SELECTIVE INCLUSION OF METHYLVIOLOGEN BY BETA-CYCLODEXTRIN - EFFECT OF CYCLODEXTRINS ON THE ELECTROCHEMISTRY OF METHYLVIOLOGEN

A study of the electrochemistry of the methylviologen dication (MV2+) in aqueous solution on glassy carbon electrodes in the presence of alpha-, beta and gamma-cyclodextrins (CD) has been carried out. The cyclic voltammograms of MV2+ obtained at low scan rates show irreversible redox behaviour for the MV+/MV0 couple and the peak current ratios are not near to one. The presence of alpha- and gamma-CDs do not greatly affect the redox behaviour. However, on the addition of beta-CD the anodic wave of the second reduction starts to develop and the MV+/MV0 redox becomes reversible in the presence of equimolar beta-CD. The plot of the anodic peak current of both reductions vs. concentration of beta-CD shows a break, revealing the selective formation of a 1:1 inclusion complex of methylviologen with beta-CD. From the values of the ratio of equilibrium binding constants it is inferred that MV+ binds more strongly to beta-CD than either MV2+ or MV0.