Repetitive cross-polarization contacts via equilibration-re-equilibration of the proton bath: Sensitivity enhancement for NMR of membrane proteins reconstituted in magnetically aligned bicelles

► Cross-polarization (CP) cannot be fully transferred in a single contact for membrane proteins refolded in bicelles. ► This is due to thermodynamic and quantum mechanical bounds, as well as Hartmann-Hahn mismatches. ► The new REP-CP sequence yields a twofold gain for bicelle-reconstituted proteins as compared to a single CP. ► The gain is achieved by employing the differences between T1 relaxation times for the high and low spins.