High frequency dynamic nuclear polarization.
High frequency dynamic nuclear polarization.
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DOI：
10.1021/ar300348n
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发表时间：
2013-09-17
影响因子：
18.3
通讯作者：
Griffin, Robert G.
中科院分区：
文献类型：
--
作者：
Ni, Qing Zhe;Daviso, Eugenio;Can, Thach V.;Markhasin, Evgeny;Jawla, Sudheer K.;Swager, Timothy M.;Temkin, Richard J.;Herzfeld, Judith;Griffin, Robert G.
在1980年至2010年的三十年间，魔角旋转(MAS)核磁共振发展成为研究许多化学、物理和生物问题的首选方法。特别是，各种测量距离和扭角的偶极重新耦合方法现在可以将分子结构限制在高分辨率。然而，应用往往受到实验低灵敏度的限制，这在很大程度上是因为必须观测低γ核的光谱，如I=1/2种13C或15N。当涉及到17O或27Al等四极核时，难度就更大了。这个问题刺激了提高MAS实验灵敏度的努力。一种特别有效的方法是动态核极化(DNP)，它利用了电子的较高平衡极化(通常表现为EPR比核磁共振具有巨大的灵敏度优势)。在DNP中，样品被掺入稳定的顺磁极化剂，并用微波照射，以将电子自旋库中的高极化转移到感兴趣的原子核。这个想法最早是由Overhauser和Slichter在1953年提出的。然而，这些实验是在静态样品上进行的，磁场以目前的标准来看是低的。要在当代的MAS核磁共振实验中实施，DNP需要工作在亚太赫兹区域的微波源-大约150-660 GHz-和低温MAS探测器。此外，需要改进偏光剂，因为产生显著增强所需的常规自由基的高浓度会影响光谱分辨率。在过去的二十年里，科学和技术的进步解决了这些问题，并使DNP达到了广泛适用的地步。这些进展包括开发工作在亚太赫兹频率范围内的高频回旋微波源。此外，还开发了低温MAS探针，允许对样品进行原位微波辐射。最后，开发了双自由基极化器，在相当低的顺磁网浓度下，将DNP实验的效率提高了~4倍。总体而言，这些发展使得在常规基础上将DNP应用于一些不同的科学努力成为可能，最突出的是在生物和材料科学方面。本文综述了这些进展，包括高频DNP中用于传递极化的主要机制，以及当前微波源和双自由基极化试剂的选择。此外，我们通过对膜和淀粉样蛋白的应用的描述来说明该技术的实用性，强调在这两种情况下可用的独特的结构信息。
During the three decades 1980–2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-γ nuclei such as the I = ½ species 13C or 15N. The difficulty is still greater when quadrupolar nuclei, like 17O or 27Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime — roughly 150–660 GHz — and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low temperature MAS probes were developed that permit in-situ microwave irradiation of the samples. And, finally, biradical polarizing agents were developed that increased the efficiency of DNP experiments by factors of ~4 at considerably lower paramagnet concentrations. Collectively these developments have made it possible to apply DNP on a routine basis to a number of different scientific endeavors, most prominently in the biological and material sciences. This Account reviews these developments, including the primary mechanisms used to transfer polarization in high frequency DNP, and the current choice of microwave sources and biradical polarizing agents. In addition, we illustrate the utility of the technique with a description of applications to membrane and amyloid proteins that emphasizes the unique structural information that is available in these two cases.
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影响因子：
2.9
作者：
Bayro, Marvin J.;Maly, Thorsten;Birkett, Neil R.;MacPhee, Cait E.;Dobson, Christopher M.;Griffin, Robert G.
通讯作者：
Griffin, Robert G.
DOI：
10.1016/j.jmr.2009.03.003
发表时间：
2009-06
期刊：
Journal of magnetic resonance (San Diego, Calif. : 1997)
影响因子：
--
作者：
Barnes AB;Mak-Jurkauskas ML;Matsuki Y;Bajaj VS;van der Wel PC;Derocher R;Bryant J;Sirigiri JR;Temkin RJ;Lugtenburg J;Herzfeld J;Griffin RG
通讯作者：
Griffin RG
影响因子：
15
作者：
Kiesewetter, Matthew K.;Corzilius, Bjoern;Smith, Albert A.;Griffin, Robert G.;Swager, Timothy M.
通讯作者：
Swager, Timothy M.
影响因子：
15
作者：
GRIFFITHS, JM;LAKSHMI, KV;GRIFFIN, RG
通讯作者：
GRIFFIN, RG
影响因子：
5.7
作者：
Michaelis, Vladimir K.;Markhasin, Evgeny;Griffin, Robert G.
通讯作者：
Griffin, Robert G.