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Pd(PPh) is widely used as a catalyst for palladium-catalyzed coupling reactions. Prominent applications include the Heck reaction, Suzuki coupling, Stille coupling, Sonogashira coupling, and Negishi coupling. These processes begin with two successive ligand dissociations followed by the oxidative addition of an aryl halide to the Pd(0) center:
:Pd(PPh) + ArBr → PdBr(Ar)(PPh) + 2 PPh | 0 | Theoretical and Fundamental Chemistry |
Much of the past research into the composition and toxicity of UCM hydrocarbons has been conducted by the Petroleum and Environmental Geochemistry Group (PEGG) at the University of Plymouth, UK. As well as the hydrocarbon UCM, oils also contain more polar compounds such as those containing oxygen, sulphur or nitrogen. These compounds can be very soluble in water and hence bioavailable to marine and aquatic organisms. Polar UCMs are present within produced waters from oil rigs and from oil sands processing. A polar UCM fraction extracted from North Sea oil produced water was reported to elicit hormonal disruption by way of both estrogen receptor agonist and androgen receptor agonist activity. Ongoing concern regarding the potential toxicity of components within Athabasca Oil Sands (Canada) tailings ponds has highlighted the need for identification of the compounds present. Until recently, such positive identification of individual so-called naphthenic acids from oil sands produced waters had so far eluded characterisation but recent research by PEGG presented at a SETAC conference in 2010 revealed that, using a new GCxGC-TOF-MS, it was possible to resolve and identify a range of new compounds within such highly complex extracts. One group of compounds found to be present were tricyclic diamondoid acids. These structures had previously not even been considered as naphthenic acids and suggests an unprecedented degree of biodegradation of some of the oil in the oil sands. | 0 | Theoretical and Fundamental Chemistry |
Clinopyroxene thermobarometry is usually used by mining industries. It is particularly helpful to the diamond industry, so many stakeholders possess pressure and temperature data regarding the formation of rocks that contain diamonds. This is important because diamonds are usually found in kimberlites, but kimberlites do not always contain diamonds. Instead of mining every kimberlite found, they can be sampled to see if they formed in an environment that would have favored the crystallization of diamonds.
Other applications are largely scientific; pressure and temperature data about magma can be used to propose detailed models of the lithosphere and mantle. These models enhance understanding of geological and volcanic activity, which may contribute to scientists' ability to predict events such as eruptions or earthquakes. | 0 | Theoretical and Fundamental Chemistry |
The earliest recorded metal employed by humans appears to be gold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves dating to the late Paleolithic period, 40,000 BC. Silver, copper, tin and meteoric iron can also be found in native form, allowing a limited amount of metalworking in early cultures. Early metallurgy using native copper is documented at sites in Anatolia and at the site of Tell Maghzaliyah in Iraq, dating from the 7th/6th millennia BC.
Certain metals, such as tin, lead, and copper can be recovered from their ores by simply heating the rocks in a fire or blast furnace in a process known as smelting. The first evidence of copper smelting, dating from the 6th millennium BC, has been found at archaeological sites in Majdanpek, Jarmovac and Pločnik, in present-day Serbia. The site of Pločnik has produced a smelted copper axe dating from 5,500 BC, belonging to the Vinča culture. The Balkans and adjacent Carpathian region were the location of major Chalcolithic cultures including Vinča, Varna, Karanovo, Gumelnița and Hamangia, which are often grouped together under the name of Old Europe. The Carpatho-Balkan region has been described as earliest metallurgical province in Eurasia, with a scale and technical quality of metal production in the 6th-5th millennia BC that totally overshadows that of any other contemporary production centre.
The earliest documented use of lead (possibly native or smelted), dating from the 6th millennium BC, is from the late Neolithic settlements of Yarim Tepe and Arpachiyah in Iraq. The artifacts suggest that lead smelting may have predated copper smelting.
Copper smelting is documented at sites in Anatolia and at the site of Tal-i Iblis in southeastern Iran from c. 5000 BC.
Copper smelting is first documented in the Delta region of northern Egypt in c. 4000 BC, associated with the Maadi culture. This represents the earliest evidence for smelting in Africa.
The Varna Necropolis, Bulgaria, is a burial site located in the western industrial zone of Varna, approximately 4 km from the city centre, internationally considered one of the key archaeological sites in world prehistory. The oldest gold treasure in the world, dating from 4,600 BC to 4,200 BC, was discovered at the site. The gold piece dating from 4,500 BC, found in 2019 in Durankulak, near Varna is another important example. Other signs of early metals are found from the third millennium BC in Palmela, Portugal, Los Millares, Spain, and Stonehenge, United Kingdom. The precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing.
In approximately 1900 BC, ancient iron smelting sites existed in Tamil Nadu.
In the Near East, about 3,500 BC, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. This represented a major technological shift known as the Bronze Age.
The extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. The process appears to have been invented by the Hittites in about 1200 BC, beginning the Iron Age. The secret of extracting and working iron was a key factor in the success of the Philistines.
Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. This includes the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Iran, ancient Egypt, ancient Nubia, and Anatolia in present-day Turkey, Ancient Nok, Carthage, the Greeks and Romans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, amongst others. Many applications, practices, and devices associated or involved in metallurgy were established in ancient China, such as the innovation of the blast furnace, cast iron, hydraulic-powered trip hammers, and double acting piston bellows.
A 16th century book by Georg Agricola, De re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. Agricola has been described as the "father of metallurgy". | 1 | Applied and Interdisciplinary Chemistry |
Photosynthesis is the process in which light energy is absorbed and converted to chemical energy. This chemical energy is eventually used in the conversion of carbon dioxide to sugar in plants. | 0 | Theoretical and Fundamental Chemistry |
Chloroplasts are one of many types of organelles in the plant cell. They are considered to have evolved from endosymbiotic cyanobacteria. Mitochondria are thought to have come from a similar endosymbiosis event, where an aerobic prokaryote was engulfed. This origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Franz Wilhelm Schimper observed in 1883 that chloroplasts closely resemble cyanobacteria. Chloroplasts are only found in plants, algae, and three species of amoeba – Paulinella chromatophora, P. micropora, and marine P. longichromatophora. | 0 | Theoretical and Fundamental Chemistry |
GenePattern is available:
# As a free public web application, hosted on Amazon Web Services. Users can create accounts, perform analyses, and create pipelines on the server.
# As open-source software that can be downloaded and installed locally.
# Public web servers hosted by other organizations. | 1 | Applied and Interdisciplinary Chemistry |
Glycals can be formed as pyranose (six-membered) or furanose (five-membered) rings, depending on the monosaccharide used as a starting material to synthesize the glycal. Glycals can also be classified as endo-glycals or exo-glycals. A glycal is an endo-glycal when the double bond is within the ring. If the hydroxyl group on carbon 1 has been replaced with another carbon atom, a double bond can also form outside the ring between carbon 1 and this new carbon. In this case, the product is called an exo-glycal. The glycal conformation that has been studied in most depth is that of the pyranose endo-glycal. The favoured conformation of this glycal is the half-chair, a result which has been confirmed by quantum mechanical calculations. | 0 | Theoretical and Fundamental Chemistry |
Although lichens had been recognized as organisms for quite some time, it was not until 1867, when Swiss botanist Simon Schwendener proposed his dual theory of lichens, that lichens are a combination of fungi with algae or cyanobacteria, whereby the true nature of the lichen association began to emerge. Schwendeners hypothesis, which at the time lacked experimental evidence, arose from his extensive analysis of the anatomy and development in lichens, algae, and fungi using a light microscope. Many of the leading lichenologists at the time, such as James Crombie and Nylander, rejected Schwendeners hypothesis because the consensus was that all living organisms were autonomous.
Other prominent biologists, such as Heinrich Anton de Bary, Albert Bernhard Frank, Beatrix Potter, Melchior Treub and Hermann Hellriegel, were not so quick to reject Schwendeners ideas and the concept soon spread into other areas of study, such as microbial, plant, animal and human pathogens. When the complex relationships between pathogenic microorganisms and their hosts were finally identified, Schwendeners hypothesis began to gain popularity. Further experimental proof of the dual nature of lichens was obtained when Eugen Thomas published his results in 1939 on the first successful re-synthesis experiment.
In the 2010s, a new facet of the fungi–algae partnership was discovered. Toby Spribille and colleagues found that many types of lichen that were long thought to be ascomycete–algae pairs were actually ascomycete–basidiomycete–algae trios The third symbiotic partner in many lichens is a basidiomycete yeast. | 1 | Applied and Interdisciplinary Chemistry |
Supercritical fluids can be used to deposit functional nanostructured films and nanometer-size particles of metals onto surfaces. The high diffusivities and concentrations of precursor in the fluid as compared to the vacuum systems used in chemical vapour deposition allow deposition to occur in a surface reaction rate limited regime, providing stable and uniform interfacial growth. This is crucial in developing more powerful electronic components, and metal particles deposited in this way are also powerful catalysts for chemical synthesis and electrochemical reactions. Additionally, due to the high rates of precursor transport in solution, it is possible to coat high surface area particles which under chemical vapour deposition would exhibit depletion near the outlet of the system and also be likely to result in unstable interfacial growth features such as dendrites. The result is very thin and uniform films deposited at rates much faster than atomic layer deposition, the best other tool for particle coating at this size scale. | 0 | Theoretical and Fundamental Chemistry |
Two-hybrid screening (originally known as yeast two-hybrid system or Y2H) is a molecular biology technique used to discover protein–protein interactions (PPIs) and protein–DNA interactions by testing for physical interactions (such as binding) between two proteins or a single protein and a DNA molecule, respectively.
The premise behind the test is the activation of downstream reporter gene(s) by the binding of a transcription factor onto an upstream activating sequence (UAS). For two-hybrid screening, the transcription factor is split into two separate fragments, called the DNA-binding domain (DBD or often also abbreviated as BD) and activating domain (AD). The BD is the domain responsible for binding to the UAS and the AD is the domain responsible for the activation of transcription. The Y2H is thus a protein-fragment complementation assay. | 1 | Applied and Interdisciplinary Chemistry |
A deuterated drug is a small molecule medicinal product in which one or more of the hydrogen atoms contained in the drug molecule have been replaced by its heavier stable isotope deuterium. Because of the kinetic isotope effect, deuterium-containing drugs may have significantly lower rates of metabolism, and hence a longer half-life. | 1 | Applied and Interdisciplinary Chemistry |
Lattice parameters of unknown crystal phases can be obtained from X-ray, neutron, or electron diffraction data. Single-crystal diffraction experiments supply orientation matrices, from which lattice parameters can be deduced. Alternatively, lattice parameters can be obtained from powder or polycrystal diffraction data via profile fitting without structural model (so-called Le Bail method).
Arbitrarily defined unit cells can be transformed to a standard setting and, from there, further reduced to a primitive smallest cell. Sophisticated algorithms compare such reduced cells with corresponding database entries. More powerful algorithms also consider derivative super- and subcells. The lattice-matching process can be further sped up by precalculating and storing reduced cells for all entries. The algorithm searches for matches within a certain range of the lattice parameters. More accurate lattice parameters allow a narrower range and, thus, a better match.
Lattice matching is useful in identifying crystal phases in the early stages of single-crystal
diffraction experiments and, thus, avoiding unnecessary full data collection and structure determination procedures for already known crystal structures. The method is particularly important for single-crystalline samples that need to be preserved. If, on the other hand, some or all of the crystalline sample material can be ground, powder diffraction fingerprinting is usually the better option for crystal phase identification, provided that the peak resolution is good enough. However, lattice matching algorithms are still better at treating derivative super- and subcells. | 0 | Theoretical and Fundamental Chemistry |
The Scripps Research Institute has a portfolio of click-chemistry patents. Licensees include Invitrogen, Allozyne, Aileron, Integrated Diagnostics, and the biotech company , a BASF spin-off created to sell products made using click chemistry. Moreover, holds a worldwide exclusive license for the research and diagnostic market for the nucleic acid field.
Fluorescent azides and alkynes are also produced by companies such as Cyandye. | 0 | Theoretical and Fundamental Chemistry |
Here the radius of the cylinder is not , but a slightly distorted form . Then the solution to first-order approximation is | 1 | Applied and Interdisciplinary Chemistry |
In the outer sphere model the donor or acceptor and the tightly bound solvation shells or the complex' ligands were considered to form rigid structures which do not change in the course of electron transfer. However, the distances in the inner sphere are dependent on the charge of donor and acceptor, e.g. the central ion-ligand distances are different in complexes carrying different charges and again the Franck–Condon principle must be obeyed: for the electron to jump to occur, the nuclei have to have an identical configuration to both the precursor and the successor complexes, of course highly distorted. In this case the energy requirement is fulfilled automatically.
In this inner sphere case the Arrhenius concept holds, the transition state of definite geometric structure is reached along a geometrical reaction coordinate determined by nuclear motions. No further nuclear motion is necessary to form the successor complex, just the electron jumps, which makes a difference to the TST theory. The reaction coordinate for inner sphere energy is governed by vibrations and they differ in the oxidized and reduces species.
For the self-exchange system Fe/Fe only the symmetrical breathing vibration of the six water molecules around the iron ions is considered. Assuming harmonic conditions this vibration has frequencies and , the force constants f and f are and the energies are
where q is the equilibrium normal coordinate and the displacement along the normal coordinate, the factor 3 stems from 6 (HO)·. Like for the outer-sphere reorganization energy potential energy curve is quadratic, here, however, as a consequence of vibrations.
The equilibrium normal coordinates differ in Fe(HO) and Fe(HO). By thermal excitation of the breathing vibration a geometry can be reached which is common to both donor and acceptor, i.e. the potential energy curves of the breathing vibrations of D and A intersect here. This is the situation where the electron may jump. The energy of this transition state is the inner sphere reorganization energy λ.
For the self-exchange reaction the metal-water distance in the transition state can be calculated
This gives the inner sphere reorganisation energy
It is fortunate that the expressions for the energies for outer and inner reorganization have the same quadratic form. Inner sphere and outer sphere reorganization energies are independent, so they can be added to give and inserted in the Arrhenius equation
Here, A can be seen to represent the probability of electron jump, that of reaching the transition state of the inner sphere and that of outer sphere adjustment.
For unsymmetrical (cross) reactions like
the expression for can also be derived, but it is more complicated. These reactions have a free reaction enthalpy ΔG which is independent of the reorganization energy and determined by the different redox potentials of the iron and cobalt couple. Consequently, the quadratic Marcus equation holds also for the inner sphere reorganization energy, including the prediction of an inverted region. One may visualizing this by (a) in the normal region both the initial state and the final state have to have stretched bonds, (b) In the Δ G = 0 case the equilibrium configuration of the initial state is the stretched configuration of the final state, and (c) in the inverted region the initial state has compressed bonds whereas the final state has largely stretched bonds.
Similar considerations hold for metal complexes where the ligands are larger than solvent molecules and also for ligand bridged polynuclear complexes. | 0 | Theoretical and Fundamental Chemistry |
Adair Crawford was born in Crumlin, Belfast, the son of Rev Thomas Crawford. He studied medicine at Glasgow and Edinburgh universities. He qualified MA in 1770 and then worked at St Georges Hospital in London before qualifying MD in 1780. He was Professor of Chemistry at the Royal Military Academy, Woolwich, London, and physician at St Thomas Hospital, London. He died at Lymington in Hampshire.
It is no coincidence that the titles of his publications usually begin with the word experiments. Crawford let the details of his experiments and their plain results do the talking, and generally refrained from theorising and over-interpretation. He did maintain the later-discredited phlogiston hypothesis, but wasn't doctrinaire about it.
In 1785, Crawford was elected a member of the American Philosophical Society in Philadelphia and the following year, in 1786, he was elected a Fellow of the Royal Society of London. In 1787 he was elected a Fellow of the Royal Society of Edinburgh. His proposers were John Playfair, James Hutton, and James Gregory.
He died in Lymington in Hampshire on 29 July 1795. | 1 | Applied and Interdisciplinary Chemistry |
*American Chemical Society PROGRESS/Dreyfus Lectureship Award (Camille and Henry Dreyfus Foundation Special Grant Program in the Chemical Sciences)
*NSF CAREER Award on Mechanistic Studies of Nucleotide Reactivity
*Alfred P. Sloan Fellow
*Faculty of Arts and Sciences Award for Distinguished Contributions to Undergraduate Education
*Sigma Chi Scientific Honor Society | 0 | Theoretical and Fundamental Chemistry |
Polycationic complexes tend to form ion pairs with anions and these ion pairs often undergo reactions via the I pathway. The electrostatically held nucleophile can exchange positions with a ligand in the first coordination sphere, resulting in net substitution. An illustrative process comes from the "anation" (reaction with an anion) of chromium(III) hexaaquo complex:
::[Cr(HO)] + SCN {[Cr(HO)], NCS}
::{[Cr(HO)], NCS} [Cr(HO)NCS] + HO | 0 | Theoretical and Fundamental Chemistry |
carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.
fixation is an addition to the ancestral and more common carbon fixation. The main carboxylating enzyme in photosynthesis is called RuBisCO, which catalyses two distinct reactions using either (carboxylation) or oxygen (oxygenation) as a substrate. RuBisCO oxygenation gives rise to phosphoglycolate, which is toxic and requires the expenditure of energy to recycle through photorespiration. photosynthesis reduces photorespiration by concentrating around RuBisCO.
To enable RuBisCO to work in an environment where there is a lot of carbon dioxide and very little oxygen, leaves generally contain two partially isolated compartments called mesophyll cells and bundle-sheath cells. is initially fixed in the mesophyll cells in a reaction catalysed by the enzyme PEP carboxylase in which the three-carbon phosphoenolpyruvate (PEP) reacts with to form the four-carbon oxaloacetic acid (OAA). OAA can then be reduced to malate or transaminated to aspartate. These intermediates diffuse to the bundle sheath cells, where they are decarboxylated, creating a -rich environment around RuBisCO and thereby suppressing photorespiration. The resulting pyruvate (PYR), together with about half of the phosphoglycerate (PGA) produced by RuBisCO, diffuses back to the mesophyll. PGA is then chemically reduced and diffuses back to the bundle sheath to complete the reductive pentose phosphate cycle (RPP). This exchange of metabolites is essential for photosynthesis to work.
Additional biochemical steps require more energy in the form of ATP to regenerate PEP, but concentrating allows high rates of photosynthesis at higher temperatures. Higher CO concentration overcomes the reduction of gas solubility with temperature (Henry's law). The concentrating mechanism also maintains high gradients of concentration across the stomatal pores. This means that plants have generally lower stomatal conductance, reduced water losses and have generally higher water-use efficiency. plants are also more efficient in using nitrogen, since PEP carboxylase is cheaper to make than RuBisCO. However, since the pathway does not require extra energy for the regeneration of PEP, it is more efficient in conditions where photorespiration is limited, typically at low temperatures and in the shade. | 0 | Theoretical and Fundamental Chemistry |
* Ashton, T. S. Iron and Steel in the Industrial Revolution (2nd edn., 1951).
* Bernal, John Desmond, Science and Industry in the Nineteenth Century, Indiana University Press, 1970.
* D’Costa, Anthony P. The Global Restructuring of the Steel Industry: Innovations, Institutions, and Industrial Change London: Routledge, 1999
* Hasegawa, Harukiyu. The Steel Industry in Japan: A Comparison with Britain 1996
* Landes, David S., The Unbound Prometheus: Technical Change and Industrial Development in Western Europe from 1750 to the Present (2nd ed. Cambridge University Press, 2003)
* Pounds, Norman J. G., and William N. Parker; Coal and Steel in Western Europe; the Influence of Resources and Techniques on Production (Indiana University Press, 1957)
* Singer, Charles Joseph, ed. A history of technology: vol 4: The Industrial Revolution c 1750–c 1860 (1960) ch 4, and vol 5: The Late Nineteenth Century, c 1850–c 1900, ch 3; [http://ets.umdl.umich.edu/cgi/t/text/text-idx?c=acls;cc=acls;view=toc;idno=heb02191.0004.001 online at ACLS e-books]
* Stoddard, Brooke C. Steel: From Mine to Mill, the Metal that Made America (2015) short, global popular history [https://www.amazon.com/Steel-Mine-Mill-Metal-America/dp/0760347425/ excerpt]
* Woytinsky, W. S., and E. S. Woytinsky. World Population and Production Trends and Outlooks (1953) pp 1098–1143, with many tables and maps on the worldwide steel industry
* Yonekura, Seiichiro. The Japanese iron and steel industry: Continuity and discontinuity, 1850–1970 (1994) [https://www.amazon.com/Japanese-Iron-Steel-Industry-1850-1990/dp/0312106734/ excerpt and text search] | 1 | Applied and Interdisciplinary Chemistry |
The vibrational properties of LAGP could be directly probed using Raman spectroscopy. LAGP shows the Raman features characteristic of all the NASICON-type materials, most of which caused by the vibrational motions of PO units. The main spectral regions in a Raman spectrum of NASICON-type materials are summarized in the following table.
The Raman spectra of LAGP are usually characterized by broad peaks, even when the material is in its crystalline form. Indeed, both the presence of aluminium ions in place of germanium ions and the extra lithium ions introduce structural and compositional disorder in the sublattice, resulting in peak broadening. | 0 | Theoretical and Fundamental Chemistry |
Almost all known substances undergo thermal expansion in response to heating, meaning that a given mass of substance contracts to a low volume at low temperatures, when little thermal energy is present. Substances, especially fluids in which intermolecular forces are weak, also undergo compression upon the application of pressure. Nearly all substances therefore reach a density maximum at very low temperatures and very high pressures, characteristic properties of the solid state of matter. | 0 | Theoretical and Fundamental Chemistry |
Aquatic biomonitoring is the science of inferring the ecological condition of rivers, lakes, streams, and wetlands by examining the organisms (fish, invertebrates, insects, plants, and algae) that live there. While aquatic biomonitoring is the most common form of biomonitoring, any ecosystem can be studied in this manner. | 1 | Applied and Interdisciplinary Chemistry |
Sensitive electronic equipment are vulnerable to interference and unauthorized surveillance. These products also require protection from high voltages. Radio frequency (RF) shielding can address these issues by reducing the transmission of electric or magnetic fields from one space to another.
Copper is an excellent material for RF shielding because it absorbs radio and magnetic waves. Other useful properties for RF shielding is that copper has a high electrical conductivity, is ductile, malleable, and solders easily.
RF shielding enclosures filter a range of frequencies for specific conditions. Properly designed and constructed copper enclosures satisfy most RF shielding needs, from computer and electrical switching rooms to hospital CAT-scan and MRI facilities. Special attention needs to be addressed regarding potential shield penetrations, such as doors, vents, and cables.
A shield can be effective against one type of electromagnetic field but not against another. For example, a copper foil or screen RF shield will be minimally effective against power frequency magnetic fields. A power frequency magnetic shield could offer little reduction of radio frequency fields. The same is true for different RF frequencies. A simple large-mesh screen shield can work well for lower frequencies, but can be ineffective for microwaves.
Sheet copper for RF shielding can be formed into essentially any shape and size. Electrical connection to a grounding system provides an effective RF enclosure. | 1 | Applied and Interdisciplinary Chemistry |
Triplet-triplet annihilation (TTA) is an energy transfer mechanism where two molecules in their triplet excited states interact to form a ground state molecule and an excited molecule in its singlet state. This mechanism is example of Dexter energy transfer mechanism. In triplet-triplet annihilation, one molecule transfers its excited state energy to the second molecule, resulting in the first molecule returning to its ground state and the second molecule being promoted to a higher excited singlet state.
Triplet-triplet annihilation was first discovered in the 1960s to explain the observation of delayed fluorescence in anthracene derivatives. | 0 | Theoretical and Fundamental Chemistry |
1,3-diaxial strain is another form of strain similar to syn-pentane. In this case, the strain occurs due to steric interactions between a substituent of a cyclohexane ring (α) and gauche interactions between the alpha substituent and both methylene carbons two bonds away from the substituent in question (hence, 1,3-diaxial interactions). When the substituent is axial, it is brought near to an axial gamma hydrogen. The amount of strain is largely dependent on the size of the substituent and can be relieved by forming into the major chair conformation placing the substituent in an equatorial position. The difference in energy between conformations is called the A value and is well known for many different substituents. The A value is a thermodynamic parameter and was originally measured along with other methods using the Gibbs free energy equation and, for example, the Meerwein–Ponndorf–Verley reduction/Oppenauer oxidation equilibrium for the measurement of axial versus equatorial values of cyclohexanone/cyclohexanol (0.7 kcal mol). | 0 | Theoretical and Fundamental Chemistry |
Different influences at the interface may cause changes in the composition of the near-surface layer. Substances may either accumulate near the surface or, conversely, move into the bulk. The movement of the molecules characterizes the phenomena of adsorption. Adsorption influences changes in surface tension and colloid stability. Adsorption layers at the surface of a liquid dispersion medium may affect the interactions of the dispersed particles in the media and consequently these layers may play crucial role in colloid stability The adsorption of molecules of liquid phase at an interface occurs when this liquid phase is in contact with other immiscible phases that may be gas, liquid, or solid | 0 | Theoretical and Fundamental Chemistry |
Tritrophic interactions in plant defense against herbivory describe the ecological impacts of three trophic levels on each other: the plant, the herbivore, and its natural enemies. They may also be called multitrophic interactions when further trophic levels, such as soil microbes, endophytes, or hyperparasitoids (higher-order predators) are considered. Tritrophic interactions join pollination and seed dispersal as vital biological functions which plants perform via cooperation with animals.
Natural enemies—predators, pathogens, and parasitoids that attack plant-feeding insects—can benefit plants by hindering the feeding behavior of the harmful insect. It is thought that many plant traits have evolved in response to this mutualism to make themselves more attractive to natural enemies. This recruitment of natural enemies functions to protect against excessive herbivory and is considered an indirect plant defense mechanism. Traits attractive to natural enemies can be physical, as in the cases of domatia and nectaries; or chemical, as in the case of induced plant volatile chemicals that help natural enemies pinpoint a food source.
Humans can take advantage of tritrophic interactions in the biological control of insect pests. | 1 | Applied and Interdisciplinary Chemistry |
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 | Theoretical and Fundamental Chemistry |
Thiophosphates (or phosphorothioates, PS) are chemical compounds and anions with the general chemical formula (x = 0, 1, 2, or 3) and related derivatives where organic groups are attached to one or more O or S. Thiophosphates feature tetrahedral phosphorus(V) centers. | 0 | Theoretical and Fundamental Chemistry |
Lumirubin is a structural isomer of bilirubin, which is formed during phototherapy used to treat neonatal jaundice. This polar isomer resulting from the blue-green lights of phototherapy has an active site to albumin, and its effects are considered less toxic than those of bilirubin. Lumirubin is excreted into bile or urine. ZZ, ZE, EE and EZ are the four structural isomers of bilirubin. ZZ is the stable, more insoluble form. Other forms are relatively soluble and are known as lumirubins. Phototherapy converts the ZZ form into lumirubins. Monoglucuronylated lumirubins are easily excreted. | 1 | Applied and Interdisciplinary Chemistry |
Senescence in cells is a state in which cells are metabolically active but are no longer able to replicate. pRb is an important regulator of senescence in cells and since this prevents proliferation, senescence is an important antitumor mechanism. pRb may occupy E2F-regulated promoters during senescence. For example, pRb was detected on the cyclin A and PCNA promoters in senescent cells. | 1 | Applied and Interdisciplinary Chemistry |
Modern spectroscopy in the Western world started in the 17th century. New designs in optics, specifically prisms, enabled systematic observations of the solar spectrum. Isaac Newton first applied the word spectrum to describe the rainbow of colors that combine to form white light. During the early 1800s, Joseph von Fraunhofer conducted experiments with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics and astronomy. Fraunhofer observed and measured dark lines in the Sun's spectrum, which now bear his name although several of them were observed earlier by Wollaston. | 0 | Theoretical and Fundamental Chemistry |
Many cross-couplings entail forming carbon–carbon bonds.
The restrictions on carbon atom geometry mainly inhibit β-hydride elimination when complexed to the catalyst. | 0 | Theoretical and Fundamental Chemistry |
There are several ways of exposure to these hepatotoxins that humans can encounter one of which is through recreational activities like swimming, surfing, fishing, and other activities involving direct contact with contaminated water. Another rare, yet extremely toxic, route of exposure that has been identified by scientists is through hemodialysis surgeries. One of the fatal cases for microcystic intoxication through hemodialysis was studied in Brazil where 48% of patients that received the surgery in a specific period of time died because the water used in the procedure was found to be contaminated.
Microcystins are chemically stable over a wide range of temperature and pH, possibly as a result of their cyclic structure.
Microcystin-LR water contamination is resistant to boiling and microwave treatments.
Microcystin-producing bacteria algal blooms can overwhelm the filter capacities of water treatment plants. Some evidence shows the toxin can be transported by irrigation into the food chain. | 1 | Applied and Interdisciplinary Chemistry |
Corinthian bronze, also named Corinthian brass or aes Corinthiacum, was a highly valuable metal alloy in classical antiquity. It is thought to be an alloy of copper with gold or silver (or both), although it has also been contended that it was simply a very high grade of bronze, or a kind of bronze that was manufactured in Corinth. It is referred to in various ancient texts, but no certain examples of Corinthian bronze exist today. However, it has been increasingly suggested that a number of artefacts previously described as niello in fact use a technique of patinated metal that may be the same as Corinthian bronze and is similar to the Japanese Shakudō.
Its composition was long a mystery, but contemporary thinking is that Corinthian bronze was "a patinated alloy of copper with some gold and silver", perhaps the same as the hesmen kem or "black copper" of Ancient Egyptian art. This is shown by ancient texts to be a prestigious material, and apparently survives in a number of statuettes of "distinctive black-patinated, inlaid metal", of which scientific analysis shows "that some have a highly unusual composition containing small amounts of gold, silver and arsenic in the alloy", and are broadly similar to Shakudō. | 1 | Applied and Interdisciplinary Chemistry |
In nuclear physics, secular equilibrium is a situation in which the quantity of a radioactive isotope remains constant because its production rate (e.g., due to decay of a parent isotope) is equal to its decay rate. | 0 | Theoretical and Fundamental Chemistry |
In land plants, the plastids that contain chlorophyll can perform photosynthesis, thereby creating internal chemical energy from external sunlight energy while capturing carbon from Earths atmosphere and furnishing the atmosphere with life-giving oxygen. These are the chlorophyll-plastids'and they are named chloroplasts; (see top graphic).
Other plastids can synthesize fatty acids and terpenes, which may be used to produce energy or as raw material to synthesize other molecules. For example, plastid epidermal cells manufacture the components of the tissue system known as plant cuticle, including its epicuticular wax, from palmitic acidwhich itself is synthesized in the chloroplasts of the mesophyll tissue. Plastids function to store different components including starches, fats, and proteins.
All plastids are derived from proplastids, which are present in the meristematic regions of the plant. Proplastids and young chloroplasts typically divide by binary fission, but more mature chloroplasts also have this capacity.
Plant proplastids (undifferentiated plastids) may differentiate into several forms, depending upon which function they perform in the cell, (see top graphic). They may develop into any of the following variants:
* Chloroplasts: typically green plastids that perform photosynthesis.
** Etioplasts: precursors of chloroplasts.
* Chromoplasts: coloured plastids that synthesize and store pigments.
* Gerontoplasts: plastids that control the dismantling of the photosynthetic apparatus during plant senescence.
* Leucoplasts: colourless plastids that synthesize monoterpenes.
Leucoplasts differentiate into even more specialized plastids, such as:
* the aleuroplasts;
** Amyloplasts: storing starch and detecting gravityfor maintaining geotropism.
** Elaioplasts: storing fats.
** Proteinoplasts: storing and modifying protein.
* or Tannosomes: synthesizing and producing tannins and polyphenols.
Depending on their morphology and target function, plastids have the ability to differentiate or redifferentiate between these and other forms. | 0 | Theoretical and Fundamental Chemistry |
The syllogism of the school was similar to that of the Nyāya school of Hinduism, but the names given by to the 5 members of syllogism are different. | 1 | Applied and Interdisciplinary Chemistry |
Consider a typical balanced chemical reaction:
The lowercase letters (, , , and ) represent stoichiometric coefficients, while the capital letters represent the reactants ( and ) and the products ( and ).
According to IUPAC's Gold Book definition
the reaction rate for a chemical reaction occurring in a closed system at constant volume, without a build-up of reaction intermediates, is defined as:
where denotes the concentration of the substance or . The reaction rate thus defined has the units of mol/L/s.
The rate of a reaction is always positive. A negative sign is present to indicate that the reactant concentration is decreasing. The IUPAC recommends that the unit of time should always be the second. The rate of reaction differs from the rate of increase of concentration of a product P by a constant factor (the reciprocal of its stoichiometric number) and for a reactant A by minus the reciprocal of the stoichiometric number. The stoichiometric numbers are included so that the defined rate is independent of which reactant or product species is chosen for measurement. For example, if and then is consumed three times more rapidly than , but is uniquely defined. An additional advantage of this definition is that for an elementary and irreversible reaction, is equal to the product of the probability of overcoming the transition state activation energy and the number of times per second the transition state is approached by reactant molecules. When so defined, for an elementary and irreversible reaction, is the rate of successful chemical reaction events leading to the product.
The above definition is only valid for a single reaction, in a closed system of constant volume. If water is added to a pot containing salty water, the concentration of salt decreases, although there is no chemical reaction.
For an open system, the full mass balance must be taken into account:
where
* is the inflow rate of in molecules per second;
* the outflow;
* is the instantaneous reaction rate of (in number concentration rather than molar) in a given differential volume, integrated over the entire system volume at a given moment.
When applied to the closed system at constant volume considered previously, this equation reduces to:
where the concentration is related to the number of molecules by Here is the Avogadro constant.
For a single reaction in a closed system of varying volume the so-called rate of conversion can be used, in order to avoid handling concentrations. It is defined as the derivative of the extent of reaction with respect to time.
Here is the stoichiometric coefficient for substance , equal to , , , and in the typical reaction above. Also is the volume of reaction and is the concentration of substance .
When side products or reaction intermediates are formed, the IUPAC recommends the use of the terms the rate of increase of concentration and rate of the decrease of concentration for products and reactants, properly.
Reaction rates may also be defined on a basis that is not the volume of the reactor. When a catalyst is used the reaction rate may be stated on a catalyst weight (mol g s) or surface area (mol m s) basis. If the basis is a specific catalyst site that may be rigorously counted by a specified method, the rate is given in units of s and is called a turnover frequency. | 0 | Theoretical and Fundamental Chemistry |
LOV-domains are a sub-class of PAS domains and were first identified in plants as part of Phototropin, which plays an essential role in the plant's growth towards light. They noncovalently bind Flavin mononucleotide (FMN) as coenzyme. Due to the bound FMN LOV-domains exhibit an intrinsic fluorescence, which is however very weak. Upon illumination with blue light, LOV-domains undergo a photocyle, during which a covalent bond is formed between a conserved cysteine-residue and the FMN. This causes a conformational change in the protein that is necessary for signal propagation and also leads to the loss of fluorescence. The covalent bond is energetically unfavorable and is cleaved with a protein specific time constant ranging from seconds to hours.
In order to make better use of the fluorescence properties of these proteins, the natural photocycle of these LOV-domains was abolished by exchanging the conserved cysteine against an alanine on a genetic level.
Thus, upon blue light irradiation, the protein remains in the fluorescent state and also exhibits a brighter fluorescence.
The first FbFPs that were generated in this fashion were subsequently further optimized using different methods of mutagenesis. Especially the brightness but also the photostability of the proteins were enhanced and their spectral characteristics altered. | 1 | Applied and Interdisciplinary Chemistry |
As carbon dioxide concentrations rise, the rate at which sugars are made by the light-independent reactions increases until limited by other factors. RuBisCO, the enzyme that captures carbon dioxide in the light-independent reactions, has a binding affinity for both carbon dioxide and oxygen. When the concentration of carbon dioxide is high, RuBisCO will fix carbon dioxide. However, if the carbon dioxide concentration is low, RuBisCO will bind oxygen instead of carbon dioxide. This process, called photorespiration, uses energy, but does not produce sugars.
RuBisCO oxygenase activity is disadvantageous to plants for several reasons:
# One product of oxygenase activity is phosphoglycolate (2 carbon) instead of 3-phosphoglycerate (3 carbon). Phosphoglycolate cannot be metabolized by the Calvin-Benson cycle and represents carbon lost from the cycle. A high oxygenase activity, therefore, drains the sugars that are required to recycle ribulose 5-bisphosphate and for the continuation of the Calvin-Benson cycle.
# Phosphoglycolate is quickly metabolized to glycolate that is toxic to a plant at a high concentration; it inhibits photosynthesis.
# Salvaging glycolate is an energetically expensive process that uses the glycolate pathway, and only 75% of the carbon is returned to the Calvin-Benson cycle as 3-phosphoglycerate. The reactions also produce ammonia (NH), which is able to diffuse out of the plant, leading to a loss of nitrogen.
::A highly simplified summary is:
:::2 glycolate + ATP → 3-phosphoglycerate + carbon dioxide + ADP + NH
The salvaging pathway for the products of RuBisCO oxygenase activity is more commonly known as photorespiration, since it is characterized by light-dependent oxygen consumption and the release of carbon dioxide. | 0 | Theoretical and Fundamental Chemistry |
Archaeology is not the only field to make use of radiocarbon dating. Radiocarbon dates can also be used in geology, sedimentology, and lake studies, for example. The ability to date minute samples using AMS has meant that palaeobotanists and palaeoclimatologists can use radiocarbon dating directly on pollen purified from sediment sequences, or on small quantities of plant material or charcoal. Dates on organic material recovered from strata of interest can be used to correlate strata in different locations that appear to be similar on geological grounds. Dating material from one location gives date information about the other location, and the dates are also used to place strata in the overall geological timeline.
Radiocarbon is also used to date carbon released from ecosystems, particularly to monitor the release of old carbon that was previously stored in soils as a result of human disturbance or climate change. Recent advances in field collection techniques also allow the radiocarbon dating of methane and carbon dioxide, which are important greenhouse gases. | 0 | Theoretical and Fundamental Chemistry |
A wide variety of techniques can be used to analyze the interfacial layer, often SAXS, NMR, AFM, STM are used, but other methods, like measuring the refractive index can reveal information as well.
Small-angle X-ray diffraction provides data about the size and dispersion of the nanoparticles, and gives information about the density of the interfacial layer. Because the amount of scattering is proportionate with the density. On top of this the thickness of the layer can be estimated. However a disadvantage is that SAXS is destructive.
AFM and STM measurements can reveal information at atomic resolution about the structure and shape of the interfacial layer. This information is limited to the surface of the nanoparticle, as you can only probe the surface. Another drawback of STM is that it's only applicable if the interfacial layer is conducting.
(Solid-state) NMR can be used to study the composition, short range ordering and dynamics in the interfacial layer. The dynamics can be studied over a wide range of timescales, which allows the intermolecular interactions, chemical reactions and transport phenomena to be analyzed. | 0 | Theoretical and Fundamental Chemistry |
The Pyrenean ibex went extinct in 2000. In 2003 frozen cells from the last one (a female killed by a falling branch) were used to clone 208 embryos, of which 7 successfully implanted in goats, and one made it to term. That one ibex died of respiratory failure just after birth; quite possibly as a result of the cloning process, its lungs had not developed properly. There may not be enough individuals' cells preserved to create a breeding population. Despite the death of the ibex, DNA analysis revealed that the offspring was a legitimate clone from its last living descendent. | 1 | Applied and Interdisciplinary Chemistry |
The French Chemical Society's Médaille Lavoisier is given for work or actions which have enhanced the perceived value of chemistry in society. | 1 | Applied and Interdisciplinary Chemistry |
Methanation is the conversion of carbon monoxide and carbon dioxide (CO) to methane (CH) through hydrogenation. The methanation reactions of CO were first discovered by Sabatier and Senderens in 1902.
CO methanation has many practical applications. It is a means of carbon oxide removal from process gases and is also being discussed as an alternative to PROX in fuel processors for mobile fuel cell applications.
Methanation as a means of producing synthetic natural gas has been considered since the 1970s. More recently it has been considered as a way to store energy produced from solar or wind power using power-to-gas systems in conjunction with existing natural gas storage. | 0 | Theoretical and Fundamental Chemistry |
*Acidification − Browning enzymes, as other enzymes, are active at a specific range of pH. For example, PPO shows optimal activity at pH 5-7 and is inhibited below pH 3. Acidifying agents and acidity regulators are widely used as food additives to maintain a desired pH in food products. Acidulants, such as citric acid, ascorbic acid, and glutathione, are used as anti-browning agents. Many of these agents also show other anti-browning effects, such as chelating and antioxidant activities.
*Antioxidants − Many antioxidants are used in food industry as food additives. These compounds react with oxygen and suppress the initiation of the browning process. Also, they interfere with intermediate products of the following reactions and inhibit melanin formation. Ascorbic acid, N-acetylcysteine, L-cysteine, 4-hexylresorcinol, erythorbic acid, cysteine hydrochloride, glutathione are examples of antioxidants that have been studied for their anti-browning properties.
*Chelating agents − Polyphenol oxidase requires copper as a cofactor for its functionality, thus copper-chelating agents inhibit the activity of this enzyme. Many agents possessing chelating activity have been studied and used in different fields of food industry, such as citric acid, sorbic acid, polyphosphates, hinokitiol, kojic acid, EDTA, porphyrins, polycarboxylic acids, different proteins. Some of these compounds also have other anti-browning effects, such as acidifying or antioxidant. Hinokitiol is used in coating materials for food packaging. | 1 | Applied and Interdisciplinary Chemistry |
It is possible to use the FSR to predict the depth of rainfall from a storm of a given duration and return period. The FSR includes values for two key variables mapped across the UK: the M5-60 minutes rainfall, and the ratio "r".
*M5-60 minutes rainfall is the expected depth of rainfall in millimetres (mm) from a storm lasting 60 minutes (1 hour) with a return period of 5 years (hence M5).
*M5-2 days rainfall is the expected depth of rainfall from a storm lasting 2 days (48 hours) with a return period of 5 years.
*The dimensionless ratio "r" is the M5-60 minutes value divided by the M5-2 days value.
*Factor Z1 is interpolated from figures based on the values of M5-2 days and "r".
*Factor Z2 (the growth factor) is found from the M5 rainfall depth, and depends on the return period.
*The Areal Reduction Factor (ARF) takes the catchment area into account. For small catchments (below 1 km) the ARF is not required.
To find the depth of a rainfall of duration D and return period T at a given location in the UK, the following should be carried out:
# Find M5-60 minutes rainfall depth and "r" for the location using FSR maps.
# Divide this rainfall depth by "r" to get the M5-2 days depth.
# Multiply the M5-2 days depth by factor Z1 to find the M5-D depth.
# Multiply the M5-D depth by factor Z2 (the growth factor) to find the MT-D depth.
# Multiply the MT-D depth by the Areal Reduction Factor (ARF). | 1 | Applied and Interdisciplinary Chemistry |
The chiral allylic stannane 1 adds to acrolein to yield the 1,5-syn diastereomer as a single stereoisomer. A subsequent sigmatropic rearrangement increased the distance between the stereocenters even further. This step was carried out en route to (±)-patulolide C.
Repeated use of the allylic stannane addition in an intramolecular sense was used in the synthesis of hemibrevetoxin B (one example is shown below). The pseudoequatorial positions of both "appendages" in the starting material lead to the observed stereoisomer. | 0 | Theoretical and Fundamental Chemistry |
The primary advantage to hyperspectral imaging is that, because an entire spectrum is acquired at each point, the operator needs no prior knowledge of the sample, and postprocessing allows all available information from the dataset to be mined. Hyperspectral imaging can also take advantage of the spatial relationships among the different spectra in a neighbourhood, allowing more elaborate spectral-spatial models for a more accurate segmentation and classification of the image.
The primary disadvantages are cost and complexity. Fast computers, sensitive detectors, and large data storage capacities are needed for analyzing hyperspectral data. Significant data storage capacity is necessary since uncompressed hyperspectral cubes are large, multidimensional datasets, potentially exceeding hundreds of megabytes. All of these factors greatly increase the cost of acquiring and processing hyperspectral data. Also, one of the hurdles researchers have had to face is finding ways to program hyperspectral satellites to sort through data on their own and transmit only the most important images, as both transmission and storage of that much data could prove difficult and costly. As a relatively new analytical technique, the full potential of hyperspectral imaging has not yet been realized. | 0 | Theoretical and Fundamental Chemistry |
Ertl is one of the editors of the Handbook of Heterogeneous Catalysis. ()
Ertl is the co-editor of Engineering Of Chemical Complexity. 2013, World Scientific Publishing. () | 0 | Theoretical and Fundamental Chemistry |
Small hole drilling EDM is used in a variety of applications.
On wire-cut EDM machines, small hole drilling EDM is used to make a through hole in a workpiece through which to thread the wire for the wire-cut EDM operation. A separate EDM head specifically for small hole drilling is mounted on a wire-cut machine and allows large hardened plates to have finished parts eroded from them as needed and without pre-drilling.
Small hole EDM is used to drill rows of holes into the leading and trailing edges of turbine blades used in jet engines. Gas flow through these small holes allows the engines to use higher temperatures than otherwise possible. The high-temperature, very hard, single crystal alloys employed in these blades makes conventional machining of these holes with high aspect ratio extremely difficult, if not impossible.
Small hole EDM is also used to create microscopic orifices for fuel system components, spinnerets for synthetic fibers such as rayon, and other applications.
There are also stand-alone small hole drilling EDM machines with an x–y axis also known as a super drill or hole popper that can machine blind or through holes. EDM drills bore holes with a long brass or copper tube electrode that rotates in a chuck with a constant flow of distilled or deionized water flowing through the electrode as a flushing agent and dielectric. The electrode tubes operate like the wire in wire-cut EDM machines, having a spark gap and wear rate. Some small-hole drilling EDMs are able to drill through 100 mm of soft or hardened steel in less than 10 seconds, averaging 50% to 80% wear rate. Holes of 0.3 mm to 6.1 mm can be achieved in this drilling operation. Brass electrodes are easier to machine but are not recommended for wire-cut operations due to eroded brass particles causing "brass on brass" wire breakage, therefore copper is recommended. | 1 | Applied and Interdisciplinary Chemistry |
The He Jiankui affair is a scientific and bioethical controversy concerning the use of genome editing following its first use on humans by Chinese scientist He Jiankui, who edited the genomes of human embryos in 2018. He became widely known on 26 November 2018 after he announced that he had created the first human genetically edited babies. He was listed in the Time 100 most influential people of 2019. The affair led to ethical and legal controversies, resulting in the indictment of He and two of his collaborators, Zhang Renli and Qin Jinzhou. He eventually received widespread international condemnation.
He Jiankui, working at the Southern University of Science and Technology (SUSTech) in Shenzhen, China, started a project to help people with HIV-related fertility problems, specifically involving HIV-positive fathers and HIV-negative mothers. The subjects were offered standard in vitro fertilisation services and in addition, use of CRISPR gene editing (CRISPR/Cas9), a technology for modifying DNA. The embryos genomes were edited to remove the CCR5 gene in an attempt to confer genetic resistance to HIV. The clinical project was conducted secretly until 25 November 2018, when MIT Technology Review' broke the story of the human experiment based on information from the Chinese clinical trials registry. Compelled by the situation, he immediately announced the birth of genome-edited babies in a series of five YouTube videos the same day. The first babies, known by their pseudonyms Lulu () and Nana (), are twin girls born in October 2018, and the second birth or the third baby born was in 2019, named Amy. He reported that the babies were born healthy.
His actions received widespread criticism, and included concern for the girls' well-being. After his presentation on the research at the Second International Summit on Human Genome Editing at the University of Hong Kong on 28 November 2018, Chinese authorities suspended his research activities the following day. On 30 December 2019, Chinese authorities announced that he was found guilty of forging documents and unethical conduct; he was sentenced to three years in prison with a three-million-yuan fine (US$430,000). Zhang Renli and Qin Jinzhou received an 18-month prison sentence, a 500,000-yuan fine and were banned from working in assisted reproductive technology for life.
He Jiankui has been variously referred to as a "rogue scientist", "China's Dr Frankenstein", and a "mad genius". The impact of human gene editing on resistance to HIV infection and other body functions in experimental infants remains controversial. The World Health Organization had issued three reports on the guidelines of human genome editing since 2019, and the Chinese government has prepared regulations since May 2019. | 1 | Applied and Interdisciplinary Chemistry |
Molecular tagging velocimetry (MTV) is a specific form of flow velocimetry, a technique for determining the velocity of currents in fluids such as air and water. In its simplest form, a single "write" laser beam is shot once through the sample space. Along its path an optically induced chemical process is initiated, resulting in the creation of a new chemical species or in changing the internal energy state of an existing one, so that the molecules struck by the laser beam can be distinguished from the rest of the fluid. Such molecules are said to be "tagged".
This line of tagged molecules is now transported by the fluid flow. To obtain velocity information, images at two instances in time are obtained and analyzed (often by correlation of the image intensities) to determine the displacement. If the flow is three-dimensional or turbulent the line will not only be displaced, it will also be deformed. | 1 | Applied and Interdisciplinary Chemistry |
Carboxylates bind to single metals by one or both oxygen atoms, the respective notation being κ- and κ-. In terms of electron counting, κ-carboxylates are "X"-type ligands, i.e., a pseudohalide-like. κ-carboxylates are "L-X ligands", i.e. resembling the combination of a Lewis base (L) and a pseudohalide (X). Carboxylates are classified as hard ligands, in HSAB theory.
For simple carboxylates, the acetate complexes are illustrative. Most transition metal acetates are mixed ligand complexes. One common example is hydrated nickel acetate, Ni(OCCH)(HO), which features intramolecular hydrogen-bonding between the uncoordinated oxygens and the protons of aquo ligands. Stoichiometrically simple complexes are often multimetallic. One family are the basic metal acetates, of the stoichiometry [MO(OAc)(HO)]. | 0 | Theoretical and Fundamental Chemistry |
LAGP-based membranes have been applied as separators in lithium-sulfur batteries. LAGP allows the transfer of lithium ions from anode to cathode but, at the same time, prevents the diffusion of polysulfides from the cathode, suppressing the polysulfide shuttle effect and enhancing the overall performance of the battery. Typically, all-solid-state lithium-sulfur batteries are not fabricated because of high interfacial resistance; therefore, hybrid electrolytes are usually realized, in which LAGP acts as a barrier against polysulfide diffusion but it is combined with liquid or polymer electrolytes to promote fast lithium diffusion and to improve the interfacial contact with electrodes. | 0 | Theoretical and Fundamental Chemistry |
In contrast to polydentate ligands, ambidentate ligands can attach to the central atom in either one of two (or more) places, but not both. An example is thiocyanate, SCN, which can attach at either the sulfur atom or the nitrogen atom. Such compounds give rise to linkage isomerism.
Polydentate and ambidentate are therefore two different types of polyfunctional ligands (ligands with more than one functional group) which can bond to a metal center through different ligand atoms to form various isomers. Polydentate ligands can bond through one atom AND another (or several others) at the same time, whereas ambidentate ligands bond through one atom OR another. Proteins are complex examples of polyfunctional ligands, usually polydentate. | 0 | Theoretical and Fundamental Chemistry |
From the quantum statistics of a completely degenerate electron gas (all the lowest quantum states are occupied), the pressure and the density of a white dwarf are calculated in terms of the maximum electron momentum standardized as , with pressure and density , where
is the mean molecular weight of the gas, and is the height of a small cube of gas with only two possible states.
When this is substituted into the hydrostatic equilibrium equation
where is the gravitational constant and is the radial distance, we get
and letting , we have
If we denote the density at the origin as , then a non-dimensional scale
gives
where . In other words, once the above equation is solved the density is given by
The mass interior to a specified point can then be calculated
The radius-mass relation of the white dwarf is usually plotted in the plane -. | 1 | Applied and Interdisciplinary Chemistry |
Historically, the theory was used to model nonuniform adsorbates and multi-components solutes. For certain pairs of adsorbates and adsorbents, the mathematical parameters of the Polyani theory can be related to the physicochemical properties of both adsorbents and adsorbates. The theory has been used to model the adsorption of carbon nanotubes and carbon nanoparticles. In the study done by Yang and Xing, the theory have been shown to better fit the adsorption isotherm than Langmuir, Freundlich, and partition. The experiment studied the adsorption of organic molecules on carbon nanoparticles and carbon nanotubes. According to the Polyani theory the surface defect curvatures of carbon nanoparticles could affect their adsorption. Flat surfaces on the particles will allow more surface atoms to approach adsorbing organic molecules which will increase the potential, leading to stronger interactions. The theory has been beneficial in trying to understand the adsorption mechanisms of organic compounds on carbon nanoparticles and estimating the adsorption capacity and affinity. Using this theory, researchers are hoping to be able to design carbon nanoparticles for specific needs such as using them as sorbents in environmental studies. | 0 | Theoretical and Fundamental Chemistry |
Malcolm Cuthbert Nokes MC MA BSc (20 May 1897 – 22 November 1986) was a British schoolteacher, soldier, research scientist and Olympic athlete, who competed in the hammer throw and discus throw. | 0 | Theoretical and Fundamental Chemistry |
Gadolin became famous for his description of the first rare-earth element, yttrium. In 1792 Gadolin received a sample of black, heavy mineral found in a quarry in a Swedish village Ytterby near Stockholm by Carl Axel Arrhenius. By careful experiments, Gadolin determined that approximately 38% of the sample was a previously unknown "earth", an oxide which was later named yttria. Yttria, or yttrium oxide, was the first known rare-earth metal compound—at that time, it was not yet regarded as an element in the modern sense. His work was published in 1794.
The mineral that Gadolin examined was named gadolinite in 1800. The element gadolinium and its oxide gadolinia were named after Gadolin by its discoverers.
In an earlier paper in 1788 Gadolin showed that the same element can show several oxidation states, in his case Sn(II) and Sn(IV) by combining itself with larger or smaller amounts of the calcinating substance. He described the disproportionation reaction:
:2 Sn(II) Sn(0) + Sn(IV). | 1 | Applied and Interdisciplinary Chemistry |
Secreted frizzled-related protein 1, also known as SFRP1, is a protein which in humans is encoded by the SFRP1 gene. | 1 | Applied and Interdisciplinary Chemistry |
It is difficult to think physically about what the Joule–Thomson coefficient, , represents. Also, modern determinations of do not use the original method used by Joule and Thomson, but instead measure a different, closely related quantity. Thus, it is useful to derive relationships between and other, more conveniently measured quantities, as described below.
The first step in obtaining these results is to note that the Joule–Thomson coefficient involves the three variables T, P, and H. A useful result is immediately obtained by applying the cyclic rule; in terms of these three variables that rule may be written
Each of the three partial derivatives in this expression has a specific meaning. The first is , the second is the constant pressure heat capacity, , defined by
and the third is the inverse of the isothermal Joule–Thomson coefficient, , defined by
This last quantity is more easily measured than . Thus, the expression from the cyclic rule becomes
This equation can be used to obtain Joule–Thomson coefficients from the more easily measured isothermal Joule–Thomson coefficient. It is used in the following to obtain a mathematical expression for the Joule–Thomson coefficient in terms of the volumetric properties of a fluid.
To proceed further, the starting point is the fundamental equation of thermodynamics in terms of enthalpy; this is
Now "dividing through" by dP, while holding temperature constant, yields
The partial derivative on the left is the isothermal Joule–Thomson coefficient, , and the one on the right can be expressed in terms of the coefficient of thermal expansion via a Maxwell relation. The appropriate relation is
where α is the cubic coefficient of thermal expansion. Replacing these two partial derivatives yields
This expression can now replace in the earlier equation for to obtain:
This provides an expression for the Joule–Thomson coefficient in terms of the commonly available properties heat capacity, molar volume, and thermal expansion coefficient. It shows that the Joule–Thomson inversion temperature, at which is zero, occurs when the coefficient of thermal expansion is equal to the inverse of the temperature. Since this is true at all temperatures for ideal gases (see expansion in gases), the Joule–Thomson coefficient of an ideal gas is zero at all temperatures. | 0 | Theoretical and Fundamental Chemistry |
The palladacycles can be neutral, cationic, or anionic. Depending on the nature of the coordinating ligands, the neutral palladacycles can be monomers, dimers, or bis-cyclopalladated. | 0 | Theoretical and Fundamental Chemistry |
Beyond the use of armourstone, closures can also be achieved solely with sand. This method necessitates a substantial dredging capacity. In the Netherlands, sand closures have been successfully implemented in various projects, including the Oesterdam, the Philipsdam, and the construction of the Second Maasvlakte. | 1 | Applied and Interdisciplinary Chemistry |
Using chiral phosphines as spectator ligands, catalysts have been developed for catalytic asymmetric hydrosilation. A well studied reaction is the addition of trichlorosilane to styrene to give 1-phenyl-1-(trichlorosilyl)ethane:
:ClSiH + PhCH=CH → (Ph)(CH)CHSiCl
Nearly perfect enantioselectivities (ee's) can be achieved using palladium catalysts supported by binaphthyl-substituted monophosphine ligands. | 0 | Theoretical and Fundamental 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). | 0 | Theoretical and Fundamental Chemistry |
Jai Pal Mittal was born on 21 September 1940 in Meerut in the Indian state of Uttar Pradesh. He completed his graduate (BSc) and master's studies (MSc) in chemistry from the Agra University and migrated to Mumbai in 1959, looking for career opportunities. He joined the Training School of Atomic Energy Establishment, erstwhile Bhabha Atomic Research Centre and did a one-year course after which he moved to USA to join the Department of Radiation Chemistry of the University of Notre Dame, Indiana. He completed his doctoral studies (PhD) in 1967, under the guidance of A. A. Lamola and W. H. Hamill. Receiving an invitation from Willard Libby, the 1960 Nobel laureate in Chemistry, to assist him, Mittal did his post doctoral research, for over a year, at the Radiation and Nuclear Chemistry laboratory of the University of California.
In 1969, Mittal returned to India to start his career as a Pool Officer at the Bhabha Atomic Research Centre (BARC) and started working in the field of photochemistry. Two years later, in 1971, he got an opportunity to work with Professor E. Hayon at the United States Army Natick Soldier Research, Development and Engineering Center and worked there for one year. On his return to India in 1972, he formed a research group at BARC for research in photochemistry and radiation chemistry. During this period, he organized the first national symposium in Thiruvananthapuram, National Symposium on Fast Reaction Chemistry and Techniques.
Mittal continued at BARC to become the Director of Chemistry and Isotope Group and the DAE Raja Ramanna Fellow of the institution. He also holds the position of M. N. Saha Distinguished Professor of the National Academy of Sciences, India and the post of a Distinguished Professor at the University of Pune and the Indian Institute of Technology, Mumbai. During his tenure at BARC, he is known to have contributed for the establishment of a nanosecond LINAC based pulse radiolysis system at BARC and promoted the nano, pico and femtosecond pump and probe techniques to study the chemical dynamics. He is reported to have initiated a new school of research in Radiation Chemistry and Photochemistry in India and his group was successful in isotopic enrichment of hydrogen, carbon and uranium isotopes. His research findings have been recorded by way of over 300 scientific papers, published in peer reviewed journals and ResearchGate, an online scientific data repository, have listed 250 of them. He has also mentored many students in their doctoral studies.
Mittal has been associated with the Board of Research in Nuclear Sciences as a chairman of many of its basic sciences committees. He is a former president of the Indian Society of Radiation and Photochem Sciences (1997-2001), the National Academy of Sciences, India (2003–04) and the Asian Photochemistry Association (2003- 2008). He has also served the Indian National Science Academy as a council member (1998-2000) and as an additional member (2005–06). He serves as the president of the Asian and Oceanian Photochemistry Association and is a member of the education council of the University of Allahabad. He is a life member of the Indian Chemical Society where has also been a past president.
Mittal lives in Navi Mumbai in Maharashtra and continues attending seminars and conferences to deliver keynote addresses. | 0 | Theoretical and Fundamental Chemistry |
Alzheimer's disease (AD) is a neurodegenerative disease resulting from synaptic plasticity failure. BC200 RNA plays a role in the dendrites of neurons thought to modulate synthesis of proteins that influence this plasticity. Researchers posit that upregulation of BC200 RNA results in an inadequate delivery of RNA to the neuronal synapses, thus resulting in neurodegeneration. In comparing healthy brains with those with AD, it was determined that BC200 RNA is upregulated in the brains of people with AD, most notably in areas of the brain that correspond to the disease. A direct relationship was observed here, the more severe the disease, the higher the levels of BC200 RNA there were. This is in contrast to a normal aging brain where a steady decrease of this RNA is observed between the ages of 49 and 86. | 1 | Applied and Interdisciplinary Chemistry |
These multiple forms (isoforms or subtypes) of phosphodiesterase were isolated from rat brain using polyacrylamide gel electrophoresis in the early 1970s by Weiss and coworkers, and were soon afterward shown to be selectively inhibited by a variety of drugs in brain and other tissues, also by Weiss and coworkers.
The potential for selective phosphodiesterase inhibitors to be used as therapeutic agents was predicted in the 1970s by Weiss and coworkers. This prediction has now come to pass in a variety of fields (e.g. sildenafil as a PDE5 inhibitor and Rolipram as a PDE4 inhibitor). | 1 | Applied and Interdisciplinary Chemistry |
The most common sources of natural gamma rays are potassium, thorium, and uranium. These elements are found in feldspars (i.e. granites, feldspathic), volcanic and igneous rocks, sands containing volcanic ash, and clays.
Gamma-ray measurement has the following applications:
* Well to well correlation: gamma-ray log fluctuates with changes in formation mineralogy. As such, gamma-ray logs from different wells within the same field or region can be very useful for correlation purposes, because similar formations show similar features.
* Logging runs correlation: Gamma-ray tools is typically run in every logging tools runs in a well. Being a common measurement, logging data can be put on depth with each other by correlating the gamma-ray feature of each run.
* Quantitative evaluation of shaliness: Since natural radioactive elements tend to have greater concentration in shales than in other sedimentary lithologies, the total gamma ray measurement is frequently used to derive a shale volume (Ellis-1987, Rider-1996). This method however, is only likely to be used in a simple sandstone-shale formation, and is subject to error when radioactive elements are present in the sand. | 0 | Theoretical and Fundamental Chemistry |
Hot blast allowed the use of anthracite in iron smelting. It also allowed use of lower quality coal because less fuel meant proportionately less sulfur and ash.
At the time the process was invented, good coking coal was only available in sufficient quantities in Great Britain and western Germany, so iron furnaces in the US were using charcoal. This meant that any given iron furnace required vast tracts of forested land for charcoal production, and generally went out of blast when the nearby woods had been felled. Attempts to use anthracite as a fuel had ended in failure, as the coal resisted ignition under cold blast conditions. In 1831, Dr. Frederick W. Gessenhainer filed for a US patent on the use of hot blast and anthracite to smelt iron. He produced a small quantity of anthracite iron by this method at Valley Furnace near Pottsville, Pennsylvania in 1836, but due to breakdowns and his illness and death in 1838, he was not able to develop the process into large-scale production.
Anthracite was displaced by coke in the US after the Civil War. Coke was more porous and able to support the heavier loads in the vastly larger furnaces of the late 19th century. | 1 | Applied and Interdisciplinary Chemistry |
Many efforts have been made to improve the Haber–Bosch process. Many metals were tested as catalysts. The requirement for suitability is the dissociative adsorption of nitrogen (i. e. the nitrogen molecule must be split into nitrogen atoms upon adsorption). If the binding of the nitrogen is too strong, the catalyst is blocked and the catalytic ability is reduced (self-poisoning). The elements in the periodic table to the left of the iron group show such strong bonds. Further, the formation of surface nitrides makes, for example, chromium catalysts ineffective. Metals to the right of the iron group, in contrast, adsorb nitrogen too weakly for ammonia synthesis. Haber initially used catalysts based on osmium and uranium. Uranium reacts to its nitride during catalysis, while osmium oxide is rare.
According to theoretical and practical studies, improvements over pure iron are limited. The activity of iron catalysts is increased by the inclusion of cobalt. | 0 | Theoretical and Fundamental Chemistry |
DeepVelo is a neural network–based ordinary differential equation that can model complex transcriptome dynamics by describing continuous-time gene expression changes within individual cells. DeepVelo has been applied to public datasets from different sequencing platforms to (i) formulate transcriptome dynamics on different time scales, (ii) measure the instability of cell states, and (iii) identify developmental driver genes via perturbation analysis. | 1 | Applied and Interdisciplinary Chemistry |
Secondary (2°) phosphines, with the formula RPH, are prepared analogously to the primary phosphines. They are also obtained by alkali-metal reductive cleavage of triarylphosphines followed by hydrolysis of the resulting phosphide salt. The latter route is employed to prepare diphenylphosphine (PhPH). Diorganophosphinic acids, RP(O)OH, can also be reduced with diisobutylaluminium hydride. Secondary phosphines are typically protic in character.
But when modified with suitable substituents, as in certain (rare) diazaphospholenes (scheme 3), the polarity of the P-H bond can be inverted (see: umpolung) and the resulting phosphine hydride can reduce a carbonyl group as in the example of benzophenone in yet another way.
Secondary phosphines occur in cyclic forms. Three-membered rings are phosphiranes (unsaturated: phosphirenes), five-membered rings are phospholanes (unsaturated: phosphole), and six-membered rings are phosphinanes. | 0 | Theoretical and Fundamental Chemistry |
One limitation is the energy loss in methane-producing bioelectrochemical systems. This occurs as a result of overpotentials occurring at the anode, membrane, and biocathode. The energy loss reduces efficiency significantly. Another limitation is the biocathode. Because the biocathode is so important in electron exchange and methane formation, its make-up can have a dramatic effect on the efficiency of the reaction. Efforts are being made to improve the biocathodes used in electromethanogenesis through combining new and existing materials, reshaping the materials, or applying different "pre-treatments" to the biocathode surface, thereby increasing biocompatibility. | 0 | Theoretical and Fundamental Chemistry |
A microbatch usually involves immersing a very small volume of protein droplets in oil (as little as 1 µl). The reason that oil is required is because such low volume of protein solution is used and therefore evaporation must be inhibited to carry out the experiment aqueously. Although there are various oils that can be used, the two most common sealing agent are paraffin oils (described by Chayen et al.) and silicon oils (described by D’Arcy). There are also other methods for microbatching that don't use a liquid sealing agent and instead require a scientist to quickly place a film or some tape on a welled plate after placing the drop in the well.
Besides the very limited amounts of sample needed, this method also has as a further advantage that the samples are protected from airborne contamination, as they are never exposed to the air during the experiment. | 0 | Theoretical and Fundamental Chemistry |
Hypothermia continues to be a major limitation to swimming or diving in cold water. The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which consequently increases the risk of other injuries.
Other factors predisposing to immersion hypothermia include dehydration, inadequate rewarming between repetitive dives, starting a dive while wearing cold, wet dry suit undergarments, sweating with work, inadequate thermal insulation, and poor physical conditioning.
Heat is lost much more quickly in water than in air. Thus, water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia in survivors, although this is not usually the direct clinical cause of death for those who are not rescued. A water temperature of can lead to death in as little as one hour, and water temperatures near freezing can cause death in as little as 15 minutes. During the sinking of the Titanic, most people who entered the water died in 15–30 minutes.
The actual cause of death in cold water is usually the bodily reactions to heat loss and to freezing water, rather than hypothermia (loss of core temperature) itself. For example, plunged into freezing seas, around 20% of victims die within two minutes from cold shock (uncontrolled rapid breathing, and gasping, causing water inhalation, massive increase in blood pressure and cardiac strain leading to cardiac arrest, and panic); another 50% die within 15–30 minutes from cold incapacitation: inability to use or control limbs and hands for swimming or gripping, as the body "protectively" shuts down the peripheral muscles of the limbs to protect its core. Exhaustion and unconsciousness cause drowning, claiming the rest within a similar time. | 1 | Applied and Interdisciplinary Chemistry |
Cast iron piping was traditionally made with one "spigot" end (plain, which was cut to length as needed) and one "socket" or "hub" end (cup-shaped). The larger-diameter hub was also called a "bell" because of its shape.
In use, the spigot of one segment was placed into the socket of the preceding one, and a ring of oakum was forced down into the joint with a caulking iron. Then the remainder of the space in the hub was filled up. Ideally, this would be done by pouring molten lead, allowing it to set, and hammering it tightly with a caulking tool. If this was not possible due to position or some other constraint, the joint could be filled with lead wool or rope, which was forcibly compacted one layer at a time.
This labor-intensive technique was durable if appropriately done but required time, skill, and patience for each joint to be made up. Quicker and lower-cost methods, such as rubber sleeve joints, have replaced mainly leaded hub connections of cast-iron piping in most new installations, but the older technology may still be used for some repairs. In addition, some conservative plumbing codes still require leaded hub joints for final connections where the sewer main leaves a building. | 1 | Applied and Interdisciplinary Chemistry |
*Heat treatment − Treating food with heat, such as blanching or roasting, de-naturates enzymes and destroys the reactants responsible for browning. Blanching is used, for example, in winemaking, tea processing, storing nuts and bacon, and preparing vegetables for freezing preservation. Meat is often partially browned under high heat before being incorporated into a larger preparation to be cooked at a lower temperature which produces less browning.
*Cold treatment − Refrigeration and freezing are the most common ways of storing food, preventing decay. The activity of browning enzymes, i.e., rate of reaction, drops in low temperatures. Thus, refrigeration helps to keep the initial look, color, and flavour of fresh vegetables and fruits. Refrigeration is also used during distribution and retailing of fruits and vegetables.
*Oxygen elimination − Presence of oxygen is crucial for enzymatic browning, therefore eliminating oxygen from the environment helps to slow down the browning reaction. Withdrawing air or replacing it with other gases (e.g., N or CO) during preservation, such as in vacuum-packaging or modified atmosphere packaging, wine or juice bottling, using impermeable films or edible coatings, dipping into salt or sugar solutions, keeps the food away from direct contact with oxygen. Impermeable films made of plastic or other materials prevent food being exposed to oxygen in the air and avoid moisture loss. There is an increasing activity in developing packaging materials impregnated with antioxidants, antimicrobial, and antifungal substances, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), tocopherols, hinokitiol, lysozyme, nisin, natamycin, chitosan, and ε-polylysine. Edible coatings can be made of polysaccharides, proteins, lipids, vegetable skins, plants or other natural products.
*Irradiation − Food irradiation using UV-C, gamma rays, x-rays, and electron beams is another method to extend the food shelf life. Ionizing radiation inhibits the vitality of microorganisms responsible for food spoilage and delays the maturation and sprouting of preserving vegetables and fruits. | 1 | Applied and Interdisciplinary Chemistry |
Crystal chemistry is the study of the principles of chemistry behind crystals and their use in describing structure-property relations in solids, as well as the chemical properties of periodic structures. The principles that govern the assembly of crystal and glass structures are described, models of many of the technologically important crystal structures (alumina, quartz, perovskite) are studied, and the effect of crystal structure on the various fundamental mechanisms responsible for many physical properties are discussed.
The objectives of the field include:
#identifying important raw materials and minerals as well as their names and chemical formulae.
#describing the crystal structure of important materials and determining their atomic details
#learning the systematics of crystal and glass chemistry.
#understanding how physical and chemical properties are related to crystal structure and microstructure.
#studying the engineering significance of these ideas and how they relate to foreign products: past, present, and future.
Topics studied are:
#Chemical bonding, Electronegativity
#Fundamentals of crystallography: crystal systems, Miller Indices, symmetry elements, bond lengths and radii, theoretical density
#Crystal and glass structure prediction: Pauling's and Zachariasen’s rules
#Phase diagrams and crystal chemistry (including solid solutions)
#Imperfections (including defect chemistry and line defects)
#Phase transitions
#Structure – property relations: Neumann's law, melting point, mechanical properties (hardness, slip, cleavage, elastic moduli), wetting, thermal properties (thermal expansion, specific heat, thermal conductivity), diffusion, ionic conductivity, refractive index, absorption, color, Dielectrics and Ferroelectrics, and Magnetism
#Crystal structures of representative metals, semiconductors, polymers, and ceramics | 0 | Theoretical and Fundamental Chemistry |
In atomic, molecular, and optical physics, a magneto-optical trap (MOT) is an apparatus which uses laser cooling and a spatially-varying magnetic field to create a trap which can produce samples of cold, neutral atoms. Temperatures achieved in a MOT can be as low as several microkelvin, depending on the atomic species, which is two or three times below the photon recoil limit. However, for atoms with an unresolved hyperfine structure, such as , the temperature achieved in a MOT will be higher than the Doppler cooling limit.
A MOT is formed from the intersection of a weak, quadrupolar, spatially-varying magnetic field and six circularly-polarized, red-detuned, optical molasses beams. As atoms travel away from the field zero at the center of the trap (halfway between the coils), the spatially-varying Zeeman shift brings an atomic transition into resonance which gives rise to a scattering force that pushes the atoms back towards the center of the trap. This is why a MOT traps atoms, and because this force arises from photon scattering in which atoms receive momentum "kicks" in the direction opposite their motion, it also slows the atoms (i.e. cools them), on average, over repeated absorption and spontaneous emission cycles. In this way, a MOT is able to trap and cool atoms with initial velocities of hundreds of meters per second down to tens of centimeters per second (again, depending upon the atomic species).
Although charged particles can be trapped using a Penning trap or a Paul trap using a combination of electric and magnetic fields, those traps are ineffective for neutral atoms. | 0 | Theoretical and Fundamental Chemistry |
* Academician Nikolai Dmitrievich Zelinsky: Ninetieth birthday. Sat. - M., 1952.
* Zelinsky A.N. [http://www.rv.ru/content.php3?id=11132 Спаси и сохрани: К 100-летию «Противогаза Зелинского»] // Russian Bulletin - 07/03/2015.
* Zelinsky Nikolai Dmitrievich // Great Soviet Encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
* Kazansky B. A., Nesmeyanov A. N., Plate A. F. Работы академика Н. Д. Зелинского и его школы в области химии углеводородов и органического катализа. / Ученые записки МГУ. Issue. 175. - M., 1956.
* Moscow University in the Great Patriotic War. - 4th, revised and supplemented. Moscow: Moscow University Press, 2020 - 1000 copies. - ISBN 978-5-19-011499-7.
* Nametkin S. S. President of the Moscow Society of Naturalists, Academician Nikolai Dmitrievich Zelinsky: On the occasion of his 80th birthday. - B. m., 1941.
* Nikolai Dmitrievich Zelinsky / USSR Academy of Sciences. — M.; L .: Publishing house of the Academy of Sciences of the USSR, 1946. - 88 p. - (Materials for the bio-bibliography of scientists of the USSR. Series of chemical sciences. Issue 1).
* Plate A.F. Nikolai Dmitrievich Zelinsky // People of Russian science: Mathematics - Mechanics - Astronomy - Physics - Chemistry. - M., 1961.
* Sysoeva E. K., Terentiev P. B. ZELINSKY Nikolai Dmitrievich // Imperial Moscow University: 1755-1917: encyclopedic dictionary / compiled by A. Yu. Andreev, D. A. Tsygankov. - M.: Russian Political Encyclopedia (ROSSPEN), 2010. - S. 254-255. — 894 p. - 2000 copies. — ISBN 978-5-8243-1429-8.
* Figurovsky N. A. Essay on the emergence and development of a coal gas mask by N. D. Zelinsky. M., 1952.
* Yuryev Yu. K., Levina R. Ya. / Sci. ed. Ioffe S.T.; Moscow Society of Naturalists. — M.: MOIP, 1953. — 120 p. - (Historical series; No. 48). - 7000 copies. | 0 | Theoretical and Fundamental Chemistry |
Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly. The atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate (multiple bonded) ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; ligands with 2, 3, 4 or even 6 bonds to the central atom are common. These complexes are called chelate complexes; the formation of such complexes is called chelation, complexation, and coordination.
The central atom or ion, together with all ligands, comprise the coordination sphere. The central atoms or ion and the donor atoms comprise the first coordination sphere.
Coordination refers to the "coordinate covalent bonds" (dipolar bonds) between the ligands and the central atom. Originally, a complex implied a reversible association of molecules, atoms, or ions through such weak chemical bonds. As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong.
The number of donor atoms attached to the central atom or ion is called the coordination number. The most common coordination numbers are 2, 4, and especially 6. A hydrated ion is one kind of a complex ion (or simply a complex), a species formed between a central metal ion and one or more surrounding ligands, molecules or ions that contain at least one lone pair of electrons.
If all the ligands are monodentate, then the number of donor atoms equals the number of ligands. For example, the cobalt(II) hexahydrate ion or the hexaaquacobalt(II) ion [Co(HO)] is a hydrated-complex ion that consists of six water molecules attached to a metal ion Co. The oxidation state and the coordination number reflect the number of bonds formed between the metal ion and the ligands in the complex ion. However, the coordination number of Pt(en) is 4 (rather than 2) since it has two bidentate ligands, which contain four donor atoms in total.
Any donor atom will give a pair of electrons. There are some donor atoms or groups which can offer more than one pair of electrons. Such are called bidentate (offers two pairs of electrons) or polydentate (offers more than two pairs of electrons). In some cases an atom or a group offers a pair of electrons to two similar or different central metal atoms or acceptors—by division of the electron pair—into a three-center two-electron bond. These are called bridging ligands. | 0 | Theoretical and Fundamental Chemistry |
The Boussinesq approximation is applied to problems where the fluid varies in temperature (or composition) from one place to another, driving a flow of fluid and heat transfer (or mass transfer). The fluid satisfies conservation of mass, conservation of momentum and conservation of energy. In the Boussinesq approximation, variations in fluid properties other than density are ignored, and density only appears when it is multiplied by , the gravitational acceleration. If is the local velocity of a parcel of fluid, the continuity equation for conservation of mass is
If density variations are ignored, this reduces to
The general expression for conservation of momentum of an incompressible, Newtonian fluid (the Navier–Stokes equations) is
where (nu) is the kinematic viscosity and is the sum of any body forces such as gravity. In this equation, density variations are assumed to have a fixed part and another part that has a linear dependence on temperature:
where is the coefficient of thermal expansion. The Boussinesq approximation states that the density variation is only important in the buoyancy term.
If is the gravitational body force, the resulting conservation equation is
In the equation for heat flow in a temperature gradient, the heat capacity per unit volume, , is assumed constant and the dissipation term is ignored. The resulting equation is
where is the rate per unit volume of internal heat production and is the thermal conductivity.
The three numbered equations are the basic convection equations in the Boussinesq approximation. | 1 | Applied and Interdisciplinary Chemistry |
The theories developed in the early 20th century to integrate Mendelian genetics with Darwinian evolution are called the modern synthesis, a term introduced by Julian Huxley.
This view of evolution was emphasized by George C. Williams' gene-centric view of evolution. He proposed that the Mendelian gene is a unit of natural selection with the definition: "that which segregates and recombines with appreciable frequency." Related ideas emphasizing the centrality of Mendelian genes and the importance of natural selection in evolution were popularized by Richard Dawkins.
The development of the neutral theory of evolution in the late 1960s led to the recognition that random genetic drift is a major player in evolution and that neutral theory should be the null hypothesis of molecular evolution. This led to the construction of phylogenetic trees and the development of the molecular clock, which is the basis of all dating techniques using DNA sequences. These techniques are not confined to molecular gene sequences but can be used on all DNA segments in the genome. | 1 | Applied and Interdisciplinary Chemistry |
Epoxidation of allyl- and vinylsilanes can be easily accomplished with peracids. Silyl epoxides can be converted into ketones, aldehydes, or alkenes after selective epoxide opening and elimination. When allylsilanes are combined with peracids, the intermediate epoxides are usually converted to allylic alcohols before isolation.
Halogen electrophiles, primarily X, react with vinyl- and allylsilanes to give a number of halogenated products. Further reaction of the initial adducts is common, and may lead, for instance, to conjugated dienes. Dienes may react further with X under the reaction conditions or undergo [4+2] cycloadditions in the presence of dienophiles.
A few metal electrophiles react with allylsilanes to give interesting products. Reactions of allylsilanes with thallium tris (trifluoroacetate) form electrophilic allylthallium(II) compounds. Palladation of allylsilanes provides π-allylpalladium compounds. | 0 | Theoretical and Fundamental Chemistry |
The process of transcription (by any polymerase) involves three main stages:
*Initiation, requiring the construction of the RNA polymerase complex on the gene's promoter
*Elongation, the synthesis of the RNA transcript
*Termination, the finishing of RNA transcription, and disassembly of the RNA polymerase complex | 1 | Applied and Interdisciplinary Chemistry |
Prior to the discovery of archaea capable of ammonia oxidation, ammonia-oxidizing bacteria (AOB) were considered the only organisms capable of ammonia oxidation. Since their discovery in 2005, two isolates of AOAs have been cultivated: Nitrosopumilus maritimus and Nitrososphaera viennensis. When comparing AOB and AOA, AOA dominate in both soils and marine environments, suggesting that Nitrososphaerota (formerly Thaumarchaeota) may be greater contributors to ammonia oxidation in these environments.
Crenarchaeol, which is generally thought to be produced exclusively by AOA (specifically Nitrososphaerota), has been proposed as a biomarker for AOA and ammonia oxidation. Crenarchaeol abundance has been found to track with seasonal blooms of AOA, suggesting that it may be appropriate to use crenarchaeol abundances as a proxy for AOA populations and thus ammonia oxidation more broadly. However the discovery of Nitrososphaerota that are not obligate ammonia-oxidizers complicates this conclusion, as does one study that suggests that crenarchaeol may be produced by Marine Group II Euryarchaeota. | 1 | Applied and Interdisciplinary Chemistry |
All the above kiln designs produce exhaust gas that carries an appreciable amount of dust. Lime dust is particularly corrosive. Equipment is installed to trap this dust, typically in the form of electrostatic precipitators or bag filters. The dust usually contains a high concentration of elements such as alkali metals, halogens and sulfur. | 1 | Applied and Interdisciplinary Chemistry |
The same procedure as used in acidic medium can be applied, for example, to balance the complete combustion of propane:
:Unbalanced reaction: CH + O → CO + HO
:Reduction: 4 H + O + 4 e → 2 HO
:Oxidation: 6 HO + CH → 3 CO + 20 e + 20 H
By multiplying the stoichiometric coefficients so the numbers of electrons in both half reaction match:
:20 H + 5 O + 20 e → 10 HO
:6 HO + CH → 3 CO + 20 e + 20 H
the balanced equation is obtained:
:CH + 5 O → 3 CO + 4 HO | 0 | Theoretical and Fundamental Chemistry |
The biofilm that develops in a trickling filter may become several millimetres thick and is typically a gelatinous matrix that may contain many species of bacteria, ciliates and amoeboid protozoa, annelids, round worms, insect larvae, other microfauna. (If annelids are abundant, the filter may be considered a vermifilter.) This is very different from many other biofilms, which may be less than 1 mm thick. Within the biofilm, both aerobic and anaerobic zones can exist supporting both oxidative and reductive biological processes. At certain times of year, especially in the spring, rapid growth of organisms in the film may cause the film to be too thick and it may slough off in patches leading to the "spring slough". | 1 | Applied and Interdisciplinary Chemistry |
These 35 primordial nuclides represent radioisotopes of 28 distinct chemical elements (cadmium, neodymium, osmium, samarium, tellurium, uranium, and xenon each have two primordial radioisotopes). The radionuclides are listed in order of stability, with the longest half-life beginning the list. These radionuclides in many cases are so nearly stable that they compete for abundance with stable isotopes of their respective elements.
For three chemical elements, indium, tellurium, and rhenium, a very long-lived radioactive primordial nuclide is found in greater abundance than a stable nuclide.
The longest-lived radionuclide known, Te, has a half-life of , which is 160 trillion times the age of the Universe. Only four of these 35 nuclides have half-lives shorter than, or equal to, the age of the universe. Most of the remaining 30 have half-lives much longer. The shortest-lived primordial isotope, U, has a half-life of 703.8 million years, about one sixth of the age of the Earth and the Solar System. Many of these nuclides decay by double beta decay, although some like Bi decay by other methods such as alpha decay.
At the end of the list, two more nuclides have been added: Sm and Pu. They have not been confirmed as primordial, but their half-lives are long enough that minute quantities should persist today. | 0 | Theoretical and Fundamental Chemistry |
The properties of a material in nanoparticle form are unusually different from those of the bulk one even when divided into micrometer-size particles. Many of them arise from spatial confinement of sub-atomic particles (i.e. electrons, protons, photons) and electric fields around these particles. The large surface to volume ratio is also significant factor at this scale. | 0 | Theoretical and Fundamental Chemistry |
Laminin–111 (also "laminin–1") is a protein of the type known as laminin isoforms. It was among the first of the laminin isoforms to be discovered. The "111" identifies the isoform's chain composition of α1β1γ1. This protein plays an important role in embryonic development. Injections of this substance are used in treatment for Duchenne muscular dystrophy, and its cellular action may potentially become a focus of study in cancer research. | 0 | Theoretical and Fundamental Chemistry |
Phosphorus tribromide, like PCl and PF, has both properties of a Lewis base and a Lewis acid. For example, with a Lewis acid such as boron tribromide it forms stable 1 :1 adducts such as BrB · PBr. At the same time PBr can react as an electrophile or Lewis acid in many of its reactions, for example with amines.
An important reaction of PBr is with alcohols, where it replaces an OH group with a bromine atom to produce an alkyl bromide. All three bromides can be transferred.
Several detailed procedures are available. In some cases, triphenylphosphine/Br is superior to PBr.
The mechanism for a primary alcohol involves formation of a phosphorous ester (to form a good leaving group), followed by an S2 substitution.
Because of the S2 substitution step, the reaction generally works well for primary and secondary alcohols, but fails for tertiary alcohols. If the reacting carbon centre is chiral, the reaction usually occurs with inversion of configuration at the carbon alpha to the alcohol, as is usual with an S2 reaction.
In a similar reaction, PBr also converts carboxylic acids to acyl bromides: | 0 | Theoretical and Fundamental Chemistry |
GCaMP is a genetically encoded calcium indicator (GECI) initially developed in 2001 by Junichi Nakai. It is a synthetic fusion of green fluorescent protein (GFP), calmodulin (CaM), and M13, a peptide sequence from myosin light-chain kinase. When bound to Ca, GCaMP fluoresces green with a peak excitation wavelength of 480 nm and a peak emission wavelength of 510 nm. It is used in biological research to measure intracellular Ca levels both in vitro and in vivo using virally transfected or transgenic cell and animal lines. The genetic sequence encoding GCaMP can be inserted under the control of promoters exclusive to certain cell types, allowing for cell-type specific expression of GCaMP. Since Ca is a second messenger that contributes to many cellular mechanisms and signaling pathways, GCaMP allows researchers to quantify the activity of Ca-based mechanisms and study the role of Ca ions in biological processes of interest. | 1 | Applied and Interdisciplinary Chemistry |
Winifred Burks-Houck was born on August 20, 1950, in Anniston, Alabama, to parents Matthew Burks and Mary Emma Goodson-Burks. She was the great, great, great-granddaughter of noted abolitionist Harriet Tubman.
Burks-Houck pledged as a member of the Delta Sigma Theta Sorority as an undergraduate student at Dillard University. After graduation, she remained a loyal member of the San Francisco-Peninsula Alumnae Chapter of the sorority to continue their mission of community advocacy and activism. She served in various leadership roles during her time in alumnae chapter, holding positions as the president from 1987 – 1989, vice-president, chair of fundraising and chapter coordinator for the annual Soul Stroll for Health. At the Delta Sigma Theta's 43rd annual national convention, Burks-Houck was recognized as a Project Cherish Honoree for her outstanding work in the field of science. | 0 | Theoretical and Fundamental Chemistry |
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