The design and application of variable angle spinning probe for dipolar local field spectroscopy in liquid crystals.

摘要

Variable Angle Spinning (VAS) is particularly valuable in structural determination for its ability to control the sample alignment and thus scale the dipolar couplings. In contrast to rotor-synchronized recoupling methods which are widely used in solid state samples, VAS can manipulate dipolar couplings in strongly aligned liquid crystalline media. Previously, one of the biggest challenges for VAS probe design was to find an ideal electric junction between the stationary tuning circuit and the mobile sample coil that is required to reorient with the spinning axis for a better filling factor. There are several previous approaches towards this goal, including sliding contact and flexible leads. As an alternative approach, RF power can transmit wirelessly via coaxial capacitive coupling where the coupling efficiency is improved by replacing the ordinary sample coil with a double frequency resonator. Our probe constructed out of this design principle has shown favorable properties at variable angle conditions. Moreover, a switched angle spinning correlation experiment is performed to demonstrate the probe's capability to resolve dipolar couplings in strongly aligned molecules.