Symmetry principles in the design of pulse sequences for structural measurements in magic angle spinning nuclear magnetic resonance

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Abstract
We introduce general symmetry principles that are useful in the design of radio‐frequency excitation sequences for magic angle spinning (MAS) NMRexperiments.Sequences derived in accordance with these symmetry principles produce excitations, evolutions, or spectra of nuclear spin systems that are insensitive to the chemical shiftanisotropies (CSA) and resonance offsets of the spins. Specific DRAMA (dipolar recovery at the magic angle) sequences are derived. These sequences allow nuclear magnetic dipole–dipole couplings, which are normally averaged to zero by MAS, to be measured or otherwise used in MAS experiments. In numerical simulations of dipolar line shapes and in both simulations and experimental 13C NMR measurements of double‐quantum filtering, DRAMA sequences with appropriate symmetries are shown to be less strongly affected by CSA and resonance offsets than sequences used in earlier work. The practicality of the DRAMA technique is thereby enhanced. We present experimental 13C MAS NMRspectra of a 13C‐labeled undecapeptide (molecular weight ≊1100) that illustrate the feasibility of applying double‐quantum filtering based on the new DRAMA sequences to the problem of simplifying MAS spectra and obtaining information about the structures of complex molecules.