Kouřilová Hana, Jurkutat Michael, Peat David, Kouřil Karel, Khan Alixander S, Horsewill Anthony J, MacDonald James F, Owers-Bradley John, Meier Benno
Institute of Biological Interfaces 4, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, 76344, Germany.
School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
Phys Chem Chem Phys. 2022 Nov 30;24(46):28242-28249. doi: 10.1039/d2cp04535d.
Radicals serve as a source of polarization in dynamic nuclear polarization, but may also act as polarization sink, in particular at low field. Additionally, if the couplings between the electron spins and different nuclear reservoirs are stronger than any of the reservoirs' couplings to the lattice, radicals can mediate hetero-nuclear polarization transfer. Here, we report radical-enhanced C relaxation in pyruvic acid doped with trityl. Up to 40 K, we find a linear carbon field dependence between 5 mT and 2 T. We model the dependence quantitatively, and find that the presence of trityl accelerates direct hetero-nuclear polarization transfer at low fields, while at higher fields C relaxation is diffusion limited. Measurements of hetero-nuclear polarization transfer up to 600 mT confirm the predicted radical-mediated proton-carbon mixing.
自由基在动态核极化中作为极化源，但也可能充当极化阱，尤其是在低场情况下。此外，如果电子自旋与不同核库之间的耦合强于任何一个核库与晶格的耦合，自由基可以介导异核极化转移。在此，我们报道了在掺杂有三苯甲基的丙酮酸中自由基增强的碳弛豫。在高达40 K的温度下，我们发现在5 mT至2 T之间碳场呈线性依赖关系。我们对这种依赖关系进行了定量建模，发现三苯甲基的存在加速了低场下的直接异核极化转移，而在较高场下碳弛豫受扩散限制。高达600 mT的异核极化转移测量证实了预测的自由基介导的质子 - 碳混合。
