大环疏水效应:冠醚在DMF+H_2O混合物中的焓对作用  

Macrocyclic Hydrophobic Effect:Enthalpic Pairwise Interactions of Crown Ethers in Mixtures of DMF and Water

作　　者：程维娜[1] 胡新根[1] 邵爽[2] 

机构地区：[1]温州大学化学与材料工程学院,浙江温州325035 [2]浙江外国语学院化学系,杭州310012

出　　处：《物理化学学报》2013年第10期2114-2122,共9页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(21073132)资助项目~~

摘　　要：利用等温滴定微量热法测定了298.15 K时12-冠-4、15-冠-5、18-冠-6和4,13-二氮杂-18-冠-6四种冠醚在纯水及不同质量分数(w=0-0.3)的N,N-二甲基甲酰胺(DMF)+H_2O混合物中的稀释焓,根据McMillan-Mayer理论计算得到相应的焓对作用系数(h_(xx)).实验发现,h_(xx)均为较大的正值,表明在冠醚-冠醚自相互作用中疏水性成分占绝对优势,主要表现为两种机制:(1)当疏水-疏水作用发生时,共球交盖使得水结构形成减少,对h_(xx)有正的贡献;(2)当疏水-亲水作用发生时,共球交盖使得水结构破坏增加,对h_(xx)有正的贡献.此外,四种冠醚h_(xx)的大小关系为:h_(xx)(18-冠-6)>h_(xx)(4,13-二氮杂-18-冠-6)≈h_(xx)(15-冠-5)>h_(xx)(12-冠-4),表明冠醚环越大,疏水-疏水作用越强,存在显著的大环疏水效应.The dilution enthalpies of four crown ethers, namely 12-crown-4, 15-crown-5, 18-crown-6, and 4,13-diaza-18-crown-6, in pure water and mixtures of N,N-dimethylformamide （DMF） and water of various mass fraction （w=0-0.3） were determined at 298.15 K by isothermal titration microcalorimetry. The corresponding enthalpic pairwise interaction coefficients （hxx） were evaluated according to the McMillan-Mayer theory. Values of hxx were all positive and large, which indicates that hydrophobic components predominate in crown-crown self-interactions. There are two main kinds of mechanisms： （1） When hydrophobic-hydrophobic interactions occur, cosphere overlapping reduces the formation of water structure, which makes a positive contribution to hxx （2） Hydrophobic-hydrophilic interactions increasingly destroy the water structure because of cosphere overlapping, which also makes a positive contribution to hxx. In addition, h,= values of the four crown ethers follow the order： hxx（18-crown-6）〉hxx（4,13-diaza-18-crown-6）= hxx（15-crown-5） 〉hxx（12-crown-4）, which indicates that the larger the size of the crown ether ring, the stronger the hydrophobic-hydrophobic interaction; namely, that crown ethers are subject to macrocyclic hydrophobic effects.

关 键 词：冠醚 二甲基甲酰胺＋水混合物 稀释焓 焓对作用 疏水-亲水平衡 大环疏水效应 等温滴定微量热法 

分 类 号：O642.1[理学—物理化学]