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Efficient DNP at high fields and fast MAS with antenna-sensitized dinitroxides
Chemical Science ( IF 7.6 ) Pub Date : 2024-09-12 , DOI: 10.1039/d4sc04473h Lorenzo Niccoli , Gilles Casano , Georges Menzildjian , Maxim Yulikov , Thomas Robinson , Salah-Eddine Akrial , Zhuoran Wang , Christian Reiter , Armin Purea , Didier Siri , Amrit Venkatesh , Lyndon Emsley , David Gajan , Moreno Lelli , Olivier Ouari , Anne Lesage
Chemical Science ( IF 7.6 ) Pub Date : 2024-09-12 , DOI: 10.1039/d4sc04473h Lorenzo Niccoli , Gilles Casano , Georges Menzildjian , Maxim Yulikov , Thomas Robinson , Salah-Eddine Akrial , Zhuoran Wang , Christian Reiter , Armin Purea , Didier Siri , Amrit Venkatesh , Lyndon Emsley , David Gajan , Moreno Lelli , Olivier Ouari , Anne Lesage
Dynamic Nuclear Polarization (DNP) can significantly enhance the sensitivity of solid-state NMR. In DNP, microwave irradiation induces polarization transfer from unpaired electron spins to 1H nuclear spins via hyperfine couplings and spin-diffusion. The structure of the polarizing agents that host the electron spins is key for DNP efficiency. Currently, only a handful of structures perform well at very high magnetic fields (≥18.8 T), and enhancements are significantly lower than those obtained at lower fields. Here, we introduce a new series of water-soluble nitroxide biradicals with a scaffold augmented by dihydroxypropyl antenna chains that perform significantly better than previous dinitroxides at 18.8 T. The new radical M-TinyPol(OH)4 yields enhancement factors of ∼220 at 18.8 T and 60 kHz MAS, which is a nearly factor 2 larger than for the previous best performing dinitroxides. The performance is understood through 2H ESEEM measurements to probe solvent accessibility, supported by Molecular Dynamics simulations, and by experiments on deuterated samples. We find that the deuterated glycerol molecules in the matrix are located mainly in the second solvation shell of the NO bond, limiting access for protonated water molecules, and restricting spin diffusion pathways. This provides a rational understanding of why the dihydroxypropyl chains present in the best-performing structures are essential to deliver the polarization to the bulk solution.
中文翻译:
高场下的高效 DNP 和具有天线敏化二硝基氧化物的快速 MAS
动态核极化 (DNP) 可以显着提高固态 NMR 的灵敏度。在 DNP 中,微波辐射通过超精细耦合和自旋扩散诱导从不成对电子自旋到1 H 核自旋的极化转移。承载电子自旋的极化剂的结构是 DNP 效率的关键。目前,只有少数结构在极高磁场(≥18.8 T)下表现良好,并且增强效果明显低于在较低磁场下获得的增强效果。在这里,我们推出了一系列新的水溶性氮氧双自由基,其支架由二羟丙基天线链增强,在 18.8 T 下的性能明显优于以前的二氮氧自由基。新的自由基 M-TinyPol(OH) 4在 18.8 T 下的增强因子为 ∼220 T 和 60 kHz MAS,比之前性能最佳的二硝基氧几乎高出 2 倍。通过2 H ESEEM 测量来了解其性能,以探测溶剂的可及性,并得到分子动力学模拟和氘代样品实验的支持。我们发现基质中的氘化甘油分子主要位于NO键的第二溶剂化壳中,限制了质子化水分子的进入,并限制了自旋扩散途径。这提供了对为什么最佳性能结构中存在的二羟丙基链对于将极化传递到本体溶液至关重要的原因的合理理解。
更新日期:2024-09-12
中文翻译:
高场下的高效 DNP 和具有天线敏化二硝基氧化物的快速 MAS
动态核极化 (DNP) 可以显着提高固态 NMR 的灵敏度。在 DNP 中,微波辐射通过超精细耦合和自旋扩散诱导从不成对电子自旋到1 H 核自旋的极化转移。承载电子自旋的极化剂的结构是 DNP 效率的关键。目前,只有少数结构在极高磁场(≥18.8 T)下表现良好,并且增强效果明显低于在较低磁场下获得的增强效果。在这里,我们推出了一系列新的水溶性氮氧双自由基,其支架由二羟丙基天线链增强,在 18.8 T 下的性能明显优于以前的二氮氧自由基。新的自由基 M-TinyPol(OH) 4在 18.8 T 下的增强因子为 ∼220 T 和 60 kHz MAS,比之前性能最佳的二硝基氧几乎高出 2 倍。通过2 H ESEEM 测量来了解其性能,以探测溶剂的可及性,并得到分子动力学模拟和氘代样品实验的支持。我们发现基质中的氘化甘油分子主要位于NO键的第二溶剂化壳中,限制了质子化水分子的进入,并限制了自旋扩散途径。这提供了对为什么最佳性能结构中存在的二羟丙基链对于将极化传递到本体溶液至关重要的原因的合理理解。