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相关概念视频

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

934
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...
934
Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

1.9K
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...
1.9K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.0K
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...
1.0K
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

971
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.
971
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

648
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.
648
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.1K
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,...
1.1K

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Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
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使用电子自旋集群的动态核极化.

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
概括
此摘要是机器生成的。

使用电子自旋集群 (ESC) 的动态核极化 (DNP) 能够显著增强核磁共振 (NMR) 信号. 这项研究详细介绍了一种TetraTrityl基因设计,用于在7T时高效的H NMR DNP,提供高效的高场DNP原理.

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科学领域:

  • 磁共振光谱学 磁共振光谱学
  • 量子化学 是一个量子化学.
  • 材料科学 材料科学 材料科学

背景情况:

  • 动态核极化 (DNP) 使用微波辐射增强NMR信号.
  • 电子自旋集群 (ESC) 为在高磁场下具有低功率要求的DNP提供了一个有前途的方法.
  • 开发高效的ESC设计对于推进DNP技术至关重要.

研究的目的:

  • 介绍一个以三基为基础的四基 (TetraTrityl) 的设计,用于H NMR DNP在7 T.
  • 为了研究电子自旋对距离和DNP增强之间的关系.
  • 建立节能ESC-DNP的设计原则.

主要方法:

  • 量子力学模拟用于模拟电子自旋相互作用.
  • 对TetraTrityl基设计的实验验证.
  • 分析电子自旋放松时间 (T1) 和电子-电子 (e-e) 旋转距离.

主要成果:

  • 缓慢放松的4-ESC需要特定的电子自旋对距离 (<8 Å和<12 Å) 以获得最佳的H ESC-DNP增强.
  • 快速放松的ESC需要敏感激素来有效地转移极化.
  • 在7T时,TetraTrityl设计证明了有效的H ESC-DNP.

结论:

  • 在ESC内部的特定电子旋转安排对于最大限度地提高DNP效率至关重要.
  • 已经阐明了使用ESC-DNP在高场高效DNP的设计原则.
  • 三基作为高场NMR信号增强的可行平台.