Thermodynamically stable vesicle formation from glycolipid biosurfactant sponge phase.
Thermodynamically stable vesicle (L(alpha1)) formation from glycolipid biosurfactant sponge phase (L(3)) and its mechanism were investigated using a "natural" biocompatible mannosyl-erythritol lipid-A (MEL-A)/L-alpha-dilauroylphosphatidylcholine (DLPC) mixture by varying the composition. The trapping efficiency for calcein and turbidity measurements clearly indicated the existence of three regions: while the trapping efficiencies of the mixed MEL-A/DLPC assemblies at the compositions with X(DLPC)< or =0.1 or X(DLPC)> or =0.8 were almost zero, the mixed assemblies at the compositions with 0.1<X(DLPC)<0.8 had some trapping efficiency, and in particular the composition with X(DLPC)=0.3 exhibited the maximum trapping efficiency. Confocal laser scanning microscopy (CLSM) and freeze-fracture electron microscopy (FFEM) determined that the assemblies in the compositions with X(DLPC)< or =0.1 were droplets with a sponge phase (L(3)) with diameter from 2 to 20 microm and those of X(DLPC)> or =0.8 were multilamellar vesicles (L(alpha)) with diameter from 2 to 10 microm. Meanwhile, dynamic light scattering (DLS) measurement revealed that the average size of the vesicles at the composition of X(DLPC)=0.3 was 633.2 nm, which is remarkably small compared to other compositions. Moreover, the mixed vesicle solution at the composition of X(DLPC)=0.3 was slightly bluish and turbid and kept its dispersion stability at 25 degrees C for more than 3 months, indicating the formation of a thermodynamically stable vesicle (L(alpha1)). These results exhibited the formation of a thermodynamically stable vesicle (L(alpha1)) with a high dispersibility from the MEL-A/DLPC mixture. The asymmetric distribution of MEL-A and DLPC in the two vesicle monolayers caused by the difference in geometrical structures is very likely to have changed their self-assembled structure from a sponge phase (L(3)) to a thermodynamically stable vesicle (L(alpha1)).
Imura
Tomohiro
T
Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan.
Yanagishita
Hiroshi
H
Ohira
Junko
J
Sakai
Hideki
H
Abe
Masahiko
M
Kitamoto
Dai
D
D005614:Freeze Fracturing; D006017:Glycolipids / Q000737:chemistry; D008823:Micelles; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D010713:Phosphatidylcholines / Q000737:chemistry; D013053:Spectrophotometry; D013501:Surface-Active Agents / Q000737:chemistry
D006017:Glycolipids; D008823:Micelles; D010713:Phosphatidylcholines; D013501:Surface-Active Agents; C439671:mannosylerythritol lipid; C015153:1,2-dilauroylphosphatidylcholine