A stable biomimetic redoxcatalyst obtained by the enzyme catalyzed amidation of iron porphyrin

Hematin, a hydroxyferriprotoporphyrin, is the more stable oxidized form of the free heme. The use of hematin as a catalyst for oxidative polymerization reactions has been restricted due to its limited aqueous solubility at low pH conditions. While there have been reports on the functionalization of hematin with poly (ethylene glycol), the esters formed are not very stable at low pH conditions. We report here the design and synthesis of hematin tethered with methoxypolyethylene glycol amine chains as a novel stable biomimetic catalyst. This one step amidation was performed under solventless conditions and catalyzed by a hydrolase (Novozyme-435). The amidation greatly improved the stability of hematin at low pH. Further, this catalyst was soluble in water and was able to catalyze the polymerization of aniline based monomers. The amide functionalized hematin serves as a robust cost-effective alternative to HRP, active even at lower pH conditions.