葫芦脲[7]与核黄素包结物的可能结构和光谱性质

Probable Configurations and Spectroscopic Properties of the Inclusion Compound of Cucurbit[7]uril and Riboflavin

利用密度泛函理论对葫芦脲[7]和核黄素包结物的可能结构进行了理论计算.从5种可能结构分析主客体在包结物中的作用得出:核黄素作为客体分子与主体葫芦脲[7]分子通过不同官能团作用可形成稳定性不同的包结物,其中以核糖醇的羟基插入到葫芦脲[7]分子的腔体与其端羰基氧原子形成较多的氢键最稳定.在理论上证明了此包结反应为一放热反应的实验事实,并进一步说明了包结物分子的相对稳定性受主客体分子的几何畸变能和主客体之间作用能的影响,说明了成键能和稳定性之间的区别.在此基础上利用时间相关的密度泛函理论进行了不同构型包结物的激发态计算并对光谱性质进行了理论预测.比较了包结物中核黄素分子的跃迁轨道的组成变化,分析得出:葫芦脲[7]的包结作用改变了核黄素分子的电子跃迁性质,使其吸收光谱发生红移.并预测出其荧光猝灭的微观机理,此理论计算结果很好地解释了相应的实验现象.

Possible configurations and optical properties of a cucurbit[7]uril（CB7） and riboflavin（VB2） inclusion compound were investigated by density functional theory（DFT）.A comparison was made among the different structures by an analysis of the interaction between the host and guest molecules.The results indicate that riboflavin sits on top of the cucurbit[7]uril molecule with a couple of hydroxyls inserting into the cavity to form H-bonds.We verify theoretically that the inclusion reaction is an exothermal reaction,which supports the findings from the experiment very well.The sequence of stability for the possible inclusion complexes is strong evidence that the interaction between the guest and host molecules and the distortion of the guest and host molecules both contribute to the stability.The bonding energy and stability should be distinguished conceptually.The time-dependent DFT method was used in the excited state calculations to explore the photochemical properties of the inclusion compounds.The component difference for the excited orbitals in the different inclusion complex configurations was compared theoretically.The results show that cucurbit[7]uril causes a red-shift absorption and fluorescence quenching for riboflavin after host-guest inclusion,which strongly support the experimental data.