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J Magn Reson. 2004 May;168(1):8-17.

Towards quantitative measurements in solid-state CPMAS NMR: A Lee-Goldburg frequency modulated cross-polarization scheme.

Author information

1
Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, USA. rfu@magnet.fsu.edu

Abstract

A new scheme combining a Lee-Goldburg (LG) sequence with frequency modulation is proposed for cross-polarization (LG-FMCP) in solid-state magic-angle-spinning nuclear magnetic resonance. During the CP contact time, the (1)H magnetization is spin-locked along the magic angle by the LG sequence and the irradiation offset of the S spins (e.g., (15)N) is modulated sinusoidally with a constant RF amplitude. It is shown experimentally that the LG sequence significantly lengthens the proton spin-lattice relaxation time in the tilted rotating frame and that the frequency modulation shortens the cross-polarization time for non-protonated S spins. As a result of substantially increasing the difference in these relaxation rates, the non-protonated and protonated S spins can be more efficiently and more uniformly polarized with a relatively long CP contact time, making quantitative CP measurements possible. A sample of (15)N-delta 1-L-histidine lyophilized from a solution of pH 6.3 and a (15)N-delta 1-L-His labeled transmembrane helical peptide in hydrated lipid bilayers were used to illustrate the advantages of this scheme.

PMID:
15082244
DOI:
10.1016/j.jmr.2004.01.012

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