Frequency-selective heteronuclear dephasing by dipole couplings in spinning and static solids

A compensated pulse sequence for the spectrally selective reintroduction of heteronuclear dipole-dipole interactions (frequency-selective dipolar recoupling) into solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments is described and shown to provide frequency-selective dipolar dephasing in weakly coupled spin systems. The experimental dipolar spin evolution is interpreted via analytical and numerical calculations, which include a simple model for the observed losses of spin coherence in the multiple pulse experiments. Tn the peptide glycylglycine, the selective dipolar evolution of two spins is observed while the influence of larger internuclear couplings is suppressed. This approach is aimed at obtaining several quantitative internuclear distances independently in dipolar ''recoupling'' MAS experiments by reducing multiple spin effects in the observed dipolar evolution. Similar frequency-selective dephasing experiments are also introduced for static solids, where an efficient application to measuring relative tensor orientations in powdered samples is demonstrated. (C) 1996 American Institute of Physics.