The Solubility of a Dye-Detergent Complex in Phospholipid Vesicles

Abstract The solubility of the dye-detergent complex, Coomassie brilliant blue-cetyltrimethylammonium bromide (CBB-CTAB), in various phospholipids vesicles and in amniotic fluid phospholipid was determined as well as the aqueous/organic distribution ratio of the solubilized products in an aqueous-organic two-phase system. The solubility of the complex depended on the phospholipid head group and decreased in the order: (PG) ≈ PI ≈ PS > PC ≈ DPPC > PE > SM (PG, phosphatidylglycerol; PI, phosphatidylinositol; PS, phosphatidylserine; PC, phosphatidylcholine; DPPC, dipalmitoylphosphatidylcholine; PE, phosphatidylethanolamine; SM, sphingomyelin). Dye solubilized in anionic phospholipid vesicles distributed to the aqueous phase, while that solubilized in zwitterionic phospholipid vesicles distributed to the organic phase. CBB solubilized in a binary mixture of lecithin and anionic phospholipid (PG, PI) vesicles containing more than 30 mol% of the anionic phospholipid distributed preferentially to the aqueous phase. On the other hand, dye solubilized in PC/PI (more than 30 mol% PI) vesicles containing SM and in amniotic fluid phospholipid distributed proportionally to the aqueous and organic phases. In both lipid mixtures, the dye products partitioning into the aqueous phase formed before those partitioning into the organic phase. The data indicated that the association between the dye complex and phospholipid is sensitive to the phospholipid composition of the vesicles.