单嘧磺隆除草剂的晶体构象-活性构象转换的密度泛函理论研究

应用密度泛函理论在B3LYP/6-31G(d)水平上对新型除草剂单嘧磺隆绕脲桥部分两个C—N键的内旋转势能面进行计算, 然后对势能面上的驻点进行构型优化和过渡态搜索, 得到单嘧磺隆4种稳定构象和构象转换过程所涉及的8个过渡态结构. 研究结果表明, 单嘧磺隆晶体构象-活性构象转换过程中涉及4种稳定构象和8条转换途径, 脲桥部分NH基团与嘧啶环上N原子所形成的分子内氢键对于构象的稳定性及转换过程起着十分重要的作用. 应用极化连续介质溶剂模型(PCM)在B3LYP/6-31＋＋G(d, p)水平下进行溶剂化效应计算, 结果表明单嘧磺隆从晶体构象转换成活性构象主要是在水相中进行的.

Density Functional Theory Study on Conformational Conversion between Crystal Conformation and Active Conformation of Herbicidal Monosulfuron

To understand how the crystal conformer converts to the active conformer, here the internal rotation potential energy surface around the two C—N bonds in the sulfonylurea bridge of monosulfuron has been studied by density functional B3LYP method and 6-31G(d) basis set. For the stationary points along the internal rotation energy surface, full geometry optimization or QST3 transition structure search and frequency analysis calculations were also performed. The calculated results indicated that there were four stable conformers and eight transition state structures corresponding to the conformational conversion of monosulfuron. The results also implied that the four stable conformers could be converted mutually through eight conversional paths. During the conversion, the internal hydrogen bond in monosulfuron can play a key role in the conformational stability and conversional process. For the obtained conformers, B3LYP/6-31＋＋G(d, p) method was also used to do single point calculation in vacuum and two PCM model solvents of water and heptane. The calculated results implied that the conversion mainly occurred in the aqueous solution.