Poly(1-vinyl-2-pyrrolidone)- and dextran-bound protoheme mono[N-[3-(imidazol-1-yl)propyl]amide] and mono[N-[5-(2-methylimidazol-1-yl)pentyl]amide] and their reversible oxygen binding in an aqueous medium

Protoheme mono[N-[3-(imidazol-1-yl)propyl]amide] and mono[N-[5-(2-methylimidazol-1-yl)pentyl]amide] were covalently bound with poly(1-vinyl-2-pyrrolidone) (1) and dextran (2). The polymer-bound hemes formed oxygen adducts with lifetimes of ca. 1 h for 1 and a few minutes for 2 in an aqueous ethylene glycol (1/1) solution cooled to -30°C, whereas nonbound heme analogues did not form under the same conditions. It is considered that the water-soluble but hydrophobic poly(vinylpyrrolidone) protects the heme-oxygen adduct from its proton-driven irreversible oxidation. Oxygen binding rate constant of 1 was reduced by the surrounding polymer, and oxygen binding affinity was close to that of hemoglobin. Mössbauer parameters of the iron-57-labeled 1 were also measured.