Behavior of cesium and thallium cations inside a calixarene cavity as probed by nuclear spin relaxation. Evidence of cation-pi interactions in water.

We have studied the complexes formed between the p-sulfonatocalix[4]arene and cesium or thallium metal cation, first by carbon-13 longitudinal relaxation of the calixarene molecule at two values of the magnetic field B(0). From the longitudinal relaxation times of an aromatic carbon directly bonded to a proton, thus subjected essentially to the dipolar interaction with that proton, we could obtain the correlation time describing the reorientation of the CH bond. The rest of this study has demonstrated that it is also the correlation time describing the tumbling of the whole calixarene assembly.

Location of a metallic cation complexed in a calixarene cavity as determined by calixarene 13C spin relaxation. application to cesium and thallium complexed by p-sulfonatocalix[4]arene in water.

This study deals with the exact location of the monovalent metal cations Cs(+) and Tl(+) which are complexed by the p-sulfonatocalix[4]arene in water. This determination rests on the measurements of longitudinal relaxation times of carbon-13 not directly bonded to protons. The difference between the relaxation times of the free calixarene and of the complex definitely demonstrates that the monovalent metal cation is well inside the calixarene cavity.