X-ray study of the pseudopolymorphism of the azithromycin monohydrate

Abstract A combination of X-ray powder diffraction and single crystal studies on azithomycin pseudopolymorphs give the precise solid state composition of all monohydrate pseudopolymorphs reported. According to the X-ray results the four monohydrates of azithromycin studied have the same crystallographic parameters. Furthermore, the analysis of the relative intensities from the powder patterns points to very similar chemical compositions and crystal structures. This result has been confirmed by the single crystal studies. The single crystal studies show that the solid state conformation of the azithromycin molecules is affected by the presence of solvents. The solvent methanol molecules were found disordered probably due to the existence of many positions where the hydrogen bonding is favoured and the large size of the available space to host the solvents.