Unveiling the Uniqueness of Crystal Structure and Crystalline Phase Behavior of Anhydrous Octyl β-D-Glucoside Using Aligned Assembly on a Surface

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.

Thermal Behavior of Anhydrous Ascorbic Acid 6‐Palmitate with Trace of Decomposition

“…In contrast, the 2D-XRD profiles from the planar lipid axes, aligned with respect to the sample surface, can inform whether each diffraction peak could be correlated or not (Figure 4a). [20][21][22] Fortunately, a relatively well-perpendicularly aligned AsP film could be prepared by spin-coating the 10 wt% AsP ethanol solution on an Si(100) substrate. The spotty reflections, rather than the Debye-Scherrer ring pattern, were obtained from the powdered materials, showing the aligned states of AsP (Figure 4b, left).…”

“…While certain purified amphiphilic lipids exhibit a composite phase consisting of both Cr and LC phases, [22] the phase separation of layered structures was reported for some phospholipid systems with specific additives. [29,30] In the latter systems, additives can partially affect the layered structures and account for different layer thicknesses.…”

“…The use of perpendicularly aligned sample films and a two-dimensional detector for the GI-WAXD analysis afforded in-depth insights into the phase behaviors of amphiphilic lipids in their bulk states. [20][21][22]…”

Short-Chain Mono-Alkyl β-D-Glucoside Crystals—Do They Form a Cubic Crystal Structure?

“…2D-GI–WAXD measurements were performed at BL03XU, SPring-8 (Hyogo, Japan) [ 27 , 30 , 37 , 38 ]. Diffraction patterns in the 0–18° range were obtained using an image-plate detector system (R-AXIS IV, Rigaku Corp., Tokyo, Japan) with an incident angle of 0.1° (wavelength = 1.00 Å).…”

“…Simple lamellar structures have always been found for single-crystal structure analysis and, as a result, the lattice constants of these typical crystals obey the following conditions: c >> a > b , where c typically corresponds to bilayer length [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. However, recently, anhydrous crystals of mono-alkyl β-D glucoside (CnG) such as heptyl (C7G) and octyl β -D-glucosides (C8G) were identified as exceptional examples, which showed c ≈ a >> b , using a grazing-incidence wide-angle X-ray diffraction analysis with a two-dimensional detector (2D-GI-WAXD) on perpendicularly aligned CnG films [ 27 ]. The large, splayed sugar head group of C7G and C8G made them form a crystal structure with a modulated lamellar structure.…”