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Research Article

Room temperature hyperpolarization of nuclear spins in bulk

Kenichiro Tateishi, Makoto Negoro, Shinsuke Nishida, Akinori Kagawa, Yasushi Morita, and Masahiro Kitagawa
PNAS May 27, 2014 111 (21) 7527-7530; first published May 12, 2014; https://doi.org/10.1073/pnas.1315778111
Kenichiro Tateishi
aDepartment of Systems Innovation, Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;
bRIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198, Japan; and
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Makoto Negoro
aDepartment of Systems Innovation, Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;
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  • For correspondence: negoro@ee.es.osaka-u.ac.jp
Shinsuke Nishida
cDepartment of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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Akinori Kagawa
aDepartment of Systems Innovation, Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;
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Yasushi Morita
cDepartment of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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Masahiro Kitagawa
aDepartment of Systems Innovation, Division of Advanced Electronics and Optical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;
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  1. Edited by Jack H. Freed, Cornell University, Ithaca, NY, and accepted by the Editorial Board April 16, 2014 (received for review August 20, 2013)

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Significance

Nuclear spins are only slightly aligned even in the strong magnetic fields of superconducting magnets because the magnetic energy of nuclear spin is much smaller than thermal energy. This is the major reason for the low sensitivity of NMR spectroscopy. Using electron spins in thermal equilibrium, which have 660 times higher magnetic energy, the sensitivity can be enhanced by at most this factor through a method called dynamic nuclear polarization. Utilizing photo-excited nonthermalized electrons instead, we demonstrate an enhancement factor of 250,000 at room temperature, which can be applied to a wide range of fields including NMR, MRI, and physics.

Abstract

Dynamic nuclear polarization (DNP), a means of transferring spin polarization from electrons to nuclei, can enhance the nuclear spin polarization (hence the NMR sensitivity) in bulk materials at most 660 times for 1H spins, using electron spins in thermal equilibrium as polarizing agents. By using electron spins in photo-excited triplet states instead, DNP can overcome the above limit. We demonstrate a 1H spin polarization of 34%, which gives an enhancement factor of 250,000 in 0.40 T, while maintaining a bulk sample (∼0.6 mg, ∼0.7 × 0.7 × 1 mm3) containing >1019 1H spins at room temperature. Room temperature hyperpolarization achieved with DNP using photo-excited triplet electrons has potentials to be applied to a wide range of fields, including NMR spectroscopy and MRI as well as fundamental physics.

  • sensitivity enhancement
  • regioselective deuteration
  • pentacene
  • quantum simulation
  • polarized target

Footnotes

  • ↵1K.T. and M.N. contributed equally to this work.

  • ↵2To whom correspondence should be addressed. E-mail: negoro{at}ee.es.osaka-u.ac.jp.
  • ↵3Present address: Department of Applied Chemistry, Faculty of Engineering, Aichi Institute of Technology, Toyota 470-0392, Japan.

  • Author contributions: K.T., M.N., Y.M., and M.K. designed research; K.T. and M.N. performed research; K.T., S.N., A.K., and Y.M. contributed new reagents/analytic tools; K.T. and M.N. analyzed data; and K.T., M.N., and M.K. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission. J.H.F. is a guest editor invited by the Editorial Board.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1315778111/-/DCSupplemental.

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Room temperature nuclear hyperpolarization
Kenichiro Tateishi, Makoto Negoro, Shinsuke Nishida, Akinori Kagawa, Yasushi Morita, Masahiro Kitagawa
Proceedings of the National Academy of Sciences May 2014, 111 (21) 7527-7530; DOI: 10.1073/pnas.1315778111

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Room temperature nuclear hyperpolarization
Kenichiro Tateishi, Makoto Negoro, Shinsuke Nishida, Akinori Kagawa, Yasushi Morita, Masahiro Kitagawa
Proceedings of the National Academy of Sciences May 2014, 111 (21) 7527-7530; DOI: 10.1073/pnas.1315778111
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