Dynamic nuclear polarization with biradicals
Dynamic nuclear polarization with biradicals
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DOI：
10.1021/ja039749a
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发表时间：
2004-09-08
影响因子：
15
通讯作者：
Griffin, RG
中科院分区：
文献类型：
--
作者：
Hu, KN;Yu, HH;Griffin, RG
首次在旋转固体中使用双自由基而不是单体顺磁中心作为极化剂进行了动态核极化实验。具体来说，两个TEMPO自由基与可变长度的聚乙二醇链相连，其中乙二醇单位的数量为2、3或4。核磁共振实验表明，DNP实验中观察到的信号与链的长度近似成反比。因此，具有较大电子偶极偶联的较短链产生较大的增强。与相同浓度的单体氮氧化物自由基相比，增强的大小是4倍大，在n= 2链上达到了~ 175的值。
Dynamic nuclear polarization (DNP) experiments in rotating solids have been performed for the first time using biradicals rather than monomeric paramagnetic centers as polarizing agents. Specifically, two TEMPO radicals were tethered with a poly(ethylene glycol) chain of variable length where the number of glycol units was 2, 3, or 4. NMR experiments show that the signal observed in DNP experiments is approximately inversely proportional to the length of the chain. Thus, the shorter chain with larger electron dipolar couplings yields larger enhancements. The size of the enhancement is a factor of 4 larger than obtained with the identical concentration of monomeric nitroxide radicals achieving a value of ∼175 for then= 2 chain.