Sensitivity-Enhanced Sim-CT HMQC PFG-HBHA(CO)NH and PFG-CBCA(CO)NH Triple-Resonance Experiments

Short transverse relaxation times of C ^α and C ^β single-quantum coherences reduce the sensitivity of triple-resonance experiments involving transfers of C ^α /C ^β or H ^α /H ^β coherences. Multiple-quantum line-narrowing techniques improve the relaxation properties of ¹³ C coherences, thereby increasing the sensitivity of the experiment. In the present work, we describe PFG-CBCA(CO)NH and PFG-HBHA(CO)NH experiments that utilize heteronuclear multiple-quantum coherences in a simultaneous constant-time period to obtain completely decoupled spectra with improved sensitivity. Results indicate that ∼30% of cross peaks show an average enhancement of ∼15% in the CBCA(CO)NH experiment. In the related HBHA(CO)NH experiment, ∼97% of the cross peaks show an average enhancement of ∼40%.