Phase separation of phospholipid multilayers incorporated with cell penetrating peptides.

We used X-ray reflectivity to investigate the structures of phospholipid multilayers with transcription-activating-factor-derived peptide (TDP) as a function of the membrane charge density. Mixed phospholipid multilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl -sn-glycero-3-phosphoserine (DPPS) with different mixing ratios (C:S) were used to elucidate the various charge densities in a plasma membrane. We fixed the peptide/lipid molar ratio (P/L) and varied the DPPC/DPPS molar ratio in the mixed multilayer. In the pure DPPC multilayer, the incorporation of TDP had nearly no effect on the bilayer thickness of the mixed lipid multilayer. However, in the mixed DPPC/DPPS multilayer, the incorporation of TDP decreased the bilayer thickness, suggesting that the TDP peptide had a stronger interaction with DPPS than with DPPC and caused disorder in the lamellar structure. Combining this with the refined X-ray reflectivity (XR) data, we concluded that the TDP existed more in the headgroup region of the TDP-induced segregated DPPS in the mixed multilayer and caused significant membrane thinning.

AFM study of phase-separated morphology in immiscible blend thin films.

Phase-separation behavior of polystyrene (PS) and poly(methyl methacrylate) (PMMA) 1:1 blend film has been studied as a function of film thickness and component by adding PS-b-PMMA diblock copolymer. After annealing, PS is phase-separated into circular-shaped bumps on a PMMA layer. The bump number is inversely proportional to the film thickness in log-log plot while the slope is invariable for the blends with and without 5% PS-b-PMMA diblock copolymer. The bump size and inter-bump spacing are also affected by both the film thickness and addition of the block copolymer.

Formation of n-alkane layers at the vapor/water interface.

We present a study on the initial wetting behaviors of two low molecular weight alkanes, heptane and octane, at the vapor/water interface using both neutron and X-ray reflectometry. Combined X-ray and neutron reflectivity studies data showed that a uniform film, which has never been reported, was formed continuously at 25 degrees C. As the adsorptive deposition continued, each adsorbed film was saturated at a specific equilibrium thickness: 48 and 36 A for deuterated heptane and octane, respectively, and 21 A for hydrogenated octane. The thickness of the adsorbed layer measured by neutron reflectivity is in agreement with that measured using X-ray reflectivity. Our observations of continuous and saturated adsorption behaviors are analyzed qualitatively using a kinetic adsorption model.

Electrochemical growth of highly oriented organic-inorganic superlattices using solid-supported multilamellar membranes as templates.

Controllable depositing of relatively thick inorganic sublayers into organic templates to fabricate organic-inorganic superlattices is of great importance. We report a novel approach to fabricating phospholipid/Ni(OH)(2) superlattices by electrochemical deposition of the inorganic component into solid-supported multilamellar templates. The well-ordered and highly oriented multilamellar templates are produced by spreading small drops of lipid solution on silicon surfaces and letting the solvent evaporate slowly. The templates which are used as working electrodes preserve the lamellar structure in the electrolyte solution. The resulting superlattices are highly oriented. The thickness of the nickel hydroxide is controlled by the concentration of nickel ions in the electrolyte bath. The electron density profiles derived from the X-ray diffraction data reveal that the thickness of the nickel hydroxide sublayers increases from 15 to 27 A as the concentration of nickel nitrate increases from 0.005 mol/L to 0.08 mol/L. We expect that the new method can be extended to depositing a variety of inorganic components including metals, oxides, and semiconductors.

Electrochemical self-assembly of highly oriented ZnO-surfactant hybrid multilayers.

Highly oriented zinc oxide-surfactant hybrid multilayers were electrochemically self-assembled on silicon substrates from Zn(NO3)2 solutions containing extremely low concentration of sodium dodecyl sulfate (SDS). The X-ray diffraction results showed that the structure of the hybrid film is sensitive to the concentration of SDS. When the concentration of SDS is below a critical value, 0.002 wt %, a surfactant bilayer is adsorbed on the silicon surface, together with electrodeposited crystalline ZnO particles. Above this concentration, lamellar ZnO-surfactant hybrid films are formed, the period of which decreases from 31.7 +/- 0.2 A at 0.003 wt % to 27.5 +/- 0.2 A at 0.005 wt %, another critical concentration. It then increases monotonically and reaches its maximum of 33.0 +/- 0.2 A above 0.05 wt %. The results implied that the kinetics of the electrochemical self-assembly depends on the relative speed of the reduction of the zinc ions and the aggregation of the surfactant. The two processes occur cooperatively at the electrolyte-electrode interface to form the hybrid films.