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In geochemistry, paleoclimatology and paleoceanography δO or delta-O-18 is a measure of the deviation in ratio of stable isotopes oxygen-18 (O) and oxygen-16 (O).
It is commonly used as a measure of the temperature of precipitation, as a measure of groundwater/mineral interactions, and as an indicator of processes that show isotopic fractionation, like methanogenesis.
In paleosciences, O:O data from corals, foraminifera and ice cores are used as a proxy for temperature.
It is defined as the deviation in "per mil" (‰, parts per thousand) between a sample and a standard:
where the standard has a known isotopic composition, such as Vienna Standard Mean Ocean Water (VSMOW). The fractionation can arise from kinetic, equilibrium, or mass-independent fractionation. | 9 | Geochemistry |
TAL effectors are proteins that are secreted by Xanthomonas bacteria via their type III secretion system when they infect plants. The DNA binding domain contains a repeated highly conserved 33–34 amino acid sequence with divergent 12th and 13th amino acids. These two positions, referred to as the Repeat Variable Diresidue (RVD), are highly variable and show a strong correlation with specific nucleotide recognition. This straightforward relationship between amino acid sequence and DNA recognition has allowed for the engineering of specific DNA-binding domains by selecting a combination of repeat segments containing the appropriate RVDs. Notably, slight changes in the RVD and the incorporation of "nonconventional" RVD sequences can improve targeting specificity. | 1 | Biochemistry |
Triboluminescence is a phenomenon in which light is generated when a material is mechanically pulled apart, ripped, scratched, crushed, or rubbed (see tribology). The phenomenon is not fully understood but appears in most cases to be caused by the separation and reunification of static electric charges, see also triboelectric effect. The term comes from the Greek τρίβειν ("to rub"; see tribology) and the Latin lumen (light). Triboluminescence can be observed when breaking sugar crystals and peeling adhesive tapes.
Triboluminescence is often a synonym for fractoluminescence (a term mainly used when referring only to light emitted from fractured crystals). Triboluminescence differs from piezoluminescence in that a piezoluminescent material emits light when deformed, as opposed to broken. These are examples of mechanoluminescence, which is luminescence resulting from any mechanical action on a solid. | 5 | Photochemistry |
Ted Ellis views education as one of his primary missions, and he is involved with several educational initiatives. He has a run a number of art workshops with children, including drawing and touching up the school mural which local sixth-graders paint every year, and joining with his wife Erania to illustrate while she reads aloud to children from books about topics like the Buffalo Soldiers. When working with children with autism, he employs a strategy of engaging the childrens creativity in a non-judgemental setting where there is no wrong way for them to express themselves; he hopes to put their art on display at the Houston Childrens Museum.
He has partnered with the Tom Joyner Foundation to fund-raise for students, while "Art with a Purpose", his own nonprofit program, was awarded a federal grant to help disadvantaged students.
Ellis serves together with Gregory Michael Carter as an artist-in-residence for an arts enrichment program at a Galveston, Texas charter school, "Ambassadors Preparatory Academy". The program, called "Ambassadors for Art", is led by school administrators and members of the community through the Gulf Coast Apollo Chapter of nonprofit volunteer service organization The Links, Incorporated. Ambassadors for Art also took part in painting a bust of US President Barack Obama. The bust was one of 45 painted by artists nationwide which were displayed in Detroit's Museum of African American History, part of a project supported by the Smithsonian Institution.
He has also worked with other arts education programs like the Peoria Public Schools' "Artreach", in the framework of which he donated five original pieces to the schools and District 150 Foundation. | 3 | Analytical Chemistry |
In proteins, crosslinks are important in generating mechanically stable structures such as hair and wool, skin, and cartilage. Disulfide bonds are common crosslinks. Isopeptide bond formation is another type of protein crosslink.
The process of applying a permanent wave to hair involves the breaking and reformation disulfide bonds. Typically a mercaptan such as ammonium thioglycolate is used for the breaking. Following this, the hair is curled and then "neutralized". The neutralizer is typically an acidic solution of hydrogen peroxide, which causes new disulfide bonds to form, thus permanently fixing the hair into its new configuration.
Compromised collagen in the cornea, a condition known as keratoconus, can be treated with clinical crosslinking.
In biological context crosslinking could play a role in atherosclerosis through advanced glycation end-products (AGEs), which have been implicated to induce crosslinking of collagen, which may lead to vascular stiffening. | 7 | Physical Chemistry |
Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the thio- prefix); however, the properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis. Thioureas are a broad class of compounds with the general structure . | 0 | Organic Chemistry |
The Superstack was built by Inco Limited (and later purchased by Vale) at an estimated cost of 25 million dollars. Construction on the structure was underway during the Sudbury tornado of August 20, 1970; the structure swayed heavily in the wind, but remained standing and suffered only minor damage. Six workers were on top of the construction platform when the storm hit, and all survived. The same day was the final day of construction on the stack, with the construction fully completed by the evening of August 21, 1970.
The stack entered into full operation in 1972. From the date of its completion until the Ekibastuz GRES-2 chimney was constructed in 1987, it was the world's tallest smokestack. Between the years 1972–75 it was the tallest freestanding structure in Canada.
Prior to the construction of the Superstack, the waste gases contributed to severe local ecological damage. The Copper Cliff smelter was already home to some of the world's tallest stacks, including two chimneys constructed in 1928-29 and 1936. However, these proved to be insufficient and compounded by open coke beds in the early to mid-20th century and logging for fuel, an inevitable near-total loss of native vegetation occurred. Of particular interest to geologists are the now exposed rocky outcrops, which have been permanently stained charcoal black, first by the pollution wafting over the decades from the roasting yards, then by the acid rain in a layer which penetrates up to three inches into the once pink-grey granite.
The Superstack was built to disperse sulphur gases and other byproducts of the smelting process away from the city of Sudbury. It did this by placing the gases high in the air, where they normally blew right past the city on the prevailing winds. As a result, these gases can be detected in the atmosphere around Greater Sudbury in a radius of the Inco plant. During the 1970s and 80s, the sulphur dioxide plume formed a permanent, opaque, cloud-like formation running across the entire horizon as seen from a distance. Periodic inversions would cause the plume to fall into the city.
Construction of the Superstack was followed by an environmental reclamation project which has included rehabilitation of existing landscapes and selected water bodies such as Lake Ramsey. An ambitious regreening plan has seen over three million new trees planted within the Greater Sudbury area. In 1992, Inco and the city were given an award by the United Nations in honour of their environmental rehabilitation programmes.
On November 3, 2014, Vale announced that they may decide to stop using the stack, following a $1 billion project to reduce emissions by 85% that negates the need for the stack. If no other use for it is found, Vale may decommission the superstack, demolish it, and replace it with a much smaller chimney. In 2017, Vale announced plans to decommission the Superstack upon the construction of two smaller, more energy efficient stacks. On July 28, 2020, Vale updated that news, stating that the stack at its Copper Cliff Complex had been taken out of service. It would remain on "hot standby" for about two months while the replacement flue connections were tested but the stack would then be demolished over the years. | 8 | Metallurgy |
Antidepressant exposure (including escitalopram) is associated with shorter duration of pregnancy (by three days), increased risk of preterm delivery (by 55%), lower birth weight (by 75 g), and lower Apgar scores (by <0.4 points). Antidepressant exposure is not associated with an increased risk of spontaneous abortion. There is a tentative association of SSRI use during pregnancy with heart problems in the baby. The advantages of their use during pregnancy may thus not outweigh the possible negative effects on the baby. | 4 | Stereochemistry |
cAMP is associated with kinases function in several biochemical processes, including the regulation of glycogen, sugar, and lipid metabolism.
In eukaryotes, cyclic AMP works by activating protein kinase A (PKA, or cAMP-dependent protein kinase). PKA is normally inactive as a tetrameric holoenzyme, consisting of two catalytic and two regulatory units (CR), with the regulatory units blocking the catalytic centers of the catalytic units.
Cyclic AMP binds to specific locations on the regulatory units of the protein kinase, and causes dissociation between the regulatory and catalytic subunits, thus enabling those catalytic units to phosphorylate substrate proteins.
The active subunits catalyze the transfer of phosphate from ATP to specific serine or threonine residues of protein substrates. The phosphorylated proteins may act directly on the cell's ion channels, or may become activated or inhibited enzymes. Protein kinase A can also phosphorylate specific proteins that bind to promoter regions of DNA, causing increases in transcription. Not all protein kinases respond to cAMP. Several classes of protein kinases, including protein kinase C, are not cAMP-dependent.
Further effects mainly depend on cAMP-dependent protein kinase, which vary based on the type of cell.
Still, there are some minor PKA-independent functions of cAMP, e.g., activation of calcium channels, providing a minor pathway by which growth hormone-releasing hormone causes a release of growth hormone.
However, the view that the majority of the effects of cAMP are controlled by PKA is an outdated one. In 1998 a family of cAMP-sensitive proteins with guanine nucleotide exchange factor (GEF) activity was discovered. These are termed Exchange proteins activated by cAMP (Epac) and the family comprises Epac1 and Epac2. The mechanism of activation is similar to that of PKA: the GEF domain is usually masked by the N-terminal region containing the cAMP binding domain. When cAMP binds, the domain dissociates and exposes the now-active GEF domain, allowing Epac to activate small Ras-like GTPase proteins, such as Rap1. | 1 | Biochemistry |
[https://www.breastcancer.org/symptoms/types/idc ] is one of the common types of breast cancer which accounts for 8 out of 10 of all invasive breast cancers. According to the American Cancer Society, more than 180,000 women in the United States find out that they have breast cancers each year, and most are diagnosed with this specific type of cancer. While it is essential to detect breast cancer early to reduce the death rate there may be already more than 10,000,000 cells in breast cancer when it can be observed by [https://www.cdc.gov/cancer/breast/basic_info/mammograms.htm#:~:text=A%20mammogram%20is%20an%20X,before%20it%20can%20be%20felt. ]. however, the IR Spectrum proposed by Szu et al seems to be more promising in detecting breast cancer cells several months ahead of a mammogram. Clinical tests have been carried out with approval of Institutional Review Board of National Taiwan University Hospital. So from August 2007 to June 2008 35 patients aged between (30-66) with an average age of 49 were enlisted in this project. the results established that about 63% of the success rate could be achieved with the cross-sectional data. Therefore the results concluded that breast cancers may be detected more accurately by maps]</u> of multiple three-points. | 7 | Physical Chemistry |
In general, hemoglobin can be saturated with oxygen molecules (oxyhemoglobin), or desaturated with oxygen molecules (deoxyhemoglobin). | 7 | Physical Chemistry |
Eilaf Egap (née Ahmed) is an adjunct assistant professor of Materials Science at Rice University. She works on imaging techniques and biomaterials for early diagnostics and drug delivery. She was a Massachusetts Institute of Technology MLK Visiting Scholar in 2011. | 0 | Organic Chemistry |
In 2016 he was co-lead of a team that discovered an insertion-deletion polymorphism, rs66698963, is under positive selective pressure depending on whether ancestral diets were primarily animal/seafood-based or plant-based. Global news widely reported that it would lead to potentially greater risk of disease, though this was corrected later. | 3 | Analytical Chemistry |
CCL7 is a multipotent chemokine involved in anti-bacterial, anti-viral and anti-fungal immune responses. For example, CCL7-mediated stimulation of CCR2 chemokine receptors on monocytes is participating in the elimination of Listeria monocytogenes infections by the recruitment of monocytes and TNF/iNOS-producing dendritic cells (TipDCs). Next, the role of the CCL7 was also observed in the mouse infected by West Nile Virus. The genetically deficient mice in CCL7 have increased mortality because of decrease in monocytes and neutrophils. Early induction of CCL7 downstream of TLR9 signaling also promotes the development of robust immunity to cryptococcal infections.
Diseases associated with CCL7 dysregulation are observed. For example, an abnormal increase of CCL7 worsens many disorders, like HIV or lesional psoriasis. Furthermore, CCL7 is implicated in various immunological diseases, as ulcerative colitis, multiple sclerosis or nonatopic and atopic asthma.
It seems, that the expression of CCL7 can activate an antitumor immune response. | 1 | Biochemistry |
Ahead of the 50th anniversary of the 1962 James Bond film Dr No, Phillips stated that the character of Dr No, with his personal nuclear reactor, helped to create a "remorselessly grim" reputation for atomic energy. and that the popularity of the movie created an enduringly negative image of nuclear power – as something dangerous that could be wielded by megalomaniacs with aspirations to world domination. Phillips claims that when nuclear power is discussed "it is not at all surprising that the public at home and abroad are sceptical" and concludes that "The Royal Society of Chemistry asserts that nuclear power has to be part of the future national energy mix, in which it plays a major role. Fossil fuels have to be eradicated for people to live in a healthy environment. Lets say yes to nuclear and no to Dr Nos nonsense." | 5 | Photochemistry |
Zero electron kinetic energy (ZEKE) spectroscopy was developed with the idea of collecting only the resonance ionization photoelectrons that have extremely low kinetic energy. The technique involves waiting for a period of time after a resonance ionization experiment and then pulsing an electric field to collect the lowest energy photoelectrons in a detector. Typically, ZEKE experiments utilize two different tunable lasers. One laser photon energy is tuned to be resonant with the energy of an intermediate state. (This may be resonant with an excited state at a multiphoton transition.) Another photon energy is tuned to be close to the ionization threshold energy. The technique worked extremely well and demonstrated energy resolution that was significantly better than the laser bandwidth. It turns out that it was not the photoelectrons that were detected in ZEKE. The delay between the laser and the electric field pulse selected the longest lived and most circular Rydberg states closest to the energy of the ion core. The population distribution of surviving long-lived near threshold Rydberg states is close to the laser energy bandwidth. The electric field pulse Stark shifts the near-threshold Rydberg states and vibrational autoionization occurs. ZEKE has provided a significant advance in the study of the vibrational spectroscopy of molecular ions. Schlag, Peatman and Müller-Dethlefs originated ZEKE spectroscopy. | 7 | Physical Chemistry |
* Conventional (C)TEM-CBED: In CTEM-CBED different shape condenser apertures are used to obtain the intensity distribution over the entire Brillouin zone.
* Large Angle (LA)CBED: (LA)CBED is performed with a large incident angle, ranging from 1˚ to 10˚. LACBED makes it possible to obtain non-overlapping disks with a larger diameter than the one determined by the Bragg angle. With LACBED I one can obtain one selected CBED disk at a time on a detector. In LACBED II, with a slight change in the focusing conditions of the intermediate lens, bright field patterns and dark field patterns can be obtained simultaneously, without overlapping each other on the fluorescent screen. A disadvantage of LACBED is that it requires a large, flat specimen.
* 4D-STEM: In 4D-STEM a convergent probing beam is raster-scanned on a specimen in a 2D array and in each position of the array, a 2D diffraction pattern is obtained, thus generating a 4D data set. After acquisition, by using different phase techniques such as ptychography, one can recover the transmittion function and the induced phase shift. In some applications, 4D-STEM is called STEM-CBED.
* Beam Rocking (BR)-CBED: With this technique, by rocking the incident beam with a rocking coil placed above the specimen, a virtual convergent beam is produced. Given that the diameter of the beam on the specimen is a few micrometers, this method has made CBED possible for materials that are susceptible to strong convergent beams. Furthermore, the large size of the illuminated specimen area and the low density current of the beam make specimen contamination insignificant.
* BR-LACBED: In this technique, in addition to the rocking coil above the specimen, there is a rocking coil placed under the projector lens, which is used to bring the preferred beam to the STEM detector. Every time the incident beam is rocked, the second coil is simultaneously driven so that the beam always falls on the STEM detector.
* Signal processing and BR-CBED: In order to enhance contrast in BR-CBED, a band-pass filter can be used that filters a certain frequency band in the CBED pattern. The combination of these two techniques makes the symmetries appearing in the patterns more clear.
* CB-LEED (Low Energy Electron Diffraction): Rocking curves are analyzed at a single energy using a convergent probe. Advantages of this method are: mapping of LEED diffraction spots into CBLEED disks, the diffraction patterns originate from a localized region of the specimen which enables the extraction of localized structural information, mapping out of the surfaces, sensitivity enhancement of small atomic displacements etc.
*Ptychography is a technique for recovering the phase of the exit electron wave. The reconstruction is done by applying an iterative phase retrieval algorithm which returns a real-space image with both phase and amplitude information. By using electron ptychography, in 2018, images of MoS with an atomic resolution of 0.39 Å were reported by Jiang et al. which set the new world record for the highest resolution microscope.
* Microdiffraction, nanodiffraction: In the literature, there are several terms used to refer to electron diffraction patterns that are acquired with a convergent beam. Such terms are CBED, microdiffraction, nanodiffraction etc. When the CBED technique is used for the acquisition of conventional diffraction information like lattice structure and interplanar spacing from very small areas, then the term microdiffraction is used. On the other hand, the term nanodiffraction is used when very small probes (< 1 nm or less in diameter) are used. | 3 | Analytical Chemistry |
The situation becomes more complex when the form of energy does not remain constant. In this context Ohta formulated the question of energy quality in terms of the conversion of energy of one form into another, that is the transformation of energy. Here, energy quality is defined by the relative ease with which the energy transforms, from form to form.
Nomenclature: Prior to Ohtas definition above, A. W. Culp produced an energy conversion table describing the different conversions from one energy to another. Culps treatment made use of a subscript to indicate which energy form is being talked about. Therefore, instead of writing "energy A", like Ohta above, Culp referred to "J", to specify electrical form of energy, where "J" refers to "energy", and the "e" subscript refers to electrical form of energy. Culps notation anticipated Sciencemans (1997) later maxim that all energy should be specified as form energy with the appropriate subscript. | 7 | Physical Chemistry |
Photoluminescence processes can be classified by various parameters such as the energy of the exciting photon with respect to the emission.
Resonant excitation describes a situation in which photons of a particular wavelength are absorbed and equivalent photons are very rapidly re-emitted. This is often referred to as resonance fluorescence. For materials in solution or in the gas phase, this process involves electrons but no significant internal energy transitions involving molecular features of the chemical substance between absorption and emission. In crystalline inorganic semiconductors where an electronic band structure is formed, secondary emission can be more complicated as events may contain both coherent contributions such as resonant Rayleigh scattering where a fixed phase relation with the driving light field is maintained (i.e. energetically elastic processes where no losses are involved), and incoherent contributions (or inelastic modes where some energy channels into an auxiliary loss mode),
The latter originate, e.g., from the radiative recombination of excitons, Coulomb-bound electron-hole pair states in solids. Resonance fluorescence may also show significant quantum optical correlations.
More processes may occur when a substance undergoes internal energy transitions before re-emitting the energy from the absorption event. Electrons change energy states by either resonantly gaining energy from absorption of a photon or losing energy by emitting photons. In chemistry-related disciplines, one often distinguishes between fluorescence and phosphorescence. The former is typically a fast process, yet some amount of the original energy is dissipated so that re-emitted light photons will have lower energy than did the absorbed excitation photons. The re-emitted photon in this case is said to be red shifted, referring to the reduced energy it carries following this loss (as the Jablonski diagram shows). For phosphorescence, electrons which absorbed photons, undergo intersystem crossing where they enter into a state with altered spin multiplicity (see term symbol), usually a triplet state. Once the excited electron is transferred into this triplet state, electron transition (relaxation) back to the lower singlet state energies is quantum mechanically forbidden, meaning that it happens much more slowly than other transitions. The result is a slow process of radiative transition back to the singlet state, sometimes lasting minutes or hours. This is the basis for "glow in the dark" substances.
Photoluminescence is an important technique for measuring the purity and crystalline quality of semiconductors such as GaN and InP and for quantification of the amount of disorder present in a system.
Time-resolved photoluminescence (TRPL) is a method where the sample is excited with a light pulse and then the decay in photoluminescence with respect to time is measured. This technique is useful for measuring the minority carrier lifetime of III-V semiconductors like gallium arsenide (GaAs). | 7 | Physical Chemistry |
Ernest Ludwig Eliel (December 28, 1921 – September 18, 2008) was an organic chemist born in Cologne, Germany. Among his awards were the Priestley Medal in 1996 and the NAS Award for Chemistry in Service to Society in 1997.
When the Nazis came to power, he left Germany and moved to Scotland, then Canada, then Cuba. He received his B.S. from the University of Havana in 1946. He moved to the United States in 1946 and taught at the University of Notre Dame from 1948. In 1972 he moved to be the W.R. Kenan, Jr. Professor of Chemistry at the University of North Carolina at Chapel Hill until his retirement in 1993. Eliel was elected a Fellow of the American Academy of Arts and Sciences in 1980. In 1981, Eliel became a founding member of the World Cultural Council. He served as president of the American Chemical Society in 1992. In 1995 he received the George C. Pimentel Award in Chemical Education, and in 1996 he was awarded the Priestley Medal of the American Chemical Society. He died in Chapel Hill, North Carolina.
His research focussed on the stereochemistry and conformational analysis of flexible organic molecules, including derivatives of cyclohexane and saturated heterocyclic rings, using nuclear magnetic resonance spectroscopy (NMR) extensively. His 1962 textbook Stereochemistry of Carbon Compounds influenced generations of organic chemists. The most recent edition is Stereochemistry of Organic Compounds, co-authored in 1994 with Samuel H. Wilen. | 4 | Stereochemistry |
Thermal spraying need not be a dangerous process if the equipment is treated with care and correct spraying practices are followed. As with any industrial process, there are a number of hazards of which the operator should be aware and against which specific precautions should be taken. Ideally, equipment should be operated automatically in enclosures specially designed to extract fumes, reduce noise levels, and prevent direct viewing of the spraying head. Such techniques will also produce coatings that are more consistent. There are occasions when the type of components being treated, or their low production levels, require manual equipment operation. Under these conditions, a number of hazards peculiar to thermal spraying are experienced in addition to those commonly encountered in production or processing industries. | 8 | Metallurgy |
Hydrogen and oxygen can be combined through by the use of a fuel cell. In this process, the reaction is broken into two half reactions which occur at separate electrodes. In this situation the reactants energy is directly converted to electricity. Useful energy can be obtained from the thermal heat of this reaction through an internal combustion engine with an upper efficiency of 60% (for compression ratio of 10 and specific heat ratio of 1.4) based on the Otto thermodynamic cycle. It is also possible to combine the hydrogen and oxygen through redox mechanism as in the case of a fuel cell. In this process, the reaction is broken into two half-reactions which occur at separate electrodes. In this situation the reactants energy is directly converted to electricity.
The standard reduction potential of hydrogen is defined as 0V, and frequently referred to as the standard hydrogen electrode (SHE).
HER can be promoted by many catalysts. | 7 | Physical Chemistry |
Aurin may cause eye, skin, and respiratory tract irritation. Ingestion and inhalation should be avoided.
Aurin was reported to have endocrine disruptor chemical (EDC) properties. | 3 | Analytical Chemistry |
A prismatic surface is a surface generated by all the lines that are parallel to a given line and intersect a broken line that is not in the same plane as the given line. The broken line is the directrix of the surface; the parallel lines are its generators (or elements). If the broken line is closed (i.e., a closed polygon), then the surface is a closed prismatic surface.
With regards to crystallography, a prismatic surface is a single face of a prismatic form, which is an open form consisting of three, four, or six identical faces related by a symmetry operator. | 3 | Analytical Chemistry |
Most low-beam headlamps produce an asymmetrical light suitable for use on only one side of the road. Low beam headlamps in LHT jurisdictions throw most of their light forward-leftward; those for RHT throw most of their light forward-rightward, thus illuminating obstacles and road signs while minimising glare for oncoming traffic.
In Europe, headlamps approved for use on one side of the road must be adaptable to produce adequate illumination with controlled glare for temporarily driving on the other side of the road,. This may be achieved by affixing masking strips or prismatic lenses to a part of the lens or by moving all or part of the headlamp optic so all or part of the beam is shifted or the asymmetrical portion is occluded. Some varieties of the projector-type headlamp can be fully adjusted to produce a proper LHT or RHT beam by shifting a lever or other movable element in or on the lamp assembly. Some vehicles adjust the headlamps automatically when the car's GPS detects that the vehicle has moved from LHT to RHT and vice versa. | 4 | Stereochemistry |
In acidic medium, H ions and water are added to balance each half-reaction.
For example, when manganese reacts with sodium bismuthate.
:Unbalanced reaction: Mn + NaBiO → Bi +
:Oxidation: 4 HO + Mn → + 8 H + 5 e
:Reduction: 2 e + 6 H + → Bi + 3 HO
Finally, the reaction is balanced by multiplying the stoichiometric coefficients so the numbers of electrons in both half reactions match
:8 HO + 2 Mn → 2 + 16 H + 10 e
:10 e + 30 H + 5 → 5 Bi + 15 HO
and adding the resulting half reactions to give the balanced reaction:
:14 H + 2 Mn + 5 NaBiO → 7 HO + 2 + 5 Bi + 5 Na | 7 | Physical Chemistry |
She married fellow metallurgist Norman Petch whom she met in Cambridge but they divorced in 1944. She went on to marry metallurgist, Alan Dennis McQuillam in 1947. Her husband died in 1987. McQuillan died in Gloucestershire in 1998. | 8 | Metallurgy |
Thomas Messinger Drown (March 19, 1842 – November 17, 1904) was the fourth University President of Lehigh University in Bethlehem, Pennsylvania, United States. He was also an analytical chemist and metallurgist. | 3 | Analytical Chemistry |
Organophosphines, like phosphine itself, are pyramidal molecules with approximate C symmetry. The C–P–C bond angles are approximately 98.6°. The C–P–C bond angles are consistent with the notion that phosphorus predominantly uses the 3p orbitals for forming bonds and that there is little sp hybridization of the phosphorus atom. The latter is a common feature of the chemistry of phosphorus. As a result, the lone pair of trimethylphosphine has predominantly s-character as is the case for phosphine, PH.
Tertiary phosphines are pyramidal. When the organic substituents all differ, the phosphine is chiral and configurationally stable (in contrast to NRR'R"). Complexes derived from the chiral phosphines can catalyse reactions to give chiral, enantioenriched products. | 0 | Organic Chemistry |
The chemical composition of sporopollenin has long been elusive due to its unusual chemical stability, insolubility and resistance to degradation by enzymes and strong chemical reagents. It was once thought to consist of polymerised carotenoids but the application of more detailed analytical methods since the 1980s has shown that this is not correct. Analyses have revealed a complex biopolymer, containing mainly long-chain fatty acids, phenylpropanoids, phenolics and traces of carotenoids in a random co-polymer. It is likely that sporopollenin derives from several precursors that are chemically cross-linked to form a rigid structure. There is also good evidence that the chemical composition of sporopollenin is not the same in all plants, indicating it is a class of compounds rather than having one constant structure.
In 2019, thioacidolysis degradation and solid-state NMR was used to determine the molecular structure of pitch pine sporopollenin, finding it primarily composed of polyvinyl alcohol units alongside other aliphatic monomers, all crosslinked through a series of acetal linkages. Its complex and heterogeneous chemical structure give some protection from the biodegradative enzymes of bacteria, fungi and animals. Some aromatic structures based on p-coumarate and naringenin were also identified within the sporopollenin polymer. These can absorb ultraviolet light and thus prevent it penetrating further into the spore. This has relevance to the role of pollen and spores in transporting and dispersing the gametes of plants. The DNA of the gametes is readily damaged by the ultraviolet component of daylight. Sporopollenin thus provides some protection from this damage as well as a physically robust container.
Analysis of sporopollenin from the clubmoss Lycopodium in the late 1980s have shown distinct structural differences from that of flowering plants. In 2020, more detailed analysis of sporopollenin from Lycopodium clavatum provided more structural information. It showed a complete lack of aromatic structures and the presence of a macrocyclic backbone of polyhydroxylated tetraketide-like monomers with pseudo-aromatic 2-pyrone rings. These were crosslinked to a poly(hydroxy acid) chain by ether linkages to form the polymer. | 1 | Biochemistry |
A sensitizer in chemiluminescence is a chemical compound, capable of light emission after it has received energy from a molecule, which became excited previously in the chemical reaction. A good example is this:
When an alkaline solution of sodium hypochlorite and a concentrated solution of hydrogen peroxide are mixed, a reaction occurs:
:ClO(aq) + HO(aq) → O*(g) + H(aq) + Cl(aq) + OH(aq)
O*is excited oxygen – meaning, one or more electrons in the O molecule have been promoted to higher-energy molecular orbitals. Hence, oxygen produced by this chemical reaction somehow absorbed the energy released by the reaction and became excited. This energy state is unstable, therefore it will return to the ground state by lowering its energy. It can do that in more than one way:
*it can react further, without any light emission
*it can lose energy without emission, for example, giving off heat to the surroundings or transferring energy to another molecule
*it can emit light
The intensity, duration and color of emitted light depend on quantum and kinetical factors. However, excited molecules are frequently less capable of light emission in terms of brightness and duration when compared to sensitizers. This is because sensitizers can store energy (that is, be excited) for longer periods of time than other excited molecules. The energy is stored through means of quantum vibration, so sensitizers are usually compounds which either include systems of aromatic rings or many conjugated double and triple bonds in their structure. Hence, if an excited molecule transfers its energy to a sensitizer thus exciting it, longer and easier to quantify light emission is often observed.
The color (that is, the wavelength), brightness and duration of emission depend upon the sensitizer used. Usually, for a certain chemical reaction, many different sensitizers can be used. | 7 | Physical Chemistry |
In 1815 the French physicist Jean-Baptiste Biot showed that certain chemicals could rotate the plane of a beam of polarised light, a property called optical activity.
The nature of this property remained a mystery until 1848, when Louis Pasteur proposed that it had a molecular basis originating from some form of dissymmetry,
with the term chirality being coined by Lord Kelvin a year later.
The origin of chirality itself was finally described in 1874, when Jacobus Henricus van t Hoff and Joseph Le Bel independently proposed the tetrahedral geometry of carbon. Structural models prior to this work had been two-dimensional, and van t Hoff and Le Bel theorized that the arrangement of groups around this tetrahedron could dictate the optical activity of the resulting compound through what became known as the Le Bel–van 't Hoff rule.
In 1894 Hermann Emil Fischer outlined the concept of asymmetric induction; in which he correctly ascribed selective the formation of -glucose by plants to be due to the influence of optically active substances within chlorophyll. Fischer also successfully performed what would now be regarded as the first example of enantioselective synthesis, by enantioselectively elongating sugars via a process which would eventually become the Kiliani–Fischer synthesis.
The first enantioselective chemical synthesis is most often attributed to Willy Marckwald, Universität zu Berlin, for a brucine-catalyzed enantioselective decarboxylation of 2-ethyl-2-methylmalonic acid reported in 1904. A slight excess of the levorotary form of the product of the reaction, 2-methylbutyric acid, was produced; as this product is also a natural product—e.g., as a side chain of lovastatin formed by its diketide synthase (LovF) during its biosynthesis—this result constitutes the first recorded total synthesis with enantioselectivity, as well other firsts (as Koskinen notes, first "example of asymmetric catalysis, enantiotopic selection, and organocatalysis"). This observation is also of historical significance, as at the time enantioselective synthesis could only be understood in terms of vitalism. At the time many prominent chemists such as Jöns Jacob Berzelius argued that natural and artificial compounds were fundamentally different and that chirality was simply a manifestation of the vital force which could only exist in natural compounds. Unlike Fischer, Marckwald had performed an enantioselective reaction upon an achiral, un-natural starting material, albeit with a chiral organocatalyst (as we now understand this chemistry). | 4 | Stereochemistry |
A wide range of Fe(III)-bearing minerals have been observed to function as terminal electron acceptors, including magnetite, hematite, goethite, lepidocrocite, ferrihydrite, hydrous ferric oxide, smectite, illite, jarosite, among others. | 1 | Biochemistry |
After some years in the planning and enabling phase, the [http://www.geotraces.org/science/science-plan GEOTRACES Science Plan] was published in 2006 and the GEOTRACES programme formally launched its seagoing effort in January 2010. This phase is expected to last a decade. | 9 | Geochemistry |
Many natural phenols are chiral. An example of such molecules is catechin. Cavicularin is an unusual macrocycle because it was the first compound isolated from nature displaying optical activity due to the presence of planar chirality and axial chirality. | 0 | Organic Chemistry |
1,3-Dienes such as butadiene and isoprene dimerize in the coordination spheres of some metals, giving chelating bis(allyl) complexes. Such complexes also arise from ring-opening of divinylcyclobutane. Chelating bis(allyl) complexes are intermediates in the metal-catalyzed dimerization of butadiene to give vinylcyclohexene and cycloocta-1,5-diene. | 0 | Organic Chemistry |
The choice of metallic substrate is determined by the dimensional, mechanical and corrosion resistance properties required of the coated product in use. The most common metallic substrates that are organically coated are:
* Hot dip galvanised steel (HDG) which consists of a cold reduced steel substrate onto which a layer of zinc is coated via a hot dip process to impart enhanced corrosion properties onto the base steel.
* Galvanized mild steel (GMS) can be used as balustrade and handrail of staircase, pipe, etc.
* Other zinc-based alloys are coated onto steel and used as a substrate for coil coating, giving different properties. They give improved corrosion resistance in particular conditions.
* Electro-galvanised (EG) coated steel consists of a cold reduced substrate onto which a layer of zinc is coated by an electrolytic process.
* Cold reduced steel (CR) without any zinc coating
* Wrought aluminium alloys
* Many other substrates are organically coated: zinc/iron, stainless steel, tinplate, brass, zinc and copper. | 8 | Metallurgy |
Trimethyloxonium tetrafluoroborate can be used for esterification of carboxylic acids under conditions where acid-catalyzed reactions are infeasible:
Although rarely employed for esterifications, carboxylate salts (often generated in situ) react with electrophilic alkylating agents, such as alkyl halides, to give esters. Anion availability can inhibit this reaction, which correspondingly benefits from phase transfer catalysts or such highly polar aprotic solvents as DMF. An additional iodide salt may, via the Finkelstein reaction, catalyze the reaction of a recalcitrant alkyl halide. Alternatively, salts of a coordinating metal, such as silver, may improve the reaction rate by easing halide elimination. | 0 | Organic Chemistry |
Electromigrated nanogaps are gaps formed in metallic bridges formed by the process of electromigration. A nanosized contact formed by electromigration acts like a waveguide for electrons. The nanocontact essentially acts like a one-dimensional wire with a conductance of . The current in a wire is the velocity of the electrons multiplied by the charge and number per unit length, or . This gives a conductance of . In nano scale bridges the conductance falls in discrete steps of multiples of the quantum conductance .
Electromigrated Nanogaps have shown great promise as electrodes in use in molecular scale electronics. Researchers have used feedback controlled electromigration to investigate the magnetoresistance of a quantum spin valve. | 7 | Physical Chemistry |
Aerobic fermentation or aerobic glycolysis is a metabolic process by which cells metabolize sugars via fermentation in the presence of oxygen and occurs through the repression of normal respiratory metabolism. Preference of aerobic fermentation over aerobic respiration is referred to as the Crabtree effect in yeast, and is part of the Warburg effect in tumor cells. While aerobic fermentation does not produce adenosine triphosphate (ATP) in high yield, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into carbon dioxide, preserving carbon-carbon bonds and promoting anabolism. | 1 | Biochemistry |
Another common method of converting between fractional and Cartesian coordinates involves the use of a cell tensor which contains each of the basis vectors of the space expressed in Cartesian coordinates. | 3 | Analytical Chemistry |
Although the underlying equations governing plasmas are relatively simple, plasma behaviour is extraordinarily varied and subtle: the emergence of unexpected behaviour from a simple model is a typical feature of a complex system. Such systems lie in some sense on the boundary between ordered and disordered behaviour and cannot typically be described either by simple, smooth, mathematical functions, or by pure randomness. The spontaneous formation of interesting spatial features on a wide range of length scales is one manifestation of plasma complexity. The features are interesting, for example, because they are very sharp, spatially intermittent (the distance between features is much larger than the features themselves), or have a fractal form. Many of these features were first studied in the laboratory, and have subsequently been recognized throughout the universe. Examples of complexity and complex structures in plasmas include: | 7 | Physical Chemistry |
The Arc transcript is dependent upon activation of the mitogen-activated protein kinase or MAP kinase (MAPK) cascade, a pathway important for regulation of cell growth and survival. Extracellular signaling to neuronal dendrites activates postsynaptic sites to increase Arc levels through a wide variety of signaling molecules, including mitogens such as epidermal growth factor (EGF), nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF), glutamate acting at NMDA receptors, dopamine through activation of the D1 receptor subtype, and dihydroxyphenylglycine (DHPG). The common factor for these signaling molecules involves activation of cyclic-AMP and its downstream target protein kinase A (PKA). As such, direct pharmacological activation of cAMP by forskolin or 8-Br-cAMP robustly increases Arc levels while H89, a PKA antagonist, blocks these effects as does further downstream blockade of mitogen-activated protein kinase kinase [sic] (MEK). Note that the MAPK cascade is a signaling pathway involving multiple kinases acting sequentially [MAPKKK→ MAPKK→ MAPK].
MAPK is able to enter the nucleus and perform its phosphotransferase activity on a number of gene regulatory components that have implications for the regulation of immediate-early genes. Several transcription factors are known to be involved in regulating the Arc gene (see above), including serum response factor (SRF), CREB, MEF2, and zif268. | 1 | Biochemistry |
Dexketoprofen is a nonsteroidal anti-inflammatory drug (NSAID). It is manufactured by Menarini, under the tradename Keral. It is available in the UK, as dexketoprofen trometamol, as a prescription-only drug and in Latin America as Enantyum, produced by Menarini. Also, in Italy and Spain it is available as an over-the-counter drug (OTC) under the trade name Enandol or Enantyum. In Hungary it is available from a pharmacy as "Ketodex". In Turkey, it is an over the counter medicine under the name "Arveles". In Latvia, Lithuania and Estonia it is available as an OTC under the tradename Dolmen
In Mexico it is available in tablet form as "Stadium" made by Menarini. It is the dextrorotatory stereoisomer of ketoprofen. | 4 | Stereochemistry |
It was proposed that increased synthesis of (p)ppGpp would cause polyphosphate (PolyP) accumulation in E. coli. The alarmone could interact with exopolyphosphatase PPX, which would inhibit the hydrolysis of PolyP, thus causing its accumulation in bacteria. Although it has recently been shown that it is actually DksA and not (p)ppGpp that causes this buildup. It has been shown in Pseudomonas aeruginosa that the phoU mutant (phoU belongs to the Pho Regulon) synthesizes more (p)ppGpp and this would be one of the reasons that it accumulates more polyphosphate. | 1 | Biochemistry |
For methanol the following parameters can be obtained:
The reference temperature has been T = 174.61 K and the reference pressure P has been set to 0 kPa.
Methanol is a component where the Simon–Glatzel works well in the given validity range. | 7 | Physical Chemistry |
Single-cell transcriptomic assays have allowed reconstruction development trajectories. Branching of these trajectories describes cell differentiation. Various methods have been developed for reconstructing branching developmental trajectories from single-cell transcriptomic data. They use various advanced mathematical concepts from optimal transportation to principal graphs. Some software libraries for reconstruction and visualization of lineage differentiation trajectories are freely available online. | 1 | Biochemistry |
The full width at half maximum (FWHM) of the Voigt profile can be found from the
widths of the associated Gaussian and Lorentzian widths. The FWHM of the Gaussian profile
is
The FWHM of the Lorentzian profile is
An approximate relation (accurate to within about 1.2%) between the widths of the Voigt, Gaussian, and Lorentzian profiles is:
By construction, this expression is exact for a pure Gaussian or Lorentzian.
A better approximation with an accuracy of 0.02% is given by (originally found by Kielkopf)
Again, this expression is exact for a pure Gaussian or Lorentzian.
In the same publication, a slightly more precise (within 0.012%), yet significantly more complicated expression can be found. | 7 | Physical Chemistry |
Inorganic phosphites (containing ) have been applied to crops to combat fungus-like pathogens of the order oomycetes (water molds). The situation is confusing because of the similarity in name between phosphite and phosphate (a major plant nutrient and fertilizer ingredient), and controversial because phosphites have sometimes been advertised as fertilizers, even though they are converted to phosphate too slowly to serve as a plant's main phosphorus source. In fact, phosphites may cause phytotoxicity when a plant is starved of phosphates. Lemoynie and others have described this complicated situation and noted that calling phosphites fertilizers avoided the regulatory complication and negative public perceptions that might have been incurred by registering them as fungicides.
A major form of inorganic phosphite used in agriculture is monopotassium phosphite. This compound does serve as a potassium fertilizer. | 0 | Organic Chemistry |
The idea that oxidation of ammonia to nitrate is in fact a biological process was first given by Louis Pasteur in 1862. Later in 1875, Alexander Müller, while conducting a quality assessment of water from wells in Berlin, noted that ammonium was stable in sterilized solutions but nitrified in natural waters. A. Müller put forward, that nitrification is thus performed by microorganisms. In 1877, Jean-Jacques Schloesing and Achille Müntz, two French agricultural chemists working in Paris, proved that nitrification is indeed microbially mediated process by the experiments with liquid sewage and artificial soil matrix (sterilized sand with powdered chalk). Their findings were confirmed soon (in 1878) by Robert Warington who was investigating nitrification ability of garden soil at the Rothamsted experimental station in Harpenden in England. R. Warington made also the first observation that nitrification is a two-step process in 1879 which was confirmed by John Munro in 1886. Although at that time, it was believed that two-step nitrification is separated into distinct life phases or character traits of a single microorganism.
The first pure nitrifier (ammonia-oxidizing) was most probably isolated in 1890 by Percy Frankland and Grace Frankland, two English scientists from Scotland. Before that, Warington, Sergei Winogradsky and the Franklands were only able to enrich cultures of nitrifiers. Frankland and Frankland succeeded with a system of serial dilutions with very low inoculum and long cultivation times counting in years. Sergei Winogradsky claimed pure culture isolation in the same year (1890), but his culture was still co-culture of ammonia- and nitrite-oxidizing bacteria. S. Winogradsky succeeded just one year later in 1891.
In fact, during the serial dilutions ammonia-oxidizers and nitrite-oxidizers were unknowingly separated resulting in pure culture with ammonia-oxidation ability only. Thus Frankland and Frankland observed that these pure cultures lose ability to perform both steps. Loss of nitrite oxidation ability was observed already by R. Warington. Cultivation of pure nitrite oxidizer happened later during 20th century, however it is not possible to be certain which cultures were without contaminants as all theoretically pure strains share same trait (nitrite consumption, nitrate production). | 1 | Biochemistry |
There are multiple different ways to fix cultural eutrophication with raw sewage being a point source of pollution. For example, sewage treatment plants can be upgraded for biological nutrient removal so that they discharge much less nitrogen and phosphorus to the receiving water body. However, even with good secondary treatment, most final effluents from sewage treatment works contain substantial concentrations of nitrogen as nitrate, nitrite or ammonia. Removal of these nutrients is an expensive and often difficult process.
Laws regulating the discharge and treatment of sewage have led to dramatic nutrient reductions to surrounding ecosystems. Because a major contributor to the nonpoint source nutrient loading of water bodies is untreated domestic sewage, it is necessary to provide treatment facilities to highly urbanized areas, particularly those in developing countries, in which treatment of domestic waste water is a scarcity. The technology to safely and efficiently reuse wastewater, both from domestic and industrial sources, should be a primary concern for policy regarding eutrophication. | 2 | Environmental Chemistry |
Many methods in ester synthesis can also be applied to that of lactones. Lactonization competes with polymerization for longer hydroxy acids, or the strained βlactones. γLactones, on the other hand, are so stable that 4-hydroxy acids (R-CH(OH)-(CH)-COH) spontaneously cyclise.
In one industrial synthesis of oxandrolone the key lactone-forming step is an organic reaction - esterification.
In halolactonization, an alkene is attacked by a halogen via electrophilic addition with the cationic intermediate captured intramolecularly by an adjacent carboxylic acid.
Specific methods include Yamaguchi esterification, Shiina macrolactonization, Corey-Nicolaou macrolactonization, Baeyer–Villiger oxidation and nucleophilic abstraction.
The γ-lactones γ-octalactone, γ-nonalactone, γ-decalactone, γ-undecalactone can be prepared in good yield in a one-step process by radical addition of primary fatty alcohols to acrylic acid, using di-tert-butyl peroxide as a catalyst.
An alternative radical reaction yielding γ-lactones is the manganese-mediated coupling. | 0 | Organic Chemistry |
Fumaric acid is produced based on catalytic isomerisation of maleic acid in aqueous solutions at low pH. It precipitates from the reaction solution. Maleic acid is accessible in large volumes as a hydrolysis product of maleic anhydride, produced by catalytic oxidation of benzene or butane. | 1 | Biochemistry |
An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently volatile for transmission via the air to the olfactory system in the upper part of the nose. As examples, various fragrant fruits have diverse aroma compounds, particularly strawberries which are commercially cultivated to have appealing aromas, and contain several hundred aroma compounds.
Generally, molecules meeting this specification have molecular weights of less than 310. Flavors affect both the sense of taste and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and the term fragrances may also apply to synthetic compounds, such as those used in cosmetics.
Aroma compounds can naturally be found in various foods, such as fruits and their peels, wine, spices, floral scent, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops. Wines have more than 100 aromas that form as byproducts of fermentation. Also, many of the aroma compounds play a significant role in the production of compounds used in the food service industry to flavor, improve, and generally increase the appeal of their products.
An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or hydrogen, as a safety measure. | 0 | Organic Chemistry |
It is possible to introduce an artificial electron acceptor into the light reaction, such as a dye that changes color when it is reduced. These are known as Hill reagents. These dyes permitted the finding of electron transport chains during photosynthesis. Dichlorophenolindophenol (DCPIP), an example of these dyes, is widely used by experimenters. DCPIP is a dark blue solution that becomes lighter as it is reduced. It provides experimenters with a simple visual test and easily observable light reaction.
In another approach to studying photosynthesis, light-absorbing pigments such as chlorophyll can be extracted from chloroplasts. Like so many important biological systems in the cell, the photosynthetic system is ordered and compartmentalized in a system of membranes. | 5 | Photochemistry |
Otto Perutz (27 July 1847, Teplice, Bohemia – 18 January 1922, Munich Germany) was an Austrian-German chemist.
From 1872 to 1876, Perutz was director of Bayerische Aktiengesellschaft für chemische und landwirtschaftlich-chemische Fabrikate (Bavarian Corporation for Chemical and Agrochemical Products Inc., later Süd-Chemie AG) in Munich-Heufeld.
In 1880, he founded his own firm Otto Perutz Trockenplattenfabrik in Munich. He developed a method for the industrial production of Eosin-Silver-Plates which had been invented by Hermann Wilhelm Vogel and Johann Baptist Obernetter. This was crucial to develop colour photography. In 1896, Perutz-Plates were used for radiography for the first time.
Perutz sold his firm in 1897. He was member of the supervisory board of Bayerische Aktiengesellschaft für chemische und landwirtschaftlich-chemische Fabrikate from 1902 until his death in 1922. The Perutz-Photowerke became part of Agfa in 1964. | 5 | Photochemistry |
* Advantages
** Some advantages to Biological and bio-hybrid drug carriers include but are not limited to offering compatibility with the human immune system, having the potential to be genetically modified, and having the capacity to hold drugs. Moreover, an essential advantage is their natural property of homing to inflammation and tumor sites. This natural property of homing to inflammation and tumor sites can enhance the targeted delivery of drugs, minimizing the risk of off-target effects and reducing the required dosage. Additionally, these systems have the potential to increase drug stability and prolong circulation time in the body, improving drug efficacy and reducing the frequency of dosing. Overall, these advantages make biological and bio-hybrid drug carriers promising for developing more effective and targeted drug delivery systems.
* Limitations
** One limitation of Biological and bio-hybrid drug carriers, especially leukocytes, is that they have a low drug-carrying capacity. A limit in the carrying capacity of a carrier means that researchers will have to use more medication to achieve the desired therapeutic effect, increasing the risk of adverse side effects and the cost of the treatment. Moreover, the short lifespan can limit their potential use for long-term drug delivery applications [35]. Coupling this aspect with an inability to penetrate deep into tumors and the potential for genetic mutations can pose significant challenges for future drug delivery systems. Therefore, despite their advantages, further research and development are needed to address current limitations and improve their clinical feasibility. | 1 | Biochemistry |
Under normal conditions, ATP and ADP cannot cross the inner mitochondrial membrane due to their high negative charges, but ADP/ATP translocase, an antiporter, couples the transport of the two molecules. The depression in ADP/ATP translocase alternatively faces the matrix and the cytoplasmic sides of the membrane. ADP in the intermembrane space, coming from the cytoplasm, binds the translocase and induces its eversion, resulting in the release of ADP into the matrix. Binding of ATP from the matrix induces eversion and results in the release of ATP into the intermembrane space, subsequently diffusing to the cytoplasm, and concomitantly brings the translocase back to its original conformation. ATP and ADP are the only natural nucleotides recognized by the translocase.
The net process is denoted by:
:ADP + ATP → ADP + ATP
ADP/ATP exchange is energetically expensive: about 25% of the energy yielded from electron transfer by aerobic respiration, or one hydrogen ion, is consumed to regenerate the membrane potential that is tapped by ADP/ATP translocase.
The translocator cycles between two states, called the cytoplasmic and matrix state, opening up to these compartments in an alternating way. There are structures available that show the translocator locked in a cytoplasmic state by the inhibitor carboxyatractyloside, or in the matrix state by the inhibitor bongkrekic acid. | 1 | Biochemistry |
One probe for testing whether or not the 2-norbornyl cation is non-classical is investigating the inherent symmetry of the cation. Many spectroscopic tools, such as nuclear magnetic resonance spectroscopy (NMR spectroscopy) and Raman spectroscopy, give hints about the reflectional and rotational symmetry present in a molecule or ion. Each of the three proposed structures of the 2-norbornyl cation illustrates a different molecular symmetry. The non-classical form contains a reflection plane through carbons 4, 5, 6, and the midpoint of carbons 1 and 2. The classical form contains neither reflectional nor rotational symmetry. The protonated nortricyclene structure contains a C-symmetric rotation axis through carbon 4.
Each peak in an NMR spectrum corresponds to a set of a particular element's atoms that are in similar chemical environments. The NMR spectrum of the antimony chloropentafluoride salt of the 2-norbornyl cation is not helpful at room temperature because hydride shifts occur faster than the timescale of an NMR experiment; most of the hydrogens are thus seen as equivalent and are accounted for in the same absorption peak. By lowering the temperature of the NMR experiment to −60 °C, hydride shifts are "frozen out" and more structural information can be gleaned from the spectrum. Researchers found that at these low temperatures, the H NMR spectrum matched what would be expected for the non-classical structure of the ion.
H and C NMR studies were able to confirm that any proposed Wagner-Meerwein rearrangements occurred faster than the timescale of the NMR experiment, even at low temperatures. For molecules in static equilibrium with respect to rearrangements, NMR reveals how many sets of symmetry-related nuclei are in the molecule and how many nuclei each of these sets accounts for via spectrum integration. For molecules in dynamic equilibrium such as the 2-norbornyl cation, nuclei within each set can also be transformed to one another through rearrangements with fast reaction rates. Since the proposed dynamic equilibrium of the classical ion proponents had very fast rates of rearrangement, the first NMR studies did not favor nor invalidate any of the three proposed structures. But by using solid-state NMR analysis, one can lower the temperature of the NMR experiment to and thus significantly slow down any rearrangement phenomena. Solid-state C NMR spectra of the 2-norbornyl cation shows that carbons 1 and 2 are in identical chemical environments, which is consistent only with the non-classical picture of the 2-norbornyl cation.
Raman spectra of the 2-norbornyl cation show a more symmetric species than would be expected for a pair of rapidly equilibrating classical ions. Since the proposed reaction rates for the classical ion rearrangements are slower than the Raman timescale, one would expect the Raman spectra to indicate a less symmetric species if the classical picture were correct.
Some studies of the C NMR in particular favored interpretation via the protonated nortricyclene structure. In addition, Raman spectra of the 2-norbornyl cation in some acidic solvents show an absorption band at 3110 cm indicative of an electron-depleted cyclopropane ring. Since that absorption band would be expected in the C-symmetric protonated nortricyclene, some scientists claimed this as convincing evidence for this interpretation. Other chemists have postulated that the properties of the 2-norbornyl cation are very dependent on the solvent environment. Though the high acidity and low nucleophilicity of the solvents used in aforementioned experiments may cause the protonated nortricylconium geometry to be the most stable, this geometry need not be the most energetically favorable in other solvents. | 7 | Physical Chemistry |
Hexamethylenetetramine or hexamine is also used as a food additive as a preservative (INS number 239). It is approved for usage for this purpose in the EU, where it is listed under E number E239, however it is not approved in the USA, Russia, Australia, or New Zealand. | 0 | Organic Chemistry |
Leber's congenital amaurosis is an inherited blinding disease caused by mutations in the RPE65 gene. The results of a small clinical trial in children were published in April. Delivery of recombinant adeno-associated virus (AAV) carrying RPE65 yielded positive results. In May, two more groups reported positive results in independent clinical trials using gene therapy to treat the condition. In all three clinical trials, patients recovered functional vision without apparent side-effects. | 1 | Biochemistry |
Tris(cyclooctatetraene)triiron or Fe(COT), also referred to as the Lavallo-Grubbs compound (after its discoverers) is an organoiron compound with the formula Fe(CH). It is a pyrophoric, black crystalline solid, which is insoluble in common organic solvents.The compound represents a rare example of a hydrocarbon analogue of the well-known Triiron dodecacarbonyl (Fe(CO)), originally prepared by Dewar and Jones in the early 20th century. | 7 | Physical Chemistry |
Perhaps no pair of valence isomers differ more strongly in appearance than colourless naphthalene and the intensely violet azulene. | 4 | Stereochemistry |
As an ordinary acid chloride, isobutyryl chloride is the subject of many reported transformations. Dehydrohalogenation of isobutyryl chloride with triethylamine gives 2,2,4,4-tetramethylcyclobutanedione. Treatment of isobutyryl chloride with hydrogen fluoride gives the acid fluoride. | 0 | Organic Chemistry |
On airless bodies, the lack of any significant greenhouse effect allows equilibrium temperatures to approach mean surface temperatures, as on Mars, where the equilibrium temperature is and the mean surface temperature of emission is . There are large variations in surface temperature over space and time on airless or near-airless bodies like Mars, which has daily surface temperature variations of 50–60 K. Because of a relative lack of air to transport or retain heat, significant variations in temperature develop. Assuming the planet radiates as a blackbody (i.e. according to the Stefan-Boltzmann law), temperature variations propagate into emission variations, this time to the power of 4. This is significant because our understanding of planetary temperatures comes not from direct measurement of the temperatures, but from measurements of the fluxes. Consequently, in order to derive a meaningful mean surface temperature on an airless body (to compare with an equilibrium temperature), a global average surface emission flux is considered, and then an effective temperature of emission that would produce such a flux is calculated. The same process would be necessary when considering the surface temperature of the Moon, which has an equilibrium temperature of , but can have temperatures of in the daytime and at night. Again, these temperature variations result from poor heat transport and retention in the absence of an atmosphere. | 7 | Physical Chemistry |
When Emerson exposed green plants to differing wavelengths of light, he noticed that at wavelengths of greater than 680 nm the efficiency of photosynthesis decreased abruptly despite the fact that this is a region of the spectrum where chlorophyll still absorbs light (chlorophyll is the green pigment in plants - it absorbs mainly the red and blue wavelengths from light). When the plants were exposed to short-wavelength light, (less than 660 nm), the efficiency also decreased.
Emerson then exposed the plants to both short and long wavelengths at the same time, causing the efficiency to increase greatly. He concluded that there must be two different photosystems involved in photosynthesis, one driven by short-wavelength light and one driven by long-wavelength (PS1 and PS2). They work together to enhance efficiency and convert the light energy to forms that can be absorbed by the plant.
The light excites the chlorophyll molecules at the reaction centre and causes an increase in energy. As the molecule becomes less excited, its energy is transported through a chain of electron carriers to the next photosystem which does much the same thing and produces energy-carrying organic molecules. | 5 | Photochemistry |
The second contribution is the induction (also termed polarization) or Debye force, arising from interactions between rotating permanent dipoles and from the polarizability of atoms and molecules (induced dipoles). These induced dipoles occur when one molecule with a permanent dipole repels another molecule's electrons. A molecule with permanent dipole can induce a dipole in a similar neighboring molecule and cause mutual attraction. Debye forces cannot occur between atoms. The forces between induced and permanent dipoles are not as temperature dependent as Keesom interactions because the induced dipole is free to shift and rotate around the polar molecule. The Debye induction effects and Keesom orientation effects are termed polar interactions.
The induced dipole forces appear from the induction (also termed polarization), which is the attractive interaction between a permanent multipole on one molecule with an induced (by the former di/multi-pole) 31 on another. This interaction is called the Debye force, named after Peter J. W. Debye.
One example of an induction interaction between permanent dipole and induced dipole is the interaction between HCl and Ar. In this system, Ar experiences a dipole as its electrons are attracted (to the H side of HCl) or repelled (from the Cl side) by HCl. The angle averaged interaction is given by the following equation:
where = polarizability.
This kind of interaction can be expected between any polar molecule and non-polar/symmetrical molecule. The induction-interaction force is far weaker than dipole–dipole interaction, but stronger than the London dispersion force. | 6 | Supramolecular Chemistry |
In thermodynamics, when is exact, the function is a state function of the system: a mathematical function which depends solely on the current equilibrium state, not on the path taken to reach that state. Internal energy , Entropy , Enthalpy , Helmholtz free energy , and Gibbs free energy are state functions. Generally, neither work nor heat is a state function. (Note: is commonly used to represent heat in physics. It should not be confused with the use earlier in this article as the parameter of an exact differential.) | 7 | Physical Chemistry |
The first serious attempt at providing a physical explanation of the material removal during electric discharge machining is perhaps that of Van Dijck. Van Dijck presented a thermal model together with a computational simulation to explain the phenomena between the electrodes during electric discharge machining. However, as Van Dijck himself admitted in his study, the number of assumptions made to overcome the lack of experimental data at that time was quite significant.
Further models of what occurs during electric discharge machining in terms of heat transfer were developed in the late eighties and early nineties. It resulted in three scholarly papers: the first presenting a thermal model of material removal on the cathode, the second presenting a thermal model for the erosion occurring on the anode and the third introducing a model describing the plasma channel formed during the passage of the discharge current through the dielectric liquid. Validation of these models is supported by experimental data provided by AGIE.
These models give the most authoritative support for the claim that EDM is a thermal process, removing material from the two electrodes because of melting or vaporization, along with pressure dynamics established in the spark-gap by the collapsing of the plasma channel. However, for small discharge energies the models are inadequate to explain the experimental data. All these models hinge on a number of assumptions from such disparate research areas as submarine explosions, discharges in gases, and failure of transformers, so it is not surprising that alternative models have been proposed more recently in the literature trying to explain the EDM process.
Among these, the model from Singh and Ghosh reconnects the removal of material from the electrode to the presence of an electrical force on the surface of the electrode that could mechanically remove material and create the craters. This would be possible because the material on the surface has altered mechanical properties due to an increased temperature caused by the passage of electric current. The authors' simulations showed how they might explain EDM better than a thermal model (melting or evaporation), especially for small discharge energies, which are typically used in μ-EDM and in finishing operations.
Given the many available models, it appears that the material removal mechanism in EDM is not yet well understood and that further investigation is necessary to clarify it, especially considering the lack of experimental scientific evidence to build and validate the current EDM models. This explains an increased current research effort in related experimental techniques. | 8 | Metallurgy |
The City of Whitwell in Tennessee is named in his honour. Tom was a founder and Chairman of the Southern States Coal, Iron and Land Company which developed coal mining in Whitwell and Iron smelting in nearby South Pittsburg. Tom visited the area at least twice hosting a banquet for five hundred workers and guests of ‘all classes’. After his death, the company was acquired by the Tennessee Coal and Iron Company. | 8 | Metallurgy |
Compared with β-carbon elimination, oxidative addition of C-C bond is a more direct way of C-C bond activation. However, it is more challenging to do for the following reasons: 1) It forms two weak M-C bonds at the expense of breaking a stable C-C bond, so it is energetically unfavorable; 2) the C-C bond is usually hindered, which makes the metal center hard to approach. As a result, the cleavage of unstrained compounds that have been achieved is mainly focused on ketone substrates. This is because the C–C bond adjacent to the carbonyl of ketones is weaker and can be much more easily cleaved. It also benefits from the less steric hindrance from the planar structure of the carbonyl motif. Suggs and Jun are pioneers in this field. They found that an Rh(I) complex, [RhCl(CH)], can be oxidatively inserted into the C–C bond of 8-acylquinolines at the 8-position to form relatively stable 5-membered rhodacycles. Subsequently, 8-acylquinoline can be coupled with ethylene to afford 8-quinolinyl ethylketone, which represented the first transition-metal-catalyzed scission of C–C bonds via oxidative addition. | 0 | Organic Chemistry |
Foldamers can vary in size, but they are defined by the presence of noncovalent, nonadjacent interactions. This definition excludes molecules like poly(isocyanates) (commonly known as polyurethane) and poly(prolines) as they fold into helices reliably due to adjacent covalent interactions. Foldamers have a dynamic folding reaction (unfolded → folded), in which large macroscopic folding is caused by solvophobic effects (hydrophobic collapse), while the final energy state of the folded foldamer is due to the noncovalent interactions. These interactions work cooperatively to form the most stable tertiary structure, as the completely folded and unfolded states are more stable than any partially folded state. | 6 | Supramolecular Chemistry |
The three principal phosphate producer countries (China, Morocco and the United States) account for about 70% of world production. | 0 | Organic Chemistry |
The simplest molecular explanation for the exchange of proteins on a surface is the adsorption/desorption model. Here, proteins interact with the surface of a biomaterial and "stick" on the material through interactions made with the protein and the biomaterial surface. Once a protein has adsorbed onto the surface of a biomaterial, the protein may change conformation (structure) and even become nonfunctional. The spaces between the proteins on the biomaterial then become available for new proteins to adsorb. Desorption occurs when the protein leaves the biomaterial surface. This simple model lacks in complexity, since Vroman-like behavior has been observed on hydrophobic surfaces as well as hydrophilic ones. Furthermore, adsorption and desorption doesn't completely explain competitive protein exchange on hydrophilic surfaces. | 7 | Physical Chemistry |
There have also been attempts to distill creosote from peat-tar, although mostly unsuccessful due to the problems with winning and drying peat on an industrial scale. Peat tar by itself has in the past been used as a wood preservative. | 7 | Physical Chemistry |
* (2007): Death of a dissident: The Poisoning of Alexander Litvinenko and the Return of the KGB. The Free Press. | 1 | Biochemistry |
The reducing agents NADH, NADPH, and FADH, as well as metal ions, act as cofactors at various steps in anabolic pathways. NADH, NADPH, and FADH act as electron carriers, while charged metal ions within enzymes stabilize charged functional groups on substrates. | 1 | Biochemistry |
Vacuum pyrolysis, with the removal of neutral volatile byproducts i.e. methanol or chloroform, has been used to prepare dihydroimidazole and triazole based carbenes. Historically the removal of chloroform by vacuum pyrolysis of adducts A was used by Wanzlick in his early attempts to prepare dihydroimidazol-2-ylidenes but this method is not widely used. The Enders laboratory has used vacuum pyrolysis of adduct B to generate a triazol-5-ylidene. | 0 | Organic Chemistry |
Carbon added to sedimentary rocks can take the form of carbonates, or organic carbon compounds. In order of source quantity the organic carbon comes from phytoplankton, plants, bacteria and zooplankton. However terrestrial sediments may be mostly from higher plants, and some oxygen deficient sediments from water may be mostly bacteria. Fungi and other animals make insignificant contributions. On the oceans the main contributor of organic matter to sediments is plankton, either dead fragments or faecal pellets termed marine snow. Bacteria degrade this matter in the water column, and the amount surviving to the ocean floor is inversely proportional to the depth. This is accompanied by biominerals consisting of silicates and carbonates. The particulate organic matter in sediments is about 20% of known molecules 80% of material that cannot be analysed. Detritivores consume some of the fallen organic materials. Aerobic bacteria and fungi also consume organic matter in the oxic surface parts of the sediment. Coarse-grained sediments are oxygenated to about half a meter, but fine grained clays may only have a couple of millimetres exposed to oxygen. The organic matter in the oxygenated zone will become completely mineralized if it stays there long enough.
Deeper in sediments where oxygen is exhausted, anaerobic biological processes continue at a slower rate. These include anaerobic mineralization making ammonium, phosphate and sulfide ions; fermentation making short chain alcohols, acids or methyl amines; acetogenesis making acetic acid; methanogenesis making methane, and sulfate, nitrite and nitrate reduction. Carbon dioxide and hydrogen are also outputs. Under freshwater, sulfate is usually very low, so methanogenesis is more important. Yet other bacteria can convert methane, back into living matter, by oxidising with other substrates. Bacteria can reside at great depths in sediments. However sedimentary organic matter accumulates the indigestible components.
Deep bacteria may be lithotrophes, using hydrogen, and carbon dioxide as a carbon source.
In the oceans and other waters there is much dissolved organic materials. These are several thousand years old on average, and are called gelbstoff (yellow substance) particularly in fresh waters. Much of this is tannins. The nitrogen containing materials here appear to be amides, perhaps from peptidoglycans from bacteria. Microorganisms have trouble consuming the high molecular weight dissolved substances, but quickly consume small molecules.
From terrestrial sources black carbon produced by charring is an important component. Fungi are important decomposers in soil. | 9 | Geochemistry |
The Racah parameters are a set of parameters used in atomic and molecular spectroscopy to describe the amount of total electrostatic repulsion in an atom that has multiple electrons.
When an atom has more than one electron, there will be some electrostatic repulsion between the electrons. The amount of repulsion varies from atom to atom, depending upon the number of electrons, their spin, and the orbitals that they occupy. The total repulsion can be expressed in terms of three parameters A, B and C which are known as the Racah parameters after Giulio Racah, who first described them. They are generally obtained empirically from gas-phase spectroscopic studies of atoms.
They are often used in transition-metal chemistry to describe the repulsion energy associated with an electronic term. For example, the interelectronic repulsion of a P term is A + 7B, and of a F term is A - 8B, and the difference between them is therefore 15B. | 7 | Physical Chemistry |
Base flipping was first observed in 1994 when researchers Klimasauskas, Kumar, Roberts, and Cheng used X-ray crystallography to view an intermediate step in the chemical reaction of a methyltransferase bound to DNA. The methyltransferase they used was the C5-cytosine methyltransferase from Haemophilus haemolyticus (M. HhaI). This enzyme recognizes a specific sequence of the DNA (5-GCGC-3) and methylates the first cytosine base of the sequence at its C5 location. Upon crystallization of the M. HhaI-DNA complex, they saw the target cytosine base was rotated completely out of the double helix and was positioned in the active site of the M. HhaI. It was held in place by numerous interactions between the M. HhaI and DNA.
The authors theorized that base flipping was a mechanism used by many other enzymes, such as helicases, recombination enzymes, RNA polymerases, DNA polymerases, and Type II topoisomerases. Much research has been done in the years subsequent to this discovery and it has been found that base flipping is a mechanism used in many of the biological processes the authors suggest. | 1 | Biochemistry |
As an example, consider the gas-phase reaction + CO → NO + . If this reaction occurred in a single step, its reaction rate (r) would be proportional to the rate of collisions between and CO molecules: r = k[][CO], where k is the reaction rate constant, and square brackets indicate a molar concentration. Another typical example is the Zel'dovich mechanism. | 7 | Physical Chemistry |
Coliform bacteria are defined as either motile or non-motile Gram-negative non-spore forming bacilli that possess β-galactosidase to produce acids and gases under their optimal growth temperature of 35–37 °C. They can be aerobes or facultative aerobes, and are a commonly used indicator of low sanitary quality of foods, milk, and water. Coliforms can be found in the aquatic environment, in soil and on vegetation; they are universally present in large numbers in the feces of warm-blooded animals as they are known to inhabit the gastrointestinal system. While coliform bacteria are not normally causes of serious illness, they are easy to culture, and their presence is used to infer that other pathogenic organisms of fecal origin may be present in a sample, or that said sample is not safe to consume. Such pathogens include disease-causing bacteria, viruses, or protozoa and many multicellular parasites.
Every drinking water source must be tested for the presence of these total coliform bacteria. | 3 | Analytical Chemistry |
Many decarboxylative cross coupling reactions involve the breaking of C–COOH bonds, therefore subsequent studies have attempted to enable cross coupling with </sub>C carboxylic acids. One such reaction by Shang et al. described a palladium catalyzed cross coupling that enables the formation of functionalized pyridines, pyrazines, quinolines, benzothiazoles, and benzoxazoles. The position of the nitrogen atom in the 2 position relative to the linkage is found to be required, therefore implying its binding to Pd in a transition state. | 0 | Organic Chemistry |
The most basic optical tweezer setup will likely include the following components: a laser (usually Nd:YAG), a beam expander, some optics used to steer the beam location in the sample plane, a microscope objective and condenser to create the trap in the sample plane, a position detector (e.g. quadrant photodiode) to measure beam displacements and a microscope illumination source coupled to a CCD camera.
An Nd:YAG laser (1064 nm wavelength) is a common choice of laser for working with biological specimens. This is because such specimens (being mostly water) have a low absorption coefficient at this wavelength. A low absorption is advisable so as to minimise damage to the biological material, sometimes referred to as opticution. Perhaps the most important consideration in optical tweezer design is the choice of the objective. A stable trap requires that the gradient force, which is dependent upon the numerical aperture (NA) of the objective, be greater than the scattering force. Suitable objectives typically have an NA between 1.2 and 1.4.
While alternatives are available, perhaps the simplest method for position detection involves imaging the trapping laser exiting the sample chamber onto a quadrant photodiode. Lateral deflections of the beam are measured similarly to how it is done using atomic force microscopy (AFM).
Expanding the beam emitted from the laser to fill the aperture of the objective will result in a tighter, diffraction-limited spot. While lateral translation of the trap relative to the sample can be accomplished by translation of the microscope slide, most tweezer setups have additional optics designed to translate the beam to give an extra degree of translational freedom. This can be done by translating the first of the two lenses labelled as "Beam Steering" in the figure. For example, translation of that lens in the lateral plane will result in a laterally deflected beam from what is drawn in the figure. If the distance between the beam steering lenses and the objective is chosen properly, this will correspond to a similar deflection before entering the objective and a resulting lateral translation in the sample plane. The position of the beam waist, that is the focus of the optical trap, can be adjusted by an axial displacement of the initial lens. Such an axial displacement causes the beam to diverge or converge slightly, the result of which is an axially displaced position of the beam waist in the sample chamber.
Visualization of the sample plane is usually accomplished through illumination via a separate light source coupled into the optical path in the opposite direction using dichroic mirrors. This light is incident on a CCD camera and can be viewed on an external monitor or used for tracking the trapped particle position via video tracking. | 1 | Biochemistry |
The first of preparation of a phosphaalkyne was achieved in 1961 when Thurman Gier produced phosphaethyne by passing phosphine gas at low pressure over an electric arc produced between two carbon electrodes. Condensation of the gaseous products in a –196 °C (–321 °F) trap revealed that the reaction had produced acetylene, ethylene, phosphaethyne, which was identified by infrared spectroscopy. | 0 | Organic Chemistry |
The project is open source - all data and all software that is produced in the project can be freely accessed and used. | 1 | Biochemistry |
In circumstances where more than one laboratory is analysing samples and feeding data into a large programme of work such as the Harmonised monitoring scheme in the UK, AQC can also be applied to validate one laboratory against another. In such cases the work may be referred to as inter-laboratory calibration. | 2 | Environmental Chemistry |
Since RuBisCO is often rate-limiting for photosynthesis in plants, it may be possible to improve photosynthetic efficiency by modifying RuBisCO genes in plants to increase catalytic activity and/or decrease oxygenation rates. This could improve sequestration of and be a strategy to increase crop yields. Approaches under investigation include transferring RuBisCO genes from one organism into another organism, engineering Rubisco activase from thermophilic cyanobacteria into temperature sensitive plants, increasing the level of expression of RuBisCO subunits, expressing RuBisCO small chains from the chloroplast DNA, and altering RuBisCO genes to increase specificity for carbon dioxide or otherwise increase the rate of carbon fixation. | 5 | Photochemistry |
The Environmental Residue Effects Database (ERED) is a database maintained by the U.S. Army Corps of Engineers that pairs data regarding the bioaccumulation of toxicants in tissue (via tissue residue) to endpoint effects such as mortality, growth, or physiological and biochemical responses. Response data also include low effect detected (LOED) and no effect detected (NOED) concentrations. This database is derived from 2329 peer-reviewed references regarding 413 chemicals. The database covers literature from 1964 to the present and includes more than 15,000 records. This database is updated with 300 or more records every year on average. The ERED database is specific to sediment toxicity and the effects of contaminates in dredged materials on freshwater organisms. It is intended to be used in evaluating the potential for contaminate concentrations of dredged sediment to have unacceptable adverse effects on aquatic organisms. Although the ERED database was designed as a tool for the Army Corps of Engineers to manage adverse effects of dredging, it is widely applicable to sediment toxicity studies and management. | 1 | Biochemistry |
Cryptoregiochemistry refers to the site of initial oxidative attack in double bond formation by enzymes such as fatty acid desaturases. This is a mechanistic parameter that is usually determined through the use of kinetic isotope effect experiments, based on the premise that the initial C-H bond cleavage step should be energetically more difficult and therefore more sensitive to isotopic substitution than the second C-H bond breaking step. | 4 | Stereochemistry |
Single doses of up to at least 32-fold (800 mg), as well as continuous therapy with 24-fold (600 mg) the usual daily dose are well tolerated. No life-threatening overdosing is known in humans, but only in animal studies with 2000- to 4000-fold doses (adjusted to body surface area). | 4 | Stereochemistry |
The images above give an indication of the compositions and scale (dimensions) associated with MAs, though these just begin to touch on the complexity of the structures; in principle, each living cell is composed of MAs, but is itself an MA as well. In the examples and other such complexes and assemblies, MAs are each often millions of daltons in molecular weight (megadaltons, i.e., millions of times the weight of a single, simple atom), though still having measurable component ratios (stoichiometries) at some level of precision. As alluded to in the image legends, when properly prepared, MAs or component subcomplexes of MAs can often be crystallized for study by protein crystallography and related methods, or studied by other physical methods (e.g., spectroscopy, microscopy).
Virus structures were among the first studied MAs; other biologic examples include ribosomes (partial image above), proteasomes, and translation complexes (with protein and nucleic acid components), procaryotic and eukaryotic transcription complexes, and nuclear and other biological pores that allow material passage between cells and cellular compartments. Biomembranes are also generally considered MAs, though the requirement for structural and spatial definition is modified to accommodate the inherent molecular dynamics of membrane lipids, and of proteins within lipid bilayers. | 1 | Biochemistry |
In the presence of two phases ( and ), the surface (surface phase) is located in between the phase and phase . Experimentally, it is difficult to determine the exact structure of an inhomogeneous surface phase that is in contact with a bulk liquid phase containing more than one solute. Inhomogeneity of the surface phase is a result of variation of mole ratios. A model proposed by Josiah Willard Gibbs proposed that the surface phase as an idealized model that had zero thickness. In reality, although the bulk regions of and phases are constant, the concentrations of components in the interfacial region will gradually vary from the bulk concentration of to the bulk concentration of over the distance x. This is in contrast to the idealized Gibbs model where the distance x takes on the value of zero. The diagram to the right illustrates the differences between the real and idealized models. | 7 | Physical Chemistry |
A relation between the apparent molar of a component of a mixture and molar mixing ratio can be obtained by dividing the definition relation
to the number of moles of one component. This gives the following relation: | 7 | Physical Chemistry |
C. albicans is a yeast with a particular feature: it translates the CUG codon into serine rather than leucine. Due to this different codon usage it is difficult to use the model system S. cerevisiae as a Y2H to check for protein-protein interactions using C. albicans genes. To provide a more native environment a C. albicans two-hybrid (C2H) system was developed. With this system protein-protein interactions can be studied in C. albicans itself. A recent addition was the creation of a high-throughput system. | 1 | Biochemistry |
The forces between the tip and the sample strongly depend on the geometry of the tip. Various studies were exploited in the past years to write the forces as a function of the tip parameters.
Among the different forces between the tip and the sample, the water meniscus forces are highly interesting, both in air and liquid environment. Other forces must be considered, like the Coulomb force, van der Waals forces, double layer interactions, solvation forces, hydration and hydrophobic forces. | 6 | Supramolecular Chemistry |
The prismanes are a class of hydrocarbon compounds consisting of prism-like polyhedra of various numbers of sides on the polygonal base. Chemically, it is a series of fused cyclobutane rings (a ladderane, with all-cis/all-syn geometry) that wraps around to join its ends and form a band, with cycloalkane edges. Their chemical formula is (CH), where n is the number of cyclobutane sides (the size of the cycloalkane base), and that number also forms the basis for a system of nomenclature within this class. The first few chemicals in this class are:
Triprismane, tetraprismane, and pentaprismane have been synthesized and studied experimentally, and many higher members of the series have been studied using computer models. The first several members do indeed have the geometry of a regular prism, with flat n-gon bases. As n becomes increasingly large, however, modeling experiments find that highly symmetric geometry is no longer stable, and the molecule distorts into less-symmetric forms. One series of modelling experiments found that starting with [11]prismane, the regular-prism form is not a stable geometry. For example, the structure of [12]prismane would have the cyclobutane chain twisted, with the dodecagonal bases non-planar and non-parallel. | 4 | Stereochemistry |
Purple bacteria is a type of photosynthetic organism with a light harvesting complex consisting of two pigment protein complexes referred to as LH1 and LH2. Within the photosynthetic membrane, these two complexes differ in terms of their arrangement. The LH1 complexes surrounds the reaction centre, while the LH2 complexes are arranged around the LH1 complexes and the reaction centre in a peripheral fashion. Purple bacteria use bacteriochlorophyll and carotenoids to gather light energy. These proteins are arranged in a ring-like fashion creating a cylinder that spans the membrane. | 5 | Photochemistry |
In organic chemistry, a ketone is an organic compound with the structure , where R and R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (which contains a carbon–oxygen double bond C=O). The simplest ketone is acetone (where R and R is methyl), with the formula . Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids (e.g., testosterone), and the solvent acetone. | 0 | Organic Chemistry |
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