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In catalytic kinetics, two basic approximations are useful (in different circumstances) to describe the behavior of many systems. The situations in which the pre-equilibrium and steady-state approximations are valid can often be distinguished by reaction progress kinetic analysis, and the two situations are closely related to the resting state of the catalyst. | 7 | Physical Chemistry |
The plastid DNA of maize seedlings is subjected to increasing damage as the seedlings develop. The DNA damage is due to oxidative environments created by photo-oxidative reactions and photosynthetic/ respiratory electron transfer. Some DNA molecules are repaired but DNA with unrepaired damage is apparently degraded to non-functional fragments.
DNA repair proteins are encoded by the cells nuclear genome and then translocated to plastids where they maintain genome stability/ integrity by repairing the plastids DNA. For example, in chloroplasts of the moss Physcomitrella patens, a protein employed in DNA mismatch repair (Msh1) interacts with proteins employed in recombinational repair (RecA and RecG) to maintain plastid genome stability. | 5 | Photochemistry |
Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, including light from frequencies beyond the visible light range, i.e. infrared and ultra-violet. It can allow extraction of additional information the human eye fails to capture with its visible receptors for red, green and blue. It was originally developed for military target identification and reconnaissance. Early space-based imaging platforms incorporated multispectral imaging technology to map details of the Earth related to coastal boundaries, vegetation, and landforms. Multispectral imaging has also found use in document and painting analysis.
Multispectral imaging measures light in a small number (typically 3 to 15) of spectral bands. Hyperspectral imaging is a special case of spectral imaging where often hundreds of contiguous spectral bands are available. | 7 | Physical Chemistry |
Note that Sides 1 and 2 are no longer in osmotic equilibrium (i.e. the total osmolytes on each side are not the same)
In vivo, ion balance does equilibriate at the proportions that would be predicted by the Gibbs–Donnan model, because the cell cannot tolerate the attendant large influx of water. This is balanced by instating a functionally impermeant cation, Na, extracellularly to counter the anionic protein. Na does cross the membrane via leak channels (the permeability is approximately 1/10 that of K, the most permeant ion) but, as per the pump-leak model, it is extruded by the Na/K-ATPase. | 7 | Physical Chemistry |
Because water has strong cohesive and adhesive forces, it exhibits capillary action. Strong cohesion from hydrogen bonding and adhesion allows trees to transport water more than 100 m upward. | 2 | Environmental Chemistry |
Because natural moissanite is extremely scarce, most silicon carbide is synthetic. Silicon carbide is used as an abrasive, as well as a semiconductor and diamond simulant of gem quality. The simplest process to manufacture silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between and . Fine SiO particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material. The silica fume, which is a byproduct of producing silicon metal and ferrosilicon alloys, can also be converted to SiC by heating with graphite at .
The material formed in the Acheson furnace varies in purity, according to its distance from the graphite resistor heat source. Colorless, pale yellow and green crystals have the highest purity and are found closest to the resistor. The color changes to blue and black at greater distance from the resistor, and these darker crystals are less pure. Nitrogen and aluminium are common impurities, and they affect the electrical conductivity of SiC.
Pure silicon carbide can be made by the Lely process, in which SiC powder is sublimed into high-temperature species of silicon, carbon, silicon dicarbide (SiC), and disilicon carbide (SiC) in an argon gas ambient at 2500 °C and redeposited into flake-like single crystals, sized up to 2 × 2 cm, at a slightly colder substrate. This process yields high-quality single crystals, mostly of 6H-SiC phase (because of high growth temperature).
A modified Lely process involving induction heating in graphite crucibles yields even larger single crystals of 4 inches (10 cm) in diameter, having a section 81 times larger compared to the conventional Lely process.
Cubic SiC is usually grown by the more expensive process of chemical vapor deposition (CVD) of silane, hydrogen and nitrogen. Homoepitaxial and heteroepitaxial SiC layers can be grown employing both gas and liquid phase approaches.
To form complexly shaped SiC, preceramic polymers can be used as precursors which form the ceramic product through pyrolysis at temperatures in the range 1000–1100 °C. Precursor materials to obtain silicon carbide in such a manner include polycarbosilanes, poly(methylsilyne) and polysilazanes. Silicon carbide materials obtained through the pyrolysis of preceramic polymers are known as polymer derived ceramics or PDCs. Pyrolysis of preceramic polymers is most often conducted under an inert atmosphere at relatively low temperatures. Relative to the CVD process, the pyrolysis method is advantageous because the polymer can be formed into various shapes prior to thermalization into the ceramic.
SiC can also be made into wafers by cutting a single crystal either using a diamond wire saw or by using a laser. SiC is a useful semiconductor used in power electronics. | 8 | Metallurgy |
Sequential double ionization is a process of formation of doubly charged ions consisting of two single-electron ionization events: the first electron is removed from a neutral atom/molecule (leaving a singly charged ion in the ground state or an excited state) followed by detachment of the second electron from the ion. | 7 | Physical Chemistry |
In 1928, German chemist H. O. Albrecht found that blood, among other substances, enhanced the luminescence of luminol in an alkaline solution of hydrogen peroxide. In 1936, Karl Gleu and Karl Pfannstiel confirmed this enhancement in the presence of haematin, a component of blood. In 1937, German forensic scientist Walter Specht made extensive studies of luminol's application to the detection of blood at crime scenes. In 1939, San Francisco pathologists Frederick Proescher and A. M. Moody made three important observations about luminol:
# although the test is presumptive, large areas of suspected material can be examined rapidly;
# dried and decomposed blood gave a stronger and more lasting reaction than fresh blood; and
# if the luminescence disappears, it may be reproduced by the application of a fresh luminol-hydrogen peroxide solution; dried bloodstains may thus be made luminescent repeatedly. | 3 | Analytical Chemistry |
Thiosulfate ion is known in the very rare mineral sidpietersite . The presence of this anion in the mineral bazhenovite was disputed. | 8 | Metallurgy |
The advent of sequencing has permitted scientists to elucidate a huge landscape of new miRNAs, to increase our knowledge of the biogenesis involved and to discover putative post-transcriptional editing processes in miRNAs ignored until now. These processes mostly generate variations of the current miRNAs that are annotated in miRBase in the 3 and 5 terminus and in minor frequencies, nucleotide substitution along the miRNA length,. The variations are mainly generated by a shift of Drosha and Dicer in the cleavage site, but also by nucleotide additions at the 3-end, resulting in new sequences different from the annotated miRNA. These were named "isomiRs" by Morin et al., 2008. IsomiRs have been well established along different species in metazoa and deeply described for the first time in human stem cells and human brain samples. Moreover, it has been proven that isomiRs are not caused by RNA degradation during sample preparation for next generation sequencing. Some studies have tried to explain the miRNA diversity by structural bases of precursors but without clear results. The functionality of adenylation or uridynilation at the 3end (3addition isomiRs) has been related to alterations in the miRNA-3-UTR stability. Furthermore, differential expression of isomiRs has been detected during development in D. melanogaster and Hippoglossus hippoglossus L., suggesting a biological function.
*Trimming variants: these are possible due to slight variations by Drosha and/or Dicer
*Nucleotide addition: Wyman et al. have described the process of nucleotide transferases adding individual nucleotides to miRNA sequences
*Nucleotide substitution: there is a huge range of possible changes in such an event, some of them can be explained by current Adenosine_deaminase like A to G or C to U, in a similar way to what happens in post-transcriptional RNA editing events involving mRNA. | 1 | Biochemistry |
The presynaptic bouton has an efficiently orchestrated process to fuse vesicles to the presynaptic membrane to release neurotransmitters and regenerate neurotransmitter vesicles. This process called the synaptic vesicle cycle maintains the number of vesicles in the presynaptic bouton and allows the synaptic terminal to be an autonomous unit. The cycle begins with (1) a region of the golgi apparatus is pinched off to form the synaptic vesicle and this vesicle is transported to the synaptic terminal. At the terminal (2) the vesicle is filled with neurotransmitter. (3) The vesicle is transported to the active zone and docked in close proximity to the plasma membrane. (4) During an action potential the vesicle is fused with the membrane, releases the neurotransmitter and allows the membrane proteins previously on the vesicle to diffuse to the periactive zone. (5) In the periactive zone the membrane proteins are sequestered and are endocytosed forming a clathrin coated vesicle. (6) The vesicle is then filled with neurotransmitter and is then transported back to the active zone.
The endocytosis mechanism is slower than the exocytosis mechanism. This means that in intense activity the vesicle in the terminal can become depleted and no longer available to be released. To help prevent the depletion of synaptic vesicles the increase in calcium during intense activity can activate calcineurin which dephosphorylate proteins involved in clathrin-mediated endocytosis. | 1 | Biochemistry |
The SI-unit for mass concentration is kg/m (kilogram/cubic metre). This is the same as mg/mL and g/L. Another commonly used unit is g/(100 mL), which is identical to g/dL (gram/decilitre). | 3 | Analytical Chemistry |
A triose is a monosaccharide, or simple sugar, containing three carbon atoms. There are only three possible trioses: the two enantiomers of glyceraldehyde, which are aldoses; and dihydroxyacetone, a ketose which is symmetrical and therefore has no enantiomers.
Trioses are important in cellular respiration. During glycolysis, fructose-1,6-bisphosphate is broken down into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. Lactic acid and pyruvic acid are later derived from these molecules. | 1 | Biochemistry |
Because the substituents attached to the imine nitrogen exert a profound influence on reactivity, few general catalyst systems exist for the enantioselective hydrogenation of imines and imine derivatives. However, catalyst systems have been developed that catalyze hydrogenation of particular classes of imines with high enantioselectivity and yield. This section describes some of these systems and is organized by the substitution pattern of the imine.
α-Carboxy imines are attractive precursors for α-amino acids. Organocatalytic reduction of these substrates is possible using a Hantzsch ester and a chiral phosphoric acid catalyst. | 0 | Organic Chemistry |
Frohring's father, William, a railroad engineer, was born in Bavaria and immigrated to the United States at 1 years old, while his mother, Martha, was born in Ohio to German emigrants. He was married to the former Gertrude Lewis, and had four children. He died of a heart attack at his home on Munn Road in Newbury, Ohio. | 7 | Physical Chemistry |
Some nutrients are complex molecules (for example vitamin B) which would be destroyed if they were broken down into their functional groups. To digest vitamin B non-destructively, haptocorrin in saliva strongly binds and protects the B molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes.
After the B-haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B molecules which rebind to intrinsic factor (IF). These B-IF complexes travel to the ileum portion of the small intestine where cubilin receptors enable assimilation and circulation of B-IF complexes in the blood. | 1 | Biochemistry |
Nayak was named after Swami Vivekananda (born Narendra Nath Datta). He has stated that seeing his father's business premises being repossessed by the bank and his father buying a lottery ticket on the advice of an astrologer to pay off the loan with the total confidence that it would get the first prize made him turn to rationalism. He married Asha Nayak, a lawyer in Mangaluru in a non-religious ceremony. Nayak started out working as a lecturer in the Department of biochemistry in the Kasturba Medical College in Mangalore in 1978. In 1982, he met Basava Premanand, a notable rationalist from Kerala, and was influenced by him.
Karnataka State Police withdrew his security wherein Nayak was quoted to say that it was an open invitation by forces to finish him. | 1 | Biochemistry |
N(6)-Carboxymethyllysine (CML), also known as N-(carboxymethyl)lysine, is an advanced glycation endproduct (AGE). CML has been the most used marker for AGEs in food analysis.
Recently, it has been demonstrated that gut microbiota mediates an aging-associated decline in gut barrier function, allowing AGEs to leak into the bloodstream from the gut and impairing microglial function in the brain. It is suggested that the amount of CML in human blood samples may correlated with age.
A humanized monoclonal antibody which binds to N6 – carboxymethyl lysine shows considerable promise as a possible therapeutic agent for treating pancreatic cancer. | 1 | Biochemistry |
RNA polymerase is composed of a core and a holoenzyme structure. The core enzymes contains the catalytic properties of RNA polymerase and is made up of ββ′α2ω subunits. This sequence is conserved across all bacterial species. The holoenzyme is composed of a specific component known as the sigma factor (σ-factor). The sigma factor functions in aiding in promoter recognition, correct placement of RNA polymerase, and beginning unwinding at the start site. After the sigma factor performs its required function, it dissociates, while the catalytic portion remains on the DNA and continues transcription. Additionally, RNA polymerase contains a core Mg+ ion that assists the enzyme with its catalytic properties. RNA polymerase works by catalyzing the nucleophilic attack of 3’ OH of RNA to the alpha phosphate of a complementary NTP molecule to create a growing strand of RNA from the template strand of DNA. Furthermore, RNA polymerase also displays exonuclease activities, meaning that if improper base pairing is detected, it can cut out the incorrect bases and replace them with the proper, correct one. | 1 | Biochemistry |
The glycosylation of proteins has an array of different applications from influencing cell to cell communication to changing the thermal stability and the folding of proteins. Due to the unique abilities of glycoproteins, they can be used in many therapies. By understanding glycoproteins and their synthesis, they can be made to treat cancer, Crohn's Disease, high cholesterol, and more.
The process of glycosylation (binding a carbohydrate to a protein) is a post-translational modification, meaning it happens after the production of the protein. Glycosylation is a process that roughly half of all human proteins undergo and heavily influences the properties and functions of the protein. Within the cell, glycosylation occurs in the endoplasmic reticulum. | 0 | Organic Chemistry |
In ecology, the term productivity refers to the rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume (unit surface) per unit of time, such as grams per square metre per day (g m d). The unit of mass can relate to dry matter or to the mass of generated carbon. The productivity of autotrophs, such as plants, is called primary productivity, while the productivity of heterotrophs, such as animals, is called secondary productivity.
The productivity of an ecosystem is influenced by a wide range of factors, including nutrient availability, temperature, and water availability. Understanding ecological productivity is vital because it provides insights into how ecosystems function and the extent to which they can support life. Productivity is typically divided into two categories: primary and secondary productivity. | 9 | Geochemistry |
Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds. It is one of the main types of bonding, along with covalent bonding and metallic bonding. Ions are atoms (or groups of atoms) with an electrostatic charge. Atoms that gain electrons make negatively charged ions (called anions). Atoms that lose electrons make positively charged ions (called cations). This transfer of electrons is known as electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be more complex, e.g. molecular ions like or . In simpler words, an ionic bond results from the transfer of electrons from a metal to a non-metal to obtain a full valence shell for both atoms.
Clean ionic bonding — in which one atom or molecule completely transfers an electron to another — cannot exist: all ionic compounds have some degree of covalent bonding or electron sharing. Thus, the term "ionic bonding" is given when the ionic character is greater than the covalent character – that is, a bond in which there is a large difference in electronegativity between the two atoms, causing the bonding to be more polar (ionic) than in covalent bonding where electrons are shared more equally. Bonds with partially ionic and partially covalent characters are called polar covalent bonds.
Ionic compounds conduct electricity when molten or in solution, typically not when solid. Ionic compounds generally have a high melting point, depending on the charge of the ions they consist of. The higher the charges the stronger the cohesive forces and the higher the melting point. They also tend to be soluble in water; the stronger the cohesive forces, the lower the solubility. | 6 | Supramolecular Chemistry |
For applications in materials science dealing with phase changes between different solid structures, pressure is often imagined to be constant (for example at one atmosphere), and is ignored as a degree of freedom, so the formula becomes:
This is sometimes incorrectly called the "condensed phase rule", but it is not applicable to condensed systems which are subject to high pressures (for example, in geology), since the effects of these pressures are important. | 7 | Physical Chemistry |
DAVID provides a comprehensive set of functional annotation tools for investigators to understand biological meaning behind large list of genes. For any given gene list, DAVID tools are able to:
* Identify enriched biological themes, particularly GO terms
* Discover enriched functional-related gene groups
* Cluster redundant annotation terms
* Visualize genes on BioCarta & KEGG pathway maps
* Display related many-genes-to-many-terms on 2-D view.
* Search for other functionally related genes not in the list
* List interacting proteins
* Explore gene names in batch
* Link gene-disease associations
* Highlight protein functional domains and motifs
* Redirect to related literatures
* Convert gene identifiers from one type to another. | 1 | Biochemistry |
A process for electrochemical production of titanium through the reduction of titanium oxide in a calcium chloride solution was first described in a 1904 German patent, and later in a US patent by Carl Marcus Olson.
The FFC Cambridge process was developed by George Chen, Derek Fray, and Thomas Farthing between 1996 and 1997 at the University of Cambridge. (The name FFC derives from the first letters of the last names of the inventors). The intellectual property relating to the technology has been acquired by Metalysis, (Sheffield, UK). | 7 | Physical Chemistry |
Raman spectroelectrochemistry is based on the inelastic scattering or Raman scattering of monochromatic light when strikes on a specific molecule, providing information about vibrational energy of that molecule. Raman spectrum provides highly specific information about the structure and composition of the molecules such as a true fingerprint of them. It has been extensively used to study single wall carbon nanotubes and graphene. | 7 | Physical Chemistry |
Tetrafluoromethane and silicon tetrafluoride can be prepared in the laboratory by the reaction of silicon carbide with fluorine.
: SiC + 4 F → CF + SiF | 2 | Environmental Chemistry |
In a manner analogous to receptor labeling, diazirine containing compounds that are analogs of natural substrates have also been used to identify binding pockets of enzymes. Examples include:
* The synthesis of a diazirine containing analog of etoposide, a widely used cancer drug targeting topoisomerase II, which holds promise for the identification of the etoposide binding site.
* The discovery that caprolactam-type gamma-secretase inhibitors target the SPP subunit of the gamma-secretase, which has been implicated in Alzheimer's disease. | 5 | Photochemistry |
Organic thiocyanates are hydrolyzed to thiocarbamates in the Riemschneider thiocarbamate synthesis.
Some thiocyanates isomerize to the isothiocyandates. This reaction is especially rapid for the allyl isothiocyanate: | 0 | Organic Chemistry |
Trithiophosphate is the anion [POS], which has C symmetry. Tetrathiophosphate is the anion [PS], which has T symmetry. | 0 | Organic Chemistry |
T-DNA contains two types of genes: the oncogenic genes, encoding for enzymes involved in the synthesis of auxins and cytokinins and responsible for tumor formation, and the genes encoding for the synthesis of opines. These compounds, produced by the condensation between amino acids and sugars, are synthesized and excreted by the crown gall cells, and they are consumed by A. tumefaciens as carbon and nitrogen sources.
The genes involved in opine catabolism, T-DNA transfer from the bacterium to the plant cell and bacterium-bacterium plasmid conjugative transfer are located outside the T-DNA. The T-DNA fragment is flanked by 25-bp direct repeats, which act as a cis-element signal for the transfer apparatus. The process of T-DNA transfer is mediated by the cooperative action of proteins encoded by genes determined in the Ti plasmid virulence region (vir genes) and in the bacterial chromosome. The Ti plasmid also contains the genes for opine catabolism produced by the crown gall cells and regions for conjugative transfer and for its own integrity and stability. The 30 kb virulence (vir) region is a regulon organized in six operons essential for the T-DNA transfer (virA, virB, virD, and virG) or for the increasing of transfer efficiency (virC and virE). Several chromosomal-determined genetic elements have shown their functional role in the attachment of A. tumefaciens to the plant cell and bacterial colonization. The loci chvA and chvB are involved in the synthesis and excretion of the b -1,2 glucan, the required for the sugar enhancement of vir genes induction and bacterial chemotaxis. The cell locus is responsible for the synthesis of cellulose fibrils. The locus is involved in the synthesis of both cyclic glucan and acid succinoglycan. The att locus is involved in the cell surface proteins. | 1 | Biochemistry |
Accumulation of tau protein is associated with neurodegenerative diseases including Alzheimers and Parkinsons diseases as well as other tauopathies. Tau protein isoforms are created by alternative splicing of exons 2, 3 and 10. The regulation of tau splicing is specific to stage of development, physiology and location. Errors in tau splicing can occur in both exons and introns and, depending on the error, result in changes to protein structure or loss of function. Aggregation of these abnormal tau proteins correlates directly with pathogenesis and disease progression. Minigenes have been used by several researchers to help understand the regulatory components responsible for mRNA splicing of the TAU gene. | 1 | Biochemistry |
A primer is a short, single-stranded nucleic acid used by all living organisms in the initiation of DNA synthesis. A synthetic primer may also be referred to as an oligo, short for oligonucleotide. DNA polymerase (responsible for DNA replication) enzymes are only capable of adding nucleotides to the 3’-end of an existing nucleic acid, requiring a primer be bound to the template before DNA polymerase can begin a complementary strand. DNA polymerase adds nucleotides after binding to the RNA primer and synthesizes the whole strand. Later, the RNA strands must be removed accurately and replace them with DNA nucleotides forming a gap region known as a nick that is filled in using an enzyme called ligase. The removal process of the RNA primer requires several enzymes, such as Fen1, Lig1, and others that work in coordination with DNA polymerase, to ensure the removal of the RNA nucleotides and the addition of DNA nucleotides. Living organisms use solely RNA primers, while laboratory techniques in biochemistry and molecular biology that require in vitro DNA synthesis (such as DNA sequencing and polymerase chain reaction) usually use DNA primers, since they are more temperature stable. Primers can be designed in laboratory for specific reactions such as polymerase chain reaction (PCR). When designing PCR primers, there are specific measures that must be taken into consideration, like the melting temperature of the primers and the annealing temperature of the reaction itself. Moreover, the DNA binding sequence of the primer in vitro has to be specifically chosen, which is done using a method called basic local alignment search tool (BLAST) that scans the DNA and finds specific and unique regions for the primer to bind. | 1 | Biochemistry |
There is a large number of methods for the determination of particle size, and it is important to acknowledge that these different methods are not expected to give identical results. The size of a particle depends on the method used for its measurement, and it is important to choose the method that is most relevant to the application.
The "See also" section covers many of these techniques. In most of them, the particle size is inferred from a measurement of, for example: light scattering; electrical resistance; particle motion, rather than a direct measurement of particle diameter. This enables rapid measurement of a particle size distribution by an instrument, but does require some form of calibration or assumptions regarding the nature of the particles. Most often this includes the assumption of spherical particles, thus giving a result which is an equivalent spherical diameter. Thus, it is usual for measured particle size distributions to be different when comparing the results between different equipment. The most appropriate method to use is normally the one where the method is aligned to the end use of the data.
For example, to choose whether a chemical compound should be measured by dynamic light scattering or laser diffraction, one generally considers the expected size range, the sample type (liquid or solid), the amount of sample available, the chemical stability, as well its application field. If designing a sedimentation vessel, then a sedimentation technique for sizing is most relevant. However, this approach is often not possible, and an alternative technique must be used. An online Expert system to assist in the selection (and elimination) of particle size analysis equipment has been developed. | 3 | Analytical Chemistry |
Gamma-ray spectroscopy is the qualitative study of the energy spectra of gamma-ray sources, such as in the nuclear industry, geochemical investigation, and astrophysics. Gamma-ray spectrometry, on the other hand, is the method used to acquire a quantitative spectrum measurement.
Most radioactive sources produce gamma rays, which are of various energies and intensities. When these emissions are detected and analyzed with a spectroscopy system, a gamma-ray energy spectrum can be produced.
A detailed analysis of this spectrum is typically used to determine the identity and quantity of gamma emitters present in a gamma source, and is a vital tool in radiometric assay. The gamma spectrum is characteristic of the gamma-emitting nuclides contained in the source, just like in an optical spectrometer, the optical spectrum is characteristic of the material contained in a sample. | 7 | Physical Chemistry |
Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements. They include gold and silver, but also the so-called platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum (see precious metals). Extraction of these metals from their corresponding hosting minerals would typically require pyrometallurgy (e.g., roasting), hydrometallurgy (cyanidation), or both as processing routes.
Early studies have demonstrated that gold dissolution rate in Ethaline compares very favourably to the cyanidation method, which is further enhanced by the addition of iodine as an oxidising agent. In an industrial process the iodine has the potential to be employed as an electrocatalyst, whereby it is continuously recovered in situ from the reduced iodide by electrochemical oxidation at the anode of an electrochemical cell. Dissolved metals can be selectively deposited at the cathode by adjusting the electrode potential. The method also allows better selectivity as part of the gangue (e.g., pyrite) tend to be dissolved more slowly.
Sperrylite (PtAs) and moncheite (PtTe), which are typically the more abundant platinum minerals in many orthomagmatic deposits, do not react under the same conditions in Ethaline because they are disulphide (pyrite), diarsenide (sperrylite) or ditellurides (calaverite and moncheite) minerals, which are particularly resistant to iodine oxidation. The reaction mechanism by which dissolution of platinum minerals is taking place is still under investigation. | 8 | Metallurgy |
Amine oxides are surfactants commonly used in consumer products such as shampoos, conditioners, detergents, and hard surface cleaners. Alkyl dimethyl amine oxide (chain lengths C10–C16) is the most commercially used amine oxide. They are considered a high production volume class of compounds in more than one member country of the Organisation for Economic Co-operation and Development (OECD); with annual production over in the US, Europe, and Japan, respectively. In North America, more than 95% of amine oxides are used in home cleaning products. They serve as stabilizers, thickeners, emollients, emulsifiers, and conditioners with active concentrations in the range of 0.1–10%. The remainder (< 5%) is used in personal care, institutional, commercial products and for unique patented uses such as photography. | 0 | Organic Chemistry |
The traditional method for attaching sugars to natural products, drugs or drug leads is by chemical glycosylation. This classical approach typically requires multiple protection/deprotection steps in addition to the key anomeric activation/coupling reaction which, depending upon the glycosyl donor/acceptor pair, can lead to a mixture of anomers. Unlike classical chemical glycosylation, glycorandomization methods are divergent (i.e., diverge from a common starting material, see divergent synthesis) and are not dependent upon sugar/aglycon protection/deprotection or sugar anomeric activation. Two complementary strategies to achieve glycorandomization/diversification have been developed: an enzyme-based strategy referred to as chemoenzymatic glycorandomization and a chemoselective method known as neoglycorandomization. Both methods start with free reducing sugars and a target aglycon to afford a library of compounds which differ solely by the sugars appended to the target natural product, drug or drug lead. | 0 | Organic Chemistry |
High-temperature corrosion typically occurs in environments that have heat and chemical such as hydrocarbon fuel sources but also other chemicals enable this form of corrosion.
Thus it can occur in boilers, automotive engines driven by diesel or gasoline, metal production furnaces and flare stacks from oil and gas production. High temperature oxidation of metals would also be included. | 8 | Metallurgy |
Every polyhedron has a dihedral angle at every edge describing the relationship of the two faces that share that edge. This dihedral angle, also called the face angle, is measured as the internal angle with respect to the polyhedron. An angle of 0° means the face normal vectors are antiparallel and the faces overlap each other, which implies that it is part of a degenerate polyhedron. An angle of 180° means the faces are parallel, as in a tiling. An angle greater than 180° exists on concave portions of a polyhedron.
Every dihedral angle in an edge-transitive polyhedron has the same value. This includes the 5 Platonic solids, the 13 Catalan solids, the 4 Kepler–Poinsot polyhedra, the two quasiregular solids, and two quasiregular dual solids. | 4 | Stereochemistry |
Methyl violet 2B (IUPAC name: N-(4-(bis(4-(dimethylamino)phenyl)methylene)cyclohexa-2,5-dien-1-ylidene)methanaminium chloride) is a green powder which is soluble in water and ethanol but not in xylene. It appears yellow in solution of low pH (~0.15) and changes to violet with pH increasing toward 3.2. | 3 | Analytical Chemistry |
The fugacity can be deduced from measurements of volume as a function of pressure at constant temperature. In that case,
This integral can also be calculated using an equation of state.
The integral can be recast in an alternative form using the compressibility factor
Then
This is useful because of the theorem of corresponding states: If the pressure and temperature at the critical point of the gas are and , we can define reduced properties and . Then, to a good approximation, most gases have the same value of for the same reduced temperature and pressure. However, in geochemical applications, this principle ceases to be accurate at pressures where metamorphism occurs.
For a gas obeying the van der Waals equation, the explicit formula for the fugacity coefficient is
This formula is based on the molar volume. Since the pressure and the molar volume are related through the equation of state; a typical procedure would be to choose a volume, calculate the corresponding pressure, and then evaluate the right-hand side of the equation. | 7 | Physical Chemistry |
Chelation is a type of bonding of ions and the molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are called chelants, chelators, chelating agents, or sequestering agents. They are usually organic compounds, but this is not a necessity.
The word chelation is derived from Greek χηλή, chēlē, meaning "claw"; the ligands lie around the central atom like the claws of a crab. The term chelate was first applied in 1920 by Sir Gilbert T. Morgan and H. D. K. Drew, who stated: "The adjective chelate, derived from the great claw or chele (Greek) of the crab or other crustaceans, is suggested for the caliperlike groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings."
Chelation is useful in applications such as providing nutritional supplements, in chelation therapy to remove toxic metals from the body, as contrast agents in MRI scanning, in manufacturing using homogeneous catalysts, in chemical water treatment to assist in the removal of metals, and in fertilizers. | 7 | Physical Chemistry |
An alternative protocol uses a solution of iodate ion (for instance potassium iodate) to which an acidified solution (again with sulfuric acid) of sodium bisulfite is added.
In this protocol, iodide ion is generated by the following slow reaction between the iodate and bisulfite:
This first step is the rate determining step. Next, the iodate in excess will oxidize the iodide generated above to form iodine:
However, the iodine is reduced immediately back to iodide by the bisulfite:
When the bisulfite is fully consumed, the iodine will survive (i.e., no reduction by the bisulfite) to form the dark blue complex with starch. | 7 | Physical Chemistry |
Ty5 is one of five endogenous retrotransposons native to the model organism Saccharomyces cerevisiae, all of which target integration to gene poor regions. Endogenous retrotransposons are hypothesized to target gene poor chromosomal targets in order to reduce the chance of inactivating host genes. Ty1-Ty4 integrate upstream of Pol III promoters, while Ty5 targets integration to loci bound in heterochromatin. In the case of Ty5, this likely occurs by means of an interaction between the C-terminus of integrase and a target protein. The tight targeting patterns seen for the Ty elements are thought to be a means to limit damage to its host, which has a very gene dense genome. Ty5 was discovered in the mid 1990s in the laboratory of Daniel Voytas at Iowa State University. Ty5 is used as a model system by which to understand the biology of the telomere and heterochromatin. The Ty5 retrotransposon is used as a genetic model to study the architecture and dynamics of the telomeres and heterochromatin. | 1 | Biochemistry |
The mercury beating heart was first observed in the year 1800 by Alessandro Volta and William Henry. The chemical phenomenon in the form best known today was first described by German chemist Friedlieb Ferdinand Runge, the discoverer of caffeine. | 7 | Physical Chemistry |
Electroslag remelting (ESR), also known as electro-flux remelting, is a process of remelting and refining steel and other alloys for mission-critical applications in aircraft, thermal power stations, nuclear power plants, military technology and others.
The electroslag remelting (ESR) process is used to remelt and refine steels and various super-alloys, resulting in high-quality ingots. This process can be started up through vacuum induction melting. The ESR process uses the as-cast alloy as a consumable electrode. Electric current (generally AC) is passed between the electrode and the new ingot, which is formed in the bottom of a water-cooled copper mold. The new ingot is covered in an engineered slag that is superheated by the electric current. The electrode tip is slowly melted from contact with the slag. These metal droplets travel through the slag to the bottom of the water-cooled mold and slowly freeze as the ingot is directionally solidified upwards from the bottom of the mold. The slag pool floats above the refined alloy, continuously floating upwards as the alloy solidifies. The molten metal is cleaned of impurities that chemically react with the slag or otherwise float to the top of the molten pool as the molten droplets pass through the slag.
Electroslag remelting uses highly reactive slags (calcium fluoride, lime, alumina, or other oxides are usually the main components) to reduce the amount of type-A sulfide present in biometal alloys. It is a common practice in European industries. ESR reduces other types of inclusions as well, and is seen as an alternative to the vacuum arc remelting (VAR) method that is prevalent in US industries.
An example of the use of the electro-slag refined (ESR) steel technique is the L30 tank gun.
CrNi60WTi is a stainless steel which is best formed by either electro-slag remelting or vacuum arc remelting. This alloy can be used for the construction of nuclear power plants. | 8 | Metallurgy |
The separating funnel relies on the concept of "like dissolves like", which describes the ability of polar solvents to dissolve polar solutes and non-polar solvents to dissolve non-polar solutes. When the separating funnel is agitated, each solute migrates to the solvent (also referred to as "phase") in which it is more soluble.
The solvents normally do not form a unified solution together because they are immiscible. When the funnel is kept stationary after agitation, the liquids form distinct physical layers - lower density liquids will stay above higher density liquids. A mixture of solutes is thus separated into two physically separate solutions, each enriched in different solutes.
The stopcock may be opened after the two phases separate to allow the bottom layer to escape the separator funnel. The top layer may be retained in the separating funnel for further extractions with additional batches of solvent or drained out into a separate vessel for other uses. If it is desired to retain the bottom layer in the separating funnel for further extractions, both layers are taken out separately, and then the former bottom layer is returned to the separating funnel.
Each independent solution can then be extracted again with additional batches of solvent, used for other physical or chemical processes. If the goal was to separate a soluble material from mixture, the solution containing that desired product can sometimes simply be evaporated to leave behind the purified solute. For this reason, it is a practical benefit to use volatile solvents for extracting the desired material from the mixture. | 3 | Analytical Chemistry |
Joan Berkowitz<br>
Paul Crutzen (Nobel Prize in Chemistry, 1995)<br>
Philip Gschwend<br>
Alice Hamilton<br>
John M. Hayes<br>
Charles David Keeling<br>
Ralph Keeling<br>
Mario Molina (Nobel Prize in Chemistry, 1995)<br>
James J. Morgan<br>
Clair Patterson<br>
Roger Revelle<br>
Sherry Roland (Nobel Prize in Chemistry, 1995)<br>
Robert Angus Smith<br>
Susan Solomon<br>
Werner Stumm<br>
Ellen Swallow Richards<br>
Hans Suess<br>
John Tyndall | 2 | Environmental Chemistry |
Multi-parametric surface plasmon resonance (MP-SPR) is based on surface plasmon resonance (SPR), an established real-time label-free method for biomolecular interaction analysis, but it uses a different optical setup, a goniometric SPR configuration. While MP-SPR provides same kinetic information as SPR (equilibrium constant, dissociation constant, association constant), it provides also structural information (refractive index, layer thickness). Hence, MP-SPR measures both surface interactions and nanolayer properties. | 7 | Physical Chemistry |
Synthetic perovskites are possible materials for high-efficiency photovoltaics – they showed a conversion efficiency of up to 26.3% and can be manufactured using the same thin-film manufacturing techniques as that used for thin film silicon solar cells. Methylammonium tin halides and methylammonium lead halides are of interest for use in dye-sensitized solar cells. Some perovskite PV cells reach a theoretical peak efficiency of 31%.
Among the methylammonium halides studied so far the most common is the methylammonium lead triiodide (). It has a high charge carrier mobility and charge carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted as current, instead of losing their energy as heat within the cell. effective diffusion lengths are some 100 nm for both electrons and holes.
Methylammonium halides are deposited by low-temperature solution methods (typically spin-coating). Other low-temperature (below 100 °C) solution-processed films tend to have considerably smaller diffusion lengths. Stranks et al. described nanostructured cells using a mixed methylammonium lead halide () and demonstrated one amorphous thin-film solar cell with an 11.4% conversion efficiency, and another that reached 15.4% using vacuum evaporation. The film thickness of about 500 to 600 nm implies that the electron and hole diffusion lengths were at least of this order. They measured values of the diffusion length exceeding 1 μm for the mixed perovskite, an order of magnitude greater than the 100 nm for the pure iodide. They also showed that carrier lifetimes in the mixed perovskite are longer than in the pure iodide. Liu et al. applied Scanning Photo-current Microscopy to show that the electron diffusion length in mixed halide perovskite along (110) plane is in the order of 10 μm.
For , open-circuit voltage (V) typically approaches 1 V, while for with low Cl content, V > 1.1 V has been reported. Because the band gaps (E) of both are 1.55 eV, V-to-E ratios are higher than usually observed for similar third-generation cells. With wider bandgap perovskites, V up to 1.3 V has been demonstrated.
The technique offers the potential of low cost because of the low temperature solution methods and the absence of rare elements. Cell durability is currently insufficient for commercial use. However, the solar cells are prone to degradation due to volatility of the organic [CHNH]I salt. The all-inorganic perovskite cesium lead iodide perovskite (CsPbI) circumvents this problem, but is itself phase-unstable, the low temperature solution methods of which have only been recently developed.
Planar heterojunction perovskite solar cells can be manufactured in simplified device architectures (without complex nanostructures) using only vapor deposition. This technique produces 15% solar-to-electrical power conversion as measured under simulated full sunlight. | 3 | Analytical Chemistry |
Seawater contains more dissolved ions than all types of freshwater. However, the ratios of solutes differ dramatically. For instance, although seawater contains about 2.8 times more bicarbonate than river water, the percentage of bicarbonate in seawater as a ratio of all dissolved ions is far lower than in river water. Bicarbonate ions constitute 48% of river water solutes but only 0.14% for seawater. Differences like these are due to the varying residence times of seawater solutes; sodium and chloride have very long residence times, while calcium (vital for carbonate formation) tends to precipitate much more quickly. The most abundant dissolved ions in seawater are sodium, chloride, magnesium, sulfate and calcium. Its osmolarity is about 1000 mOsm/L.
Small amounts of other substances are found, including amino acids at concentrations of up to 2 micrograms of nitrogen atoms per liter, which are thought to have played a key role in the origin of life. | 9 | Geochemistry |
Examples of Fano resonances can be found in atomic physics, nuclear physics, condensed matter physics, electrical circuits, microwave engineering, nonlinear optics, nanophotonics, magnetic metamaterials, and in mechanical waves.
Fano can be observed with photoelectron spectroscopy and Raman spectroscopy. The phenomenon can be also observed at visible frequencies using simple glass microspheres, which may allow enhancing the magnetic field of light (which is typically small) by a few orders of magnitude. | 7 | Physical Chemistry |
Sigma hole interactions have applications in a variety of fields. The ability to induce stabilizing and strongly directional intermolecular interactions which can be easily tuned via minor structural substitutions makes leveraging these interactions particularly value in fields in which control over supramolecular organization is desired. As such, sigma hole interactions have been used in the field of crystal engineering to design molecular building blocks for self-assembly, to improve the properties of liquid crystals, and to design magnetic materials. | 6 | Supramolecular Chemistry |
Like the complex multicellularity seen in animals, the multicellularity of land plants is developmentally organized into tissue and organ units via transcription factor genes with homeotic effects.
Although plants have homeobox-containing genes, plant homeotic factors tend to possess MADS-box DNA binding domains.
Animal genomes also possess a small number MADS-box factors.
Thus, in the independent evolution of multicellularity in plants and animals, different eukaryotic transcription factor families were co-opted to serve homeotic functions.
MADS-domain factors have been proposed to function as co-factors to more specialized factors and thereby help to determine organ identity.
This has been proposed to correspond more closely to the interpretation of animal homeotics outlined by Michael Akam. | 1 | Biochemistry |
In 1923, Debye and Hückel reported the first successful theory for the distribution of charges in ionic solutions.
The framework of linearized Debye–Hückel theory subsequently was applied to colloidal dispersions by Levine and Dube
who found that charged colloidal particles should experience a strong medium-range repulsion and a weaker long-range attraction.
This theory did not explain the observed instability of colloidal dispersions against irreversible aggregation in solutions of high ionic strength.
In 1941, Derjaguin and Landau introduced a theory for the stability of colloidal dispersions that invoked a fundamental instability driven by strong but short-ranged van der Waals attractions countered by the stabilizing influence of electrostatic repulsions.
In 1948, Verwey and Overbeek independently arrived at the same result.
This so-called DLVO theory resolved the failure of the Levine–Dube theory to account for the dependence of colloidal dispersions' stability on the ionic strength of the electrolyte. | 7 | Physical Chemistry |
Pure lisinopril powder is white to off white in color. Lisinopril is soluble in water (approximately 13 mg/L at room temperature), less soluble in methanol, and virtually insoluble in ethanol. | 4 | Stereochemistry |
Isaac Newton has been credited with the first description of conformal interaction observed through the interference phenomenon known as Newton's rings, though it was S. D. Poisson in 1823 who first described the optical characteristics of two identical surfaces in contact. It was not until the 19th century that objects were made of such precision that the binding phenomenon was observed. The clinging together was described as "wringing together", or as "ansprengen" in German. By 1900 optical contact bonding was being employed in the construction of optical prisms, and the following century saw further research into the phenomenon at the same time that ideas of inter-atom interactions were first being studied. | 6 | Supramolecular Chemistry |
Transition metal alkyne complexes are often formed by the displacement of labile ligands by the alkyne. For example, a variety of cobalt-alkyne complexes arise by the reaction of alkynes with dicobalt octacarbonyl.
Many alkyne complexes are produced by reduction of metal halides:
: CpTiCl + Mg + MeSiC≡CSiMe → CpTi[(CSiMe)] + MgCl | 0 | Organic Chemistry |
Upon treatment of ortho-carboranes with organolithium reagents such as n-Butyllithium, the CH vertices of the carborane cage can be deprotonated, affording the dilithiated ortho-carborane cage. Taking advantage of this more active carbon-lithium bond, the metalated carborane cages can then be treated with copper(I) chloride while in organic solvents, resulting in a copper-mediated carbon-carbon coupling reaction of the carborane cages. The copper salt is needed to avoid unwanted carbon-boron and boron-boron coupling reactions. The reaction mixture is allowed to stir at room temperature for two days, forming a copper-metalated carborane cage. Finally, the mixture is treated with 3M hydrochloric acid to quench the reaction process. The crude product is then purified via column chromatography and affords one half-equivalent of the carbon-carbon linked dimer of the original ortho-carborane in high yields. Worth noting is the effect of donating solvents on the yields of the reactions, as yields in solvents such as tetrahydrofuran and diethyl ether afford product in greatly decreased yields. | 7 | Physical Chemistry |
The measurement time required for a single impedance measurement point strongly depends on the frequency of interest. While frequencies above about 1 Hz can be measured within seconds, the measurement time increases significantly in the lower frequency range.
Although the exact duration for measuring a complete impedance spectrum depends on the measauring device as well as on internal settings, the following measurement times can be considered as rules of thumb when measuring the frequency measurement points sequentially, with the upper frequency assumed as 100 kHz or 1 MHz:
* Down to approx. 1 Hz, the measuring time is approx. 1 minute
* Down to 0.1 Hz approx. 5 minutes
* Down to 0.05 Hz approx. 10 minutes
* Down to 0.02 Hz approx. 15 minutes
* Down to 0.01 Hz approx. 30 minutes
Measurements down to or below 0.01 Hz are typically associated with measurement times in the range of several hours. Therefore, a spectrum can be roughly divided into three sub-ranges with regard to the occurrence of artifacts: in the high-frequency domain (approx. > 100 to 1000 Hz), induction or mutual induction can dominate. In the low frequency region (< 1 Hz), drift can occur due to noticeable change in the system. The range between about 1 Hz and 1000 Hz is usually not affected by high- or low-frequency artifacts. However, the mains frequency (50/60 Hz) may come into play as distorting artifact in this region. | 7 | Physical Chemistry |
Interfering with insects' reproduction can be accomplished by sterilizing males of the target species and releasing them, so that they mate with females but do not produce offspring. This technique was first used on the screwworm fly in 1958 and has since been used with the medfly, the tsetse fly, and the gypsy moth. This is a costly and slow approach that only works on some types of insects. | 2 | Environmental Chemistry |
Asymmetrical flow field flow fractionation (AF4) is nowadays a common and state-of-the art method for fractionation and separation of macromolecules and particles in a suspension. AF4 is an alternative to HPLC and SEC in cases where column chromatography is not suitable for the analyte. HPLC or SEC would be used for liquid separations for molecules up to 1000 kDa and nanoparticles up to 10 nm. As the size increases above 10 nm, AF4 becomes superior in terms of resolution and recovery.
AF4's applications are flexible for many analytical conditions where a column-based method would be unable to properly separate the desired particles. For macromolecules and nanoparticles AF4 is an alternative method especially when the stationary phase in columns interacts with the sample. AF4 is specifically powerful for inhomogeneous samples where it can separate soluble macromolecules from particles or aggregates.
AF4 and other FFF methods have been extensively used in environmental research on the impact of nano materials and to characterize condensed tannins oxidation.
For high molar mass and branched polymers, AF4 has been shown to achieve good separation, whereas SEC fails, and AF4 has been applied to polyolefines at temperatures above 150 C.
Detection methods are the same as for FFF in general, UV is most popular as a concentration detector, but most AF4 systems include a multi-angle light scattering detector for direct measurement or size and molar mass. | 3 | Analytical Chemistry |
The lipid pump sequesters carbon from the oceans surface to deeper waters via lipids associated with overwintering vertically migratory zooplankton. Lipids are a class of hydrocarbon rich, nitrogen and phosphorus deficient compounds essential for cellular structures. The lipid associated carbon enters the deep ocean as carbon dioxide produced by respiration of lipid reserves and as organic matter from the mortality of zooplankton. Compared to the more general biological pump, the lipid pump also results in a lipid shunt, where other nutrients like nitrogen and phosphorus that are consumed in excess must be excreted back to the surface environment, and thus are not removed from the surface mixed layer of the ocean. This means that the carbon transported by the lipid pump does not limit the availability of essential nutrients in the ocean surface. Carbon sequestration via the lipid pump is therefore decoupled from nutrient removal, allowing carbon uptake by oceanic primary production to continue. In the Biological Pump, nutrient removal is always coupled to carbon sequestration; primary production is limited as carbon and nutrients are transported to depth together in the form of organic matter. The contribution of the lipid pump to the sequestering of carbon in the deeper waters of the ocean can be substantial: the carbon transported below 1,000 metres (3,300 ft) by copepods of the genus Calanus' in the Arctic Ocean almost equals that transported below the same depth annually by particulate organic carbon (POC) in this region. A significant fraction of this transported carbon would not return to the surface due to respiration and mortality. Research is ongoing to more precisely estimate the amount that remains at depth. The export rate of the lipid pump may vary from 1–9.3 g C m y across temperate and subpolar regions containing seasonally-migrating zooplankton. The role of zooplankton, and particularly copepods, in the food web is crucial to the survival of higher trophic level organisms whose primary source of nutrition is copepods. With warming oceans and increasing melting of ice caps due to climate change, the organisms associated with the lipid pump may be affected, thus influencing the survival of many commercially important fish and endangered marine mammals. As a new and previously unquantified component of oceanic carbon sequestration, further research on the lipid pump can improve the accuracy and overall understanding of carbon fluxes in global oceanic systems. | 9 | Geochemistry |
Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability. Mental disability is a result which occurs primarily when babies or small children are rendered hypothyroidic by a lack of dietary iodine (new hypothyroidism in adults may cause temporary mental slowing, but not permanent damage).
In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency also gives rise to hypothyroidism, the most serious symptoms of which are epidemic goitre (swelling of the thyroid gland), extreme fatigue, mental slowing, depression, weight gain, and low basal body temperatures.
The addition of iodine to table salt (so-called iodized salt) has largely eliminated the most severe consequences of iodine deficiency in wealthier nations, but deficiency remains a serious public health problem in the developing world. Iodine deficiency is also a problem in certain areas of Europe; in Germany, an estimated one billion dollars in healthcare costs is spent each year in combating and treating iodine deficiency. | 1 | Biochemistry |
In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.
Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The first of these concepts was provided by the French chemist Antoine Lavoisier, around 1776.
It is important to think of the acid–base reaction models as theories that complement each other. For example, the current Lewis model has the broadest definition of what an acid and base are, with the Brønsted–Lowry theory being a subset of what acids and bases are, and the Arrhenius theory being the most restrictive. | 7 | Physical Chemistry |
The isomeric shift on atomic spectral lines is the energy or frequency shift in atomic spectra, which occurs when one replaces one nuclear isomer by another. The effect was predicted by Richard M. Weiner in 1956, whose calculations showed that it should be measurable by atomic (optical) spectroscopy (see also). It was observed experimentally for the first time in 1958. The theory of the atomic isomeric shift is also used in the interpretation of the Mössbauer isomeric shift. | 7 | Physical Chemistry |
Catalytic DNA (deoxyribozyme or DNAzyme) catalyze a reaction when interacting with the appropriate input, such as a matching oligonucleotide. These DNAzymes are used to build logic gates analogous to digital logic in silicon; however, DNAzymes are limited to 1-, 2-, and 3-input gates with no current implementation for evaluating statements in series.
The DNAzyme logic gate changes its structure when it binds to a matching oligonucleotide and the fluorogenic substrate it is bonded to is cleaved free. While other materials can be used, most models use a fluorescence-based substrate because it is very easy to detect, even at the single molecule limit. The amount of fluorescence can then be measured to tell whether or not a reaction took place. The DNAzyme that changes is then "used", and cannot initiate any more reactions. Because of this, these reactions take place in a device such as a continuous stirred-tank reactor, where old product is removed and new molecules added.
Two commonly used DNAzymes are named E6 and 8-17. These are popular because they allow cleaving of a substrate in any arbitrary location. Stojanovic and MacDonald have used the E6 DNAzymes to build the MAYA I and MAYA II machines, respectively; Stojanovic has also demonstrated logic gates using the 8-17 DNAzyme. While these DNAzymes have been demonstrated to be useful for constructing logic gates, they are limited by the need for a metal cofactor to function, such as Zn or Mn, and thus are not useful in vivo.
A design called a stem loop, consisting of a single strand of DNA which has a loop at an end, are a dynamic structure that opens and closes when a piece of DNA bonds to the loop part. This effect has been exploited to create several logic gates. These logic gates have been used to create the computers MAYA I and MAYA II which can play tic-tac-toe to some extent. | 1 | Biochemistry |
A neutron moisture meter is a moisture meter utilizing neutron scattering. The meters are most frequently used to measure the water content in soil or rock. The technique is non-destructive, and is sensitive to moisture in the bulk of the target material, not just at the surface.
Water, due to its hydrogen content, is an effective neutron moderator, slowing high-energy neutrons. With a source of high-energy neutrons and a detector sensitive to low-energy neutrons (thermal neutrons), the detection rate will be governed by the water content of the soil between the source and the detector. The neutron source typically contains a small amount of a radionuclide. Sources may emit neutrons during spontaneous fission, as with californium; alternatively, an alpha emitter may be mixed with a light element for a nuclear reaction yielding excess neutrons, as with americium in a beryllium matrix. | 7 | Physical Chemistry |
These are the crystallographic groups of a cubic crystal system: 23, 432, , 3m, and . All of them contain four diagonal 3-fold axes. These axes are arranged as 3-fold axes in a cube, directed along its four space diagonals (the cube has symmetry). These symbols are constructed the following way:
* First position – symmetrically equivalent directions of the coordinate axes x, y, and z. They are equivalent due to the presence of diagonal 3-fold axes.
* Second position – diagonal 3 or axes.
* Third position – diagonal directions between any two of the three coordinate axes x, y, and z. These can be 2, m, or .
All Hermann–Mauguin symbols presented above are called full symbols. For many groups they can be simplified by omitting n-fold rotation axes in positions. This can be done if the rotation axis can be unambiguously obtained from the combination of symmetry elements presented in the symbol. For example, the short symbol for is mmm, for is mm, and for is mm. In groups containing one higher-order axis, this higher-order axis cannot be omitted. For example, symbols and can be simplified to 4/mmm (or mm) and 6/mmm (or mm), but not to mmm; the short symbol for is m. The full and short symbols for all 32 crystallographic point groups are given in crystallographic point groups page.
Besides five cubic groups, there are two more non-crystallographic icosahedral groups (I and I in Schoenflies notation) and two limit groups (K and K in Schoenflies notation). The Hermann–Mauguin symbols were not designed for non-crystallographic groups, so their symbols are rather nominal and based on similarity to symbols of the crystallographic groups of a cubic crystal system. Group I can be denoted as 235, 25, 532, 53. The possible short symbols for I are m, m, mm, m. The possible symbols for limit group K are ∞∞ or 2∞, and for K are ∞ or m or ∞∞m. | 3 | Analytical Chemistry |
The best-studied example of cap-independent translation initiation in eukaryotes uses the internal ribosome entry site (IRES). Unlike cap-dependent translation, cap-independent translation does not require a 5 cap to initiate scanning from the 5 end of the mRNA until the start codon. The ribosome can localize to the start site by direct binding, initiation factors, and/or ITAFs (IRES trans-acting factors) bypassing the need to scan the entire 5' UTR. This method of translation is important in conditions that require the translation of specific mRNAs during cellular stress, when overall translation is reduced. Examples include factors responding to apoptosis and stress-induced responses. | 1 | Biochemistry |
In spectroscopy, hypsochromic shift () is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a shorter wavelength (higher frequency). Because the blue color in the visible spectrum has a shorter wavelength than most other colors, this effect is also commonly called a blue shift. It should not be confused with a bathochromic shift, which is the opposite process – the molecule's spectra are changed to a longer wavelength (lower frequency).
Hypsochromic shifts can occur because of a change in environmental conditions: for example, a change in solvent polarity will result in solvatochromism. A series of structurally related molecules in a substitution series can also show a hypsochromic shift. Hypsochromic shift is a phenomenon seen in molecular spectra, not atomic spectra - it is thus more common to speak of the movement of the peaks in the spectrum rather than lines.
where is the wavelength of the spectral peak of interest and
For example, β-acylpyrrole will show a hypsochromic shift of 30-40 nm in comparison with α-acylpyrroles. | 7 | Physical Chemistry |
The field of building-integrated photovoltaics (BIPV) has gained attention from the scientific community due to its potential to reduce pollution and materials and electricity costs, as well as to improve the aesthetics of a building. In recent years, scientists have looked at ways to incorporate DSSC’s in BIPV applications, since the dominant Si-based PV systems in the market have a limited presence in this field due to their energy-intensive manufacturing methods, poor conversion efficiency under low light intensities, and high maintenance requirements. In 2021, a group of researchers from the Silesian University of Technology in Poland developed a DSSC in which the classic glass counter electrode was replaced by an electrode based on a ceramic tile and nickel foil. The motivation for this change was that, despite that glass substrates have resulted in the highest recorded efficiencies for DSSC’s, for BIPV applications like roof tiles or building facades, lighter and more flexible materials are essential. This includes plastic films, metals, steel, or paper, which may also reduce manufacturing costs. The team found that the cell had an efficiency of 4% (close to that of a solar cell with a glass counter electrode), demonstrated the potential for creating building-integrated DSSC’s that are stable and low-cost. | 5 | Photochemistry |
The term "biotoxin" is sometimes used to explicitly confirm the biological origin as opposed to environmental or anthropogenic origins. Biotoxins can be classified by their mechanism of delivery as poisons (passively transferred via ingestion, inhalation, or absorption across the skin), toxungens (actively transferred to the target's surface by spitting, spraying, or smearing), or venoms (delivered through a wound generated by a bite, sting, or other such action). They can also be classified by their source, such as fungal biotoxins, microbial toxins, plant biotoxins, or animal biotoxins.
Toxins produced by microorganisms are important virulence determinants responsible for microbial pathogenicity and/or evasion of the host immune response.
Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snail can contain over 100 unique peptides, which target specific nerve channels or receptors).
Biotoxins in nature have two primary functions:
* Predation, such as in the spider, snake, scorpion, jellyfish, and wasp
* Defense as in the bee, ant, termite, honey bee, wasp, poison dart frog and plants producing toxins
** The toxins used as defense in species among the poison dart frog can also be used for medicinal purposes
Some of the more well known types of biotoxins include:
* Cyanotoxins, produced by cyanobacteria
* Dinotoxins, produced by dinoflagellates
* Necrotoxins cause necrosis (i.e., death) in the cells they encounter. Necrotoxins spread through the bloodstream. In humans, skin and muscle tissues are most sensitive to necrotoxins. Organisms that possess necrotoxins include:
** The brown recluse or "fiddle back" spider
** Most rattlesnakes and vipers produce phospholipase and various trypsin-like serine proteases
** Puff adder
** Necrotizing fasciitis (caused by the "flesh eating" bacterium Streptococcus pyogenes) – produces a pore forming toxin
* Neurotoxins primarily affect the nervous systems of animals. The group neurotoxins generally consists of ion channel toxins that disrupt ion channel conductance. Organisms that possess neurotoxins include:
** The black widow spider.
** Most scorpions
** The box jellyfish
** Elapid snakes
** The cone snail
** The Blue-ringed octopus
** Venomous fish
** Frogs
** Palythoa coral
** Various different types of algae, cyanobacteria and dinoflagellates
* Myotoxins are small, basic peptides found in snake and lizard venoms, They cause muscle tissue damage by a non-enzymatic receptor based mechanism. Organisms that possess myotoxins include:
** rattlesnakes
** Mexican beaded lizard
* Cytotoxins are toxic at the level of individual cells, either in a non-specific fashion or only in certain types of living cells:
** Ricin, from castor beans
** Apitoxin, from honey bees
** T-2 mycotoxin, from certain toxic mushrooms
** Cardiotoxin III, from Chinese cobra
** Hemotoxin, from vipers | 1 | Biochemistry |
Lipofuscin appears to be the product of the oxidation of unsaturated fatty acids and may be symptomatic of membrane damage, or damage to mitochondria and lysosomes. Aside from a large lipid content, lipofuscin is known to contain sugars and metals, including mercury, aluminium, iron, copper and zinc. Lipofuscin is also accepted as consisting of oxidized proteins (30–70%) as well as lipids (20–50%). It is a type of lipochrome and is specifically arranged around the nucleus.
The accumulation of lipofuscin-like material may be the result of an imbalance between formation and disposal mechanisms. Such accumulation can be induced in rats by administering a protease inhibitor (leupeptin); after a period of three months, the levels of the lipofuscin-like material return to normal, indicating the action of a significant disposal mechanism. However, this result is controversial, as it is questionable if the leupeptin-induced material is true lipofuscin. There exists evidence that "true lipofuscin" is not degradable in vitro; whether this holds in vivo over longer time periods is not clear.
The ABCR -/- knockout mouse has delayed dark adaptation but normal final rod threshold relative to controls. Bleaching the retina with strong light leads to formation of toxic cationic bis-pyridinium salt, N-retinylidene-N-retinyl-ethanolamine (A2E), which causes dry and wet age-related macular degeneration. From this experiment, it was concluded that ABCR has a significant role in preventing formation of A2E in extracellular photoreceptor surfaces during bleach recovery. | 1 | Biochemistry |
Electrochemical fluorination (ECF) (also known as the Simons' process) involves electrolysis of a substrate dissolved in hydrogen fluoride. As fluorine is itself manufactured by the electrolysis of hydrogen fluoride, ECF is a rather more direct route to fluorocarbons. The process proceeds at low voltage (5 – 6 V) so that free fluorine is not liberated. The choice of substrate is restricted as ideally it should be soluble in hydrogen fluoride. Ethers and tertiary amines are typically employed. To make perfluorohexane, trihexylamine is used, for example:
The perfluorinated amine will also be produced: | 2 | Environmental Chemistry |
Classical examples of polymorphism are the pair of minerals calcite and aragonite, both forms of calcium carbonate. Allotropy is the term used for elements, for example diamond versus graphite, and in metallurgy.
β-HgS precipitates as a black solid when Hg(II) salts are treated with HS. With gentle heating of the slurry, the black polymorph converts to the red form. | 3 | Analytical Chemistry |
Mediator is a crucial component for transcription initiation. Mediator interacts with the pre-initiation complex, composed of RNA Polymerase II and general transcription factors TFIIB, TFIID, TFIIE, TFIIF, and TFIIH to stabilize and initiate transcription. Studies of Mediator-RNA Pol II contacts in budding yeast have emphasized the importance of TFIIB-Mediator contacts in the formation of the complex. Interactions of Mediator with TFIID in the initiation complex has been shown.
The Structure of a core Mediator (cMed) that's associated with a core pre-initiation complex was elucidated. | 1 | Biochemistry |
* Eli Samuels: Eli is 18 years old, 6′9″ (201 centimeters) tall. Hes an A student, and is the salutatorian in high school. His mother has Huntingtons disease, which he could have too.
* Jonathan Samuels: Jonathan Samuels is Elis father, who loved his wife. He has a problem with Eli working at Wyatt Transgenics, because of things that went down in the past. He is initially completely unwilling to tell Eli anything about his mother's relationships with Dr. Wyatt.
* Dr. Quincy Wyatt: Dr. Quincy Wyatt is a famed geneticist, who is considered to be on par with Mendel, Watson, and Crick. He offers Eli a job. He displays an unexplained interest in Eli.
* Vivian Fadiman: Vivian Fadiman is Elis girlfriend and Valedictorian at his high school. All she wants is to be part of his life and she supports him in everything he does. Its hard for her to understand why Eli hides major parts of his life from her. Eli is devoted to her, though they do go through some rough times.
* Kayla Matheson: A year older than Eli, he gets to know her via Dr. Wyatt. He is attracted to her because of her beauty and athleticism.
* Ava Samuels: Ava Samuels was Elis mother and lived in a nursing home because of her Huntingtons disease. She had a mysterious connection with Dr. Wyatt. | 1 | Biochemistry |
Most sulfilimines are N-substituted with electron-withdrawing groups. These compounds are typically prepared by oxidation of thioethers with electrophilic amine reagents, such as chloramine-T in the presence of a base:
An alternative route involves reactions of electrophilic sulfur compounds with amines. The imidosulfonium reagents provide a source of "", which are attacked by amines. | 0 | Organic Chemistry |
Peculiarly, above 1,394 °C (2,541 °F) iron changes back into the bcc structure, known as δ-Fe. δ-iron can dissolve as much as 0.08% of carbon by mass at 1,475 °C. It is stable up to its melting point of 1,538 °C (2,800 °F). δ-Fe cannot exist above 5.2 GPa, with austenite instead transitioning directly to a molten phase at these high pressures. | 8 | Metallurgy |
Schuster married his wife Carlotta, a psychiatrist, in 1962. He is a lifelong classical music enthusiast and serious pianist. | 5 | Photochemistry |
The hijack of an enhancer from another gene allows the analysis of the function of that enhancer. This, especially if the reporter gene is for a fluorescent protein, can be used to help map expression of the mutated gene through the organism, and is a very powerful tool. It is a useful tool for looking at gene expression patterns (temporally and spatially). | 1 | Biochemistry |
:K = 24 × (M / M)
where
: K is the karat rating of the material,
: M is the mass of pure gold in the alloy, and
: M is the total mass of the material.
24-karat gold is pure (while 100% purity is very difficult to attain, 24-karat as a designation is permitted in commerce for a minimum of 99.95% purity), 18-karat gold is 18 parts gold, 6 parts another metal (forming an alloy with 75% gold), 12-karat gold is 12 parts gold (12 parts another metal), and so forth.
In England, the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of fineness (that is, 99.2% purity) could have been described as being 23-karat, 3-grain, 1-quart gold.
The karat fractional system is increasingly being complemented or superseded by the millesimal system, described above for bullion, though jewelry generally tends to still use the karat system.
Conversion between percentage of pure gold and karats:
* 58.33–62.50% = 14 k (acclaimed 58.33%)
* 75.00–79.16% = 18 k (acclaimed 75.00%)
* 91.66–95.83% = 22 k (acclaimed 91.66%)
* 95.83–99.95% = 23 k (acclaimed 95.83%)
* 99.95–100% = 24 k (acclaimed 99.95%) | 8 | Metallurgy |
* [http://vlp.mpiwg-berlin.mpg.de/library/data/lit16635 Über den Niederschlag, welchen Pikrinsäre in normalem Harn erzeugt und über eine neue Reaction des Kreatinins] by Max Jaffe (1886) | 1 | Biochemistry |
CDP works with corporations, cities, states, and regions to help develop carbon emissions reductions strategies. The collection of self-reported data from the companies is supported by over 800 institutional investors with about US$100 trillion in assets.
Much of the data elicited has never been collected before. This information is helpful to investors, corporations, and regulators in making informed decisions on taking action towards a sustainable economy by measuring and understanding their environmental impact and taking steps to address and limit their risk to climate change, deforestation and water security. | 2 | Environmental Chemistry |
Seventeen individuals, both men and women, journeyed across the remote region known as Arnhem Land in northern Australia for nine months. From varying disciplinary perspectives, and under the guidance of expedition leader Charles Mountford, they investigated the Indigenous populations and the environment of Arnhem Land. In addition to an ethnographer, archaeologist, photographer, and filmmaker, the expedition included a botanist, a mammalogist, an ichthyologist, an ornithologist, and a team of medical and nutritional scientists.
Their first base camp was Groote Eylandt in the Gulf of Carpentaria. Three months later they moved to Yirrkala on the Gove Peninsula and three months following that to Oenpelli (now Gunbalanya) in west Arnhem Land. The journey involved the collaboration of different sponsors and partners (among them the National Geographic Society, the Smithsonian Institution, and various agencies of the Commonwealth of Australia).
A Bulletin article in 1956 noted that the scientists collected 13,500 plants, 30,000 fish, 850 birds, 460 animals, thousands of implements, amounting to twenty-five tons, and photographed and filmed in colour and black-and-white and made tracings of cave-paintings from Chasm Island, Groote Eylandt and Oenpelli. The Australian Broadcasting Commission promoted the Expedition in its ABC Weekly magazine by appealing to readers curiosity about "...a fish that looks exactly like a leaf, a multi-coloured praying mantis, intricate string games the aborigines play, a fungus used to cure wounds..."
In the wake of the expedition came volumes of scientific publications. The legacy of the 1948 Arnhem Land Expedition is vast, complex, and, at times, contentious. Human remains collected by Setzler and later held by the Smithsonian Institution have since been repatriated to Gunbalanya. | 1 | Biochemistry |
During mania, there is an increase in neurotransmission of dopamine that causes a secondary homeostatic down-regulation, resulting in decreased neurotransmission of dopamine, which can cause depression. Additionally, the post-synaptic actions of dopamine are mediated through G-protein coupled receptors. Once dopamine is coupled to the G-protein receptors, it stimulates other secondary messenger systems that modulate neurotransmission. Studies found that in autopsies (which do not necessarily reflect living people), people with bipolar disorder had increased G-protein coupling compared to people without bipolar disorder. Lithium treatment alters the function of certain subunits of the dopamine associated G-protein, which may be part of its mechanism of action. | 1 | Biochemistry |
In at least one plant, Juglans regia, progesterone has been detected. In addition, progesterone-like steroids are found in Dioscorea mexicana. Dioscorea mexicana is a plant that is part of the yam family native to Mexico. It contains a steroid called diosgenin that is taken from the plant and is converted into progesterone. Diosgenin and progesterone are also found in other Dioscorea species, as well as in other plants that are not closely related, such as fenugreek.
Another plant that contains substances readily convertible to progesterone is Dioscorea pseudojaponica native to Taiwan. Research has shown that the Taiwanese yam contains saponins — steroids that can be converted to diosgenin and thence to progesterone.
Many other Dioscorea species of the yam family contain steroidal substances from which progesterone can be produced. Among the more notable of these are Dioscorea villosa and Dioscorea polygonoides. One study showed that the Dioscorea villosa contains 3.5% diosgenin. Dioscorea polygonoides has been found to contain 2.64% diosgenin as shown by gas chromatography-mass spectrometry. Many of the Dioscorea species that originate from the yam family grow in countries that have tropical and subtropical climates. | 0 | Organic Chemistry |
Thermometric titrations employing sodium salts of ethylenediaminetetra-acetic acid (EDTA) have been demonstrated for the determination of a range of metal ions. Reaction enthalpies are modest, so titrations are normally carried out with titrant concentrations of 1 mol/L. This necessitates the use of the tetra-sodium salt of EDTA rather than the more common di-sodium salt which is saturated at a concentration of only approximately 0.25 mol/L.
An excellent application is the sequential determination of calcium and magnesium. Although calcium reacts exothermically with EDTA (heat of chelation ~-23.4 kJ/mol), magnesium reacts endothermically with a heat of chelation of ~+20.1 kJ/mol. This is illustrated in the titration plot of EDTA with calcium and magnesium in sea water (Figure 14). Following the solution temperature curve, the breakpoint for the calcium content (red-tagged endpoint) is followed by a region of modest temperature rise due to competition between the heats of dilution of the titrant with the solution, and the endothermic reaction of Mg and EDTA. The breakpoint for the consumption of Mg (blue-tagged endpoint) by EDTA is revealed by upswing in temperature caused purely by the heat of dilution.
Direct EDTA titrations with metal ions are possible when reaction kinetics are fast, for example zinc, copper, calcium and magnesium. However, with slower reaction kinetics such as those exhibited by cobalt and nickel, back-titrations are used. Titrations for cobalt and nickel are carried out in an ammoniacal environment; buffered with ammonia:ammonium chloride solution. An excess of EDTA is added, and is back-titrated with Cu(II) solution. It is postulated that the breakpoint is revealed by the difference in reaction enthalpies between the formation of the Cu-EDTA complex, and that for the formation of the Cu-amine complex.
A catalyzed endpoint procedure to determine trace amounts of metal ions in solution (down to approximately 10 mg/L) employs 0.01 mol/L EDTA. This has been applied to the determination of low level Cu(II) in specialized plating baths, and to the determination of total hardness in water. The reaction enthalpies of EDTA with most metal ions are often quite low, and typically titrant concentrations around 1 mol/L are employed with commensurately high amounts of titrand in order to obtain sharp, reproducible endpoints. Using a catalytically indicated endpoint, very low EDTA titrant concentrations can be used. A back-titration is used. An excess of EDTA solution is added. The excess of EDTA is back-titrated with a suitable metal ion such as Mn or Cu. At the endpoint, the first excess of metal ion catalyzes a strongly exothermic reaction between a polyhydric phenol (such as resorcinol) and hydrogen peroxide. | 3 | Analytical Chemistry |
As the internal energy is a convex function of entropy and volume, the stability condition requires that the second derivative of internal energy with entropy or volume to be positive. It is commonly expressed as . Since the maximum principle of entropy is equivalent to minimum principle of internal energy, the combined criteria for stability or thermodynamic equilibrium is expressed as and for parameters, entropy and volume. This is analogous to and condition for entropy at equilibrium. The same concept can be applied to the various thermodynamic potentials by identifying if they are convex or concave of respective their variables.
and
Where Helmholtz energy is a concave function of temperature and convex function of volume.
and
Where enthalpy is a concave function of pressure and convex function of entropy.
and
Where Gibbs potential is a concave function of both pressure and temperature.
In general the thermodynamic potentials (the internal energy and its Legendre transforms), are convex functions of their extrinsic variables and concave functions of intrinsic variables. The stability conditions impose that isothermal compressibility is positive and that for non-negative temperature, . | 7 | Physical Chemistry |
An ion-neutral complex in chemistry is an aggregate of an ion with one or more neutral molecules in which at least one of the partners has a rotational degree of freedom about an axis perpendicular to the intermolecular direction In chemistry, the dissociation of a molecule into two or more fragments can take place in the gas phase, provided there is sufficient internal energy for the requisite barriers to be overcome.
For many years, it was assumed that the fragments of a gas phase dissociation simply fly apart. In 1958, Allan Maccoll suggested that the decomposition of alkyl halides (RX) might take place via the intermediacy of ion pairs, [R X], in which the charged fragments were no longer covalently bonded but were held together by electrostatic attraction. Maccoll and coworkers subsequently examined chlorine isotope effects in the thermal decomposition of chloroethane and concluded that the data did not support that interpretation; however, he had provided the germ of an idea that came to fruition two decades later in the study of decompositions of electrically charged molecules.
In the late 1970s three research groups—in England, the United States, and France—independently provided evidence for the occurrence of ion-neutral complexes (sometimes called ion-dipole complexes or ion-molecule complexes) in the unimolecular dissociations of positive ions under the conditions associated with mass spectrometry (i.e. as isolated species in a vacuum). The general idea is that a charged species, RY, can give rise to dissociation fragments via a transient complex, [R Y], in which the electrically charged partner, R, can undergo molecular rearrangements at the same time as it rotates relative to the neutral partner, Y. Similarly, the neutral partner, Y, can also rotate relative to the charged partner, as well as having the ability to exchange Hydrogens and internal energy with it.
More recently several research groups have provided evidence that revives Maccoll's original hypothesis, but with the variation that the fragments that sojourn in the presence of one another are both electrically uncharged. In other words, dissociations of a neutral molecule RX can take place in the gas phase via the intermediacy of radical pairs [R· X·], where X· can be as small as a hydrogen atom. In the gas phase such intermediates are often called roaming radicals. | 7 | Physical Chemistry |
In addition to the reconstruction of the impedance from the phase shift, the reverse approach is also possible. However, the herein presented procedure possesses several advantages:
* When calculating the phase shift from the impedance, a function of the angular frequency ω comes into play which is more difficult to determine compared to the constant C in equation (3).
* Generally, the phase shift is more stable than the impedance. This is based on the fact that for impedance elements (more precisely: Constant phase element, CPE ) the property "phase shift" remains constant even if the value of the impedance drastically changes. Such Constant Phase-elements are the typical electronic elements, among others such as the electrical resistor, capacitor and coil. For illustration, Figure 2 shows the impedance spectrum of an NTC resistor heated during the measurement (starting between 1 kHz and 10 kHz down to lower frequencies). It can clearly be seen that the value of the impedance (red curve) changes with temperature, while the phase shift (blue curve) remains constant. In other words, "a resistor remains a resistor".
* The reconstruction of the impedance from the phase shift further restores the "inner (= complex)" relationship between these two quantities. This relationship is lost by the independent construction of the supporting point splines for impedance and phase (Figure 1). Depending on the system under investigation, this restored correlation - even in the absence of artifacts - can lead to an improved evaluation of the spectra. In such cases, the gain in accuracy due to the reconstruction of the complex impedance outweighs the approximation error according to equation (3), which results from the neglection of the higher derivatives. | 7 | Physical Chemistry |
Water contains hydrogen in the oxidation state +1 and oxygen in the oxidation state −2. It oxidizes chemicals such as hydrides, alkali metals, and some alkaline earth metals. One example of an alkali metal reacting with water is:
:2 Na + 2 → + 2 + 2
Some other reactive metals, such as aluminium and beryllium, are oxidized by water as well, but their oxides adhere to the metal and form a passive protective layer. Note that the rusting of iron is a reaction between iron and oxygen that is dissolved in water, not between iron and water.
Water can be oxidized to emit oxygen gas, but very few oxidants react with water even if their reduction potential is greater than the potential of . Almost all such reactions require a catalyst. An example of the oxidation of water is:
:4 + 2 → 4 AgF + 4 HF + | 2 | Environmental Chemistry |
In Southeast Asia during the Vietnam War, the Rainbow Herbicides were a group of tactical-use chemicals used by the United States military. The environmental destruction caused by this defoliation has been described by Swedish Prime Minister Olof Palme, lawyers, historians and other academics as an ecocide. | 2 | Environmental Chemistry |
*Beridze TG, Odintsova MS, Sissakian NM (1967) Distribution of bean leaf DNA components in the cell organelle fractions. Molek.Biol.USSR. 1,142-153
*Beridze TG (1972) DNA nuclear satellites of the genus Phaseolus. Biochim. Biophys. Acta 262,393-396
*Beridze TG (1975) DNA nuclear satellites of the genus Brassica: variation between species. Biochim.Biophys.Acta. 395,274-279
*Beridze T. Satellite DNA, 1986, Springer-Verlag, Berlin, Heidelberg, New York, Tokio
*Beridze T, Pipia I, Beck J., Hsu S.-CT, Gamkrelidze M, Gogniashvili M, Tabidze V, This R,Bacilieri P, Gotsiridze V, Glonti M, Schaal B (2011). Plastid DNA sequence diversity in a worldwide set of grapevine cultivars (Vitis vinifera L. subsp. vinifera). Bulletin of the Georgian National Academy of Sciences. 5, 2011, 98–103.
*Pipia I, Gogniashvili M, Tabidze V, Beridze T, Gamkrelidze M, Gotsiridze V, Melyan G, Musayev M, Salimov V, Beck J, Schaal B (2012) Plastid DNA sequence diversity in wild grapevine samples (Vitis vinifera subsp. sylvestris) from the Caucasus region. Vitis 51 (3), 119–124
*Tabidze V, Baramidze G, Pipia I, Gogniashvili M, Ujmajuridze L, Beridze T, Hernandez AG, Schaal B (2014) The Complete Chloroplast DNA Sequence of Eleven Grape Cultivars. Simultaneous Resequencing Methodology. Journal International des Sciences de la Vigne et du Vin J Int Sci Vigne Vin. 48, 99-109
*Tabidze V, Pipia I, Gogniashvili M, Kunelauri N, Ujmajuridze L, Pirtskhalava M, Vishnepolsky B, Hernandez AG, Fields CJ, BeridzeT (2017) Whole genome comparative analysis of four Georgian grape cultivars. Molecular Genetics and Genomics. 292, 1377-1389
*Gogniashvili M., Naskidashvili P., Bedoshvili D., Kotorashvili A., Kotaria N., Beridze T. (2015) Complete chloroplast DNA sequences of Zanduri wheat (Triticum spp.) Genet Resour Crop Evol
*Gogniashvili M, Jinjikhadze T, Maisaia M, Akhalkatsi M, Kotorashvili A, Kotaria N, Beridze T, Dudnikov AJ (2016) Complete chloroplast genomes of Aegilops tauschii Coss. and Ae.cylindrica Host sheds light on plasmon D evolution. Current Genetics.
*Gogniashvili M, Maisaia I, Kotorashvili A, Kotaria N, Beridze T (2018) Complete chloroplast DNA sequences of Georgian indigenous polyploid wheats (Triticum spp.) and B plasmon evolution. Genet Resour Crop Evol 65:1995–2002 | 1 | Biochemistry |
The high stereospecificity and stereoselectivity inherent in many TMM cycloaddition reactions is a significant advantage; for instance, the trans ring junction in TMM cycloaddition adduct 2 was carried through in a synthesis of (+)-brefeldin A. | 0 | Organic Chemistry |
The Jackson Laboratory in Bar Harbor, Maine, USA with the University of Southampton, UK identified ALMS1 as the single gene responsible for Alström syndrome. | 1 | Biochemistry |
Most metal alkyl complexes contain other, non-alkyl ligands. Great interest, mainly theoretical, has focused on the homoleptic complexes. Indeed, the first reported example of a complex containing a metal-sp carbon bond was the homoleptic complex diethylzinc. Other examples include hexamethyltungsten, tetramethyltitanium, and tetranorbornylcobalt.
Mixed ligand, or heteroleptic, complexes containing alkyls are numerous. In nature, vitamin B12 and its many derivatives contain reactive Co-alkyl bonds. | 0 | Organic Chemistry |
A similar procedure that uses radiofrequency energy for back pain appears to have short-term benefit, but it is unclear if it has a long-term effect. | 1 | Biochemistry |
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