Dramatic solvent effect on the ligand wrapping around a complexed cation: a MD study of p-tert-butylcalix[4]arene tetramide and its complexes with alkali cations and europium(3+) in acetonitrile

A series of molecular dynamics (MD) simulations have been performed on tert-butylcalix[4]arene tetramide ligand L and its complexes with cations Li + to Cs + and Eu 3+ in acetonitrile solution in order to elucidate the structural basis of complexation of cations by an ionophore possessing a highly flexible nonpreorganized pseudocavity. Comparison of its dynamic behavior in acetonitrile and in water demonstrates the dramatic solvent effect on the extent of ligand wrapping around the complexed ions. The binding mode of cation complexes in acetonitrile differs significantly from the picture provided by the solid-state structure of LK + complex and from structures simulated in gas phase and in water