HYDROXAMIC ACID

A 'hydroxamic acid' is a class of chemical compounds sharing the same functional group in which an amine is inserted into an carboxylic acid. Its general structure is R-CO-NH-OH, with in R as an organic residue, a CO as a carbonyl group, and a hydroxylamine as NH₂-OH. They are used as metal chelators.
Hydroxamic acids can be synthesized from aldehydes via the Angeli-Rimini reaction. A well-known hydroxamic acid reaction is the Lossen rearrangement.
Hydroxamates are essential growth factors, or vitamins, for some microbes. They function as iron-binding compounds (siderophores) that solubilise iron and transport it into the cell.
Iron is a key component of cytochromes and iron-sulphur proteins (involved in electron transport) and is thus important in cellulr respiration. In an environment, absent from oxygen (anoxic); iron will be present in the ferrous +2 oxidation state (Fe²⁺), which is water-soluble. Under oxic conditions; iron will be in the ferric +3 oxidation state (Fe³⁺), in insoluble mineral form. The powerful chelating properties of hydoxamic acid and its derivatives is exploited by bacteria to obtain ferric iron. Once the iron-hydroxamate complex has entered the cell, the iron is liberated and the hydroxamic acid can be excreted and reused for iron transport.