An electrochemical study of mixed solutions of β-cyclodextrin and sodium dodecyl sulfate

Abstract

Abstract The association of β-cyclodextrin with sodium dodecyl sulfate, evidenced by an increase in the critical micelle concentration of SDS, is first studied using conductivity and pNa measurements. The conductivity of the mixed 10 −2 M β-CD/SDS solution at SDS concentrations below the apparent critical micelle concentration is found to depend mainly on the concentration of free sodium counterions and nonassociated amphiphilic ions. The variation of the conductivity with SDS concentration is not uniform and the curve indicates an increase of nonassociated monomer when the SDS concentration reaches 8–9 × 10 −3 M . The two-step oxidation of tetrathiofulvalene (TTF) solubilized in water + 10 −2 M β-CD shows that the diffusion of the probe included in the cavity of the large cycloamylose molecule is about 2.9 times lower than that in water. On the contrary, the diffusion coefficient of the nonassociated radical cation TTF + is equal to that obtained in water; this leads to an enhancement of the second wave with respect to the first, unlike in SDS micelles where the diffusion coefficients of TTF and TTF + are almost equal. The effect of added SDS on the water/β-CD/TTF system is then studied on the basis of the change in potential oxidation and current ratio between the two waves. The results reveal that the release of TTF from cyclodextrin and its subsequent resolubilization in SDS micelles proceed from a saturation effect of the cyclodextrin by amphiphilic monomers.