Browsing by Author "Dong, YD"
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- ItemImpurities in commercial phytantriol significantly alter its lyotropic liquid-crystalline phase behavior(American Chemical Society, 2008-07-01) Dong, YD; Dong, AW; Larson, I; Rappolt, M; Amenitsch, H; Hanley, TL; Boyd, BJThe lyotropic liquid-crystalline phase behavior of phytantriol is receiving increasing interest in the literature as a result of similarities with glyceryl monooleate, despite its very different molecular structure. Some differences in the phase-transition temperature for the bicontinuous cubic to reverse hexagonal phase have been reported in the literature. In this study, we have investigated the influence that the commercial source and hence the purity has on the lyotropic phase behavior of phytantriol. Suppression of the phase-transition temperatures (by up to 15 degrees C for the bicontinuous cubic to reverse hexagonal phase transition) is apparent with lower-purity phytantriol. In addition, the composition boundaries were also found to depend significantly on the source and purity of phytantriol, with the bicontinuous cubic phase + excess water boundary occurring at a water content above that reported previously (i.e., > 5% higher). Both the temperature and compositional changes in phase boundaries have significant implications on the use of these materials and highlight the impact that subtle levels of impurities can play in the phase behavior of these types of materials. © 2008, American Chemical Society
- ItemNonequilibrium effects in self-assembled mesophase materials: unexpected supercooling effects for cubosomes and hexosomes(American Chemical Society, 2010-06-01) Dong, YD; Tilley, AJ; Larson, I; Lawrence, MJ; Amenitsch, H; Rappolt, M; Hanley, TL; Boyd, BJPolar lipids often exhibit equilibrium liquid crystalline structures in excess water, such as the bicontinuous cubic phases (QII) at low temperatures and inverse hexagonal phase (HII) at higher temperatures. In this study, the equilibrium and nonequilibrium phase behavior of glyceryl monooleate (GMO) and phytantriol (PHYT) systems in excess water were investigated using both continuous heating and cooling cycles, and rapid temperature changes. Evolution of the phase structure was followed using small-angle X-ray scattering (SAXS). During cooling, not only was supercooling of the liquid crystalline systems by up to 25 °C observed, but evidence for nonequilibrium phase structures (not present on heating; such as the gyroid cubic phase only present at low water content in equilibrium) was also apparent. The nonequilibrium phases were surprisingly stable, with return to equilibrium structure for dispersed submicrometer sized particle systems taking more than 13 h in some cases. Inhibition of phase nucleation was the key to greater supercooling effects observed for the dispersed particles compared to the bulk systems. These findings highlight the need for continued study into the nonequilibrium phase structures for these types of systems, as this may influence performance in applications such as drug delivery. © 2010, American Chemical Society
- ItemSensitivity of nanostructure in charged cubosomes to phase changes triggered by ionic species in solution(American Chemical Society, 2013-11-07) Liu, Q; Dong, YD; Hanley, TL; Boyd, BJThe phase behavior of dispersions comprising mixed ionic surfactant and phytantriol was precisely controlled by varying the ionic surfactant content in the mixed lipid and the ionic strength in the system. Two important trends in the phase transition of the mixed lipid systems were identified: (1) An increase in the ionic surfactant content increased the curvature of the self-assembled system toward the hydrophobic region, resulting in the phase transition from cubic phase to lamellar phase. (2) An increase in ionic strength decreased repulsion between the headgroups of the ionic surfactant, resulting in a phase transition from lamellar phase to cubic phase. The phase transitions were confirmed using small-angle X-ray scattering and cryo-TEM and were strongly correlated with the visual turbidity of the dispersions. The lipid mixture with anionic surfactant showed high sensitivity to multivalent cations for triggering the phase transition, which may be a potential strategy to develop a detection/treatment system for toxic multivalent metallic cations such as chromium. © 2013, American Chemical Society.
- ItemTransfer of lipid between triglyceride dispersions and lyotropic liquid crystal nanostructured particles using time-resolved SAXS(Royal Society of Chemistry., 2012-04-16) Tilley, AJ; Dong, YD; Chong, JYT; Hanley, TL; Kirby, N; Drummond, CJ; Boyd, BJLipid-based lyotropic liquid crystalline nanostructured phases, such as the reverse bicontinuous cubic phase (V-2) and the reverse hexagonal phase (H-2), can be dispersed into submicron sized particles with often preserved internal nanostructure, termed cubosomes and hexosomes respectively. The internal nanostructure of the particles imparts desirable characteristics such as the ability to provide sustained release of active ingredients but is susceptible to change upon the incorporation of other lipids used as an active ingredient delivery system. These are complex systems in which the direction of lipid transfer, role of the stabiliser and formation of different phase structures, such as the frustrated H-2 phase are all likely to play a role but are not yet completely understood. Consequently, we have investigated the interparticle transfer of lipids between cubosomes/hexosomes and other dispersed lipids, namely triglycerides and vitamin E acetate emulsions. Time-resolved synchrotron small angle X-ray scattering was used to follow changes to nanostructure, attributed to the transfer of lipids into or out of the cubosomes. It was found that transfer of lipid occurred due to compositional ripening via a micelle-mediated mechanism, evident from the rate of lipid transfer increasing with Pluronic concentration. The rate of transfer of alkanes between liquid crystalline particles and emulsions has been shown previously to depend inversely on chain length. However in the triglyceride systems in the current study, the rate of lipid transfer (trilaurin > tricaprylin > supercooled trimyristin >> crystallised trimyristin and tristearin) did not decrease with increase in the chain length of triglyceride as might be anticipated. The equilibrium phase diagrams of triglyceride + phytantriol in excess water were determined. These diagrams showed that the transfer of phytantriol away from cubosomes to the emulsions, which increases the local triglyceride to phytantriol concentration in the cubosomes, would require formation of H-2 phase more readily for tricaprylin than for trilaurin. Therefore, the lack of correlation of transfer rate with chain length of the triglyceride was attributed to the system seeking to avoid the unfavourable formation of the H-2 phase, competing with the driving force from the entropy of mixing, and was therefore attributed as the reason for the greater rate of transfer of trilaurin compared to the less lipophilic tricaprylin. © 2012 Royal Society of Chemistry