Effects of cyclodextrin complexation on one-electron reduction and electron transfer of aromatic sulfonates

Abstract

Pulse radiolysis of argon-saturated aqueous solutions of sodium biphenyl-4-sulfonate (BPS–Na+) and sodium pyrene-1-sulfonate (PyS–Na+) results in the one-electron reduction of the aromatic moieties of the sulfonates by the hydrated electron to give the radical anions, BPS˙2– and PyS˙2–. The effects of cyclodextrin (CD) complexation of the sulfonates on the reaction rates of the one-electron reduction have been investigated. The rate constants for the one-electron reduction of BPS– and PyS– are significantly reduced by β- and γ-CDs, respectively, through complexation, but are hardly influenced by the other CDs including α-CD. The selective reduction of a mixed sulfonate system has been achieved by using β- and γ-CDs. The electron transfer from BPS˙2– to PyS– is also retarded effectively by the complexation of PyS– with γ-CD. The change in the transient absorption spectrum after the pulse irradiation of the PyS–Na+ solutions containing γ-CD has suggested that the reduced 2:2 complex is unstable and dissociates into the 1 : 1 complexes.