BaBa-xy16: Robust and broadband homonuclear DQ recoupling for applications in rigid and soft solids up to the highest MAS frequencies

• Published in: Journal of magnetic resonance (1997) Vol. 212; no. 1; pp. 204 - 215
• Main Authors: Saalwächter, Kay, Lange, Frank, Matyjaszewski, Krzysztof, Huang, Chih-Feng, Graf, Robert
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-09-2011
• Subjects: 31P NMR; Accumulation; Algorithms; Anisotropy; Biomolecular solid-state NMR; Broadband; Computer Simulation; Couplings; Double-quantum NMR; Elastomers; Electromagnetic Fields; Magnesium; Magnesium Compounds - chemistry; Multiple-quantum NMR; Networks; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular - methods; Nuclear power generation; Phosphates; Phosphates - chemistry; Polymers; Recoupling; Simulation; Trains; Phosphates; Networks; Recoupling; 31P NMR; Elastomers; Biomolecular solid-state NMR; Multiple-quantum NMR; Double-quantum NMR; Polymers
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2011.07.001

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►An improved and truly broadband, supercycled variant of the popular DQ MAS experiment BaBa is introduced. ► The sequence is exceptionally robust and tolerant to large CSA and offsets, with improving performance under ultra-fast MAS. ► We demonstrate the site-resolved determination of weak RDCs and their distributions in anisotropically mobile polymer systems.
We here present a substantially improved version of the popular Back-to-Back (BaBa) homonuclear double-quantum (DQ) MAS recoupling pulse sequence. By combining the original pulse sequence with a virtual
π pulse train with xy-16 phase cycling along with time-reversed DQ reconversion, a truly broadband and exceptionally robust pulse sequence is obtained. The sequence has moderate radio-frequency power requirements, amounting to only one 360° nutation per rotor cycle, it is robust with respect to rf power and tune-up errors, and its broadband performance increases with increasing spinning frequency, here tested up to 63
kHz. The experiment can be applied to many spin-1/2 nuclei in rigid solids with substantial frequency offsets and CSAs, which is demonstrated on the example of
31P NMR of a magnesium ultraphosphate, comparing experimental data with multi-spin simulations, and we also show simulations addressing the performance in
13C NMR of bio(macro)molecules.
1H-based studies of polymer dynamics are highlighted for the example of a rigid solid with strongly anisotropic mobility, represented by a polymer inclusion compound, and for the example of soft materials with weak residual dipole–dipole couplings, represented by homogeneous and inhomogeneous elastomers. We advocate the use of normalized (relaxation-corrected) DQ build-up curves for a quantitative assessment of weak average dipole–dipole couplings and even distributions thereof.