RAMPED-AMPLITUDE CROSS-POLARIZATION IN MAGIC-ANGLE-SPINNING NMR
RAMPED-AMPLITUDE CROSS-POLARIZATION IN MAGIC-ANGLE-SPINNING NMR
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DOI：
10.1006/jmra.1994.1208
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发表时间：
1994-10-01
期刊：
影响因子：
--
通讯作者：
SMITH, SO
中科院分区：
文献类型：
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作者：
METZ, G;WU, XL;SMITH, SO
CP-MAS核磁共振的Hartmann-Hahn匹配分布表明，如果MAS频率在样品中偶极耦合的数量级上，则显示出强烈的失配相关性。在这些条件下，型材分解成一系列由纺速分隔的窄匹配带，并且很难建立和保持有效的匹配条件。可变幅度CP(VACP)，如前所述(Peersen等人，J.Magn.雷森。A104,334,1993)，已被证明在高速纺丝时恢复扁平型材是有效的。这里，描述了一种使用斜坡幅度交叉极化序列(RAMP-CP)的VACP的改进实现。幅度调制的顺序对于交叉极化过程是重要的。具有线性幅度斜坡的新脉冲序列不仅更容易设置，而且还提高了可变幅度实验的性能，因为即使在总接触时间较短的情况下，它也可以在更大范围的匹配条件下产生平坦的轮廓。与传统的CP序列和最初提出的VACP序列相比，获得了信号强度的增加。(C)1994年学术出版社。
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.