1.
Organic compound
–
An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry. Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. Vitalism survived for a while even after the rise of modern atomic theory and it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate, urea had long been considered an organic compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by others, in which increasingly complex organic substances were produced from inorganic ones without the involvement of any living organism. Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic. Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially
2.
Ketone
–
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
3.
Aldehyde
–
The group—without R—is the aldehyde group, also known as the formyl group. Aldehydes are common in organic chemistry, Aldehydes feature an sp2-hybridized, planar carbon center that is connected by a double bond to oxygen and a single bond to hydrogen. The C–H bond is not ordinarily acidic, because of resonance stabilization of the conjugate base, an α-hydrogen in an aldehyde is far more acidic, with a pKa near 15, compared to the acidity of a typical alkane. This acidification is attributed to the quality of the formyl center and the fact that the conjugate base. Related to, the group is somewhat polar. Aldehydes can exist in either the keto or the enol tautomer, keto-enol tautomerism is catalyzed by either acid or base. Usually the enol is the minority tautomer, but it is more reactive, the common names for aldehydes do not strictly follow official guidelines, such as those recommended by IUPAC, but these rules are useful. IUPAC prescribes the following nomenclature for aldehydes, Acyclic aliphatic aldehydes are named as derivatives of the longest carbon chain containing the aldehyde group, thus, HCHO is named as a derivative of methane, and CH3CH2CH2CHO is named as a derivative of butane. The name is formed by changing the suffix -e of the parent alkane to -al, so that HCHO is named methanal, in other cases, such as when a -CHO group is attached to a ring, the suffix -carbaldehyde may be used. Thus, C6H11CHO is known as cyclohexanecarbaldehyde, if the presence of another functional group demands the use of a suffix, the aldehyde group is named with the prefix formyl-. This prefix is preferred to methanoyl-, the word aldehyde was coined by Justus von Liebig as a contraction of the Latin alcohol dehydrogenatus. In the past, aldehydes were sometimes named after the corresponding alcohols, for example, the term formyl group is derived from the Latin word formica ant. This word can be recognized in the simplest aldehyde, formaldehyde, Aldehydes have properties that are diverse and that depend on the remainder of the molecule. Smaller aldehydes are more soluble in water, formaldehyde and acetaldehyde completely so, the volatile aldehydes have pungent odors. Aldehydes degrade in air via the process of autoxidation, the two aldehydes of greatest importance in industry, formaldehyde and acetaldehyde, have complicated behavior because of their tendency to oligomerize or polymerize. They also tend to hydrate, forming the geminal diol, the oligomers/polymers and the hydrates exist in equilibrium with the parent aldehyde. Aldehydes are readily identified by spectroscopic methods, using IR spectroscopy, they display a strong νCO band near 1700 cm−1. In their 1H NMR spectra, the formyl hydrogen center absorbs near δH =9 and this signal shows the characteristic coupling to any protons on the alpha carbon
4.
Functional group
–
In organic chemistry, functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of, however, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to other and to the rest of the molecule by covalent bonds. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, Functional groups can also be charged, e. g. in carboxylate salts, which turns the molecule into a polyatomic ion or a complex ion. Complexation and solvation is also caused by interactions of functional groups. In the common rule of thumb like dissolves like, it is the shared or mutually well-interacting functional groups give rise to solubility. For example, sugar dissolves in water because both share the functional group and hydroxyls interact strongly with each other. Combining the names of groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the group is called the alpha carbon, the second, beta carbon. IUPAC conventions call for numeric labeling of the position, e. g. 4-aminobutanoic acid, in traditional names various qualifiers are used to label isomers, for example isopropanol is an isomer is n-propanol. The following is a list of functional groups. In the formulas, the symbols R and R usually denote an attached hydrogen, or a side chain of any length. Functional groups, called hydrocarbyl, that only carbon and hydrogen. Each one differs in type of reactivity, there are also a large number of branched or ring alkanes that have specific names, e. g. tert-butyl, bornyl, cyclohexyl, etc. Hydrocarbons may form charged structures, positively charged carbocations or negative carbanions, examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion. Haloalkanes are a class of molecule that is defined by a carbon–halogen bond and this bond can be relatively weak or quite stable. In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions, the substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity. Compounds that contain nitrogen in this category may contain C-O bonds, compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their lighter analogue on the periodic table
5.
Dinitrophenylhydrazine
–
2, 4-Dinitrophenylhydrazine is the chemical compound C6H32NHNH2. Dinitrophenylhydrazine is a red to orange solid and it is a substituted hydrazine, and is often used to qualitatively test for carbonyl groups associated with aldehydes and ketones. The hydrazone derivatives can also be used as evidence toward the identity of the original compound, the melting point of the derivative is often used, with reference to a database of values, to determine the identity of a specific carbonyl compound. It is relatively sensitive to shock and friction, it is a shock explosive so care must be taken with its use, to reduce its explosive hazard, it is usually supplied wet. 2, 4-Dinitrophenylhydrazine is commercially available usually as a wet powder,2, 4-Dinitrophenylhydrazine can be used to qualitatively detect the carbonyl functionality of a ketone or aldehyde functional group. It is also considered a reaction, nucleophilic addition of the -NH2 group to the C=O carbonyl group. In particular, the use of 2, 4-dinitrophenylhydrazine was developed by Brady, modern spectroscopic and spectrometric techniques have since superseded these techniques. Dinitrophenylhydrazine does not react with other carbonyl-containing functional groups such as acids, amides. This stability would be lost by addition of a reagent to the carbonyl group, hence, these compounds are more resistant to addition reactions. Also with carboxylic acids there is the effect of the acting as a base. Tollens reagent Fehlings reagent Schiff test
6.
Sorbent
–
A sorbent is a material used to absorb or adsorb liquids or gases. Examples include, A material similar to molecular sieve material, which acts by adsorption and it has a large internal surface area and good thermal conductivity. It is typically supplied in pellets of 1 mm to 2 mm diameter, occasionally as beads up to 5 mm diameter. They are typically made from aluminium oxide with a porous structure, materials used to absorb other materials due to their high affinity for doing so. Examples include, In composting, dry materials absorb many odoriferous chemicals, a sponge absorbs many times its own weight in water. A polypropylene fiber mat may be used to absorb oil, a cellulose fiber product may be used to absorb oil. The granular gel material in a baby diaper will absorb several times its weight in urine. Polymethylsiloxane polyhydrate is a gelly-like polymeric organosilicon compound, PMSPG is an sorbent designed for binding toxic substances of different nature, pathogens and metabolites in the gastrointestinal tract and their excretion. Desiccants absorb water, drying out the surrounding materials
7.
Adsorption
–
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent and this process differs from absorption, in which a fluid is dissolved by or permeates a liquid or solid, respectively. Adsorption is a process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it, similar to surface tension, adsorption is a consequence of surface energy. In a bulk material, all the requirements of the constituent atoms of the material are filled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms, the exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption or chemisorption. It may also occur due to electrostatic attraction, pharmaceutical industry applications, which use adsorption as a means to prolong neurological exposure to specific drugs or parts thereof, are lesser known. The word adsorption was coined in 1881 by German physicist Heinrich Kayser, adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure or concentration at constant temperature. The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different materials, to date,15 different isothem models were developed. The function is not adequate at very high pressure because in reality x / m has a maximum as pressure increases without bound. As the temperature increases, the k and n change to reflect the empirical observation that the quantity adsorbed rises more slowly. Irving Langmuir was the first to derive a scientifically based adsorption isotherm in 1918, the model applies to gases adsorbed on solid surfaces. It is a semi-empirical isotherm with a basis and was derived based on statistical thermodynamics. It is the most common isotherm equation to use due to its simplicity and it is based on four assumptions, All of the adsorption sites are equivalent and each site can only accommodate one molecule. The surface is energetically homogeneous and adsorbed molecules do not interact, at the maximum adsorption, only a monolayer is formed. Adsorption only occurs on localized sites on the surface, not with other adsorbates, the fourth condition is the most troublesome, as frequently more molecules will adsorb to the monolayer, this problem is addressed by the BET isotherm for relatively flat surfaces. The Langmuir isotherm is nonetheless the first choice for most models of adsorption, Langmuir suggested that adsorption takes place through this mechanism, A g + S ⇌ A S, where A is a gas molecule and S is an adsorption site. The direct and inverse rate constants are k and k−1, vmon is related to the number of adsorption sites through the ideal gas law
8.
High-performance liquid chromatography
–
High-performance liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pass a pressurized liquid solvent containing the mixture through a column filled with a solid adsorbent material. HPLC has been used for manufacturing, legal, research, Chromatography can be described as a mass transfer process involving adsorption. HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, the active component of the column, the adsorbent, is typically a granular material made of solid particles, 2–50 micrometers in size. The components of the mixture are separated from each other due to their different degrees of interaction with the adsorbent particles. The pressurized liquid is typically a mixture of solvents and is referred to as a mobile phase and its composition and temperature play a major role in the separation process by influencing the interactions taking place between sample components and adsorbent. These interactions are physical in nature, such as hydrophobic, dipole–dipole and ionic, due to the small sample amount separated in analytical HPLC, typical column dimensions are 2. 1–4.6 mm diameter, and 30–250 mm length. Also HPLC columns are made with smaller sorbent particles and this gives HPLC superior resolving power when separating mixtures, which makes it a popular chromatographic technique. The schematic of an HPLC instrument typically includes a sampler, pumps, the sampler brings the sample mixture into the mobile phase stream which carries it into the column. The pumps deliver the flow and composition of the mobile phase through the column. The detector generates a signal proportional to the amount of sample component emerging from the column, a digital microprocessor and user software control the HPLC instrument and provide data analysis. Some models of pumps in a HPLC instrument can mix multiple solvents together in ratios changing in time. Various detectors are in use, such as UV/Vis, photodiode array or based on mass spectrometry. Most HPLC instruments also have an oven that allows for adjusting the temperature at which the separation is performed. The sample mixture to be separated and analyzed is introduced, in a small volume. The components of the move through the column at different velocities. The velocity of each component depends on its nature, on the nature of the stationary phase. The time at which an analyte elutes is called its retention time
9.
Ultraviolet
–
Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
10.
Uncoupling protein
–
An uncoupling protein is a mitochondrial inner membrane protein that is a regulated proton channel or transporter. An uncoupling protein is capable of dissipating the proton gradient generated by NADH-powered pumping of protons from the mitochondrial matrix to the mitochondrial intermembrane space. The energy lost in dissipating the proton gradient via UCPs is not used to do biochemical work and this is what links UCP to thermogenesis. UCPs are positioned in the membrane as the ATP synthase. The two proteins thus work in parallel with one generating heat and the other generating ATP from ADP and inorganic phosphate, mitochondria respiration is coupled to ATP synthesis but is regulated by UCPs. Some plants species use the heat generated by uncoupling proteins for special purposes, skunk cabbage, for example, keeps the temperature of its spikes as much as 20° higher than the environment, spreading odor and attracting insects that fertilize the flowers. However, other substances, such as 2, 4-dinitrophenol and carbonyl cyanide m-chlorophenyl hydrazone, also serve the same uncoupling function, salicylic acid is also an uncoupling agent and will decrease production of ATP and increase body temperature if taken in excess. Uncoupling proteins are increased by thyroid hormone, norepinephrine, epinephrine, scientists observed the thermogenic activity in brown adipose tissue, which eventually led to the discovery of the UCP. The brown tissue revealed elevated levels of mitochondria respiration and another respiration not coupled to ATP synthesis, the UCP was the protein discovered responsible for activating a proton pathway that was not coupled to ADP phosphorylation. Uncoupling Agents at the US National Library of Medicine Medical Subject Headings
11.
Adenosine triphosphate
–
Adenosine triphosphate is a nucleotide, also called a nucleoside triphosphate, is a small molecule used in cells as a coenzyme. It is often referred to as the unit of currency of intracellular energy transfer. ATP transports chemical energy within cells for metabolism, most cellular functions need energy in order to be carried out, synthesis of proteins, synthesis of membranes, movement of the cell, cellular division, transport of various solutes etc. The ATP is the molecule that carries energy to the place where the energy is needed, when ATP breaks into ADP and Pi, the breakdown of the last covalent link of phosphate liberates energy that is used in reactions where it is needed. Substrate-level phosphorylation, oxidative phosphorylation in cellular respiration, and photophosphorylation in photosynthesis are three mechanisms of ATP biosynthesis. Metabolic processes that use ATP as an energy source convert it back into its precursors, ATP is therefore continuously recycled in organisms, the human body, which on average contains only 250 grams of ATP, turns over its own body weight equivalent in ATP each day. ATP is used as a substrate in signal transduction pathways by kinases that phosphorylate proteins and it is also used by adenylate cyclase, which uses ATP to produce the second messenger molecule cyclic AMP. The ratio between ATP and AMP is used as a way for a cell to sense how much energy is available and control the metabolic pathways that produce and consume ATP. Apart from its roles in signaling and energy metabolism, ATP is also incorporated into nucleic acids by polymerases in the process of transcription, ATP is the neurotransmitter believed to signal the sense of taste. The structure of this consists of a purine base attached by the 9′ nitrogen atom to the 1′ carbon atom of a pentose sugar. Three phosphate groups are attached at the 5′ carbon atom of the pentose sugar and it is the addition and removal of these phosphate groups that inter-convert ATP, ADP and AMP. When ATP is used in DNA synthesis, the sugar is first converted to deoxyribose by ribonucleotide reductase. ATP was discovered in 1929 by Karl Lohmann, and independently by Cyrus Fiske and Yellapragada Subbarow of Harvard Medical School and it was proposed to be the intermediary molecule between energy-yielding and energy-requiring reactions in cells by Fritz Albert Lipmann in 1941. It was first artificially synthesized by Alexander Todd in 1948, ATP consists of adenosine – composed of an adenine ring and a ribose sugar – and three phosphate groups. The phosphoryl groups, starting with the group closest to the ribose, are referred to as the alpha, beta, consequently, it is closely related to the adenosine nucleotide, a monomer of RNA. ATP is highly soluble in water and is stable in solutions between pH6.8 and 7.4, but is rapidly hydrolysed at extreme pH. Consequently, ATP is best stored as an anhydrous salt, ATP is an unstable molecule in unbuffered water, in which it hydrolyses to ADP and phosphate. This is because the strength of the bonds between the groups in ATP is less than the strength of the hydrogen bonds, between its products, and water
12.
ATP synthase
–
ATP synthase is an important enzyme that creates the energy storage molecule adenosine triphosphate. ATP is the most commonly used energy currency of cells for most organisms and it is formed from adenosine diphosphate and inorganic phosphate, and needs energy for its formation. Located within the membrane and the inner mitochondrial membrane, ATP synthase consists of two regions the FO portion embedded within the membrane. The F1 portion of the ATP synthase is outside the membrane, the nomenclature of the enzyme has a long history. These functional regions consist of different protein subunits — refer to tables, the F1 particle is large and can be seen in the transmission electron microscope by negative staining. These are particles of 9 nm diameter that pepper the inner mitochondrial membrane and this ATPase activity was further associated with the creation of ATP by a long series of experiments in many laboratories. The FO region of ATP synthase is a pore that is embedded in the mitochondrial membrane. It consists of three main subunits A, B, and C, and six additional subunits, d, e, f, g, F6, and 8. The research group of John E. Walker, then at the MRC Laboratory of Molecular Biology in Cambridge, the structure, at the time the largest asymmetric protein structure known, indicated that Boyers rotary-catalysis model was, in essence, correct. For elucidating this, Boyer and Walker shared half of the 1997 Nobel Prize in Chemistry, the crystal structure of the F1 showed alternating alpha and beta subunits, arranged like segments of an orange around a rotating asymmetrical gamma subunit. A portion of the FO rotates as the pass through the membrane. The major F1 subunits are prevented from rotating in sympathy with the central stalk rotor by a stalk that joins the alpha3beta3 to the non-rotating portion of FO. The structure of the intact ATP synthase is currently known at low-resolution from electron cryo-microscopy studies of the complex, the cryo-EM model of ATP synthase suggests that the peripheral stalk is a flexible structure that wraps around the complex as it joins F1 to FO. Under the right conditions, the reaction can also be carried out in reverse. The binding change mechanism involves the active site of a β subunits cycling between three states, in the open state, ADP and phosphate enter the active site, in the adjacent diagram, this is shown in red. The protein then closes up around the molecules and binds them loosely — the loose state, finally, the active site cycles back to the open state, releasing ATP and binding more ADP and phosphate, ready for the next cycle of ATP production. Like other enzymes, the activity of F1FO ATP synthase is reversible, the overall process of creating energy in this fashion is termed oxidative phosphorylation. The same process takes place in the mitochondria, where ATP synthase is located in the mitochondrial membrane
13.
Redox
–
Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
14.
Oxygen
–
Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
15.
Oxidative phosphorylation
–
Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to reform ATP. In most eukaryotes, this takes place inside mitochondria, almost all aerobic organisms carry out oxidative phosphorylation. This pathway is probably so pervasive because it is an efficient way of releasing energy. During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen and these redox reactions release energy, which is used to form ATP. These linked sets of proteins are called electron transport chains, in eukaryotes, five main protein complexes are involved, whereas in prokaryotes many different enzymes are present, using a variety of electron donors and acceptors. The energy released by electrons flowing through this electron transport chain is used to transport protons across the mitochondrial membrane. This generates potential energy in the form of a pH gradient and this store of energy is tapped by allowing protons to flow back across the membrane and down this gradient, through a large enzyme called ATP synthase, this process is known as chemiosmosis. This enzyme uses energy to generate ATP from adenosine diphosphate. This reaction is driven by the flow, which forces the rotation of a part of the enzyme. The enzymes carrying out this metabolic pathway are also the target of many drugs and this means one cannot occur without the other. These enzymes are like a battery, as they work to drive current through the circuit. The movement of protons creates an electrochemical gradient across the membrane and it has two components, a difference in proton concentration and a difference in electric potential, with the N-side having a negative charge. ATP synthase releases this energy by completing the circuit and allowing protons to flow down the electrochemical gradient. The electrochemical gradient drives the rotation of part of the enzymes structure, inversely, chloroplasts operate mainly on ΔpH. However, they require a small membrane potential for the kinetics of ATP synthesis. At least in the case of the fusobacterium P. modestum it drives the counter-rotation of subunits a and c of the FO motor of ATP synthase, the amount of energy released by oxidative phosphorylation is high, compared with the amount produced by anaerobic fermentation. These ATP yields are theoretical maximum values, in practice, some protons leak across the membrane, the electron transport chain carries both protons and electrons, passing electrons from donors to acceptors, and transporting protons across a membrane. These processes use both soluble and protein-bound transfer molecules, in mitochondria, electrons are transferred within the intermembrane space by the water-soluble electron transfer protein cytochrome c
16.
Molecular biology
–
Writing in Nature in 1961, William Astbury described molecular biology as. It is concerned particularly with the forms of biological molecules and is predominantly three-dimensional and structural—which does not mean, however and it must at the same time inquire into genesis and function. Researchers in molecular biology use specific techniques native to molecular biology but increasingly combine these techniques and ideas from genetics. There is not a line between these disciplines. Biochemists focus heavily on the role, function, and structure of biomolecules, the study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry. Genetics is the study of the effect of differences on organisms. This can often be inferred by the absence of a normal component, the study of mutants – organisms which lack one or more functional components with respect to the so-called wild type or normal phenotype. Genetic interactions can often confound simple interpretations of such knockout studies, molecular biology is the study of molecular underpinnings of the processes of replication, transcription, translation, and cell function. This picture, however, is undergoing revision in light of emerging novel roles for RNA, much of molecular biology is quantitative, and recently much work has been done at its interface with computer science in bioinformatics and computational biology. In the early 2000s, the study of structure and function. There is also a tradition of studying biomolecules from the ground up in biophysics. One of the most basic techniques of molecular biology to study protein function is molecular cloning, in this technique, DNA coding for a protein of interest is cloned using PCR and/or restriction enzymes into a plasmid. A vector has 3 distinctive features, an origin of replication, a multiple cloning site, the origin of replication will have promoter regions upstream from the replication/transcription start site. This plasmid can be inserted into either bacterial or animal cells, introducing DNA into bacterial cells can be done by transformation via uptake of naked DNA, conjugation via cell-cell contact or by transduction via viral vector. Introducing DNA into eukaryotic cells, such as cells, by physical or chemical means is called transfection. Several different transfection techniques are available, such as calcium phosphate transfection, electroporation, microinjection, the plasmid may be integrated into the genome, resulting in a stable transfection, or may remain independent of the genome, called transient transfection. DNA coding for a protein of interest is now inside a cell, a variety of systems, such as inducible promoters and specific cell-signaling factors, are available to help express the protein of interest at high levels. Large quantities of a protein can then be extracted from the bacterial or eukaryotic cell, polymerase chain reaction is an extremely versatile technique for copying DNA
17.
Osazone
–
Osazones are a class of carbohydrate derivatives found in organic chemistry formed when sugars are reacted with excess of phenylhydrazine. The famous German chemist Emil Fischer developed and used the reaction to identify sugars whose stereochemistry differed by only one chiral carbon, osazones formation test involves the reaction of a reducing sugar with excess of phenylhydrazine when kept at boiling temperature. Therefore, sucrose, for example, does not form osazone crystals because it is a non reducing sugar as it has no free carbonyl group, the reaction involves formation of a pair of phenylhydrazone functionalities, concomitant with the oxidation of the hydroxymethyl group in alpha carbon. The reaction can be used to identify monosaccharides, firstly glucose with phenylhydrazine gives glucosephenylhydrazone by elimination of a water molecule from the functional group. The next step involves reaction of one equivalent of glucosephenylhydrazone with two equivalents of phenylhydrazine, the alpha carbon is attacked here because its more reactive than the others. Osazones are highly coloured and crystalline compounds and can be easily detected, each sugar has a characteristic crystal form of osazones. Glucose, fructose and mannose form broomstick or needle-shaped crystals
18.
Hydrazone iodination
–
Hydrazone iodination is an organic reaction in which a hydrazone is converted into a vinyl iodide by reaction of iodine and a non-nucleophilic base such as DBU. First published by D. H. R, Barton in 1962 the reaction is sometimes referred to as the Barton reaction or, more descriptively, as the Barton vinyl iodine procedure. The reaction has earlier roots with the 1911 discovery by Wieland, in the original Barton publication the reaction was optimized by using a strong guanidine base, the inverse addition of the hydrazone to an iodine solution, and by exclusion of water. In the next step, iodine reacts as an electrophile, displacement of nitrogen then generates an iodocarbonium ion, when the reaction site is not sterically hindered, a second iodide can recombine to form the geminal di-iodide, otherwise an elimination reaction leads to the vinyliodide. When water is present, the product can revert to the ketone. This reaction is related to the Shapiro reaction, another example can be found in the Danishefsky Taxol total synthesis. In one study it is attempted to trap any reactive intermediate of this reaction with an internal alkene. When the hydrazone 1 in scheme 5 is reacted with iodine and triethylamine in toluene, the actual process taking place is path A with elimination of HI to the diazo compound 4 followed by a diazoalkane 1, 3-dipolar cycloaddition to the pyrazoline 5 in 85% yield
19.
Shapiro reaction
–
The reaction was discovered by Robert H. Shapiro in 1967. The Shapiro reaction was used in the Nicolaou Taxol total synthesis, in a prelude to the actual Shapiro reaction a ketone or an aldehyde is reacted with p-toluenesulfonylhydrazide to a p-toluenesulfonylhydrazone which is an imine or hydrazone. Two equivalents of a base, such as n-butyllithium, then abstract first the proton from the hydrazone and then the less acidic proton α to the hydrazone carbon. The carbanion proceeds in a reaction to create the carbon–carbon double bond. This step results in expulsion of the group and formation of a diazonium anion. The anion then collapses, falling off as a nitrogen molecule. The result is a vinyllithium at the position where the nitrogen had been attached and this organolithium carbon is both nucleophilic and basic. It can be reacted with electrophiles or simply neutralized with water or an acid. The position of the alkene in the product is controlled by the site of deprotonation by the organolithium base, in general, the kinetically favored, less substituted site of differentially substituted tosylhydrazones is deprotonated selectively, leading to the less substituted vinyllithium intermediate. Although many secondary reactions exist for the functional group, in the Shapiro reaction in particular water is added. Other reactions of compounds include alkylation reactions with for instance alkyl halides. Traditional Shapiro reactions require stoichiometric amounts of base to generate the alkenyllithium reagents, the required phenylaziridinylhydrazone was prepared from the condensation of 6-undecanone with 1-amino-2-phenyl-aziridine. Treatment of the phenylaziridinylhydrazone with 0.3 equivalents of LDA in ether resulted in the alkene shown below with an cis, the ratio was determined by capillary GLC analysis after conversion to the corresponding epoxides with mCPBA. The catalyst loading can be reduced to 0.05 equivalents in the case of a 30 mmol scale reaction, the Shapiro reaction can also be combined with the Suzuki reaction to produce a variety of olefin products. Keay and coworkers have developed methodology that combines these reactions in a one pot process that does not require the isolation of the boronic acid and this reaction has a wide scope, tolerating a slew of trisylhydrazones and aryl halides, as well as several solvents and Pd sources. The Shapiro reaction has been used to generate olefins en route to complex natural products, K. Mori and coworkers wanted to determine the absolute configuration of the phytocassane group of a class of natural products called phytoalexins. This was accomplished by preparing the naturally occurring -phytocassane D from -Wieland-Miescher ketone, en route to -phytocassane D, a tricyclic ketone was subjected to Shapiro reaction conditions to yield the cyclic alkene product
20.
Vinyl group
–
In chemistry, vinyl or ethenyl is the functional group −CH=CH2, namely the ethylene molecule minus one hydrogen atom. The name is used for any compound containing that group. An industrially important example is vinyl chloride, precursor to PVC, vinyl is one of the alkenyl functional groups. On a carbon skeleton, sp2-hybridized carbons or positions are often called vinylic, allyls, acrylates and styrenics contain vinyl groups. The etymology of vinyl is the Latin vinum = wine, because of its relationship with alcohol, the term vinyl was coined by the German chemist Hermann Kolbe in 1851. Vinyl groups can polymerize with the aid of an initiator or a catalyst. In these polymers, the bonds of the vinyl monomers turn into single bonds. Vinyl groups do not exist in polymer, the term refers to the precursor. It is sometimes important to ascertain the absence of unreacted vinyl monomer in the product when the monomer is toxic or reduces the performance of the plastic. The following table gives examples of vinyl polymers. The vinylidene and vinylene derivatives can polymerize in the same manner, allyl Grignard reagents can attack with the vinyl end first. If next to a group, conjugate addition occurs. Vinyl organometallics, e. g. vinyl lithium, participate in coupling reactions such as in Negishi coupling
21.
Azine
–
Azines are a functional class of organic compounds with the connectivity RRC=N-N=CRR. These compounds are the product of the condensation of hydrazine with ketones and aldehydes, the usual method of industrial production is the Peroxide process, starting from the ketone, ammonia, and hydrogen peroxide. In the laboratory, azines are typically prepared by the reaction of a carbonyl compound with hydrazine hydrate. Azines characteristically undergo hydrolysis to hydrazines, azines have been used as precursors to hydrazones and diazo compounds. The coordination chemistry of azines has also been studied, ketazines are also important intermediates in the industrial production of hydrazine hydrate by the Peroxide process. They may be classified as aldazines or ketazines, depending on the nature of the carbonyl compound. Azines may also be named by substitutive or functional class nomenclature, in functional class nomenclature, the functional modifier azine is appended to the name of the carbonyl compound, hence, acetone azine. In older nomenclature, the class name ketazine has been used with the names of the hydrocarbyl substituents. In substitutive nomenclature, azines are named as derivatives of hydrazine, hence, in the presence of groups of higher seniority, the prefixes hydrazinylidene and hydrazinediylidene are used. US3965097, Eichenhofer, Kurt-Wilhelm & Reinhard Schliebs, Production of ketazines, US3972878, Schirmann, Jean-Pierre, Jean Combroux & Serge Yvon Delavarenne, Method for preparing azines and hydrazones, issued 1976-08-03. US3978049, Schirmann, Jean-Pierre, Pierre Tellier & Henri Mathais et al, process for the preparation of hydrazine compounds, issued 1976-08-31. US4093656, Schirmann, Jean-Pierre, Jean Combroux & Serge Yvon Delavarenne, Method for making azines, US4724133, Schirmann, Jean-Pierre, Jean Combroux & Serge Y. Delavarenne, Preparation of an aqueous solution of hydrazine hydrate
22.
Pyrazole
–
Pyrazole is an organic compound with the formula C3H3N2H. It is a characterized by a 5-membered ring of three carbon atoms and two adjacent nitrogen atoms. Pyrazole is a base, with pKb 11.5. Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms, notable drugs containing a pyrazole ring are celecoxib and the anabolic steroid stanozolol. In a classical method developed by German chemist Hans von Pechmann in 1898, Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate. In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of watermelons, imidazole is an analog of pyrazole with two non-adjacent nitrogen atoms. In isoxazole, another analog, the atom in position 1 replaced by oxygen. Recent Advances in the Chemistry of Pyrazoles, reactions and N-Heterocyclic Carbenes of Pyrazole
23.
Enders SAMP/RAMP hydrazone-alkylation reaction
–
The Enders SAMP/RAMP hydrazone alkylation reaction is an asymmetric carbon-carbon bond formation reaction facilitated by pyrrolidine chiral auxiliaries. It was pioneered by E. J. Corey and D. Enders in 1976 and this method is usually a three-step sequence. The first step is to form the hydrazone between -1-amino-2-methoxymethylpyrrolidine or -1-amino-2-methoxymethylpyrrolidine and a ketone or aldehyde, finally, the alkylated ketone or aldehyde can be regenerated by ozonolysis or hydrolysis. Regioselective and stereoselective formation of carbon-carbon bonds adjacent to carbonyl group is an important procedure in organic chemistry, alkylation reaction of enolates has been the main focus of the field. Both A. G. Myers and D. A. Evans developed asymmetric alkylation reactions for enolates, the apparent shortcoming for enolate alkylation reactions is over-alkylation, even if the amount of base added for enolization as well as the reaction temperature are carefully controlled. The ketene formation during the process for substrates possessing Evans oxazolidinone is also a main side reaction for the related alkylation reactions. Development in the field of chemistry and the utilization of imine derivatives of enolates managed to provide an alternative for enolate alkylation reactions. In 1963, G. Stork reported the first enamine alkylation reaction for ketones - Stork enamine alkylation reaction, in 1976, Meyers reported the first alkylation reaction of metallated azaenolates of hydrazones with an acyclic amino acid-based auxiliary. Compared with the carbonyl compounds and the chiral enamine species reported previously. The combination of amino acid derivatives and the powerful hydrazone techniques were pioneered by E. J. Corey and D. Enders in 1976. Both SAMP and RAMP are synthesized from amino acids, the detailed synthesis of these two auxiliaries are shown below. This anion is a good nucleophile and readily attacks electrophiles, such as alkyl halides. The stereochemistry of this reaction is discussed in detail in next section, after the deprotonation, the imine turns into an azaenolate with lithium cation chelating both the nitrogen and oxygen. There are two options for lithium chelation. There are also two available orientations for the nitrogen and R2 group, being either EC=C or ZC=C. This leads to four possible azaenolate intermediates for the Enders SAMP/RAMP hydrazone alkylation reaction, experiments and calculations show that one specific stereoisomer of the azaenolate is favored over the other three possible candidates. The favored azaenolate is the dominant starting molecule for the subsequent alkylation reaction, there are two possible faces of accessing for any electrophile to react with. The steric interaction between the ring and the electrophilic reagent hinders the attack of the electrophile from the top face
24.
Lithium diisopropylamide
–
Lithium diisopropylamide is a chemical compound with the molecular formula 2NLi. It is used as a base and has been widely accepted due to its good solubility in non-polar organic solvents. It is a solid, but is usually generated and observed only in solution. LDA is commonly formed by treating a cooled solution of diisopropylamine with n-butyllithium. When dissociated, the anion can become protonated to form Diisopropylamine. Diisopropylamine has pKa value of 36, therefore, its conjugate base is suitable for the deprotonation of compounds with greater acidity. Importantly, such weakly acidic compounds carbon acids of the type R2CHZ, where Z = CR, CO2R, conventional protic functional groups such as alcohols and carboxylic acids are of course readily deprotonated. Like most organolithium reagents, LDA is not a salt, but is highly polar and it forms aggregates in solution, with the extent of aggregation depending on the nature of the solvent. In THF its structure is primarily that of a solvated dimer, in nonpolar solvents such as toluene, it forms a temperature-dependent oligomer equilibrium. At room temperature trimers and tetramers are the most likely structures, with increasing temperature the aggregation extends to pentameric and higher oligomeric structures. Solid LDA is pyrophoric, but its solutions are generally not, as such it is commercially available as a solution in polar aprotic solvents such as THF and ether, however for small scale use, it is common and more cost effective to prepare LDA in situ. The deprotonation of carbon acids can proceed with either kinetic or thermodynamic reaction control, kinetic controlled deprotonation requires a base that is sterically hindered. For example, in the case of phenylacetone, deprotonation can produce two different enolates, LDA has been shown to deprotonate the methyl group, which is the kinetic course of the deprotonation. A weaker base such as an alkoxide, which deprotonates the substrate. An alternative to the base is to use a strong base which is present at a lower concentration than the ketone. For instance, with a slurry of sodium hydride in THF or dimethylformamide, a ketone molecule might be deprotonated at the kinetic site. This enolate may then encounter other ketones and the thermodynamic enolate will form through the exchange of protons, LDA can, however, act as a nucleophile under certain conditions. Lithium amide Lithium bisamide Lithium tetramethylpiperidide
25.
Elias James Corey
–
Corey is an American organic chemist. In 1990, he won the Nobel Prize in Chemistry for his development of the theory and methodology of organic synthesis, Corey was born to Christian Lebanese immigrants in Methuen, Massachusetts,50 km north of Boston. His mother changed his name to Elias to honor his father and his widowed mother, brother, two sisters and an aunt and uncle all lived together in a spacious house, struggling through the Great Depression. As a young boy, Corey was rather independent and enjoyed such as baseball, football. He attended a Catholic elementary school and Lawrence High School in Lawrence, at the age of 16, Corey entered MIT, where he earned both a bachelors degree in 1948 and a Ph. D. under Professor John C. Upon entering MIT, Coreys only experience with science was in mathematics, after his first chemistry class in his sophomore year he began rethinking his long-term career plans and graduated with a bachelors degree in chemistry. Immediately thereafter, at the invitation of Professor John C, sheehan, Corey remained at MIT for his Ph. D. After his graduate career he was offered an appointment at the University of Illinois at Urbana–Champaign and he was initiated as a member of the Zeta Chapter of Alpha Chi Sigma at the University of Illinois in 1952. In 1959, he moved to Harvard University, where he is currently a professor of organic chemistry with an active Corey Group research program. He chose to work in organic chemistry because of its intrinsic beauty and he has also been an advisor to Pfizer for more than 50 years. Among numerous honors, Corey was awarded the National Medal of Science in 1998, the Nobel Prize in Chemistry in 1990, and the American Chemical Societys greatest honor, the Priestley Medal, in 2004. Corey has developed several new synthetic reagents, PCC, also referred to as the Corey-Suggs reagent, is used for the oxidation of alcohols to corresponding ketones and aldehydes. PCC has several advantages over other commercial oxidants, one of these advantages is that the compound is available as an air-stable yellow solid that is not very hygroscopic. Unlike other oxidizing agents, PCC can accomplish single oxidations with only about 1.5 equivalents, the alcohol performs nucleophilic attack to the electropositive chromium metal displacing chlorine. The chloride anion then acts as a base to afford the aldehyde product, the slightly acidic character of PCC makes it useful for cyclization reactions with alcohols and alkenes. The initial oxidation yields the corresponding aldehyde, which can undergo a Prins reaction with the neighboring alkene. After elimination and further oxidation, the product is a cyclic ketone, if this product is undesired, powdered sodium acetate can be used as a buffer to achieve only initial oxidation. The robustness of PCC as an agent has also rendered it useful in the realm of total synthesis
26.
Dieter Enders
–
Dieter Enders is an organic chemist who has done work developing asymmetric synthesis, in particular using modified prolines as asymmetric auxiliaries. The most widely applied of his chiral auxiliaries are the complementary SAMP and RAMP auxiliaries, in 1974 he obtained his doctorate from the University of Gießen studying under Dieter Seebach and followed this with a postdoc at Harvard University studying with Elias James Corey. He then moved back to Gießen to obtain his Habilitation in 1979, whereupon he became a lecturer, in 1985 he moved to Aachen, where he has remained as Full Professor of Organic Chemistry and Director. He is editor-in-chief of Synthesis and is on the boards of many other journals including Letters in Organic Chemistry. During his career he has won many awards
27.
Enantioselective synthesis
–
Enantioselective synthesis, also called chiral synthesis or asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as, a reaction in which one or more new elements of chirality are formed in a substrate molecule. Put more simply, it is the synthesis of a compound by a method that favors the formation of a specific enantiomer or diastereomer, many of the building blocks of biological systems, such as sugars and amino acids, are produced exclusively as one enantiomer. As a result, living systems possess a degree of chemical chirality. Examples of this selectivity include, Flavour, the sweetener aspartame has two enantiomers. L-aspartame tastes sweet, yet D-aspartame is tasteless Odor, R--carvone smells like spearmint yet S--carvone, drug effectiveness, the antidepressant drug Citalopram is sold as a racemic mixture. However, studies have shown only the - enantiomer is responsible for the drugs beneficial effects. Drug safety, D‑penicillamine is used in therapy and for the treatment of rheumatoid arthritis. However L‑penicillamine is toxic as it inhibits the action of pyridoxine, as such, enantioselective synthesis is of great importance, but it can also be difficult to achieve. Asymmetric induction can occur intramolecularly when given a starting material. This behaviour can be exploited, especially when the goal is to make several consecutive chiral centres to give a specific enantiomer of a specific diastereomer. An aldol reaction, for example, is inherently diastereoselective, if the aldehyde is enantiopure, enantioselective catalysis is a widely practiced method for generating chiral compounds. Enantiomers possess identical enthalpies and entropies and hence should be produced in equal amounts by an undirected process – leading to a racemic mixture, the nonselectivity can be biased using a chiral feature that favors the formation of one enantiomer over another via interactions at the transition state. Enantioselectivity is usually determined by the rates, k1/k2, of an enantiodifferentiating step. The differing barrier heights, ΔΔG*, for these divergent steps determines the rates, k1/k2 = 10^ k1/k2 is also sensitive to temperature. In general, enantioselective catalysis are chiral coordination complexes, catalysis is effective for a broader range of transformations than any other method of enantioselective synthesis. The catalysts are almost invariably rendered chiral by using chiral ligands, most enantioselective catalysts are effective at low substrate/catalyst ratios. Given their high efficiencies, they are suitable for industrial scale synthesis
28.
Chiral auxiliary
–
A chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions, the auxiliary can then be typically recovered for future use. Chiral auxiliaries are one of many strategies available to chemists to selectively produce the desired stereoisomer of a given compound. Chiral auxiliaries were introduced by E. J, Corey in 1975 with chiral 8-phenylmenthol and by B. M. Trost in 1980 with chiral mandelic acid, the menthol compound is difficult to prepare and as an alternative trans-2-phenyl-1-cyclohexanol was introduced by J. K. Whitesell in 1985. Chiral auxiliaries are incorporated into synthetic routes to control the configuration of stereogenic centers. The cost of employing stoichiometric auxiliary and the need to spend synthetic steps appending and removing the auxiliary make this approach appear inefficient, however, for many transformations, the only available stereoselective methodology relies on chiral auxiliaries. In addition, transformations with chiral auxiliaries tend to be versatile and very well-studied, furthermore, the products of auxiliary-directed reactions are diastereomers, which enables their facile separation by methods such as column chromatography or crystallization. In an early example of the use of an auxiliary in asymmetric synthesis. Corey and coworkers conducted an asymmetric Diels-Alder reaction between -8-phenylmenthol acrylate ester and 5-benzyloxymethylcyclopentadiene, the cycloaddition product was carried forward to the iodolactone shown below, an intermediate in the classic Corey synthesis of the prostaglandins. It is proposed that the face of the acrylate is blocked by the auxiliary. -8-phenylmenthol can be prepared from either enantiomer of pulegone, though neither route is very efficient,1, 1’-Binaphthyl-2, 2’-diol, or BINOL, has been used as chiral auxiliary for the asymmetric synthesis since 1983. Hisashi Yamamoto first utilized -BINOL as an auxiliary in the asymmetric synthesis of limonene. -BINOL monoeryl ether was prepared by the monosilylation and alkylation of -BINOL as the chiral auxiliary, followed with the reduction by organoaluminum reagent, limonene was synthesized with low yields and moderate enantiomeric excesses up to 64% ee. The preparation of a variety of enantiomerically pure uncommon R-amino acids can be achieved by the alkylation of chiral glycine derivatives possessing axially chiral BINOL as an auxiliary and it has been depicted by Fuji et al. Based on different electrophile, the diastereomeric excess varied from 69% to 86, Trans-2-phenylcyclohexanol is one type of chiral auxiliary, which was first introduced by James K. Whitesell and his coworkers in 1985. This chiral auxiliary was used in ene reactions of the derived glyoxylate ester, trans-2-cumylcyclohexanol has a similar structure to Trans-2-phenylcyclohexanol. In 2015, Brown group published an efficient method in permanganate-mediated oxidative cyclization with this type of chiral auxiliary, oxazolidinone auxiliaries, popularized by David Evans, have been applied to many stereoselective transformations, including aldol reactions, alkylation reactions, and Diels-Alder reactions
29.
Azo compound
–
Azo compounds are compounds bearing the functional group R–N=N–R′, in which R and R′ can be either aryl or alkyl. IUPAC defines azo compounds as, Derivatives of diazene, HN=NH, the more stable derivatives contain two aryl groups. The N=N group is called an azo group, the name azo comes from azote, the French name for nitrogen that is derived from the Greek ἀ- + ζωή. Most colored textile and leather articles are treated with azo dyes, as a consequence of п-delocalization, aryl azo compounds have vivid colors, especially reds, oranges, and yellows. Therefore, they are used as dyes, and are known as azo dyes. Some azo compounds, e. g. methyl orange, are used as acid-base indicators due to the different colors of their acid, most DVD-R/+R and some CD-R discs use blue azo dye as the recording layer. The development of azo dyes was an important step in the development of the chemical industry, azo pigments consist of colorless particles colored using an azo compound. Azo pigments are important in a variety of paints including artists paints and they have excellent coloring properties, again mainly in the yellow to red range, as well as good lightfastness. The lightfastness depends not only on the properties of the azo compound. Aryl azo compounds are stable, crystalline species. Azobenzene is the prototypical aromatic azo compound and it exists mainly as the trans isomer, but upon photolysis, converts to the cis isomer. The oxidation of hydrazines also gives azo compounds, typical aniline partners are shown below. Illustrative azo compounds that are precursors to dyes Aliphatic azo compounds are commonly encountered than the aryl azo compounds. A commercially important alkyl azo compound is azobisisobutyronitrile, which is used as an initiator in free radical polymerizations. A simple dialkyl diazo compound is diethyldiazene, EtN=NEt, because of their instability, aliphatic azo compounds pose the risk of explosion. Likewise, several studies have linked azo pigments with basal cell carcinoma. Azo dyes derived from benzidine are carcinogens, exposure to them has classically been associated with bladder cancer, accordingly, the production of benzidine azo dyes was discontinued in the 1980s in the most important western industrialized countries. Certain azo dyes can break down under reductive conditions to any of a group of defined aromatic amines
30.
Imine
–
An imine is a functional group or chemical compound containing a carbon–nitrogen double bond. The Nitrogen atom can be attached to a hydrogen or an organic group, if this group is not a hydrogen atom, then the compound can sometimes be referred to as a Schiff base. The carbon atom has two single bonds. Usually imines refer to compounds with the connectivity R2C=NR, as discussed below, in the older literature, imine refers to the aza analogue of an epoxide. Thus, ethyleneimine is the ring species C2H4NH. Imines are related to ketones and aldehydes by replacement of the oxygen with an NR group, when R = H, the compound is a primary imine, when R is hydrocarbyl, the compound is a secondary imine. Imines exhibit diverse reactivity and are encountered throughout chemistry. When R3 is OH, the imine is called an oxime, a primary imine in which C is attached to both a hydrocarbyl and a H is called a primary aldimine, a secondary imine with such groups is called a secondary aldimine. A primary imine in which C is attached to two hydrocarbyls is called a primary ketimine, an imine with such groups is called a secondary ketimine. One way of naming aldimines is to take the name of the radical, remove final e, see the aldimine article for other naming conventions. N-Sulfinyl imines are a class of imines having a sulfinyl group attached to the nitrogen atom. In recent years, several such as Trisborate, pyrrolidine or Titanium Ethoxide have been shown to catalyse imine formation. Several other methods exist for the synthesis of imines, reaction of organic azides with metal carbenoids. Condensation of carbon acids with nitroso compounds, the rearrangement of trityl N-haloamines in the Stieglitz rearrangement. By reaction of alkenes with hydrazoic acid in the Schmidt reaction, by reaction of a nitrile, hydrochloric acid, and an arene in the Hoesch reaction. Multicomponent synthesis of 3-thiazolines in the Asinger reaction, primary ketimines can be synthesized via a Grignard reaction with a nitrile. The most important reactions of imines are their hydrolysis to the corresponding amine, otherwise this functional group participates in many other reactions, many of which are analogous to the reactions of aldehydes and ketones. An imine is reduced in reductive amination, an imine reacts with an amine to an aminal, see for example the synthesis of cucurbituril
31.
Nitrosamine
–
Nitrosamines are chemical compounds of the chemical structure R1N–N=O, that is, a nitroso group bonded to an amine. Nitrosamines are used in the manufacture of cosmetics, pesticides. Nitrosamines occur in products such as balloons, and in many foods. Nitrosamines from condoms are not expected to be of toxicological significance, in foods, nitrosamines are produced from nitrites and secondary amines, which often occur in the form of proteins. Their formation can occur only under conditions, including strongly acidic conditions such as that of the human stomach. High temperatures, as in frying, can enhance the formation of nitrosamines. The presence of nitrosamines may be identified by the Liebermann nitroso reaction, under acidic conditions the nitrite forms nitrous acid, which is protonated and splits into the nitrosonium cation N≡O+ and water, H 2NO+2 → H2O + NO+. The nitrosonium cation then reacts with an amine to produce nitrosamine and these processes lead to significant levels of nitrosamines in many foodstuffs, especially beer, fish, and fish byproducts, and also in meat and cheese products preserved with nitrite compounds. The U. S. government established limits on the amount of used in meat products in order to decrease cancer risk in the population. There are also rules about adding ascorbic acid or related compounds to meat, tobacco-specific nitrosamines can also be found in tobacco smoke, American dip snuff, chewing tobacco, and to a much lesser degree, snus. Nitrosamines can also be found in e-cigarette vapour, though this is reported to be trace amounts, Nitrosamines can be formed from nitrates in drinking water upon ingestion. The EPA standard is 10 ppm but is considered by the National Academy of Sciences as lacking margin of safety for sensitive individuals and this standard has not changed in over 40 years despite repeated warnings from the Academy. In 1956, two British scientists, John Barnes and Peter Magee, reported that dimethylnitrosamine produced liver tumours in rats, research was undertaken and approximately 90% of nitrosamine compounds were deemed to be carcinogenic. In the 1970s, there was a frequency of liver cancer found in Norwegian farm animals. The farm animals had been fed on herring meal, which was preserved using sodium nitrite, the sodium nitrite had reacted with dimethylamine in the fish and produced dimethylnitrosamine. Nitrosamines can cause cancers in a variety of animal species. At present, available evidence from case-control studies on nitrite. Hydrazines derived from these nitrosamines, e. g. UDMH, are also carcinogenic, endogenous nitrosamine formation can be inhibited by ascorbic acid
32.
International Standard Book Number
–
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
33.
PubMed Identifier
–
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
. PMID 18712739.