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Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

1.9K
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 one, the...
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Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

1.2K
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
1.2K
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

1.1K
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.
1.1K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

3.4K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
3.4K
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

1.1K
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
1.1K
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

870
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
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Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR
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在光化学诱导的动态核偏振光谱学中,对具有强烈异构的超细合的核的旋转放松效应.

Ilya Kuprov1, Timothy D Craggs, Sophie E Jackson

  • 1Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK. ilya.kuprov@chem.ox.ac.uk

Journal of the American Chemical Society
|July 3, 2007
PubMed
概括

这项研究模拟了19F标记激素对中的核和电子旋转放松. 横向的超细合-g-tensor异构性交叉相关性占主导地位,导致化学诱导的动态核极化 (CIDNP) 中的相反,用于探测蛋白质的移动性.

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科学领域:

  • 物理化学 物理化学
  • 化学物理 化学物理
  • 频谱学是一种光谱学.

背景情况:

  • 核和电子自旋放松在激进对进化中至关重要.
  • 了解这些过程是解释磁力运动系统中的实验数据的关键.
  • 以前的模型可能无法完全捕捉复杂的放松动态.

研究的目的:

  • 开发和验证一个理论模型,用于 19F-标记的双基对的旋转放松.
  • 在高磁场中,在纳秒时间尺度上识别主导放松机制.
  • 解释化学诱导动态核极化 (CIDNP) 中观察到的相反及其应用.

主要方法:

  • 利用实验结果和旋转放松过程的理论建模.
  • 采用完整的旋转状态空间和放松超操作器,以实现精确的旋转动力学.
  • 在超过10特斯拉的磁场中调查系统.

主要成果:

  • 电子核双极交叉放松和纵向高精度合异性质-g-电阻异性质交叉相关性在高电场下是可以忽略不计的.
  • 横向的高精度合-g-tensor异质性交叉相关性是主导的放松过程.
  • 这一过程导致19F CIDNP信号的相位逆转,以获得较大的旋转相关时间.

结论:

  • 开发的旋转动力学模型为磁动力学系统提供了可靠的治疗,具有显著的放松效应.
  • 观察到的CIDNP相位逆转是横向DeltaHFC-Deltag交叉相关性的直接结果.
  • 这种现象是局部移动性的宝贵探测器,特别是在复杂的生物系统中,如部分变性蛋白质.