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π Electron Effects on Chemical Shift: Overview01:27

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An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
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Hyperpolarized Xenon for NMR and MRI Applications
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Biradical Polarizing Agents at High Fields.

Vladimir K Michaelis1,2, Eric G Keeler1,3, Salima Bahri1,4

  • 1Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139, Massachusetts, United States.

The Journal of Physical Chemistry. B
|October 4, 2022
PubMed
Summary
This summary is machine-generated.

Dynamic nuclear polarization (DNP) significantly boosts nuclear magnetic resonance (NMR) sensitivity. This study reveals conventional biradicals offer similar 1H DNP enhancements across varying conditions, challenging prior assumptions.

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Area of Science:

  • Nuclear Magnetic Resonance (NMR) Spectroscopy
  • Dynamic Nuclear Polarization (DNP)

Background:

  • DNP is revolutionizing NMR spectroscopy by enhancing sensitivity for complex chemical and structural analyses.
  • Significant advancements have been made in DNP methods over the last decade, with ongoing efforts to further improve capabilities.

Purpose of the Study:

  • To investigate the impact of static magnetic field strength and temperature on 1H DNP enhancements.
  • To evaluate the performance of three conventional organic biradicals (TOTAPOL, AMUPol, SPIROPOL) under specific DNP conditions.
  • To explore the influence of temperature, microwave power, magnetic field strength, and protein sample deuteration on NMR experimental outcomes.

Main Methods:

  • Experimental assessment of 1H DNP enhancements using TOTAPOL, AMUPol, and SPIROPOL biradicals.
  • Measurements conducted at liquid nitrogen temperatures and 700 MHz/460.5 GHz.
  • Systematic variation of experimental parameters including temperature, microwave power, magnetic field strength, and sample deuteration.

Main Results:

  • Contrary to expectations, TOTAPOL, AMUPol, and SPIROPOL exhibited comparable 1H DNP enhancements (ε ≈ 60) at liquid nitrogen temperatures and 700 MHz/460.5 GHz.
  • Detailed analysis of how various experimental factors affect DNP-enhanced NMR results was performed.

Conclusions:

  • Conventional organic biradicals demonstrate robust and similar performance in DNP-enhanced NMR under the tested conditions.
  • The findings provide valuable insights for optimizing DNP-NMR experiments and expand its applicability in structural and chemical problem-solving.