hydroxylatie

Hydroxylation is the chemical process of inserting a hydroxyl group (-OH) into an organic substrate, converting nonpolar C–H bonds into more polar C–OH bonds. This oxidation typically increases solubility and alters reactivity. Hydroxylation can be catalyzed by enzymes or occur as a non-enzymatic radical reaction, and it is a common step in metabolism, synthesis, and environmental chemistry.

Enzymatic hydroxylation is carried out by oxygenases, notably cytochrome P450 monooxygenases in many organisms. P450 enzymes use molecular oxygen and electrons from NADPH to insert one oxygen atom into RH to form ROH while reducing the second oxygen to water. Other enzymes include non-heme iron(II)/α-ketoglutarate-dependent dioxygenases, which couple substrate hydroxylation with oxidative decarboxylation of α-ketoglutarate. These reactions are typically regio- and stereoselective.

Non-enzymatic hydroxylation branches include reactions mediated by hydroxyl radicals (OH•) formed by Fenton chemistry or photochemical processes. OH• is highly reactive and can hydroxylate many substrates but is difficult to control, contributing to oxidative damage in biology and to atmospheric and environmental chemistry.

Biological role: In humans and other animals, hydroxylation is a key Phase I metabolic step that makes drugs and xenobiotics more polar for excretion, and it can also generate reactive metabolites. An example is phenylalanine hydroxylation to tyrosine, catalyzed by phenylalanine hydroxylase. Industrially, hydroxylation is used in biocatalysis and chemical synthesis to introduce alcohol groups into hydrocarbons or to generate phenols.

Environmental relevance: hydroxylation by natural enzymes or radical hydroxylation contributes to the breakdown of pollutants; atmospheric OH radicals initiate oxidation of volatile organic compounds.

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