Reorientational dynamics of p ‐sulfonatocalix[4]arene and of its La(III) complex in water

The reorientational dynamics of p ‐sulfonatocalix[4]arene and of its La(III) complex in deuterated water were studied by 1 H NMR longitudinal relaxation rates. It is shown that the relaxation is purely dipolar in the non‐extreme narrowing regime. The distance between the geminal protons could be determined from the NMR data, giving good agreement with the values generally used in correlation time calculations. The correlation times show an Arrhenius behaviour in good agreement with previously reported data from 13 C measurements for a similar uncomplexed calixarene. The Arrhenius energies of activation are identical for the uncomplexed and the complexed calixarenes, suggesting a reorientational motion strongly dependent on the structure of the water cage around the complex. This is also in agreement with a complexation of the La(III) cation in the second sphere of solvation of the sulfonate groups, as shown by molecular dynamics simulations. Copyright © 2004 John Wiley & Sons, Ltd.