中文摘要：

采用密度函数理论的B3LYP交换关联能泛函在6-311＋G（2df,2p）基组水平上,优化计算了Ca^＋,Mg^＋与RNA碱基嘧啶各同分异构体形成稳定复合物的结构,发现其中C1M,T1M和U1M（M=Ca^＋和Mg^＋）为最稳定复合物,并对这些复合物红外振动进行了计算。计算结果显示碱基嘧啶单体主要存在的两个红外特征振动,是由环振动和环外氧原子及与其成键的环上碳原子之间产生伸缩振动引起的。当形成复合物时,由于离子的参与,使单体碱基分子的振动情况发生了改变,主要表现在离子倾向于与环外负电子原子N和O原子成键,使与离子直接作用环外原子参与的特征振动频率减小,谱线红移;不与离子直接作用环外原子引起的特征振动频率增大,谱线蓝移。

英文摘要：

A density functional investigation of the interaction between calcium and magnesium univalent cations and RNA pyrimidine base（cytosine,thymine and uracil） was performed to determine geometric coordinates and free energies for all possible stable isomers at B3LYP/6-311＋G（2df,2p） level.The most stable isomers C1M,T1M and U1M（M=Ca＋ and Mg＋） with the lowest free energy among the same pyrimidine base tautomers were calculated to determine the characters of infrared vibrations.According to the results,two characteristic infrared vibrations at wave numbers 1 684 and 1 765 cm^-1 were found for single pyrimidine base C1,at 1 747 and 1 792 cm^-1 for T1,1 763 and at 1 796 cm^-1 for U1.In addition,spectrum shifts were found when the cations interact with the pyrimidine base tautomers.For deeper analysis,we found that when the stable complexes are formed,the cations are prone to act on the oxygen atoms,and cause the vibrational frequencies to change,the spectral lines belonging to the vibration of C—O—M turn out to redshift and the others turn out to blueshift.When the stable complex C1M is formed,the characteristic infrared vibration at 1 684 cm^-1 mainly caused by the ring＇s vibration turns out to blueshift about 10 cm^-1,and the another characteristic vibration of 1 765 cm^-1 caused by vibration of bond C—O with oxygen atom acting on cations directly turns out to redshift by 112 cm^-1 for complex C1Ca＋ and by 110 cm^-1 for C1Mg＋.When the stable complexes T1M are formed,the characteristic vibration of bond C—O—M turns out to redshift about 130 cm^-1 and the vibration of bond C—O turns out to blueshift about 55 cm^-1.When the stable complexes U1M are formed,the vibration of bond C—O—M truns out to redshift about 90 cm^-1 and about 50 cm^-1 for another C—O.The characteristic infrared vibration frequencies are changed obviously when tautomers act on the cations,which is mainly because cations take part in molecule＇s vibrations and change the force constants and reduced masses.