Abstract
Although the anomalous low crystallinity of octyl β-D-glucoside (β-OGlu) was first proposed more than 30 years ago, many fundamental aspects of its crystal structure and of the crystalline phase behavior of the pure substance have remained uncertain. In this paper, we employ grazing-incidence wide-angle X-ray-diffraction measurements using a two-dimensional detector (2D-GI-WAXD) and perpendicularly aligned crystalline films to demonstrate that β-OGlu forms crystal structures consisting of an intermediate phase—like a ripple phase with two large crystal-lattice constants, a and c, comparable to the lengths of its bilayer structures. Furthermore, solid-to-solid phase transitions accompanied by latent heat confirm the existence of a solid-solution-like phase consisting of a crystalline and a liquid-crystal (LC) phase, which persists over a 20 °C temperature range, in a single-component system. In addition, the system forms a superlattice, accompanied by a change in packing of the component sugars in the partial-melting state; this shift is different from the gel-crystal transition observed for a typical lipid system. These facts indicate that even in the crystalline phase formed from a single component, each individual β-OGlu molecule in a single-component phase plays a versatile role in the crystallisation and melting processes. These findings must somewhat explain the specific co-assembling features with proteins of β-OGlu, which has long been used empirically in biochemistry.
Highlights
As a pivotal lipid among numerous synthetic glycolipids, octyl β-D-glucoside (β-OGlu) has long attracted attention owing to its versatile biochemical applications
The validity of the identification is supported by analyzing a crystal of n-heptyl β-D-glucoside (β-HGlu), which we studied for comparison
In the powder X-ray diffraction (PXRD) profiles obtained for this study, we observed several diffraction peaks at lower diffraction angles for β-OGlu and for β-HGlu
Summary
As a pivotal lipid among numerous synthetic glycolipids, octyl β-D-glucoside (β-OGlu) has long attracted attention owing to its versatile biochemical applications. Intriguing features are that the compound mimics membrane lipids, binding with protein molecules via hydrogen bonding or hydrophobic interactions, and it co-crystallizes with protein molecules [1,2,3,4,5,6,7,8,9]. It is intrinsically self-assembling, a characteristic that emerges from the various phase behaviors that depend upon the concentration and temperature. The glass-transition behavior both in the absence and presence of ice, and the water-cluster-like responsive behavior under magnetic and electric fields have been
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