Aqueous Vesicle Suspensions Research Articles

Brillouin study of elastic properties of nanometric phospholipid layers in aqueous suspensions of vesicles

This work is devoted to the development of an experimental technique based on Brillouin spectroscopy for the study of aqueous suspensions of multilayer vesicles of phospholipids at different temperatures using the example of DPPC phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine). The temperature dependence of the Brillouin line position is studied. A comparison of the behavior of Brillouin lines of polycrystalline ice, dry vesicles, and vesicles suspension reveals the contribution of phospholipid layers to the Brillouin spectrum. Analysis of the data makes it possible to estimate the value of sound velocity of the vesicles membranes and its temperature dependence. [AQ1] [AQ2]

Lipid‐Containing Polymer Vesicles with pH/Ca2+‐Ion‐Manipulated, Size‐Selective Permeability

AbstractPolymeric vesicles attained from the self‐assembly of distearin (a diacylglycerol lipid)‐conjugated poly(acrylic acid) (PAAc) with various distearin contents in the aqueous phase show the capability of control over the vesicular‐wall permeability to hydrophilic solutes of varying sizes by a simple manipulation of the external pH. The pH sensitivity of the vesicle membranes in size‐selective permeability is largely dependent upon the lipid content of copolymer. By the addition of CaCl2 in aqueous vesicle suspensions, the pH‐evolved assembly structure and the membrane permeability can be immobilized with promoted resistance to further pH alteration, along with an additional counterion screening effect that reduces the pH required for the onset of polar solutes of certain sizes to pass through the membranes. Small‐angle X‐ray scattering (SAXS) measurements of the vesicle structure in the aqueous phase indicate that the pH‐regulated permeability to polar solutes is virtually governed by the extent of hydration and swelling of the vesicle membranes, and the lipid residues within each vesicle wall are packed into the ≈4–5 repeating lamellar islet structure surrounded by PAAc segments.

AFM characterization of spin-coated multilayered dry lipid films prepared from aqueous vesicle suspensions

We present a detailed AFM study on multilayered dry lipid films prepared from aqueous vesicle suspensions. Different preparation techniques were applied in order to optimize the preparation of homogeneous lipid films of various film thicknesses. Suspensions of preformed DOPC/DPPC vesicles were adsorbed onto indium tin oxide-coated glass coverslips, a substrate also commonly employed for the formation of giant liposomes. We found that the homogeneity of the lipid films could substantially be improved when applying a spin-coating step during the film preparation. These films were much more homogeneous than those prepared by conventional drop-casting and in addition the film thickness could be controlled. When using a combination of vesicle adsorption and spin-coating the quality and thickness of the films depended crucially on the lipid concentration of the vesicle suspension, the adsorption temperature and the adsorption time. For lipid films prepared by direct spin-coating the lipid concentration and the applied spin-coating sequence were critical parameters for the quality and thickness of the deposited lipid films.

Frequency dependent2H N.M.R. relaxation rates of small unilamellar phospholipid vesicles

Deuterium (2H) N.M.R. spectroscopy has been used to investigate experimentally the molecular dynamics of phospholipid vesicles. 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) was deuterated specifically in both acyl chains, and aqueous suspensions of vesicles were studied above the main orderdisorder transition temperature. 2H spin-lattice relaxation rates (R 1) were measured at nine different magnetic field strengths, corresponding to Larmor frequencies (v o = ωo/2π) spanning 2·5 MHz to 61·4 MHz. Of three models considered, a model in which R 1 ∝ ω-1/2 0 best described the 2H N.M.R. results, whereas fits to R 1 ∝ ω-1 0 or to a lorentzian plus a constant dispersion were less satisfactory. Thus a broad distribution of motions exists, which must be explained by any model for the N.M.R. relaxation of liquid-crystalline phospholipids.