摘要
采用量子化学密度泛函理论在B3LYP/6-311G^(**)水平对标题化合物可能存在的A、B、C三类互变异构体进行全优化,采用AIM 2000程序包计算了分子内氢键及相应的成键临界点电荷密度和关键原子的电荷;在计算的基础上,分析了异构体几何构型、相对稳定性和电荷分布,讨论分子内质子转移的难易程度.采用含时密度泛函理论在相同水平上对其进行了电子吸收光谱研究.为模拟真实条件,计算还考虑了水溶液对电子结构和光谱性质的影响.研究结果表明:烯胺式B为最稳定结构,三个异构体稳定性为B>A>C.A、B、C的λ_(max)均来源于分子的π→π~*跃迁,且存在明显的分子内电荷转移现象.异构体A、B之间易通过分子内质子转移进行互变,质子转移的能垒较低;质子供体和受体之间的电荷转移可能是通过共轭体系的π电子跃迁产生的.水溶液中A、B电子光谱的λ_(max)发生红移,振子强度增大,吸收增强;而C的λ_(max)基本不改变,振子强度减小,吸收减弱.
The structures of three possible tautomers of the title compound （A, B and C） were fully optimized by using density functional theory （DFT） at the B3LYP/6-311G＊ level, and the electronic charge densities of critical points and charges of some atoms were calculated with AIM 2000 program package. On the basis of calculations, the geometries, relative stability, charge density population and intramolecular proton transferring were discussed. Using TD-DFT method, the electronic spectrum of each isomer was studied at the same level. For simulating the real conditions, the solvent （water） effects were evaluated with the polarized continuum model （PCM）. The theoretical calculation confirms that the eneamine tautomer is most stable with the stability order of B〉 A〉 C. The λmax of all tautomers originate mainly from the π→π＊ electronic transition, and all involve the intramolecular charge transfer. The intramolecular proton transfer may be caused to undergo the conversion of A to B （or B to A） with a low energy barrier by the π electron transitions in conjugated system. In water medium, A and B both have the red shift of λmax, the oscillator strength increases, and the absorption tends to be enhanced. Instead, the λmax of C in water remains almost the same as that in gas, the oscillator strength decreases, and the absorption tends to be weakened.
出处
《原子与分子物理学报》
CAS
CSCD
北大核心
2010年第5期979-985,共7页
Journal of Atomic and Molecular Physics
基金
重庆市科委自然科学基金项目(CSTC
2008BB6061)
重庆市教委科学技术研究项目(KJ080703)
科技部项目(2009GJF10005)
关键词
姜黄素
苯丙氨酸
席夫碱
衍生物
理论研究
curcumin, phenylalanine, schiff base, derivative, theoretical study
