SELECTIVE RECOGNITION OF CARBOXYLATE ANIONS BY POLYAMMONIUM RECEPTORS IN 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 carboxylic species, 1,2- benzenedicarboxylic (1), 1.3-benzenedicarboxylic (2), 1.2,3-benzenetricarboxylic (3), 1,3,5-benzenetricarboxylic (4), cis,cis-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (5), cis,trans-1.3.5-trimethyl-1,3.5-cyclohexanetricarboxylic (6). and citric (7) acids has been followed 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 potentiometric 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 protonation possibilities is introduced. Preorganization of the substrates in a shape complementary to the receptor yields interesting features such 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.