超低磁场下仲氢对顺式15 N，15 N '-偶氮苯的超极化作用
Hyperpolarization of cis-15N,15N'-azobenzene by parahydrogen at ultralow magnetic fields
摘要：
开发利用核超极化的方法和寻找核自旋可以有效超极化的分子是核磁共振的一个活跃领域。特别令人感兴趣的是具有长的核弛豫时间的那些分子，使它们成为磁共振成像中作为造影剂的合适候选物。在这项工作中，我们提出了一个详细的研究SABRE鞘（信号放大通过可逆交换屏蔽使能对准转移到异核）的实验15 N，15 N '偶氮苯。在SABRE SHEATH实验中，靶的核自旋通过在可逆化学过程期间在超低场下从仲氢转移自旋极化而超极化。所研究的系统是复杂的，我们只关心的数据的一个子集，呈现的细节的分子，经历快速的化学交换在催化复合物，从而参与极化的游离偶氮苯。偶氮苯存在两种异构体，反式和顺式。我们发现，在合适的磁场下，SABRE可以有效地超极化顺式偶氮苯中的所有核自旋。增强因子（相对于9.4T）对于15 N自旋达到几千倍，对于1H自旋达到几十倍。有两种方法可以观察到15 N/1H自旋的超极化磁化强度或15 N自旋对的超极化单重态。我们比较了这些方法，并提出了SABRE实验对它们的依赖性。反式~（15）N，~（15）N '偶氮苯的超极化现象不明显。本文的结果将有助于进一步的实验，即超极化顺式-15 N，15 N '偶氮苯被光转换为反式-15 N，15 N'偶氮苯，以将所产生的超极化存储在反式-15 N，15 N '偶氮苯的15 N对的长寿命自旋态中。
英文摘要：
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.
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