Surface-Enhanced Vibrational Spectroelectrochemistry: Electric-Field Effects on Redox and Redox-Coupled Processes of Heme Proteins

4 Concluding Remarks

Surface-enhanced vibrational spectroelectrochemistry constitutes a powerful approach for elucidating the reaction mechanisms and dynamics of immobilized redox proteins. In contrast to traditional electrochemical methods, the combination of SERR and SEIRA provides a direct and detailed molecular picture of all potential-dependent processes of the adsorbed species, including those that are non-Faradaic reactions. In this respect, these techniques may gain increasing importance in both fundamental and applied science. On the one hand, a profound knowledge of the molecular structure and dynamics of immobilized proteins and enzymes that can be obtained by these methods is a prerequisite for the rational design of bioelectronic devices of technological importance. On the other hand, surface-enhanced vibrational spectroscopies open new possibilities to study complex biomimetic systems, thereby providing novel insight into fundamental biological processes.

In this contribution we have presented a simple way for studying the influence of electric-fields on the various parameters that control electron-and proton-transfer reactions of soluble and membrane-bound proteins like Cyt-c and CcO. We have shown that electric fields of a magnitude comparable to those at the interfaces of biomembranes, i.e., the natural reaction environment, may have a substantial influence on redox potentials, protein structure, redox-linked conformational changes and orientation/reorientation of electrostatic complexes. These studies do not directly prove a functional role of the electric-field effects in vivo, but they clearly indicate that such effects might be present and deserve further investigation. The application of surfaceenhanced vibrational spectroscopic methods in combination with more realistic model systems appears to be a promising strategy towards that goal.