text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Members of the genus Dinophysis have a phycobilin-containing chloroplast taken from a cryptophyte. However, the cryptophyte is not an endosymbiont—only the chloroplast seems to have been taken, and the chloroplast has been stripped of its nucleomorph and outermost two membranes, leaving just a two-membraned chloroplast. Cryptophyte chloroplasts require their nucleomorph to maintain themselves, and Dinophysis species grown in cell culture alone cannot survive, so it is possible (but not confirmed) that the Dinophysis chloroplast is a kleptoplast—if so, Dinophysis chloroplasts wear out and Dinophysis species must continually engulf cryptophytes to obtain new chloroplasts to replace the old ones. | 5 | Photochemistry |
In terms of the imaginary system, it is a general term for various types of remote sensor systems that acquire remote sensing images of objects without photography. Scanning is usually used for imaging, tape recording or indirect recording on film. According to the structure of the system, the scanning method and the detector parts are roughly divided into:
1. Optomechanical scanning. Such as multi-spectral scanners. The mirror is used to scan the object surface, and the image data is output after being split, detected and photoelectrically converted.
2. Electronic scanning. For example, a return beam guiding TV camera, is an image-side scanning method. The process is optical imaging on the target surface of the light guide, and the signal is amplified and output after being scanned by the electron beam.
3. Robust self-scanning. For example, the photoelectric scanning sensor of the French SPOT satellite is also an image scanning method. The object is imaged by an objective lens on a detector array consisting of a plurality of charge coupled devices (CCDs) that are photoelectrically converted and output.
4. Antenna scanning. Such as side-view radar, which is an active remote sensing imaging system that is a surface scanning method. It transmits the microwave beam through the antenna and receives an echo reflected by the scene, which is demodulated and output. | 7 | Physical Chemistry |
Layering graphene on top of gold has been shown to improve SPR sensor performance. Its high electrical conductivity increases the sensitivity of detection. The large surface area of graphene also facilitates the immobilization of biomolecules while its low refractive index minimizes its interference. Enhancing SPR sensitivity by incorporating graphene with other materials expands the potential of SPR sensors, making them practical in a broader range of applications. For instance, the enhanced sensitivity of graphene can be used in conjunction with a silver SPR sensor, providing a cost-effective alternative for measuring glucose levels in urine.
Graphene has also been shown to improve the resistance of SPR sensors to high-temperature annealing up to 500 °C. | 7 | Physical Chemistry |
Levobetaxolol inhibits the beta-1-adrenergic receptor. When applied topically, it reduces intra-ocular pressure (IOP) by 16-23% depending on time of day and the individual. It also has neuroprotective effects. Levobetaxolol has fewer cardiovascular side effects than other beta blockers. | 4 | Stereochemistry |
The history of oligopeptidases originates in the late 1960s, when the rabbit brain was searched for enzymes that cause inactivation of the nonapeptide bradykinin. In the early and mid 1970s two thiol-activated endopeptidases, responsible for more than 90% of bradykinin inactivation, were isolated from cytosol of rabbit brain, and characterized. They correspond to EOPA (endooligopeptidase A, EC 3.4.22.19), and Prolyl endopeptidase or Prolyl oligopeptidase (POP) (EC 3.4.21.26). Since their activities are restricted to oligopeptides (usually from 8-13 amino acid residues), and do not hydrolyze proteins or large peptides (>30 amino acid residues), they were designated oligopeptidases. In the early and mid 1980s other oligopeptidases, mostly metallopeptidases, were described in the cytosol of mammalian tissues, such as the TOP (thimet oligopeptidase, EC 3.4.24.15), and the neurolysin (EC 3.4.24.16). Earlier on, the ACE (angiotensin-converting enzyme, EC 3.4.15.1), and the NEP (neprilysin, EC 3.4.24.11), had been described, at the end of the 1960s, and in 1973, respectively. | 1 | Biochemistry |
The heat collected from this process generates steam, which can be used in a conventional steam turbine system to make electricity. In contrast to the low-temperature solar thermal systems that are used for air or water heating in domestic or commercial buildings, these solar thermal electricity plants operate at high temperatures, requiring both concentrated sunlight and a large collection area, making the Moroccan desert an ideal location.
This is an alternative approach to the more widely used “photovoltaic” technology for producing electricity from sunlight. In a photovoltaic system, the sunlight is absorbed in the photovoltaic device (commonly called a solar cell) and energy is passed to electrons in the material, converting the solar energy directly into electricity. Sometimes, solar thermal electricity and photovoltaics are portrayed as competing technologies and, while this may be true when deciding on the way forward for a specific site, in general they are complementary, using solar energy as extensively as possible. | 7 | Physical Chemistry |
The general formula for the action of an element of a space group is
: y = M.x + D
where M is its matrix, D is its vector, and where the element transforms point x into point y. In general, D = D (lattice) + , where is a unique function of M that is zero for M being the identity. The matrices M form a point group that is a basis of the space group; the lattice must be symmetric under that point group, but the crystal structure itself may not be symmetric under that point group as applied to any particular point (that is, without a translation). For example, the diamond cubic structure does not have any point where the cubic point group applies.
The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group. For (overall dimension, lattice dimension):
* (1,1): One-dimensional line groups
* (2,1): Two-dimensional line groups: frieze groups
* (2,2): Wallpaper groups
* (3,1): Three-dimensional line groups; with the 3D crystallographic point groups, the rod groups
* (3,2): Layer groups
* (3,3): The space groups discussed in this article | 4 | Stereochemistry |
Reactants of the photoreactions can be both gaseous and liquids. In general, it is necessary to bring the reactants close to the light source in order to obtain the highest possible luminous efficacy. For this purpose, the reaction mixture can be irradiated either directly or in a flow-through side arm of a reactor with a suitable light source.
A disadvantage of photochemical processes is the low efficiency of the conversion of electrical energy in the radiation energy of the required wavelength. In addition to the radiation, light sources generate plenty of heat, which in turn requires cooling energy. In addition, most light sources emit polychromatic light, even though only monochromatic light is needed. A high quantum yield, however, compensates for these disadvantages.
Working at low temperatures is advantageous since side reactions are avoided (as the selectivity is increased) and the yield is increased (since gaseous reactants are driven out less from the solvent).
The starting materials can sometimes be cooled before the reaction to such an extent that the reaction heat is absorbed without further cooling of the mixture. In the case of gaseous or low-boiling starting materials, work under overpressure is necessary. Due to the large number of possible raw materials, a large number of processes have been described. Large scale reactions are usually carried out in a stirred tank reactor, a bubble column reactor or a tube reactor, followed by further processing depending on the target product. In case of a stirred tank reactor, the lamp (generally shaped as an elongated cylinder) is provided with a cooling jacket and placed in the reaction solution. Tube reactors are made from quartz or glass tubes, which are irradiated from the outside. Using a stirred tank reactor has the advantage that no light is lost to the environment. However, the intensity of light drops rapidly with the distance to the light source due to adsorption by the reactants.
The influence of the radiation on the reaction rate can often be represented by a power law based on the quantum flow density, i.e. the mole light quantum (previously measured in the unit einstein) per area and time. One objective in the design of reactors is therefore to determine the economically most favorable dimensioning with regard to an optimization of the quantum current density. | 5 | Photochemistry |
Another category of plant defenses are those features that indirectly protect the plant by enhancing the probability of attracting the natural enemies of herbivores. Such an arrangement is known as mutualism, in this case of the "enemy of my enemy" variety. One such feature are semiochemicals, given off by plants. Semiochemicals are a group of volatile organic compounds involved in interactions between organisms. One group of semiochemicals are allelochemicals; consisting of allomones, which play a defensive role in interspecies communication, and kairomones, which are used by members of higher trophic levels to locate food sources. When a plant is attacked it releases allelochemics containing an abnormal ratio of these s (HIPVs). Predators sense these volatiles as food cues, attracting them to the damaged plant, and to feeding herbivores. The subsequent reduction in the number of herbivores confers a fitness benefit to the plant and demonstrates the indirect defensive capabilities of semiochemicals. Induced volatiles also have drawbacks, however; some studies have suggested that these volatiles attract herbivores. Crop domestication has increased yield sometimes at the expense of HIPV production. Orre Gordon et al 2013 tests several methods of artificially restoring the plant-predator partnership, by combining companion planting and synthetic predator attractants. They describe several strategies which work and several which do not.
Plants sometimes provide housing and food items for natural enemies of herbivores, known as "biotic" defense mechanisms, as a means to maintain their presence. For example, trees from the genus Macaranga have adapted their thin stem walls to create ideal housing for an ant species (genus Crematogaster), which, in turn, protects the plant from herbivores. In addition to providing housing, the plant also provides the ant with its exclusive food source; from the food bodies produced by the plant. Similarly, several Acacia tree species have developed stipular spines (direct defenses) that are swollen at the base, forming a hollow structure that provides housing for protective ants. These Acacia trees also produce nectar in extrafloral nectaries on their leaves as food for the ants.
Plant use of endophytic fungi in defense is common. Most plants have endophytes, microbial organisms that live within them. While some cause disease, others protect plants from herbivores and pathogenic microbes. Endophytes can help the plant by producing toxins harmful to other organisms that would attack the plant, such as alkaloid producing fungi which are common in grasses such as tall fescue (Festuca arundinacea), which is infected by Neotyphodium coenophialum.
Trees of the same species form alliances with other tree species in order to improve their survival rate. They communicate and have dependent relationships through connections below the soil called underground mycorrhiza networks, which allows them to share water/nutrients and various signals for predatory attacks while also protecting its immune system. Within a forest of trees, the ones getting attacked send communication distress signals that alerts neighboring trees to alter their behavior (defense). The tree and fungi relationship is a symbiotic relationship. Fungi, intertwined with the trees roots, support communication between trees to locate nutrients. In return, the fungi receive some of the sugar that trees photosynthesize. Trees send out several forms of communication including chemical, hormonal, and slow pulsing electric signals. Farmers investigated the electrical signals between trees, using a voltage-based signal system, similar to an animals nervous system, where a tree faces distress and releases a warning signal to surrounding trees. | 1 | Biochemistry |
Van Bekkum was born on 26 September 1932 in Rotterdam. He studied technological chemistry at Delft University of Technology and graduated in 1959. He subsequently worked two years for Royal Dutch Shell before returning to Delft University to work as lecturer. In 1971 he was named professor of Catalysis in Organic Chemistry. From 1975 to 1976 he served as rector magnificus of the university. As professor van Bekkum specialized in carbohydrate chemistry and the study of zeolites. In 1995 van Bekkum was appointed as the first president of the newly-founded Federation of the European Zeolite Association.
In 1998 he officially retired, however, by 2013 he was still working at the university. In his period at Delft University van Bekkum was doctoral advisor to 75 students.
Van Bekkum was elected member of the Royal Netherlands Academy of Arts and Sciences in 1995. He became an honorary member of the Royal Netherlands Chemical Society in 1998.
Apart from his career in chemistry van Bekkum was a competitive chess player.
He died on 30 November 2020 in Rotterdam, at age 88. | 0 | Organic Chemistry |
Most ceramics are extremely hard and must be wet-sawed with a circular blade embedded with diamond particles. A metallography or lapidary saw equipped with a low-density diamond blade is usually suitable. The blade must be cooled by a continuous liquid spray. | 8 | Metallurgy |
Life in sea ice is energetically demanding, and sets limits at any hierarchical, organizational, and organismic level, ranging from molecules to everything that an organism does. Despite this fact, the brine-containing interstices and pockets found in sea ice host a variety of organisms, including bacteria, autotrophic and heterotrophic protists, microalgae, and metazoa. | 9 | Geochemistry |
In statistical physics, a system is said to present quenched disorder when some parameters defining its behavior are random variables which do not evolve with time. These parameters are said to be quenched or frozen. Spin glasses are a typical example. Quenched disorder is contrasted with annealed disorder in which the parameters are allowed to evolve themselves.
Mathematically, quenched disorder is more difficult to analyze than its annealed counterpart as averages over thermal noise and quenched disorder play distinct roles. Few techniques to approach each are known, most of which rely on approximations. Common techniques used to analyzed systems with quenched disorder include the replica trick, based on analytic continuation, and the cavity method, where a system's response to the perturbation due to an added constituent is analyzed. While these methods yield results agreeing with experiments in many systems, the procedures have not been formally mathematically justified. Recently, rigorous methods have shown that in the Sherrington-Kirkpatrick model, an archetypal spin glass model, the replica-based solution is exact. The generating functional formalism, which relies on the computation of path integrals, is a fully exact method but is more difficult to apply than the replica or cavity procedures in practice. | 3 | Analytical Chemistry |
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the titrant or titrator, is prepared as a standard solution of known concentration and volume. The titrant reacts with a solution of analyte (which may also be termed the titrand) to determine the analytes concentration. The volume of titrant that reacted with the analyte is termed the titration volume'. | 3 | Analytical Chemistry |
Photopyroelectric As known that Photopyroelectric can be regarded as –Photo +Pyroelectric，which means any optical systems using a pyroelectric detector or imaging system, In addition, pyroelectricity could be depicted as the capability of the components formulating the transient voltage when heated or cooled. Once the temperature on which they depend changes, the position of the atom will change slightly in the crystal structure. This process of change can also be referred to as the polarization of the material. As a result, the voltage across the crystal will be triggered by this change in polarization. To further explain, when the temperature in the engine is kept constant for a period of time, the voltage in the photovoltage will gradually disappear due to the leakage current. In this sense, leakage is mainly caused by several ways, for example, electrons going through the crystal, ions going through the air, or current leaking through a voltmeter connected to the crystal.<br /> | 7 | Physical Chemistry |
Chemical defense is a strategy employed by many organisms to avoid consumption by producing toxic or repellent metabolites or chemical warnings which incite defensive behavioral changes. The production of defensive chemicals occurs in plants, fungi, and bacteria, as well as invertebrate and vertebrate animals. The class of chemicals produced by organisms that are considered defensive may be considered in a strict sense to only apply to those aiding an organism in escaping herbivory or predation. However, the distinction between types of chemical interaction is subjective and defensive chemicals may also be considered to protect against reduced fitness by pests, parasites, and competitors. Repellent rather than toxic metabolites are allomones, a sub category signaling metabolites known as semiochemicals. Many chemicals used for defensive purposes are secondary metabolites derived from primary metabolites which serve a physiological purpose in the organism. Secondary metabolites produced by plants are consumed and sequestered by a variety of arthropods and, in turn, toxins found in some amphibians, snakes, and even birds can be traced back to arthropod prey. There are a variety of special cases for considering mammalian antipredatory adaptations as chemical defenses as well. | 1 | Biochemistry |
Remineralisation refers to the breakdown or transformation of organic matter (those molecules derived from a biological source) into its simplest inorganic forms. These transformations form a crucial link within ecosystems as they are responsible for liberating the energy stored in organic molecules and recycling matter within the system to be reused as nutrients by other organisms. What fraction does escape remineralisation varies depending on the location. For example, in the North Sea, values of carbon deposition are ~1% of primary production while that value is <0.5% in the open oceans on average. Therefore, most of nutrients remain in the water column, recycled by the biota. Heterotrophic organisms will utilize the materials produced by the autotrophic (and chemotrophic) organisms and via respiration will remineralise the compounds from the organic form back to inorganic, making them available for primary producers again.
For most areas of the ocean, the highest rates of carbon remineralisation occur at depths between in the water column, decreasing down to about where remineralisation rates remain pretty constant at 0.1 μmol kg yr. This provides the most nutrients available for primary producers within the photic zone, though it leaves the upper surface waters starved of inorganic nutrients. Most remineralisation is done with dissolved organic carbon (DOC). Studies have shown that it is larger sinking particles that transport matter down to the sea floor while suspended particles and dissolved organics are mostly consumed by remineralisation. This happens in part due to the fact that organisms must typically ingest nutrients smaller than they are, often by orders of magnitude. With the microbial community making up 90% of marine biomass, it is particles smaller than the microbes (on the order of ) that will be taken up for remineralisation. | 9 | Geochemistry |
The stereotypic inflammatory response provoked by toll-like receptor activation has prompted speculation that endogenous activators of toll-like receptors might participate in autoimmune diseases. TLRs have been suspected of binding to host molecules including fibrinogen (involved in blood clotting), heat shock proteins (HSPs), HMGB1, extracellular matrix components and self DNA (it is normally degraded by nucleases, but under inflammatory and autoimmune conditions it can form a complex with endogenous proteins, become resistant to these nucleases and gain access to endosomal TLRs as TLR7 or TLR9). These endogenous ligands are usually produced as a result of non-physiological cell death. | 1 | Biochemistry |
Rotary vacuum drum filter (RVDF), patented in 1872, is one of the oldest filters used in the industrial liquid-solids separation. It offers a wide range of industrial processing flow sheets and provides a flexible application of dewatering, washing and/or clarification.
A rotary vacuum filter consists of a large rotating drum covered by a cloth. The drum is suspended on an axial over a trough containing liquid or solids slurry with approximately 50-80% of the screen area immersed in the slurry.
As the drum rotates into and out of the trough, the slurry is sucked on the surface of the cloth and rotated out of the liquid or solids suspension as a cake. When the cake is rotating out, it is dewatered in the drying zone. The cake is dry because the vacuum drum is continuously sucking the cake and taking the water out of it. At the final step of the separation, the cake is discharged as solids products and the drum rotates continuously to another separation cycle. | 3 | Analytical Chemistry |
A constant magnetic force is applied to unzip the DNA hairpin, and reducing the force allows the hairpin to rezip. Prior to performing the downstream applications several unzipping and rezipping cycles are performed. While the magnetic force required to unzip and rezip may vary depending on the DNA sequence and hairpin length, their absolute values are not critical as long as they are consistent within a sequencing run. | 1 | Biochemistry |
Unlike in marine sediments, diagenesis does not pose a large threat to the integrity of the C/N ratio in lacustrine sediments. Though wood from living trees around lakes have consistently higher C/N ratios than wood buried in sediment, the change in elemental composition is not large enough to remove the vascular versus non-vascular plant signals due to the refractory nature of terrestrial organic matter. Abrupt shifts in the C/N ratio down-core can be interpreted as shifts in the organic source material.
For example, two separate studies on Mangrove Lake, Bermuda and Lake Yunoko, Japan show irregular, abrupt fluctuations between C/N around 11 to around 18. These fluctuations are attributed to shifts from mainly algal dominance to land-based vascular dominance. Results of studies that show abrupt shifts in algal dominance and vascular dominance often lead to conclusions about the state of the lake during these distinct periods of isotopic signatures. Times in which lakes are dominated by algal signals suggest the lake is a deep-water lake, while times in which lakes are dominated by vascular plant signals suggest the lake is shallow, dry, or marshy. Using the C/N ratio in conjunction with other sediment observations, such as physical variations, D/H isotopic analyses of fatty acids and alkanes, and δ13C analyses on similar biomarkers can lead to further regional climate interpretations that describe the larger phenomena at play. | 9 | Geochemistry |
*Natural agents − Different natural products and their extracts, such as onion, pineapple, lemon, and white wine, are known to inhibit or slow the browning of some products. Onion and its extract exhibit potent anti-browning properties by inhibiting the PPO activity. Pineapple juice have shown to possess anti-browning effect on apples and bananas. Lemon juice is used in making doughs to make the pastry products look brighter. This effect is possibly explained by the anti-browning properties of citric and ascorbic acids in the lemon juice.
*Genetic modification − Arctic apples have been genetically modified to silence the expression of PPO, thereby delaying the browning effect, and improving apple eating quality. | 1 | Biochemistry |
The book begins by discussing the history of parasites in human knowledge, from the earliest writings about them in ancient cultures, up through modern times. The focus comes to rest extensively on the views and experiments conducted by scientists in the 17th, 18th, and 19th centuries, such as those done by Antonie van Leeuwenhoek, Japetus Steenstrup, Friedrich Küchenmeister, and Ray Lankester. Among them, Leeuwenhoek was the first to ever physically view cells through a microscope, Steenstrup was the first to explain and confirm the multiple stages and life cycles of parasites that are different from most other living organisms, and Küchenmeister, through his religious beliefs and his views on every creature having a place in the natural order, denied the ideas of his time and proved that all parasites are a part of active evolutionary niches and not biological dead ends by conducting morally ambiguous experiments on prisoners. Lankester is given a specific focus and repeated discussion throughout the book due to his belief that parasites are examples of degenerative evolution, especially in regards to Sacculina, and Zimmer's repeated refutation of this idea.
Several chapters are taken to discuss various types of parasites and how they infect and control their hosts, along with the biochemistry involved in their take-over or evasion of their hosts immune system, eventually leading to their dispersal into their next form and life cycle. An extended time is also given on the workings of immunology and how the immune systems of living beings respond to parasite infection, along with the methods that bodily functions use to counteract and potentially kill invading microorganisms. Woven into this discussion are several specific sites that Zimmer visited during his writing of Parasite Rex' and the scientists he worked with to understand different biosystems and all the parasites that live within them, including human sleeping sickness infections in Sudan from the tsetse fly, the parasites of frogs in Costa Rica, primarily showcased by filarial worms that infect humans and a variety of species, and the USDA National Parasite Collection based out of Maryland.
The final chapters focus on an overall effect parasites have had on the evolution of life and the theory that it is due to parasitic infection that sexual reproduction evolved to become dominant, in contrast to previous asexual reproduction methods, due to the increased genetic variety and thus potential parasitic resistance that this would confer. This research was showcased by W. D. Hamilton and his theories on the evolution of sex, along with the Red Queen hypothesis and the idea of an evolutionary arms race between parasites and their hosts. Zimmer then discusses a final time the wide variety of parasites that evolved to have humans as their primary hosts and our attempts through scientific advancement to eradicate them. The closing chapter considers the positive benefits of parasites and how humans have used them to improve agriculture and medical technology, but also how ill-considered usage of parasites could also destroy various habitats by having them act as invasive species. In the end, Zimmer ponders whether humanity counts as a parasite on the planet and what the effects of this relationship could be. | 1 | Biochemistry |
Where primary energy is used to describe fossil fuels, the embodied energy of the fuel is available as thermal energy and around 70% is typically lost in conversion to electrical or mechanical energy. There are very much less significant conversion losses when hydroelectricity, wind and solar power produce electricity, but today's UN conventions on energy statistics counts the electricity made from hydroelectricity, wind and solar as the primary energy itself for these sources. One consequence of employing primary energy as an energy metric is that the contribution of hydro, wind and solar energy is under reported compared to fossil energy sources, and there is hence an international debate on how to count energy from non thermal renewables, with many estimates having them undercounted by a factor of about three. | 7 | Physical Chemistry |
The purpose of single cell metabolomics is to gain a better understanding at the molecular level of major biological topics such as: cancer, stem cells, aging, as well as the development of drug resistance. In general the focus of metabolomics is mostly on understanding how cells deal with environmental stresses at the molecular level, and to give a more dynamic understanding of cellular functions. | 1 | Biochemistry |
Although the concept of circles and spheres can be extended to hyperbolic space, finding the densest packing becomes much more difficult. In a hyperbolic space there is no limit to the number of spheres that can surround another sphere (for example, Ford circles can be thought of as an arrangement of identical hyperbolic circles in which each circle is surrounded by an infinite number of other circles). The concept of average density also becomes much more difficult to define accurately. The densest packings in any hyperbolic space are almost always irregular.
Despite this difficulty, K. Böröczky gives a universal upper bound for the density of sphere packings of hyperbolic n-space where n ≥ 2. In three dimensions the Böröczky bound is approximately 85.327613%, and is realized by the horosphere packing of the order-6 tetrahedral honeycomb with Schläfli symbol {3,3,6}. In addition to this configuration at least three other horosphere packings are known to exist in hyperbolic 3-space that realize the density upper bound. | 3 | Analytical Chemistry |
An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them. These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating. On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions. Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO) as the "central external trigger for euxinia."
Human activities in the Holocene epoch, such as the release of nutrients from farms and sewage, cause relatively small-scale dead zones around the world. British oceanologist and atmospheric scientist Andrew Watson says full-scale ocean anoxia would take "thousands of years to develop." The idea that modern climate change could lead to such an event is also referred to as Kump's hypothesis, | 9 | Geochemistry |
Imidates may be generated by a number of synthetic routes, but are in general formed by the Pinner reaction. This proceeds via the acid catalyzed attack of nitriles by alcohols.
Imidates produced in this manner are formed as their hydrochloride salts, which are sometimes referred to as Pinner salts. Carboximidates are also formed as intermediates in the Mumm rearrangement and the Overman rearrangement. | 0 | Organic Chemistry |
In cell biology, protein kinase A (PKA) is a family of serine-threonine kinase whose activity is dependent on cellular levels of cyclic AMP (cAMP). PKA is also known as cAMP-dependent protein kinase (). PKA has several functions in the cell, including regulation of glycogen, sugar, and lipid metabolism. It should not be confused with 5'-AMP-activated protein kinase (AMP-activated protein kinase). | 1 | Biochemistry |
The V comformation of COT has an angle at 135° and is thought to be highly stabilized via bonding with the iron atoms (in free COT, this comformation is disfavored by approximately 36 kcal/mol.
Fascinatingly, in benzene solution, H NMR reveals a single broadened resonance with a chemical shift at -3.15 ppm. This suggests that the cyclooctatetraene ligands are highly fluxional and some degree of paramagnetism.
COT is known to be a highly fluxional ligand in other compounds too, such compounds being deemed “ring-whizzers” (like the related (cyclooctatetraene)iron tricarbony<nowiki/>l).
The conformational fluxionality is supported by computational studies which show very low barriers to COT rotation (on the scale of 1.4 kcal/mol) and rocking (0.1 kcal/mol). The transformation from the C singlet comformation to the triplet C comformation have been calculated to be nearly isoenergetic, driving the possibility of the singlet state existing in equilibrium with the triplet state- an explanation for the observation of paramagnetic NMR resonances at ambient temperatures. | 7 | Physical Chemistry |
At the minimum in the system can be approximated to a linear one, the residuals in the case of unit weights are related to the observations by
The symmetric, idempotent matrix is known in the statistics literature as the hat matrix, . Thus,
and
where is an identity matrix and and are the variance-covariance matrices of the residuals and observations, respectively. This shows that even though the observations may be uncorrelated, the residuals are always correlated.
The diagram at the right shows the result of a refinement of the stability constants of Ni(Gly), Ni(Gly) and (where GlyH = glycine). The observed values are shown a blue diamonds and the species concentrations, as a percentage of the total nickel, are superimposed. The residuals are shown in the lower box. The residuals are not distributed as randomly as would be expected. This is due to the variation of liquid junction potentials and other effects at the glass/liquid interfaces. Those effects are very slow compared to the rate at which equilibrium is established. | 7 | Physical Chemistry |
IR-visible sum frequency generation spectroscopy uses two laser beams (an infrared probe, and a visible pump) that spatially and temporally overlap at a surface of a material or the interface between two media. An output beam is generated at a frequency of the sum of the two input beams. The two input beams must be able to access the surface with sufficiently high intensities, and the output beam must be able to reflect off (or transmit through) the surface in order to be detected. Broadly speaking, most sum frequency spectrometers can be considered as one of two types, scanning systems (those with narrow bandwidth probe beams) and broadband systems (those with broad bandwidth probe beams). For the former type of spectrometer, the pump beam is a visible wavelength laser held at a constant frequency, and the other (the probe beam) is a tunable infrared laser — by tuning the IR laser, the system can scan across molecular resonances and obtain a vibrational spectrum of the interfacial region in a piecewise fashion. In a broadband spectrometer, the visible pump beam is once again held at a fixed frequency, while the probe beam is spectrally broad. These laser beams overlap at a surface, but may access a wider range of molecular resonances simultaneously than a scanning spectrometer, and hence spectra can be acquired significantly faster, allowing the ability to perform time-resolved measurements with interfacial sensitivity. | 7 | Physical Chemistry |
In a mixture of gases, the fugacity of each component has a similar definition, with partial molar quantities instead of molar quantities (e.g., instead of and instead of ):
and
where is the partial pressure of component . The partial pressures obey Dalton's law:
where is the total pressure and is the mole fraction of the component (so the partial pressures add up to the total pressure). The fugacities commonly obey a similar law called the Lewis and Randall rule:
where is the fugacity that component would have if the entire gas had that composition at the same temperature and pressure. Both laws are expressions of an assumption that the gases behave independently. | 7 | Physical Chemistry |
Some typical Doppler-broadened NICE-OHMS signals, from 13 ppb (10 μTorr, 13•10 atm) of CH detected in a cavity with a finesse of 4800, are shown in the figure. (a) fm- and (b) wm-signal. Individual markers: measured data; Solid curves: theoretical fits. | 7 | Physical Chemistry |
More than half of the regional land in Campania is used for agriculture, and therefore the economy of the region is adversely affected by the waste crisis. Between January and March 2007, 30,000 kilograms of waste were burned on agricultural land, with a revenue of more than €118,000. In the region, over 12,000 cattle, river buffaloes and sheep had been culled before 2006. High levels of mortality and abnormal foetuses were also recorded in farms in Acerra linked to elevated levels of dioxin. Local studies have shown higher than permissible levels of lead in vegetables grown in the area. The government blames the Mafia's illegal garbage disposal racket.
In March 2008, dioxin were found in buffalo milk from farms in Caserta. While only 2.8% of farms in Campania were affected, the sale of dairy products from Campania collapsed in both domestic and global markets.
A chain reaction followed, in which several countries including Japan, China, Russia and Germany took various measures ranging from the mere raising of the attention threshold to the suspension of imports. The Italian institutions activated almost immediately, even in response to pressing requests from the European Union, a series of checks and suspended, in some cases, the sale of dairy products from the incriminated provinces. Tests had shown levels of dioxins higher than normal in at least 14% of samples taken in the provinces of Naples, Caserta and Avellino. In the provinces of Salerno and Benevento, no control indicated dioxins positivity. In any case, the contamination has affected, in a limited defined manner, the farms used to produce the PDO buffalo mozzarella DOP. On 19 April, China definitively removed the ban on mozzarella, originally activated on 28 March 2008, and tests held in December 2013 in Germany on behalf of four Italian consumer associations have highlighted dioxin and heavy metal levels at least five times lower than the legal limit. | 2 | Environmental Chemistry |
The presence of atmospheric methane has a role in the scientific search for extra-terrestrial life. The justification is that on an astronomical timescale, methane in the atmosphere of an Earth-like celestial body will quickly dissipate, and that its presence on such a planet or moon therefore indicates that something is replenishing it. If methane is detected (by using a spectrometer for example) this may indicate that life is, or recently was, present.
This was debated when methane was discovered in the Martian atmosphere by M.J. Mumma of NASAs Goddard Flight Center, and verified by the Mars Express Orbiter (2004) and in Titans atmosphere by the Huygens probe (2005). This debate was furthered with the discovery of transient, spikes of methane on Mars by the Curiosity Rover.
It is argued that atmospheric methane can come from volcanoes or other fissures in the planet's crust and that without an isotopic signature, the origin or source may be difficult to identify.
On 13 April 2017, NASA confirmed that the dive of the Cassini orbiter spacecraft on 28 October 2015 discovered an Enceladus plume which has all the ingredients for methanogenesis-based life forms to feed on. Previous results, published in March 2015, suggested hot water is interacting with rock beneath the sea of Enceladus; the new finding supported that conclusion, and add that the rock appears to be reacting chemically. From these observations scientists have determined that nearly 98 percent of the gas in the plume is water, about 1 percent is hydrogen, and the rest is a mixture of other molecules including carbon dioxide, methane and ammonia. | 1 | Biochemistry |
The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid are of increasing importance due to stricter controls on emissions of sulfur compounds. 70 Tg(S) per year in the form of SO comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires, and 7–8 Tg(S) per year from volcanoes. | 2 | Environmental Chemistry |
The Chen-Kao reaction (named after Ko Kuei Chen and Chung-Hsi Kao, Madison, Wisconsin 1926) is a chemical method for determining the presence of pseudoephedrine, ephedrine, and similar phenylalkylamines.
The reaction is used in spot tests and is also known as Chen-Kao test (or simply as Chen, Test T in UN Precursor Test Kit).
The test is often used to distinguish ephedrine, pseudoephedrine, norephedrine, cathinone and methcathinone from amphetamine and methamphetamine,
which do not react with Chen’s test reagent. | 3 | Analytical Chemistry |
Yuri Andreyevich Zhdanov (; 20 August 1919 – 19 December 2006) was a Soviet and Russian chemistry professor and rector of the University of Rostov. He was the son of Soviet politician Andrei Zhdanov and a former husband of Joseph Stalin's daughter, Svetlana Alliluyeva. | 0 | Organic Chemistry |
Tetrafluoromethane is sometimes used as a low temperature refrigerant (R-14). It is used in electronics microfabrication alone or in combination with oxygen as a plasma etchant for silicon, silicon dioxide, and silicon nitride. It also has uses in neutron detectors. | 2 | Environmental Chemistry |
The amylolytic process is used in the brewing of alcohol from grains. Since grains contain starches but little to no simple sugars, the sugar needed to produce alcohol is derived from starch via the amylolytic process. In beer brewing, this is done through malting. In sake brewing, the mold Aspergillus oryzae provides amylolysis, and in Tapai, Saccharomyces cerevisiae. The amylolytic process can also be used to allow for maximum results in production. For instance, glucose formation, when amylolytic enzymes are added to a given compound, the enzymes work to give maximum formation. The amylolytic process is also useful in the breaking down of molecules, it can be closely associated with the process of hydrolysis. | 0 | Organic Chemistry |
The Standard Model hypothesises a field called the Higgs field (symbol: ), which has the unusual property of a non-zero amplitude in its ground state (zero-point) energy after renormalization; i.e., a non-zero vacuum expectation value. It can have this effect because of its unusual "Mexican hat" shaped potential whose lowest "point" is not at its "centre". Below a certain extremely high energy level the existence of this non-zero vacuum expectation spontaneously breaks electroweak gauge symmetry which in turn gives rise to the Higgs mechanism and triggers the acquisition of mass by those particles interacting with the field. The Higgs mechanism occurs whenever a charged field has a vacuum expectation value. This effect occurs because scalar field components of the Higgs field are "absorbed" by the massive bosons as degrees of freedom, and couple to the fermions via Yukawa coupling, thereby producing the expected mass terms. The expectation value of in the ground state (the vacuum expectation value or VEV) is then , where . The measured value of this parameter is approximately . It has units of mass, and is the only free parameter of the Standard Model that is not a dimensionless number.
The Higgs mechanism is a type of superconductivity which occurs in the vacuum. It occurs when all of space is filled with a sea of particles which are charged and thus the field has a nonzero vacuum expectation value. Interaction with the vacuum energy filling the space prevents certain forces from propagating over long distances (as it does in a superconducting medium; e.g., in the Ginzburg–Landau theory). | 7 | Physical Chemistry |
The local solidification time can be calculated using Chvorinov's rule, which is:
Where t is the solidification time, V is the volume of the casting, A is the surface area of the casting that contacts the mold, n is a constant, and B is the mold constant. It is most useful in determining if a riser will solidify before the casting, because if the riser does solidify first then it is worthless. | 8 | Metallurgy |
Levocetirizine is referred to as a non-sedating antihistamine as it does not enter the brain in significant amounts and is therefore unlikely to cause drowsiness. Cardiac safety with repolarization may be better than some other antihistamines, as levocetirizine does not significantly prolong the QT interval in healthy individuals. However, some people may still experience some slight sleepiness, headache, mouth dryness, lightheadedness, vision problems (mainly blurred vision), palpitations and fatigue. | 4 | Stereochemistry |
Research carried out in 2008 in the Siberian Arctic showed methane releases on the annual scale of millions of tonnes, which was a substantial increase on the previous estimate of 0.5 millions of tonnes per year. apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal levels. The excess methane has been detected in localized hotspots in the outfall of the Lena River and the border between the Laptev Sea and the East Siberian Sea. At the time, some of the melting was thought to be the result of geological heating, but more thawing was believed to be due to the greatly increased volumes of meltwater being discharged from the Siberian rivers flowing north.
By 2013, the same team of researchers used multiple sonar observations to quantify the density of bubbles emanating from subsea permafrost into the ocean (a process called ebullition), and found that 100–630 mg methane per square meter is emitted daily along the East Siberian Arctic Shelf (ESAS), into the water column. They also found that during storms, when wind accelerates air-sea gas exchange, methane levels in the water column drop dramatically. Observations suggest that methane release from seabed permafrost will progress slowly, rather than abruptly. However, Arctic cyclones, fueled by global warming, and further accumulation of greenhouse gases in the atmosphere could contribute to more rapid methane release from this source. Altogether, their updated estimate had now amounted to 17 millions of tonnes per year.
However, these findings were soon questioned, as this rate of annual release would mean that the ESAS alone would account for between 28% and 75% of the observed Arctic methane emissions, which contradicts many other studies. In January 2020, it was found that the rate at which methane enters the atmosphere after it had been released from the shelf deposits into the water column had been greatly overestimated, and observations of atmospheric methane fluxes taken from multiple ship cruises in the Arctic instead indicate that only around 3.02 million tonnes of methane are emitted annually from the ESAS. A modelling study published in 2020 suggested that under the present-day conditions, annual methane release from the ESAS may be as low as 1000 tonnes, with 2.6 – 4.5 million tonnes representing the peak potential of turbulent emissions from the shelf. | 6 | Supramolecular Chemistry |
In spectroscopy, oscillator strength is a dimensionless quantity that expresses the probability of absorption or emission of electromagnetic radiation in transitions between energy levels of an atom or molecule. For example, if an emissive state has a small oscillator strength, nonradiative decay will outpace radiative decay. Conversely, "bright" transitions will have large oscillator strengths. The oscillator strength can be thought of as the ratio between the quantum mechanical transition rate and the classical absorption/emission rate of a single electron oscillator with the same frequency as the transition. | 7 | Physical Chemistry |
* Reduction of an epoxide with lithium aluminium hydride or aluminium hydride produces the corresponding alcohol. This reduction process results from the nucleophilic addition of hydride (H).
* Reductive cleavage of epoxides gives β-lithioalkoxides.
* Epoxides undergo ring expansion reactions, illustrated by the insertion of carbon dioxide to give cyclic carbonates.
* When treated with thiourea, epoxides convert to the episulfide, which are called thiiranes.
* An epoxide adjacent to an alcohol can undergo the Payne rearrangement in base. | 0 | Organic Chemistry |
One of the oldest, and perhaps the most studied, families of photochromes are the spiropyrans. Very closely related to these are the spirooxazines. For example, the spiro form of an oxazine is a colorless leuco dye; the conjugated system of the oxazine and another aromatic part of the molecule is separated by a sp³-hybridized "spiro" carbon. After irradiation with UV light, the bond between the spiro-carbon and the oxazine breaks, the ring opens, the spiro carbon achieves sp² hybridization and becomes planar, the aromatic group rotates, aligns its π-orbitals with the rest of the molecule, and a conjugated system forms with ability to absorb photons of visible light, and therefore appear colorful. When the UV source is removed, the molecules gradually relax to their ground state, the carbon-oxygen bond reforms, the spiro-carbon becomes sp³ hybridized again, and the molecule returns to its colorless state.
This class of photochromes in particular are thermodynamically unstable in one form and revert to the stable form in the dark unless cooled to low temperatures. Their lifetime can also be affected by exposure to UV light. Like most organic dyes they are susceptible to degradation by oxygen and free radicals. Incorporation of the dyes into a polymer matrix, adding a stabilizer, or providing a barrier to oxygen and chemicals by other means prolongs their lifetime. | 5 | Photochemistry |
The reaction involving benzaldehyde was discovered by Claisen using sodium benzylate as base. The reaction produces benzyl benzoate.
Enolizable aldehydes are not amenable to Claisen's conditions. Vyacheslav Tishchenko discovered that aluminium alkoxides allowed the conversion of enolizable aldehydes to esters. | 0 | Organic Chemistry |
As particles and droplets in an aerosol collide with one another, they may undergo coalescence or aggregation. This process leads to a change in the aerosol particle-size distribution, with the mode increasing in diameter as total number of particles decreases. On occasion, particles may shatter apart into numerous smaller particles; however, this process usually occurs primarily in particles too large for consideration as aerosols. | 7 | Physical Chemistry |
Higher values of TFQI are associated with obesity, metabolic syndrome, impaired renal function, diabetes, and diabetes-related mortality. In a large population of community-dwelling euthyroid subjects the thyroid feedback quantile-based index predicted all-cause mortality, even after adjustment for other established risk factors and comorbidities.
A cross-sectional study from Spain observed increased prevalence of type 2 diabetes, atrial fibrillation, ischemic heart disease and hypertension in persons with elevated PTFQI.
Serum Concentrations of Adipocyte Fatty Acid-Binding Protein (A-FABP) are significantly correlateted to TFQI, suggesting some form of cross-talk between adipose tissue and HPT axis.
TFQI results are also elevated in takotsubo syndrome, potentially reflecting type 2 allostatic load in the situation of psychosocial stress. Reductions have been observed in subjects with schizophrenia after initiation of therapy with oxcarbazepine and quetiapine, potentially reflecting declining allostatic load.
Despite positive association to metabolic syndrome and type 2 allostatic load a large population-based study failed to identify an association to risks of dyslipidemia and non-alcoholic fatty liver disease (NAFLD). | 1 | Biochemistry |
The conformation of any polymer is affected by a number of factors, notably the polymer architecture and the solvent affinity. In the case of polyelectrolytes, charge also has an effect. Whereas an uncharged linear polymer chain is usually found in a random conformation in solution (closely approximating a self-avoiding three-dimensional random walk), the charges on a linear polyelectrolyte chain will repel each other via double layer forces, which causes the chain to adopt a more expanded, rigid-rod-like conformation. The charges will be screened if the solution contains a great deal of added salt. Consequently, the polyelectrolyte chain will collapse to a more conventional conformation (essentially identical to a neutral chain in good solvent).
Polymer conformation affects many bulk properties (such as viscosity, turbidity, etc.). Although the statistical conformation of polyelectrolytes can be captured using variants of conventional polymer theory, it is, in general, quite computationally intensive to properly model polyelectrolyte chains, owing to the long-range nature of the electrostatic interaction.
Techniques such as static light scattering can be used to study polyelectrolyte conformation and conformational changes. | 7 | Physical Chemistry |
The concentration of calcium in the cell nucleus can increase in response to signals from the environment. Nuclear calcium is an evolutionary conserved potent regulator of gene expression that allows cells to undergo long-lasting adaptive responses. The 'Nuclear Calcium Hypothesis’ by Hilmar Bading describes nuclear calcium in neurons as an important signaling end-point in synapse-to-nucleus communication that activates gene expression programs needed for persistent adaptations. In the nervous system, nuclear calcium is required for long-term memory formation, acquired neuroprotection, and the development of chronic inflammatory pain. In the heart, nuclear calcium is important for the development of cardiac hypertrophy. In the immune system, nuclear calcium is required for human T cell activation. Plants use nuclear calcium to control symbiosis signaling. | 1 | Biochemistry |
Makemake exhibits methane, large amounts of ethane and tholins, as well as smaller amounts of ethylene, acetylene and high-mass alkanes may be present, most likely created by photolysis of methane by solar radiation. | 9 | Geochemistry |
Table 1: Reaction times and yield vary on the substrate. The β-glucopyranoside was found to be the best substrate for the Tipson–Cohen reaction as the reaction time and yield were much superior that any other substrate proposed in the study.
Substrates possess benzylidene protecting groups at C-4 and C-6, OMe groups at anomeric position and OTs groups at C-2 and C-3. Reaction temperature 95–100 ˚C | 0 | Organic Chemistry |
SPEARpesticides (Species At Risk) is a trait based biological indicator system for streams which quantitatively links pesticide contamination to the composition of invertebrate communities. The approach uses species traits that characterize the ecological requirements posed by pesticide contamination in running waters. Therefore, it is highly specific and only slightly influenced by other environmental factors. SPEARpesticides is linked to the quality classes of the EU Water Framework Directive (WFD) | 2 | Environmental Chemistry |
The deformation gradient for a simple shear deformation has the form
where are reference orthonormal basis vectors in the plane of deformation and the shear deformation is given by
In matrix form, the deformation gradient and the left Cauchy–Green deformation tensor may then be expressed as
Therefore,
and the Cauchy stress is given by | 7 | Physical Chemistry |
* Zur Kenntnis der thermischen Zersetzung der Salpetersäure, 1926.
* Zur Erklärung der abnormen Osmose an nichtquellbaren Membranen, I.-III. Teil, 1933.
* The Structure of the Colladion Membrane and Its Electrical Behavior, an Experimental Test of Some Aspects of the Teorell and Meyer-sievers Theories of Electrical Membrane Behavior, 1944. | 7 | Physical Chemistry |
Standard methods such as microarrays and standard bulk RNA-Seq analysis analyze the expression of RNAs from large populations of cells. In mixed cell populations, these measurements may obscure critical differences between individual cells within these populations.
Single-cell RNA sequencing (scRNA-Seq) provides the expression profiles of individual cells. Although it is not possible to obtain complete information on every RNA expressed by each cell, due to the small amount of material available, patterns of gene expression can be identified through gene clustering analyses. This can uncover the existence of rare cell types within a cell population that may never have been seen before. For example, rare specialized cells in the lung called pulmonary ionocytes that express the Cystic fibrosis transmembrane conductance regulator were identified in 2018 by two groups performing scRNA-Seq on lung airway epithelia. | 1 | Biochemistry |
Pre-mRNAs from the D. melanogaster gene dsx contain 6 exons. In males, exons 1,2,3,5,and 6 are joined to form the mRNA, which encodes a transcriptional regulatory protein required for male development. In females, exons 1,2,3, and 4 are joined, and a polyadenylation signal in exon 4 causes cleavage of the mRNA at that point. The resulting mRNA is a transcriptional regulatory protein required for female development.
This is an example of exon skipping. The intron upstream from exon 4 has a polypyrimidine tract that doesnt match the consensus sequence well, so that U2AF proteins bind poorly to it without assistance from splicing activators. This 3 splice acceptor site is therefore not used in males. Females, however, produce the splicing activator Transformer (Tra) (see below). The SR protein Tra2 is produced in both sexes and binds to an ESE in exon 4; if Tra is present, it binds to Tra2 and, along with another SR protein, forms a complex that assists U2AF proteins in binding to the weak polypyrimidine tract. U2 is recruited to the associated branchpoint, and this leads to inclusion of exon 4 in the mRNA. | 1 | Biochemistry |
Mukaiyama studied chemistry at the Tokyo Institute of Technology, earning his BSc in synthetic organic chemistry in 1948. He became assistant professor at Gakushuin University in 1953, where he stayed until he received his Ph.D. in synthetic organic chemistry from the University of Tokyo in 1957. | 0 | Organic Chemistry |
The formyl group can be readily reduced to a primary alcohol (). Typically this conversion is accomplished by catalytic hydrogenation either directly or by transfer hydrogenation. Stoichiometric reductions are also popular, as can be effected with sodium borohydride. | 0 | Organic Chemistry |
Glycogen is cleaved from the nonreducing ends of the chain by the enzyme glycogen phosphorylase to produce monomers of glucose-1-phosphate:
In vivo, phosphorolysis proceeds in the direction of glycogen breakdown because the ratio of phosphate and glucose-1-phosphate is usually greater than 100. Glucose-1-phosphate is then converted to glucose 6 phosphate (G6P) by phosphoglucomutase. A special debranching enzyme is needed to remove the α(1→6) branches in branched glycogen and reshape the chain into a linear polymer. The G6P monomers produced have three possible fates:
* G6P can continue on the glycolysis pathway and be used as fuel.
* G6P can enter the pentose phosphate pathway via the enzyme glucose-6-phosphate dehydrogenase to produce NADPH and 5 carbon sugars.
* In the liver and kidney, G6P can be dephosphorylated back to glucose by the enzyme glucose 6-phosphatase. This is the final step in the gluconeogenesis pathway. | 1 | Biochemistry |
Mycophenolic acid is a Penicillium metabolite that was originally prepared via a key benzannulation step. An alkyne and a cyclobutenone were reacted to form a substituted phenol in a single step in a 73% yield (Scheme 14). Mycophenolic acid was prepared in nine steps in an overall yield of 17-19%.
In the synthesis of highly substituted indoles performed by Danheiser, the key step was a benzannulation reaction using cyclobutenone and ynamides to produce highly substituted aniline derivatives. In this case, the ortho position can be functionalized with various substituents. Following the benzannulation reaction with various heterocyclization reactions can provide access to substituted indoles (Scheme 15).
Danheiser also used the benzannulation with ynamides for the synthesis of polycyclic benzofused nitrogen heterocycles followed by ring-closing metathesis (Scheme 16) for the total synthesis of (+)-FR900482, an anticancer agent.
Kowalski used the benzannulation reaction with siloxyacetylenes for the first time, reacting them with cyclobutenones to synthesize a substituted phenol for the total synthesis of Δ-6-tetrahydrocannabinol (Scheme 17).
The benzannulation reaction was used by Smith in the total synthesis of cylindrocyclophanes specifically (−)-Cylindrocyclophane F. He utilized the reaction of a siloxyalkyne and a cyclobutenone to construct the dihydroxyl aromatic intermediate for an olefin metathesis reaction to access the target (Scheme 18).
An outstanding application of Danheiser benzannulation in 6-step synthesis of dictyodendrins was demonstrated by Zhang and Ready. They obtained the cyclobutenone substrate using a hetero-[2+2] cycloaddition between aryl ynol ethers (aryl ketene precursors), and the following benzannulation enabled the rapid construction of the carbazole cole of dictyodendrins F, H and I. The successful usage of Danheiser benzannulation allows Zhang and Ready to achieve the so-far shortest synthesis of dictyodendrin natural products. | 0 | Organic Chemistry |
Reverse transfection is a technique for the transfer of genetic material into cells. As DNA is printed on a glass slide for the transfection process (the deliberate introduction of nucleic acids into cells) to occur before the addition of adherent cells, the order of addition of DNA and adherent cells is reverse that of conventional transfection. Hence, the word “reverse” is used. | 1 | Biochemistry |
The targeted deletion or alteration of genes relies on the integration of a DNA strand at a specific and predictable position into the genome of the host cell. This DNA strand must be engineered in such a way that both ends are identical to this specific gene locus. This is a prerequisite for being efficiently integrated via homologous recombination (HR). This is similar to the process used for creating knockout mice.
So far, this method of gene targeting in land plants has been carried out in the mosses Physcomitrella patens and Ceratodon purpureus, since in these non-seed plant species the efficiency of HR is several orders of magnitude higher than in seed plants.
Knockout mosses are stored at and distributed by a specialized biobank, the International Moss Stock Center. | 1 | Biochemistry |
The critical micelle concentration (CMC) in water at 25 °C is 8.2 mM, and the aggregation number at this concentration is usually considered to be about 62. The micelle ionization fraction (α) is around 0.3 (or 30%). | 1 | Biochemistry |
Shimomura worked in the department of biology at Princeton for Professor Johnson to study the bioluminescent jellyfish Aequorea victoria, which they collected during many summers at the Friday Harbor Laboratories of the University of Washington. In 1962, their work culminated in the discovery of the proteins aequorin and green fluorescent protein (GFP) in A. victoria; for this work, he was awarded a third of the Nobel Prize in Chemistry in 2008. | 0 | Organic Chemistry |
In chemistry, pi stacking (also called π–π stacking) refers to the presumptive attractive, noncovalent pi interactions (orbital overlap) between the pi bonds of aromatic rings. However this is a misleading description of the phenomena since direct stacking of aromatic rings (the "sandwich interaction") is electrostatically repulsive. What is more commonly observed (see figure to the right) is either a staggered stacking (parallel displaced) or pi-teeing (perpendicular T-shaped) interaction both of which are electrostatic attractive For example, the most commonly observed interactions between aromatic rings of amino acid residues in proteins is a staggered stacked followed by a perpendicular orientation. Sandwiched orientations are relatively rare.
Pi stacking is repulsive as it places carbon atoms with partial negative charges from one ring on top of other partial negatively charged carbon atoms from the second ring and hydrogen atoms with partial positive charges on top of other hydrogen atoms that likewise carry partial positive charges. In staggered stacking, one of the two aromatic rings is offset sideways so that the carbon atoms with partial negative charge in the first ring are placed above hydrogen atoms with partial positive charge in the second ring so that the electrostatic interactions become attractive. Likewise, pi-teeing interactions in which the two rings are oriented perpendicular to either other is electrostatically attractive as it places partial positively charged hydrogen atoms in close proximity to partially negatively charged carbon atoms. An alternative explanation for the preference for staggered stacking is due to the balance between van der Waals interactions (attractive dispersion plus Pauli repulsion).
These staggered stacking and π-teeing interactions between aromatic rings are important in nucleobase stacking within DNA and RNA molecules, protein folding, template-directed synthesis, materials science, and molecular recognition. Despite the wide use of term pi stacking in the scientific literature, there is no theoretical justification for its use. | 6 | Supramolecular Chemistry |
Saponifiable lipids have relevant applications as a source of biofuel and can be extracted from various forms of biomass to produce biodiesel. | 1 | Biochemistry |
An example of a mineral containing hydroxyl groups is garnet. Garnet is an anhydrous mineral commonly analyzed within geological subdisciplines because of its general stability. One study analyzed the presence of garnets within the upper mantle through infrared spectroscopy and showed absorption at approximately 3500 cm, which is consistent with the presence of hydroxyl groups. These garnets have been shown to vary in composition dependent on its geographic origin. One particular study in Southern Africa determined concentrations ranging from 1 ppm - 135 ppm. However, this is significantly lower than the hydroxyl content in regions such as the Colorado Plateau. It was also demonstrated that there is an inverse correlation regarding the concentration of OH and Mg + Fe. | 9 | Geochemistry |
Without the aid of the whole-genome sequences, pre-genomics investigations looked at select regions of the genome, often with only minimal knowledge of the gene sequences they were looking at. Genetic techniques capable of providing this sort of information include Restriction Fragment Length Polymorphism (RFLP) analysis and microsatellite analysis. | 1 | Biochemistry |
In statistical mechanics, the following molecular equation is derived from first principles
where is the absolute pressure of the gas, is the number density of the molecules (given by the ratio , in contrast to the previous formulation in which is the number of moles), is the absolute temperature, and is the Boltzmann constant relating temperature and energy, given by:
where is the Avogadro constant.
From this we notice that for a gas of mass , with an average particle mass of times the atomic mass constant, , (i.e., the mass is Da) the number of molecules will be given by
and since , we find that the ideal gas law can be rewritten as
In SI units, is measured in pascals, in cubic metres, in kelvins, and in SI units. | 7 | Physical Chemistry |
Other salts of the dimethylaminomethylene cation:
*Dimethyl(methylidene)ammonium trifluoroacetate.
*Dimethyl(methylidene)ammonium chloride (Böhmes salt', after Horst Böhme) | 0 | Organic Chemistry |
Grain boundaries are interfaces where crystals of different orientations meet. A grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. The term "crystallite boundary" is sometimes, though rarely, used. Grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary.
Treating a grain boundary geometrically as an interface of a single crystal cut into two parts, one of which is rotated, we see that there are five variables required to define a grain boundary. The first two numbers come from the unit vector that specifies a rotation axis. The third number designates the angle of rotation of the grain. The final two numbers specify the plane of the grain boundary (or a unit vector that is normal to this plane).
Grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve strength, as described by the Hall–Petch relationship. Since grain boundaries are defects in the crystal structure they tend to decrease the electrical and thermal conductivity of the material. The high interfacial energy and relatively weak bonding in most grain boundaries often makes them preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep.
Grain boundaries are in general only a few nanometers wide. In common materials, crystallites are large enough that grain boundaries account for a small fraction of the material. However, very small grain sizes are achievable. In nanocrystalline solids, grain boundaries become a significant volume fraction of the material, with profound effects on such properties as diffusion and plasticity. In the limit of small crystallites, as the volume fraction of grain boundaries approaches 100%, the material ceases to have any crystalline character, and thus becomes an amorphous solid. | 3 | Analytical Chemistry |
Macroinvertebrates are useful and convenient indicators of the ecological health of water bodies and terrestrial ecosystems. They are almost always present, and are easy to sample and identify. This is largely due to the fact that most macro-invertebrates are visible to the naked eye, they typically have a short life-cycle (often the length of a single season) and are generally sedentary. Pre-existing river conditions such as river type and flow will affect macro invertebrate assemblages and so various methods and indices will be appropriate for specific stream types and within specific eco-regions. While some benthic macroinvertebrates are highly tolerant to various types of water pollution, others are not. Changes in population size and species type in specific study regions indicate the physical and chemical state of streams and rivers. Tolerance values are commonly used to assess water pollution and environmental degradation, such as human activities (e.g. selective logging and wildfires) in tropical forests. | 2 | Environmental Chemistry |
Deep cycling involves the exchange of materials with the mantle. The deep water cycle involves exchange of water with the mantle, with water carried down by subducting oceanic plates and returning through volcanic activity, distinct from the water cycle process that occurs above and on the surface of Earth. Some of the water makes it all the way to the lower mantle and may even reach the outer core.
In the conventional view of the water cycle (also known as the hydrologic cycle), water moves between reservoirs in the atmosphere and Earth's surface or near-surface (including the ocean, rivers and lakes, glaciers and polar ice caps, the biosphere and groundwater). However, in addition to the surface cycle, water also plays an important role in geological processes reaching down into the crust and mantle. Water content in magma determines how explosive a volcanic eruption is; hot water is the main conduit for economically important minerals to concentrate in hydrothermal mineral deposits; and water plays an important role in the formation and migration of petroleum. Petroleum is a fossil fuel derived from ancient fossilized organic materials, such as zooplankton and algae.
Water is not just present as a separate phase in the ground. Seawater percolates into oceanic crust and hydrates igneous rocks such as olivine and pyroxene, transforming them into hydrous minerals such as serpentines, talc and brucite. In this form, water is carried down into the mantle. In the upper mantle, heat and pressure dehydrates these minerals, releasing much of it to the overlying mantle wedge, triggering the melting of rock that rises to form volcanic arcs. However, some of the "nominally anhydrous minerals" that are stable deeper in the mantle can store small concentrations of water in the form of hydroxyl (OH), and because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans.
The conventional view of the ocean's origin is that it was filled by outgassing from the mantle in the early Archean and the mantle has remained dehydrated ever since. However, subduction carries water down at a rate that would empty the ocean in 1–2 billion years. Despite this, changes in the global sea level over the past 3–4 billion years have only been a few hundred metres, much smaller than the average ocean depth of 4 kilometres. Thus, the fluxes of water into and out of the mantle are expected to be roughly balanced, and the water content of the mantle steady. Water carried into the mantle eventually returns to the surface in eruptions at mid-ocean ridges and hotspots. Estimates of the amount of water in the mantle range from to 4 times the water in the ocean.
The deep carbon cycle is the movement of carbon through the Earth's mantle and core.
It forms part of the carbon cycle and is intimately connected to the movement of carbon in the Earth's surface and atmosphere. By returning carbon to the deep Earth, it plays a critical role in maintaining the terrestrial conditions necessary for life to exist. Without it, carbon would accumulate in the atmosphere, reaching extremely high concentrations over long periods of time. | 9 | Geochemistry |
In inorganic chemistry, sulfonyl halide groups occur when a sulfonyl () functional group is singly bonded to a halogen atom. They have the general formula , where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides > chlorides > bromides > iodides, all four types being well known. The sulfonyl chlorides and fluorides are of dominant importance in this series. | 0 | Organic Chemistry |
There are two common methods for carbene generation.
In α elimination, two substituents eliminate from the same carbon atom. This occurs with reagents with no good leaving groups vicinal to an acidic proton are exposed to strong base; for example, phenyllithium will abstract HX from a haloform (CHX). Such reactions typically require phase-transfer conditions.
Molecules with no acidic proton can also form carbenes. A geminal dihalide exposed to organolithiums with undergo metal-halogen exchange and then eliminate a lithium salt to give a carbene, and zinc metal abstracts halogens similarly in the Simmons–Smith reaction.
:RCBr + BuLi → RCLi(Br) + BuBr
:RCLi(Br) → RC + LiBr
It remains uncertain if these conditions form truly free carbenes or a metal-carbene complex. Nevertheless, metallocarbenes so formed give the expected organic products. In a specialized but instructive case, α-halomercury compounds can be isolated and separately thermolyzed. The "Seyferth reagent" releases CCl upon heating:
:CHHgCCl → CCl + CHHgCl
Separately, carbenes can be produced from an extrusion reaction with a large free energy change. Diazirines and epoxides photolyze with a tremendous release in ring strain to carbenes. The former extrude inert nitrogen gas, but epoxides typically give reactive carbonyl wastes, and asymmetric epoxides can potentially form two different carbenes. Typically, the C-O bond with lesser fractional bond order (fewer double-bond resonance structures) breaks. For example, when one substituent is alkyl and another aryl, the aryl-substituted carbon is usually released as a carbene fragment.
Ring strain is not necessary for a strong thermodynamic driving force. Photolysis, heat, or transition metal catalysts (typically rhodium and copper) decompose diazoalkanes to a carbene and gaseous nitrogen; this occurs in the Bamford-Stevens reaction and Wolff rearrangement. As with the case of metallocarbenes, some reactions of diazoalkanes that formally proceed via carbenes may instead form a [[1,3-Dipolar cycloaddition|[3+2] cycloadduct]] intermediate that extrudes nitrogen. To generate an alkylidene carbene a ketone can be exposed to trimethylsilyl diazomethane and then a strong base. | 0 | Organic Chemistry |
A metal-ion buffer provides a controlled source of free metal ions in a manner similar to the regulation of hydrogen ion concentration by a pH buffer A metal-ion buffer solution contains the free (hydrated) metal ion along with a complex compound formed by the association of the ion with a ligand in excess. The concentration of free metal ion depends on the total concentration of each component (ligand and metal ion) as well as on the stability constant of the complex. If the ligand can undergo protonation, the concentration of the free metal ion depends also on solution pH.
A considerable improvement in the detection limit of a liquid-membrane ion-selective electrode has been achieved by using a metal-ion buffer as internal solution. | 7 | Physical Chemistry |
DNA as well as RNA are normally visualized by staining with ethidium bromide, which intercalates into the major grooves of the DNA and fluoresces under UV light. The intercalation depends on the concentration of DNA and thus, a band with high intensity will indicate a higher amount of DNA compared to a band of less intensity. The ethidium bromide may be added to the agarose solution before it gels, or the DNA gel may be stained later after electrophoresis. Destaining of the gel is not necessary but may produce better images. Other methods of staining are available; examples are MIDORI Green, SYBR Green, GelRed, methylene blue, brilliant cresyl blue, Nile blue sulphate, and crystal violet. SYBR Green, GelRed and other similar commercial products are sold as safer alternatives to ethidium bromide as it has been shown to be mutagenic in Ames test, although the carcinogenicity of ethidium bromide has not actually been established. SYBR Green requires the use of a blue-light transilluminator. DNA stained with crystal violet can be viewed under natural light without the use of a UV transilluminator which is an advantage, however it may not produce a strong band.
When stained with ethidium bromide, the gel is viewed with an ultraviolet (UV) transilluminator. The UV light excites the electrons within the aromatic ring of ethidium bromide, and once they return to the ground state, light is released, making the DNA and ethidium bromide complex fluoresce. Standard transilluminators use wavelengths of 302/312-nm (UV-B), however exposure of DNA to UV radiation for as little as 45 seconds can produce damage to DNA and affect subsequent procedures, for example reducing the efficiency of transformation, in vitro transcription, and PCR. Exposure of DNA to UV radiation therefore should be limited. Using a higher wavelength of 365 nm (UV-A range) causes less damage to the DNA but also produces much weaker fluorescence with ethidium bromide. Where multiple wavelengths can be selected in the transilluminator, shorter wavelength can be used to capture images, while longer wavelength should be used if it is necessary to work on the gel for any extended period of time.
The transilluminator apparatus may also contain image capture devices, such as a digital or polaroid camera, that allow an image of the gel to be taken or printed.
For gel electrophoresis of protein, the bands may be visualised with Coomassie or silver stains. | 1 | Biochemistry |
Recyclability is a key factor of a sustainable material. It reduces the need to mine new resources and requires less energy than mining. Copper and its alloys are virtually 100% recyclable and can be recycled infinitely without any loss of quality (i.e., copper does not degrade (i.e., downcycle) after each recycling loop as do most non-metallic materials, if they are recyclable at all). Copper retains much of its primary metal value: premium-grade scrap normally contains at least 95% of the value of primary metal from newly mined ore. Scrap values for competing materials range from about 60% down to 0%. And copper recycling requires only around 20% of the energy needed to extract and process primary metal.
Currently, around 40% of Europe's annual copper demand and about 55% of copper used in architecture come from recycled sources. New copper coil and sheet often have 75%-100% recycled content.
By 1985, more copper was recycled than the total amount of copper that was consumed in 1950. This is due to the relative ease of reusing processing waste and salvaging copper from products after their useful life. | 8 | Metallurgy |
In chemistry, stereospecificity is the property of a reaction mechanism that leads to different stereoisomeric reaction products from different stereoisomeric reactants, or which operates on only one (or a subset) of the stereoisomers.
In contrast, stereoselectivity is the property of a reactant mixture where a non-stereospecific mechanism allows for the formation of multiple products, but where one (or a subset) of the products is favored by factors, such as steric access, that are independent of the mechanism.
A stereospecific mechanism specifies the stereochemical outcome of a given reactant, whereas a stereoselective reaction selects products from those made available by the same, non-specific mechanism acting on a given reactant. Given a single, stereoisomerically pure starting material, a stereospecific mechanism will give 100% of a particular stereoisomer (or no reaction), although loss of stereochemical integrity can easily occur through competing mechanisms with different stereochemical outcomes. A stereoselective process will normally give multiple products even if only one mechanism is operating on an isomerically pure starting material.
The term stereospecific reaction is ambiguous, since the term reaction itself can mean a single-mechanism transformation (such as the Diels–Alder reaction), which could be stereospecific, or the outcome of a reactant mixture that may proceed through multiple competing mechanisms, specific and non-specific. In the latter sense, the term stereospecific reaction is commonly misused to mean highly stereoselective reaction.
Chiral synthesis is built on a combination of stereospecific transformations (for the interconversion of existing stereocenters) and stereoselective ones (for the creation of new stereocenters), where also the optical activity of a chemical compound is preserved.
The quality of stereospecificity is focused on the reactants and their stereochemistry; it is concerned with the products too, but only as they provide evidence of a difference in behavior between reactants. Of stereoisomeric reactants, each behaves in its own specific way. Stereospecificity towards enantiomers is called enantiospecificity. | 4 | Stereochemistry |
A useful alternative to the methods described here that avoids the site selectivity concerns of the SHJ reaction is tandem Michael reaction/cyclization to simultaneously form the heterocyclic base and establish its connection to the sugar moiety.
A second alternative is enzymatic transglycosylation, which is completely kinetically controlled (avoiding issues of chemical transglycosylation associated with thermodynamic control). However, operational complications associated with the use of enzymes are a disadvantage of this method. | 0 | Organic Chemistry |
The compressive strength and hardness of diamond and various other materials, such as boron nitride, (which has the closely related zincblende structure) is attributed to the diamond cubic structure.
Similarly, truss systems that follow the diamond cubic geometry have a high capacity to withstand compression, by minimizing the unbraced length of individual struts. The diamond cubic geometry has also been considered for the purpose of providing structural rigidity though structures composed of skeletal triangles, such as the octet truss, have been found to be more effective for this purpose. | 3 | Analytical Chemistry |
In nuclear physics these methods are used to study properties of the nucleus itself.
Methods for studies of the nucleus:
* Gamma spectroscopy
* Hypernuclear spectroscopy
Methods for condensed matter studies:
* Nuclear magnetic resonance (NMR)
* Mössbauer spectroscopy
* Perturbed angular correlation (PAC, TDPAC, PAC spectroscopy)
* Muon spin spectroscopy
* Nuclear orientation
* Channeling
* Nuclear reaction analysis
* Nuclear quadrupole resonance (NQR)
Methods for trace element analysis:
* Neutron activation analysis (NAA)
* Associated particle imaging (API) | 7 | Physical Chemistry |
Recently, LIBS has been investigated as a fast, micro-destructive food analysis tool. It is considered a potential analytical tool for qualitative and quantitative chemical analysis, making it suitable as a PAT (Process Analytical Technology) or portable tool. Milk, bakery products, tea, vegetable oils, water, cereals, flour, potatoes, palm date and different types of meat have been analyzed using LIBS. Few studies have shown its potential as an adulteration detection tool for certain foods. LIBS has also been evaluated as a promising elemental imaging technique in meat.
In 2019, researchers of the University of York and of the Liverpool John Moores University employed LIBS for studying 12 European oysters (Ostrea edulis, Linnaeus, 1758) from the Late Mesolithic shell midden at Conors Island (Republic of Ireland). The results highlighted the applicability of LIBS to determine prehistoric seasonality practices as well as biological age and growth at an improved rate and reduced cost than was previously achievable. | 7 | Physical Chemistry |
Ion-exchange chromatography (IEC) or ion chromatography (IC) is an analytical technique for the separation and determination of ionic solutes in aqueous samples from environmental and industrial origins such as metal industry, industrial waste water, in biological systems, pharmaceutical samples, food, etc. Retention is based on the attraction between solute ions and charged sites bound to the stationary phase. Solute ions charged the same as the ions on the column are repulsed and elute without retention, while solute ions charged oppositely to the charged sites of the column are retained on it. Solute ions that are retained on the column can be eluted from it by changing the mobile phase composition, such as increasing its salt concentration and pH or increasing the column temperature, etc.
Types of ion exchangers include polystyrene resins, cellulose and dextran ion exchangers (gels), and controlled-pore glass or porous silica gel. Polystyrene resins allow cross linkage, which increases the stability of the chain. Higher cross linkage reduces swerving, which increases the equilibration time and ultimately improves selectivity. Cellulose and dextran ion exchangers possess larger pore sizes and low charge densities making them suitable for protein separation.
In general, ion exchangers favor the binding of ions of higher charge and smaller radius.
An increase in counter ion (with respect to the functional groups in resins) concentration reduces the retention time, as it creates a strong competition with the solute ions. A decrease in pH reduces the retention time in cation exchange while an increase in pH reduces the retention time in anion exchange. By lowering the pH of the solvent in a cation exchange column, for instance, more hydrogen ions are available to compete for positions on the anionic stationary phase, thereby eluting weakly bound cations.
This form of chromatography is widely used in the following applications: water purification, preconcentration of trace components, ligand-exchange chromatography, ion-exchange chromatography of proteins, high-pH anion-exchange chromatography of carbohydrates and oligosaccharides, and others. | 3 | Analytical Chemistry |
TLRs are believed to function as dimers. Though most TLRs appear to function as homodimers, TLR2 forms heterodimers with TLR1 or TLR6, each dimer having a different ligand specificity. TLRs may also depend on other co-receptors for full ligand sensitivity, such as in the case of TLR4's recognition of LPS, which requires MD-2. CD14 and LPS-Binding Protein (LBP) are known to facilitate the presentation of LPS to MD-2.
A set of endosomal TLRs comprising TLR3, TLR7, TLR8 and TLR9 recognize nucleic acid derived from viruses as well as endogenous nucleic acids in context of pathogenic events. Activation of these receptor leads to production of inflammatory cytokines as well as type I interferons (interferon type I) to help fight viral infection.
The adapter proteins and kinases that mediate TLR signaling have also been targeted. In addition, random germline mutagenesis with ENU has been used to decipher the TLR signaling pathways. When activated, TLRs recruit adapter molecules within the cytoplasm of cells to propagate a signal. Four adapter molecules are known to be involved in signaling. These proteins are known as MyD88, TIRAP (also called Mal), TRIF, and TRAM (TRIF-related adaptor molecule).
TLR signaling is divided into two distinct signaling pathways, the MyD88-dependent and TRIF-dependent pathway. | 1 | Biochemistry |
Bacteriophage Φ29 DNA polymerase is a high-processivity enzyme that can produce DNA amplicons greater than 70 kilobase pairs. Its high fidelity and 3’–5 proofreading activity reduces the amplification error rate to 1 in 10−10 bases compared to conventional Taq polymerase with a reported error rate of 1 in 9,000. The reaction can be carried out at a moderate isothermal condition of 30 °C and therefore does not require a thermocycler. It has been actively used in cell-free cloning, which is the enzymatic method of amplifying DNA in vitro without cell culturing and DNA extraction. The large fragment of Bst' DNA polymerase is also used in MDA, but Ф29 is generally preferred due to its sufficient product yield and proofreading activity. | 1 | Biochemistry |
In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound.
In biochemistry, the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway, such as a protein precursor. | 1 | Biochemistry |
The ketone carbon is often described as sp hybridized, a description that includes both their electronic and molecular structure. Ketones are trigonal planar around the ketonic carbon, with C–C–O and C–C–C bond angles of approximately 120°. Ketones differ from aldehydes in that the carbonyl group (C=O) is bonded to two carbons within a carbon skeleton. In aldehydes, the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains. Ketones are also distinct from other carbonyl-containing functional groups, such as carboxylic acids, esters and amides.
The carbonyl group is polar because the electronegativity of the oxygen is greater than that for carbon. Thus, ketones are nucleophilic at oxygen and electrophilic at carbon. Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to themselves. Because of their inability to serve both as hydrogen-bond donors and acceptors, ketones tend not to "self-associate" and are more volatile than alcohols and carboxylic acids of comparable molecular weights. These factors relate to the pervasiveness of ketones in perfumery and as solvents. | 0 | Organic Chemistry |
Refer to the figure on the bottom right plotting the heat capacity as a function of temperature. In this context, T is the temperature corresponding to point A on the curve.
Different operational definitions of the glass transition temperature T are in use, and several of them are endorsed as accepted scientific standards. Nevertheless, all definitions are arbitrary, and all yield different numeric results: at best, values of T for a given substance agree within a few kelvins. One definition refers to the viscosity, fixing T at a value of 10 poise (or 10 Pa·s). As evidenced experimentally, this value is close to the annealing point of many glasses.
In contrast to viscosity, the thermal expansion, heat capacity, shear modulus, and many other properties of inorganic glasses show a relatively sudden change at the glass transition temperature. Any such step or kink can be used to define T. To make this definition reproducible, the cooling or heating rate must be specified.
The most frequently used definition of T uses the energy release on heating in differential scanning calorimetry (DSC, see figure). Typically, the sample is first cooled with 10 K/min and then heated with that same speed.
Yet another definition of T uses the kink in dilatometry (a.k.a. thermal expansion): refer to the figure on the top right. Here, heating rates of are common. The linear sections below and above T are colored green. T is the temperature at the intersection of the red regression lines.
Summarized below are T values characteristic of certain classes of materials. | 7 | Physical Chemistry |
Once in the cytoplasmic space of root cells Mg, along with the other cations, is probably transported radially into the stele and the vascular tissue. From the cells surrounding the xylem the ions are released or pumped into the xylem and carried up through the plant. In the case of Mg, which is highly mobile in both the xylem and phloem, the ions will be transported to the top of the plant and back down again in a continuous cycle of replenishment. Hence, uptake and release from vascular cells is probably a key part of whole plant Mg homeostasis. Figure 1 shows how few processes have been connected to their molecular mechanisms (only vacuolar uptake has been associated with a transport protein, AtMHX).
The diagram shows a schematic of a plant and the putative processes of Mg transport at the root and leaf where Mg is loaded and unloaded from the vascular tissues. Mg is taken up into the root cell wall space (1) and interacts with the negative charges associated with the cell walls and membranes. Mg may be taken up into cells immediately (symplastic pathway) or may travel as far as the Casparian band (4) before being absorbed into cells (apoplastic pathway; 2). The concentration of Mg in the root cells is probably buffered by storage in root cell vacuoles (3). Note that cells in the root tip do not contain vacuoles. Once in the root cell cytoplasm, Mg travels toward the centre of the root by plasmodesmata, where it is loaded into the xylem (5) for transport to the upper parts of the plant. When the Mg reaches the leaves it is unloaded from the xylem into cells (6) and again is buffered in vacuoles (7). Whether cycling of Mg into the phloem occurs via general cells in the leaf (8) or directly from xylem to phloem via transfer cells (9) is unknown. Mg may return to the roots in the phloem sap.
When a Mg ion has been absorbed by a cell requiring it for metabolic processes, it is generally assumed that the ion stays in that cell for as long as the cell is active. In vascular cells, this is not always the case; in times of plenty, Mg is stored in the vacuole, takes no part in the day-to-day metabolic processes of the cell (Stelzer et al., 1990), and is released at need. But for most cells it is death by senescence or injury that releases Mg and many of the other ionic constituents, recycling them into healthy parts of the plant. In addition, when Mg in the environment is limiting, some species are able to mobilise Mg from older tissues. These processes involve the release of Mg from its bound and stored states and its transport back into the vascular tissue, where it can be distributed to the rest of the plant. In times of growth and development, Mg is also remobilised within the plant as source and sink relationships change.
The homeostasis of Mg within single plant cells is maintained by processes occurring at the plasma membrane and at the vacuole membrane (see Figure 2). The major driving force for the translocation of ions in plant cells is ΔpH. H-ATPases pump H ions against their concentration gradient to maintain the pH differential that can be used for the transport of other ions and molecules. H ions are pumped out of the cytoplasm into the extracellular space or into the vacuole. The entry of Mg into cells may occur through one of two pathways, via channels using the ΔΨ (negative inside) across this membrane or by symport with H ions. To transport the Mg ion into the vacuole requires a Mg/H antiport transporter (such as AtMHX). The H-ATPases are dependent on Mg (bound to ATP) for activity, so that Mg is required to maintain its own homeostasis.
A schematic of a plant cell is shown including the four major compartments currently recognised as interacting with Mg. H-ATPases maintain a constant ΔpH across the plasma membrane and the vacuole membrane. Mg is transported into the vacuole using the energy of ΔpH (in A. thaliana by AtMHX). Transport of Mg into cells may use either the negative ΔΨ or the ΔpH. The transport of Mg into mitochondria probably uses ΔΨ as in the mitochondria of yeast, and it is likely that chloroplasts take Mg by a similar system. The mechanism and the molecular basis for the release of Mg from vacuoles and from the cell is not known. Likewise, the light-regulated Mg concentration changes in chloroplasts are not fully understood, but do require the transport of H ions across the thylakoid membrane. | 1 | Biochemistry |
Clay minerals can be classified as 1:1 or 2:1. A 1:1 clay would consist of one tetrahedral sheet and one octahedral sheet, and examples would be kaolinite and serpentinite. A 2:1 clay consists of an octahedral sheet sandwiched between two tetrahedral sheets, and examples are talc, vermiculite, and montmorillonite. The layers in 1:1 clays are uncharged and are bonded by hydrogen bonds between layers, but 2:1 layers have a net negative charge and may be bonded together either by individual cations (such as potassium in illite or sodium or calcium in smectites) or by positively charged octahedral sheets (as in chlorites).
Clay minerals include the following groups:
* Kaolin group which includes the minerals kaolinite, dickite, halloysite, and nacrite (polymorphs of ).
** Some sources include the kaolinite-serpentine group due to structural similarities.
* Smectite group which includes dioctahedral smectites, such as montmorillonite, nontronite and beidellite, and trioctahedral smectites, such as saponite. In 2013, analytical tests by the Curiosity rover found results consistent with the presence of smectite clay minerals on the planet Mars.
* Illite group which includes the clay-micas. Illite is the only common mineral in this group.
* Chlorite group includes a wide variety of similar minerals with considerable chemical variation.
* Other 2:1 clay types exist such as palygorskite (also known as attapulgite) and sepiolite, clays with long water channels internal to their structure.
Mixed layer clay variations exist for most of the above groups. Ordering is described as a random or regular order and is further described by the term reichweite, which is German for range or reach. Literature articles will refer to an R1 ordered illite-smectite, for example. This type would be ordered in an illite-smectite-illite-smectite (ISIS) fashion. R0 on the other hand describes random ordering, and other advanced ordering types are also found (R3, etc.). Mixed layer clay minerals which are perfect R1 types often get their own names. R1 ordered chlorite-smectite is known as corrensite, R1 illite-smectite is rectorite.
X-ray rf(001) is the spacing between layers in nanometers, as determined by X-ray crystallography. Glycol (mg/g) is the adsorption capacity for glycol, which occupies the interlayer sites when the clay is exposed to a vapor of ethylene glycol at for eight hours. CEC is the cation exchange capacity of the clay. (%) is the percent content of potassium oxide in the clay. DTA describes the differential thermal analysis curve of the clay. | 9 | Geochemistry |
Molecular medicine is a broad field, where physical, chemical, biological, bioinformatics and medical techniques are used to describe molecular structures and mechanisms, identify fundamental molecular and genetic errors of disease, and to develop molecular interventions to correct them. The molecular medicine perspective emphasizes cellular and molecular phenomena and interventions rather than the previous conceptual and observational focus on patients and their organs. | 1 | Biochemistry |
Huntington's disease (HD) results from a mutation in the huntingtin gene that causes an excess of CAG repeats. The gene then forms a mutated huntingtin protein with polyglutamine repeats near the amino terminus. This disease is incurable and known to cause motor, cognitive, and behavioral deficits. Researchers have been looking to gene silencing as a potential therapeutic for HD.
Gene silencing can be used to treat HD by targeting the mutant huntingtin protein. The mutant huntingtin protein has been targeted through gene silencing that is allele specific using allele specific oligonucleotides. In this method, the antisense oligonucleotides are used to target single nucleotide polymorphism (SNPs), which are single nucleotide changes in the DNA sequence, since HD patients have been found to share common SNPs that are associated with the mutated huntingtin allele. It has been found that approximately 85% of patients with HD can be covered when three SNPs are targeted. In addition, when antisense oligonucleotides were used to target an HD-associated SNP in mice, there was a 50% decrease in the mutant huntingtin protein.
Non-allele specific gene silencing using siRNA molecules has also been used to silence the mutant huntingtin proteins. Through this approach, instead of targeting SNPs on the mutated protein, all of the normal and mutated huntingtin proteins are targeted. When studied in mice, it was found that siRNA could reduce the normal and mutant huntingtin levels by 75%. At this level, they found that the mice developed improved motor control and a longer survival rate when compared to the controls. Thus, gene silencing methods may prove to be beneficial in treating HD. | 1 | Biochemistry |
Zinc is the second most abundant transition metal present in living organisms second only to iron. It is critical for the growth and survival of cells. In humans, zinc is primarily found in various organs and tissues such as the brain, intestines, pancreas and mammary glands. In prokaryotes, zinc can function as an antimicrobial, zinc oxide nano-particles can function as an antibacterial or antibiotic. Zinc homeostasis is highly controlled to allow for its benefits without risk of death via its high toxicity. Because of zinc's antibiotic nature, it is often used in many drugs against bacterial infections in humans. Inversely, due to the bacterial nature of mitochondria, zinc antibiotics are also lethal to mitochondria and results in cell death at high concentrations. Zinc is also used in a number of transcription factors, proteins and enzymes. | 1 | Biochemistry |
MDA generates sufficient yield of DNA products. It is a powerful tool of amplifying DNA molecules from samples, such as uncultured microorganism or single cells to the amount that would be sufficient for sequencing studies. The large size of MDA-amplified DNA products also provides desirable sample quality for identifying the size of polymorphic repeat alleles. Its high fidelity also makes it reliable to be used in the single-nucleotide polymorphism (SNP) allele detection. Due to its strand displacement during amplification, the amplified DNA has sufficient coverage of the source DNA molecules, which provides a high-quality product for genomic analysis. The products of displaced strands can be subsequently cloned into vectors to construct library for subsequent sequencing reactions. | 1 | Biochemistry |
* 1945–1946 – Nikolay Bogoliubov develops a general method for a microscopic derivation of kinetic equations for classical statistical systems using BBGKY hierarchy
* 1947 – Nikolay Bogoliubov and Kirill Gurov extend this method for a microscopic derivation of kinetic equations for quantum statistical systems
* 1948 – Claude Elwood Shannon establishes information theory
* 1957 – Aleksandr Solomonovich Kompaneets derives his Compton scattering Fokker–Planck equation
* 1957 – Ryogo Kubo derives the first of the Green-Kubo relations for linear transport coefficients
* 1957 – Edwin T. Jaynes publishes two papers detailing the MaxEnt interpretation of thermodynamics from information theory
* 1960–1965 – Dmitry Zubarev develops the method of non-equilibrium statistical operator, which becomes a classical tool in the statistical theory of non-equilibrium processes
* 1972 – Jacob Bekenstein suggests that black holes have an entropy proportional to their surface area
* 1974 – Stephen Hawking predicts that black holes will radiate particles with a black-body spectrum which can cause black hole evaporation
*1977 – Ilya Prigogine wins the Nobel prize for his work on dissipative structures in thermodynamic systems far from equilibrium. The importation and dissipation of energy could reverse the 2nd law of thermodynamics | 7 | Physical Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.