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A quantum chemical approach to the study of a novel reaction path and its control in the supercritical water

研究超临界水中新型反应路径及其控制的量子化学方法

基本信息

批准号：
15360422
负责人：
NITTA Tomoshige
金额：
$ 7.55万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

The results obtained by present work can be summarized by the following two subjects. One is that a novel methodology (QM/MM-ER) has been developed to compute the free energy change associated with a chemical reaction in a condensed phase. The other is that a novel reaction pathway has been explored by means of the QM/MM-ER simulations. It has been suggested that the proton transfers along the hydrogen bonds of water molecules promote the dehyderation of butanediol in hot water. The details of the results have been itemized as follows.(1)Quantum chemical approach to the free energy calculation in condensed phaseIn order to compute the free energy change associated with a chemical reaction in aqueous solution, we have combined the quantum mechanical/molecular mechanical approach with the theory of energy representation. Within the theory of the energy representation, the solvation free energy of a solute is described in terms of the distribution functions of the solute-solvent interaction energy instead of the spatial distribution function used in the conventional theory of solution. Since the method of the energy representation does not need the concept of the interaction site, the combination with the quantum chemical treatment is straightforward.(2)Quantum chemical calculation for the dehydration reaction of alcoholQuantum chemical calculations have revealed that butanediol forms a biradical electronic structure at the transition state (TS) of the proton transferring reaction. The activation energy is extremely high (〜70 kcal/mol) in the gaseous phase, however, it reduces to 〜50 kcal/mol in hot water. The electronic state of the TS forms a zwitterionic structure in the polar solvent, which leads to the stabilization of the TS as compared to the reactant. Thus it has been suggested that the proton-transfer mechanism catalyzes the dehydration reaction of alcohol in hot water.

目前的工作所获得的结果可以概括为以下两个主题。一是开发了一种新的方法（QM/MM-ER）来计算与凝聚相化学反应相关的自由能变化。另一个是通过QM/MM-ER模拟探索了一种新的反应途径。有人提出，沿着水分子氢键的质子转移促进了丁二醇在热水中的脱水。具体结果如下： (1)凝聚相自由能计算的量子化学方法为了计算水溶液中化学反应的自由能变化，我们将量子力学/分子力学方法与能量表示理论相结合。在能量表示理论中，溶质的溶剂化自由能是用溶质-溶剂相互作用能的分布函数来描述的，而不是传统溶液理论中使用的空间分布函数。由于能量表示方法不需要相互作用位点的概念，因此与量子化学处理的结合非常简单。(2)醇脱水反应的量子化学计算量子化学计算揭示了丁二醇在质子转移反应的过渡态(TS)形成双自由基电子结构。气相中的活化能极高（〜70 kcal/mol），但在热水中则降至〜50 kcal/mol。 TS 的电子态在极性溶剂中形成两性离子结构，这使得 TS 与反应物相比更加稳定。因此，有人提出质子转移机制催化了乙醇在热水中的脱水反应。