Spectroelectrochemistry methods

While the redox titration method is potentiometric, the spectroelectrochemistry method is potentiostatic [99]. In this method, the protein solution is introduced into an optically transparent thin layer electrochemical cell. The potential of the transparent electrode is held constant until the ratio of the oxidized to reduced forms of the protein attains equilibrium, according to the Nemst equation. The oxidation-reduction state of the protein is determined by directly measuring the spectra through the tranparent electrode. In this method, as in the redox titration method, the spectral characterization of redox species is required. A series of potentials are sequentially potentiostated so that different oxidized/reduced ratios are obtained. The data is then adjusted to the Nemst equation in order to calculate the standard redox potential of the proteic species. Errors in redox potentials estimated with this method may be in the order of 3 mV. 

Refs. [i] Hamberg I, Granqvist CG (1986) / AppI Phys 60-.R123 [ii] Granqvist CG, Hultaker A (2002) Thin Solid Films 411 1 [iii] Mortimer R) (1999) Electronic spectroscopy Spectroelectrochemistry, methods and instrumentation. In Lindon JC, Tranter GE, Holmes ]L (eds), Encyclopedia of spectroscopy and spectrometry. Academic Press, London, pp 2174-2181 jivj Bard AJ, Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, Chap. 17... 

Infrared spectroelectrochemical methods, particularly those based on Fourier transform infrared (FTIR) spectroscopy can provide structural information that UV-visible absorbance techniques do not. FTIR spectroelectrochemistry has thus been fruitful in the characterization of reactions occurring on electrode surfaces. The technique requires very thin cells to overcome solvent absorption problems. 

K. Itaya, T. Ataka, and S. Toshima, Spectroelectrochemistry and electrochemical preparation method of... 

The electrosynthesized (0EP)Ge(CgHs)C10, was characterized in situ by thin-layer spectroelectrochemistry. The final product of electrosynthesis was spectrally compared with the same compounds which were synthesized using chemical and photochemical methods(35). (0EP)Ge(C6H5)Ci and (0EP)Ge(CsHs)0H were also electrochemically generated by the use of specific solvent/supporting electrolyte systems(35). 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

Although the instrumental techniques described here give detailed mechanistic information, they do not provide an insight into the structure of intermediates. If we, however, combine electrochemical and spectroscopic methods, this is advantageously accomplished (spectroelectrochemistry) [73]. Various spectroscopies have been coupled with electrochemical experiments, among them ESR [74], optical [75], and NMR spectroscopy [76, 77], as well as mass spectrometry [78, 79]. 

The two reviews, Spectroelectrochemistry Applications and Spectroelectro-chemistry Methods and instrumentation , both by Mortimer, R. J., appear in The Encyclopedia of Spectroscopy and Spectrometry, Lindon, J. C., Trantor, G. E. and Holmes J. L. (Eds), Academic Press, London, 2000, pp. 2161-2174 and 2174-2181, respectively, and give excellent coverage of this combined spectroscopic and electrochemical technique. 

Combination of Electrochemical and Nonelectrochemical Techniques 271 Spectroelectrochemistry 271 Electrochemical-ESR Method 276 Electrochemical Mass Spectroscopy 279... 

Electron spin resonance and electrochemistry Spectroelectrochemistry— transparent electrodes Digital simulation methods in electrochemistry... 

In general, the redox potential data for Compound I and Compound II is unavailable. Direct methods such as cyclic voltammetry cannot be used due to the short lifetime of the activated intermediates and irreversibility of the reactions to generate them. The methods that may be found in the literature to estimate redox potential of the catalytic species, Compound I and Compound II, are redox titrations [64, 97, 98], spectroelectrochemistry [99], and catalytic-based estimation [53]. 

The chemical stability and electrochemical reversibility of PVF films makes them potentially useful in a variety of applications. These include electrocatalysis of organic reductions [20] and oxidations [21], sensors [22], secondary batteries [23], electrochemical diodes [24] and non-aqueous reference electrodes [25]. These same characteristics also make PVF attractive as a model system for mechanistic studies. Classical electrochemical methods, such as voltammetry [26-28] chronoamperometry [26], chronopotentiometry [27], and electrochemical impedance [29], and in situ methods, such as spectroelectrochemistry [30], the SECM [26] and the EQCM [31-38] have been employed to this end. Of particular relevance here are the insights they have provided on anion exchange [31, 32], permselectivity [32, 33] and the kinetics of ion and solvent transfer [34-... 

Feb. 28,1934, Camden, NJ, USA - Mar. 3,2003, Cincinnati, OH, USA) Mark received a B.A. in chemistry from the University of Virginia and a Ph.D. from Duke University. He was postdoc at the University of North Carolina and at the California Institute of Technology. After a faculty position at the University of Michigan he served from 1970 until his death as Professor in the Chemistry Department of the University of Cincinnati. Mark was electrochemist and analytical chemist. His major contributions concern spectroelectrochemistry and conducting polymer electrodes. He was among the pioneers of kinetic methods of analysis. His scientific work is documented in over 300 publications and 14 books which he either has written or edited. 

The time range of the electrochemical measurements has been decreased considerably by using more powerful -> potentiostats, circuitry, -> microelectrodes, etc. by pulse techniques, fast -> cyclic voltammetry, -> scanning electrochemical microscopy the 10-6-10-1° s range has become available [iv,v]. The electrochemical techniques have been combined with spectroscopic ones (see -> spectroelectrochemistry) which have successfully been applied for relaxation studies [vi]. For the study of the rate of heterogeneous -> electron transfer processes the ILIT (Indirect Laser Induced Temperature) method has been developed [vi]. It applies a small temperature perturbation, e.g., of 5 K, and the change of the open-circuit potential is followed during the relaxation period. By this method a response function of the order of 1-10 ns has been achieved. 

Spectroelectrochemistry — Many - electrode processes are complex and difficult to study quantitatively and unambiguously. The current signal from voltammetric experiments provides only very limited structural information about reaction intermediates at surfaces or in solution. In order to improve the level of quantitative and structural information available from electrochemical experiments, spectroscopic techniques are directly (or in situ ) coupled to electrochemical methods [i, ii]. 

Ref [i] Holze R (2008) Surface and interface analysis an electrochemists toolbox. Springer, Berlin [ii] Neudeck A, Marken F, Compton RG (2005) UV/Vis/NIR spectroelectrochemistry. In Electroanalytical Methods. Scholz F (ed), Springer, Berlin, pp 167... 

We find LSV to be the kinetic method which gives the most detailed information related to the mechanism of the reaction of the intermediate. As will be discussed in some detail later, the reaction orders in all species appearing in the rate law can be derived from the LSV response (Parker, 1981f). The reaction orders in substrate and primary intermediate are not directly separable using the data from the other techniques. Because of the possibility of obtaining homogeneous relaxation data in addition to the direct response, spectroelectrochemistry can offer more kinetic detail than the other direct techniques. 

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