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The IUPAC International Chemical Identifier (InChI or ) is a textual identifier for chemical substances, designed to provide a standard and human-readable way to encode molecular information and to facilitate the search for such information in databases and on the web. Initially developed by IUPAC and NIST from 2000 to 2005, the format and algorithms are non-proprietary. The continuing development of the standard has been supported since 2010 by the not-for-profit InChI Trust, of which IUPAC is a member. The current version is 1.04 and was released in September 2011. Prior to 1.04, the software was freely available under the open source LGPL license, but it now uses a custom license called IUPAC-InChI Trust License.〔http://www.inchi-trust.org/download/104/LICENCE.pdf〕 ==Overview== The identifiers describe chemical substances in terms of ''layers'' of information — the atoms and their bond connectivity, tautomeric information, isotope information, stereochemistry, and electronic charge information. Not all layers have to be provided; for instance, the tautomer layer can be omitted if that type of information is not relevant to the particular application. InChIs differ from the widely used CAS registry numbers in three respects: * they are freely usable and non-proprietary; * they can be computed from structural information and do not have to be assigned by some organization; * most of the information in an InChI is human readable (with practice). InChIs can thus be seen as akin to a general and extremely formalized version of IUPAC names. They can express more information than the simpler SMILES notation and differ in that every structure has a unique InChI string, which is important in database applications. Information about the 3-dimensional coordinates of atoms is not represented in InChI; for this purpose a format such as PDB can be used. The InChI algorithm converts input structural information into a unique InChI identifier in a three-step process: normalization (to remove redundant information), canonicalization (to generate a unique number label for each atom), and serialization (to give a string of characters). The InChIKey, sometimes referred to as a hashed InChI, is a fixed length (25 character) condensed digital representation of the InChI that is not human-understandable. The InChIKey specification was released in September 2007 in order to facilitate web searches for chemical compounds, since these were problematic with the full-length InChI. It should be noted that, unlike the InChI, the InChIKey is not unique: though collisions can be calculated to be very rare, they happen. In January 2009 the final 1.02 version of the InChI software was released. This provided a means to generate so called standard InChI, which does not allow for user selectable options in dealing with the stereochemistry and tautomeric layers of the InChI string. The standard InChIKey is then the hashed version of the standard InChI string. The standard InChI will simplify comparison of InChI strings and keys generated by different groups, and subsequently accessed via diverse sources such as databases and web resources. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「International Chemical Identifier」の詳細全文を読む スポンサード リンク
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