Effect of water/glycerol polymorphism on dynamic nuclear polarization
Effect of water/glycerol polymorphism on dynamic nuclear polarization
复制标题
水/甘油多态对动态核极化的影响
DOI：
10.1039/c8cp00358k
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发表时间：
2018-04-21
影响因子：
3.3
通讯作者：
Han, Songi
中科院分区：
文献类型：
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作者：
Leavesley, Alisa;Wilson, Christopher B.;Han, Songi
稳健实验方法的一个最重要的特点是获得一致的数据。然而，在动态核极化(DNP)中，已经观察到DNP对名义上相同的样品的核磁共振信号增强在不同的实验阶段可能会有所不同。我们研究了不同的冷冻条件对DNP结果的影响，标准样品是体积为50/40/10的d(8)-甘油/D2O/H2O溶液，4-氨基节奏为40 mm，发现与快速冷冻样品相比，在玻璃化转变温度(T-g)以上10K热处理样品会引起DNP图谱的显著变化和增强。当改变甘油组成以产生60/30/10d(8)-甘油/D2O/H2O的溶液时，DNP的性能变得明显更一致，即使是在非常不同的样品冷冻方法下制备的样品，这与50/40/10溶液的情况形成了鲜明的对比。在与DNP实验相同的样品和实验条件下，测量了EPR线形T-m和玻璃化转变温度T-g，以支持不同冻结方法由于形成不同晶型的玻璃而改变了4-氨基节奏径向在50/40/10溶液中的分布的结论，这在60/30/10溶液中有所减轻，与水/甘油玻璃化文献一致。
A paramount feature of robust experimental methods is acquiring consistent data. However, in dynamic nuclear polarization (DNP), it has been observed that the DNP-induced NMR signal enhancement of nominally the same sample can vary between different experimental sessions. We investigated the impact of various freezing conditions on the DNP results for a standard sample, a 50/40/10 by volume d(8)-glycerol/D2O/H2O solution of 40 mM 4-amino TEMPO, and found that annealing the samples 10 K above the glass transition temperature (T-g) causes significant changes to the DNP profiles and enhancements compared to that in rapidly frozen samples. When varying the glycerol composition to yield a solution of 60/30/10 d(8)-glycerol/D2O/H2O, the DNP performance became markedly more consistent, even for samples prepared under vastly different sample freezing methods, in stark contrast with that of the 50/40/10 solution. The EPR lineshapes, T-m, and glass transition temperature, T-g, were measured under the same sample and experimental conditions as used for the DNP experiments to support the conclusion that different freezing methods change the distribution of 4-amino TEMPO radials in the 50/40/10 solution due to the formation of different polymorphs of the glass, which is mitigated in the 60/30/10 solution and is consistent with the water/glycerol vitrification literature.