Direct Electrochemistry and Electrocatalysis of Heme Proteins Entrapped in Agarose Hydrogel Films in Room-Temperature Ionic Liquids

Abstract

The electrochemistry and electrocatalysis of a number of heme proteins entrapped in agarose hydrogel films in the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) have been investigated. UV−vis and FTIR spectroscopy show that the heme proteins retain their native structure in agarose film. The uniform distribution of hemoglobin in agarose−dimethylformamide film was demonstrated by atomic force microscopy. Cyclic voltammetry shows that direct electron transfer between the heme proteins and glassy carbon electrode is quasi-reversible in [bmim][PF₆]. The redox potentials for hemoglobin, myoglobin, horseradish peroxidase, cytochrome c, and catalase were found to be more negative than those in aqueous solution. The charge-transfer coefficient and the apparent electron-transfer rate constant for these heme proteins in [bmim][PF₆] were calculated from the peak-to-peak separation as a function of scan rate. The heme proteins catalyze the electroreduction of trichloroacetic acid and tert-butyl hydroperoxide in [bmim][PF₆]. The kinetic parameter I_max (maximum current at saturation concentration of substrate) and the apparent K_m (Michaelis−Menten constant) for the electrocatalytic reactions were evaluated.