标题： 基于金属离子的动态核极化：MI-DNP 显示英文标题

标题： Metal Ions based Dynamic Nuclear Polarization: MI-DNP

摘要： 在过去二十年中，魔角旋转动态核极化（MAS DNP）彻底改变了材料表征的核磁共振（NMR），解决了其固有的低灵敏度这一主要限制。理论理解、仪器和样品制备方面的进展扩大了可以受益于MAS DNP的材料应用和研究问题的范围。目前，MAS下最常用的一种超极化方法是将感兴趣的样品浸渍在含有氮氧自由基的溶液中，这些自由基在微波照射下作为外源性极化剂。另一方面，在基于金属离子（MI）的DNP中，无机材料被掺杂有顺磁性金属中心，这些中心可以作为内源性极化剂使用。在本工作中，我们概述了用于表征金属离子所需的电子顺磁共振（EPR）概念，并讨论了由于顺磁性物质的存在而预期在NMR响应中的变化。我们强调了哪些电子自旋特性有利于作为DNP中的极化剂以及如何从EPR和NMR数据中识别它们。给出了主要DNP机制的理论描述，采用量子力学形式，并利用这些概念来解释DNP实验中观察到的自旋动力学。此外，我们突出了MI-DNP与更常见的MAS DNP方法之间的主要差异，后者使用有机自由基作为外源性极化源。最后，我们回顾了金属离子作为极化剂的一般应用，然后特别关注可以受益于MI-DNP的材料科学中的研究问题。 显示英文摘要

摘要： Over the last two decades magic angle spinning dynamic nuclear polarization (MAS DNP) has revolutionized NMR for materials characterization, tackling its main limitation of intrinsically low sensitivity. Progress in theoretical understanding, instrumentation, and sample formulation expanded the range of materials applications and research questions that can benefit from MAS DNP. Currently the most common approach for hyperpolarization under MAS consists in impregnating the sample of interest with a solution containing nitroxide radicals, which upon microwave irradiation serve as exogenous polarizing agents. On the other hand, in metal ion based (MI)-DNP, inorganic materials are doped with paramagnetic metal centres, which then can be used as endogenous polarizing agents. In this work we give an overview of the electron paramagnetic resonance (EPR) concepts required to characterize the metal ions and discuss the expected changes in the NMR response due to the presence of paramagnetic species. We highlight which properties of the electron spins are beneficial for applications as polarizing agents in DNP and how to recognize them, both from the EPR and NMR data. A theoretical description of the main DNP mechanisms is given, employing a quantum mechanical formalism, and these concepts are used to explain the spin dynamics observed in the DNP experiment. In addition, we highlight the main differences between MI-DNP and the more common approaches in MAS DNP, which use organic radicals as exogenous polarizing source. Finally, we review some applications of metal ions as polarizing agents in general and then focus particularly on research questions in materials science that can benefit from MI-DNP.