Leavesley Alisa, Shimon Daphna, Siaw Ting Ann, Feintuch Akiva, Goldfarb Daniella, Vega Shimon, Kaminker Ilia, Han Songi
Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
Weizmann Institute of Science, Rehovot, Israel.
Phys Chem Chem Phys. 2017 Feb 1;19(5):3596-3605. doi: 10.1039/c6cp06893f.
Here, we present an integrated experimental and theoretical study of H dynamic nuclear polarization (DNP) of a frozen aqueous glass containing free radicals at 7 T, under static conditions and at temperatures ranging between 4 and 20 K. The DNP studies were performed with a home-built 200 GHz quasi-optics microwave bridge, powered by a tunable solid-state diode source. DNP using monochromatic and continuous wave (cw) irradiation applied to the electron paramagnetic resonance (EPR) spectrum of the radicals induces the transfer of polarization from the electron spins to the surrounding nuclei of the solvent and solutes in the frozen aqueous glass. In our systematic experimental study, the DNP enhanced H signals are monitored as a function of microwave frequency, microwave power, radical concentration, and temperature, and are interpreted with the help of electron spin-lattice relaxation times, experimental MW irradiation parameters, and the electron spectral diffusion (eSD) model introduced previously. This comprehensive experimental DNP study with mono-nitroxide radical spin probes was accompanied with theoretical calculations. Our results consistently demonstrate that eSD effects can be significant at 7 T under static DNP conditions, and can be systematically modulated by experimental conditions.
在此，我们展示了一项关于含自由基的冷冻水玻璃在7 T、静态条件及4至20 K温度范围内氢动态核极化（DNP）的综合实验与理论研究。DNP研究使用了由可调谐固态二极管源供电的自制200 GHz准光学微波桥进行。对自由基的电子顺磁共振（EPR）谱施加单色连续波（cw）辐射的DNP会促使极化从电子自旋转移至冷冻水玻璃中溶剂和溶质的周围原子核。在我们的系统实验研究中，监测DNP增强的氢信号作为微波频率、微波功率、自由基浓度和温度的函数，并借助电子自旋 - 晶格弛豫时间、实验微波辐射参数以及先前引入的电子光谱扩散（eSD）模型进行解释。这项使用单硝基自由基自旋探针的全面实验DNP研究伴随着理论计算。我们的结果一致表明，在静态DNP条件下，eSD效应在7 T时可能很显著，并且可以通过实验条件进行系统调节。
