Determination of the relative orientation between 15N-1H dipolar coupling and 1H chemical shift anisotropy tensors under fast MAS solid-state NMR

Abstract

In this work, we have proposed a proton-detected three-dimensional (3D) 15N-1H dipolar coupling (DIP)/1H chemical shift anisotropy (CSA)/1H chemical shift (CS) correlation experiment to measure the relative orientation between the 15N-1H dipolar coupling and the 1H CSA tensors under fast magic angle spinning (MAS) solid-state NMR. In the 3D correlation experiment, the 15N-1H dipolar coupling and 1H CSA tensors are recoupled using our recently developed windowless C-symmetry-based C331-ROCSA (recoupling of chemical shift anisotropy) DIPSHIFT and C331-ROCSA pulse-based methods, respectively. The 2D 15N-1H DIP/1H CSA powder lineshapes extracted using the proposed 3D correlation method are shown to be sensitive to the sign and asymmetry of the 1H CSA tensor, a feature that allows the determination of the relative orientation between the two correlating tensors with improved accuracy. The experimental method developed in this study is demonstrated on a powdered U-15N L-Histidine.HCl·H2O sample.