Microscale Crystals of Cytochrome c and Calixarene on Electrodes: Interprotein Electron Transfer between Defined Sites

The assembly of redox proteins on electrodes is an important step in biosensor development. Recently, p-sulfonato-calix[4]arene was shown to act as "molecular glue" for the assembly and crystallization of cytochrome c (cyt c). Electrochemical data are presented for microscale cyt c-calixarene crystals grown on self-assembled monolayers (SAM)-modified Au electrodes. The crystals were characterized by cyclic voltammetry and exceptionally high concentrations of electroactive cyt c were obtained. The peak currents were found to increase linearly with the square root of the scan rate, thus allowing an evaluation of the rate constant for electron self-exchange. This study revealed high electroactivity accompanied by fast interprotein electron transfer in crystals, which may have implications for the construction of novel bioelectronic devices.