The effect of pH on cyclodextrin complexation of trifluoperazine.

The characteristics of host-guest complexation between cyclodextrins (beta-CD, DM-beta-CD, HP-beta-CD) and protonated (pH 1.9, 6.2) or basic (pH 10.2) forms of trifluoperazine (TF) were investigated by spectrometric method. The association constants of complexes obtained at different temperatures and pH were calculated using Scott's equation and the thermodynamic parameters (deltaH, deltaS and deltaG) associated with the inclusion process were determined from Van't Hoff plot. The influence of pH and CD complexation on photostability of TF in solutions of different pH was followed. It was found that the photochemical decomposition of TF alone and in the presence of CD proceeds according to the first order reaction. It was also established that the increase in the TF photostability was dependent on the stability of TF-CD association. Spatial configuration of obtained complexes has been proposed on the basis of 2D NMR technique.