Studies of Biological Redox Systems by Thin-Layer Electrochemical Techniques

Abstract

Thin-layer electrochemical techniques were developed for measuring E°' and n-values of biological redox systems. A spectropotentiostatic method combines optical measurements of the biocomponent with potential control of a thin solution layer. Coupling of the biocomponent to the electrode potential is achieved by chemical modification of the electrode or by addition of a mediator-titrant. The temperature dependence of E°' is determined easily. This condition is exemplified by cytochrome c for which measurements were sufficiently precise to resolve a nonlinear behavior in the E°' temperature dependence. Biocomponents with no observable optical properties can be studied by thin-layer pulse coulometry and thin-layer staircase coulometry. In these techniques, E°' and n are determined by measuring charge as a function of potential. The activity of galactose oxidase was measured while simultaneously controlling its oxidation state. The oxidation state is controlled by a gold electrode (coupled with ferricyanide as a mediator-titrant) in a thin-layer cell with a peroxide electrode inserted in one side. The relative activity of the enzyme is monitored by measuring peroxide production from the enzyme-catalyzed reaction of substrate. Thin-Layer Cells

Long Optical Path Length Cell for Thin-Layer Spectroelectrochemistry

“…Equilibrium Redox Studies. One of the most used applications of thin-layer spectroelectrochemical cells is the determination of E °‘ and the stoichiometry, n , of redox reactions. ,,, These determinations take advantage of the rapid establishment of the redox equilibrium for a solution species confined in the thin-layer cavity with E appl . Using the absorbance of ferricyanide to calculate the relative amounts of the oxidized and reduced forms of the redox couple as a function of E appl , − the values of the slope and y -intercept of a plot of E appl vs log({Fe(CN) 6 4- }/{Fe(CN) 6 3- }) can be used to determine the respective values of n and E °'.…”

“…Recent studies have exploited the advantages of thin-layer spectroelectrochemistry in explorations of a variety of heterogeneous and homogeneous electrochemical processes. − In many instances, optical monitoring is accomplished by irradiating the solution confined in the thin-layer cavity with the propagation axis of the optical beam parallel to the electrode/solution interface. − ,− ,,, The configuration of such long optical path length thin-layer spectroelectrochemical cells (LOPTLCs) yields path lengths of ∼1 cm. These path lengths result in an enhancement in sensitivity of ∼100-fold over that generally achieved using conventional thin-layer cells and optically transparent electrodes that have path lengths of ∼100 μm.…”

In situ Time-Resolved Spectroelectrochemistry Reveals Limitations of Biohybrid Photoelectrode Performance

“…Absorbance spectroscopy offers a tool to probe electron transfer, 9 and has been applied to electrochemical systems for many decades. 10,11 For example, transient absorption spectroscopy of dye-sensitized solar cells has revealed the kinetics of electron injection, 10,12 resolved reaction mechanisms 13 and reaction intermediates, 14 and has been used to characterize loss processes such as charge recombination. 15,16 Additionally, extensive transient absorption measurements have been applied RCs suspended in solution, revealing the mechanisms of charge separation and stabilization of the charge separated state that underpin high quantum efficiencies (see supplemental information for details).…”

Thin-layer spectroelectrochemical cell

“…where t' is the hypothetical origin for the current-time curve (in the linear sweep experiment scale) which matches the diffusion part of the stationary electrode voltammogram. In particular, with reference to Figure 1, this equation will be obeyed by the current ¿x, recorded at the switching potential Ex, as well as by the current ¿x relative to the potential EK chosen in such a way that E* ~ ~~Epb (2) This last current represents the actual contribution of the forward process at Epb and hence it must be added to (tpb)°f or a correct computation of the peak-current ratio íph/ " K¿pb) "t ¿x|/¿pf…”