Structural Insights into Solid-to-Solid Phase Transition and Modulated Crystal Formation in Octyl-β-d-Galactoside Crystals.

Abstract

Despite the significance of synthetic monotailed β-linked galactolipids, for a detailed understanding of natural galactolipids, many aspects of these β-linked galactolipids' crystal structures such as temperature-dependence and hydration characteristics remain inadequately understood. In this manuscript, we demonstrated detailed insight of crystal characteristics of one of the simplest monotailed galactolipids, octyl-β-d-galactoside (MOβ-Gal), using thermal analyses, Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) measurements and grazing-incidence wide-angle X-ray diffraction (GI-WAXD) analysis. As a result, it was revealed that the MOβ-Gal anhydrous crystal showed a continuous structural change from the high-symmetry structure to low-symmetry crystal lattice via the strengthened hydrogen bonding interaction as the temperature decreased. In addition, the hemihydrate crystal was found to be in the modulated "ribbon phase". These insights strongly suggest that β-linked galactolipids possess intrinsic characteristics necessary to form a modulated structure even in the crystal state and demonstrate the importance of the presence of tiny amounts of water as cushioning media for preventing order parameter evolution.