Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP

Lloyd Lumata, Zoltan Kovacs, A. Dean Sherry, Craig Malloy, Stephen Hill, Johan Van Tol, Lu Yu, Likai Song, Matthew E. Merritt

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Abstract

We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e -1 of other free radicals used in DNP at the same concentration, trityl OX063 has slower T 1e -1 than BDPA and 4-oxo-TEMPO. At T > 20 K, the T 1e -1vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd3+ doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e -1 especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx = g y = 2.00319(3) and gz = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T 1e -1 is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.

Original languageEnglish (US)
Pages (from-to)9800-9807
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume15
Issue number24
DOIs
StatePublished - Jun 28 2013

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Paramagnetic resonance
electron paramagnetic resonance
Polarization
polarization
free radicals
Free Radicals
Spin-lattice relaxation
spin-lattice relaxation
Linewidth
electron spin
Temperature
Tensors
temperature
tris(8-carboxyl-2,2,6,6-benzo(1,2-d-4,5-d)-bis(1,3)dithiole-4-yl)methyl sodium salt
dissolving
Dissolution
Anisotropy
Doping (additives)
tensors
Magnetic fields

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Physics and Astronomy(all)

Cite this

Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP. / Lumata, Lloyd; Kovacs, Zoltan; Sherry, A. Dean; Malloy, Craig; Hill, Stephen; Van Tol, Johan; Yu, Lu; Song, Likai; Merritt, Matthew E.

In: Physical Chemistry Chemical Physics, Vol. 15, No. 24, 28.06.2013, p. 9800-9807.

Research output: Contribution to journalArticle

Lumata, Lloyd ; Kovacs, Zoltan ; Sherry, A. Dean ; Malloy, Craig ; Hill, Stephen ; Van Tol, Johan ; Yu, Lu ; Song, Likai ; Merritt, Matthew E. / Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP. In: Physical Chemistry Chemical Physics. 2013 ; Vol. 15, No. 24. pp. 9800-9807.
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AU - Lumata, Lloyd

AU - Kovacs, Zoltan

AU - Sherry, A. Dean

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AU - Hill, Stephen

AU - Van Tol, Johan

AU - Yu, Lu

AU - Song, Likai

AU - Merritt, Matthew E.

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N2 - We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e -1 of other free radicals used in DNP at the same concentration, trityl OX063 has slower T 1e -1 than BDPA and 4-oxo-TEMPO. At T > 20 K, the T 1e -1vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd3+ doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e -1 especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx = g y = 2.00319(3) and gz = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T 1e -1 is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.

AB - We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e -1 of other free radicals used in DNP at the same concentration, trityl OX063 has slower T 1e -1 than BDPA and 4-oxo-TEMPO. At T > 20 K, the T 1e -1vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd3+ doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e -1 especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx = g y = 2.00319(3) and gz = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T 1e -1 is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.

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