Solubilization of ubiquinone-10 in the lamellar and bicontinuous cubic phases of aqueous monoolein

Using X-ray diffraction measurements and polarizing microscopy, the solubilization of ubiquinone-10 (UQ(10)) was investigated in the lamellar and reversed bicontinuous cubic phases of aqueous monoolein (MO, 86 wt% of monooleoylglycerol). At 25 degrees C and UQ(10) content below 0.5 wt%, a partial phase diagram of the MO/UQ(10)/H2O system indicated the same sequence of hydration-induced phases as found in the MO/H2O system. This low amount of coenzyme had no effect on the MO bilayer thickness and swelling behavior of phases, but it promoted thermotropic Q(230)-->H-II phase transition. We suggested that the effect was determined by the UQ(10) partitioning into the H-II phase regions where the MO chains must be stressed upon the phase transition. At UQ(10) contents above 0.5 wt%, a solid 'UQ(10)-rich' phase appeared inside the initially homogeneous phases within a few days. It was proposed that this process was driven by the coenzyme lateral diffusion in the MO bilayer. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.