title: Limits in Proton Nuclear Singlet-State Lifetimes Measured with para-Hydrogen-Induced Polarization.
abstract: 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 A2systems), 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).
authors.affiliation: Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY, 10003, USA.
authors.forename: Yuning
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY, 10003, USA.
authors.forename: Xueyou
authors.initials: X
authors.lastname: Duan
authors.affiliation: Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY, 10003, USA.
authors.forename: Pei Che
authors.initials: PC
authors.lastname: Soon
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo náměstí 2, 166 10, Praha 6, Czech Republic.|Department of Electrotechnology, Electrical Engineering, Czech Technical University, Technická 2, 166 27, Prague 6, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Sychrovský
authors.affiliation: Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY, 10003, USA. james.canary@nyu.edu.
authors.forename: James W
authors.initials: JW
authors.lastname: Canary
authors.affiliation: Department of Chemistry, New York University, 100 Washington Sq. East, New York, NY, 10003, USA. alexej.jerschow@nyu.edu.
authors.forename: Alexej
authors.initials: A
authors.lastname: Jerschow
keywords: chemical shift anisotropy; dimethyl fumarate; hyperpolarization; paramagnetic relaxation; singlet lifetime limits