Host–guest interactions between 4-sulfonatocalix[8]arene and 1-alkyl-3-methylimidazolium type ionic liquids
2012
Wintgens, Véronique | Amiel, Catherine | Biczók, László | Miskolczy, Zsombor | Megyesi, Mónika
The inclusion of 1-alkyl-3-methylimidazolium ions (Cₙmim⁺) in 4-sulfonatocalix[8]arene was studied by isothermal titration calorimetry in aqueous solution at 298K. Sequential formation of 1:1 and 2:1 complexes occurred in enthalpy driven reactions. The alteration of the molecular structure of the guest barely affected the driving force of the confinement of the first Cₙmim⁺. However, the binding affinity of the second Cₙmim⁺ went through a maximum when the number of carbon atoms in the side chain was increased. The enthalpy and entropy change diminished linearly with the length of the aliphatic substituent of Cₙmim⁺ for 1:1 complexation, but reached a minimum for the hexyl homologue in the case of 2:1 inclusion. Linear entropy–enthalpy correlations were found with smaller slope and intercept for the second binding step.
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