Multidimensional Dipolar Exchange-Assisted Recoupling Measurements in Solid-State NMR
β Scribed by Joseph R. Sachleben; Peter Beverwyk; Lucio Frydman
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 369 KB
- Volume
- 144
- Category
- Article
- ISSN
- 1090-7807
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β¦ Synopsis
A series of uni-and multidimensional variants of the dipolar exchange-assisted recoupling (DEAR) NMR experiment is described and applied to determinations of 13 C-14 N dipolar local field spectra in amino acids and dipeptides. The DEAR protocol recouples nearby nuclei by relying on differences in their relative rates of longitudinal relaxation, and has the potential to give quantitative geometric results without requiring radiofrequency pulsing on both members of a coupled spin pair. One-and twodimensional variants of this recoupling strategy on generic I-S pairs are discussed, and measurements of 13 C-14 N distances and 2D local field experiments sensitive to the relative orientation of CN vectors with respect to the 13 C shielding tensor are presented. Since these measurements did not involve pulsing on the broad nitrogen resonance, their results were independent of the quadrupolar parameters of this nucleus. High-resolution 3D NMR versions of the 2D experiments were also implemented in order to separate their resulting local field patterns according to the isotropic shifts of inequivalent 13 C sites. These high-resolution 3D acquisitions involved collecting a series of 2D DEAR NMR data sets on rotating samples as a function of spinning angle, and then subjecting the resulting data to a processing akin to that involved in variable-angle correlation NMR. Once successfully tested on L-alanine this experiment was applied to the analysis of a series of dipeptides, allowing us to extract separate local field 13 C-14 N spectra from this type of multisite systems.
π SIMILAR VOLUMES
Practical heteronuclear dipolar recoupling performances under magic angle spinning for SFAM and REDOR have been investigated under well-defined rf inhomogeneity environments with variation of resonance offsets for the irradiated nucleus. The heteronuclear dipolar recoupling efficiencies were quantit