Hydrostatic Pressure Effects on the Lamellar to Gyroid Cubic Phase Transition of Monolinolein at Limited Hydration

• Published in: Langmuir Vol. 28; no. 36; pp. 13018 - 13024
• Main Authors: Tang, T.-Y. Dora, Brooks, Nicholas J, Jeworrek, Christoph, Ces, Oscar, Terrill, Nick J, Winter, Roland, Templer, Richard H, Seddon, John M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.09.2012
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Glycerides - chemistry; Hydrostatic Pressure; Membranes; Membranes, Artificial; Models, Molecular; Phase Transition; Thermodynamics; Water - chemistry; Water; Encapsulation; Self assembly; Phase diagram; Lipids; High temperature; Liquid phase; Phase transitions; Thermodynamics; Water content; Membrane; Inverse; Structure; Low temperature; Drug; Crystalline phase; Composition; Stability; Hydration; Fluid; Carbon; X ray diffraction; High pressure; Double bond; Hydrostatics; Pressure effect; Low pressure; Models; Monoacylglycerol
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la3025843

Monoacylglycerol based lipids are highly important model membrane components and attractive candidates for drug encapsulation and as delivery agents. However, optimizing the properties of these lipids for applications requires a detailed understanding of the thermodynamic factors governing the self-assembled structures that they form. Here, we report on the effects of hydrostatic pressure, temperature, and water composition on the structural behavior and stability of inverse lyotropic liquid crystalline phases adopted by monolinolein (an unsaturated monoacylglycerol having cis-double bonds at carbon positions 9 and 12) under limited hydration conditions. Six pressure–temperature phase diagrams have been determined using small-angle X-ray diffraction at water contents between 15 wt % and 27 wt % water, in the range 10–40 °C and 1–3000 bar. The gyroid bicontinuous cubic (QII G) phase is formed at low pressure and high temperatures, transforming to a fluid lamellar (Lα) phase at high pressures and low temperature via a region of QII G/Lα coexistence. Pressure stabilizes the lamellar phase over the QII G phase; at fixed pressure, increasing the water content causes the coexistence region to move to lower temperature. These trends are consistent throughout the hydration range studied. Moreover, at fixed temperature, increasing the water composition increases the pressure at which the QII G to Lα transition takes place. We discuss the qualitative effect of pressure, temperature, and water content on the stability of the QII G phase.