Study of clathration between α-/β-cyclodextrin and quaternary ammonium surfactants

Interactions of α-/β-CD with 3-alkoxyl-2-hydroxypropyltrimethylammonium chlorides(CnNCl)in aqueous solutions were investigated with titration microcalorimetry at temperature 298.15 K.Results showed that both the reactions between C8NCl and α-CD as well as between C8NCl and β-CD can form stable clathrates of same mole ratio of 1∶1 with the apparent experimental stability constants of 1.41×103 dm3·mol-1 and 6.50×102 dm3·mol-1 respectively;while C12NCl will react with α-CD and β-CD forming clathrates of mole ratio of 1∶2 and 1∶1 respectively with apparent experimental stability constants of 1.05×106 dm6·mol-2 and 8.83×103 dm3·mol-1 respectively.The standard enthalpy change(ΔHθ)and standard entropy change(ΔSθ)of the clathration between C12NCl that has the longer carbon chain and α-/β-CD are smaller than that of C8NCl that has the shorter carbon chain.It has been proved that the formation process of clathrates of α-CD is driven by enthalpy and hindered by entropy;while the formation process of clathrates of β-CD is commonly driven by both enthalpy and entropy.