Conductivity and Surface Tension Study for Cucurbit[7]uril Inclusion Complex of Cetyltrimethylammonium Chloride in Aqueous Solution

Abstract

Conductivity and surface tension measurements have been carried out at temperatures between 298.15 K for cetyltrimethylammonium Chloride (CTAC) + H₂O and CTAC + Cucurbit[7]uril (CB[7]) + H₂O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the hydrophobic contribution of the transfer free energy for the hydrocarbon chain of CTAC, the stoichoimetry and inclusion constants for the inclusion complex of CTAC with CB[7] have been determined. The influence of CB[7] and its complex on the micellization processes of CTAC is analyzed. It is shown that CB[7] partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium, and retarded the formation of CTAC micelles in a certain extent. CB[7] and the inclusion complex do not have any surface activity. The CB[7] and its complexes do not participate the formation of micelles of CTAC, and the complex has no effect on the micelle properties once the micelles are formed. The result suggests that β-CB[7] forms strong complex with CTAC, and the stoichoimetry is found to be 1:1, and the inclusion constants of CB[7]-CTAC complex are almost the same in different CB[7] solutions.

Keywords:

• Cetyltrimethylammonium chloride
• conductivity
• cucurbit[7]uril
• micellization
• stoichoimetry
• surface tension

This work was financially supported by the National Natural Science Foundation of China (Grant No. 20703023 and 20963007), the Natural Science Foundation of Jiangxi Province (Grant No. 2007GQH2100), and the Science Research Program of the Education Department in Jiangxi Province (Grant No. [2007] 14).