Milani Jonas, Vuichoud Basile, Bornet Aurélien, Melzi Roberto, Jannin Sami, Bodenhausen Geoffrey
Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, CH-1015 Lausanne, Switzerland.
Bruker Italia S.r.l., Viale V. Lancetti 43, 20158 Milano, Italy.
Rev Sci Instrum. 2017 Jan;88(1):015109. doi: 10.1063/1.4973777.
Dynamic Nuclear Polarization (DNP) is often achieved by the direct transfer of polarization from electrons to nuclei such as C, induced by microwave saturation of the wings of narrow EPR lines of radicals like trityl. In the indirect approach on the other hand, DNP is used to transfer the polarization from the electrons of radicals such as nitroxides that have broad EPR lines to nuclear spins I = H, followed by cross-polarization (CP) from I = H to S = C or other nuclei with low gyromagnetic ratios. This approach is particularly attractive for S = N, since direct DNP yields modest polarizations P(N) < 4% with build-up times that can be as long as τ(N) > 2 h. In this paper, we show that CP from H to N at 1.2 K can yield P(N) = 25% with τ(N) = 10-15 min. After rapid dissolution and transfer to a solution-state NMR spectrometer, a polarization P(N) = 20% was observed at 300 K. The longitudinal relaxation times in solution can be as long as T(N) > 800 s in favorable cases.
动态核极化（DNP）通常是通过将极化从电子直接转移到原子核（如碳原子核）来实现的，这是由三苯甲基等自由基的窄电子顺磁共振（EPR）线的边带微波饱和所诱导的。另一方面，在间接方法中，DNP用于将极化从具有宽EPR线的自由基（如氮氧化物）的电子转移到核自旋I = H，然后从I = H交叉极化（CP）到S = C或其他具有低旋磁比的原子核。这种方法对S = N特别有吸引力，因为直接DNP产生的极化程度适中，P(N) < 4%，且极化建立时间可能长达τ(N) > 2小时。在本文中，我们表明在1.2 K下从H到N的CP可以产生P(N) = 25%，τ(N) = 10 - 15分钟。快速溶解并转移到溶液态核磁共振光谱仪后，在300 K下观察到极化P(N) = 20%。在有利的情况下，溶液中的纵向弛豫时间可以长达T(N) > 800秒。
