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相关概念视频

Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

1.0K
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.
1.0K
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

248
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...
248
Insensitive Nuclei Enhanced by Polarization Transfer (INEPT)01:15

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT)

408
Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) is an advanced Nuclear Magnetic Resonance (NMR) technique specifically designed to detect and enhance the signals of low-abundance nuclei, such as carbon-13 and nitrogen-15, in small molecules. The fundamental principle behind INEPT is the transfer of polarization from a more abundant and highly polarizable nucleus, typically hydrogen-1, to the low-abundance nucleus of interest. This process effectively boosts the NMR signal of the...
408
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

683
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.
683
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

847
A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
847
Other Nuclides: 31P, 19F, 15N NMR01:16

Other Nuclides: 31P, 19F, 15N NMR

418
Many organic, inorganic, and biological molecules contain spin-half nuclei such as nitrogen-15, fluorine-19, and phosphorus-31. As a result, NMR studies of these nuclei have found extensive applications in chemical and biological research.
While fluorine-19 and phosphorous-31 have high natural abundances (100%) and positive gyromagnetic ratios, nitrogen-15 has a low natural abundance and a negative gyromagnetic ratio. However, nitrogen-15 is still preferred over nitrogen-14 (which has a...
418

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Updated: Jul 25, 2025

Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR
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Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR

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频率交换的动态核极化

Michael Mardini1, Ravi Shankar Palani1, Iram M Ahmad2

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

Journal of magnetic resonance (San Diego, Calif. : 1997)
|June 29, 2023
PubMed
概括
此摘要是机器生成的。

一个新的微波源可以实现动态核极化 (DNP) NMR的频率,振幅和相位调制. 这一进步可以提高水样的灵敏度,并为新的时间域实验打开了大门.

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Preparation of Fungal and Plant Materials for Structural Elucidation Using Dynamic Nuclear Polarization Solid-State NMR
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Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
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Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR
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Preparation of Fungal and Plant Materials for Structural Elucidation Using Dynamic Nuclear Polarization Solid-State NMR
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Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
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科学领域:

  • 核磁共振光谱学 核磁共振光谱学
  • 电子对磁共振是一种电子对磁共振.
  • 微波工程 微波工程

背景情况:

  • 动态核极化 (DNP) 通过将电子极化转移到核中,显著提高了NMR光谱的灵敏度.
  • 传统的DNP方法依赖于具有固定的频率和功率的连续波 (CW) 微波源,限制了探索的机制.
  • 高磁场 (>5 T) 需要140 GHz以上的微波源,历史上偏好了陀螺仪或固定频振荡器.

研究的目的:

  • 引入一种能够轻松调节频率,振幅和相位的新型微波源,用于9 T (250 GHz) 的DNP-NMR实验.
  • 研究调制微波辐射对DNP机制的影响,并探索新的实验可能性.
  • 为了证明经济实惠和紧的微波源的潜力,在水样中实现显著的灵敏度增强.

主要方法:

  • 将频率,振幅和相敏捷微波源集成到一个9 T (250 GHz) 魔形角旋转 (MAS) NMR 装置中.
  • 在调节辐射下对连续波 (CW) DNP机制的实验研究.
  • 频率切割辐射的应用和使用水溶性BDPA基的Overhauser效应增强的演示.

主要成果:

  • 成功实现了用于DNP-MAS NMR实验的多功能微波源.
  • 证明频率切割辐射对DNP的优势.
  • 通过使用BDPA基,在水溶液中达到大约25的Overhauser显著增强.

结论:

  • 开发的微波源为DNP-NMR提供了前所未有的控制,使新的机制的探索成为可能.
  • 负担得起和紧的微波源可以在含水样本中实现显著的灵敏度增长,包括生物巨分子.
  • 微波放大器的未来发展将促进先进的时间域DNP实验.