用密度泛函理论研究苦参碱质子转移的异构化

Theoretical study on the proton transfer isomerization of matrine

采用密度泛函B3LYP/6-311G(d,p)方法和分子内质子迁移及水助质子迁移2种途径,计算苦参碱酮式与烯醇式互变异构反应,得到各异构体和过渡态的结构及变化过程中的活化能、反应焓、活化吉布斯自由能等性质。结果表明:苦参碱结构中有3个椅式和1个近扭船式六元环。无论是孤立分子还是一水合物,其酮式是最稳定结构。水助质子迁移可以大大降低反应活化能,其氢键起重要作用。得到了非平面四元环及六元环的过渡态,其碳原子杂化方式均为sp^3。

The reaction mechanism of the proton transfer between the keto tautomer and the enol tautomer for matrine has been investigated by B3LYP method with 6-311G（d,p） basis set.The intramolecular proton transfer and water-assisted intermolecular transfer pathways were used.The geometrical structures,reaction enthalpies,activation energies,activation free energies of tautomerism were obtained.The results showed that the keto A1 is the most stable tautomer of all the tautomers in the form of isolated or hydrated isomers.The water-assisted intermolecular transfer processes has lower activation energies because hydrogen bonds formed in the hydrated isomers play an important role.The four-membered and six-membered cyclic transition states are not planarity because structure of molecule is not planarity,and the carbons on which proton transfer were took place in transition states adopts sp^3 hybridized orbitals.