Poly(1-vinyl-2-methylimidazole) and poly(1-vinyl-2-methylimidazole-co-1-vinylpyrrolidone) predominantly form five-coordinate heme complexes in aqueous solution. The apparent formation constants (K) of the heme complexes were estimated spectroscopically. The K values of the polymer-heme complexes were about 102 to 103 times those of the corresponding monomeric ones. These large K values were canceled by adding poly(1-vinylpyrrolidone), alcohol, or dimethylformamide. The viscometric measurement of the polymer-heme solution showed that the polymer complex took a compact shape. These results indicate a hydrophobic interaction of heme with the polymer-ligand. Poly(1-vinyl-2-methylimidazole) could form the five-coordinate heme complex, even in the presence of a large amount of imidazole.
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