RAMPED-AMPLITUDE CROSS-POLARIZATION IN MAGIC-ANGLE-SPINNING NMR

被引:1073
作者
METZ, G
WU, XL
SMITH, SO
机构
[1] YALE UNIV,DEPT MOLEC BIOPHYS & BIOCHEM,NEW HAVEN,CT 06520
[2] YALE UNIV,DEPT CHEM,NEW HAVEN,CT 06520
关键词
D O I
10.1006/jmra.1994.1208
中图分类号
O64 [物理化学(理论化学)、化学物理学]; O56 [分子物理学、原子物理学];
学科分类号
070203 ; 070304 ; 081704 ; 1406 ;
摘要
The Hartmann-Hahn matching profile in CP-MAS NMR shows a strong mismatch dependence if the MAS frequency is on the order of the dipolar couplings in the sample. Under these conditions, the profile breaks down into a series of narrow matching bands separated by the spinning speed, and it becomes difficult to establish and maintain an efficient matching condition. Variable-amplitude CP (VACP), as introduced previously (Peersen et al., J. Magn. Reson. A 104, 334, 1993), has been proven to be effective for restoring flat profiles at high spinning speeds. Here, a refined implementation of VACP using a ramped-amplitude cross-polarization sequence (RAMP-CP) is described. The order of the amplitude modulation is shown to be of importance for the cross-polarization process. The new pulse sequence with a linear amplitude ramp is not only easier to set up but also improves the performance of the variable-amplitude experiment in that it produces flat profiles over a wider range of matching conditions even with short total contact times. An increase in signal intensity is obtained compared to both con ventional CP and the originally proposed VACP sequence. (C) 1994 Academic Press, Inc.
引用
收藏
页码:219 / 227
页数:9
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