Approaches to Artificial Macromolecular Oxygen Carriers

Construction of artificial oxygen carriers by use of iron or cobalt complexes bound to synthetic polymers was attempted. Radical copolymerization of porphyrin vinyl monomers with styrene gave the metalloporphyrins covalently bonded to a polymer chain at low concentration. For these metalloporphyrin polymers, irreversible oxidation via dimerization was prevented in aprotic solvents and reversible oxygenation was observed. The chemical environment around the oxygen-binding site was presumed to play an important role on the stability of oxygenated complex as in the case of the tetraamide groups on the porphyrin plane. When ethylenebis(salicylideniminato)cobalt chelate coordinated to a polymer-ligand, it formed a stable oxygenated complex at room temperature. Rotational motion of the chelate was decreased markedly by the polymer chain to enhance the coordinate bond between the metal ion and the bound oxygen molecule. Furthermore, the iron porphyrin with bulky substituents was oxygenated even in homogeneous aqueous solutions by combining it with the rigid, hydrophobic domain of a water-soluble block copolymer.