An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects from landing or climbing on that surface. Insect repellents help prevent and control the outbreak of insect-borne diseases such as malaria, Lyme disease, dengue fever, bubonic plague, river blindness and West Nile fever. Pest animals serving as vectors for disease include insects such as flea and mosquito; some insect repellents are insecticides, but most discourage insects and send them flying or crawling away. Any might kill at a massive dose without reprieve, but classification as an insecticide implies death at lower doses. Methyl anthranilate and other anthranilate-based insect repellents Benzaldehyde, for bees DEET Dimethyl carbate Dimethyl phthalate, not as common as it once was but still an active ingredient in commercial insect repellents Ethylhexanediol known as Rutgers 612 or "6-12 repellent," discontinued in the US in 1991 due to evidence of causing developmental defects in animals Icaridin known as picaridin, KBR 3023 Butopyronoxyl.
Used in a "6-2-2" mixture during the 1940s and 1950s before the commercial introduction of DEET Ethyl butylacetylaminopropionate Metofluthrin Permethrin is different in that it is a contact insecticide A more recent repellent being researched is SS220, shown to provide better protection than DEET Tricyclodecenyl allyl ether, a compound found in synthetic perfumes Beautyberry leaves Birch tree bark is traditionally made into tar. Combined with another oil at 1/2 dilution, it is applied to the skin for repelling mosquitos Bog Myrtle Catnip oil whose active compound is Nepetalactone Citronella oil Essential oil of the lemon eucalyptus and its active compound p-menthane-3,8-diol Neem oil Lemongrass Tea tree oil from the leaves of Melaleuca alternifolia Tobacco Synthetic repellents tend to be more effective and/or longer lasting than "natural" repellents. For protection against mosquito bites, the U. S. Centers for Disease Control recommends DEET, oil of lemon eucalyptus, ethyl butylacetylaminopropionate and 2-undecanone with the caveat that higher percentages of the active ingredient provide longer protection.
In 2015, Researchers at New Mexico State University tested 10 commercially available products for their effectiveness at repelling mosquitoes. On the mosquito Aedes aegypti, the vector of Zika virus, only one repellent that did not contain DEET had a strong effect for the duration of the 240 minutes test: a lemon eucalyptus oil repellent. All DEET-containing mosquito repellents were active. In one comparative study from 2004, ethyl butylacetylaminopropionate was as effective or better than DEET in protection against Aedes aegypti and Culex quinquefasciatus mosquitoes. Other sources (official publications of the associations of German physicians as well as of German druggists suggest the contrary and state DEET is still the most efficient substance available and the substance of choice for stays in malaria regions, while ethyl butylacetylaminopropionate has little effect. However, some plant-based repellents may provide effective relief as well. Essential oil repellents can be short-lived in their effectiveness, since essential oils can evaporate completely.
A test of various insect repellents by an independent consumer organization found that repellents containing DEET or picaridin are more effective than repellents with "natural" active ingredients. All the synthetics gave 100% repellency for the first 2 hours, where the natural repellent products were most effective for the first 30 to 60 minutes, required reapplication to be effective over several hours. Permethrin is recommended as protection against mosquitoes for gear, or bed nets. In an earlier report, the CDC found oil of lemon eucalyptus to be more effective than other plant-based treatments, with a similar effectiveness to low concentrations of DEET. However, a 2006 published study found in both cage and field studies that a product containing 40% oil of lemon eucalyptus was just as effective as products containing high concentrations of DEET. Research has found that neem oil is mosquito repellent for up to 12 hours. Citronella oil's mosquito repellency has been verified by research, including effectiveness in repelling Aedes aegypti, but requires reapplication after 30 to 60 minutes.
There are products available based on sound production ultrasound which purport to be insect repellents. However, these electronic devices have been shown to be ineffective based on studies done by the United States Environmental Protection Agency and many universities. Regarding safety with insect repellent use on children and pregnant women: Children may be at greater risk for adverse reactions to repellents, in part, because their exposure may be greater. Keep repellents out of the reach of children. Do not allow children to apply repellents to themselves. Use only small amounts of repellent on children. Do not apply repellents to the hands of young children because this may result in accidental eye contact or ingestion. Try to reduce the use of repellents by dressing children in long sleeves and long trousers tucked into boots or socks whenever possible. Use netting over strollers, etc; as with chemical exposures in general, pregnant
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
An essential oil is a concentrated hydrophobic liquid containing volatile chemical compounds from plants. Essential oils are known as volatile oils, ethereal oils, aetherolea, or as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived; the term essential used here does not mean indispensable as with the terms essential amino acid or essential fatty acid which are so called since they are nutritionally required by a given living organism. In contrast to fatty oils, essential oils evaporate without leaving a stain or residue. Essential oils are extracted by distillation by using steam. Other processes include expression, solvent extraction, absolute oil extraction, resin tapping, wax embedding, cold pressing, they are used in perfumes, cosmetics and other products, for flavoring food and drink, for adding scents to incense and household cleaning products.
Essential oils are used for aromatherapy, a form of alternative medicine in which healing effects are ascribed to aromatic compounds. Aromatherapy may be useful to induce relaxation, but there is not sufficient evidence that essential oils can treat any condition. Improper use of essential oils may cause harm including allergic reactions and skin irritation, children may be susceptible to the toxic effects of improper use. Essential oils have been used in folk medicine throughout history; the earliest recorded mention of the techniques and methods used to produce essential oils is believed to be that of Ibn al-Baitar, an Al-Andalusian physician and chemist. Rather than refer to essential oils themselves, modern works discuss specific chemical compounds of which the essential oils are composed. For example: methyl salicylate rather than "oil of wintergreen". Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that uses essential oils and other aromatic compounds.
Oils are volatilized, diluted in a carrier oil and used in massage, diffused in the air by a nebulizer, heated over a candle flame, or burned as incense. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer and are based on historical accounts of use of essential oils for these purposes. Claims for the efficacy of medical treatments, treatment of cancers in particular, are now subject to regulation in most countries. Most common essential oils such as lavender, tea tree oil and eucalyptus are distilled. Raw plant material, consisting of the flowers, wood, roots, seeds, or peel, is put into an alembic over water; as the water is heated, the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil, where they condense back to liquid, collected in the receiving vessel. Most oils are distilled in a single process. One exception is ylang-ylang, purifed through a fractional distillation; the recondensed water is referred to as a hydrosol, herbal distillate, or plant water essence, which may be sold as another fragrant product.
Hydrosols include rose water, lavender water, lemon balm, clary sage, orange blossom water. The use of herbal distillates in cosmetics is increasing. Most citrus peel oils are expressed cold-pressed. Due to the large quantities of oil in citrus peel and low cost to grow and harvest the raw materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet orange oils are obtained as byproducts of the citrus industry. Before the discovery of distillation, all essential oils were extracted by pressing. Most flowers contain too little volatile oil to undergo expression, but their chemical components are too delicate and denatured by the high heat used in steam distillation. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvents are called concretes, which are a mixture of essential oil, waxes and other lipophilic plant material. Although fragrant, concretes contain large quantities of non-fragrant waxes and resins.
Another solvent, such as ethyl alcohol, is used to extract the fragrant oil from the concrete. The alcohol solution is chilled to −18 °C for more than 48 hours which causes the waxes and lipids to precipitate out; the precipitates are filtered out and the ethanol is removed from the remaining solution by evaporation, vacuum purge, or both, leaving behind the absolute. Supercritical carbon dioxide is used as a solvent in supercritical fluid extraction; this method can avoid petrochemical residues in the product and the loss of some "top notes" when steam distillation is used. It does not yield an absolute directly; the supercritical carbon dioxide will extract both the waxes and the essential oils that make up the concrete. Subsequent processing with liquid carbon dioxide, achieved in the same extractor by lowering the extraction temperature, will separate the waxes from the essential oils; this lower temperature process prevents the denaturing of compounds. When the extraction is complete, the pressure is reduced to ambient and the carbon dioxide reverts to a gas, leaving no residue.
Florasol is another solvent used to obtain essential oils. It was developed as a refrigerant to replac
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the 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 been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open 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 considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of 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; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is 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, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R -- O -- R ′, where R ′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl groups are the same on both sides of the oxygen atom it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anesthetic diethyl ether referred to as "ether". Ethers are common in organic chemistry and more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin. Ethers feature C–O–C linkage defined by a bond angle of about 110° and C–O distances of about 140 pm; the barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3. Oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons.
They are far less acidic than hydrogens alpha to carbonyl groups, however. Depending on the groups at R and R′, ethers are classified into two types:Simple ethers or symmetrical ethers. Mixed ethers or asymmetrical ethers. In the IUPAC nomenclature system, ethers are named using the general formula "alkoxyalkane", for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a more-complex molecule, it is described as an alkoxy substituent, so –OCH3 would be considered a "methoxy-" group; the simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane. IUPAC rules are not followed for simple ethers; the trivial names for simple ethers are a composite of the two substituents followed by "ether". For example, ethyl methyl ether, diphenylether; as for other organic compounds common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called "ether", but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed.
The aromatic ethers include furans. Acetals are another class of ethers with characteristic properties. Polyethers are compounds with more than one ether group; the crown ethers are examples of small polyethers. Some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are large and are known as cyclic or ladder polyethers. Polyether refers to polymers which contain the ether functional group in their main chain; the term glycol is reserved for low to medium range molar mass polymer when the nature of the end-group, a hydroxyl group, still matters. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties; the phenyl ether polymers are a class of aromatic polyethers containing aromatic cycles in their main chain: Polyphenyl ether and Poly. Many classes of compounds with C–O–C linkages are not considered ethers: Esters, carboxylic acid anhydrides. Ether molecules cannot form hydrogen bonds with each other, resulting in low boiling points compared to those of the analogous alcohols.
The difference in the boiling points of the ethers and their isomeric alcohols becomes lower as the carbon chains become longer, as the van der Waals interactions of the extended carbon chain dominates over the presence of hydrogen bonding. Ethers are polar; the C–O–C bond angle in the functional group is about 110°, the C–O dipoles do not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structure; the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible. Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to linear aliphatic ethers. Other properties are: The lower ethers are volatile and flammable. Lower ethers act as anaesthetics. Ethers are good organic solvents. Simple ethers are tasteless. Ethers are quite stable chemical compounds which do not react with bases, active metals, dilute acids, oxidising agents, reducing agents.
They are of low chemical reactivity, but they are more reactive than alkanes. Epoxides and acetals are unrepresentative classes of ethers and are discussed in separate articles. Important reactions are listed below. Although ethers resist hydrolysis, their polar bonds are cloven by mineral acids such as hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers afford methyl halides: ROCH3 + HBr → CH3Br + ROHThese reactions proceed via onium intermediates, i.e. +Br−. Some ethers undergo rapid cleavage with boron tribromide to give the alkyl bromide. Depending on the substituents, some ethers can be cloven with a variety of reagents, e.g. strong base. When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether peroxide; the reaction is accelerated by light, metal catalysts, aldehydes. In addition to avoiding storage conditions to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatil
Artemisia is a large, diverse genus of plants with between 200 and 400 species belonging to the daisy family Asteraceae. Common names for various species in the genus include mugwort and sagebrush. Artemisia comprises hardy herbaceous plants and shrubs, which are known for the powerful chemical constituents in their essential oils. Artemisia species grow in temperate climates of both hemispheres in dry or semiarid habitats. Notable species include A. vulgaris, A. tridentata, A. annua, A. absinthium, A. dracunculus, A. abrotanum. The leaves of many species are covered with white hairs. Most species have strong aromas and bitter tastes from terpenoids and sesquiterpene lactones, which discourage herbivory, may have had a selective advantage; the small flowers are wind-pollinated. Artemisia species are used as food plants by the larvae of a number of Lepidoptera species; some botanists split the genus into several genera, but DNA analysis does not support the maintenance of the genera Crossostephium, Neopallasia and Sphaeromeria.
Some of the species are called sages, causing confusion with the Salvia sages in the family Lamiaceae. The name "artemisia" derives from the Greek goddess Artemis, the namesake of Greek Queens Artemisia I and II. A more specific reference may be to Artemisia II of Caria, a botanist and medical researcher who died in 350 BC; the aromatic leaves of some species are used for flavouring. Most species have an bitter taste. A. dracunculus is used as a culinary herb important in French cuisine. Artemisia vulgaris was used to repel midges and moths, intestinal worms, in brewing as a remedy against hangovers and nightmares. Artemisia absinthium is used to make the potent spirits absinthe. Malört contains wormwood; the aperitif vermouth is a wine flavored with aromatic herbs, but with wormwood. Artemisia arborescens is an aromatic herb indigenous to the Middle East used in tea with mint. A few species are grown as the fine-textured ones used for clipped bordering. All grow best in free-draining sandy soil, in full sun.
Artemisia stelleriana is known as Dusty Miller, but several other species bear that name, including Jacobaea maritima, Silene coronaria, Centaurea cineraria. The largest collection of living Artemisia species and cultivars is held in the National Collection of Artemisia in Sidmouth, Devon, UK, which holds about 400 taxa; the National Collection scheme is administered by Plant Heritage in the British Isles. Artemisinin and derivatives are a group of compounds with the most rapid action of all current drugs used to treat malaria. Treatments containing an artemisinin derivative are now standard treatment worldwide for malaria caused by Plasmodium falciparum. Artemisia cina and other Old World species are the source of santonin. Chinese mugwort, Artemisia argyi, is used in traditional Chinese medicine. Artemisia capillaris Thunberg has been found to have potent sedative-hypnotic effects, which are mediated through potentiation of the GABAA receptor- Cl− ion channel complex Artemisia austriaca has beneficial effects in reducing the withdrawal syndrome of morphine.
Artemisia has been used in popular culture for centuries. A few examples are: Artemisia herba-alba is thought to be the plant translated as "wormwood" in English language versions of the Bible. Wormwood is mentioned seven times in the Jewish Bible, always with the implication of bitterness, it is mentioned once in the New Testament. Wormwood is the "name of the star" in the Book of Revelation 8:11 that John of Patmos envisions as cast by the angel and falling into the waters, making them undrinkably bitter. Further references in the Bible show wormwood was a common herb known for its bitter taste. In Shakespeare's Hamlet, the titular character says "Wormwood, wormwood" to comment on the bitter implications of what the Player Queen has just said. Classification of Artemisia is difficult. Divisions of Artemisia prior to 2000 into subgenera or sections have not been backed up by molecular data, but much of the molecular data, as of 2006, are not strong; the following identified. Section Tridentatae consists of eleven to thirteen species of coarse shrubs, which are prominent parts of the flora in western North America.
In some classifications, they are part of the genus or subgenus Seriphidium, although recent studies have contested this lineage to Old World species. Tridentatae was first articulated as a section by Rydberg in 1916, it was not until McArthur et al. in 1981 that Tridentatae was elevated to a separate subgenus from Seriphidium. The principal motive for their separation was geographical distribution, chemical makeup, karyotype. Much of the debate surrounding Tridentatae is phytogeographic, thus habitat and geography are cited when understanding the evolution of this endemic North American subgenus. Evolutionary cycles of wet and dry climates encouraged “dip