466478 Quantitative Monitoring of Microphase Separation Behaviors in Cationic Liposomes Using Multiple Fluorescent Probes

Thursday, November 17, 2016: 3:35 PM
Plaza A (Hilton San Francisco Union Square)
Keishi Suga, Kei Akizaki, Yukihiro Okamoto and Hiroshi Umakoshi, Div. of Chem. Eng., Grad. Sch. of Eng. Sci., Osaka University, Toyonaka, Japan

Microphase separation behaviors of cationic liposomes have been investigated using a pH-sensitive fluorescent probe with 4-heptadecyl-7-hydroxycoumarin (HHC), 1,6-diphenyl-1,3,5-hexatriene, and 6-lauroyl-2-dimethylaminonaphthalene, and to estimate localized electrostatic potentials. Shifts of the apparent pKa values of HHC were observed in cationic liposomes in proportion to the amount of cationic lipids. Two pKa values were obtained with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/3ß-[N(N',N'-dimethylaminoethane)-carbamoyl] cholesterol hydrochloride (DC-Ch) liposomes, while only one pKa value was generated with either DOPC/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or DOPC/dimethyldioctadecylammonium-bromide (DODAB) liposomes. The physicochemical membrane property analyses, focusing on membrane fluidity and membrane polarity, revealed heterogeneity among DOPC/DC-Ch liposomes. By analyzing the pH titration curves using sigmoidal fitting, the localized electrostatic potentials were estimated. For DOPC/DOTAP=(7/3), the membrane was in the liquid-disordered phase and the density of cationic molecules was 0.41 cation/nm2. For DOPC/DC-Ch=(7/3), the membrane was heterogeneous and the densities of cationic molecules in liquid-disordered and liquid-ordered phases were 0.25 and 1.24 cation/nm2, respectively. We thereby conclude that the DC-Ch molecules can form nanodomains when these molecules are concentrated to 59%.

Extended Abstract: File Not Uploaded
See more of this Session: Self-Assembled Soft Materials for Membrane Applications
See more of this Group/Topical: Separations Division