SELECTIVE RECOGNITION OF CARBOXYLATE ANIONS BY POLYAMMONIUM RECEPTORSIN AQUEOUS-SOLUTION - CRITERIA FOR SELECTIVITY IN MOLECULAR RECOGNITION

The interaction in aqueous solution of the polyammonium receptor 1,4,7 ,10.13,16,19-heptaazacyclohenicosane (8, [21]aneN(7)) with the carboxy lic species, 1,2- benzenedicarboxylic (1), 1.3-benzenedicarboxylic (2) , 1.2,3-benzenetricarboxylic (3), 1,3,5-benzenetricarboxylic (4), cis- 1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (5), ans-1.3.5-trimethy l-1,3.5-cyclohexanetricarboxylic (6). and citric (7) acids has been fo llowed by potentiometry and cyclic voltammetry at 298.1 K in 0.15 mol dm(-3) NaClO4, as well as by NMR spectroscopy. The analysis of the pot entiometric and electrochemical data show the formation of 1:1 adducts . A novel method based on both potentiometry and cyclic voltammetry to establish selectivity patterns in systems presenting different proton ation possibilities is introduced. Preorganization of the substrates i n a shape complementary to the receptor yields interesting features su ch as the selective recognition of 5 over its epimer 6 and recognition of the dicarboxylic species 1 and 2 over the tricarboxylic ones 6 and 7.