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Efficient low‐power heteronuclear decoupling in 13 C high‐resolution solid‐state NMR under fast magic angle spinning
Author(s) -
Kotecha Mrignayani,
Wickramasinghe Nalinda P.,
Ishii Yoshitaka
Publication year - 2007
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2151
Subject(s) - decoupling (probability) , chemistry , heteronuclear molecule , pulse sequence , spinning , nuclear magnetic resonance , magic angle , magic angle spinning , analytical chemistry (journal) , physics , nuclear magnetic resonance spectroscopy , stereochemistry , chromatography , engineering , control engineering , polymer chemistry
The use of a low‐power two‐pulse phase modulation (TPPM) sequence is proposed for efficient 1 H radio frequency (rf) decoupling in high‐resolution 13 C solid‐state NMR (SSNMR) under fast MAS conditions. Decoupling efficiency for different low‐power decoupling sequences such as continuous‐wave (cw), TPPM, XiX, and π‐pulse (PIPS) train decoupling has been investigated at a spinning speed of 40 kHz for 13 C CPMAS spectra of uniformly 13 C ‐ and 15 N ‐labeled L ‐alanine. It was found that the TPPM decoupling sequence, which was originally designed for high‐power decoupling, provides the best decoupling efficiency at low power among all the low‐power decoupling sequences examined here. Optimum performance of the low‐power TPPM sequence was found to be obtained at a decoupling field intensity (ω 1 ) of ∼ω R /4 with a pulse flip angle of ∼π and a phase alternation between ± ϕ(ϕ = ∼20° ), where ω R /2π is the spinning speed. The sensitivity obtained for 13 CO 2 − , 13 CH, and 13 CH 3 in L ‐alanine under low‐power TPPM at ω 1 /2π of 10 kHz was only 5–15% less than that under high‐power TPPM at ω 1 /2π of 200 kHz, despite the fact that only 0.25% of the rf power was required in low‐power TPPM. Analysis of the 13 CH 2 signals for uniformly 13 C‐ and 15 N‐labeled L ‐isoleucine under various low‐power decoupling sequences also confirmed superior performance of the low‐power TPPM sequence, although the intensity obtained by low‐power TPPM was 61% of that obtained by high‐power TPPM. 13 C CPMAS spectra of 13 C ‐labeled ubiquitin micro crystals obtained by low‐power TPPM demonstrates that the low‐power TPPM sequence is a practical option that provides excellent resolution and sensitivity in 13 C SSNMR for hydrated proteins. Copyright © 2007 John Wiley & Sons, Ltd.