Title: Hyperpolarization of cis-15N,15N'-azobenzene by parahydrogen at ultralow magnetic fields Show Chinese title

Title: 超低磁场下通过仲氢对顺式-15N,15N'-偶氮苯的超极化

Abstract: Development of the methods to exploit nuclear hyperpolarization and search for molecules whose nuclear spins can be efficiently hyperpolarized is an active area in nuclear magnetic resonance. Of particular interest are those molecules that have long nuclear relaxation times, making them to be suitable candidates as contrast agents in magnetic resonance imaging. In this work, we present a detailed study of SABRE SHEATH (Signal Amplification By Reversible Exchange in Shield Enabled Alignment Transfer to Heteronuclei) experiments of 15N,15N' azobenzene. In SABRE SHEATH experiments nuclear spins of the target are hyperpolarized by transfer of spin polarization from parahydrogen at ultralow fields during a reversible chemical process. The studied system is complicated, and we are concerned only about a subset of the data, presenting details for the molecules that experience fast chemical exchange at the catalytic complex and thus are involved in polarizing the free azobenzene. Azobenzene exists in two isomers trans- and cis-. We show that all nuclear spins in cis-azobenzene can be efficiently hyperpolarized by SABRE at suitable magnetic fields. Enhancement factors (relative to 9.4 T) reach several thousands of times for 15N spins and a few tens of times for the 1H spins. There are two approaches to observe either hyperpolarized magnetization of 15N/1H spins or hyperpolarized singlet order of the 15N spin pair. We compare these approaches and present the field dependencies of SABRE experiments for them. No hyperpolarization of trans 15N,15N' azobenzene was observed. The results presented here will be useful for further experiments where hyperpolarized cis-15N,15N' azobenzene is switched by light to trans 15N,15N' azobenzene for storing the produced hyperpolarization in the long-lived spin state of the 15N pair of trans-15N,15N' azobenzene. Show Chinese abstract

Abstract: 开发利用核超极化的技术并寻找能够被有效超极化的分子是核磁共振中的一个活跃领域。 特别感兴趣的是那些具有长核弛豫时间的分子，这使它们成为磁共振成像中对比剂的合适候选者。 在本工作中，我们对15N,15N'偶氮苯的SABRE SHEATH（通过可逆交换在屏蔽增强对齐传递到异核的信号放大）实验进行了详细研究。 在SABRE SHEATH实验中，目标核自旋通过可逆化学过程在超低磁场下从邻氢转移自旋极化而被超极化。 研究系统较为复杂，我们仅关注数据的一个子集，详细描述那些在催化复合物中经历快速化学交换的分子，因此参与极化自由偶氮苯的分子。 偶氮苯存在两种异构体顺式和反式。 我们展示了在适当的磁场下，顺式-偶氮苯中的所有核自旋都可以通过SABRE高效地超极化。 相对于9.4 T，15N自旋的增强因子可达数千倍，而1H自旋的增强因子为几十倍。 有两种方法可以观察15N/1H自旋的超极化磁化或15N自旋对的超极化单重态序。 我们比较了这些方法，并展示了针对它们的SABRE实验的场依赖性。 未观察到反式15N,15N'偶氮苯的超极化。 这里展示的结果将有助于进一步的实验，在这些实验中，通过光将超极化的顺式15N,15N'偶氮苯转换为反式15N,15N'偶氮苯，以将产生的超极化存储在反式15N,15N'偶氮苯的15N对的长寿命自旋态中。