Modified β-cylclodextrins as enhancers of fluorescence emission of carbazole alkaloid derivatives

✍ Scribed by M. Sbai; S.Ait Lyazidi; D.A. Lerner; B. del Castillo; M.A. Martin

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 769 KB
• Volume: 303
• Category: Article
• ISSN: 0003-2670
• DOI: 10.1016/0003-2670(94)00475-2

✦ Synopsis

Experimental conditions for formation of inclusion complexes between carbazole and ellipticine and several cyclodextrins (CDs): /3-cyclodextrin ( p-CD), hydroxypropyl B-cyclodextrin @@CD), (2,6-di-O-methyl)-P-cyclodextrin (DM p-CD), (2,3,6-t&0-methyl)-&cyclodextrin (TMP_CD) and -y-cyclodextrin (YCD), are described. A notable increase of fluorescence intensity of the host molecules is observed upon complexation, attributed to protection of the excited state within the cyclodextrin cavity. This allows the quantitation of both compounds in aqueous media in concentration levels of 10e7 M to 10e6 M. Inclusion also affects the deprotonation equilibrium of the pyrrolic nitrogen of both compounds. Thus, P-CD facilitates the deprotonation of carbazole while HPfi-CD, DMPCD, TM@CD and y-CD make it more difficult. Similar observations were made for ellipticine, although its behaviour was more complex because of the coexistence of two ionization equilibria owing to the presence of a basic pyridine-like nitrogen. Finally, the effect of cyclodextrins on fluorescence quenching caused by heavy halogen atoms was also studied. In the case of carbazole, a static quenching was observed, which is prevented by modified /~-CDS. In the case of ellipticine, the quenching effect was related to acid-base equilibria, and therefore it has been studied under acidic (A,, = 305 nm, A,, = 520 nm) and basic (A,, = 292 nm, A,, = 430 nm) conditions.