Prednisone/Cyclodextrin Inclusion Complexation: Phase Solubility, Thermodynamic, Physicochemical and Computational Analysis

Abstract

Guest–host interaction of prednisone (PN) with cyclodextrins (CDs) have been investigated using phase solubility diagrams (PSD), differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), scanning electron microscopy (SEM) and molecular mechanical modeling (MM). Estimates of the complex formation constant (K 11) show that the tendency of PN to complex with CDs follows the order: β-CD>γ-CD>HP-β-CD>α-CD. At the same pH of 7.0, β-CD forms soluble 1:1 and insoluble 1:2 PN/CD complexes (BS-type PSDs). The thermodynamic functions for 1:1 PN/β-CD estimated at pH = 7.0 (ΔG 11 o =−20.8 kJ⋅mol−1) show that complexation is driven by enthalpy (−30.7 kJ⋅mol−1) but retarded by entropy (ΔS 11 o =−33.1 J⋅mol−1⋅K−1) changes. The MM modeling study indicates the formation of different isomeric 1:1 complexes with CDs. PSD, DSC, XRPD, SEM and MM studies established the formation of inclusion complexes in solution and the solid state.