Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei
Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei
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DOI：
10.1016/j.jmr.2009.12.016
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发表时间：
2010-03-01
影响因子：
2.2
通讯作者：
Schurko, Robert W.
中科院分区：
文献类型：
--
作者：
O'Dell, Luke A.;Harris, Kristopher J.;Schurko, Robert W.
利用SIMPSON 2.0中实现的最优控制程序，产生了用于半整数四极核静态NMR粉末谱图观测的各种振幅和相位调制的激发脉冲。这种脉冲既能激发中心跃迁，又能通过来自卫星的布居转移增强信号。与选择性π/2脉冲相比，对于自旋3/2 Rb-87核的中心跃迁已经实现了超过100%的增强。这些脉冲被示出对RF功率和发射机偏移的变化相对不敏感，并且可以实现比双频扫描（DFS）更均匀的信号增强，导致更准确的光谱线型，我们还研究了“校准自由”优化脉冲的可能性，一般用于半-具有未知相互作用参数的整数四极子这样的脉冲对于研究低丰度或不敏感的核是非常有用的，对于这些核，DFS方案的实验优化可能是我们证明了针对任意自旋3/2系统优化的脉冲可以在多个样品上很好地起作用，并且还可以激发更高自旋数的中心跃迁，尽管增强较小。这些优化的脉冲实现信号增强的机制是高度复杂的，并且与DFS不同，涉及卫星过渡流形的非线性激发，以及显著的多量子相干的产生和操纵。(C)2010爱思唯尔公司版权所有
Various amplitude- and phase-modulated excitation Pulses for the observation of static NMR powder patterns from half-integer quadrupolar nuclei have been generated using the optimal control routines implemented in SIMPSON 2 0 Such pulses are capable of both excitation of the central transition and signal enhancement by Population transfer from the satellites. Enhancements in excess of 100% have been achieved for the central transition of the spin-3/2 Rb-87 nucleus compared with a selective pi/2 pulse These pulses are shown to be relatively insensitive to changes in RF power and transmitter offsets, and can achieve a more uniform signal enhancement than double-frequency sweeps (DFS), resulting in more accurate spectral lineshapes We also investigate the possibility of "calibration-free" optimized pulses for general use on half-integer quadrupoles With unknown interaction parameters Such pulses could prove extremely useful for Studying low abundance or insensitive nuclei for which experimental optimization of the DFS scheme may be difficult We demonstrate that a Pulse optimized for an arbitrary spin-3/2 system can function well on multiple samples, and can also excite the central transition of higher spin numbers, albeit with a smaller enhancement. The mechanism by which these optimized Pulses achieve the signal enhancement is highly complex and, unlike DFS, involves a non-linear excitation of the satellite transition manifold, as well as the generation and manipulation of significant multiple-quantum coherences. (C) 2010 Elsevier Inc All rights reserved