Ionization and Structural Changes of the DMPG Vesicle along Its Anomalous Gel-Fluid Phase Transition: A Study with Different Lipid Concentrations

Ionization and Structural Changes of the DMPG Vesicle along Its Anomalous Gel-Fluid Phase Transition: A Study with Different Lipid Concentrations

Author Barroso, Rafael P. Google Scholar
Riske, Karin A. Autor UNIFESP Google Scholar
Henriques, Vera B. Google Scholar
Teresa Lamy, M. Google Scholar
Institution Universidade de São Paulo (USP)
Universidade Federal de São Paulo (UNIFESP)
Abstract Dispersions of saturated anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG) have been extensively studied regarding their peculiar thermostructural behavior. At low ionic strength, the gel-fluid transition is spread along nearly 17 degrees C, displaying several thermal events in the calorimetric profile that is quite different from the single sharp peak around 23 degrees C found for higher ionic strength DMPG dispersions. To investigate the role of charge in the bilayer transition, we carefully examine the temperature dependence of the electrical conductivity of DMPG dispersions at different concentrations, correlating the data with the corresponding differential scanning calorimetry (DSC) traces. Electrical conductivity together with electrophoretic mobility measurements allowed the calculation of the dependence of the degree of ionization of DMPG vesicles on lipid concentration and temperature. It was shown that there is a decrease in vesicle charge as the lipid concentration increases, which is probably correlated with the increase in the concentration of bulk Na(+). Apart from the known increase in the electrical conductivity along the DMPG temperature transition region, a sharp rise was observed at the bilayer pretransition for all lipid concentrations studied, possibly indicating that the beginning of the chain melting process is associated with an increase in bilayer ionization. It is confirmed here that the gel-fluid transition of DMPG at low ionic strength is accompanied by a huge increase in the dispersion viscosity. However, it is shown that this measured macroviscosity is distinct from the local viscosity felt by either charged ions or DMPG charged aggregates in measurements of electrical conductivity or electrophoretic mobility, Data presented here give support to the idea that DMPG vesicles, at low ionic strength, get more ionized along the temperature transition region and could be perforated and/or deformed vesicle structures.
Language English
Sponsor USP
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Date 2010-09-07
Published in Langmuir. Washington: Amer Chemical Soc, v. 26, n. 17, p. 13805-13814, 2010.
ISSN 0743-7463 (Sherpa/Romeo, impact factor)
Publisher Amer Chemical Soc
Extent 13805-13814
Access rights Closed access
Type Article
Web of Science ID WOS:000281354000016

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