• K. Saalwächter, F. Lange, K. Matyjaszewski, C.-F. Huang, R. Graf.
  BaBa-xy16: Robust and broadband homonuclear DQ recoupling for applications in rigid and soft solids up to the highest MAS frequencies.
  J. Magn. Reson. x, submitted (2011). DOI 10.1016/j.jmr.2011.07.001.

  Abstract

  We here present a substantially improved version of the popular Back-to-Back (BaBa) homonu- clear double-quantum (DQ) MAS recoupling pulse sequence. By combining the orignal 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 CSA, which is demonstrated on the example of ³¹P NMR of a magnesium ultraphosphate, comparing experimental data with multi-spin simulations. 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.

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