1-palmitoyl-2-oleoylphosphatidylcholine and didodecyldimethylammonium

The cationic large unilamellar mixed liposomes from 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and didodecyldimethylammonium bromide (DDAB) or dioctadecyldimethylammonium bromide (DODAB) were prepared. The influence of the addition of Triton X-100 (TX-100) or octaethylene glycol mono-n-dodecylether (C(12)E(8)) on the membrane integrity was investigated turbidimetrically. The stability of the liposomal systems was estimated by monitoring fluorimetrically at 25 °C the rate of spontaneous and surfactant-induced release of entrapped 5(6)-carboxyfluorescein (CF). In order to evaluate the interaction of the cationic DODAB guest with the host POPC membrane, the main phase transition temperatures (T(m)) were determined by electron paramagnetic resonance spectroscopy (EPR). All the results obtained show that the presence of DODAB and DDAB stabilizes the POPC liposomes. The extent of stabilization depends on the concentration and nature of the cationic guest.

Topics: Cations; Electron Spin Resonance Spectroscopy; Kinetics; Lipid Bilayers; Liposomes; Molecular Dynamics Simulation; Nephelometry and Turbidimetry; Octoxynol; Phase Transition; Phosphatidylcholines; Polyethylene Glycols; Quaternary Ammonium Compounds; Transition Temperature

The fusion between synthetic vesicles is an interesting mechanism for the stepwise construction of vesicle compartments for origins of life models and synthetic biology. In this communication, we report an innovative study on the not well-known case of fusion between oppositely charged vesicles, in particular by using fatty acid vesicles and DDAB as cationic surfactant. By combining fluorescence, turbidity vs. time profiles and vesicle size distribution obtained by dynamic light scattering, we show that POPC/oleate 1/4 mol/mol anionic vesicles can be fused with POPC/DDAB 1/1 mol/mol cationic vesicles with about 20% yield. Other non-fusion processes also occur, vesicle fusion being more effective by reducing the ionic strength of the buffer. This study also contributes to clarify the term "vesicle fusion", which is not always properly used in describing reactivity among vesicles.

Topics: Models, Chemical; Oleic Acid; Osmolar Concentration; Phosphatidylcholines; Quaternary Ammonium Compounds; Surface-Active Agents

When a giant vesicle composed of POPC (rendered anionic with 5 mol % POPG) touches a giant POPC vesicle (rendered cationic with 5 mol % of DDAB), the two vesicles adhere strongly. When, however, low levels (0.1-2 mol %) of a perylene-substituted lipid are incorporated in to the bilayer, the vesicles separate at a rate that depends on the additive concentration. The vesicles that drift apart lose charge, indicating that the anionic and cationic components of the vesicles have interchanged upon contact. Presumably, the large perylene disrupts bilayer packing to allow the intervesicular exchange, and subsequent charge neutralization, to occur with up to 104 rate increases. It is possible that adhered living cells release one another by, similarly, producing low levels of a membrane-bound lipid or protein that induces so-called "kiss-and-run" vesicle events by promoting the release of adhesive elements.

Topics: Anions; Catalysis; Liposomes; Membrane Lipids; Phosphatidylcholines; Phosphatidylglycerols; Quaternary Ammonium Compounds

The entrapment efficiency of three main methods used in the literature for the encapsulation of nucleic acids in liposomes were studied using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes. In particular the reverse phase method, the dehydration/rehydration method, and the freeze/thawing method were compared to each other under standardised conditions, i.e. using in every case the same concentration of guest molecules (DNA, tRNA and ATP as low molecular weight analogue) and equally extruded liposomes. The percentage of entrapment strictly referred to the material localized inside the liposomes, i.e. particular care was devoted to ruling out the contribution of the nucleic acid material bound to the outer surface of the liposomes: this was eliminated by extensive enzymatic digestion prior to column chromatography. Depending on the conditions used, the percentage of the entrapped material varied between 10 and 54% of the initial amount. Further, the encapsulation efficiency was markedly affected by the salt concentration, by the size of liposomes, but to a lower degree by the molecular weight of the guest molecules. In general, we observed that the freeze/thawing encapsulation procedure was the most efficient one. In a second part of the work the freeze/thawing method was applied to encapsulate DNA (369 bp and 3368 bp, respectively) using liposomes obtained from POPC mixed with 1-10% charged cosurfactant, i.e. phosphatidylserine (PS) or didodecyldimethylammonium bromide (DDAB), respectively. Whereas PS had no significant effect, the entrapment efficiency went up to 60% in POPC/DDAB (97.5:2.5) liposomes. The large entrapment efficiency of DNA permits spectroscopic investigations of the DNA encapsulated in the water pool of the liposomes. UV absorption and circular dichroism spectra were practically the same as in water, indicating no appreciable perturbation of the electronic transitions or of the conformation of the entrapped biopolymer. This was in contrast to the DNA bound externally to the POPC/DDAB liposomes which showed significant spectral changes with respect to DNA dissolved in water.

Topics: Adenosine Triphosphate; Circular Dichroism; Deoxyribonuclease I; DNA; Drug Compounding; Electrophoresis, Polyacrylamide Gel; Exodeoxyribonucleases; Freeze Fracturing; Liposomes; Microscopy, Electron; Molecular Conformation; Particle Size; Phosphatidylcholines; Phosphatidylserines; Quaternary Ammonium Compounds; RNA, Transfer; Sodium Chloride; Spectrophotometry; Ultrafiltration