Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, USA.
J Chem Phys. 2019 Dec 28;151(24):245102. doi: 10.1063/1.5131452.
Low-concentration photochemically induced dynamic nuclear polarization (LC-photo-CIDNP) has recently emerged as a powerful technology for the detection of aromatic amino acids and proteins in solution in the low-micromolar to nanomolar concentration range. LC-photo-CIDNP is typically carried out in the presence of high-power lasers, which are costly and maintenance-heavy. Here, we show that LC-photo-CIDNP can be performed with light-emitting diodes (LEDs), which are inexpensive and much less cumbersome than lasers, laser diodes, flash lamps, or other light sources. When nuclear magnetic resonance (NMR) sample concentration is within the low-micromolar to nanomolar range, as in LC-photo-CIDNP, replacement of lasers with LEDs leads to no losses in sensitivity. We also investigate the effect of optical-fiber thickness and compare excitation rate constants of an Ar ion laser (488 nm) and a 466 nm LED, taking LED emission bandwidths into account. In addition, importantly, we develop a novel pulse sequence (C RASPRINT) to perform ultrarapid LC-photo-CIDNP data collection. Remarkably, C RASPRINT leads to 4-fold savings in data collection time. The latter advance relies on the fact that photo-CID nuclear hyperpolarization does not suffer from the longitudinal-relaxation recovery requirements of conventional NMR. Finally, we combine both the above improvements, resulting in facile and rapid (≈16 s-2.5 min) collection of 1 and 2D NMR data on aromatic amino acids and proteins in solution at nanomolar to low micromolar concentration.
低浓度光诱导动态核极化（LC-photo-CIDNP）最近成为一种强大的技术，可用于检测溶液中低至纳摩尔浓度范围内的芳香族氨基酸和蛋白质。LC-photo-CIDNP 通常在高功率激光器的存在下进行，这些激光器成本高且维护复杂。在这里，我们展示了可以使用发光二极管（LED）进行 LC-photo-CIDNP，与激光器、激光二极管、闪光灯或其他光源相比，LED 价格低廉且体积小巧得多。当核磁共振（NMR）样品浓度处于低至纳摩尔浓度范围内时，如在 LC-photo-CIDNP 中，用 LED 代替激光器不会导致灵敏度损失。我们还研究了光纤厚度的影响，并比较了氩离子激光器（488nm）和 466nm LED 的激发速率常数，同时考虑了 LED 发射带宽。此外，重要的是，我们开发了一种新的脉冲序列（C RASPRINT）来进行超快 LC-photo-CIDNP 数据采集。值得注意的是，C RASPRINT 使数据采集时间缩短了 4 倍。这一进步依赖于这样一个事实，即光 CID 核极化不受传统 NMR 的纵向弛豫恢复要求的影响。最后，我们结合了上述两项改进，使溶液中芳香族氨基酸和蛋白质的 1D 和 2D NMR 数据能够在纳摩尔至低微摩尔浓度范围内轻松快速（≈16 s-2.5 min）采集。
