Determination of formation constants of cyclodextrin inclusion complexes using affinity capillary electrophoresis

The present study describes the application of the method of affinity capillary electrophoresis (ACE) to investigate interactions between five types of cyclodextrins (CD) and model drugs. While the drugs were injected as sample solution, the effect of different CD types and concentrations in the run buffer was studied. Mathematical models were developed to evaluate the inclusion complex formation constants and the mobilities of the complexes. Further stoichiometric constants were determined, and different models for interpretation of these results were suggested. It was evident that size and hydrophobicity of drugs have a stronger influence on the formation of inclusion complexes than the charge of drugs. β-CD and its derivatives show the strongest interactions with drugs. The handling of the described technique as well as the mathematical description are very simple. The evaluation of the different mathematical models yielded similar results. The use of a nonlinear equation enables an improved fit to experimental data. The present results demonstrate that ACE is valuable as a rapid screening method to characterize inclusion complexes between drugs and CDs. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 215–222, 1999

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