Semiquinones (or ubisemiquinones, if their origin is

ubiquinone Coenzyme Q10 (CoQ10 ), also known as ubiquinone, is a naturally occurring Cofactor (biochemistry), biochemical cofactor (coenzyme) and an antioxidant produced by the human body. It can also be obtained from dietary sources, such as meat, fish, ...

) are

free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabolic disorders Metabolism ...

s resulting from the removal of one hydrogen atom with its electron during the process of

dehydrogenation In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At ...

of a hydroquinone, such as

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para' ...

itself or

catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amounts. It ...

, to a

quinone The quinones are a class of organic compounds that are formally "derived from aromatic compounds benzene.html" ;"title="uch as benzene">uch as benzene or naphthalene] by conversion of an even number of –CH= groups into –C(=O)– groups with ...

or alternatively the addition of a single hydrogen atom with its electron to a quinone. Semiquinones are highly unstable. E.g. ubisemiquinone is the first of two stages in reducing the supplementary form of CoQ₁₀ (ubiquinone) to its active form

ubiquinol A ubiquinol is an electron-rich (reduced) form of coenzyme Q (ubiquinone). The term most often refers to ubiquinol-10, with a 10-unit tail most commonly found in humans. The natural ubiquinol form of coenzyme Q is 2,3-dimethoxy-5-methyl-6-poly p ...

References

Light reactions Cellular respiration {{Carbohydrate-stub