FREQUENCY-SELECTIVE HETERONUCLEAR DEPHASING BY DIPOLE COUPLINGS IN SPINNING AND STATIC SOLIDS

A compensated pulse sequence for the spectrally selective reintroducti on of heteronuclear dipole-dipole interactions (frequency-selective di polar 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 obse rved losses of spin coherence in the multiple pulse experiments. Tn th e peptide glycylglycine, the selective dipolar evolution of two spins is observed while the influence of larger internuclear couplings is su ppressed. This approach is aimed at obtaining several quantitative int ernuclear distances independently in dipolar ''recoupling'' MAS experi ments by reducing multiple spin effects in the observed dipolar evolut ion. Similar frequency-selective dephasing experiments are also introd uced for static solids, where an efficient application to measuring re lative tensor orientations in powdered samples is demonstrated. (C) 19 96 American Institute of Physics.