Coenzyme Models. IX. Micellar Catalysis of Isoalloxazine (Flavin) Oxidation of Dithiol

The influence of micelles on the reaction of isoalloxazines and 1,4-butanedithiol(BDT) was studied. The pKa of BDT was lowered by 0.3 pK unit in the presence of the hexadecyltrimethylammonium bromide(CTAB) micelle, indicating the formation of “hydrophobic ion pairs.” The apparent second-order rate constant for the reaction of 3-methyl-10-ethylisoalloxazine and BDT increased by 18-fold on addition of CTAB(3 mM). The UV-visible spectrum of 3-hexadecyl-10-butylisoalloxazine in the presence of the CTAB micelle was similar to that in organic solvents, the rate being enhanced by more than 400-fold as compared with that in a nonmicellar system. Anionic(SDS) and nonionic(Brij-35) micelles suppressed the reaction. The results show that the flavin oxidation of dithiol is facilitated by the environments of the CTAB micelle.