Characterization of Oleic Acid/CHAPSO Bicellar Mixture Formation via Lipid Transfer

Oleic acid/3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxypropane sulfonate (OA/CHAPSO) bicellar mixtures are potential functional membrane materials. The lipid transfer during the formation of these bicellar mixtures was evaluated. The OA/CHAPSO bicellar mixture was prepared by mixing a solution of OA vesicles as a source of bilayer membranes with a solution of CHAPSO as a detergent at different composition ratios, x _OA (= [OA] / ([OA] + [CHAPSO])). The lipid transfer was evaluated based on the leakage of fluorescent probe molecules, i.e., carboxyl boron-dipyrromethene (BODIPY C12), from the OA bilayer membranes. Mixing the CHAPSO solution with the OA vesicle eliminated the self-quenching of BODIPY C12 because of the leakage of BODIPY C12 molecules. The apparent rate constant of the leakage increased with decrease in x _OA to 0.60. However, at x _OA ≤ 0.60, the apparent rate constants barely changed. The correlation between the leakage of the BODIPY C12 molecules and the transfer of OA molecules enables the evaluation of the lipid transfer during the OA/CHAPSO bicellar mixture formation through the observation of the self-quenching of BODIPY C12.