Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (10): 2114-2122.doi: 10.3866/PKU.WHXB201305103

• THERMALANALYSIS KINETICS ANDTHERMOKINETICS • Previous Articles     Next Articles

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

CHENG Wei-Na1, HU Xin-Gen1, SHAO Shuang2   

  1. 1 College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, Zhejiang Province, P. R. China;
    2 Department of Chemistry, Zhejiang International Studies University, Hangzhou 310012, P. R. China
  • Received:2013-03-26 Revised:2013-05-09 Published:2013-09-26
  • Contact: HU Xin-Gen E-mail:hxgwzu@126.com
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21073132).

Abstract:

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, hxx 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.

Key words: Crown ether, N,N-dimethylformamide+H2Omixture, Dilution enthalpy, Enthalpic pairwise interaction, Hydrophobic-hydrophilic equilibrium, Macrocyclic hydrophobic effect, Isothermal titration calorimetry

MSC2000: 

  • O645