Dioxygen solubility in aqueous phosphatidylcholine dispersions

The solubility of molecular oxygen, or dioxygen, in low weight percent (1.5%) sonicated dimyristoylphosphatidylcholine (DMPC) aqueous dispersions saturated with air has been measured as a function of temperature between 10 degrees C and 40 degrees C. A modified Winkler technique was used involving a dual cell coulometric titration with voltammetric endpoint detection in a mixed solvent (methanol/water). The results indicate that dioxygen is approximately four times more soluble in the liquid crystalline bilayers (above 24 degrees C) than in the gel state bilayers (below 24 degrees C). The solubility of dioxygen in the bilayer does not appear to be strongly temperature dependent on either side of the 24 degrees C phase transition. The dioxygen solubility in gel state DMPC is approximately equal to that in water at the same temperature. Our result are contrasted with recent measurements made using EPR spin labels.