Hydroxyl radical

The hydroxyl radical (·OH) is a neutral species of one oxygen atom and one hydrogen atom with an unpaired electron. Its high reactivity gives it a lifetime too short for significant accumulation in most environments.

Fenton reaction: A reaction in which iron(II) reacts with hydrogen peroxide to produce iron(III), hydroxide, and often hydroxyl radicals. This iron-catalyzed route generates ·OH from hydrogen peroxide.
Atmospheric chemistry: The study of chemical reactions and composition in Earth’s atmosphere. Atmospheric ·OH controls the oxidation of many trace gases.
Oxidative stress: A state in which oxidant production exceeds the capacity of biological defenses to control reactive species and their effects. Excess ·OH formation can contribute to oxidative damage in cells.
Free radical: An atom, molecule, or ion containing one or more unpaired electrons. The unpaired electron places ·OH in this broader chemical class.
Haber–Weiss reaction: A net reaction between superoxide and hydrogen peroxide that produces oxygen and hydroxide; iron can catalyze it. Its iron-catalyzed chemistry can supply hydroxyl radicals in biological systems.
Atmospheric lifetime: The average time a substance remains in the atmosphere before removal by chemical or physical processes. Reactions with ·OH help determine the lifetimes of many atmospheric pollutants.
DNA damage: Chemical or structural changes to DNA that can disrupt replication, transcription, or genome stability. ·OH can attack DNA bases and the sugar-phosphate backbone.
Unpaired electron: An electron that occupies an orbital without a partner of opposite spin. Its unpaired electron underlies the hydroxyl radical’s reactive character.
Hydrogen peroxide: A reactive oxygen compound with formula H₂O₂ that can act as an oxidant and radical precursor. It is a common reactant in pathways that form ·OH.
Methane: A simple hydrocarbon, CH₄, and a potent greenhouse gas. Atmospheric ·OH initiates the main chemical removal pathway for methane.

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