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一个多模式驱动的分子航天器:光化学和热反应性阿佐本罗塔克桑
Hiroto Murakami1, Atsushi Kawabuchi, Rika Matsumoto
1Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki 852-8521, Japan.
Journal of the American Chemical Society
|November 10, 2005
概括
研究了阿尔法-环氧化 (alpha-CyD) 在罗塔克桑中的穿作用. 光异构化和NMR揭示了alpha-CyD运动,溶剂影响了这些分子机器中的阿佐本光异构化.
科学领域:
- 超分子化学 超分子化学
- 摄影化学的使用.
- 材料科学 材料科学 材料科学
背景情况:
- 罗塔克桑是机械互锁的分子架构,在分子机器中具有潜在的应用.
- 阿尔法-环极德 (alpha-CyD) 是一种宏环宿主分子,通常用作基于罗他森的系统中的组成部分.
- 亚博和维奥单元经常被纳入罗塔中,以赋予光响应和能量屏障功能.
研究的目的:
- 为了研究三种不同的轮素系统中的α-环氧化 (alpha-CyD) 的穿行为.
- 探索溶剂 (DMSO和水) 对这些轮素的光异构和分子运动的影响.
- 阐明alpha-CyD在应对光和热等外部刺激时的位置动态.
主要方法:
- 三种罗塔克桑的合成和表征,其中包括α-cyclodextrin,azobenzene,viologen和2,4-dinitrobenzene.
- 紫外线-Vis光谱法用于监测亚博烯部分的跨光异构化.
- 核磁共振 (NMR) 光谱,包括NOE差分光谱,以探测分子结构和动态.
- 可变温度的NMR研究,以调查分子运动和宿主-客人相互作用.
主要成果:
- 罗他素1的光异构化发生在DMSO和水中,表明alpha-CyD向乙烯组移动.
- 罗素2在DMSO中表现出光异构,但在水中没有,这表明依赖于溶剂的分子运动.
- 罗塔3在任何一种溶剂中都没有显示出光异构.
- 核磁共振 (NMR) 数据证实了阿尔法-CyD在罗他素2中的转移,并提供了关于其在不同条件下在罗他素结构中的位置的见解.
- 在交替光照照射后,观察到罗塔xane 1 的诱导循环二重化 (ICD) 的可逆变化.
结论:
- 罗塔克桑中的α-CyD的穿动力学受到亚博烯光异构化和周围溶剂环境的显著影响.
- 溶剂极性在调节光响应行为和轮素系统的分子运动方面起着至关重要的作用.
- 核磁共振和ICD光谱仪是特征复杂的动态和位置的变化,在基于罗他森的分子机器内组件的强大的工具.
相关概念视频
Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Radical Reactivity: Overview
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
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