Bretschneider Christian O, Akbey Ümit, Aussenac Fabien, Olsen Greg L, Feintuch Akiva, Oschkinat Hartmut, Frydman Lucio
Chemical Physics Department, Weizmann Institute of Science, Rehovot, Israel.
NMR Supported Structural Biology, Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany.
Chemphyschem. 2016 Sep 5;17(17):2691-701. doi: 10.1002/cphc.201600301. Epub 2016 Jul 15.
Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid-state polarization enhancement at ambient conditions, and the maximization of (13) C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's (13) C behavior in nano- and micro-particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid-state experiments. It was found that (13) C NMR signals could be boosted by orders of magnitude in either low- or room-temperature solid-state DNP experiments by utilizing naturally occurring paramagnetic P1 substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin-lattice relaxation times characteristic of diamond, coupled with a time-independent cross-effect-like polarization transfer mechanism facilitated by a matching of the nitrogen-related hyperfine coupling and the (13) C Zeeman splitting. The efficiency of this solid-state polarization process, however, is harder to exploit in dissolution DNP-enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed.
动态核极化（DNP）是提高核磁共振（NMR）和磁共振成像（MRI）灵敏度的一种通用方法。这种通用性引发了人们对克服这些技术潜在局限性的兴趣，包括在环境条件下实现固态极化增强，以及最大化用于进行体内MRI扫描的¹³C信号寿命。本研究探讨了纳米和微粒中金刚石的¹³C行为是否可用于实现这些目标。在溶液和固态实验中，针对不同磁场、晶粒尺寸以及从低温到环境温度的样品环境，分析了金刚石DNP增强的特性。研究发现，通过利用天然存在的顺磁性P1替代氮缺陷，在低温或室温固态DNP实验中，¹³C NMR信号可提高几个数量级。我们将这种行为归因于金刚石特有的异常长的电子/核自旋晶格弛豫时间，以及由氮相关超精细耦合与¹³C塞曼分裂相匹配所促进的与时间无关的类似交叉效应的极化转移机制。然而，在溶解DNP增强的MRI环境中，这种固态极化过程的效率更难利用。本文简要讨论了将接近纳米尺度的极化金刚石用于固态和溶液应用的前景。
