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The most potent narcotic component of opium is the alkaloid morphine, which acts as an opioid receptor agonist. The N-type calcium channel blocker ziconotide is an analgesic based on a cyclic peptide cone snail toxin (ω-conotoxin MVIIA) from the species Conus magus. Numerous anti-infectives are based on natural product... | Wikipedia - Natural product - Medical uses > Modern natural product-derived drugs | 343 | 1,345 | null |
Section: Medical uses > Limiting and enabling factors. Numerous challenges limit the use of natural products for drug discovery, resulting in 21st century preference by pharmaceutical companies to dedicate discovery efforts toward high-throughput screening of pure synthetic compounds with shorter timelines to refinemen... | Wikipedia - Natural product - Medical uses > Limiting and enabling factors | 213 | 1,204 | null |
Section: Isolation and purification. All natural products begin as mixtures with other compounds from the natural source, often very complex mixtures, from which the product of interest must be isolated and purified. The isolation of a natural product refers, depending on context, either to the isolation of sufficient ... | Wikipedia - Natural product - Isolation and purification | 332 | 1,694 | null |
Section: Synthesis. Many natural products have complex structures. The complexity is determined by factors like molecular mass, arrangement of substructures (e.g., functional groups, rings), number and density of these groups, their stability, stereochemical elements, and physical properties, as well as the novelty of ... | Wikipedia - Natural product - Synthesis | 170 | 900 | null |
Section: Synthesis > Semisynthesis. Isolating a natural product from its source can be costly in terms of time and materials, and may impact the availability of the natural resource or have ecological consequences. For example, it is estimated that harvesting enough paclitaxel for a single dose of therapy would require... | Wikipedia - Natural product - Synthesis > Semisynthesis | 282 | 1,374 | null |
Section: Synthesis > Biomimetic synthesis. Biomimetic synthesis is a branch of organic chemistry which aims at designing and preparing natural product compounds in the laboratory using the biosynthetic pathways as a blueprint. This method is based on the mechanisms used by the living organisms for the synthesis of vari... | Wikipedia - Natural product - Synthesis > Biomimetic synthesis | 210 | 1,064 | null |
Section: Synthesis > Symmetry. Examination of dimerized and trimerized natural products has shown that an element of bilateral symmetry is often present. Bilateral symmetry refers to a molecule or system that contains a C2, Cs, or C2v point group identity. C2 symmetry tends to be much more abundant than other types of ... | Wikipedia - Natural product - Synthesis > Symmetry | 197 | 937 | null |
Section: Research and teaching > Chemistry. Natural products chemistry is a distinct area of chemical research which was important in the development and history of chemistry. Isolating and identifying natural products has been important to source substances for early preclinical drug discovery research, to understand ... | Wikipedia - Natural product - Research and teaching > Chemistry | 308 | 1,625 | null |
Section: History > Isolation. Lavoisier showed at the end of the 18th century that organic substances consisted of a limited number of elements: primarily carbon and hydrogen and supplemented by oxygen and nitrogen. He quickly focused on the isolation of these substances, often because they had an interesting pharmacol... | Wikipedia - Natural product - History > Isolation | 237 | 1,076 | null |
Section: History > Synthesis. A second important step was the synthesis of organic compounds. While the synthesis of inorganic substances had been known for a long time, creating organic substances was a major challenge. In 1827, the Swedish chemist Jöns Jacob Berzelius argued that a vital force or life force was essen... | Wikipedia - Natural product - History > Synthesis | 307 | 1,377 | null |
Section: History > Structural theories. The third key development was the structure elucidation of organic substances. While the elemental composition of pure organic compounds could be determined accurately, their molecular structures remained unclear. This issue became evident in a dispute between Friedrich Wöhler an... | Wikipedia - Natural product - History > Structural theories | 239 | 1,271 | null |
Section: History > Milestones. By the 1930s, several major classes of natural products had been identified and studied extensively. Key milestones in the field of natural product research include: Terpenes: First systematically studied by Otto Wallach (Nobel Prize 1910) and later by Leopold Ružička (Nobel Prize 1939). ... | Wikipedia - Natural product - History > Milestones | 341 | 1,550 | null |
Their work on steroid hormones paved the way for modern endocrinology. Alkaloids and anthocyanins: Researched by Robert Robinson (Nobel Prize 1947) and others. These compounds, particularly alkaloids, have been crucial in the development of many pharmaceuticals. Polypeptide hormones: Investigated by Vincent du Vigneaud... | Wikipedia - Natural product - History > Milestones | 239 | 1,132 | null |
Article: Nuclear chemistry. Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties. It is the chemistry of radioactive elements such as the actinides, radium and radon together with t... | Wikipedia - Nuclear chemistry - Summary | 350 | 1,955 | null |
Section: History. After Wilhelm Röntgen discovered X-rays in 1895, many scientists began to work on ionizing radiation. One of these was Henri Becquerel, who investigated the relationship between phosphorescence and the blackening of photographic plates. When Becquerel (working in France) discovered that, with no exter... | Wikipedia - Nuclear chemistry - History | 288 | 1,443 | null |
This injury resulted in the biological properties of radiation being investigated, which in time resulted in the development of medical treatment. Ernest Rutherford, working in Canada and England, showed that radioactive decay can be described by a simple equation (a linear first degree derivative equation, now called ... | Wikipedia - Nuclear chemistry - History | 338 | 1,640 | null |
In the early 1920s Otto Hahn created a new line of research. Using the "emanation method", which he had recently developed, and the "emanation ability", he founded what became known as "applied radiochemistry" for the researching of general chemical and physical-chemical questions. In 1936 Cornell University Press publ... | Wikipedia - Nuclear chemistry - History | 259 | 1,288 | null |
Section: Main areas > Radiation chemistry. Radiation chemistry is the study of the chemical effects of radiation on matter; this is very different from radiochemistry as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into hy... | Wikipedia - Nuclear chemistry - Main areas > Radiation chemistry | 156 | 841 | null |
Section: Main areas > Study of nuclear reactions. A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as fission and fusion. Some early evidence for nuclear fission was the formation of a short-lived radioisotope of barium which was isolated from neutron irradiated uranium (1... | Wikipedia - Nuclear chemistry - Main areas > Study of nuclear reactions | 218 | 1,018 | null |
Section: Main areas > The nuclear fuel cycle > Reprocessing > Law. In the United States, it is normal to use fuel once in a power reactor before placing it in a waste store. The long-term plan is currently to place the used civilian reactor fuel in a deep store. This non-reprocessing policy was started in March 1977 be... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > Law | 186 | 945 | null |
Section: Main areas > The nuclear fuel cycle > Reprocessing > PUREX chemistry. The current method of choice is to use the PUREX liquid-liquid extraction process which uses a tributyl phosphate/hydrocarbon mixture to extract both uranium and plutonium from nitric acid. This extraction is of the nitrate salts and is clas... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > PUREX chemistry | 300 | 1,342 | null |
It is normal to then back extract the loaded organic phase to create a medium active liquor which contains mostly uranium and plutonium with only small traces of fission products. This medium active aqueous mixture is then extracted again by tributyl phosphate/hydrocarbon to form a new organic phase, the metal bearing ... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > PUREX chemistry | 250 | 1,210 | null |
Section: Main areas > The nuclear fuel cycle > Reprocessing > New methods being considered for future use. The PUREX process can be modified to make a UREX (URanium EXtraction) process which could be used to save space inside high level nuclear waste disposal sites, such as Yucca Mountain nuclear waste repository, by r... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > New methods being considered for future use | 341 | 1,455 | null |
Adding a second extraction agent, octyl(phenyl)-N,N-dibutyl carbamoylmethyl phosphine oxide (CMPO) in combination with tributylphosphate, (TBP), the PUREX process can be turned into the TRUEX (TRansUranic EXtraction) process this is a process which was invented in the US by Argonne National Laboratory, and is designed ... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > New methods being considered for future use | 331 | 1,446 | null |
As part of the management of minor actinides, it has been proposed that the lanthanides and trivalent minor actinides should be removed from the PUREX raffinate by a process such as DIAMEX or TRUEX. In order to allow the actinides such as americium to be either reused in industrial sources or used as fuel the lanthanid... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Reprocessing > New methods being considered for future use | 320 | 1,369 | null |
Section: Main areas > The nuclear fuel cycle > Absorption of fission products on surfaces. Another important area of nuclear chemistry is the study of how fission products interact with surfaces; this is thought to control the rate of release and migration of fission products both from waste containers under normal con... | Wikipedia - Nuclear chemistry - Main areas > The nuclear fuel cycle > Absorption of fission products on surfaces | 314 | 1,503 | null |
Section: Education. Despite the growing use of nuclear medicine, the potential expansion of nuclear power plants, and worries about protection against nuclear threats and the management of the nuclear waste generated in past decades, the number of students opting to specialize in nuclear and radiochemistry has decrease... | Wikipedia - Nuclear chemistry - Education | 240 | 1,277 | null |
Section: Spinout areas > Kinetics (use within mechanistic chemistry). The mechanisms of chemical reactions can be investigated by observing how the kinetics of a reaction is changed by making an isotopic modification of a substrate, known as the kinetic isotope effect. This is now a standard method in organic chemistry... | Wikipedia - Nuclear chemistry - Spinout areas > Kinetics (use within mechanistic chemistry) | 190 | 890 | null |
Section: Spinout areas > Uses within geology, biology and forensic science > Biology. Within living things, isotopic labels (both radioactive and nonradioactive) can be used to probe how the complex web of reactions which makes up the metabolism of an organism converts one substance to another. For instance a green pla... | Wikipedia - Nuclear chemistry - Spinout areas > Uses within geology, biology and forensic science > Biology | 309 | 1,560 | null |
15N, a stable isotope of nitrogen, has also been used. It is incorporated mainly into proteins. Radioactive isotopes have the advantages of being detectable in very low quantities, in being easily measured by scintillation counting or other radiochemical methods, and in being localizable to particular regions of a cell... | Wikipedia - Nuclear chemistry - Spinout areas > Uses within geology, biology and forensic science > Biology | 336 | 1,677 | null |
11C, carbon-11 is usually produced by cyclotron bombardment of 14N with protons. The resulting nuclear reaction is 14N(p,α)11C. Additionally, carbon-11 can also be made using a cyclotron; boron in the form of boric oxide is reacted with protons in a (p,n) reaction. Another alternative route is to react 10B with deutero... | Wikipedia - Nuclear chemistry - Spinout areas > Uses within geology, biology and forensic science > Biology | 334 | 1,401 | null |
Article: Oilfield scale inhibition. Oilfield scale inhibition is the process of preventing the formation of scale from blocking or hindering fluid flow through pipelines, valves, and pumps used in oil production and processing. Scale inhibitors (SIs) are a class of specialty chemicals that are used to slow or prevent s... | Wikipedia - Oilfield scale inhibition - Summary | 196 | 1,034 | null |
Section: Background. The three prevailing water-related problems that upset oil companies today are corrosion, gas hydrates and scaling in production systems. The reservoir water has a high composition of dissolved minerals equilibrated over millions of years at constant physicochemical conditions. As the reservoir flu... | Wikipedia - Oilfield scale inhibition - Background | 167 | 872 | null |
Section: Types of scales > Inorganic scale. Inorganic scales refer to mineral deposits that occur when the formation water mixes with different brines such as injection water. The mixing changes causes reaction between incompatible ions and changes the thermodynamic and equilibrium state of the reservoir fluids. Supers... | Wikipedia - Oilfield scale inhibition - Types of scales > Inorganic scale | 315 | 1,529 | null |
Section: Types of scales > Calcium carbonate scale. Water, noted for its high solvation power can dissolve certain gases such as carbon dioxide (CO2) to form aqueous CO2(aq). Under the right conditions of temperature and/or pressure, H2O and CO2(aq) molecules react to yield carbonic acid (H2CO3) whose solubility increa... | Wikipedia - Oilfield scale inhibition - Types of scales > Calcium carbonate scale | 324 | 1,067 | null |
Section: Types of scales > Sulfate scales. Sulfates of Group (II) metal ions (M2+), generally decrease in solubility down the group. The most difficult scales to remove are those of Barium sulfate because of its high insolubility forming very hard scale deposits. A general representation of the reaction is summarized i... | Wikipedia - Oilfield scale inhibition - Types of scales > Sulfate scales | 316 | 1,524 | null |
The scaling-tendency of an oil-well can be predicted based on the prevailing conditions such as pH, temperature, pressure, ionic strength and the mole fraction of CO2 in the vapor and aqueous phases. For instance the saturation index for CaCO3 scale is calculated using the formula; Fs= {[Ca2+][CO32−]}/Ksp Where Fs is t... | Wikipedia - Oilfield scale inhibition - Types of scales > Sulfate scales | 161 | 684 | null |
Section: Scale remediation > Scale inhibitors. Scale inhibitors are specialty chemicals that are added to oil production systems to delay, reduce and/or prevent scale deposition. acrylic acid polymers, maleic acid polymers and phosphonates have been used extensively for scale treatment in water systems due to their exc... | Wikipedia - Oilfield scale inhibition - Scale remediation > Scale inhibitors | 350 | 1,370 | null |
The inhibitor molecules essentially bind ions in aqueous phase of production fluids that could potentially precipitate as scales. For instance, to bind positively charged ions in the water, anions must be present in the inhibitor molecular backbone structure and vice versa. Group (II) metal ions are commonly sequestere... | Wikipedia - Oilfield scale inhibition - Scale remediation > Scale inhibitors | 265 | 1,198 | null |
Section: Environmental considerations. Generally, the environmental impacts of SIs are complicated further by combination of other chemicals applied through exploratory, drilling, well-completion and start-up operations. Produced fluids, and other wastes from oil and gas operations with high content of different toxic ... | Wikipedia - Oilfield scale inhibition - Environmental considerations | 304 | 1,687 | null |
Another alternative, polysaccharide SIs meet the requirements for environmentally friendly materials; they contain no Phosphorus or Nitrogen and are noted for their non-toxic, renewable, and biodegradable properties. Carboxymethyl inulin (CMI), which is isolated from the roots of Inula helenium has been used in oil exp... | Wikipedia - Oilfield scale inhibition - Environmental considerations | 241 | 1,229 | null |
Article: Organic chemistry. Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms. Study of structure determines their structural formula. St... | Wikipedia - Organic chemistry - Summary | 326 | 1,756 | null |
Section: History. Before the 18th century, chemists generally believed that compounds obtained from living organisms were endowed with a vital force that distinguished them from inorganic compounds. According to the concept of vitalism (vital force theory), organic matter was endowed with a "vital force". During the fi... | Wikipedia - Organic chemistry - History | 337 | 1,723 | null |
His discovery, made widely known through its financial success, greatly increased interest in organic chemistry. A crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently in 1858 by both Friedrich August Kekulé and Archibald Scott Couper. Both researchers suggested that... | Wikipedia - Organic chemistry - History | 346 | 1,846 | null |
In the early part of the 20th century, polymers and enzymes were shown to be large organic molecules, and petroleum was shown to be of biological origin. The multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of complex natural compounds increased in complexity to glucose an... | Wikipedia - Organic chemistry - History | 273 | 1,567 | null |
Section: Characterization. Since organic compounds often exist as mixtures, a variety of techniques have also been developed to assess purity; chromatography techniques are especially important for this application, and include HPLC and gas chromatography. Traditional methods of separation include distillation, crystal... | Wikipedia - Organic chemistry - Characterization | 335 | 1,849 | null |
Section: Melting and boiling properties. Organic compounds typically melt and many boil. In contrast, while inorganic materials generally can be melted, many do not boil, and instead tend to degrade. In earlier times, the melting point (m.p.) and boiling point (b.p.) provided crucial information on the purity and ident... | Wikipedia - Organic chemistry - Melting and boiling properties | 152 | 745 | null |
Section: Nomenclature. The names of organic compounds are either systematic, following logically from a set of rules, or nonsystematic, following various traditions. Systematic nomenclature is stipulated by specifications from IUPAC (International Union of Pure and Applied Chemistry). Systematic nomenclature starts wit... | Wikipedia - Organic chemistry - Nomenclature | 324 | 1,470 | null |
Section: Classification of organic compounds > Functional groups. The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties. A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be... | Wikipedia - Organic chemistry - Classification of organic compounds > Functional groups | 337 | 1,708 | null |
Different functional groups have different pKa values and bond strengths (single, double, triple) leading to increased electrophilicity with lower pKa and increased nucleophile strength with higher pKa. More basic/nucleophilic functional groups desire to attack an electrophilic functional group with a lower pKa on anot... | Wikipedia - Organic chemistry - Classification of organic compounds > Functional groups | 224 | 873 | null |
Section: Classification of organic compounds > Aliphatic compounds. The aliphatic hydrocarbons are subdivided into three groups of homologous series according to their state of saturation: alkanes (paraffins): aliphatic hydrocarbons without any double or triple bonds, i.e. just C-C, C-H single bonds alkenes (olefins): ... | Wikipedia - Organic chemistry - Classification of organic compounds > Aliphatic compounds | 314 | 1,272 | null |
Section: Classification of organic compounds > Heterocyclic compounds. The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter... | Wikipedia - Organic chemistry - Classification of organic compounds > Heterocyclic compounds | 298 | 1,244 | null |
Section: Classification of organic compounds > Biomolecules. Biomolecular chemistry is a major category within organic chemistry which is frequently studied by biochemists. Many complex multi-functional group molecules are important in living organisms. Some are long-chain biopolymers, and these include peptides, DNA, ... | Wikipedia - Organic chemistry - Classification of organic compounds > Biomolecules | 348 | 1,529 | null |
Section: Classification of organic compounds > Fullerenes. Fullerenes and carbon nanotubes, carbon compounds with spheroidal and tubular structures, have stimulated much research into the related field of materials science. The first fullerene was discovered in 1985 by Sir Harold W. Kroto of the United Kingdom and by R... | Wikipedia - Organic chemistry - Classification of organic compounds > Fullerenes | 208 | 983 | null |
Section: Organic reactions. Organic reactions are chemical reactions involving organic compounds. Many of these reactions are associated with functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and steric hindrance. ... | Wikipedia - Organic chemistry - Organic reactions | 251 | 1,373 | null |
Section: Organic synthesis. Synthetic organic chemistry is an applied science as it borders engineering, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem-solving task, where a synthesis is designed for a target molecule by selecting optimal ... | Wikipedia - Organic chemistry - Organic synthesis | 269 | 1,451 | null |
Article: Particle aggregation. Particle agglomeration refers to the formation of assemblages in a suspension and represents a mechanism leading to the functional destabilization of colloidal systems. During this process, particles dispersed in the liquid phase stick to each other, and spontaneously form irregular parti... | Wikipedia - Particle aggregation - Summary | 338 | 1,601 | null |
Section: Early stages. A well dispersed colloidal suspension consists of individual, separated particles and is stabilized by repulsive inter-particle forces. When the repulsive forces weaken or become attractive through the addition of a coagulant, particles start to aggregate. Initially, particle doublets A2 will for... | Wikipedia - Particle aggregation - Early stages | 350 | 1,719 | null |
When salt is added to the suspension, the electrical double layer repulsion is screened, and van der Waals attraction become dominant and induce fast aggregation. The figure on the right shows the typical dependence of the stability ratio W versus the electrolyte concentration, whereby the regimes of slow and fast aggr... | Wikipedia - Particle aggregation - Early stages | 343 | 1,768 | null |
Other mechanisms of colloid stabilization are equally possible, particularly, involving polymers. Adsorbed or grafted polymers may form a protective layer around the particles, induce steric repulsive forces, and lead to steric stabilization at it is the case with polycarboxylate ether (PCE), the last generation of che... | Wikipedia - Particle aggregation - Early stages | 180 | 881 | null |
Section: Later stages. As the aggregation process continues, larger clusters form. The growth occurs mainly through encounters between different clusters, and therefore one refers to cluster-cluster aggregation process. The resulting clusters are irregular, but statistically self-similar. They are examples of mass frac... | Wikipedia - Particle aggregation - Later stages | 295 | 1,391 | null |
Section: Homoaggregation versus heteroaggregation. When aggregation occurs in a suspension composed of similar monodisperse colloidal particles, the process is called homoaggregation (or homocoagulation). When aggregation occurs in a suspension composed of dissimilar colloidal particles, one refers to heteroaggregation... | Wikipedia - Particle aggregation - Homoaggregation versus heteroaggregation | 347 | 1,294 | null |
Section: Experimental techniques. Numerous experimental techniques have been developed to study particle aggregation. Most frequently used are time-resolved optical techniques that are based on transmittance or scattering of light. Light transmission. The variation of transmitted light through an aggregating suspension... | Wikipedia - Particle aggregation - Experimental techniques | 342 | 1,911 | null |
The aggregating suspension is forced through a narrow capillary particle counter and the size of each aggregate is being analyzed by light scattering. From the scattering intensity, one can deduce the size of each aggregate, and construct a detailed aggregate size distribution. If the suspensions contain high amounts o... | Wikipedia - Particle aggregation - Experimental techniques | 319 | 1,796 | null |
Section: Relevance. Particle aggregation is a widespread phenomenon, which spontaneously occurs in nature but is also widely explored in manufacturing. Some examples include. Formation of river delta. When river water carrying suspended sediment particles reaches salty water, particle aggregation may be one of the fact... | Wikipedia - Particle aggregation - Relevance | 336 | 1,705 | null |
Article: Particle deposition. Particle deposition is the spontaneous attachment of particles to surfaces. The particles in question are normally colloidal particles, while the surfaces involved may be planar, curved, or may represent particles much larger in size than the depositing ones (e.g., sand grains). Deposition... | Wikipedia - Particle deposition - Summary | 292 | 1,533 | null |
Section: Initial stages. A particle may diffuse to a surface in quiescent conditions, but this process is inefficient as a thick depletion layer develops, which leads to a progressive slowing down of the deposition. When particle deposition is efficient, it proceeds almost exclusively in a system under flow. In such co... | Wikipedia - Particle deposition - Initial stages | 344 | 1,673 | null |
Section: Blocking. When depositing particles repel each other, the deposition will stop by the time when enough particles have deposited. At one point, such a surface layer will repel any particles that may still make attempts to deposit. The surface is said to be saturated or blocked by the deposited particles. The bl... | Wikipedia - Particle deposition - Blocking | 344 | 1,332 | null |
One disk after another is placed randomly at a surface. Once a disk is placed, it sticks at the same spot, and cannot be removed. When an attempt to deposit a disk would result in an overlap with an already deposited disk, this attempt is rejected. Within this model, the surface is initially filled rapidly, but the mor... | Wikipedia - Particle deposition - Blocking | 286 | 1,404 | null |
Section: Experimental techniques. Particle deposition can be followed by various experimental techniques. Direct observation of deposited particles is possible with an optical microscope, scanning electron microscope, or the atomic force microscope. Optical microscopy has the advantage that the deposition of particles ... | Wikipedia - Particle deposition - Experimental techniques | 271 | 1,540 | null |
Section: Relevance. Particle deposition occurs in numerous natural and industrial systems. Few examples are given below. Coatings and surface functionalization. Paints and adhesives often are concentrated suspensions of colloidal particles, and in order to adhere well to the surface the particles must deposit to the su... | Wikipedia - Particle deposition - Relevance | 251 | 1,223 | null |
Article: Random sequential adsorption. Random sequential adsorption (RSA) refers to a process where particles are randomly introduced in a system, and if they do not overlap any previously adsorbed particle, they adsorb and remain fixed for the rest of the process. RSA can be carried out in computer simulation, in a ma... | Wikipedia - Random sequential adsorption - Summary | 348 | 1,688 | null |
For circular disks, saturation occurs at a coverage of 0.547. When the depositing particles are polydisperse, much higher surface coverage can be reached, since the small particles will be able to deposit into the holes in between the larger deposited particles. On the other hand, rod like particles may lead to much sm... | Wikipedia - Random sequential adsorption - Summary | 320 | 1,161 | null |
The accuracy of this conjecture in higher dimensions is not known. For k {\displaystyle k} -mers on a one-dimensional lattice, we have for the fraction of vertices covered, θ k = k ∫ 0 ∞ exp ( − u − 2 ∑ j = 1 k − 1 1 − e − j u j ) d u = k ∫ 0 1 exp ( − 2 ∑ j = 1 k − 1 1 − v j j ) d v {\displaystyle \theta _{k}=k\in... | Wikipedia - Random sequential adsorption - Summary | 305 | 751 | null |
Article: Phenol sulfur transferase deficiency. Phenol sulfur transferase deficiency, in short PST deficiency, is the lack or the reduced activity of the functional enzyme phenol sulfur transferase, which is crucial in the detoxification of mainly phenolic compounds by catalysing the sulfate conjugation of the hydroxyl ... | Wikipedia - Phenol sulfur transferase deficiency - Summary | 296 | 1,471 | null |
Section: Phenol sulfur transferase. Phenol sulfur transferase, in short PST or SULT1, is a subfamily of the enzyme cytosolic sulfotransferases (SULTs) consisting of at least 8 isoforms in humans that catalyze the transfer of sulfuryl group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to phenolic compounds, resulti... | Wikipedia - Phenol sulfur transferase deficiency - Phenol sulfur transferase | 278 | 1,114 | null |
Section: Discovery. PST deficiency was first discovered in the late 1990s by Dr. Rosemary Waring through a series of tests during her researches on the mechanisms and characteristics of sulfation in autistic children. From the result of the test administering individuals with paracetamol, it was found that the level of... | Wikipedia - Phenol sulfur transferase deficiency - Discovery | 168 | 812 | null |
Section: Pathophysiology > Causes. PST deficiency can be caused by inherited mutations in the PST genes, for example the SULT1A1*2 polymorphism, which is a single nucleotide polymorphism at the 638th base of the SULT1A1 gene from guanine to adenosine that causes the change of the 213th amino acid residue of the resulta... | Wikipedia - Phenol sulfur transferase deficiency - Pathophysiology > Causes | 219 | 994 | null |
Section: Pathophysiology > Disease-causing mechanisms. PST deficiency can directly cause diseases by the resulted phenol sulfoconjugation defect which reduces the removal of toxic phenolic compounds. In the liver, where PST serves as one of the important enzymes involved in detoxification, the reduced transcriptional a... | Wikipedia - Phenol sulfur transferase deficiency - Pathophysiology > Disease-causing mechanisms | 240 | 1,077 | null |
Section: Clinical impact > Related disorders > Autism. It is suspected that mutations, including both microdeletion and microduplication, of the PST genes are the risk factors of autism spectrum disorder, especially the mutation causing decreased SULT1A activity which is usually reported in autistic individuals. Some s... | Wikipedia - Phenol sulfur transferase deficiency - Clinical impact > Related disorders > Autism | 251 | 1,192 | null |
Section: Clinical impact > Pharmacological impacts. Drug metabolism of phenolic drugs, such as paracetamol and salicylamide, is greatly dependent on the phenol sulfoconjugation by PST, and therefore careful controls on the dosage forms, routes, rates, and duration of administration of those drugs are important for PST ... | Wikipedia - Phenol sulfur transferase deficiency - Clinical impact > Pharmacological impacts | 187 | 827 | null |
Section: Foundations of chemistry. Major philosophical questions arise as soon as one attempts to define chemistry and what it studies. Atoms and molecules are often assumed to be the fundamental units of chemical theory, but traditional descriptions of molecular structure and chemical bonding fail to account for the p... | Wikipedia - Philosophy of chemistry - Foundations of chemistry | 337 | 1,931 | null |
Organic (i.e., carbon-based) molecules are those most often chiral. Amino acids, nucleic acids and sugars, all of which are found exclusively as a single enantiomer in organisms, are the basic chemical units of life. Chemists, biochemists, and biologists alike debate the origins of this homochirality. Philosophers deba... | Wikipedia - Philosophy of chemistry - Foundations of chemistry | 248 | 1,197 | null |
Section: Philosophers of chemistry. Friedrich Wilhelm Joseph Schelling was among the first philosophers to use the term "philosophy of chemistry". Several philosophers and scientists have focused on the philosophy of chemistry in recent years, notably, the Dutch philosopher Jaap van Brakel, who wrote The Philosophy of ... | Wikipedia - Philosophy of chemistry - Philosophers of chemistry | 286 | 1,527 | null |
Article: Phosphorimidazolide. A phosphorimidazolide is a chemical compound in which a phosphoryl mono-ester is covalently bound to a nitrogen atom in an imidazole ring. They are a type of phosphoramidate. These phosphorus (V) compounds are encountered as reagents used for making new phosphoanhydride bonds with phosphat... | Wikipedia - Phosphorimidazolide - Summary | 182 | 681 | null |
Section: Role in oligonucleotide formation. Phosphorimidazolides have been investigated for their mechanistic role in abiogenesis (the natural process by which life arose from non-living matter). Specifically, they have been proposed as the active electrophilic species which may have mediated the formation of inter-nuc... | Wikipedia - Phosphorimidazolide - Role in oligonucleotide formation | 348 | 1,463 | null |
Section: Phosphoanhydride bond formation. While early studies of phosphorimidazolide derivatives of nucleotides found that oligonucleotides could form in the presence of a complementary template, pyrophosphate-linked dimers formed predominantly in the absence of a template. This proclivity for forming new phosphoanhydr... | Wikipedia - Phosphorimidazolide - Phosphoanhydride bond formation | 192 | 745 | null |
Section: Synthesis. Phosphorimidazolide reagents have been synthesized from phosphate mono-esters. In one method, a phosphate mono-ester is dissolved in anhydrous pyridine or N,N-dimethylformamide (DMF) and activated using triphenylphosphine (PPh3) and 2,2’-Dithiodipyridine (2,2’-DTDP) in the presence of triethylamine ... | Wikipedia - Phosphorimidazolide - Synthesis | 263 | 941 | null |
Article: Photochemistry. Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750 nm), or infrared radiation (750–2500 nm). In nature, photoch... | Wikipedia - Photochemistry - Summary | 178 | 928 | null |
Section: Concept > Grotthuss–Draper law and Stark–Einstein law. Photoexcitation is the first step in a photochemical process where the reactant is elevated to a state of higher energy, an excited state. The first law of photochemistry, known as the Grotthuss–Draper law (for chemists Theodor Grotthuss and John W. Draper... | Wikipedia - Photochemistry - Concept > Grotthuss–Draper law and Stark–Einstein law | 161 | 724 | null |
Section: Concept > Fluorescence and phosphorescence. When a molecule or atom in the ground state (S0) absorbs light, one electron is excited to a higher orbital level. This electron maintains its spin according to the spin selection rule; other transitions would violate the law of conservation of angular momentum. The ... | Wikipedia - Photochemistry - Concept > Fluorescence and phosphorescence | 324 | 1,404 | null |
This triplet state can relax to the ground state S0 by radiationless ISC or by a radiation pathway called phosphorescence. This process implies a change of electronic spin, which is forbidden by spin selection rules, making phosphorescence (from T1 to S0) much slower than fluorescence (from S1 to S0). Thus, triplet sta... | Wikipedia - Photochemistry - Concept > Fluorescence and phosphorescence | 182 | 827 | null |
Section: Concept > Experimental setup. Photochemical reactions require a light source that emits wavelengths corresponding to an electronic transition in the reactant. In the early experiments (and in everyday life), sunlight was the light source, although it is polychromatic. Mercury-vapor lamps are more common in the... | Wikipedia - Photochemistry - Concept > Experimental setup | 326 | 1,655 | null |
Section: Concept > Principles. In the case of photochemical reactions, light provides the activation energy. Simplistically, light is one mechanism for providing the activation energy required for many reactions. If laser light is employed, it is possible to selectively excite a molecule so as to produce a desired elec... | Wikipedia - Photochemistry - Concept > Principles | 344 | 1,776 | null |
Section: Photochemical reactions > Examples of photochemical reactions. Photosynthesis: Plants use solar energy to convert carbon dioxide and water into glucose and oxygen. Human formation of vitamin D by exposure to sunlight. Bioluminescence: e.g. In fireflies, an enzyme in the abdomen catalyzes a reaction that produc... | Wikipedia - Photochemistry - Photochemical reactions > Examples of photochemical reactions | 339 | 1,501 | null |
Section: Photochemical reactions > Organic photochemistry. Examples of photochemical organic reactions are electrocyclic reactions, radical reactions, photoisomerization, and Norrish reactions. Alkenes undergo many important reactions that proceed via a photon-induced π to π* transition. The first electronic excited st... | Wikipedia - Photochemistry - Photochemical reactions > Organic photochemistry | 347 | 1,532 | null |
Section: Photochemical reactions > Inorganic and organometallic photochemistry. Coordination complexes and organometallic compounds are also photoreactive. These reactions can entail cis-trans isomerization. More commonly, photoreactions result in dissociation of ligands, since the photon excites an electron on the met... | Wikipedia - Photochemistry - Photochemical reactions > Inorganic and organometallic photochemistry | 235 | 977 | null |
Section: Photochemical reactions > Historical. Although bleaching has long been practiced, the first photochemical reaction was described by Trommsdorff in 1834. He observed that crystals of the compound α-santonin when exposed to sunlight turned yellow and burst. In a 2007 study the reaction was described as a success... | Wikipedia - Photochemistry - Photochemical reactions > Historical | 152 | 668 | null |
Article: Photopharmacology. Photopharmacology is an emerging multidisciplinary field that combines photochemistry and pharmacology. Built upon the ability of light to change the pharmacokinetics and pharmacodynamics of bioactive molecules, it aims at regulating the activity of drugs in vivo by using light. The light-ba... | Wikipedia - Photopharmacology - Summary | 205 | 920 | null |
Section: History. Though photopharmacology is a relatively new field, the concept of using light in therapeutic applications came into practice a few decades ago. Photodynamic therapy (PDT) is a well-established clinically practiced protocol in which photosensitizers are used to produce singlet oxygen for destroying di... | Wikipedia - Photopharmacology - History | 336 | 1,769 | null |
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