Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, United States.
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
J Phys Chem B. 2021 May 27;125(20):5171-5190. doi: 10.1021/acs.jpcb.0c10937. Epub 2021 May 7.
Nuclear magnetic resonance (NMR) spectroscopy is a powerful method to study the molecular structure and dynamics of materials. The inherently low sensitivity of NMR spectroscopy is a consequence of low spin polarization. Hyperpolarization of a spin ensemble is defined as a population difference between spin states that far exceeds what is expected from the Boltzmann distribution for a given temperature. Dynamic nuclear polarization (DNP) can overcome the relatively low sensitivity of NMR spectroscopy by using a paramagnetic matrix to hyperpolarize a nuclear spin ensemble. Application of DNP to NMR can result in sensitivity gains of up to four orders of magnitude compared to NMR without DNP. Although DNP NMR is now more routinely utilized for solid-state (ss) NMR spectroscopy, it has not been exploited to the same degree for liquid-state samples. This Review will consider challenges and advances in the application of DNP NMR to liquid-state samples. The Review is organized into four sections: (i) mechanisms of DNP NMR relevant to hyperpolarization of liquid samples; (ii) applications of liquid-state DNP NMR; (iii) available detection schemes for liquid-state samples; and (iv) instrumental challenges and outlook for liquid-state DNP NMR.
核磁共振（NMR）光谱学是研究材料分子结构和动力学的一种强大方法。NMR 光谱学固有的低灵敏度是自旋极化低的结果。自旋系统的超极化被定义为自旋态之间的种群差异，远远超过给定温度下玻尔兹曼分布所预期的差异。动态核极化（DNP）可以通过使用顺磁基质来超极化核自旋系统，克服 NMR 光谱学的相对低灵敏度。与没有 DNP 的 NMR 相比，DNP NMR 的应用可使灵敏度提高多达四个数量级。尽管 DNP NMR 现在更常用于固态（ss）NMR 光谱学，但它在液态样品中的应用并没有达到相同的程度。本综述将考虑 DNP NMR 在液态样品中的应用所面临的挑战和进展。综述分为四个部分：（i）与液态样品超极化相关的 DNP NMR 机制；（ii）液态 DNP NMR 的应用；（iii）液态样品的可用检测方案；以及（iv）液态 DNP NMR 的仪器挑战和展望。
