Selective cross-polarization in solution state NMR

In two influential paper, Ernst and coworkers argued that cross-polarization, originally proposed by Hartmann and Hahn, can be very useful in isotropic liqs. to transfer coherence between scalar-coupled nuclei such as protons and carbon-13 (Maudsley, A. A., Muller, L., and Ernst, R. R., 1977; J. Magn. Reson., 28, 463; Muller, L., and Ernst, R. R., 1979, Molec. Phys., 38, 963). Unfortunately, the efficiency of cross-polarization in liqs. tends to be strongly attenuated if the radiofrequency fields are not perfectly homogeneous. In this paper, it is demonstrated by expts. and simulations that imperfections in RF fields have little effect on the efficiency of magnetization transfer, provided that the RF amplitudes are comparable with the magnitudes of the heteronuclear scalar coupling consts. A comparison between selective cross-polarization and selective INEPT shows clearly that cross-polarization is more efficient. Selective cross-polarization does not require any careful calibration and is insensitive to exptl. instabilities. [on SciFinder (R)]