Synthesis of Reversible Oxygen Complex of Polymeric Hemochrome

Abstract

Iron—protoporphyrin IX was bound to poly(vinylpyridine) and poly(vinylimidazole) at the axial site of the iron atom. The equilibrium constant for the complexation of heme with the polymeric ligand is 102 times as large as that of the monomeric analogue. Such a polymeric hemochrome can take up molecular oxygen (O2) more rapidly than does the corresponding monomeric hemochrome. The degree of oxygen saturation of the polymer complex is appreciably higher than that of the monomer complex.The rate constant of oxygenation in water (ka\\simeq10 sec−1) is much larger than that in an organic solvent (ka\\simeq10−4sec−1). The rate constant (ka) at the adsorption step is appreciably affected by the conformational change of the polymer ligand; ka is enhanced by about 10 times under the optimal conditions.On the other hand, the rate constant (kd) at the decomposition step of the oxygen complex is drastically affected by the environment around an active site. Upon adding an appropriate agent such as a salt, poly electrolyte, or surface-active agent, kd decreased drastically with increasing concentration of additives, so that an oxygen complex remained stable even in an aqueous solution.