Coherence transfer by single-transition cross-polarization: Quantitation of cross-correlation effects in nuclear magnetic resonance

It is shown that selective single-transition cross-polarization (ST-CP) may be achieved in four-level systems such as encountered in NMR (nuclear magn etic resonance) of scalar-coupled two-spin systems (for example, N-15-H-1 g roups in peptides), by employing two selective resonant fields applied to a pair of connected transitions with RF amplitudes much weaker than the sepa ration of the parallel transitions (e.g., the scalar coupling constant J(NH )). The transfer benefits from differential line narrowing due to interfere nce between the N-15 chemical shift anisotropy and N-15-H-1 dipolar couplin g, which is clearly observed in N-15-labeled human ubiquitin at 600 MHz. (C ) 2000 American Institute of Physics. [S0021-9606(00)00327-5].