InChIKey

A fixed-length hashed form of the IUPAC InChI structure identifier — 27 characters that make one chemical structure searchable and comparable across databases.

The IUPAC International Chemical Identifier (InChI) is a structure-derived text string that encodes a molecule's atoms, bonds, charges and stereochemistry in standardised layers, so that any software given the same structure produces the same string. The InChIKey is its fixed-length companion: a 27-character hash in three hyphen-separated blocks, designed to be practical where the full string is unwieldy.

The first fourteen characters encode the molecular skeleton and the next block covers stereochemistry and other layers, which gives the key a useful property: two structures sharing the first block share a skeleton, while a full match indicates the same standardised structure. Because the key is deterministic and license-free, it works as a cross-database join — the same structure yields the same key in PubChem, ChEMBL or a vendor's own records.

A hash is one-way: the structure cannot be reconstructed from the key, only looked up. For peptides, InChI handles well-defined small-to-mid-size molecules better than large or ambiguously specified ones, so an InChIKey on a research page indicates a fully specified structure stood behind it — verified, on this site, against the registry record before publication.

SourceInChI Trust — about the InChI standard

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.