Relaxation Dynamics of Nuclear Long-Lived Spin States in Propane and Propane-d6 Hyperpolarized by Parahydrogen
Relaxation Dynamics of Nuclear Long-Lived Spin States in Propane and Propane-d6 Hyperpolarized by Parahydrogen
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DOI：
10.1021/acs.jpcc.9b01538
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发表时间：
2019-05-09
影响因子：
3.7
通讯作者：
Chekmenev, Eduard Y.
中科院分区：
文献类型：
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作者：
Ariyasingha, Nuwandi M.;Salnikov, Oleg G.;Chekmenev, Eduard Y.
本文报道了超极化（HP）丙烷和HP丙烷-d（6）的弛豫动力学的系统研究。仲氢诱导的过量仲氢（pH（2））分别加成到丙烯和丙烯-d（6）。在HP丙烷LLS的低磁场下为这些分子创建的长寿命自旋态（LLS）以指数方式衰减，时间常数（T-LLS）比相应的T-1值大大约三倍。T-LLS和T-1在1 atm（肺MRI的最生物医学相关条件）至5 atm范围内随丙烷压力线性增加。高压丙烷气在1atm下的T-LLS值与3s相似。基质（丙烯-d（6））的氘化产生HP丙烷-d（6）气体，其T-LLS值比HP完全质子化的丙烷气体的T-LLS值短约20%，表明氘化对LLS HP状态的寿命没有益处。在非均相氢化反应期间使用pH（2）或NH 4/N-2缓冲气体[导致纯HP丙烷（100：0，即，无缓冲气体）与HP丙烷气体与缓冲气体的43：57混合物]的比较，导致（i）T-1无显著变化，（ii）T-LLS值降低（分别为35 +/-7%和8 +/-7%）;以及（iii）随着丙烷浓度的降低，高压丙烷气体的极化水平增加（分别增加1.6 +/- 0.1倍和1.4 +/- 0.1倍，尽管T-LLS降低，这导致在HP气体输送期间不成比例地更大的极化损耗）。此外，我们还证明了高压丙烷低温收集的可行性（当使用缓冲气体时，这可能有助于制备更大量的浓缩高压丙烷），并且液化高压丙烷的T-LLS达到14.7 s，大于T-LLS值在任何研究压力下的高压丙烷气体。最后，我们探讨了使用部分自旋锁定诱导交叉（SLIC）的射频（RF）脉冲序列转换成可观察的H-1核磁在低磁场的人口过剩的LLS的效用。我们发现，（i）即使采用SLIC脉冲持续时间的最佳或接近最佳值时，也保留了大量的过填充LLS，以及（ii）丙烷的过填充LLS也相对不受强RF脉冲的影响，从而表明LLS非常适合作为NMR/MRI检测应用中的自旋极化库。所提出的研究结果可能是有用的，通过使用惰性缓冲气体的HET-PHIP产生的HP丙烷的极化水平的改善;增加的HP状态的寿命在制备和存储过程中;和开发高效的方法的超快MR成像的HP丙烷的HP丙烷气体的生物医学应用的背景下，包括其潜在的用途作为可吸入的造影剂。
We report a systematic study of relaxation dynamics of hyperpolarized (HP) propane and HP propane-d(6) prepared by heterogeneous pairwise 0.0475 T were employed for this study. The parahydrogen-induced overpopulation parahydrogen (pH(2)) addition to propylene and propylene-d(6), respectively. Long-lived spin states (LLSs) created for these molecules at a low magnetic field of of a HP propane LLS decays exponentially with a time constant (T-LLS) approximately threefold greater than the corresponding T-1 values. Both T-LLS and T-1 increase linearly with propane pressure in the range of 1 atm (the most biomedically relevant conditions for pulmonary MRI) to 5 atm. The T-LLS value of HP propane gas at 1 atm is similar to 3 s. Deuteration of the substrate (propylene-d(6)) yields HP propane-d(6) gas with T-LLS values approximately 20% shorter than those of HP fully protonated propane gas, indicating that deuteration does not benefit the lifetime of the LLS HP state. The use of pH(2) or Xe/N-2 buffering gas during heterogeneous hydrogenation reaction [leading to production of pure HP propane (100:0, i.e., no buffering gas) versus a 43:57 mixture of HP propane gas with buffering gas] results in (i) no significant changes in T-1, (ii) decrease of T-LLS values (by 35 +/- 7 and 8 +/- 7%, respectively); and (iii) an increase of the polarization levels of HP propane gas with a propane concentration decrease (by 1.6 +/- 0.1-fold and 1.4 +/- 0.1-fold, respectively, despite the decrease in T-LLS, which leads to disproportionately greater polarization losses during HP gas transport). Moreover, we demonstrate the feasibility of HP propane cryocollection (which can be potentially useful for preparing larger amounts of concentrated HP propane, when buffering gas is employed), and T-LLS of liquefied HP propane reaches 14.7 s, which is greater than the T-LLS value of HP propane gas at any pressure studied. Finally, we have explored the utility of using a partial spin-lock induced crossing (SLIC) radio-frequency (RF) pulse sequence for converting the overpopulated LLS into observable H-1 nuclear magnetization at a low magnetic field. We find that (i) the bulk of the overpopulated LLS is retained even when the optimal or near-optimal values of SLIC pulse duration are employed, and (ii) the overpopulated LLS of propane is also relatively immune to strong RF pulses, thereby indicating that LLS is highly suitable as a spin-polarization reservoir in the context of NMR/MRI detection applications. The presented findings may be useful for improving the levels of polarization of HP propane produced by HET-PHIP via the use of an inert buffer gas; increasing the lifetime of the HP state during preparation and storage; and developing efficient approaches for ultrafast MR imaging of HP propane in the context of biomedical applications of HP propane gas, including its potential use as an inhalable contrast agent.