Changes in the surface potential of Lactobacillus acidophilus under freeze-thawing stress

The zeta potential of Lactobacillus acidophilux CRL 640, a measure of the net distribution of electrical charges on the bacterial surface, is a function of the glucose concentration in the growing media. With 2% glucose, cells in the stationary phase showed a zeta potential of -45 ± 2 mV. With these cells, the zeta potential after freezing and thawing decreased to -32 ± 2 mV and there was a decrease in viability. The changes in the surface potential correlated with damage to the cell surface as shown by electron microscopy. Freeze-thawed cells incubated in a rich medium recovered a zeta potential of -38 ± 2 mV without cell growth. L. acidophilus CRL 640 showed the same value of surface potential as control cells when they were frozen and thawed in 2 M glycerol.Fil: Fernandez Murga, María Leonor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; ArgentinaFil: Font, Graciela Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; ArgentinaFil: Disalvo, Anibal E.. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentin

Coordination forces between lipid bilayers produced by ferricyanide and Ca2+

© 2011 Elsevier B.V. All rights reserved.Attractive forces usually invoked to take place in membrane–membrane contact in aggregation are hydrogen bonding cross-linkings and hydrophobic interactions between opposing surfaces. However, little is known in relation to the presence of coordination forces in the membrane–membrane interaction. These are understood as those that may be favoured by the formation or the participation of coordination complexes between surface specific groups. In this work, we have analyzed the formation of this type of aggregates between phosphatidylcholine vesicles mediated by a coadsorption of ferricyanide and Ca2+ ions to the interface. The results obtained by surface potential measures, optical and electronic microscopy, FTIR and 1H NMR spectroscopies indicate that ferricyanide [Fe(CN)6]3− but not of ferrocyanide [Fe(CN)6]4− can form the complex when Ca2+ has been adsorbed previously to the membrane surface. In this condition, the anion is likely to act as a bridge between two opposing membranes causing a tight aggregation in which geometry and the polarizability of the ligands to Fe3+ play a role

Water and Membranes

I. INTRODUCTION Water is unquestionably playing a very important part in the functioning of biomolecular assemblies. Depending on the character of the functional groups of biomolecules, the interactions of these groups with water and with themselves while solvated in water, are called hydrophobic or hydrophilic. These interactions are responsible for protein folding, the subject of a very intense study in the recent past and at the present time.1 The same interactions are also responsible for the creation of membrane structures in biology.2,3 The subject of water and its influence on the biomembrane properties is very broad, so we decided to concentrate here on the discussion of water properties in the region between lipid membranes and permeability of water across membranes. It is believed that water between membrane surfaces strongly influences the interactions between the surfaces. These interactions are determining the process of primary significance in biology: membrane and vesicle fusion.4 Understanding the basic mechanistic steps in the fusion process can result in the ability to mimic fusion for pharmacological applications, such as liposomal drug delivery. The interaction between membranes across water will be discussed in the part of our review dealing with the hydration force

A Molecular View of the Surface Pressure/Area Per Lipid Isotherms Assessed by FTIR/ATR Spectroscopy

The macroscopic behavior of a lipid monolayer in terms of packing and compressibility properties is classically obtained from surface pressure/area per molecule isotherms. Molecular interpretations trying to fit the II/A curves have been attempted by molecular dynamics. In this regard, the simulation is performed by introducing parameters accounting for the lipid-lipid interaction in the monolayer plane. However, water, as an essential component of the interfacial phenomena, is not explicitly included in terms of molecular arrays. This drawback appears to be a consequence of the lack of experimental evidence that may complement the macroscopic view with the microscopic features. In this work, we propose that II/A curves can be reproduced from microscopic molecular data obtained with FTIR/ATR spectroscopy. The changes in surface pressure, in fact, changes in the surface tension of the lipid–water interphase, can be related to the acyl regions exposed to water and evaluated by the ratio of isolated-to-connected CH2 populations. In turn, the area changes correspond to the variations in the primary and secondary hydration shells of the phosphate region. The isolated/connected CH2 ratio represents the extension of the non-polar region exposed to water and is linked to the resulting water surface tension. The area per lipid is determined by the excluded volume of the hydration shells around the phosphate groups in correlation to the carbonyl groups. The derivative of the frequencies of the -CH2 groups with respect to the water content gives an insight into the influence of water arrangements on the compressibility properties, which is important in understanding biologically relevant phenomena, such as osmotic stress in cells and the mechanical response of monolayers. It is concluded that the water population distributed around the different groups dominates, to a great extent, the physical properties of the lipid membranes

Water as a Link between Membrane and Colloidal Theories for Cells

This review is an attempt to incorporate water as a structural and thermodynamic component of biomembranes. With this purpose, the consideration of the membrane interphase as a bidimensional hydrated polar head group solution, coupled to the hydrocarbon region allows for the reconciliation of two theories on cells in dispute today: one considering the membrane as an essential part in terms of compartmentalization, and another in which lipid membranes are not necessary and cells can be treated as a colloidal system. The criterium followed is to describe the membrane state as an open, non-autonomous and responsive system using the approach of Thermodynamic of Irreversible Processes. The concept of an open/non-autonomous membrane system allows for the visualization of the interrelationship between metabolic events and membrane polymorphic changes. Therefore, the Association Induction Hypothesis (AIH) and lipid properties interplay should consider hydration in terms of free energy modulated by water activity and surface (lateral) pressure. Water in restricted regions at the lipid interphase has thermodynamic properties that explain the role of H-bonding networks in the propagation of events between membrane and cytoplasm that appears to be relevant in the context of crowded systems

A compact device for simultaneous dielectric spectroscopy and microgravimetric analysis under controlled humidity

Water plays a key role in the functioning of natural and synthetic molecular systems. Despite several hydration studies, different techniques are employed individually for monitoring different physical features such as kinetics, dynamics and absorption. This study describes a compact hydration cell, which enables simultaneous dielectric relaxation spectroscopy (DRS) and mass loss/uptake measurements in thin organic layers under controlled humidity conditions and in a wide temperature range. This approach enabled us to correlate the physical quantities obtained during the same experiment by complementary techniques. To demonstrate the performance of this device, a 200 nm thick Poly(methyl methacrylate) (PMMA) layer was measured at various relative humidity levels (0 – 75 %), temperatures (25 – 75 ˚C) and frequencies (DRS: 0.1 Hz – 1 MHz) to study how hydration and dehydration processes affect its molecular dynamics. The results show the capability of this setup to study the changes in the PMMA film regarding the kinetics and molecular dynamics upon variation of the water content.status: publishe

Interaction of S-layer proteins of <i>Lactobacillus kefir</i> with model membranes and cells

<p>In previous works, it was shown that S-layer proteins from <i>Lactobacillus kefir</i> were able to recrystallize and stabilize liposomes, this feature reveling a great potential for developing liposomal-based carriers. Despite previous studies on this subject are important milestones, a number of questions remain unanswered. In this context, the feasibility of S-layer proteins as a biomaterial for drug delivery was evaluated in this work. First, S-layer proteins were fully characterized by electron microscopy, 2D-electrophoresis, and anionic exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). Afterward, interactions of S-layer proteins with model lipid membranes were evaluated, showing that proteins adsorb to the lipid surface following a non-fickean or anomalous diffusion, when positively charged lipid were employed, suggesting that electrostatic interaction is a key factor in the recrystallization process on these proteins. Finally, the interaction of S-layer coated liposomes with Caco-2 cell line was assessed: First, cytotoxicity of formulations was tested showing no cytotoxic effects in S-layer coated vesicles. Second, by flow cytometry, it was observed an increased ability to transfer cargo molecules into Caco-2 cells from S-layer coated liposomes in comparison to control ones. All data put together, supports the idea that a combination of adhesive properties of S-layer proteins concomitant with higher stability of S-layer coated liposomes represents an exciting starting point in the development of new drug carriers.</p