Spontaneous vesicle formation in catanionic mixtures of amino acid-based surfactants: chain length symmetry effects.
The use of amino acids for the synthesis of novel surfactants with vesicle-forming properties potentially enhances the biocompatibility levels needed for a viable alternative to conventional lipid vesicles. In this work, the formation and characterization of catanionic vesicles by newly synthesized lysine- and serine-derived surfactants have been investigated by means of phase behavior mapping and PFG-NMR diffusometry and cryo-TEM methods. The lysine-derived surfactants are double-chained anionic molecules bearing a pseudogemini configuration, whereas the serine-derived amphiphile is cationic and single-chained. Vesicles form in the cationic-rich side for narrow mixing ratios of the two amphiphiles. Two pairs of systems were studied: one symmetric with equal chain lengths, 2C12/C12, and the other highly asymmetric with 2C8/C16 chains, where the serine-based surfactant has the longest chain. Different mechanisms of the vesicle-to-micelle transition were found, depending on symmetry: the 2C12/C12 system entails limited micellar growth and intermediate phase separation, whereas the 2C8/C16 system shows a continuous transition involving large wormlike micelles. The results are interpreted on the basis of currently available models for the micelle-vesicle transitions and the stabilization of catanionic vesicles (energy of curvature vs mixing entropy).
Marques
Eduardo F
EF
Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, no. 687, P 4169-007 Porto, Portugal. efmarque@fc.up.pt
Brito
Rodrigo O
RO
Silva
Sandra G
SG
Rodríguez-Borges
J Enrique
JE
do Vale
Maria Luísa
ML
Gomes
Paula
P
Araújo
Maria J
MJ
Söderman
Olle
O
D000596:Amino Acids / Q000737:chemistry*; D020285:Cryoelectron Microscopy; D004058:Diffusion; D007477:Ions / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D015394:Molecular Structure; D013237:Stereoisomerism; D013501:Surface-Active Agents / Q000737:chemistry*
D000596:Amino Acids; D007477:Ions; D008823:Micelles; D013501:Surface-Active Agents