Properties of mixed DOTAP-DPPC bilayer membranes as reported by differential scanning calorimetry and dynamic light scattering measurements.
We have investigated the effect of a cationic lipid [DOTAP] on both the thermotropic phase behavior and the structural organization of aqueous dispersions of dipalmitoyl-phosphatidylcholine [DPPC] by means of high-sensitivity differential scanning calorimetry and dynamic light scattering measurements. We find that the incorporation of increasing quantities of DOTAP progressively reduces the temperature and the enthalpy of the gel-to-liquid crystalline transition. We are further showing that, in mixed DOTAP-DPPC systems, the reduction of the phase transition temperature is accompanied by a reduction of the average size of the structures present in the aqueous mixtures, whatever the DOTAP concentration is. These results, which extend a previous investigation by Campbell et al. (Campbell, R. B.; Balasubramanian, S. V.; Straubinger, R. M.; Biochim. Biosphys. Acta 2001, 27, 1512.) limited to a DOTAP concentration below 20 mol %, confirm that the insertion of cationic head groups in zwitterionic phosphatidylcholine bilayers facilitates the formation of stable, relatively small, unilamellar vesicles. This self-assembling restructuring from an aqueous multilamellar structure toward a liposomal phase is favored by decreasing the phospholipid phase transition temperature and by increasing the temperature of the system. This reduction of the average size and the appearance of a stable liposomal phase is also promoted by a heating and cooling thermal treatment.
Cinelli
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S
Dipartimento di Fisica, UniversitA di Perugia and CEMIN (Centro Eccellenza Materiali Innovativi Nanostrutturati) Via A. Pascoli, I-06123, Perugia, Italy.
Onori
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G
Zuzzi
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S
Bordi
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F
Cametti
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C
Sennato
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S
Diociaiuti
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D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D005229:Fatty Acids, Monounsaturated / Q000737:chemistry*; D008027:Light; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D008560:Membrane Fluidity; D046529:Microscopy, Electron, Transmission; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012542:Scattering, Radiation
D005229:Fatty Acids, Monounsaturated; D008051:Lipid Bilayers; D008081:Liposomes; D000644:Quaternary Ammonium Compounds; D015060:1,2-Dipalmitoylphosphatidylcholine; C070046:1,2-dioleoyloxy-3-(trimethylammonium)propane