A SUPRAMOLECULAR CYTOCHROME-P450 MIMIC

An amphiphilic rhodium(III) complex has been incorporated in closed bi layers of surfactants with positive, zwitterionic, or negative charges . In the presence of formate this rhodium complex efficiently catalyze s the reduction of a variety of electron carriers and manganese(III) p orphyrins. The charge of the surfactant head groups determines the aci dity of the reduced Rh-III hydride complex and the rate of reduction, which increases on going from negatively to positively charged surfact ants. A manganese(III) porphyrin, incorporated in the bilayers togethe r with the Rh complex, can be used as an artificial cytochrome P450-ty pe epoxidation catalyst. The relative concentrations of Mn-II and Mn-I II porphyrin depend on the reduction and reoxidation rates, and an osc illating reaction is observed at a Rh complex/Mn porphyrin ratio of 10 . A variety of substrates are epoxidized by reductive activation of O- 2 by this model system with turnover numbers of the same order of magn itude as those of the enzyme system. The charge on the surfactant has a dramatic effect on the catalytic epoxidation activity of the model s ystem. Aggregates of positively charged surfactant molecules do not di splay catalytic activity in this reaction, probably because the proton s required for cleavage of the oxygen-oxygen bond are repelled at the aggregate surface.