Physicochemical characterization of 6-O-acyl trehalose fatty acid monoesters in desiccated system

• Published in: Chemistry and physics of lipids 2018-11, Vol.216, p.80-90
• Main Authors: Ogawa, Shigesaburo, Honda, Koji, Tsubomura, Taro, Totani, Kiichiro, Takahashi, Isao, Hara, Setsuko
• Format: Article
• Language: English
• Subjects: Chemistry, Physical; Esters - chemistry; Fatty Acids - chemistry; Glass transition; Hydrate crystal; Lamellar gel glass; Lipids - chemistry; Liquid crystal; Trehalose - chemistry; Trehalose fatty acid ester; Trehalose lipids
• ISSN: 0009-3084; 1873-2941
• DOI: 10.1016/j.chemphyslip.2018.09.012

[Display omitted] •TREn (n = 10, 12, 14, 16) formed LC phases such as Lα and Q phases, which became glassy LC phases below Tg (ca. 78 °C).•A reversible phase transition between the Lα and the Lβ phases occurred in the glassy phase for TREn (n = 14, 16).•A strong evidence that the hydrocarbon chain in the glassy state can be fluid-like rather than glassy-like was provided.•TREn formed monohydrate Cr, which showed similar dehydration temperature independent on the acyl chain length.•The glassy Lα (Lα-G) phase kinetically formed when the dehydration occurred under vacuum condition below Tg. The understanding of the basic physicochemical properties of trehalose lipid is indispensable to extending their availability. In this study, the hydrate crystal (Cr), the liquid crystalline (LC) phase and the glassy state formations of 6-O-acyl trehalose fatty acid monoester (TREn) were examined under in a desiccated system. TREn (n = 10, 12, 14, 16) formed monohydrate Cr and showed the hydrate Cr-glassy fluid lamellar LC (Lα) phase transition via dehydration in the heating process. Here, Lα phase for TRE10 and TRE12 was kinetically formed by the dehydration below the glass transition temperature (Tg). On the dehydration temperature (Tdeh), Tgs, and heat capacity changes (ΔCps) at these Tgs, no distinct effects by the difference of the acyl chain length were recognized, possibly because the core structure of containing sugar hydrate Cr or sugar moieties should be similar regardless of the acyl chain length. Besides, TRE10 having a relatively high hydrophilic/hydrophobic balance (HLB) afforded to form the cubic LC (Q) phase and the corresponding glassy phase, while TRE14 and TRE16 having low HLB afforded the Lα phase as well as the corresponding glassy phases above Tg. TRE12 having middle HLB afforded both LCs and the corresponding glassy phase by controlling the kinetics of LC-LC phase transition between Lα and Q phases. Furthermore, the anomalous reversible phase transition during both the heating and cooling processes was also ascertained in the glassy phase for TRE16, which was considered the phase transition between glassy Lα and glassy lamellar gel (Lβ) phase. It greatly empathizes the two-dimensional trehalose glass layer and fluid hydrocarbon chains in the TREn glassy phase. Thus, in this study, it was demonstrated that TREn as the simplest trehalose lipid exhibited the glassy formation performance as well as the hydrate Cr formation, which showed less chain length