Dipole Potential of Monolayers with Biologically Relevant Lipid Compositions.

The membrane dipole potential that arises from the interfacial water and constitutive dipolar groups of lipid molecules modulates the interaction of amphiphiles and proteins with membranes. Consequently, its determination for lipid mixtures resembling the existing diversity in biological membranes is very relevant. In this work, the dipole potentials of monolayers, formed at the air-water interface, from pure or mixed lipids (1-palmitoyl-2-oleoyl--glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl--glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl--glycero-3-phosphatidyserine (POPS), sphingomyelin (SpM) and cholesterol) were measured and correlated with the mean area per lipid.

Impact of chlorogenic acid on surface and phase properties of cholesterol-enriched phosphatidylcholine membranes.

This study analyses the insertion of Chlorogenic acid (CGA) in phosphatidylcholine (PC) membranes enriched with cholesterol (Chol). While cholesterol decreases the area per lipid and increases the dipole potential, CGA increases and decreases these values, respectively. When CGA is inserted into cholesterol-containing DMPC membranes, these effects cancel out, resulting in values that overlap with those of DMPC monolayers without Chol and CGA.

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.

Breakdown of classical paradigms in relation to membrane structure and functions.

Updates of the mosaic fluid membrane model implicitly sustain the paradigms that bilayers are closed systems conserving a state of fluidity and behaving as a dielectric slab. All of them are a consequence of disregarding water as part of the membrane structure and its essential role in the thermodynamics and kinetics of membrane response to bioeffectors. A correlation of the thermodynamic properties with the structural features of water makes possible to introduce the lipid membrane as a responsive structure due to the relaxation of water rearrangements in the kinetics of bioeffectors' interactions.

Effect of cholesterol on the hydration properties of ester and ether lipid membrane interphases.

Fluorescence spectroscopy and Molecular Dynamics results show that cholesterol reduces water along the chains in ether lipids by changing the water distribution pattern between tightly and loosely bound water molecules. Water distribution was followed by emission spectra and generalized polarization of 6-dodecanoyl-2-dimethyl aminonaphthalene (Laurdan) inserted in 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14: 0 Diether PC) membranes. Molecular Dynamics simulations indicate that the action of cholesterol could be different in ether PC in comparison to ester PC.

Interaction of chlorogenic acid with model lipid membranes and its influence on antiradical activity.

Chlorogenic acid (CGA) is a strong phenolic antioxidant with antibacterial properties composed by a caffeoyl ester of quinic acid. Although a number of benefits has been reported and related to interactions with the red blood cell membranes, details on its membrane action and how composition and membrane state may affect it, is not yet well defined. In this work, the interaction of CGA with lipid monolayers and bilayers composed by 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC); 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14:0 diether PC); 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-di-O-hexadecyl-sn-glycero-3-phosphocholine (16:0 diether PC) were studied at different surface pressures (π).

Water Behavior at the Phase Transition of Phospholipid Matrixes Assessed by FTIR Spectroscopy.

Lipid membranes are one of the most important biological matrixes in which biochemical processes take place. This particular lipid arrangement is driven by different water disposition interacting with it, which is related to different water states with different energy levels at the interphase. In our work, we report changes in water content and distinctive water states by Fourier transform infrared (FTIR) spectroscopy of this self-assembled matrix at different water contents and temperatures.

Modulation of Interfacial Hydration by Carbonyl Groups in Lipid Membranes.

The lack of carbonyl groups and the presence of ether bonds give the lipid interphase a different water organization around the phosphate groups that affects the compressibility and electrical properties of lipid membranes. Generalized polarization of 1,2-di--tetradecyl--glycero-3-phosphocholine (14:0 diether PC) in correlation with Fourier transform infrared (FTIR) analysis indicates a higher level of polarizability of water molecules in the membrane phase around the phosphate groups both below and above . This reorganization of water promotes a different response in compressibility and dipole moment of the interphase, which is related to different H bonding of water molecules with phosphates (PO) and carbonyl (CO) groups.

Therapeutic effects of forced exercise cycling in individuals with Parkinson's disease.

Currently there is no cure for the progressive movement disorders associated with Parkinson's Disease (PD). Pharmacological management of movement disorders in PD are associated with significant negative side effects. Exercise improves the efficacy of anti-parkinsonian medication, but does not ameliorate the side effects.

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 that 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.

A new model for lipid monolayer and bilayers based on thermodynamics of irreversible processes.

Lipid monolayers are used as experimental model systems to study the physical chemical properties of biomembranes. With this purpose, surface pressure/area per molecule isotherms provide a way to obtain information on packing and compressibility properties of the lipids. These isotherms have been interpreted considering the monolayer as a two dimensional ideal or van der Waals gas without contact with the water phase.

Correlation between the hydration of acyl chains and phosphate groups in lipid bilayers: Effect of phase state, head group, chain length, double bonds and carbonyl groups.

This paper demonstrates by means of FTIR/ATR analysis that water molecules intercalate at different extents in the acyl chain region of lipid membranes in correlation with the hydration of the phosphate groups. This correlation is sensible to the chain length, the presence of double bonds and the phase state of the lipid membrane. The presence of carbonyl groups CO modifies the profile of hydration of the two regions as observed from the comparison of DMPC and 14:0 Diether PC.

Effects of Phenylalanine on the Liquid-Expanded and Liquid-Condensed States of Phosphatidylcholine Monolayers.

Background: Phenylalanine (Phe) is involved in physiological and pathological processes in cell membranes in which expanded and condensed states coexist. In this direction, it was reported that surface hydration is important for the binding affinity of the amino acid which significantly perturbs 1,2-dipalmitoyl--glycero-3-phosphocholine (DPPC) monolayer structure and morphology. A deeper insight showed that Phe inserts in DPPC monolayer defects as a monomer at pH 5 and forms aggregates that adsorb to the membrane surface generating a reconfiguration of the lipid arrangement in areas of higher packing.

Zeta potential changes of Saccharomyces cerevisiae during fermentative and respiratory cycles.

Saccharomyces cerevisiae is a type of yeast, widely used in diverse biotechnological food-beverage processes. Although the performance of an industrial fermentation process depends largely on the number of cells, it is necessary to consider the physiological state of the cultures. In this context, the aim of this study was to determine in a yeast culture how factors such as growth conditions affect surface properties at the different growth stages.

Nebulizing novel multifunctional nanovesicles: the impact of macrophage-targeted-pH-sensitive archaeosomes on a pulmonary surfactant.

In this study, a NE-U22 vibrating mesh Omron nebulizer was used to deliver the Lissamine™ rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (Rh-PE) and 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS)/p-xylene-bis-pyridinium bromide (DPX) double-labelled macrophage-targeted pH-sensitive archaeosomes (ApH, 174 ± 48 nm, -30 ± 13 mV unilamellar nanovesicles made of dioleoyl-sn-glycero-3-phosphoethanolamine: [total polar archaeolipids from the hyperhalophile archaebacteria Halorubrum tebenquichense]: cholesteryl hemisuccinate 4.2 : 2.8 : 3 w : w : w) to J774A.

Lipid selectivity in novel antimicrobial peptides: Implication on antimicrobial and hemolytic activity.

Antimicrobial peptides (AMPs) are small cationic molecules that display antimicrobial activity against a wide range of bacteria, fungi and viruses. For an AMP to be considered as a therapeutic option, it must have not only potent antibacterial properties but also low hemolytic and cytotoxic activities [1]. Even though many studies have been conducted in order to correlate the antimicrobial activity with affinity toward model lipid membranes, the use of these membranes to explain cytotoxic effects (especially hemolysis) has been less explored.

Interaction of S-layer proteins of Lactobacillus kefir with model membranes and cells.

In previous works, it was shown that S-layer proteins from Lactobacillus kefir 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.

The use of zeta potential as a tool to study phase transitions in binary phosphatidylcholines mixtures.

Temperature dependence of the zeta potential (ZP) is proposed as a tool to analyze the thermotropic behavior of unilamellar liposomes prepared from binary mixtures of phosphatidylcholines in the absence or presence of ions in aqueous suspensions. Since the lipid phase transition influences the surface potential of the liposome reflecting a sharp change in the ZP during the transition, it is proposed as a screening method for transition temperatures in complex systems, given its high sensitivity and small amount of sample required, that is, 70% less than that required in the use of conventional calorimeters. The sensitivity is also reflected in the pre-transition detection in the presence of ions.

Interaction of Phenylalanine with DPPC Model Membranes: More Than a Hydrophobic Interaction.

The negative free energy previously reported is explained by the stabilization of a PC-Phe (phosphocholine-phenylalanine) complex in the presence of water shown by the decrease in the symmetric stretching frequency of the phosphate group of the lipid (PO2(-)). An entropic contribution due to the disruption of the water network around the phenyl and in the membrane defect may be invoked. The dipole potential decrease is explained by the orientation of the carboxylate opposing to the CO of the lipids with oxygen moiety toward the low hydrated hydrocarbon core.

Hydration in Lipid Monolayers: Correlation of Water Activity and Surface Pressure.

In order to give a physical meaning to each region of the membrane we define the interphase as the region in a lipid membrane corresponding to the polar head groups imbibed in water with net different properties than the hydrocarbon region and the water phase. The interphase region is analyzed under the scope of thermodynamics of surface and solutions based on the definition of Defay-Prigogine of an interphase and the derivation that it has in the understanding of membrane processeses in the context of biological response. In the view of this approach, the complete monolayer is considered as the lipid layer one molecule thick plus the bidimensional solution of the polar head groups inherent to it (the interphase region).

Membrane Hydration: A Hint to a New Model for Biomembranes.

The classical view of a biological membrane is based on the Singer-Nicholson mosaic fluid model in which the lipid bilayer is the structural backbone. Under this paradigm, many studies of biological processes such as, permeability, active transport, enzyme activity and adhesion and fusion processes have been rationalized considering the lipid membrane as a low dielectric slab of hydrocarbon chains with polar head groups exposed to water at each side in which oil/water partition prevails. In spite of several analyses and evidence available in relation to membrane hydration, water is not taken into account as a functional component.

Phenylalanine interaction with lipid monolayers at different pHs.

The influence of Phe on the surface pressure of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers at the air-water interface was studied at different initial surface pressures (26 and 40 mN/m) and two pHs (5.0 and 7.3) at constant temperature (20 °C).

Phenylalanine Blocks Defects Induced in Gel Lipid Membranes by Osmotic Stress.

We study the binding of phenylalanine (Phe) with dipalmitoylphosphocholine (DPPC) vesicles in gel (25 °C) and in liquid crystalline states (50 °C) and in gel large unilamellar vesicles (LUVs) subjected to osmotic dehydration with merocyanine (MC 540) as a fluorescent surface membrane marker. Phe does not produce significant changes in MC 540 monomer concentration in DPPC LUVs at 50 °C. In contrast, it significantly decreases the monomer adsorption in defects present in DPPC LUVs at 25 °C.

Influence of temperature, anions and size distribution on the zeta potential of DMPC, DPPC and DMPE lipid vesicles.

The purpose of the work is to compare the influence of the multilamellarity, phase state, lipid head groups and ionic media on the origin of the surface potential of lipid membranes. With this aim, we present a new analysis of the zeta potential of multilamellar and unilamellar vesicles composed by phosphatidylcholines (PC) and phosphatidylethanolamines (PE) dispersed in water and ionic solutions of polarizable anions, at temperatures below and above the phase transition. In general, the adsorption of anions seems to explain the origin of the zeta potential in vesicles only above the transition temperature (Tc).