Spectroelectrochemistry of Proteins

Abstract

This mini review addresses the evolution of spectroelectrochemistry from the laboratories of Professor Theodore Kuwana into the examination of proteins. Synchronizing electrochemical and spectral properties of proteins enables the identification of functions of redox centers, and their kinetics and thermodynamics. Changes in conformation and redox states are examined by a variety of spectroscopic techniques by directly observing protein reactions at electrodes with modified surfaces.

Spectroelectrochemistry Using Optically Transparent Electrodes – Ted Kuwana and the Early Years

“…The article by George Wilson in this issue links the pioneering work described here by Kuwana and his groups with subsequent research milestones leading to our contemporary understanding of redox proteins [35].…”

Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy

“…Monitoring of electrochemical processes can be obtained by so-called operando approaches. Such methods are established in electrocatalysis, battery, and bioelectrochemistry research, and they describe the spectroscopic or microscopic monitoring of electrochemical processes under operational conditions. − Among them, spectroelectrochemistry relies on the optical transparency of the working electrode, and with the implementation of ITO electrodes, this method was commenced to study redox-active proteins about 60 years ago . Up to now, the operando combination of electrochemistry and spectroscopic ellipsometry is rather rarely applied, possibly due to the challenges of optical modeling and the limitations of continuous and reasonably smooth layers. − Nonetheless, ellipsometry is a powerful tool to obtain both the dielectric optical response function (i.e., complex refractive index) of thin films as well as the electric properties for Drude-like behavior, which apply well to ITO thin films. − Furthermore, ellipsometry is a sensitive probe to monitor the adsorption of ultrathin layers at solid–liquid interfaces such as self-assembled monolayers and biomolecules. − Even specific immobilization of biomolecules and cells at functionalized hybrid interfaces for biosensing purposes can be traced. − More specifically, operando ellipsometry allows to study reversible ion intercalation processes upon electrochemical cycling in battery-related research. − For spatially resolved investigation, operando imaging ellipsometry is an emerging probe for battery electrodes, and it provides insights by monitoring the local change of ellipsometric parameters at selected wavelengths. , …”

“… 37 − 46 Among them, spectroelectrochemistry relies on the optical transparency of the working electrode, 47 and with the implementation of ITO electrodes, this method was commenced to study redox-active proteins about 60 years ago. 48 Up to now, the operando combination of electrochemistry and spectroscopic ellipsometry is rather rarely applied, possibly due to the challenges of optical modeling and the limitations of continuous and reasonably smooth layers. 49 − 56 Nonetheless, ellipsometry is a powerful tool to obtain both the dielectric optical response function (i.e., complex refractive index) of thin films as well as the electric properties for Drude-like behavior, which apply well to ITO thin films.…”

Spectroelectrochemistry for determination of the redox potential in heme enzymes: Dye-decolorizing peroxidases

“…Determination of E°' Fe(III)/Fe(II) of heme proteins can be performed by i) chemical redox titrations (sometimes referred to as potentiometric titrations in the literature), in which stepwise chemical reduction or oxidation of the protein in solution is monitored by spectroscopic changes of the heme group; the most commonly used methods are UV–Visible [ 11 , 12 ], electron paramagnetic resonance (EPR) [ 13 ], nuclear magnetic resonance (NMR) [ [14] , [15] , [16] ], resonance Raman (RR) [ 17 ], Magnetic Circular Dichroism (MCD) [ 18 ], and to a lower extent Infrared (IR) spectroscopies [ 19 ]; ii) electrochemical methods, such as cyclic voltammetry (CV), in which the current changes due to protein oxidation / reduction are monitored as the electrode potential is swept upward or downward across the protein's E°' [ 20 , 21 ]; and iii) spectroelectrochemical methods, in which spectroscopic changes (most commonly UV–Vis, IR and surface-enhanced RR (SERR)) of the protein are monitored along an electrochemical redox titration. The spectroelectrochemical methods enable the identification of electroactive species of interest and simultaneously provide information about their molecular structure in situ [ [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] ].…”