Application of cyclodextrin-mediated capillary electrophoresis to simultaneously determine the apparent binding constants and thermodynamic parameters of naphthalenesulfonate derivatives

Application of capillary electrophoresis (CE) to simultaneously determine the apparent binding constants and thermodynamic parameters for six positional and structural naphthalenesulfonate derivatives with β-cyclodextrin (β-CD) is presented. The change in electrophoresis mobilities was used to assess the binding constants by non-linear regression and three different linear plots methods (named double reciprocal, x-reciprocal and y-reciprocal). The substituent group(s) attached to the naphthalene ring considerably affected the inclusion behaviors of these naphthalenesulfonate derivatives. The binding constant varies over almost one order of magnitude and a highly selective sequence is obtained between these guest model compounds. Naphthalenesulfonates with the substituent(s) at the 2-position(s) displayed stronger interaction with β-CD, and gave well compatible results by these four plot methods. While at least one substituent was substituted into the 1-position of naphthalene showed the weak interaction or no interaction with β-CD. Comparison to three linear regression methods, the non-linear regression method proves to be the most suitable for these determinations. Additionally, apparent binding constants for each structural isomer with β-CD at several temperature, and thermodynamic parameters for binding were also calculated and discussed.