在10-脱乙巴丁III中对固态多态的13C核磁共振检测
James K Harper1, Julio C Facelli, Dewey H Barich
1Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, USA.
Journal of the American Chemical Society
|August 29, 2002
概括
固态NMR揭示了形状变化,而不仅仅是格子相互作用,导致NMR转移差异在10-deacetylbaccatin III多态. 这些替代剂和环素环的变化是理解固态NMR行为的关键.
科学领域:
- 固态NMR光谱学 固态NMR光谱学
- 晶体学 晶体学是指结晶学.
- 计算化学计算化学
背景情况:
- 多态性显著影响固态化合物的物理和化学特性.
- 了解固态核磁共振 (NMR) 转移差异的起源对于描述不同的晶体形式至关重要.
研究的目的:
- 为了调查固态NMR化学转移的主要原因,研究10-脱乙巴卡III的多态体之间的差异.
- 为了区分格子相互作用与分子构成对观察到的NMR光谱变化的贡献.
主要方法:
- 固态碳-13 (13C) NMR化学转移张量测量在二甲基硫氧化物 (DMSO) 溶酸盐和未溶化形式的10-甲基乙巴卡丁III上进行.
- 进行了NMR化学转移张数的初始计算,包括和排除DMSO分子.
- 对六种baccatin III类似物进行了X射线衍射分析.
主要成果:
- 单独的格子相互作用无法完全解释两种多态体之间的观察到的NMR转移差异.
- 鉴定出循环烯,烯和乙部分的形状变化是转移差异的可能来源.
- 在X射线分析中,支持了循环烯和烯系统中拟议的构造变化.
- 计算的13C化学转移与两种形式的实验数据密切匹配,表明B,C和D环的刚性.
结论:
- 观察到的10-甲乙巴卡III多态体中的固态NMR张量差异主要是由形状变化驱动的.
- 特定环替代剂和环基环的形状变化是这些NMR光谱差异的主要贡献者.
- 10 - 脱乙巴丁III的B,C和D环在固态中表现出显著的刚性.
更多相关视频
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...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.


