THE DISTINCTIVE PROPERTIES OF DIOXYGEN COMPLEXES FORMED IN THE COBALT(II)-ASPARAGINE-OH SYSTEMS (IN RELATION TO OTHER AMINO-ACIDS AND MIXEDCOMPLEXES WITH N-BASE)

Dioxygen complexes forming in the Cobalt(II)- asparagine-OH- system in aqueous solution have been investigated by potentiometric, volumetric and spectroscopic methods. In contrast to the corresponding complexes with other bidentate amino acids the asparagine ligand acts at high p H (> 13) as a tridentate ligand, the stability of the oxygen adduct be ing evidently enhanced thereby. This result has been interpreted as co ordination of the side chain amide group deprotonated in presence of t he metal, followed by structurally stimulated formation of a monobridg ed dimer. Additionally it has been proved that in weakly basic solutio ns the cobalt(II)-alpha-amino acid active complexes, able to bind diox ygen, are generally of ML3 type (not ML2 as it was assumed up to now).