Voltammetry of Viologens Revealing Reduction of Hydrophobic Interaction in Frozen Aqueous Electrolyte Solutions

Abstract

AbstractVoltammetry of viologens, methylviologen (MV2+) and benzylviologen (BV2+) in frozen aqueous solutions reveals that freezing suppresses the hydrophobic interactions. Reduced viologen species (MV0 or BV+.), which have intrinsically poor solubility in water, give sharp adsorption peaks in cyclic voltammograms. Freezing makes the peaks broader and peak broadening increases with decreasing the liquid phase volume in a frozen solution. This obviously indicates that the surface wave is transferred into the usual diffusion controlled wave. Thus, the interaction between adsorbates is weakened by freezing. In addition, freezing reduces the complexation constant of β‐cyclodextrin (β‐CD) with MV0 but slightly enhances that with BV+.. This is also interpreted as the suppression of the hydrophobic interactions in the frozen concentrated solution.