Enhanced direct electron transfer reactivity of hemoglobin in cationic gemini surfactant–room temperature ionic liquid composite film on glassy carbon electrodes

A novel composite film comprising cationic gemini surfactant butyl-α,ω-bis(dimethylcetylammonium bromide) (C16H33N(CH3)2–C4H8–N(CH3)2C16H33, C16–C4–C16) and ionic liquid 1-octyl-3-methylimidazolium hexafluorophate (OMIMPF6) has been prepared. The composite film shows good biocompatibility and it can promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. On the C16–C4–C16 (dissolved in ethanol)-OMIMPF6 film coated GC electrode, the immobilized Hb can exhibit a pair of well-defined, quasi-reversible and stable redox peaks with a formal potential of −0.317 V (vs SCE) in 0.10 M pH 7 phosphate buffer solutions. The electron transfer coefficient (α) of Hb is calculated to be 0.44 and the heterogeneous electron transfer rate constant is 6.08 s−1. With the length of alkyl chains of gemini surfactant increasing and the ethanol concentration rising, the redox peaks of the resulting electrode C16–C4–C16–OMIMPF6–Hb/GC become bigger. The electrode presents good electrocatalytic response to peroxide hydrogen. The kinetic parameters Imax and km for the catalytic reaction are estimated. In addition, UV–vis spectra and reflectance absorption infrared spectra demonstrate that the Hb immobilized in the C16–C4–C16–OMIMPF6 film almost retains the structure of native Hb.