title: 13C dynamic nuclear polarization using isotopically enriched 4-oxo-TEMPO free radicals.
abstract: The nitroxide-based free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) is a widely used polarizing agent in NMR signal amplification via dissolution dynamic nuclear polarization (DNP). In this study, we have thoroughly investigated the effects of15N and/or2H isotopic labeling of 4-oxo-TEMPO free radical on13C DNP of 3 M [1-13C] sodium acetate samples in 1 : 1 v/v glycerol : water at 3.35 T and 1.2 K. Four variants of this free radical were used for13C DNP: 4-oxo-TEMPO, 4-oxo-TEMPO-15N, 4-oxo-TEMPO-d16and 4-oxo-TEMPO-15N,d16. Our results indicate that, despite the striking differences seen in the electron spin resonance (ESR) spectral features, the13C DNP efficiency of these15N and/or2H-enriched 4-oxo-TEMPO free radicals are relatively the same compared with13C DNP performance of the regular 4-oxo-TEMPO. Furthermore, when fully deuterated glassing solvents were used, the13C DNP signals of these samples all doubled in the same manner, and the13C polarization buildup was faster by a factor of 2 for all samples. The data here suggest that the hyperfine coupling contributions of these isotopically enriched 4-oxo-TEMPO free radicals have negligible effects on the13C DNP efficiency at 3.35 T and 1.2 K. These results are discussed in light of the spin temperature model of DNP. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, TX, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Niedbalski
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, TX, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Parish
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, TX, USA.
authors.forename: Andhika
authors.initials: A
authors.lastname: Kiswandhi
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, TX, USA.
authors.forename: Lloyd
authors.initials: L
authors.lastname: Lumata
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D002247:Carbon Isotopes; D003497:Cyclic N-Oxides / Q000737:chemistry*; D003903:Deuterium; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry*; D007553:Isotope Labeling; D008872:Microwaves; D012997:Solvents
chemical_list: D000975:Antioxidants; D002247:Carbon Isotopes; D003497:Cyclic N-Oxides; D005609:Free Radicals; D012997:Solvents; D003903:Deuterium; C003959:TEMPO
keywords: DNP; NMR; TEMPO; dynamic nuclear polarization; thermal mixing