Stoichiometry and association constants of the inclusion complexes of ellipticine with modified β-cyclodextrin

Abstract

Ellipticine is the most representative compound of the small family of pyrido[4,3-b]carbazole alkaloids which exhibit antitumour activity. However, its use is plagued by problems associated with its insolubility in water and with its detection in clinical analysis. As the use of cyclodextrins (CDs) may alleviate these problems, the inclusion complexes obtained from ellipticine and γ-CD as well as a set of complexes with β-CD or modified β-CDs were characterized by means of their stoichiometry and association constants. The stoichoimetry was 1:1 (ellipticine: CD) for complexes with β-CD and modified β-CDs and 1:2 for the ellipticine–γ-CD complex. Association constants were calculated using spectrofluorimetric data. As they depend on the pH of the medium, they were calculated for different pH values (1.0, 9.1 and 13.0). Modified β-CDs together with γ-CD gave the highest association constants. The association constants obtained for cationic and neutral ellipticine with the different β-CDs did not differ significantly. These results might lead to an improvement in the chromatographic analysis and clinical use of ellipticine.