Multiple Equilibria Interaction Pattern between the Ionic Liquids C(n)mimPF(6) and beta-Cyclodextrin in Aqueous Solutions

作者：Zhang Jingjing; Shen Xinghai^*

来源：Journal of Physical Chemistry B, 2011, 115(41): 11852-11861.

DOI：10.1021/jp206418m

The interactions of ionic liquids (ILs) 1-alkyl-3-methylimidazolium hexafluorophosphate (C(n)mimPF(6), n = 2, 4, 6, 8) with beta-cyclodextrin (beta-CD) in aqueous solutions are investigated in this article. The stoichiometry and apparent association constants were obtained by the competitive fluorescence method, NMR measurements, and isothermal titration calorimetry (ITC). The results showed that C(2)mimPF(6), C(4)mimPF(6), and C(6)mimPF(6) form 1:1 (guest:host) inclusion complexes with beta-CD whereas the 1:2 inclusion complex can be formed between C(8)mimPF(6) and beta-CD. We studied the existence state of the ILs and found that they exist mainly as separated ions with a minor percentage existing as associated ion pairs within the concentration studied. By ESI/HRMS, the coexistence of different complexes including C(n)mim(+).PF(6)(-) -beta-CD, C(n)mim(+) -beta-CD (or C(n)mim(+) -beta-CD(2)), and PF(6)(-) -beta-CD was observed. It is also deduced that the intermediate complex, (beta-CD cation).(anion beta l-CD), may dissociate into cation beta-CD and anion beta-CD complexes. Thermodynamic parameters determined by ITC indicate that, while the inclusion process for C(6)mimPF(6)/beta-CD complex is entropy and enthalpy driven, the interactions of other C(n)mimPF(6) (n = 2, 4, 8) with beta-CD are enthalpy controlled. Based on these results, a more comprehensive pattern involving multiple equilibria on the interaction between C(n)mimPF(6) and beta-CD in aqueous solutions is presented herein.

• 出版日期2011-10-20
• 单位北京大学