Order-resolved sideband separation in magic-angle-spinning NMR. 31P NMR of oriented DNA fibers

✍ Scribed by Zhiyan Song; Oleg N. Antzutkin; Allan Rupprecht; Malcolm H. Levitt

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 405 KB
• Volume: 253
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(96)00249-7

✦ Synopsis

We report new radiofrequency pulse schemes for deriving the orientation distribution function of chemical shift anisotropy tensors in the nuclear magnetic resonance of ordered solids. Sample spinning at the magic-angle is combined with radiofrequency pulse schemes for spinning sideband separation. We separate the sidebands associated with molecular order using only 5 radiofrequency ~r-pulses and avoiding a three-dimensional Fourier transformation.

Solid-state NMR spectra depend in general on the relative orientation of the principal axes of the spin interaction tensors and the external magnetic field. This fact may be exploited to obtain the orientation distribution function (odf) of the spin interaction tensors in an external reference frame. Information about microscopic orientational distributions can be obtained under suitable assumptions of microscopic and macroscopic ordering, and knowledge of local tensor orientations [l]. The molecular orientational distribution function has been shown to correlate with macroscopic properties such as the tensile strength of drawn polymers [2,3], and molecular conformational changes such as the transition between the A and B forms of DNA .

A variety of NMR methods exist for probing the microscopic odf's . If the number of distinct chemical sites is small, it is possible to analyze the