MODIFIED BETA-CYLCLODEXTRINS AS ENHANCERS OF FLUORESCENCE EMISSION OFCARBAZOLE ALKALOID DERIVATIVES

Experimental conditions for formation of inclusion complexes between c arbazole and ellipticine and several cyclodextrins (CDs): beta-cyclode xtrin( beta-CD), hydroxypropyl beta-cyclodextrin (HP beta-CD), (2,6-di -O-methyl)-beta-cyclodextrin (DM beta CD), (2,3,6-tri-O-methyl)-beta-c yclodextrin (TM beta-CD) and gamma-cyclodextrin (gamma-CD), are descri bed. A notable increase of fluorescence intensity of the host molecule s is observed upon complexation, attributed to protection of the excit ed state within the cyclodextrin cavity. This allows the quantitation of both compounds in aqueous media in concentration levels of 10(-7) M to 10(-6) M. Inclusion also affects the deprotonation equilibrium of the pyrrolic nitrogen of both compounds. Thus, beta-CD facilitates the deprotonation of carbazole while HP beta-CD, DM beta-CD, TM beta-CD a nd gamma-CD make it more difficult. Similar observations were made for ellipticine, although its behaviour was more complex because of the c oexistence of two ionization equilibria owing to the presence of a bas ic pyridine-like nitrogen. Finally, the effect of cyclodextrins on flu orescence quenching caused by heavy halogen atoms was also studied. In the case of carbazole, a static quenching was observed, which is prev ented by modified beta-CDs. In the case of ellipticine, the quenching effect was related to acid-base equilibria, and therefore it has been studied under acidic (lambda(ex) = 305 nm, lambda(em) = 520 nm) and ba sic (lambda(ex) = 292 nm, lambda(em) = 430 nm) conditions.