Band-selective hetero- and homonuclear cross-polarization using trains of shaped pulses

Abstract

The performance of solution cross-polarization using trains of shaped pulses on two channels is investigated by computer simulation and experiment. It is determined that a Waltz modulation pattern of Gaussian pulses of individual flip angles of 225°, issued to two coupled spins simulatneously, yields excellent coherence transfer with good phasing behavior. Simulations and experimental verification were carried out for both heteronuclear cross-polarization between two restricted areas (e.g. 1 H α − 13 C α ) and for homonuclear cross-polarization between two spectral regions (e.g. 13 CO− 13 C α ). It is shown that shaped cross-polarization behaves as pure heteronuclear cross-polarization when the two radiofrequency (rf) fields are far apart, while it behaves in some aspects analogous to homonuclear cross-polarization when the two rf fields approach each other. The novel coherence-transfer sequence, referred to as ‘cosine-modulated shaped Waltz’ (CSW), was implemented in a 3D (H)C(CCO)NH experiment using an 18-kDa isotopically labeled protein.