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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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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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Atomic Nuclei: Nuclear Spin01:08

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All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not...
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

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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.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

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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 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
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Dynamic Nuclear Polarization Using Electron Spin Cluster.

Raj K Chaklashiya1, Asif Equbal2,3, Andrey Shernyukov4

  • 1Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, United States.

The Journal of Physical Chemistry Letters
|May 12, 2024
PubMed
Summary
This summary is machine-generated.

Dynamic nuclear polarization (DNP) using electron spin clusters (ESCs) enables significant nuclear magnetic resonance (NMR) signal enhancement. This study details a TetraTrityl radical design for efficient 1H NMR DNP at 7 T, offering power-efficient high-field DNP principles.

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Area of Science:

  • Magnetic Resonance Spectroscopy
  • Quantum Chemistry
  • Materials Science

Background:

  • Dynamic nuclear polarization (DNP) enhances NMR signals using microwave irradiation.
  • Electron spin clusters (ESCs) offer a promising approach for DNP with low power requirements at high magnetic fields.
  • Developing efficient ESC designs is crucial for advancing DNP technology.

Purpose of the Study:

  • To present the design of a trityl-based tetra-radical (TetraTrityl) for 1H NMR DNP at 7 T.
  • To investigate the relationship between electron spin pair distances and DNP enhancement.
  • To establish design principles for power-efficient ESC-DNP.

Main Methods:

  • Quantum mechanical simulations to model electron spin interactions.
  • Experimental validation of the TetraTrityl radical design.
  • Analysis of electron spin relaxation times (T1) and electron-electron (e-e) spin distances.

Main Results:

  • A slow-relaxing 4-ESC requires specific electron spin pair distances (<8 Å and <12 Å) for optimal 1H ESC-DNP enhancement.
  • Fast-relaxing ESCs necessitate a sensitizer radical for efficient polarization transfer.
  • The TetraTrityl design demonstrates effective 1H ESC-DNP at 7 T.

Conclusions:

  • Specific electron spin arrangements within ESCs are critical for maximizing DNP efficiency.
  • Design principles for power-efficient DNP at high fields using ESC-DNP have been elucidated.
  • The TetraTrityl radical serves as a viable platform for high-field NMR signal enhancement.