Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR.
Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR.
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DOI：
10.1021/jp505752c
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发表时间：
2014-08-07
期刊：
影响因子：
--
通讯作者：
Ashbrook SE
中科院分区：
文献类型：
--
作者：
Colaux H;Dawson DM;Ashbrook SE
多量子相干性和单量子相干性之间的转换是许多四极核核磁共振 (NMR) 实验不可或缺的一部分。当由单个脉冲实现时，这种转换效率相对较低，并且已经开发了许多复合脉冲方案来提高这种效率。为了提供最大程度的改进，此类方案通常需要耗时的实验优化。在这里，我们演示了一种生成调幅脉冲的方法，以提高三量子到单量子转换的效率。使用 SIMPSON 和 MATLAB 软件包执行优化，产生无需重新优化实验即可使用的高效脉冲。当对固有射频章动率和四极耦合幅度的良好估计用作优化的输入时，可以获得最显着的信号增强，但脉冲对于任一参数的合理变化都表现出鲁棒性，与单脉冲转换相比产生显着的增强，并且与其他常用方法相比，效率也相当或更高。在所有情况下，我们的方法易于实施是有利的，特别是对于最需要改进的低灵敏度情况（例如，低旋磁比或高四极耦合）。我们的方法提供了常规提高核和系统高分辨率核磁共振谱灵敏度的潜力，否则可能会被认为“太具有挑战性”。
The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed “too challenging”.
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影响因子：
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作者：
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