Conformational Characteristics of Free and Cesium Complexed p-H-Calix[6]arene Alkyl Ester Derivatives

Calixarenes have received much interest because of their versatile recognition properties toward a variety of ionic and organic guests including biomolecules, which result from the ease of functionalization at the lower rim or upper rim. 1-4 The conformational characteristics of calixarenes are also known to have strong effects on their complex formation behaviors. 1 Among the calixarene series, the appropriately functionalized calix[6]arenes are known to have a prefer-ence for cesium ion, which is one of the major components of nuclear wastes. 1,5 Nevertheless, there are only a few reports on the complexation of cesium ion by calix[6]arenes and on the conformational behaviors of the complex and/or the free host itself. 6,7 In this paper, we report the unusual conformational characteristics of p-H-calix[6]arene deriva-tives and their cesium ion complexes revealed by usin