title: BaBa-xy16: robust and broadband homonuclear DQ recoupling for applications in rigid and soft solids up to the highest MAS frequencies.
abstract: 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.
authors.affiliation: Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, D-06120 Halle, Germany. kay.saalwaechter@physik.uni-halle.de
authors.forename: Kay
authors.initials: K
authors.lastname: Saalwächter
authors.forename: Frank
authors.initials: F
authors.lastname: Lange
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Matyjaszewski
authors.forename: Chih-Feng
authors.initials: CF
authors.lastname: Huang
authors.forename: Robert
authors.initials: R
authors.lastname: Graf
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D003198:Computer Simulation; D020724:Elastomers; D004574:Electromagnetic Fields; D017616:Magnesium Compounds / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010710:Phosphates / Q000737:chemistry; D011108:Polymers
chemical_list: D020724:Elastomers; D017616:Magnesium Compounds; D010710:Phosphates; D011108:Polymers; C030781:magnesium phosphate