碱基分子中单电子作用势判断化学键强弱的研究

碱基是遗传物质DNA和RNA的基本结构单元,与基因突变、癌症及遗传疾病许多健康问题息息相关.使用MELD精密从头计算及自编程序,计算了常见碱基分子腺嘌呤、鸟嘌呤、胸腺嘧啶、胞嘧啶和尿嘧啶中沿各化学键方向上的单电子作用势,并根据单电子作用势势垒——Dpb对各化学键的强弱进行了比较.结果表明,N—H键的Dpb值明显高于C—H键的Dpb值,且胸腺嘧啶分子的C7—H键的Dpb相对于其他分子的C—H键明显偏低.由于Dpb可以用来表征化学键的强弱,因此,碱基分子中N—H键要强于C—H键,且胸腺嘧啶中的C7—H键最弱,在DNA中易被自由基或其他基团进攻,该结论与实验结果一致,为进一步探讨碱基分子的相关性质奠定了基础.

Study on the strengths of chemical bonds evaluated by the PAEM for nucleobases

Nucleobases are the most important components of the genetic materials DNA and RNA, and may contribute to a variety of health-related problems including mutagenesis,carcinogenesis and inherited disease. In this paper,the potential energy barrier along all the C--H and N--H bonds for some familiar bases,including adenine, guanine, thymine, cytosine and uracil, have been calculated by using the MELD ab initio method and our own program,denoted by Dpb. The results showed that the N--H Dpb values are higher than the C--H Dpb values of all these nucleobases,and the Dpb of C7--H bond in thymine is the lowest. Dpb is a new indicator for charactering the strength of the chemical bond. As a result,the N--H bonds are stronger than the C--H bonds in all these molecules,and the C7--H bond of thymine should be also a sensitive site for DNA damage with the lowest Dpb value. The results are in agreement with the experimental results. This work provides a new tool for explo- ring the properties for nucleobases.