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Lichens come in many colors. Coloration is usually determined by the photosynthetic component. Special pigments, such as yellow usnic acid, give lichens a variety of colors, including reds, oranges, yellows, and browns, especially in exposed, dry habitats. In the absence of special pigments, lichens are usually bright green to olive gray when wet, gray or grayish-green to brown when dry. This is because moisture causes the surface skin (cortex) to become more transparent, exposing the green photobiont layer. Different colored lichens covering large areas of exposed rock surfaces, or lichens covering or hanging from bark can be a spectacular display when the patches of diverse colors "come to life" or "glow" in brilliant displays following rain.
Different colored lichens may inhabit different adjacent sections of a rock face, depending on the angle of exposure to light. Colonies of lichens may be spectacular in appearance, dominating much of the surface of the visual landscape in forests and natural places, such as the vertical "paint" covering the vast rock faces of Yosemite National Park.
Color is used in identification. The color of a lichen changes depending on whether the lichen is wet or dry. Color descriptions used for identification are based on the color that shows when the lichen is dry. Dry lichens with a cyanobacterium as the photosynthetic partner tend to be dark grey, brown, or black.
The underside of the leaf-like lobes of foliose lichens is a different color from the top side (dorsiventral), often brown or black, sometimes white. A fruticose lichen may have flattened "branches", appearing similar to a foliose lichen, but the underside of a leaf-like structure on a fruticose lichen is the same color as the top side. The leaf-like lobes of a foliose lichen may branch, giving the appearance of a fruticose lichen, but the underside will be a different color from the top side.
The sheen on some jelly-like gelatinous lichens is created by mucilaginous secretions. | 2 | Environmental Chemistry |
In crystallography, the basis and lattice are treated separately. For a perfect crystal the lattice gives the reciprocal lattice, which determines the positions (angles) of diffracted beams, and the basis gives the structure factor which determines the amplitude and phase of the diffracted beams:
where the sum is over all atoms in the unit cell, are the positional coordinates of the -th atom, and is the scattering factor of the -th atom. The coordinates have the directions and dimensions of the lattice vectors . That is, (0,0,0) is at the lattice point, the origin of position in the unit cell; (1,0,0) is at the next lattice point along and (1/2, 1/2, 1/2) is at the body center of the unit cell. defines a reciprocal lattice point at which corresponds to the real-space plane defined by the Miller indices (see Bragg's law).
is the vector sum of waves from all atoms within the unit cell. An atom at any lattice point has the reference phase angle zero for all since then is always an integer. A wave scattered from an atom at (1/2, 0, 0) will be in phase if is even, out of phase if is odd.
Again an alternative view using convolution can be helpful. Since [crystal structure] = [lattice] [basis], [crystal structure] = [lattice] [basis]; that is, scattering [reciprocal lattice] [structure factor]. | 3 | Analytical Chemistry |
The combinatorial complexity of signaling systems involving multi-state proteins poses two kinds of problems. The first problem is concerned with how such a system can be specified; i.e. how a modeler can specify all complexes, all changes those complexes undergo and all parameters and conditions governing those changes in a robust and efficient way. This problem is called the "specification problem". The second problem concerns computation. It asks questions about whether a combinatorially complex model, once specified, is computationally tractable, given the large number of states and the even larger number of possible transitions between states, whether it can be stored electronically, and whether it can be evaluated in a reasonable amount of computing time. This problem is called the "computation problem". Among the approaches that have been proposed to tackle combinatorial complexity in multi-state modeling, some are mainly concerned with addressing the specification problem, some are focused on finding effective methods of computation. Some tools address both specification and computation. The sections below discuss rule-based approaches to the specification problem and particle-based approaches to solving the computation problem. A wide range of computational tools exist for multi-state modeling. | 1 | Biochemistry |
Effectors are central to the pathogenic or symbiotic potential of microbes and microscopic plant-colonizing animals such as nematodes. Effectors typically are proteins that are delivered outside the microbe and into the host cell. These colonist-derived effectors manipulate the host's cell physiology and development. As such, effectors offer examples of co-evolution (example: a fungal protein that functions outside of the fungus but inside of plant cells has evolved to take on plant-specific functions). Pathogen host range is determined, among other things, by the presence of appropriate effectors that allow colonization of a particular host. Pathogen-derived effectors are a powerful tool to identify plant functions that play key roles in disease and in disease resistance. Apparently most effectors function to manipulate host physiology to allow disease to occur. Well-studied bacterial plant pathogens typically express a few dozen effectors, often delivered into the host by a Type III secretion apparatus. Fungal, oomycete and nematode plant pathogens apparently express a few hundred effectors.
So-called "core" effectors are defined operationally by their wide distribution across the population of a particular pathogen and their substantial contribution to pathogen virulence. Genomics can be used to identify core effectors, which can then be used to discover new R gene alleles, which can be used in plant breeding for disease resistance. | 1 | Biochemistry |
For incident photon energies E larger than two times the rest mass of the electron (1.022 MeV), pair production can occur. The resulting positron annihilates with one of the surrounding electrons, typically producing two photons with 511 keV. In a real detector (i.e. a detector of finite size) it is possible that after the annihilation:
* Both photons deposit their energy in the detector. This results in a 511 keV peak.
* One of the two photons escapes the detector and only one of the photons deposits its energy in the detector, resulting in a peak with E − 511 keV, the single escape peak.
* Both photons escape the detector, resulting in a peak with E − 2 × 511 keV, the double escape peak.
The above Am-Be-source spectrum shows an example of single and double escape peak in a real measurement. | 7 | Physical Chemistry |
Thermogravimetric analysis (TGA) is conducted on an instrument referred to as a thermogravimetric analyzer. A thermogravimetric analyzer continuously measures mass while the temperature of a sample is changed over time. Mass, temperature, and time are considered base measurements in thermogravimetric analysis while many additional measures may be derived from these three base measurements.
A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a furnace with a programmable control temperature. The temperature is generally increased at constant rate (or for some applications the temperature is controlled for a constant mass loss) to incur a thermal reaction. The thermal reaction may occur under a variety of atmospheres including: ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases, carburizing gases, vapors of liquids or "self-generated atmosphere"; as well as a variety of pressures including: a high vacuum, high pressure, constant pressure, or a controlled pressure.
The thermogravimetric data collected from a thermal reaction is compiled into a plot of mass or percentage of initial mass on the y axis versus either temperature or time on the x-axis. This plot, which is often smoothed, is referred to as a TGA curve. The first derivative of the TGA curve (the DTG curve) may be plotted to determine inflection points useful for in-depth interpretations as well as differential thermal analysis.
A TGA can be used for materials characterization through analysis of characteristic decomposition patterns. It is an especially useful technique for the study of polymeric materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers, coatings, paints, and fuels. | 7 | Physical Chemistry |
Solar energy production in the U.S. has doubled from 2013 to 2019. This was driven first by the falling price of quality silicon, and later simply by the globally plunging cost of photovoltaic modules. In 2018, the U.S. added 10.8GW of installed solar photovoltaic energy, an increase of 21%.
Latin America : Latin America has emerged as a promising region for solar energy development in recent years, with over 10 GW of installations in 2020. The solar market in Latin America has been driven by abundant solar resources, falling costs, competitive auctions and growing electricity demand. Some of the leading countries for solar energy in Latin America are Brazil, Mexico, Chile and Argentina. However, the solar market in Latin America also faces some challenges, such as political instability, financing gaps and power transmission bottlenecks.
Middle East and Africa : The Middle East and Africa has also experienced significant growth in solar energy deployment in recent years, with over 8 GW installations in 2020. The solar market in the Middle East and Africa has been driven by the low-cost generation of solar energy, the diversification of energy sources, the fight against climate change and rural electrification are motivated. Some of the notable countries for solar energy in the Middle East and Africa are Saudi Arabia, United Arab Emirates, Egypt, Morocco and South Africa. However, the solar market in the Middle East and Africa also faces several obstacles, including social unrest, regulatory uncertainty and technical barriers. | 7 | Physical Chemistry |
The Henderson–Hasselbach equation gives the pH of a solution relative to the pK of the acid–base pair. However the pK is dependent on ionic strength and temperature, and as it shifts so will the pH of a solution based on that acid–base pair. Because the doubly charged [HPO] is stabilized more by high ionic strength than is the singly-charged [HPO], their pK is somewhat dependent on ionic strength. The often-cited pK of ~7.2 is the value extrapolated to zero ionic strength, and is not applicable at physiological ionic strength.
Phillips et al. measured the pK at 10, 25, and 37 °C at various ionic strengths. For the latter two temperatures they report pK in Debye-Hückel equations (plotted in the accompanying figure for µ up to 0.5 M):<br>
at 25 °C: pKa = 7.18 − 1.52 sqrt(µ) + 1.96 µ <br>
at 37 °C: pKa = 7.15 − 1.56 sqrt(µ) + 1.22 µ
The pK is weakly dependent on temperature. Phillips et al. reported ∆H at 25 °C of 760 cal/mol (3180 J/mol) and a linear dependence of pK on 1/T (Van t Hoff equation). The positive ∆H results in an increase in K, and thus a decrease in pK with rising temperature, the change in pKa being 166 × the change in (1/T), which around 25 °C results in a change in pK of −0.00187 per degree. This applies strictly to the extrapolated thermodynamic pK' at infinite dilution, and as the figure shows, the temperature effect can be much larger at higher ionic strength. | 1 | Biochemistry |
An optode requires three components to function: a chemical that responds to an analyte, a polymer to immobilise the chemical transducer and instrumentation (optical fibre, light source, detector and other electronics). Optodes usually have the polymer matrix coated onto the tip of an optical fibre, but in the case of evanescent wave optodes the polymer is coated on a section of fibre that has been unsheathed. | 7 | Physical Chemistry |
Recent research indicates that hyperspectral imaging may be useful to detect the development of cracks in pavements which are hard to detect from images taken with visible spectrum cameras. | 7 | Physical Chemistry |
To perform a pulsed EDMR experiment, the system is first initialised by placing it in a magnetic field. This orients the spins of the electrons occupying the donor and acceptor in the direction of the magnetic field. To study the donor, we apply a microwave pulse ("γ" in the diagram) at a resonant frequency of the donor. This flips the spin of the electron on the donor. The donor electron can then decay to the acceptor energy state (it was forbidden from doing that before it was flipped due to the Pauli exclusion principle) and from there to the valence band, where it recombines with a hole. With more recombination, there will be fewer conduction electrons in the conduction band and a corresponding increase in the resistance, which can be directly measured. Above-bandgap light is used throughout the experiment to ensure that there are many electrons in the conduction band.
By scanning the frequency of the microwave pulse, we can find which frequencies are resonant, and with knowledge of the strength of the magnetic field, we can identify the donors energy levels from the resonant frequency and knowledge of the Zeeman effect. The donors energy levels act as a fingerprint by which we can identify the donor and its local electronic environment. By changing the frequency slightly, we can study the acceptor instead. | 7 | Physical Chemistry |
Work from the Widom laboratory has shown that nucleosomal DNA is in equilibrium between a wrapped and unwrapped state. Measurements of these rates using time-resolved FRET revealed that DNA within the nucleosome remains fully wrapped for only 250 ms before it is unwrapped for 10-50 ms and then rapidly rewrapped. This implies that DNA does not need to be actively dissociated from the nucleosome but that there is a significant fraction of time during which it is fully accessible. Indeed, this can be extended to the observation that introducing a DNA-binding sequence within the nucleosome increases the accessibility of adjacent regions of DNA when bound. This propensity for DNA within the nucleosome to "breathe" has important functional consequences for all DNA-binding proteins that operate in a chromatin environment. In particular, the dynamic breathing of nucleosomes plays an important role in restricting the advancement of RNA polymerase II during transcription elongation. | 1 | Biochemistry |
Amine oxides are common metabolites of medication and psychoactive drugs. Examples include nicotine, Zolmitriptan, and morphine.
Amine oxides of anti-cancer drugs have been developed as prodrugs that are metabolized in the oxygen-deficient cancer tissue to the active drug. | 0 | Organic Chemistry |
In 1955, Siekevitz and Potter demonstrated that adenine nucleotides were distributed in cells in two pools located in the mitochondrial and cytosolic compartments. Shortly thereafter, Pressman hypothesized that the two pools could exchange nucleotides. However, the existence of an ADP/ATP transporter was not postulated until 1964 when Bruni et al. uncovered an inhibitory effect of atractyloside on the energy-transfer system (oxidative phosphorylation) and ADP binding sites of rat liver mitochondria.
Soon after, an overwhelming amount of research was done in proving the existence and elucidating the link between ADP/ATP translocase and energy transport. cDNA of ADP/ATP translocase was sequenced for bovine in 1982 and a yeast species Saccharomyces cerevisiae in 1986 before finally Battini et al. sequenced a cDNA clone of the human transporter in 1989. The homology in the coding sequences between human and yeast ADP/ATP translocase was 47% while bovine and human sequences extended remarkable to 266 out of 297 residues, or 89.6%. In both cases, the most conserved residues lie in the ADP/ATP substrate binding pocket. | 1 | Biochemistry |
Located within the , the Institute of Analytical Sciences (UMR 5280) is a French research, training and expertise center specializing in analytical chemistry. It is a Joint Research Unit (French: Unité mixte de recherche or UMR) affiliated with the National Centre for Scientific Research (CNRS), Claude Bernard University Lyon 1, and École normale supérieure de Lyon. | 3 | Analytical Chemistry |
Ingram began her academic studies at Yavapai Community College in Arizona where she earned an associates degree. She subsequently studied at New Mexico State University and earned a bachelors degree in chemistry. Her Ph.D. is in chemistry from the University of Arizona. | 3 | Analytical Chemistry |
The outcomes of manganese-mediated coupling reactions depend on both the structure of the substrate(s) and the reaction conditions. This section describes the scope and limitations of inter- and intramolecular manganese-mediated radical coupling reactions and is organized according to the carbonyl compound employed as the substrate.
Intermolecular reactions between ketones/aldehydes and alkenes tend to result in low yields. In the absence of copper(II) acetate, hydrogen atom abstraction occurs, yielding saturated ketones or aldehydes.
When Cu(OAc) is present, further oxidation to carbocations followed by elimination takes place, leading to the formation of β,γ-unsaturated carbonyl compounds in moderate yields.
Aromatic compounds are also useful radical acceptors in manganese(III)-mediated coupling reactions. Furan reacts selectively at the α position to afford substituted products in high yield.
Lactonization of alkenes in the presence of acetic acid and acetate salts is a synthetically useful method for the synthesis of γ-lactones. Selectivity is high for the radical addition that leads to the more stable adduct radical, and trans lactones are selectively formed from either cis or trans acyclic alkenes.
β-Dicarbonyl compounds are useful substrates for the formation of dihydrofurans. Copper(II) acetate is not necessary in this case because of the high resonance stabilization of the intermediate diphenylmethyl radical.
When alkenes or carbonyl compounds containing pendant unsaturated moiety are treated with manganese(III) acetate, tandem intramolecular cyclization reactions may occur. Generally, exo cyclization of terminal double bonds is favored, as shown in equation (10). A variety of substitution patterns may be employed for this transformation, and yields are generally higher than intermolecular coupling reactions.
The stereochemical course of tandem reactions can be understood in some cases by invoking a chairlike transition state with as many substituents as possible in pseudoequatorial positions; however, a number of examples exhibiting unpredictable stereochemistry are known.
Nitriles are useful as radical acceptors in tandem cyclizations. Hydrolysis of the resulting imine leads to polycyclic ketones in moderate yields with good stereoselectivity. | 0 | Organic Chemistry |
Amorphous phases are important constituents of thin films. Thin films are solid layers of a few nanometres to tens of micrometres thickness that are deposited onto a substrate. So-called structure zone models were developed to describe the microstructure of thin films as a function of the homologous temperature (T), which is the ratio of deposition temperature to melting temperature. According to these models, a necessary condition for the occurrence of amorphous phases is that (T) has to be smaller than 0.3. The deposition temperature must be below 30% of the melting temperature. | 7 | Physical Chemistry |
Measuring the extent and kinetics of radioligand binding is important in determining information about binding sites of radioligands, and subsequent affinity to potential drugs. Three different binding assays are typically used for radioligand binding; these are saturation, competition, and kinetic binding. | 1 | Biochemistry |
High-pressure lamps are much more similar to HID lamps than fluorescent lamps.
These lamps radiate a broad-band UVC radiation, rather than a single line. They are widely used in industrial water treatment, because they are very intense radiation sources. High-pressure lamps produce very bright bluish white light. | 5 | Photochemistry |
Methionine sulfoximine (MSO, also known as MetSox) is an irreversible glutamine synthetase inhibitor. It is the sulfoximine derivative of methionine with convulsant effects.
Methionine sulfoximine is composed of two different diastereomers, which are L-S-Methionine sulfoximine and L-R-Methionine sulfoximine. These affect the longevity of the model mouse for Lou Gehrig's disease. Overproduction of glutamate results to excitotoxicity, which kills the cell. Since methionine sulfoximine inhibits glutamate production in the brain, it prevents excitotoxicity. Thus, increasing the longevity of the mice. | 1 | Biochemistry |
Theory and instrumentation of Raman/AFM and IR/AFM combine the theory of SPR (AFM and NSOM) and Raman scattering, and this combination is based on TERS. In TERS, the electric field of excitation source induces an SPR in the tip of the probe. If the electric field vector of the incidence light is perpendicular (s-polarized) to the metal tip axis, the free electrons are driven to the sides lateral of the tip. If it is parallel (p-polarized) to the tip axis, the free electrons on the surface of the metal are confined to the end of the apex of tip. As a consequence, there is a very large electric-field enhancement which is sensed by the molecules close to it leading to a stronger signal.
A typical approach in a TERS experiment is to focus the laser beam on a metal tip with the light polarized along the tip axis, followed by collection of the surface-enhanced Raman scattered light from the sample in the enhancement zone of the tip using optics.
Depending on the sample and experiment, different illumination geometries have been applied in TERS experiments, as shown in figure 4. With p-polarized (parallel to the surface normal) incidence light, the plasmon excitation at the tip is most efficient. If the focusing objective lens is also used for collecting the scattered photons (backscattering geometry), the optimum angle is around 55° with respect to the surface normal. This is because the scattering lobe is maximum with this configuration and it provides a much enhanced signal. The setup of figure 4(A) is usually used for the large thick samples. Setup (B) handles semi-transparent or transparent samples, such as single cells, tissue samples and biopolymers. The setup of figure 4(C) is preferred for opaque samples because all the light would be focused by the parabolic mirror. | 7 | Physical Chemistry |
Antimonide bromides or bromide antimonides are compounds containing anions composed of bromide (Br) and antimonide (Sb). They can be considered as mixed anion compounds. They are in the category of pnictidehalides. Related compounds include the antimonide chlorides, antimonide iodides, arsenide chlorides, arsenide bromides, arsenide iodides, phosphide chlorides, phosphide bromides, and phosphide iodides. The bromoantimonates have antimony in positive oxidation states.
The antimony can be linked into chains, in which case it has a formal oxidation state of −1. Alternately it can be in pairs as Sb, with an oxidation state of −2 for each atom.
Many of these compounds are clathrates, whereby there are two interpenetrating structures that are only weakly bound to each other by van der Waals force. | 6 | Supramolecular Chemistry |
4-Nitrophenol can be prepared by nitration of phenol using dilute nitric acid at room temperature. The reaction produces a mixture of 2-nitrophenol and 4-nitrophenol. | 3 | Analytical Chemistry |
The monomers, 3-hydroxybutanoic acid and 3-hydroxypentanoic acid, are joined by ester bonds; the back bone of the polymer is made up of carbon and oxygen atoms.
The property of the PHBV depends upon the ratio of these two monomers in it.
3-hydroxybutanoic acid provides stiffness while 3-hydroxypentanoic acid promotes flexibility. Thus PHBV can be made to resemble either polypropylene or polyethylene by changing the ratio of monomers. Increase in the ratio of 3-hydroxybutanoic acid to 3-hydroxypentanoic acid results in an increase in melting point, water permeability, glass transition temperature (T) and tensile strength. However impact resistance is reduced. | 1 | Biochemistry |
Trifluoromethylation in organic chemistry describes any organic reaction that introduces a trifluoromethyl group in an organic compound. Trifluoromethylated compounds are of some importance in pharmaceutical industry and agrochemicals. Several notable pharmaceutical compounds have a trifluoromethyl group incorporated: fluoxetine, mefloquine, Leflunomide, nulitamide, dutasteride, bicalutamide, aprepitant, celecoxib, fipronil, fluazinam, penthiopyrad, picoxystrobin, fluridone, norflurazon, sorafenib and triflurazin. A relevant agrochemical is trifluralin. The development of synthetic methods for adding trifluoromethyl groups to chemical compounds is actively pursued in academic research. | 0 | Organic Chemistry |
Polysorbates are a class of emulsifiers used in some pharmaceuticals and food preparation. They are commonly used in oral and topical pharmaceutical dosage forms. They are also often used in cosmetics to solubilize essential oils into water-based products. Polysorbates are oily liquids derived from ethoxylated sorbitan (a derivative of sorbitol) esterified with fatty acids. Common brand names for polysorbates include Kolliphor, Scattics, Alkest, Canarcel, Tween, and Kotilen. | 0 | Organic Chemistry |
Thalidomide, sold under the brand names Contergan and Thalomid among others, is an oral medication used to treat a number of cancers (e.g., multiple myeloma), graft-versus-host disease, and many skin disorders (e.g., complications of leprosy such as skin lesions). While thalidomide has been used in a number of HIV-associated conditions, such use is associated with increased levels of the virus.
Common side effects include sleepiness, rash, and dizziness. Severe side effects include tumor lysis syndrome, blood clots, and peripheral neuropathy. Thalidomide is a known human teratogen and carries an extremely high risk of severe, life-threatening birth defects if administered during pregnancy. It causes skeletal deformities such as amelia (absence of legs and/or arms), absence of bones, and phocomelia (malformation of the limbs). A single dose of thalidomide, regardless of dosage, is enough to cause teratogenic effects.
Thalidomide was first marketed in 1957 in West Germany, where it was available over the counter. When first released, thalidomide was promoted for anxiety, trouble sleeping, "tension", and morning sickness. While it was initially thought to be safe in pregnancy, concerns regarding birth defects arose, resulting in its removal from the market in Europe in 1961. The total number of infants affected by thalidomide use during pregnancy is estimated at 10,000, of whom about 40% died around the time of birth. Those who survived had limb, eye, urinary tract, and heart problems. Its initial entry into the US market was prevented by Frances Kelsey, a reviewer at the FDA. The birth defects caused by thalidomide led to the development of greater drug regulation and monitoring in many countries.
It was approved in the United States in 1998 for use as a treatment for cancer. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. | 4 | Stereochemistry |
The optical density is generated from equation:
:Optical density= Log (Intensity of incident light / Intensity of<br /> Transmitted light)
In practical terms, a sample that contains no DNA or RNA should not<br /> absorb any of the ultraviolet light and therefore produce an OD of 0
Optical density= Log (100/100)=0
When using spectrophotometric analysis to determine the concentration of DNA or RNA, the Beer–Lambert law is used to determine unknown concentrations without the need for standard curves. In essence, the Beer Lambert Law makes it possible to relate the amount of light absorbed to the concentration of the absorbing molecule. The following absorbance units to nucleic acid concentration conversion factors are used to convert OD to concentration of unknown nucleic acid samples:
:A260 dsDNA = 50 µg/ml
:A260 ssDNA = 33 µg/ml
:A260 ssRNA = 40 µg/ml | 7 | Physical Chemistry |
Single nucleotide polymorphism (SNP) in langerin gene may affect the stability as well as the affinity of the protein for some carbohydrates. The most common polymorphism is a replacement of alanine for valine in the 278. position (rs741326). Allelic frequency of this polymorphism is up to 48 %, but it probably does not have any influence on stability and affinity of langerin. Substitution of asparagine for aspartic acid in the 288. position leads to 10-fold reduction in the ability to recognize mannose-BSA. A substitution of tryptophane for arginine in the 264. position leads to a loss of Birbeck granules. | 1 | Biochemistry |
While the idea of non-synaptic interactions between neurons has existed since the 19th century, there has historically been considerable skepticism in the field of neuroscience. Many people believed that the micro electrical fields produced by the neurons themselves were so small that they were negligible. While many supporters of the ephaptic coupling theory have been trying to prove its existence through experiments that block both chemical and electrical synapses, still some opponents in the field express caution. For example, in 2014, one scientist published a review that presents his skepticism on the idea of ephaptic coupling, saying “The agreement between their simulations and Poelzing’s data is impressive, but I will need a more definitive experimental confirmation before I can embrace the ephaptic hypothesis.” He bases his caution in wanting more distinction between gap junctions' propagation of charge and true ephaptic coupling. Whether it is a true lack of evidence or simply obstinance in the face of change, many in the field are still not entirely convinced there is unambiguous evidence of ephaptic coupling.
Research continues and in 2018 what appears to be a definitive experiment was published. A process of slow wave propagation in the brain of about 0.1m per second has been shown in vivo. Slow wave propagation was also recorded by inserting two electrodes into two ends of a piece of mouse brain taken from a freshly killed mouse. The tissue was then cut between the two electrode positions, severing any possible link by neurons or gap junctions between the two electrodes. The slow wave continued to propagate and could only be stopped by separating the two pieces of tissue with a 400-micron gap. Assuming the reproducibility of this experiment skeptics of ephaptic coupling should be satisfied it is a real phenomenon and investigations will focus now on its mechanisms and role rather than its existence. | 1 | Biochemistry |
Fischer carbenes are used with alkynes as the starting reagents for the Wulff–Dötz reaction, forming phenols. | 0 | Organic Chemistry |
An application of dendritic growth in directional solidification is gas turbine engine blades which are used at high temperatures and must handle high stresses along the major axes. At high temperatures, grain boundaries are weaker than grains. In order to minimize the effect on properties, grain boundaries are aligned parallel to the dendrites. The first alloy used in this application was a nickel-based alloy (MAR M-200) with 12.5% tungsten, which accumulated in the dendrites during solidification. This resulted in blades with high strength and creep resistance extending along the length of the casting, giving improved properties compared to the traditionally-cast equivalent. | 8 | Metallurgy |
Condensation polymers tend to be more biodegradable than addition polymers. The peptide or ester bonds between monomers can be hydrolysed, especially in the presence of catalysts or bacterial enzymes. | 7 | Physical Chemistry |
The I. I. Rabi Award, founded in 1983, is awarded annually by IEEE.
: "The Rabi Award is to recognize outstanding contributions related to the fields of atomic and molecular frequency standards, and time transfer and dissemination."
The award is named after Isidor Isaac Rabi, Nobel Prize winner in 1944. He was the first recipient of the award, for his experimental and theoretical work on atomic beam resonance spectroscopy. | 7 | Physical Chemistry |
The symbiotic relationship between the Hawaiian bobtail squid Euprymna scolopes and the marine gram-negative bacterium Aliivibrio fischeri has been well studied. The two organisms exhibit a mutualistic relationship in which bioluminescence produced by A. fischeri helps to attract pray to the squid host, which provides nutrient-rich tissues and a protected environment forA. fischeri. Bioluminescence provided by A. fischeri also aids in the defense of the squid E. scolopes by providing camouflage during its nighttime foraging activity. Following bacterial colonization, the specialized organs of the squid undergo developmental changes and a relationship becomes established. The squid expels 90% of the bacterial population each morning, because it no longer needs to produce bioluminescence in the daylight. This expulsion benefits the bacteria by aiding in their dissemination. A single expulsion by one bobtail squid produces enough bacterial symbionts to fill 10,000m of seawater at a concentration that is comparable to what is found in coastal waters. Thus, in at least some habitats, the symbiotic relationship between A. fischeri and E. scolopes plays a key role in determining the abundance and distribution of E. scolopes. There is a higher abundance of A. fischeri in the vicinity of a population of E. scolopes and this abundance markedly decreases with increasing distance from the host's habitat.
Bioluminescent Photobacterium species also engage in mutually beneficial associations with fish and squid. Dense populations of P. kishitanii, P. leiogathi, and P. mandapamensis can live in the light organs of marine fish and squid, and are provided with nutrients and oxygen for reproduction in return for providing bioluminescence to their hosts, which can aid in sex-specific signaling, predator avoidance, locating or attracting prey, and schooling.<!-- Empty reference | 1 | Biochemistry |
Water is particularly common solvent to be found in crystals because it is small and polar. But all solvents can be found in some host crystals. Water is noteworthy because it is reactive, whereas other solvents such as benzene are considered to be chemically innocuous. Occasionally more than one solvent is found in a crystal, and often the stoichiometry is variable, reflected in the crystallographic concept of "partial occupancy". It is common and conventional for a chemist to "dry" a sample with a combination of vacuum and heat "to constant weight".
For other solvents of crystallization, analysis is conveniently accomplished by dissolving the sample in a deuterated solvent and analyzing the sample for solvent signals by NMR spectroscopy. Single crystal X-ray crystallography is often able to detect the presence of these solvents of crystallization as well. Other methods may be currently available. | 3 | Analytical Chemistry |
Clarification is a name for the method of separating fluid from solid particles. Often clarification is used along with flocculation to make the solid particles sink faster to the bottom of the clarification pool while fluid is obtained from the surface which is free of solid particles.
Thickening is the same as clarification except reverse. Solids that sink to the bottom are obtained and fluid is rejected from the surface.
The difference of these methods could be demonstrated with the methods used in waste water processing: in the clarification phase, sludge sinks to the bottom of the pool and clear water flows over the clear water grooves and continues its journey. The obtained sludge is then pumped into the thickeners, where sludge thickens farther and is then obtained to be pumped into digestion to be prepared into fertilizer. | 3 | Analytical Chemistry |
Isolobal fragments of tetrahedral and octahedral molecules can be related. Structures with the same number of frontier orbitals are isolobal to one another. For example, the methane with two hydrogen atoms removed, CH is isolobal to a d ML complex formed from an octahedral starting complex (Figure 4). | 0 | Organic Chemistry |
The Fowkes hypothesis (after F. M. Fowkes) is a first order approximation for surface energy. It states the surface energy is the sum of each component's forces:
γ=γ+γ+γ+...
where γ is the dispersion component, γ is the polar, γ is the dipole and so on.
The Fowkes hypothesis goes further making the approximation that the interface between an apolar liquid and apolar solid where there are only dispersive interactions acting across the interface can be estimated using the geometric mean of the contributions from each surface i.e.
γ=γ+γ-2(γ x γ) | 7 | Physical Chemistry |
The α-amylases () (CAS 9014-71-5) (alternative names: 1,4-α--glucan glucanohydrolase; glycogenase) are calcium metalloenzymes. By acting at random locations along the starch chain, α-amylase breaks down long-chain saccharides, ultimately yielding either maltotriose and maltose from amylose, or maltose, glucose and "limit dextrin" from amylopectin. They belong to glycoside hydrolase family 13 (https://www.cazypedia.org/index.php/Glycoside_Hydrolase_Family_13).
Because it can act anywhere on the substrate, α-amylase tends to be faster-acting than β-amylase. In animals, it is a major digestive enzyme, and its optimum pH is 6.7–7.0.
In human physiology, both the salivary and pancreatic amylases are α-amylases.
The α-amylase form is also found in plants, fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus). | 1 | Biochemistry |
The 3-Hydroxypropionate bicycle, also known as 3-HP/malyl-CoA cycle, discovered only in 1989, is utilized by green non-sulfur phototrophs of Chloroflexaceae family, including the maximum exponent of this family Chloroflexus auranticus by which this way was discovered and demonstrated. The 3-Hydroxipropionate bicycle is composed of two cycles and the name of this way comes from the 3-Hydroxyporopionate which corresponds to an intermediate characteristic of it.
The first cycle is a way of synthesis of glyoxylate. During this cycle, two equivalents of bicarbonate are fixed by the action of two enzymes: the Acetyl-CoA carboxylase catalyzes the carboxylation of the Acetyl-CoA to Malonyl-CoA and Propionyl-CoA carboxylase catalyses the carboxylation of propionyl-CoA to methylamalonyl-CoA. From this point a series of reactions lead to the formation of glyoxylate which will thus become part of the second cycle.
In the second cycle, glyoxylate is approximately one equivalent of propionyl-CoA forming methylamalonyl-CoA. This, in turn, is then converted through a series of reactions into citramalyl-CoA. The citramalyl-CoA is split into pyruvate and Acetyl-CoA thanks to the enzyme MMC lyase. At this point the pyruvate is released, while the Acetyl-CoA is reused and carboxylated again at Malonyl-CoA thus reconstituting the cycle.
A total of 19 reactions are involved in 3-hydroxypropionate bicycle and 13 multifunctional enzymes are used. The multifunctionality of these enzymes is an important feature of this pathway which thus allows the fixation of three bicarbonate molecules.
It is a very expensive pathway: 7 ATP molecules are used for the synthesis of the new pyruvate and 3 ATP for the phosphate triose.
An important characteristic of this cycle is that it allows the co-assimilation of numerous compounds making it suitable for the mixotrophic organisms. | 5 | Photochemistry |
Photocatalyst activity indicator ink (paii) is a substance used to identify the presence of an underlying heterogeneous photocatalyst and to measure its activity. Such inks render visible the activity of photocatalytic coatings applied to various "self-cleaning" products. The inks contain a dyestuff that reacts to ultraviolet radiation in the presence of the photocatalytic agent in the coating. They are applied to the coated product (usually by a pen, brush, or drawdown bar) and show a color change or disappearance when exposed to ultraviolet radiation. The use of a paii based on the dye resazurin forms the basis of an ISO standard test for photocatalytic activity. | 5 | Photochemistry |
There are ten known isoforms of adenylyl cyclases in mammals:
These are also sometimes called simply AC1, AC2, etc., and, somewhat confusingly, sometimes Roman numerals are used for these isoforms that all belong to the overall AC class III. They differ mainly in how they are regulated, and are differentially expressed in various tissues throughout mammalian development. | 1 | Biochemistry |
* 999.999—six nines fine: The purest gold ever produced. Refined by the Perth Mint in 1957.
* 999.99—five nines fine: The purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness, including the world's largest, at 100 kg.
* 999.9—four nines fine: Most popular. E.g. ordinary Canadian Gold Maple Leaf and American Buffalo coins.
* 999—24 karat, also occasionally known as three nines fine: e.g., Chinese Gold Panda coins.
* 995: The minimum allowed in Good Delivery gold bars.
* 990—two nines fine
* 986—Ducat fineness: Formerly used by Venetian and Holy Roman Empire mints; still in use in Austria and Hungary.
* 958.3—23 karat
* 916—22 karat: Crown gold. Historically the most widely used fineness for gold bullion coins, such as the oldest American Eagle denominations from 1795–1833. Currently used for British Sovereigns, South African Krugerrands, and the modern (1986—present) American Gold Eagles.
* 900—one nine fine: American Eagle denominations for 1837–1933; currently used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs).
* 899—American Eagles briefly for 1834—1836.
* 834—20 karat
* 750—18 karat: In Spain oro de primera ley (first law gold).
* 625—15 karat
* 585—14 karat
* 583.3—14 karat: In Spain oro de segunda ley (second law gold).
* 500—12 karat
* 417—10 karat: Lowest legal solid gold karat made in the US prior to the August 2018 revision of the FTC Guides (Now 1 karat is legal).
* 375—9 karat: Minimum standard for gold in some of the Commonwealth realms: Australia, Canada, New Zealand, UK, etc. It is also the minimum in Austria, Ireland, Portugal and France.
* 333—8 karat: Minimum standard for gold in Germany after 1884. It is also the minimum for Denmark, Greece and Mexico.
* 1 karat: Legal minimum for gold in the US since the revision of the FTC Guides of August 2018. | 8 | Metallurgy |
The R is the functional group attached to a tertiary carbon. If the functional group was an OH group, this compound would be commonly called tert-butanol or t-butanol. When a functional group is attached to a tertiary carbon, the prefix -tert (-t) is used in the common name for the compound. An example of this is shown in the figure. | 0 | Organic Chemistry |
The major neurotransmitter systems are the noradrenaline (norepinephrine) system, the dopamine system, the serotonin system, and the cholinergic system. Drugs targeting the neurotransmitter of such systems affect the whole system, which explains the mode of action of many drugs.
Most other neurotransmitters, on the other hand, e.g. glutamate, GABA and glycine, are used very generally throughout the central nervous system. | 1 | Biochemistry |
Chromosome jumping (or chromosome hopping) was first described in 1984 by Collins and Weissman.
At the time, cloning techniques allowed for generation of clones of limited size (up to 240kb), and cytogenetic techniques allowed for mapping such clones to a small region of a particular chromosome to a resolution of around 5-10Mb. Therefore, a major gap remained in resolution between available technologies, and no methods were available for mapping larger areas of the genome. | 1 | Biochemistry |
In chemistry, the capped trigonal prismatic molecular geometry describes the shape of compounds where seven atoms or groups of atoms or ligands are arranged around a central atom defining the vertices of an augmented triangular prism. This shape has C symmetry and is one of the three common shapes for heptacoordinate transition metal complexes, along with the pentagonal bipyramid and the capped octahedron.
Examples of the capped trigonal prismatic molecular geometry are the heptafluorotantalate () and the heptafluoroniobate () ions. | 4 | Stereochemistry |
Some commonly used types of genetic markers are:
* RFLP (or Restriction fragment length polymorphism)
* SSLP (or Simple sequence length polymorphism)
* AFLP (or Amplified fragment length polymorphism)
* RAPD (or Random amplification of polymorphic DNA)
* VNTR (or Variable number tandem repeat)
* SSCP (or Single-strand conformation polymorphism)
* Microsatellite polymorphism, (or Simple sequence repeat)
* SNP (or Single nucleotide polymorphism)
* STR (or Short tandem repeat)
* SFP (or Single feature polymorphism)
* DArT (or Diversity Arrays Technology)
* RAD markers (or Restriction site associated DNA markers)
* (using Sequence-tagged sites)
Molecular genetic markers can be divided into two classes: a) biochemical markers which detect variation at the gene product level such as changes in proteins and amino acids and b) molecular markers which detect variation at the DNA level such as nucleotide changes: deletion, duplication, inversion and/or insertion. Markers can exhibit two modes of inheritance, i.e. dominant/recessive or co-dominant. If the genetic pattern of homo-zygotes can be distinguished from that of hetero-zygotes, then a marker is said to be co-dominant. Generally co-dominant markers are more informative than the dominant markers. | 1 | Biochemistry |
Amines are the most prevalent absorbent in postcombustion carbon capture technology today. In particular, monoethanolamine (MEA) has been used in industrial scales in postcombustion carbon capture, as well as in other CO separations, such as "sweetening" of natural gas. However, amines are corrosive, degrade over time, and require large industrial facilities. Ionic liquids on the other hand, have low vapor pressures . This property results from their strong Coulombic attractive force. Vapor pressure remains low through the substance's thermal decomposition point (typically >300 °C). In principle, this low vapor pressure simplifies their use and makes them "green" alternatives. Additionally, it reduces risk of contamination of the CO gas stream and of leakage into the environment.
The solubility of CO in ionic liquids is governed primarily by the anion, less so by the cation. The hexafluorophosphate (PF) and tetrafluoroborate (BF) anions have been shown to be especially amenable to CO capture.
Ionic liquids have been considered as solvents in a variety of liquid-liquid extraction processes, but never commercialized. Beside that, ionic liquids have replaced the conventional volatile solvents in industry such as absorption of gases or extractive distillation. Additionally, ionic liquids are used as co-solutes for the generation of aqueous biphasic systems, or purification of biomolecules. | 7 | Physical Chemistry |
Surface modification makes paper hydrophobic and oleophilic. This combination allows ink oil to penetrate the paper, but prevents dampening water absorption, which increases papers printability.
Three different plasma-solid interactions are used: etching/ablation, plasma activation, and plasma coating. Etching or ablation is when material is removed from the surface of the solid. Plasma activation is where species in the plasma like ions, electrons, or radicals are used to chemically or physically modify the surface. Lastly, plasma coating is where material is coated to the surface in the form of a thin film. Plasma coating can be used to add hydrocarbons to surfaces which can make a surface non-polar or hydrophobic. The specific type of plasma coating used to add hydrocarbons is called plasma enhanced chemical vapor deposition process or PCVD. | 7 | Physical Chemistry |
Though there are many methods to detect protein–protein interactions, the majority of these methods—such as co-immunoprecipitation, fluorescence resonance energy transfer (FRET) and dual polarisation interferometry—are not screening approaches. | 1 | Biochemistry |
The BCA Micro BCA assay is a 3-component protocol which uses concentrated stocks of the Biuret reaction, BCA, and copper(II) reagents. It allows for an improved sensitivity of ~2 - 40 μg/mL vs 20 - 2000 µg/mL of the original BCA assay. However, it has a different, and generally speaking more sensitive, interference from non-protein components. Kits for the Micro BCA assay are available from at least two commercial vendors. Notably, the composition and use of a "Micro BCA Reagent and Protocol" was described in the original manuscript by Smith, and modern kits likely consist of an exact or highly similar formulation. The protocol consists of mixing Micro-Reagent B and the Copper Solution 25:1 to form Micro-Reagent C (MC), which is not shelf stable and should be freshly prepared, and then mixing MC 1:1 with Micro-Reagent A to produce the final (also unstable) assay working solution. Micro-Reagent A, Micro-Reagent B, and Copper Solution are stable indefinitely at room temperature.
Micro-Reagent A (MA)
* 8% w/v NaCO·HO (CAS: 5968-11-6)
* 1.6% w/v NaOH (CAS: 1310-73-2)
* 1.6% w/v Na tartrate (CAS: 868-18-8) (10x concentration as Reagent A in Original BCA Assay above)
* Sufficient NaHCO (CAS: 144-55-8) to adjust pH to 11.25
Micro-Reagent B (MB)
* 4% w/v BCA-Na (CAS: 979-88-4) (4x concentration as Reagent A in Original BCA Assay above)
Copper Solution
* 4% w/v CuSO·5HO (CAS: 7758-99-8) (Same concentration as Reagent B in Original BCA Assay above) | 1 | Biochemistry |
A fecal coliform (British: faecal coliform) is a facultatively anaerobic, rod-shaped, gram-negative, non-sporulating bacterium. Coliform bacteria generally originate in the intestines of warm-blooded animals. Fecal coliforms are capable of growth in the presence of bile salts or similar surface agents, are oxidase negative, and produce acid and gas from lactose within 48 hours at 44 ± 0.5°C. The term thermotolerant coliform is more correct and is gaining acceptance over "fecal coliform".
Coliform bacteria include genera that originate in feces (e.g. Escherichia) as well as genera not of fecal origin (e.g. Enterobacter, Klebsiella, Citrobacter). The assay is intended to be an indicator of fecal contamination; more specifically of E. coli which is an indicator microorganism for other pathogens that may be present in feces. Presence of fecal coliforms in water may not be directly harmful, and does not necessarily indicate the presence of feces. | 3 | Analytical Chemistry |
In chemistry, T-shaped molecular geometry describes the structures of some molecules where a central atom has three ligands. Ordinarily, three-coordinated compounds adopt trigonal planar or pyramidal geometries. Examples of T-shaped molecules are the halogen trifluorides, such as ClF.
According to VSEPR theory, T-shaped geometry results when three ligands and two lone pairs of electrons are bonded to the central atom, written in AXE notation as AXE. The T-shaped geometry is related to the trigonal bipyramidal molecular geometry for AX molecules with three equatorial and two axial ligands. In an AXE molecule, the two lone pairs occupy two equatorial positions, and the three ligand atoms occupy the two axial positions as well as one equatorial position. The three atoms bond at 90° angles on one side of the central atom, producing the T shape.
The trifluoroxenate(II) anion, , has been investigated as a possible first example of an AXE molecule, which might be expected by VSEPR reasoning to have six electron pairs in an octahedral arrangement with both the three lone pairs and the three ligands in a mer or T-shaped orientations. Although this anion has been detected in the gas phase, attempts at synthesis in solution and experimental structure determination were unsuccessful. A computational chemistry study showed a distorted planar Y-shaped geometry with the smallest F–Xe–F bond angle equal to 69°, rather than 90° as in a T-shaped geometry. | 4 | Stereochemistry |
In Chaetomium thermophilum, a complex of a metabolon exists between fatty acid synthase and a MDa carboxylase, and was observed using chemical cross-linking coupled to mass spectrometry and visualized by cryo-electron microscopy. The Fatty acid synthesis metabolon in C. thermophilum is highly flexible, and although a high-resolution structure of Fatty acid synthase was possible, the metabolon was highly flexible, hindering high-resolution structure determination. | 1 | Biochemistry |
A single water molecule can participate in a maximum of four hydrogen bonds because it can accept two bonds using the lone pairs on oxygen and donate two hydrogen atoms. Other molecules like hydrogen fluoride, ammonia, and methanol can also form hydrogen bonds. However, they do not show anomalous thermodynamic, kinetic, or structural properties like those observed in water because none of them can form four hydrogen bonds: either they cannot donate or accept hydrogen atoms, or there are steric effects in bulky residues. In water, intermolecular tetrahedral structures form due to the four hydrogen bonds, thereby forming an open structure and a three-dimensional bonding network, resulting in the anomalous decrease in density when cooled below 4 °C. This repeated, constantly reorganizing unit defines a three-dimensional network extending throughout the liquid. This view is based upon neutron scattering studies and computer simulations, and it makes sense in the light of the unambiguously tetrahedral arrangement of water molecules in ice structures.
However, there is an alternative theory for the structure of water. In 2004, a controversial paper from Stockholm University suggested that water molecules in the liquid state typically bind not to four but only two others; thus forming chains and rings. The term "string theory of water" (which is not to be confused with the string theory of physics) was coined. These observations were based upon X-ray absorption spectroscopy that probed the local environment of individual oxygen atoms. | 2 | Environmental Chemistry |
The antibodies from lymphocyte secretions (ALS) assay is an immunological assay to detect active diseases like tuberculosis, cholera, typhoid etc. Recently, ALS assay nods the scientific community as it is rapidly used for diagnosis of Tuberculosis. The principle is based on the secretion of antibody from in vivo activated plasma B cells found in blood circulation for a short period of time in response to TB-antigens during active TB infection rather than latent TB infection. | 1 | Biochemistry |
A wide range of possible FCS experiments involve chemical reactions that continually fluctuate from equilibrium because of thermal motions (and then "relax"). In contrast to diffusion, which is also a relaxation process, the fluctuations cause changes between states of different energies. One very simple system showing chemical relaxation would be a stationary binding site in the measurement volume, where particles only produce signal when bound (e.g. by FRET, or if the diffusion time is much faster than the sampling interval). In this case the autocorrelation is:
where
is the relaxation time and depends on the reaction kinetics (on and off rates), and:
is related to the equilibrium constant K.
Most systems with chemical relaxation also show measurable diffusion as well, and the autocorrelation function will depend on the details of the system. If the diffusion and chemical reaction are decoupled, the combined autocorrelation is the product of the chemical and diffusive autocorrelations. | 7 | Physical Chemistry |
An intein is a "parasitic" segment of a protein that is able to excise itself from the chain of amino acids as they emerge from the ribosome and rejoin the remaining portions with a peptide bond in such a manner that the main protein "backbone" does not fall apart. This is a case of a protein changing its own primary sequence from the sequence originally encoded by the DNA of a gene. Additionally, most inteins contain a homing endonuclease or HEG domain which is capable of finding a copy of the parent gene that does not include the intein nucleotide sequence. On contact with the intein-free copy, the HEG domain initiates the DNA double-stranded break repair mechanism. This process causes the intein sequence to be copied from the original source gene to the intein-free gene. This is an example of protein directly editing DNA sequence, as well as increasing the sequence's heritable propagation. | 1 | Biochemistry |
Edward Roberts pursued his undergraduate studies in biochemistry with a minor in music at the University of Sussex, Brighton, England, earning a Bachelor of Science with Honors degree in 1979. He continued his academic journey with a Ph.D. in synthetic organic chemistry at the University of Newcastle-upon-Tyne, England, under Richard J Stoodley, completing his doctoral studies in 1982. | 0 | Organic Chemistry |
DnaA has the ability to bind its own promoter. When DnaA binds to its own promoter it blocks RNA polymerase from binding the promoter and inhibits initiation of transcription. In this way, DnaA is able to regulate its own expression. This process is called autoregulation. | 1 | Biochemistry |
While at Harvard, Woodward took on the directorship of the
Woodward Research Institute, based at Basel, Switzerland, in 1963. He also became a trustee of his alma mater, MIT, from 1966 to 1971, and of the Weizmann Institute of Science in Israel.
Woodward died in Cambridge, Massachusetts, from a heart attack in his sleep. At the time, he was working on the synthesis of an antibiotic, erythromycin. A student of his said about him:
:I owe a lot to R. B. Woodward. He showed me that one could attack difficult problems without a clear idea of their outcome, but with confidence that intelligence and effort would solve them. He showed me the beauty of modern organic chemistry, and the relevance to the field of detailed careful reasoning. He showed me that one does not need to specialize. Woodward made great contributions to the strategy of synthesis, to the deduction of difficult structures, to the invention of new chemistry, and to theoretical aspects as well. He taught his students by example the satisfaction that comes from total immersion in our science. I treasure the memory of my association with this remarkable chemist. | 4 | Stereochemistry |
The Eötvös rule, named after the Hungarian physicist Loránd (Roland) Eötvös (1848–1919) enables the prediction of the surface tension of an arbitrary liquid pure substance at all temperatures. The density, molar mass and the critical temperature of the liquid have to be known. At the critical point the surface tension is zero.
The first assumption of the Eötvös rule is:
1. The surface tension is a linear function of the temperature.
:This assumption is approximately fulfilled for most known liquids. When plotting the surface tension versus the temperature a fairly straight line can be seen which has a surface tension of zero at the critical temperature.
The Eötvös rule also gives a relation of the surface tension behaviour of different liquids in respect to each other:
2. The temperature dependence of the surface tension can be plotted for all liquids in a way that the data collapses to a single master curve. To do so either the molar mass, the density, or the molar volume of the corresponding liquid has to be known.
More accurate versions are found on the main page for surface tension. | 7 | Physical Chemistry |
Other uses are assessment of tissue breakdown in general; this is possible when there are no other indicators of hemolysis. It is used to follow up cancer (especially lymphoma) patients, as cancer cells have a high rate of turnover, with destroyed cells leading to an elevated LDH activity. | 1 | Biochemistry |
Photochemical reactions require a light source that emits wavelengths corresponding to an electronic transition in the reactant. In the early experiments (and in everyday life), sunlight was the light source, although it is polychromatic. Mercury-vapor lamps are more common in the laboratory. Low-pressure mercury-vapor lamps mainly emit at 254 nm. For polychromatic sources, wavelength ranges can be selected using filters. Alternatively, laser beams are usually monochromatic (although two or more wavelengths can be obtained using nonlinear optics), and LEDs have a relatively narrow band that can be efficiently used, as well as Rayonet lamps, to get approximately monochromatic beams.
The emitted light must reach the targeted functional group without being blocked by the reactor, medium, or other functional groups present. For many applications, quartz is used for the reactors as well as to contain the lamp. Pyrex absorbs at wavelengths shorter than 275 nm. The solvent is an important experimental parameter. Solvents are potential reactants, and for this reason, chlorinated solvents are avoided because the C–Cl bond can lead to chlorination of the substrate. Strongly-absorbing solvents prevent photons from reaching the substrate. Hydrocarbon solvents absorb only at short wavelengths and are thus preferred for photochemical experiments requiring high-energy photons. Solvents containing unsaturation absorb at longer wavelengths and can usefully filter out short wavelengths. For example, cyclohexane and acetone "cut off" (absorb strongly) at wavelengths shorter than 215 and 330 nm, respectively.
Typically, the wavelength employed to induce a photochemical process is selected based on the absorption spectrum of the reactive species, most often the absorption maximum. Over the last years, however, it has been demonstrated that, in the majority of bond-forming reactions, the absorption spectrum does not allow selecting the optimum wavelength to achieve the highest reaction yield based on absorptivity. This fundamental mismatch between absorptivity and reactivity has been elucidated with so-called photochemical action plots. | 5 | Photochemistry |
The expression of genes in the operon is controlled by three differentially regulated promoters, two of which are controlled by RpoS encoded sigma factor σ.
* csiD : is σ-dependent and is activated exclusively upon carbon starvation because cAMP-CRP acts an essential activator for σ containing RNA polymerase at the csiD promoter.
* gabD: is σ -dependent and is induced by multiple stresses.
* gabD: is σ dependent and is controlled by Nac (Nitrogen Assimilation Control) regulatory proteins expressed under nitrogen limitation. | 1 | Biochemistry |
With other types of pans, some oil or fat is required to prevent hot food from sticking to the pan's surface. Food does not have the same tendency to stick to a non-stick surface; pans can be used with less, or no oil, and are easier to clean as residues do not stick to the surface.
According to writer Tony Polombo, pans that are not non-stick are better for producing pan gravy, because the fond (the caramelized drippings that stick to the pan when meat is cooked) sticks to them, and can be turned into pan gravy by deglazing them—dissolving them in liquid. | 7 | Physical Chemistry |
Light2CAT was a project funded by the European Commission from 2012 to 2015. It aimed to develop a modified that can absorb visible light and include this modified into construction concrete. The degrades harmful pollutants such as NOx into NO. The modified TiO is in use in Copenhagen and Holbæk, Denmark, and Valencia, Spain. This “self-cleaning” concrete led to a 5-20% reduction in NOx over the course of a year. | 5 | Photochemistry |
The Arrhenius equation is an elementary treatment that gives the quantitative basis of the relationship between the activation energy and the reaction rate at which a reaction proceeds. The rate constant as a function of thermodynamic temperature is then given by:
The reaction rate is given by:
where E is the activation energy, and R is the gas constant, and m and n are experimentally determined partial orders in [A] and [B], respectively. Since at temperature T the molecules have energies according to a Boltzmann distribution, one can expect the proportion of collisions with energy greater than E to vary with e. The constant of proportionality A is the pre-exponential factor, or frequency factor (not to be confused here with the reactant A) takes into consideration the frequency at which reactant molecules are colliding and the likelihood that a collision leads to a successful reaction. Here, A has the same dimensions as an (m + n)-order rate constant (see Units below).
Another popular model that is derived using more sophisticated statistical mechanical considerations is the Eyring equation from transition state theory:
where ΔG is the free energy of activation, a parameter that incorporates both the enthalpy and entropy change needed to reach the transition state. The temperature dependence of ΔG is used to compute these parameters, the enthalpy of activation ΔH and the entropy of activation ΔS, based on the defining formula ΔG = ΔH − TΔS. In effect, the free energy of activation takes into account both the activation energy and the likelihood of successful collision, while the factor kT/h gives the frequency of molecular collision.
The factor (c) ensures the dimensional correctness of the rate constant when the transition state in question is bimolecular or higher. Here, c is the standard concentration, generally chosen based on the unit of concentration used (usually c = 1 mol L = 1 M), and M is the molecularity of the transition state. Lastly, κ, usually set to unity, is known as the transmission coefficient, a parameter which essentially serves as a "fudge factor" for transition state theory.
The biggest difference between the two theories is that Arrhenius theory attempts to model the reaction (single- or multi-step) as a whole, while transition state theory models the individual elementary steps involved. Thus, they are not directly comparable, unless the reaction in question involves only a single elementary step.
Finally, in the past, collision theory, in which reactants are viewed as hard spheres with a particular cross-section, provided yet another common way to rationalize and model the temperature dependence of the rate constant, although this approach has gradually fallen into disuse. The equation for the rate constant is similar in functional form to both the Arrhenius and Eyring equations:
where P is the steric (or probability) factor and Z is the collision frequency, and ΔE is energy input required to overcome the activation barrier. Of note, , making the temperature dependence of k different from both the Arrhenius and Eyring models. | 7 | Physical Chemistry |
Defined by flows through a system, a flow process is a steady state of flow into and out of a vessel with definite wall properties. The internal state of the vessel contents is not the primary concern. The quantities of primary concern describe the states of the inflow and the outflow materials, and, on the side, the transfers of heat, work, and kinetic and potential energies for the vessel. The states of the inflow and outflow materials consist of their internal states, and of their kinetic and potential energies as whole bodies. Very often, the quantities that describe the internal states of the input and output materials are estimated on the assumption that they are bodies in their own states of internal thermodynamic equilibrium. Because rapid reactions are permitted, the thermodynamic treatment may be approximate, not exact. | 7 | Physical Chemistry |
In electron spectroscopy, depending on the technique, irradiating the sample with high-energy particles such as X-ray photons, electron beam electrons, or ultraviolet radiation photons, causes Auger electrons and photoelectrons to be emitted. Figure 1 illustrates this on the basis of a single particle in which, for example, the incoming X-ray photon from a particular energy range (E=hν) transfers its energy to an electron in the inner shell of an atom. Photon absorption caused electron emission leaves a hole in the atomic shell (see figure 1 (a)). The hole can be filled in two ways, forming different characteristic rays that are specific to each element. As the electron in the shell of a higher energy level fills the hole, a fluorescent photon is emitted (figure 1 (b)). In the Auger phenomenon, the electron in the shell of the higher energy level fills the hole that causes the adjacent or nearby electron to emit, forming the Auger electron (figure 1 (c)).
As can be seen from discussed above and figure 1, Auger electrons and photoelectrons are different in their physical origin, however, both types of electrons carry similar information about the chemical elements in material surfaces. Each element has its own special Auger electron or photon electron energy from which these can be identified. The binding energy of a photoelectron can be calculated by the formula below.
where E is the binding energy of the photoelectron, hν is the energy of the incoming radiation particle, E is the kinetic energy of the photoelectron measured by the device and is the work function.
The kinetic energy of the Auger electron is approximately equal to the energy difference between the binding energies of the electron shells involved in the Auger process. This can be calculated as follows:
where E is the kinetic energy of the Auger electron, hν is the energy of the incoming radiation particle and E is first outer shell binding energy and E is second outer shell binding energies. | 7 | Physical Chemistry |
Recently, CBED was applied to study graphene and other 2D monolayer crystals and van der Waals structures. For 2D crystals, the analysis of CBED patterns is simplified, because the intensity distribution in a CBED disk is directly related to the atomic arrangement in the crystal. The deformations at a nanometer resolution have been retrieved, the interlayer distance of a bilayer crystal has been reconstructed, and so on, by using CBED. | 3 | Analytical Chemistry |
A heterogeneous mixture (e. g. liquid and solid) can be separated by mechanical separation processes like filtration or centrifugation. Homogeneous mixtures can be separated by molecular separation processes; these are either equilibrium-based or rate-controlled. Equilibrium-based processes are operating by the formation of two immiscible phases with different compositions at equilibrium, an example is distillation (in distillation the vapor has another composition than the liquid). Rate-controlled processes are based on different transport rates of compounds through a medium, examples are adsorption, ion exchange or crystallization.
Separation of a mixture into two phases can be done by an energy separating agent, a mass separating agent, a barrier or external fields. Energy-separating agents are used for creating a second phase (immiscible of different composition than the first phase), they are the most common techniques used in industry. For example, leads the addition of heat (the separating agent) to a liquid (first phase) to the formation of vapor (second phase). Mass-separating agents are other chemicals. They selectively dissolve or absorb one of the products; they are either a liquid (for sorption, extractive distillation or extraction) or a solid (for adsorption or ion exchange). The use of a barrier which restricts the movement of one compound but not of the other one (semipermeable membranes) is less common; external fields are used just in special applications. | 3 | Analytical Chemistry |
In the United States, eszopiclone is a schedule IV controlled substance under the Controlled Substances Act. Use of eszopiclone may lead to physical and psychological dependence. The risk of non-medical use and dependence increases with the dose and duration of usage and concomitant use of other psychoactive substances. The risk is also greater in patients with a history of alcohol use disorder or other substance use disorder or history of psychiatric disorders. Tolerance may develop after repeated use of benzodiazepines and benzodiazepine-like drugs for a few weeks.
A study funded and carried out by Sepracor, the manufacturer of eszopiclone, found no signs of tolerance or dependence in a group of patients followed for up to six months. | 4 | Stereochemistry |
Nickel monosilicide can be prepared by depositing a nickel layer on silicon and subsequent annealing. In the case of Ni films with thicknesses above 4 nm, the normal phase transition is given by NiSi at 250 °C followed by NiSi at 350 °C and NiSi at approximately 800 °C. For films with an initial Ni thickness below 4 nm a direct transition from orthorhombic NiSi to epitaxial NiSi, skipping the nickel monosilicide phase, is observed. | 8 | Metallurgy |
Massively parallel single molecule direct RNA-Seq has been explored as an alternative to traditional RNA-Seq, in which RNA-to-cDNA conversion, ligation, amplification, and other sample manipulation steps may introduce biases and artifacts. Technology platforms that perform single-molecule real-time RNA-Seq include Oxford Nanopore Technologies (ONT) Nanopore sequencing, PacBio IsoSeq, and Helicos (bankrupt). Sequencing RNA in its native form preserves modifications like methylation, allowing them to be investigated directly and simultaneously. Another benefit of single-molecule RNA-Seq is that transcripts can be covered in full length, allowing for higher confidence isoform detection and quantification compared to short-read sequencing. Traditionally, single-molecule RNA-Seq methods have higher error rates compared to short-read sequencing, but newer methods like ONT direct RNA-Seq limit errors by avoiding fragmentation and cDNA conversion. Recent uses of ONT direct RNA-Seq for differential expression in human cell populations have demonstrated that this technology can overcome many limitations of short and long cDNA sequencing. | 1 | Biochemistry |
The signal generated by probe modulation is much smaller than the original pump beam, so the two are spectrally separated within the detection path using a dichroic mirror. The probe signal can be collected with many different types of photodetectors, typically a photodiode. Then, the modulated signal is amplified using a lock-in amplifier tuned to the pump modulation frequency. | 7 | Physical Chemistry |
The first nitridoiron(V) compound was synthesised and characterized by Wagner and Nakamoto (1988, 1989) using photolysis and Raman spectroscopy at low temperatures. | 7 | Physical Chemistry |
The euplotid nuclear code (translation table 10) is the genetic code used by Euplotidae. The euplotid code is a socalled "symmetrical code", which results from the symmetrical distribution of the codons. This symmetry allows for arythmic exploration of the codon distribution. In 2013, shCherbak and Makukov, reported that "the patterns are shown to match the criteria of an intelligent signal." | 1 | Biochemistry |
Melt inclusions are generally small - most are less than 80 micrometres across (a micrometre is one thousandth of a millimeter, or about 0.00004 inches). They may contain a number of different constituents, including glass (which represents melt that has been quenched by rapid cooling), small crystals and a separate vapour-rich bubble. They occur in the crystals that can be found in igneous rocks, such as for example quartz, feldspar, olivine, pyroxene, nepheline, magnetite, perovskite and apatite. Melt inclusions can be found in both volcanic and plutonic rocks. In addition, melt inclusions can contain immiscible (non-miscible) melt phases and their study is an exceptional way to find direct evidence for presence of two or more melts at entrapment. | 9 | Geochemistry |
The basic leaching chemical formula that drives this process is:
This is achieved in practice through a process called double leaching. The calcine is first leached in a neutral or slightly acidic solution (of sulfuric acid) in order to leach the zinc out of the zinc oxide. The remaining calcine is then leached in strong sulfuric acid to leach the rest of the zinc out of the zinc oxide and zinc ferrite. The result of this process is a solid and a liquid; the liquid contains the zinc and is often called leach product; the solid is called leach residue and contains precious metals (usually lead and silver) which are sold as a by-product. There is also iron in the leach product from the strong acid leach, which is removed in an intermediate step, in the form of goethite, jarosite, and haematite. There is still cadmium, copper, arsenic, antimony, cobalt, germanium, nickel, and thallium in the leach product. Therefore, it needs to be purified. | 8 | Metallurgy |
Thermosetting plastics are generally stronger than thermoplastic materials due to the three-dimensional network of bonds (crosslinking), and are also better suited to high-temperature applications up to the decomposition temperature since they keep their shape as strong covalent bonds between polymer chains cannot be broken easily. The higher the crosslink density and aromatic content of a thermoset polymer, the higher the resistance to heat degradation and chemical attack. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. They normally decompose before melting.
Hard, plastic thermosets may undergo permanent or plastic deformation under load. Elastomers, which are soft and springy or rubbery and can be deformed and revert to their original shape on loading release.
Conventional thermoset plastics or elastomers cannot be melted and re-shaped after they are cured. This usually prevents recycling for the same purpose, except as filler material. New developments involving thermoset epoxy resins which on controlled and contained heating form crosslinked networks permit repeatedly reshaping, like silica glass by reversible covalent bond exchange reactions on reheating above the glass transition temperature. There are also thermoset polyurethanes shown to have transient properties and which can thus be reprocessed or recycled. | 7 | Physical Chemistry |
ViroCap is a test announced in 2015 by researchers at Washington University in St. Louis which can detect most of the infectious viruses which affect both humans and animals. It was demonstrated to be as sensitive as the various Polymerase chain reaction assays for the viruses. It will not be available for clinical use until validation studies are done, which may take years. The test examines two million sequences of genetic data from viruses. The research was published in September 2015 in the online journal Genome Research. | 1 | Biochemistry |
The growth and development of normal cells follow a cycle in a controlled and ordered manner. When they are damaged, they will die through a process called apoptosis. However, apoptosis is disrupted in cancer cells, allowing them to divide and grow uncontrollably, potentially invading other tissues or organs. They will not undergo the normal death process of body cells.
Hepatocellular carcinoma (HCC) is a prevalent type of liver cancer that accounts for over 80% of cases. It is lethal cancer due to the remarkable drug tolerance, spread potential and high chance of relapse. Scientists have carried out many kinds of research in finding out the risk factors of HCC progression. | 1 | Biochemistry |
Noyori believes strongly in the power of catalysis and of green chemistry; in a 2005 article he argued for the pursuit of "practical elegance in synthesis". In this article he stated that "our ability to devise straightforward and practical chemical syntheses is indispensable to the survival of our species." Elsewhere he has said that "Research is for nations and mankind, not for researchers themselves." He encourages scientists to be politically active: "Researchers must spur public opinions and government policies toward constructing the sustainable society in the 21st century."
Noyori is currently a chairman of the Education Rebuilding Council, which was set up by Japan's PM Shinzō Abe after he came to power in 2006.
Noyori is most famous for asymmetric hydrogenation using as catalysts complexes of rhodium and ruthenium, particularly those based on the BINAP ligand. Asymmetric hydrogenation of an alkene in the presence of ((S)-BINAP)Ru(OAc) is used for the commercial production of enantiomerically pure (97% ee) naproxen, a nonsteriodal anti-inflammatory drug. The antibacterial agent levofloxacin is manufactured by asymmetric hydrogenation of ketones in the presence of a Ru(II) BINAP halide complex.
He has also worked on other asymmetric processes. Each year 3000 tonnes (after new expansion) of menthol are produced (in 94% ee) by Takasago International Corporation, using Noyori's method for isomerisation of allylic amines.
More recently with Philip G. Jessop, Noyori has developed an industrial process for the manufacture of N,N-dimethylformamide from hydrogen, dimethylamine and supercritical carbon dioxide in the presence of as catalyst. | 4 | Stereochemistry |
ChemPhysChem is a biweekly peer-reviewed scientific journal published by Wiley-VCH on behalf of Chemistry Europe. It was established in 2000 and covers all aspects of chemical physics and physical chemistry. Initially published monthly, the journal moved to 18 issues per year in 2007, and further to biweekly in 2016. | 7 | Physical Chemistry |
The society makes a number of merit awards, four annually and others either biennially or triennially, to acknowledge excellence and achievement in both specific and general fields of science. The annual awards comprise the Morton Lecture, the Colworth Medal, the Centenary Award and the Novartis Medal and Prize. | 1 | Biochemistry |
Perfluoroaromatic compounds contain only carbon and fluorine, like other fluorocarbons, but also contain an aromatic ring. The three most important examples are hexafluorobenzene, octafluorotoluene, and octafluoronaphthalene.
Perfluoroaromatic compounds can be manufactured via the Fowler process, like fluoroalkanes, but the conditions must be adjusted to prevent full fluorination. They can also be made by heating the corresponding perchloroaromatic compound with potassium fluoride at high temperature (typically 500 °C), during which the chlorine atoms are replaced by fluorine atoms. A third route is defluorination of the fluoroalkane; for example, octafluorotoluene can be made from perfluoromethylcyclohexane by heating to 500 °C with a nickel or iron catalyst.
Perfluoroaromatic compounds are relatively volatile for their molecular weight, with melting and boiling points similar to the corresponding aromatic compound, as the table below shows. They have high density and are non-flammable. For the most part, they are colorless liquids. Unlike the perfluoralkanes, they tend to be miscible with common solvents. | 2 | Environmental Chemistry |
For xDNA to be used as a substitute structure for information storage, it requires a reliable replication mechanism. Research into xDNA replication using a Klenow fragment from DNA polymerase I shows that a natural base partner is selectively added in instances of single-nucleotide insertion. However, DNA polymerase IV (Dpo4) has been able to successfully use xDNA for these types of insertions with high fidelity, making it a promising candidate for future research in extending replicates of xDNA. xDNA's mismatch sensitivity is similar to that of B-DNA. | 1 | Biochemistry |
The previously described study by Timby et al. (2015) also assessed the effects of MFGM supplementation in term infants on the risk of infectious diseases and other disease symptoms. In particular, the cumulative incidence of acute otitis media was analyzed between the two randomized feeding groups (control formula or MFGM- supplemented formula to 6 months of age), and compared to a breastfed reference group. The MFGM-supplemented group experienced a significant reduction in episodes of acute otitis media up to 6 months of age compared with infants fed control formula (1% vs 9%; P=0.034); with no significant difference in otitis media incidence compared to the breastfed group (0%). In addition, a significantly lower incidence and longitudinal prevalence of antipyretic drug use was seen in the MFGM-supplemented group (25%) compared with the control formula group (43%). Timby et al. (2017) further showed that the MFGM supplementation influenced the infants’ oral microbiota; the authors noted that, Moraxella catarrhalis, a common bacterial cause of acute otitis media, was less prevalent in infants fed the MFGM-supplemented formula than in those fed control formula.
Zavaleta et al. (2011) evaluated the effects of an MFGM-enriched complementary food on health outcomes in term infants 6 to 11 months of age in Peru. In this double-blind RCT, 499 primarily breast-fed infants were fed for 6 months with a daily milk-based complementary food that included either whey protein concentrate enriched in MFGM, or an equal amount of additional protein from skim milk (control). Results showed that the group with the MFGM-supplemented diet had a significantly lower prevalence of diarrhea during the study compared to the control group (3.84% vs 4.37%; P<0.05), as well as a significant reduction (46%) in episodes of bloody diarrhea compared to the control group (P=0.025).
Later through analyzing the metabolome and immune markers of those infants, Lee et al. (2018) reported that supplementation with MFGM may improve micronutrient status, amino acid, and energy metabolism along with a reduced proinflammatory response (e.g. interleukin-2).
The previously described study by Veereman-Wauters et al. (2012) in preschool-age children (2.5 to 6 years old) also reported the effect of MFGM-supplemented formula consumption on health outcomes. Children receiving the MFGM-supplemented formula reported a significant reduction in the number of days with fever, and particularly the number of short febrile episodes (<3 days), compared to the control group. | 1 | Biochemistry |
The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride, chlorine has a valence of 1. Chlorine, as it has a valence of one, can be substituted for hydrogen in many compounds. Phosphorus has a valence 3 in phosphine () and a valence of 5 in phosphorus pentachloride (), which shows that an element may exhibit more than one valence. The structural formula of a compound represents the connectivity of the atoms, with lines drawn between two atoms to represent bonds. The two tables below show examples of different compounds, their structural formulas, and the valences for each element of the compound. | 3 | Analytical Chemistry |
Hash rosin has recently become a top quality, highly prized product in the cannabis market. For dabbing, it is considered to be the cleanest form of concentrating cannabis, as it requires only ice, water (instead of organic solvents like butane), heat, pressure, and collection tools. Cannabis flower material is washed with ice water, and strained using filters in sequential micron size to isolate intact trichomes and their heads into ice water hash. The microns that are held in highest regards are the 73u and 90u, as this is where the resin heads reside. These are sometimes isolated and sold as one of the highest quality, most expensive cannabis products in the market today, known as "full melt" because it will dab fine without having to be pressed. "Full spectrum" hash rosin will normally come from 45u-159u, as smaller and larger particles are likely to be too unrefined or broken stalks of the trichomes.
This hash is then pressed at the appropriate temperature and pressure to squeeze the oils out of the hash, and is collected with metal tools and parchment paper. Just like hydrocarbon extraction, the quality of the final product depends greatly on the quality of the starting material. This is emphasized even more so with hash rosin due to its lower yield percentages compared to solvent-derived concentrates (.3-8% rosin vs 10-20% hydrocarbon). Hash rosin producers often touch on how growing cannabis for hash production is different than growing for flower production, as some strains will be deceptive with their looks regarding yields. | 7 | Physical Chemistry |
π systems are important building blocks in supramolecular assembly because of their versatile noncovalent interactions with various functional groups.
A notable example of applying π–π interactions in supramolecular assembly is the synthesis of catenane. The major challenge for the synthesis of catenane is to interlock molecules in a controlled fashion. Stoddart and co-workers developed a series of systems utilizing the strong π–π interactions between electron-rich benzene derivatives and electron-poor pyridinium rings. [2]Catanene was synthesized by reacting bis(pyridinium) (A), bisparaphenylene-34-crown-10 (B), and 1, 4-bis(bromomethyl)benzene (C) (Fig. 2). The π–π interaction between A and B directed the formation of an interlocked template intermediate that was further cyclized by substitution reaction with compound C to generate the [2]catenane product. | 6 | Supramolecular Chemistry |
For example, one could use a cation exchange (negatively charged) surface chemistry for ERLIC separations to reduce the influence on retention of anionic (negatively charged) groups (the phosphates of nucleotides or of phosphonyl antibiotic mixtures; or sialic acid groups of modified carbohydrates) to now allow separation based more on the basic and/or neutral functional groups of these molecules. Modifying the polarity of a weakly ionic group (e.g. carboxyl) on the surface is easily accomplished by adjusting the pH to be within two pH units of that groups pKa. For strongly ionic functional groups of the surface (i.e. sulfates or phosphates) one could instead use a lower amount of buffer so the residual charge is not completely ion paired. An example of this would be the use of a 12.5mM (rather than the recommended >20mM buffer), pH 9.2 mobile phase on a polymeric, zwitterionic, betaine-sulfonate surface to separate phosphonyl antibiotic mixtures (each containing a phosphate group). This enhances the influence of the columns sulfonic acid functional groups of its surface chemistry over its, slightly diminished (by pH), quaternary amine. Commensurate with this, these analytes will show a reduced retention on the column eluting earlier, and in higher amounts of organic solvent, than if a neutral polar HILIC surface were used. This also increases their detection sensitivity by negative ion mass spectrometry. | 1 | Biochemistry |
There are >50 human diseases associated with SINEs. When inserted near or within the exon, SINEs can cause improper splicing, become coding regions, or change the reading frame, often leading to disease phenotypes in humans and other animals. Insertion of Alu elements in the human genome is associated with breast cancer, colon cancer, leukemia, hemophilia, Dent's disease, cystic fibrosis, neurofibromatosis, and many others. | 1 | Biochemistry |
Beerstone is a buildup that forms when oxalate, proteins, and calcium or magnesium salts from the grains and water in the beer brewing process precipitate and form scale on kegs, barrels and tap lines. The minerals adsorb to the surface of the container first, driven by charge attractions. Proteins are often coordinated to these minerals in the solution and can bind with them to the surface. In other cases proteins also adsorb to the minerals on the surface, making deposits difficult to remove, as well as providing a surface that can easily harbor microorganisms. If built-up beer stone inside tap lines flakes off, it can negatively affect the quality of the finished product by making beer hazy and contributing "off" flavors. It is also harmful from a nutritional standpoint: oxalates can decrease absorption of calcium in the body, in addition to increasing risk of kidney stone formation. | 1 | Biochemistry |
The other context of agricultural issues involves the transport of agricultural chemicals (nitrates, phosphates, pesticides, herbicides, etc.) via surface runoff. This result occurs when chemical use is excessive or poorly timed with respect to high precipitation. The resulting contaminated runoff represents not only a waste of agricultural chemicals, but also an environmental threat to downstream ecosystems. Pine straws are often used to protect soil from soil erosion and weed growth. However, harvesting these crops may result in the increase of soil erosion. | 2 | Environmental Chemistry |
Though to a far lesser extent than estrogen, which is the major mediator of mammary ductal development (via the ERα), progesterone may be involved in ductal development of the mammary glands to some extent as well. PR knockout mice or mice treated with the PR antagonist mifepristone show delayed although otherwise normal mammary ductal development at puberty. In addition, mice modified to have overexpression of PRA display ductal hyperplasia, and progesterone induces ductal growth in the mouse mammary gland. Progesterone mediates ductal development mainly via induction of the expression of amphiregulin, the same growth factor that estrogen primarily induces the expression of to mediate ductal development. These animal findings suggest that, while not essential for full mammary ductal development, progesterone seems to play a potentiating or accelerating role in estrogen-mediated mammary ductal development. | 0 | Organic Chemistry |
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