Modulatory resonance recoupling of heteronuclear dipolar interactions under magic angle spinning

A new solid-state NMR technique for recoupling heteronuclear dipolar interactions under magic angle spinning is proposed. In this method, the recoupling is achieved by interference between two non-commutable time-dependent Hamiltonians in the doubly rotating frame: one is the heteronuclear dipolar interaction modulated by MAS and the other is the rf interaction whose amplitude is modulated. When the two modulation frequencies are matched to each other, the cross term between the two interactions becomes time-independent. Since the recoupling condition does not include the intensity of the rf field, this recoupling method is insensitive to inhomogeneity of the rf field. This new recoupling method is demonstrated for 2-13C/15N doubly labeled glycine.