Interacción y detección de sondas fluorescentes con p-sulfonatocalix[8]areno

VEGLIA, ALICIA V

Porto Alegre, Brasil

Conferencia; Programa de pos-Graduación en Química; 2009

Universidad Federal de Río Grande del Sur, Instituto de Química.

In recent years molecular containers have attracted considerable attention owing to theirpotential application in catalysis, stabilization of reactive intermediates, and binding, separation, andsensing of small molecules and ions. Among them, a system of current interest is that formed bycalixarenes (CA) as a result of their intrinsic shape, with makes them versatile receptors for neutraland charged molecules. The CA are basket-shaped metacyclophanes synthesized by condensationof p-alkyl-substituted phenols and formaldehyde in the presence of alkalis. Furthermore, they can befunctionalized by substitution of R by groups such as HSO3-, increasing their water solubility.The CA constituted by eight monomers of 4-hydroxybenzene sulphonic acid is the psulphonatocalix[8]arene (C8S). In this report we evaluate the binding and sensor ability of C8S withorganic compounds with different electronic and structural characteristics such as the fluorescentprobes, methyl orange (MO) and 1-anilino-8-naphtalene sulphonate (ANS), and the benzoimidazolicpesticides, benomyl (BY) and carbendazim (CZ).The spectrophotometric and spectrofluorimetric determinations were carried out at pH= 1.00 and25 ºC in water. The Uv-vis spectra of all substrates did not change in the presence of C8S. A similarbehaviour was observed on the fluorescence of ANS.In the case of MO, fluorescence quenching was produced on the increase of C8S. This effect was rationalized by Stern-Volmer equation given an association constant (KA / M-1) with a value of(32 4) 102, indicating the formation of a 1:1 complex less fluorescent than the free substrate. A similar tendency was found for BY at concentrations of C8S higher than 8 _M. However, in this case, fluorescence enhancement was produced when C8S concentration changes increasedfrom 0 to 8 _M. In this region, from the exponential fitting of the data of fluorescence vs [C8S] it waspossible determine a value of KA = (4 2) 104 M-1 and a fluorescence quantum yield ratio betweenthe complex and the free substrate (c/f) of 3.1 0.7, indicating the ability of C8S as nanosensor. Inaddition, the 1:1 stoichiometry was confirmed with a molar ratio plot. Similar results were found forCZ.We will discuss the differences observed on the basis of the nature of the interactions producedbetween each substrates and C8S and we will compare them with previous results with C6S.