Use of evolutionary factor analysis in the spectroelectrochemistry of Escherichia coli sulfite reductase hemoprotein and a Mo/Fe/S cluster

The deconvolution of spectroelectrochemical data is often quite difficult i f the spectra of intermediates are not known. Factor analysis, however, has been shown to be a powerful technique which can make it possible to deconv olute overlapping spectra. In this work, evolving factor analysis will be u sed to determine the number of intermediates and the spectra of those speci es for two typical spectroelectrochemical experiments: linear scan voltamme try and chronoabsorptometry in a thin-layer cell. The first system was the reduction of E. coli sulfite reductase hemoprotein (SiR-HP). Principal fact or analysis indicated that three species were present. By using evolving fa ctor analysis, the potential regions where each of the species were present were identified, and their concentrations and spectra were determined by t he use of the mass balance equation. The spectra of the one-electron (SiR-H P1-) and two-electron (SiR-HP2-) reduced product were compared with previou s work. The second experiment was the chronoabsorptometry of Cl2FeS2MoS2FeC l22- in methylene chloride. This experiment indicated that five species wer e present during the experiment. The entire set of 61 spectra were fit by a ssuming that there were 4 species present during the electrolysis. The rate constant for the appearance of subsequent species fit quite well with the rate constant for the disappearance of previous species. The spectra of the intermediates and final product were obtained using evolving factor analys is and a mass balance equation. Identification of the fifth species, which was probably the initial reduction product, Cl2FeS2MoS2FeCl22-, was difficu lt due to its low concentration and the fact that it was present in the sam e time region as the starting material.