6-硫代鸟嘌呤磺化异构体热力学稳定性的计算研究

采用量子化学密度泛函理论B3LYP方法在6-311++G(d,p)基组水平上,对6-硫代鸟嘌呤硫醇式与硫酮式两类共14种磺化异构体的热力学稳定性进行了计算研究,全自由度优化了各物种构型,进行了振动分析,获得了各磺化异构体的零点能、焓、热力学能以及吉布斯自由能等热力学数据.分析了各异构体磺化前后稳定性的变化情况,探讨了磺化异构体的稳定性问题.结果表明,不论是硫酮式还是硫醇式磺化异构体,当H原子连接到N7上时磺化异构体稳定性均比连接到N9上时较高一些.在6-硫代鸟嘌呤磺化异构体中,STG(3,7,10,10)是最稳定的异构体,STG(1,7,10,10)、STG(1,9,10,10)和STG(1,3,7,10)等异构体也可共存,其他异构体存在的可能性均较小.

Calculational investigation of the thermodynamic stability on sulfonated tautomers of 6-thioguanine

The thermodynamic stability of fourteen sulfonated tautomers for keto and enol 6-thioguanine was investigated using DFT-B3LYP method combined with 6-311++G(d,p) basis set. All the structures were optimized with full freedom and the frequency analysis was also carried out at the same level. Zero point energies, enthalpies, total energies and Gibbs free energies of each tautomer were also obtained. The results show that the N7H configuration stability of sulfonated tautomers for 6- thioguanine is higher than the N9H form. The geometrical configuration STG(3,7,10,10) is the most stable of all the tautomers and the STG(1,7,10,10), STG(1,9,10,10) and STG(1,3,7,10) tautomers can exist in some quantity.