CD studies on mixed complexes of cobalt with acetylacetone and amino acids or dipeptides, and observations on oxygen reaction of the 1:1 histidine-Co(II) complex

Abstract

The coordination of the imidazole ring in formation of the 1:1 histidine-Co(II) chelate complex gives a distinctive CD spectrum. Even at pH 5–6 the complex rapidly captures elemental oxygen and more slowly oxidizes to a mixture of two positively charged Co(III) complex isomers, which have distinctive CD spectra. The attempt to form mixed bischelate complexes of Co(II) from acetylacetone and amino acids or dipeptides, at pH 5–6, very slowly yields a product which is a mixture of Co(III) isomeric bischelates. These are mainly neutral, presumably holding a hydroxyl ion formed through oxygen oxidation as in the histidine complex case. The isomers are separable by passage through a bed of cation-exchange resin, and most reliably identified by their CD spectra, usually assisted by their visual coloration. The CD spectra of the mixed bischelate dipeptide complexes are characteristically different from those with amino acid.