(1-Deoxy)ceramides in bilayers containing sphingomyelin and cholesterol

An X-ray diffraction study of the effect of α-tocopherol on the structure and phase behaviour of bilayers of dimyristoylphosphatidylethanolamine

The partition of cholesterol between ordered and fluid bilayers of phosphatidylcholine: A synchrotron X-ray diffraction study

Anisothermal solid-state reactions of Ni/Al nanometric multilayers

Characterization of a Quasicrystalline Phase in Codispersions of Phosphatidylethanolamine and Glucocerebroside

The effect of dolichol C(95) on the structure and thermotropic phase behaviour of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine and stearoyloleoylphosphatidylethanolamine has been examined by synchrotron X-ray diffraction and differential scanning calorimetry. The presence of dolichol C(95) had no detectable effects on the temperature of either the gel to ripple or the ripple to liquid-crystal phase transition of dipalmitoylphosphatidylcholine. A proportionate increase of a few degrees in the temperature of the gel to lamellar liquid-crystal phase transition is observed in dispersions of dipalmitoylphosphatidylethanolamine and significantly there is a decrease in the temperature of the lamellar to non-lamellar phase transition of stearoyloleoylphosphatidylethanolamine. There was no significant change in the bilayer repeat spacing of all three mixed dispersions in gel phase in the presence of up to 20 mol% dolichol C(95). Electron density calculations showed that there was no change of bilayer thickness of dipalmitoylphosphatidylcholine with incorporation of up to 7.5 mol% dolichol C(95). These data suggest that effect of dolichol on the phospholipid model membranes depend on both the head group and the hydrocarbon chains of the phospholipid molecules. The presence of dolichol in phosphatidylcholine bilayers conforms to a model in which the polyisoprene compound is phase separated into a central domain sandwiched between the two monolayers in gel phase. In bilayers of phosphatidylethanolamines dolichol tends to stabilize the bilayers in gel phase at low temperatures and destabilize the bilayers in lamellar disordered structure at high temperatures. Non-lamellar structures coexist with lamellar disordered phase over a wide temperature range suggesting that dolichol is enriched in domains of non-lamellar structure and depleted from lamellar phase. These findings are useful to understand the function of dolichol in cell membranes.

We investigated the partitioning behavior of gramicidin A′ in various binary phospholipid mixtures in which gel and liquid crystalline phase coexistence had been induced. The quenching of the gramicidin A′ tryptophanyl fluorescence by a spin-labeled phosphatidylcholine was used to determine the equilibrium ratio of gramicidin A′ concentration in the liquid crystalline phase to that in the gel phase (i.e. the partition coefficient, KP). Three multilamellar vesicular systems, differing in the order and rigidity of the gel phase, were compared. The phospholipid content of the gel phase was rich in dipalmitoylphosphatidylcholine or distearoylphosphatidylcholine, or was entirely Ca(dioleoylphosphatidylserine)2. In all cases the gel phase was depleted of gramicidin A′, with KP = 10 ± 2, 25 ± 5, and ≥30, respectively. These data suggest that the more ordered the gel phase, the less it can accommodate a transmembrane polypeptide.

Influence of the interdigitated gel phase in mixtures of ether-linked and monofluorinated ester-linked phospholipids

Two types of microcontainers were prepared by using the adsorption of polyamide on the surface of micrometer-sized inorganic porous calcium carbonate microparticles followed by thermal conversion of the polyamide layers into polyimide coatings. The effect of the preparation conditions on the structure and morphology of the microcontainers was studied by transmission electron microscopy and scanning electron microscopy. The smoothest and defect-free coatings were prepared using polyethylenimine as the supporting polymer. The thickness of the polyamide/polyimide shells was estimated by atomic force microscopy and scanning electron microscopy between 50 and 150 nm depending on the quantity of the layers. The water-soluble antibiotic, doxorubicin hydrochloride, was used as a model compound to demonstrate the efficiency of the microcontainers for encapsulation. The resistance of the novel microcontainers to solvent treatment was visualized by the confocal scanning fluorescence microscopy. It was demonstrated that the combination of the high thermal and chemical resistance of polyamide/polyimide shell and the sorption capacity of the CaCO3 is very useful for development of highly protective microcontainers and thermal detectors for smart fabrics.

Structural Correlations and Thermodynamics of the Gel Phase in Lipid Bilayers

Miscibility and surface crystal morphology of blends containing poly(vinylidene fluoride) by atomic force microscopy

The synergistic interaction between xanthan and glucomannan in solution and in the gel phase has been studied by circular dichroism spectroscopy and differential scanning calorimetry. The study in solution of the polysaccharidic mixture indicates a preferred stoichiometry of the interaction corresponding to a weight fraction of xanthan around 0.55. This finding is in reasonable agreement with the differential scanning calorimetry measurements carried out on the gel phase. Models from conformational analysis based on these results were formulated in terms of 1:1 and 2:1 Konjac glucomannan/xanthan molecular assemblies. The experimental and calculation results clearly indicate the involvement of the side chains of xanthan and suggest that the ordered portions of the macromolecular complex in solution act in the gel phase as junction zones.

The gel-liquid crystal phase transitions of the pseudo-binary systems of cephalins DMPE and DHPE in excess water were studied by differential scanning calorimetry. The phase diagram of the pseudebinary systems has been given. The experiments showed that the partial phase separation in gel phase might occur at least at the mole fractions of DHPE below 0.1. The analysis by the model of ideal solution showed that both the cephalins were non-ideally miscible both in the gel phases and in the liquid crystal phases. The analysis by the model of regular solution showed that all the non-ideality parameters in the gel phases were larger than those in the liquid crystal phases at the same temperature. All the non-ideality parameters were not constant, but rather dependent on temperature.

Interactions between L-α-dipalmitoylphosphatidylcholine (DPPC) and 2S, 3S, 4R-2-stearoylamide-1, 3, 4-octadecanetriol (Ceramide 3) in mixed monolayers and bilayers were investigated by surface pressure measurements, atomic force microscopy (AFM) and differential scanning calorimetry (DSC).AFM images for mixed DPPC/Ceramide 3 monolayers (single-layer LB films) deposited at 10mN/m surface pressure on mica indicated elliptical domains. DSC curves indicated the phase transition temperature of DPPC liposomal bilayer membranes to shift upwards with the addition of Ceramide 3 and a sharp DPPC peak to become broad in mixed DPPC/Ceramide 3 systems. A DSC peak was noted to split at higher mole fractions of Ceramide 3.The phase separation was evident in mixed DPPC/Ceramide 3 monolayers and bilayers, and Ceramide 3 may possibly interact with DPPC in the liquid-expanded phase with consequent phase separation accompanied with domain formation.

Nanographene oxide (NGO) was prepared from natural graphite flakes via modified Hummer’s method. Nanocomposite of NGO and zinc oxide (NGO–ZnO) in the ratio of 1:1 was prepared by sol–gel method. Structural and physiochemical properties of the synthesized NGO and NGO–ZnO nanocomposite were investigated with the help of powder X ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope coupled with energy-dispersive X ray analysis (SEM/EDX), thermal gravimetric analysis and differential scanning calorimetry (TGA/DSC) and atomic force microscopy (AFM). The PXRD results showed the conversion of graphite to nanographene oxide. It was observed from the FTIR spectra that graphite oxidized by strong oxidant KMnO4 showed the presence of oxygen atoms on the graphite layer. Thus, certifies the presence of oxygen-containing functional groups COOH, C=O, C–O–C in GO films. SEM image indicated the morphology of NGO and inclusion of nano-zinc oxide in graphene layer. EDS analyzed the components in the material. Percentage of oxygen in NGO shows extensive oxidation of graphene layer and percentage of zinc calculated by EDS agreed with theoretical ratio. TGA/DSC analyzer indicated the thermal stability of the material. AFM indicated exfoliation of graphite to graphene. Photocatalytic activities of the prepared samples were evaluated by degradation of rhodamine 6B (Rh 6B) azo dye in aqueous solution. From the measured absorbance values, the photocatalytic activity of NGO–ZnO nanocomposite was found to be excellent than pure NGO.

Hyperbranched fluoropolymers (HBFPs), based on benzyl ether linkages and having a large number of pentafluorophenyl chain ends, were crosslinked by a reaction with diamino‐terminated poly(ethylene glycol) (PEG) or diamino‐terminated poly(dimethyl siloxane) (PDMS) to form hyperbranched–linear copolymer networks of different compositions, structures, and properties. The crosslinking reactions involved the nucleophilic aromatic substitution of the pentafluorophenyl para‐fluorines of HBFP by the amine functionalities of the respective telechelic linear segments. The contact angles, differential scanning calorimetry, thermogravimetric analysis, tensile measurements, and atomic force microscopy (AFM) were used to characterize the resulting network film samples. The surface wettability of the crosslinked materials was affected by the nature and amount of the linear polymer crosslinking agent employed. Amphiphilic polymer networks were formed by the incorporation of diamino‐terminated PEG as a crosslinker, whereas diamino‐terminated PDMS produced polymer networks of a hydrophobic character. The mechanical properties improved upon crosslinking, as measured by tensile testing. The mechanical integrity of the films was also found to improve upon crosslinking, as measured by AFM machining protocols. The AFM images revealed topographical morphologies that appeared to be the result of phase segregation of HBFP from PEG or PDMS; the dimensions of the phase‐segregated domains were dependent on the stoichiometry of HBFP to the linear polymer and the thickness of the coating. As the content of PEG increased, fouling by human fibrinogen, used as a model protein, decreased. Further studies are in progress to determine the effects of the surface composition, morphology, and topography on the biofouling characteristics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3531–3540, 2003