Abstract:

The complexation of six tricyclic antidepressant drugs {[}amitriptylin (AMN), nortriptylin (NRN), imipramin (IMN), doxepin (DXN), protriptylin (PTN), and maprotilin (MPN)] with alpha-and-beta-cyclodextrins (CDs) using ion-selective electrodes (ISEs) as drug ion sensors is described. Binding parameters were calculated by nonlinear fitting of the model described by the Scatchard equation, to the experimental data of a titration of a CD solution with the ion of interest. One binding site (the CD cavity) was found in all cases with both CDs. The calculated association constants at 25-degrees-C using CD concentrations in the range of 0.0100-0.0010 M, varied from 4.81 x 10(3) M-1 (MPN) to 23.9 x 10(3) M-1 (AMN) in the case of beta-CD and from 50 M-1 (DXN) to 123 M-1 (MPN) in the case of alpha-CD. The precision for the estimation of the binding parameters was 0.1-5.0% (within-run RSD%) and 8-10% (between-run RSD%; n = 3). The complexation of the drugs with beta-CD was also examined as a function of temperature in the range of 5-37-degrees-C; it was found to decrease by increasing temperature. Van't Hoff analysis gave good correlations (r greater-than-or-equal-to 0.989) for all drug ions studied. The estimates of the thermodynamic parameters indicate that the formation of inclusion complexes is enthalpy driven. A compensation plot based on the thermodynamic parameters DELTA-H and DELTA-S resulted in a linear relationship, which is indicative of a common type of force involved in the complexation of drugs to beta-CD.