Hydrogen Peroxide-Triggered Release of Catalytically Active Manganese Porphyrin Species from a PEG Hydrogel

A cross-linked hydrogel was prepared by coupling manganese tetrakis(4-carboxyphenyl)porphyrin with poly(ethylene glycol) diamine and evaluated as an H2O2-responsive catalytic material. The resulting hydrogel exhibited both superoxide dismutase-like and catalase-like activities, although the apparent activity of the immobilized manganese porphyrin was lower than that of soluble manganese tetrakis(4-carboxyphenyl)porphyrin under the examined conditions. Upon exposure to H2O2, manganese-porphyrin-containing species were released from the cross-linked poly(ethylene glycol) network. The released species had an apparent hydrodynamic diameter of approximately 63 nm and were largely retained by a membrane with a 10 kDa cutoff. The released species retained both superoxide dismutase-like and catalase-like activities. Aerobic ascorbate oxidation by the hydrogel and released species was limited compared with that promoted by a cationic manganese porphyrin reference. These results show that hydrogen peroxide acts not only as a substrate for the manganese porphyrin catalyst but also as a chemical stimulus that releases catalytically active manganese-porphyrin-containing species from the cross-linked poly(ethylene glycol) network. H2O2-triggered release therefore modulates manganese porphyrin catalyst accessibility in the hydrogel system.