Recoupled separated-local-field experiments and applications to study intermediate-regime molecular motions
Recoupled separated-local-field experiments and applications to study intermediate-regime molecular motions
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DOI：
10.1016/j.jmr.2012.05.003
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发表时间：
2012-08-01
影响因子：
2.2
通讯作者：
Saalwaechter, Kay
中科院分区：
文献类型：
--
作者：
Cobo, Marcio Fernando;Achilles, Anja;Saalwaechter, Kay
一个特定的分离局部场NMR实验，被称为偶极化学位移相关（DIPORA），经常用于通过XH偶极耦合和T-2的变化探测重定向来研究分子运动。在耦合较弱或重定向角较小的系统中，应用DIPORE实验的再耦合变体，其中有效偶极耦合被类似REDOR的π脉冲串放大。然而，先前描述的这个实验的恒定时间变量对运动引起的T-2效应不敏感，这排除了在从数百Hz到大约MHz的大范围速率上观察运动。我们提出了一个DIPOND实现放大偶极耦合，仍然是敏感的T-2效应。自旋动力学模拟、分析计算和实验证明了该技术对分子运动的敏感性，并提出了避免缺陷的最佳实验条件。此外，基于平均-哈密顿理论，对REDOR类再耦合和质子去耦合的相互作用进行了深入的理论分析，这使得可以解释文献数据中发现的许多伪像的起源。(C)2012 Elsevier Inc. All rights reserved.
A specific separated-local-field NMR experiment, dubbed Dipolar-Chemical-Shift Correlation (DIPSHIFT) is frequently used to study molecular motions by probing reorientations through the changes in XH dipolar coupling and T-2. In systems where the coupling is weak or the reorientation angle is small, a recoupled variant of the DIPSHIFT experiment is applied, where the effective dipolar coupling is amplified by a REDOR-like pi-pulse train. However, a previously described constant-time variant of this experiment is not sensitive to the motion-induced T-2 effect, which precludes the observation of motions over a large range of rates ranging from hundreds of Hz to around a MHz. We present a DIPSHIFT implementation which amplifies the dipolar couplings and is still sensitive to T-2 effects. Spin dynamics simulations, analytical calculations and experiments demonstrate the sensitivity of the technique to molecular motions, and suggest the best experimental conditions to avoid imperfections. Furthermore, an in-depth theoretical analysis of the interplay of REDOR-like recoupling and proton decoupling based on Average-Hamiltonian Theory was performed, which allowed explaining the origin of many artifacts found in literature data. (C) 2012 Elsevier Inc. All rights reserved.