Modifications of the structure and dynamics of dimyristoylphosphatidic acid model membranes by calcium ions and poly-L-lysines. A Raman and deuterium NMR study
Interactions of calcium ions (Ca2+) or poly-L-lysines (PLL) of different molecular weight with negatively charged model membranes (dimyristoylphosphatidic acid
(DMPA) dispersions) have been followed by Raman and deuterium (2H) NMR spectroscopies.
Results show that both short (m.v.=3 300 to 4 000) and long (m.w.=180 000 to 260 000) PLL increase the degree of ordering
of the lipid acyl chains either in gel or fluid phases. This effect is attributed to a neutralizing action of the PLL positive
charges on the phospholipid head group negative charges, which leads to a better chain packing. In addition, a 20 °C upshift
in the temperature, T
, of the gel-to-fluid phase transition is promoted by long PLL, whereas no change in T
is observed with short PLL. These observations are correlated to temperature-induced conformational changes of the polypeptides.
As detected by Raman amide I bands, long PLL retain their β-sheet conformation over all the temperature range of the study, whereas short PLL undergo at about T
, a transition from β-sheet (T<T
) to random coil (T>T
Effect of calcium leads to an increase in ordering such that lipids are in their gel state up to 75 °C. Above this temperature
a structural modification occurs which is not yet identified but which cannot be attributed to a conventional gel-to-fluid
Available from: Filipe E. Antunes
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ABSTRACT: Mixed polymer-surfactant systems have been intensively investigated in the last two decades, with the main focus on surfactant micelles as the surfactant aggregate in interaction. The main types of phase behavior, driving forces and structural/rheological effects at stake are now fairly well understood. Polymer-vesicle systems, on the other hand, have received comparatively less attention from a physico-chemical perspective. In this review, our main goal has been to bridge this gap, taking a broad approach to cover a field that is in clear expansion, in view of its multiple implications for colloid and biological sciences and in applied areas. We start by a general background on amphiphile self-assembly and phase separation phenomena in mixed polymer-surfactant solutions. We then address vesicle formation, properties and stability not only in classic lipids, but also in various other surfactant systems, among which catanionic vesicles are highlighted. Traditionally, lipid and surfactant vesicles have been studied separately, with little cross-information and comparison, giving duplication of physico-chemical interpretations. This situation has changed in more recent times. We then proceed to cover more in-depth the work done on different aspects of the associative behavior between vesicles (of different composition and type of stability) and different types of polymers, including polysaccharides, proteins and DNA. Thus, phase behavior features, effects of vesicle structure and stability, and the forces/mechanisms of vesicle-macromolecule interaction are addressed. Such association may generate gels with interesting rheological properties and high potential for applications. Finally, special focus is also given to DNA, a high charge polymer, and its interactions with surfactants, and vesicles, in particular, in the context of gene transfection studies.
Advances in Colloid and Interface Science 11/2008; 147-148:18-35. DOI:10.1016/j.cis.2008.10.001 · 7.78 Impact Factor
Available from: Alexey Nesterenko
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ABSTRACT: The topic correlates electrostatic effects induced by polylysine (PL) adsorption at the lipid membrane surface with data of alternative methods sensitive to lipid bilayer structure. Comparison of electrokinetic data for liposomes from anionic lipids (cardiolipin, phosphatidylserine) and results of boundary potential (BP) measurements with lipid membranes shows effects in two opposite directions: fast positive changes of BP due to adsorption of polycations at the outer membrane surface and slow negative changes that can be attributed to alteration of the dipole component of BP. The latter effect does not depend on the polymer length and may be caused by lipid interaction with lysine as a basic unit of these polypeptides. Molecular dynamic simulation points out the possible mechanism of the dipole effect, which could be caused by reduced number of H-bonds to PO4 groups upon the lysine adsorption. Atomic force microscopy visualized the geometry of clusters formed by PL of different lengths at the lipid bilayer. Isotherm titration calorimetry and the technique of lipid monolayers reveal the similarity in polypeptide and inorganic multivalent cation effects on the lateral lipid condensation accompanied by dipole effects.
Advances in Planar Lipid Bilayers and Liposomes 01/2013; 17(29):139-166. DOI:10.1016/B978-0-12-411516-3.00006-1
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