Complex formation analysis of water-soluble calixarenes by capillary zone electrophoresis

The equilibria of complex formation reactions between various kinds of cati ons and anionic calixarenes in an aqueous solution were analyzed by capilla ry zone electrophoresis on the basis of the change in electrophoretic mobil ity of the calixarenes. The apparent electrophoretic mobility of the calixa renes decreased with increasing concentrations of alkali metal ions and qua ternary ammonium ions. Equilibrium constants were determined by a non-liner least-squares analysis using the changes in apparent electrophoretic mobil ity. The complex formation constants obtained with alkali metal ions were i n the order of 10(2.3)-10(3.0), and those with quaternary ammonium ions wer e 10(2.9)-10(4.2), providing less selectivity among them. The selectivity o f the calixarene toward alkali metal and quaternary ammonium ions in aqueou s solution involves flexible structure, and compensative interactions of el ectrostatic and hydrophobic interactions. From the results obtained in this work, the electrophoretic method has proved to be useful for analyzing the reactivity of anionic calixarene in aqueous solution. (C) 2001 Elsevier Sc ience B.V. All rights reserved.