{"term":{"id":"03518","title":"ligands","longtitle":"IUPAC Gold Book - ligands","doi":"10.1351\/goldbook.L03518","code":"L03518","status":"current","definitions":[{"id":1,"text":"In an inorganic coordination entity, the atoms or groups joined to the central atom.","links":[{"term":"central atom","url":"https:\/\/goldbook.iupac.org\/terms\/view\/C00930"},{"term":"coordination entity","url":"https:\/\/goldbook.iupac.org\/terms\/view\/C01330"}],"sources":["Red Book, 3rd ed., p. 146"]},{"id":2,"text":"In biochemistry: if it is possible or convenient to regard part of a polyatomic molecular entity as central, then the atoms, groups or molecules bound to that part are called ligands. Biochemical usage is thus wider, in that the central entity can be polyatomic. Thus H+ may be a ligand for proteins and for citrate as well as for $\\ce{O^{2−}}$. It may even be a ligand for a univalent entity such as acetate: in other circumstances, $\\ce{AcO^{−}}$ may be the ligand for $\\ce{H^{+}}$, since the definition makes it clear that the view of which entity is central may change for convenience. Thus, four calcium ions are ligands for calmodulin, when the protein is regarded as central: four carboxylate groups of calmodulin ligate (are ligands of) each calcium ion when this ion is regarded as central. It is the ligand that is said to ligate the central entity, which is said to be ligated. When the hormone binding to a receptor is called a ligand, the receptor is thus regarded as the central entity. Biochemists should bear in mind that the usage in inorganic chemistry has been that ligands bind only single atoms, so they should be cautious in fields such as bioinorganic chemistry where confusion may be possible.","links":[{"term":"ligate","url":"https:\/\/goldbook.iupac.org\/terms\/view\/L03522"},{"term":"proteins","url":"https:\/\/goldbook.iupac.org\/terms\/view\/P04898"},{"term":"receptor","url":"https:\/\/goldbook.iupac.org\/terms\/view\/RT06841"}],"sources":["PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1136 (https:\/\/doi.org\/10.1351\/pac199466051077)","White Book, 2nd ed., p. 335 (https:\/\/iupac.qmul.ac.uk\/bibliog\/white.html)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/L03518\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/L03518\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/L03518\/plain"},"citation":"Citation: 'ligands' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351\/goldbook.L03518","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-10T00:14:31+00:00"}}