ELECTROCHEMICAL STUDIES ON MOLECULAR RECOGNITION OF ANIONS - COMPLEX-FORMATION BETWEEN XYLYLENYL BIS-IMINOIMIDAZOLINIUM AND DICARBOXYLATES IN NITROBENZENE AND WATER

This paper reports studies of complex formation between the synthetic dicarboxylate receptor para-xylylenylbis-(iminoimidazolinium) (1(2+)) and dicarboxylates in electrolyte-containing nitrobenzene and water us ing cyclic voltammetry resulting from charge transfer across a liquid\ liquid interface. A series of dicarboxylate-tetrabutylammonium salts w as prepared and investigated systematically. The receptor 1(2+) shows modest selectivity in binding glutarate in nitrobenzene over longer di carboxylates. The interactions between 1(2+) and glutarate are very we ak in the aqueous phase, and the association constant for the binding reaction is 190 +/- 100 M-1. The association constants between 1(2+) a nd glutarate in electrolyte-containing nitrobenzene saturated with an aqueous phase and in electrolyte-containing nitrobenzene that has not been saturated with an aqueous phase are 7.46 +/- 0.39 x 10(4) and 2.1 2 +/- 0.28 x 10(5) M-1, respectively. 1(2+) transfers across the water /nitrobenzene interface reversibly. However, it does not facilitate th e transfer of shorter chain dicarboxylates, as crown ethers do for alk ali metals. The failure to observe facilitated transfer is not due to a lack of complexation between glutarate and 1(2+). Rather it arises b ecause at potentials sufficiently negative (water phase vs. nitrobenze ne phase) to drive the anionic dicarboxylate into the receptor-enriche d nitrobenzene, the cationic receptor has already been driven in the o pposite direction, depleting it from the organic side of the interface . (C) 1998 Elsevier Science S.A.