title: DSPC/DLPC mixed films supported on silica: a QCM-D and friction force study.
abstract: The membrane properties of phospholipid mixtures supported on silica were studied by means of a quartz crystal microbalance with dissipation monitoring (QCM-D) technique, in situ soft-contact atomic force microscopy (AFM), and friction force microscopy (FFM). The phospholipids used in this study were di-stearoylphosphatidylcholine (DSPC) and dilauroylphosphatidylcholine (DLPC). The phospholipid films were prepared by a vesicle-fusion method, in which DSPC/DLPC mixed liposomes dispersed in an aqueous medium are adsorbed on silica and their structure is transformed into a bilayer on the substrate. The changes in QCM-D (frequency and dissipation) and friction responses of DSPC single systems (gel state at 25°C) are relatively large compared with those of DLPC single systems (liquid-crystalline state at 25°C) and those of mixed DSPC/DLPC systems. This suggests that (i) the gel-state DSPC liposomes are somewhat flattened on the silica, by keeping their solid-like molecular rigidity, whereas (ii) both the liquid-crystalline DLPC and mixed liposomes experience instantaneous structural transformation at the silica/water interface and form a normally flattened bilayer on the substrate. The friction force response is dependent on the phase state of the phospholipids, and the liquid-crystalline DLPC has a more significant impact on the overall membrane properties (i.e., the degree of swelling and the friction response on the surface) than does the gel-state DSPC.
authors.affiliation: Department of Pure and Applied Chemistry in Faculty of Science and Technology and Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Chiba, Japan.
authors.forename: Takakuni
authors.initials: T
authors.lastname: Oguchi
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
mesh_terms: D017276:Friction; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D018625:Microscopy, Atomic Force; D010713:Phosphatidylcholines / Q000737:chemistry*; D058525:Quartz Crystal Microbalance Techniques; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; C015153:1,2-dilauroylphosphatidylcholine; D012822:Silicon Dioxide; C010942:1,2-distearoyllecithin