Bioelectrocatalytic Reduction of Oxygen by Hemoglobin-Adsorbed Carbon-Felt, and its Inhibition by Azide

Abstract

Hemoglobin (Hb) was adsorbed onto a carbon-felt (CF), which is a microelectrode ensemble of microcarbon fiber (ca. 7 µm diameter) and possesses a random three-dimensional structure. Direct electron transfer between Hb heme and the CF was achieved without any electron mediating species and special materials. The Hb-adsorbed CF (Hb-CF) showed a pair of well-defined cyclic voltammetric peaks with the formal potential of −0.221 V (vs. Ag/AgCl) at pH 5.0 (0.1 M phosphate/citrate buffer), which is attributed to Hb Fe(III)/Fe(II) redox couple. The apparent heterogeneous electron-transfer rate constant (k s ) was estimated to be 14.6 s −1 . Furthermore, the Hb-CF exhibited an excellent bioelectrocatalytic activity for the reduction of O 2 . This bioelectrocatalytic activity was inhibited by azide, which binds to active heme center of Hb.