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.
Reson. x, submitted (2011). DOI 10.1016/j.jmr.2011.07.001.
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.