H CSA parameters by ultrafast MAS NMR: Measurement and applications to structure refinement.

A H anisotropic-isotropic chemical shift correlation experiment which employs symmetry-based recoupling sequences to reintroduce the chemical shift anisotropy in ν and ultrafast MAS to resolve H sites in ν is described. This experiment is used to measure H shift parameters for L-ascorbic acid, a compound with a relatively complex hydrogen-bonding network in the solid. The H CSAs of hydrogen-bonded sites with resolved isotropic shifts can be extracted directly from the recoupled lineshapes.

Measuring (19)F shift anisotropies and (1)H-(19)F dipolar interactions with ultrafast MAS NMR.

A new (19)F anisotropic-isotropic shift correlation experiment is described that operates with ultrafast MAS, resulting in good resolution of isotropic (19)F shifts in the detection dimension. The new experiment makes use of a recoupling sequence designed using symmetry principles that reintroduces the (19)F chemical shift anisotropy in the indirect dimension. The situations in which the new experiment is appropriate are discussed, and the (19)F shift anisotropy parameters in poly(difluoroethylene) (PVDF) are measured.

Measuring proton shift tensors with ultrafast MAS NMR.

A new proton anisotropic-isotropic shift correlation experiment is described which operates with ultrafast MAS, resulting in good resolution of isotropic proton shifts in the detection dimension. The new experiment makes use of a recoupling sequence designed using symmetry principles which reintroduces the proton chemical shift anisotropy in the indirect dimension. The experiment has been used to measure the proton shift tensor parameters for the OH hydrogen-bonded protons in tyrosine·HCl and citric acid at Larmor frequencies of up to 850 MHz.