Calixarenes and related compounds as polyprotic acids and containers

GUADALUPE G. MIÑAMBRES; MATÍAS E. CARRANZA; SANTIAGO D. SALAS; MARCIO LAZZAROTTO; MARÍA T. BAUMGARTNER; VEGLIA, A. V.

Foz Iguazú

Conferencia; 12th Latin American Conference on Physical Organic Chemistry; 2013

Universidad Federal de Santa Catarina

The final objective of our studies is to develop new and enhanced analytical methods based onsupramolecular interactions for analytes of biological implications in human health. Macrocycliccompounds are building blocks in supramolecular systems, acting as receptors of inorganic andorganic analytes. The interactions involved are of different kind and magnitude as van der Wallsforces, hydrogen bond and electrostatic interactions. Calixarenes (CA), thiacalixarenes (TCA)and resorcarenes (RA) are macrocyclic compounds of phenol from the family of cyclophanes.These macrocycles have different solubility and polyprotic acid-base properties in aqueous oraqueous/ organic media, depending of their subtituents. These characteristics make possiblethe study of the same host with different electronic charge establishing different interactions withothers compounds depending on pH.In this report we present the results obtained in our lab for the determinations of the pKai (i = 1;2; n) of p-t-butylcalix[4]arene, p-t-butylcalix[6]arene, p-t-butylthiacalix[4]arene and nbutyl[4]resorcarenein the appropriate aqueous medium of solubilization (75% ethanol:water forCA and TCA; or 2% methanol:water for RA) by potentiometric and spectrophotometric methods.Also we discuss the ability of these macrocycles as receptor for inorganic and organicmolecules.In all cases, an enhanced acidity (7-2 pKa units) was observed compared with that of thecorresponding phenol monomer as in the case of p-sulphonato-calix[n]arenes in water;1 butsome particular effect with the metallic ion (Li+, Na+,K+) of the tritan base is observed, mainly inthe case of CA. These findings indicate some particular interaction between the receptor andthe inorganic cation that can not be explained only by the size of the ion.The ability of these macrocycles as container for organic compounds was explored in thefollowing cases: a) n-butyl[4]resorcarene for Promecarb (pesticide), b) TCA for Cafeic Acid(natural product and dietary supplement) and c) p-sulphonato-calix[n]arene for Carbazol(contaminant) at different pH values by spectrophotometric and spectrofluorimetric methods.These results will be interpreted in base of the possible interactions produced by the electroniccharacteristic of the macrocycle and the analyte at the pH and the medium employed.