Catalyses by polymer complexes. Part 3. Polymer micellar catalysis of isoalloxazine (flavin) oxidation of thiols

Abstract

The effect of cationic polymer micelles on the isoalloxazine (flavin) oxidation of thiols is reported: the polymers employed were poly-(2-ethyl-1-vinylimidazole) quaternized with ethyl bromide and lauryl bromide [lauryl group content: 8.8 mol %(L-9), 28.9 mol %(L-29), and 40.9 mol %(L-41)]. Addition of L-29 and L-41 polymers caused a red shift of the u.v. absorption maximum of thiophenoxide ion and an increase in its acid dissociation constant, while L-9 polymer scarcely affected these values. Under anaerobic conditions, the oxidation of thiophenol and 2-mercaptoethanol by 10-ethyl-3-methylisoalloxazine in the presence of micelle-like polymers (L-29 and L-41) was 10²–10⁵ times faster than the corresponding reaction in a non-polymeric system, whereas L-9, a polyelectrolyte-like polymer, produced almost no acceleration. The thiolate anion bound to the polymer domain is activated probably due to the formation of a hydrophobic ion pair. On the other hand, the oxidation of butane-1,4-dithiol was not much affected by the polymer micelle. The difference in mechanism of dithiol oxidation is discussed in connection with the microenvironmental effect.