高磁场下的溶液态动态核极化
Solution-state dynamic nuclear polarization at high magnetic field.
作者信息
Loening Nikolaus M, Rosay Melanie, Weis Volker, Griffin Robert G
机构信息
Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
出版信息
J Am Chem Soc. 2002 Jul 31;124(30):8808-9. doi: 10.1021/ja026660g.
The goal of dynamic nuclear polarization (DNP) is to enhance NMR signals by transferring electron spin polarization to the nuclei. Although mechanisms such as the solid effect and thermal mixing can be used for DNP in the solid state, currently, the only practical mechanism in solutions is the Overhauser effect (OE), which usually arises due to dipolar relaxation between electrons and the nuclei. At magnetic fields greater than approximately 1 T, dipolar relaxation does not result in a useful enhancement and therefore the conventional wisdom is that DNP should not work in solutions at high magnetic fields. However, scalar relaxation due to time-dependent scalar couplings has a different magnetic field dependence and can lead to substantial OE enhancements. At room temperature and at a magnetic field of 5 T (211 MHz for protons, 140 GHz for electrons), we have observed that scalar relaxation between electrons and nuclei results in NMR signal enhancements of 180, 42, -36, and 8, for 31P, 13C, 15N, and 19F, respectively.
动态核极化（DNP）的目标是通过将电子自旋极化转移到原子核来增强核磁共振（NMR）信号。尽管诸如固体效应和热混合等机制可用于固态的DNP，但目前，溶液中唯一实用的机制是奥弗豪泽效应（OE），它通常源于电子与原子核之间的偶极弛豫。在大于约1 T的磁场中，偶极弛豫不会产生有用的增强，因此传统观点认为DNP在高磁场溶液中不起作用。然而，由于随时间变化的标量耦合引起的标量弛豫具有不同的磁场依赖性，并且可以导致显著的OE增强。在室温以及5 T的磁场（质子为211 MHz，电子为140 GHz）下，我们观察到电子与原子核之间的标量弛豫分别导致31P、13C、15N和19F的NMR信号增强了180、42、-36和8。
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