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Abstract
To understand the electron transfer mechanism of cytochrome C in the intermembrane space of mitochondria, two kinds of electrochemical interfaces, single 3-mercaptopropionic acid self-assembled monolayer modified porous gold electrodes and binary 3-mercaptopropionic acid-octadecanethiol self-assembled monolayer modified porous gold electrodes, were constructed. The binary 3-mercaptopropionic acid-octadecanethiol self-assembled monolayer was prepared by the oxidation of the preassembled 3-mercaptopropionic acid self-assembled monolayer coupled with the replacement reaction of octadecanethiol. Atomic force microscopy showed that both interfaces had relatively uniform pores with dimensions of a few nanometers that mimicked the confined environments of cytochrome C in the intermembrane space of mitochondria. The self-assembly of cytochrome C on the two interfaces occurred via electrostatic interactions between the polar amino acid residues of the cytochrome C molecules and the -COOH terminal groups of the self-assembled monolayer. Electrochemical results showed that cytochrome C at the conductive 3-mercaptopropionic acid self-assembled monolayer modified porous gold electrode displayed enhanced electrochemical activity and a faster electron transfer rate when compared to a gold electrode interface. However, the electron transport behavior of cytochrome C was prevented when the insulated octadecanethiol component was in the self-assembled monolayer. This work suggests that the electrochemical behavior of proteins in confined environments differs from the behavior when unconfined.