Spectroelectrochemistry principles

We can deduce the meaning of the word spectroelectrochemistry by dissecting it piece by piece. Spectroelectrochemistry follows an electrochemical process by the use of electromagnetic radiation (hence spectra- ). In principle, any form of spectroscopy can be used to follow the progress of an electrode reaction, but in practice we tend to concentrate on two, namely UV—visible ( UV—vis ) spectroscopy and a form of microwave spectroscopy known as electron paramagnetic resonance (EPR), as described below. 

Optical Spectroscopy General principles and overview, 246, 13 absorption and circular dichroism spectroscopy of nucleic acid duplexes and triplexes, 246, 19 circular dichroism, 246, 34 bioinorganic spectroscopy, 246, 71 magnetic circular dichroism, 246, 110 low-temperature spectroscopy, 246, 131 rapid-scanning ultraviolet/visible spectroscopy applied in stopped-flow studies, 246, 168 transient absorption spectroscopy in the study of processes and dynamics in biology, 246, 201 hole burning spectroscopy and physics of proteins, 246, 226 ultraviolet/visible spectroelectrochemistry of redox proteins, 246, 701 diode array detection in liquid chromatography, 246, 749. 

The following chapters are devoted to single methods or to closely related families of methods. A brief overview, including some joint features of a given method, will precede the description of the individual techniques. The principle of organization of methods and techniques is a common feature. These are either probes shared by several techniques or particular surface/interphase properties studied with the methods. An introduction to spectroelectrochemistry in molecular inorganic chemistry is available [128]. 

The principles that govern infrared spectroelectrochemistry have been reported in a number of papers. This chapter highlights recent progress and discusses spectroscopic instrumentation and measurement concepts that have received little coverage in previous reports. Applications in the study of molecules on well-defined surfaces, bimetallic alloys, and nanoparticle catalysts are described. 

The second section of this volume is concerned with electroanalytical techniques, starting with the principles of standard voltammetric and amperometric methods, then progressing to more specialized, but equally important, experimental approaches that can provide major insights into electrochemical processes. Finally, the last section of this volume focuses on spectroelectrochemistry and surface microscopy techniques. 

The measurements of electrochemical impedance, voltammetric (po-larographic) analysis, and spectroelectrochemistry represent a basis for analysis of molecules of biological significance in bulk of solution and at interfaces. These principles are reviewed in the first four chapters. The next three chapters demonstrate how these principles are utilized in voltammetric and interfacial analysis of biomacromolecules such as nucleic acids, proteins, polysaccharides, and viruses in vitro, in the development of biosensors with electrochemical transducers and in in vivo voltammetry. The last two chapters of this volume are devoted to the principles of electrophoresis used for separation analysis of biomolecules and to the theoretical principles and practical description of the patch-clamp technique to an extent suitable for those wishing to initiate research in electrophysiology. 

IR spectroelectrochemistry has been the subject of a sizeable amount of early reviews, where the experimental details and applications have been described [5-7]. Regardless the fact that electrochemistry is an extremely broad field, the following discussion will be restricted to classical electrochemical systems where a solid electrode is in contact with a liquid electrolyte solution which may contain electroactive species. Since the typically used electrolyte solutions (mostly aqueous solutions) are strongly IR absorbing, it is not possible to use a standard laboratory electrochemical cell, but for spectroelectrochemical experiments, special cell designs and beam paths have to be employed. There are two general principles on how the IR beam is directed to the electrode surface called internal reflection and external reflection, respectively. 

Spectroelectrochemistry encompasses a group of techniques that allow simultaneous acquisition of electrochemical and spectroscopic information in situ in an electrochemical cell. A wide range of spectroscopic techniques may be combined with electrochemistry, including electronic (UV-visible) absorption and reflectance spectroscopy, luminescence spectroscopy, infrared and Raman spectroscopies, electron spin resonance spectroscopy and ellipsometry. Molecular properties such as molar absorption coefficients, vibrational absorption frequencies and electronic or magnetic resonance frequencies, in addition to electrical parameters such as current, voltage or charge, are now being used routinely for the study of electron transfer reaction pathways and the fundamental molecular states at interfaces. In this article the principles and practice of electronic spectroelectrochemistry are introduced. 

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