monooxygenated

Monooxygenated describes a compound that has undergone monooxygenation, an oxidation reaction in which one atom of molecular oxygen is incorporated into the substrate while the other is reduced, typically to water. In biochemical systems this process is most commonly mediated by monooxygenase enzymes, which transfer one oxygen atom from O2 into the substrate and reduce the other oxygen atom to H2O. The general reaction can be represented as RH + O2 + NADPH + H+ → ROH + H2O + NADP+. The inserted oxygen often appears as a hydroxyl group, yielding hydroxylated metabolites, but monooxygenation can also produce epoxides or rearranged products depending on the substrate and enzyme.

Monooxygenation plays a central role in phase I metabolism, where lipophilic compounds such as drugs and xenobiotics are converted to more polar, excretable metabolites. Cytochrome P450 enzymes are the most widely known monooxygenases, but other enzymes such as flavin-containing monooxygenases (FMOs) and various peroxidases also perform monooxygenation in different contexts. The reaction requires cofactors and, in vivo, is linked to cellular redox systems.

Examples include the hydroxylation of aromatic compounds (benzene to phenol) and alkanes (methane to methanol) by methane monooxygenase. In pharmacology, many drug metabolites are monooxygenated, which can affect activity and toxicity. Analytical approaches to detect monooxygenated products include mass spectrometry and isotope labeling (for example using 18O2) to confirm oxygen incorporation.

Monooxygenation is distinct from dioxygenation, where both atoms of O2 are incorporated, and from subsequent oxidations leading to higher oxidation states.