硫尿嘧啶特征振动的密度泛函理论分析

硫尿嘧啶特征振动的密度泛函理论分析 Characteristic Vibration Analysis of Thiouracil by DFT 张兴初 ZHANG Xingchu1 1 2 first-author 胡义华 HU Yihua2 2 王小涓 WANG Xiaojuan3 3 广州科技贸易职业学院机电系 广州科技贸易职业学院机电系 Department of Mechanical and Electronic,Guangzhou Vocational College of Technology and Business Department of Mechanical and Electronic,Guangzhou Vocational College of Technology and Business 广东工业大学物理与光电工程学院 广东工业大学物理与光电工程学院 Faculty of Physics and Optoelectronic Engineering,Guangdong University of Technology Faculty of Physics and Optoelectronic Engineering,Guangdong University of Technology 广东工业大学继续教育学院 广东工业大学继续教育学院 College of Contining Education,Guangdong University of Technology College of Contining Education,Guangdong University of Technology 采用密度泛函理论的B3LYP交换关联能泛函,在6-311+G（2df,2p）基组水平上,对尿嘧啶及硫尿嘧啶分子进行优化计算,发现硫尿嘧啶两个互变异构体中,硫取代7位置氧（U7S）的总能量为-20080.0636eV,硫取代3位置氧（U3S）的总能量为-20079.9896eV,U7S的总能量较小,较为稳定.在同样基组水平上对这些分子进行振动频率分析,发现尿嘧啶分子C—O健伸缩振动频率约为1770cm-1,而形成硫尿嘧啶时,与之相对应的S—O键伸缩振动频率约为1160cm-1,发生了约600cm-1的红移,且红外活性减弱.对应于该振动模式的力常数从16N·cm-1降低至3N·cm-1,折合质量由8amu降至3.8amu,力常数的减弱是产生这一振动红移的主要原因. A density functional investigation of uracil and thiouracil tautomers was performed to determine geometric coordinates and characteristic vibrations at B3LYP/6-311+G（2df,2p） level. The geometry optimizations of thiouracil tautomers have been carried out. According to the result,the total energy 3-thiouracil（U3S） is -20 079.989 6 eV,and 7-thiouracil（U7S） is -20 080.063 6 eV. The total energy for U7S is lower than U3S,so U7S is more stable than U3S.What’s more,the frequencies of optimized structures are calculated for characters of infrared vibration. We find that the stretching vibration frequencies of C—O for the three molecules is about 1 770 cm-1 and changes a little,but the stretching vibration of C—S for two thiouracil tautomers have more than 600 cm-1 redshift compared with the stretching vibration of C—O at the same position for uracil,which is about 1 160 cm-1. The reason for the redshift is that the sulfur atom taking place of the oxygen atom in uracil changes the force constants and the reduced masses. The force constant reduces from 16 N·cm-1 to 3 N·cm-1,and the reduced mass from 8 amu to 3.8 amu,so the decrease of the force constants is the main reason for redshift. 密度泛函理论（DFT） 红外振动谱 硫尿嘧啶 density function theory （DFT） infrared vibrational spectrum thiouracil 10.14188/j.1671-8836.2010.01.008 O621.13 国家自然科学基金资助项目（20471018） 2010-01-01 2021-04-01 1 56