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Sickle cell disease can be treated in mice. The mice – which have essentially the same defect that causes human cases – used a viral vector to induce production of fetal hemoglobin (HbF), which normally ceases to be produced shortly after birth. In humans, the use of hydroxyurea to stimulate the production of HbF temporarily alleviates sickle cell symptoms. The researchers demonstrated this treatment to be a more permanent means to increase therapeutic HbF production.
A new gene therapy approach repaired errors in messenger RNA derived from defective genes. This technique has the potential to treat thalassaemia, cystic fibrosis and some cancers.
Researchers created liposomes 25 nanometers across that can carry therapeutic DNA through pores in the nuclear membrane. | 1 | Applied and Interdisciplinary Chemistry |
Trifluoroacetic acid, often used in these reductions, is a strong, corrosive acid. Some hydrosilanes are pyrophoric. | 0 | Theoretical and Fundamental Chemistry |
In Russia, starting from May 18, 2012, modafinil is Schedule II controlled substance. Being classified as a schedule II controlled substance in Russia means that it is seen as a drug with a high potential for abuse and dependence. This classification imposes strict regulations on the production, distribution, and use of modafinil. Possession of a few modafinil pills can lead to three to ten years imprisonment. Modafinil is not approved for medical use in Russia and cannot be bought even in pharmacies. It also cannot be imported from abroad, even if you have a prescription issued outside Russia. There are multiple cases of criminal proceedings initiated against Russian residents who tried to import modafinil by mail from abroad. | 0 | Theoretical and Fundamental Chemistry |
GCaMP consists of three key domains: an M13 domain at the N-terminus, a calmodulin (CaM) domain at the C-terminus, and a GFP domain in the center. The GFP domain is circularly permuted such that the native N- and C-termini are fused together by a six-amino-acid linking sequence, and the GFP sequence is split in the middle, creating new N- and C-termini that connect to the M13 and CaM domains.
In the absence of Ca, the GFP chromophore is exposed to water and exists in a protonated state with minimal fluorescence intensity. Upon Ca binding, the CaM domain undergoes a conformational change and tightly binds to the M13 domain alpha helix, preventing water molecules from accessing the chromophore. As a result, the chromophore rapidly deprotonates and converts into an anionic form that fluoresces brightly, similar to native GFP. | 1 | Applied and Interdisciplinary Chemistry |
A variety of supramolecular polymers can be synthesized by using monomers with host-guest complementary binding motifs, such as crown ethers/ammonium ions, cucurbiturils/viologens, calixarene/viologens, cyclodextrins/adamantane derivatives, and pillar arene/imidazolium derivatives [30–33]. When the monomers are "heteroditopic", supramolecular copolymers results, provided the monomers does not homopolymerize. Akira Harada was one of the firstwhorecognize the importance of combining polymers and cyclodextrins. Feihe Huang showed an example of supramolecular alternating copolymer from two heteroditopic monomers carrying both crown ether and ammonium ion termini. Takeharo Haino demonstrated an extreme example of sequence control in supramolecular copolymer, where three heteroditopic monomers are arranged in an ABC sequence along the copolymer chain. The design strategy utilizing three distinct binding interactions; ball-and-socket (calix[5]arene/C60), donor-acceptor (bisporphyrin/trinitrofluorenone), and Hamilton's H-bonding interactions is the key to attain a high orthogonality to form an ABC supramolecular terpolymer. | 0 | Theoretical and Fundamental Chemistry |
A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time. These basins are also called dry ponds, holding ponds or dry detention basins if no permanent pool of water exists.
Detention ponds that are designed to permanently retain some volume of water at all times are called retention basins. In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality, unless it includes a permanent pool feature. | 1 | Applied and Interdisciplinary Chemistry |
No truly smooth surfaces really exist, and surface imperfections are visible under a microscope. As a result, when two bodies are pressed together, contact is only performed in a finite number of points, separated by relatively large gaps, as can be shown in Fig. 2. Since the actual contact area is reduced, another resistance for heat flow exists. The gases/fluids filling these gaps may largely influence the total heat flow across the interface. The thermal conductivity of the interstitial material and its pressure, examined through reference to the Knudsen number, are the two properties governing its influence on contact conductance, and thermal transport in heterogeneous materials in general.
In the absence of interstitial materials, as in a vacuum, the contact resistance will be much larger, since flow through the intimate contact points is dominant. | 0 | Theoretical and Fundamental Chemistry |
Zinc (Zn), alongside Magnesium (Mg) and Iron (Fe), constitutes one of the three families of biodegradable metals. Zinc, as an abundant trace element, ranks sixth among all the essential metallic elements crucial for sustaining life within the human body. Zinc exhibits an intermediate biodegradation rate, falling between that of Fe (relatively slow) and Mg (relatively high) which positions it as a promising material for use in biodegradable implants. | 1 | Applied and Interdisciplinary Chemistry |
With an FFT based spectrum analyzer, the frequency resolution is , the inverse of the time T over which the waveform is measured and Fourier transformed.
With Fourier transform analysis in a digital spectrum analyzer, it is necessary to sample the input signal with a sampling frequency that is at least twice the bandwidth of the signal, due to the Nyquist limit. A Fourier transform will then produce a spectrum containing all frequencies from zero to . This can place considerable demands on the required analog-to-digital converter and processing power for the Fourier transform, making FFT based spectrum analyzers limited in frequency range. | 0 | Theoretical and Fundamental Chemistry |
Magnetic circular dichroism (MCD) is the differential absorption of left and right circularly polarized (LCP and RCP) light, induced in a sample by a strong magnetic field oriented parallel to the direction of light propagation. MCD measurements can detect transitions which are too weak to be seen in conventional optical absorption spectra, and it can be used to distinguish between overlapping transitions. Paramagnetic systems are common analytes, as their near-degenerate magnetic sublevels provide strong MCD intensity that varies with both field strength and sample temperature. The MCD signal also provides insight into the symmetry of the electronic levels of the studied systems, such as metal ion sites. | 0 | Theoretical and Fundamental Chemistry |
RT-PCR can be used to diagnose genetic disease such as Lesch–Nyhan syndrome. This genetic disease is caused by a malfunction in the HPRT1 gene, which clinically leads to the fatal uric acid urinary stone and symptoms similar to gout. Analyzing a pregnant mother and a fetus for mRNA expression levels of HPRT1 will reveal if the mother is a carrier and if the fetus will likely to develop Lesch–Nyhan syndrome. | 1 | Applied and Interdisciplinary Chemistry |
A simple application of dimensional analysis to mathematics is in computing the form of the volume of an -ball (the solid ball in n dimensions), or the area of its surface, the -sphere: being an -dimensional figure, the volume scales as , while the surface area, being -dimensional, scales as . Thus the volume of the -ball in terms of the radius is , for some constant . Determining the constant takes more involved mathematics, but the form can be deduced and checked by dimensional analysis alone. | 1 | Applied and Interdisciplinary Chemistry |
Bimolecular reactions are highly dependent on the concentration of substrates. Therefore, when a supramolecular container encapsulates both reactants within its small cavity, the effective local concentration of the reactants is increased and, as a result of an entropic effect, the rate of the reaction is accelerated. That is to say an intramolecular reaction is faster than its corresponding intermolecular reaction.
Although high raise in effective concentration is observed, molecules that employ this mode of catalysis have tiny rate acceleration compared to that of enzymes. A proposed explanation is that in a container the substrates are not as tightly bound as in enzyme. The reagents have room to wiggle in a cavity and so the entropic effect might not be as important. Even in the case of enzymes, computational studies have shown that the entropic effect might also be overestimated.
Examples of molecules that work via this mechanism are Rebeks tennis ball and Fujitas octahedral complex. | 0 | Theoretical and Fundamental Chemistry |
Highly repetitive DNA consists of short stretches of DNA that are repeated many times in tandem (one after the other). The repeat segments are usually between 2 bp and 10 bp but longer ones are known. Highly repetitive DNA is rare in prokaryotes but common in eukaryotes, especially those with large genomes. It is sometimes called satellite DNA.
Most of the highly repetitive DNA is found in centromeres and telomeres (see above) and most of it is functional although some might be redundant. The other significant fraction resides in short tandem repeats (STRs; also called microsatellites) consisting of short stretches of a simple repeat such as ATC. There are about 350,000 STRs in the human genome and they are scattered throughout the genome with an average length of about 25 repeats.
Variations in the number of STR repeats can cause genetic diseases when they lie within a gene but most of these regions appear to be non-functional junk DNA where the number of repeats can vary considerably from individual to individual. This is why these length differences are used extensively in DNA fingerprinting. | 1 | Applied and Interdisciplinary Chemistry |
The c-ANCA antigen is specifically proteinase 3 (PR3). p-ANCA antigens include myeloperoxidase (MPO) and bacterial permeability increasing factor Bactericidal/permeability-increasing protein (BPI). Other antigens exist for c-ANCA (atypical), however many are as yet unknown. Classical p-ANCA occurs with antibodies directed to MPO. p-ANCA without nuclear extension occurs with antibodies to BPI, cathepsin G, elastase, lactoferrin and lysozyme. GS-ANA are antibodies directed to granulocyte specific nuclear antigens. Atypical ANCA are thought to be antigens similar to that of the p-ANCAs, however may occur due to differences in neutrophil processing.
Other less common antigens include HMG1 (p-ANCA pattern), HMG2 (p-ANCA pattern), alpha enolase (p and c-ANCA pattern), catalase (p and c-ANCA pattern), beta glucuronidase (p-ANCA pattern), azurocidin (p and c-ANCA pattern), actin (p and a-ANCA) and h-lamp-2 (c-ANCA). | 1 | Applied and Interdisciplinary Chemistry |
Electrons that are bound in atoms, molecules and solids each occupy distinct states of well-defined binding energies. When light quanta deliver more than this amount of energy to an individual electron, the electron may be emitted into free space with excess (kinetic) energy that is higher than the electron's binding energy. The distribution of kinetic energies thus reflects the distribution of the binding energies of the electrons in the atomic, molecular or crystalline system: an electron emitted from the state at binding energy is found at kinetic energy . This distribution is one of the main characteristics of the quantum system, and can be used for further studies in quantum chemistry and quantum physics. | 0 | Theoretical and Fundamental Chemistry |
Synthesis for a standard β-blocker begins with the mono-alkylation of catechol to give an ether (see figure 4).
The fundamental step, and usually the last, in the synthesis of β-blockers consists of adding a propanolamine side chain. This can be done following two paths which both involve alkylation of an appropriate phenoxide with epichlorohydrin (ECH). The first way is shown as the upper way in figure 5. It consists of phenoxide reacting at the oxirane and resulting in an alkoxide, that displaces the adjacent chloride to form a new epoxide ring. The second way is shown as the lower route in figure 5. It consists of displacement of the halogen directly with a S2 reaction to give the same glycidic ether. When following both pathways, the central chiral carbon preserves its configuration, which is an important part to consider when synthesizing enantiomerically defined drugs. The ring opening of the epoxide ring in glycidic ether is done with an appropriate amine, such as isopropyl amine or tert-butylamine, and leads to the aryloxypropanolamine compound that consist of a secondary amine. This amine is typically known as the structural requirement for the β-adrenergic blocking activity. | 1 | Applied and Interdisciplinary Chemistry |
While application of inorganic nanoparticles in bionanotechnology shows encouraging advancements from a materials science perspective, the use of such materials in vivo is limited by issues related with toxicity, biodistribution and bioaccumulation. Because metal inorganic nanoparticle systems degrade into their constituent metal atoms, challenges may arise from the interactions of these materials with biosystems, and a considerable amount of the particles may remain in the body after treatment, leading to buildup of metal particles potentially resulting in toxicity.
Recently, however, some studies have shown that certain nanoparticle environmental toxicity effects aren't apparent until nanoparticles undergo transformations to release free metal ions. Under aerobic and anaerobic conditions, it was found that copper, silver, and titanium nanoparticles released low or insignificant levels of metal ions. This is evidence that copper, silver, and titanium NP are slow to release metal ions, and may therefore appear at low levels in the environment. Additionally, nanoshell coatings significantly protect against degradation in the cellular environment and also reduce QDs toxicity by reducing metal ion leakage from the core. | 0 | Theoretical and Fundamental Chemistry |
Drug discovery is the process by which potential drugs are discovered or designed. In the past, most drugs have been discovered either by isolating the active ingredient from traditional remedies or by serendipitous discovery. Modern biotechnology often focuses on understanding the metabolic pathways related to a disease state or pathogen, and manipulating these pathways using molecular biology or biochemistry. A great deal of early-stage drug discovery has traditionally been carried out by universities and research institutions.
Drug development refers to activities undertaken after a compound is identified as a potential drug in order to establish its suitability as a medication. Objectives of drug development are to determine appropriate formulation and dosing, as well as to establish safety. Research in these areas generally includes a combination of in vitro studies, in vivo studies, and clinical trials. The cost of late stage development has meant it is usually done by the larger pharmaceutical companies. The pharmaceuticals and biotechnology industry spends more than 15% of its net sales for Research & Development which is in comparison with other industries by far the highest share.
Often, large multinational corporations exhibit vertical integration, participating in a broad range of drug discovery and development, manufacturing and quality control, marketing, sales, and distribution. Smaller organizations, on the other hand, often focus on a specific aspect such as discovering drug candidates or developing formulations. Often, collaborative agreements between research organizations and large pharmaceutical companies are formed to explore the potential of new drug substances. More recently, multi-nationals are increasingly relying on contract research organizations to manage drug development. | 1 | Applied and Interdisciplinary Chemistry |
Soon after the publication of Libbys 1949 paper in Science', universities around the world began establishing radiocarbon-dating laboratories, and by the end of the 1950s there were more than 20 active research laboratories. It quickly became apparent that the principles of radiocarbon dating were valid, despite certain discrepancies, the causes of which then remained unknown.
The development of radiocarbon dating has had a profound impact on archaeologyoften described as the "radiocarbon revolution". In the words of anthropologist R. E. Taylor, " data made a prehistory possible by contributing a time scale that transcends local, regional and continental boundaries". It provides more accurate dating within sites than previous methods, which usually derived either from stratigraphy or from typologies (e.g. of stone tools or pottery); it also allows comparison and synchronization of events across great distances. The advent of radiocarbon dating may even have led to better field methods in archaeology since better data recording leads to a firmer association of objects with the samples to be tested. These improved field methods were sometimes motivated by attempts to prove that a date was incorrect. Taylor also suggests that the availability of definite date information freed archaeologists from the need to focus so much of their energy on determining the dates of their finds, and led to an expansion of the questions archaeologists were willing to research. For example, from the 1970s questions about the evolution of human behaviour were much more frequently seen in archaeology.
The dating framework provided by radiocarbon led to a change in the prevailing view of how innovations spread through prehistoric Europe. Researchers had previously thought that many ideas spread by diffusion through the continent, or by invasions of peoples bringing new cultural ideas with them. As radiocarbon dates began to prove these ideas wrong in many instances, it became apparent that these innovations must sometimes have arisen locally. This has been described as a "second radiocarbon revolution", and with regard to British prehistory, archaeologist Richard Atkinson has characterized the impact of radiocarbon dating as "radical[...] therapy" for the "progressive disease of invasionism". More broadly, the success of radiocarbon dating stimulated interest in analytical and statistical approaches to archaeological data. Taylor has also described the impact of AMS, and the ability to obtain accurate measurements from very small samples, as ushering in a third radiocarbon revolution.
Occasionally, radiocarbon dating techniques date an object of popular interest, for example, the Shroud of Turin, a piece of linen cloth thought by some to bear an image of Jesus Christ after his crucifixion. Three separate laboratories dated samples of linen from the Shroud in 1988; the results pointed to 14th-century origins, raising doubts about the shroud's authenticity as an alleged 1st-century relic.
Researchers have studied other isotopes created by cosmic rays to determine if they could also be used to assist in dating objects of archaeological interest; such isotopes include Helium-3|, Beryllium-10|, Neon-21|, Aluminium-26|, and Chlorine-36|. With the development of AMS in the 1980s it became possible to measure these isotopes precisely enough for them to be the basis of useful dating techniques, which have been primarily applied to dating rocks. Naturally occurring radioactive isotopes can also form the basis of dating methods, as with potassium–argon dating, argon–argon dating, and uranium series dating. Other dating techniques of interest to archaeologists include thermoluminescence, optically stimulated luminescence, electron spin resonance, and fission track dating, as well as techniques that depend on annual bands or layers, such as dendrochronology, tephrochronology, and varve chronology. | 0 | Theoretical and Fundamental Chemistry |
Ehrlich joined the Institute of Experimental Therapy (Institut für experimentelle Therapie) at Frankfurt am Main, Germany, in 1899, becoming the director of its research institute the Georg–Speyer Haus in 1906. Here his research focused on testing arsenical dyes for killing microbes. Arsenic was an infamous poison, and his attempt was criticised. He was publicly lampooned as an imaginary "Dr Phantasus". But Ehrlichs rationale was that the chemical structure called side chain forms antibodies that bind to toxins (such as pathogens and their products); similarly, chemical dyes such as arsenic compounds could also produce such side chains to kill the same microbes. This led him to propose a new concept called "side-chain theory". (Later in 1900, he revised his concept as "receptor theory".) Based on his new theory, he postulated that in order to kill microbes, "wir müssen chemisch zielen lernen'" ("we have to learn how to aim chemically").
His institute was convenient as it was adjacent to a dye factory. He began testing a number of compounds against different microbes. It was during his research that he coined the terms "chemotherapy" and "magic bullet". Although he used the German word zauberkugel in his earlier writings, the first time he introduced the English term "magic bullet" was at a Harben Lecture in London in 1908. By 1901, with the help of Japanese microbiologist Kiyoshi Shiga, Ehrlich experimented with hundreds of dyes on mice infected with trypanosome, a protozoan parasite that causes sleeping sickness. In 1904 they successfully prepared a red azo dye they called Trypan Red for the treatment of sleeping sickness. | 1 | Applied and Interdisciplinary Chemistry |
The competition between orientation produced by surface anchoring and by electric field effects is often exploited in liquid crystal devices. Consider the case in which liquid crystal molecules are aligned parallel to the surface and an electric field is applied perpendicular to the cell. At first, as the electric field increases in magnitude, no change in alignment occurs. However at a threshold magnitude of electric field, deformation occurs. Deformation occurs where the director changes its orientation from one molecule to the next. The occurrence of such a change from an aligned to a deformed state is called a Fréedericksz transition and can also be produced by the application of a magnetic field of sufficient strength.
The Fréedericksz transition is fundamental to the operation of many liquid crystal displays because the director orientation (and thus the properties) can be controlled easily by the application of a field. | 0 | Theoretical and Fundamental Chemistry |
Vanadium is often purified from aqueous extracts of slags and ore by selective precipitation of ammonium metavanadate. The material is then roasted to give vanadium pentoxide:
:2 NHVO → VO + 2 NH + HO | 0 | Theoretical and Fundamental Chemistry |
In the winter of 1856–57, Dirichlet found some solutions of Euler equations and he presented those in his lectures on partial differential equations in July 1857 and published the results in the same month. His work was left unfinished at his sudden death in 1859, but his notes were collated and published by Richard Dedekind posthumously in 1860.
Bernhard Riemann said, "In his posthumous paper, edited for publication by Dedekind, Dirichlet has opened up, in a most remarkable way, an entirely new avenue for investigations on the motion of a self-gravitating homogeneous ellipsoid. The further development of his beautiful discovery has a particular interest to the mathematician even apart from its relevance to the forms of heavenly bodies which initially instigated these investigations." | 1 | Applied and Interdisciplinary Chemistry |
The LHCGRs become desensitized when exposed to LH for some time. A key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic) receptor domain by protein kinases. This process uncouples Gs protein from the LHCGR. | 1 | Applied and Interdisciplinary Chemistry |
The three TET genes are expressed as different isoforms, including at least two isoforms of TET1, three of TET2 and three of TET3. Different isoforms of the TET genes are expressed in different cells and tissues. The full-length canonical TET1 isoform appears virtually restricted to early embryos, embryonic stem cells and primordial germ cells (PGCs). The dominant TET1 isoform in most somatic tissues, at least in the mouse, arises from alternative promoter usage which gives rise to a short transcript and a truncated protein designated TET1s. The three isoforms of TET2 arise from different promoters. They are expressed and active in embryogenesis and differentiation of hematopoietic cells. The isoforms of TET3 are the full length form TET3FL, a short form splice variant TET3s, and a form that occurs in oocytes designated TET3o. TET3o is created by alternative promoter use and contains an additional first N-terminal exon coding for 11 amino acids. TET3o only occurs in oocytes and the one cell stage of the zygote and is not expressed in embryonic stem cells or in any other cell type or adult mouse tissue tested. Whereas TET1 expression can barely be detected in oocytes and zygotes, and TET2 is only moderately expressed, the TET3 variant TET3o shows extremely high levels of expression in oocytes and zygotes, but is nearly absent at the 2-cell stage. It appears that TET3o, high in oocytes and zygotes at the one cell stage, is the major TET enzyme utilized when almost 100% rapid demethylation occurs in the paternal genome just after fertilization and before DNA replication begins (see DNA demethylation). | 1 | Applied and Interdisciplinary Chemistry |
Air or other gas dissolved in the fluid it can come out of solution as small bubbles (entrained air). If these small bubbles have sufficient buoyancy, they can rise to the surface and together form foam. Mechanical factors that may generate entrapped air:
* Leaky seals on pumps
* High pressure pumps
* Poor system design (tank, pump inlet, outlet and manifold design)
* Pressure release | 0 | Theoretical and Fundamental Chemistry |
Convergence of the Stokes expansion was first proved by for the case of small-amplitude waves – on the free surface of a fluid of infinite depth. This was extended shortly afterwards by for the case of finite depth and small-amplitude waves.
Near the end of the 20th century, it was shown that for finite-amplitude waves the convergence of the Stokes expansion depends strongly on the formulation of the periodic wave problem. For instance, an inverse formulation of the periodic wave problem as used by Stokes – with the spatial coordinates as a function of velocity potential and stream function – does not converge for high-amplitude waves. While other formulations converge much more rapidly, e.g. in the Eulerian frame of reference (with the velocity potential or stream function as a function of the spatial coordinates). | 1 | Applied and Interdisciplinary Chemistry |
The idea of sequence quality scores can be traced back to the original description of the SCF file format by Staden's group in 1992. In 1995, Bonfield and Staden proposed a method to use base-specific quality scores to improve the accuracy of consensus sequences in DNA sequencing projects.
However, early attempts to develop base-specific quality scores had only limited success.
The first program to develop accurate and powerful base-specific quality scores was the program Phred. Phred was able to calculate highly accurate quality scores that were logarithmically linked to the error probabilities. Phred was quickly adopted by all the major genome sequencing centers as well as many other laboratories; the vast majority of the DNA sequences produced during the Human Genome Project were processed with Phred.
After Phred quality scores became the required standard in DNA sequencing, other manufacturers of DNA sequencing instruments, including Li-Cor and ABI, developed similar quality scoring metrics for their base calling software. | 1 | Applied and Interdisciplinary Chemistry |
Post-Irradiation Examination (PIE) is the study of used nuclear materials such as nuclear fuel. It has several purposes. It is known that by examination of used fuel that the failure modes which occur during normal use (and the manner in which the fuel will behave during an accident) can be studied. In addition information is gained which enables the users of fuel to assure themselves of its quality and it also assists in the development of new fuels. After major accidents the core (or what is left of it) is normally subject to PIE to find out what happened. One site where PIE is done is the ITU which is the EU centre for the study of highly radioactive materials.
Materials in a high-radiation environment (such as a reactor) can undergo unique behaviors such as swelling and non-thermal creep. If there are nuclear reactions within the material (such as what happens in the fuel), the stoichiometry will also change slowly over time. These behaviors can lead to new material properties, cracking, and fission gas release.
The thermal conductivity of uranium dioxide is low; it is affected by porosity and burn-up. The burn-up results in fission products being dissolved in the lattice (such as lanthanides), the precipitation of fission products such as palladium, the formation of fission gas bubbles due to fission products such as xenon and krypton and radiation damage of the lattice. The low thermal conductivity can lead to overheating of the center part of the pellets during use. The porosity results in a decrease in both the thermal conductivity of the fuel and the swelling which occurs during use.
According to the International Nuclear Safety Center the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations.
The bulk density of the fuel can be related to the thermal conductivity.
Where ρ is the bulk density of the fuel and ρ is the theoretical density of the uranium dioxide.
Then the thermal conductivity of the porous phase (K) is related to the conductivity of the perfect phase (K, no porosity) by the following equation. Note that s is a term for the shape factor of the holes.
:K = K(1 − p/1 + (s − 1)p)
Rather than measuring the thermal conductivity using the traditional methods such as Lees disk, the Forbes method, or Searle's bar, it is common to use Laser Flash Analysis where a small disc of fuel is placed in a furnace. After being heated to the required temperature one side of the disc is illuminated with a laser pulse, the time required for the heat wave to flow through the disc, the density of the disc, and the thickness of the disk can then be used to calculate and determine the thermal conductivity.
:λ = ρCα
*λ thermal conductivity
*ρ density
*C heat capacity
*α thermal diffusivity
If t is defined as the time required for the non illuminated surface to experience half its final temperature rise then.
:α = 0.1388 L/t
*L is the thickness of the disc
For details see K. Shinzato and T. Baba (2001). | 0 | Theoretical and Fundamental Chemistry |
In SEC, mass is not measured so much as the hydrodynamic volume of the polymer molecules, that is, how much space a particular polymer molecule takes up when it is in solution. However, the approximate molecular weight can be calculated from SEC data because the exact relationship between molecular weight and hydrodynamic volume for polystyrene can be found. For this, polystyrene is used as a standard. But the relationship between hydrodynamic volume and molecular weight is not the same for all polymers, so only an approximate measurement can be obtained.
Another drawback is the possibility of interaction between the stationary phase and the analyte. Any interaction leads to a later elution time and thus mimics a smaller analyte size.
When performing this method, the bands of the eluting molecules may be broadened. This can occur by turbulence caused by the flow of the mobile phase molecules passing through the molecules of the stationary phase. In addition, molecular thermal diffusion and friction between the molecules of the glass walls and the molecules of the eluent contribute to the broadening of the bands. Besides broadening, the bands also overlap with each other. As a result, the eluent usually gets considerably diluted. A few precautions can be taken to prevent the likelihood of the bands broadening. For instance, one can apply the sample in a narrow, highly concentrated band on the top of the column. The more concentrated the eluent is, the more efficient the procedure would be. However, it is not always possible to concentrate the eluent, which can be considered as one more disadvantage. | 1 | Applied and Interdisciplinary Chemistry |
Three successive generations of the same family all bearing the name Abraham Darby are renowned for their contributions to the development of the English iron industry. Their works at Coalbrookdale in Shropshire nurtured the start of improvements in metallurgy that allowed large-scale production of the iron that made the development of steam engines and railways possible, although their most notable innovation was The Iron Bridge. | 1 | Applied and Interdisciplinary Chemistry |
Plutonium normally has six allotropes and forms a seventh (zeta, ζ) under high temperature and a limited pressure range. to 19.86 g/cm. | 0 | Theoretical and Fundamental Chemistry |
While there are several configurations of SBRs, the basic process is similar. The installation consists of one or more tanks that can be operated as plug flow or completely mixed reactors. The tanks have a “flow through” system, with raw wastewater (influent) coming in at one end and treated water (effluent) flowing out the other. In systems with multiple tanks, while one tank is in settle/decant mode the other is aerating and filling. In some systems, tanks contain a section known as the bio-selector, which consists of a series of walls or baffles which direct the flow either from side to side of the tank or under and over consecutive baffles. This helps to mix the incoming influent and the returned activated sludge (RAS), beginning the biological digestion process before the liquor enters the main part of the tank. | 1 | Applied and Interdisciplinary Chemistry |
Use of mass spectrometry as a second component of an operando experiment allows for optical spectra to be obtained before obtaining a mass spectrum of the analytes. Electrospray ionization allows a wider range of substances to be analysed than other ionization methods, due to its ability to ionize samples without thermal degradation. In 2017, Prof. Frank Crespilho and coworks introduced a new approach to operando DEMS, aiming the enzyme activity evaluation by differential electrochemical mass spectrometry (DEMS). NAD-dependent alcohol dehydrogenase (ADH) enzymes for ethanol oxidation were investigated by DEMS. The broad mass spectra obtained under bioelectrochemical control and with unprecedented accuracy were used to provide new insight into the enzyme kinetics and mechanisms. | 0 | Theoretical and Fundamental Chemistry |
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a magnetic tunnel junction.
This article deals with the term as a measurement of a devices electrical sensitivity to light. In a charge-coupled device (CCD) or other photodetector, it is the ratio between the number of charge carriers collected at either terminal and the number of photons hitting the devices photoreactive surface. As a ratio, QE is dimensionless, but it is closely related to the responsivity, which is expressed in amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. For typical semiconductor photodetectors, QE drops to zero for photons whose energy is below the band gap. A photographic film typically has a QE of much less than 10%, while CCDs can have a QE of well over 90% at some wavelengths. | 0 | Theoretical and Fundamental Chemistry |
The third-generation of Glycoazodyes was first reported in 2015. These Glycoazodyes use an amido-ester linker. An amide group bonds the sugar to an n-alkane spacer, and the spacer is bonded to the dye through an ester group. | 0 | Theoretical and Fundamental Chemistry |
The side-chain of the nucleophilic residue performs covalent catalysis on the substrate. The lone pair of electrons present on the oxygen or sulfur attacks the electropositive carbonyl carbon. The 20 naturally occurring biological amino acids do not contain any sufficiently nucleophilic functional groups for many difficult catalytic reactions. Embedding the nucleophile in a triad increases its reactivity for efficient catalysis. The most commonly used nucleophiles are the hydroxyl (OH) of serine and the thiol/thiolate ion (SH/S) of cysteine. Alternatively, threonine proteases use the secondary hydroxyl of threonine, however due to steric hindrance of the side chains extra methyl group such proteases use their N'-terminal amide as the base, rather than a separate amino acid.
Use of oxygen or sulfur as the nucleophilic atom causes minor differences in catalysis. Compared to oxygen, sulfurs extra d orbital makes it larger (by 0.4 Å) and softer, allows it to form longer bonds (d and d by 1.3-fold), and gives it a lower pK (by 5 units). Serine is therefore more dependent than cysteine on optimal orientation of the acid-base triad members to reduce its pK in order to achieve concerted deprotonation with catalysis. The low pK' of cysteine works to its disadvantage in the resolution of the first tetrahedral intermediate as unproductive reversal of the original nucleophilic attack is the more favourable breakdown product. The triad base is therefore preferentially oriented to protonate the leaving group amide to ensure that it is ejected to leave the enzyme sulfur covalently bound to the substrate N-terminus. Finally, resolution of the acyl-enzyme (to release the substrate C-terminus) requires serine to be re-protonated whereas cysteine can leave as S. Sterically, the sulfur of cysteine also forms longer bonds and has a bulkier van der Waals radius and if mutated to serine can be trapped in unproductive orientations in the active site.
Very rarely, the selenium atom of the uncommon amino acid selenocysteine is used as a nucleophile. The deprotonated Se state is strongly favoured when in a catalytic triad. | 1 | Applied and Interdisciplinary Chemistry |
Bio-available nitrogen occurs in the ocean in several forms, including simple ionic forms such as nitrate (NO), nitrite (NO) and ammonium (NH), and more complex organic forms such as urea ((NH)CO). These forms are used by autotrophic phytoplankton to synthesise organic molecules such as amino acids (the building blocks of proteins). Grazing of phytoplankton by zooplankton and larger organisms transfers this organic nitrogen up the food chain and throughout the marine food-web.
When nitrogenous organic molecules are ultimately metabolised by organisms, they are returned to the water column as ammonium (or more complex molecules that are then metabolised to ammonium). This is known as regeneration, since the ammonium can be used by phytoplankton, and again enter the food-web. Primary production fuelled by ammonium in this way is thus referred to as regenerated production.
However, ammonium can also be oxidised to nitrate (via nitrite), by the process of nitrification. This is performed by different bacteria in two stages :
:::NH + O → NO + 3H + 2e
:::NO + HO → NO + 2H + 2e
Crucially, this process is believed to only occur in the absence of light (or as some other function of depth). In the ocean, this leads to a vertical separation of nitrification from primary production, and confines it to the aphotic zone. This leads to the situation whereby any nitrate in the water column must be from the aphotic zone, and must have originated from organic material transported there by sinking. Primary production fuelled by nitrate is, therefore, making use of a "fresh" nutrient source rather than a regenerated one. Production by nitrate is thus referred to as new production.
The figure at the head of this section illustrates this. Nitrate and ammonium are taken up by primary producers, processed through the food-web, and then regenerated as ammonium. Some of this return flux is released into the surface ocean (where it is available again for uptake), while some is returned at depth. The ammonium returned at depth is nitrified to nitrate, and ultimately mixed or upwelled into the surface ocean to repeat the cycle.
Consequently, the significance of new production lies in its connection to sinking material. At equilibrium, the export flux of organic material sinking into the aphotic zone is balanced by the upward flux of nitrate. By measuring how much nitrate is consumed by primary production, relative to that of regenerated ammonium, one should be able to estimate the export flux indirectly.
As an aside, the f-ratio can also reveal important aspects of local ecosystem function. High f-ratio values are typically associated with productive ecosystems dominated by large, eukaryotic phytoplankton (such as diatoms) that are grazed by large zooplankton (and, in turn, by larger organisms such as fish). By contrast, low f-ratio values are generally associated with low biomass, oligotrophic food webs consisting of small, prokaryotic phytoplankton (such as Prochlorococcus) which are kept in check by microzooplankton. | 0 | Theoretical and Fundamental Chemistry |
FRET-based probes can detect the presence of various molecules: the probe's structure is affected by small molecule binding or activity, which can turn the FRET system on or off. This is often used to detect anions, cations, small uncharged molecules, and some larger biomacromolecules as well. Similarly, FRET systems have been designed to detect changes in the cellular environment due to such factors as pH, hypoxia, or mitochondrial membrane potential. | 1 | Applied and Interdisciplinary Chemistry |
Macromolecular crystallography was preceded by the older field of small-molecule x-ray crystallography (for structures with less than a few hundred atoms). Small-molecule diffraction data extends to much higher resolution than feasible for macromolecules, and has a very clean mathematical relationship between the data and the atomic model. The residual, or R-factor, measures the agreement between the experimental data and the values back-calculated from the atomic model. For a well-determined small-molecule structure the R-factor is nearly as small as the uncertainty in the experimental data (well under 5%). Therefore, that one test by itself provides most of the validation needed, but a number of additional consistency and methodology checks are done by automated software as a requirement for small-molecule crystal structure papers submitted to the International Union of Crystallography (IUCr) journals such as Acta Crystallographica section B or C. Atomic coordinates of these small-molecule structures are archived and accessed through the Cambridge Structural Database (CSD) or the Crystallography Open Database (COD).
The first macromolecular validation software was developed around 1990, for proteins. It included Rfree cross-validation for model-to-data match, bond length and angle parameters for covalent geometry, and sidechain and backbone conformational criteria. For macromolecular structures, the atomic models are deposited in the Protein Data Bank (PDB), still the single archive of this data. The PDB was established in the 1970s at Brookhaven National Laboratory, moved in 2000 to the [http://www.rcsb.org/pdb RCSB] (Research Collaboration for Structural Biology) centered at Rutgers, and expanded in 2003 to become the [http://www.wwpdb.org/ wwPDB] (worldwide Protein Data Bank), with access sites added in Europe ([http://pdbe.org|PDBe]) and Asia ([http://www.pdbj.org|PDBj]), and with NMR data handled at the [http://www.bmrb.wisc.edu BioMagResBank (BMRB)] in Wisconsin.
Validation rapidly became standard in the field, with further developments described below. *Obviously needs expansion*
A large boost was given to the applicability of comprehensive validation for both x-ray and NMR as of February 1, 2008, when the worldwide Protein Data Bank (wwPDB) made mandatory the deposition of experimental data along with atomic coordinates. Since 2012 strong forms of validation have been in the process of being adopted for [http://www.wwpdb.org/validation.html wwPDB deposition] from recommendations of the wwPDB Validation Task Force committees for x-ray crystallography, for NMR, for SAXS (small-angle x-ray scattering), and for cryoEM (cryo-Electron Microscopy). | 1 | Applied and Interdisciplinary Chemistry |
There are two types of twinning that can occur during growth, accidental and ones where the twinned structure has lower energy.
In accidental growth twinning an atom joins a crystal face in a less than ideal position, forming a seed for growth of a twin. The original crystal and its twin then grow together and closely resemble each other. This is characteristic enough of certain minerals to suggest that it is thermodynamically or kinetically favored under conditions of rapid growth.
Different from these are twins found in nanoparticles such as the image here, these fivefold or decahedral nanoparticles being one of the most common. These cyclic twins occur as they are lower in energy at small sizes. For the five-fold case shown, there is a disclination along the common axis which leads to an additional strain energy. Balancing this there is a reduction in the surface free energy, in large part due to more (111) surface facets. In small nanoparticles the decahedral and a more complicated icosahedral structure (with twenty units) are lower energy, but at larger energies single crystals become lower energy. However, they do not have to transform into single crystals and can grow very large, and are known as fivelings, documented as early as 1831 by Gustav Rose; further drawings are available in the Atlas der Kristallformen, and see also the article on fiveling<nowiki/>s. | 0 | Theoretical and Fundamental Chemistry |
Industrial source waste can contain alpha, beta, neutron or gamma emitters. Gamma emitters are used in radiography while neutron emitting sources are used in a range of applications, such as oil well logging. | 0 | Theoretical and Fundamental Chemistry |
Dimethylcalcium is obtained by metathesis reaction of calcium bis(trimethylsilyl)amide and methyllithium in diethyl ether:
A well known organocalcium compound is (Cp)calcium(I). Bis(allyl)calcium was described in 2009. It forms in a metathesis reaction of allylpotassium and calcium iodide as a stable non-pyrophoric off-white powder:
The bonding mode is η. This compound is also reported to give access to an η polymeric (CaCHCHCH) compound.
The compound [(thf)Ca{μ-CH-1,3,5-Ph}Ca(thf)] also described in 2009 is an inverse sandwich compound with two calcium atoms at either side of an arene.
Olefins tethered to cyclopentadienyl ligands have been shown to coordinate to calcium(II), strontium(II), and barium(II):
Organocalcium compounds have been investigated as catalysts. | 0 | Theoretical and Fundamental Chemistry |
According to Rangan, an Australian concrete expert, the growing worldwide demand for concrete is a great opportunity for the development of geopolymer cements of all types, with their much lower tally of carbon dioxide .
Geopolymer cements do not rely on calcium carbonate as a key ingredient, and generate much less than Portland cement during manufacture, with claimed reductions in the range of 40% to 80-90% . Joseph Davidovits delivered the first paper on this subject in March 1993 at a symposium organized by the American Portland Cement Association, Chicago, Illinois.
This section compares the energy needs and emissions for regular Portland cement, rock-based geopolymer cements and fly ash-based geopolymer cements. The comparison proceeds between Portland cement and geopolymer cements with similar strength, i.e. average 40 MPa at 28 days. There have been several studies published on the subject that may be summarized in the following way:
Rock-based geopolymer cement manufacture involves:
* 70% by weight geological compounds (calcined at 700°C);
* blast furnace slag;
* alkali-silicate solution (industrial chemical, user-friendly).
The presence of blast furnace slag provides room-temperature hardening and increases the mechanical strength.
Energy needs
According to the US Portland Cement Association (2006), energy needs for Portland cement is commonly in the range of 4700 MJ/tonne. The calculation for rock-based geopolymer cement is performed considering that the blast furnace slags are available as a by-product from the steel industry (no additional energy needed), or must be manufactured (re-smelting from non granulated slag or from geological resources).
In the most favorable case — slag availability as a by-product — there is a reduction of 59% of the energy needs in the manufacture of rock-based geopolymer-cement in comparison with Portland cement. In the least favorable case —slag manufacture — the reduction reaches 43%.
emissions during manufacture
In the most favorable case — slag availability as by-product — there is a reduction of 80% of the emission during manufacture of rock-based geopolymer cement in comparison with Portland cement. In the least favorable case —slag manufacture — the reduction reaches 70%.
Fly ash-based cements Class F fly ashes
They do not require any further heat treatment. The calculation is therefore easier. One achieves emissions in the range of 0.09 to 0.25 tonnes of / 1 tonne of fly ash-based cement, i.e. emissions that are reduced in the range of 75 to 90%. | 0 | Theoretical and Fundamental Chemistry |
Several methods exist to rank electrophiles in order of reactivity and one of them is devised by Robert Parr with the electrophilicity index ω given as:
with the electronegativity and chemical hardness. This equation is related to the classical equation for electrical power:
where is the resistance (Ohm or Ω) and is voltage. In this sense the electrophilicity index is a kind of electrophilic power. Correlations have been found between electrophilicity of various chemical compounds and reaction rates in biochemical systems and such phenomena as allergic contact dermititis.
An electrophilicity index also exists for free radicals. Strongly electrophilic radicals such as the halogens react with electron-rich reaction sites, and strongly nucleophilic radicals such as the 2-hydroxypropyl-2-yl and tert-butyl radical react with a preference for electron-poor reaction sites. | 0 | Theoretical and Fundamental Chemistry |
Accurately measuring V̇O max involves a physical effort sufficient in duration and intensity to fully tax the aerobic energy system. In general clinical and athletic testing, this usually involves a graded exercise test in which exercise intensity is progressively increased while measuring:
* ventilation and
* oxygen and carbon dioxide concentration of the inhaled and exhaled air.
V̇O max is measured during a cardiopulmonary exercise test (CPX test). The test is done on a treadmill or cycle ergometer. In untrained subjects, V̇O max is 10% to 20% lower when using a cycle ergometer compared with a treadmill. However, trained cyclists' results on the cycle ergometer are equal to or even higher than those obtained on the treadmill.
The classic V̇O max, in the sense of Hill and Lupton (1923), is reached when oxygen consumption remains at a steady state ("plateau") despite an increase in workload. The occurrence of a plateau is not guaranteed and may vary by person and sampling interval, leading to modified protocols with varied results. | 1 | Applied and Interdisciplinary Chemistry |
In 1953, Paul Flory first classified polymerization as "step-growth polymerization" and "chain-growth polymerization". IUPAC recommends to further simplify "chain-growth polymerization" to "chain polymerization". It is a kind of polymerization where an active center (free radical or ion) is formed, and a plurality of monomers can be polymerized together in a short period of time to form a macromolecule having a large molecular weight. In addition to the regenerated active sites of each monomer unit, polymer growth will only occur at one (or possibly more) endpoint.
Many common polymers can be obtained by chain polymerization such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyvinyl acetate (PVA).
Typically, chain-growth polymerization can be understood with the chemical equation:
In this equation, P is the polymer while x represents degree of polymerization, * means active center of chain-growth polymerization, M is the monomer which will react with active center, and L may be a low-molar-mass by-product obtained during chain propagation. For most chain-growth polymerizations, there is no by-product L formed. However there are some exceptions, such as the polymerization of amino acid N-carboxyanhydrides to oxazolidine-2,5-diones.
This type of polymerization is described as "chain" or "chain-growth" because the reaction mechanism is a chemical chain reaction with an initiation step in which an active center is formed, followed by a rapid sequence of chain propagation steps in which the polymer molecule grows by addition of one monomer molecule to the active center in each step. The word "chain" here does not refer to the fact that polymer molecules form long chains. Some polymers are formed instead by a second type of mechanism known as step-growth polymerization without rapid chain propagation steps. | 0 | Theoretical and Fundamental Chemistry |
Crystalline material may be divided into single crystals, twin crystals, polycrystals, and crystal powder. In a single crystal, the arrangement of atoms, ions, or molecules is defined by a single crystal structure in one orientation. Twin crystals, on the other hand, consist of single-crystalline twin domains, which are aligned by twin laws and separated by domain walls.
Polycrystals are made of a large number of small single crystals, or crystallites, held together by thin layers of amorphous solid. Crystal powder is obtained by grinding crystals, resulting in powder particles, made up of one or more crystallites. Both polycrystals and crystal powder consist of many crystallites with varying orientation.
Crystal phases are defined as regions with the same crystal structure, irrespective of orientation or twinning. Single and twinned crystalline specimens therefore constitute individual crystal phases. Polycrystalline or crystal powder samples may consist of more than one crystal phase. Such a phase comprises all the crystallites in the sample with the same crystal structure.
Crystal phases can be identified by successfully matching suitable crystallographic parameters with their counterparts in database entries. Prior knowledge of the chemical composition of the crystal phase can be used to reduce the number of database entries to a small selection of candidate structures and thus simplify the crystal phase identification process considerably. | 0 | Theoretical and Fundamental Chemistry |
Hydrastine is an isoquinoline alkaloid which was discovered in 1851 by Alfred P. Durand. Hydrolysis of hydrastine yields hydrastinine, which was patented by Bayer as a haemostatic drug during the 1910s. It is present in Hydrastis canadensis (thus the name) and other plants of the family Ranunculaceae. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction
known as dissociation in the context of acid–base reactions. The chemical species HA is an acid that dissociates into , the conjugate base of the acid and a hydrogen ion, . The system is said to be in equilibrium when the concentrations of its components will not change over time, because both forward and backward reactions are occurring at the same rate.
The dissociation constant is defined by
: or
where quantities in square brackets represent the concentrations of the species at equilibrium. As a simple example for a weak acid with K = 10, log K is the exponent which is -5, so that pK = 5. And for acetic acid with K = 1.8 x 10, pK is close to 5. A higher K corresponds to a stronger acid which is more dissociated at equilibrium. For the more convenient logarithmic scale, a lower pK means a stronger acid. | 0 | Theoretical and Fundamental Chemistry |
Light is what algae primarily need for growth as it is the most limiting factor. Many companies are investing for developing systems and technologies for providing artificial light. One of them is OriginOil that has developed a Helix BioReactorTM that features a rotating vertical shaft with low-energy lights arranged in a helix pattern. Water temperature also influences the metabolic and reproductive rates of algae. Although most algae grow at low rate when the water temperature gets lower, the biomass of algal communities can get large due to the absence of grazing organisms. The modest increases in water current velocity may also affect rates of algae growth since the rate of nutrient uptake and boundary layer diffusion increases with current velocity.
Other than light and water, phosphorus, nitrogen, and certain micronutrients are also useful and essential in growing algae. Nitrogen and phosphorus are the two most significant nutrients required for algal productivity, but other nutrients such as carbon and silica are additionally required. Of the nutrients required, phosphorus is one of the most essential ones as it is used in numerous metabolic processes. The microalgae D. tertiolecta was analyzed to see which nutrient affects its growth the most. The concentrations of phosphorus (P), iron (Fe), cobalt (Co), zinc (Zn), manganese (Mn) and molybdenum (Mo), magnesium (Mg), calcium (Ca), silicon (Si) and sulfur (S) concentrations were measured daily using inductively coupled plasma (ICP) analysis. Among all these elements being measured, phosphorus resulted in the most dramatic decrease, with a reduction of 84% over the course of the culture. This result indicates that phosphorus, in the form of phosphate, is required in high amounts by all organisms for metabolism.
There are two enrichment media that have been extensively used to grow most species of algae: Walne medium and the Guillard's F/ medium. These commercially available nutrient solutions may reduce time for preparing all the nutrients required to grow algae. However, due to their complexity in the process of generation and high cost, they are not used for large-scale culture operations. Therefore, enrichment media used for mass production of algae contain only the most important nutrients with agriculture-grade fertilizers rather than laboratory-grade fertilizers. | 1 | Applied and Interdisciplinary Chemistry |
DNA nucleotides are held together with hydrogen bonds, which are relatively weak and can be easily broken. Base flipping occurs on a millisecond timescale by breaking the hydrogen bonds between bases and unstacking the base from its neighbors. The base is rotated out of the double helix by 180 degrees., typically via the major groove, and into the active site of an enzyme. This opening leads to small conformational changes in the DNA backbone which are quickly stabilized by the increased enzyme-DNA interactions. Studies looking at the free-energy profiles of base flipping have shown that the free-energy barrier to flipping can be lowered by 17 kcal/mol for M.HhaI in the closed conformation.
There are two mechanisms of DNA base flipping: active and passive. In the active mechanism, an enzyme binds to the DNA and then actively rotates the base, while in the passive mechanism a damaged base rotates out spontaneously first, then is recognized and bound by the enzyme. Research has demonstrated both mechanisms: uracil-DNA glycosylase follows the passive mechanism and Tn10 transposase follows the active mechanism.
Furthermore, studies have shown that DNA base flipping is used by many different enzymes in a variety biological processes such as DNA methylation, various DNA repair mechanisms, RNA transcription and DNA replication. | 1 | Applied and Interdisciplinary Chemistry |
An increasingly popular method of cleaning windows is the "water-fed pole" system. Instead of washing windows with conventional detergent, they are scrubbed with purified water, typically containing less than 10 ppm dissolved solids, using a brush on the end of a pole wielded from ground level. RO is commonly used to purify the water. | 0 | Theoretical and Fundamental Chemistry |
Kubista holds several positions and advisory roles within the scientific and biotechnology communities including: Roche, ThermoFisher, Qiagen, Bio-Rad, and RealSeq Biosciences. He is also a member of the Scientific Advisory Council of Genetic Engineering News.
Kubista has also been involved in the establishment of modern molecular diagnostics in developing countries. Since 1999, he has served as an advisor to UNESCO, providing guidance and assistance to countries such as: Libya, Egypt, Iran, Grenada, and Ghana.
Kubista is an expert advisor for the European Commission Research Directorate General. He also works as a special consultant in the Life Science field for AFRY and Pharma Relations. Kubista advises the United Nations Educational Scientific and Cultural Organization (UNESCO) and is part of the scientific advisory board for the International Biotechnology Research in Tripoli, Libya, under UNESCO. | 1 | Applied and Interdisciplinary Chemistry |
Boronic acid self-condensation or condensation with diols is a well-documented dynamic covalent reaction. The boronic acid condensation has the characteristic of forming two dynamic bonds with various substrates. This is advantageous when designing systems where high rigidity is desired, such as 3-D cages and COFs. | 0 | Theoretical and Fundamental Chemistry |
Introduction of too many siRNA can result in nonspecific events due to activation of innate immune responses. Most evidence to date suggests that this is probably due to activation of the dsRNA sensor PKR, although retinoic acid-inducible gene I (RIG-I) may also be involved. The induction of cytokines via toll-like receptor 7 (TLR7) has also been described. Chemical modification of siRNA is employed to reduce in the activation of the innate immune response for gene function and therapeutic applications. One promising method of reducing the nonspecific effects is to convert the siRNA into a microRNA. MicroRNAs occur naturally, and by harnessing this endogenous pathway it should be possible to achieve similar gene knockdown at comparatively low concentrations of resulting siRNAs. This should minimize nonspecific effects. | 1 | Applied and Interdisciplinary Chemistry |
A protein mimetic is a molecule such as a peptide, a modified peptide or any other molecule that biologically mimics the action or activity of some other protein.
Protein mimetics are commonly used in drug design and discovery. | 1 | Applied and Interdisciplinary Chemistry |
Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula . It is commonly abbreviated as LiHMDS or Li(HMDS) (lithium hexamethyldisilazide - a reference to its conjugate acid HMDS) and is primarily used as a strong non-nucleophilic base and as a ligand. Like many lithium reagents, it has a tendency to aggregate and will form a cyclic trimer in the absence of coordinating species. | 0 | Theoretical and Fundamental Chemistry |
The atomic beam is formed through a supersonic expansion, which is a standard technique used in helium atom scattering. The centreline of the gas is selected by a skimmer to form an atom beam with a narrow velocity distribution. The gas is then further collimated by a pinhole to form a narrow beam, which is typically between 1–10 μm. The use of a focusing element (such as a zone plate) allows beam spot sizes below 1 μm to be achieved, but currently still comes with low signal intensity.
The gas then scatters from the surface and is collected into a detector. In order to measure the flux of the neutral helium atoms, they must first be ionised. The inertness of helium that makes it a gentle probe means that it is difficult to ionise and therefore reasonably aggressive electron bombardment is typically used to create the ions. A mass spectrometer setup is then used to select only the helium ions for detection.
Once the flux from a specific part of the surface is collected, the sample is moved underneath the beam to generate an image. By obtaining the value of the scattered flux across a grid of positions, then values can then be converted to an image.
The observed contrast in helium images has typically been dominated by the variation in topography of the sample. Typically, since the wavelength of the atom beam is small, surfaces appear extremely rough to the incoming atom beam. Therefore, the atoms are diffusely scattered and roughly follow Knudsens Law [citation?] (the atom equivalent of Lamberts cosine law in optics). However, more recently work has begun to see divergence from diffuse scattering due to effects such as diffraction and chemical contrast effects. However, the exact mechanisms for forming contrast in a helium microscope is an active field of research. Most cases have some complex combination of several contrast mechanisms making it difficult to disentangle the different contributions.
Combinations of images from multiple perspectives allows stereophotogrammetry to produce partial three dimensional images, especially valuable for biological samples subject to degradation in electron microscopes. | 0 | Theoretical and Fundamental Chemistry |
Because water molecules absorb microwaves and other radio wave frequencies, water in the atmosphere attenuates radar signals. In addition, atmospheric water will reflect and refract signals to an extent that depends on whether it is vapor, liquid or solid.
Generally, radar signals lose strength progressively the farther they travel through the troposphere. Different frequencies attenuate at different rates, such that some components of air are opaque to some frequencies and transparent to others. Radio waves used for broadcasting and other communication experience the same effect.
Water vapor reflects radar to a lesser extent than do water's other two phases. In the form of drops and ice crystals, water acts as a prism, which it does not do as an individual molecule; however, the existence of water vapor in the atmosphere causes the atmosphere to act as a giant prism.
A comparison of GOES-12 satellite images shows the distribution of atmospheric water vapor relative to the oceans, clouds and continents of the Earth. Vapor surrounds the planet but is unevenly distributed. The image loop on the right shows monthly average of water vapor content with the units are given in centimeters, which is the precipitable water or equivalent amount of water that could be produced if all the water vapor in the column were to condense. The lowest amounts of water vapor (0 centimeters) appear in yellow, and the highest amounts (6 centimeters) appear in dark blue. Areas of missing data appear in shades of gray. The maps are based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on NASA's Aqua satellite. The most noticeable pattern in the time series is the influence of seasonal temperature changes and incoming sunlight on water vapor. In the tropics, a band of extremely humid air wobbles north and south of the equator as the seasons change. This band of humidity is part of the Intertropical Convergence Zone, where the easterly trade winds from each hemisphere converge and produce near-daily thunderstorms and clouds. Farther from the equator, water vapor concentrations are high in the hemisphere experiencing summer and low in the one experiencing winter. Another pattern that shows up in the time series is that water vapor amounts over land areas decrease more in winter months than adjacent ocean areas do. This is largely because air temperatures over land drop more in the winter than temperatures over the ocean. Water vapor condenses more rapidly in colder air.
As water vapor absorbs light in the visible spectral range, its absorption can be used in spectroscopic applications (such as DOAS) to determine the amount of water vapor in the atmosphere. This is done operationally, e.g. from the Global Ozone Monitoring Experiment (GOME) spectrometers on ERS (GOME) and MetOp (GOME-2). The weaker water vapor absorption lines in the blue spectral range and further into the UV up to its dissociation limit around 243 nm are mostly based on quantum mechanical calculations and are only partly confirmed by experiments. | 1 | Applied and Interdisciplinary Chemistry |
Adverse respiratory health effects are associated with occupancy in buildings with moisture and mold damage. Infants may develop respiratory symptoms due to exposure to a specific type of fungal mold, called Penicillium. Signs that an infant may have mold-related respiratory problems include (but are not limited to) a persistent cough and wheeze. Increased exposure increases the probability of developing respiratory symptoms during their first year of life. Studies have shown that a correlation exists between the probability of developing asthma and increased exposure to Penicillium. The levels are deemed no mold to low level, from low to intermediate, and intermediate to high. Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.
Mold exposures have a variety of health effects depending on the person. Some people are more sensitive to mold than others. Exposure to mold can cause several health issues such as; throat irritation, nasal stuffiness, eye irritation, cough, and wheezing, as well as skin irritation in some cases. Exposure to mold may also cause heightened sensitivity depending on the time and nature of exposure. People at higher risk for mold allergies are people with chronic lung illnesses and weak immune systems, which can often result in more severe reactions when exposed to mold.
There has been sufficient evidence that damp indoor environments are correlated with upper respiratory tract symptoms such as coughing, and wheezing in people with asthma. | 1 | Applied and Interdisciplinary Chemistry |
Tang's research interests encompass photocatalytic/thermocatalytic small molecule activation (e.g. CH, N, HO, CH and CO) and microwave catalysis (e.g. plastic recycling), together with the investigation of the underlying charge dynamics and kinetics by state-of-the-art spectroscopies. According to Google Scholar, these research activities result into >250 journal papers in reputable journals. | 0 | Theoretical and Fundamental Chemistry |
If the rate constants for the following reaction are and ; , then the rate equation is:
:For reactant A:
:For reactant B:
:For product C:
With the individual concentrations scaled by the total population of reactants to become probabilities, linear systems of differential equations such as these can be formulated as a master equation. The differential equations can be solved analytically and the integrated rate equations are
The steady state approximation leads to very similar results in an easier way. | 0 | Theoretical and Fundamental Chemistry |
Discovered in 1937 by Robin Hill, Hill reagents allowed the discovery of electron transport chains during photosynthesis.
These are dyes that act as artificial electron acceptors, changing color when they are reduced.
An example of a Hill reagent is 2,6-dichlorophenolindophenol (DCPIP). | 0 | Theoretical and Fundamental Chemistry |
This research, published in 2017, aimed to solve the solar neutrino and antineutrino flux for extremely low energies (keV range). Processes at these low energies consisted vital information that told researchers about the solar metallicity. Solar metallicity is the measure of elements present in the particle that are heavier than hydrogen and helium, typically in this field this element is usually iron. The results from this research yielded significantly different findings compared to past research in terms of the overall flux spectrum. Currently technology does not yet exist to put these findings to the test. | 0 | Theoretical and Fundamental Chemistry |
In 1980 Ferguson-Miller et al. at Michigan State developed n-dodecyl-β--maltopyranoside (DDM) as part of a successful effort to purify an active, stable, monodisperse form of cytochrome c oxidase. Maltosides have been used extensively to stabilize membrane proteins for biophysical and structural studies. | 1 | Applied and Interdisciplinary Chemistry |
Protein chemical shift re-referencing is a post-assignment process of adjusting the assigned NMR chemical shifts to match IUPAC and BMRB recommended standards in protein chemical shift referencing. In NMR chemical shifts are normally referenced to an internal standard that is dissolved in the NMR sample. These internal standards include tetramethylsilane (TMS), 4,4-dimethyl-4-silapentane-1-sulfonic acid (DSS) and trimethylsilyl propionate (TSP). For protein NMR spectroscopy the recommended standard is DSS, which is insensitive to pH variations (unlike TSP). Furthermore, the DSS 1H signal may be used to indirectly reference 13C and 15N shifts using a simple ratio calculation [1]. Unfortunately, many biomolecular NMR spectroscopy labs use non-standard methods for determining the 1H, 13C or 15N “zero-point” chemical shift position. This lack of standardization makes it difficult to compare chemical shifts for the same protein between different laboratories. It also makes it difficult to use chemical shifts to properly identify or assign secondary structures or to improve their 3D structures via chemical shift refinement. Chemical shift re-referencing offers a means to correct these referencing errors and to standardize the reporting of protein chemical shifts across laboratories. | 0 | Theoretical and Fundamental Chemistry |
The Fukuyama synthesis (chiral (-), 2004) started from cyclic amine 1. Chirality was at some point introduced into this starting material by enzymatic resolution of one of the precursors. Acyloin 2 was formed by Rubottom oxidation and hydrolysis. Oxidative cleavage by lead acetate formed aldehyde 3, removal of the nosyl group (thiophenol / cesium carbonate) triggered an amine-carbonyl condensation with iminium ion 4 continuing to react in a transannular cyclization to diester 5 which could be converted to the Wieland-Gumlich aldehyde by known chemistry. | 0 | Theoretical and Fundamental Chemistry |
Some metering pumps can be used for dispensing. A metering pump is designed to deliver a continuous rate of flow, however, a dispensing pump is designed to deliver a precise total amount. | 1 | Applied and Interdisciplinary Chemistry |
The research on dnaA(Ts) mutants provided the first proof that the dnaA gene is autoregulated. DnaA protein is still produced at non-permissive temperatures where it is inactive, but in some mutants it can be made active again by returning to a temperature that is conducive to development. This reversible initiation capacity—which was larger than anticipated given the mass gain of the culture—could be seen in the absence of protein synthesis at the permissive temperature and suggested that the DnaA protein synthesis was derepressed at the high growth temperature. These results prompted a thorough investigation of the dnaA46 mutant under permissive, intermediate, and non-permissive development conditions. The studys findings revealed that as growth temperature increased, the DnaA46 proteins activity decreased, leading to progressively decreasing DNA and origin concentrations at intermediate temperatures. An increase in initiation capacity was seen concurrently with a decrease in DnaA protein activity. Hansen and Rasmussen (1977) argued that the DnaA protein had a positive effect in replication initiation aing transcripts entering the dnaA gene were found as a result of sequencing the dnaA promoter region and the dnaA gene. The DnaA promoter region has nine GATC sites within 225 base pairs, and a sequence that is similar to nd a negative role in its own synthesis based on these observations. Two promoters providrepetitions (DnaA-boxes) in the oriC region was found between the two promoters. According to several studies, the DnaA protein negatively regulates both promoters. In these research, it was discovered that the dnaA transcription was upregulated by 4- to 5-fold at non-permissive temperatures in dnaATs mutants and repressed by the same amount when DnaA protein was overproduced. The autoregulation of the dnaA gene requires the DnaA-box. The sequence of the dnaA2p promoter region has some intriguing characteristics that can be seen more clearly. This promoter contains two GATC sites, one in the 10 sequence and the other in the 35 sequence, and both in vivo and in vitro, methylation increases transcription from this promoter by a factor of two. In addition, DnaA protein binds to regions upstream of the dnaA2p promoter with a high affinity. | 1 | Applied and Interdisciplinary Chemistry |
In order to study its potential as a cancer therapy target, Globo H has been synthesized in the laboratory. One synthesis is achieved by first building two trisaccharides from their component sugars, and then linking them. The trisaccharides, with most of their functional groups protected to prevent side reactions, are linked by creating the GalNAcβ(1-3)Gal bond. A thioethyl group is added to the 1 position on one of the protected galactose rings, and in the presence of methyl triflate, this reacts with the hydroxyl group on the 3 position of the other galactose to link the trisaccharides and form the hexasaccharide. The ceramide is added to the 1 position of the terminal glucose ring after hexasaccharide formation. | 1 | Applied and Interdisciplinary Chemistry |
The outer mitochondrial membrane, which encloses the entire organelle, is 60 to 75 angstroms (Å) thick. It has a protein-to-phospholipid ratio similar to that of the cell membrane (about 1:1 by weight). It contains large numbers of integral membrane proteins called porins. A major trafficking protein is the pore-forming voltage-dependent anion channel (VDAC). The VDAC is the primary transporter of nucleotides, ions and metabolites between the cytosol and the intermembrane space. It is formed as a beta barrel that spans the outer membrane, similar to that in the gram-negative bacterial outer membrane. Larger proteins can enter the mitochondrion if a signaling sequence at their N-terminus binds to a large multisubunit protein called translocase in the outer membrane, which then actively moves them across the membrane. Mitochondrial pro-proteins are imported through specialised translocation complexes.
The outer membrane also contains enzymes involved in such diverse activities as the elongation of fatty acids, oxidation of epinephrine, and the degradation of tryptophan. These enzymes include monoamine oxidase, rotenone-insensitive NADH-cytochrome c-reductase, kynurenine hydroxylase and fatty acid Co-A ligase. Disruption of the outer membrane permits proteins in the intermembrane space to leak into the cytosol, leading to cell death. The outer mitochondrial membrane can associate with the endoplasmic reticulum (ER) membrane, in a structure called MAM (mitochondria-associated ER-membrane). This is important in the ER-mitochondria calcium signaling and is involved in the transfer of lipids between the ER and mitochondria. Outside the outer membrane are small (diameter: 60 Å) particles named sub-units of Parson. | 1 | Applied and Interdisciplinary Chemistry |
The releases of fission products and uranium from uranium dioxide (from spent BWR fuel, burnup was 65 GWd t) which was heated in a Knudsen cell has been repeated. Fuel was heated in the Knudsen cell both with and without preoxidation in oxygen at c 650 K. It was found even for the noble gases that a high temperature was required to liberate them from the uranium oxide solid. For unoxidized fuel 2300 K was required to release 10% of the uranium while oxidized fuel only requires 1700 K to release 10% of the uranium.
According to the report on Chernobyl used in the above table 3.5% of the following isotopes in the core were released Np, Pu, Pu, Pu, Pu and Cm. | 0 | Theoretical and Fundamental Chemistry |
In intense light, plants use various mechanisms to prevent damage to their photosystems. They are able to release some light energy as heat, but the excess light can also produce reactive oxygen species. While some of these can be detoxified by antioxidants, the remaining oxygen species will be detrimental to the photosystems of the plant. More specifically, the D1 subunit in the reaction center of PSII can be damaged. Studies have found that deg1 proteins are involved in the degradation of these damaged D1 subunits. New D1 subunits can then replace these damaged D1 subunits in order to allow PSII to function properly again. | 0 | Theoretical and Fundamental Chemistry |
If it is the liver that cannot effectively transfer the indirect bilirubin into bilirubin glucuronide and further into bilirubin di-glucuronide, the consequence will be hyperbilirubinemia or intrahepatic (or hepatocellular) jaundice.
Moreover, the unconjugated hyperbilirubinemia arises in case the components of liver transfer the indirect bilirubin into bilirubin glucuronide in the rate slower than they should be. This condition is associated with either decreased uptake of bilirubin into hepatocytes (Rotor syndrome) or defective intracellular protein binding.
In similar fashion, the conjugated hyperbilirubinemia emerges in case the components of the liver have difficulty turning bilirubin glucuronide into bilirubin di-glucuronide. Note that biliary duct blockage can also lead to conjugated hyperbilirubinemia but the pathophysiology is that backflow of bilirubin di-glucuronide with little indirect bilirubin and bilirubin glucuronide from bile duct through liver into blood plasma. These conditions are associated with either defective intracellular protein binding (for the second time) or disturbed secretion into the bile canaliculi (Dubin–Johnson syndrome).
Liver failure and hepatitis are the most etiological in liver-genesis hyperbilirubinemia. In case of hyperbilirubinemia due to intrahepatic or extrahepatic bile ducts blockage, e.g. gallstone, the name is given as Post-hepatic (or obstructive) jaundice.
Bilirubin concentration is not a sensitive early indicator of liver diseases as the liver may have reserved its capacity in removal of bilirubin to save energy and unreserved the previously reserved capacity when encountering a sudden rise of unconjugated bilirubin. In short, there is still a chance for an ill liver to get rid of excessive unconjugated bilirubin in the blood plasma, displaying a total bilirubin level that is within normal reference range. | 1 | Applied and Interdisciplinary Chemistry |
Lignin is a highly crosslinked polymer that comprises the main structural material of higher plants. A hydrophobic material, it is derived from precursor monolignols. Heterogeneity arises from the diversity and degree of crosslinking between these lignols. | 0 | Theoretical and Fundamental Chemistry |
The carbonate pump is sometimes referred to as the “hard tissue” component of the biological pump. Some surface marine organisms, like coccolithophores, produce hard structures out of calcium carbonate, a form of particulate inorganic carbon, by fixing bicarbonate. This fixation of DIC is an important part of the oceanic carbon cycle.
Ca + 2 HCO → CaCO + CO + HO
While the biological carbon pump fixes inorganic carbon (CO) into particulate organic carbon in the form of sugar (CHO), the carbonate pump fixes inorganic bicarbonate and causes a net release of CO. In this way, the carbonate pump could be termed the carbonate counter pump. It works counter to the biological pump by counteracting the CO flux into the biological pump. | 0 | Theoretical and Fundamental Chemistry |
Potential flow does not include all the characteristics of flows that are encountered in the real world. Potential flow theory cannot be applied for viscous internal flows, except for flows between closely spaced plates. Richard Feynman considered potential flow to be so unphysical that the only fluid to obey the assumptions was "dry water" (quoting John von Neumann). Incompressible potential flow also makes a number of invalid predictions, such as dAlemberts paradox, which states that the drag on any object moving through an infinite fluid otherwise at rest is zero. More precisely, potential flow cannot account for the behaviour of flows that include a boundary layer. Nevertheless, understanding potential flow is important in many branches of fluid mechanics. In particular, simple potential flows (called elementary flows) such as the free vortex and the point source possess ready analytical solutions. These solutions can be superposed to create more complex flows satisfying a variety of boundary conditions. These flows correspond closely to real-life flows over the whole of fluid mechanics; in addition, many valuable insights arise when considering the deviation (often slight) between an observed flow and the corresponding potential flow. Potential flow finds many applications in fields such as aircraft design. For instance, in computational fluid dynamics, one technique is to couple a potential flow solution outside the boundary layer to a solution of the boundary layer equations inside the boundary layer. The absence of boundary layer effects means that any streamline can be replaced by a solid boundary with no change in the flow field, a technique used in many aerodynamic design approaches. Another technique would be the use of Riabouchinsky solids. | 1 | Applied and Interdisciplinary Chemistry |
In general, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans. An example of a small hydrocarbon displaying cis–trans isomerism is but-2-ene. 1,2-Dichlorocyclohexane is another example. | 0 | Theoretical and Fundamental Chemistry |
Processive enzymes are proteins that catalyze consecutive reactions without releasing its substrate. An example of processive enzymes is RNA polymerase which binds to a DNA strand and repeatedly catalyzes nucleotide transfers, effectively synthesizing a corresponding RNA strand.
Nolte and coworkers developed an artificial processive enzyme in a form of manganese porphyrin rotaxane that treads along a long polymer of alkene and catalyze multiple rounds of alkene epoxidation. Manganese (III) ion in the porphyrin is the molecule's catalytic center, capable of epoxidation in the presence of an oxygen donor and an activating ligand. With a small ligand such pyridine that binds manganese from inside the cavity of the rotaxane, epoxidation happens outside the catalyst. With a large bulky ligand such as tert-butyl pyridine that does not fit inside the cavity however, epoxidation happens on the inside of the catalyst. | 0 | Theoretical and Fundamental Chemistry |
The method was first described by Cunningham & Jones in 1993 for the analysis of dynamic PET data obtained in the brain. It assumes that the tissue impulse response function (IRF) can be described as a combination of many exponentials. Since A tissue TAC can be expressed as a convolution of measured arterial input function with IRF, C(t) can be expressed as:
where, is a convolution operator, C(t) is the bone tissue activity concentration of tracer (in units: MBq/ml) over a period of time t, C(t) is the plasma concentration of tracer (in units: MBq/ml) over a period of time t, IRF(t) is equal to the sum of exponentials, β values are fixed between 0.0001 sec and 0.1 sec in intervals of 0.0001, n is the number of α components that resulted from the analysis and β, β,..., β corresponds to the respective α, α,..., α components from the resulted spectrum. The values of α are then estimated from the analysis by fitting multi-exponential to the IRF. The intercept of the linear fit to the slow component of this exponential curve is considered the plasma clearance (K) to the bone mineral. | 1 | Applied and Interdisciplinary Chemistry |
# Excitatory synapse: Enhances the probability of depolarization in postsynaptic neurons and the initiation of an action potential.
# Inhibitory Synapse: Diminishes the probability of depolarization in postsynaptic neurons and the initiation of an action potential.
An influx of Na+ driven by excitatory neurotransmitters opens cation channels, depolarizing the postsynaptic membrane toward the action potential threshold. In contrast, inhibitory neurotransmitters cause the postsynaptic membrane to become less depolarized by opening either Cl- or K+ channels, reducing firing. Depending on their release location, the receptors they bind to, and the ionic circumstances they encounter, various transmitters can be either excitatory or inhibitory. For instance, acetylcholine can either excite or inhibit depending on the type of receptors it binds to. For example, glutamate serves as an excitatory neurotransmitter, in contrast to GABA, which acts as an inhibitory neurotransmitter. Additionally, dopaminergic is a neurotransmitter that exerts dual effects, displaying both excitatory and inhibitory impacts through binding to distinct receptors.
The membrane potential prevents Cl- from entering the cell, even when its concentration is much higher outside than inside. The resting potential for Cl- in many neurons is quite negative, nearly equal to the resting potential. Opening Cl- channels tends to buffer the membrane potential, but this effect is countered when the membrane starts to depolarize, allowing more negatively charged Cl- ions to enter the cell. Consequently, it becomes more difficult to depolarize the membrane and excite the cell when Cl- channels are open. Similar effects result from the opening of K+ channels. The significance of inhibitory neurotransmitters is evident from the effects of toxins that impede their activity. For instance, strychnine binds to glycine receptors, blocking the action of glycine and leading to muscle spasms, convulsions, and death. | 1 | Applied and Interdisciplinary Chemistry |
* Intracoronary Administration of Bone Marrow-Derived Progenitor Cells: an in vivo technique in which progenitor cells derived from bone marrow are administered into an infarct artery to differentiate into functional cardiac cells and recover contractile function after an acute, ST-elevation myocardial infarction, thus preventing adverse remodeling of the left ventricle.
* Human Cardiac Organoids:an in vitro, scaffold-free technique for producing a functioning cardiac organoid; cardiac spheroids made from a mixed cell population derived from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) cultured on gelatin-coated well plates, without a scaffold, resulted in the generation of a functioning cardiac organoid | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry, hydroxamic acids are a class of organic compounds having a general formula bearing the functional group , where R and R' are typically organyl groups (e.g., alkyl or aryl) or hydrogen. They are amides () wherein the nitrogen atom has a hydroxyl () substituent. They are often used as metal chelators.
Common example of hydroxamic acid is aceto-N-methylhydroxamic acid (). Some uncommon examples of hydroxamic acids are formo-N-chlorohydroxamic acid () and chloroformo-N-methylhydroxamic acid (). | 0 | Theoretical and Fundamental Chemistry |
The advantages of supercritical fluid extraction (compared with liquid extraction) are that it is relatively rapid because of the low viscosities and high diffusivities associated with supercritical fluids. Alternative solvents to supercritical fluids may be poisonous, flammable or an environmental hazard to a much larger extent than water or carbon dioxide are. The extraction can be selective to some extent by controlling the density of the medium, and the extracted material is easily recovered by simply depressurizing, allowing the supercritical fluid to return to gas phase and evaporate leaving little or no solvent residues. Carbon dioxide is the most common supercritical solvent. It is used on a large scale for the decaffeination of green coffee beans, the extraction of hops for beer production, and the production of essential oils and pharmaceutical products from plants. A few laboratory test methods include the use of supercritical fluid extraction as an extraction method instead of using traditional solvents. | 0 | Theoretical and Fundamental Chemistry |
When homebrewing grew in popularity during the economic depression that followed the Finnish banking crisis of the early 1990s, yeast strains known as "turbo yeast" ("turbohiiva", "pikahiiva") were introduced to the market. These yeast strains enable a very rapid fermentation to full cask strength, in some cases in as little as three days (compared to several weeks required by traditional wine yeast strains). Such a short production time naturally does not allow the yeast to become lees. The introduction of turbo yeast reinforced the public's view of kilju as an easy method of procuring cheap alcohol. | 1 | Applied and Interdisciplinary Chemistry |
Paclitaxel total synthesis in organic chemistry is a major ongoing research effort in the total synthesis of paclitaxel (Taxol). This diterpenoid is an important drug in the treatment of cancer but, also expensive because the compound is harvested from a scarce resource, namely the Pacific yew (Taxus brevifolia). Not only is the synthetic reproduction of the compound itself of great commercial and scientific importance, but it also opens the way to paclitaxel derivatives not found in nature but with greater potential.
The paclitaxel molecule consists of a tetracyclic core called baccatin III and an amide tail. The core rings are conveniently called (from left to right) ring A (a cyclohexene), ring B (a cyclooctane), ring C (a cyclohexane) and ring D (an oxetane).
The paclitaxel drug development process took over 40 years. The anti-tumor activity of a bark extract of the Pacific yew tree was discovered in 1963 as a follow-up of a US government plant screening program already in existence 20 years before that. The active substance responsible for the anti-tumor activity was discovered in 1969 and structure elucidation was completed in 1971. Robert A. Holton of Florida State University succeeded in the total synthesis of paclitaxel in 1994, a project that he had started in 1982. In 1989 Holton had also developed a semisynthetic route to paclitaxel starting from 10-deacetylbaccatin III. This compound is a biosynthetic precursor and is found in larger quantities than paclitaxel itself in Taxus baccata (the european yew). In 1990
Bristol-Myers Squibb bought a licence to the patent for this process which in the years to follow earned Florida State University and Holton (with a 40% take) over 200 million US dollars. | 0 | Theoretical and Fundamental Chemistry |
Bramwell was awarded the 2010 Holweck Prize of the British Institute of Physics and the Société Française de Physique (SFP) for "pioneering new concepts in the experimental and theoretical study of spin systems". He shared the 2012 Europhysics Prize of the European Physical Society Condensed Matter Division "for the prediction and experimental observation of magnetic monopoles in spin ice". He is a Fellow of the Institute of Physics.
In 2010 he won the Times Higher Education research project of the year for "magnetricity", and was named by The Times on their list of the 100 top UK scientists. | 0 | Theoretical and Fundamental Chemistry |
Hemoglobin consists of protein subunits (globin molecules), which are polypeptides, long folded chains of specific amino acids which determine the proteins chemical properties and function. The amino acid sequence of any polypeptide is translated from a segment of DNA, the corresponding gene. The amino acid sequence that determines the proteins chemical properties and function.
There is more than one hemoglobin gene. In humans, hemoglobin A (the main form of hemoglobin in adults) is coded by genes HBA1, HBA2, and HBB. Alpha 1 and alpha 2 subunits are respectively coded by genes HBA1 and HBA2 close together on chromosome 16, while the beta subunit is coded by gene HBB on chromosome 11. The amino acid sequences of the globin subunits usually differ between species, with the difference growing with evolutionary distance. For example, the most common hemoglobin sequences in humans, bonobos and chimpanzees are completely identical, with exactly the same alpha and beta globin protein chains. Human and gorilla hemoglobin differ in one amino acid in both alpha and beta chains, and these differences grow larger between less closely related species.
Mutations in the genes for hemoglobin can result in variants of hemoglobin within a single species, although one sequence is usually "most common" in each species. Many of these mutations cause no disease, but some cause a group of hereditary diseases called hemoglobinopathies. The best known hemoglobinopathy is sickle-cell disease, which was the first human disease whose mechanism was understood at the molecular level. A mostly separate set of diseases called thalassemias involves underproduction of normal and sometimes abnormal hemoglobins, through problems and mutations in globin gene regulation. All these diseases produce anemia.
Variations in hemoglobin sequences, as with other proteins, may be adaptive. For example, hemoglobin has been found to adapt in different ways to the thin air at high altitudes, where lower partial pressure of oxygen diminishes its binding to hemoglobin compared to the higher pressures at sea level. Recent studies of deer mice found mutations in four genes that can account for differences between high- and low-elevation populations. It was found that the genes of the two breeds are "virtually identical—except for those that govern the oxygen-carrying capacity of their hemoglobin. . . . The genetic difference enables highland mice to make more efficient use of their oxygen." Mammoth hemoglobin featured mutations that allowed for oxygen delivery at lower temperatures, thus enabling mammoths to migrate to higher latitudes during the Pleistocene. This was also found in hummingbirds that inhabit the Andes. Hummingbirds already expend a lot of energy and thus have high oxygen demands and yet Andean hummingbirds have been found to thrive in high altitudes. Non-synonymous mutations in the hemoglobin gene of multiple species living at high elevations (Oreotrochilus, A. castelnaudii, C. violifer, P. gigas, and A. viridicuada) have caused the protein to have less of an affinity for inositol hexaphosphate (IHP), a molecule found in birds that has a similar role as 2,3-BPG in humans; this results in the ability to bind oxygen in lower partial pressures.
Birds unique circulatory lungs also promote efficient use of oxygen at low partial pressures of O. These two adaptations reinforce each other and account for birds remarkable high-altitude performance.
Hemoglobin adaptation extends to humans, as well. There is a higher offspring survival rate among Tibetan women with high oxygen saturation genotypes residing at 4,000 m. Natural selection seems to be the main force working on this gene because the mortality rate of offspring is significantly lower for women with higher hemoglobin-oxygen affinity when compared to the mortality rate of offspring from women with low hemoglobin-oxygen affinity. While the exact genotype and mechanism by which this occurs is not yet clear, selection is acting on these women's ability to bind oxygen in low partial pressures, which overall allows them to better sustain crucial metabolic processes. | 0 | Theoretical and Fundamental Chemistry |
There are many factors at play in even a basic melt spinning process. The quality and dimensions of the product are determined by how the machine is operated and configured. Consequently, there are many studies exploring the effects of variations in the melt spinner's configuration on specific alloys. For example, [https://www.jstage.jst.go.jp/article/matertrans1960/21/4/21_4_219/_article here] is an article about the specific conditions that were found to work well for melt spinning Fe-B and Fe-Si-B alloys.
In general, melt spinners will run with some variation in the following variables depending on the desired product.
* Nozzle gap: The distance between the nozzle and the cooled drum. Primarily affects ribbon thickness.
* Nozzle shape: The shape of the nozzle ejecting the molten material onto the drum. Nozzles allowing for a larger melt puddle on the drum's surface result in wider ribbons.
* Flow rate: The flow rate of melt onto the drum. The flow rate is usually closely related to the rotational speed of the drum. Mainly affects the width and thickness of the ribbons.
* Rotational speed: The speed at which the drum rotates. In general, a faster drum makes thinner ribbons.
* Drum temperature: The temperature at which the drum operates. Mainly affects the atomic structure of the resulting ribbon. Different alloys form best at specific temperatures.
Since every material acts differently, the exact cause-effect relationship between each of these variables and the resulting ribbon is usually determined experimentally. Other less commonly adjusted variables exist, but their effects on the final ribbon dimensions and structure aren't all documented. | 1 | Applied and Interdisciplinary Chemistry |
Lipid:In marine sediments, a stable lipid called IP25 (Ice Proxy with 25 carbon atoms), which is biosynthesized by sea-ice dwelling diatom, has been found to be generally related to spring sea-ice cover in the Arctic region, Thus this proxy could be used to reconstruct sea-ice coverage. A different biomarker, IPSO25 (Ice Proxy Southern Ocean with 25 carbon atoms) has been documented as a useful proxy for the sea-ice cover in the Antarctic region. | 0 | Theoretical and Fundamental Chemistry |
* Respiratory tract infections (such as tonsillitis, pharyngitis, and lobar pneumonia) caused by group A beta-hemolytic streptococci and S. pneumoniae (formerly D. pneumonia).
* Otitis media caused by group A beta-hemolytic streptococci, S. pneumoniae, H. influenzae, and staphylococci.
* Skin and skin structure infections caused by staphylococci (penicillin-susceptible and penicillin-resistant) and beta-hemolytic streptococci.
* Urinary tract infections, including prostatitis, caused by E. coli, P. mirabilis and Klebsiella species. | 0 | Theoretical and Fundamental Chemistry |
The term benzannulated compounds refers to derivatives of cyclic compounds (usually aromatic) which are fused to a benzene ring. Examples are listed in the table below:
In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors". | 0 | Theoretical and Fundamental Chemistry |
In metals and minerals, grains are ordered structures in different crystal orientations. Subgrains are defined as grains that are oriented at a < 10–15 degree angle at the grain boundary, making it a low-angle grain boundary (LAGB). Due to the relationship between the energy versus the number of dislocations at the grain boundary, there is a driving force for fewer high-angle grain boundaries (HAGB) to form and grow instead of a higher number of LAGB. The energetics of the transformation depend on the interfacial energy at the boundaries, the lattice geometry (atomic and planar spacing, structure [i.e. FCC/BCC/HCP] of the material, and the degrees of freedom of the grains involved (misorientation, inclination). The recrystallized material has less total grain boundary area, which means that failure via brittle fracture along the grain boundary is less probable. | 1 | Applied and Interdisciplinary Chemistry |
For deriving the analytical solution of this non-stationary flow velocity profile, the following assumptions are taken:
* Fluid is homogeneous, incompressible and Newtonian;
* Tube wall is rigid and circular;
* Motion is laminar, axisymmetric and parallel to the tube's axis;
* Boundary conditions are: axisymmetry at the centre, and no-slip condition on the wall;
* Pressure gradient is a periodic function that drives the fluid;
* Gravitation has no effect on the fluid.
Thus, the Navier-Stokes equation and the continuity equation are simplified as
and
respectively. The pressure gradient driving the pulsatile flow is decomposed in Fourier series,
where is the imaginary number, is the angular frequency of the first harmonic (i.e., ), and are the amplitudes of each harmonic . Note that, (standing for ) is the steady-state pressure gradient, whose sign is opposed to the steady-state velocity (i.e., a negative pressure gradient yields positive flow). Similarly, the velocity profile is also decomposed in Fourier series in phase with the pressure gradient, because the fluid is incompressible,
where are the amplitudes of each harmonic of the periodic function, and the steady component () is simply Poiseuille flow
Thus, the Navier-Stokes equation for each harmonic reads as
With the boundary conditions satisfied, the general solution of this ordinary differential equation for the oscillatory part () is
where is the Bessel function of first kind and order zero, is the Bessel function of second kind and order zero, and are arbitrary constants, and is the dimensionless Womersley number. The axisymmetric boundary condition () is applied to show that for the derivative of above equation to be valid, as the derivatives and approach infinity. Next, the wall non-slip boundary condition () yields . Hence, the amplitudes of the velocity profile of the harmonic becomes
where is used for simplification.
The velocity profile itself is obtained by taking the real part of the complex function resulted from the summation of all harmonics of the pulse, | 1 | Applied and Interdisciplinary Chemistry |
Cell cultures of Berberis beaniana (B. beaniana), which in this certain experiment are taken as an example, were harvested 10–12 days, contained large amounts of proto-berberines, mainly jatrorrhizine. These quaternary alkaloids have a strong inhibitory effect on the BBE, so they had to be removed. In order to eliminate most of these interfering cationic substances, the enzyme solution was treated first with carboxymethyl-Sepharose and subsequently with dextrancoated charcoal.
After that, the resulting solution was fractionated using standard procedures and generated, after isoelectric focusing, a single protein band in SDS gel electrophoresis. In the end, the obtained enzyme had been purified 450 times and contained 0.7% of the activity present in the crude extract at the beginning. | 1 | Applied and Interdisciplinary Chemistry |
The discoveries of the 118 chemical elements known to exist as of 2024 are presented here in chronological order. The elements are listed generally in the order in which each was first defined as the pure element, as the exact date of discovery of most elements cannot be accurately determined. There are plans to synthesize more elements, and it is not known how many elements are possible.
Each element's name, atomic number, year of first report, name of the discoverer, and notes related to the discovery are listed. | 1 | Applied and Interdisciplinary Chemistry |
Ribosomal frameshifting, also known as translational frameshifting or translational recoding, is a biological phenomenon that occurs during translation that results in the production of multiple, unique proteins from a single mRNA. The process can be programmed by the nucleotide sequence of the mRNA and is sometimes affected by the secondary, 3-dimensional mRNA structure. It has been described mainly in viruses (especially retroviruses), retrotransposons and bacterial insertion elements, and also in some cellular genes.
Small molecules, proteins, and nucleic acids have also been found to stimulate levels of frameshifting. In December 2023, it was reported that in vitro-transcribed (IVT) mRNAs in response to BNT162b2 (Pfizer–BioNTech) anti-COVID-19 vaccine caused ribosomal frameshifting. | 1 | Applied and Interdisciplinary Chemistry |
Professor Abiodun Adewale Oladipo (born January 1, 1958, Ile-Ife, Nigeria) is a Nigerian academician, administrator, and politician. His Contribution includes, the field of nuclear chemistry, as well as his involvement in Nigerian politics. He serves as the [https://www.uniosun.edu.ng/index.php/admin-management/the-pro-chancellor.html Pro-chancellor] and Chairman of the Governing Council of Osun State University. | 0 | Theoretical and Fundamental Chemistry |
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