Spectroelectrochemical techniques

Infrared spectroelectrochemical technique proved to be an excellent method to look at time and potential dependent changes of various types of chemical species. The employment of this technique will surely be significant on the mechanistic study of electron-transfer reactions of rhenium complexes. 

Spectroelectrochemistry [3] is the field in which electrochemistry is combined with spectroscopy. Spectroelectrochemical techniques are useful in studying the electrochemical phenomena that occur both in solutions and at electrode surfaces. Here, only the phenomena in solutions are considered. 

We characterized and further studied this basic mechanism of covalent affinity labeling using spectroelectrochemical techniques. The kinetics and stability of quinone oxidation products at high dilution and low pH were consistent with the proposed mechanism, as was the concentration dependence of rapid labeling reactions of the more reactive catechol with the receptor.1215 Spectroelectrochemical and direct cyclic voltametric determination of the half-potentials of the hydroxylated quinones were further consistent with their intermediacy in the labeling reactions of TMC.15 The quinone oxidation products of 4- and 5-HTMC were characterized in part as cyclopentadiene Diels-Alder adducts.15 The instantaneous reactions of these hydroxy TMCs with receptor were consistent with their intermediacy in the TMC reactions. From the concentration dependence of the half-of-sites labeling reactions we could deduce Kd for each isomer fC,(4-HTMC) = 224 98 pM, K/5-HTMC) = 39 17 juM. 

Considerable progress. However, has been achieved in the recent past due to the development of techniques for the detection of intermediates in low concentrations, such as the rotating ring—disc electrode and in situ spectroelectrochemical techniques such as electron spin resonance (ESR). 

The formation of the live-coordinate axial complexes ZnTPP(L) has been studied electro-chemically, and thin-layer spectroelectrochemical techniques have been used to demonstrate the electrochemical and spectrochemical reversibility of the process 1184,1185... 

In situ eiectrolysis-EPR methods usually employ a wire or grid electrode contained in a conventional flat or tube EPR cell. The constraints on the geometric configuration are such that secondary and reference electrodes are usually remote from the generating electrode, which often leads to problems in the control of the potential nevertheless it is a valuable technique for recording spectra of EPR active intermediates. These and related spectroelectrochemical techniques have been reviewed by Robinson.5... 

Figure 3.7 Spectroelectrochemical techniques (A) transmission, (B) internal reflectance, (C) specular reflectance, (D) parallel.

The application of thin-layer spectroelectrochemical techniques to the study of electrode reactions in molten salts is becoming increasingly popular. Experiments have been conducted in both the ultraviolet-visible and infrared spectral regions. Background information about thin-layer spectroelectrochemical techniques is given in Chapter 3. In addition, Norvell and Mamantov [72] have reviewed the application of spectroelectrochemical techniques to molten salts. 

Two of the more common spectroelectrochemical techniques that have been employed for investigations in molten salts are chronoabsorptometry and spectro-... 

Simultaneous application of spectroscopy in voltammetry — Numerous spectroelectrochemical methods employ spectrometers fast enough to acquire complete spectra within seconds or fractions of a second. Acquisition of spectra during a slow electrode potential scan as employed in -> cyclic voltammetry or during single scan voltammetry can thus be related to a single electrode potential (within a range of a few millivolts or even more narrow). Thus interfacial phenomena as detected with the applied spectroelectrochemical technique can be related to the electrode potential directly even in case of unstable intermediates. 

Finally, in proteins with multiple binding sites e.g. transferrin), or in complex protein assemblies with multiple subunits e.g. hemoglobin) there is an opportunity for allosteric interactions between redox-active iron sites. These allosteric interactions are readily probed by the spectroelectrochemical technique, as illustrated in Sections 2.3.2.2 and 2.4.2.3. 

In this chapter we describe the spectroelectrochemical technique as it applies to nonheme and heme iron proteins containing single or multiple iron-binding sites, and as single protein or multiple subunit assemblies. In this discussion, we will address the influence of the following on the spectroelectrochemical... 

The influence of pH on the formal reduction potential was also examined using the spectroelectrochemical technique. The 1/2 value for MHpx at pH... 

Summarising, spectroelectrochemical techniques are ideal for studying mixed-valence intermediates ... 

E. Alessio, S. Daff, M. Elliot, E. lengo, L. A. Jack, K. G. Macnamara, J. M. Pratt and L. J. Yellowlees, Chapter 11, Spectroelectrochemical Techniques in Trends in Molecular Electrochemistry, A. J. L. Pombeiro and C. Amotore (ed.), Fontis Media and Marcel Dekker, Netherlands, 2004. 

V(IV) complexes that are coordinated by six sulfur donor atoms are also known. For example, [AsPh4]2[V(mnt)3] (mnt = maleonitriledithiolate) displays three redox features on cyclic voltammetry, which correspond to the reversible V(V/IV), V(IV/III), and quasireversible V(III/II) couples at 0.17, —0.87, and —2.12 V versus Cp2Fe/CH2Cl2 [55]. The surface normalized incident Fourier transform infrared spectroscopy (SNIFTIRS) spectroelectrochemical technique was used to determine that the extent of tt bonding of the mnt ligand increases as the metal s oxidation state is lowered through examination of the v(CN) frequencies in the various oxidation states. This technique was particularly effective in the determination of the spectral features of the short-lived V(I I) species. 

The final in-situ infrared spectroelectrochemical technique was reported in a preliminary note in 1987 by Roe et al. [121], The paper reported the development of a new design of a spectroelectrochemical cell with a faster response time to enable the recording of transient IR spectra using the recently developed pulsed IR tunable lasers [122], A reflection-absorption spectrum was given of CO adsorbed on Pt at + 0.2 V (vs. SCE) in 1M HC104... 

In-situ spectroelectrochemical techniques are covered by chapters on infrared, Raman EPR, ellipsometry, electroreflectance, and photocurrent spectroscopy. Ex-situ UHV experiments are treated in a separate chapter. New electrochemical directions are described in chapters on hydrodynamic methods, channel electrodes, and microelectrodes. A final chapter covers computing strategies for the on-line accumulation and processing of elec-trochemial data. 

This contains a good overview of spectroelectrochemical techniques. 

One of the main advantages of the optically transparent thin-layer spectroelectrochemical technique (OTTLSET) is that the oxidized and reduced forms of the analyte adsorbed on the electrode and in the bulk solution can be quickly adjusted to an equilibrium state when the appropriate potential is applied to the thin-layer cell, thereby providing a simple method for measuring the kinetics of a redox system. The formal potential E° and the electron transfer number n can be obtained from the Nernst equation by monitoring the absorbance changes in situ as a function of potential. Other thermodynamic parameters, such as AH, AS, and AG, can also be obtained. Most redox proteins do not undergo direct redox reactions on a bare metal electrode surface. However, they can undergo indirect electron transfer processes in the presence of a mediator or a promoter the determination of their thermodynamic parameters can then... 

This section treats the theory of homogeneous mediated bioelectrocatalysis in a quiet solution. An empirical equation explaining the catalytic current is presented, which is conveniently used for the determination of kinetic parameters of the enzyme reaction. A novel method of protein redox potential measurements is also described using a mediated continuous-flow column electrolytic spectroelectrochemical technique. 

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