论文标题
用振荡脉冲序列增强剑刀：对称性降低鲁棒性
SABRE Enhancement with Oscillating Pulse Sequences: Symmetry Reduces Robustness
论文作者
论文摘要
SABER（通过可逆交换进行信号扩增）提供了一种简单，快速且具有成本效益的方法，可以使溶液中的各种分子过极化，并已通过质子进行证明，并且最近与Heteronuclei（X-Sabre）一起证明。 SABER效应的常规分析是基于水平抗跨（LAC）的，它需要非常低的磁场（〜0.6UT）才能实现共振和转移自旋顺序，并将自旋顺序从para-hydrdogen到靶杂核。我们在最近的研究中已经证明，在Saber中使用的LAC的有效性非常有限，因此用LACS预测的最大剑翼极化是不正确的。在这里，我们提出了几个振荡脉冲序列，这些脉冲序列使用远离共振条件的磁场，并且通常可以将极化三倍地化。与平均哈密顿理论的分析表明，振荡脉冲实际上可以调整氢化物和靶核之间的J耦合，并且耦合较弱的耦合会产生最大的极化。这种理论处理与模拟和实验结合在一起，相对于传统的X-S-S-S-S-S-S-S-S-S-S-S-Sabre方法显示出很大的磁化改进。它还表明，与大多数脉冲序列应用相比，切换框架中具有时间对称性的波形使磁化化生成对实验缺陷更强大。
SABRE (Signal Amplification by Reversible Exchange) methods provide a simple, fast, and cost-effective method to hyperpolarize a wide variety of molecules in solution, and have been demonstrated with protons and, more recently, with heteronuclei (X-SABRE). The conventional analysis of the SABRE effect is based on level anti-crossings (LACs), which requires very low magnetic fields (~ 0.6uT) to achieve resonance and transfer spin order from the para-hydrogen to target heteronuclei. We have demonstrated in our recent study that the validity of LACs used in SABRE is very limited, so the maximum SABRE polarization predicted with LACs is not correct. Here, we present several oscillating pulse sequences that use magnetic fields far away from the resonance condition and can commonly triple the polarization. An analysis with average Hamiltonian theory indicates that the oscillating pulse, in effect, adjusts the J-couplings between hydrides and target nuclei and that a much weaker coupling produces maximum polarization. This theoretical treatment, combined with simulations and experiment, show substantial magnetization improvements relative to traditional X-SABRE methods. It also shows that, in contrast to most pulse sequence applications, waveforms with reduced time symmetry in the toggling frame make magnetization generation more robust to experimental imperfections.
