Parish Christopher, Niedbalski Peter, Wang Qing, Khashami Fatemeh, Hayati Zahra, Liu Mengtian, Song Likai, Lumata Lloyd
Department of Physics, University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080, USA.
National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, USA.
J Chem Phys. 2019 Jun 21;150(23):234307. doi: 10.1063/1.5096036.
Glassing matrix deuteration could be a beneficial sample preparation method for C dynamic nuclear polarization (DNP) when large electron paramagnetic resonance (EPR) width free radicals are used. However, it could yield the opposite DNP effect when samples are doped with small EPR width free radicals. Herein, we have investigated the influence of solvent deuteration on the C nuclear and electron relaxation that go along with the effects on C DNP intensities at 3.35 T and 1.2 K. For C DNP samples doped with trityl OX063, the C DNP signals decreased significantly when the protons are replaced by deuterons in glycerol:water or DMSO:water solvents. Meanwhile, the corresponding solid-state C T relaxation times of trityl OX063-doped samples generally increased upon solvent deuteration. On the other hand, C DNP signals improved by a factor of ∼1.5 to 2 upon solvent deuteration of samples doped with 4-oxo-TEMPO. Despite this C DNP increase, there were no significant differences recorded in C T values of TEMPO-doped samples with nondeuterated or fully deuterated glassing matrices. While solvent deuteration appears to have a negligible effect on the electron T relaxation of both free radicals, the electron T relaxation times of these two free radicals generally increased upon solvent deuteration. These overall results suggest that while the solid-phase C DNP signals are dependent upon the changes in total nuclear Zeeman heat capacity, the C relaxation effects are related to H/H nuclear spin diffusion-assisted C polarization leakage in addition to the dominant paramagnetic relaxation contribution of free radical centers.
当使用大电子顺磁共振（EPR）线宽的自由基时，玻璃化基质氘代可能是一种有利于碳动态核极化（DNP）的样品制备方法。然而，当样品掺杂小EPR线宽的自由基时，可能会产生相反的DNP效应。在此，我们研究了溶剂氘代对碳核弛豫和电子弛豫的影响，以及在3.35 T和1.2 K下对碳DNP强度的影响。对于掺杂三苯甲基OX063的碳DNP样品，当甘油：水或二甲基亚砜：水溶剂中的质子被氘取代时，碳DNP信号显著降低。同时，掺杂三苯甲基OX063的样品相应的固态碳横向弛豫时间通常随着溶剂氘代而增加。另一方面，掺杂4-氧代-TEMPO的样品在溶剂氘代后，碳DNP信号提高了约1.5至2倍。尽管碳DNP有所增加，但对于掺杂TEMPO且玻璃化基质未氘代或完全氘代的样品，其碳横向弛豫时间值没有显著差异。虽然溶剂氘代似乎对两种自由基的电子横向弛豫影响可忽略不计，但这两种自由基的电子横向弛豫时间通常随着溶剂氘代而增加。这些总体结果表明，虽然固相碳DNP信号取决于总核塞曼热容量的变化，但碳弛豫效应除了自由基中心的主要顺磁弛豫贡献外，还与氢/氢核自旋扩散辅助的碳极化泄漏有关。
