A homonuclear rotational echo double-resonance method for measuring site-resolved distance distributions in I=½ spin pairs, clusters, and multispin systems.
A homonuclear rotational echo double-resonance method for measuring site-resolved distance distributions in I=½ spin pairs, clusters, and multispin systems.
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DOI：
10.1002/anie.201207094
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发表时间：
2012-12
影响因子：
--
通讯作者：
Jinjun Ren;H. Eckert
中科院分区：
文献类型：
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作者：
Jinjun Ren;H. Eckert
高分辨率固态核磁共振光谱在原子水平上为复杂、无序和分子固体提供结构信息的独特能力和潜力已得到充分证明。[1，2]特别是，核间偶极偶极耦合的分析可以提供有关距离，键连接性和空间自旋分布的信息。[3]对于异向自旋系统，以位置分辨方式实现这一点的最有效方法之一是旋转回波双共振（REDOR）技术，[4]其中测量信号幅度S 0的差异信号，其中没有相互作用（由于魔角自旋，MAS）和减少的信号幅度S '，其中相互作用重新耦合（通过在转子周期期间应用反转脉冲）。REDOR已被广泛用于测量核间距及其在生物系统和无机材料中的分布，并已被改编成许多不同的版本和变体。[5-11]相比之下，对于多自旋系统，迄今为止还没有实现具有类似通用性的类似的同向差分策略。虽然已经发表了大量的homopolymer再耦合方法，[12-32]它们的校准，以产生基于模拟或模型化合物工作的偶极耦合信息，仍然是一个困难的问题。虽然最近使用改进的双量子激发策略报道了有希望的进展，[14]但重要的剩余问题包括双量子相干激发的有限效率，T2弛豫和偶极截断效应。[33-35]到目前为止已知的唯一的homestrant差分方法涉及使用“用于旋转回波幅度的移相的transverseecho简单激发（t-SEESTRM）”方法的零量子相干性的激发，[28]其中横向磁化Ix 1 + Ix 2的移相与有效哈密顿量影响下的移相进行比较[Eq.①]。虽然横向回波SEEDS确实成功地消除了T2弛豫对实验数据的影响，但到目前为止，还没有报道将其应用于孤立双自旋对以外的系统。
The unique power and potential of high-resolution solid-state NMR spectroscopy to provide structure information at the atomic level for complex, disordered, and molecular solids have been amply demonstrated.[1, 2] In particular, the analysis of internuclear dipole–dipole couplings can provide information about distances, bond connectivities, and spatial spin distributions.[3] For heteronuclear spin systems, one of the most powerful methods to accomplish this in a site-resolved fashion has been the rotational echo double-resonance (REDOR) technique,[4] where a difference signal is measured of signal amplitudes S0 with the interaction absent (owing to magic-angle spinning, MAS) and reduced signal amplitudes S’with the interaction recoupled (through application of inversion pulses during the rotor period). REDOR has been widely used for measuring internuclear distances and their distributions in biological systems and inorganic materials alike and has been adapted in many different versions and variants.[5–11] In contrast, an analogous homonuclear difference strategy of similar versatility has up to now not yet been realized for multispin systems. Although a large variety of homonuclear recoupling approaches have been published,[12–32] their calibration to yield information on dipolar couplings on the basis of simulations or model compound work has remained a difficult issue. While promising progress was recently reported using improved double-quantum excitation strategies,[14] important remaining issues include the limited efficiency of double-quantum coherence excitation, T2 relaxation, and dipolar truncation effects.[33–35] The only homonuclear difference method known so far involves an excitation of zero-quantum coherences using the “transverseecho simple excitation for the dephasing of rotational-echo amplitude (t-SEDRA)” method,[28] where the dephasing of transverse magnetization Ix1+ Ix2 is compared with that under the influence of an effective Hamiltonian [Eq.(1)]. While transverse-echo SEDRA does succeed in eliminating the influence of T2 relaxation upon the experimental data, applications to systems beyond isolated two-spin pairs have not been reported so far.