Two-Dimensional Nuclear Magnetic Resonance Experiments for Studying Molecular Order and Dynamics in Static and in Rotating Solids

PATROS—A New MAS Exchange Method Using Sideband Separation: Application to Poly(n-butylmethacrylate)

“…3c the mixing period was correctly adjusted according to Eq. [11], with G ϭ 2, while in Fig. 3d it was intentionally set, incorrectly, to m ϭ (G Ϫ 1 2 )T R (the tr-ODESSA condition).…”

“…[11]) implies that for each increment a slightly different mixing period is used. The largest variation in m within one PATROS sequence is a single rotation period.…”

Initial Conditions for Carbon-13 MAS NMR 1D Exchange Involving Chemically Equivalent and Inequivalent Nuclei

“…For such measurements, an ODESSA type sequence (20, 21) must be used. The original ODESSA sequence is the same as for the rotor-synchronized MAS 2D-exchange experiment (13,14), except that the evolution time is fixed at T R /2 (Fig. 2d).…”

“…The principal values of their chemical shift (CS) tensors are identical, but their principal axes (PAS) are not, although they are related by the crystal symmetry; (iii) exchange between inequivalent nuclei, which have different CS tensors. Spin exchange between magnetically equivalent nuclei does usually not affect the MAS spectra, while the other two types of exchange processes can readily be distinguished from the nature of the cross-peaks between the spinning sidebands (ssb) in the spectra of rotorsynchronized 2D-exchange experiments (13)(14)(15). Thus, exchange between congruent nuclei (type ii) shows up as auto cross-peaks (i.e., cross-peaks between ssb belonging to the same manifold), while exchange between inequivalent nuclei (type iii) is manifested in the appearance of hetero cross-peaks linking ssb belonging to different manifolds.…”

Sideband Patterns from Rotor-Encoded Longitudinal Magnetization in MAS Recoupling Experiments

“…For instance, early attempts to combine chemical-shift exchange spectroscopy with slow MAS led to spurious sidebands in two dimensions when the phase of the rotor at the end of the mixing time was not the same as the phase at either the start or the end of the t 1 period (15)(16)(17). Clearly, these extra sidebands are manifestations of a type of spectral "encoding" of the change in rotor phase.…”