ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
A new 13C polarization technique in solids is presented on the basis of a recently proposed 13C–13C recoupling sequence [13C–1H dipolar-assisted rotational resonance (DARR), K. Takegoshi, S. Nakamura, and T. Terao, Chem. Phys. Lett. 344, 631 (2001)] operative under fast magic angle spinning (MAS), in which a rf field is applied to 1H with a rotary resonance condition but none to 13C. The 1H irradiation in DARR saturates 1H signals, leading to the 13C signal enhancement due to the nuclear Overhauser effect for fast rotating methyl groups, if any. If we use a uniformly 13C labeled sample, 13C–13C polarization transfer enhanced by DARR successively distributes the enhanced methyl carbon polarization to the other 13C spins, leading to uniform enhancement for all 13C spins even under very fast MAS. In uniformly 13C labeled rotating samples, the enhancement factor in cross polarization (CP) is about 2.4, while in the present nuclear Overhauser polarization (NOP), it is 3.0 in the fast rotation limit of the methyl groups. While the CP enhancement becomes smaller for molecules with short T1ρ of 1H or 13C, NOP would work well for such mobile molecules, and also NOP enables us to acquire a signal with a short repetition time even if 1H T1 is long. Further, NOP has the advantage of quantitativeness, and is very easy to carry out, being insensitive to the adjustment of rf field intensity and requiring only very low rf power. These features are demonstrated for uniformly 13C, 15N-labeled L-threonine and uniformly 13C, 15N-labeled glycylisoleucine. NOP-MAS is also applied for a naturally abundant 13C sample. © 2002 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1485062
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