液晶相中的二糖化物的符合分布函数,使用NMR光谱学确定
Baltzar Stevensson1, Clas Landersjö, Göran Widmalm
1Division of Physical Chemistry and Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
Journal of the American Chemical Society
|May 23, 2002
概括
一种新的APME方法使用液晶中的NMR数据准确地确定分子构造. 这种方法克服了以前模型的局限性,使灵活分子的精确结构确定成为可能.
科学领域:
- 生物物理化学 生物物理化学
- 结构生物学 结构生物学
- 核磁共振光谱学 核磁共振光谱学
背景情况:
- 对NMR参数的分析,特别是残余二极合,对于分子结构的确定至关重要.
- 现有的模型,如添加潜力 (AP) 和最大 (ME),在描述形态分布方面存在局限性,特别是在低阶系统中.
- 稀释液晶中的柔性分子对传统的结构分析方法构成挑战.
研究的目的:
- 引入和验证一种新的分析方法,增量潜在最大 (APME),用于确定结构分布函数.
- 应用APME方法来分析在稀释液晶环境中脱糖的NMR参数.
- 证明APME在克服灵活分子分析现有模型局限性的有效性.
主要方法:
- 开发APME方法,结合添加物潜力和最大模型的方面.
- 使用内部残余双极合来确定方向顺序参数.
- 使用残余二极合,J合和核重复效应 (NOE) 构建构造分布函数.
主要成果:
- APME方法在低阶极限中证明了有效性,提供了准确的形状分布.
- 在实验测量和计算计算的NMR参数之间取得了很好的一致性.
- 使用单个分子构造的分析结果与APME方法相比,误差明显更大.
结论:
- APME方法是分析NMR参数和确定灵活分子的结构分布函数的强大工具.
- 这种方法对于具有低定向顺序的系统特别有效,例如稀释液晶中的分子.
- 该研究强调了APME在复杂分子系统中推进结构确定方面的潜力.
相关概念视频
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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:192D 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...
01:15NMR 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...
01:03IR Frequency Region: Fingerprint Region
IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the C=O, C=N, and C=C occur between 1600–1850 cm−1.
The...
The...
01:24Mass Spectrum: Interpretation
An unknown compound can be established by identifying the molecular ion peak in the mass spectrum. The molecular ion peak is often weak or absent due to the predominance of fragmentation in high-energy electron beams. In such cases, a soft-energy electron beam can be used to scan the spectrum to enhance the intensity of the molecular ion peak. Additionally, chemical ionization, field ionization, and desorption ionization spectra are used to obtain a relatively intense molecular ion peak.To...
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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...