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Global sales of proprietary drugs are estimated $735 billion in 2010, or almost 90% of the total pharma market. Global sales of generics are about $100 billion, or just over 10% of the total pharma market. Due to the much lower unit price, their market share will be close to 30% on an API volume/volume basis. | 0 | Organic Chemistry |
Sulfur trioxide pyridine complex is the compound with the formula CHNSO. It is a colourless solid that dissolves in polar organic solvents. It is the adduct formed from the Lewis base pyridine and the Lewis acid sulfur trioxide. The compound is mainly used as a source of sulfur trioxide, for example in the synthesis of sulfate esters from alcohols:
:ROH + CHNSO → [CHNH][ROSO]
It also is useful for sulfamations:
:RNH + CHNSO → CHN + RNSOH
The compound is used for sulfonylation reactions, especially in the sulfonylation of furans. It is also an activating electrophile in a Parikh-Doering oxidation. | 0 | Organic Chemistry |
Photothermal effect is a phenomenon associated with electromagnetic radiation. It is produced by the photoexcitation of material, resulting in the production of thermal energy (heat).
It is sometimes used during treatment of blood vessel lesions, laser resurfacing, laser hair removal and laser surgery. | 7 | Physical Chemistry |
This is the oldest and still most commonly used technique, particularly for flame AAS. In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background absorption over the entire width of the exit slit of the spectrometer. The use of a separate lamp makes this technique the least accurate one, as it cannot correct for any structured background. It also cannot be used at wavelengths above about 320 nm, as the emission intensity of the deuterium lamp becomes very weak. The use of deuterium HCL is preferable compared to an arc lamp due to the better fit of the image of the former lamp with that of the analyte HCL. | 3 | Analytical Chemistry |
According to ISO 13600, an energy carrier is either a substance or a phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes. It is any system or substance that contains energy for conversion as usable energy later or somewhere else. This could be converted for use in, for example, an appliance or vehicle. Such carriers include springs, electrical batteries, capacitors, pressurized air, dammed water, hydrogen, petroleum, coal, wood, and natural gas.
ISO 13600 series (ISO 13600, ISO 13601, and ISO 13602) are intended to be used as tools to define, describe, analyse and compare technical energy systems (TES) at micro and macro levels:
*ISO 13600 (Technical energy systems — Basic concepts) covers basic definitions and terms needed to define and describe TESs in general and TESs of energyware supply and demand sectors in particular.
*ISO 13601 (Technical energy systems — Structure for analysis — Energyware supply and demand sectors) covers structures that shall be used to describe and analyse sub-sectors at the macro level of energyware supply and demand
*ISO 13602 (all parts) facilitates the description and analysis of any technical energy systems. | 7 | Physical Chemistry |
Flexibility
Your DNA sequence of interest can be moved across any expression system in just one recombination step when you create the entry clone with it.
Speed
Instead of taking two or more days with conventional restriction and ligation cloning, the Gateway approach allows for the creation of the expression construct in just one day. The attB-PCR products can also be immediately cloned into the target vectors by performing the BP and LR reactions in the same tube. There are no procedures for restriction, ligation, or gel purification during the cloning process.
Multiple fragment cloning
Gateway cloning can be used to simultaneously insert several DNA pieces into numerous vectors in a single tube. To create the necessary expression clone, up to four DNA segments can be cloned into a single Gateway vector in a precise order and orientation in a single tube. The design of the Gateway vectors makes this possible.
High efficiency
The Gateway Cloning Method uses positive and negative selection markers to increase the chance of successfully cloning a gene. This means that the process is more efficient, meaning it is more likely to produce successful results.
Universality
All types of DNA fragments can be cloned using PCR techniques. Cloning is available for many different kinds of organisms, from mammals to bacteria. | 1 | Biochemistry |
The European Union Waste Electrical and Electronic Equipment Directive and Restriction of Hazardous Substances Directive were adopted in early 2003 and came into effect on July 1, 2006, restricting the inclusion of lead in most consumer electronics sold in the EU, and having a broad effect on consumer electronics sold worldwide. In the US, manufacturers may receive tax benefits by reducing the use of lead-based solder. Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 50 to 200 °C higher, though there are also solders with much lower melting points. Lead-free solder typically requires around 2% flux by mass for adequate wetting ability.
When lead-free solder is used in wave soldering, a slightly modified solder pot may be desirable (e.g. titanium liners or impellers) to reduce maintenance cost due to increased tin-scavenging of high-tin solder.
Lead-free solder is prohibited in critical applications, such as aerospace, military and medical projects, because joints are likely to suffer from metal fatigue failure under stress (such as that from thermal expansion and contraction). Although this is a property that conventional leaded solder possesses as well (like any metal), the point at which stress fatigue will usually occur in leaded solder is substantially above the level of stresses normally encountered.
Tin-silver-copper (Sn-Ag-Cu, or SAC) solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior (), which is below the 22/78 Sn-Ag (wt.%) eutectic of and the 99.3/0.7 Sn-Cu eutectic of . The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.
Much recent research has focused on the addition of a fourth element to Sn-Ag-Cu solder, in order to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays. Examples of these four-element compositions are 18/64/14/4 tin-silver-copper-zinc (Sn-Ag-Cu-Zn) (melting range 217–220 °C) and 18/64/16/2 tin-silver-copper-manganese (Sn-Ag-Cu-Mn; melting range of 211–215 °C).
Tin-based solders readily dissolve gold, forming brittle intermetallic joins; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layers as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silver are suitable; tin-free alloys are also a choice, though their wetting ability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull. | 8 | Metallurgy |
As discussed above in types, a swept-tuned spectrum analyzer down-converts a portion of the input signal spectrum to the center frequency of a band-pass filter by sweeping the voltage-controlled oscillator through a range of frequencies, enabling the consideration of the full frequency range of the instrument.
The bandwidth of the band-pass filter dictates the resolution bandwidth, which is related to the minimum bandwidth detectable by the instrument. As demonstrated by the animation to the right, the smaller the bandwidth, the more spectral resolution. However, there is a trade-off between how quickly the display can update the full frequency span under consideration and the frequency resolution, which is relevant for distinguishing frequency components that are close together. For a swept-tuned architecture, this relation for sweep time is useful:
Where ST is sweep time in seconds, k is proportionality constant, Span is the frequency range under consideration in hertz, and RBW is the resolution bandwidth in Hertz.
Sweeping too fast, however, causes a drop in displayed amplitude and a shift in the displayed frequency.
Also, the animation contains both up- and down-converted spectra, which is due to a frequency mixer producing both sum and difference frequencies. The local oscillator feedthrough is due to the imperfect isolation from the IF signal path in the mixer.
For very weak signals, a pre-amplifier is used, although harmonic and intermodulation distortion may lead to the creation of new frequency components that were not present in the original signal. | 7 | Physical Chemistry |
For the special case of simple cubic crystals, the lattice vectors are orthogonal and of equal length (usually denoted a); similarly for the reciprocal lattice. So, in this common case, the Miller indices (ℓmn) and [ℓmn] both simply denote normals/directions in Cartesian coordinates. For cubic crystals with lattice constant a, the spacing d between adjacent (ℓmn) lattice planes is (from above):
Because of the symmetry of cubic crystals, it is possible to change the place and sign of the integers and have equivalent directions and planes:
*Coordinates in angle brackets such as denote a family of directions that are equivalent due to symmetry operations, such as [100], [010], [001] or the negative of any of those directions.
*Coordinates in curly brackets or braces such as {100} denote a family of plane normals that are equivalent due to symmetry operations, much the way angle brackets denote a family of directions.
For face-centered cubic (fcc) and body-centered cubic (bcc) lattices, the primitive lattice vectors are not orthogonal. However, in these cases the Miller indices are conventionally defined relative to the lattice vectors of the cubic supercell and hence are again simply the Cartesian directions. | 3 | Analytical Chemistry |
* Gene therapy for color blindness
* Gene therapy for epilepsy
* Gene therapy for osteoarthritis
* Gene therapy in Parkinson's disease
* Gene therapy of the human retina
Gene therapies are under development for:
* Usher syndrome deafness
* Otoferlin mutation deafness | 1 | Biochemistry |
In instances in which DNA samples are degraded, like if there are intense fires or all that remains are bone fragments, standard STR testing on those samples can be inadequate. When standard STR testing is done on highly degraded samples, the larger STR loci often drop out, and only partial DNA profiles are obtained. Partial DNA profiles can be a powerful tool, but the probability of a random match is larger than if a full profile was obtained. One method that has been developed to analyse degraded DNA samples is to use miniSTR technology. In the new approach, primers are specially designed to bind closer to the STR region.
In normal STR testing, the primers bind to longer sequences that contain the STR region within the segment. MiniSTR analysis, however, targets only the STR location, which results in a DNA product that is much smaller.
By placing the primers closer to the actual STR regions, there is a higher chance that successful amplification of this region will occur. Successful amplification of those STR regions can now occur, and more complete DNA profiles can be obtained. The success that smaller PCR products produce a higher success rate with highly degraded samples was first reported in 1995, when miniSTR technology was used to identify victims of the Waco fire. | 1 | Biochemistry |
Common crystals exhibit broken translation symmetry: they have repeated patterns in space and are not invariant under arbitrary translations or rotations. The laws of physics are unchanged by arbitrary translations and rotations. However, if we hold fixed the atoms of a crystal, the dynamics of an electron or other particle in the crystal depend on how it moves relative to the crystal, and particle momentum can change by interacting with the atoms of a crystal — for example in Umklapp processes. Quasimomentum, however, is conserved in a perfect crystal.
Time crystals show a broken symmetry analogous to a discrete space-translation symmetry breaking. For example, the molecules of a liquid freezing on the surface of a crystal can align with the molecules of the crystal, but with a pattern less symmetric than the crystal: it breaks the initial symmetry. This broken symmetry exhibits three important characteristics:
* the system has a lower symmetry than the underlying arrangement of the crystal,
* the system exhibits spatial and temporal long-range order (unlike a local and intermittent order in a liquid near the surface of a crystal),
* it is the result of interactions between the constituents of the system, which align themselves relative to each other. | 3 | Analytical Chemistry |
Protein adsorption often results in significant conformational changes, which refers to changes in the secondary, tertiary, and quartary structures of proteins. In addition to adsorption rates and amounts, orientation and conformation are of critical importance. These conformational changes can affect protein interaction with ligands, substrates, and antigens which are dependent on the orientation of the binding site of interest. These conformational changes, as a result of protein adsorption, can also denature the protein and change its native properties. | 1 | Biochemistry |
Ammonolysis can be used to synthesize nitrides (and oxynitrides) by reacting various metal precursors with ammonia, some options include chemical vapor deposition, treating metals or metal oxides with ammonia gas, or liquid supercritical ammonia (also known as "ammonothermal" synthesis, analogous to hydrothermal synthesis).
The products of these reactions may be complex, with mixtures of oxygen, nitrogen, and hydrogen that can be difficult to characterize. | 1 | Biochemistry |
Some polysilicates are ladder polymers. One example is provided by the mineral tremolite.
In the area of coordination chemistry, the ladder structure is seen in some coordination polymers. Illustrative is the polymer [CuI(2-picoline]. When the 2-picoline is replaced by a tertiary phosphine, it forms a tetrameric cubane-type cluster, [CuI(PR. In both cases, the Cu(I) centers adopt tetrahedral molecular geometry. | 7 | Physical Chemistry |
The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring. It was the German chemist Carl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene). In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene. | 2 | Environmental Chemistry |
Lactobacillus fermentation and accompanying production of acid provides a protective vaginal microbiome that protects against the proliferation of pathogenic organisms. | 1 | Biochemistry |
The saprobic index is only regarded as a valid estimate if the sum of the abundance classes is at least 20. For example, if a survey only found a total of 500 individuals of any species, the sample would still be valid if the survey found four species with 125 individuals each (abundance class 5).
Likewise, a single water body has to be surveyed several times in different months in order to account for fluctuations.
During its history, several correcting factors have been introduced. For example, they deal with the flow rate of the river (fast-flowing water bodies are inherently better oxygenated, thus speeding up organic matter degradation), water acidification, and human-made changes to the water body. Likewise, corrections must be applied for the altitude of the ecosystem (lowland rivers naturally carry more organic matter than mountainous ones, where biomass production is lower), and for the different size of catchment areas.
The saprobic system was never designed to accurately indicate water quality if only a selection of organisms is surveyed. Deviations can be sizeable if a survey only studies ciliates and members of the macrozoobenthos (benthos animals larger than 1 millimeter), as the latter's abundance can be easily influenced by oxygen levels and not by the availability of organic matter. | 2 | Environmental Chemistry |
The sample suspended in a suitable medium is placed in a hermetically closed metabolic chamber. The mitochondria are brought into defined “states” by the sequential addition of substrates or inhibitors. Since the mitochondria consume oxygen, the oxygen concentration drops. This change of oxygen concentration is recorded by an oxygen sensor in the chamber. From the rate of the oxygen decline (taking into account correction for oxygen diffusion) the respiratory rate of the mitochondria can be computed. | 1 | Biochemistry |
*Vibration - either sinusoidal vibration or gyratory vibration.
**Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The vibration is in a wave pattern determined by frequency and amplitude.
**Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion.
*Gravity - This physical interaction is after material is thrown from the screen causing it to fall to a lower level. Gravity also pulls the particles through the screen media.
*Density - The density of the material relates to material stratification.
*Electrostatic Force - This force applies to screening when particles are extremely dry or is wet. | 8 | Metallurgy |
The primary convention for expressing tacticity is in terms of the relative weight fraction of triad or higher-order components, as described above. An alternative expression for tacticity is the average length of meso and racemo sequences within the polymer molecule. The average meso sequence length may be approximated from the relative abundance of pentads as follows: | 4 | Stereochemistry |
Hydrogen atom transfer (HAT) is distinct from PCET. In HAT, the proton and electron start in the same orbitals and move together to the final orbital. HAT is recognized as a radical pathway, although the stoichiometry is similar to that for PCET. | 7 | Physical Chemistry |
Several routes exist for the production of cyclohexenone. For the laboratory scale, it can be produced from resorcinol via 1,3-cyclohexanedione.
Cyclohexenone is obtained by Birch reduction of anisole followed by acid hydrolysis.
It can be obtained from cyclohexanone by α-bromination followed by treatment with base. Hydrolysis of 3-chloro cyclohexene followed by oxidation of the cyclohexenol is yet another route.
Cyclohexenone is produced industrially by catalytic oxidation of cyclohexene, for example with hydrogen peroxide and vanadium catalysts. Several patents describe diverse oxidizing agents and catalysts. | 0 | Organic Chemistry |
Effluent spreading is a process in which a slurry of effluent from a dairy farm's milking parlor is pumped and spread on pasture. Commonly a rotating sprinkler is used. Dairy manure contains ammonium NH4-N.
In New Zealand the application of effluent is a permitted activity, although spreading in excess is an environmental hazard. | 9 | Geochemistry |
In classical thermodynamics, a commonly considered model is the heat engine. It consists of four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A cyclic process leaves the working body in an unchanged state, and is envisaged as being repeated indefinitely often. Work transfers between the working body and the work reservoir are envisaged as reversible, and thus only one work reservoir is needed. But two thermal reservoirs are needed, because transfer of energy as heat is irreversible. A single cycle sees energy taken by the working body from the hot reservoir and sent to the two other reservoirs, the work reservoir and the cold reservoir. The hot reservoir always and only supplies energy and the cold reservoir always and only receives energy. The second law of thermodynamics requires that no cycle can occur in which no energy is received by the cold reservoir. Heat engines achieve higher efficiency when the ratio of the initial and final temperature is greater. | 7 | Physical Chemistry |
Crayfish have also been hypothesized as being suitable bioindicators, under the appropriate conditions. One example of use is an examination of accumulation of microplastics in the digestive tract of red swamp crayfish (Procambarus clarkii) being used as a bioindicator of wider microplastics pollution. | 2 | Environmental Chemistry |
The Sleeping Beauty (SB) transposase is the recombinase that drives the Sleeping Beauty transposon system. SB transposase belongs to the DD[E/D] family of transposases, which in turn belong to a large superfamily of polynucleotidyl transferases that includes RNase H, RuvC Holliday resolvase, RAG proteins, and retroviral integrases. The SB system is used primarily in vertebrate animals for gene transfer, including gene therapy, and gene discovery. The engineered SB100X is an enzyme that directs the high levels of transposon integration. | 1 | Biochemistry |
The properties of many polymers are affected by hydrogen bonds within and/or between the chains. Prominent examples include cellulose and its derived fibers, such as cotton and flax. In nylon, hydrogen bonds between carbonyl and the amide NH effectively link adjacent chains, which gives the material mechanical strength. Hydrogen bonds also affect the aramid fibre, where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong. Hydrogen-bond networks make both polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids, and nylon 6 more sensitive than nylon-11. | 6 | Supramolecular Chemistry |
A kaliapparat is a laboratory device invented in 1831 by Justus von Liebig (1803–1873) for the analysis of carbon in organic compounds. The device, made of glass, consists of a series of five bulbs connected and arranged in a triangular shape.
To determine the carbon in an organic compound with a kaliapparat, the substance is first burned, converting any carbon present into carbon dioxide (CO). The gaseous products along with the water vapor produced by combustion are passed through the kaliapparat, which is filled with a potassium hydroxide (KOH) solution. The potassium hydroxide reacts with the CO to trap it as potassium carbonate. The global reaction, ignoring intermediate steps and the corresponding ionic dissociation, can be written as follows:
:2 KOH + CO CO + HO.
Subtracting the mass of the kaliapparat before the combustion from that measured after the combustion gives the amount of CO absorbed. From the mass of CO thus determined, standard stoichiometric calculations then give the mass of carbon in the original sample.
A stylized symbol of a kaliapparat is used in the American Chemical Society logo since 1909, originally designed in the early 20th century by Tiffany's Jewelers. | 0 | Organic Chemistry |
Stays made from puddled iron bar were used as a cheaper alternative to copper for joining the inner and outer firebox plates of steam locomotives. The incorporated stringers gave flexibility akin to stranded wire rope and stays made of the material were therefore resistant to snapping in service. Wrought iron rivets made from iron bar typically contained stringer filaments running the length of the rivet, but filaments at right angles to the tension, particularly beneath the head, caused weakness. | 8 | Metallurgy |
The Peter Debye Award in Physical Chemistry is awarded annually by the American Chemical Society "to encourage and reward outstanding research in physical chemistry". The award is named after Peter Debye and
granted without regard to age or nationality. | 7 | Physical Chemistry |
Nucleic acid extraction apparatus based on the Tajima pipette (see Fig. 2) are one of the most widespread instruments to perform the Boom method.
The Tajima pipette was invented by Hideji Tajima, founder and president of
Precision System Sciences (PSS) Inc., a Japanese manufacturer of precision and measuring instruments.
Tajima pipette is a Core Technology of PSS Inc.
PSS Inc. provides OEM product based on this technology (for example MagNA Pure(R) )
for several leading reagent manufacturers such as Hoffmann-La Roche, Life Technologies, ... and so on.
After the Tajima et al. patent was filed, similar patent applications have also been filed by other parties.
The Tajima pipette performs magnetic particle control method and procedure, which can separate magnetic particles combined with a target substance from the liquid by magnetic force and suspend them in a liquid. | 1 | Biochemistry |
Viruses (i.e., measles, mumps, or parainfluenza), especially viruses that have an RNA genome, have been shown to have evolved to utilize RNA modifications in many ways when taking over the host cell. Viruses are known to utilize the RNA modifications in different parts of their infection cycle from immune evasion to protein translation enhancement. RNA editing is used for stability and generation of protein variants. Viral RNAs are transcribed by a virus-encoded RNA-dependent RNA polymerase, which is prone to pausing and "stuttering" at certain nucleotide combinations. In addition, up to several hundred non-templated As are added by the polymerase at the 3 end of nascent mRNA. These As help stabilize the mRNA. Furthermore, the pausing and stuttering of the RNA polymerase allows the incorporation of one or two Gs or As upstream of the translational codon. The addition of the non-templated nucleotides shifts the reading frame, which generates a different protein.
Additionally, the RNA modifications are shown to have both positive and negative effects on the replication and translation efficiency depending on the virus. For example, Courtney et al. showed that an RNA modification called 5-methylcytosine is added to the viral mRNA in infected host cells in order to enhance the protein translation of HIV-1 virus. The inhibition of the mC modification on viral mRNA results in significant reduction in viral protein translation, but interestingly it has no effect on the expression of viral mRNAs in the cell. On the other hand, Lichinchi et al. showed that the N6-methyladenosine modification on ZIKV mRNA inhibits the viral replication. | 1 | Biochemistry |
The translational energy of the molecule is given by the kinetic energy expression:
where is the mass of the molecule and is its velocity. | 4 | Stereochemistry |
RNA velocity is based on bridging measurements to a underlying mechanism, mRNA splicing, with two modes indicating the current and future state. It is a method used to predict the future gene expression of a cell based on the measurement of both spliced and unspliced transcripts of mRNA.
RNA velocity could be used to infer the direction of gene expression changes in single-cell RNA sequencing (scRNA-seq) data. It provides insights into the future state of individual cells by using the abundance of unspliced to spliced RNA transcripts. This ratio can indicate the transcriptional dynamics and potential fate of a cell, such as whether it is transitioning from one cell type to another or undergoing differentiation. | 1 | Biochemistry |
Born in Fukuchiyama, Kyoto in 1928, Shimomura was brought up in Manchukuo (Manchuria, China) and Osaka, Japan while his father served as an officer in the Imperial Japanese Army. Later, his family moved to Isahaya, Nagasaki, 25 km from the epicenter of the August 1945 atomic bombing of the city. He recalled hearing, as a 16-year-old boy, the bomber plane Bockscar before the atom bomb exploded. The explosion flash blinded Shimomura for about thirty seconds, and he was later drenched by the "black rain" bomb fallout. He overcame great odds in the following 11 years to earn an education and achieve academic success.
Shimomuras education opportunities were starkly limited in devastated, post-war Japan. Although he later recalled having no interest in the subject, he enrolled in the College of Pharmaceutical Sciences of Nagasaki Medical College (now Nagasaki University School of Pharmaceutical Sciences). The Medical College campus had been entirely destroyed by the atomic bomb blast, forcing the pharmacy school to relocate to a temporary campus near Shimomuras home. This proximity was the fortuitous reason he embarked upon the studies and career which would ultimately lead to unanticipated rewards. Shimomura was awarded a BS degree in pharmacy in 1951, and he stayed on as a lab assistant through 1955.
Shimomuras mentor at Nagasaki helped him find employment as an assistant to Professor Yoshimasa Hirata at Nagoya University in 1956. While working for Professor Hirata, he received a MS degree in organic chemistry in 1958 and, before leaving Japan for an appointment at Princeton University, a Ph.D. in organic chemistry in 1960 at Nagoya University. At Nagoya, Hirata assigned Shimomura the challenging task of determining what made the crushed remains of a type of crustacean (Jp. umi-hotaru, lit. "sea-firefly", Vargula hilgendorfii) glow when moistened with water. This assignment led Shimomura to the successful identification of the protein causing the phenomenon, and he published the preliminary findings in the Bulletin of the Chemical Society of Japan' in a paper titled "Crystalline Cypridina luciferin." The article caught the attention of Professor Frank Johnson at Princeton University, and Johnson successfully recruited Shimomura to work with him in 1960. | 0 | Organic Chemistry |
A collection of data from the United States found that about half the water stations tested had hardness over 120 mg per litre of calcium carbonate equivalent, placing them in the categories "hard" or "very hard". The other half were classified as soft or moderately hard. More than 85% of American homes have hard water. The softest waters occur in parts of the New England, South Atlantic-Gulf, Pacific Northwest, and Hawaii regions. Moderately hard waters are common in many of the rivers of the Tennessee, Great Lakes, and Alaska regions. Hard and very hard waters are found in some of the streams in most of the regions throughout the country. The hardest waters (greater than 1,000 ppm) are in streams in Texas, New Mexico, Kansas, Arizona, Utah, parts of Colorado, southern Nevada, and southern California. | 3 | Analytical Chemistry |
Archaeometallurgical study has many uses in both the chemical and anthropological fields. Analysis contributes valuable insights into many archaeological questions, from technological choice to social organisation. Any project concerned with the relationship that the human species has had to the metals known to us is an example of archaeometallurgical study. | 8 | Metallurgy |
AFM-IR has been used to study the surface plasmon resonance in heavily silicon-doped indium arsenide microparticles. Gold split ring resonators have been studied for use with Surface-Enhanced Infrared Absorption Spectroscopy. In this case AFM-IR was used to measure the local field enhancement of the plasmonics structures (~30X) at 100 nm spatial resolution. | 3 | Analytical Chemistry |
Sputtering (in particular radio-frequency magnetron sputtering) has been applied to the fabrication of LAGP thin-films starting from a LAGP target. Depending on the temperature of the substrate during the deposition, LAGP can be deposited in the cold sputtering or hot sputtering configuration.
The film stoichiometry and microstructure can be tuned by controlling the deposition parameters, especially the power density, the chamber pressure, and the substrate temperature. Both amorphous and crystalline films are obtained, with a typical thickness around 1 μm. The room-temperature ionic conductivity and the activation energy of sputtered and annealed LAGP films are comparable with those of bulk pellets, i.e. 10 S/cm and 0.31 eV. | 7 | Physical Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), and Valine (Val, V). | 1 | Biochemistry |
There is a need for a computer program that is easier to operate and that requires a simpler data structure than most currently available models. Therefore, the SaltModod program was designed keeping in mind a relative simplicity of operation to facilitate the use by field technicians, engineers and project planners instead of specialized geo-hydrologists.
It aims at using input data that are generally available, or that can be estimated with reasonable accuracy, or that can be measured with relative ease. Although the calculations are done numerically and have to be repeated many times, the final results can be checked by hand using the formulas in the manual.
SaltMod's objective is to predict the long-term hydro-salinity in terms of general trends, not to arrive at exact predictions of how, for example, the situation would be on the first of April in ten years from now.
Further, SaltMod gives the option of the re-use of drainage and well water (e.g. for irrigation) and it can account for farmers' response to waterlogging, soil salinity, water scarcity and over-pumping from the aquifer. Also it offers the possibility to introduce subsurface drainage systems at varying depths and with varying capacity so that they can be optimized.
Other features of Saltmod are found in the next section. | 9 | Geochemistry |
Since 1 January 2010, it has been illegal to use newly manufactured HCFCs to service refrigeration and air-conditioning equipment; only reclaimed and recycled HCFCs may be used. In practice this means that the gas has to be removed from the equipment before servicing and replaced afterwards, rather than refilling with new gas.
Since 1 January 2015, it has been illegal to use any HCFCs to service refrigeration and air-conditioning equipment; broken equipment that used HCFC refrigerants must be replaced with equipment that does not use them. | 2 | Environmental Chemistry |
The other function of retromer is the recycling of protein cargo directly back to the plasma membrane. Dysfunction of this branch of the retromer recycling pathway causes endosomal protein traffic jams that are linked to Alzheimer’s disease. It has been suggested that recycling dysfunction is the “fire” that drives the common form of Alzheimer’s, leading to the production of amyloid and tau tangle “smoke”. | 1 | Biochemistry |
The apparatus for testing consists of a closed testing cabinet/chamber, where a salt water (5% NaCl) solution is atomized by means of spray nozzle(s) using pressurized air. This produces a corrosive environment of dense salt water fog (also referred to as a mist or spray) in the chamber, so that test samples exposed to this environment are subjected to severely corrosive conditions. Chamber volumes vary from supplier to supplier. If there is a minimum volume required by a particular salt spray test standard, this will be clearly stated and should be complied with. There is a general historical consensus that larger chambers can provide a more homogeneous testing environment.
Variations to the salt spray test solutions depend upon the materials to be tested. The most common test for steel based materials is the Neutral Salt Spray test (often abbreviated to NSS) which reflects the fact that this type of test solution is prepared to a neutral pH of 6.5 to 7.2. To maintain a neutral pH, hydrochloric acid or sodium hydroxide are added to reduce or increase pH into the required range. Results are represented generally as testing hours in NSS without appearance of corrosion products (e.g. 720 h in NSS according to ISO 9227). Synthetic seawater solutions are also commonly specified by some companies and standards. Other test solutions have other chemicals added including acetic acid (often abbreviated to ASS) and acetic acid with copper chloride (often abbreviated to CASS) each one chosen for the evaluation of decorative coatings, such as electroplated copper-nickel-chromium, electroplated copper-nickel or anodized aluminum. These acidified test solutions generally have a pH of 3.1 to 3.3
Some sources do not recommend using ASS or CASS test cabinets interchangeably for NSS tests, due to the risk of cross-contamination. It is claimed that a thorough cleaning of the cabinet after CASS test is very difficult. ASTM does not address this issue, but ISO 9227 does not recommend it and if it is to be done, advocates a thorough cleaning.
Although the majority of salt spray tests are continuous, i.e.; the samples under test are exposed to the continuous generation of salt fog for the entire duration of the test, a few do not require such exposure. Such tests are commonly referred to as modified salt spray tests. ASTM G85 is an example of a test standard which contains several modified salt spray tests which are variations to the basic salt spray test. | 8 | Metallurgy |
The urea molecule is planar when in a solid crystal because of sp hybridization of the N orbitals. It is non-planar with C symmetry when in the gas phase or in aqueous solution, with C–N–H and H–N–H bond angles that are intermediate between the trigonal planar angle of 120° and the tetrahedral angle of 109.5°. In solid urea, the oxygen center is engaged in two N–H–O hydrogen bonds. The resulting dense and energetically favourable hydrogen-bond network is probably established at the cost of efficient molecular packing: The structure is quite open, the ribbons forming tunnels with square cross-section. The carbon in urea is described as sp hybridized, the C-N bonds have significant double bond character, and the carbonyl oxygen is relatively basic. Urea's high aqueous solubility reflects its ability to engage in extensive hydrogen bonding with water.
By virtue of its tendency to form porous frameworks, urea has the ability to trap many organic compounds. In these so-called clathrates, the organic "guest" molecules are held in channels formed by interpenetrating helices composed of hydrogen-bonded urea molecules.
As the helices are interconnected, all helices in a crystal must have the same molecular handedness. This is determined when the crystal is nucleated and can thus be forced by seeding. The resulting crystals have been used to separate racemic mixtures. | 0 | Organic Chemistry |
The Open Regulatory Annotation Database (also known as ORegAnno) is designed to promote community-based curation of regulatory information. Specifically, the database contains information about regulatory regions, transcription factor binding sites, regulatory variants, and haplotypes. | 1 | Biochemistry |
The behaviour of the coals ash residue at high temperature is a critical factor in selecting coals for steam power generation. Most furnaces are designed to remove ash as a powdery residue. Coal which has ash that fuses into a hard glassy slag known as clinker' is usually unsatisfactory in furnaces as it requires cleaning. However, furnaces can be designed to handle the clinker, generally by removing it as a molten liquid.
Ash fusion temperatures are determined by viewing a moulded specimen of the coal ash through an observation window in a high-temperature furnace. The ash, in the form of a cone, pyramid or cube, is heated steadily past 1000 °C to as high a temperature as possible, preferably . The following temperatures are recorded;
* Deformation temperature: This is reached when the corners of the mould first become rounded.
* Softening (sphere) temperature: This is reached when the top of the mould takes on a spherical shape.
* Hemisphere temperature: This is reached when the entire mould takes on a hemisphere shape.
* Flow (fluid) temperature: This is reached when the molten ash collapses to a flattened button on the furnace floor. | 3 | Analytical Chemistry |
The misorientation distribution (MD) is analogous to the ODF used in characterizing texture. The MD describes the probability of the misorientation between any two grains falling into a range around a given misorientation . While similar to a probability density, the MD is not mathematically the same due to the normalization. The intensity in an MD is given as "multiples of random density" (MRD) with respect to the distribution expected in a material with uniformly distributed misorientations. The MD can be calculated by either series expansion, typically using generalized spherical harmonics, or by a discrete binning scheme, where each data point is assigned to a bin and accumulated. | 3 | Analytical Chemistry |
Eogan (1994) noted that around 250 surviving gold objects are known to date to the Early Bronze Age, 165 of those from Ireland, and the other 83 from Britain. From analysing the designs of the earliest gold artefacts in Britain, Eogan noted that they "form a homogeneous group" which, when "taken in conjunction with other metal types demonstrate that a new technology was introduced." Early Bronze Age pieces are generally much smaller, with very thin decorated discs or plaques common. Two small gold cups have been found in England, the Rillaton Cup and the similar but now crushed Ringlemere Cup.
Due to its natural resources, Ireland had a "rich Early Bronze Age [metal-working] industry", producing large quantities of metal axes, halberds and daggers, and as a part of this also had a "major gold industry", seeing the production of lunulae and gold disks on a far larger scale than Britain. | 8 | Metallurgy |
The usual equipment includes a seal-able metabolic chamber, an oxygen sensor, and devices for data recording, stirring, thermostatisation and a way to introduce chemicals into the chamber. As described above for whole-animal respirometry the choice of materials is very important. Plastic materials are not suitable for the chamber because of their oxygen storage capacity. When plastic materials are unavoidable (e.g. for o-rings, coatings of stirrers, or stoppers) polymers with a very low oxygen permeability (like PVDF as opposed to e.g. PTFE) may be used. Remaining oxygen diffusion into or out of the chamber materials can be handled by correcting the measured oxygen fluxes for the instrumental oxygen background flux. The entire instrument comprising the mentioned components is often called an oxygraph. The companies providing equipment for whole-animal rspirometry mentioned above are usually not involved in mitochondrial respiromety. The community is serviced at widely varying levels of price and sophistication by companies like Oroboros Instruments, Hansatech, Respirometer Systems & Applications, YSI Life Sciences or Strathkelvin Instruments . | 1 | Biochemistry |
Studies published in 2000 considered this hypothetical effect to be responsible for warming events in and at the end of the Last Glacial Maximum. Although periods of increased atmospheric methane match periods of continental-slope failure, later work found that the distinct deuterium/hydrogen (D/H) isotope ratio indicated that wetland methane emissions was the main contributor to atmospheric methane concentrations. While there were major dissociation events during the last deglaciation, with Bølling–Allerød warming triggering the disappearance of the entire methane hydrate deposit in the Barents Sea within 5000 years, those events failed to counteract the onset of a major Younger Dryas cooling period, suggesting that most of the methane stayed within the seawater after being liberated from the seafloor deposits, with very little entering the atmosphere.
In 2008, it was suggested that equatorial permafrost methane clathrate may have had a role in the sudden warm-up of "Snowball Earth", 630 million years ago.
Other events potentially linked to methane hydrate excursions are the Permian–Triassic extinction event and the Paleocene–Eocene Thermal Maximum. | 6 | Supramolecular Chemistry |
In enzymatic analysis (which is widely used in medical laboratories) the color reaction is preceded by a reaction catalyzed by an enzyme. As the enzyme is specific to a particular substrate, more accurate results can be obtained. Enzymatic analysis is always carried out in a buffer solution at a specified temperature (usually 37°C) to provide the optimum conditions for the enzymes to act. Examples follow. | 3 | Analytical Chemistry |
* In emulsions a phase inversion is when the dispersed phase becomes the dispersion medium and the dispersion medium becomes the dispersed phase, for example when cream becomes butter. | 7 | Physical Chemistry |
The clay hypothesis for the origin of life was proposed by Graham Cairns-Smith in 1985. It postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in contact with an aqueous solution. The clay mineral montmorillonite has been shown to catalyze the polymerization of RNA in aqueous solution from nucleotide monomers, and the formation of membranes from lipids. In 1998, Hyman Hartman proposed that "the first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic acid and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hot spring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids." | 9 | Geochemistry |
Less ambiguous than the above ichnogenera, are the traces left behind by invertebrates such as Hibbertopterus, a giant "sea scorpion" or eurypterid of the early Paleozoic era. This marine arthropod produced a spectacular track preserved in Scotland.
Bioerosion through time has produced a magnificent record of borings, gnawings, scratchings and scrapings on hard substrates. These trace fossils are usually divided into macroborings and microborings. Bioerosion intensity and diversity is punctuated by two events. One is called the Ordovician Bioerosion Revolution (see Wilson & Palmer, 2006) and the other was in the Jurassic. For a comprehensive bibliography of the bioerosion literature, please see the External links below.
The oldest types of tetrapod tail-and-footprints date back to the latter Devonian period. These vertebrate impressions have been found in Ireland, Scotland, Pennsylvania, and Australia. A sandstone slab containing the track of tetrapod, dated to 400 million years, is amongst the oldest evidence of a vertebrate walking on land.
Important human trace fossils are the Laetoli (Tanzania) footprints, imprinted in volcanic ash 3.7 Ma (million years ago) – probably by an early Australopithecus. | 2 | Environmental Chemistry |
Long intergenic Non-coding RNA (LincRNA) is defined as RNA transcripts that are longer than 200 nucleotides. These RNAs must not have open reading frames that encode proteins. The term “intergenic” refers to the identification of these transcripts from regions of the genome that do not contain protein-encoding genes. LncRNAs also contain promoter - or enhancer-associated RNAs that are gene proximal and can be either in the sense or antisense orientation. | 1 | Biochemistry |
Enzymes can catalyze up to several million reactions per second. Enzyme rates depend on solution conditions and substrate concentration. Like other enzymes POLR2 has a saturation curve and a maximum velocity (V). It has a K (substrate concentration required for one-half V) and a k (the number of substrate molecules handled by one active site per second). The specificity constant is given by k/K. The theoretical maximum for the specificity constant is the diffusion limit of about 10 to 10 (Ms), where every collision of the enzyme with its substrate results in catalysis. In yeast, mutation in the Trigger-Loop domain of the largest subunit can change the kinetics of the enzyme.
Bacterial RNA polymerase, a relative of RNA Polymerase II, switches between inactivated and activated states by translocating back and forth along the DNA. Concentrations of [NTP] = 10 μM GTP, 10 μM UTP, 5 μM ATP and 2.5 μM CTP, produce a mean elongation rate, turnover number, of ~1 bp (NTP) for bacterial RNAP, a relative of RNA polymerase II.
RNA polymerase II undergoes extensive co-transcriptional pausing during transcription elongation. This pausing is especially pronounced at nucleosomes, and arises in part through the polymerase entering a transcriptionally incompetent backtracked state. The duration of these pauses ranges from seconds to minutes or longer, and exit from long-lived pauses can be promoted by elongation factors such as TFIIS. In turn, the transcription rate influences whether the histones of transcribed nucleosomes are evicted from chromatin, or reinserted behind the transcribing polymerase. | 1 | Biochemistry |
Selegiline is considered by some to be a nootropic, both at clinical and sub-clinical dosages, and has been used off-label to improve cognitive performance. It has been shown to have protective activity against a range of neurotoxins and to increase the production of several brain growth factors, such as nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor. It has been demonstrated in numerous animal models to improve learning ability and preserve it during both ischemia and aging. | 4 | Stereochemistry |
The source material was pig iron produced by a blast furnace using charcoal and the manganese rich iron ore from the Dannemora mine. A V-shaped hearth using charcoal was used to heat up the pig iron bar that was presented to a tuyere that decarbonized it and made it melt and fall in drops that solidified in a pool of slag where the decarburization continued. The iron drops were picked up with an iron bar and presented again in front of the tuyere and one by one agglomerated into a ball. That heterogeneous iron was full of slag and the carbon content ranged from pure iron to nearly pig iron. It was therefore reheated in a chafery and hammered and folded using a waterwheel powered trip hammer.
The ore from Dannemora was very low in sulphur and high in manganese. It is possible the manganese bonded with the impurities during the oxidation, creating a pretty pure wrought iron. The use of charcoal prevented the contamination with impurities usually associated with the usage of coal or coke, of which Sweden has none. In England, the chafery might use coal or coke, as in this stage the iron is solidified and the contamination remain low.
The iron was sold to England, where it was recarbonized into blister steel using the cementation process. This steel still contain some slag, and if the carbon was around 1% at the surface, it was lower in the center. The blister steel was than purchased by Benjamin Huntsman who melted it in a crucible heated using coke and poured it. This modern crucible steel was different from the medieval wootz, but was homogeneous and without slag. | 8 | Metallurgy |
Cibacron Blue F3GA, Procion Blue HB, or Reactive blue 2 is a purinergic receptor antagonist, such as P2Y purinoceptor, and also an ATP receptor channels antagonist. It has a formula of CHClNOS and a molecular weight of 774.2 g/mol. Cibacron blue is soluble in water and DMSO, however insoluble in ethanol. In water, saturated concentration is reached at 12.92 mM with the help of sonication. Cibacron Blue F3GA has a wide specificity for nucleotide-binding proteins or just a stereoselectivity electrostatic binding. It can be used to purify interferons, dehydrogenases, kinases, and serum albumin. For example, interferon purification from human gingival fibroblast extract using Cibacron Blue F3G-A on poly(2-hydroxyethyl methacrylate), the supporting matrix, in the form of cryogels. It has shown 97.6% purity of interferon. | 3 | Analytical Chemistry |
Electroviscous effects, in chemistry of colloids and surface chemistry, according to an IUPAC definition, are the effects of the particle surface charge on viscosity of a fluid.
Viscoelectric is an effect by which an electric field near a charged interface influences the structure of the surrounding fluid and affects the viscosity of the fluid.
Kinematic viscosity of a fluid, η, can be expressed as a function of electric potential gradient (electric field), , by an equation in the form:
where f is the viscoelectric coefficient of the fluid.
The value of f for water (ambient temperature) has been estimated to be (0.5–1.0) × 10 V m. | 7 | Physical Chemistry |
For many years, alongside scientific research, he has carried out an intense dissemination activity, also on the relationship between science and society and between science and peace, with particular reference to energy and resource issues. He is convinced that scientists have a great responsibility that derives from their knowledge and therefore it is their duty to actively contribute to solving the problems of humanity, particularly those connected to the current energy-climate crisis. Every year he holds dozens of seminars in primary or secondary schools and public conferences to illustrate to students and citizens the problems created by the use of fossil fuels: climate change, ecological unsustainability and the social unease deriving from growing inequalities. He believes that three transitions are necessary: from fossil fuels to renewable energies, from the linear economy to the circular economy and from consumerism to sobriety. On these themes he is coauthor of books much appreciated by students and teachers of secondary schools: Chimica (2000); Energia oggi e domani: Prospettive, sfide, speranze (2004); Energia per lastronave Terra (2017), whose first edition (2007) won the Galileo award for scientific dissemination; Chimica! Leggere e scrivere il libro della natura (2012), english version: Chemistry! Reading and writing the book of Nature (2014); Energia, risorse, ambiente (2014); Le macchine molecolari' (2018), finalist in the National Award for Scientific Dissemination Giancarlo Dosi. | 5 | Photochemistry |
Photodegradation of plastics and other materials can be inhibited with polymer stabilizers, which are widely used. These additives include antioxidants, which interrupt degradation processes. Typical antioxidants are derivatives of aniline. Another type of additive are UV-absorbers. These agents capture the photon and convert it to heat. Typical UV-absorbers are hydroxy-substituted benzophenones, related to the chemicals used in sunscreen. Restoration of yellowed plastic of old toys is nicknamed retrobright. | 5 | Photochemistry |
Once the TALEN constructs have been assembled, they are inserted into plasmids; the target cells are then transfected with the plasmids, and the gene products are expressed and enter the nucleus to access the genome. Alternatively, TALEN constructs can be delivered to the cells as mRNAs, which removes the possibility of genomic integration of the TALEN-expressing protein. Using an mRNA vector can also dramatically increase the level of homology directed repair (HDR) and the success of introgression during gene editing. | 1 | Biochemistry |
To fix carbon dioxide into sugar molecules in the process of photosynthesis, chloroplasts use an enzyme called RuBisCO. RuBisCO has trouble distinguishing between carbon dioxide and oxygen, so at high oxygen concentrations, RuBisCO starts accidentally adding oxygen to sugar precursors. This has the result of ATP energy being wasted and being released, all with no sugar being produced. This is a big problem, since O is produced by the initial light reactions of photosynthesis, causing issues down the line in the Calvin cycle which uses RuBisCO.
plants evolved a way to solve this—by spatially separating the light reactions and the Calvin cycle. The light reactions, which store light energy in ATP and NADPH, are done in the mesophyll cells of a leaf. The Calvin cycle, which uses the stored energy to make sugar using RuBisCO, is done in the bundle sheath cells, a layer of cells surrounding a vein in a leaf.
As a result, chloroplasts in mesophyll cells and bundle sheath cells are specialized for each stage of photosynthesis. In mesophyll cells, chloroplasts are specialized for the light reactions, so they lack RuBisCO, and have normal grana and thylakoids, which they use to make ATP and NADPH, as well as oxygen. They store in a four-carbon compound, which is why the process is called photosynthesis. The four-carbon compound is then transported to the bundle sheath chloroplasts, where it drops off and returns to the mesophyll. Bundle sheath chloroplasts do not carry out the light reactions, preventing oxygen from building up in them and disrupting RuBisCO activity. Because of this, they lack thylakoids organized into grana stacks—though bundle sheath chloroplasts still have free-floating thylakoids in the stroma where they still carry out cyclic electron flow, a light-driven method of synthesizing ATP to power the Calvin cycle without generating oxygen. They lack photosystem II, and only have photosystem I—the only protein complex needed for cyclic electron flow. Because the job of bundle sheath chloroplasts is to carry out the Calvin cycle and make sugar, they often contain large starch grains.
Both types of chloroplast contain large amounts of chloroplast peripheral reticulum, which they use to get more surface area to transport stuff in and out of them. Mesophyll chloroplasts have a little more peripheral reticulum than bundle sheath chloroplasts. | 5 | Photochemistry |
The metals involved in a bimetallic strip can vary in composition so long as their thermal expansion coefficients differ. The metal of lower thermal expansion coefficient is sometimes called the passive metal, while the other is called the active metal. Copper, steel, brass, iron, and nickel are commonly used metals in bimetallic strips. Metal alloys have been used in bimetallic strips as well, such as invar and constantan. Material selection has a significant impact on the working temperature range of a bimetallic strip, with some having a temperature limit up to 500°C, with others only reaching 150°C before failing. | 8 | Metallurgy |
Diastereoselective conjugate addition reactions of chiral organocuprates provide β-functionalized ketones in high yield and diastereoselectivity. A disadvantage of these reactions is the requirement of a full equivalent of enantiopure starting material.
More recently, catalytic enantioselective methods have been developed based on the copper(I)-catalyzed conjugate addition of Grignard reactions to enones. The proposed mechanism involves transmetalation from the Grignard reagent to copper, conjugate addition, and rate-determining reductive elimination (see the analogous upper pathway in equation (2)). | 0 | Organic Chemistry |
Carbon dioxide affects the curve in two ways. First, CO accumulation causes carbamino compounds to be generated through chemical interactions, which bind to hemoglobin forming carbaminohemoglobin. CO is considered an Allosteric regulation as the inhibition happens not at the binding site of hemoglobin. Second, it influences intracellular pH due to formation of bicarbonate ion. Formation of carbaminohemoglobin stabilizes T state hemoglobin by formation of ion pairs. Only about 5–10% of the total CO content of blood is transported as carbamino compounds, whereas (80–90%) is transported as bicarbonate ions and a small amount is dissolved in the plasma. The formation of a bicarbonate ion will release a proton into the plasma, decreasing pH (increased acidity), which also shifts the curve to the right as discussed above; low CO levels in the blood stream results in a high pH, and thus provides more optimal binding conditions for hemoglobin and O. This is a physiologically favored mechanism, since hemoglobin will drop off more oxygen as the concentration of carbon dioxide increases dramatically where tissue respiration is happening rapidly and oxygen is in need. | 1 | Biochemistry |
Sea salt is salt that is produced by the evaporation of seawater. It is used as a seasoning in foods, cooking, cosmetics and for preserving food. It is also called bay salt, solar salt, or simply salt. Like mined rock salt, production of sea salt has been dated to prehistoric times. | 9 | Geochemistry |
The slides are then immersed in a solution that cause the cells to lyse. The lysis solution often used in the comet assay consists of a highly concentrated aqueous salt (often, common table salt can be used) and a detergent (such as Triton X-100 or sarcosinate). The pH of the lysis solution can be adjusted (usually between neutral and alkaline pH) depending upon the type of damage the researcher is investigating.
The aqueous salt disrupts proteins and their bonding patterns within the cell as well as disrupting the RNA content of the cell. The detergent dissolves the cellular membranes. Through the action of the lysis solution the cells are destroyed. All proteins, RNA, membranes and cytoplasmic and nucleoplasmic constituents are disrupted and diffuse into the agarose matrix. Only the DNA of the cell remains, and unravels to fill the cavity in the agarose that the whole cell formerly filled. This structure is called nucleoid (a general term for a structure in which DNA is concentrated). | 1 | Biochemistry |
Clustering of genes in prokaryotes was known for a long time. Their genes are grouped in operons, genes within operons share a common promoter unit. These genes are mostly functionally related. The genome of prokaryotes is relatively very simple and compact. In eukaryotes the genome is huge and only a small amount of it are functionally genes, furthermore the genes are not arranged in operons. Except for nematodes and trypanosomes; although their operons are different from the prokaryotic operons. In eukaryotes each gene has a transcription regulation site of its own. Therefore, genes don't have to be in close proximity to be co-expressed. Therefore, it was long assumed that eukaryotic genes were randomly distributed across the genome due to the high rate of chromosome rearrangements. But because the complete sequence of genomes became available it became possible to absolutely locate a gene and measure its distance to other genes.
The first eukaryote genome ever sequenced was that of Saccharomyces cerevisiae, or budding yeast, in 1996. Half a year after that Velculescu et al. (1997) published a research in which they had integrated SAGE data with the now available genome map. During a cell cycle different genes are active in a cell. Therefore, they used SAGE data from three moments of the cell cycle (log phase, S phase-arrested and G2/M-phase arrested cells). Because in yeast all genes have a promoter unit of their own it was not suspected that genes would cluster near to each other but they did. Clusters were present on all 16 yeast chromosomes.
A year later Cho et al. also reported (although in more detail) that certain genes are located near to each other in yeast. | 1 | Biochemistry |
The reversibility of the interconversion of 3-sulfolene with buta-1,3-diene and sulfur dioxide suggests the use of sulfolene as a recyclable aprotic dipolar solvent, in replacement for dimethyl sulfoxide (DMSO), which is often used but difficult to separate and poorly reusable. As a model reaction, the reaction of benzyl azide with 4-toluenesulfonic acid cyanide forming 1-benzyl-5-(4-toluenesulfonyl)tetrazole was investigated. The formation of the tetrazole can also be carried out as a one-pot reaction without the isolation of the benzyl azide with 72% overall yield.
After the reaction, the solvent 3-sulfolene is decomposed at 135 °C and the volatile butadiene (b.p. −4.4 °C) and sulfur dioxide (b.p. −10.1 °C) are deposited in a cooling trap at −76 °C charged with excess sulfur dioxide. After the addition of hydroquinone as polymerization inhibition, 3-sulfoles is formed again quantitatively upon heating to room temperature. It appears questionable though, if 3-sulfolene with a useful liquid phase range of only 64 to a maximum of about 100 °C can be used as DMSO substitutes (easy handling, low cost, environmental compatibility) in industrial practice. | 0 | Organic Chemistry |
Often called a "squirrel cage" (because of its general similarity in appearance to exercise wheels for pet rodents) or "scroll fan", the centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades that form a spiral, or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in leaf blowers, blowdryers, air mattress inflators, inflatable structures, climate control in air handling units and various industrial purposes. They are typically noisier than comparable axial fans (although some types of centrifugal fans are quieter such as in air handling units). | 7 | Physical Chemistry |
Neurotrophins that interact with p75NTR include NGF, NT-3, BDNF, and NT-4/5. Neurotrophins activating p75NTR may initiate apoptosis (for example, via c-Jun N-terminal kinases signaling, and subsequent p53, Jax-like proteins and caspase activation). This effect can be counteracted by anti-apoptotic signaling by TrkA.
Neurotrophin binding to p75NTR, in addition to apoptotic signaling, can also promote neuronal survival (for example, via NF-kB activation). There are multiple targets of Akt that could play a role in mediating p75NTR-dependent survival, but one of the more intriguing possibilities is that Ant-induced phosphorylation of IkB kinase 1 (IKK1) plays a role in the induction of NF-kB. | 1 | Biochemistry |
Following the action potential, characteristically generated by the influx of Na through voltage gated Na channels, there is a period of repolarization in which the Na channels are inactivated while K channels are activated. Further study of K channels shows that there are four types which influence the repolarization of the cell membrane to re-establish the resting potential. The four types are K1, K2, K3 and K4. The K1 channel primarily influences the repolarization of the axon. The K2 channel is characteristically activated slower. The K4 channels are characteristically activated rapidly. When K2 and K4 channels are blocked, the action potential predictably widens. The K3 channels open at a more positive membrane potential and deactivate 10 times faster than the other K channels. These properties allow for the high-frequency firing that mammalian neurons require. Areas with dense K3 channels include the neocortex, basal ganglia, brain stem and hippocampus as these regions create microsecond action potentials that requires quick repolarization.
Utilizing voltage-clamp data from experiments based on rodent neurons, the K4 channels are associated with the primary repolarization conductance following the depolarization period of a neuron. When the K4 channel is blocked, the action potential becomes broader, resulting in an extended repolarization period, delaying the neuron from being able to fire again. The rate of repolarization closely regulates the amount of Ca ions entering the cell. When large quantities of Ca ions enter the cell due to extended repolarization periods, the neuron may die, leading to the development of stroke or seizures.
The K1 channels are found to contribute to repolarization of pyramidal neurons, likely associated with an upregulation of the K4 channels. The K2 channels were not found to contribute to repolarization rate as blocking these channels did not result in changes in neuron repolarization rates. | 7 | Physical Chemistry |
Glycogen serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue. Glycogen is made primarily by the liver, and the muscles but can also be made by glycogenesis within the brain and stomach.
Glycogen is analogous to starch, a glucose polymer in plants, and is sometimes referred to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α(1→4) glycosidic bonds linked with α(1→6)-linked branches. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact and more immediately available as an energy reserve than triglycerides (lipids).
In the liver hepatocytes, glycogen can compose up to 8 percent (100–120 grams in an adult) of the fresh weight soon after a meal. Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a low concentration of one to two percent of the muscle mass. The amount of glycogen stored in the body—especially within the muscles, liver, and red blood cells—varies with physical activity, basal metabolic rate, and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo.
Glycogen is composed of a branched chain of glucose residues. It is primarily stored in the liver and muscles.
* It is an energy reserve for animals.
* It is the chief form of carbohydrate stored in animal organisms.
* It is insoluble in water. It turns brown-red when mixed with iodine.
* It also yields glucose on hydrolysis. | 0 | Organic Chemistry |
Biological carbon sequestration (also called biosequestration) is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual or enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation and sustainable forest management. Land-use changes that enhance natural carbon capture have the potential to capture and store large amounts of carbon dioxide each year. These include the conservation, management, and restoration of ecosystems such as forests, peatlands, wetlands, and grasslands, in addition to carbon sequestration methods in agriculture.
Methods and practices exist to enhance soil carbon sequestration in both sectors of agriculture and forestry. | 5 | Photochemistry |
More recently, starting in the 1920s, organic farming and horticulture have made frequent use of companion planting, since many other means of fertilizing, weed reduction and pest control are forbidden. Permaculture advocates similar methods.
The list of companion plants used in such systems is large, and includes vegetables, fruit trees, kitchen herbs, garden flowers, and fodder crops. The number of pairwise interactions both positive (the pair of species assist each other) and negative (the plants are best not grown together) is larger, though the evidence for such interactions ranges from controlled experiments to hearsay. For example, plants in the cabbage family (Brassicaceae) are traditionally claimed to grow well with celery, onion family plants (Allium), and aromatic herbs, but are thought best not grown with strawberry or tomato.
In 2022, agronomists recommended that multiple tools including plant disease resistance in crops, conservation of natural enemies (parasitoids and predators) to provide biological pest control, and companion planting such as with aromatic forbs to repel pests should be used to achieve "sustainable" protection of crops. They considered a multitrophic approach that took into account the many interactions between crops, companion plants, herbivorous pests, and their natural enemies essential. Many studies have looked at the effects of plants on crop pests, but relatively few interactions have been studied in depth or using field trials. | 1 | Biochemistry |
A large number of biologically important modified monosaccharides exist:
* Amino sugars such as:
** galactosamine
** glucosamine
** sialic acid
** N-acetylglucosamine
* Sulfosugars such as:
** sulfoquinovose
* Others such as:
** ascorbic acid
** mannitol
** glucuronic acid | 0 | Organic Chemistry |
The cylindrospermopsin biosynthetic gene cluster (BGC) was described from Cylindrospermopsis raciborskii AWT205 in 2008. | 0 | Organic Chemistry |
Compounds containing 2 geminal phosphonate groups are known as bisphosphonates. They were first synthesized in 1897 by Von Baeyer and Hofmann and now form the basis for an important class of drugs, used to treat osteoporosis and similar diseases. Examples include HEDP (etidronic acid or Didronel), which is prepared from phosphorous acid and acetic anhydride:
:2 HPO + (CHCO)O → CHC(OH)(POH) + CHCOH | 0 | Organic Chemistry |
Anaerobic microbial mineralization of recalcitrant organic pollutants is of great environmental significance and involves intriguing novel biochemical reactions. In particular, hydrocarbons and halogenated compounds have long been doubted to be degradable in the absence of oxygen, but the isolation of hitherto unknown anaerobic hydrocarbon-degrading and reductively dehalogenating bacteria during the last decades provided ultimate proof for these processes in nature. While such research involved mostly chlorinated compounds initially, recent studies have revealed reductive dehalogenation of bromine and iodine moieties in aromatic pesticides. Other reactions, such as biologically induced abiotic reduction by soil minerals, has been shown to deactivate relatively persistent aniline-based herbicides far more rapidly than observed in aerobic environments. Many novel biochemical reactions were discovered enabling the respective metabolic pathways, but progress in the molecular understanding of these bacteria was rather slow, since genetic systems are not readily applicable for most of them. However, with the increasing application of genomics in the field of environmental microbiology, a new and promising perspective is now at hand to obtain molecular insights into these new metabolic properties. Several complete genome sequences were determined during the last few years from bacteria capable of anaerobic organic pollutant degradation. The ~4.7 Mb genome of the facultative denitrifying Aromatoleum aromaticum strain EbN1 was the first to be determined for an anaerobic hydrocarbon degrader (using toluene or ethylbenzene as substrates). The genome sequence revealed about two dozen gene clusters (including several paralogs) coding for a complex catabolic network for anaerobic and aerobic degradation of aromatic compounds. The genome sequence forms the basis for current detailed studies on regulation of pathways and enzyme structures. Further genomes of anaerobic hydrocarbon degrading bacteria were recently completed for the iron-reducing species Geobacter metallireducens (accession nr. NC_007517) and the perchlorate-reducing Dechloromonas aromatica (accession nr. NC_007298), but these are not yet evaluated in formal publications. Complete genomes were also determined for bacteria capable of anaerobic degradation of halogenated hydrocarbons by halorespiration: the ~1.4 Mb genomes of Dehalococcoides ethenogenes strain 195 and Dehalococcoides sp. strain CBDB1 and the ~5.7 Mb genome of Desulfitobacterium hafniense strain Y51. Characteristic for all these bacteria is the presence of multiple paralogous genes for reductive dehalogenases, implicating a wider dehalogenating spectrum of the organisms than previously known. Moreover, genome sequences provided unprecedented insights into the evolution of reductive dehalogenation and differing strategies for niche adaptation.
Recently, it has become apparent that some organisms, including Desulfitobacterium chlororespirans, originally evaluated for halorespiration on chlorophenols, can also use certain brominated compounds, such as the herbicide bromoxynil and its major metabolite as electron acceptors for growth. Iodinated compounds may be dehalogenated as well, though the process may not satisfy the need for an electron acceptor. | 2 | Environmental Chemistry |
In 2005, Myriad Genetics reported the results of its Phase II clinical trial of Flurizan; it was the largest ever Alzheimers drug treatment trial using R-flurbiprofen. Patients were split into three treatment groups, receiving placebo, 400 or 800 mg R-flurbiprofen twice daily for a year. Result from this trial showed that the drug was well tolerated, and positive trends were observed with the 800 mg twice-daily dose in patients with mild Alzheimers disease. A subgroup of patients that were diagnosed with mild disease, and had high plasma drug levels had significantly less decline in two primary behavioral outcomes (Activities of Daily Living scale (ADCS-ADL) and Global Function (CDR-SB)). Approximately 80 patients enrolled in the optional follow-on study showed continuing benefits with R-flurbiprofen, with increasing positive trends over this period for all primary outcomes after 24 months. On March 5, 2007 Myriad reported final results of the two-year trial, showing that 42% of those 80 patients showed improvement or no decline in one or more of the three primary endpoints of cognition, global function and activities of daily living, compared to a typical 10% of patients on placebo.
A Phase III clinical study evaluated 800 mg R-flurbiprofen twice-daily versus placebo for 18 months exclusively in 1800 patients with mild Alzheimers disease. This second trial concluded in February 2008 with results reported in the summer. After Phase III testing, which included nearly 1,700 patients with mild Alzheimers disease treated for 18 months with either Flurizan or placebo, Myrial Genetics concluded that the drug did not improve thinking ability or the ability of patients to carry out daily activities significantly more than those patients with placebo. Peter Meldrum, the chief executive of Myriad, announced on June 30, 2008, that the company will no longer be developing Flurizan. Prior to this termination, Myriad had sold distribution rights in the European Union to Lundbeck for an initial payment of $100 million, which Lundbeck has indicated it will now take as a write-down. | 4 | Stereochemistry |
Phycoerythrocyanin is a kind of phycobiliprotein, magenta chromoprotein involved in photosynthesis of some Cyanobacteria. This chromoprotein consists of alpha- and beta-subunits, generally aggregated as hexamer. Alpha-phycoerythrocyanin contains a phycoviolobilin, a violet bilin, that covalently attached at Cys-84, and beta-phycoerythrocyanin contains two phycocyanobilins, a blue bilin, that covalently attached at Cys-84 and -155, respectively. Phycoerythrocyanin is similar to phycocyanin, an important component of the light-harvesting complex (phycobilisome) of cyanobacteria and red algae.
While only phycocyanobilin is covalently bound to phycocyanin, leading to an absorption maximum around 620 nm, phycoerythrocyanin containing both phycoviolobilin and phycocyanobilin leads to an absorption maximum around 575 nm. As both phycoerythrocyanin and phycocyanin have phycocyanobilin acting as the terminal acceptor of energy transfer, they fluoresce around 635 nm, which is absorbed by allophycocyanins that have maximal absorption around 650 nm and maximal fluorescence around 670 nm. Finally, the light energy absorbed by phycoerythrocyanin is transferred to photosynthetic reaction center. | 1 | Biochemistry |
Often, reactivity and reaction mechanisms are pictured as the behavior of isolated molecules in which the solvent is treated as a passive support. However, the nature of the solvent can actually influence reaction rates and order of a chemical reaction.
Performing a reaction without solvent can affect reaction-rate for reactions with bimolecular mechanisms, for example, by maximizing the concentration of the reagents. Ball milling is one of several mechanochemical techniques where physical methods are used to control reactions rather than solvents are methods are methods for affecting reactions in the absence of solvent. | 7 | Physical Chemistry |
Mechanical spalling occurs at high-stress contact points, for example, in a ball bearing. Spalling occurs in preference to brinelling, where the maximal shear stress occurs not at the surface, but just below, shearing the spall off.
One of the simplest forms of mechanical spalling is plate impact, in which two waves of compression are reflected on the free-surfaces of the plates and then interact to generate a region of high tensile stress inside one of the plates.
Spalling can also occur as an effect of cavitation, where fluids are subjected to localized low pressures that cause vapour bubbles to form, typically in pumps, water turbines, vessel propellers, and even piping under some conditions. When such bubbles collapse, a localized high pressure can cause spalling on adjacent surfaces. | 8 | Metallurgy |
The Potential of Mean Force of a system with N particles is by construction the potential that gives the average force over all the configurations of all the n+1...N particles acting on a particle j at any fixed configuration keeping fixed a set of particles 1...n
Above, is the averaged force, i.e. "mean force" on particle j. And is the so-called potential of mean force. For , is the average work needed to bring the two particles from infinite separation to a distance . It is also related to the radial distribution function of the system, , by: | 7 | Physical Chemistry |
Recovery of metals from oxide matrixes is generally carried out using mineral acids. However, electrochemical dissolution of metal oxides in DES can allow to enhance the dissolution up to more than 10 000 times in pH neutral solutions.
Studies have shown that ionic oxides such as ZnO tend to have high solubility in ChCl:malonic acid, ChCl:urea and Ethaline, which can resemble the solubilities in aqueous acidic solutions, e.g., HCl. Covalent oxides such as TiO, however, exhibits almost no solubility. The electrochemical dissolution of metal oxides is strongly dependent on the proton activity from the HBD, i.e. capability of the protons to act as oxygen acceptors, and on the temperature. It has been reported that eutectic ionic fluids of lower pH-values, such as ChCl:oxalic acid and ChCl:lactic acid, allow a better solubility than that of higher pH (e.g., ChCl:acetic acid). Hence, different solubilities can be obtained by using, for instance, different carboxylic acids as HBD. | 8 | Metallurgy |
When a dry porous medium is brought into contact with a liquid, it will absorb the liquid at a rate which decreases over time. When considering evaporation, liquid penetration will reach a limit dependent on parameters of temperature, humidity and permeability. This process is known as evaporation limited capillary penetration and is widely observed in common situations including fluid absorption into paper and rising damp in concrete or masonry walls. For a bar shaped section of material with cross-sectional area A that is wetted on one end, the cumulative volume V of absorbed liquid after a time t is
where S is the sorptivity of the medium, in units of m·s or mm·min. This time dependence relation is similar to Washburn's equation for the wicking in capillaries and porous media. The quantity
is called the cumulative liquid intake, with the dimension of length. The wetted length of the bar, that is the distance between the wetted end of the bar and the so-called wet front, is dependent on the fraction f of the volume occupied by voids. This number f is the porosity of the medium; the wetted length is then
Some authors use the quantity S/f as the sorptivity.
The above description is for the case where gravity and evaporation do not play a role.
Sorptivity is a relevant property of building materials, because it affects the amount of rising dampness. Some values for the sorptivity of building materials are in the table below. | 7 | Physical Chemistry |
The typical impurity in triflic anhydride is triflic acid, which is also a colorless liquid. Samples of triflic anhydride can be assayed by F NMR spectroscopy: −72.6 ppm vs. −77.3 for TfOH (std CFCl). | 0 | Organic Chemistry |
Particular advantages of the powder technology include:
# Very high levels of purity and uniformity in starting materials
# Preservation of purity, due to the simpler subsequent fabrication process (fewer steps) that it makes possible
# Stabilization of the details of repetitive operations, by control of grain size during the input stages
# Absence of binding contact between segregated powder particles – or "inclusions" (called stringering) – as often occurs in melting processes
# No deformation needed to produce directional elongation of grains
# Capability to produce materials of controlled, uniform porosity.
# Capability to produce nearly net-shaped objects.
# Capability to produce materials which cannot be produced by any other technology.
# Capability to fabricate high-strength material like turbine blades.
# After sintering the mechanical strength to handling becomes higher.
The literature contains many references on sintering dissimilar materials to produce solid/solid-phase compounds or solid/melt mixtures at the processing stage. Almost any substance can be obtained in powder form, through either chemical, mechanical or physical processes, so basically any material can be obtained through sintering. When pure elements are sintered, the leftover powder is still pure, so it can be recycled. | 8 | Metallurgy |
The previous derivations assumed that there is only one species, A, adsorbing onto the surface. This section considers the case when there are two distinct adsorbates present in the system. Consider two species A and B that compete for the same adsorption sites. The following hypotheses are made here:
# All the sites are equivalent.
# Each site can hold at most one molecule of A, or one molecule of B, but not both simultaneously.
# There are no interactions between adsorbate molecules on adjacent sites.
As derived using kinetic considerations, the equilibrium constants for both A and B are given by
and
The site balance states that the concentration of total sites [S] is equal to the sum of free sites, sites occupied by A and sites occupied by B:
Inserting the equilibrium equations and rearranging in the same way we did for the single-species adsorption, we get similar expressions for both θ and θ: | 7 | Physical Chemistry |
The significance of CIA for astrophysics was recognized early-on, especially where dense atmospheres of mixtures of molecular hydrogen and helium gas exist. | 7 | Physical Chemistry |
In microholography, focused beams of light are used to record submicrometre-sized holograms in a photorefractive material, usually by the use of collinear beams. The writing process may use the same kinds of media that are used in other types of holographic data storage, and may use two–photon processes to form the holograms. | 5 | Photochemistry |
An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body. | 1 | Biochemistry |
The mechanism for chloroplast DNA (cpDNA) replication has not been conclusively determined, but two main models have been proposed. Scientists have attempted to observe chloroplast replication via electron microscopy since the 1970s. The results of the microscopy experiments led to the idea that chloroplast DNA replicates using a double displacement loop (D-loop). As the D-loop moves through the circular DNA, it adopts a theta intermediary form, also known as a Cairns replication intermediate, and completes replication with a rolling circle mechanism. Transcription starts at specific points of origin. Multiple replication forks open up, allowing replication machinery to transcribe the DNA. As replication continues, the forks grow and eventually converge. The new cpDNA structures separate, creating daughter cpDNA chromosomes.
In addition to the early microscopy experiments, this model is also supported by the amounts of deamination seen in cpDNA. Deamination occurs when an amino group is lost and is a mutation that often results in base changes. When adenine is deaminated, it becomes hypoxanthine. Hypoxanthine can bind to cytosine, and when the XC base pair is replicated, it becomes a GC (thus, an A → G base change).
In cpDNA, there are several A → G deamination gradients. DNA becomes susceptible to deamination events when it is single stranded. When replication forks form, the strand not being copied is single stranded, and thus at risk for A → G deamination. Therefore, gradients in deamination indicate that replication forks were most likely present and the direction that they initially opened (the highest gradient is most likely nearest the start site because it was single stranded for the longest amount of time). This mechanism is still the leading theory today; however, a second theory suggests that most cpDNA is actually linear and replicates through homologous recombination. It further contends that only a minority of the genetic material is kept in circular chromosomes while the rest is in branched, linear, or other complex structures.
One of competing model for cpDNA replication asserts that most cpDNA is linear and participates in homologous recombination and replication structures similar to the linear and circular DNA structures of bacteriophage T4. It has been established that some plants have linear cpDNA, such as maize, and that more species still contain complex structures that scientists do not yet understand. When the original experiments on cpDNA were performed, scientists did notice linear structures; however, they attributed these linear forms to broken circles. If the branched and complex structures seen in cpDNA experiments are real and not artifacts of concatenated circular DNA or broken circles, then a D-loop mechanism of replication is insufficient to explain how those structures would replicate. At the same time, homologous recombination does not expand the multiple A --> G gradients seen in plastomes. Because of the failure to explain the deamination gradient as well as the numerous plant species that have been shown to have circular cpDNA, the predominant theory continues to hold that most cpDNA is circular and most likely replicates via a D loop mechanism. | 5 | Photochemistry |
Possibly the most exciting potential use for PECO is producing hydrogen to be used as a source of renewable energy. Photoelectrochemical oxidation reactions that take place within PEC cells are the key to water splitting for hydrogen production. While the main concern with this technology is stability, systems that use PECO technology to create hydrogen from vapor rather than liquid water has demonstrated potential for greater stability. Early researchers working on vapor fed systems developed modules with 14% solar to hydrogen (STH) efficiency, while remaining stable for 1000+ hours. More recently, further technological developments have been made, demonstrated by the direct air electrolysis (DAE) module developed by Jining Guo and his team, which produces 99% pure hydrogen from the air and has demonstrated stability of 8 months thus far.
Promising research and technological advancement using PECO for different applications like water and air treatment and hydrogen production suggests that it is a valuable tool that can be utilized in a variety of ways. | 5 | Photochemistry |
T-1123 can be produced from m-diethylaminophenol, methyl isocyanate and methyl iodide. First, m-diethylaminophenol is reacted with methyl isocyanate to produce a methylcarbamate. The resulting methylcarbamate is then reacted with methyl iodide to produce T-1123. | 1 | Biochemistry |
This large and diverse class of steroids are biosynthesized from isoprenoids and structurally resemble cholesterol. Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens. | 1 | Biochemistry |
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