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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
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Related Experiment Video

Updated: May 7, 2025

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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Two-electron two-nucleus effective Hamiltonian and the spin diffusion barrier.

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  • 1Institute for Biomedical Engineering, University and ETH Zurich, 8092 Zurich, Switzerland.

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Summary

Dynamic nuclear polarization (DNP) enables quantum technologies by transferring electron spins to nuclei. This study reveals a four-spin flip-flop mechanism that overcomes spin diffusion barriers, allowing efficient bulk nuclear hyperpolarization.

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Area of Science:

  • Quantum Information Science
  • Magnetic Resonance Spectroscopy
  • Condensed Matter Physics

Background:

  • Dynamic nuclear polarization (DNP) and quantum technologies depend on electron-nuclear spin transfer.
  • Hyperfine couplings can create a "spin diffusion barrier," hindering spin transfer by suppressing nuclear dipolar flip-flops.

Purpose of the Study:

  • To investigate spin transfer processes in electron-nuclear hybrid quantum systems.
  • To analyze the role of tensorial dipolar and hyperfine couplings in spin transfer.
  • To develop a model explaining efficient bulk nuclear hyperpolarization in DNP.

Main Methods:

  • Application of the Schrieffer-Wolff transformation to a two-electron, two-nucleus spin system.
  • Analysis of tensorial dipolar and hyperfine couplings.
  • Investigation of energy-conserving four-spin flip-flop processes.
  • Model fitting of HypRes-on experimental data.

Main Results:

  • Identified an energy-conserving electron-nuclear four-spin flip-flop mechanism.
  • Demonstrated that this mechanism facilitates nuclear spin diffusion near electrons.
  • Provided experimental evidence supporting the relevance of this four-spin flip-flop.
  • Developed a model explaining how all nuclear spins can contribute to hyperpolarization without a spin diffusion barrier.

Conclusions:

  • The electron-nuclear four-spin flip-flop is crucial for overcoming spin diffusion barriers in DNP.
  • This mechanism enables efficient hyperpolarization of bulk nuclear spins.
  • Connects magnetic resonance and quantum information by providing a pathway for enhanced spin transfer.