A Slowly Relaxing Rigid Biradical for Efficient Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy: Expeditious Characterization of Functional Group Manipulation in Hybrid Materials
A Slowly Relaxing Rigid Biradical for Efficient Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy: Expeditious Characterization of Functional Group Manipulation in Hybrid Materials
复制标题
DOI：
10.1021/ja210177v
复制
发表时间：
2012-02-01
影响因子：
15
通讯作者：
Emsley, Lyndon
中科院分区：
文献类型：
--
作者：
Zagdoun, Alexandre;Casano, Gilles;Emsley, Lyndon
开发了一种具有长电子自旋-晶格弛豫时间（T-1e）的新型氮基双自由基，作为DNP固体核磁共振实验的外源极化源。在含1,1,2,2-四氯乙烷自由基溶液浸渍的杂化硅基介结构材料以及冷冻体溶液中，这种新型双自由基的性能得到了证明，在9.4 T的磁场和类似100 K的样品温度下，DNP增强因子（epsilon）超过100。报道了自由基浓度对DNP增强因子和总体灵敏度增强（Sigma(dagger)）的影响。双基相对较高的DNP效率归因于T-1e的增加，这使得电子共振更有效地饱和。这种新的双自由基被证明优于迄今为止在DNP表面增强材料核磁共振光谱中使用的极化剂，与室温下的传统核磁共振实验相比，硅-29 CPMAS光谱的总体灵敏度提高了113倍。这使得实验时间减少了1 / 12 700倍，使得C-13和N-15在自然同位素丰度下的一维和二维核磁共振光谱的获取快速（小时）。在这里，它被用来监测在有机硅杂化材料的表面功能上进行的一系列化学反应。
A new nitroxide-based biradical having a long electron spin-lattice relaxation time (T-1e) has been developed as an exogenous polarization source for DNP solid-state NMR experiments. The performance of this new biradical is demonstrated on hybrid silica-based mesostructured materials impregnated with 1,1,2,2-tetrachloroethane radical containing solutions, as well as in frozen bulk solutions, yielding DNP enhancement factors (epsilon) of over 100 at a magnetic field of 9.4 T and sample temperatures of similar to 100 K. The effects of radical concentration on the DNP enhancement factors and on the overall sensitivity enhancements (Sigma(dagger)) are reported. The relatively high DNP efficiency of the biradical is attributed to an increased T-1e, which enables more effective saturation of the electron resonance. This new biradical is shown to outperform the polarizing agents used so far in DNP surface-enhanced NMR spectroscopy of materials, yielding a 113-fold increase in overall sensitivity for silicon-29 CPMAS spectra as compared to conventional NMR experiments at room temperature. This results in a reduction in experimental times by a factor >12 700, making the acquisition of C-13 and N-15 one- and two-dimensional NMR spectra at natural isotopic abundance rapid (hours). It has been used here to monitor a series of chemical reactions carried out on the surface functionalities of a hybrid organic-silica material.