Supramolecular chemistry: calixarenes vs cyclodextrins. Analytical applications.

NATALIA PACIONI; GUILLERMO BRACAMONTE; VALERIA SUELDO OCCELLO; ALICIA VEGLIA

Los Cocos, Córdoba, Argentina

Conferencia; 9th Latin American Conference on Physical Organic Chemistry.; 2007

IUPAC-Universidad Nacional de Córdoba-Universidad Nacional de Río Cuarto

Over the last years, the objective of our research has been to study the potential analyticalcapability of supramolecular host compounds as selective and reversible sensors for organiccompounds of biological, pharmaceutical, agrochemical or environmental interest.Individual host molecules possessing an intrinsic cavity are termed cavitands. Inclusion of guestspecies within a cavitand results in a host-guest complex. The formation of host-guest complexesgenerally changes the physicochemical properties of the binding analyte. Detection methods basedon changes in UV-vis absorbances or on fluorescence emissions have a broad applicability. Thesetechniques are of particular promise for sensor technology.Among the cavitands for organic compounds we selected for this study calixarenes andcyclodextrins. The calixarenes (CA) are a versatile class of macrocycle formed from thecondensation of phenol and formaldehyde and they are termed as metacyclophanes. Thecyclodextrins (CD) are cyclic oligosaccharides comprising six to eight D-glucopyranoside units (α, β,γ-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 andhydroxypropyl-β-CD as cavitants in aqueous media for some aromatic organic compoundsderivatives of: indole (6-hydroxymelatonin and 2-I-melatonin); benzothiazole(mercaptobenzothiazole and 2-(methylthio)benzothiazol) and carbamates (benomyl andcarbendazim).The UV-vis of all the substrates did not change in the presence of CA or CDs, but fluorescenceenhancements were observed for 6-hydroxymelatonin with CDs and for carbamate compounds withboth cavitands. The association constants (KA, M-1) were determined for spectrofluorimetry beinghigher for CA complex (~ 105) than for CDs ones (~ 102 ). In all cases the increase in the quantumfluorescence yield of the included substrate shows a more restrictive motion environment and whichcan be applied to develop a more sensitive analytical method of quantification.The different behaviours observed between the substrates and the hosts, and the differences inthe KA values between CA and CDs complexes were interpreted on the basis of the different drivingbinding forces operating in each case, mainly electrostatic for CA and hydrophobic for CD. Theanalytical applicability of the methods with both cavitands were also compared between them andwith other reported methods.