Reversible oxygen binding by the complex of poly(2-methyl-1-vinylimidazole) and heme in cold aqueous media

Poly(2-methyl-1-vinylimidazole), molecular weight > 10⁴, forms a stable five-co-ordinated complex with heme in aqueous ethylene glycol solution. This complex gave an oxygen adduct at -30 °C, whereas an irreversible oxidation was observed for low-molecular-weight heme complexes with 2-methyl-imidazoles and for the six-co-ordinated heme complex with poly(1-vinylimidazole). Oxygenation was also observed for heme complexes with copolymers of 2-methyl-1-vinylimidazole but not for those with ionic copolymers. The lifetime of the oxygen adduct decreased with increasing hydrogen-ion concentration and upon adding alcohol or urea. Oxygen-binding and -dissociation rate constants and oxygen-binding equilibrium constants were also measured in cold aqueous media.