Ordering and lyotropic behavior of a silicon-supported cationic and neutral lipid system studied by neutron reflectivity

Abstract

Self-assembling of amphipathic lipid films on solid support allows the structural investigation of important biological model systems, such as the vectorlike lipid membranes, in order to improve DNA transfection in nonviral gene therapy. We present a neutron reflectivity study of a binary lipid system composed of dioleoylphosphatidylcholine (DOPC) and dimethyldioctadecylammonium bromide (DDAB) deposited on [100] silicon support by means of spin coating technique. We underline their lyotropic behavior under saturated deuterium oxide (D2 O) vapor thus pointing out that the lipid mixture is organized in ordered domains composed of plane lamellar bilayers of noninteractive DOPC and DDAB. © 2008 American Institute of Physics

Alamethicin–lipid interaction studied by energy dispersive X-ray diffraction

“…5, a Bragg peak is present in every pattern of the four steps, proving that the DOPC keeps the lamellar structure during the lyotropic transition and a continuous increase of its bilayer thickness is observed. As it has previously been observed [13] the swelling process of the membrane lattice constant is due to the increase of the number of water molecules organized between the planes composed of DOPC hydrophilic heads. Moreover, as plotted in the step 4 of the Fig.…”

“…1% with a maximum count rate of 10 k counts/s. We exploit the follow Bragg's diffraction law: q = 4/(hc) Esin  (h and c represent the Plank constant and the speed of light in the vacuum, respectively) to relate the energy of diffracted photons E at grazing incident angle and the reciprocal lattice vector q along the vertical direction, permitting to obtain the lattice constant of (0 0 l) lamellar lipid structure [13,17]. Diffraction spectra were acquired setting to 0.45 • and were fitted with Levenberg-Marquardt algorithm to obtain the bilayer thickness from the position of the first order Bragg peak through the relation d = 2/q where q is the mean value of the Gaussian fit.…”

“…Moreover, the characterization of the structural modifications due to a specific class of antimicrobial peptides allows us a clear recognition of a cytotoxic peptide presence, highlighting biosensing properties of the solid supported lipid membranes. The main aim of this work is to detect ordering variations in the direction normal to the substrate plane (which we call vertical direction) of the lecithin 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) multi-lamellar structure [13] in presence of alamethicin antimicrobial peptide by EDXD technique. In this paper we demonstrate the capability of such a diffraction method to clarify the role of the lipid-peptide ratio and the influence of the hydration level on the lipid membrane-amphipathic peptide interaction which allowed us to postulate a mechanism for the alamethicin cytotoxicity at low peptide concentration.…”

Vertical ordering sensitivity of solid supported DPPC membrane to alamethicin and the related loss of cell viability

“…During the X-ray measurements, the sample was kept inside a controlled humidity-temperature chamber at T = 25°C, where the bare DPPC was in the L β phase. The influence of water hydration on the vertical ordering of the Ala-DPPC films was investigated by choosing two RH environmental conditions: at 50% RH, the membrane underwent dehydration down to the thermodynamic equilibrium, ensuring, in turn, that only a small number of water molecules remained absorbed onto the polar membrane surface [13]; at 100% RH, the membrane could instead reach the maximum amount of adsorbed water [13]. In all of the experiments, Milli-Q quality water was employed (18.2 MΩ cm, resistivity).…”

“…Therefore, varied model assemblies have been employed to mimic the lipid bilayer organisation of the membrane [11][12][13][14][15][16]. These models include multilamellar and unilamellar liposomes, colorimetric biomimetic membranes, and planar lipid mono-, bi-and multi-layers deposited on solid supports.…”