Development of DNP-Enhanced High-Resolution Solid-State NMR System for the Characterization of the Surface Structure of Polymer Materials
Development of DNP-Enhanced High-Resolution Solid-State NMR System for the Characterization of the Surface Structure of Polymer Materials
复制标题
用于表征聚合物材料表面结构的 DNP 增强高分辨率固态核磁共振系统的开发
DOI：
10.1007/s10762-012-9874-1
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
F.D. Doty
中科院分区：
文献类型：
--
作者：
F. Horii;T.Idehara;Y. Fujii;I.Ogawa;A. Horii;G. Entzminger;F.D. Doty
通过将在4.7 T下运行的200 MHz Chemagnetics CMX-200光谱仪与高功率131.5 GHz Gyrotron FU CW IV相结合，开发了动态核极化（DNP）增强交叉极化/魔角旋转（DNP/CP/MAS）核磁共振系统。在长脉冲TE模式下产生的频率为5 Hz的30 W亚太赫兹波通过光滑铜圆波导成功地传输到改进的Doty Scientific低温CP/MAS探头。由于高功率的连续亚太赫兹波脉冲辐射会引起探针电路中电弧放电和不期望的样品加热对NMR信号产生严重的RF噪声，开发了与NMR检测同步的开-关亚太赫兹波脉冲辐照，并确定了对应于非太赫兹波的辐照时间和冷却时间的适当设置。发现照射时间对于抑制电弧和样品加热非常有效。C113-enrichedD-葡萄糖溶解在含有单自由基4-amino-TEMPO的冷冻培养基中，可达到的最大DNP增强超过30倍。首次获得了聚甲基丙烯酸甲酯（PMMA）亚微米颗粒在相同冷冻介质中分散状态下的DNP/CP/MAS ~（13）C NMR谱，表明DNP增强的~ 1H自旋有效地从介质通过PMMA颗粒表面扩散到PMMA颗粒，并在~ 1H自旋到达的表面区域被检测为高分辨率~（13）C谱。在此基础上，探讨了DNP/CP/MAS NMR表征纳米材料（包括高分子材料）表面结构的可能性。
A dynamic nuclear polarization (DNP)-enhanced cross-polarization/magic-angle spinning (DNP/CP/MAS) NMR system has been developed by combining a 200 MHz Chemagnetics CMX-200 spectrometer operating at 4.7 T with a high-power 131.5 GHz Gyrotron FU CW IV. The 30 W sub-THz wave generated in a long pulse TEmode with a frequency of 5 Hz was successfully transmitted to the modified Doty Scientific low-temperature CP/MAS probe through copper smooth-wall circular waveguides. Since serious RF noises on NMR signals by arcing in the electric circuit of the probe and undesired sample heating were induced by the continuous sub-THz wave pulse irradiation with higher powers, the on-off sub-THz wave pulse irradiation synchronized with the NMR detection was developed and the appropriate setting of the irradiation time and the cooling time corresponding to the non-irradiation time was found to be very effective for the suppression of the arcing and the sample heating. The attainable maximum DNP enhancement was more than 30 folds for C113C-enrichedD-glucose dissolved in the frozen medium containing mono-radical 4-amino-TEMPO. The first DNP/CP/MAS13C NMR spectra of poly(methyl methacrylate) (PMMA) sub-micron particles were obtained at the dispersed state in the same frozen medium, indicating that DNP-enhanced1H spins effectively diffuse from the medium to the PMMA particles through their surface and are detected as high-resolution13C spectra in the surficial region to which the1H spins reach. On the basis of these results, the possibility of the DNP/CP/MAS NMR characterization of the surface structure of nanomaterials including polymer materials was discussed.