Solvent-Induced Transformation of Myo-Iositol Crystal

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The objective of our study is to investigate the effect of organic solvents on pseudopolymorph transformation kinetics for clarifying the transformation phenomena. In our previous study, we observed anhydrate and dihydrate crystals of myo-inositol in a water and/or water-ethanol system and transformation phenomena. However, we could not determine the detailed transformation mechanism in organic solvents. Therefore, we attempted seeding crystals in different alcohol solvents, which resulted in the transformation of the seed crystals of dihydrate into anhydrate crystals. The transformation kinetics increased with the decrease in alkyl carbon number in the solvents and also with the ethanol mass fraction. In the transformation process, fine anhydrate crystals were observed on the surface of dihydrate crystals, and the dihydrate crystals were found to dissolve and gradually decrease in size. On the basis of the results, we propose that the hydrophilic nature of organic solvents is a significant factor determining the pseudopolymorph transformation kinetics of myo-inositol. The transformation phenomena proceeded easily by the addition of seed dihydrate crystals, as if the solvent had the driving force for the crystallization of a stable polymorph. We classified this unique mechanism as ‘solvent-induced transformation’.