Micelle-Enhancing Effect on a Flavin-Photosensitized Reaction of Benzyl Alcohols in Aqueous Solution

Abstract

The tetra-O-acetylriboflavin (Fl)-photosensitized dehydrogenation of benzyl alcohols 1 proceeded more efficiently in aqueous solutions in the presence of sodium dodecyl sulfate (H₂O/SDS) than acetonitrile solutions. The fluorescence quenching of Fl with 1 occurred efficiently in H₂O/SDS. The apparent rate constants (k_Q) for the fluorescence quenching were determined by Stern–Volmer plots. The plots of k_Q vs the free-energy changes for the electron transfer from 1 to the excited singlet of Fl showed the Rehm–Weller-type correlation. However, plots for H₂O/SDS were deviated from a curve calculated by the Rehm–Weller equation, although plots for MeCN were fitted to the calculated curve. The deviation in H₂O/SDS is attributable to the incorporation of Fl and 1 into the hydrophobic domain of the SDS micelle, where the condensation, less-polar medium, and exteior negative charge operate favorably for efficient electron transfer.