High-field solution state DNP using cross-correlations
High-field solution state DNP using cross-correlations
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DOI：
10.1016/j.jmr.2021.106940
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发表时间：
2021-04-14
影响因子：
2.2
通讯作者：
Kuprov, Ilya
中科院分区：
文献类型：
--
作者：
Concilio, Maria Grazia;Soundararajan, Murari;Kuprov, Ilya
在普通核磁共振仪器的磁场中，电子塞曼频率太高，无法在溶液中发生有效的电子-核偶极交叉弛豫。该过程的速率随着电子塞曼频率 omega(-2) 的变化而衰减 - 在缺乏各向同性超精细耦合的情况下，高场磁体中的液态动态核极化 (DNP) 因此是不切实际的。然而，接触耦合和偶极交叉弛豫并不是将电子磁化强度移动到液体中的原子核的唯一机制：还存在多个互相关（CC）弛豫过程，涉及相互作用张量各向异性的各种组合。其中一些过程的速率比偶极交叉弛豫具有更有利的高场行为，但由于其数值处理（尤其是分析处理）的困难，它们在很大程度上仍然是未知的。在本次交流中，我们报告了 1e1n 和 2e1n 自旋系统在液态下每个旋转驱动弛豫过程的分析评估，以及稳态 DNP 相对于自旋哈密顿参数的数值优化。 2e1n 系统发现了一种先前未报道的互相关 DNP (CCDNP) 机制，涉及多重弛豫干扰效应和电子间交换耦合。通过模拟，我们发现了真实的自旋哈密顿参数，在高磁场下产生比偶极交叉弛豫更强的核极化。 (C) 2021 Elsevier Inc. 保留所有权利。
At the magnetic fields of common NMR instruments, electron Zeeman frequencies are too high for efficient electron-nuclear dipolar cross-relaxation to occur in solution. The rate of that process fades with the electron Zeeman frequency as omega(-2) - in the absence of isotropic hyperfine couplings, liquid state dynamic nuclear polarisation (DNP) in high-field magnets is therefore impractical. However, contact coupling and dipolar cross-relaxation are not the only mechanisms that can move electron magnetisation to nuclei in liquids: multiple cross-correlated (CC) relaxation processes also exist, involving various combinations of interaction tensor anisotropies. The rates of some of those processes have more favourable high-field behaviour than dipolar cross-relaxation, but due to the difficulty of their numerical - and particularly analytical - treatment, they remain largely uncharted. In this communication, we report analytical evaluation of every rotationally driven relaxation process in liquid state for 1e1n and 2e1n spin systems, as well as numerical optimisations of the steady-state DNP with respect to spin Hamiltonian parameters. A previously unreported cross-correlated DNP (CCDNP) mechanism was identified for the 2e1n system, involving multiple relaxation interference effects and inter-electron exchange coupling. Using simulations, we found realistic spin Hamiltonian parameters that yield stronger nuclear polarisation at high magnetic fields than dipolar cross-relaxation. (C) 2021 Elsevier Inc. All rights reserved.