Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128, Mainz, Germany.
J Am Chem Soc. 2012 Jun 27;134(25):10393-6. doi: 10.1021/ja304285s. Epub 2012 Jun 15.
Nuclear magnetic resonance (NMR) is a very powerful tool in physics, chemistry, and life sciences, although limited by low sensitivity. This problem can be overcome by hyperpolarization techniques dramatically enhancing the NMR signal. However, this approach is restricted to relatively short time scales depending on the nuclear spin-lattice relaxation time T(1) in the range of seconds. This makes long-lived singlet states very useful as a way to extend the hyperpolarization lifetimes. Para-hydrogen induced polarization (PHIP) is particularly suitable, because para-H(2) possesses singlet symmetry. Most PHIP experiments, however, are performed on asymmetric molecules, and the initial singlet state is directly converted to a NMR observable triplet state decaying with T(1), in the order of seconds. We demonstrate that in symmetric molecules, a long-lived singlet state created by PHIP can be stored for several minutes on protons in high magnetic fields. Subsequently, it is converted into observable high nonthermal magnetization by controlled singlet-triplet conversion via level anticrossing.
核磁共振（NMR）是物理学、化学和生命科学中非常强大的工具，尽管灵敏度有限。这个问题可以通过超极化技术来克服，该技术可以显著增强 NMR 信号。然而，这种方法受限于相对较短的时间尺度，这取决于核自旋晶格弛豫时间 T(1)在秒的范围内。这使得长寿命的单重态非常有用，可以延长超极化寿命。氘诱导极化（PHIP）特别适合，因为氘（2）具有单重态对称性。然而，大多数 PHIP 实验都是在不对称分子上进行的，初始单重态直接转化为 NMR 可观测的三重态，以秒为单位衰减。我们证明，在对称分子中，通过 PHIP 产生的长寿命单重态可以在高磁场中的质子上储存几分钟。随后，通过通过能级交叉实现受控单重态-三重态转换，将其转化为可观测的高非热磁化。
