Stepwise electrocatalytic reduction of nitric oxide by cationic picket-fence porphyrin in an ultrathin phospholipid film

Abstract

The electrochemical reduction of nitric oxide (NO) catalyzed by metal porphyrins as enzyme mimics provides a promising way to understand its roles in biological denitrification. Here, a stepwise electrocatalytic reduction of NO was demonstrated by a cationic picket-fence porphyrin incorporated in an ultrathin phospholipid film. The mass transport-corrected Tafel slopes demonstrated −117 mV/dec and −60 mV/dec for the first and second reduction of NO at physiological pH (pH 7.0), respectively, suggesting a distinguish mechanism for the two-step reduction of NO. More significantly, the potential of the first reduction is constant at −0.37 V vs. NHE while the second potential shifted positively with decreasing pH, giving pH dependence with a slope of −43 mV/pH. A kinetic mechanism of electrocatalytic NO reduction is thus proposed, and provides a promising hint for decoding the functions of the various enzymes. Keywords: Iron porphyrin, Electrocatalysis, Nitric oxide, Kinetic mechanism, Phospholipid