Compound Complex Formation in Phospholipid Membranes Induced by a Nonionic Surfactant of the Oligo(ethylene oxide)–Alkyl Ether Type: A Comparative DSC and FTIR Study
✍ Scribed by B. Mädler; H. Binder; G. Klose
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 288 KB
- Volume
- 202
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
lipid matrix and thus to vary the hydrophilic/hydrophobic
The phase behavior of pseudobinary mixtures DMPC/C 12 E 4 at balance in a definite way. The incorporation of nonionic high water excess was studied between 0 and 50ЊC as a function surfactants of the oligo(ethylene oxide) -alkyl ether type of the surfactant mole fraction x using DSC and FTIR. The phase (C m E n ) into phospholipid bilayers is known to modulate transitions of each component could be followed separately by membrane properties such as hydration (1-3), structural FTIR spectroscopy mixing acyl-chain-deuterated DMPC-d 54 and and dynamic properties of the membrane/water interface alkyl-chain-protonated C 12 E 4 . Changes of the corresponding meth-(4-7), partition of the surfactant between the lipid/surfacylene stretching band frequencies yield the solidus and liquidus
tant mixed membrane and water (8), the morphology of the lines in the temperature-composition phase diagram. Two eutectics appear at x É 0.55 and x É 0.85. In the concentration range aggregates formed (9-11), the type of phase transitions in between these values, the existence of a gel compound complex of , and the repulsive forces between the membranes about 1:2 lipid:surfactant composition was established. A peritectic . The lateral arrangement of membrane components point was suggested at low surfactant concentration between the such as mixing properties, cluster formation, and the solubilirippled, gel, and liquid crystalline states of the lipid-rich bilayers zation of lamellar membrane structures to structures with on the basis of the Gibbs phase rule. A micellar transition (cloud lower symmetry and higher curvatures are of fundamental point) precedes the formation of lamellar aggregates as the surfacinterest. tant rich mixtures are heated. The phase transformations are dis-In a manner similar to that found for fatty acids and alkacussed in terms of fluidity and hydration of the molecules on the nols and their derivatives (16, 17), C m E n surfactants usually basis of spectral data obtained from selected infrared absorption destabilize the bilayer and cause their solubilization into bands of the lipid and of the surfactant. The phase behavior of C 12 E 4 /DMPC was compared with literature data of related systems mixed micelles after reaching a critical fraction in the lipid with respect to the chain melting transition, membrane solubilizamembrane. The pure surfactants dissolved in water can protion, and complex formation. ᭧ 1998 Academic Press vide a variety of lamellar and nonlamellar phases in depen-Key Words: thermotropic phase behavior; eutectic mixture; ladence on the water concentration and temperature (18-20, mellar and micellar phases; hydration; molecular order. 24, 25). Hence, reversible transformations between lamellar and micellar phases can be controlled by external parameters. Therefore nonionic surfactants of the C m E n type have (PC, phosphatidylcholine; DPPC, dipalmitoyl-PC). Com-124