Department of Pharmacognosy and Natural Products Chemistry, School of Pharmacy, National and Kapodistrian University of Athens, Athens, Greece.
CICECO-Chemistry Department, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.
J Magn Reson. 2019 Aug;305:175-179. doi: 10.1016/j.jmr.2019.07.003. Epub 2019 Jul 5.
Dynamic Nuclear Polarization (DNP) can substantially enhance the sensitivity of NMR experiments. Among the implementations of DNP, ex-situ dissolution DNP (dDNP) achieves high signal enhancement levels owing to a combination of a large temperature factor between 1.4 and 300 K with the actual DNP effect in the solid state at 1.4 K. For sufficiently long T relaxation times much of the polarization can be preserved during dissolution with hot solvent, thus enabling fast experiments during the life time of the polarization. Unfortunately, for many metabolites found in biological samples such as blood, relaxation times are too short to achieve a significant enhancement. We have therefore introduced C-carbonyl labeled acetyl groups as probes into amino acid metabolites using a simple reaction protocol. The advantage of such tags is a sufficiently long T relaxation time, the possibility to enhance signal intensity by introducing C, and the possibility to identify tagged metabolites in NMR spectra. We demonstrate feasibility for mixtures of amino acids and for blood serum. In two-dimensional dDNP-enhanced HMQC experiments of these samples acquired in 8 s we can identify acetylated amino acids and other metabolites based on small differences in chemical shifts.
动态核极化（DNP）可以显著提高 NMR 实验的灵敏度。在 DNP 的各种实现方法中，由于在 1.4 K 下固态中的实际 DNP 效应与 1.4 到 300 K 之间的大温度因子相结合，因此离体溶解 DNP（dDNP）实现了高的信号增强水平。对于足够长的 T 弛豫时间，在热溶剂中溶解时可以保留大部分极化，从而在极化寿命期间实现快速实验。不幸的是，对于在生物样品（如血液）中发现的许多代谢物，弛豫时间太短而无法实现显著的增强。因此，我们使用简单的反应方案将 C-羰基标记的乙酰基作为探针引入到氨基酸代谢物中。这些标签的优点是 T 弛豫时间足够长，可以通过引入 C 来增强信号强度，并且可以在 NMR 谱中识别标记的代谢物。我们证明了混合物和血清中的可行性。在 8 秒内采集的这些样品的二维 dDNP 增强 HMQC 实验中，我们可以根据化学位移的微小差异来识别乙酰化氨基酸和其他代谢物。
