Temperature effect on the bilayer stacking in multilamellar lipid vesicles.

The small-angle region of the Bragg diffraction of MLV samples is a simple and powerful tool for the study of mesoscopic lipid structures either alone or in interaction with molecules of biological interest. It is also a helpful tool to obtain the much needed thermotropic phase diagrams of lipid mixtures. In the course of our work, we found that the analysis of the diffractograms obtained as a function of temperature is not as straightforward as we expected.

Study of the miscibility of cholesteryl oleate in a matrix of ceramide, cholesterol and fatty acid.

Cholesteryl esters (CE) are not generally abundant but are ubiquitous in living organisms and have markedly different properties from cholesterol because of their acyl chain. The miscibility/immiscibility of CE with biological lipid structures is a key property for their functions. In this work we study the solubility of cholesteryl oleate (ChO) in a model of the stratum corneum lipid matrix composed of ceramide C16, cholesterol and palmitic acid in excess water.

The thermotropism and prototropism of ternary mixtures of ceramide C16, cholesterol and palmitic acid. An exploratory study.

Mixtures of ceramides with other lipids in the presence of water are key components of the structure of the lipid matrix of the stratum corneum and are involved in lateral phase separation processes occurring in lipid membranes. Besides their structural role, ceramides are functional for cell signaling and trafficking. We elected, as our object of study, a mixture of N-hexadecanoylceroyl-d-erythro-sphyngosine, C16-Cer, with cholesterol, Ch, in a molar proportion 54:46 in excess water to which palmitic acid, PA, is added in varying amounts.

Phase behavior of aqueous dispersions of mixtures of N-palmitoyl ceramide and cholesterol: a lipid system with ceramide-cholesterol crystalline lamellar phases.

Ceramides are particularly abundant in the stratum corneum lipid matrix, where they determine its unusual mesostructure, are involved in the lateral segregation of lipid domains in biological cell membranes, and are also known to act as signaling agents in cells. The importance attributed to ceramides in several biological processes has heightened in recent years, demanding a better understanding of their interaction with other membrane components, namely, cholesterol. Structural data concerning pure ceramides in water are relatively scarce, and this is even more the case for mixtures of ceramides with other lipids commonly associated with them in biological systems.

On the self-aggregation and fluorescence quenching aptitude of surfactant ionic liquids.

The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and (1)H NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [Cnmpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n=4, 10, 12, 14, 16, or 18), [C12mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C12mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C12mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide).

Encapsulation of adenoviral vectors into chitosan-bile salt microparticles for mucosal vaccination.

The objective of this study is the incorporation of adenoviral vectors into a microparticulate system adequate for mucosal delivery. Microencapsulation of the vectors was accomplished by ionotropic coacervation of chitosan, using bile salts as counter-anion. The process was optimized in order to promote high encapsulation efficiency, with a minimal loss of viral infectivity.

Kinetics of bimolecular reactions in model bilayers and biological membranes. A critical review.

The quantitative study of the probability of molecular encounters giving rise to a reaction in membranes is a challenging discipline. Model systems, model in the sense that they use model bilayers and model reactants, have been widely used for this purpose, but the methodologies employed for the analysis of the results obtained in experiments, and for experimental design, are so disparate that a concerned experimentalist has difficulty in deciding about the value of each approach. This review intends to examine the several approaches that can be found in the literature showing, when feasible, the weakness, strengths and limits of application of each of them.

Incorporation of a model protein into chitosan-bile salt microparticles.

In order to develop a mucosal delivery system based on biocompatible polymers, a new methodology for production of protein-loaded microparticles is developed. Chitosan anionic precipitation/coacervation is accomplished by the addition of sodium deoxycholate (DCA). These microparticles were prepared under mild conditions, where bovine serum albumin (BSA) and DCA were simply dipped into a chitosan solution under stirring.

Reappraisal of four different approaches for finding the mean reaction time in the multi-trap variant of the Adam-Delbrück problem.

Adam and Delbrück argued that the dimensionality of the diffusion space determines the average lifetime of a diffusing particle confined to a region with a central trap. Doubts have often been aired as to whether their calculation is relevant to real biological systems, where the number of traps is usually much larger than unity; or whether the rate enhancement is merely a manifestation of an increase in the concentration of the traps; or whether the diverse multi-trap versions of their expression for the mean lifetime in two dimensions are trustworthy. These issues are addressed, and the long-standing problem of finding the low-density limit of trapping time in two dimensions solved, by examining previous treatments of the problem, and by carrying out simulations of two-dimensional systems in which the particles undergo a Pearsonian random walk, and the traps are distributed randomly or on a square lattice.

Partition of fish pheromones between water and aggregates of humic acids. Consequences for sexual signaling.

High-molecular-weight suspended organic matter of soil and aquatic origins competes with water for the dissolution of relatively water insoluble organic substances. The same happens with microalgae and other organisms present in natural waters. Several pheromones, which play a specific role in the reproductive cycle of fish, are secreted to the water and are generally, if not always, molecules with hydrophobic or amphiphilic characteristics.

Solubility of amphiphiles in membranes: influence of phase properties and amphiphile head group.

The solubilities of two fluorescent lipid amphiphiles with comparable apolar structures and different polar head groups, NBD-hexadecylamine and RG-tetradecylamine (or -octadecylamine), were compared in lipid bilayers at a molar ratio of 1/50 at 23 degrees C. Bilayers examined were in the solid, liquid-disordered, or liquid-ordered phases. While NBD-hexadecylamine was soluble in all the examined bilayer membrane phases, RG-tetradecylamine was stably soluble only in the liquid-disordered phase.