A microcalorimetric study of β-cyclodextrin with 3-alkoxyl-2-hydroxypropyl trimethyl ammonium bromides in aqueous solutions

We have investigated with titration microcalorimetry β-cyclodextrin with 3-alkoxyl-2-hydroxypropyl trimethyl ammonium bromides, which is a new surfactant synthesized in this laboratory, in aqueous solutions at a temperature of 298.15 K. The results are discussed in the light of amphiphilic interaction and the complex formed of water molecules around a hydrophobic surfactant tail. The stoichiometry of the (host + guest) complex changes from 1:1 to 2:1, as the number of carbon atoms n in the hydrophobic chain, CnH2n + 1O, increases from 8 to 14. All the complexes are stable with the apparent experimentally determined stability constants of β1 = 1.08 · 103 dm3 · mol−1, β1 = 28.66 · 103 dm3 · mol−1 and β2 = 141.9 · 103 dm6 · mol−2 for n = 8, 12 and 14, respectively. The enthalpy decreases with increasing n of the hydrophobic chain.