Phospholipid vesicles headgroups

Starke-Peterkovic T, Clarke RJ (2009) Effect of headgroup on the dipole potential of phospholipid vesicles. Eur Biophys J 39 103-110... 

Moghimi, S. M., and Hunter, A. S. (2001), Recognition by macrophages and liver cells of opsonized phospholipid vesicles and phospholipid headgroups, Pharm. Res., 18, 1-8. 

Figure 11.9. Contrast formation in cryo-TEM. (a) Schematic image of a vesicle formed with phospholipid molecules, (b) Schematic representation of a phospholipid molecule with polar headgroup and apolar tail. (c)(d) Projection of the polar head group, which is the strongest scattering center, (e) Calculated line scan considering the projection of the polar head groups, (d) Schematic image of a vesicle. (e)(f) Experimental images of vesicles where the double layer with a thickness of about 3.5 nm is clearly seen. Adapted from Sagalowicz et al. 2003.

Vibrational spectroscopy shows that inclusion of cholesterol in phospholipid bilayers tends to decrease the fluidity of the hydrophobic region above the main transition point Tm and to increase it below Tm. The presence of cholesterol in DPPC or DMPC muti-layered vesicles does not affect the transition point but simply broadens the transition by decreasing the CH2-stretching wavenumber in the liquid crystalline phase and by increasing it in the gel-like phase (Lippert and Peticolas, 1971 Spiker and Levin, 1976 Casal and Mantsch, 1984). There is also evidence that lipid-cholesterol interaction increases the amount of bound water in the headgroups (Levin et al., 1985). 

In this work, we will mainly focus on DMPC and DMPG lipids but some other phospholipids work as well. However, if the geometry of a phospholipid molecule (i.e., the contribution of the polar headgroup versus the apolar part - see ref (22, 23)) does not allow the formation of small unilamellar vesicles it will be difficult to generate stable MLs. For instance, in selected experimental conditions, pure phosphatidyletha-nolamine membranes are known to be destabilized (24). 

Liposomes are vesicles formed through the association of phospholipid molecules in an aqueous environment, yielding a structure with the hydrocarbon tails forming a lipid bilayer and hydrophilic headgroups directed at both the aqueous core and... 

A biological membrane is a structure particularly suitable for study by the LB technique. The eukaryotic cell membrane is a barrier that serves as a highway and controls the transfer of important molecules in and out of the cell (Roth etal., 2000). The cell membrane consists of a bilayer or a two-layer LB film (Tien etal, 1998). Lipid bilayers are composed of a variety of amphiphilic molecules, mainly phospholipids and sterols which in turn consist of a hydrophobic tail, and a hydrophilic headgroup. The complexity of the biomembrane is such that frequently simpler systems are used as models for physical investigations. They are based on the spontaneous self-organization of the amphiphilic lipid molecules when brought in contact with an aqueous medium. The three most frequently used model systems are monolayers, black lipid membranes, and vesicles or liposomes. 

Previous studies have shown that surfactant vesicles and tubules can be metallized in a nonselective manner. Since phospholipids with negatively charged headgroups bind metal ions much more strongly than phospholipids with zwitterionic headgroups, Che Pdbind selectively to the negatively charged phospholipids. As a result, selective metallization should occur. 

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