1.
Chemistry
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Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
2.
Amount of substance
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Amount of substance is a standards-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount, the International System of Units defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is the mole and it has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant, the mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 12g of the isotope carbon-12. This number is called Avogadros number and has the value 6. 022140857×1023 and it is the numerical value of the Avogadro constant which has the unit 1/mol, and relates the molar mass of an amount of substance to its mass. Therefore, the amount of substance of a sample is calculated as the sample mass divided by the mass of the substance. Amount of substance appears in thermodynamic relations such as the gas law. Another unit of amount of substance in use in engineering in the United States is the pound-mole. When quoting an amount of substance, it is necessary to specify the entity involved, unless there is no risk of ambiguity. One mole of chlorine could refer either to chlorine atoms, as in 58.44 g of sodium chloride, or to chlorine molecules, the simplest way to avoid ambiguity is to replace the term substance by the name of the entity or to quote the empirical formula. The main derived quantity in which amount of substance enters into the numerator is amount of substance concentration and this name is often abbreviated to amount concentration, except in clinical chemistry where substance concentration is the preferred term to avoid ambiguity with mass concentration. The term molar concentration is incorrect, but commonly used, the alchemists, and especially the early metallurgists, probably had some notion of amount of substance, but there are no surviving records of any generalization of the idea beyond a set of recipes. In 1758, Mikhail Lomonosov questioned the idea that mass was the measure of the quantity of matter. The development of the concept of amount of substance was coincidental with, and vital to,1777, Wenzel publishes Lessons on Affinity, in which he demonstrates that the proportions of the base component and the acid component remain the same during reactions between two neutral salts. 1789, Lavoisier publishes Treatise of Elementary Chemistry, introducing the concept of a chemical element,1792, Richter publishes the first volume of Stoichiometry or the Art of Measuring the Chemical Elements. The term stoichiometry is used for the first time, the first tables of equivalent weights are published for acid–base reactions. Richter also notes that, for an acid, the equivalent mass of the acid is proportional to the mass of oxygen in the base. 1794, Prousts Law of definite proportions generalizes the concept of equivalent weights to all types of chemical reaction,1805, Dalton publishes his first paper on modern atomic theory, including a Table of the relative weights of the ultimate particles of gaseous and other bodies
3.
Enantiomer
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A single chiral atom or similar structural feature in a compound causes that compound to have two possible structures which are non-superposable, each a mirror image of the other. Each member of the pair is termed an enantiomorph, the property is termed enantiomerism. The presence of multiple features in a given compound increases the number of geometric forms possible. Enantiopure compounds refer to samples having, within the limits of detection and they are sometimes called optical isomers for this reason. Enantiomer members often have different chemical reactions with other enantiomer substances, since many biological molecules are enantiomers, there is sometimes a marked difference in the effects of two enantiomers on biological organisms. Owing to this discovery, drugs composed of one enantiomer can be developed to enhance the pharmacological efficacy. An example is eszopiclone, which is enantiopure and therefore administered in doses that are exactly 1/2 of the older, in the case of eszopiclone, the S enantiomer is responsible for all the desired effects, while the other enantiomer seems to be inactive. A dose of 2 mg of zopiclone must be administered to produce the therapeutic effect as 1 mg of eszopiclone. In chemical synthesis of enantiomeric substances, non-enantiomeric precursors inevitably produce racemic mixtures, in the absence of an effective enantiomeric environment, separation of a racemic mixture into its enantiomeric components is impossible. The R/S system is an important nomenclature system for denoting distinct enantiomers, another system is based on prefix notation for optical activity, - and - or d- and l-. The Latin for left and right is laevus and dexter, respectively, left and right have always had moral connotations, and the Latin words for these are sinister and rectus. The English word right is a cognate of rectus and this is the origin of the D, L and S, R notations, and the employment of prefixes levo- and dextro- in common names. Most compounds that one or more asymmetric carbon atoms show enantiomerism. There are a few compounds that do have asymmetric carbon atoms. An example of such an enantiomer is the sedative thalidomide, which was sold in a number of countries across the world from 1957 until 1961 and it was withdrawn from the market when it was found to cause of birth defects. One enantiomer caused the desirable effects, while the other, unavoidably present in equal quantities. The herbicide mecoprop is a mixture, with the --enantiomer possessing the herbicidal activity. Another example is the antidepressant drugs escitalopram and citalopram, citalopram is a racemate, escitalopram is a pure enantiomer
4.
Chirality (chemistry)
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Chirality /kaɪˈrælɪti/ is a geometric property of some molecules and ions. A chiral molecule/ion is non-superposable on its mirror image, the presence of an asymmetric carbon center is one of several structural features that induce chirality in organic and inorganic molecules. The term chirality is derived from the Greek word for hand, the mirror images of a chiral molecule/ion are called enantiomers or optical isomers. Individual enantiomers are often designated as either right- or left-handed, Chirality is an essential consideration when discussing the stereochemistry in organic and inorganic chemistry. The concept is of practical importance because most biomolecules and pharmaceuticals are chiral. Chirality is based on molecular symmetry elements, specifically, a chiral compound can contain no improper axis of rotation, which includes planes of symmetry and inversion center. Chiral molecules are always dissymmetric but not always asymmetric, in general, chiral molecules have point chirality at a single stereogenic atom, which has four different substituents. The two enantiomers of such compounds are said to have different absolute configurations at this center, the stereogenic atom is usually carbon, as in many biological molecules. However chirality can exist in any atom, including metals, phosphorus, Chiral nitrogen is equally possible, although the effects of nitrogen inversion can make many of these compounds impossible to isolate. While the presence of a stereogenic atom describes the great majority of cases, for instance it is not necessary for the chiral substance to have a stereogenic atom. Examples include 1-bromo-1-chloro-1-fluoroadamantane, methylethylphenyltetrahedrane, certain calixarenes and fullerenes, which have inherent chirality, the C2-symmetric species 1, 1-bi-2-naphthol,1, 3-dichloro-allene have axial chirality. -cyclooctene and many ferrocenes have planar chirality, when the optical rotation for an enantiomer is too low for practical measurement, the species is said to exhibit cryptochirality. Even isotopic differences must be considered when examining chirality, illustrative is the derivative of benzyl alcohol PhCHDOH is chiral. The S enantiomer has D = +0. 715°, many biologically active molecules are chiral, including the naturally occurring amino acids and sugars. In biological systems, most of these compounds are of the chirality, most amino acids are levorotatory. Typical naturally occurring proteins, made of L amino acids, are known as left-handed proteins, d-amino acids are very rare in nature and have only been found in small peptides attached to bacteria cell walls. The origin of this homochirality in biology is the subject of much debate, however, there is some suggestion that early amino acids could have formed in comet dust. Enzymes, which are chiral, often distinguish between the two enantiomers of a chiral substrate, one could imagine an enzyme as having a glove-like cavity that binds a substrate
5.
Louis Pasteur
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Louis Pasteur was a French biologist, microbiologist and chemist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization. He is remembered for his breakthroughs in the causes and prevention of diseases. He reduced mortality from puerperal fever, and created the first vaccines for rabies and his medical discoveries provided direct support for the germ theory of disease and its application in clinical medicine. He is best known to the public for his invention of the technique of treating milk and wine to stop bacterial contamination. He is regarded as one of the three founders of bacteriology, together with Ferdinand Cohn and Robert Koch, and is popularly known as the father of microbiology. Pasteur was responsible for disproving the doctrine of spontaneous generation and he performed experiments that showed that without contamination, microorganisms could not develop. Under the auspices of the French Academy of Sciences, he demonstrated that in sterilized and sealed flasks nothing ever developed, although Pasteur was not the first to propose the germ theory, his experiments indicated its correctness and convinced most of Europe that it was true. Today, he is regarded as one of the fathers of germ theory. Pasteur also made significant discoveries in chemistry, most notably on the basis for the asymmetry of certain crystals. Early in his career, his investigation of tartaric acid resulted in the first resolution of what is now called optical isomers and his work led the way to the current understanding of a fundamental principle in the structure of organic compounds. He was the director of the Pasteur Institute, established in 1887, till his death, although Pasteur made groundbreaking experiments, his reputation became associated with various controversies. Historical reassessment of his notebook revealed that he practiced deception to overcome his rivals, Louis Pasteur was born on December 27,1822, in Dole, Jura, France, to a Catholic family of a poor tanner. He was the child of Jean-Joseph Pasteur and Jeanne-Etiennette Roqui. The family moved to Marnoz in 1826 and then to Arbois in 1827, Pasteur entered primary school in 1831. He was a student in his early years, and not particularly academic. He drew many pastels and portraits of his parents, friends, Pasteur attended secondary school at the Collège dArbois. In October 1838, he left for Paris to join the Pension Barbet, in 1839, he entered the Collège Royal de Besançon to study philosophy and earned his Bachelor of Letters degree in 1840. He was appointed a tutor at the Besançon college while continuing a degree course with special mathematics
6.
Isomer
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An isomer is a molecule with the same molecular formula as another molecule, but with a different chemical structure. That is, isomers contain the number of atoms of each element. Isomers do not necessarily share similar properties, unless they also have the functional groups. There are two forms of isomerism, structural isomerism and stereoisomerism. In structural isomers, sometimes referred to as constitutional isomers, the atoms, Structural isomers have different IUPAC names and may or may not belong to the same functional group. For example, two position isomers would be 2-fluoropropane and 1-fluoropropane, illustrated on the side of the diagram above. In skeletal isomers the main chain is different between the two isomers. This type of isomerism is most identifiable in secondary and tertiary alcohol isomers, tautomers are structural isomers that spontaneously interconvert with each other, even when pure. They have different chemical properties and, as a consequence, distinct reactions characteristic to each form are observed, if the interconversion reaction is fast enough, tautomers cannot be isolated from each other. An example is when they differ by the position of a proton, such as in keto/enol tautomerism, there is, however, another isomer of C3H8O that has significantly different properties, methoxyethane. Unlike the isomers of propanol, methoxyethane has an oxygen connected to two carbons rather than to one carbon and one hydrogen. Methoxyethane is an ether, not an alcohol, because it lacks a hydroxyl group, propadiene and propyne are examples of isomers containing different bond types. Propadiene contains two double bonds, whereas propyne contains one triple bond, in stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers which are non-superposable mirror-images of each other, and diastereomers, enantiomers always contain chiral centers and diastereomers often do, but there are some diastereomers that neither are chiral nor contain chiral centers. Another type of isomer, conformational isomers, may be rotamers, diastereomers, for example, ortho- position-locked biphenyl systems have enantiomers. E/Z isomers, which have restricted rotation at a bond, are configurational isomers. They are classified as diastereomers, whether or not they contain any chiral centers, e/Z notation depicts absolute stereochemistry, which is an unambiguous descriptor based on CIP priorities. Cis–trans isomers are used to describe any molecules with restricted rotation in the molecule, for molecules with C=C double bonds, these descriptors describe relative stereochemistry only based on group bulkiness or principal carbon chain, and so can be ambiguous
7.
IUPAC
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The International Union of Pure and Applied Chemistry /ˈaɪjuːpæk/ or /ˈjuːpæk/ is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science, IUPAC is registered in Zürich, Switzerland, and the administrative office, known as the IUPAC Secretariat, is in Research Triangle Park, North Carolina, United States. This administrative office is headed by IUPACs executive director, currently Lynn Soby, IUPAC was established in 1919 as the successor of the International Congress of Applied Chemistry for the advancement of chemistry. Its members, the National Adhering Organizations, can be national chemistry societies, national academies of sciences, there are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPACs Inter-divisional Committee on Nomenclature and Symbols is the world authority in developing standards for the naming of the chemical elements. Since its creation, IUPAC has been run by different committees with different responsibilities. These committees run different projects which include standardizing nomenclature, finding ways to bring chemistry to the world, IUPAC is best known for its works standardizing nomenclature in chemistry and other fields of science, but IUPAC has publications in many fields including chemistry, biology and physics. IUPAC is also known for standardizing the atomic weights of the elements through one of its oldest standing committees, the need for an international standard for chemistry was first addressed in 1860 by a committee headed by German scientist Friedrich August Kekulé von Stradonitz. This committee was the first international conference to create an international naming system for organic compounds, the ideas that were formulated in that conference evolved into the official IUPAC nomenclature of organic chemistry. IUPAC stands as a legacy of this meeting, making it one of the most important historical international collaborations of chemistry societies, since this time, IUPAC has been the official organization held with the responsibility of updating and maintaining official organic nomenclature. IUPAC as such was established in 1919, one notable country excluded from this early IUPAC is Germany. Germanys exclusion was a result of prejudice towards Germans by the Allied powers after World War I, Germany was finally admitted into IUPAC during 1929. However, Nazi Germany was removed from IUPAC during World War II, during World War II, IUPAC was affiliated with the Allied powers, but had little involvement during the war effort itself. After the war, East and West Germany were eventually readmitted to IUPAC, since World War II, IUPAC has been focused on standardizing nomenclature and methods in science without interruption. In 2016, IUPAC denounced the use of chlorine as a chemical weapon, the letter stated, Our organizations deplore the use of chlorine in this manner. According to the CWC, the use, stockpiling, distribution, IUPAC is governed by several committees that all have different responsibilities. Each committee is made up of members of different National Adhering Organizations from different countries, the steering committee hierarchy for IUPAC is as follows, All committees have an allotted budget to which they must adhere. Any committee may start a project, if a projects spending becomes too much for a committee to continue funding, it must take the issue to the Project Committee
8.
Optical rotation
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Optical rotation or optical activity is the rotation of the plane of polarization of linearly polarized light as it travels through certain materials. Optical activity occurs only in chiral materials, those lacking microscopic mirror symmetry, unlike other sources of birefringence which alter a beams state of polarization, optical activity can be observed in fluids. This can include gases or solutions of chiral molecules such as sugars, molecules with helical secondary structure such as some proteins and it can also be observed in chiral solids such as certain crystals with a rotation between adjacent crystal planes or metamaterials. The rotation of the plane of polarization may be either clockwise, to the right, for instance, sucrose and camphor are d-rotary whereas cholesterol is l-rotary. For a given substance, the angle by which the polarization of light of a wavelength is rotated is proportional to the path length through the material and proportional to its concentration. The rotation is not dependent on the direction of propagation, unlike the Faraday effect where the rotation is dependent on the direction of the applied magnetic field. Optical activity is measured using a source and polarimeter. Modulation of a liquid crystals optical activity, viewed between two polarizers, is the principle of operation of liquid-crystal displays. The rotation of the orientation of polarized light was first observed in 1811 in quartz by French physicist François Jean Dominique Arago. Jean Baptiste Biot also observed the rotation of the axis of polarization in certain liquids, simple polarimeters have been used since this time to measure the concentrations of simple sugars, such as glucose, in solution. In fact one name for D-glucose, is dextrose, referring to the fact that it causes linearly polarized light to rotate to the right or dexter side. In a similar manner, levulose, more known as fructose. Fructose is even more strongly levorotatory than glucose is dextrorotatory, in 1849, Louis Pasteur resolved a problem concerning the nature of tartaric acid. Pasteur noticed that the crystals come in two forms that are mirror images of one another. Sorting the crystals by hand gave two forms of the compound, Solutions of one form rotate polarized light clockwise, while the other form rotate light counterclockwise, an equal mix of the two has no polarizing effect on light. If the 4 neighbors are all different, then there are two possible orderings of the neighbors around the tetrahedron, which will be mirror images of each other and this led to a better understanding of the three-dimensional nature of molecules. Optical activity occurs due to molecules dissolved in a fluid or due to the fluid itself only if the molecules are one of two stereoisomers, this is known as an enantiomer, the structure of such a molecule is such that it is not identical to its mirror image. In mathematics, this property is known as chirality
9.
Polarization (waves)
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Polarization is a parameter applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave the direction of the oscillation is transverse to the direction of motion of the wave, a simple example of a polarized transverse wave is vibrations traveling along a taut string for example in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a direction, horizontal direction. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, in some types of transverse waves the wave displacement is limited to a single direction, so these also dont exhibit polarization. For example, in waves in liquids the wave displacement of the particles is always in a vertical plane. In linear polarization the fields oscillate in a single direction, in circular or elliptical polarization the fields rotate at a constant rate in a plane as the wave travels. Polarized light can be produced by passing unpolarized light through a polarizing filter, some of these are used to make polarizing filters. Light is also partially polarized when it reflects from a surface, according to quantum mechanics, electromagnetic waves consist of particles called photons. When viewed in this way, the polarization of a wave is determined by a quantum mechanical property of photons called their spin. A photon has one of two spins, it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with one type of spin. Linearly polarized waves consist of numbers of right and left hand spinning photons. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar. And incoherent states can be modeled stochastically as a combination of such uncorrelated waves with some distribution of frequencies, phases. Considering a monochromatic wave of optical frequency f, let us take the direction of propagation as the z axis. Being a transverse wave the E and H fields must then contain components only in the x and y directions whereas Ez=Hz=0. Using complex notation, we understand the instantaneous electric and magnetic fields to be given by the real parts of the complex quantities occurring in the following equations. Here ex, ey, hx, and hy are complex numbers, in the second more compact form, as these equations are customarily expressed, these factors are described using the wavenumber k =2 π n / λ and angular frequency ω =2 π f
10.
Boiling point
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The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the environmental pressure. A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a boiling point than when that liquid is at atmospheric pressure. For a given pressure, different liquids boil at different temperatures, for example, water boils at 100 °C at sea level, but at 93.4 °C at 2,000 metres altitude. The normal boiling point of a liquid is the case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level,1 atmosphere. At that temperature, the pressure of the liquid becomes sufficient to overcome atmospheric pressure. The standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar, the heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation, evaporation is a surface phenomenon in which molecules located near the liquids edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, a saturated liquid contains as much thermal energy as it can without boiling. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase, the liquid can be said to be saturated with thermal energy. Any addition of energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed, similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the pressure of the liquid equals the surrounding environmental pressure. Thus, the point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, at higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, the boiling point cannot be increased beyond the critical point. Likewise, the point decreases with decreasing pressure until the triple point is reached
11.
Methamphetamine
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Methamphetamine is a strong central nervous system stimulant that is mainly used as a recreational drug and less commonly as a treatment for attention deficit hyperactivity disorder and obesity. Methamphetamine was discovered in 1893 and exists as two enantiomers, levo-methamphetamine and dextro-methamphetamine, Methamphetamine properly refers to a specific chemical, the racemic free base, which is an equal mixture of levomethamphetamine and dextromethamphetamine in their pure amine forms. Dextromethamphetamine is a much stronger CNS stimulant than levomethamphetamine, both methamphetamine and dextromethamphetamine are illicitly trafficked and sold owing to their potential for recreational use. Levomethamphetamine is available as a drug for use as an inhaled nasal decongestant in the United States. While dextromethamphetamine is a potent drug, racemic methamphetamine is sometimes illicitly produced due to the relative ease of synthesis. In low doses, methamphetamine can elevate mood, increase alertness, concentration and energy in fatigued individuals, at higher doses, it can induce psychosis, breakdown of skeletal muscle, seizures and bleeding in the brain. Chronic high-dose use can precipitate unpredictable and rapid mood swings, prominent delusions, Methamphetamine is known to have a high addiction liability and dependence liability. Heavy recreational use of methamphetamine may lead to a post-acute-withdrawal syndrome, unlike amphetamine, methamphetamine is neurotoxic to human midbrain dopaminergic neurons. It has also shown to damage serotonin neurons in the CNS. This damage includes adverse changes in structure and function, such as reductions in grey matter volume in several brain regions. Methamphetamine belongs to the phenethylamine and substituted amphetamine chemical classes. It is related to the other dimethylphenethylamines as an isomer of these compounds. Methamphetamine is sometimes prescribed off label for narcolepsy and idiopathic hypersomnia, in the United States, methamphetamines levorotary form is available in some over-the-counter nasal decongestant products. As methamphetamine is associated with a potential for misuse, the drug is regulated under the Controlled Substances Act and is listed under schedule II in the United States. Methamphetamine hydrochloride dispensed in the United States is required to include a warning regarding its potential for recreational misuse. Methamphetamine is often used recreationally for its effects as a potent euphoriant and stimulant as well as aphrodisiac qualities, according to a National Geographic TV documentary on methamphetamine, an entire subculture known as party and play is based around methamphetamine use. Members of this San Francisco sub-culture, which consists almost entirely of gay male methamphetamine users, due to its strong stimulant and aphrodisiac effects and inhibitory effect on ejaculation, with repeated use, these sexual encounters will sometimes occur continuously for several days on end. The crash following the use of methamphetamine in this manner is often severe
12.
Melting point
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The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
13.
Malic acid
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Malic acid is an organic compound with the molecular formula C4H6O5. It is an acid that is made by all living organisms, contributes to the pleasantly sour taste of fruits. Malic acid has two forms, though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates, the malate anion is an intermediate in the citric acid cycle. L-Malic acid is the naturally occurring form, whereas a mixture of L-, malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of CO2 in the Calvin cycle, in the citric acid cycle, -malate is an intermediate, formed by the addition of an -OH group on the si face of fumarate. It can also be formed from pyruvate via anaplerotic reactions, malate is also synthesized by the carboxylation of phosphoenolpyruvate in the guard cells of plant leaves. Malate, as an anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the cell decreases the solute potential, allowing water to enter the cell. Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785, antoine Lavoisier in 1787 proposed the name acide malique, which is derived from the Latin word for apple, mālum—as is its genus name Malus. In German it is named Äpfelsäure after plural or singular of the fruit apple, Malic acid contributes to the sourness of green apples. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/l and it confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb and it is also a component of some artificial vinegar flavors, such as salt and vinegar flavored potato chips. The process of malolactic fermentation converts malic acid to much milder lactic acid, Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism. Malic acid, when added to products, is denoted by E number E296. Malic acid is the source of extreme tartness in United States-produced confectionery and it is also used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth and it is approved for use as a food additive in the EU, US and Australia and New Zealand. Malic acid provides 10 kJ of energy per gram during digestion, racemic malic acid is produced industrially by the double hydration of maleic anhydride
14.
Dumbbell
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The dumbbell, a type of free weight, is a piece of equipment used in weight training. It can be used individually or in pairs, with one in each hand, the forerunner of the dumbbell, halteres, were used in ancient Greece as lifting weights and also as weights in the ancient Greek version of the long jump. A kind of dumbbell was also used in India for more than a millennium, despite their common English name implying an Indian origin, the so-called Indian clubs were in fact created in the Near East. Properly referred to as meels, they are first recorded as being used by wrestlers in ancient Persia, Egypt, the practice has continued to the present day, notably in the Varzesh-e Bastan tradition practiced in the zurkaneh of Iran. From Persia, the Mughals brought the meels to South Asia where are still used by pehlwan, british colonists first came across Persian meels in India, and erroneously referred to them as Indian clubs despite their Middle Eastern origin. The design of the Nal, as the equipment was referred to and it was generally used in pairs, in workouts by wrestlers, bodybuilders, sports players, and others wishing to increase strength and muscle size. The term dumbbell or dumb bell originated in late Stuart England, in 1711 the poet Joseph Addison mentioned exercising with a dumb bell in an essay published in The Spectator. By the early 17th century, the shape of the dumbbell. There are currently three main types of dumbbell, Adjustable dumbbells consist of a metal bar whose centre portion is engraved with a crosshatch pattern to improve grip. Weight plates are slid onto the outer portions of the dumbbell, shown to the right is a spinlock dumbbell, whose ends are threaded to accept large nuts as collars. Alternatively, a dumbbell may have smooth ends with plates being secured by a sprung collar, nowadays, many commercially sold dumbbells are available with sophisticated, and easy-to-use methods for weight increments adjustments. Fixed-weight dumbbells are weights created in a dumbbell shape, inexpensive varieties consist of cast iron, sometimes coated with rubber or neoprene for comfort, and even cheaper versions consist of a rigid plastic shell that is filled with concrete. Selectorized dumbbells are adjustable dumbbells whose number of plates can be changed when resting in the dumbbell stand. This is achieved by adjusting the number of plates that follow the handle when lifted and this makes it very easy to change the weight of the dumbbell between exercises, and the stand typically doubles as storage for the additional weights not being used for a particular exercise. Barbell Kettlebell Weights Weight lifting belt Pool dumbbell Bulgarian Bag Media related to Dumbbells at Wikimedia Commons Guide to different types of dumbbell
15.
Chiral resolution
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Chiral resolution in stereochemistry is a process for the separation of racemic compounds into their enantiomers. It is an important tool in the production of optically active drugs, other terms with the same meaning are optical resolution and mechanical resolution. One disadvantage of chiral resolution of racemates compared to direct asymmetric synthesis of one of the enantiomers is that only 50% of a desired enantiomer is obtained, 5-10% of all racemates are known to crystallize as mixtures of enantiopure crystals, so-called conglomerates. Louis Pasteur was the first to conduct chiral resolution when he discovered the concept of activity by the manual separation of left-handed and right-handed tartaric acid crystals in 1849. This type of resolution, called spontaneous resolution, has also demonstrated with racemic methadone. In a typical setup 50 grams dl-methadone is dissolved in petroleum ether, two millimeter-sized d- and l-crystals are added and after stirring for 125 hours at 40 °C two large d- and l-crystals are recovered in 50% yield. Another form of direct crystallization is preferential crystallization also called resolution by entrainment of one of the enantiomers, for example, an added seed of -hydrobenzoin to an ethanol solution of -hydrobenzoin will have the -enantiomer crystallizing out and after 15 cycles 97% optical purity can be obtained. Derivatization of racemic compounds is possible with optically pure reagents forming pairs of diastereomers which can be separated by conventional techniques in physical chemistry, derivatization is possible by salt formation between an amine and a carboxylic acid. Simple deprotonation affords the pure enantiomer, examples of chiral derivatizing agents are tartaric acid and brucine. The method was introduced by Louis Pasteur in 1853 by resolving racemic tartaric acid with optically active -cinchotoxine, the alcohol -enantiomer forms an insoluble diastereomeric salt with the mandelic acid and can be filtered from the solution. Simple deprotonation with sodium hydroxide liberates free -alcohol, in the meanwhile the -alcohol remains in solution unaffected and is recycled back to the racemic mixture by epimerization with hydrochloric acid in toluene. This process is known as RRR synthesis in which the Rs stand for Resolution-Racemization-Recycle, in chiral column chromatography the stationary phase is made chiral with similar resolving agents as described above
16.
Chromatography
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Chromatography is a laboratory technique for the separation of a mixture. The mixture is dissolved in a called the mobile phase. The various constituents of the mixture travel at different speeds, causing them to separate, the separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in a partition coefficient result in differential retention on the stationary phase. Chromatography may be preparative or analytical, the purpose of preparative chromatography is to separate the components of a mixture for later use, and is thus a form of purification. Analytical chromatography is done normally with smaller amounts of material and is for establishing the presence or measuring the proportions of analytes in a mixture. The two are not mutually exclusive, Chromatography was first employed in Russia by the Italian-born scientist Mikhail Tsvet in 1900. He continued to work with chromatography in the first decade of the 20th century, primarily for the separation of plant pigments such as chlorophyll, carotenes, since these components have different colors they gave the technique its name. New types of chromatography developed during the 1930s and 1940s made the technique useful for separation processes. Since then, the technology has advanced rapidly, researchers found that the main principles of Tsvets chromatography could be applied in many different ways, resulting in the different varieties of chromatography described below. Advances are continually improving the performance of chromatography, allowing the separation of increasingly similar molecules. The analyte is the substance to be separated during chromatography and it is also normally what is needed from the mixture. Analytical chromatography is used to determine the existence and possibly also the concentration of analyte in a sample, a bonded phase is a stationary phase that is covalently bonded to the support particles or to the inside wall of the column tubing. A chromatogram is the output of the chromatograph. In the case of a separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture. Plotted on the x-axis is the time and plotted on the y-axis a signal corresponding to the response created by the analytes exiting the system. In the case of a system the signal is proportional to the concentration of the specific analyte separated. A chromatograph is equipment that enables a sophisticated separation, e. g. gas chromatographic or liquid chromatographic separation, Chromatography is a physical method of separation that distributes components to separate between two phases, one stationary, the other moving in a definite direction
17.
Enzyme
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Enzymes /ˈɛnzaɪmz/ are macromolecular biological catalysts. Enzymes accelerate, or catalyze, chemical reactions, the molecules at the beginning of the process upon which enzymes may act are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology, enzymes are known to catalyze more than 5,000 biochemical reaction types. Most enzymes are proteins, although a few are catalytic RNA molecules, enzymes specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy, some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example is orotidine 5-phosphate decarboxylase, which allows a reaction that would take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules, inhibitors are molecules that decrease enzyme activity, many drugs and poisons are enzyme inhibitors. An enzymes activity decreases markedly outside its optimal temperature and pH, some enzymes are used commercially, for example, in the synthesis of antibiotics. French chemist Anselme Payen was the first to discover an enzyme, diastase and he wrote that alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells. In 1877, German physiologist Wilhelm Kühne first used the term enzyme, the word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms. Eduard Buchner submitted his first paper on the study of yeast extracts in 1897, in a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts even when there were no living yeast cells in the mixture. He named the enzyme that brought about the fermentation of sucrose zymase, in 1907, he received the Nobel Prize in Chemistry for his discovery of cell-free fermentation. Following Buchners example, enzymes are usually named according to the reaction they carry out, the biochemical identity of enzymes was still unknown in the early 1900s. Sumner showed that the enzyme urease was a protein and crystallized it. These three scientists were awarded the 1946 Nobel Prize in Chemistry, the discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. This high-resolution structure of lysozyme marked the beginning of the field of structural biology, an enzymes name is often derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase
18.
Catalysis
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Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. In most cases, reactions occur faster with a catalyst because they require less activation energy, furthermore, since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle, in the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations, the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have an activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature. However, the mechanics of catalysis is complex. Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst, in heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst, analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, in heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a system or sublimate in a solid–gas system. The production of most industrially important chemicals involves catalysis, similarly, most biochemically significant processes are catalysed. Research into catalysis is a field in applied science and involves many areas of chemistry, notably organometallic chemistry. Catalysis is relevant to aspects of environmental science, e. g. the catalytic converter in automobiles. Many transition metals and transition metal complexes are used in catalysis as well, Catalysts called enzymes are important in biology. A catalyst works by providing a reaction pathway to the reaction product. The rate of the reaction is increased as this route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates water and oxygen, as shown below,2 H2O2 →2 H2O + O2 This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow. In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available and this reaction is strongly affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms
19.
Homochirality
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Homochirality describes a geometric property of some materials that are composed of chiral units. Chiral bodies are objects which are non-superposable on their mirror images, for example, left and right hands are chiral. A substance is said to be if all the constituent units are molecules of the same chiral form. In biology, homochirality is a property of amino acids. The origin of phenomenon is not clearly understood. It is unclear if homochirality has a purpose, however it appears to be a form of information storage, one suggestion is that it reduces entropy barriers in the formation of large organized molecules. It has been verified that amino acids form large aggregates in larger abundance from enantiopure substrates than from racemic ones. The emergence of chirality consensus as a natural process has been associated with the 2nd law of thermodynamics. Once established, chirality would be selected for, a small enantiomeric excess can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction. In asymmetric autocatalysis, the catalyst is a molecule, which means that a chiral molecule is catalysing its own production. An initial enantiomeric excess, such as can be produced by polarized light, another speculation suggests that fundamental chirality of physical processes such as that of the beta decay leads to slightly different half-lives of biologically relevant molecules. Homochirality may also result from spontaneous absolute asymmetric synthesis, in the Soai reaction, pyrimidine-5-carbaldehyde is alkylated by diisopropylzinc to the corresponding pyrimidyl alcohol. Because the initial product is also an effective catalyst the reaction is autocatalytic. The presence of just 0.2 equivalent of the alcohol S-enantiomer at the start of the reaction is sufficient to amplify the enantiomeric excess to 93%, another study concerns the proline catalyzed aminoxylation of propionaldehyde by nitrosobenzene. In this system too the presence of enantioenriched catalyst drives the reaction one of the two possible optical isomers. Serine octamer clusters are also contenders, partial sublimation processes can take place on the surface of meteors where large variations in temperature exist. When sodium chlorate is allowed to crystallize from water and the collected crystals examined in a polarimeter, each crystal turns out to be chiral, in an ordinary experiment the amount of L crystals collected equals the amount of D crystals. However, when the sodium chlorate solution is stirred during the process the crystals are either exclusively L or exclusively D
20.
Stereospecificity
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A stereoselective process will normally give multiple products even if only one mechanism is operating on an isomerically pure starting material. In the latter sense, the term stereospecific reaction is commonly misused to mean highly stereoselective reaction, chiral synthesis is built on a combination of stereospecific transformations and stereoselective ones, where also the optical activity of a chemical compound is preserved. Of stereoisomeric reactants, each behaves in its own specific way, the choice of mechanism adopted by a particular reactant combination depends on other factors. For example, tertiary centres react almost exclusively by the SN1 mechanism whereas primary centres react almost exclusively by the SN2 mechanism. When a nucleophilic substitution results in inversion, it is because of a competition between the two mechanisms, as often occurs at secondary centres, or because of double inversion. The addition of singlet carbenes to alkenes is stereospecific in that the geometry of the alkene is preserved in the product, for example, dibromocarbene and cis-2-butene yield cis-2, 3-dimethyl-1, 1-dibromocyclopropane, whereas the trans isomer exclusively yields the trans cyclopropane. This addition remains stereospecific even if the alkene is not isomerically pure. The disrotatory ring closing reaction of conjugated trienes is stereospecific in that isomeric reactants will give isomeric products
21.
Stereoselectivity
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The selectivity arises from differences in steric effects and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the energy difference between the two pathways is finite. However, in cases, the minor stereoisomer may not be detectable by the analytic methods used. The degree of selectivity is measured by the enantiomeric excess, a diastereoselective reaction is one in which one diastereomer is formed in preference to another, establishing a preferred relative stereochemistry. The degree of selectivity is measured by the diastereomeric excess. Stereoconvergence can be considered an opposite of stereoselectivity, when the reaction of two different stereoisomers yield a single product stereoisomer, the quality of stereoselectivity is concerned solely with the products, and their stereochemistry. Of a number of possible products, the reaction selects one or two to be formed. An example of modest stereoselectivity is the dehydrohalogenation of 2-iodo-butane which yields 60% trans-2-butene, since alkene geometric isomers are also classified as diastereomers, this reaction would also be called diastereoselective. The chiral center need not be pure, as the relative stereochemistry will be the same for both enantiomers. In the case of chiral alcohols, kinetic resolution results. Another example is Sharpless asymmetric dihydroxylation, in the example below the achiral alkene yields only one of possible 4 stereoisomers. With a stereogenic center next to the carbocation the substitution can be stereoselective in inter-, the first dirigent protein was discovered in Forsythia intermedia. This protein has found to direct the stereoselective biosynthesis of -pinoresinol from coniferyl alcohol monomers. Recently, a second, enantiocomplementary dirigent protein was identified in Arabidopsis thaliana, stereospecific Dynamic stereochemistry Torquoselectivity Regioselectivity Chemoselectivity
22.
Stereoisomerism
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Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms, but differ in the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the same molecular formula, by definition, molecules that are stereoisomers of each other represent the same structural isomer. Enantiomers, also known as optical isomers, are two stereoisomers that are related to other by a reflection, They are mirror images of each other that are non-superimposable. Human hands are an analog of stereoisomerism. Every stereogenic center in one has the configuration in the other. As a result, different enantiomers of a compound may have different biological effects. Pure enantiomers also exhibit the phenomenon of optical activity and can be separated only with the use of a chiral agent, in nature, only one enantiomer of most chiral biological compounds, such as amino acids, is present. Diastereomers are stereoisomers not related through a reflection operation and they are not mirror images of each other. These include meso compounds, cis–trans isomers, and non-enantiomeric optical isomers, diastereomers seldom have the same physical properties. In the example shown below, the form of tartaric acid forms a diastereomeric pair with both levo and dextro tartaric acids, which form an enantiomeric pair. Please refer to Chirality for more regarding the D- and L- labels. Stereoisomerism about double bonds arises because rotation about the bond is restricted. The simplest examples of cis-trans isomerism are the 1, 2-disubstituted ethenes, molecule I is cis-1, 2-dichloroethene and molecule II is trans-1, 2-dichloroethene. Due to occasional ambiguity, IUPAC adopted a rigorous system wherein the substituents at each end of the double bond are assigned priority based on their atomic number. If the high-priority substituents are on the side of the bond. If they are on sides, it is E. Since chlorine has an atomic number than hydrogen, it is the highest-priority group. Using this notation to name the above pictured molecules, molecule I is -1, 2-dichloroethene and molecule II is -1 and it is not the case that Z and cis or E and trans are always interchangeable
23.
Carbocation
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A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are methenium CH+3, methanium CH+5, some carbocations may have two or more positive charges, on the same carbon atom or on different atoms, such as the ethylene dication C 2H2+4. Until the early 1970s, all carbocations were called carbonium ions and this nomenclature was proposed by G. A. Olah. One textbook retains the name of carbonium ion for carbenium ion to this day. The history of carbocations dates back to 1891 when G. Merling reported that he added bromine to tropylidene and then heated the product to obtain a crystalline, water-soluble material, C 7H 7Br. He did not suggest a structure for it, however, Doering and this ion is predicted to be aromatic by Hückels rule. In 1902, Norris and Kehrman independently discovered that colorless triphenylmethanol gives deep-yellow solutions in concentrated sulfuric acid, triphenylmethyl chloride similarly formed orange complexes with aluminium and tin chlorides. In 1902, Adolf von Baeyer recognized the character of the compounds formed. He dubbed the relationship between color and salt formation halochromy, of which green is a prime example. Carbocations are reactive intermediates in organic reactions. This idea, first proposed by Julius Stieglitz in 1899, was developed by Hans Meerwein in his 1922 study of the Wagner–Meerwein rearrangement. Carbocations were also found to be involved in the SN1 reaction, the E1 reaction, the chemical establishment was reluctant to accept the notion of a carbocation and for a long time the Journal of the American Chemical Society refused articles that mentioned them. The first NMR spectrum of a carbocation in solution was published by Doering et al. in 1958. It was the ion, made by treating hexamethylbenzene with methyl chloride. The stable 7-norbornadienyl cation was prepared by Story et al. in 1960 by reacting norbornadienyl chloride with silver tetrafluoroborate in sulfur dioxide at −80 °C, the NMR spectrum established that it was non-classically bridged. In 1962, Olah directly observed the tert-butyl carbocation by nuclear magnetic resonance as a species on dissolving tert-butyl fluoride in magic acid. The NMR of the norbornyl cation was first reported by Schleyer et al. the charged carbon atom in a carbocation is a sextet, i. e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability. Therefore, carbocations are often reactive, seeking to fill the octet of electrons as well as regain a neutral charge
24.
Small molecule
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In molecular biology and pharmacology, a small molecule is a low molecular weight organic compound that may help regulate a biological process, with a size on the order of 1 nm. In addition, this molecular weight cutoff is a necessary but insufficient condition for oral bioavailability, Small molecules can have a variety of biological functions, serving as cell signaling molecules, as drugs in medicine, as pesticides in farming, and in many other roles. These compounds can be natural or artificial, they may have an effect against a disease or may be detrimental. Larger structures such as acids and proteins, and many polysaccharides, are not small molecules—though their constituent monomers are often considered small molecules. Very small oligomers are also usually considered small molecules, such as dinucleotides, peptides such as the antioxidant glutathione, Small molecules may also be used as research tools to probe biological function as well as leads in the development of new therapeutic agents. Some can inhibit a specific function of a protein or disrupt protein–protein interactions. Most pharmaceuticals are small molecules, although some drugs can be proteins, many proteins are degraded if administered orally and most often cannot cross cell membranes. Small molecules are likely to be absorbed, although some of them are only absorbed after oral administration if given as prodrugs. One advantage small molecule drugs have over large molecule biologics is that many SMDs can be taken orally whereas biologics generally require injection or another parenteral administration, secondary metabolites are a rich source of biologically active compounds and hence are often used as research tools and leads for drug discovery. Examples of secondary metabolites include, Alkaloids Glycosides Lipids Nonribosomal peptides, such as actinomycin-D Phenazines Natural phenols Polyketide Terpenes, including steroids Tetrapyrroles. An example is the teratogen and carcinogen phorbol 12-myristate 13-acetate, which is a plant terpene that activates protein kinase C, there is also interest in creating small molecule artificial transcription factors to regulate gene expression, examples include wrenchnolol. Small-molecule anti-genomic therapeutics, or SMAT, refers to a technology that targets DNA signatures found in many biological warfare agents. Metabolite Chemogenomics Neurotransmitter Peptidomimetic Small Molecule Libraries at the US National Library of Medicine Medical Subject Headings
25.
Salbutamol
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Salbutamol, also known as albuterol and marketed as Ventolin among other names, is a medication that opens up the medium and large airways in the lungs. It is used to treat asthma, exercise-induced bronchoconstriction, and chronic pulmonary disease. It may also be used to high blood potassium levels. It is usually used by inhaler or nebulizer but is available as a pill. Onset of action of the version is typically within 15 minutes. Common side effects include shakiness, headache, fast heart rate, dizziness, serious side effects may include worsening bronchospasm, irregular heartbeat, and low blood potassium levels. It can be used during pregnancy and breastfeeding, but safety is not entirely clear, salbutamol is a short-acting β2 adrenergic receptor agonist which works by causing airway smooth muscles to relax. Salbutamol was first made in 1967 in Britain and it was approved for medical use in the United States in 1982. It is on the World Health Organizations List of Essential Medicines and it is available as a generic medication. The wholesale cost in the world of an inhaler which contains 200 doses is between $1.12 and $2.64 as of 2014. In the United States it is between $25 and $50 for a month supply. Salbutamol is typically used to treat bronchospasm, as well as chronic obstructive pulmonary disease, as a β2 agonist, salbutamol also finds use in obstetrics. Intravenous salbutamol can be used as a tocolytic to relax the smooth muscle to delay premature labor. Salbutamol has been used to treat acute hyperkalemia, as it stimulates potassium flow into cells thus lowering the level in the blood, the most common side effects are fine tremor, anxiety, headache, muscle cramps, dry mouth, and palpitation. Other symptoms may include tachycardia, arrhythmia, flushing, myocardial ischemia, rarely occurring, but of importance, are allergic reactions of paradoxical bronchospasm, urticaria, angioedema, hypotension, and collapse. High doses or prolonged use may cause hypokalaemia, which is of concern especially in patients with renal failure and this drug is sold as a racemic mixture. With regard to structure-activity relationships, the tertiary butyl group in salbutamol makes it selective for β2 receptors. Salbutamol may be quantified in blood or plasma, practical needs for this include to confirm a diagnosis of poisoning in hospitalized patients, or to aid in a forensic investigation
26.
Amphetamine
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Amphetamine is a potent central nervous system stimulant that is used in the treatment of attention deficit hyperactivity disorder, narcolepsy, and obesity. Amphetamine was discovered in 1887 and exists as two enantiomers, levoamphetamine and dextroamphetamine, amphetamine properly refers to a specific chemical, the racemic free base, which is equal parts of the two enantiomers, levoamphetamine and dextroamphetamine, in their pure amine forms. The term is used informally to refer to any combination of the enantiomers. Historically, it has used to treat nasal congestion and depression. Amphetamine is also used as a performance enhancer and cognitive enhancer. The first amphetamine pharmaceutical was Benzedrine, a brand which was used to treat a variety of conditions, currently, pharmaceutical amphetamine is prescribed as racemic amphetamine, Adderall, dextroamphetamine, or the inactive prodrug lisdexamfetamine. At therapeutic doses, amphetamine causes emotional and cognitive effects such as euphoria, change in desire for sex, increased wakefulness and it induces physical effects such as decreased reaction time, fatigue resistance, and increased muscle strength. Larger doses of amphetamine may impair cognitive function and induce rapid muscle breakdown, drug addiction is a serious risk with large recreational doses but is unlikely to arise from typical long-term medical use at therapeutic doses. Very high doses can result in psychosis which rarely occurs at therapeutic doses even during long-term use, recreational doses are generally much larger than prescribed therapeutic doses and carry a far greater risk of serious side effects. Amphetamine belongs to the phenethylamine class and it is also the parent compound of its own structural class, the substituted amphetamines, which includes prominent substances such as bupropion, cathinone, MDMA, and methamphetamine. Phenethylamine is the parent compound of amphetamine, while N-methylphenethylamine is an isomer of amphetamine that differs only in the placement of the methyl group. Amphetamine is used to attention deficit hyperactivity disorder, narcolepsy, and obesity. Reviews of clinical stimulant research have established the safety and effectiveness of long-term continuous amphetamine use for the treatment of ADHD, randomized controlled trials of continuous stimulant therapy for the treatment of ADHD spanning two years have demonstrated treatment effectiveness and safety. Psychostimulants like methylphenidate and amphetamine are effective in treating ADHD because they increase neurotransmitter activity in these systems, approximately 80% of those who use these stimulants see improvements in ADHD symptoms. A systematic review from 2014 found that low doses of amphetamine also improve memory consolidation, therapeutic doses of amphetamine also enhance cortical network efficiency, an effect which mediates improvements in working memory in all individuals. Amphetamine and other ADHD stimulants also improve task saliency and increase arousal, stimulants such as amphetamine can improve performance on difficult and boring tasks and are used by some students as a study and test-taking aid. However, high doses that are above the therapeutic range can interfere with working memory. Amphetamine improves endurance and reaction time primarily through reuptake inhibition and effluxion of dopamine in the nervous system
27.
Omeprazole
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Omeprazole, sold under the brand names Prilosec and Losec among others, is a medication used in the treatment of gastroesophageal reflux disease, peptic ulcer disease, and Zollinger–Ellison syndrome. It is also used to prevent upper gastrointestinal bleeding in people who are at high risk and it can be taken by mouth or injected into a vein. Common side effects include nausea, vomiting, headaches, and increased intestinal gas, serious side effects may include Clostridium difficile colitis, an increased risk of pneumonia, an increased risk of bone fractures, and the potential of masking stomach cancer. It is unclear if it is safe for use in pregnancy, Omeprazole is a proton pump inhibitor and as such blocks the release of stomach acid. It is on the World Health Organizations List of Essential Medicines and it is available as a generic medication. The wholesale cost in the world as of 2014 is US$0.01 to US$0.07 per dose. In the United States it costs on average US$0.50 per pill, Omeprazole can be used in the treatment of gastroesophageal reflux disease, peptic ulcers, erosive esophagitis, and Zollinger-Ellison syndrome. Peptic ulcers may be treated with omeprazole, treatment of H. pylori infection can be completed by taking a triple therapy combination of omeprazole, amoxicillin, and clarithromycin for 7–14 days. Amoxicillin may be replaced with metronidazole in patients who are allergic to penicillin, long-term use of PPIs is strongly associated with the development of benign polyps from fundic glands, these polyps do not cause cancer and resolve when PPIs are discontinued. No association is seen between PPI use and cancer, but use of PPIs may mask gastric cancers or other serious gastric problems, epidemiological data do not show an increased risk of major birth defects after maternal use of omeprazole during pregnancy. No clinical trials have evaluated the potential consequences of the use of omeprazole in breastfeeding. Omeprazole needs to be administrated in a formulation due to its rapid degradation in the acidic conditions of the stomach. This suggests that most of the free molecules ingested by the infant are likely degraded before being absorbed, Omeprazole at normal doses is likely safe during breastfeeding. However, the most significant major drug interaction concern is the activation of clopidogrel when taken together with omeprazole. Although still controversial, this may increase the risk of stroke or heart attack in people taking clopidogrel to prevent these events and this interaction is possible because omeprazole is an inhibitor of the enzymes CYP2C19 and CYP3A4. Clopidogrel is a prodrug that partially depends on CYP2C19 for conversion to its active form. Inhibition of CYP2C19 may block the activation of clopidogrel, which could reduce its effects, almost all benzodiazepines are metabolised by the CYP3A4 and CYP2D6 pathway, and inhibition of these enzymes results in a higher AUC. Other examples of drugs dependent on CYP3A4 for their metabolism are escitalopram, warfarin, oxycodone, tramadol, the concentrations of these drugs may increase if they are used concomitantly with omeprazole
28.
Levomethamphetamine
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Levomethamphetamine is the levorotary form of methamphetamine. Levomethamphetamine is a sympathomimetic vasoconstrictor which is the ingredient in some over-the-counter nasal decongestant inhalers in the United States. It does not possess the potential for euphoria or addiction that dextromethamphetamine possesses, among its physiological effects are the vasoconstriction that makes it useful for nasal decongestion. The elimination half-life of levomethamphetamine is between 13.3 and 15 hours, whereas dextromethamphetamine has a half-life of about 10.5 hours, levomethamphetamine is the chemical precursor of the antiparkinsons drug selegiline. Selegiline, a monoamine oxidase B inhibitor at low doses, is also metabolized into levomethamphetamine and levoamphetamine. This has caused users to test positive for amphetamines, central side effects may include anxiety, insomnia, and anorexia. The study did not test the oral administration of levomethamphetamine, levomethamphetamine can register on urine drug screens as either methamphetamine, amphetamine, or both, depending on the subjects metabolism and dosage. L-methamphetamine metabolizes completely into L-amphetamine after a period of time
29.
Over-the-counter drug
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In many countries, OTC drugs are selected by a regulatory agency to ensure that they are ingredients that are safe and effective when used without a physicians care. OTC drugs are regulated by active pharmaceutical ingredients, not final products. By regulating APIs instead of specific drug formulations, governments allow manufacturers freedom to formulate ingredients, or combinations of ingredients, into proprietary mixtures. The term over-the-counter may be somewhat counterintuitive, since, in many countries, in contrast, prescription drugs are almost always passed over a counter from the pharmacist to the customer. Some drugs may be classified as over-the-counter, but may only be dispensed by a pharmacist after an assessment of the patients needs or the provision of patient education. In many countries, a number of OTC drugs are available in establishments without a pharmacy, such as stores, supermarkets. Regulations detailing the establishments where drugs may be sold, who is authorized to dispense them, as of 2011, around a third of older adults in the U. S. reportedly use OTC drugs. In Canada, there are four drug schedules, Schedule 1, Schedule 2, Do not require a prescription, but require an assessment by a pharmacist prior to sale. These drugs are kept in an area of the pharmacy where there is no public access, Schedule 3, Do not require a prescription, but must be kept in an area under the supervision of a pharmacist. These drugs are kept in an area of the outlet where self-selection is possible. Unscheduled, Do not require a prescription and may be sold in any retail outlet, all medications outside of Schedule 1 may be considered an OTC drug, as they do not require prescriptions for sale. While the National Association of Pharmacy Regulatory Authorities provides recommendations on the scheduling of drugs for sale in Canada, due to this, the exact drugs found in each schedule may vary from province to province. The drug can be on the shelves like any other product, examples are domperidone,400 mg ibuprofen up to 50 tablets and dextromethorphan. The drugs are usually on the shelves and the store sells items like toys, gadgets, perfumes. The drugs in this category have limited risk and addiction potential, examples are naproxen and diclofenac in small amounts, cinnarizine,400 mg ibuprofen up to 20 tablets and also 500 mg paracetamol up to 50 tablets. In the United States, the manufacture and sale of OTC substances is regulated by the Food, the FDA requires that all new drugs obtain a New Drug Application before entering interstate commerce, but the act exempts any drugs generally recognized as safe and effective from this requirement. Thus, in the United States an OTC drug product is allowed to be marketed either pursuant to an FDA monograph, the Federal Trade Commission regulates advertising of OTC products. This is in contrast to prescription drug advertising, which is regulated by the FDA, the FDA requires that OTC products are labeled with an approved Drug Facts label to educate consumers about their medications
30.
Otto Wallach
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Otto Wallach was a German chemist and recipient of the 1910 Nobel Prize in Chemistry for his work on alicyclic compounds. Wallach was born in Königsberg, the son of a Prussian civil servant and his father, Gerhard Wallach, descended from a Jewish family that had converted to Lutheranism. His mother, Otillie, was an ethnic German of Protestant religion, Wallachs father was transferred to Stettin and later to Potsdam. Otto Wallach went to school, a Gymnasium, in Potsdam, where he learned about literature, at this time he also started private chemical experiments at the house of his parents. In 1867 he started studying chemistry at the University of Göttingen, during his work with Friedrich Kekulé in Bonn he started a systematic analysis of the terpenes present in essential oils. Up to this only a few had been isolated in pure form. Melting point comparison and the measurement of mixtures was one of the methods to confirm identical substances, for this method the mostly liquid terpenes had to be transformed into crystalline compounds. With stepwise derivatisation, especially additions to the double bond present in some of the terpenes, with these principal methods he opened the path to systematic research on terpenes. He was responsible for naming terpene and pinene, and for undertaking the first systematic study of pinene^ and he wrote a book about the chemistry of terpenes, Terpene und Campher. Otto Wallach is known for Wallachs rule, Wallach degradation, the Leuckart-Wallach reaction, digital edition of the University and State Library Düsseldorf. Verhalten der Elemente und ihrer Verbindungen, methoden zur Auffindung und Trennung der Elemente. Aufl. von Hülfstabellen für den chemisch-analytischen Unterricht 1880 Terpene und Campher, digital edition of the University and State Library Düsseldorf. Nobel Lecture Alicyclic Compounds from Nobelprize. org website Biography Biography from Nobelprize. org website Otto Wallach at the NNDB website
31.
Merriam-Webster
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Merriam-Webster, Incorporated, is an American company that publishes reference books, especially known for its dictionaries. In 1831, George and Charles Merriam founded the company as G & C Merriam Co. in Springfield, in 1843, after Noah Webster died, the company bought the rights to An American Dictionary of the English Language from Websters estate. All Merriam-Webster dictionaries trace their lineage to this source, in 1964, Encyclopædia Britannica, Inc. acquired Merriam-Webster, Inc. as a subsidiary. The company adopted its current name in 1982, in 1806, Webster published his first dictionary, A Compendious Dictionary of the English Language. In 1807 Webster started two decades of work to expand his publication into a fully comprehensive dictionary, An American Dictionary of the English Language. To help him trace the etymology of words, Webster learned 26 languages, Webster hoped to standardize American speech, since Americans in different parts of the country used somewhat different vocabularies and spelled, pronounced, and used words differently. Webster completed his dictionary during his year abroad in 1825 in Paris and his 1820s book contained 70,000 words, of which about 12,000 had never appeared in a dictionary before. He also added American words, including skunk and squash, that did not appear in British dictionaries, at the age of 70 in 1828, Webster published his dictionary, it sold poorly, with only 2,500 copies putting him in debt. However, in 1840, he published the edition in two volumes with much greater success. He shows ways that American poetry inherited Websters ideas and draws on his lexicography to develop the language, in 1843, after Websters death, George Merriam and Charles Merriam secured publishing and revision rights to the 1840 edition of the dictionary. They published a revision in 1847, which did not change any of the text but merely added new sections. This began a series of revisions that were described as being unabridged in content, in 1884 it contained 118,000 words,3000 more than any other English dictionary. With the edition of 1890, the dictionary was retitled Websters International, the Collegiate Dictionary was introduced in 1898 and the series is now in its eleventh edition. Following the publication of Websters International in 1890, two Collegiate editions were issued as abridgments of each of their Unabridged editions, with the ninth edition, the Collegiate adopted changes which distinguish it as a separate entity rather than merely an abridgment of the Third New International. Some proper names were returned to the word list, including names of Knights of the Round Table, the most notable change was the inclusion of the date of the first known citation of each word, to document its entry into the English language. The eleventh edition includes more than 225,000 definitions, a CD-ROM of the text is sometimes included. This dictionary is preferred as a source for general matters of spelling by the influential The Chicago Manual of Style, the Chicago Manual states that it normally opts for the first spelling listed. Merriam overhauled the dictionary again with the 1961 Websters Third New International under the direction of Philip B, gove, making changes that sparked public controversy
