Dioxygen Chemistry

Absorption of sunlight in green plants through chlorophyll (that consists of magnesium;) gives energy for photosynthesis, that converts CO₂ and H₂O into organic compounds and dioxygen. Respiration through both plants and animals gives metabolic energy through oxidation of organic matter by using atmospheric O₂. Both respiration and photosynthesis include complex electron-transfer chains, that are including redox reactions of organic (example quinones) and inorganic compounds (example Fe proteins). The terminal step within photosynthesis is

and is carried out through a unit containing four Mn ions. The O₂-consuming unit in respiration (termed as cytochrome c oxidase like it acquires electrons from the heme-iron protein cytochrome c) consists of both heme-Fe and Cu at the active site. The many-electron redox step is make easy through the existence of two or more transition metals along with a number of available redox states, Mn^II/^III/^IV, Cu^I/^II and Fe^II/^III/^IV with the ferryl (Fe^IV=O) state that is not general for Fe.

Intermediate oxidation states of O, peroxide (O^2-₂) and (O^-₂) superoxide are usually toxic and are undesirable side results of the exceeding reactions. Superoxide dismutase is a Cu-Zn-consisting of enzyme catalyzing the disproportionation of to O^-₂ and O^2-₂H2O; several catalases and peroxidases work to decompose peroxide.

Oxygenase enzymes catalyze particular oxidation reactions through O₂. Cytochrome P-450 enzymes carry out reactions like R-H→R-OH and include a ferryl intermediate. Copper-consisting of oxygenases are usually found outside cells (than inside like with Fe; the variation is thought to reflect the later adoption of Cu in evolution) and are particularly significant in reactions that create connective tissue like collagen.