Determining the relative orientation between the chemical shift anisotropy and heteronuclear dipolar tensors in static solids by SEDOR NMR

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

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.