Comparative effect of cyclodextrin nanocavities versus organic solvents on the fluorescence of carbamate and indole compounds

NATALIA L. PACIONI; A. GUILLERMO BRACAMONTE; ALICIA V. VEGLIA

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

Elsevier B.V.

Año: 2008 vol. 198 p. 179 - 185

1010-6030

The effect of the addition of different amounts of organic solvents (S) on the fluorescence of aromatic compounds (C) and their inclusion complexes with -cyclodextrin ( CD) and hydroxypropyl-beta -cyclodextrin (HPCD) has been examined using steady-state measurements. Carbamate pesticides with different aromatic moiety, such as carbofuran (CF), promecarb (PC), carbaryl (CY) and bendiocarb (BC) were used, as well as indole derivatives with different polarity in their lateral chains, such as melatonin (M, neutral), 5-methoxytryptamine (MT, cation) and auxin (IA, anion). Their complexes in water show a fluorescence signal higher than that obtained for the free substrates in solvent:water mixtures (30%, v/v n-propanol or acetonitrile, and 50%, v/vmethanol). The isofluorescent point (IF), the %IF and the F85% are defined in order to evaluate the use of CD nanocavities as a non-polluting alternative for the analysis of the compounds analyzed. Apparent formation constants (KAP, M−1) for the complexes of C:HPCD at different solvent percentages were determined for CF and PC with methanol (MeOH), n-propanol (ProOH) and acetonitrile (ACN), and for indole compounds with ACN. A decrease in the KAP values for the CF:HPCD (120–30) and PC:HPCD (2000–400) complexes occurs in accordance with the solvent affinities for CDs (MeOH< ACN< ProOH). Nevertheless, in the indolic series, the polar characteristics of MT, IA and M determine their behaviour in the presence of ACN. For the neutral substrate M, KAP decreases with the increasing percentage of ACN (100–10). In contrast, for IA and MT (ionic substrates) KAP increases (10–100). These resultsmay be accounted for by two different mechanisms: the competition between C and S for the cavity of the receptor or the formation of ternary complexes C:S:CD with additional stabilization.