The minus sign is necessary. It reflects that the J is rotating in left-hand when the thumb is pointing as the H field.
when turned on the rotating magnetic field (B), with angular frequency ω. In the rotating frame of the rotating field, the equation of motion is:
or
if , the static field is cancelled, and the spin now precesses around H with angular frequency Rabi frequency
Since the rotating field is perpendicular to the static field, the spin in rotating frame is now able to flip between up and down.
By sweeping ω, one can obtain a maximum flipping and determine the magnetic moment. | 7 | Physical Chemistry |
N-Methylmorpholine N-oxide (more correctly 4-methylmorpholine 4-oxide), NMO or NMMO is an organic compound. This heterocyclic amine oxide and morpholine derivative is used in organic chemistry as a co-oxidant and sacrificial catalyst in oxidation reactions for instance in osmium tetroxide oxidations and the Sharpless asymmetric dihydroxylation or oxidations with TPAP. NMO is commercially supplied both as a monohydrate CHNO·HO and as the anhydrous compound. The monohydrate is used as a solvent for cellulose in the lyocell process to produce cellulose fibers. | 0 | Organic Chemistry |
Pradeep Mathur (born 1955) is an Indian organometallic and cluster chemist and the founder director of the Indian Institute of Technology, Indore. He is a former professor of the Indian Institute of Technology, Mumbai and is known for his studies on mixed metal cluster compounds. He is an elected fellow of the Indian Academy of Sciences The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 2000, for his contributions to chemical sciences. He has also been honoured by the award of an honorary Doctor of Science degree by the University of Keele in the U.K. | 0 | Organic Chemistry |
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