Frequency selective polarization transfer based on multiple chemical shift precession

In this Letter, we have demonstrated a novel strategy for frequency selective polarization transfer in solid-state NMR spectroscopy under magic-angle spinning condition. The polarization transfer during the mixing time is mediated by scalar spin-spin coupling. The frequency selectivity is achieved by inserting free precession periods (windows) in the mixing time, during which the system evolves under the chemical shift difference of the coupled spin pair. Experimental data are obtained for [U 13C, 15N]-alanine and the results can be fully explained by a simple theoretical framework based on the isotropic chemical shifts and the scalar spin-spin coupling.