Effects of hydrophilic room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate on direct electrochemistry and bioelectrocatalysis of heme proteins entrapped in agarose hydrogel films

The effects of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) on direct electrochemistry and bioelectrocatalysis of hemoglobin (Hb), myoglobin (Mb), and catalase (Cat) entrapped in agarose hydrogel films were investigated. A small amount of water in [bmim][BF4] is necessary to maintain the electrochemical activities of these heme proteins. The direct electron transfer between heme proteins and glassy carbon electrode (GC) is a surface-confined quasi-reversible process, corresponding to heme Fe(III) + e → heme Fe(II). Several electrochemical parameters of these processes, such as the charge-transfer coefficient (a) and the apparent electron transfer rate constant (ks), were calculated by nonlinear regression analysis of square wave voltammetry (SWV) experimental data. Furthermore, highly electrocatalytic activities of the heme protein–agarose films toward hydrogen peroxide (H2O2) were observed, indicating that heme proteins entrapped in agarose films retained their bioelectrocatalytic activities in [bmim][BF4] solution. The apparent Michaelis-Menten constant (Kmapp) of Mb for H2O2 was evaluated to be 5.93 × 10−4 mol L−1. The catalytic reduction peak current is directly proportional to the concentration of H2O2 between 1.28 × 10−6 mol L−1 and 7.08 × 10−4 mol L−1. Experiments for Hb and Cat received similar results.