Host-guest complexation of β-, γ-cyclodextrin with alkyl trimethyl ammonium bromides in aqueous solution

As a continuation of our previous investigation, interactions between cyclodextrin (beta-CD), gamma-cyclodextrin (gamma-CD) and alkyl trimethylammonium bromides in aqueous solutions have been studied with titration calorimetry and H-1 NMR at 298.15 K. The results are discussed in terms of the amphiphilic interaction of CD with surfactants and the iceberg structure formed by water molecules existing around the hydrophobic tail of surfactant molecules. The stoichiometry of the beta-CD-surfactant system is 1:1 whereas that of the gamma-CD-surfactant system is 1:2. The corresponding formation enthalpy (negative) of the complexes of the two systems decreases with an increase in the number of carbon atoms (n) in hydrophobic chain of surfactant molecule, CnH2n+1, whereas the entropy increases with the enlargement of n.