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首页> 外文期刊>Journal of magnetic resonance >Distance measurements in spin-1/2 systems by ~(13)C and ~(31)P solid-state NMR in dense dipolar networks
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Distance measurements in spin-1/2 systems by ~(13)C and ~(31)P solid-state NMR in dense dipolar networks

机译：在稠密偶极网络中用〜（13）C和〜（31）P固态NMR测量spin / 1/2系统中的距离

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摘要

In this article solid-state NMR methods for the determination of internuclear dipole-dipole couplings between homonuclear spin-1/2 nuclei are presented. They are suitable for relatively dense dipolar networks which are still dominated by 2-spin interactions. C-/R-symmetry theory is applied to create a double-quantum average Hamiltonian using phase-modulated radio-frequency irradiation and magic-angle samplerotation. Symmetry derived pulse sequences with improved compensation against chemical shift anisotropies were found assuming a small isotropic chemical shift difference and using numerical calculations of the spin dynamics. Moreover it is shown that a constant time procedure can be used to acquire reliable double-quantum build-up curves even in systems in which damping obscures oscillations in their symmetric build-up curve. This technique is demonstrated on four crystalline model compounds with ~(31)P and ~(13)C spin systems typical for inorganic and biological applications. Comparison to crystal structure data indicates that the distance derived this way from ~(31)P and ~(13)C double-quantum NMR carry only small systematic errors caused for example by anisotropic J-coupling, dipolar contributions from adjacent spins and relaxation.
机译：本文介绍了用于确定同核自旋1/2核之间的核间偶极-偶极偶合的固态NMR方法。它们适用于相对密集的偶极网络，该网络仍以2自旋相互作用为主。应用C / R对称理论，通过调相射频辐射和幻角样本旋转来创建双量子平均哈密顿量。在假设小的各向同性化学位移差并使用自旋动力学的数值计算的情况下，发现了对称偏移衍生的脉冲序列，其对化学位移各向异性的补偿得到了改善。此外，表明即使在其中阻尼掩盖了其对称累积曲线中的振荡的系统中，恒定时间程序也可用于获取可靠的双量子累积曲线。这项技术在具有〜（31）P和〜（13）C自旋系统的四种晶体模型化合物上得到了证明，该化合物通常用于无机和生物应用。与晶体结构数据的比较表明，以这种方式从〜（31）P和〜（13）C双量子NMR得出的距离仅带有很小的系统误差，例如，由各向异性J耦合，相邻自旋的偶极贡献和弛豫引起。

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