胞嘧啶-胸腺嘧啶二核苷SP光损伤反应的理论研究

在DNA光损伤产物中，有一种特殊的UV诱导生成的嘧啶二聚体(SP)．尽管胞嘧啶C和胸腺嘧啶T在分子结构上非常相似，在实验中还没有发现DNA相邻的C和T之间形成类似的SP产物．用密度泛函理论，以DNA中的片段CpT为模型分子，在B3LYP/6-311++G(d,p)//B3LYP/6-31G(d,p)计算水平上从理论的角度揭示 了阻碍CpT生成SP类似物的关键因素． 与生成类似SP产物相比较，CpT更倾向于通过光物理失活途径回到基态反应物

Theoretical Investigation on the Absence of Spore Photoproduct Analogue at Cytosine-Thymine Site

As a well known DNA photolesion product, the special UV induced pyrimidine dimmer called spore photoproduct (SP), has aroused strong research interests. The SP formation was reported solely between two adjacent thymidine residues. It remains unclear in pervious experimental observations why there is an absence of the cytosine-derived SP-like photoprod-uct formation at the cytosine containing DNA strand, although the cytosine residue holds great similarity to thymine in terms of molecular structure. From a theoretical perspec-tive, we have explored this issue in this work by means of density functional theory at the B3LYP/6-311++G(d,p) //B3LYP/6-31G(d,p) level for the DNA dinucleotide fragment, cy-tosine phosphate thymine (CpT). Key factors blocking the formation of the SP-like product between two adjacent cytosine and thymidine residues are revealed. Instead of undergoing photochemical SP reaction, a photophysical deactivation pathway back to the ground state turns out to be favorable for the CpT dinucleotide fragment.