UPTAKE OF MOLECULAR-OXYGEN BY CO(II) CHELATES WITH PEPTIDES IN AQUEOUS-SOLUTIONS .9. TERNARY COBALT(II) - HISTIDINE-CONTAINING DIPEPTIDE-IMIDAZOLE SYSTEMS - EFFECTIVE DIOXYGEN CARRIERS

The Co(II) - glycyl-L-histidine-imidazole - O-2 and Co(II)-L-histydylg lycine-imidazole - O-2 systems were studied besides the corresponding ones with L-histidine and glycylglycine. Potentiometric, gas-volumetri c and spectroscopic (UV/VIS, near IR, ESR) measurements indicated tile presence of two types of ternary species: with parent complexes conta ining a deprotonated amide group (as for glycylglycine and similar dip eptides) and with parent histidine-like active complexes. The overall stability constants of the ternary complexes have been determined. A r ise in reversibility of oxygen uptake was evident in both cases when c ompared with the systems without imidazole.