Guarin David, Marhabaie Sina, Rosso Alberto, Abergel Daniel, Bodenhausen Geoffrey, Ivanov Konstantin L, Kurzbach Dennis
Département de Chimie, Ecole Normale Supérieure, PSL Research University, UPMC Univ Paris 06, CNRS, Laboratoire des Biomolécules (LBM), 24 rue Lhomond, 75005 Paris, France.
Sorbonne Universités, UPMC Univ Paris 06, Ecole Normale Supérieure, CNRS, Laboratoire des Biomolécules (LBM), 75005 Paris, France.
J Phys Chem Lett. 2017 Nov 16;8(22):5531-5536. doi: 10.1021/acs.jpclett.7b02233. Epub 2017 Nov 1.
Dynamic nuclear polarization (DNP) embraces a family of methods to increase signal intensities in nuclear magnetic resonance (NMR) spectroscopy. Despite extensive theoretical work that allows one to distinguish at least five distinct mechanisms, it remains challenging to determine the relative weights of the processes that are responsible for DNP in state-of-the-art experiments operating with stable organic radicals like nitroxides at high magnetic fields and low temperatures. Specifically, determining experimental conditions where DNP involves thermal mixing, which denotes a spontaneous heat exchange between different spin reservoirs, remains challenging. We propose an experimental approach to ascertain the prevalence of the thermal mixing regime by monitoring characteristic signature properties of the time evolution of the hyperpolarization. We find that thermal mixing is the dominant DNP mechanism at high nitroxide radical concentrations, while a mixture of different mechanisms prevails at lower concentrations.
动态核极化（DNP）包含一系列用于提高核磁共振（NMR）光谱中信号强度的方法。尽管有大量的理论工作使人们能够区分至少五种不同的机制，但在使用诸如硝基氧等稳定有机自由基在高磁场和低温下进行的前沿实验中，确定导致DNP的各过程的相对权重仍然具有挑战性。具体而言，确定DNP涉及热混合的实验条件（热混合是指不同自旋库之间的自发热交换）仍然具有挑战性。我们提出了一种实验方法，通过监测超极化时间演化的特征性标志性特性来确定热混合机制的普遍性。我们发现，在高硝基氧自由基浓度下，热混合是主要的DNP机制，而在较低浓度下，不同机制的混合占主导地位。
