Second-order average Hamiltonian theory of symmetry-based pulse schemes in the Nuclear Magnetic Resonance of rotating solids: Application to triple-quantum dipolar recoupling,

A. Brinkmann, and M. Edén,
J. Chem. Phys. 120, 11726-11745, (2004).
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The average Hamiltonian theory (AHT) of several classes of symmetry-based radio frequency pulse sequences is developed to second order, allowing quantitative analyses of a wide range of recoupling and decoupling applications in magic-angle spinning solid state nuclear magnetic resonance. General closed analytical expressions are presented for a cross-term between any two interactions recoupled to second order AHT. We classify them into different categories and show that some properties of the recoupling pulse sequence may be predicted directly from this classification. These results are applied to examine a novel homonuclear recoupling strategy, effecting a second order average dipolar Hamiltonian comprising trilinear triple quantum (3Q) spin operators. We discuss general features and design principles of such 3Q recoupling sequences and demonstrate by numerical simulations and experiments that they provide more efficient excitation of 13C 3Q coherences compared to previous techniques. We passed up to 15 % of the signal through a state of 3Q coherence in rotating powders of uniformly 13C-labeled alanine and tyrosine. Second order recoupling-based 13C homonuclear 3Q correlation spectroscopy is introduced and demonstrated on tyrosine.