Cooxidant

Cooxidant is a term used in chemistry and biochemistry to denote a second oxidant that participates in an oxidation reaction alongside a primary oxidant. The cooxidant can help transfer electrons, regenerate the active oxidizing species, or broaden the range of substrates that can be oxidized. In many catalytic oxidation systems, a metal catalyst cycles between oxidation states in the presence of a primary oxidant (such as oxygen or hydrogen peroxide). A cooxidant serves to reoxidize the catalyst or to mediate electron transfer, thereby enabling catalytic turnover.

In enzymatic or microbial systems, cooxidants may refer to cosubstrates or additional oxidants that enable the enzyme to oxidize substrates not normally accepted, often via indirect or cooxidative pathways. For example, an enzyme may oxidize a target compound only in the presence of a cooxidant that accepts electrons from the enzyme’s reduced cofactor and transfers them to an external oxidant. In environmental science, cooxidation describes incidental oxidation of pollutants by reactive species produced during the metabolism of another substrate.

The term is context-dependent and may overlap with related concepts such as oxidants, co-substrates, and redox mediators. Practical usage varies by field, and precise definitions are typically specified in experimental methods or review articles.