15N 甘三中的化学屏蔽:通过固态NMR进行测量并与X射线结构相关联
Eduard Y Chekmenev1, Qianwen Zhang, Kevin W Waddell
1Department of Chemistry, 2320 South Brook Street, University of Louisville, Louisville, Kentucky 40292, USA.
Journal of the American Chemical Society
|January 8, 2004
概括
这项研究详细介绍了15N在各种结构中的糖基残留中的化学屏蔽. 研究结果揭示了结和形状如何影响这些屏蔽参数,从而使二次结构预测成为可能.
科学领域:
- 固态核磁共振 (NMR) 光谱学 固态核磁共振 (NMR) 光谱学
- 结构生物学 结构生物学
- 计算化学的计算化学
背景情况:
- 甘氨基残留物是和蛋白质中的基本构建块.
- 了解化学屏蔽与二次结构之间的关系对于蛋白质结构的确定至关重要.
- 之前的研究已经探讨了各种光谱参数,但缺乏对15N屏蔽在各种糖基构造中的全面分析.
研究的目的:
- 准确确定 15N 化学屏蔽参数,用于不同二次结构 (α-螺旋,β-链,多聚甘油II 和扩展) 中的甘残留物.
- 为了研究结和局部构成对15N屏蔽的影响.
- 开发基于屏蔽参数的甘残留二次结构的预测模型.
主要方法:
- 采用了固态魔术角度旋转 (MAS) 和静止NMR光谱学.
- 合成了含有同位素标记为 [2-(13) C,(15) N] Gly 的.
- 使用二维二极合器,特别是 (1) H - 15 N 和 (13) C - alpha) - 15 N,在分子框架内定位15N屏蔽张量.
主要成果:
- 精确的15N化学屏蔽成分 (2-5ppm) 确定了糖残留物.
- 发现15N屏蔽张量体的delta{11},delta{33}平面与平面不一致.
- 同位变位变化为13ppm,与结合和形状相关;张量跨度和偏离轴对称被按二级结构分组.
结论:
- 15N化学屏蔽参数对糖基残留中的局部构成和结合敏感.
- 15N屏蔽张量的定向为本地分子几何学提供了洞察力.
- 使用屏蔽参数,可以建立蛋白质中糖基残留二次结构的预测方案,以补充现有的13C(alpha) 数据.
相关概念视频
Carbon-13 (¹³C) NMR: Overview
Carbon-13 is a naturally occurring NMR-active isotope of carbon with a low natural abundance of 1.1%. In contrast, carbon-12 is the most abundant isotope of carbon with zero nuclear spin. Therefore, it is NMR inactive. The gyromagnetic ratio of carbon-13 is smaller than that of protons. As a result, carbon-13 resonance is about 6000 times weaker than proton resonance. For a given magnetic field strength, the resonance frequency of carbon-13 is about one-fourth of the resonance frequency for...
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)
Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
NMR Spectroscopy: Chemical Shift Overview
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
For instance, the proton...
Chemical Shift: Internal References and Solvent Effects
In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
Other Nuclides: 31P, 19F, 15N NMR
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 high...
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 high...


