Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy at Very High Field and Fast MAS

极高场和快速 MAS 下的动态核极化增强固态核磁共振波谱

基本信息

项目摘要

Over the last two decades, magic angle spinning (MAS) solid-state NMR spectroscopy has evolved into a cornerstone technique for the structural characterization of a broad range of organic compounds, inorganic and hybrid materials. However, the main weakness of NMR is its intrinsically low sensitivity, preventing its use in many of the most exciting areas in materials science. Dynamic Nuclear Polarization (DNP) has emerged as the most promising approach to overcome the sensitivity issue of NMR. In a DNP experiment, the large polarization of unpaired electrons is transferred upon microwave irradiation to surrounding nuclei. For this purpose, a significant number of stable radicals as polarization sources has been developed which provide signal enhancements of two orders of magnitude at magnetic fields of 5–9.4 T. The most commonly used polarizing agents however, binitroxides relying on the Cross Effect, suffer from their unfavorable dependence on the magnetic field, as drastic reductions in enhancements are observed when going to very high field. At fast MAS frequencies, their performance is further attenuated due to depolarization processes, which decrease the real sensitivity of the NMR experiment. These major bottlenecks need to be overcome to further extend the application range of DNP enhanced solid-state NMR spectroscopy.This project is dedicated to the development of new DNP MAS NMR approaches at high magnetic field and fast MAS for the structural characterization of challenging materials. In a first task, new polarizing agents for high field Cross Effect DNP NMR will be developed by evaluating the performance of a new series of mixed Cross Effect radicals which are expected to outperform current binitroxide radicals at high field (18.8 T).In a second step, new sample formulations for Overhauser Effect DNP will be introduced, including the investigation of BDPA derivatives designed for this polarizing scheme as well as the optimization of the glassy matrices.Finally, DNP solid-state NMR methods at high field and fast MAS will be applied to surface organometallic catalysts. The newly developed strategies will be employed to characterize the detailed structure of active sites in alkene-metathesis catalysts supported on alumina-silica supports and more specifically, understand at a molecular level the role of the surface in the catalytic activity.Advances are expected in the field of DNP MAS NMR itself, from the introduction of new polarization sources tailored for high field DNP NMR, to sample formulation and to the implementation of state of the art pulse sequences under DNP conditions. In addition, the project shall provide new insights into the structure of alumina-silica surfaces and a better understanding of their key role in the activation of supported organometallic catalysts.
在过去的二十年中,魔角旋转(MAS)固态核磁共振波谱已经发展成为广泛的有机化合物,无机和杂化材料的结构表征的基石技术。然而,核磁共振的主要弱点是其固有的低灵敏度,这阻碍了它在材料科学中许多最激动人心的领域的应用。动态核极化(DNP)已成为克服核磁共振灵敏度问题的最有前途的方法。在DNP实验中,未配对电子的大极化在微波照射下被转移到周围的原子核。为此,大量稳定自由基作为极化源已经被开发出来,它们在5-9.4 t的磁场下提供两个数量级的信号增强。然而,最常用的极化剂,依赖于交叉效应的二氮氧化物,由于它们对磁场的不利依赖,当进入非常高的磁场时,观察到增强的急剧减少。在快速MAS频率下,由于退极化过程,其性能进一步衰减,降低了核磁共振实验的实际灵敏度。为了进一步扩大DNP增强固体核磁共振波谱的应用范围,需要克服这些主要的瓶颈。该项目致力于在高磁场和快速MAS下开发新的DNP MAS NMR方法,用于具有挑战性的材料的结构表征。在第一项任务中,将通过评估一系列新的混合交叉效应自由基的性能来开发用于高场交叉效应DNP NMR的新型极化剂,这些混合交叉效应自由基有望在高场(18.8 T)下优于当前的二氮氧化物自由基。在第二步中,将引入新的样品配方,包括为这种偏振方案设计的BDPA衍生物的研究以及玻璃矩阵的优化。最后,在高场和快速MAS下,DNP固态核磁共振方法将应用于表面有机金属催化剂。新开发的策略将用于表征氧化铝-二氧化硅载体上的烯烃复分解催化剂活性位点的详细结构,更具体地说,在分子水平上理解表面在催化活性中的作用。从为高场DNP NMR量身定制的新型极化源,到样品配方,再到DNP条件下最先进脉冲序列的实施,DNP MAS NMR领域本身有望取得进展。此外,该项目将为氧化铝-二氧化硅表面的结构提供新的见解,并更好地了解它们在负载型有机金属催化剂活化中的关键作用。

项目成果

期刊论文数量(1)
专著数量(0)
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Dr. Dorothea Wisser其他文献

Dr. Dorothea Wisser的其他文献

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{{ truncateString('Dr. Dorothea Wisser', 18)}}的其他基金

Operando Investigation of Heterogeneous Photocatalysis by Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
魔角旋转核磁共振波谱对异相光催化的操作研究
  • 批准号:
    503810318
  • 财政年份:
  • 资助金额:
    --
  • 项目类别:
    Research Grants

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