相关概念视频
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
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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.
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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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.
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01:26Photochemical Electrocyclic Reactions: Stereochemistry
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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
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02:50Catalysis
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The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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01:07Catalytically Perfect Enzymes
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The theory of catalytically perfect enzymes was first proposed by W.J. Albery and J. R. Knowles in 1976. These enzymes catalyze biochemical reactions at high-speed. Their catalytic efficiency values range from 108-109 M-1s-1. These enzymes are also called 'diffusion-controlled' as the only rate-limiting step in the catalysis is that of the substrate diffusion into the active site. Examples include triose phosphate isomerase, fumarase, and superoxide dismutase.
Most enzymes...
Most enzymes...
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01:14Keto–Enol Tautomerism: Mechanism
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The keto and enol forms are known as tautomers and they constantly interconvert (or tautomerize) between the two forms under acid or base catalyzed conditions. Both the reactions involve the same steps—protonation and deprotonation— although in the reverse order.
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通过烯合成酶解码催化.
Joshua N Whitehead1, Nicole G H Leferink2, Linus O Johannissen1
1Manchester Institute of Biotechnology, Department of Chemistry, The University of Manchester, Manchester, M1 7DN, United Kingdom.
ACS catalysis
|October 12, 2023
概括
本综述更新了合成酶/循环酶 (TS) 生物催化学的领域,详细介绍了了解TS反应化学和工程方面的最新进展. 未来的目标包括合理设计"设计合成体"用于新型应用.
科学领域:
- 生物化学和合成生物学
- 酶催化和工程 酶催化和工程
背景情况:
- 合成酶 (TSs) 是生产各种类的关键酶.
- 2017年的一项审查总结了基础的TS发现;这项工作更新了自那时以来的领域.
研究的目的:
- 审查最近的TS文献,重点关注反应化学和工程策略.
- 探索合成酶的合理设计的未来.
主要方法:
- 2017年以后发表的TS研究的文献综述.
- 综合实验和计算方法的分析,以了解TS催化.
- 检查最近的TS工程策略,包括机器学习.
主要成果:
- 确定控制TS产品结果的催化动机.
- 详细探讨TS酶如何将简单的基质转化为复杂的 terpenoids.
- 新兴的TS工程数据驱动方法.
结论:
- 对TS的理性和预测性工程正在成为一个现实的目标.
- 了解催化动机是解读TS复杂性的关键.
- "设计者合成酶"已经在地平线上.
