Feng Yesu, Davis Ryan M, Warren Warren S
Department of Chemistry, Duke University, Durham, North Carolina 27708, USA ; Center for Molecular and Biomolecular Imaging, Duke University, Durham, North Carolina 27708, USA.
Nat Phys. 2012 Nov;8(11):831-837. doi: 10.1038/nphys2425. Epub 2012 Sep 16.
Long-lived nuclear spin states could greatly enhance the applicability of hyperpolarized nuclear magnetic resonance. Using singlet states between inequivalent spin pairs has been shown to extend the signal lifetime by more than an order of magnitude compared to the spin lattice relaxation time (), but they have to be prevented from evolving into other states. In the most interesting case the singlet is between chemically equivalent spins, as it can then be inherently an eigenstate. However this presents major challenges in the conversion from bulk magnetization to singlet. In the only case demonstrated so far, a reversible chemical reaction to break symmetry was required. Here we present a pulse sequence technique that interconverts between singlet spin order and bulk magnetization without breaking the symmetry of the spin system. This technique is independent of field strength and is applicable to a broad range of molecules.
长寿命核自旋态可极大地提高超极化核磁共振的适用性。与自旋晶格弛豫时间（）相比，利用不等价自旋对之间的单重态已被证明能将信号寿命延长一个多数量级，但必须防止它们演变成其他状态。在最有趣的情况下，单重态存在于化学等价的自旋之间，因为此时它本质上可以是一个本征态。然而，这在从体磁化强度转换为单重态时带来了重大挑战。在迄今为止唯一展示的案例中，需要一个可逆化学反应来打破对称性。在此，我们提出一种脉冲序列技术，该技术可在单重态自旋序和体磁化强度之间相互转换，而不会破坏自旋系统的对称性。该技术与场强无关，适用于广泛的分子。
