How does β-cyclodextrin affect oxygen solubility in aqueous solutions of sodium perfluoroheptanoate?

The solubility of oxygen in aqueous solutions of sodium perfluoroheptanoate (NaPFHept) at different concentrations was measured at 310.15 K with an apparatus based on the saturation method. The effect of adding beta-cyclodextrin (beta CD) on the solubility of oxygen was also studied. Conductimetry measurements showed that the presence of CD in aqueous solutions of NaPFHept increases its critical micellar concentration (CMC). In the presence of beta CD (15 mM), the characteristic minimum of oxygen solubility observed at the CMC is shifted from 83 to 114 mM, and the curvature at the minimum is reduced to 64% of the value in the absence of beta CD. Chemical shift changes for the H5 protons of CD, recorded as functions of the initial concentration of NaPFHept, point to the formation of a relatively strong 1:1 inclusion in CD of the perfluoroheptanoate anion. Hence, it is suggest that the effect of adding CD on the solubility of oxygen cannot be accounted for only by the perfluoroheptanoate anion inclusion in CD, but has to be ascribed to the direct influence of this inclusion complex on disrupting the aggregation process reducing the increase of oxygen solubility after the CMC value. (c) 2006 Elsevier Inc. All rights reserved.