Inclusion complexes of hydroxypropyl-β-cyclodextrin with novel cytotoxic compounds: Solubility and thermodynamic properties

Complexation processes in the systems of 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) – pharmacologically active substances within the temperature range of 293–315 K were studied by the UV-spectroscopy method. 2HP-β-CD was shown to improve the solubility of the studied drugs in aqueous systems. It was proved that complexation leads to the formation of supramolecular inclusion compounds with a 1:1 component ratio. The obtained complex 2HP-β-CD–methylium, tris(1-pentyl-1H-indol-3-yl)-, chloride was found to be unstable in buffer pH 7.4. Stability constants of the complexes and thermodynamic parameters of the formation of the inclusion compound 2HP-β-CD-1H-indole-3-methanol and 1-pentyl-α,α-bis(1-pentyl-1H-indol-3-yl) were calculated. The negative values of the changes in the Gibbs energy and the enthalpy indicate that the inclusion process is spontaneous and exothermic. The excess of the enthalpy term over the entropic one indicates that the inclusion process is enthalpy-determined.