Interaction between Heme Bonded to Polyvinylpyridine or Polyvinylimidazole and Molecular Oxygen

Abstract

Iron-protoporphyrin chloride was allowed to bond to such a polymeric derivative as poly-4- vinylpyridine (PVP) or poly-1-vinyl-2-methylimidazole (PVMI) in various solvents and the interaction between the above hemochrome and molecular oxygen (O₂) was examined in com- parison with the analogous monomeric complexes.
The equilibrium constants in the complexation between heme (Fe2+) and the following axial ligands are as follows: pyridine; 51.3 (//mol), imidazole; 45.5 (l/mol), PVP; 1.14 X 1O₂ (l/mol), PVMI; 2.55 x 108 (l/mol). This result indicates that a polymeric hemochrome is more stable than a monomeric one.
It is known that a central iron ( II ) ion is immediately oxidized, when a Fe ( II ) protoporphyrin complex is exposed to O₂ in an aqueous solution. However, since the oxidation of the polymeric complex retarded under an appropriate condition, the stable oxygen complex formed and then the reversible oxygenation could occur. In addition, the oxygenation rate of the polymeric complex was higher than that of the monomeric complex and the degree of saturation of oxygen of the polymeric complex was approximately 100%.