Spectrophotometric and Thermodynamic Studies of the Inclusion Complexation of Thiourea Substrate with Hydroxypropyl-β-cyclodextrin

A simple and fast spectrophotometric method has been used to determine the thermodynamic parameters of the inclusion complex formed between N-(2-ethylphenyl)-N'-(2- methylphenyl) thiourea, a hydrophobic substrate trap and hydroxypropyl-β-cyclodextrin (HP -β-CD). The overall association constants have been calculated at different temperatures using the Scott's method and are found to decrease with increase in temperature. The free energy change ( ΔG°) and the enthalpy of formation ( ΔH°) as well as the entropy ( ΔS°) have been determined for the various inclusions. The method has been applied with satisfactory precision; the values of relative standard deviations did not exceed 2%.