Hartmann–Hahn polarization transfer in liquids: An ideal tool for selective experiments

Cross-polarization using continuous-wave spin-locking fields has never become routine in liquid-state nuclear magnetic resonance. Efficiency of cross-polarization tends to be strongly attenuated if radio-frequency (RF) fields are not perfectly homogeneous. It has recently been demonstrated that imperfections in RF-fields have little effect on efficiency of polarization transfer, provided that RF-amplitudes are comparable to magnitudes of heteronuclear scalar coupling constants, rendering this method ideal for selective experiments. The technique can be exploited for the excitation of nuclei with a low gyromagnetic factor like 13C and 15N, as well as of nuclei with a high gyromagnetic factor like 1H. Several useful applications are discussed.