Crystallization of Ergosterol Using the Water-Immiscible Solvent Hexane and the Characterization of Precipitates

Abstract

The crystallization of ergosterol was performed using water-immiscible hexane as a solvent. It was found that a ppm-level of water contained in hexane plays an important role in the change in the morphology of precipitates. The morphology of the ergosterol precipitates changed from thin needle-like crystals to spherical precipitates with a decrease in the water content of hexane. The thin needle-like crystals were monohydrate crystals and obtained when a sufficient amount of water was dispersed in hexane as many small droplets. On the other hand, the spherical precipitates were obtained under less water content, for instance under 185 ppm water. The spherical precipitates had a good filtration property, compared with the thin needle-like crystals. The precipitates were a mixture of the monohydrate crystals and amorphous solid. As long as it was observed with a 10000-fold scanning electron microscope, the surface of the spherical precipitate was covered with small thin needle-like monohydrate crystals and the inside was smooth solid. We named the spherical precipitate the broccoli-like precipitate. A possible mechanism for the formation of the broccoli-like precipitate is as follows. As the first step, ergosterol precipitates as a mixture of the monohydrate micro crystals and amorphous solid from the solution containing a ppm-level of water. Then, the monohydrate crystals preferentially grow or the amorphous solid transforms to the monohydrate crystals on the surface of the precipitates by contacting with fresh solvent containing water.