Effect of counterions on the interactions in solid dispersions between polyethylene glycol, griseofulvin and alkali dodecyl sulphates

Abstract

Solid dispersions of polyethylene glycol (PEG) 3000 and 10% w/w griseofulvin with or without different surfactants incorporated were prepared by the melting method. The anionic surfactants lithium dodecyl sulphate (LiDS), sodium dodecyl sulphate (SDS) and potassium dodecyl sulphate (KDS) were added in equivalent amounts, ~ 2% w/w. Phase analysis was performed by X-ray powder diffraction and investigation of short-range structure by 13C-CP/MAS solid-state NMR. In all samples with surfactant added, solid solutions (PEG/MDS) 1− x griseofulvin x were formed. The properties of the solid solutions with Na + and K + ions were almost identical. The addition of LiDS created a structure of the solid solution that was more crystalline than that structure of the sodium- and potassium-containing compounds. The ion with the highest charge-to-radius ratio, Li +, formed chemical bonds that were different from those of the other ions. This was indicated by a changed influence on the hydrophilic parts of the griseofulvin molecules in the lithium compound. The melting behaviour of the solid solutions, investigated by DSC, showed a second transformation in the melt at 186–196°C, indicating a two-phase region in the liquid phase. For the lithium-containing compounds the transformation appeared at lower temperature than for the sodium- and potassium-containing compounds.