H2Cit

H2Cit is a shorthand term used in chemistry and related fields to denote a hydrogen-containing citrate species. Because citrate chemistry involves different protonation states depending on pH, H2Cit can refer to several forms in practice, most commonly a dihydrogen citrate-related species. In many contexts, the exact identity of H2Cit depends on the solution conditions, and it may be discussed alongside other protonated or deprotonated forms of citrate such as H3Cit (citric acid), H2Cit−, HCit2−, and Cit3−.

Chemical basis and properties

Citrate derives from citric acid, a tricarboxylic acid with a central hydroxyl group. The citrate framework contains three carboxyl groups and one hydroxyl, making it a versatile multidentate ligand and a capable buffering system. Hydrogen-containing citrate forms act as weak acids with multiple dissociation steps; their speciation shifts with pH, influencing metal binding, solubility, and buffering performance. These species are often employed in citrate buffers for biochemical and analytical applications due to their gentle pH transition ranges and metal-chelating capabilities.

Production and sources

Citric acid, the precursor for citrate species, is primarily produced by microbial fermentation of sugars. Neutralization or partial neutralization of citric acid yields various citrate forms, including hydrogen-containing species used in buffers and analytical reagents. In practical use, H2Cit is encountered in solutions prepared to achieve specific pH ranges or chelation requirements.

Applications and safety

H2Cit-related citrate species are widely used as buffering agents in laboratory assays, chromatography, and biochemical workflows. They also serve as sequestrants to bind metal ions in foods, pharmaceuticals, and cleaning products. Citrates are generally regarded as safe in standard food and laboratory contexts, though handling guidelines and concentration limits should be followed.

See also: citric acid, citrate, citrate buffer, H3Cit.