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.
Calcium peroxide or calcium dioxide is the inorganic compound with the formula CaO2. It is the peroxide salt of Ca2+. Commercial samples can be yellowish, it is insoluble in water. As a solid, it is stable against decomposition. In contact with water however it hydrolyzes with release of oxygen. Upon treatment with acid, it forms hydrogen peroxide. Calcium peroxide is produced by combining calcium salts and hydrogen peroxide: Ca2 + H2O2 → CaO2 + 2 H2OThe octahydrate precipitates upon the reaction of calcium hydroxide with dilute hydrogen peroxide. Upon heating it dehydrates, it is used as an oxidant to enhance the extraction of precious metals from their ores. In its second main application, it is used as a food additive under the E number E930 it is used as flour bleaching agent and improving agent. In agriculture it is used in the presowing treatments of rice seed. Calcium peroxide has found use in the aquaculture to oxygenate and disinfect water. In the ecological restoration industry it is used in the treatment of soils.
Calcium peroxide is used in a similar manner to magnesium peroxide for environmental restoration programs. It is used to restore soil and groundwater contaminated with petroleum by the process of enhanced in-situ bioremediation
Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid, it occurs as the mineral fluorite, deeply coloured owing to impurities. The compound crystallizes in a cubic motif called the fluorite structure. Ca2 + centres are eight-coordinate; each F− centre is coordinated to four Ca2+ centres. Although packed crystalline samples are colorless, the mineral is deeply colored due to the presence of F-centers; the same crystal structure is found in numerous ionic compounds with formula AB2, such as CeO2, cubic ZrO2, UO2, ThO2, PuO2. A related structure is the antifluorite structure, where the anions and cations are swapped, such as Be2C; the mineral fluorite is abundant, of interest as a precursor to HF. Thus, little motivation exists for the industrial production of CaF2. High purity CaF2 is produced by treating calcium carbonate with hydrofluoric acid: CaCO3 + 2 HF → CaF2 + CO2 + H2O Naturally occurring CaF2 is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials.
Calcium fluoride in the fluorite state is of significant commercial importance as a fluoride source. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid: CaF2 + H2SO4 → CaSO4 + 2 HF Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy and excimer lasers, it is transparent over a broad range from ultraviolet to infrared frequencies. Its low refractive index reduces the need for anti-reflection coatings, its insolubility in water is convenient as well. Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces toxic hydrofluoric acid. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air. List of laser types Photolithography Skeletal fluorosis NIST webbook thermochemistry data Charles Townes on the history of lasers National Pollutant Inventory - Fluoride and compounds fact sheet Crystran Material Data MSDS
Boric acid called hydrogen borate, boracic acid, orthoboric acid and acidum boricum, is a weak, monobasic Lewis acid of boron, used as an antiseptic, flame retardant, neutron absorber, or precursor to other chemical compounds. It has the chemical formula H3BO3, exists in the form of colorless crystals or a white powder that dissolves in water; when occurring as a mineral, it is called sassolite. Boric acid, or sassolite, is found in its free state in some volcanic districts, for example, in the Italian region of Tuscany, the Lipari Islands and the US state of Nevada. In these volcanic settings it mixed with steam, from fissures in the ground, it is found as a constituent of many occurring minerals – borax, boracite and colemanite. Boric acid and its salts are found in seawater, it is found in plants, including all fruits. Boric acid was first prepared by Wilhelm Homberg from borax, by the action of mineral acids, was given the name sal sedativum Hombergi; however borates, including boric acid, have been used since the time of the ancient Greeks for cleaning, preserving food, other activities.
Boric acid may be prepared by reacting borax with a mineral acid, such as hydrochloric acid: Na2B4O7·10H2O + 2 HCl → 4 B3 + 2 NaCl + 5 H2OIt is formed as a by product of hydrolysis of boron trihalides and diborane: B2H6 + 6 H2O → 2 B3 + 6 H2BX3 + 3 H2O → B3 + 3 HX Boric acid is soluble in boiling water. When heated above 170 °C, it dehydrates, forming metaboric acid: H3BO3 → HBO2 + H2OMetaboric acid is a white, cubic crystalline solid and is only soluble in water. Metaboric acid melts at about 236 °C, when heated above about 300 °C further dehydrates, forming tetraboric acid called pyroboric acid: 4 HBO2 → H2B4O7 + H2OThe term boric acid may sometimes refer to any of these compounds. Further heating leads to boron trioxide. H2B4O7 → 2 B2O3 + H2OThere are conflicting interpretations for the origin of the acidity of aqueous boric acid solutions. Raman spectroscopy of alkaline solutions has shown the presence of B−4 ion, leading some to conclude that the acidity is due to the abstraction of OH− from water: B3 + H2O ↽ − ⇀ B−4 + H+ or more properly expressed in the aqueous solution: B3 + 2 H2O ↽ − ⇀ B−4 + H3O+This may be characterized as Lewis acidity of boron toward OH−, rather than as Brønsted acidity.
Polyborate anions are formed at pH 7–10 if the boron concentration is higher than about 0.025 mol/L. The best known of these is the'tetraborate' ion, found in the mineral borax: 4− + 2 H+ ⇌ 2− + 7H2OBoric acid makes an important contribution to the absorption of low frequency sound in seawater. With polyols such as glycerol and mannitol the acidity of the solution is increased. With mannitol for example the pK decreases to 5.15. This is due to the formation of a chelate, −, this feature is used in analytical chemistry. Boric acid dissolves in anhydrous sulfuric acid: B3 + 6H2SO4 → 3H3O+ + 2HSO4− + B4−Boric acid reacts with alcohols to form borate esters, B3 where R is alkyl or aryl. A dehydrating agent, such as concentrated sulfuric acid is added: B3 + 3 ROH → B3 +3 H2O The three oxygen atoms form a trigonal planar geometry around the boron; the B-O bond length is 136 pm and the O-H is 97 pm. The molecular point group is C3h. Crystalline boric acid consists of layers of B3 molecules held together by hydrogen bonds of length 272 pm.
The distance between two adjacent layers is 318 pm. Based on mammalian median lethal dose rating of 2,660 mg/kg body mass, boric acid is only poisonous if taken internally or inhaled in large quantities; the Fourteenth Edition of the Merck Index indicates that the LD50 of boric acid is 5.14 g/kg for oral dosages given to rats, that 5 to 20 g/kg has produced death in adult humans. For comparison's sake, the LD50 of salt is reported to be 3.75 g/kg in rats according to the Merck Index. According to the Agency for Toxic Substances and Disease Registry, "The minimal lethal dose of ingested boron was reported to be 2–3 g in infants, 5–6 g in children, 15–20 g in adults. However, a review of 784 human poisonings with boric acid reported no fatalities, with 88% of cases being asymptomatic."Long-term exposure to boric acid may be of more concern, causing kidney damage and kidney failure. Although it does not appear to be carcinogenic, studies in dogs have reported testicular atrophy after exposure to 32 mg/kg bw/day for 90 days.
This level is far lower than the LD50. According to the CLH report for boric acid published by the Bureau for Chemical Substances Lodz, boric acid in high doses shows significant developmental toxicity and teratogenicity in rabbit and mouse fetuses as well as cardiovascular defects, skeletal variations, mild kidney lesions; as a consequence in the 30th ATP to EU directive 67/548/EEC of August 2008, the European Commission decided to amend its classification as reprotoxic category 2, to apply the risk phrases R60 and R61. At a 2010 European Diagnostics Manufacturing Association Meeting, several new additions to the Substance of Very High Concern candidate list in relation to the Registration, Evaluation and Restriction of Chemicals Regulations 20
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having low coefficients of thermal expansion, making them resistant to thermal shock, more so than any other common glass; such glass is less subject to thermal stress and is used for the construction of reagent bottles. Borosilicate glass is sold under such trade names as Borcam, Borosil, DURAN, Simax, BSA 60, BSC 51, Endural, Refmex, Kimble, MG and some items sold under different trade names. Borosilicate glass was first developed by the German glassmaker Otto Schott in the late 19th century. Otto Schott was the founder of today's Schott AG, which has sold borosilicate glass under the brand name DURAN; as part of an equity carve-out in 2005, the DURAN Group was founded and the manufacture of Duran was transferred to it. After Corning Glass Works introduced Pyrex in 1915, the name became synonymous for borosilicate glass in the English-speaking world.
However, borosilicate glass is the name of a glass family with various members tailored to different purposes. Most common today is borosilicate 3.3 glass such as Duran, International Cookware's NIPRO BSA 60, BSC 51. In addition to quartz, sodium carbonate, aluminium oxide traditionally used in glassmaking, boron is used in the manufacture of borosilicate glass; the composition of low-expansion borosilicate glass, such as those laboratory glasses mentioned above, is 80% silica, 13% boric oxide, 4% sodium oxide and 2–3% aluminium oxide. Though more difficult to make than traditional glass due to the high melting temperature required, it is economical to produce, its superior durability and heat resistance finds use in chemical laboratory equipment, lighting, in certain kinds of windows. Borosilicate glass is created by combining and melting boric oxide, silica sand, soda ash, alumina. Since borosilicate glass melts at a higher temperature than ordinary silicate glass, some new techniques were required for industrial production.
The manufacturing process depends on the product geometry and can be differentiated between different methods like floating, tube drawing, or moulding. The common type of borosilicate glass used for laboratory glassware has a low thermal expansion coefficient, about one-third that of ordinary soda-lime glass; this reduces material stresses caused by temperature gradients, which makes borosilicate a more suitable type of glass for certain applications. Fused quartzware is better in this respect. While more resistant to thermal shock than other types of glass, borosilicate glass can still crack or shatter when subjected to rapid or uneven temperature variations. Among the characteristic properties of this glass family are: Different borosilicate glasses cover a wide range of different thermal expansions, enabling direct seals with various metals and alloys like molybdenum glass with a CTE of 4,6, tungsten with a CTE around 4,0 and Kovar with a CTE around 5,0 because of the matched CTE with the sealing partner Allowing high maximum temperatures of about 500 °C Showing an high chemical resistance in corrosive environments.
Norm tests for example for acid resistance create extreme conditions and reveal low impacts on glassThe softening point of type 7740 Pyrex is 820 °C. Borosilicate glass is less dense than typical soda-lime glass due to the low atomic mass of boron, its mean specific heat capacity at constant pressure is 0.83 J/ one fifth of water's. The temperature differential that borosilicate glass can withstand before fracturing is about 165 °C; this compares well with soda lime glass, which can withstand only a 37 °C change in temperature and is why typical kitchenware made from traditional soda-lime glass will shatter if a vessel containing boiling water is placed on ice, but Pyrex or other borosilicate laboratory glass will not. Optically, borosilicate glasses are crown glasses with low dispersion and low refractive indices. For the purposes of classification, borosilicate glass can be arranged in the following groups, according to their oxide composition. Characteristic of borosilicate glasses is the presence of substantial amounts of silica and boric oxide as glass network formers.
The amount of boric oxide affects the glass properties in a particular way. Apart from the resistant varieties, there are others that – due to the different way in which the boric oxide is incorporated into the structural network – have only low chemical resistance. Hence we differentiate between the following subtypes; the B2O3 content for borosilicate glass is 12–13% and the SiO2 content over 80%. High chemical durability and low thermal expansion – the lowest of all commercial glasses for large-scale technical applications – make this a multitalented glass material. High-grade borosilicate flat glasses are used in a wide variety of industries for technical applications that require either good thermal resistance, excellent chemical durability, or high light transmission in c
Calcium hydride is the chemical compound with the formula CaH2, is therefore an alkaline earth hydride. This grey powder reacts vigorously with water liberating hydrogen gas. CaH2 is thus used as a drying agent. CaH2 is a saline hydride; the alkali metals and the alkaline earth metals heavier than beryllium all form saline hydrides. A well-known example is sodium hydride; these species are insoluble in all solvents. CaH2 crystallizes in the PbCl2 structure. Calcium hydride is prepared from its elements by direct combination of calcium and hydrogen at 300 to 400 °C. CaH2 is a reducing agent for the production of metal powders from the oxides of Ti, V, Nb, Ta, U, it is proposed to operate via its decomposition to Ca metal: TiO2 + 2 CaH2 → Ti + 2 CaO + 2 H2 CaH2 has been used for hydrogen production. In the 1940s, it was available under the trade name "Hydrolith" as a source of hydrogen:'The trade name for this compound is "hydrolith", it is rather expensive for this use.' The reference to "emergency" refers to wartime use.
The compound has, been used for decades as a safe and convenient means to inflate weather balloons. It is used in laboratories to produce small quantities of pure hydrogen for experiments; the moisture content of diesel fuel is estimated by the hydrogen evolved upon treatment with CaH2. The reaction of CaH2 with water can be represented as follows: CaH2 + 2 H2O → Ca2 + 2 H2The two hydrolysis products, gaseous H2 and Ca2, are separated from the dried solvent. Calcium hydride is a mild desiccant and, compared to molecular sieves inefficient, its use is safer than more reactive agents such as sodium-potassium alloy. Calcium hydride is used as a desiccant for basic solvents such as amines and pyridine, it is used to dry alcohols. Despite its convenience, CaH2 has a few drawbacks: It is insoluble in all solvents with which it does not react vigorously, in contrast to LiAlH4, thus the speed of its drying action can be slow; because CaH2 and Ca2 are indistinguishable in appearance, the quality of a sample of CaH2 is not obvious visually.
During the Battle of the Atlantic, German submarines used calcium hydride as a sonar decoy called bold. Calcium monohydride
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