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Limits in Proton Nuclear Singlet‐State Lifetimes Measured with para ‐Hydrogen‐Induced Polarization
Author(s) -
Zhang Yuning,
Duan Xueyou,
Soon Pei Che,
Sychrovský Vladimír,
Canary James W.,
Jerschow Alexej
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201600663
Subject(s) - chemistry , intramolecular force , deuterium , singlet state , proton , photochemistry , atomic physics , stereochemistry , excited state , physics , quantum mechanics
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′X 3 X 3 ′ and A 2 systems), the singlet‐state readout requires either a chemical desymmetrization 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).