通过增强动态核极化来改善NMR

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Nuclear magnetic resonance (NMR) spectroscopy is a sophisticated analytical tool for investigating the structure, dynamics, reaction state, and chemical environment of molecules. NMR can simultaneously identify and quantify numerous constituent components of a sample. In addition, it can be targeted to detect the amount of a particular species. Furthermore, since NMR is based on the application of a magnetic field rather than radiation, it does not damage the sample and can be applied to both solutions and solids. It is thus widely used in many research areas and also in industry quality control protocols.

尽管NMR提供了极大的详细信息，但当天然丰度低的核（例如¹³C，正在研究。尽管可以使用较大的样品，增加扫描持续时间或使用较高的磁场来提高灵敏度，但最好使用更精确的方法，例如动态核极化（DNP）¹。

Dynamic nuclear polarization

DNP可以通过使用高极化电子来改善核自旋极化，从而通过几个数量级来增强NMR信号²。来自电子的自旋极化被转移到要分析的样品的核中。

核自旋在固态上极化，然后使用过热的溶剂快速溶解，以产生“超极化”溶液，该溶液的NMR信号比热平衡大几千倍。该技术已被证明对¹³C metabolic imaging^3,4。

提供游离电子的偏振剂通常是稳定的有机自由基。氮氧化物和三乙醇是溶解DNP的最常用的自由基。氮氧化物的宽电子顺磁共振（EPR）光谱使它们最有效地极化¹h，而狭窄的EPR光谱却最适合¹³C polarization.

DNP优化

¹³C可以通过添加顺磁化合物（例如基于Gadolinium的对比剂（GBCA））进一步增强C极化。这种掺杂已显示出增强¹³C DNP through reduction of electron T1 of the polarizing agent⁵。Changes in electron spectra do not occur with the addition of paramagnetic agents alone. Thus the increase in polarization is thought to be a consequence of the T1 effect and the interaction between the paramagnetic agent and the nuclei of the sample.

With NMR being used for increasingly complex investigations, research continues into optimization of the polarization procedure and the underlying physics of DNP in order to achieve the best results. A range of other metal ions, but most commonly manganese (Mn²⁺）和铜（Cu²⁺), have been used as to effectively enhance trityl DNP, supporting further investigation into the use of metal ion contrast agents as additives to optimise DNP NMR.

过渡金属掺杂

最近的研究首次研究了与顺磁过渡金属复合物在效率上使用掺杂¹³C DNP⁶。

偏振剂Trityl OX063，用顺磁过渡金属复合物Mn-Nota，Cu-Nota或Co-Nota掺杂用于分析¹³C乙酸钠。此外，准备了对照样品，没有添加过渡金属。使用带有TE011圆柱形腔的Bruker E680 EPR光谱仪，通过EPR在国家高磁场实验室进行EPR评估每个溶液。

Data showed that doping with Mn-NOTA substantially improved the solid-state¹³C DNP signal, giving a three-fold increase in signal⁶。In contrast, neither of the other two transition metal complexes, Cu-NOTA and Co-NOTA, provided enhancement of solid-state¹³C DNP EPR signals.

W频段EPR测量随后显示，在掺杂MN的样品中，Trityl OX063电子T1显着降低²⁺。Interestingly, this was not observed in DNP samples doped with either Cu²⁺或co²⁺, despite their paramagnetic nature.

这项最新的研究突出了对一组金属成员观察到的影响的最新研究，不一定会转化为该组的其他成员。它清楚地表明，并非所有的顺磁性添加剂都对增强DNP的增强有益于提高NMR的灵敏度。重要的是，它还提供了直接证据，表明通过顺磁性添加剂减少偏振剂的电子T1是实现固态改善的必不可少的必需品¹³C DNP signals.

参考

1. Abragam A，Goldman M.Rep。Prog。物理。1978;41：395–467。
2. Ardenkjaer-Larsen JH。J. Magn。reson。2016;264：3–12。
3. Gallagher FA, et al. Prog. Nucl. Magn. Reson. Spectrosc. 2009; 55:285–295.
4. Nelson SJ, et al. Sci. Transl Med. 2013;5:198ra108.
5. Niedbalski P等。J. Chem. Phys. 2017;146:014303.
6. Niedbalski P等。J Phys Chem。A. 2017; 121（48）：9221–9228。

This information has been sourced, reviewed and adapted from materials provided by Bruker BioSpin - NMR, EPR and Imaging.

For more information on this source, please visitBruker Biospin -NMR，EPR和成像。