Journal of Chemical Thermodynamics, Vol.97, 242-250, 2016
Calorimetric study on the interaction of didecyldimethylammonium and decyltrimethylammonium cations with native cyclodextrins in water
The interaction of two decylammonium surfactants, didecyldimethylammonium bromide (D) and decyltrimethylammonium bromide (S), with native alpha-, beta-, and gamma-cyclodextrins (CDs) was systematically examined using the isothermal titration calorimetry (ITC). The measured heat data at five temperatures ranging from (283.15 to 318.15) K were treated simultaneously allowing the estimation of thermodynamically consistent temperature dependence of the equilibrium constant, the enthalpy and heat capacity for the formation of inclusion complexes. The heat data for D/alpha-CD interaction were analysed by the sequential binding model with 1:1, 1:2 and 1:3 (D:alpha-CD) stoichiometries, while other surfactant-CD combinations were examined using only 1:1 and 1:2/2:1 stoichiometries. Thermodynamic quantities for complexation are discussed in terms of structural features and their temperature dependence. The enthalpy-entropy compensation analysis of selected surfactant-CD 1:1 complexes obeys a linear relationship. Due to entropical stabilization caused to a high extent by alkyl chain desolvation, the >C-10 bearing ions were found not to follow the patterns previously published on binding of other guests. The prediction of the binding thermodynamic properties of D/CD from the S/CD interaction was tested and found surprisingly accurate. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords:Didecyldimethylammonium;Decyltrimethylammonium;Water;Cyclodextrin;Inclusion complex stability;Binding thermodynamics