3-Dimensional Variable-Angle Nuclear-Magnetic-Resonance Exchange Spectroscopy without Rotor Axis Hopping

Title3-Dimensional Variable-Angle Nuclear-Magnetic-Resonance Exchange Spectroscopy without Rotor Axis Hopping
Publication TypeJournal Article
Year of Publication1994
AuthorsLee Y.K, Emsley L., Larsen R.G, Schmidt-Rohr K., Hong M., Frydman L., Chingas G.C, Pines A
JournalJournal of Chemical Physics
Volume101
Issue3
Pagination1852-1864
Date PublishedAug 1
ISBN Number0021-9606
Accession NumberWOS:A1994NY00200011
Keywordsdistributions
Abstract

Slow, large-amplitude chain motions play an important role in determining the macroscopic mechanical properties of polymers. Although such motions have been studied quantitatively by two-dimensional (2D) nuclear: magnetic resonance (NMR) exchange experiments, overlapping anisotropic patterns hamper spectral analysis, and limit applications. Variable angle correlation spectroscopy (VACSY) has proven useful in resolving such problems for rapidly spinning samples by separating anisotropic spectral patterns according to isotropic chemical shifts. In a previous study [J. Am. Chem. Sec. 115, 4825 (1993)], we described a three-dimensional (3D) NMR experiment that incorporates; the VACSY method and a hop of the rotor axis to correlate the isotropic chemical shifts to 2D anisotropic exchange patterns. The hop of the rotor axis, however, presents experimental difficulties and limits the range of motional rates that may be studied. We present in this paper a new 3D VACSY exchange experiment that obtains the same correlations without the need for the rotor axis hop. A series of 2D exchange spectra are recorded with the sample spinning at different rotation axis angles.' Then using the scaling of the anisotropic frequency at the different angles, we construct the data onto a 3D matrix so that a Fourier transformation directly yields the desired correlations. The technique is applied to C-13 exchange NMR to study the slow molecular motion of ordered isotactic polypropylene.

URL<Go to ISI>://WOS:A1994NY00200011
DOI10.1063/1.467696
Short Title3-Dimensional Variable-Angle Nuclear-Magnetic-Resonance Exchange Spectroscopy without Rotor Axis Hopping
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