1.
Drug
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A drug is any substance that, when inhaled, injected, smoked, consumed, absorbed via a patch on the skin, or dissolved under the tongue, causes a physiological change in the body. In pharmacology, a drug, also called a medication or medicine, is a chemical substance used to treat, cure, prevent. Traditionally drugs were obtained through extraction from plants, but more recently also by organic synthesis. Pharmaceutical drugs may be used for a duration, or on a regular basis for chronic disorders. Another major classification system is the Biopharmaceutics Classification System and this classifies drugs according to their solubility and permeability or absorption properties. Psychoactive drugs are chemical substances that affect the function of the nervous system, altering perception. They include alcohol, a depressant, and the nicotine and caffeine. These three are the most widely consumed psychoactive drugs worldwide and are also considered recreational drugs since they are used for rather than medicinal purposes. Other recreational drugs include hallucinogens, opiates and amphetamines and some of these are used in spiritual or religious settings. Some drugs can cause addiction and all drugs can have side effects, excessive use of stimulants can promote stimulant psychosis. Many recreational drugs are illicit and international such as the Single Convention on Narcotic Drugs exist for the purpose of their prohibition. The transitive verb to drug arose later and invokes the psychoactive rather than properties of a substance. A medication or medicine is a drug taken to cure or ameliorate any symptoms of an illness or medical condition, the use may also be as preventive medicine that has future benefits but does not treat any existing or pre-existing diseases or symptoms. In the United Kingdom, behind-the-counter medicines are called pharmacy medicines which can only be sold in registered pharmacies and these medications are designated by the letter P on the label. The range of medicines available without a prescription varies from country to country, medications are typically produced by pharmaceutical companies and are often patented to give the developer exclusive rights to produce them. Those that are not patented are called generic drugs since they can be produced by other companies without restrictions or licenses from the patent holder, pharmaceutical drugs are usually categorised into drug classes. A group of drugs will share a chemical structure, or have the same mechanism of action. Another major classification system is the Biopharmaceutics Classification System and this groups drugs according to their solubility and permeability or absorption properties
2.
Dopamine
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Dopamine is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the brain and body. It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, dopamine is also synthesized in plants and most multicellular animals. In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons to send signals to nerve cells. The brain includes several distinct dopamine pathways, one of plays a major role in reward-motivated behavior. Most types of rewards increase the level of dopamine in the brain, other brain dopamine pathways are involved in motor control and in controlling the release of various hormones. These pathways and cell groups form a system which is neuromodulatory. Outside the central system, dopamine functions primarily as a local chemical messenger. With the exception of the vessels, dopamine in each of these peripheral systems is synthesized locally. Several important diseases of the system are associated with dysfunctions of the dopamine system. Parkinsons disease, a condition causing tremor and motor impairment, is caused by a loss of dopamine-secreting neurons in an area of the midbrain called the substantia nigra. Its metabolic precursor L-DOPA can be manufactured, and in its pure form marketed as Levodopa is the most widely used treatment for the condition. There is evidence that schizophrenia involves altered levels of dopamine activity, similar dopamine antagonist drugs are also some of the most effective anti-nausea agents. Restless legs syndrome and attention deficit hyperactivity disorder are associated with decreased dopamine activity, dopaminergic stimulants can be addictive in high doses, but some are used at lower doses to treat ADHD. A dopamine molecule consists of a structure with one amine group attached via an ethyl chain. As such, dopamine is the simplest possible catecholamine, a family that includes the neurotransmitters norepinephrine and epinephrine. The presence of a ring with this amine attachment makes it a substituted phenethylamine. Like most amines, dopamine is an organic base, as a base, it is generally protonated in acidic environments. The protonated form is highly water-soluble and relatively stable, but can become oxidized if exposed to oxygen or other oxidants, in basic environments, dopamine is not protonated
3.
Jmol
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Jmol is computer software for molecular modelling chemical structures in 3-dimensions. Jmol returns a 3D representation of a molecule that may be used as a teaching tool and it is written in the programming language Java, so it can run on the operating systems Windows, macOS, Linux, and Unix, if Java is installed. It is free and open-source software released under a GNU Lesser General Public License version 2.0, a standalone application and a software development kit exist that can be integrated into other Java applications, such as Bioclipse and Taverna. A popular feature is an applet that can be integrated into web pages to display molecules in a variety of ways, for example, molecules can be displayed as ball-and-stick models, space-filling models, ribbon diagrams, etc. Jmol supports a range of chemical file formats, including Protein Data Bank, Crystallographic Information File, MDL Molfile. There is also a JavaScript-only version, JSmol, that can be used on computers with no Java, the Jmol applet, among other abilities, offers an alternative to the Chime plug-in, which is no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS9. Jmol requires Java installation and operates on a variety of platforms. For example, Jmol is fully functional in Mozilla Firefox, Internet Explorer, Opera, Google Chrome, fast and Scriptable Molecular Graphics in Web Browsers without Java3D
4.
European Chemicals Agency
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ECHA is the driving force among regulatory authorities in implementing the EUs chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and it is located in Helsinki, Finland. The Agency, headed by Executive Director Geert Dancet, started working on 1 June 2007, the REACH Regulation requires companies to provide information on the hazards, risks 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 commonly used substances have been registered, the information is technical but gives detail on the impact of each chemical on people and the environment. This also gives European consumers the right to ask whether the goods they buy contain dangerous substances. The Classification, Labelling 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, companies need to notify ECHA of the classification and labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100000 substances, the information is freely available on their website. Consumers can check chemicals in the products they use, Biocidal products include, for example, insect repellents and disinfectants used in hospitals. The Biocidal Products Regulation ensures that there is 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 export and import of hazardous chemicals. Through this mechanism, countries due to hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have effects on human health and the environment are identified as Substances of Very High Concern 1. These are mainly substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment, other substances considered as SVHCs include, for example, endocrine disrupting chemicals. Companies manufacturing or importing articles containing these substances in a concentration above 0 and 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 officially identified in the EU as being of very 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 then move to another list
5.
Substituted amphetamine
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The compounds in this class span a variety of pharmacological subclasses, including stimulants, empathogens, and hallucinogens, among others. Some of amphetamines substituted derivatives occur in nature, for example in the leaves of Ephedra and these have been used since antiquity for their pharmacological effects. Amphetamine was first produced at the end of the 19th century, by the 1930s, amphetamine and some of its derivative compounds found use as decongestants in the symptomatic treatment of colds and also occasionally as psychoactive agents. Their effects on the nervous system are diverse, but can be summarized by three overlapping types of activity, psychoanaleptic, hallucinogenic and empathogenic. Various substituted amphetamines may cause these actions either separately or in combination, amphetamines are a subgroup of the substituted phenethylamine class of compounds. Substitution of hydrogen results in a large class of compounds. Natives of Yemen and Ethiopia have a tradition of chewing khat leaves to achieve a stimulating effect. The active substances of khat are cathinone and, to a lesser extent, amphetamine was first synthesized in 1887 by Romanian chemist Lazăr Edeleanu, although its pharmacological effects remained unknown until the 1930s. MDMA was produced in 1912 as an intermediate product, however, this synthesis also went largely unnoticed. In the 1920s, both methamphetamine and the dextrorotatory optical isomer of amphetamine, dextroamphetamine, were synthesized and this synthesis was a by-product of a search for ephedrine, a bronchodilator used to treat asthma extracted exclusively from natural sources. Over-the-counter use of substituted amphetamines was initiated in the early 1930s by the pharmaceutical company Smith, Kline & French, as a medicine for colds and nasal congestion. Subsequently, amphetamine was used in the treatment of narcolepsy, obesity, hay fever, orthostatic hypotension, epilepsy, Parkinsons disease, alcoholism, the reinforcing effects of substituted amphetamines were quickly discovered, and the misuse of substituted amphetamines had been noted as far back as 1936. During World War II, amphetamines were used by the German military to keep their tank crews awake for long periods and it was noticed that extended rest was required after such artificially induced activity. The widespread use of substituted amphetamines began in postwar Japan and quickly spread to other countries, modified designer amphetamines gained popularity since the 1960s, such as MDA and PMA. In 1970, the United States adopted the Controlled Substances Act that limited non-medical use of substituted amphetamines, street use of PMA was noted in 1972. MDMA emerged as a substitute to MDA in the early 1970s, american chemist Alexander Shulgin first synthesized the drug in 1976 and through him the drug was briefly introduced into psychotherapy. Recreational use grew and in 1985 MDMA was banned by the US authorities in an emergency scheduling initiated by the Drug Enforcement Administration, since the mid-1990s, MDMA has become a popular entactogenic drug among the youth and quite often non-MDMA substances were sold as ecstasy. Ongoing trials are investigating its efficacy as an adjunct to psychotherapy in the management of treatment-resistant post-traumatic stress disorder
6.
Chemical synapse
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Chemical synapses are biological junctions through which neurons signals can be exchanged to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the nervous system. They are crucial to the computations that underlie perception and thought. They allow the system to connect to and control other systems of the body. At a chemical synapse, one neuron releases neurotransmitter molecules into a space that is adjacent to another neuron. The neurotransmitters are kept within small sacs called vesicles, and are released into the synaptic cleft by exocytosis and these molecules then bind to receptors on the postsynaptic cells side of the synaptic cleft. The adult human brain is estimated to contain from 1014 to 5 ×1014 synapses, every cubic millimeter of cerebral cortex contains roughly a billion of them. The word synapse comes from synaptein, which Sir Charles Scott Sherrington and colleagues coined from the Greek syn-, chemical synapses are not the only type of biological synapse, electrical and immunological synapses also exist. Without a qualifier, however, synapse commonly means chemical synapse, synapses are functional connections between neurons, or between neurons and other types of cells. A typical neuron gives rise to several thousand synapses, although there are types that make far fewer. Most synapses connect axons to dendrites, but there are other types of connections, including axon-to-cell-body, axon-to-axon. Chemical synapses pass information directionally from a cell to a postsynaptic cell and are therefore asymmetric in structure. Synaptic vesicles are docked at the plasma membrane at regions called active zones. Immediately opposite is a region of the cell containing neurotransmitter receptors. Immediately behind the postsynaptic membrane is a complex of interlinked proteins called the postsynaptic density. Proteins in the PSD are involved in anchoring and trafficking neurotransmitter receptors, the receptors and PSDs are often found in specialized protrusions from the main dendritic shaft called dendritic spines. Synapses may be described as symmetric or asymmetric, when examined under an electron microscope, asymmetric synapses are characterized by rounded vesicles in the presynaptic cell, and a prominent postsynaptic density. Symmetric synapses in contrast have flattened or elongated vesicles, and do not contain a prominent postsynaptic density, the synaptic cleft is a gap between the pre- and postsynaptic cells that is about 20 nm wide
7.
Weight gain
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Weight gain is an increase in body weight. This can involve an increase in mass, fat deposits. Weight gain can be a symptom of a medical condition. If enough weight is gained due to increased body fat deposits, one may become overweight or obese, the Body Mass Index measures body weight in proportion to the square of height and defines optimal, insufficient, and excessive weight based on the ratio. Weight gain has a latency period, typical latency periods vary from three days to two weeks after ingestion. Having excess adipose tissue is a condition, especially where food supplies are plentiful. As much as 64% of the United States adult population is considered overweight or obese. A commonly asserted rule for weight gain or loss is based on the assumption that one pound of human fat tissue contains about 3,500 kilocalories, thus, eating 500 fewer calories than one needs per day should result in a loss of about a pound per week. Similarly, for every 3500 calories consumed above the amount one needs and he notes that previous research suggested that a pound of human adipose tissue is 87% fat, which equals 395 grams of fat. He further assumes that animal fat contains 9.5 calories per gram, thus one pound of human fat tissue should contain 3750 calories. He concludes that a 3500 calorie excess or deficit for a person meeting his assumptions, would lead to the gain or loss, respectively, of one pound of body weight. He notes that if the assumptions he makes are not met, in any case, Wishnofsky did not take into account numerous aspects of human physiology and biochemistry which refute this simple equivalence. Unfortunately, the claim has achieved the status of a rule of thumb and is repeated in numerous sources, used for planning by dietitians. In regard to adipose tissue increases, a person gains weight by increasing food consumption, becoming physically inactive. When energy intake exceeds energy expenditure, the body can store the energy as fat. However, the physiology of weight gain and loss is complex involving numerous hormones, body systems, the human microbiota facilitates fermentation of indigestible carbohydrates to short-chain fatty acids, SCFAs, contributing to weight gain. A change in the proportion of Bacteroidetes and Firmicutes may determine host’s risk of obesity, lack of sufficient sleep has been suggested as a cause for weight gain or the difficulty in maintaining a healthy weight. As a result, sleep deprivation over time may contribute to increased caloric intake and decreased self-control over food cravings, weight gain is a common side-effect of certain psychiatric medications
8.
Norepinephrine
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Norepinephrine, also called noradrenaline or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter. Norepinephrine is also the international nonproprietary name given to the drug, regardless of which name is used for the substance itself, parts of the body that produce or are affected by it are referred to as noradrenergic. In the brain, norepinephrine is produced in closely packed brain cell neurons or nuclei that are small yet exert powerful effects on brain areas. The most important of these nuclei is the locus coeruleus, located in the pons, regardless of how and where it is released, norepinephrine acts on target cells by binding to and activating noradrenergic receptors located on the cell surface. The general function of norepinephrine is to mobilize the brain and body for action, norepinephrine release is lowest during sleep, rises during wakefulness, and reaches much higher levels during situations of stress or danger, in the so-called fight-or-flight response. In the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, a variety of medically important drugs work by altering the actions of norepinephrine systems. Norepinephrine itself is used as an injectable drug for the treatment of critically low blood pressure. Beta blockers, which some of the effects of norepinephrine, are frequently used to treat glaucoma, migraine. Alpha blockers, which counter a different set of effects, are used to treat several cardiovascular. Alpha-2 agonists often have an effect, and are commonly used as anesthesia-enhancers in surgery. Many important psychiatric drugs exert strong effects on systems in the brain. Norepinephrine is a catecholamine and a phenethylamine and its structure differs from that of epinephrine only in that epinephrine has a methyl group attached to its nitrogen, whereas the methyl group is replaced by a hydrogen atom in norepinephrine. The prefix nor- is derived as an abbreviation of the word normal, norepinephrine is synthesized from the amino acid tyrosine by a series of enzymatic steps in the adrenal medulla and postganglionic neurons of the sympathetic nervous system. These amino acids are found in nearly every protein and, as such, are provided by ingestion of protein-containing food, phenylalanine is converted into tyrosine by the enzyme phenylalanine hydroxylase, with molecular oxygen and tetrahydrobiopterin as cofactors. Tyrosine is converted into L-DOPA by the tyrosine hydroxylase, with tetrahydrobiopterin, O2. L-DOPA is converted into dopamine by the enzyme aromatic L-amino acid decarboxylase, dopamine is then converted into norepinephrine by the enzyme dopamine β-monooxygenase, with O2 and ascorbic acid as cofactors. Norepinephrine itself can further be converted into epinephrine by the enzyme phenylethanolamine N-methyltransferase with S-adenosyl-L-methionine as cofactor, in mammals, norepinephrine is rapidly degraded to various metabolites. The initial step in the breakdown can be catalyzed by either of the monoamine oxidase or COMT
9.
Serotonin
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Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is found in the gastrointestinal tract, blood platelets. It is popularly thought to be a contributor to feelings of well-being, approximately 90% of the human bodys total serotonin is located in the enterochromaffin cells in the GI tract, where it is used to regulate intestinal movements. The remainder is synthesized in serotonergic neurons of the CNS, where it has various functions and these include the regulation of mood, appetite, and sleep. Serotonin also has some functions, including memory and learning. Modulation of serotonin at synapses is thought to be an action of several classes of pharmacological antidepressants. Serotonin secreted from the cells eventually finds its way out of tissues into the blood. There, it is taken up by blood platelets, which store it. When the platelets bind to a clot, they release serotonin, Serotonin is also a growth factor for some types of cells, which may give it a role in wound healing. Serotonin is metabolized mainly to 5-HIAA, chiefly by the liver, metabolism involves first oxidation by monoamine oxidase to the corresponding aldehyde. This is followed by oxidation by aldehyde dehydrogenase to 5-HIAA, the acetic acid derivative. The latter is then excreted by the kidneys, in addition to animals, serotonin is found in fungi and plants. Serotonins presence in insect venoms and plant spines serves to cause pain, Serotonin is produced by pathogenic amoebae, and its effect on the gut causes diarrhea. Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds, Serotonin is a neurotransmitter and is found in all bilateral animals, where it mediates gut movements and the animals perceptions of resource availability. In less complex animals, such as invertebrates, resources simply mean food availability. In more complex animals, such as arthropods and vertebrates, resources also can mean social dominance, in response to the perceived abundance or scarcity of resources, an animals growth, reproduction or mood may be elevated or lowered. This may somewhat depend on how much serotonin the organism has at its disposal, except for the 5-HT3 receptor, a ligand-gated ion channel, all other 5-HT receptors are G-protein-coupled receptors that activate an intracellular second messenger cascade. Serotonergic action is terminated primarily via uptake of 5-HT from the synapse and this is accomplished through the specific monoamine transporter for 5-HT, SERT, on the presynaptic neuron
10.
Simplified molecular-input line-entry system
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The simplified molecular-input line-entry system is a specification in form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules, the original SMILES specification was initiated in the 1980s. It has since modified and extended. In 2007, a standard called OpenSMILES was developed in the open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. The Environmental Protection Agency funded the project to develop SMILES. It has since modified and extended by others, most notably by Daylight Chemical Information Systems. In 2007, a standard called OpenSMILES was developed by the Blue Obelisk open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, in July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is generally considered to have the advantage of being slightly more human-readable than InChI, the term SMILES refers to a line notation for encoding molecular structures and specific instances should strictly be called SMILES strings. However, the term SMILES is also used to refer to both a single SMILES string and a number of SMILES strings, the exact meaning is usually apparent from the context. The terms canonical and isomeric can lead to confusion when applied to SMILES. The terms describe different attributes of SMILES strings and are not mutually exclusive, typically, a number of equally valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol, algorithms have been developed to generate the same SMILES string for a given molecule, of the many possible strings, these algorithms choose only one of them. This SMILES is unique for each structure, although dependent on the algorithm used to generate it. These algorithms first convert the SMILES to a representation of the molecular structure. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database, there is currently no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, and these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES
11.
Heart valve
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A heart valve normally allows blood to flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart, a heart valve opens or closes incumbent on differential blood pressure on each side. The four main valves in the heart are, The two atrioventricular valves, the valve, and the tricuspid valve, which are between the upper chambers and the lower chambers. The two semilunar valves, the valve and the pulmonary valve, which are in the arteries leaving the heart. The mitral valve and the valve are in the left heart, the tricuspid valve. There are also the coronary sinus and the inferior vena cava valves, the heart valves and the chambers are lined with endocardium. Heart valves separate the atria from the ventricles, or the ventricles from a blood vessel, heart valves are situated around the fibrous rings of the cardiac skeleton. The valves incorporate leaflets or cusps, which are pushed open to allow blood flow, the mitral valve has two cusps, whereas the others have three. There are nodules at the tips of the cusps that make the seal tighter, the pulmonary valve has left, right, and anterior cusps. The aortic valve has left, right, and posterior cusps, the tricuspid valve has anterior, posterior, and septal cusps, and the mitral valve has just anterior and posterior cusps. These are the mitral and tricuspid valves, which are situated between the atria and the ventricles and prevent backflow from the ventricles into the atria during systole and they are anchored to the walls of the ventricles by chordae tendineae, which prevent the valves from inverting. The chordae tendineae are attached to muscles that cause tension to better hold the valve. Together, the muscles and the chordae tendineae are known as the subvalvular apparatus. The function of the apparatus is to keep the valves from prolapsing into the atria when they close. The subvalvular apparatus has no effect on the opening and closure of the valves, however, the peculiar insertion of chords on the leaflet free margin, however, provides systolic stress sharing between chords according to their different thickness. The closure of the AV valves is heard as lub, the first heart sound, the closure of the SL valves is heard as dub, the second heart sound. The mitral valve is called the bicuspid valve because it contains two leaflets or cusps. The mitral valve gets its name from the resemblance to a bishops mitre and it is on the left side of the heart and allows the blood to flow from the left atrium into the left ventricle
12.
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
