Selective recognition of carboxylate anions by polyammonium receptors in aqueous solution. Criteria for selectivity in molecular recognition

Abstract

The interaction in aqueous solution of the polyammonium receptor 1,4,7,10,13,16,19-heptaazacyclohenicosane (8, [21]aneN₇) 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.