ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.
NMR Signal Enhancement Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
J Phys Chem Lett. 2022 Jan 13;13(1):98-104. doi: 10.1021/acs.jpclett.1c03714. Epub 2021 Dec 28.
We demonstrate a method to quantify and manipulate nuclear spin decoherence mechanisms that are active in zero to ultralow magnetic fields. These include (i) nonadiabatic switching of spin quantization axis due to residual background fields and (ii) scalar pathways due to through-bond couplings between H and heteronuclear spin species, such as H used partially as an isotopic substitute for H. Under conditions of free evolution, scalar relaxation due to H can significantly limit nuclear spin polarization lifetimes and thus the scope of magnetic resonance procedures near zero field. It is shown that robust trains of pulsed dc magnetic fields that apply π flip angles to one or multiple spin species may switch the effective symmetry of the nuclear spin Hamiltonian, imposing decoupled or coupled dynamic regimes on demand. The method should broaden the spectrum of hyperpolarized biomedical contrast-agent compounds and hyperpolarization procedures that are used near zero field.
我们展示了一种量化和操纵零场到超低场中活跃的核自旋退相干机制的方法。这些机制包括：（i）由于残余背景场导致的自旋量子化轴的非绝热切换，以及（ii）由于 H 和异核自旋物种（如 H 部分用作 H 的同位素替代物）之间的键间耦合导致的标量途径。在自由演化条件下，由于 H 引起的标量弛豫会显著限制核自旋极化寿命，从而限制了零场附近磁共振程序的范围。结果表明，施加给一个或多个自旋物种的π翻转角的脉冲直流磁场的强磁场脉冲可以切换核自旋哈密顿量的有效对称性，根据需要施加解耦或耦合的动态状态。该方法应该拓宽在零场附近使用的超极化生物医学对比剂化合物和超极化方法的范围。
