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In the first step of the mechanism, the glycosyl bromide reacts with silver carbonate upon elimination of silver bromide and the silver carbonate anion to the oxocarbenium ion. From this structure a dioxolanium ring is formed, which is attacked by methanol via an mechanism at the carbonyl carbon atom. This attack leads to the inversion. After deprotonation of the intermediate oxonium, the product glycoside is formed.
The reaction can also be applied to carbohydrates with other protecting groups. In the oligosaccharide synthesis in place of the methanol other carbohydrates are used, which have been modified with protective groups in such a way that only one hydroxyl group is accessible. | 0 | Organic Chemistry |
* International Symposium on the Origin of Life on the Earth (held at Moscow, 19–24 August 1957)
* Proceedings of the SPIE held at San Jose, California, 22–24 January 2001
* Proceedings of the SPIE held at San Diego, California, 31 July–2 August 2005 | 9 | Geochemistry |
This modification involves the addition of a methyl group to the 2 hydroxyl (-OH) group of the ribose sugar of RNA molecules. In contrast with the mA modification, it is the ribose sugar, a part of the backbone rather than the base that is altered. It is present in various kinds of cellular RNA, providing coding and structural support. 2-O-methylation of viral RNA is often accompanied by the addition of an inverted N-7methylguanosine to the 5 end on the phosphate group. These modifications regulate important functions of viral RNA such as metabolism and immune system interactions.
Different viruses have their mechanisms for acquiring this modification. Cytoplasmic RNA viruses like flaviridae and coronaviruses encode the required to catalyze cap formation reactions, with some needing one enzyme for the 5' cap and 2-O-methylation while others require two enzymes like poxviruses. Others, like influenza virus can hijack the methylguanosine caps from host cell mRNA and be preferentially translated. | 1 | Biochemistry |
The main function of chemokines is to manage the migration of leukocytes (homing) in the respective anatomical locations in inflammatory and homeostatic processes.
Basal: homeostatic chemokines are basal produced in the thymus and lymphoid tissues. Their homeostatic function in homing is best exemplified by the chemokines CCL19 and CCL21 (expressed within lymph nodes and on lymphatic endothelial cells) and their receptor CCR7 (expressed on cells destined for homing in cells to these organs). Using these ligands is possible routing antigen-presenting cells (APC) to lymph nodes during the adaptive immune response. Among other homeostatic chemokine receptors include: CCR9, CCR10, and CXCR5, which are important as part of the cell addresses for tissue-specific homing of leukocytes. CCR9 supports the migration of leukocytes into the intestine, CCR10 to the skin and CXCR5 supports the migration of B-cell to follicles of lymph nodes. As well CXCL12 (SDF-1) constitutively produced in the bone marrow promotes proliferation of progenitor B cells in the bone marrow microenvironment.
Inflammatory: inflammatory chemokines are produced in high concentrations during infection or injury and determine the migration of inflammatory leukocytes into the damaged area. Typical inflammatory chemokines include: CCL2, CCL3 and CCL5, CXCL1, CXCL2 and CXCL8. A typical example is CXCL-8, which acts as a chemoattractant for neutrophils. In contrast to the homeostatic chemokine receptors, there is significant promiscuity (redundancy) associated with binding receptor and inflammatory chemokines. This often complicates research on receptor-specific therapeutics in this area. | 1 | Biochemistry |
Initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data-flow management software. However, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. In doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. Instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces—remnants of criminal activity. Embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners' mindset to accept concepts and methodologies in forensic intelligence.
Recent calls advocating for the integration of forensic scientists into the criminal justice system, as well as policing and intelligence missions, underscore the necessity for the establishment of educational and training initiatives in the field of forensic intelligence. This article contends that a discernible gap exists between the perceived and actual comprehension of forensic intelligence among law enforcement and forensic science managers, positing that this asymmetry can be rectified only through educational interventions
The primary challenge in forensic intelligence education and training is identified as the formulation of programs aimed at heightening awareness, particularly among managers, to mitigate the risk of making suboptimal decisions in information processing. The paper highlights two recent European courses as exemplars of educational endeavors, elucidating lessons learned and proposing future directions at an initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data-flow management software.
However, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. In doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. Instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces—remnants of criminal activity. Embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners' mindset to accept concepts and methodologies in forensic intelligence.
The overarching conclusion is that the heightened focus on forensic intelligence has the potential to rejuvenate a proactive approach to forensic science, enhance quantifiable efficiency, and foster greater involvement in investigative and managerial decision-making. A novel educational challenge is articulated for forensic science university programs worldwide: a shift in emphasis from a fragmented criminal trace analysis to a more comprehensive security problem-solving approach. | 3 | Analytical Chemistry |
In a crystal, a superstructure manifests itself through additional reflections in diffraction patterns, e.g., in low energy electron diffraction (LEED) or X-ray diffraction experiments. Often a set of weak diffraction spots appears between the stronger spots belonging to what is referred to as the substructure. In some cases a phase transition occurs, e.g., at higher temperatures, where the superstructure disappears and the material reverts to the simpler substructure. Not all compounds exhibit a superstructure.
The superspots in diffraction patterns represent a modulation of the substructure that causes the inherent translation symmetry of the (substructure) lattice to be violated slightly or the size of the repeat motif of the structure to be increased. One could speak of symmetry breaking of the translation symmetry of the lattice, although rotational symmetry may be lost simultaneously. | 3 | Analytical Chemistry |
In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula . It can be viewed as a methylene radical (:) with an added proton (), or as a methyl radical (•) with one electron removed. It is a carbocation and an enium ion, making it the simplest of the carbenium ions. | 7 | Physical Chemistry |
Matrix isolation has its origins in the first half of the 20th century with the experiments by photo-chemists and physicists freezing samples in liquefied gases. The earliest isolation experiments involved the freezing of species in transparent, low temperature organic glasses, such as EPA (ether/isopentane/ethanol 5:5:2). The modern matrix isolation technique was developed extensively during the 1950s, in particular by George C. Pimentel. He initially used higher-boiling inert gases like xenon and nitrogen as the host material, and is often said to be the "father of matrix isolation".
Laser vaporization in matrix isolation spectroscopy was first brought about in 1969 by Schaeffer and Pearson using a yttrium aluminum garnet (YAG) laser to vaporize carbon which reacted with hydrogen to produce acetylene. They also showed that laser-vaporized boron would react with HCl to create BCl. In the 1970s, Koerner von Gustorfs lab used the technique to produce free metal atoms which were then deposited with organic substrates for use in organometallic chemistry. Spectroscopic studies were done on reactive intermediates in around the early 1980s by Bell Labs. They used laser-induced fluorescence to characterize multiple molecules like SnBi and SiC. Smalleys group employed the use of this method with time-of-flight mass spectrometry by analyzing Al clusters. With the work of chemists like these, laser-vaporization in matrix isolation spectroscopy rose in popularity due to its ability to generate transients involving metals, alloys and semi-conductor molecules and clusters. | 7 | Physical Chemistry |
Oil reservoirs are routinely mapped by injecting a PFT down one bore hole and measuring the concentration at adjacent boreholes. In this way, geologists can build up an image of the reservoir.
Traditional underground high-tension cables are constructed either with internal oil ducts or channels or by the use of a pipe through which the insulated conductor is installed. In either design the system is then filled with pressurised, de-gassed oil. The oils primary function is to improve the insulating properties of the cable but occasionally leaks can occur through cable joints, oil system fittings or cable sheath damage. The leak is initially identified by the loss of liquid from the system, but its location used to involve engineers digging up the road, freezing a section of cable and seeing if the level was still going down, then choosing a new point to dig and re-freeze. It could take several holes to isolate the leak. If a PFT is injected into the oil, there will be a relatively high concentration of PFT above the leak, which can be pin-pointed to within a few feet, requiring only a single hole to be dug right where the leak is.
PFTs have been used to follow air movement, for tracing the flow of pollutants, for example, the Big Bend Regional Aerosol and Visibility Observational study. measuring the effectiveness of ventilation and studying the possible effects of terrorist attacks (for example in New York ).
PFTs have even been used to track ransom money after a kidnapping. | 2 | Environmental Chemistry |
Kullback gives the following example (Table 2.1, Example 2.1). Let and be the distributions shown in the table and figure. is the distribution on the left side of the figure, a binomial distribution with and . is the distribution on the right side of the figure, a discrete uniform distribution with the three possible outcomes , , (i.e. ), each with probability .
Relative entropies and are calculated as follows. This example uses the natural log with base E (mathematical constant)|, designated to get results in nats (see units of information): | 7 | Physical Chemistry |
Flavin adenine dinucleotide is a group bound to many enzymes including ferredoxin-NADP+ reductase, monoamine oxidase, D-amino acid oxidase, glucose oxidase, xanthine oxidase, and acyl CoA dehydrogenase. | 1 | Biochemistry |
The great majority of contemporary spectrometers use a mixture of commercially available and bespoke components which users integrate according to their particular needs. Instruments can be broadly categorised according to their general operating principles. Although rotational transitions can be found across a very broad region of the electromagnetic spectrum, fundamental physical constraints exist on the operational bandwidth of instrument components. It is often impractical and costly to switch to measurements within an entirely different frequency region. The instruments and operating principals described below are generally appropriate to microwave spectroscopy experiments conducted at frequencies between 6 and 24 GHz. | 7 | Physical Chemistry |
Lisa Michelle Jones (born February 1977) is an associate professor of pharmaceutical sciences at the University of Maryland, Baltimore (UMB). Her research is in structural proteomics, using mass spectrometry together with fast photochemical oxidation of proteins (FPOP), allowing researchers to study the solvent accessibility of proteins experimentally. | 1 | Biochemistry |
Carbon-carbon bond activation reactions have numerous applications in organic synthesis, materials science, and pharmaceuticals. In organic synthesis, these reactions are used to construct complex molecules in a highly efficient and selective manner. For example, in 2021 Dong Group described the first enantioselective total synthesis of the natural product penicibilaenes using a late-stage carbon-carbon bond activation strategy. There are also a lot of other examples highlighting the potential of carbon-carbon bond activation strategies in the total synthesis of complex natural products with high stereocontrol. | 0 | Organic Chemistry |
It can be used in practical applications such as malting, to represent the grain–air–moisture system.
The underlying property data for the Mollier diagram is identical to a psychrometric chart. At first inspection, there may appear little resemblance between the charts, but if the user rotates a chart ninety degrees and looks at it in a mirror, the resemblance is apparent. The Mollier diagram coordinates are enthalpy h and humidity ratio x. The enthalpy coordinate is skewed and the constant enthalpy lines are parallel and evenly spaced. | 7 | Physical Chemistry |
Plants for the production of pre-reduced iron ore are known as direct reduction plants. The principle involves exposing iron ore to the reducing action of a high-temperature gas (around 1000 °C). This gas is composed of carbon monoxide and dihydrogen, the proportions of which depend on the production process.
Generally speaking, there are two main types of processes:
* processes where the reducing gas is obtained from natural gas. In this case, the ore is reduced in tanks;
* processes where the reducing gas is obtained from coal. The reactor is generally an inclined rotary kiln, similar to those used in cement plants, in which coal is mixed with limestone and ore, then heated.
Another way of classifying processes is to distinguish between those where the reducing gases are produced in specific facilities separate from the reduction reactor - which characterizes most processes using natural gas - and those where the gases are produced inside the fusion reactor: coal-fired processes generally fall into this category. However, many "gas-fired" processes can be fed by gasification units producing a reducing gas from coal.
In addition, since the melting stage is necessary to obtain alloys, reduction-melting processes have been developed which, like blast furnaces, produce a more or less carburized liquid metal. Finally, many more or less experimental processes have been developed. | 8 | Metallurgy |
An autoreceptor is a type of receptor located in the membranes of nerve cells. It serves as part of a negative feedback loop in signal transduction. It is only sensitive to the neurotransmitters or hormones released by the neuron on which the autoreceptor sits. Similarly, a heteroreceptor is sensitive to neurotransmitters and hormones that are not released by the cell on which it sits. A given receptor can act as either an autoreceptor or a heteroreceptor, depending upon the type of transmitter released by the cell on which it is embedded.
Autoreceptors may be located in any part of the cell membrane: in the dendrites, the cell body, the axon, or the axon terminals.
Canonically, a presynaptic neuron releases a neurotransmitter across a synaptic cleft to be detected by the receptors on a postsynaptic neuron. Autoreceptors on the presynaptic neuron will also detect this neurotransmitter and often function to control internal cell processes, typically inhibiting further release or synthesis of the neurotransmitter. Thus, release of neurotransmitter is regulated by negative feedback. Autoreceptors are usually G protein-coupled receptors (rather than transmitter-gated ion channels) and act via a second messenger. | 1 | Biochemistry |
PHBV is synthesized by bacteria as storage compounds under growth limiting conditions. It can be produced from glucose and propionate by the recombinant Escherichia coli strains. Many other bacteria like Paracoccus denitrificans and Ralstonia eutropha are also capable of producing it.
It can also be synthesized from genetically engineered plants.
PHBV is a copolymer of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHBV may also be synthesized from butyrolactone and valerolactone in the presence of oligomeric aluminoxane as catalyst. | 1 | Biochemistry |
In organic chemistry, isothiocyanate is a functional group as found in compounds with the formula . Isothiocyanates are the more common isomers of thiocyanates, which have the formula . | 0 | Organic Chemistry |
Quantum crystallography is a branch of crystallography that investigates crystalline materials within the framework of quantum mechanics, with analysis and representation, in position or in momentum space, of quantities like wave function, electron charge and spin density, density matrices and all properties related to them (like electric potential, electric or magnetic moments, energy densities, electron localization function, one electron potential, etc.).
Like the quantum chemistry, Quantum crystallography involves both experimental and computational work. The theoretical part of quantum crystallography is based on quantum mechanical calculations of atomic/molecular/crystal wave functions, density matrices or density models, used to simulate the electronic structure of a crystalline material. While in quantum chemistry, the experimental works mainly rely on spectroscopy, in quantum crystallography the scattering techniques (X-rays, neutrons, γ-Rays, electrons) play the central role, although spectroscopy as well as atomic microscopy are also sources of information.
The connection between crystallography and quantum chemistry has always been very tight, after X-ray diffraction techniques became available in crystallography. In fact, the scattering of radiation enables mapping the one-electron distribution or the elements of a density matrix.
The kind of radiation and scattering determines the quantity which is represented (electron charge or spin) and the space in which it is represented (position or momentum space).
Although the wave function is typically assumed not to be directly measurable, recent advances enable also to compute wave functions that are restrained to some experimentally measurable observable (like the scattering of a radiation).
The term Quantum Crystallography was first introduced in revisitation articles by L. Huang, L. Massa and Nobel Prize winner Jerome Karle, who associated it with two mainstreams: a) crystallographic information that enhances quantum mechanical calculations and b) quantum mechanical approaches to improve crystallography information. This definition mainly refers to studies started in the 1960s and 1970s, when first attempts to obtain wave functions from scattering experiments appeared, together with other methods to constrain a wavefunction to experimental observations like the dipole moment. This field has been recently reviewed, within the context of this definition.
Parallel to studies on wave function determination, R. F. Stewart and P. Coppens investigated the possibilities to compute models for one-electron charge density from X-ray scattering (for example by means of pseudoatoms multipolar expansion), and later of spin density from polarized neutron diffraction, that originated the scientific community of charge, spin and momentum density.
In a recent review article, V. Tsirelson gave a more general definition: "Quantum crystallography is a research area exploiting the fact that parameters of quantum-mechanically valid electronic model of a crystal can be derived from the accurately measured set of X-ray coherent diffraction structure factors".
The book Modern Charge Density Analysis offers a survey of the research involving Quantum Crystallography and of the most adopted experimental or theoretical methodologies.
The International Union of Crystallography has recently established a commission on Quantum Crystallography, as extension of the previous commission on Charge, Spin and Momentum density, with the purpose of coordinating research activities in this field. | 3 | Analytical Chemistry |
There are two main types of anaerobic photosynthetic electron transport chains in bacteria. The type I reaction centers are found in GSB, Chloracidobacterium, and Heliobacteria, while the type II reaction centers are found in FAPs and purple bacteria. | 5 | Photochemistry |
*Spectra cannot be acquired quickly due to the monochromatic laser source which is used. Having said this, some groups are now beginning to develop the use of broadband LED or supercontinuum sources for CRDS, the light of which can then be dispersed by a grating onto a CCD, or Fourier transformed spectrometer (mainly in broadband analogues of CRDS). Perhaps more importantly, the development of CRDS based techniques have now been demonstrated over the range from the near UV to the mid-infrared. In addition, the frequency-agile rapid scanning (FARS) CRDS technique has been developed to overcome the mechanical or thermal frequency tuning which typically limits CRDS acquisition rates. The FARS method utilizes an electro-optic modulator to step a probe laser side band to successive cavity modes, eliminating tuning time between data points and allowing for acquisition rates about 2 orders of magnitude faster than traditional thermal tuning.
*Analytes are limited both by the availability of tunable laser light at the appropriate wavelength and also the availability of high reflectance mirrors at those wavelengths.
*Expense: the requirement for laser systems and high reflectivity mirrors often makes CRDS orders of magnitude more expensive than some alternative spectroscopic techniques. | 7 | Physical Chemistry |
In organic chemistry, organocatalysis is a form of catalysis in which the rate of a chemical reaction is increased by an organic catalyst. This "organocatalyst" consists of carbon, hydrogen, sulfur and other nonmetal elements found in organic compounds. Because of their similarity in composition and description, they are often mistaken as a misnomer for enzymes due to their comparable effects on reaction rates and forms of catalysis involved.
Organocatalysts which display secondary amine functionality can be described as performing either enamine catalysis (by forming catalytic quantities of an active enamine nucleophile) or iminium catalysis (by forming catalytic quantities of an activated iminium electrophile). This mechanism is typical for covalent organocatalysis. Covalent binding of substrate normally requires high catalyst loading (for proline-catalysis typically 20–30 mol%).
Noncovalent interactions such as hydrogen-bonding facilitates low catalyst loadings (down to 0.001 mol%).
Organocatalysis offers several advantages. There is no need for metal-based catalysis thus making a contribution to green chemistry. In this context, simple organic acids have been used as catalyst for the modification of cellulose in water on multi-ton scale. When the organocatalyst is chiral an avenue is opened to asymmetric catalysis; for example, the use of proline in aldol reactions is an example of chirality and green chemistry. Organic chemists David MacMillan and Benjamin List were both awarded the 2021 Nobel Prize in chemistry for their work on asymmetric organocatalysis. | 0 | Organic Chemistry |
The mathematical resolution to Loschmidt's paradox is called the (steady state) fluctuation theorem (FT), which is a generalisation of the second law of thermodynamics. The FT shows that as a system gets larger or the trajectory duration becomes longer, entropy-consuming trajectories become more unlikely, and the expected second law behaviour is recovered.
The FT was first put forward by and much of the work done in developing and extending the theorem was accomplished by theoreticians and mathematicians interested in nonequilibrium statistical mechanics.
The first observation and experimental proof of Evan's fluctuation theorem (FT) was performed by | 7 | Physical Chemistry |
The natural time scale of electron motion in atoms, molecules, and solids is the attosecond (1 as= 10 s). This fact is a direct consequence of quantum mechanics.
Indeed, for simplicity, consider a quantum particle in superposition between ground-level, of energy , and the first excited level, of energy :
with and chosen as the square roots of the quantum probability of observing the particle in the corresponding state.
are the time-dependent ground and excited state respectively, with the reduced Planck constant.
The expectation value of a generic hermitian and symmetric operator, , can be written as , as a consequence the time evolution of this observable is:
While the first two terms do not depend on time, the third, instead, does. This creates a dynamic for the observable with a characteristic time, , given by .
As a consequence, for energy levels in the range of 10 eV, which is the typical electronic energy range in matter, the characteristic time of the dynamics of any associated physical observable is approximately 400 as.
To measure the time evolution of , one needs to use a controlled tool, or a process, with an even shorter time-duration that can interact with that dynamic.
This is the reason why attosecond light pulses are used to disclose the physics of ultra-fast phenomena in the few-femtosecond and attosecond time-domain. | 7 | Physical Chemistry |
Mass-difference impurity scattering is given by:
where is a measure of the impurity scattering strength. Note that is dependent of the dispersion curves. | 7 | Physical Chemistry |
A key characteristic of amorphous brazing foils (ABFs) is their relatively low melting points, which typically range from 830 to 1200°C. This attribute is crucial for their application as filler metals in brazing. Due to their ductility and flexibility, ABFs present a viable alternative to filler metals in paste or powder form. This substitution offers notable advantages, such as the elimination of soot formation, a common drawback associated with residual organic solvents in paste-based fillers. Additionally, ABFs help minimize the formation of surface oxides, an issue frequently encountered with gas-atomized powder fillers, thereby enhancing the quality and integrity of the brazed joint. | 8 | Metallurgy |
Hemoglobin binds with carbon monoxide 210 times more readily than with oxygen. Because of this higher affinity of hemoglobin for carbon monoxide than for oxygen, carbon monoxide is a highly successful competitor that will displace oxygen even at minuscule partial pressures. The reaction HbO + CO → HbCO + O almost irreversibly displaces the oxygen molecules forming carboxyhemoglobin; the binding of the carbon monoxide to the iron centre of hemoglobin is much stronger than that of oxygen, and the binding site remains blocked for the remainder of the life cycle of that affected red blood cell. With an increased level of carbon monoxide, a person can suffer from severe tissue hypoxia while maintaining a normal pO because carboxyhemoglobin does not carry oxygen to the tissues. | 1 | Biochemistry |
Past studies suggest that repeats are a common feature of eukaryotes unlike the prokaryotes and archaea. Other reports suggest that irrespective of the comparative shortage of repeat elements in prokaryotic genomes, they nevertheless contain hundreds or even thousands of large repeats. Current genomic analysis seem to suggest the existence of a large excess of perfect inverted repeats in many prokaryotic genomes as compared to eukaryotic genomes.
For quantification and comparison of inverted repeats between several species, namely on archaea, see | 1 | Biochemistry |
Like most other community analysis methods, TRFLP is also based on PCR amplification of a target gene. In the case of TRFLP, the amplification is performed with one or both the primers having their 5’ end labeled with a fluorescent molecule. In case both primers are labeled, different fluorescent dyes are required. While several common fluorescent dyes can be used for the purpose of tagging such as 6-carboxyfluorescein (6-FAM), ROX, carboxytetramethylrhodamine (TAMRA, a rhodamine-based dye), and [https://en.wiktionary.org/wiki/hexachlorofluorescein hexachlorofluorescein] (HEX), the most widely used dye is 6-FAM. The mixture of amplicons is then subjected to a restriction reaction, normally using a four-cutter restriction enzyme. Following the restriction reaction, the mixture of fragments is separated using either capillary or polyacrylamide electrophoresis in a DNA sequencer and the sizes of the different terminal fragments are determined by the fluorescence detector. Because the excised mixture of amplicons is analyzed in a sequencer, only the terminal fragments (i.e. the labeled end or ends of the amplicon) are read while all other fragments are ignored. Thus, T-RFLP is different from ARDRA and RFLP in which all restriction fragments are visualized. In addition to these steps the TRFLP protocol often includes a cleanup of the PCR products prior to the restriction and in case a capillary electrophoresis is used a desalting stage is also performed prior to running the sample. | 1 | Biochemistry |
Early experiments measured the force between mica surfaces in air or vacuum. The technique has been extended, however, to enable an arbitrary vapor or solvent to be introduced between the two surfaces. In this way, interactions in various media can be carefully probed, and the dielectric constant of the gap between the surfaces can be tuned. Moreover, use of water as a solvent enables the measurement of interactions between biological molecules (such as lipids in biological membranes or proteins) in their native environment. In a solvent environment, SFA can even measure the oscillatory solvation and structural forces arising from the packing of individual layers of solvent molecules. It can also measure the electrostatic double layer forces between charged surfaces in an aqueous medium with electrolyte. | 6 | Supramolecular Chemistry |
Han Zuilhof (born 1965) holds the chair of organic chemistry at Wageningen University. His interests focus on surface-bound (bio-)organic chemistry and bionanotechnology. He obtained an MSc in chemistry and MA in philosophy from Leiden University (both highest honors). After a PhD in organic chemistry (Leiden University, 1994; highest honors), and postdoctoral work at the University of Rochester, NY, and Columbia University, he joined the faculty at Wageningen University. He has been a professor of organic chemistry since 2007. He has written over 340 research papers, and more than 10 patents. He is a distinguished adjunct professor of chemical engineering at the King Abdulaziz University in Jeddah, Saudi Arabia, and a perennial distinguished guest professor of molecular science and medicinal chemistry at the school of pharmaceutical science and technology (SPST) at Tianjin University, China.
He serves/served on the editorial advisory boards of Langmuir, [http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%292196-7350 Advanced Materials Interfaces] and Applied Surface Science and was a senior editor of Langmuir from 2016 to 2020. In 2018, Han Zuilhof was elected as a "Fellow of the Royal Society of Chemistry (RSC) for his outstanding contributions to chemical science, and in 2021 was awarded the Robert Robinson Award in Synthetic Organic Chemistry by the RSC for contributions to click chemistry. He is also the founder (2011) of a spin-off company, Surfix.
Among his recent accomplishments are the discovery of tiara[5]arenes, the first intrinsically chiral click reaction (no chiral auxiliary or catalyst needed), and the synthesis and structure elucidation of SOF4-based SuFEx-derived polymers. | 0 | Organic Chemistry |
Dai was born in Taiwan. He completed a BSc in chemistry at National Taiwan University in 1974, following military service, and went to the United States in 1976 for graduate studies. He obtained his doctorate in chemistry from the University of California at Berkeley in 1981, and then did postdoctoral research at the Massachusetts Institute of Technology until 1984. That year he began teaching in the chemistry department of the University of Pennsylvania in Philadelphia, where he remained for twenty-two years and became department chair and the Hirschmann-Makineni Professor. He founded the Penn Science Teacher Institute that eventually trained 300 in-service science teachers and was named as a model for training science teachers in a 2005 National Academy of Sciences white paper. In 2007 he became Dean of the College of Science and Technology of Temple University, also in Philadelphia, Pennsylvania, and was Provost of Temple University during 2012 - 2016. During his time as provost, Temple's USNWR ranking went from #135 to #115 and Temple became a Carnegie R1 Highest Research Activity University. In 2017, Dai was appointed vice president for International Affairs at Temple University. | 7 | Physical Chemistry |
ELPs can be synthetically conjugated to poly (ethylene glycol) by adding a cyclooctyne functional motif to the poly (ethylene glycol) and an azide group to the ELP. Through a cycloaddition reaction involving both of the functional groups and manipulation of the solvent pH, diblock and star polymers can be formed. Rather than forming the canonical spherical clumps above the transition temperature, this specific conjugated ELP forms a micelle with amphiphillic properties, in which the polar head groups face outward and the hydrophobic domains face inward. Such micelles may be helpful in delivering nonpolar drugs to the body. | 7 | Physical Chemistry |
Methoxy arachidonyl fluorophosphonate, commonly referred as MAFP, is an irreversible active site-directed enzyme inhibitor that inhibits nearly all serine hydrolases and serine proteases. It inhibits phospholipase A2 and fatty acid amide hydrolase with special potency, displaying IC values in the low-nanomolar range. In addition, it binds to the CB receptor in rat brain membrane preparations (IC = 20 nM), but does not appear to agonize or antagonize the receptor, though some related derivatives do show cannabinoid-like properties. | 1 | Biochemistry |
Canuel has a B.S. in Chemistry from Stonehill College (1981) and earned her Ph.D.in Marine Science (1992) from the University of North Carolina at Chapel Hill. Following her Ph.D. she was a postdoctoral researcher at the United States Geological Survey until 1994 when she joined the faculty at the College of William & Mary. She was promoted to professor in 2006, and named Chancellor Professor in 2018.
From 2018 until 2020 Canuel was a program officer at the National Science Foundation, and she returned there in 2021. | 9 | Geochemistry |
The cellular level of β-catenin is mostly controlled by its ubiquitination and proteosomal degradation. The E3 ubiquitin ligase TrCP1 (also known as β-TrCP) can recognize β-catenin as its substrate through a short linear motif on the disordered N-terminus. However, this motif (Asp-Ser-Gly-Ile-His-Ser) of β-catenin needs to be phosphorylated on the two serines in order to be capable to bind β-TrCP. Phosphorylation of the motif is performed by Glycogen Synthase Kinase 3 alpha and beta (GSK3α and GSK3β). GSK3s are constitutively active enzymes implicated in several important regulatory processes. There is one requirement, though: substrates of GSK3 need to be pre-phosphorylated four amino acids downstream (C-terminally) of the actual target site. Thus it also requires a "priming kinase" for its activities. In the case of β-catenin, the most important priming kinase is Casein Kinase I (CKI). Once a serine-threonine rich substrate has been "primed", GSK3 can "walk" across it from C-terminal to N-terminal direction, phosphorylating every 4th serine or threonine residues in a row. This process will result in dual phosphorylation of the aforementioned β-TrCP recognition motif as well. | 1 | Biochemistry |
Intermolecular forces such as Van der Waals forces, hydrogen bonds, and dipole–dipole interactions are typically not sufficiently strong to hold two apparently conformal rigid bodies together, since the forces drop off rapidly with distance, and the actual area in contact between the two bodies is small due to surface roughness and minor imperfections.
However, if the bodies are conformal to an accuracy of better than 10 angstroms (1 nanometer), then a sufficient surface area is in close enough contact for the intermolecular interactions to have an observable macroscopic effect—that is, the two objects stick together. Such a condition requires a high degree of accuracy and surface smoothness, which is typically found in optical components, such as prisms. | 6 | Supramolecular Chemistry |
Israel has the highest rate of IVF in the world, with 1,657 procedures performed per million people per year. Couples without children can receive funding for IVF for up to two children. The same funding is available for people without children who will raise up to two children in a single parent home. IVF is available for people aged 18 to 45. The Israeli Health Ministry says it spends roughly $3450 per procedure. | 1 | Biochemistry |
Current scRNA-Seq protocols involve the following steps: isolation of single cell and RNA, reverse transcription (RT), amplification, library generation and sequencing. Single cells are either mechanically separated into microwells (e.g., BD Rhapsody, Takara ICELL8, Vycap Puncher Platform, or CellMicrosystems CellRaft) or encapsulated in droplets (e.g., 10x Genomics Chromium, Illumina Bio-Rad ddSEQ, 1CellBio InDrop, Dolomite Bio Nadia). Single cells are labeled by adding beads with barcoded oligonucleotides; both cells and beads are supplied in limited amounts such that co-occupancy with multiple cells and beads is a very rare event. Once reverse transcription is complete, the cDNAs from many cells can be mixed together for sequencing; transcripts from a particular cell are identified by each cell's unique barcode. Unique molecular identifier (UMIs) can be attached to mRNA/cDNA target sequences to help identify artifacts during library preparation.
Challenges for scRNA-Seq include preserving the initial relative abundance of mRNA in a cell and identifying rare transcripts. The reverse transcription step is critical as the efficiency of the RT reaction determines how much of the cells RNA population will be eventually analyzed by the sequencer. The processivity of reverse transcriptases and the priming strategies used may affect full-length cDNA production and the generation of libraries biased toward the 3’ or 5 end of genes.
In the amplification step, either PCR or in vitro transcription (IVT) is currently used to amplify cDNA. One of the advantages of PCR-based methods is the ability to generate full-length cDNA. However, different PCR efficiency on particular sequences (for instance, GC content and snapback structure) may also be exponentially amplified, producing libraries with uneven coverage. On the other hand, while libraries generated by IVT can avoid PCR-induced sequence bias, specific sequences may be transcribed inefficiently, thus causing sequence drop-out or generating incomplete sequences.
Several scRNA-Seq protocols have been published:
Tang et al.,
STRT,
SMART-seq,
CEL-seq,
RAGE-seq, Quartz-seq and C1-CAGE. These protocols differ in terms of strategies for reverse transcription, cDNA synthesis and amplification, and the possibility to accommodate sequence-specific barcodes (i.e. UMIs) or the ability to process pooled samples.
In 2017, two approaches were introduced to simultaneously measure single-cell mRNA and protein expression through oligonucleotide-labeled antibodies known as REAP-seq, and CITE-seq. | 1 | Biochemistry |
The presence of humic acid in water intended for potable or industrial use can have a significant impact on the treatability of that water and the success of chemical disinfection processes. For instance, humic and fulvic acids can react with the chemicals used in the chlorination process to form disinfection byproducts such as dihaloacetonitriles, which are toxic to humans. Accurate methods of establishing humic acid concentrations are therefore essential in maintaining water supplies, especially from upland peaty catchments in temperate climates.
As a lot of different bio-organic molecules in very diverse physical associations are mixed together in natural environments, it is cumbersome to measure their exact concentrations in the humic superstructure. For this reason, concentrations of humic acid are traditionally estimated out of concentrations of organic matter, typically from concentrations of total organic carbon (TOC) or dissolved organic carbon (DOC).
Extraction procedures are bound to alter some of the chemical linkages present in the soil humic substances (mainly ester bonds in biopolyesters such as cutins and suberins). The humic extracts are composed of large numbers of different bio-organic molecules that have not yet been totally separated and identified. However, single classes of residual biomolecules have been identified by selective extractions and chemical fractionation, and are represented by alkanoic and hydroxy alkanoic acids, resins, waxes, lignin residues, sugars, and peptides. | 9 | Geochemistry |
A thermodynamic system is a body of matter and/or radiation separate from its surroundings that can be studied using the laws of thermodynamics.
Thermodynamic systems can be passive and active according to internal processes. According to internal processes, passive systems and active systems are distinguished: passive, in which there is a redistribution of available energy, active, in which one type of energy is converted into another.
Depending on its interaction with the environment, a thermodynamic system may be an isolated system, a closed system, or an open system. An isolated system does not exchange matter or energy with its surroundings. A closed system may exchange heat, experience forces, and exert forces, but does not exchange matter. An open system can interact with its surroundings by exchanging both matter and energy.
The physical condition of a thermodynamic system at a given time is described by its state, which can be specified by the values of a set of thermodynamic state variables. A thermodynamic system is in thermodynamic equilibrium when there are no macroscopically apparent flows of matter or energy within it or between it and other systems. | 7 | Physical Chemistry |
Researchers at the École Polytechnique Fédérale de Lausanne and at the Université du Québec à Montréal claim to have overcome two of the DSC's major issues:
* "New molecules" have been created for the electrolyte, resulting in a liquid or gel that is transparent and non-corrosive, which can increase the photovoltage and improve the cell's output and stability.
* At the cathode, platinum was replaced by cobalt sulfide, which is far less expensive, more efficient, more stable and easier to produce in the laboratory. | 5 | Photochemistry |
Degenerate matter occurs when the Pauli exclusion principle significantly alters a state of matter at low temperature. The term is used in astrophysics to refer to dense stellar objects such as white dwarfs and neutron stars, where thermal pressure alone is not enough to avoid gravitational collapse. The term also applies to metals in the Fermi gas approximation.
Degenerate matter is usually modelled as an ideal Fermi gas, an ensemble of non-interacting fermions. In a quantum mechanical description, particles limited to a finite volume may take only a discrete set of energies, called quantum states. The Pauli exclusion principle prevents identical fermions from occupying the same quantum state. At lowest total energy (when the thermal energy of the particles is negligible), all the lowest energy quantum states are filled. This state is referred to as full degeneracy. This degeneracy pressure remains non-zero even at absolute zero temperature. Adding particles or reducing the volume forces the particles into higher-energy quantum states. In this situation, a compression force is required, and is made manifest as a resisting pressure. The key feature is that this degeneracy pressure does not depend on the temperature but only on the density of the fermions. Degeneracy pressure keeps dense stars in equilibrium, independent of the thermal structure of the star.
A degenerate mass whose fermions have velocities close to the speed of light (particle kinetic energy larger than its rest mass energy) is called relativistic degenerate matter.
The concept of degenerate stars, stellar objects composed of degenerate matter, was originally developed in a joint effort between Arthur Eddington, Ralph Fowler and Arthur Milne. Eddington had suggested that the atoms in Sirius B were almost completely ionised and closely packed. Fowler described white dwarfs as composed of a gas of particles that became degenerate at low temperature; he also pointed out that ordinary atoms broadly similar in regards to the filling of energy levels by fermions. Milne proposed that degenerate matter is found in most of the nuclei of stars, not only in compact stars. | 7 | Physical Chemistry |
Aluminium smelting is the process of extracting aluminium from its oxide, alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery.
This is an electrolytic process, so an aluminium smelter uses huge amounts of electric power; smelters tend to be located close to large power stations, often hydro-electric ones, in order to hold down costs and reduce the overall carbon footprint. Smelters are often located near ports, since many smelters use imported alumina. | 8 | Metallurgy |
(-)-C-demethyl arteannuin B is a structural analog of the antimalarial artemisinin. It exhibits potent antimalarial activity even against a drug-resistant strain. Little and coworkers obtained the alkylated hydrazone in diastereomerically pure form (de > 95%) through the Enders' alkylation reaction. This intermediate was then elaborated into (-)-C-demethyl arteannuin B. | 0 | Organic Chemistry |
Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HOCC(O)CHCOH. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes that occur in animals. It takes part in gluconeogenesis, the urea cycle, the glyoxylate cycle, amino acid synthesis, fatty acid synthesis and the citric acid cycle. | 1 | Biochemistry |
Metal–π interactions play a major role in organometallics. Linear and cyclic π systems bond to metals allowing organic complexes to bond to metals. | 6 | Supramolecular Chemistry |
Georg-Maria Schwab (, ; 3 February 1899 – 23 December 1984) was a German-Greek physical chemist recognised for his important contributions in the field of catalysis and the kinetics thereof.
Schwab's early academic career in Berlin and Würzburg (1923–1928) was characterised by meticulous experimental work as a kineticist, before starting his specialisation in heterogeneous catalysis in Munich (1928–1938). Dismissed by Nazi Germany on anti-Semitic grounds, he emigrated to Greece with the help of his future wife Elly Schwab-Agallidis, where together, they continued conducting physico-chemical research (1939–1950). Eventually returning to West Germany in the 1950s, Schwab served as professor of physical chemistry in the University of Munich until retirement (1951–1967). | 7 | Physical Chemistry |
In genetics, the term horizontal resistance was first used by J. E. Vanderplank to describe many-gene resistance, which is sometimes also called generalized resistance. This contrasts with the term vertical resistance which was used to describe single-gene resistance. Raoul A. Robinson further refined the definition of horizontal resistance. Unlike vertical resistance and parasitic ability, horizontal resistance and horizontal parasitic ability are entirely independent of each other in genetic terms.
In the first round of breeding for horizontal resistance, plants are exposed to pathogens and selected for partial resistance. Those with no resistance die, and plants unaffected by the pathogen have vertical resistance and are removed. The remaining plants have partial resistance and their seed is stored and bred back up to sufficient volume for further testing. The hope is that in these remaining plants are multiple types of partial-resistance genes, and by crossbreeding this pool back on itself, multiple partial resistance genes will come together and provide resistance to a larger variety of pathogens.
Successive rounds of breeding for horizontal resistance proceed in a more traditional fashion, selecting plants for disease resistance as measured by yield. These plants are exposed to native regional pathogens, and given minimal assistance in fighting them. | 1 | Biochemistry |
Desorption is the physical process where adsorbed atoms or molecules are released from a surface into the surrounding vacuum or fluid. This occurs when a molecule gains enough energy to overcome the activation barrier and the binding energy that keep it attached to the surface.
Desorption is the reverse of the process of adsorption, which differs from absorption in that adsorption it refers to substances bound to the surface, rather than being absorbed into the bulk.
Desorption can occur from any of several processes, or a combination of them: it may result from heat (thermal energy); incident light such as infrared, visible, or ultraviolet photons; or a incident beam of energetic particles such as electrons. It may also occur following chemical reactions such as oxidation or reduction in an electrochemical cell or after a chemical reaction of a adsorbed compounds in which the surface may act as a catalyst. | 7 | Physical Chemistry |
The notion of energy quality was also recognised in the economic sciences. In the context of biophysical economics energy quality was measured by the amount of economic output generated per unit of energy input (C.J. Cleveland et al. 2000). The estimation of energy quality in an economic context is also associated with embodied energy methodologies. Another example of the economic relevance of the energy quality concept is given by Brian Fleay. Fleay says that the "Energy Profit Ratio (EPR) is one measure of energy quality and a pivotal index for assessing the economic performance of fuels. Both the direct and indirect energy inputs embodied in goods and services must be included in the denominator." (2006; p. 10) Fley calculates the EPR as the energy output/energy input. | 7 | Physical Chemistry |
The reaction can be under kinetic or thermodynamic control depending on the exact reaction conditions, catalyst, and substrate. Common rings, 5- through 7-membered cycloalkenes, have a high tendency for formation and are often under greater thermodynamic control due to the enthalpic favorability of the cyclic products, as shown by Illuminati and Mandolini on the formation of lactone rings. Smaller rings, between 5 and 8 atoms, are more thermodynamically favored over medium to large rings due to lower ring strain. Ring strain arises from abnormal bond angles resulting in a higher heat of combustion relative to the linear counterpart. If the RCM product contains a strained olefin, polymerization becomes preferable through ring-opening metathesis polymerization of the newly formed olefin. Medium rings in particular have greater ring strain, in part due to greater transannular interactions from opposing sides of the ring, but also the inability to orient the molecule in such a way to prevent penalizing gauche interactions. RCM may be considered to have a kinetic bias if the products cannot reenter the catalytic cycle or interconvert through an equilibrium. A kinetic product distribution could lead to mostly RCM products or may lead to oligomers and polymers, which are most often disfavored. | 0 | Organic Chemistry |
*cis-1,4-polyisoprene (synthetic analogue of rubber) and trans-1,4-polyisoprene (synthetic analogue of gutta percha) are obtained by coordination polymerisation using suitable Ziegler-Natta catalysts.
* Polyhydroxoalkanoates such as poly(3-hydroxobutyrate), poly(hydroxovaleric acid) etc. obtained by polycondensation and polyaddition. Low-molecular weight polylactide and other polyglycolides can also be obtained by chemical synthesis.
*Oligonucleotides and polynucleotides (DNA or RNA) can be obtain by chemical synthesis through a variety of established approaches.
*A variety of proteins have been obtained by chemical synthesis. A successful approach relies on native chemical ligation, which achieves the synthesis of proteins by linking shorter unprotected peptides. This strategy allowed to obtain, amongst many others, proteins such as insulin-like growth factor 1, the precursor of Aequorea green fluorescent protein and the influenza A virus M2 membrane protein. | 1 | Biochemistry |
In these cells the electrolyte between the electrodes is a water solution of some salt or hydrophylic compound. An essential property of these compounds is that they must be able to undergo redox reactions in order to shuttle electrons from one electrode to the other during the cell operation. | 7 | Physical Chemistry |
In environments where nuclear safety and radiation protection are required, radioactive contamination is a concern. Radioactive substances can appear on surfaces, or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirable, and processes can give rise to their presence in such places. Several examples of radioactive contamination include:
* residual radioactive material remaining at a site after the completion of decommissioning of a site where there was a nuclear reactor, such as a power plant, experimental reactor, isotope reactor, or a nuclear powered ship or submarine
* ingested or absorbed radioactive material that contaminates a biological entity, whether unintentionally or intentionally (such as with radiopharmaceuticals
* escape of elements after nuclear accident, such as the contamination of Iodine-131 and Caesium-137 after the nuclear disaster in Chernobyl, Ukraine.
Note that the term "radioactive contamination" may have a connotation that is not intended. The term refers only to the presence of radioactivity and gives no indication itself of the magnitude of the hazard involved. However, radioactivity can be measured as a quantity in a given location or on a surface, or on a unit area of a surface, such as a square meter or centimeter.
Like environmental monitoring, radiation monitoring can be employed to catch contamination-causing activities before much harm. | 9 | Geochemistry |
The products and services offered by the fine chemical industry fall into two broad categories: (1) "Exclusives", a.k.a. custom manufacturing (CM) and (2) "standard" or "catalogue" products. "Exclusives", provided mostly under contract research or custom manufacturing arrangements, prevail in business with life science companies; "standards" prevail in other target markets. Service-intense custom manufacturing (CM) constitutes the most prominent activity of the fine chemical industry. CM is the antonym of outsourcing. In custom manufacturing, a specialty-chemicals company outsources the process development, pilot plant, and, finally, industrial-scale production of an active ingredient, or a predecessor thereof, to one, or a few, fine chemical companies. The intellectual property of the product, and generally also the manufacturing process, stay with the customer. The customer-supplier relationship is governed by an exclusive supply agreement. At the beginning of cooperation, the customer provides a "tech package", which in its simplest version, includes a laboratory synthesis description and SHE recommendations. In this case, the whole scale up, which comprises a factor of about one million (10 gram → 10 ton quantities), is done by the fine chemical company. | 0 | Organic Chemistry |
The tetratricopeptide repeat domain provides the concave surface necessitated for SIP recognition. RopB-CTD houses 5 stacked TPR motifs, each having sets of paired antiparallel helices that aid in the formation of a concave inner pathway and a convex exterior. The base of the recognition site is constructed by α6 and α8 helices [See Also: alpha helix], while the supporting walls are constructed from helices α2, and α12. The exterior portion of the recognition site is flanked by asparagines N152 and N192 thus providing a ridge of support for the peptide-protein complex. | 1 | Biochemistry |
As a catalyst, ArMs have three advantages,
# thanks to the development in molecular biology, it is quite easy to generate a library of ArM mutants which has a size up to 10. Using proper selection method, the ArM has a large potential to gain unique catalytic properties.
# ArMs are proteins, it can have both hydrophilic and hydrophobic surface in the aqueous solution. Anchoring the artificial cofactor which is not easily dissolve in water would help it function in aqueous phase. In some structure, the hydrophobic cavity would protect some labile bond (like many carbene or nitrene-metal complex in Arnold ArMs).
# The backbone itself in ArM is a asymmetric environment. In some cases, the enantioselective synthesis can be tuned by changing one or two amino acid residues around the metal catalytic center.
So far, ArMs can catalyze a lot of chemical reactions, such as: allylic alkylation, allylic amination, aldol reaction, alcohol oxidation, C-H activation, click reaction, catechol oxidation, reduction, cyclopropanation, Diels-Alder reaction, epoxidation, epoxide ring opening, Friedel-Crafts alkylation, hydrogenation, hydroformylation, Heck reaction, metathesis, Michael addition, nitrite reduction, NO reduction, Suzuki reaction, Si-H insertion, polymerization (atom transfer radical polymerization). | 0 | Organic Chemistry |
Quantitative PCR is also used by microbiologists working in the fields of food safety, food spoilage and fermentation and for the microbial risk assessment of water quality (drinking and recreational waters) and in public health protection.
qPCR may also be used to amplify taxonomic or functional markers of genes in DNA taken from environmental samples. Markers are represented by genetic fragments of DNA or complementary DNA. By amplifying a certain genetic element, one can quantify the amount of the element in the sample prior to amplification. Using taxonomic markers (ribosomal genes) and qPCR can help determine the amount of microorganisms in a sample, and can identify different families, genera, or species based on the specificity of the marker. Using functional markers (protein-coding genes) can show gene expression within a community, which may reveal information about the environment. | 1 | Biochemistry |
Focusing on crystallographic data and applications of the group theory in solid state physics, the server is built on a core of databases and contains different shells. | 3 | Analytical Chemistry |
Taking (the Planck constant divided by ), (the speed of light), and (the electromagnetic coupling constant i.e. a measure of the strength of the electromagnetic force (where is the absolute value of the electronic charge and is the vacuum permittivity)) we can form a dimensionless quantity called the fine-structure constant:
The fine-structure constant is the coupling constant of quantum electrodynamics (QED) determining the strength of the interaction between electrons and photons. It turns out that the fine-structure constant is not really a constant at all owing to the zero-point energy fluctuations of the electron-positron field. The quantum fluctuations caused by zero-point energy have the effect of screening electric charges: owing to (virtual) electron-positron pair production, the charge of the particle measured far from the particle is far smaller than the charge measured when close to it.
The Heisenberg inequality where , and , are the standard deviations of position and momentum states that:
It means that a short distance implies large momentum and therefore high energy i.e. particles of high energy must be used to explore short distances. QED concludes that the fine-structure constant is an increasing function of energy. It has been shown that at energies of the order of the Z boson rest energy, 90 GeV, that:
rather than the low-energy . The renormalization procedure of eliminating zero-point energy infinities allows the choice of an arbitrary energy (or distance) scale for defining . All in all, depends on the energy scale characteristic of the process under study, and also on details of the renormalization procedure. The energy dependence of has been observed for several years now in precision experiment in high-energy physics. | 7 | Physical Chemistry |
The total synthesis of Aflatoxin B2 is a multistep sequence that begins with a [2+3]cycloaddition between the quinone 1 and the 2,3-Dihydrofuran. This reaction is catalyzed by a CBS catalyst and is enantioselective. The next step is the orthoformylation of reaction product 2 in a Duff reaction. The hydroxyl group in 3 is esterified with triflic anhydride which adds a triflate protecting group. This step enables a Grignard reaction of the aldehyde group in 4 with methylmagnesiumbromide to the alcohol 5 which is then oxidized with the Dess-Martin periodinane to the ketone 6. A Baeyer-Villiger oxidation converts the ketone to an ester (7) and a reduction with Raney nickel converts the ester into an alcohol and removes the triflic acid group. In the final step the coumarin skeleton is added to 9 by a combined coupling reaction with zinc carbonate of the vinyl bromide in 8 and a transesterification step between the phenol group and the ethyl ester group. | 0 | Organic Chemistry |
The Journal of Photochemistry and Photobiology A: Chemistry is published biweekly. There is no editor-in-chief; editorial responsibility is shared and divided geographically with Hiroshi Masuhara covering Asia, Russ Schmehl covering America, and Monique Martin covering Europe. | 5 | Photochemistry |
Metals such as iron, copper, chromium, vanadium, and cobalt are capable of redox cycling in which a single electron may be accepted or donated by the metal. This action catalyzes production of reactive radicals and reactive oxygen species. The presence of such metals in biological systems in an uncomplexed form (not in a protein or other protective metal complex) can significantly increase the level of oxidative stress. These metals are thought to induce Fenton reactions and the Haber-Weiss reaction, in which hydroxyl radical is generated from hydrogen peroxide. The hydroxyl radical then can modify amino acids. For example, meta-tyrosine and ortho-tyrosine form by hydroxylation of phenylalanine. Other reactions include lipid peroxidation and oxidation of nucleobases. Metal-catalyzed oxidations also lead to irreversible modification of arginine, lysine, proline, and threonine. Excessive oxidative-damage leads to protein degradation or aggregation.
The reaction of transition metals with proteins oxidated by reactive oxygen or nitrogen species can yield reactive products that accumulate and contribute to aging and disease. For example, in Alzheimer's patients, peroxidized lipids and proteins accumulate in lysosomes of the brain cells. | 1 | Biochemistry |
Tisza was the author of the 1966 book, Generalized Thermodynamics. The 1982 publication, Physics as Natural Philosophy: Essays in Honor of László Tisza, was written by Tisza's colleagues and former students in honor of his 75th birthday. | 7 | Physical Chemistry |
Although the modern electric arc furnace is a highly efficient recycler of steel scrap, operation of an arc furnace shop can have adverse environmental effects. Much of the capital cost of a new installation will be devoted to systems intended to reduce these effects, which include:
* Enclosures to reduce high sound levels
* Dust collector for furnace off-gas
* Slag production
* Cooling water demand
* Heavy truck traffic for scrap, materials handling, and product
* Environmental effects of electricity generation
Since EAF steelmaking mainly use recycled materials like scrap iron and scrap steel, as their composition varies the resulting EAF slag and EAF dust can be toxic. EAF dust is collected by air pollution control equipment. It is called collected dust and usually contains heavy metals, such as zinc, lead and dioxins, etc. It is categorized as hazardous industrial waste and disposal is regulated.
Because of the very dynamic quality of the arc furnace load, power systems may require technical measures to maintain the quality of power for other customers; flicker and harmonic distortion are common power system side-effects of arc furnace operation. | 8 | Metallurgy |
A reactive center, also called a propagating center, in chemistry is a particular location, usually an atom, within a chemical compound that is the likely center of a reaction in which the chemical is involved. In chain-growth polymer chemistry, this is also the point of propagation for a growing chain. The reactive center is commonly radical, anionic, or cationic, but can also take other forms. | 7 | Physical Chemistry |
A restriction fragment is a DNA fragment resulting from the cutting of a DNA strand by a restriction enzyme (restriction endonucleases), a process called restriction. Each restriction enzyme is highly specific, recognising a particular short DNA sequence, or restriction site, and cutting both DNA strands at specific points within this site. Most restriction sites are palindromic, (the sequence of nucleotides is the same on both strands when read in the 5 to 3 direction of each strand), and are four to eight nucleotides long. Many cuts are made by one restriction enzyme because of the chance repetition of these sequences in a long DNA molecule, yielding a set of restriction fragments. A particular DNA molecule will always yield the same set of restriction fragments when exposed to the same restriction enzyme. Restriction fragments can be analyzed using techniques such as gel electrophoresis or used in recombinant DNA technology. | 1 | Biochemistry |
*[http://www.nature.com/nature/journal/v446/n7134/full/446391a.html Bergman FAQ in Nature on C-H activation (2007)]
*[https://web.archive.org/web/20160303224214/http://stoltz.caltech.edu/seminars/2004_Ramtohul.pdf Literature Presentation by Ramtohul in Stoltz group on applications of C-H activation]
*[http://www.chem.tamu.edu/rgroup/marcetta/chem636/Presentations/C-H%20Activation=Sam.pdf Powerpoint on John Bercaw's work]
*[http://www.nsf-cchf.com/index.html Center for Selective C-H Functionalization] | 0 | Organic Chemistry |
The lysophosphatidic acid receptors (LPARs) are a group of G protein-coupled receptors for lysophosphatidic acid (LPA) that include:
* Lysophosphatidic acid receptor 1 (LPAR1; formerly known as EDG2, GPR26)
* Lysophosphatidic acid receptor 2 (LPAR2; formerly known as EDG4)
* Lysophosphatidic acid receptor 3 (LPAR3; formerly known as EDG7)
* Lysophosphatidic acid receptor 4 (LPAR4; formerly known as GPR23, P2RY9)
* Lysophosphatidic acid receptor 5 (LPAR5; formerly known as GPR92)
* Lysophosphatidic acid receptor 6 (LPAR6; formerly known as GPR87, P2RY5) | 1 | Biochemistry |
PyAOP ((7-Azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate) is a coupling reagent used in solid phase peptide synthesis. It is a derivative of the HOAt family of coupling reagents. It is preferred over HATU, because it does not side react at the N-terminus of the peptide. Compared to the HOBt derivates, PyAOP (and HOAt in general) are more reactive due to the additional nitrogen. | 1 | Biochemistry |
Many biological proteins and enzymes can possess more than one binding site.
Usually, when a ligand binds with a macromolecule , it can influence binding kinetics of other ligands binding to the macromolecule.
A simplified mechanism can be formulated if the affinity of all binding sites can be considered independent of the number of ligands bound to the macromolecule.
This is valid for macromolecules composed of more than one, mostly identical, subunits. It can be then assumed that each of these subunits are identical, symmetric and that they possess only a single binding site. Then the concentration of bound ligands becomes
In this case, , but comprises all partially saturated forms of the macromolecule:
where the saturation occurs stepwise
For the derivation of the general binding equation a saturation function is defined as the quotient from the portion of bound ligand to the total
amount of the macromolecule:
K′ are so-called macroscopic or apparent dissociation constants and can result from multiple individual reactions. For example, if a macromolecule M has three binding sites, K′ describes a ligand being bound to any of the three binding sites. In this example, K′ describes two molecules being bound and K′ three molecules being bound to the macromolecule. The microscopic or individual dissociation constant describes the equilibrium of ligands binding to specific binding sites. Because we assume identical binding sites with no cooperativity, the microscopic dissociation constant must be equal for every binding site and can be abbreviated simply as K. In our example, K′ is the amalgamation of a ligand binding to either of the three possible binding sites (I, II and III), hence three microscopic dissociation constants and three distinct states of the ligand–macromolecule complex. For K′ there are six different microscopic dissociation constants (I–II, I–III, II–I, II–III, III–I, III–II) but only three distinct states (it does not matter whether you bind pocket I first and then II or II first and then I). For K′ there are three different dissociation constants — there are only three possibilities for which pocket is filled last (I, II or III) — and one state (I–II–III).
Even when the microscopic dissociation constant is the same for each individual binding event, the macroscopic outcome (K′, K′ and K′) is not equal. This can be understood intuitively for our example of three possible binding sites. K′ describes the reaction from one state (no ligand bound) to three states (one ligand bound to either of the three binding sides). The apparent K′ would therefore be three times smaller than the individual K. K′ describes the reaction from three states (one ligand bound) to three states (two ligands bound); therefore, K′ would be equal to K. K′ describes the reaction from three states (two ligands bound) to one state (three ligands bound); hence, the apparent dissociation constant K′ is three times bigger than the microscopic dissociation constant K.
The general relationship between both types of dissociation constants for n binding sites is
Hence, the ratio of bound ligand to macromolecules becomes
where is the binomial coefficient.
Then the first equation is proved by applying the binomial rule | 7 | Physical Chemistry |
The Tepper-García function, named after German-Mexican Astrophysicist Thor Tepper-García, is a combination of an exponential function and rational functions that approximates the line broadening function over a wide range of its parameters.
It is obtained from a truncated power series expansion of the exact line broadening function.
In its most computationally efficient form, the Tepper-García function can be expressed as
where , , and .
Thus the line broadening function can be viewed, to first order, as a pure Gaussian function plus a correction factor that depends linearly on the microscopic properties of the absorbing medium (encoded in ); however, as a result of the early truncation in the series expansion, the error in the approximation is still of order , i.e. . This approximation has a relative accuracy of
over the full wavelength range of , provided that .
In addition to its high accuracy, the function is easy to implement as well as computationally fast. It is widely used in the field of quasar absorption line analysis. | 7 | Physical Chemistry |
Nuclear magnetic resonance (NMR) is a technique used to obtain physical, chemical, electronic and structural information about molecules due to the chemical shift of the resonance frequencies of nuclear spins in the sample. Its combination with electrochemical techniques can provide detailed and quantitative information about the functional groups, topology, dynamics and the three-dimensional structure of molecules in solution during a charge transfer process. The area under an NMR peak is related to the ratio of the number of turns involved and the peak integrals to determine the composition quantitatively. | 7 | Physical Chemistry |
This compound is prepared by a modified Williamson ether synthesis in the presence of a templating cation:(CHOCHCHCl) + (CHOCHCHOH) + 2 KOH → (CHCHO) + 2 KCl + 2 HO
It can be also prepared by the oligomerization of ethylene oxide. It can be purified by distillation, where its tendency to supercool becomes evident. 18-Crown-6 can also be purified by recrystallisation from hot acetonitrile. It initially forms an insoluble solvate. Rigorously dry material can be made by dissolving the compound in THF followed by the addition of NaK to give [K(18-crown-6)]Na, an alkalide salt.
Crystallographic analysis reveals a relatively flat molecule but one where the oxygen centres are not oriented in the idealized 6-fold symmetric geometry usually shown. The molecule undergoes significant conformational change upon complexation. | 6 | Supramolecular Chemistry |
Justus von Liebig and Friedrich Wöhler in Giessen, Germany, had investigated the purple product, murexide, obtained from snake excrement in the 1830s, but this was not an abundant raw material, and a method of using it as a dyestuff was not established at that time. In the 1850s, French colourists and dye-producers, such as Depoully in Paris, succeeded in making murexide from abundant South American guano and of applying it to natural fibres. It was then widely adopted in Britain, France and Germany. | 3 | Analytical Chemistry |
Because malate dehydrogenase is closely tied to the citric acid cycle, studies have proposed and experimentally demonstrated that citrate is an allosteric regulator of malate dehydrogenase depending on the concentrations of L-malate and NAD. This may be due to deviations observed in the kinetic behavior of malate dehydrogenase at high oxaloacetate and L-malate concentrations. Experiments have shown that Citrate can both allosterically activate and inhibit the enzymatic activity of malate dehydrogenase. Citrate has been shown to inhibit the oxidation of L-malate when there are low levels of L-malate and NAD. However, in the presence of high levels of malate and NAD, citrate can stimulate the production of oxaloacetate. Although malate dehydrogenase is typically considered a reversible enzyme, it is believed that there is an allosteric regulatory site on the enzyme where citrate can bind to and drive the reaction equilibrium in either direction.
Glutamate has also been shown to inhibit malate dehydrogenase activity. Furthermore, it has been shown that alpha ketoglutarate dehydrogenase can interact with mitochondrial aspartate aminotransferase to form a complex, which can then bind to malate dehydrogenase, forming a ternary complex that reverses inhibitory action on malate dehydrogenase enzymatic activity by glutamate. Additionally, the formation of this complex enables glutamate to react with aminotransferase without interfering activity of malate dehydrogenase. The formation of this ternary complex also facilitates the release of oxaloacetate from malate dehydrogenase to aminotransferase. Kinetically, the binding of malate dehydrogenase to the binary complex of alpha ketoglutarate dehydrogenase and aminotrannferase has been shown to increase reaction rate of malate dehydrogenase because the Km of malate dehydrogenase is decreased when it is bound as part of this complex. | 1 | Biochemistry |
See also
* Chiral resolution
*Chiral chromatography
* Chiral drugs
* Chiral switch
* Enantiomer
* Chirality | 4 | Stereochemistry |
Semicarbazide is frequently reacted with aldehydes and ketones to produce semicarbazones via a condensation reaction. This is an example of imine formation resulting from the reaction of a primary amine with a carbonyl group. The reaction is useful because semicarbazones, like oximes and 2,4-DNPs, typically have high melting points and crystallize, facilitating purification or identification of reaction products. | 0 | Organic Chemistry |
Patches have been demonstrated to be a promising detection platform for sweat diagnostics. Simple, long-term collection devices which check for drugs of abuse or alcohol are already on the market and operate on the following principle: a user applies the patch which then collects sweat over a period of hours or days, then the patch is analyzed utilizing techniques such as GC-MS which are accurate but have the drawback of lack of continuous measurements and high costs. For example, sweat diagnostic products for illicit drugs and alcohol are manufactured and supplied by PharmChek and AlcoPro, respectively. Recently several efforts have been made to develop low cost polymer based continuous perspiration monitoring devices and are in early stages of commercialization.
More recently, startup companies such as [http://www.Xsensio.com Xsensio] have begun developing products targeted towards the consumer, healthcare and athletics market for sweat diagnostics. Ultimately, it is the hope that these devices will have the ability to detect changes in human physiology within minutes without the need for repeated sample collection and analysis. | 1 | Biochemistry |
After initial reports of a "homoaromatic" structure for the tris-homocyclopropenyl cation were published by Winstein, many groups began to report observations of similar compounds. One of the best studied of these molecules is the homotropylium cation, the parent compound of which was first isolated as a stable salt by Pettit, et al. in 1962, when the group reacted cyclooctatraene with strong acids. Much of the early evidence for homoaromaticity comes from observations of unusual NMR properties associated with this molecule. | 7 | Physical Chemistry |
Non-specific binding of primers frequently occurs and may occur for several reasons. These include repeat sequences in the DNA template, non-specific binding between primer and template, high or low G-C content in the template, or incomplete primer binding, leaving the 5' end of the primer unattached to the template. Non-specific binding of degenerate primers is also common. Manipulation of annealing temperature and magnesium ion concentration may be used to increase specificity. For example, lower concentrations of magnesium or other cations may prevent non-specific primer interactions, thus enabling successful PCR. A "hot-start" polymerase enzyme whose activity is blocked unless it is heated to high temperature (e.g., 90–98˚C) during the denaturation step of the first cycle, is commonly used to prevent non-specific priming during reaction preparation at lower temperatures. Chemically mediated hot-start PCRs require higher temperatures and longer incubation times for polymerase activation, compared with antibody or aptamer-based hot-start PCRs.
Other methods to increase specificity include Nested PCR and Touchdown PCR.
Computer simulations of theoretical PCR results (Electronic PCR) may be performed to assist in primer design.
Touchdown polymerase chain reaction or touchdown style polymerase chain reaction is a method of polymerase chain reaction by which primers will avoid amplifying nonspecific sequences. The annealing temperature during a polymerase chain reaction determines the specificity of primer annealing. The melting point of the primer sets the upper limit on annealing temperature. At temperatures just below this point, only very specific base pairing between the primer and the template will occur. At lower temperatures, the primers bind less specifically. Nonspecific primer binding obscures polymerase chain reaction results, as the nonspecific sequences to which primers anneal in early steps of amplification will "swamp out" any specific sequences because of the exponential nature of polymerase amplification.
The earliest steps of a touchdown polymerase chain reaction cycle have high annealing temperatures. The annealing temperature is decreased in increments for every subsequent set of cycles (the number of individual cycles and increments of temperature decrease is chosen by the experimenter). The primer will anneal at the highest temperature which is least-permissive of nonspecific binding that it is able to tolerate. Thus, the first sequence amplified is the one between the regions of greatest primer specificity; it is most likely that this is the sequence of interest. These fragments will be further amplified during subsequent rounds at lower temperatures, and will out compete the nonspecific sequences to which the primers may bind at those lower temperatures. If the primer initially (during the higher-temperature phases) binds to the sequence of interest, subsequent rounds of polymerase chain reaction can be performed upon the product to further amplify those fragments. | 1 | Biochemistry |
Studies in 2007 have catalogued nucleosome positions in yeast and shown that nucleosomes are depleted in promoter regions and origins of replication.
About 80% of the yeast genome appears to be covered by nucleosomes and the pattern of nucleosome positioning clearly relates to DNA regions that regulate transcription, regions that are transcribed and regions that initiate DNA replication. Most recently, a new study examined dynamic changes in nucleosome repositioning during a global transcriptional reprogramming event to elucidate the effects on nucleosome displacement during genome-wide transcriptional changes in yeast (Saccharomyces cerevisiae). The results suggested that nucleosomes that were localized to promoter regions are displaced in response to stress (like heat shock). In addition, the removal of nucleosomes usually corresponded to transcriptional activation and the replacement of nucleosomes usually corresponded to transcriptional repression, presumably because transcription factor binding sites became more or less accessible, respectively. In general, only one or two nucleosomes were repositioned at the promoter to effect these transcriptional changes. However, even in chromosomal regions that were not associated with transcriptional changes, nucleosome repositioning was observed, suggesting that the covering and uncovering of transcriptional DNA does not necessarily produce a transcriptional event. After transcription, the rDNA region has to protected from any damage, it suggested HMGB proteins play a major role in protecting the nucleosome free region. | 1 | Biochemistry |
Pre-emption prevents damage from happening. This is done either by converting reactive metabolites to less harmful ones, or by speeding up an insufficiently fast chemical reaction. The reactive metabolite can be either a side product, or a normal, but highly reactive intermediate.
For example, a side activity of Rubisco yields small amounts of xylulose-1,5-bisphosphate, which can inhibit Rubisco activity. The CbbY enzyme dephosphorylates xylulose-1,5-bisphosphate to the natural metabolite xylulose-5-phosphate, thereby preventing inhibition of Rubisco. | 1 | Biochemistry |
SOLID was designed for automatic in situ detection and identification of substances from liquid and crushed samples under the conditions of outer space. The system uses hundreds of carefully selected antibodies to detect lipids, proteins, polysaccharides, and nucleic acids. These are complex biological polymers that could only be synthesized by life forms, and are therefore strong indicators —biosignatures— of past or present life.
SOLID consists of two separate functional units: a Sample Preparation Unit (SPU) for extractions by ultrasonication, and a Sample Analysis Unit (SAU), for fluorescent immunoassays. The antibody microarrays are separated in hundreds of small compartments inside a biochip only a few square centimeters in size.
SOLID instrument is able to perform both "sandwich" and competitive immunoassays using hundreds of well characterized and highly specific antibodies. The technique called "sandwich immunoassay" is a non-competitive immunoassay in which the analyte (compound of interest in the unknown sample) is captured by an immobilized antibody, then a labeled antibody is bound to the analyte to reveal its presence. In other words, the "sandwich" quantify antigens (i.e. biomolecules) between two layers of antibodies (i.e. capture and detection antibody). For the competitive assay technique, unlabeled analyte displaces bound labelled analyte, which is then detected or measured.
An optical system is set up so that a laser beam excites the fluorochrome label and a CCD detector captures an image of the microarray that can be measured.
The instrument is able to detect a broad range of molecular size compounds, from the amino acid size, peptides, proteins, to whole cells and spores, with sensitivities at 1–2 ppb (ng/mL) for biomolecules and 104 to 103 spores per milliliter. Some compartments in the microarray are reserved for samples of known nature and concentrations, that are used as controls for reference and comparison. SOLID instrument concept avoids the high-temperature treatments of other techniques that may destroy organic matter in the presence of Martian oxidants such as perchlorates. | 1 | Biochemistry |
: Genomic selection is a novel approach to traditional marker-assisted selection where selection is made based on only a few markers. Rather than seeking to identify individual loci significantly associated with a trait, genomics uses all marker data as predictors of performance and consequently delivers more accurate predictions. Selection can be based on genomic selection predictions, potentially leading to more rapid and lower cost gains from breeding. Genomic prediction combines marker data with phenotypic and pedigree data (when available) in an attempt to increase the accuracy of the prediction of breeding and genotypic values. | 1 | Biochemistry |
This sequencing method was originally developed by 10x Genomics in 2015, and was launched under the name GemCode or Chromium. GemCode employed a method of gel bead-based barcoding to amalgamate short DNA fragments. The longer fragments produced by this could then be sequenced using validated technology such as Illumina next-generation sequencing. An updated version of linked-read sequencing was introduced by the same company in 2018, termed Linked-Reads V2. While GemCode uses a single barcode for tagging of both the gel bead and the DNA fragment, Linked-Reads V2 uses separate barcodes for improved detection of genetic variants.
The group developed the linked-read sequencing technology published their first paper regarding this technology in 2016. The authors of this paper developed the linked-read sequencing technology initially to sequence the genomes of both healthy individuals and cancer patients to determine somatic mutations, copy number variations, and structural variations in cancer genomes. Later that year, another research group combined linked-read sequencing technology with long-read sequencing technology to assemble human genome. Both studies demonstrated the utility of linked-read sequencing in comprehensive genome analysis and in understanding genetic diseases. However, in 2019, a lawsuit relating to patent infringement resulted in 10x Genomics discontinuing their line of linked-read products. | 1 | Biochemistry |
The equilibrium phase diagram of the alloy formed between the two components tantalum and tungsten is a binary diagram, where the two components are totally soluble on each other. In this diagram the melting temperature of the two elements are shown. It can be seen that there are two lines, representing the solidus and liquidus. | 8 | Metallurgy |
T-symmetry or time reversal symmetry is the theoretical symmetry of physical laws under the transformation of time reversal,
Since the second law of thermodynamics states that entropy increases as time flows toward the future, in general, the macroscopic universe does not show symmetry under time reversal. In other words, time is said to be non-symmetric, or asymmetric, except for special equilibrium states when the second law of thermodynamics predicts the time symmetry to hold. However, quantum noninvasive measurements are predicted to violate time symmetry even in equilibrium, contrary to their classical counterparts, although this has not yet been experimentally confirmed.
Time asymmetries (see Arrow of time) generally are caused by one of three categories:
# intrinsic to the dynamic physical law (e.g., for the weak force)
# due to the initial conditions of the universe (e.g., for the second law of thermodynamics)
# due to measurements (e.g., for the noninvasive measurements) | 7 | Physical Chemistry |
Chloride is an anion in the human body needed for metabolism (the process of turning food into energy). It also helps keep the body's acid-base balance. The amount of serum chloride is carefully controlled by the kidneys.
Chloride ions have important physiological roles. For instance, in the central nervous system, the inhibitory action of glycine and some of the action of GABA relies on the entry of Cl into specific neurons. Also, the chloride-bicarbonate exchanger biological transport protein relies on the chloride ion to increase the blood's capacity of carbon dioxide, in the form of the bicarbonate ion; this is the mechanism underpinning the chloride shift occurring as the blood passes through oxygen-consuming capillary beds.
The normal blood reference range of chloride for adults in most labs is 96 to 106 milliequivalents (mEq) per liter. The normal range may vary slightly from lab to lab. Normal ranges are usually shown next to results in the lab report. A diagnostic test may use a chloridometer to determine the serum chloride level.
The North American Dietary Reference Intake recommends a daily intake of between 2300 and 3600 mg/day for 25-year-old males. | 1 | Biochemistry |
Fibrosis or scar formation is another pro-oxidant-related symptom. E.g., interocular copper or vitreous chalicosis is associated with severe vitreous fibrosis, as is interocular iron. Liver cirrhosis is also a major symptom of Wilson's disease. The pulmonary fibrosis produced by paraquat and the antitumor agent bleomycin is also thought to be induced by the pro-oxidant properties of these agents. It may be that oxidative stress produced by such agents mimics a normal physiological signal for fibroblast conversion to myofibroblasts. | 1 | Biochemistry |
Several genetic diseases may be the result of splice site mutations. For example, mutations that cause the incorrect splicing of β-globin mRNA are responsible of some cases of β-thalassemia. Another Example is TTP (thrombotic thrombocytopenic purpura). TTP is caused by deficiency of ADAMTS-13. A splice site mutation of ADAMTS-13 gene can therefore cause TTP. It is estimated that 15% of all point mutations causing human genetic diseases occur within a splice site. | 1 | Biochemistry |
One unique property of dendrimers such as PAMAM is the high density of surface functional groups, which allow many alterations to be made to the surface of each dendrimer molecule. In putative PAMAM dendrimers, the surface is rife with primary amines, with higher generations expressing exponentially greater densities of amino groups. Although the potential to attach many things to each dendrimer is one of their greatest advantages, the presence of highly localized positive charges can be toxic to cells. Surface modification via attachment of acetyl and lauroyl groups help mask these positive charges, attenuating cytotoxicity and increasing permeability to cells. Thus, these types of modifications are especially beneficial for biological applications. Secondary and tertiary amino surface groups are also found to be less toxic than primary amino surface groups, suggesting it is charge shielding which has major bearing on cytotoxicity and not some secondary effect from a particular functional group. Furthermore, other studies point to a delicate balance in charge which must be achieved to obtain minimal cytotoxicity. Hydrophobic interactions can also cause cell lysis, and PAMAM dendrimers whose surfaces are saturated with nonpolar modifications such as lipids or polyethylene glycol (PEG) suffer from higher cytotoxicity than their partially substituted analogues. PAMAM dendrimers with nonpolar internal components have also been shown to induce hemolysis. | 6 | Supramolecular Chemistry |
Xylenol orange is an organic reagent, most commonly used as a tetrasodium salt as an indicator for metal titrations. When used for metal titrations, it will appear red in the titrand and become yellow once it reaches its endpoint. Historically, commercial preparations of it have been notoriously impure, sometimes consisting of as little as 20% xylenol orange, and containing large amounts of semi-xylenol orange and iminodiacetic acid. Purities as high as 90% are now available.
It is fluorescent, and has excitation maximums of 440 & 570 nm and an emission maximum of 610 nm. | 3 | Analytical Chemistry |
DnaA is a protein that activates initiation of DNA replication in bacteria. Based on the Replicon Model, a positively active initiator molecule contacts with a particular spot on a circular chromosome called the replicator to start DNA replication. It is a replication initiation factor which promotes the unwinding of DNA at oriC. The DnaA proteins found in all bacteria engage with the DnaA boxes to start chromosomal replication. In addition to the DnaA protein, its concentration, binding to DnaA-boxes, and binding of ATP or ADP, we will cover the regulation of the DnaA gene, the unique characteristics of the DnaA gene expression, promoter strength, and translation efficiency. The onset of the initiation phase of DNA replication is determined by the concentration of DnaA. DnaA accumulates during growth and then triggers the initiation of replication. Replication begins with active DnaA binding to 9-mer (9-bp) repeats upstream of oriC. Binding of DnaA leads to strand separation at the 13-mer repeats. This binding causes the DNA to loop in preparation for melting open by the helicase DnaB. | 1 | Biochemistry |
Imaging of biophotons from leaves has been used as a method for assaying R gene responses. These genes and their associated proteins are responsible for pathogen recognition and activation of defense signaling networks leading to the hypersensitive response, which is one of the mechanisms of the resistance of plants to pathogen infection. It involves the generation of reactive oxygen species (ROS), which have crucial roles in signal transduction or as toxic agents leading to cell death.
Biophotons have been also observed in the roots of stressed plants. In healthy cells, the concentration of ROS is minimized by a system of biological antioxidants. However, heat shock and other stresses changes the equilibrium between oxidative stress and antioxidant activity, for example, the rapid rise in temperature induces biophoton emission by ROS. | 1 | Biochemistry |
In this technique a square or rectangular paper is used. Here the sample is applied to one of the corners and development is performed at a right angle to the direction of the first run. | 3 | Analytical Chemistry |
Eva Smolková-Keulemansová, Weilová (27 April 1927 – 27 February 2024) was a survivor of Auschwitz, Neuengamme, and Bergen-Belsen concentration camps. After her liberation, she became a renowned Czech scientist and professor of analytical science at Charles University in Prague. | 3 | Analytical Chemistry |
The city of Oslo, Norway installed a system for converting domestic food waste to fuel in 2012. A thermal hydrolysis system produces biogas from the food waste, which provides fuel for the city bus system and is also used for agricultural fertilizer. | 7 | Physical Chemistry |
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