Proton-detected separated local field spectroscopy

PISEMO, a separated local field experiment that can be performed with either direct 15N (or 13C) detection or indirect 1H detection, is demonstrated on a single crystal of a model peptide. The 1H signals modulated by 1H-15N heteronuclear dipole-dipole couplings are observed stroboscopically in the windows of the multiple-pulse sequence used to attenuate 1H-1H homonuclear dipole-dipole couplings. 1H-detection yields spectra with about 2.5 times the signal to noise ratio observed with 15N-detection under equivalent conditions. Resolution in both the 15N chemical shift and 1H-15N heteronuclear dipole-dipole coupling dimensions is similar to that observed with PISEMA, however, since only on-resonance pulses are utilized, the bandwidth is better.