A phase cycle scheme that significantly suppresses offset-dependent artifacts in the R2-CPMG 15N relaxation experiment
A phase cycle scheme that significantly suppresses offset-dependent artifacts in the R2-CPMG 15N relaxation experiment
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DOI：
10.1016/j.jmr.2004.06.021
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发表时间：
2004-11-01
影响因子：
2.2
通讯作者：
Zuiderweg, ERP
中科院分区：
文献类型：
--
作者：
Yip, GNB;Zuiderweg, ERP
R-2-CPMG N-15 弛豫实验构成了 NMR 动力学测量的基础，可用于纳皮秒动力学和毫微秒动力学（动力学）的分析。一段时间以来，人们已经知道，在有限脉冲宽度的实际极限中（当使用低温探针时，这种极限变得很严重），对于远离 RE 载体的自旋，表观 R-2 弛豫行为中会出现系统误差。 R-2 速率的不准确测量会传播到定量模型中，例如无模型松弛分析、旋转扩散张量分析和松弛色散。问题的根源在于在脉冲期间以及脉冲之间磁化矢量在 XY 平面外的演化。这些偏差随脉冲长度、施加的 CPMG 脉冲数量和 CPMG 脉冲间延迟而变化。在这里，我们通过实验、数值模拟和解析方程详细分析了这些影响。我们的工作表明 CPMG 脉冲的相位进展发生了令人惊讶的简单变化，这导致了性能的显着提高。首先，CPMG实验的适用范围在谱宽上增加了两倍；其次，可以评估的动力/动力学过程显着扩展到较慢的时间尺度；最后，弛豫色散实验的稳健性大大提高。 (C) 2004 Elsevier Inc. 保留所有权利。
R-2-CPMG N-15 relaxation experiments form the basis of NMR dynamics measurements, both for analysis of nano-pico second dynamics and milli-micro second dynamics (kinetics). It has been known for some time that in the practical limit of finite pulse widths, which becomes acute when using cryogenic probes, systematic errors in the apparent R-2 relaxation behavior occur for spins far off-resonance from the RE carrier. Inaccurate measurement of R-2 rates propagates into quantitative models such as model-free relaxation analysis, rotational diffusion tensor analysis, and relaxation dispersion. The root of the problem stems from evolution of the magnetization vectors out of the XY-plane, both during the pulses as well as between the pulses. These deviations vary as a function of pulse length, number of applied CPMG pulses, and CPMG inter-pulse delay. Herein, we analyze these effects in detail with experimentation, numerical simulations, and analytical equations. Our work suggests a surprisingly simple change in the phase progression of the CPMG pulses, which leads to a remarkable improvement in performance. First, the applicability range of the CPMG experiment is increased by a factor of two in spectral width; second, the dynamical/kinetic processes that can be assessed are significantly extended towards the slower time scale; finally, the robustness of the relaxation dispersion experiments is greatly improved. (C) 2004 Elsevier Inc. All rights reserved.