C-13-H-1 dipolar recoupling under very fast magic-angle spinning using virtual pulses

A new solid-state NMR pulse sequence for recoupling C-13-H-1 dipolar intera ctions under magic-angle spinning is proposed, which works under a spinning speed of a few to several tens kilohertz. The sequence is composed of two different frequency switched Lee-Goldburg sequences, and the modulation of the spin part of the C-13-H-1 dipolar interaction is introduced by a virtua l pulse sequence consisting of unitary operators connecting the rotating fr ame and the tilted rotating frame. When the cycle time of the spinning is e qual to or twice the cycle time of the sequence, the C-13-H-1 dipolar inter actions can be recoupled. The sequence is insensitive to experimental imper fections such as rf inhomogeneity or frequency offset, and the resulting li neshape can be represented by a simple analytical equation based on the zer oth-order average Hamiltonian. Experimental results for [2-C-13] L-valine H Cl are reported. (C) 1999 Elsevier Science B.V. All rights reserved.