论文标题
自由基诱导的异核混合和低场$^{13} $ c在固体丙酮酸中放松
Radical-induced Hetero-Nuclear Mixing and Low-field $^{13}$C Relaxation in Solid Pyruvic Acid
论文作者
论文摘要
自由基充当动态核极化的来源，但也可能充当极化。如果电子旋转与不同的核储层之间的耦合比任何储层与晶格的耦合都更强，则自由基可以介导杂核混合。在这里，我们报告了以trityl掺杂的丙酮酸中的激进增强$^{13} $ c放松。我们发现碳$ t_1 $在5吨和2吨之间的线性依赖性。我们扩展了一种模型，先前用于质子，碳，预测通过自由基非Zeman储层的有效质子 - 碳混合，从20吨到以上的1 t超过1 t。线路的行驶，以及从根部附近到散装的田间依赖碳扩散。杂核极化转移的测量最高600吨，证实了预测的混合以及从弛豫分析推断出的两种效果。
Radicals serve as source in dynamic nuclear polarization, but may also act as polarization sink. If the coupling between the electron spins and different nuclear reservoirs is stronger than any of the reservoirs' couplings to the lattice, radicals can mediate hetero-nuclear mixing. Here, we report radical-enhanced $^{13}$C relaxation in pyruvic acid doped with trityl. We find a linear dependence of the carbon $T_1$ on field between 5 mT and 2 T. We extend a model, employed previously for protons, to carbon, and predict efficient proton-carbon mixing via the radical Non-Zeeman reservoir, for fields from 20 mT to beyond 1 T. Discrepancies between the observed carbon relaxation and the model are attributed to enhanced direct hetero-nuclear mixing due to trityl-induced linebroadening, and a field-dependent carbon diffusion from the radical vicinity to the bulk. Measurements of hetero-nuclear polarization transfer up to 600 mT confirm the predicted mixing as well as both effects inferred from the relaxation analysis.
