Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel.
J Magn Reson. 2011 Jul;211(1):96-100. doi: 10.1016/j.jmr.2011.04.001. Epub 2011 Apr 5.
Dynamic nuclear polarization (DNP) followed by sudden sample dissolution, is a topic of active investigation owing to the method's unique prospects for the delivery of NMR spectra and images with unprecedented sensitivity. This experiment achieves hyperpolarization by the combined effects of electron-nuclear irradiation and cryogenic operation; the exploitation of these states occurs following a sudden melting and flushing of the resulting pellet from its original environment into a conventional, liquid-state setting. This melting and flushing usually demands using the equivalent of a few milliliters of hot solvent, a procedure which although well suited for in vivo studies leads to an excessive sample volume when considering typical analytical settings. The present study explores a way of reducing the ensuing dilution of the hyperpolarized analytes, by employing a combination of immiscible liquids for performing the melting and flushing. It is shown that suitable combinations of immiscible solvents - both in terms of their heat capacities and densities - allow one to melt the targeted cryogenic pellet and dissolve the hyperpolarized analytes in a fraction of the solvent hitherto required. By tailoring the resulting volume to the needs of a conventional 5mm NMR probe, a substantial sensitivity enhancement can be added to the hyperpolarization process. An extra benefit may arise from using radicals that preferentially dissolve in the immiscible organic phase, by way of a lengthening of the relaxation time of the investigated analytes. Examples of these principles are given, and further potential extensions of this approach are discussed.
动态核极化（DNP）随后是样品的突然溶解，由于该方法在提供具有空前灵敏度的 NMR 谱和图像方面具有独特的前景，因此是一个活跃的研究课题。该实验通过电子-核辐照和低温操作的综合效应实现超极化；在将所得的颗粒从其原始环境突然熔化和冲洗到常规的液态环境中后，会利用这些状态。这种熔化和冲洗通常需要使用几毫升热溶剂的等效物，尽管该程序非常适合体内研究，但在考虑典型的分析设置时，会导致样品体积过大。本研究通过使用不混溶的液体组合来减少随后的超极化分析物的稀释，从而探索了一种方法。结果表明，不混溶溶剂的合适组合 - 就其热容和密度而言 - 可以使目标低温颗粒熔化，并将超极化分析物溶解在迄今所需溶剂的一小部分中。通过将所得体积调整为常规 5mm NMR 探头的需求，可以为超极化过程添加实质性的灵敏度增强。通过使用优先溶解在不混溶有机相中的自由基，可能会延长研究分析物的弛豫时间，从而带来额外的好处。给出了这些原理的示例，并讨论了这种方法的进一步潜在扩展。
