Highly efficient heteronuclear polarization transfer using dipolar-echo edited R-symmetry sequences in solid-state NMR

Abstract

In solid-state NMR, dipolar-based heteronuclear polarization transfer has been extensively used for sensitivity enhancement and multidimensional correlations, but its efficiency often suffers from undesired spin interactions and hardware limitations. Herein, we propose a novel dipolar-echo edited R-symmetry (DEER) sequence, which is further incorporated into the INEPT-type scheme, dubbed DEER-INEPT, for achieving highly efficient heteronuclear polarization transfer. Numerical simulations and NMR experiments demonstrate that DEER-INEPT offers significantly improved robustness, enabling efficient polarization transfer under a wide range of MAS conditions, from slow to ultrafast rates, outperforming existing methods. Its high efficiency leads to noticeably enhanced sensitivity in both ¹H → X and X → ¹H transfers, applicable to both spin-1/2 and spin-half-integer quadrupolar nuclei. DEER-INEPT is expected to be widely used in various systems, offering advantages in both sensitivity enhancement and structural analysis.