title: Nuclear spin hyperpolarization of the solvent using signal amplification by reversible exchange (SABRE).
abstract: Here we report the polarization of the solvent OH protons by SABRE using standard iridium-based catalysts under slightly acidic conditions. Solvent polarization was observed in the presence of a variety of structurally similar N-donor substrates while no solvent enhancement was observed in the absence of substrate or para-hydrogen (p-H2). Solvent polarization was sensitive to the polarizing field and catalyst:substrate ratio in a manner similar to that of substrate protons. SABRE experiments with pyridine-d5 suggest a mechanism where hyperpolarization is transferred from the free substrate to the solvent by chemical exchange while measured hyperpolarization decay times suggest a complimentary mechanism which occurs by direct coordination of the solvent to the catalytic complex. We found the solvent hyperpolarization to decay nearly 3 times more slowly than its characteristic spin-lattice relaxation time suggesting that the hyperpolarized state of the solvent may be sufficiently long lived (∼20s) to hyperpolarize biomolecules having exchangeable protons. This route may offer future opportunities for SABRE to impact metabolic imaging.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, United States. Electronic address: Karlos.Moreno@UTSouthwestern.edu.
authors.forename: Karlos X
authors.initials: KX
authors.lastname: Moreno
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, United States. Electronic address: Khaled.nasr@utsouthwestern.edu.
authors.forename: Khaled
authors.initials: K
authors.lastname: Nasr
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, United States. Electronic address: Mark.Milne@utsouthwestern.cdu.
authors.forename: Mark
authors.initials: M
authors.lastname: Milne
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, United States. Electronic address: Dean.Sherry@utsouthwestern.edu.
authors.forename: A Dean
authors.initials: AD
authors.lastname: Sherry
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Road, Richardson, TX 75080, United States. Electronic address: wgoux@utdallas.edu.
authors.forename: Warren J
authors.initials: WJ
authors.lastname: Goux
mesh_terms: D002384:Catalysis; D017665:Hydroxyl Radical / Q000737:chemistry; D007495:Iridium / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000706:statistics & numerical data; D011522:Protons; D012997:Solvents / Q000737:chemistry*
chemical_list: D011522:Protons; D012997:Solvents; D017665:Hydroxyl Radical; D007495:Iridium
keywords: Chemical exchange; Hyperpolarization; Iridium catalyst; MR imaging; SABRE; Solvent enhancement