1H DNP at 1.4 T of water doped with a triarylmethyl-based radical.
1H DNP at 1.4 T of water doped with a triarylmethyl-based radical.
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1H DNP 在 1.4 T 水中掺杂三芳基甲基自由基。
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
J. Ardenkjær
中科院分区：
文献类型：
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作者：
Robert A. Wind;J. Ardenkjær
最近开发了一种基于三芳基甲基（TAM）的自由基，用于生物和其他水溶液体系的研究，并且已经报道了在10 mT或更低的低磁场中，大的（1）H动态核极化（DNP）增强。在本文中，该自由基的DNP性质进行了研究，在一个相当大的领域1.4 T，对应于质子和电子拉莫尔频率为60 MHz和40 GHz，分别。为了避免过度的微波加热的样品，现有的DNP NMR探头进行了修改与屏蔽线圈，缠绕在样品毛细管和其轴垂直的微波场的电组件。发现使用该探针，在入射功率为10 W的微波照射4 s后，样品中的温度升高仅为16 ℃。为了研究，将IOmM的TAM自由基溶解在去离子但未脱气的水中，并放入Imm i.d.和6 mm长的毛细管。在26 ℃下，获得了以下结果：（I）自由基的弛豫率为0.07（mMs）（-1），与从低场结果外推的值一致;（II）泄漏因子为0.63，最大功率下的饱和因子为0.85，耦合因子为-0.0187。结果表明，这些结果同意非常好的分析，其中的电子-偶极相互作用是占主导地位的DNP机制，并从这些相互作用产生的弛豫过渡由平移扩散的水分子。最后，结合DNP与磁共振显微镜（MRM）的可能性进行了讨论。它示出，在26摄氏度的整体DNP增强质子极化应成为最大的在一个外部场为0.3 T，并成为可比的热平衡极化在一个字段为30 T，大大大于最大的高分辨率磁铁可用的日期。它的结论是，DNP MRM在这一领域，这对应于一个标准的微波频率为9 GHz的，有可能显着增加的灵敏度在NMR和MRI实验的小水溶液样品掺杂的TAM自由基。
Recently a triarylmethyl-based (TAM) radical has been developed for research in biological and other aqueous systems, and in low magnetic fields, 10 mT or less, large (1)H dynamic nuclear polarization (DNP) enhancements have been reported. In this paper the DNP properties of this radical have been investigated in a considerably larger field of 1.4 T, corresponding to proton and electron Larmor frequencies of 60 MHz and 40 GHz, respectively. To avoid excessive microwave heating of the sample, an existing DNP NMR probe was modified with a screening coil, wound around the sample capillary and with its axis perpendicular to the electric component of the microwave field. It was found that with this probe the temperature increase in the sample after 4 s of microwave irradiation with an incident power of 10 W was only 16 degrees C. For the investigations, 10 mM of the TAM radical was dissolved in deionized, but not degassed, water and put into a 1-mm i.d. and 6-mm long capillary tube. At 26 degrees C the following results were obtained: (I) The relaxivity of the radical is 0.07 (mMs)(-1), in accordance with the value extrapolated from low-field results; (II) The leakage factor is 0.63, the saturation factor at maximum power is 0.85, and the coupling factor is -0.0187. It is shown that these results agree very well with an analysis where the electron-dipolar interactions are the dominant DNP mechanism, and where the relaxation transitions resulting from these interactions are governed by translational diffusion of the water molecules. Finally, the possibilities of combining DNP with magnetic resonance microscopy (MRM) are discussed. It is shown that at 26 degrees C the overall DNP-enhanced proton polarization should become maximal in an external field of 0.3 T and become comparable to the thermal equilibrium polarization in a field of 30 T, considerably larger than the largest high-resolution magnet available to date. It is concluded that DNP MRM in this field, which corresponds to a standard microwave frequency of 9 GHz, has the potential to significantly increase the sensitivity in NMR and MRI experiments of small aqueous samples doped with the TAM radical.