核碱基在 ⩽200 K 低温下直接和水介导的同分异构反应动力学

IF 1.5 4区 化学 Q4 CHEMISTRY, PHYSICAL
Judith Würmel, John M. Simmie
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引用次数: 0

摘要

星际介质中合成复杂有机分子的详细化学动力学机制尚处于早期发展阶段。通过对小行星取样进行化学分析,我们已经知道这种合成必须发生。随着分子复杂性的增加,可能的结构异构体的数量也在增加,其结果是新生的物种可能会采用不同的空间排列,而不是能量最低的排列。作为氢原子转移反应或酰亚胺酸-酰胺物种 H-O=C-N- ⇌ $\rightleftharpoons$ O=C-N-H 的同分异构体研究计划的一部分,我们研究了一些核碱基(即胞嘧啶、胸腺嘧啶和尿嘧啶)的动力学,在这些核碱基中会出现一种环状的同分异构形式(内酰胺)。我们报告了在 50-200 K 低温条件下,直接单分子过程和由额外水分子介导的类似转化过程的反应速率,其中第四种是 5-氮杂脲嘧啶(1,3,5-三嗪-2,4(1H,3H)-二酮)。我们的研究表明,这些同分异构反应可分为三类,并强调了量子力学隧道效应在这些低温条件下对速率常数的重要性。我们进一步介绍了一些热化学数据,如形成焓、熵、等压热容和焓函数。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Kinetics of direct and water-mediated tautomerization reactions of nucleobases at low temperatures ⩽200 K

Kinetics of direct and water-mediated tautomerization reactions of nucleobases at low temperatures ⩽200 K

Detailed chemical kinetic mechanisms for the synthesis of complex organic molecules in the interstellar medium are at an early stage of developement. That such synthesis must take place is well-known from chemical analysis of sampled asteroids. As molecular complexity increases the number of possible structural isomers also increases with the consequence that the nascent species may adopt a different spatial arrangement, to the lowest energy one. As part of a program of investigations of the hydrogen atom transfer reaction or tautomerization of imidic acid–amide species H-O=C-N- $\rightleftharpoons$ O=C-N-H we have studied the kinetics for a number of nucleobases, namely cytosine, thymine and uracil where a cyclic form of tautomerism (lactim–lactam) is encountered. Together with a fourth, 5-aza-uracil (1,3,5-triazine-2,4(1H,3H)-dione), we report on the rates of reaction at low temperatures 50–200 K for both the direct unimolecular process and the similar transformation mediated by an additional water molecule. We show that these tautomerization reactions can be categorized into three classes, and highlight the importance of quantum mechanical tunneling on the rate constants at these low temperatures. We further present some thermochemistry data, such as formation enthalpies, entropies, isobaric heat capacities and enthalpy functions.

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来源期刊
CiteScore
3.30
自引率
6.70%
发文量
74
审稿时长
3 months
期刊介绍: As the leading archival journal devoted exclusively to chemical kinetics, the International Journal of Chemical Kinetics publishes original research in gas phase, condensed phase, and polymer reaction kinetics, as well as biochemical and surface kinetics. The Journal seeks to be the primary archive for careful experimental measurements of reaction kinetics, in both simple and complex systems. The Journal also presents new developments in applied theoretical kinetics and publishes large kinetic models, and the algorithms and estimates used in these models. These include methods for handling the large reaction networks important in biochemistry, catalysis, and free radical chemistry. In addition, the Journal explores such topics as the quantitative relationships between molecular structure and chemical reactivity, organic/inorganic chemistry and reaction mechanisms, and the reactive chemistry at interfaces.
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