Limits in Proton Nuclear Singlet-State Lifetimes Measured with para-Hydrogen-Induced Polarization

作者：Zhang Yuning; Duan Xueyou; Soon Pei Che; Sychrovsky Vladimir; Canary James W; Jerschow Alexej

来源：ChemPhysChem, 2016, 17(19): 2967-2971.

DOI：10.1002/cphc.201600663

• chemical shift anisotropy
• dimethyl fumarate
• hyperpolarization
• paramagnetic relaxation
• singlet lifetime limits

The synthesis of a hyperpolarized molecule was developed, where the polarization and the singlet state were preserved over two controlled chemical steps. Nuclear singlet-state lifetimes close to 6 min for protons are reported in dimethyl fumarate. Owing to the high symmetry (AA'X3X3' and A(2) systems), the singlet-state readout requires either a chemical de-symmetrization or a long and repeated spin lock. Using DFT calculations and relaxation models, we further determine nuclear spin singlet lifetime limiting factors, which include the intramolecular dipolar coupling mechanism (proton-proton and proton-deuterium), the chemical shift anisotropy mechanism (symmetric and antisymmetric), and the intermolecular dipolar coupling mechanism (to oxygen and deuterium). If the limit of paramagnetic relaxation caused by residual oxygen could be lifted, the intramolecular dipolar coupling to deuterium would become the limiting relaxation mechanism and proton lifetimes upwards of 26 min could become available in the molecules considered here (dimethyl maleate and dimethyl fumarate).

• 出版日期2016-10-5