Cyclodextrins as modifiers of the luminescence characteristics of aflatoxins

Abstract

The fluorescence properties in solution of the four main aflatoxins, B 1, B 2, G 1 and G 2, in the presence of various cyclodextrin derivatives were studied. A preliminary study was made in order to determine the absorbance and fluorescence spectra, relative quantum fluorescence yields (φ F), Stokes shifts, E S1 (0-0) energy levels and low-temperature (77 K) data for these aflatoxins. The effect of cyclodextrins on the fluorescence emission was then investigated. A substantial enhancement of the fluorescence emission of aflatoxins with an unsaturated furan ring (B 1 and G 1) in the presence of aqueous solutions of α,β-heptakis-di- O-methyl-β-cyclodextrin and hydroxypropyl-β-cyclodextrin was observed. Surprisingly, γ-cyclodextrin was inefficient in this respect. Conversely, neither aflatoxin B 2 or G 2, with a saturated furan ring, showed such an interaction and their emission characteristics remained constant in the presence of cyclodextrins. From a mechanistic point of view, the selectivity of the interaction seems to involve partially a non-inclusion process, because of the high molar ratio of cyclodextrin to aflatoxin needed for the fluorescence enhancement. The correlation between the behaviour in the presence of cyclodextrins and the solvent effect on the furan-unsaturated aflatoxins is discussed.