在金属氨酸离子基中发生的对称性破坏现象
Torgil Vangberg1, Renate Lie, Abhik Ghosh
1Department of Chemistry, Faculty of Science, University of Tromsø, N-9037 Tromsø, Norway.
Journal of the American Chemical Society
|July 4, 2002
概括
对于金属氨酸离子基的常见A(1u) /A(2u) 描述往往是不准确的. 密度函数理论的计算表明,这些基因经历了伪约翰-泰勒扭曲,最好用不同的对称性来描述.
科学领域:
- 计算化学计算化学
- 量子化学 是一个量子化学.
- 材料科学 材料科学 材料科学
背景情况:
- 在各种化学过程中,金属氨酸基离子基具有至关重要的作用.
- 现有的模型经常简化其电子结构,使用A(1u) /A(2u) 二分法.
- 以前的研究暗示了超出这种简单描述的复杂性.
研究的目的:
- 通过先进的计算方法研究金属氨酸离子基的电子结构和能量.
- 确定这些物种的普遍A(1u) /A(2u) 描述是否准确.
- 探索影响它们结构扭曲和旋转密度概况的因素.
主要方法:
- 使用密度函数理论 (DFT) 的计算.
- 分析了能量,分子结构和旋转密度概况.
- 在各种对称性约束下进行了几何优化.
主要成果:
- 由于边界轨道的接近退化,A(1u) /A(2u) 二分法往往是不合理的.
- 金属氨酸离子基经历伪约翰-泰勒 (pJT) 扭曲,最好用 (2)A(u) 对称性来描述.
- 在A(1u) 和A(2u) 状态之间的能量差异为0.15 eV的值预测了pJT扭曲.
- 模化对单个环内键长度交替的影响很小.
结论:
- 伪约翰-泰勒效应是金属氨酸基离子基的结构的一个重要因素.
- (2)A(u) 对称性提供了一个比传统的A(1u) /A(2u) 模型更准确的描述.
- 计算标准可以预测这些系统中pJT扭曲的发生和性质.
相关概念视频
Bonding in Metals
Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Drüde called the “Electron Sea Model”.
Mass Spectrometry: Molecular Fragmentation Overview
The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
Radical Formation: Homolysis
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
Mass Spectrometry: Alcohol Fragmentation
Alcohols (R-OH) ionize to lose one non-bonded electron from the oxygen atom, forming molecular ions. Due to their tendency to fragment rapidly, the intensity of the molecular ion peak in the mass spectrum is weak or sometimes absent. The fragmentation patterns for alcohols occur in two ways, i.e. ⍺-cleavage and dehydration. During ⍺-cleavage, the bond at the ⍺-position adjacent to the hydroxyl group cleaves to give a resonance-stabilized cation and a radical. However, intramolecular dehydration...
Mass Spectrometry: Carboxylic Acid, Ester, and Amide Fragmentation
The fragmentation patterns observed for compounds such as carboxylic acids, esters, and amides in the mass spectra include ⍺-cleavage and McLafferty rearrangement. Fragmentation by ⍺-cleavage preferentially occurs at the carbon-carbon bond at the ⍺-position next to the carboxylic group to generate a neutral radical and a cation. Long chain compounds with hydrogen at their γ-carbon undergo McLafferty rearrangement to give a radical cation and a neutral alkene.
For example, the fragmentation of...
For example, the fragmentation of...
Imperfections in Crystal Structure: Non-Stoichiometric Defects
Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...


