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

作者：Cheng Wei Na; Hu Xin Gen^*; Shao Shuang

来源：Acta Physico - Chimica Sinica, 2013, 29(10): 2114-2122.

DOI：10.3866/PKU.WHXB201305103

• Crown ether
• N,N-dimethylformamide+H2O mixture
• Dilution enthalpy
• Enthalpic pairwise interaction
• Hydrophobic-hydrophilic equilibrium
• Macrocyclic hydrophobic effect
• Isothermal titration calorimetry

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 (h(xx)) were evaluated according to the McMillan-Mayer theory. Values of h(xx) 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 h(xx). (2) Hydrophobic-hydrophilic interactions increasingly destroy the water structure because of cosphere overlapping, which also makes a positive contribution to h(xx). In addition, h(xx) values of the four crown ethers follow the order: h(xx)(18-crown-6)>h(xx)(4,13-diaza-18-crown-6)approximate to h(xx)(15-crown-5) >h(xx)(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.

• 出版日期2013-10
• 单位浙江外国语学院; 温州大学