Surface Enhanced Raman Spectra from Flavins Adsorbed on a Silver Electrode: Observation of unstable semiquinone intermediate

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Ohio State University

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The surface enhanced Raman scattering (SERS) spectroscopy of protein-free flavin in different redox states was investigated at a silver electrode. Good quality SERS spectra of oxidized flavin with an excitation frequency within the flavin absorption band (488 or 514.5 nm) and out of the absorption band (yellow-red region) are reported. Fluorescence interference from the flavin is nearly completely quenched by the surface interaction. The flavin molecules were determined to be bound at the silver surface via its $N_{5}$ and $O_{4}$ atoms based upon the results of $N_{3}-H$ deuterium substiution, effect of pH and electrolyte type on SERS spectra, and the SERS spectral analysis. Reduced flavin did not exhibit a well defined SERS spectrum probably because of the break down of the surface complex. The SERS spectro of neutral semiquinone radical, as an intermediate of the two single electron reduction steps, were observed in acidic solution with yellow or red excitation. This is the first time that the SERS spectroscopic technique has been used for probing the existence of the unstable intermediate species at the electrode surface.


Address of all authors: Department of chemistry, city college of New York, New York, N.Y. 10031
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