BINDING AND SENSING OF FLUORESCENT PROBES BY p-SULPHONATOCALIX(8)ARENE

VALERIA N. SUELDO OCCELLO; GUADALUPE G. MIÑAMBRES; GRACIELA FORTUNATO; MARCIO LAZZAROTTO; ALICIA V. VEGLIA

Florianópolis, SC, Brazil

Congreso; the 10th Latin American Conference on Physical Organic Chemistry (CLAFQO-10); 2009

CLAFQO

In recent years molecular containers have attracted considerable attention owing to their potential application in catalysis, stabilization of reactive intermediates, and binding, separation, and sensing of small molecules and ions. Among them, a system of current interest is that formed by calixarenes (CA) as a result of their intrinsic shape, with makes them versatile receptors for neutral and charged molecules. The CA are basket-shaped metacyclophanes synthesized by condensation of p-alkyl-substituted phenols and formaldehyde in the presence of alkalis. Furthermore, they can be functionalized 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 with organic compounds with different electronic and structural characteristics such as the fluorescent probes, methyl orange (MO) and 1-anilino-8-naphtalene sulphonate (ANS), and the benzoimidazolic pesticides, benomyl (BY) and carbendazim (CZ). The spectrophotometric and spectrofluorimetric determinations were carried out at pH= 1.00 and 25 ºC in water. The Uv-vis spectra of all substrates did not change in the presence of C8S. A similar behaviour 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) 10(2), 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 µM. However, in this case, fluorescence enhancement was produced when C8S concentration changes increased from 0 to 8 µM. In this region, from the exponential fitting of the data of fluorescence vs [C8S] it was possible determine a value of KA = (4 ± 2) 10(4) M(-1) and a fluorescence quantum yield ratio between the complex and the free substrate (φ c /φ f ) of 3.1 ± 0.7, indicating the ability of C8S as nanosensor. In addition, the 1:1 stoichiometry was confirmed with a molar ratio plot. Similar results were found for CZ. We will discuss the differences observed on the basis of the nature of the interactions produced between each substrates and C8S and we will compare them with previous results with C6S.