Observing and preventing rubidium runaway in a direct-infusion xenon-spin hyperpolarizer optimized for high-resolution hyper-CEST (chemical exchange saturation transfer using hyperpolarized nuclei) NMR
Observing and preventing rubidium runaway in a direct-infusion xenon-spin hyperpolarizer optimized for high-resolution hyper-CEST (chemical exchange saturation transfer using hyperpolarized nuclei) NMR
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DOI：
10.1063/1.4865944
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发表时间：
2014-02-28
影响因子：
4.4
通讯作者：
Schroeder, L.
中科院分区：
文献类型：
--
作者：
Witte, C.;Kunth, M.;Schroeder, L.
众所周知，氙会与蛋白质和合成分子发生主客体相互作用。由于氙还可以通过自旋交换光泵浦进行超极化，从而可以研究高度稀释的系统，因此它成为此类主体分子的理想核磁共振探针。使用超极化核的化学交换饱和转移 (Hyper-CEST) 可以进一步提高氙作为探针的效用，但对于高精度实验，需要针对此类测量进行优化的偏振器和氙注入系统。我们提出了专为满足 Hyper-CEST 测量要求而设计的超极化器和氙气注入系统的设计。该设计的一个关键要素是防止铷失控，这是一种由激光加热引起的链式反应，可防止高光子密度的有效利用。使用沿着泵浦单元放置的热电偶，我们确定了热源和发生铷失控的条件。然后，我们展示了主动冷却光学单元以防止紧凑装置中铷失控的有效性。这导致极化率比未冷却时高 2-3 倍，使我们能够在 Xe-129 的连续流速为 9 毫升/分钟的情况下实现 25% 的极化率。这种设计的简单性还使其可以改装到许多现有的偏光器上。结合可将射击噪声降低至 0.56% 的定向注入系统，我们以前所未有的细节捕获了 Hyper-CEST 光谱，使我们能够完全解析仅相距 1.62 ppm 的峰。由于其高偏振性和出色的稳定性，我们的设计可以将主客体系统的基础理论与低浓度的实验进行比较，这对于以前的偏振器来说是极其困难的。 (C) 2014 AIP 出版有限责任公司。
Xenon is well known to undergo host-guest interactions with proteins and synthetic molecules. As xenon can also be hyperpolarized by spin exchange optical pumping, allowing the investigation of highly dilute systems, it makes an ideal nuclear magnetic resonance probe for such host molecules. The utility of xenon as a probe can be further improved using Chemical Exchange Saturation Transfer using hyperpolarized nuclei (Hyper-CEST), but for highly accurate experiments requires a polarizer and xenon infusion system optimized for such measurements. We present the design of a hyperpolarizer and xenon infusion system specifically designed to meet the requirements of Hyper-CEST measurements. One key element of this design is preventing rubidium runaway, a chain reaction induced by laser heating that prevents efficient utilization of high photon densities. Using thermocouples positioned along the pumping cell we identify the sources of heating and conditions for rubidium runaway to occur. We then demonstrate the effectiveness of actively cooling the optical cell to prevent rubidium runaway in a compact setup. This results in a 2-3-fold higher polarization than without cooling, allowing us to achieve a polarization of 25% at continuous flow rates of 9 ml/min of Xe-129. The simplicity of this design also allows it to be retrofitted to many existing polarizers. Combined with a direction infusion system that reduces shot-to-shot noise down to 0.56% we have captured Hyper-CEST spectra in unprecedented detail, allowing us to completely resolve peaks separated by just 1.62 ppm. Due to its high polarization and excellent stability, our design allows the comparison of underlying theories of host-guest systems with experiment at low concentrations, something extremely difficult with previous polarizers. (C) 2014 AIP Publishing LLC.