International Chemical Identifier

International Chemical Identifier (InChI) is a textual identifier for chemical substances, designed to provide a standard way to encode molecular information and to facilitate the search for such information in databases and on the web. Initially developed by the International Union of Pure and Applied Chemistry (IUPAC), it has become a widely used standard in chemical informatics.

Overview

The InChI algorithm converts a chemical structure into a unique, machine-readable string of characters. This string, which is the InChI, can be used to generate a digital representation of a chemical substance, allowing for easy sharing and searching of chemical data. The InChI includes layers and sub-layers of information that can describe not only the molecular structure but also specific tautomeric forms, isotopic information, stereochemistry, and electronic charge.

Components

The InChI consists of several components, each representing different aspects of the chemical substance:

• Main Layer: Contains the most fundamental information about the molecule, including the chemical formula, atom connections, and hydrogen atoms.
• Charge Layer: Indicates the net charge of the molecule.
• Stereochemical Layer: Provides information about the stereochemistry of the molecule, including double bond and tetrahedral stereochemistry.
• Isotopic Layer: Contains information about isotopic atoms within the molecule.
• Fixed-H Layer: Specifies the tautomeric form of the molecule.
• Reconnected Layer: Used for disconnected structures, such as salts or complexes, to provide a non-standard representation focusing on connectivity.

Advantages

The InChI provides several advantages for the scientific community:

• Standardization: Offers a consistent, standardized format for representing chemical substances.
• Interoperability: Facilitates the exchange and comparison of chemical data across different databases and software.
• Searchability: Enhances the ability to search for chemical substances and related information on the internet and within scientific databases.
• Openness: As an open standard, InChI is freely available for use by anyone, promoting widespread adoption and use.

Applications

InChI identifiers are used in a wide range of applications, including:

• Chemical Databases: Many chemical databases use InChI as a standard identifier to index and retrieve chemical substances.
• Scientific Publications: Researchers include InChIs in publications to enable easy access to the chemical substances discussed.
• Chemical Inventory Management: InChIs are used in inventory management systems for tracking and managing chemical substances.
• Web Searching: InChIs can be used in web searches to find information about specific chemical substances.

Challenges

Despite its advantages, the use of InChI also presents some challenges:

• Complexity: The detailed representation of chemical substances can result in long and complex InChI strings that may be difficult to interpret without specialized software.
• Adoption: While widely used, the adoption of InChI is not universal, and some databases and software may use alternative identifiers.

Future Directions

The development and adoption of InChI continue to evolve, with ongoing efforts to extend its applicability to new types of chemical substances and to enhance its functionality. Future developments may include improved handling of polymers, mixtures, and complex natural products.

See Also

• Chemical nomenclature
• Molecular structure
• Chemical database
• IUPAC nomenclature

External Links

• International Chemical Identifier (InChI) Trust - Official website