title: Dissolution DNP-NMR spectroscopy using galvinoxyl as a polarizing agent.
abstract: The goal of this work was to test feasibility of using galvinoxyl (2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy) as a polarizing agent for dissolution dynamic nuclear polarization (DNP) NMR spectroscopy. We have found that galvinoxyl is reasonably soluble in ethyl acetate, chloroform, or acetone and the solutions formed good glasses when mixed together or with other solvents such as dimethyl sulfoxide. W-band electron spin resonance (ESR) measurements revealed that galvinoxyl has an ESR linewidth D intermediate between that of carbon-centered free radical trityl OX063 and the nitroxide-based 4-oxo-TEMPO, thus the DNP with galvinoxyl for nuclei with low gyromagnetic ratio γ such as (13)C and (15)N is expected to proceed predominantly via the thermal mixing process. The optimum radical concentration that would afford the highest (13)C nuclear polarization (approximately 6% for [1-(13)C]ethyl acetate) at 3.35 T and 1.4 K was found to be around 40 mM. After dissolution, large liquid-state NMR enhancements were achieved for a number of (13)C and (15)N compounds with long spin-lattice relaxation time T(1). In addition, the hydrophobic galvinoxyl free radical can be easily filtered out from the dissolution liquid when water is used as the solvent. These results indicate that galvinoxyl can be considered as an easily available free radical polarizing agent for routine dissolution DNP-NMR spectroscopy.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, 75390, United States.
authors.forename: Lloyd L
authors.initials: LL
authors.lastname: Lumata
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Merritt
authors.forename: Craig R
authors.initials: CR
authors.lastname: Malloy
authors.forename: A Dean
authors.initials: AD
authors.lastname: Sherry
authors.forename: Johan
authors.initials: J
authors.lastname: van Tol
authors.forename: Likai
authors.initials: L
authors.lastname: Song
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Kovacs
mesh_terms: D001559:Benzhydryl Compounds / Q000032:analysis* / Q000737:chemistry*; D005609:Free Radicals / Q000032:analysis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D055672:Static Electricity
chemical_list: D001559:Benzhydryl Compounds; D005609:Free Radicals; C020338:galvinoxyl