Heteronuclear coherence transfer in solid-state nuclear magnetic resonance using a γ-encoded transferred echo experiment

Abstract

A novel type of solid-state nuclear magnetic resonance experiment for efficient transfer of coherence between different nuclear spin I=1/2 species under magic-angle spinning conditions is introduced. The method combines the attractive features of γ-encoded dipolar recoupling [Nielsen et al., J. Chem. Phys. 101, 1805 (1995)] with coherence transfer mediated by a longitudinal spin-order operator in a transferred echo experiment. Using two-channel rotary resonance recoupling with different phase and amplitude modulation schemes, the transferred echo sequence can be tuned to achieve dipolar recoupling and coherence transfer over a well-defined range of chemical shifts while keeping the ratio between the rf field strength and the sample spinning frequency relatively low. The method, referred to as gamma-encoded transfer echo, is described analytically, by numerical simulations for various different spin systems, and experimentally by N15 to C13 coherence transfers in a powder sample of C13, N15-labeled glycine.