Preparation and Function of Poly(acrylic acid)s Modified by Supramolecular Complex Composed of Porphinatoiron and a Cyclodextrin Dimer That Bind Diatomic Molecules (O2 and CO) in Aqueous Solution

Abstract

Poly(acrylic acid) (PAA) is modified by 5-(4-β-alanylaminophenyl)-10,15,20-tris(4-sulfonatophenyl) porphinatoiron(III) to yield iron porphyrin-bearing PAAs (FeP(n)s) through a condensation reaction. FeP(n)s were further functionalized by Py3CD, which is a per-O-methylated β-cyclodextrin (CD) dimer with a pyridine linker and includes the porphyrin pendants to form ferric hemoCD-P(n)s. Ferrous hemoCD-P(3), having three porphyrin chromophores in a polymer chain, is shown to bind molecular oxygen (P(1/2)=7.9±1.4 Torr) in aqueous solution at pH 7.0 and 25 °C, affording oxy-hemoCD-P(3). Oxy-hemoCD-P(3) is biphasically autoxidized to ferric hemoCD-P(3), with 27% of the dioxygen adducts being rapidly oxidized. The rate of autoxidation of oxy-hemoCD-P(15), having 15 porphyrin chromophores in a polymer chain, was much faster than that of oxy-hemoCD-P(3), thus suggesting self-catalyzed autoxidation of oxy-hemoCD-P(n)s. Oxy-hemoCD-P(n)s are markedly stabilized by catalase, thereby indicating that hydrogen peroxide generated from oxy-hemoCD-P(n) accelerates the autoxidation. Most of the hemoCD-P(3) molecules injected into the femoral vein of a rat remained in the body, though about 16% of the hemoCD-P(3) molecules were excreted in the urine as a carbon monoxide adduct.