“Supramolecular chemistry: calixarenes vs cyclodextrins. Analytical applications”

NATALIA L. PACIONI,; A. GUILLERMO BRACAMONTE,; VALERIA N. SUELDO OCCELLO,; ALICIA V. VEGLIA

Los Cocos, Cordoba, Argentina

Congreso; IX Conferencia Latinoamericana de Fisico-quimica Organica; 2007

Facultad de Ciencias Químicas. U.N.C.

  Individual host molecules possessing an intrinsic cavity are termed cavitands. Inclusion of guest species within a cavitand results in a host-guest complex. The formation of host-guest complexes generally changes the physicochemical properties of the binding analyte. Detection methods based on changes in UV-vis absorbances or on fluorescence emissions have a broad applicability. These techniques are of particular promise for sensor technology.  Among the cavitands for organic compounds we selected for this study calixarenes and cyclodextrins. The calixarenes (CA) are a versatile class of macrocycle formed from the condensation of phenol and formaldehyde and they are termed as metacyclophanes. The cyclodextrins (CD) are cyclic oligosaccharides comprising six to eight D-glucopyranoside units (á, â, ã-CD) linked by a 1,4-glycosidic bond and they are named native CD. We present here the comparative results found using p-sulphonatocalix[6]arene,1 native CD and hydroxypropyl-â-CD as cavitants in aqueous media for some aromatic organic compounds derivatives of: indole (6-hydroxymelatonin and 2-I-melatonin);  benzothiazole (mercaptobenzothiazole and 2-(methylthio)benzothiazol) and carbamates (benomyl and carbendazim). The Uv-vis of all the substrates did not change in the presence of CA or CDs, but fluorescence enhancements were observed for 6-hydroxymelatonin with CDs and for carbamate compounds with both cavitands. The association constants (KA, M-1) were determined for spectrofluorimetry being higher for CA complex (~ 105) than for CDs ones (~ 102 ).  In all cases the increase in the quantum fluorescence yield of the included substrate shows a more restrictive motion environment and which can be applied to develop a more sensitive analytical method of quantification. The different behaviours observed between the substrates and the hosts, and the differences in the KA values between CA and CDs complexes were interpreted on the basis of the different driving binding forces operating in each case, mainly electrostatic for CA and hydrophobic for CD. The analytical applicability of the methods with both cavitands were also compared between them and with other reported methods.