Lipoic aci is the organic compound, one enantiomer of which is an essential cofactor for many enzyme complexes. The molecule consists of a carboxylic acid and a cyclic disulfide. Only the R-enantiomer is biologically significant. It is essential for aerobic life and a common dietary supplement. Dihydrolipoic acid is the reduced form of lipoic acid although it is sometimes also called "lipoic acid." "Lipoate" is the conjugate base of lipoic acid, and this form is mainly present at physiological conditions.