Langmuir 2002, 18, 10509-10511
Giant Vesicle Formation from Oleic Acid/ Sodium Oleate on Glass Surfaces Induced by Adsorbed Hydrocarbon Molecules Kenichi Morigaki† and Peter Walde* Institut fu¨ r Polymere, Department of Materials Science, ETH-Zentrum, Universita¨ tstrasse 6, CH-8092 Zu¨ rich, Switzerland Received September 19, 2002. In Final Form: October 7, 2002
Introduction Long chain fatty acids (such as oleic acid) are known to form bilayer structures in water if approximately half of their carboxyl groups are ionized.1 Colloidal suspensions of these bilayers in aqueous solution typically contain spherical vesicles that encapsulate a part of the aqueous solution.1,2 Fatty acids are attractive for basic physicochemical studies of surfactant self-assembly phenomena, because they are chemically simple and because they can form a wide range of aggregation structures, including spherical micelles, lamellar bilayers, and inverted structures, due to the ability of their carboxyl headgroup to be ionized and to form hydrogen bonds.1,3 Herein, we report a novel observation that submicrometer-sized large unilamellar vesicles (LUVs) prepared from a mixture of oleic acid and sodium oleate transform into cell-sized giant vesicles (GVs) with dimensions of several micrometers on (or close to) glass surfaces and in the presence of adsorbed hydrocarbons such as squalane. GV growth was observed generally for fatty acids but not for double-chain phospholipids, suggesting that the dynamic nature of the single-chain surfactants may play an important role for the vesicle growth and transformation. Experimental Section Materials. Fatty acids and squalane were purchased from Fluka, polyethyleneimine (PEI) was from Sigma, and polystyrenesulfonate (PSS) and polymethacrylate (PMA) were from Aldrich (all Buchs, Switzerland). OTS (octadecyltriethoxysilane) was obtained from Lancaster Synthesis (Lancashire, U.K.). POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) was from Avanti Polar Lipids (Alabaster, AL). Hellmanex was from Hellma (Mu¨hlheim, Germany). All other chemicals were of reagent grade and used as received. Microscopy cover glasses were obtained from either Knittel or Menzel (both Braunschweig, Germany) or VWR Scientific, Inc. (Media, PA). * To whom correspondence should be addressed. E-mail:
[email protected]. Fax: +41-1-63-21265. Telephone: +41-1-6320473. † Present address: National Institute of Advanced Industrial Science and Technology (AIST), Midorigaoka, Ikeda, Osaka 5638577, Japan. (1) (a) Haines, T. H. Proc. Natl. Acad. Sci. U.S.A. 1983, 80, 160-164. (b) Cistola, D. P.; Hamilton, J. A.; Jackson, D.; Small, D. M. Biochemistry 1988, 27, 1881-1888. (c) Fukuda, H.; Goto, A.; Yoshioka, H.; Goto, R.; Morigaki, K.; Walde, P. Langmuir 2001, 17, 4223-4231. (2) (a) Gebicki, J. M.; Hicks, M. Nature 1973, 243, 232-234. (b) Gebicki, J. W.; Hicks, M. Chem. Phys. Lipids 1976, 16, 142-169. (c) Hargreaves, W. R.; Deamer, D. W. Biochemistry 1978, 17, 3759-3768. (d) Walde, P.; Wick, R.; Fresta, M.; Mangone, A.; Luisi, P. L. J. Am. Chem. Soc. 1994, 116, 11649-11654. (e) Morigaki, K.; Dallavalle, S.; Walde, P.; Colonna, S.; Luisi, P. L. J. Am. Chem. Soc. 1997, 119, 292301. (f) Blo¨chliger, E.; Blocher, M.; Walde, P.; Luisi, P. L. J. Phys. Chem. B 1998, 102, 10383-10390. (g) Zepik, H. H.; Blo¨chliger, E.; Luisi, P. L. Angew. Chem., Int. Ed. Engl. 2001, 40, 199-202. (3) Edwards, K.; Silvander, M.; Karlsson, G. Langmuir 1995, 11, 2429-2434.
10509
Cover Glass Surface Cleaning and Modification. The microscopy cover glasses were first cleaned with 0.5% v/v Hellmanex/water, rinsed with deionized water, treated with a warm solution of NH4OH (28%)/H2O2 (30%)/H2O (1:1:5, v/v/v) (65 °C for 15 min), extensively rinsed with deionized water, and then dried in an oven at 110 °C. The polyelectrolytes were adsorbed onto the surface of cleaned cover glasses from dilute aqueous solutions (0.1 mM). For the adsorption of PSS and PMA, PEI was first adsorbed onto the glass surface in order to provide a positive surface charge. Silanization of the glass surface was performed in an OTS solution (0.04% w/v in THF/cyclohexane (1:20, v/v)). Cover Glass Surface Analyses. XPS (X-ray photoelectron spectroscopy) analyses were performed using a PHI 5700 spectrophotometer equipped with a concentric hemispherical analyzer in the standard configuration. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra were recorded on a PHI 7200 time-of-flight secondary ion mass spectrometer in the mass range 0-500 m/e for positive ions and 0-200 m/e for negative ions. The total ion dose of the 8 kV Cs+ primary ion beam (100 m diameter) was below the static limit (
