在魔术角度旋转下从二极点顺序的交叉极化:ADRF-CPMAS NMR实验
Tamar Wolf1, Sundaresan Jayanthi2, Adonis Lupulescu3
1Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel.
The Journal of chemical physics
|December 14, 2023
概括
在旋转框架 (ADRF) 中的附磁去磁化可以有效地增强固态NMR中不敏感核的信号. 这种ADRF-CPMAS技术在某些情况下超过了传统的哈特曼-哈恩交叉偏振 (HH-CPMAS).
科学领域:
- 固态核磁共振 (NMR) 光谱学. 固态核磁共振 (NMR) 光谱学.
- 在凝聚物质中的量子动力学和旋转操纵.
背景情况:
- 增强来自低马的信号,不敏感的核在固态NMR中至关重要.
- 哈特曼-哈恩交叉极化 (HH-CP) 是一种成熟的方法,用于在魔法角度旋转 (MAS) 下使这些核敏感.
研究的目的:
- 调查利用在旋转框架 (ADRF) 中通过附磁性去磁生成的1H双极顺序来增强MAS下不敏感核信号的潜力.
- 为了比较这种基于ADRF的新型交叉极化 (ADRF-CPMAS) 与已建立的哈特曼-哈恩交叉极化 (HH-CPMAS) 的效率.
主要方法:
- 使用ADRF创建的1H双极顺序在MAS下向不敏感核 (I-spin) 进行极化转移.
- 对ADRF-CPMAS的实验和理论分析,包括对匹配条件和多旋转转移过程的调查.
- 在静态和旋转固体中分析推导和数值模拟ADRF过程,将其视为连贯的演变.
主要成果:
- 通过ADRF-CPMAS证明了有效的极化转移.
- ADRF-CPMAS可以实现比优化的HH-CPMAS更高的效率,特别是在塑料晶体中.
- 这种技术需要低射频核化场,并表现出独特的零频匹配条件,涉及多个旋转.
- 分析推导和数值模拟准确地预测了模型化合物中13C和15N的实验结果.
结论:
- ADRF-CPMAS是HH-CPMAS的可行和潜在的优越替代品,用于增强固态NMR中不敏感核的信号.
- 该研究提供了基于连贯演变的理论框架,以了解ADRF过程和多旋转转移.
- 进一步探索化学转移异构和射频异质等因素证实了ADRF-CPMAS技术的稳定性.
相关概念视频
Double Resonance Techniques: Overview
214
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...
Spin decoupling is usually achieved by...
214
¹H NMR: Interpreting Distorted and Overlapping Signals
1.0K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.0K
Spin–Spin Coupling Constant: Overview
932
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.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
932
¹H NMR Signal Multiplicity: Splitting Patterns
5.2K
When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
5.2K
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...
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
2D NMR: Overview of Homonuclear Correlation Techniques
202
Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
COSY90 is the standard two-dimensional (2D) COSY experiment that...
202


