13C/15N distance determination by CPMAS NMR in uniformly 13C labeled molecules

The REDOR and CPMAS techniques are applied for measuring C-13-N-15 dipolar coupling constants in glycine. It is shown that the selective CP or SPECIFIC CP technique removes the coherent evolution of the spin system under homonuclear C-13-C-13 J couplings. While the large coupling constant (similar to 900 Hz) is readily determined because of the presence of large oscillations in the CPMAS dynamics, their absence precludes the measurement of the small coupling constant (similar to 200 Hz). The experimental results and numerical simulations demonstrate that the determination of C-13-N-15 coupling constants of medium size (< 1 kHz) by the CPMAS technique is mainly limited by the strength of the H-1 decoupling field and the size of the C-13 and N-15 chemical shift anisotropies. Copyright (c) 2005 John Wiley & Sons, Ltd.