Kushida Yo, Saito Nozomi, Shigeno Masanori, Yamaguchi Masahiko
Department of Organic Chemistry , Graduate School of Pharmaceutical Sciences , Tohoku University , Aoba , Sendai , 980-8578 , Japan . Email:
Chem Sci. 2017 Feb 1;8(2):1414-1421. doi: 10.1039/c6sc01893a. Epub 2016 Oct 14.
Competition among multiple pathways in a chemical reaction exhibits notable kinetic phenomena, particularly when amplification by self-catalysis is involved. A pseudoenantiomeric 1 : 1 mixture of an aminomethylene helicene ()-tetramer and an ()-pentamer formed enantiomeric hetero-double helices and in solution when random coil was cooled. When a solution of at 70 °C was directly cooled to 25 °C, the -to- reaction was predominant, then was slowly converted to over 60 h. The slow conversion in the -to--to- reaction was due to the formation of the hetero-double helix , which was an off-pathway intermediate, and the slow -to- conversion. In contrast, when a solution of at 70 °C was snap-cooled to -25 °C before then maintaining the solution at 25 °C, the -to- reaction predominated, and the formation of was complete within 4 h. The reactions involve competition between the self-catalytic -to- and -to- pathways, where and catalyze the -to- and -to- reactions, respectively. Subtle differences in the initial states generated by thermal pretreatment were amplified by the self-catalytic process, which resulted in a drastic reaction shortcut.
化学反应中多条途径之间的竞争呈现出显著的动力学现象，特别是当涉及自催化放大作用时。当无规卷曲的氨基亚甲基螺旋烯（）-四聚体和（）-五聚体的假对映体1:1混合物在溶液中冷却时，形成了对映体异质双螺旋和。当70℃的溶液直接冷却至25℃时，向的反应占主导，然后在60小时内缓慢转化为。向向反应的缓慢转化是由于异质双螺旋的形成，它是一条偏离途径的中间体，以及向的缓慢转化。相比之下，当70℃的溶液快速冷却至-25℃，然后将溶液保持在25℃时，向的反应占主导，并且在4小时内完全形成。这些反应涉及自催化的向和向途径之间的竞争，其中和分别催化向和向反应。热预处理产生的初始状态的细微差异通过自催化过程被放大，这导致了反应的大幅捷径。
