Windowless dipolar recoupling: the detection of weak dipolar couplings between spin 12 nuclei with large chemical shift anisotropies

A new homonuclear dipolar recoupling technique is described which uses a sequence of phase-shifted, windowless irradiations applied synchronously with sample spinning. Experiments performed on a series of doubly labeled dicarboxylic acids, alanine-1,3-13C2, and 2′-deoxythymidine-4,6-13C2 demonstrate that this new windowless dipolar recoupling pulse sequence can accurately determine internuclear distances from polycrystalline solids in cases where the coupled spins have large chemical shift anisotropies and large differences in isotropic chemical shift.