Moreno Karlos X, Nasr Khaled, Milne Mark, Sherry A Dean, Goux Warren J
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, United States.
Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Road, Richardson, TX 75080, United States.
J Magn Reson. 2015 Aug;257:15-23. doi: 10.1016/j.jmr.2015.04.013. Epub 2015 May 14.
Here we report the polarization of the solvent OH protons by SABRE using standard iridium-based catalysts under slightly acidic conditions. Solvent polarization was observed in the presence of a variety of structurally similar N-donor substrates while no solvent enhancement was observed in the absence of substrate or para-hydrogen (p-H2). Solvent polarization was sensitive to the polarizing field and catalyst:substrate ratio in a manner similar to that of substrate protons. SABRE experiments with pyridine-d5 suggest a mechanism where hyperpolarization is transferred from the free substrate to the solvent by chemical exchange while measured hyperpolarization decay times suggest a complimentary mechanism which occurs by direct coordination of the solvent to the catalytic complex. We found the solvent hyperpolarization to decay nearly 3 times more slowly than its characteristic spin-lattice relaxation time suggesting that the hyperpolarized state of the solvent may be sufficiently long lived (∼20s) to hyperpolarize biomolecules having exchangeable protons. This route may offer future opportunities for SABRE to impact metabolic imaging.
在此，我们报告了在弱酸性条件下，使用基于铱的标准催化剂通过SABRE实现溶剂OH质子的极化。在存在多种结构相似的含氮供体底物的情况下观察到了溶剂极化，而在没有底物或仲氢（p-H2）的情况下未观察到溶剂增强。溶剂极化对极化场和催化剂与底物的比例敏感，其方式与底物质子类似。用吡啶-d5进行的SABRE实验表明了一种机制，即超极化通过化学交换从游离底物转移到溶剂，而测得的超极化衰减时间表明了一种互补机制，该机制是通过溶剂与催化络合物的直接配位发生的。我们发现溶剂超极化的衰减速度比其特征性自旋晶格弛豫时间慢近3倍，这表明溶剂的超极化状态可能具有足够长的寿命（约20秒），足以使具有可交换质子的生物分子超极化。这条途径可能为SABRE影响代谢成像提供未来机会。
