1.
Lactam
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A lactam is a cyclic amide. The term is a portmanteau of the words lactone + amide, general synthetic methods exist for the organic synthesis of lactams. Lactams form by the rearrangement of oximes in the Beckmann rearrangement. Lactams form from cyclic ketones and hydrazoic acid in the Schmidt reaction, lactams form from cyclisation of amino acids. Lactams form from intramolecular attack of linear acyl derivatives from the nucleophilic abstraction reaction, in iodolactamization an iminium ion reacts with an halonium ion formed in situ by reaction of an alkene with iodine. At lower temp, β-lactam is the preferred product, at optimum temperatures, a highly useful γ-lactam known as Vince Lactam is obtained. Lactim is a cyclic carboximidic acid compound characterized by an endocyclic carbon-nitrogen double bond and it is formed when lactam undergoes tautomerization. β-Lactam β-Lactam antibiotics, which includes penicillins 2-Pyrrolidone 2-Piperidinone Caprolactam
2.
Amide
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An amide, also known as an acid amide, is a compound with the functional group RnExNR′2. Most common are carboxamides, but many other important types of amides are known, the term amide refers both to classes of compounds and to the functional group within those compounds. Amide can also refer to the base of ammonia or of an organic amine. For discussion of these anionic amides, see Alkali metal amides, the remainder of this article is about the carbonyl–nitrogen sense of amide. The simplest amides are derivatives of ammonia wherein one hydrogen atom has replaced by an acyl group. The ensemble is represented as RCNH2 and is described as a primary amide. Closely related and even more numerous are secondary amides which can be derived from amines and have the formula RCNHR′. Tertiary amides are commonly derived from amines and have the general structure RCNR′R″. Amides are usually regarded as derivatives of carboxylic acids in which the group has been replaced by an amine or ammonia. The lone pair of electrons on the nitrogen is delocalized into the carbonyl, consequently, the nitrogen in amides is not pyramidal. It is estimated that acetamide is described by resonance structure A for 62%, in the usual nomenclature, one adds the term amide to the stem of the parent acids name. For instance, the derived from acetic acid is named acetamide. IUPAC recommends ethanamide, but this and related names are rarely encountered. When the amide is derived from a primary or secondary amine, thus, the amide formed from dimethylamine and acetic acid is N, N-dimethylacetamide. Usually even this name is simplified to dimethylacetamide, cyclic amides are called lactams, they are necessarily secondary or tertiary amides. Functional groups consisting of –PNR2 and –SO2NR2 are phosphonamides and sulfonamides, some chemists make a pronunciation distinction between the two, saying /əˈmiːd/ for the carbonyl–nitrogen compound and /ˈeɪmaɪd/ for the anion. Others replace one of these with /ˈæmᵻd/, while others pronounce both /ˈæmᵻd/, making them homonyms. Compared to amines, amides are very weak bases, while the conjugate acid of an amine has a pKa of about 9.5, the conjugate acid of an amide has a pKa around −0.5
3.
Alpha and beta carbon
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The alpha carbon in organic molecules refers to the first carbon atom that attaches to a functional group, such as a carbonyl. The second carbon atom is called the beta carbon, and the system continues naming in alphabetical order with Greek letters, the nomenclature can also be applied to the hydrogen atoms attached to the carbon atoms. A hydrogen atom attached to a carbon atom is called an alpha-hydrogen atom, a hydrogen atom on the beta-carbon atom is a beta hydrogen atom. Organic molecules with more than one group can be a source of confusion. Generally the functional group responsible for the name or type of the molecule is the group for purposes of carbon-atom naming. For example, the molecules nitrostyrene and phenethylamine are very similar, alpha-carbon is also a term that applies to proteins and amino acids. It is the carbon before the carbonyl carbon. Therefore, reading along the backbone of a protein would give a sequence of –n– etc. The α-carbon is where the different substituents attach to different amino acid. That is, the groups hanging off the chain at the α-carbon are what give amino acids their diversity and these groups give the α-carbon its stereogenic properties for every amino acid except for glycine. Therefore, the α-carbon is a stereocenter for every amino acid except glycine, glycine also does not have a β-carbon, while every other amino acid does. The α-carbon of an acid is significant in protein folding. When describing a protein, which is a chain of amino acids, in general, α-carbons of adjacent amino acids in a protein are about 3.8 ångströms apart. The α-carbon is important for enol- and enolate-based carbonyl chemistry as well, an exception is in reaction with silyl- chlorides, -bromides, and -iodides, where the oxygen acts as the nucleophile to produce silyl enol ether. ^ Hackhs Chemical Dictionary,1969, page 30, ^ Hackhs Chemical Dictionary,1969, page 95
4.
Antibiotic
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Antibiotics, also called antibacterials, are a type of antimicrobial drug used in the treatment and prevention of bacterial infections. They may either kill or inhibit the growth of bacteria, a limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the cold or influenza. Drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics, sometimes the term antibiotic is used to refer to any substance used against microbes, synonymous with antimicrobial. Some sources distinguish between antibacterial and antibiotic, antibacterials are used in soaps and disinfectants, while antibiotics are used as medicine, Antibiotics revolutionized medicine in the 20th century, and have together with vaccination led to the near eradication of diseases such as tuberculosis in the developed world. However, their effectiveness and easy access led to overuse, especially in raising, prompting bacteria to develop resistance. All classes of antibiotics in use today were first discovered prior to the mid 1980s, substances with antibiotic properties had been used for various purposes since ancient times. Before the early 20th century, treatments for infections were based primarily on medicinal folklore, mixtures with antimicrobial properties that were used in treatments of infections were described over 2000 years ago. Many ancient cultures, including the ancient Egyptians and ancient Greeks, used specially selected mold and plant materials, more recent observations made in the laboratory of antibiosis between microorganisms led to the discovery of natural antibacterials produced by microorganisms. Louis Pasteur observed, if we could intervene in the antagonism observed between some bacteria, it would offer perhaps the greatest hopes for therapeutics. In 1874, physician Sir William Roberts noted that cultures of the mold Penicillium glaucum that is used in the making of types of blue cheese did not display bacterial contamination. In 1876, physicist John Tyndall also contributed to this field, Louis Pasteur conducted research showing that Bacillus anthracis would not grow in the presence of the related mold Penicillium notatum. In his thesis, Duchesne proposed that bacteria and molds engage in a battle for survival. Duchesne observed that E. coli was eliminated by the fungus Penicillium glaucum when they were grown in the same culture. He also observed that when he inoculated animals with lethal doses of typhoid bacilli together with Penicillium glaucum. Unfortunately Duchesnes army service after getting his degree prevented him from doing any further research, Duchesne died of tuberculosis, a disease now treated by antibiotics. In 1928, Sir Alexander Fleming identified penicillin, a molecule produced by molds that kills or stops the growth of certain kinds of bacteria. Fleming was working on a culture of disease-causing bacteria when he noticed the spores of a mold, Penicillium chrysogenum
5.
Penicillin
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Penicillin is a group of antibiotics which include penicillin G, penicillin V, procaine penicillin, and benzathine penicillin. Penicillin antibiotics were among the first medications to be effective against many bacterial infections caused by staphylococci and streptococci, penicillins are still widely used today, though many types of bacteria have developed resistance following extensive use. About 10% of people report that they are allergic to penicillin, however, serious allergies only occur in about 0. 03%. Penicillin was discovered in 1928 by Scottish scientist Alexander Fleming, people began using it to treat infections in 1942. There are several enhanced penicillin families which are effective against additional bacteria, these include the penicillins, aminopenicillins. They are derived from Penicillium fungi, the term penicillin is often used generically to refer to benzylpenicillin, procaine benzylpenicillin, benzathine benzylpenicillin, and phenoxymethylpenicillin. Procaine penicillin and benzathine penicillin have the same activity as benzylpenicillin. Phenoxymethylpenicillin is less active against gram-negative bacteria than benzylpenicillin, infrequent adverse effects include fever, vomiting, erythema, dermatitis, angioedema, seizures, and pseudomembranous colitis. About 10% of people report that they are allergic to penicillin, however, serious allergies only occur in about 0. 03%. Penicillin can also induce serum sickness or a serum sickness-like reaction in some individuals, serum sickness is a type III hypersensitivity reaction that occurs one to three weeks after exposure to drugs including penicillin. It is not a drug allergy, because allergies are type I hypersensitivity reactions. Pain and inflammation at the site is also common for parenterally administered benzathine benzylpenicillin, benzylpenicillin. Significantly, there is a reaction to Streptolysin S, a toxin released by certain killed bacteria and associated with Penicillin injection. Allergic reactions to any β-lactam antibiotic may occur in up to 1% of patients receiving that agent, the allergic reaction is a Type I hypersensitivity reaction. Anaphylaxis will occur in approximately 0. 01% of patients and it has previously been accepted that there was up to a 10% cross-sensitivity between penicillin-derivatives, cephalosporins, and carbapenems, due to the sharing of the β-lactam ring. Assessments in 2006 found no risk for cross-allergy for second-generation or later cephalosporins than the first generation. However, as a risk, research shows that all beta lactams have the intrinsic hazard of very serious hazardous reactions in susceptible patients. Only the frequency of these reactions vary, based on the structure, bacteria constantly remodel their peptidoglycan cell walls, simultaneously building and breaking down portions of the cell wall as they grow and divide
6.
Carbapenem
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Carbapenems are antibiotics used for the treatment of infections known or suspected to be caused by multidrug-resistant bacteria. Their use is primarily in people who are hospitalized, like the penicillins and cephalosporins, they are members of the beta lactam class of antibiotics, which kill bacteria by binding to penicillin-binding proteins and inhibiting cell wall synthesis. They exhibit a spectrum of activity compared to cephalosporins and penicillins. Their effectiveness is less affected by many mechanisms of antibiotic resistance than other beta lactams. Carbapenem antibiotics were developed at Merck & Co. from the carbapenem thienamycin. Concern has arisen in recent years over increasing rates of resistance to carbapenems, agents with anti-pseudomonal activity, including doripenem, imipenem, and meropenem are not recommended in this population. Doripenem, imipenem, and meropenem are recommended for high-risk community-acquired abdominal infections, combination therapy, typically with an aminoglycoside, is recommended for Pseudomonas infections to avoid resistance development during treatment. Imipenem and meropenem are useful in cases in which P. aeruginosa is a suspected pathogen, in 2015, the National Institute for Health and Care Excellence recommended piperacillin-tazobactam as first line therapy for the treatment of bloodstream infections in neutropenic cancer patients. For bloodstream infections known to be due to extended spectrum beta-lactamase producing Enterobacteriaceace, carbapenems exhibit broad spectrum activity against gram-negative bacteria and somewhat narrower activity against gram-positive bacteria. For empiric therapy they are combined with a second drug having broader spectrum gram-positive activity. Activity is maintained against most strains of E. coli and K. pneumoniae that are resistant to cephalosporins due to the production of extended spectrum beta-lactamases, imipenem, doripenem, and meropenem also exhibit good activity against most strains of Pseudomonas aeruginosa and Acinetobacter species. The observed activity against these pathogens is especially valued as they are resistant to many other antibiotic classes. The spectrum of activity of the carbapenems against gram-positive bacteria is fairly broad, good activity is seen against methicillin-sensitive strains of Staphylococcus species, but many other antibiotics provide coverage for such infections. Good activity is observed for most Streptococcus species, including penicillin-resistant strains. Carbapenems generally exhibit good activity against anaerobes such as Bacteriodes fragilis, like other beta lactam antibiotics, they lack activity against atypical bacteria, which do not have a cell wall and are thus not affected by cell wall synthesis inhibitors. Carbapenems are contraindicated in patients with allergic reactions to beta lactam antibiotics. Serious and occasionally fatal allergic reactions can occur in people treated with carbapenems, seizures are a dose-limiting toxicity for both imipenem and meropenem. Clostridium difficile-related diarrhea may occur in people treated with carbapenems or other broad spectrum antibiotics, imipenem, the first clinically used carbapenem, was developed at Merck and Co
7.
Monobactam
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Monobactams are β-lactam compounds wherein the β-lactam ring is alone and not fused to another ring, in contrast to most other β-lactams. They are effective only against aerobic Gram-negative bacteria, currently the only commercially available monobactam antibiotic is aztreonam. Other examples of monobactams are tigemonam, nocardicin A, and tabtoxin, adverse effects to monobactams can include skin rash and occasional abnormal liver functions. They have no cross-hypersensitivity reactions with penicillin but like penicillins can trigger seizures in patients with history of seizures, monobactams at the US National Library of Medicine Medical Subject Headings
8.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength
9.
Bacteria
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Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea
10.
Antimicrobial resistance
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Antimicrobial resistance is the ability of a microbe to resist the effects of medication previously used to treat them. This broader term also covers antibiotic resistance, which applies to bacteria, resistance arises through one of three ways, natural resistance in certain types of bacteria, genetic mutation, or by one species acquiring resistance from another. Resistance can appear spontaneously because of mutations, or more commonly following gradual buildup over time. Resistant microbes are increasingly difficult to treat, requiring alternative medications or higher doses, microbes resistant to multiple antimicrobials are called multidrug resistant, or sometimes superbugs. Antimicrobial resistance is on the rise with millions of deaths every year, Antibiotics should only be used when needed as prescribed by health professionals. The prescriber should closely adhere to the five rights of administration, the right patient, the right drug, the right dose, the right route. Narrow-spectrum antibiotics are preferred over broad-spectrum antibiotics when possible, as effectively and accurately targeting specific organisms is less likely to cause resistance, cultures should be taken before treatment when indicated and treatment potentially changed based on the susceptibility report. For people who take these medications at home, education about proper use is essential, rising drug resistance is caused mainly by improper use of antimicrobials in humans as well as in animals, and spread of resistant strains between the two. Antibiotics increase selective pressure in bacterial populations, causing vulnerable bacteria to die, with resistance to antibiotics becoming more common there is greater need for alternative treatments. Calls for new antibiotic therapies have been issued, but new development is becoming rarer. Antibiotic resistance—when bacteria change so antibiotics no longer work in people who need them to treat infections—is now a threat to public health. Increasing public calls for collective action to address the threat include proposals for international treaties on antimicrobial resistance. Worldwide antibiotic resistance is not fully mapped, but poorer countries with weak healthcare systems are more affected, the WHO defines antimicrobial resistance as a microorganisms resistance to an antimicrobial drug that was once able to treat an infection by that microorganism. A person cannot become resistant to antibiotics, resistance is a property of the microbe, not a person or other organism infected by a microbe. Bacteria with resistance to antibiotics predate medical use of antibiotics by humans, however and this may result in emergence of resistance in any remaining bacteria. Antibiotic use in feed at low doses for growth promotion is an accepted practice in many industrialized countries and is known to lead to increased levels of resistance. It is uncertain whether antibacterials in soaps and other products contribute to antibiotic resistance, increasing bacterial resistance is linked with the volume of antibiotic prescribed, as well as missing doses when taking antibiotics. Up to half of antibiotics used in humans are unnecessary and inappropriate, a single regimen of antibiotics even in compliant individuals leads to a greater risk of resistant organisms to that antibiotic in the person for a month to possibly a year
11.
Beta-lactamase
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Beta-lactamase provides antibiotic resistance by breaking the antibiotics structure. These antibiotics all have an element in their molecular structure. Through hydrolysis, the lactamase enzyme breaks the β-lactam ring open, beta-lactam antibiotics are typically used to treat a broad spectrum of Gram-positive and Gram-negative bacteria. Beta-lactamases produced by Gram-negative organisms are usually secreted, especially when antibiotics are present in the environment, the structure of a Streptomyces β-lactamase is given by 1BSG. Penicillinase is a type of β-lactamase, showing specificity for penicillins. Molecular weights of the various penicillinases tend to cluster near 50 kiloDaltons, penicillinase-resistant beta-lactams such as methicillin were developed, but there is now widespread resistance to even these. Additionally, many class A TEM β-lactamases are inhibited by β-lactamase inhibitor protein, because of the increasing number of TEM- and SHV-derived β-lactamases, they were divided into two subclasses, 2a and 2b. GROUP 2a PENICILLINASE, Molecular Class A The 2a subgroup contains just penicillinases, GROUP 2b BROAD-SPECTRUM, Molecular Class A 2b Opposite to 2a, 2b are broad-spectrum β-lactamases, meaning that they are capable of inactivating penicillins and cephalosporins at the same rate. GROUP 2c CARBENICILLINASE, Molecular Class A Latersubgroup 2c was segregated from group 2 because these enzymes inactivate carbenicillin more than benzylpenicillin and these enzymes are able to inactivate the oxazolylpenicillins like oxacillin, cloxacillin, dicloxacillin. The enzymes belong to the molecular class D not molecular class A. Metallo B-lactamases are able to hydrolyse penicillins, cephalosporins and this group has been omitted from the current scheme, as when it was described originally it included enzymes not classifiable into other groups. The molecular classification of β-lactamases is based on the nucleotide and amino acid sequences in these enzymes, to date, four classes are recognised, correlating with the functional classification. Among Gram-negative bacteria, the emergence of resistance to expanded-spectrum cephalosporins has been a major concern and it appeared initially in a limited number of bacterial species that could mutate to hyperproduce their chromosomal class C β-lactamase. A few years later, resistance appeared in bacterial species not naturally producing AmpC enzymes due to the production of TEM- or SHV-type ESBLs, members of the family commonly express plasmid-encoded β-lactamases. Which confer resistance to penicillins but not to expanded-spectrum cephalosporins, in the mid-1980s, a new group of enzymes, the extended-spectrum β-lactamases, was detected. The prevalence of ESBL-producing bacteria have been increasing in acute care hospitals. ESBLs are beta-lactamases that hydrolyze extended-spectrum cephalosporins with a side chain. These cephalosporins include cefotaxime, ceftriaxone, and ceftazidime, as well as the oxyimino-monobactam aztreonam, thus ESBLs confer multi-resistance to these antibiotics and related oxyimino-beta lactams. In typical circumstances, they derive from genes for TEM-1, TEM-2, a broader set of β-lactam antibiotics are susceptible to hydrolysis by these enzymes
12.
Hermann Staudinger
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Hermann Staudinger was a German organic chemist who demonstrated the existence of macromolecules, which he characterized as polymers. For this work he received the 1953 Nobel Prize in Chemistry and he is also known for his discovery of ketenes and of the Staudinger reaction. Hermann Staudinger was born in 1881 in Worms, after receiving his Ph. D. from the University of Halle in 1903, Staudinger took a position at the University of Strasbourg. It was here that he discovered the ketenes, a family of molecules characterized by the general depicted in Figure 1. Ketenes would prove an important intermediate for the production of yet-to-be-discovered antibiotics such as penicillin and amoxicillin. In 1907, Staudinger began an assistant professorship at the Technical University of Karlsruhe, here, he successfully isolated a number of useful organic compounds as more completely reviewed by Rolf Mülhaupt. In 1912, Staudinger took on a new position at the Swiss Federal Institute of Technology in Zurich, one of his earliest discoveries came in 1919, when he and colleague Meyer reported that azides react with triphenylphosphine to form phosphazide. This reaction – commonly referred to as the Staudinger reaction – produces a high phosphazide yield. While at Karlsruhe and later, Zurich, Staudinger began research in the chemistry of rubber, for very high molecular weights had been measured by the physical methods of Raoult. In other words, polymers are like chains of paper clips, at first the majority of Staudinger’s colleagues refused to accept the possibility that small molecules could link together covalently to form high-molecular weight compounds. As Mülhaupt aptly notes, this is due in part to the fact that molecular structure, in 1926 he was appointed lecturer of chemistry at the University of Freiburg at Freiburg in Breisgau, where he spent the rest of his career. In 1927, he married the Latvian botanist, Magda Voita (also shown as, further evidence to support his polymer hypothesis emerged in the 1930s. High molecular weights of polymers were confirmed by membrane osmometry, the X-ray diffraction studies of polymers by Herman Mark provided direct evidence for long chains of repeating molecular units. And the synthetic work led by Carothers demonstrated that such as nylon. His theory opened up the subject to development, and helped place polymer science on a sound basis. Staudinger’s groundbreaking elucidation of the nature of the high-molecular weight compounds he termed Makromoleküle paved the way for the birth of the field of polymer chemistry, Staudinger himself saw the potential for this science long before it was fully realized. e. Staudinger founded the first polymer chemistry journal in 1940, and in 1953 received the Nobel Prize in Chemistry for “his discoveries in the field of macromolecular chemistry. ”In 1999, heidegger and Nazism, denounced or demoted non-Nazis Polymer science Helmut Ringsdorf. Hermann Staudinger and the Future of Polymer Research Jubilees – Beloved Occasions for Cultural Piety, ogilvie, Marilyn Bailey, Harvey, Joy Dorothy
13.
Schiff base
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A Schiff base is a compound with the general structure R2C=NR. They can be considered a sub-class of imines, being either secondary ketimines or secondary depending on their structure. The term is synonymous with azomethine which refers specifically to secondary aldimines. A number of naming systems exist for these compounds. For instance a Schiff base derived from an aniline, where R3 is a phenyl or a substituted phenyl, can be called an anil, the term Schiff base is normally applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. Such complexes do occur naturally, for instance in Corrin, but the majority of Schiff bases are artificial and are used to form many important catalysts, such as Jacobsens catalyst. Schiff bases can be synthesized from an aliphatic or aromatic amine, the common enzyme cofactor PLP forms a Schiff base with a lysine residue and is transaldiminated to the substrate. Similarly, the cofactor retinal forms a Schiff base in rhodopsins, including human rhodopsin, an example where the substrate forms a Schiff base to the enzyme is in the fructose 1, 6-bisphosphate aldolase catalyzed reaction during glycolysis and in the metabolism of amino acids. Schiff bases are common ligands in coordination chemistry, the imine nitrogen is basic and exhibits pi-acceptor properties. The ligands are derived from alkyl diamines and aromatic aldehydes. Chiral Schiff bases were one of the first ligands used for asymmetric catalysis, in 1968 Ryōji Noyori developed a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene. For this work he was awarded a share of the 2001 Nobel Prize in Chemistry. Their simple and clean chemistry make them a candidate as a low cost alternative to currently used conjugated materials. Schiff base chemistry is used to prepare covalent organic framework
14.
Aniline
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Aniline is an organic compound with the formula C6H5NH2. Consisting of a group attached to an amino group, aniline is the prototypical aromatic amine. Its main use is in the manufacture of precursors to polyurethane, like most volatile amines, it possesses the odour of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds, the amine is nearly planar owing to conjugation of the lone pair with the aryl substituent. The C-N distance is correspondingly shorter, in aniline, the C-N and C-C distances are close to 1.39 Å, indicating the π-bonding between N and C. Industrial aniline production involves two steps, first, benzene is nitrated with a concentrated mixture of nitric acid and sulfuric acid at 50 to 60 °C to yield nitrobenzene. The nitrobenzene is then hydrogenated in the presence of metal catalysts, the reduction of nitrobenzene to aniline was first performed by Nikolay Zinin in 1842 using inorganic sulfide as a reductant. Aniline can alternatively be prepared from ammonia and phenol derived from the cumene process, many analogues of aniline are known where the phenyl group is further substituted. These include toluidines, xylidines, chloroanilines, aminobenzoic acids, nitroanilines and they often are prepared by nitration of the substituted aromatic compounds followed by reduction. For example, this approach is used to convert toluene into toluidines, the chemistry of aniline is rich because the compound has been cheaply available for many years. Below are some classes of its reactions, the oxidation of aniline has been heavily investigated, and can result in reactions localized at nitrogen or more commonly results in the formation of new C-N bonds. In alkaline solution, azobenzene results, whereas arsenic acid produces the violet-coloring matter violaniline, chromic acid converts it into quinone, whereas chlorates, in the presence of certain metallic salts, give aniline black. Hydrochloric acid and potassium chlorate give chloranil, potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene, ammonia and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives 4-aminophenol and para-amino diphenylamine, oxidation with persulfate affords a variety of polyanilines compounds. These polymers exhibit rich redox and acid-base properties, like phenols, aniline derivatives are highly susceptible to electrophilic substitution reactions. Its high reactivity reflects that it is an enamine, which enhances the ability of the ring. For example, reaction of aniline with sulfuric acid at 180 °C produces sulfanilic acid, if bromine water is added to aniline, the bromine water is decolourised and a white precipitate of 2,4, 6-tribromophenylamine is formed. The largest scale industrial reaction of aniline involves its alkylation with formaldehyde, an idealized equation is shown,2 C6H5NH2 + CH2O → CH22 + H2O The resulting diamine is the precursor to 4, 4-MDI and related diisocyanates
15.
Benzaldehyde
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Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful and this colorless liquid has a characteristic almond-like odor. Benzaldehyde is the component of bitter almond oil and can be extracted from a number of other natural sources. Synthetic benzaldehyde is the agent in imitation almond extract, which is used to flavor cakes. Benzaldehyde was first extracted from bitter almonds in 1803 by the French pharmacist Martrès, in 1832 German chemists Friedrich Wöhler and Justus von Liebig first synthesized benzaldehyde. Benzaldehyde can be obtained by many processes, in the 1980s, an estimated 18 million kilograms were produced annually in Japan, Europe, and North America, a level that can be assumed to continue. Currently liquid phase chlorination and oxidation of toluene are the main routes, numerous other methods have been developed, such as the partial oxidation of benzyl alcohol, alkali hydrolysis of benzal chloride, and the carbonylation of benzene. Site-specific nuclear magnetic resonance spectroscopy, which evaluates 1H/2H isotope ratios, has used to differentiate between naturally occurring and synthetic benzaldehyde. Benzaldehyde and similar chemicals occur naturally in many foods, most of the benzaldehyde that people eat is from natural, traditional foods, such as almonds. Almonds, apricots, apples and cherry kernels, contain significant amounts of amygdalin and this glycoside breaks up under enzyme catalysis into benzaldehyde, hydrogen cyanide and two molecules of glucose. Benzaldehyde contributes to the scent of oyster mushrooms, on oxidation, benzaldehyde is converted into the odorless benzoic acid, which is a common impurity in laboratory samples. Benzyl alcohol can be formed from benzaldehyde by means of hydrogenation, benzaldehyde is commonly employed to confer almond flavor to foods and scented products. It is sometimes used in cosmetics products, in industrial settings, benzaldehyde is used chiefly as a precursor to other organic compounds, ranging from pharmaceuticals to plastic additives. The aniline dye malachite green is prepared from benzaldehyde and dimethylaniline and it is a precursor to certain acridine dyes as well. Via aldol condensations, benzaldehyde is converted into derivatives of cinnamaldehyde, the synthesis of mandelic acid starts from benzaldehyde, First hydrocyanic acid is added to benzaldehyde, and the resulting nitrile is subsequently hydrolysed to mandelic acid. It is used as a bee repellant, a small amount of benzaldehyde-containing solution is placed on a fume board near the honey combs. The bees promptly move away from the combs to get away from the fumes. Benzaldehyde allows the beekeeper to remove the honey frames from the bee hive with greater safety to both bees and the beekeeper, for a 70-kg human, the lethal dose is estimated at 50 mL
16.
Diphenylketene
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Diphenylketene is a chemical substance of the ketene family. Diphenylketene, like most disubstituted ketenes, is an oil at room temperature and pressure. Diphenylketene can undergo attack from a host of nucleophiles, including alcohols, amines and these rates can be increased in the presence of catalysts. At present the mechanism of attack is unknown, but work is underway to determine the exact mechanism, diphenylketene is produced by the elimination of hydrogen chloride from diphenylacetyl chloride in the presence of triethylamine
17.
Cycloaddition
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A cycloaddition is a pericyclic chemical reaction, in which two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity. The resulting reaction is a cyclization reaction, many but not all cycloadditions are concerted. As a class of reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation, an older, but still common, notation is based on the size of linear arrangements of atoms in the reactants. It uses parentheses, where the variables are the numbers of atoms in each reactant. The product is a cycle of size, in this system, the standard Diels-Alder reaction a cycloaddition, the 1, 3-dipolar cycloaddition is a cycloaddition and cyclopropanation of a carbene with an alkene a cycloaddition. A more recent, IUPAC-preferred notation uses square brackets to indicate the number of electrons, rather than carbon atoms, in the notation, the standard Diels-Alder reaction is a cycloaddition, the 1, 3-dipolar cycloaddition is. Thermal cycloadditions are those cycloadditions where the reactants are in the electronic state. They usually have π electrons participating in the material, for some integer n. These reactions occur, for reasons of symmetry, in a suprafacial-suprafacial or antarafacial-antarafacial manner. Cycloadditions in which 4n π electrons participate can also occur via photochemical activation, here, one component has an electron promoted from the HOMO to the LUMO. Orbital symmetry is then such that the reaction can proceed in a suprafacial-suprafacial manner, an example is the DeMayo reaction. Another example is shown below, the dimerization of cinnamic acid. The two trans alkenes react head-to-tail, and the isomers are called truxillic acids. Supramolecular effects can influence these cycloadditions, the cycloaddition of trans-1, 2-bisethene is directed by resorcinol in the solid-state in 100% yield. Some cycloadditions instead of π bonds operate through strained cyclopropane rings, for example, an analog for the Diels-Alder reaction is the quadricyclane-DMAD reaction, In the cycloaddition notation i and j refer to the number of atoms involved in the cycloaddition. In this notation a Diels-Alder reaction is a cycloaddition and a 1, the IUPAC preferred notation however, with takes electrons into account and not atoms. In this notation the DA reaction and the dipolar reaction both become a cycloaddition, the reaction between norbornadiene and an activated alkyne is a cycloaddition
18.
Grignard reaction
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The Grignard reaction is an organometallic chemical reaction in which alkyl, vinyl, or aryl-magnesium halides add to a carbonyl group in an aldehyde or ketone. This reaction is an important tool for the formation of carbon–carbon bonds, the reaction of an organic halide with magnesium is not a Grignard reaction, but provides a Grignard reagent. Grignard reagents are similar to organolithium reagents because both are strong nucleophiles that can form new carbon–carbon bonds, the nucleophilicity increases if the alkyl substituent is replaced by an amido group. These amido magnesium halides are called Hauser bases, the Grignard reagent functions as a nucleophile, attacking the electrophilic carbon atom that is present within the polar bond of a carbonyl group. The addition of the Grignard reagent to the carbonyl typically proceeds through a ring transition state. However, with hindered Grignard reagents, the reaction may proceed by single-electron transfer, similar pathways are assumed for other reactions of Grignard reagents, e. g. in the formation of carbon–phosphorus, carbon–tin, carbon–silicon, carbon–boron and other carbon–heteroatom bonds. Grignard reagents form via the reaction of an alkyl or alkyl halide with magnesium metal, the reaction is conducted by adding the organic halide to a suspension of magnesium in an etherial solvent, which provides ligands required to stabilize the organomagnesium compound. Empirical evidence suggests that the reaction takes place on the surface of the metal, the reaction proceeds through single electron transfer, In the Grignard formation reaction, radicals may be converted into carbanions through a second electron transfer. R−X + Mg → R−X•− + Mg•+ R−X•− → R• + X− R• + Mg•+ → RMg+ RMg+ + X− → RMgX A limitation of Grignard reagents is that they do not readily react with alkyl halides via an SN2 mechanism. In reactions involving Grignard reagents, it is important to water and air. Since most Grignard reactions are conducted in diethyl ether or tetrahydrofuran. Small-scale or quantitative preparations should be conducted under nitrogen or argon atmospheres, although the reagents still need to be dry, ultrasound can allow Grignard reagents to form in wet solvents by activating the magnesium such that it consumes the water. As is common for reactions involving solids and solution, initiation follows a period during which reactive magnesium becomes exposed to the organic reagents. After this induction period, the reactions can be highly exothermic, Alkyl and aryl bromides and iodides are common, with chlorides being seen as well. However, fluorides are generally unreactive, except with specially activated magnesium, typical Grignard reactions involve the use of magnesium ribbon. All magnesium is coated with a layer of magnesium oxide. Specially activated magnesium, such as Rieke magnesium, circumvents this problem, the oxide layer can also be broken up using ultrasound, or by adding a few drops of iodine or 1, 2-Diiodoethane. Most Grignard reactions are conducted in solvents, especially diethyl ether
19.
Ring strain
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In organic chemistry, ring strain is a type of instability that exists when bonds in a molecule form angles that are abnormal. Strain is most commonly discussed for small rings such as cyclopropanes and cyclobutanes, because of their high strain, the heat of combustion for these small rings is elevated. Ring strain results from a combination of angle strain, conformational strain or Pitzer strain, the simplest examples of angle strain are small cycloalkanes such as cyclopropane and cyclobutane. Furthermore, there is often eclipsing in cyclic systems which cannot be relieved, in alkanes, optimum overlap of atomic orbitals is achieved at 109. 5°. The most common compounds have five or six carbons in their ring. Adolf von Baeyer received a Nobel Prize in 1905 for the discovery of the Baeyer strain theory, angle strain occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation. Angle strain typically affects cyclic molecules, which lack the flexibility of acyclic molecules, angle strain destabilizes a molecule, as manifested in higher reactivity and elevated heat of combustion. Maximum bond strength results from effective overlap of orbitals in a chemical bond. A quantitative measure for angle strain is strain energy, angle strain and torsional strain combine to create ring strain that affects cyclic molecules. ΔHcombustion per CH2 -658.6 kJ = strain per CH2 The value 658.6 kJ per mole is obtained from an unstrained long-chain alkane, cyclic alkenes are subject to strain resulting from distortion of the sp2-hybridized carbon centers. Illustrative is C60 where the centres are pyramidalized. This distortion enhances the reactivity of this molecule, angle strain also is the basis of Bredts rule which dictates that bridgehead carbon centers are not incorporated in alkenes because the resulting alkene would be subject to extreme angle strain. In cycloalkanes, each carbon is bonded nonpolar covalently to two carbons and two hydrogen, the carbons have sp3 hybrization and should have ideal bond angles of 109. 5°. Due to the limitations of cyclic structure, however, the angle is only achieved in a six carbon ring — cyclohexane in chair conformation. For other cycloalkanes, the bond angles deviate from ideal, in cyclopropanes and cyclobutanes the C-C bonds are 60° and ~90° respectively. These molecules have bond angles between ring atoms which are more acute than the tetrahedral and trigonal planar bond angles required by their respective sp3. Because of the bond angles, the bonds have higher energy. In addition, the structures of cyclopropanes/enes and cyclclobutanes/enes offer very little conformational flexibility
20.
Hydrolysis
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Hydrolysis usually means the cleavage of chemical bonds by the addition of water. When a carbohydrate is broken into its component sugar molecules by hydrolysis, generally, hydrolysis or saccharification is a step in the degradation of a substance. Hydrolysis can be the reverse of a reaction in which two molecules join together into a larger one and eject a water molecule. Thus hydrolysis adds water to break down, whereas condensation builds up by removing water, usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both substance and water molecule to split into two parts, in such reactions, one fragment of the target molecule gains a hydrogen ion. A common kind of hydrolysis occurs when a salt of an acid or weak base is dissolved in water. Water spontaneously ionizes into hydroxide anions and hydronium cations, the salt also dissociates into its constituent anions and cations. For example, sodium acetate dissociates in water into sodium and acetate ions, sodium ions react very little with the hydroxide ions whereas the acetate ions combine with hydronium ions to produce acetic acid. In this case the net result is an excess of hydroxide ions. For example, dissolving sulfuric acid in water is accompanied by hydrolysis to give hydronium and bisulfate, for a more technical discussion of what occurs during such a hydrolysis, see Brønsted–Lowry acid–base theory. Acid–base-catalysed hydrolyses are very common, one example is the hydrolysis of amides or esters and their hydrolysis occurs when the nucleophile attacks the carbon of the carbonyl group of the ester or amide. In an aqueous base, hydroxyl ions are better nucleophiles than polar molecules such as water, in acids, the carbonyl group becomes protonated, and this leads to a much easier nucleophilic attack. The products for both hydrolyses are compounds with carboxylic acid groups, perhaps the oldest commercially practiced example of ester hydrolysis is saponification. It is the hydrolysis of a triglyceride with a base such as sodium hydroxide. During the process, glycerol is formed, and the fatty acids react with the base and these salts are called soaps, commonly used in households. In addition, in living systems, most biochemical reactions take place during the catalysis of enzymes, the catalytic action of enzymes allows the hydrolysis of proteins, fats, oils, and carbohydrates. As an example, one may consider proteases and they catalyse the hydrolysis of interior peptide bonds in peptide chains, as opposed to exopeptidases. However, proteases do not catalyse the hydrolysis of all kinds of proteins and their action is stereo-selective, Only proteins with a certain tertiary structure are targeted as some kind of orienting force is needed to place the amide group in the proper position for catalysis
21.
Plane (geometry)
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In mathematics, a plane is a flat, two-dimensional surface that extends infinitely far. A plane is the analogue of a point, a line. When working exclusively in two-dimensional Euclidean space, the article is used, so. Many fundamental tasks in mathematics, geometry, trigonometry, graph theory and graphing are performed in a space, or in other words. Euclid set forth the first great landmark of mathematical thought, a treatment of geometry. He selected a small core of undefined terms and postulates which he used to prove various geometrical statements. Although the plane in its sense is not directly given a definition anywhere in the Elements. In his work Euclid never makes use of numbers to measure length, angle, in this way the Euclidean plane is not quite the same as the Cartesian plane. This section is concerned with planes embedded in three dimensions, specifically, in R3. In a Euclidean space of any number of dimensions, a plane is determined by any of the following. A line and a point not on that line, a line is either parallel to a plane, intersects it at a single point, or is contained in the plane. Two distinct lines perpendicular to the plane must be parallel to each other. Two distinct planes perpendicular to the line must be parallel to each other. Specifically, let r0 be the vector of some point P0 =. The plane determined by the point P0 and the vector n consists of those points P, with position vector r, such that the vector drawn from P0 to P is perpendicular to n. Recalling that two vectors are perpendicular if and only if their dot product is zero, it follows that the plane can be described as the set of all points r such that n ⋅ =0. Expanded this becomes a + b + c =0, which is the form of the equation of a plane. This is just a linear equation a x + b y + c z + d =0 and this familiar equation for a plane is called the general form of the equation of the plane
22.
Orbital hybridisation
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In chemistry, hybridisation is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory. Hybrid orbitals are very useful in the explanation of molecular geometry, although sometimes taught together with the valence shell electron-pair repulsion theory, valence bond and hybridisation are in fact not related to the VSEPR model. Chemist Linus Pauling first developed the theory in 1931 in order to explain the structure of simple molecules such as methane using atomic orbitals. In reality however, methane has four bonds of equivalent strength separated by the bond angle of 109. 5°. It gives a simple orbital picture equivalent to Lewis structures, hybridisation theory finds its use mainly in organic chemistry. Orbitals are a representation of the behaviour of electrons within molecules. In heavier atoms, such as carbon, nitrogen, and oxygen, hybrid orbitals are assumed to be mixtures of atomic orbitals, superimposed on each other in various proportions. For example, in methane, the C hybrid orbital which forms each carbon–hydrogen bond consists of 25% s character and 75% p character and is thus described as sp3 hybridised. Quantum mechanics describes this hybrid as an sp3 wavefunction of the form N, the ratio of coefficients is √3 in this example. Since the electron density associated with an orbital is proportional to the square of the wavefunction, the p character or the weight of the p component is N2λ2 = 3/4. The amount of p character or s character, which is decided mainly by orbital hybridisation, molecules with multiple bonds or multiple lone pairs can have orbitals represented in terms of sigma and pi symmetry or equivalent orbitals. The sigma and pi representation of Erich Hückel is the common one compared to the equivalent orbital representation of Linus Pauling. The two have mathematically equivalent total many-electron wave functions, and are related by a transformation of the set of occupied molecular orbitals. Hybridisation describes the bonding atoms from a point of view. For a tetrahedrally coordinated carbon, the carbon should have 4 orbitals with the symmetry to bond to the 4 hydrogen atoms. The carbon atom can also bond to four hydrogen atoms by an excitation of an electron from the doubly occupied 2s orbital to the empty 2p orbital, producing four singly occupied orbitals. The energy released by formation of two additional bonds more than compensates for the energy required, energetically favouring the formation of four C-H bonds. Quantum mechanically, the lowest energy is obtained if the four bonds are equivalent, a set of four equivalent orbitals can be obtained that are linear combinations of the valence-shell s and p wave functions, which are the four sp3 hybrids
23.
Resonance (chemistry)
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In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis structure. A molecule or ion with such delocalized electrons is represented by several contributing structures, each contributing structure can be represented by a Lewis structure, with only an integer number of covalent bonds between each pair of atoms within the structure. Several Lewis structures are used collectively to describe the molecular structure. Electron delocalization lowers the energy of the substance and thus makes it more stable than any of the contributing structures. The difference between the energy of the actual structure and that of the contributing structure with the lowest potential energy is called the resonance energy or delocalization energy. An isomer is a molecule with the chemical formula but with different arrangements of atoms in space. Resonance contributors of a molecule, on the contrary, can differ by the arrangements of electrons. Therefore, the resonance hybrid cannot be represented by a combination of isomers, benzene undergoes substitution reactions, rather than addition reactions as typical for alkenes. He proposed that the bond in benzene is intermediate of a single and double bond. The mechanism of resonance was introduced into quantum mechanics by Werner Heisenberg in 1926 in a discussion of the states of the helium atom. He compared the structure of the atom with the classical system of resonating coupled harmonic oscillators. Linus Pauling used this mechanism to explain the partial valence of molecules in 1928, the alternative term mesomerism popular in German and French publications with the same meaning was introduced by C. K. Ingold in 1938, but did not catch on in the English literature. The current concept of effect has taken on a related. The double headed arrow was introduced by the German chemist Fritz Arndt who preferred the German phrase zwischenstufe or intermediate stage, the real structure is an intermediate of these structures represented by a resonance hybrid. The contributing structures are not isomers and they differ only in the position of electrons, not in the position of nuclei. Each Lewis formula must have the number of valence electrons. Bonds that have different bond orders in different contributing structures do not have typical bond lengths, the real structure has a lower total potential energy than each of the contributing structures would have. This means that it is more stable than each separate contributing structure would be and it is a common misconception that resonance structures are actual transient states of the molecule, with the molecule oscillating between them or existing as an equilibrium between them
24.
Trigonal planar molecular geometry
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In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands are identical and all angles are 120°. Such species belong to the point group D3h, molecules where the three ligands are not identical, such as H2CO, deviate from this idealized geometry. Examples of molecules with trigonal planar geometry include boron trifluoride, formaldehyde, phosgene, some ions with trigonal planar geometry include nitrate, carbonate, and guanidinium. In organic chemistry, planar, three-connected carbon centers that are trigonal planar are often described as having sp2 hybridization, nitrogen inversion is the distortion of pyramidal amines through a transition state that is trigonal planar. Pyramidalization is a distortion of this molecular shape towards a tetrahedral molecular geometry, one way to observe this distortion is in pyramidal alkenes
25.
Pyramid (geometry)
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In geometry, a pyramid is a polyhedron formed by connecting a polygonal base and a point, called the apex. Each base edge and apex form a triangle, called a lateral face and it is a conic solid with polygonal base. A pyramid with a base has n +1 vertices, n +1 faces. A right pyramid has its apex directly above the centroid of its base, nonright pyramids are called oblique pyramids. A regular pyramid has a polygon base and is usually implied to be a right pyramid. When unspecified, a pyramid is usually assumed to be a square pyramid. A triangle-based pyramid is often called a tetrahedron. Among oblique pyramids, like acute and obtuse triangles, a pyramid can be called if its apex is above the interior of the base and obtuse if its apex is above the exterior of the base. A right-angled pyramid has its apex above an edge or vertex of the base, in a tetrahedron these qualifiers change based on which face is considered the base. Pyramids are a subclass of the prismatoids, pyramids can be doubled into bipyramids by adding a second offset point on the other side of the base plane. A right pyramid with a base has isosceles triangle sides, with symmetry is Cnv or. It can be given an extended Schläfli symbol ∨, representing a point, a join operation creates a new edge between all pairs of vertices of the two joined figures. The trigonal or triangular pyramid with all equilateral triangles faces becomes the regular tetrahedron, a lower symmetry case of the triangular pyramid is C3v, which has an equilateral triangle base, and 3 identical isosceles triangle sides. The square and pentagonal pyramids can also be composed of convex polygons. Right pyramids with regular star polygon bases are called star pyramids, for example, the pentagrammic pyramid has a pentagram base and 5 intersecting triangle sides. A right pyramid can be named as ∨P, where is the point, ∨ is a join operator. It has C1v symmetry from two different base-apex orientations, and C2v in its full symmetry, a rectangular right pyramid, written as ∨, and a rhombic pyramid, as ∨, both have symmetry C2v. The volume of a pyramid is V =13 b h and this works for any polygon, regular or non-regular, and any location of the apex, provided that h is measured as the perpendicular distance from the plane containing the base
26.
Ketone
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In chemistry, a ketone /ˈkiːtoʊn/ is an organic compound with the structure RCR, where R and R can be a variety of carbon-containing substituents. Ketones and aldehydes are simple compounds that contain a carbonyl group and they are considered simple because they do not have reactive groups like −OH or −Cl attached directly to the carbon atom in the carbonyl group, as in carboxylic acids containing −COOH. Many ketones are known and many are of importance in industry. Examples include many sugars and the industrial solvent acetone, which is the smallest ketone, the word ketone is derived from Aketon, an old German word for acetone. According to the rules of IUPAC nomenclature, ketones are named by changing the suffix -ane of the parent alkane to -anone, the position of the carbonyl group is usually denoted by a number. For the most important ketones, however, traditional names are still generally used. The common names of ketones are obtained by writing separately the names of the two alkyl groups attached to the group, followed by ketone as a separate word. The names of the groups are written alphabetically. When the two groups are the same, the prefix di- is added before the name of alkyl group. The positions of other groups are indicated by Greek letters, the α-carbon being the adjacent to carbonyl group. If both alkyl groups in a ketone are the same then the ketone is said to be symmetrical, although used infrequently, oxo is the IUPAC nomenclature for a ketone functional group. Other prefixes, however, are also used, for some common chemicals, keto or oxo refer to the ketone functional group. The term oxo is used widely through chemistry, for example, it also refers to an oxygen atom bonded to a transition metal. The ketone carbon is often described as sp2 hybridized, a description that includes both their electronic and molecular structure, ketones are trigonal planar around the ketonic carbon, with C−C−O and C−C−C bond angles of approximately 120°. Ketones differ from aldehydes in that the group is bonded to two carbons within a carbon skeleton. In aldehydes, the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains, ketones are also distinct from other carbonyl-containing functional groups, such as carboxylic acids, esters and amides. The carbonyl group is polar because the electronegativity of the oxygen is greater than that for carbon, thus, ketones are nucleophilic at oxygen and electrophilic at carbon. Because the carbonyl group interacts with water by bonding, ketones are typically more soluble in water than the related methylene compounds
27.
Robert Burns Woodward
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Robert Burns Woodward was an American organic chemist. He also worked closely with Roald Hoffmann on theoretical studies of chemical reactions and he was awarded the Nobel Prize in Chemistry in 1965. Woodward was born in Boston, Massachusetts, to Margaret and Arthur Chester Woodward, son of Roxbury, Massachusetts apothecary, when Robert was one year old, his father died in the flu pandemic of 1918. From a very early age, Woodward was attracted to and engaged in study of chemistry while he attended a public primary school. By the time he entered school, he had already managed to perform most of the experiments in Ludwig Gattermanns then widely used textbook of experimental organic chemistry. In 1928, Woodward contacted the Consul-General of the German consulate in Boston, later, in his Cope lecture, he recalled how he had been fascinated when, among these papers, he chanced upon Diels and Alders original communication about the Diels–Alder reaction. Throughout his career, Woodward was to repeatedly and powerfully use and investigate this reaction, in 1933, he entered the Massachusetts Institute of Technology, but neglected his formal studies badly enough to be excluded at the end of the 1934 fall term. MIT readmitted him in the 1935 fall term, and by 1936 he had received the Bachelor of Science degree, only one year later, MIT awarded him the doctorate, when his classmates were still graduating with their bachelors degrees. Woodwards doctoral work involved investigations related to the synthesis of the sex hormone estrone. MIT required that students have research advisors. Woodwards advisors were James Flack Norris and Avery Adrian Morton, although it is not clear whether he took any of their advice. In the 1960s, Woodward was named Donner Professor of Science, in 1944, with his post doctoral researcher, William von Eggers Doering, Woodward reported the synthesis of the alkaloid quinine, used to treat malaria. Nevertheless, it was a landmark for chemical synthesis, Woodwards particular insight in this synthesis was to realise that the German chemist Paul Rabe had converted a precursor of quinine called quinotoxine to quinine in 1905. Hence, a synthesis of quinotoxine would establish a route to synthesizing quinine, when Woodward accomplished this feat, organic synthesis was still largely a matter of trial and error, and nobody thought that such complex structures could actually be constructed. Woodward showed that organic synthesis could be made into a science. This synthesis was the first one in a series of exceedingly complicated, Woodward was perhaps the first synthetic organic chemist who used these ideas as a predictive framework in synthesis. Woodwards style was the inspiration for the work of hundreds of successive synthetic chemists who synthesized medicinally important, during the late 1940s, Woodward synthesized many complex natural products including quinine, cholesterol, cortisone, strychnine, lysergic acid, reserpine, chlorophyll, cephalosporin, and colchicine. Many of Woodwards syntheses were described as spectacular by his colleagues and before he did them, Woodwards syntheses were also described as having an element of art in them, and since then, synthetic chemists have always looked for elegance as well as utility in synthesis
28.
Apex (geometry)
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In geometry, an apex is the vertex which is in some sense the highest of the figure to which it belongs. The term is used to refer to the vertex opposite from some base. In an isosceles triangle, the apex is the vertex where the two sides of equal length meet, opposite the third side. In a pyramid or cone, the apex is the vertex at the top, in a pyramid, the vertex is the point that is part of all the lateral faces, or where all the lateral edges meet
29.
Polymerization
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In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them, in chemical compounds, polymerization occurs via a variety of reaction mechanisms that vary in complexity due to functional groups present in reacting compounds and their inherent steric effects. Alkanes can also be polymerized, but only with the help of strong acids, further compounds either being referred to as oligomers in smaller molecules. Polymerization that is not sufficiently moderated and proceeds at a fast rate can be very hazardous and this phenomenon is known as hazardous polymerization and can cause fires and explosions. Step-growth polymers are defined as polymers formed by the reaction between functional groups of monomers, usually containing heteroatoms such as nitrogen or oxygen. Most step-growth polymers are classified as condensation polymers, but not all step-growth polymers release condensates, in this case. Step-growth polymers increase in weight at a very slow rate at lower conversions. To alleviate inconsistencies in these methods, adjusted definition for condensation and addition polymers have been developed. Chain-growth polymerization involves the linking together of molecules incorporating double or triple carbon-carbon bonds and these unsaturated monomers have extra internal bonds that are able to break and link up with other monomers to form a repeating chain, whose backbone typically contains only carbon atoms. Chain-growth polymerization is involved in the manufacture of such as polyethylene, polypropylene. A special case of chain-growth polymerization leads to living polymerization, in the radical polymerization of ethylene, its π bond is broken, and the two electrons rearrange to create a new propagating center like the one that attacked it. The form this propagating center takes depends on the type of addition mechanism. There are several mechanisms through which this can be initiated, the free radical mechanism is one of the first methods to be used. Free radicals are very reactive atoms or molecules that have unpaired electrons, taking the polymerization of ethylene as an example, the free radical mechanism can be divided into three stages, chain initiation, chain propagation, and chain termination. Free radical addition polymerization of ethylene must take place at temperatures and pressures. While most other free radical polymerizations do not require such extreme temperatures and pressures, one effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains, a newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst, especially with respect to polymer branching. Other forms of chain growth polymerization include cationic addition polymerization and anionic addition polymerization, cationic and anionic mechanisms are also more ideally suited for living polymerizations, although free radical living polymerizations have also been developed
30.
Antimicrobial peptides
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Antimicrobial peptides, also called host defense peptides are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for antimicrobial peptides and these peptides are potent, broad spectrum antibiotics which demonstrate potential as novel therapeutic agents. Antimicrobial peptides have been demonstrated to kill Gram negative and Gram positive bacteria, enveloped viruses, fungi, unlike the majority of conventional antibiotics it appears as though antimicrobial peptides may also have the ability to enhance immunity by functioning as immunomodulators. Marine fish sources have high levels of compounds with in vivo testing confirming the efficacy of fish peptides used in food/feed ingredients. Antimicrobial peptides are a unique and diverse group of molecules, which are divided into subgroups on the basis of their amino acid composition, Antimicrobial peptides are generally between 12 and 50 amino acids. These peptides include two or more positively charged residues provided by arginine, lysine or, in environments, histidine. Many of these peptides are unstructured in free solution, and fold into their final configuration upon partitioning into biological membranes and it contains hydrophilic amino acid residues aligned along one side and hydrophobic amino acid residues aligned along the opposite side of a helical molecule. This amphipathicity of the antimicrobial peptides allows them to partition into the lipid bilayer. The ability to associate with membranes is a feature of antimicrobial peptides although membrane permeabilization is not necessary. These peptides have a variety of activities ranging from membrane permeabilization to action on a range of cytoplasmic targets. The modes of action by which antimicrobial peptides kill microbes are varied, some antimicrobial peptides kill both bacteria and fungi, e. g. psoriasin kills E. coli and several filamentous fungi. The cytoplasmic membrane is a frequent target, but peptides may also interfere with DNA and protein synthesis, protein folding, and cell wall synthesis. The initial contact between the peptide and the organism is electrostatic, as most bacterial surfaces are anionic, or hydrophobic. Alternately, they may penetrate into the cell to bind intracellular molecules which are crucial to cell living, however, in many cases, the exact mechanism of killing is not known. One emerging technique for the study of such mechanisms is dual polarisation interferometry, in contrast to many conventional antibiotics these peptides appear to be bactericidal instead of bacteriostatic. In general the antimicrobial activity of peptides is determined by measuring the minimal inhibitory concentration. Animal models indicate that host defence peptides are crucial for both prevention and clearance of infection and it appears as though many peptides initially isolated as and termed antimicrobial peptides have been shown to have more significant alternative functions in vivo. Several methods have used to determine the mechanisms of antimicrobial peptide activity
31.
3T3 cells
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3T3 cells come from a cell line established in 1962 by two scientists then at the Department of Pathology in the New York University School of Medicine, George Todaro and Howard Green. The 3T3 cell line has become the standard fibroblast cell line, Todaro and Green originally obtained their 3T3 cells from Swiss albino mouse embryo tissue. The 3T3 designation refers to the abbreviation of 3-day transfer, inoculum 3 x 105 cells and this cell line was originally established from the primary mouse embryonic fibroblast cells that were cultured by the designated protocol, so-called 3T3 protocol. The primary mouse embryonic fibroblast cells were transferred every 3 days, the spontaneously immortalized cells with stable growth rate were established after 20-30 generations in culture, and then named 3T3 cells. Specifically, 3T3-L1 is one of the current lines, Swiss 3T3 can be inhibited by temazepam and other benzodiazepines. These cells are also contact inhibited, the cells are sensitive to sarcoma virus and leukemia virus focus formation. 3T3 cells can be transformed with SV40 and some other polyomaviruses, lysophosphatidylcholine induces AP-1 activity and c-jun N-terminal kinase activity by a protein kinase C-independent pathway. The modal chromosome number is 68, which occurs in 30% of cells, higher ploidies occur at a much lower rate of 2. 4%. 3T3 cells are used in the cultivation of keratinocytes, with the 3T3 cells secreting growth factors favourable to these kinds of cells. Todaro GJ, Green H. Quantitative studies of the growth of mouse cells in culture. Nikon MicroscopyU Digital Video Gallery, 3T3 Cell Motility - a set of films of 3T3 cells in culture Cellosaurus entry for 3T3
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Stem cell
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Stem cells are undifferentiated biological cells that can differentiate into specialized cells and can divide to produce more stem cells. They are found in multicellular organisms, in mammals, there are two broad types of stem cells, embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues. In adult organisms, stem cells and progenitor cells act as a system for the body. There are three known accessible sources of adult stem cells in humans, Bone marrow, which requires extraction by harvesting. Adipose tissue, which requires extraction by liposuction, Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk, by definition, autologous cells are obtained from ones own body, just as one may bank his or her own blood for elective surgical procedures. Adult stem cells are used in various medical therapies. Stem cells can now be artificially grown and transformed into specialized cell types with characteristics consistent with cells of tissues such as muscles or nerves. Embryonic cell lines and autologous stem cells generated through somatic cell nuclear transfer or dedifferentiation have also been proposed as promising candidates for future therapies. Research into stem cells grew out of findings by Ernest A. McCulloch, till at the University of Toronto in the 1960s. The classical definition of a cell requires that it possess two properties, Self-renewal, the ability to go through numerous cycles of cell division while maintaining the undifferentiated state. Potency, the capacity to differentiate into specialized cell types, apart from this it is said that stem cell function is regulated in a feed back mechanism. Stochastic differentiation, when one cell develops into two differentiated daughter cells, another stem cell undergoes mitosis and produces two stem cells identical to the original. Potency specifies the differentiation potential of the stem cell, totipotent stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism and these cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the egg are also totipotent. Pluripotent stem cells are the descendants of totipotent cells and can differentiate into all cells. Multipotent stem cells can differentiate into a number of cell types, oligopotent stem cells can differentiate into only a few cell types, such as lymphoid or myeloid stem cells
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Azetidine
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Azetidine is a saturated heterocyclic organic compound containing three carbon atoms and one nitrogen atom. It is a liquid at room temperature with an odor of ammonia and is strongly basic compared to most secondary amines. Azetidines do not occur as frequently in nature and have been studied far less closely related chemical compounds such as pyrrolidine. Azetidine and its derivatives are relatively rare structural motifs in natural products, notably, they are a key component of mugineic acids and penaresidins. Perhaps the most abundant azetidine containing natural product is azetidine-2-carboxylic acid, azete, the unsaturated analog Pubchem ChemSynthesis
34.
Lactone
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Lactones are cyclic esters of hydroxycarboxylic acids, containing a 1-oxacycloalkan-2-one structure, or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by esterification of the corresponding hydroxycarboxylic acids. Lactones with three- or four-membered rings are very reactive, making their isolation difficult, special methods are normally required for the laboratory synthesis of small-ring lactones as well as those that contain rings larger than six-membered. The first carbon atom after the carbon in the group on the parent compound is labelled α, the second will be labeled β. Therefore, the prefixes also indicate the size of the ring, α-lactone = 3-membered ring, β-lactone = 4-membered, γ-lactone = 5-membered. The other suffix used to denote a lactone is -olide, used in substance class names like butenolide, macrolide, cardenolide or bufadienolide, the name lactone derives from the ring compound called lactide, which is formed from the dehydration of 2-hydroxypropanoic acid CH3-CH-COOH. Lactic acid, in turn, derives its name from its isolation from soured milk. An internal dehydration within the molecule of lactic acid would have produced alpha-propiolactone. Naturally occurring lactones are mainly saturated and unsaturated γ- and δ-lactones, the γ- and δ-lactones are intramolecular esters of the corresponding hydroxy fatty acids. They contribute to the aroma of butter, cheese and various foods, cyclopentadecanolide is responsible for the musklike odor of angelica root oil. Of the naturally occurring bicyclic lactones, phthalides are responsible for the odors of celery and lovage oils, many methods in ester synthesis can also be applied to that of lactones. In one industrial synthesis of oxandrolone the key lactone-forming step is an organic reduction - esterification, in halolactonization, an alkene is attacked by a halogen via electrophilic addition with the cationic intermediate captured intramolecularly by an adjacent carboxylic acid. Specific methods include Yamaguchi esterification, Shiina macrolactonization, Baeyer–Villiger oxidation, the most stable structure for lactones are the 5-membered γ-lactones and 6-membered δ-lactones because, as in all organic cycles,5 and 6 membered rings minimize the strain of bond angles. γ-lactones are so stable that, in the presence of acids at room temperature. β-lactones do exist, but can only be made by special methods, α-lactones can be detected as transient species in mass spectrometry experiments. Like straight-chained esters, the reaction of lactones is a reversible reaction. However, the constant of the hydrolysis reaction of the lactone is lower than that of the straight-chained ester i. e. the products are less favored in the case of the lactones. This is because although the enthalpies of the hydrolysis of esters and lactones are about the same, straight-chained esters give two products upon hydrolysis, making the entropy change more favorable than in the case of lactones which give only a single product
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International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
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PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
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