First spectroelectrochemical experiment

Mamantov et al. (46) studied the oxidation and reduction of sulfur, selenium, and iodine beginning in 1975, and later suggested sulfur (IV) as am oxidant in molten salt batteries. In 1980, Mamantov, Norvell, and Klatt carried out what appear to be the first spectroelectrochemical experiments in chloroaluminate melts using optically transparent electrodes to observe absorption spectra of species formed at the electrode (47). 

Adams prophetic statement did not go unheeded by Kuwana (Figure 1). While still a graduate student, he attempted his first spectroelectrochemical experiment by passing a light beam parallel to the surface of a platinum electrode. Inability to focus... 

The electrogeneration of [(TPP)Co] from (TPP)Co, and the reaction of this species with CHjI can be followed by cyclic voltammetry as shown in Figures lc and Id. In the absence of any added reagent, there are two reversible reduction waves which occur at Ei/2 = 0.85 jind -1.86 V (see Figure lc). These are due to the formation of [(TPP)CoJ and [(TPP)Co]2-, where the second reduction has occurred at the porphyrin ir ring system. The first reduction of (TPP)Co is not reversible in the presence of CH3I, and occurs at Ep = -0.86 V (see Figure Id). A new reversible reduction also appears at Ej/2 = -1.39 V. This process is due to (TPP)Co(CHj) which is formed as shown by Equation 8. The formation of (TPP)Co(CHj) as the final product of the electrosynthesis was confirmed by spectroelectrochemical experiments which were carried out under the same experimental conditions(26). 

A very simple spectroelectrochemical experiment based on a conventional cuvette for UVA is spectroscopy with electrodes immersed in the solution phase is shown in Fig. II.6.4. The optically transparent working electrode is located directly in the beam path and additionally a large surface area counter electrode (Pt wire) and a reference electrode (e.g. a coated silver wire) are located in the solution phase above the beam path. After filling the cuvette with electrolyte solution, the reference spectrum can be recorded taking into account the transparency of the OTE and optical properties of the solution. This reference spectrum is later used to subtract the absorption of the cuvette, the electrolyte, and the OTE from experimental data obtained after applying a potential. Next, the redox reagent is added and the first spectrum of the starting material is recorded. The potential is applied... 

Optical spectra of transferrin C-lobe docked with the transferrin receptor showed a characteristic broad absorption band centred at 465 nm, just as in the receptor-free /zo/o-protein (Figure 2.1 inset). The intensity of this absorbance band declined as more negative potentials were applied in a spectroelectrochemistry experiment, but did not qualitatively change in its overall features. An EPR spectrum of the Fec/TfR complex at pH 5.8, recovered from the OTTLE cell after completion of spectroelectrochemical studies allowed us to conclude that the first coordination shell of Fe " in transferrin is intact and unperturbed when C-lobe is complexed with TfR. Consequently, we assume that C-lobe and Fec/TfR complex have similar if not identical Fe " and Fe binding constants, and so we take for binding of Fe " in the protein-receptor complex to be 10 M as calculated for free Tf. This value was used to correct the observed Nernst plot data by accounting for the dissociation of Fe that occurs upon reduction. Nernst plots for the observed spectroelectrochemical data for FccTf/TfR, and data corrected for Fe dissociation, are presented in Figure 2.7. The corrected plot exhibits typical Nernstian behaviour for a one-electron transfer and a E1/2 value of —285 mV. 

In order to calculate A.I/ I) from the measured PM IRRAS spectra, one has to determine functions J2 and Jq in an independent experiment. A reliable method to measure the PEM response functions was described by Buffeteau et al. [69]. Below we describe a similar method that we adapted with minor changes to use for electrochemical systems [81]. The spectroelectrochemical cell is replaced by the dielectric total external reflection mirror (a Cap2 equilateral prism can be used for this purpose). The second polarizer is inserted just after the PEM and set to admit p-polarized light (identical setting to that of the first polarizer). The PEM is turned off and the reference spectrum is acquired. This spectrum gives the intensity of the p-polarized light Ip (cal), which passes through the whole optical bench. 

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