133Cs NMR Spectroscopic Investigation of the Interaction of 133Cs+ with Monovalent Cations in Aqueous Solution

Abstract

133Cs NMR spectroscopy was used to study the interaction of 133Cs+ with monovalent cations in aqueous solution. The interaction between 133Cs+ and the cations causes a repulsive polarization in the electron environment of 133Cs+, which is detected by a change in its resonance frequency. The resulting 133Cs chemical shift seemed to be dependent on the activities and the single-ion enthalpies and entropies of hydration of the cations. The hydration cospheres of an ion are the barriers through which 133Cs+ must pass in order to come into contact with the cation. These hydration cosphere barriers can be related to the single-ion enthalpy and entropy of hydration of the cation. The experiments revealed that 133Cs+ is not nearly as sensitive a probe as 129Xe, presumably due to its more tightly bound hydration cospheres. However, 133Cs NMR was moderately successful in predicting trends in the chemical shift behavior induced by the cations studied.