European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio; these spectra are used to determine the elemental or isotopic signature of a sample, the masses of particles and of molecules, to elucidate the chemical structures of molecules and other chemical compounds. In a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons; this may cause some of the sample's molecules to break into charged fragments. These ions are separated according to their mass-to-charge ratio by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection.
The ions are detected by a mechanism capable of detecting charged particles, such as an electron multiplier. Results are displayed as spectra of the relative abundance of detected ions as a function of the mass-to-charge ratio; the atoms or molecules in the sample can be identified by correlating known masses to the identified masses or through a characteristic fragmentation pattern. In 1886, Eugen Goldstein observed rays in gas discharges under low pressure that traveled away from the anode and through channels in a perforated cathode, opposite to the direction of negatively charged cathode rays. Goldstein called these positively charged anode rays "Kanalstrahlen". Wilhelm Wien found that strong electric or magnetic fields deflected the canal rays and, in 1899, constructed a device with perpendicular electric and magnetic fields that separated the positive rays according to their charge-to-mass ratio. Wien found. English scientist J. J. Thomson improved on the work of Wien by reducing the pressure to create the mass spectrograph.
The word spectrograph had become part of the international scientific vocabulary by 1884. Early spectrometry devices that measured the mass-to-charge ratio of ions were called mass spectrographs which consisted of instruments that recorded a spectrum of mass values on a photographic plate. A mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be observed. Once the instrument was properly adjusted, a photographic plate was exposed; the term mass spectroscope continued to be used though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope. The use of the term mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy. Mass spectrometry is abbreviated as mass-spec or as MS. Modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F.
W. Aston in 1918 and 1919 respectively. Sector mass spectrometers known as calutrons were developed by Ernest O. Lawrence and used for separating the isotopes of uranium during the Manhattan Project. Calutron mass spectrometers were used for uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during World War II. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt and Wolfgang Paul for the development of the ion trap technique in the 1950s and 1960s. In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the development of electrospray ionization and Koichi Tanaka for the development of soft laser desorption and their application to the ionization of biological macromolecules proteins. A mass spectrometer consists of three components: an ion source, a mass analyzer, a detector; the ionizer converts a portion of the sample into ions. There is a wide variety of ionization techniques, depending on the phase of the sample and the efficiency of various ionization mechanisms for the unknown species.
An extraction system removes ions from the sample, which are targeted through the mass analyzer and into the detector. The differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio; the detector measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present. Some detectors give spatial information, e.g. a multichannel plate. The following example describes the operation of a spectrometer mass analyzer, of the sector type. Consider a sample of sodium chloride. In the ion source, the sample is ionized into sodium and chloride ions. Sodium atoms and ions are monoisotopic, with a mass of about 23 u. Chloride atoms and ions come in two isotopes with masses of 35 u and 37 u; the analyzer part of the spectrometer contains electric and magnetic fields, which exert forces on ions traveling through these fields. The speed of a charged particle may be increased or decreased while passing through the electric field, its direction may be altered by the magnetic field.
The magnitude of the deflection of the moving ion's trajectory depends on its mass-to-charge ratio. L
A methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms — CH3. In formulas, the group is abbreviated Me; such hydrocarbon groups occur in many organic compounds. It is a stable group in most molecules. While the methyl group is part of a larger molecule, it can be found on its own in any of three forms: anion, cation or radical; the anion has the radical seven and the cation six. All three forms are reactive and observed; the methylium cation is otherwise not encountered. Some compounds are considered to be sources of the CH3+ cation, this simplification is used pervasively in organic chemistry. For example, protonation of methanol gives a electrophilic methylating reagent: CH3OH + H+ → CH3+ + H2OSimilarly, methyl iodide and methyl triflate are viewed as the equivalent of the methyl cation because they undergo SN2 reactions by weak nucleophiles; the methanide anion exists only under exotic conditions. It can be produced by electrical discharge in ketene at low pressure and its enthalpy of reaction is determined to be about 252.2±3.3 kJ/mol.
In discussions mechanisms of organic reactions, methyl lithium and related Grignard reagents are considered to be salts of "CH3−". Such reagents are prepared from the methyl halides: 2 M + CH3X → MCH3 + MXwhere M is an alkali metal; the methyl radical has the formula CH3. It exists in dilute gases, but in more concentrated form it dimerizes to ethane, it can be produced by thermal decomposition of only certain compounds those with an -N=N- linkage. The reactivity of a methyl group depends on the adjacent substituents. Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by the strongest acids; the oxidation of a methyl group occurs in nature and industry. The oxidation products derived from methyl are CH2OH, CHO, CO2H. For example, permanganate converts a methyl group to a carboxyl group, e.g. the conversion of toluene to benzoic acid. Oxidation of methyl groups gives protons and carbon dioxide, as seen in combustion. Demethylation is a common process, reagents that undergo this reaction are called methylating agents.
Common methylating agents are dimethyl sulfate, methyl iodide, methyl triflate. Methanogenesis, the source of natural gas, arises via a demethylation reaction. Certain methyl groups can be deprotonated. For example, the acidity of the methyl groups in acetone is about 1020 more acidic than methane; the resulting carbanions are key intermediates in many reactions in organic synthesis and biosynthesis. Fatty acids are produced in this way; when placed in benzylic or allylic positions, the strength of the C-H bond is decreased, the reactivity of the methyl group increases. One manifestation of this enhanced reactivity is the photochemical chlorination of the methyl group in toluene to give benzyl chloride. In the special case where one hydrogen is replaced by deuterium and another hydrogen by tritium, the methyl substituent becomes chiral. Methods exist to produce optically pure methyl compounds, e.g. chiral acetic acid. Through the use of chiral methyl groups, the stereochemical course of several biochemical transformations have been analyzed.
A methyl group may rotate around the R—C-axis. This is a free rotation only in the simplest cases like gaseous CClH3. In most molecules, the remainder R breaks the C ∞ symmetry of the R—C-axis and creates a potential V that restricts the free motion of the three protons. For the model case of C2H6 this is discussed under the name ethane barrier. In condensed phases, neighbour molecules contribute to the potential. Methyl group rotation can be experimentally studied using quasielastic neutron scattering. French chemists Jean-Baptiste Dumas and Eugene Peligot, after determining methanol's chemical structure, introduced "methylene" from the Greek methy "wine" and hȳlē "wood, patch of trees" with the intention of highlighting its origins, "alcohol made from wood"; the term "methyl" was derived in about 1840 by back-formation from "methylene", was applied to describe "methyl alcohol". Methyl is the IUPAC nomenclature of organic chemistry term for an alkane molecule, using the prefix "meth-" to indicate the presence of a single carbon
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain polar bonds due to a difference in electronegativity between the bonded atoms. A polar molecule with two or more polar bonds must have a geometry, asymmetric in at least one direction, so that the bond dipoles do not cancel each other. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Polarity underlies a number of physical properties including surface tension and melting and boiling points. Not all atoms attract electrons with the same force; the amount of "pull" an atom exerts on its electrons is called its electronegativity. Atoms with high electronegativities – such as fluorine and nitrogen – exert a greater pull on electrons than atoms with lower electronegativities such as alkali metals and alkaline earth metals. In a bond, this leads to unequal sharing of electrons between the atoms, as electrons will be drawn closer to the atom with the higher electronegativity.
Because electrons have a negative charge, the unequal sharing of electrons within a bond leads to the formation of an electric dipole: a separation of positive and negative electric charge. Because the amount of charge separated in such dipoles is smaller than a fundamental charge, they are called partial charges, denoted as δ+ and δ−; these symbols were introduced by Sir Christopher Ingold and Dr. Edith Hilda Ingold in 1926; the bond dipole moment is calculated by multiplying the amount of charge separated and the distance between the charges. These dipoles within molecules can interact with dipoles in other molecules, creating dipole-dipole intermolecular forces. Bonds can fall between one of two extremes – being nonpolar or polar. A nonpolar bond occurs when the electronegativities are identical and therefore possess a difference of zero. A polar bond is more called an ionic bond, occurs when the difference between electronegativities is large enough that one atom takes an electron from the other.
The terms "polar" and "nonpolar" are applied to covalent bonds, that is, bonds where the polarity is not complete. To determine the polarity of a covalent bond using numerical means, the difference between the electronegativity of the atoms is used. Bond polarity is divided into three groups that are loosely based on the difference in electronegativity between the two bonded atoms. According to the Pauling scale: Nonpolar bonds occur when the difference in electronegativity between the two atoms is less than 0.5 Polar bonds occur when the difference in electronegativity between the two atoms is between 0.5 and 2.0 Ionic bonds occur when the difference in electronegativity between the two atoms is greater than 2.0Pauling based this classification scheme on the partial ionic character of a bond, an approximate function of the difference in electronegativity between the two bonded atoms. He estimated that a difference of 1.7 corresponds to 50% ionic character, so that a greater difference corresponds to a bond, predominantly ionic.
As a quantum-mechanical description, Pauling proposed that the wave function for a polar molecule AB is a linear combination of wave functions for covalent and ionic molecules: ψ = aψ + bψ. The amount of covalent and ionic character depends on the values of the squared coefficients a2 and b2. While the molecules can be described as "polar covalent", "nonpolar covalent", or "ionic", this is a relative term, with one molecule being more polar or more nonpolar than another. However, the following properties are typical of such molecules. A molecule is composed of one or more chemical bonds between molecular orbitals of different atoms. A molecule may be polar either as a result of polar bonds due to differences in electronegativity as described above, or as a result of an asymmetric arrangement of nonpolar covalent bonds and non-bonding pairs of electrons known as a full molecular orbital. A polar molecule has a net dipole as a result of the opposing charges from polar bonds arranged asymmetrically.
Water is an example of a polar molecule since it has a slight positive charge on one side and a slight negative charge on the other. The dipoles do not cancel out resulting in a net dipole. Due to the polar nature of the water molecule itself, polar molecules are able to dissolve in water. Other examples include sugars, which have many polar oxygen–hydrogen groups and are overall polar. If the bond dipole moments of the molecule do not cancel, the molecule is polar. For example, the water molecule contains two polar O−H bonds in a bent geometry; the bond dipole moments do not cancel, so that the molecule forms a molecular dipole with its negative pole at the oxygen and its positive pole midway between the two hydrogen atoms. In the figure each bond joins the central O atom with a negative charge to an H atom with a positive charge; the hydrogen fluoride, HF, molecule is polar by virtue of polar covalent bonds – in the covalent bond electrons are displaced toward the more electronegative fluorine atom.
Ammonia, NH3, molecule. The molecule has two lone electrons in an orbital, that points towards the fourth apex of the approximate tetrahedron; this orbital is not participating in covalent bonding.
Casein pronounced "kay-seen" in British English, is a family of related phosphoproteins. These proteins are found in mammalian milk, comprising c. 80% of the proteins in cow's milk and between 20% and 45% of the proteins in human milk. Sheep and buffalo milk have a higher casein content than other types of milk with human milk having a low casein content. Casein has a wide variety of uses, from being a major component of cheese, to use as a food additive; the most common form of casein is sodium caseinate. As a food source, casein supplies amino acids and two essential elements and phosphorus. Casein contains a high number of proline residues. There are no disulfide bridges; as a result, it has little tertiary structure. It is hydrophobic, making it poorly soluble in water, it is found in milk as a suspension of particles, called casein micelles, which show only limited resemblance with surfactant-type micelles in a sense that the hydrophilic parts reside at the surface and they are spherical. However, in sharp contrast to surfactant micelles, the interior of a casein micelle is hydrated.
The caseins in the micelles are held together by hydrophobic interactions. Any of several molecular models could account for the special conformation of casein in the micelles. One of them proposes the micellar nucleus is formed by several submicelles, the periphery consisting of microvellosities of κ-casein. Another model suggests; the most recent model proposes a double link among the caseins for gelling to take place. All three models consider micelles as colloidal particles formed by casein aggregates wrapped up in soluble κ-casein molecules; the isoelectric point of casein is 4.6. Since milk's pH is 6.6, casein has a negative charge in milk. The purified protein is water-insoluble. While it is insoluble in neutral salt solutions, it is dispersible in dilute alkalis and in salt solutions such as aqueous sodium oxalate and sodium acetate; the enzyme trypsin can hydrolyze a phosphate-containing peptone. It is used to form a type of organic adhesive. Casein paint is a water-soluble medium used by artists.
Casein paint has been used since ancient Egyptian times as a form of tempera paint, was used by commercial illustrators as the material of choice until the late 1960s when, with the advent of acrylic paint, casein became less popular. It is still used by scene painters, although acrylic has made inroads in that field as well. Casein-based glues, formulated from casein, hydrated lime and sodium hydroxide were popular for woodworking, including for aircraft, as late as the de Havilland Albatross airliner. Casein glue is used in transformer manufacturing due to its oil permeability. While replaced with synthetic resins, casein-based glues still have a use in certain niche applications, such as laminating fireproof doors and the labeling of bottles; the popular Elmer's School Glue was made from casein because it was non-toxic and would wash out of clothing. Several foods and toppings all contain a variety of caseinates. Sodium caseinate acts as a greater food additive for stabilizing processed foods, however companies could opt to use calcium caseinate to increase calcium content and decrease sodium levels in their products.
The main food uses of casein are for powders requiring rapid dispersion into water, ranging from coffee creamers to instant cream soups. Mead Johnson introduced a product in the early 1920s named Casec to ease gastrointestinal disorders and infant digestive problems which were a common cause of death in children at that time, it is believed to neutralize capsaicin, the active ingredient of peppers, jalapeños, other chili peppers. Cheese consists of proteins and fat from milk the milk of cows, goats, or sheep, it is produced by coagulation, caused by destabilization of the casein micelle, which begins the processes of fractionation and selective concentration. The milk is acidified and coagulated by the addition of rennet, containing a proteolytic enzyme known as rennin; the solids are separated and pressed into final form. Unlike many proteins, casein is not coagulated by heat. During the process of clotting, milk-clotting proteases act on the soluble portion of the caseins, κ-casein, thus originating an unstable micellar state that results in clot formation.
When coagulated with chymosin, casein is sometimes called paracasein. Chymosin is an aspartic protease that hydrolyzes the peptide bond in Phe105-Met106 of κ-casein, is considered to be the most efficient protease for the cheese-making industry. British terminology, on the other hand, uses the term caseinogen for the uncoagulated protein and casein for the coagulated protein; as it exists in milk, it is a salt of calcium. Some of the earliest plastics were based on casein. In particular, galalith was well known for use in buttons. Fiber can be made from extruded casein. Lanital, a fabric made from casein fiber, was popular in Italy during the 1930s. Recent innovations such as QMilch are offering a more refined use of the fiber for modern fabrics. An attractive property of the casein molecule is its ability to form a gel or clot in the stomach, which makes it efficient in nutrient supply; the clot is able to provide a sustained slow release of amino acids into the blood stream
The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are 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. 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 not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. 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 and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the 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, 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; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
Valerian is a perennial flowering plant native to Europe and Asia. In the summer when the mature plant may have a height of 1.5 metres, it bears sweetly scented pink or white flowers that attract many fly species hoverflies of the genus Eristalis. It is consumed as food including the grey pug. Crude extract of valerian root may have sedative and anxiolytic effects, is sold in dietary supplement capsules to promote sleep. Valerian has been used as a medicinal herb since at least the time of ancient Rome. Hippocrates described its properties, Galen prescribed it as a remedy for insomnia. In medieval Sweden, it was sometimes placed in the wedding clothes of the groom to ward off the "envy" of the elves. In the 16th century, the Anabaptist reformer Pilgram Marpeck prescribed valerian tea for a sick woman. John Gerard's Herball states that his contemporaries found Valerian "excellent for those burdened and for such as be troubled with croup and other like convulsions, for those that are bruised with falls."
He says that the dried root was valued as a medicine by the poor in the north of England and the south of Scotland, so that "no broth or pottage or physicall meats be worth anything if Setewale be not there."The seventeenth century astrological botanist Nicholas Culpeper thought the plant was "under the influence of Mercury, therefore hath a warming faculty." He recommended both herb and root, said that "the root boiled with liquorice and aniseed is good for those troubled with cough. It is of special value against the plague, the decoction thereof being drunk and the root smelled; the green herb being bruised and applied to the head taketh away pain and pricking thereof." The name of the herb is derived from the Latin verb valere. Other names used for this plant include garden valerian, garden heliotrope and all-heal. Red valerian grown in gardens, is sometimes referred to as "valerian", but is a different species, from the same family but not closely related. Known compounds detected in valerian that may contribute to its method of action are: Alkaloids: actinidine, shyanthine and valerine Isovaleramide may be created in the extraction process.
Gamma-aminobutyric acid Isovaleric acid Iridoids, including valepotriates: isovaltrate and valtrate Sesquiterpenes: valerenic acid, hydroxyvalerenic acid and acetoxyvalerenic acid Flavanones: hesperidin, 6-methylapigenin, linarin Because of valerian's historical use as a sedative, anticonvulsant, migraine treatment, pain reliever, most basic science research has been directed at the interaction of valerian constituents with the GABA receptor. Many studies remain all require clinical validation; the mechanism of action of valerian in general, as a mild sedative in particular, has not been elucidated. However, some of the GABA-analogs valerenic acids as components of the essential oil along with other semivolatile sesquiterpenoids are believed to have some affinity for the GABAA receptor, a class of receptors on which benzodiazepines are known to act. Valeric acid, responsible for the typical odor of older valerian roots, does not have any sedative properties. Valeric acid is related to valproic acid, a prescribed anticonvulsant.
Valerian contains isovaltrate, shown to be an inverse agonist for adenosine A1 receptor sites. This action does not contribute to the herb's possible sedative effects, which would be expected from an agonist, rather than an inverse agonist, at this particular binding site. Hydrophilic extractions of the herb sold over the counter, however do not contain significant amounts of isovaltrate. Valerenic acid in valerian stimulates serotonin receptors as a partial agonist, including 5-HT5A, implicated in the sleep-wake cycle; the chief constituent of valerian is a yellowish-green to brownish-yellow oil present in the dried root, varying in content from 0.5 to 2.0%. This variation in quantity may be determined by location; the volatile oils that form the active ingredient are pungent, somewhat reminiscent of well-matured cheese. Though some people remain partial to the earthy scent, some find it unpleasant, comparing the odor to that of unwashed feet. Although valerian is a common traditional medicine used for treating insomnia, there is no good evidence it is effective for this purpose.
Valerian is not helpful in treating anxiety. There is insufficient evidence for safety of valerian for anxiety disorders; the European Medicines Agency approved the health claim that valerian can be used as a traditional herbal medicine to relieve mild nervous tension and to aid sleep. In the United States, valerian extracts are sold as a nutritional supplement under the Dietary Supplement Health and Education Act of 1994. Oral forms are available in both unstandardized forms. Standardized products may be preferable considering the wide variation of the chemicals in the dried root, as noted above; when standardized, it is done so as a percentage of valeric acid. Because th