Global and distribution analysis of fluorescence decays and spectrofluorimetric determination of stoichiometry and association constant of the inclusion complex of 2-amino-5,6-dimethyl-benzimidazole with beta-cyclodextrin.

The steady state and time-resolved fluorescence study of 2-amino-5,6-dimethyl-benzimidazole (ADBI) have been studied in aqueous solution of beta-cyclodextrin (beta-CD). The fluorescence decays were analyzed by global analysis and distribution analysis in order to get insight about the inclusion process. The fluorescence lifetime of ADBI is increased in beta-CD and an enhancement of the emission, is observed, together with negligible changes in the energy of ADBI in beta-CD. The experimental data show that beta-CD reacts with ADBI to form a 1:1 host-guest complex with association constant was determined to be 2074+/-77M(-1). Both global analysis and distribution analysis of the fluorescence decays support the formation of only 1:1 inclusion complex. AM1 calculation shows that the size of ADBI was appropriate for good insertion within the beta-CD cavity and the inclusion of ADBI inside the beta-CD cavity should takes place from the side of the amino group substituent.