Carbon-13 NMR Longitudinal Relaxation Time Study of an Ionophoric 1,3-Alternate-Shaped Calix[4]arene Ester

Abstract

The carbon-13 NMR longitudinal relaxation times (T₁) studies on the 1,3-alternate-shaped calix[4]arene possessing two ester groups 1 in the absence and the presence of Na⁺ were carried out for the first time. The T₁ values were measured under proton-noise-decoupling conditions by the inversion-recovery technique. The T₁-value of 1 is primarily governed by dipole-dipole relaxation. When calixarene 1 forms an ensemble with Na⁺, the T₁-values for all carbons are decreased. This suggests that the molecular motion of species 1 is efficiently frozen through complexation with Na⁺. Eventually, Na⁺ ion plays an important role as a template ion specifically to freeze the fluctuational motion of two ethoxycarbonylmethoxybenzene units of 1.