左旋尤利沙星电子结构及ECD谱的理论研究

Theoretical study on the structure and ECD spectrum of S-ulifoxacin

采用DFT及TD-DFT方法在B3LYP/6-311++G**水平对左旋尤利沙星的电子结构及ECD谱进行了理论研究.研究发现,环A、环B、环C及羰基之间共轭,成刚性平面结构.电子密度拓扑分析发现,H(23)与O(19)之间存在分子内氢键;水溶液中,分子内氢键作用加强,键长缩短为0.1624nm,键鞍点电荷密度增加为0.0581a.u..理论研究获得的ECD谱与实验谱基本吻合.水溶液中,左旋尤利沙星在244nm处存在负性康登效应,在253、278、333nm处存在正性康登效应.轨道成份分析显示,电子跃迁所涉及的轨道均为π轨道;因此,所有的康登效应均由π→π*荷移跃迁引起.这些结论对于深入理解尤利沙星的电子结构和手性光学性质具有一定的意义.

The structure and ECD spectrum of S-ulifoxacin were studied by using density functional theory（DFT） and time-dependent density function theory（TD-DFT） at the B3LYP/6-311＋＋G＊ ＊ level.The calculation results demonstrate that the conjugated effect is observed among rings A,B,C and carboxyl group.The topology analysis shows that there is a bond critical point between the H（7） atom and N（4） atom,namely to indicate the formation of intramolecular hydrogen bond.In water,the bond length is shortened to 0.1624 nm and the electronic charge density of bond critical point is increased to 0.0581 a.u.,verifying the enhancement of the bond in this solution.The calculated Electronic Circular Dichroism（ECD） spectrum agrees well with the experimental ECD spectrum.Detailed analyses of the ECD spectra in water solution reveal that negative cotton effect could be observed at 244 nm,and positive cotton effects could be observed at 253,278,333 nm.The orbital composition analysis shows that the molecular orbitals referring to above charge transfer transition are π orbital.This means that all the cotton effects in the ECD spectrum are caused by the π→π＊ charge transfer transition.Above findings could provide a deep insight into the electronic structure and chioptical properties of ulifoxacin.