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Founded in 1877 the North Australian Pastoral Company is one of Australia's leading agricultural enterprises as well as being one of its oldest and largest. NAPCO’S rangelands span 6.4 million hectares across both Queensland and the Northern Territory where a variety of stations have been established. The company is currently in possession of cattle heads amounting to some 190,000 cows spread throughout each station from Queensland to the Northern Territory. There are currently twelve stations located in Queensland, and only two located in the Northern Territory. However, whilst Queensland contains more stations in comparison to the Northern Territory, its capacity of cattle is far less. For example, the Goldsborough station in Queensland only holds a capacity of 4,000 cattle, whereas the Northern Territory station of Mittiebah holds an approximate capacity of 80,000 cows.
The company's standing in the Australian agricultural industry is attributed to its advanced composite breeding programs, from which it has developed two of its own cattle species known as the Alexandria composite and Kynuna composite. The company has also engaged in an Environmental Management System (EMS) which is a policy implementation that aims to reduce carbon emissions by engaging in environmentally sound beef production. By introducing an Environmental Management Strategy, the company is in step with the work of fellow pastoralists operating in the Northern Rangeland industry who have also implemented a particular model of EMS to specifically target the impact they have on the environment. | 2 | Environmental Chemistry |
Bacteriochlorophyll and carotenoids are two molecules responsible for harvesting light energy. Current models of the organization of bacteriochlorophyll and carotenoids (the main constituents) inside the chlorosomes have put them in a lamellar organization, where the long farnesol tails of the bacteriochlorophyll intermix with carotenoids and each other, forming a structure resembling a lipid multilayer.
Recently, another study has determined the organization of the bacteriochlorophyll molecules in green sulfur bacteria. Because they have been so difficult to study, the chlorosomes in green sulfur bacteria are the last class of light-harvesting complexes to be characterized structurally by scientists. Each individual chlorosome has a unique organization and this variability in composition had prevented scientists from using X-ray crystallography to characterize the internal structure. To get around this problem, the team used a combination of different experimental approaches. Genetic techniques to create a mutant bacterium with a more regular internal structure, cryo-electron microscopy to identify the larger distance constraints for the chlorosome, solid-state nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the chlorosome's component chlorophyll molecules, and modeling to bring together all of the pieces and create a final picture of the chlorosome.
To create the mutant, three genes were inactivated that green sulfur bacteria acquired late in their evolution. In this way it was possible to go backward in evolutionary time to an intermediate state with much less variable and better ordered chlorosome organelles than the wild-type. The chlorosomes were isolated from the mutant and the wild-type forms of the bacteria. Cryo-electron microscopy was used to take pictures of the chlorosomes. The images reveal that the chlorophyll molecules inside chlorosomes have a nanotube shape. The team then used MAS NMR spectroscopy to resolve the microscopic arrangement of chlorophyll inside the chlorosome. With distance constraints and DFT ring current analyses, the organization was found to consist of unique syn-anti monomer stacking. The combination of NMR, cryo-electron microscopy and modeling enabled the scientists to determine that the chlorophyll molecules in green sulfur bacteria are arranged in helices. In the mutant bacteria, the chlorophyll molecules are positioned at a nearly 90-degree angle in relation to the long axis of the nanotubes, whereas the angle is less steep in the wild-type organism. The structural framework can accommodate disorder to improve the biological light harvesting function, which implies that a less ordered structure has a better performance. | 5 | Photochemistry |
Among Palestinians, the liquid is known simply as "shit". Amnesty International, BTselem, and the Association for Civil Rights in Israel have been critical of the IDFs use of the product. Concerns have included accusations of indiscriminate use against people, homes, and businesses not involved in demonstrations. The IDF has also been accused of deployment in a manner described as punitive. The IDF has at times sprayed Palestinian houses after protests as a form of collective punishment. In response to a negative B'tselem report, the Israel Defense Forces stated that "Skunk" is used only when demonstrators become violent or engage in vandalism and has specific rules of engagement for its use.
Skunk was criticized in a joint 2016 Physicians for Human Rights (PHR) and International Network of Civil Liberties Organizations (INCLO) report on crowd control weapons published by the American Civil Liberties Union (ACLU). | 1 | Biochemistry |
Camphorsultam, or Oppolzer's sultam, is a classic chiral auxiliary.
In the total synthesis of manzacidin B, Ohfune group utilized camphorsultam to construct the core oxazoline ring asymmetrically. Comparing with oxazolidinone as the chiral auxiliary, camphorsultam had a significant (2S,3R)-selectivity.
Camphorsultam also acts as a chiral auxiliary in Michael addition. Lithium base promoted stereoselective Michael addition of thiols to N-mcthacryloylcamphorsultam produced the corresponding addition products in high diastereoselectivity.
Camphorsultam was used as a chiral auxiliary for the asymmetric Claisen rearrangement. In the presence of butylated hydroxytoluene (BHT) used as a radical scavenger, a toluene solution of the adduct between geraniol and camphorsultam was heated in a sealed tube at 140 °C, to provide mainly the (2R,3S)-isomer as the major rearrangement product in 72% yield, securing the two contiguous stereocenters including the quaternary carbon. | 4 | Stereochemistry |
Upon the identification of the early targets of arginylation by ATE1 (in vitro and in vivo), a pattern emerged. This pattern showed that ATE1 displayed a high affinity for proteins and peptides containing the acidic amino acids asparagine or glutamine which were exposed on the N-terminal side of the protein or peptide. Further studies aided by high precision mass spectrometry have revealed hundreds of proteins from different cells and tissues which have been arginylated. Several of these proteins also displayed arginylation at their N-chain termini, but contained residues other than asparagine or glutamine. As such, arginylation studies are still in the introductory stages and further research into the specificity of arginylation must be performed.
However, the assumption that arginylation only occurs at the N-terminus severely limited the amount of proteins which were likely to be arginylated. This is due to the fact that, if the preference of arginylation to occur only at the N-terminus assumption was true, then arginylation would never be able to happen on intact proteins due to protein sequences beginning with methionine at the N-terminus and not the preferred asparagine or glutamine. This assumption was soon proved false when a protein was discovered with an arginylated residue in the middle of its sequence. | 1 | Biochemistry |
Other organelles of the microbody family related to peroxisomes include glyoxysomes of plants and filamentous fungi, glycosomes of kinetoplastids, and Woronin bodies of filamentous fungi. | 1 | Biochemistry |
Dose-dependent changes of heart rate and cardiac output are observed within the first hour after administration of ractopamine and gradually return to baseline values. The systolic blood pressure will also increase in a dose-dependent manner, while the diastolic pressure remains unchanged. | 4 | Stereochemistry |
* The Bay, a 2012 found footage-style eco-horror movie about a pandemic due to deadly pollution from chicken factory farm run-off and mutant isopods and aquatic parasites able to infect humans.
* Expedition Chesapeake, A Journey of Discovery, a 2019 film starring Jeff Corwin created by The Whitaker Center for Science and the Arts. | 2 | Environmental Chemistry |
The polymer-supported synthesis of β-mannosides based on the Crich’s protocol has also been studied in the same laboratories. As shown in Scheme 4, diol 17 was first reacted with polystyrylboronic acid (18) to offer the bound donor 19, in which 4,6-O-phenylboronates served as the torsionally disarming protecting group. With that, activation of the thioglycoside 19 was readily achieved, and the coupling reaction with the acceptor alcohol underwent smoothly to provide the bound β-mannoside 20. After removal of the excess reagents and byproducts from the resin, 20 was then treated with aqueous acetone to release 4,6-diol 21. Overall, this is a powerful method for solid-phase synthesis of β-mannosides, which has great potential to be further extended, was established. | 0 | Organic Chemistry |
Most modern laboratories use a refinement of total plate count in which serial dilutions of the sample are vacuum filtered through purpose made membrane filters and these filters are themselves laid on nutrient medium within sealed plates. The methodology is otherwise similar to conventional total plate counts. Membranes have a printed millimetre grid printed on and can be reliably used to count the number of colonies under a binocular microscope. | 3 | Analytical Chemistry |
Section 1.3 explains the rules for writing scientific symbols and names, for example, where to use capital letters or italics, and where their use is incorrect. The typographical rules are extensive, including even such detail as whether "20°C" or "20 °C" is the correct form. | 3 | Analytical Chemistry |
The "hard ionization" process of electron ionization can be softened by the cooling of the molecules before their ionization, resulting in mass spectra that are richer in information. In this method named cold electron ionization (cold-EI) the molecules exit the GC column, mixed with added helium make up gas and expand into vacuum through a specially designed supersonic nozzle, forming a supersonic molecular beam (SMB). Collisions with the make up gas at the expanding supersonic jet reduce the internal vibrational (and rotational) energy of the analyte molecules, hence reducing the degree of fragmentation caused by the electrons during the ionization process. Cold-EI mass spectra are characterized by an abundant molecular ion while the usual fragmentation pattern is retained, thus making cold-EI mass spectra compatible with library search identification techniques. The enhanced molecular ions increase the identification probabilities of both known and unknown compounds, amplify isomer mass spectral effects and enable the use of isotope abundance analysis for the elucidation of elemental formulas. | 3 | Analytical Chemistry |
Since NMR spectroscopy has been available to chemists, there have been numerous studies on the applications of this technique. One of these noted the difference in the chemical shift (i.e. the distance between the peaks) of two diastereomers. Conversely, two compounds that are enantiomers have the same NMR spectral properties. It was reasoned that if a mix of enantiomers could be converted into a mix of diastereomers by bonding them to another chemical that was itself chiral, it would be possible to distinguish this new mixture using NMR, and therefore learn about the original enantiomeric mixture. The first popular example of this technique was published in 1969 by Harry S. Mosher. The chiral agent used was a single enantiomer of MTPA (α-methoxy-α-(trifluoromethyl)phenylacetic acid), also known as Moshers acid. The corresponding acid chloride is also known as Moshers acid chloride, and the resultant diastereomeric esters are known as Moshers esters. Another system is Pirkles Alcohol developed in 1977. | 4 | Stereochemistry |
In plant physiology, the Warburg effect is the decrease in the rate of photosynthesis due to high oxygen concentrations. Oxygen is a competitive inhibitor of carbon dioxide fixation by RuBisCO which initiates photosynthesis. Furthermore, oxygen stimulates photorespiration which reduces photosynthetic output. These two mechanisms working together are responsible for the Warburg effect. | 5 | Photochemistry |
Visiting professor: University of British Columbia, Vancouver, Canada 1972; Energy Research Center, Hebrew University of Jerusalem, Israel, 1979; University of Strasbourg, France, 1990; University of Leuven, Belgium, 1991; University of Bordeaux, France, 1994. Chairman: Gruppo Italiano di Fotochimica (1982–1986), European Photochemistry Association (1988–92); XII IUPAC Symposium on Photochemistry (1988); International Symposium on "Photochemistry and Photophysics of Coordination Compounds (since 1989, now Honorary Chairman); PhD course in Chemistry Sciences (2002–2007) e Laurea specialistica in Photochemistry and Chemistry of Materials (2004–2007), University of Bologna.
Director: Institute of Photochemistry and High Energy Radiations (FRAE), National Research Council (Italy), Bologna (1977–1988) and Center for the Photochemical Conversion of Solar Energy, University of Bologna (1981–1998). Member of the Scientific Committee of several international scientific journals. Member of the Scientific Committee of the Urban Plan for Sustainable Mobility (PUMS), of the Bologna metropolitan area (2008–).
Political activity: In 2009 he started the Science and Society interdisciplinary course at the University of Bologna with the aim of bridging the gap between University and City; it has long been hoping for the strengthening of similar initiatives for the cultural growth of the Metropolitan City. In 2014 he founded the Energia per l'Italia group,[2] formed by 22 professors and researchers of the University and of the most important research centers of Bologna, with the aim of offering the Government and local politicians guidelines to tackle the energy problem according to a broad perspective that includes scientific, social, environmental and cultural aspects.
Coordinator and editor: Supramolecular Photochemistry, NATO ASI Series n. 214, Reidel, Dordrecht (1987); Supramolecular Chemistry, NATO ASI Series n. 371, Reidel, Dordrecht (1992) (with L. De Cola); Guest Editor, Supramolecular Photochemistry, New J. Chem., N.7–8, vol. 20 (1996); Editor in chief of the Handbook on Electron Transfer in Chemistry, in five volumes, Wiley-VCH, Weinheim (2001); Topics in Current Chemistry, volumes 280 and 281 on Photochemistry and Photophysics of Coordination Compounds (2007). | 5 | Photochemistry |
Pre-mRNAs of the Transformer (Tra) gene of Drosophila melanogaster undergo alternative splicing via the alternative acceptor site mode. The gene Tra encodes a protein that is expressed only in females. The primary transcript of this gene contains an intron with two possible acceptor sites. In males, the upstream acceptor site is used. This causes a longer version of exon 2 to be included in the processed transcript, including an early stop codon. The resulting mRNA encodes a truncated protein product that is inactive. Females produce the master sex determination protein Sex lethal (Sxl). The Sxl protein is a splicing repressor that binds to an ISS in the RNA of the Tra transcript near the upstream acceptor site, preventing U2AF protein from binding to the polypyrimidine tract. This prevents the use of this junction, shifting the spliceosome binding to the downstream acceptor site. Splicing at this point bypasses the stop codon, which is excised as part of the intron. The resulting mRNA encodes an active Tra protein, which itself is a regulator of alternative splicing of other sex-related genes (see dsx above). | 1 | Biochemistry |
A variety of organisms regulate their light production using different luciferases in a variety of light-emitting reactions. The majority of studied luciferases have been found in animals, including fireflies, and many marine animals such as copepods, jellyfish, and the sea pansy. However, luciferases have been studied in luminous fungi, like the Jack-O-Lantern mushroom, as well as examples in other kingdoms including bioluminescent bacteria, and dinoflagellates. | 1 | Biochemistry |
Dextroamphetamine is available as a transdermal patch containing dextroamphetamine base under the brand name Xelstrym. | 4 | Stereochemistry |
The eastern meadow vole (Microtus pennsylvanicus), sometimes called the field mouse or meadow mouse, is a North American vole found in eastern Canada and the United States. Its range extends farther south along the Atlantic coast.
The western meadow vole, Florida salt marsh vole, and beach vole were formerly considered regional variants or subspecies of M. pennsylvanicus, but have all since been designated as distinct species.
The eastern meadow vole is active year-round, usually at night. It also digs burrows, where it stores food for the winter and females give birth to their young. Although these animals tend to live close together, they are aggressive towards one another. This is particularly evident in males during the breeding season. They can cause damage to fruit trees, garden plants, and commercial grain crops. | 2 | Environmental Chemistry |
Inert solids are produced in all montane rivers as the energy of the water helps grind away rocks into gravel, sand and finer material. Much of this settles very quickly and provides an important substrate for many aquatic organisms. Many salmonid fish require beds of gravel and sand in which to lay their eggs. Many other types of solids from agriculture, mining, quarrying, urban run-off and sewage may block-out sunlight from the river and may block interstices in gravel beds making them useless for spawning and supporting insect life. | 2 | Environmental Chemistry |
Müllerian mimicry relies on aposematism, or warning signals. Dangerous organisms with these honest signals are avoided by predators, which quickly learn after a bad experience not to pursue the same unprofitable prey again. Learning is not actually necessary for animals which instinctively avoid certain prey; however, learning from experience is more common. The underlying concept with predators that learn is that the warning signal makes the harmful organism easier to remember than if it remained as well camouflaged as possible. Aposematism and camouflage are in this way opposing concepts, but this does not mean they are mutually exclusive. Many animals remain inconspicuous until threatened, then suddenly employ warning signals, such as startling eyespots, bright colours on their undersides or loud vocalizations. In this way, they enjoy the best of both strategies. These strategies may also be employed differentially throughout development. For instance, large white butterflies are aposematic as larvae, but are Müllerian mimics once they emerge from development as adult butterflies. | 1 | Biochemistry |
In NMR spectroscopy, e.g. of the nuclei H, C and Si, frequencies depend on the magnetic field, which is not the same across all experiments. Therefore, frequencies are reported as relative differences to tetramethylsilane (TMS), an internal standard that George Tiers proposed in 1958 and that the International Union of Pure and Applied Chemistry has since endorsed. The relative difference to TMS is called chemical shift.
TMS works as an ideal standard because it is relatively inert and its identical methyl protons produce a strong upfield signal, isolated from most other protons. It is soluble in most organic solvents and is removable via distillation due to its low boiling point.
In practice, the difference between the signals of common solvents and TMS are known. Therefore, no TMS needs to be added to commercial deuterated solvents, as modern instruments are capable of detecting the small quantities of protonated solvent present. By specifying the lock solvent to be used, modern spectrometers are able to correctly reference the sample; in effect, the solvent itself serves as the internal standard. | 3 | Analytical Chemistry |
In chemistry, hydration energy (also hydration enthalpy) is the amount of energy released when one mole of ions undergoes hydration. Hydration energy is one component in the quantitative analysis of solvation. It is a particular special case of water. The value of hydration energies is one of the most challenging aspects of structural prediction. Upon dissolving a salt in water, the cations and anions interact with the positive and negative dipoles of the water. The trade-off of these interactions vs those within the crystalline solid comprises the hydration energy. | 7 | Physical Chemistry |
Many varieties of coordination cages exist.
In general, coordination cages are either homoleptic or heteroleptic. That is, they assembled either from a single type of ligand or multiple types. Generic coordination cages are often classified just as coordination complexes, with a MxLy formula. Heteroleptic complexes typically form more complex geometries, as illustrated with the following cages: [M(L)] and [M(μ-L)(μ-L)](BF). The former cage is assembled from a 2:3 ratio of metal (M) and ligand (L), where the metal can be copper, zinc, or cadmium. This cage is homoleptic and assembles into a hexadecanuclear framework. The second cage is assembled from a 4:1:4 ratio of MBF, the ligand L and the ligand L. This cage is heteroleptic and assembles into a dodecanuclear cuboctohedral framework. Four of the triangular faces of this shape are occupied by L, which acts as a triply bridging ligand. The twelve remaining edges are spanned with the edge ligands, L. Ligands are the building blocks of coordination cages, and the choice and ratio of ligands determine the final structure. Due to their highly symmetrical nature, coordination cages are also often referred to by their geometry. The geometry of high-symmetry cages is often that of Platonic or Archimedean solids; sometimes cages are casually referred to by their geometries.
Of the named categories of coordination cages, cavitand cages and metalloprisms are some of the more common. | 6 | Supramolecular Chemistry |
As a trigonal bipyramidal molecule undergoes Berry pseudorotation, it proceeds via an intermediary stage with the square pyramidal geometry. Thus even though the geometry is rarely seen as the ground state, it is accessed by a low energy distortion from a trigonal bipyramid.
Pseudorotation also occurs in square pyramidal molecules. Molecules with this geometry, as opposed to trigonal bipyramidal, exhibit heavier vibration. The mechanism used is similar to the Berry mechanism. | 4 | Stereochemistry |
Luciferin () is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The resulting transformation, which usually involves breaking off a molecular fragment, produces an excited state intermediate that emits light upon decaying to its ground state. The term may refer to molecules that are substrates for both luciferases and photoproteins. | 1 | Biochemistry |
While at PAEC, Qureshi joined the chemistry department of Quaid-e-Azam University as an associate professor. In the 1990s, he joined the Punjab University to teach post-graduate course on physical chemistry. In the 2000s, he joined the Lahore University of Management Sciences's School of Science and Engineering as director of engineering and safety.
Over the years, he became known for his strong scientific advocacy of peaceful usage of nuclear energy, safety, and security, following the Fukushima disaster. A member of Khwarizmi Science Society, he has lectured on safety issues regarded the nuclear power and topics in nuclear chemistry. He has also authored numerous articles on chemical safety and securities around the world in worlds leading research journal. In 2011, he lectured on physical chemistry and spoke about how nuclear technology was being used currently and different ways of disposing nuclear waste at the Forman Christian College University in Lahore. He is the recipient of Pakistans highest honours– the Hilal-i-Imtiaz bestowed in 2003 and the Sitara-e-Imtiaz bestowed in 1999 by the Government of Pakistan. | 7 | Physical Chemistry |
Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon in which certain energetically favorable grains (crystallites) grow rapidly in a matrix of finer grains, resulting in a bimodal grain-size distribution.
In ceramic materials, this phenomenon can result in the formation of elongated prismatic, acicular (needle-like) grains in a densified matrix. This microstructure has the potential to improve fracture toughness by impeding the propagation of cracks. | 3 | Analytical Chemistry |
A molecular demon or biological molecular machine is a biological macromolecule that resembles and seems to have the same properties as Maxwells demon. These macromolecules gather information in order to recognize their substrate or ligand within a myriad of other molecules floating in the intracellular or extracellular plasm. This molecular recognition represents an information gain which is equivalent to an energy gain or decrease in entropy. When the demon is reset i.e. when the ligand is released, the information is erased, energy is dissipated and entropy increases obeying the second law of thermodynamics. The difference between biological molecular demons and the thought experiment of Maxwells demon is the latter's apparent violation of the second law. | 6 | Supramolecular Chemistry |
Arguably, the most common hemiacetals are sugars, for example glucose. The favorability of the formation of a strain-free six-membered ring and the electrophilicity of an aldehyde combine to strongly favor the acetal form. | 0 | Organic Chemistry |
Due to the binding of metal ions being essential for various enzymes to maintain their enzymatic activity, thiomers are potent reversible enzyme inhibitors. Many non-invasively administered drugs such as therapeutic peptides or nucleic acids are degraded on the mucosa by membrane bound enzymes strongly reducing their bioavailability. In case of oral administration this ‘enzymatic barrier’ is even more pronounced as an additional degradation caused by luminally secreted enzymes takes place. Because of their capability to bind zinc ions via thiol groups, thiomers are potent inhibitors of most membrane bound and secreted zinc-dependent enzymes. Due to this enzyme inhibitory effect, thiolated polymers can significantly improve the bioavailability of non-invasively administered drugs | 7 | Physical Chemistry |
Organic scavenger resins have been used commercially in water filters as early as 1997. As an alternative to reverse osmosis, organic anion resins (scavenger resins) have been used to remove impurities from drinking water. These types of resins are able to remove the negatively charged organic molecules in water, like bicarbonates, sulfates, and nitrates. It has been estimated that 60–80% of organic impurities in water may be remove using these methods. | 0 | Organic Chemistry |
Coupled reactions are reactions whose rate or equilibrium constant is not the same for the oxidized and reduced forms of the species that is being investigated. For example, reduction should favour protonation (): the protonation reaction is coupled to the reduction at . The binding of a small molecule (other than the proton) may also be coupled to a redox reaction.
Two cases must be considered depending on whether the coupled reaction is slow or fast (meaning that the time scale of the coupled reaction is larger or smaller than the voltammetric time scale ).
* Fast chemical reactions that are coupled to electron transfer (such as protonation) only affect the apparent values of and , but the peaks remain symmetrical. The dependence of on ligand concentration (e.g. the dependence of on pH plotted in a Pourbaix diagram) can be interpreted to obtain the dissociation constants (e.g. acidity constants) from the oxidized or reduced forms of the redox species.
* Asymmetry may result from slow chemical reactions that are coupled to (and gate) the electron transfer. From fast scan voltammetry, information can be gained about the rates of the reactions that are coupled to electron transfer. The case of and reversible surface electrochemical reactions followed by irreversible chemical reactions was addressed by Laviron in refs but the data are usually interpreted using the numerical solution of the appropriate differential equations. | 7 | Physical Chemistry |
The rate of carboxylation (V) is the rate that RuBisCO fixes CO to RuBP under substrate saturated conditions. A higher value of V corresponds to a higher rate of carboxylation. This rate of carboxylation can also be represented through its Michaelis-Menten constant K, with a higher value of K corresponding to a higher rate of carboxylation. V is represented by V, and K is represented as K in the generalized Michaelis-Menten curve. Although the rate of carboxylation varies among RuBisCO types, RuBisCO on average fixes only three molecules of CO per second. This is remarkably slow compared to typical enzyme catalytic rates, which usually catalyze reactions at the rate of thousands of molecules per second. | 7 | Physical Chemistry |
Chromatin remodeling is the dynamic modification of chromatin architecture to allow access of condensed genomic DNA to the regulatory transcription machinery proteins, and thereby control gene expression. Such remodeling is principally carried out by 1) covalent histone modifications by specific enzymes, e.g., histone acetyltransferases (HATs), deacetylases, methyltransferases, and kinases, and 2) ATP-dependent chromatin remodeling complexes which either move, eject or restructure nucleosomes. Besides actively regulating gene expression, dynamic remodeling of chromatin imparts an epigenetic regulatory role in several key biological processes, egg cells DNA replication and repair; apoptosis; chromosome segregation as well as development and pluripotency. Aberrations in chromatin remodeling proteins are found to be associated with human diseases, including cancer. Targeting chromatin remodeling pathways is currently evolving as a major therapeutic strategy in the treatment of several cancers. | 1 | Biochemistry |
A standard configuration for a Penning trap consists of a ring electrode and two end caps. A static voltage differential between the ring and end caps confines ions along the axial direction (between end caps). However, as expected from Earnshaw's theorem, the static electric potential is not sufficient to trap an ion in all three dimensions. To provide the radial confinement, a strong axial magnetic field is applied.
For a uniform electric field , the force accelerates a positively charged ion along the -axis. For a uniform magnetic field , the Lorentz force causes the ion to move in circular motion with cyclotron frequency
Assuming an ion with zero initial velocity placed in a region with and , the equations of motion are
The resulting motion is a combination of oscillatory motion around the -axis with frequency and a drift velocity in the -direction. The drift velocity is perpendicular to the direction of the electric field.
For the radial electric field produced by the electrodes in a Penning trap, the drift velocity will precess around the axial direction with some frequency , called the magnetron frequency. An ion will also have a third characteristic frequency between the two end cap electrodes. The frequencies usually have widely different values with . | 7 | Physical Chemistry |
Neutrophil apoptosis, or programmed cell death, is vital in controlling the duration of the early inflammatory response, thus restricting damage to tissues by the neutrophils. ANCA may be developed either via ineffective apoptosis or ineffective removal of apoptotic cell fragments, leading to the exposure of the immune system to molecules normally sequestered inside the cells. This theory solves the paradox of how it could be possible for antibodies to be raised against the intracellular antigenic targets of ANCA. | 1 | Biochemistry |
This branch of engineering emerged gradually from chemical engineering as electrical power sources became available in the mid-19th century. Michael Faraday described his laws of electrolysis in 1833, relating for the first time the amount of electrical charge and converted mass. In 1886 Charles Martin Hall developed a cheap electrochemical process for extracting aluminium from its ore in molten salts, constituting the first true large-scale electrochemical industry. Later, Hamilton Castner improved the process aluminium manufacturing and devised the electrolysis of brine in large mercury cells for the production of chlorine and caustic soda, effectively founding the chlor-alkali industry with Karl Kellner in 1892. The next year, Paul L. Hulin patented filter-press type electrochemical cells in France. Charles Frederick Burgess developed the electrolytic refining of iron ca. 1904 and later ran a successful battery company. Burgess published one of the first texts on the field in 1920. Industrial electrochemistry followed an empirical approach during the first three decades of the 20th century.
After the Second World War, interest focused on the fundaments of electrochemical reactions. Among other developments, the potentiostat (1937) enabled such studies. A critical advance was provided by the work of Carl Wagner and Veniamin Levich in 1962, who linked the hydrodynamics of a flowing electrolyte towards a rotating disc electrode with the mass transport control of the electrochemical reaction through a rigorous mathematical treatment. The same year, Wagner described "The Scope of Electrochemical Engineering" for the first time as a separate discipline from a physicochemical perspective. During the 60s and 70s Charles W. Tobias, who is regarded as the "father of electrochemical engineering" by the Electrochemical Society, was concerned with ionic transport by diffusion, migration, and convection, exact solutions of potential and current distribution problems, conductance in heterogeneous media, quantitative description of processes in porous electrodes. Also in the 60s, John Newman pioneered the study of many of the physicochemical laws that govern electrochemical systems, demonstrating how complex electrochemical processes could be analysed mathematically to correctly formulate and solve problems associated with batteries, fuel cells, electrolyzer, and related technologies. In Switzerland, Norbert Ibl contributed to experimental and theoretical studies of mass transfer and potential distribution in electrolyses, especially at porous electrodes. Fumio Hine carried out equivalent developments in Japan. In addition, several individuals, including Kuhn, Kreysa, Rousar, Fleischmann, Alkire, Coeuret, Pletcher, and Walsh established many other training centers and, with their colleagues, developed important experimental and theoretical methods of study. Currently, the main tasks of electrochemical engineering consist of the development of efficient, safe, and sustainable technologies for the production of chemicals, metal recovery, remediation, and decontamination technologies as well as the design of fuel cells, flow batteries, and industrial electrochemical reactors.
The history of electrochemical engineering has been summarised by Wendt, Lapicque, and Stankovic. | 7 | Physical Chemistry |
There is evidence for multiple euxinic events during the Phanerozoic. It is most likely that euxinia was periodic during the Paleozoic and Mesozoic, but geologic data is too sparse to draw any large scale conclusions. In this eon, there is some evidence that euxinic events are potentially linked with mass extinction events including the Late Devonian and Permian–Triassic. | 9 | Geochemistry |
Progesterone also appears to be involved in the pathophysiology of breast cancer, though its role, and whether it is a promoter or inhibitor of breast cancer risk, has not been fully elucidated. Most progestins, or synthetic progestogens, like medroxyprogesterone acetate, have been found to increase the risk of breast cancer in postmenopausal women in combination with estrogen as a component of menopausal hormone therapy. The combination of natural oral progesterone or the atypical progestin dydrogesterone with estrogen has been associated with less risk of breast cancer than progestins plus estrogen. However, this may simply be an artifact of the low progesterone levels produced with oral progesterone. More research is needed on the role of progesterone in breast cancer. | 0 | Organic Chemistry |
Quantitative PCR (Q-PCR) is used to measure the quantity of a PCR product (preferably real-time, QRT-PCR). It is the method of choice to quantitatively measure amounts of transgene DNA in a food or feed sample. Q-PCR is commonly used to determine whether a DNA sequence is present in a sample and the number of its copies in the sample. The method with currently the highest level of accuracy is quantitative real-time PCR. QRT-PCR methods use fluorescent dyes, such as Sybr Green, or fluorophore-containing DNA probes, such as TaqMan, to measure the amount of amplified product in real time. If the targeted genetic sequence is unique to a certain GMO, a positive PCR test proves that the GMO is present in the sample. | 1 | Biochemistry |
Erythrolitmin (also called erythrolein) is the active ingredient extracted from the Litmus lichen, used in chemistry as a pH indicator. Erythrolitmin is related to the orceins, and consists essentially of several phenoxazone and orcinol residues. | 3 | Analytical Chemistry |
Many methods exist for the preparation of ketones in industrial scale and academic laboratories. Ketones are also produced in various ways by organisms; see the section on biochemistry below.
In industry, the most important method probably involves oxidation of hydrocarbons, often with air. For example, a billion kilograms of cyclohexanone are produced annually by aerobic oxidation of cyclohexane. Acetone is prepared by air-oxidation of cumene.
For specialized or small scale organic synthetic applications, ketones are often prepared by oxidation of secondary alcohols:
Typical strong oxidants (source of "O" in the above reaction) include potassium permanganate or a Cr(VI) compound. Milder conditions make use of the Dess–Martin periodinane or the Moffatt–Swern methods.
Many other methods have been developed, examples include:
* By geminal halide hydrolysis.
* By hydration of alkynes. Such processes occur via enols and require the presence of an acid and mercury(II) sulfate (). Subsequent enol–keto tautomerization gives a ketone. This reaction always produces a ketone, even with a terminal alkyne, the only exception being the hydration of acetylene, which produces acetaldehyde.
*From Weinreb Amides using stoichiometric organometallic reagents.
* Aromatic ketones can be prepared in the Friedel–Crafts acylation, the related Houben–Hoesch reaction, and the Fries rearrangement.
* Ozonolysis, and related dihydroxylation/oxidative sequences, cleave alkenes to give aldehydes or ketones, depending on alkene substitution pattern.
* In the Kornblum–DeLaMare rearrangement ketones are prepared from peroxides and base.
* In the Ruzicka cyclization, cyclic ketones are prepared from dicarboxylic acids.
* In the Nef reaction, ketones form by hydrolysis of salts of secondary nitro compounds.
* In the Fukuyama coupling, ketones form from a thioester and an organozinc compound.
* By the reaction of an acid chloride with organocadmium compounds or organocopper compounds.
* The Dakin–West reaction provides an efficient method for preparation of certain methyl ketones from carboxylic acids.
* Ketones can be prepared by the reaction of Grignard reagents with nitriles, followed by hydrolysis.
* By decarboxylation of carboxylic anhydride.
* Ketones can be prepared from haloketones in reductive dehalogenation of halo ketones.
* In ketonic decarboxylation symmetrical ketones are prepared from carboxylic acids.
* Hydrolysis of unsaturated secondary amides, β-Keto acid esters, or β-diketones (the acetoacetic ester synthesis).
* Acid-catalysed rearrangement of 1,2-diols, or Criegee oxidation of the same. | 0 | Organic Chemistry |
Sevoflurane is a potent vasodilator, as such it induces a dose dependent reduction in blood pressure and cardiac output. It is a bronchodilator, however, in patients with pre-existing lung pathology, it may precipitate coughing and laryngospasm. It reduces the ventilatory response to hypoxia and hypercapnia, and impedes hypoxic pulmonary vasoconstriction. Sevoflurane vasodilatory properties also cause it to increase intracranial pressure and cerebral blood flow. However, it reduces cerebral metabolic rate. | 2 | Environmental Chemistry |
Climate change is likely to increase the frequency, intensity and duration of cyanobacterial blooms in many eutrophic lakes, reservoirs and estuaries. Bloom-forming cyanobacteria produce a variety of neurotoxins, hepatotoxins and dermatoxins, which can be fatal to birds and mammals (including waterfowl, cattle and dogs) and threaten the use of waters for recreation, drinking water production, agricultural irrigation and fisheries. Toxic cyanobacteria have caused major water quality problems, for example in Lake Taihu (China), Lake Erie (USA), Lake Okeechobee (USA), Lake Victoria (Africa) and the Baltic Sea.
Climate change favours cyanobacterial blooms both directly and indirectly. Many bloom-forming cyanobacteria can grow at relatively high temperatures. Increased thermal stratification of lakes and reservoirs enables buoyant cyanobacteria to float upwards and form dense surface blooms, which gives them better access to light and hence a selective advantage over nonbuoyant phytoplankton organisms. Protracted droughts during summer increase water residence times in reservoirs, rivers and estuaries, and these stagnant warm waters can provide ideal conditions for cyanobacterial bloom development.
The capacity of the harmful cyanobacterial genus Microcystis to adapt to elevated CO levels was demonstrated in both laboratory and field experiments. Microcystis spp. take up CO and and accumulate inorganic carbon in carboxysomes, and strain competitiveness was found to depend on the concentration of inorganic carbon. As a result, climate change and increased CO levels are expected to affect the strain composition of cyanobacterial blooms. | 5 | Photochemistry |
An old-standing topic in grain growth is the evolution of the grains size distribution. Inspired by the work of Lifshitz and Slyozov on Ostwald ripening, Hillert has suggested that in a normal grain growth process the size distribution function must converge to a self-similar solution, i.e. it becomes invariant when the grain size is scaled with a characteristic length of the system that is proportional to the average grain size .
Several simulation studies, however, have shown that the size distribution deviates from the Hillerts self-similar solution. Hence a search for a new possible self-similar solution was initiated that indeed led to a new class of self-similar distribution functions. Large-scale phase field simulations have shown that there is indeed a self-similar behavior possible within the new distribution functions. It was shown that the origin of the deviation from Hillerts distribution is indeed the geometry of grains specially when they are shrinking. | 8 | Metallurgy |
Nucleotides can be synthesized by a variety of means, both in vitro and in vivo.
In vitro, protecting groups may be used during laboratory production of nucleotides. A purified nucleoside is protected to create a phosphoramidite, which can then be used to obtain analogues not found in nature and/or to synthesize an oligonucleotide.
In vivo, nucleotides can be synthesized de novo or recycled through salvage pathways. The components used in de novo nucleotide synthesis are derived from biosynthetic precursors of carbohydrate and amino acid metabolism, and from ammonia and carbon dioxide. Recently it has been also demonstrated that cellular bicarbonate metabolism can be regulated by mTORC1 signaling. The liver is the major organ of de novo synthesis of all four nucleotides. De novo synthesis of pyrimidines and purines follows two different pathways. Pyrimidines are synthesized first from aspartate and carbamoyl-phosphate in the cytoplasm to the common precursor ring structure orotic acid, onto which a phosphorylated ribosyl unit is covalently linked. Purines, however, are first synthesized from the sugar template onto which the ring synthesis occurs. For reference, the syntheses of the purine and pyrimidine nucleotides are carried out by several enzymes in the cytoplasm of the cell, not within a specific organelle. Nucleotides undergo breakdown such that useful parts can be reused in synthesis reactions to create new nucleotides. | 1 | Biochemistry |
When a liquid drop is put onto a flat surface, two situations may result. If the contact angle is zero, the situation is referred to as complete wetting. If the contact angle is between 0 and 180°, the situation is called partial wetting. A wetting transition is a surface phase transition from partial wetting to complete wetting. | 7 | Physical Chemistry |
Cleavage is a physical property traditionally used in mineral identification, both in hand-sized specimen and microscopic examination of rock and mineral studies. As an example, the angles between the prismatic cleavage planes for the pyroxenes (88–92°) and the amphiboles (56–124°) are diagnostic.
Crystal cleavage is of technical importance in the electronics industry and in the cutting of gemstones.
Precious stones are generally cleaved by impact, as in diamond cutting.
Synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Simply pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is usually enough to cause cleavage; however, when dicing a wafer to form chips, a procedure of scoring and breaking is often followed for greater control. Elemental semiconductors (silicon, germanium, and diamond) are diamond cubic, a space group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved. Most other commercial semiconductors (GaAs, InSb, etc.) can be made in the related zinc blende structure, with similar cleavage planes. | 3 | Analytical Chemistry |
Based on the physical method of electroporation, nucleofection uses a combination of electrical parameters, generated by a device called Nucleofector, with cell-type specific reagents. The substrate is transferred directly into the cell nucleus and the cytoplasm. In contrast, other commonly used non-viral transfection methods rely on cell division for the transfer of DNA into the nucleus. Thus, nucleofection provides the ability to transfect even non-dividing cells, such as neuron and resting blood cells. Before the introduction of the Nucleofector Technology, efficient gene transfer into primary cells had been restricted to the use of viral vectors, which typically involve disadvantages such as safety risks, lack of reliability, and high cost. The non-viral gene transfer methods available were not suitable for the efficient transfection of primary cells. Non-viral delivery methods may require cell division for completion of transfection, since the DNA enters the nucleus during breakdown of the nuclear envelope upon cell division or by a specific localization sequence.
Optimal nucleofection conditions depend upon the individual cell type, not on the substrate being transfected. This means that identical conditions are used for the nucleofection of DNA, RNA, siRNAs, shRNAs, mRNAs and pre-mRNAs, BACs, peptides, morpholinos, PNA, or other biologically active molecules. | 1 | Biochemistry |
Cholesterol is precursor for steroid hormones including progestogens, glucocorticoids, mineralocorticoids, androgens, and estrogens. | 1 | Biochemistry |
Amphipathic Lipid Packing Sensor (ALPS) motifs were first identified in 2005 in ARFGAP1 and have been reviewed.
The curving of a phospholipid bilayer, for example into a liposome, causes disturbances to the packing of the lipids on the side of the bilayer that has the larger surface area (the outside of a liposome for example). The less "ordered" or "looser" packing of the lipids is recognized by ALPS motifs.
ALPS motifs are 20 to 40 amino acid long portions of proteins that have important collections of types of amino acid residues. Bulky hydrophobic amino acid residues, such as Phenylalanine, Leucine, and Tryptophan are present every 3 or 4 positions, with many polar but uncharged amino acid residues such as Glycine, Serine and Threonine between. The ALPS is unstructured in solution but folds as an alpha helix when associated with the membrane bilayer, such that the hydrophobic residues insert between loosely packed lipids and the polar residues point toward the aqueous cytoplasm. | 1 | Biochemistry |
*Protection: Cushions the plasma membrane and protects it from chemical injury
*Immunity to infection: Enables the immune system to recognize and selectively attack foreign organisms
*Defense against cancer: Changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them.
*Transplant compatibility: Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants
*Cell adhesion: Binds cells together so that tissues do not fall apart
*Inflammation regulation: Glycocalyx coating on endothelial walls in blood vessels prevents leukocytes from rolling/binding in healthy states.
*Fertilization: Enables sperm to recognize and bind to eggs
*Embryonic development: Guides embryonic cells to their destinations in the body | 1 | Biochemistry |
The first synthetic ion channel was constructed by partial substitution on the primary rim of β-cyclodextrin. Other substituted β-cyclodextrins have since been reported, including thiol-modified cyclodextrins, an anion-selective oligobutylene channel, and various poly-ethyleneoxide linked starburst oligomers. Structure-activity relationships for a large suite of cyclodextrin "half-channels" prepared by "click"-chemistry has been recently reported. | 6 | Supramolecular Chemistry |
The oxidative photosynthetic carbon cycle reaction is catalyzed by RuBP oxygenase activity:
:RuBP + → Phosphoglycolate + 3-phosphoglycerate + 2
During the catalysis by RuBisCO, an activated intermediate is formed (an enediol intermediate) in the RuBisCO active site. This intermediate is able to react with either or . It has been demonstrated that the specific shape of the RuBisCO active site acts to encourage reactions with . Although there is a significant "failure" rate (~25% of reactions are oxygenation rather than carboxylation), this represents significant favouring of , when the relative abundance of the two gases is taken into account: in the current atmosphere, is approximately 500 times more abundant, and in solution is 25 times more abundant than .
The ability of RuBisCO to specify between the two gases is known as its selectivity factor (or Srel), and it varies between species, with angiosperms more efficient than other plants, but with little variation among the vascular plants.
A suggested explanation of RuBisCO's inability to discriminate completely between and is that it is an evolutionary relic: The early atmosphere in which primitive plants originated contained very little oxygen, the early evolution of RuBisCO was not influenced by its ability to discriminate between and . | 5 | Photochemistry |
Two waste products, dust and chips, form at the working surface during woodworking operations such as sawing, milling and sanding. These operations both shatter lignified wood cells and break out whole cells and groups of cells. Shattering of wood cells creates dust, while breaking out of whole groups of wood cells creates chips. The more cell-shattering that occurs, the finer the dust particles that are produced. For example, sawing and milling are mixed cell shattering and chip forming processes, whereas sanding is almost exclusively cell shattering. | 2 | Environmental Chemistry |
One of Ted Ellis more famous works is an abstract depiction of Barack Obamas signature hope pose. Ellis painted the portrait in honor of Obamas 2008 Presidential inauguration. In Obama, the 44th President', Ellis uses red, blue, yellow, and green acrylic paint to portray Obama as someone who unites people across lines of color, ethnicity, and religion.
The piece was presented at a January 19, 2009, gala held by the National Black Chamber of Commerce and the National Newspaper Publishers Association Foundation at the Embassy of France in Washington, D.C. The proceeds from the autographed prints sold at the event supported NNPA Foundation and the Howard University School of Communications Building Fund (NNPA Media Wing). | 3 | Analytical Chemistry |
Crystal violet is used as a textile and paper dye, and is a component of navy blue and black inks for printing, ball-point pens, and inkjet printers. It is sometimes used to colourize diverse products such as fertilizer, antifreeze, detergent, and leather.
The dye is used as a histological stain, particularly in Gram staining for classifying bacteria.
When conducting DNA gel electrophoresis, crystal violet can be used as a nontoxic DNA stain as an alternative to fluorescent, intercalating dyes such as ethidium bromide. Used in this manner, it may be either incorporated into the agarose gel or applied after the electrophoresis process is finished. Used at a 0.001% concentration and allowed to stain a gel after electrophoresis for 30 minutes, it can detect as little as 16 ng of DNA. Through use of a methyl orange counterstain and a more complex staining method, sensitivity can be improved further to 8 ng of DNA. When crystal violet is used as an alternative to fluorescent stains, it is not necessary to use ultraviolet illumination; this has made crystal violet popular as a means of avoiding UV-induced DNA destruction when performing DNA cloning in vitro.
In biomedical research, crystal violet can be used to stain the nuclei of adherent cells. In this application, crystal violet works as an intercalating dye and allows the quantification of DNA which is proportional to the number of cells.
In forensics, crystal violet was used to develop fingerprints. Crystal violet is also used as a tissue stain in the preparation of light microscopy sections. In laboratory, solutions containing crystal violet and formalin are often used to simultaneously fix and stain cells grown in tissue culture to preserve them and make them easily visible, since most cells are colourless. It is also sometimes used as a cheap way to put identification markings on laboratory mice; since many strains of lab mice are albino, the purple colour stays on their fur for several weeks.
In body piercing, gentian violet is commonly used to mark the location for placing piercings, including surface piercings.
Marking blue, used to mark out pieces in metalworking, is composed of methylated spirits, shellac, and gentian violet. | 3 | Analytical Chemistry |
In the asymmetric Diels–Alder reactions, instead of using chiral ligands or chiral auxiliaries to differentiate the side selectivity of the dienolphiles, the differentiation of face selectivity of the dienes (especially for cyclopentadiene derivatives) using stereoelectronic effects have been reported by Woodward since 1955. A systematic research of facial selectivity using substituted cyclopentadiene or permethylcyclopentadiene derivatives have been conducted and the results can be listed as below.
The stereoelectronic effect affecting the outcome of the facial selectivity of the diene in the Diels–Alder reaction is the interaction between the σ(C(sp)–CH) (when σ(C(sp)–X) is a better acceptor than a donor) or σ(C(sp)–X) (when σ(C(sp)–X) is a better donor than an acceptor) and the σ* orbital of the forming bond between the diene and the dienophile.
If the two geminal substituents are both aromatic rings with different substituents tuning the electron density, the differentiation of the facial selectivity is also facile where the dienophile approaches the diene anti to the more electron-rich C–C bond where the stereoelectronic effect, in this case, is similar to the previous one.
The ring opening of cyclobutene under heating conditions can have two products: inward and outward rotation.
The inward rotation transition state of the structure shown below is relatively favored for acceptor R substituents (e.g. NO) but is especially disfavored by donor R substituents (e.g. NMe). | 4 | Stereochemistry |
Together with the formula above, the boiling-point elevation can in principle be used to measure the degree of dissociation or the molar mass of the solute. This kind of measurement is called ebullioscopy (Latin-Greek "boiling-viewing"). However, since superheating is difficult to avoid, precise ΔT measurements are difficult to carry out, which was partly overcome by the invention of the Beckmann thermometer. Furthermore, the cryoscopic constant that determines freezing-point depression is larger than the ebullioscopic constant, and since the freezing point is often easier to measure with precision, it is more common to use cryoscopy. | 7 | Physical Chemistry |
Bharat graduated with a BA in Biological Sciences from the University of Oxford, UK. His studies were supported by a Rhodes Scholarship. He then undertook research at the European Molecular Biology Laboratory in Heidelberg, Germany for his PhD working with John A. G. Briggs. He studied the structure and assembly of pathogenic viruses using cryogenic electron microscopy and tomography. His work on several viral capsid proteins improved understanding of how viruses are assembled within infected cells. | 1 | Biochemistry |
Harmful algal bloom in coastal areas are also often referred to as "red tides". The term "red tide" is derived from blooms of any of several species of dinoflagellate, such as Karenia brevis. However, the term is misleading since algal blooms can widely vary in color, and growth of algae is unrelated to the tides. Not all red tides are produced by dinoflagellates. The mixotrophic ciliate Mesodinium rubrum produces non-toxic blooms coloured deep red by chloroplasts it obtains from the algae it eats.
As a technical term, it is being replaced in favor of more precise terminology, including the generic term "harmful algal bloom" for harmful species, and "algal bloom" for benign species. | 3 | Analytical Chemistry |
Metals in Earths inner core could possibly be in the chain-melted state, as suggested by several simulations, where metals such as titanium and iron displayed partially molten states, or quasi-solid properties. It is also possible that Earths mantle may contain metals like potassium in the chain-melted state; however, potassium is usually not found in pure form.
These suggestions may also possibly be proven by the Kola superdeep borehole, where according to declassified documents, the rock at the bottom of the borehole was found to be in a texture between solid and liquid. | 7 | Physical Chemistry |
*Hydrogenolysis of ester compounds to the corresponding alcohols, and carbon–carbon and carbon–oxygen double bonds to single bonds. For example, sebacoin, derived from the acyloin condensation of dimethyl sebacate, is hydrogenated to 1,2-cyclodecanediol by this catalyst. Phenanthrene is also reduced, at the 9,10 position.
*Hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5-pentanediol at 250–300 °C under 3300-6000 psi of H.
*Decarboxylation of α-phenylcinnamic acid to cis-stilbene.
Reactions involving hydrogen are conducted at relatively high gas pressure (135 atm) and high temperatures (150–300 °C) in a so-called hydrogenation bomb. More active catalysts, such as W-6 grade Raney nickel, also catalyze hydrogenations such as ester reductions. The latter catalyst benefits from requiring less vigorous conditions (i.e., it works at room temperature under similar hydrogenation pressures) but requires the chemist to use a higher ratio of catalyst to reagents. | 0 | Organic Chemistry |
A variety of further synthetic procedures are particularly useful in opening carbocyclic and other rings, generally which contain a double bound or other functional group "handle" to facilitate chemistry; these are termed ring-opening reactions. Examples include:
* ring opening metathesis, which can also be used to accomplish a specific type of polymerization. | 4 | Stereochemistry |
Perera is a Chartered Chemist (CChem.)by profession and a Registered Analytical Chemist of the Royal Society of Chemistry (RSC) in the United Kingdom. He is a Fellow (FRSC) of the RSC of which he is an honorary life member and the former hony. secretary / treasurer (1984–1992) of its section in Sri Lanka.
He is also a life member and a Fellow (FIChemC) of the Institute of Chemistry Ceylon and a Fellow (FIQA) of the Institute of Quality Assurance UK.
His professional career started in August 1978 as an assistant lecturer at the department of Chemistry, University of Colombo. His work thereafter in the multinational pharmaceutical manufacturing industry extended for almost 14 years, from September 1978 until July 1992.
Perera started his career in industry as a production executive with Glaxo Ceylon Limited and stayed until March 1982.
Mackwoods-Winthrop Limited then hired hm as the senior manager in charge of their quality assurance and analytical control divisions until March 1989, and thereafter as the senior manager of the newly established technical services department.
Perera then changed over to the cosmetics and healthcare industry when Hemas Manufacturing Limited invited him to join them in August 1992 as the Director – Senior Manager of quality assurance and product development.
But it was only 14 weeks service there for Perera, as a freak road accident on 12 November 1992 made him instantaneously a paraplegic for life and cut short tragically, at the age of 36, his professional career that was just blossoming out. | 3 | Analytical Chemistry |
Releaser pheromones are pheromones that cause an alteration in the behavior of the recipient. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. In general, this type of pheromone elicits a rapid response, but is quickly degraded. In contrast, a primer pheromone has a slower onset and a longer duration. For example, rabbit (mothers) release mammary pheromones that trigger immediate nursing behavior by their babies. | 1 | Biochemistry |
Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects protected metal to a more easily corroded "sacrificial anode" to act as the anode. The sacrificial metal, instead of the protected metal, then corrodes. A common application of cathodic protection is in galvanized steel, in which a sacrificial coating of zinc on steel parts protects them from rust.
Oxidation is used in a wide variety of industries such as in the production of cleaning products and oxidizing ammonia to produce nitric acid.
Redox reactions are the foundation of electrochemical cells, which can generate electrical energy or support electrosynthesis. Metal ores often contain metals in oxidized states such as oxides or sulfides, from which the pure metals are extracted by smelting at high temperature in the presence of a reducing agent. The process of electroplating uses redox reactions to coat objects with a thin layer of a material, as in chrome-plated automotive parts, silver plating cutlery, galvanization and gold-plated jewelry. | 9 | Geochemistry |
When studying urease at about the same time as Michaelis and Menten were studying invertase, Donald Van Slyke and G. E. Cullen made essentially the opposite assumption, treating the first step not as an equilibrium but as an irreversible second-order reaction with rate constant . As their approach is never used today it is sufficient to give their final rate equation:
and to note that it is functionally indistinguishable from the Henri–Michaelis–Menten equation. One cannot tell from inspection of the kinetic behaviour whether is equal to or to or to something else. | 7 | Physical Chemistry |
Alkylidenecyclopropanes more readily undergo C-C bond oxidative addition than cyclopropanes.
Following oxidative addition, 1,2-insertion mechanisms are common and reductive elimination yields the desired product. The 1,2-insertion step usually occurs with an alkyne, alkene, or allene and the final product is often a 5 or 7 membered ring. Six-membered rings may be formed after dimerization of the metallocyclobutane intermediate with another alkylidenecyclopropane substrate and subsequent reductive elimination. Common transition metals utilized with alkylidenecyclopropanes are nickel, rhodium, and palladium. It has been shown that the metallacyclobutane intermediate following oxidative addition to the distal C-C bond can isomerize. | 0 | Organic Chemistry |
Plasma protein binding refers to the degree to which medications attach to blood proteins within the blood plasma. A drug's efficacy may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse or diffuse through cell membranes. Common blood proteins that drugs bind to are human serum albumin, lipoprotein, glycoprotein, and α, β‚ and γ globulins. | 1 | Biochemistry |
In chemistry, persulfide refers to the functional group R-S-S-H. Persulfides are intermediates in the biosynthesis of iron-sulfur proteins and are invoked as precursors to hydrogen sulfide, a signaling molecule. | 0 | Organic Chemistry |
With polymerase chain reaction (PCR) being among the most popular contexts in which DNA denaturation is desired, heating is the most frequent method of denaturation. Other than denaturation by heat, nucleic acids can undergo the denaturation process through various chemical agents such as formamide, guanidine, sodium salicylate, dimethyl sulfoxide (DMSO), propylene glycol, and urea. These chemical denaturing agents lower the melting temperature (T) by competing for hydrogen bond donors and acceptors with pre-existing nitrogenous base pairs. Some agents are even able to induce denaturation at room temperature. For example, alkaline agents (e.g. NaOH) have been shown to denature DNA by changing pH and removing hydrogen-bond contributing protons. These denaturants have been employed to make Denaturing Gradient Gel Electrophoresis gel (DGGE), which promotes denaturation of nucleic acids in order to eliminate the influence of nucleic acid shape on their electrophoretic mobility. | 1 | Biochemistry |
A wealth of literature exists on the defensive chemistry of secondary metabolites produced by terrestrial plants and their antagonistic effects on pests and pathogens, likely owing to the fact that human society depends upon large-scale agricultural production to sustain global commerce. Since the 1950s, over 200,000 secondary metabolites have been documented in plants. These compounds serve a variety of physiological and allelochemical purposes, and provide a sufficient stock for the evolution of defensive chemicals. Examples of common secondary metabolites used as chemical defenses by plants include alkaloids, phenols, and terpenes. Defensive chemicals used to avoid consumption may be broadly characterized as either toxins or substances reducing the digestive capacity of herbivores. Although toxins are defined in a broad sense as any substance produced by an organism that reduces the fitness of another, in a more specific sense toxins are substances which directly affect and diminish the functioning of certain metabolic pathways. Toxins are minor constituents (<2% dry weight), active in small concentrations, and more present in flowers and young leaves. On the other hand, indigestible compounds make up to 60% dry weight of tissue and are predominately found in mature, woody species. Many alkaloids, pyrethrins, and phenols are toxins. Tannins are major inhibitors of digestion and are polyphenolic compounds with large molecular weights. Lignin and cellulose are important structural elements in plants and are also usually highly indigestible. Tannins are also toxic against pathogenic fungi at natural concentrations in a variety of woody tissues. Not only useful as deterrents to pathogens or consumers, some of the chemicals produced by plants are effective in inhibiting competitors as well. Two separate shrub communities in the California chaparral were found to produce phenolic compounds and volatile terpenes which accumulated in soil and prevented various herbs from growing near the shrubs. Other plants were only observed to grow when fire removed shrubs, but herbs subsequently died off after shrubs returned. Although the focus has been on broad-scale patterns in terrestrial plants, Paul and Fenical in 1986 demonstrated a variety of secondary metabolites in marine algae which prevented feeding or induced mortality in bacteria, fungi, echinoderms, fishes, and gastropods. In nature, pests are a severe problem to plant communities as well, leading to the co-evolution of plant chemical defenses and herbivore metabolic strategies to detoxify their plant food. A variety of invertebrates consume plants, but insects have received a majority of the attention. Insects are pervasive agricultural pests and sometimes occur in such high densities that they can strip fields of crops. | 1 | Biochemistry |
The centrifugal partition chromatograph instrument is constituted with a unique rotor which contains the column. This rotor rotates on its central axis (while HSCCC column rotates on its planetary axis and simultaneously rotates eccentrically about another solar axis). With less vibrations and noise, the CPC offers a typical rotation speed range from 500 to 2000 rpm. Contrary to hydrodynamic CCC, the rotation speed is not directly proportional to the retention volume ratio of the stationary phase. Like DCCC, CPC can be operated in either descending or ascending mode, where the direction is relative to the force generated by the rotor rather than gravity. A redesigned CPC column with larger chambers and channels has been named centrifugal partition extraction (CPE). In the CPE design, faster flow rates and increased column loading can be achieved. | 3 | Analytical Chemistry |
Since 1990 the number of European producers has been declining. The French SNPE factory closed in 1990; in 1993, the production of hexamethylenetetramine in Leuna, Germany ceased; in 1996, the Italian facility of Agrolinz closed down; in 2001, the UK producer Borden closed; in 2006, production at Chemko, Slovak Republic, was closed. Remaining producers include INEOS in Germany, Caldic in the Netherlands, and Hexion in Italy. In the US, Eli Lilly and Company stopped producing methenamine tablets in 2002. In Australia, Hexamine Tablets for fuel are made by Thales Australia Ltd. In México, Hexamine is produced by Abiya. | 0 | Organic Chemistry |
Dexketoprofen is the (S)-enantiomer of ketoprofen. Technically it is a chiral switch of (±)-ketoprofen. The switch was done for a faster onset of action, a better therapeutic value. Dexketoprofen consists of a propionic acid moiety connected to a benzophenone molecule by its second carbon. | 4 | Stereochemistry |
*Rapid purification time: Products can be purified in short periods of time, relative to traditional techniques
*Product remains in solution: The product is not removed from solution, as in crystallization techniques.
*Reaction may be monitored: The purification process is controlled
*Traditional purity techniques may be employed
*Can be used in excess
*Removed by filtration
*Allow for the synthesis of complex compound libraries
*Can be customized: Different scavenger resins employed for different impurities.
*High solvent compatibility (can be used with many solvents) | 0 | Organic Chemistry |
Primer pheromones trigger a change of developmental events (in which they differ from all the other pheromones, which trigger a change in behavior). They were first described in Schistocerca gregaria by Maud Norris in 1954. | 1 | Biochemistry |
In vertebrates, the majority of gene promoters contain a CpG island with numerous CpG sites. When many of a gene's promoter CpG sites are methylated the gene becomes silenced. Colorectal cancers typically have 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. However, transcriptional silencing may be of more importance than mutation in causing progression to cancer. For example, in colorectal cancers about 600 to 800 genes are transcriptionally silenced by CpG island methylation (see regulation of transcription in cancer). Transcriptional repression in cancer can also occur by other epigenetic mechanisms, such as altered expression of microRNAs. In breast cancer, transcriptional repression of BRCA1 may occur more frequently by over-expressed microRNA-182 than by hypermethylation of the BRCA1 promoter (see Low expression of BRCA1 in breast and ovarian cancers). | 1 | Biochemistry |
5-Diphosphomevalonic acid (or mevalonate-5-pyrophosphate, or 5-pyrophosphomevalonate) is an intermediate in the mevalonate pathway. | 1 | Biochemistry |
There are attempts to provide partition coefficients for drugs at a single-cell level. This strategy requires methods for the determination of concentrations in individual cells, i.e., with Fluorescence correlation spectroscopy or quantitative Image analysis. Partition coefficient at a single-cell level provides information on cellular uptake mechanism. | 7 | Physical Chemistry |
The continuum in the spectrum is the light with wavelengths between the lines. Polarization in the continuum is due to Rayleigh scattering by neutral hydrogen atoms (H I) and Thomson scattering by free electrons. Most of the opacity in the sun is due to the hydride ion, H which however does not alter polarization. In 1950 Subrahmanyan Chandrasekhar came up with a solution for the degree of polarization due to scattering, and predicted 11.7% polarization at the limb of the Sun. But nowhere near this level is observed. What happens at the limb is that there is a forest of spicules poking out from the edge, so it is not possible to get parallel to such a rough surface.
For most of the solar disk the degree of linear polarization of the continuum is under 0.1%, but it rises to 1% at the limb. The polarization also depends strongly on the wavelength, and for near ultraviolet 3000 Å the light near the limb is 100 times more polarized than red light at 7000 Å. At the limit of the Balmer series a change happens where at shorter wavelengths more bound-bound Balmer series transitions cause more opacity. This extra opacity drops the polarization degree by a factor of two near 3746 Å. | 7 | Physical Chemistry |
Jannik Bjerrum (son of Niels Bjerrum) developed the first general method for the determination of stability constants of metal-ammine complexes in 1941. The reasons why this occurred at such a late date, nearly 50 years after Alfred Werner had proposed the correct structures for coordination complexes, have been summarised by Beck and Nagypál. The key to Bjerrum's method was the use of the then recently developed glass electrode and pH meter to determine the concentration of hydrogen ions in solution. Bjerrum recognised that the formation of a metal complex with a ligand was a kind of acid–base equilibrium: there is competition for the ligand, L, between the metal ion, M, and the hydrogen ion, H. This means that there are two simultaneous equilibria that have to be considered. In what follows electrical charges are omitted for the sake of generality. The two equilibria are
Hence by following the hydrogen ion concentration during a titration of a mixture of M and HL with base, and knowing the acid dissociation constant of HL, the stability constant for the formation of ML could be determined. Bjerrum went on to determine the stability constants for systems in which many complexes may be formed.
The following twenty years saw a veritable explosion in the number of stability constants that were determined. Relationships, such as the Irving-Williams series were discovered. The calculations were done by hand using the so-called graphical methods. The mathematics underlying the methods used in this period are summarised by Rossotti and Rossotti. The next key development was the use of a computer program, LETAGROP to do the calculations. This permitted the examination of systems too complicated to be evaluated by means of hand-calculations. Subsequently, computer programs capable of handling complex equilibria in general, such as SCOGS and MINIQUAD were developed so that today the determination of stability constants has almost become a "routine" operation. Values of thousands of stability constants can be found in two commercial databases. | 7 | Physical Chemistry |
A fishs hypoxia tolerance can be represented in different ways. A commonly used representation is the critical O tension (P), which is the lowest water O tension (P consumption rate (M is therefore thought to be more hypoxia-tolerant than a fish with a higher P. But while P is often used to represent hypoxia tolerance, it more accurately represents the ability to take up environmental O at hypoxic P is nevertheless closely tied to a fishs hypoxia tolerance, in part because some fish prioritize their use of aerobic metabolism over anaerobic metabolism and metabolic suppression. It therefore remains a widely used hypoxia tolerance metric.
A fish's hypoxia tolerance can also be represented as the amount of time it can spend at a particular hypoxic P</sub>-of-LOE value therefore imply enhanced hypoxia tolerances. In either case, LOE is a more holistic representation of overall hypoxia tolerance because it incorporates all contributors to hypoxia tolerance, including aerobic metabolism, anaerobic metabolism and metabolic suppression. | 9 | Geochemistry |
The Adamkiewicz reaction is part of a biochemical test used to detect the presence of the amino acid tryptophan in proteins. When concentrated sulfuric acid is combined with a solution of protein and glyoxylic acid, a red/purple colour is produced. It was named after its discoverer, Albert Wojciech Adamkiewicz. Pure sulfuric acid and a minimal amount of pure formaldehyde, along with an oxidizing agent introduced into the sulfuric acid, allow the reaction to proceed. | 0 | Organic Chemistry |
Ordinary spectroscopy is concerned with the spectra of single atoms or molecules. Here we outline the very different spectra of complexes consisting of two or more interacting atoms or molecules: the "interaction-induced" or "collision-induced" spectroscopy. Both ordinary and collision-induced spectra may be observed in emission and absorption and require an electric or magnetic multipole moment - in most cases an electric dipole moment - to exist for an optical transition to take place from an initial to a final quantum state of a molecule or a molecular complex. (For brevity of expression we will use here the term "molecule" interchangeably for atoms as well as molecules). A complex of interacting molecules may consist of two or more molecules in a collisional encounter, or else of a weakly bound van der Waals molecule. On first sight, it may seem strange to treat optical transitions of a collisional complex, which may exist just momentarily, for the duration of a fly-by encounter (roughly 10 seconds), in much the same way as this was long done for molecules in ordinary spectroscopy. But even transient complexes of molecules may be viewed as a new, "supermolecular" system which is subject to the same spectroscopic rules as ordinary molecules. Ordinary molecules may be viewed as complexes of atoms that have new and possibly quite different spectroscopic properties than the individual atoms the molecule consists of, when the atoms are not bound together as a molecule (or are not "interacting"). Similarly, complexes of interacting molecules may (and usually do) acquire new optical properties, which often are absent in the non-interacting, well separated individual molecules.
Collision-induced absorption (CIA) and emission (CIE) spectra are well known in the microwave and infrared regions of the electromagnetic spectrum, but they occur in special cases also in the visible and near ultraviolet regions. Collision-induced spectra have been observed in nearly all dense gases, and also in many liquids and solids. CIA and CIE are due to the intermolecular interactions, which generate electric dipole moments. We note that an analogous collision-induced light scattering
(CILS) or Raman process also exists, which is well studied and is in many ways completely analogous to CIA and CIE. CILS arises from interaction-induced polarizability increments of molecular complexes; the excess polarizability of a complex, relative the sum of polarizabilities of the noninteracting molecules. | 7 | Physical Chemistry |
Dendrosomes have been explored as vectors in gene delivery and genetic immunization.
Poly (propyleneimine) dendrosome based genetic immunization against Hepatitis B was found to be highly effective as compared to Dendrimer-Plasmid DNA complex. It has been postulated that in dendrosomes, the poly (propyleneimine) dendrimer–DNA complex is largely protected by multilamelarity of the vesicles. Moreover, it has been hypothesized that the lipoidal layers of the dendrosomes modifies the release pattern of the poly (propyleneimine) dendrimer –DNA complex, while some of the larger vesicles remain at the site of injection following their degradation by tissue phospholipases, the smaller ones delivering and transfecting efficiently the antigen-presenting cells (APC) in the draining lymph nodes. Dendrosomes have also been explored for the delivery of s10siRNA targeting E6/E7 oncogenes in cervical cancer. It has been reported that polyamidoamine dendrimer based dendrosomes are efficient systems for the delivery of siRNA for effective management of cervical cancer. | 6 | Supramolecular Chemistry |
The cyclopentadienyl cation is another textbook example of an antiaromatic compound. It is conventionally understood to be planar, cyclic, and have 4 π electrons (4n for n=1) in a conjugated system.
However, it has long been questioned if the cyclopentadienyl cation is genuinely antiaromatic and recent discoveries have suggested that it may not be. The lowest-energy singlet state is antiaromatic, but the lowest-energy triplet state is aromatic due to Baird's rule, and research in 2007 showed the triplet state to be the ground state. | 7 | Physical Chemistry |
Bilirubin consists of an open-chain tetrapyrrole. It is formed by oxidative cleavage of a porphyrin in heme, which affords biliverdin. Biliverdin is reduced to bilirubin. After conjugation with glucuronic acid, bilirubin is water-soluble and can be excreted.
Bilirubin is structurally similar to the pigment phycobilin used by certain algae to capture light energy, and to the pigment phytochrome used by plants to sense light. All of these contain an open chain of four pyrrolic rings.
Like these other pigments, some of the double-bonds in bilirubin isomerize when exposed to light. This isomerization is relevant to the phototherapy of jaundiced newborns: the E,Z-isomers of bilirubin formed upon light exposure are more soluble than the unilluminated Z,Z-isomer, as the possibility of intramolecular hydrogen bonding is removed. Increased solubility allows the excretion of unconjugated bilirubin in bile.
Some textbooks and research articles show the incorrect geometric isomer of bilirubin. The naturally occurring isomer is the Z,Z-isomer. | 1 | Biochemistry |
Daltons law (also called Daltons law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases. This empirical law was observed by John Dalton in 1801 and published in 1802. Dalton's law is related to the ideal gas laws. | 7 | Physical Chemistry |
Geostandards and Geoanalytical Research is a quarterly peer-reviewed scientific journal covering reference materials, analytical techniques, and data quality relevant to the chemical analysis of geological and environmental samples. The journal was established in 1977 as Geostandards Newsletter and modified its title in 2004. The editors-in-chief are Thomas C. Meisel, Jacinta Enzweiler, Mary F. Horan, Kathryn L. Linge, Christophe R. Quétel and Paul J. Sylvester. It is published by Wiley-Blackwell on behalf of the International Association of Geoanalysts. The journal is a hybrid open-access journal, publishing both subscription and open access articles. | 9 | Geochemistry |
The FIDA principle is based on measuring the change in the apparent size (diffusivity) of a selective indicator interacting with the analyte molecule. The apparent indicator size is measured by Taylor dispersion analysis in a capillary under hydrodynamic flow. | 1 | Biochemistry |
Gold–aluminium intermetallic is a type of intermetallic compound of gold and aluminium which usually forms at contacts between the two metals. Gold–aluminium intermetallic have different properties from the individual metals, such as low conductivity and high melting point depending on their composition. Furthermore, Due to the difference of density between the metals and intermetallics, the growth of the intermetallic layers causes reduction in volume, and therefore creates gaps in the metal near the interface between gold and aluminium. The production of gaps lowers the strength of the metal compound, which can cause mechanical failure at the joint, fostering the problems that the intermetallics causes in metal compounds. These properties can cause problems in wire bonding in microelectronics. The main compounds formed are usually AuAl (white plague) and AuAl (purple plague), which both form at high temperatures, then AuAl and AuAl can further react with Au to form more stable compound, AuAl. | 8 | Metallurgy |
α-Neoendorphin is an endogenous opioid peptide with a decapeptide structure and the amino acid sequence Tyr-Gly-Gly-Phe-Leu-Arg-Lys-Tyr-Pro-Lys.
α-Neoendorphin is a neuropeptide. Prodynorphin or Proenkephalin B is its precursor. Researchers and anatomists have not yet studied the distribution of α-neoendorphin in the human in detail. However, some studies have been done which supports the presence of α-neoendorphin immunoreactive fibers throughout the human brainstem. According to a study done by Duque, Ewing, Arturo Mangas, Pablo Salinas, Zaida Díaz-cabiale, José Narváez, and Rafael Coveñas; α-neoendorphin immunoreactive fibers can be found in the caudal part of the solitary nucleus, in the caudal and the gelatinosa parts of the spinal trigeminal nucleus, and only low density was found in the central grey matter of medulla. | 1 | Biochemistry |
A carbamoyl chloride is the functional group with the formula RNC(O)Cl. The parent carbamoyl chloride, HNCOCl is unstable, but many N-substituted analogues are known. Most examples are moisture sensitive, colourless, and soluble in nonpolar organic solvents. An example is dimethylcarbamoyl chloride (m.p. −90 °C and b.p. 93 °C). Carbamoyl chlorides are used to prepare a number of pesticides, e.g. carbofuran and aldicarb. | 0 | Organic Chemistry |
Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP or Ins3P or IP is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP), a phospholipid that is located in the plasma membrane, by phospholipase C (PLC).
Together with diacylglycerol (DAG), IP is a second messenger molecule used in signal transduction in biological cells. While DAG stays inside the membrane, IP is soluble and diffuses through the cell, where it binds to its receptor, which is a calcium channel located in the endoplasmic reticulum. When IP binds its receptor, calcium is released into the cytosol, thereby activating various calcium regulated intracellular signals. | 1 | Biochemistry |
MoOPH is synthesized from molybdenum trioxide by oxidation with hydrogen peroxide and addition of the HMPA and pyridine ligands: | 0 | Organic Chemistry |
Pressure jump is a technique used in the study of chemical kinetics. It involves making rapid changes to the pressure of an experimental system and observing the return to equilibrium or steady state. This allows the study of the shift in equilibrium of reactions that equilibrate in periods between milliseconds to hours (or longer), these changes often being observed using absorption spectroscopy, or fluorescence spectroscopy though other spectroscopic techniques such as CD, FTIR or NMR can also be used.
Historically, pressure jumps were limited to one direction. Most commonly fast drops in pressure were achieved by using a quick release valve or a fast burst membrane. Modern equipment can achieve pressure changes in both directions using either double reservoir arrangements (good for large changes in pressure) or pistons operated by piezoelectric actuators (often faster than valve based approaches). Ultra fast pressure drops can be achieved using electrically disintegrated burst membranes. The ability to automatically repeat measurements and average the results is useful since the reaction amplitudes are often small.
The fractional extent of the reaction (i.e. the percentage change in concentration of a measurable species) depends on the molar volume change (ΔV°) between the reactants and products and the equilibrium position. If K is the equilibrium constant and P is the pressure then the volume change is given by:
where R is the universal gas constant and T is the absolute temperature. The volume change can thus be understood to be the pressure dependency of the change in Gibbs free energy associated with the reaction.
When a single step in a reaction is perturbed in a pressure jump experiment, the reaction follows a single exponential decay function with the reciprocal time constant (1/τ) equal to the sum of the forward and reverse intrinsic rate constants. In more complex reaction networks, when multiple reaction steps are perturbed, then the reciprocal time constants are given by the eigenvalues of the characteristic rate equations. The ability to observe intermediate steps in a reaction pathway is one of the attractive features of this technology. | 7 | Physical Chemistry |
Phosphinates or hypophosphites are a class of phosphorus compounds conceptually based on the structure of hypophosphorous acid. IUPAC prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species (e.g. sodium hypophosphite), while phosphinate typically refers to organophosphorus species. | 0 | Organic Chemistry |
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