Phase behavior of synthetic amphiphile vesicles investigated by calorimetry and fluorescence methods

Benatti, Carlos R.; Tiera, Márcio José; Feitosa, Eloi; Olofsson, Gerd

doi:10.1016/s0040-6031(98)00634-0

Cited by 38 publications

(45 citation statements)

References 10 publications

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“…27,42 In the polymer-vesicle samples here investigated no such maximum has been detected, due to the intrinsic viscosity of the polymer solution. Instead, a continuous and steep decrease in viscosity with temperature for both polymers is observed.…”

Section: Dscmentioning

confidence: 81%

Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

et al. 2006

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Vesicles composed of an anionic and a cationic surfactant, with a net negative charge, associate strongly with a hydrophobically modified polycation (LM200) and with an unmodified polycation with higher charge density (JR400), forming viscoelastic gel-like structures. Calorimetric results show that in these gels, LM200 induces a rise of the chain melting temperature (T m ) of the vesicles, whereas JR400 has the opposite effect. For both polymer-vesicle systems, the shear viscosity exhibits an inflection point at T m , and for the LM200 system the measured relaxation times are significantly higher below T m . The neat vesicles and the polycationbound vesicles have a polygonal-like faceted shape when the surfactant chains in the bilayer are crystallized, as probed by cryo-transmission electron microscopy. Above T m , the neat and the LM200-bound vesicles regain a spheroidal shape, whereas those in the JR400 system remain with a deformed faceted shape even above T m . These shape changes are interpreted in terms of different mechanisms for the polymer-vesicle interaction, which seem to be highly dependent on polymer architecture, namely charge density and hydrophobic modification. A crystallization-segregation mechanism is proposed for the LM200-vesicle system, while, for the JR400-vesicle one, charge polarization-lateral segregation effects induced by the polycation in the catanionic bilayer are envisaged.

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Section: Dscmentioning

confidence: 81%

Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

et al. 2006

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“…1.4) for systems forming vesicles. [10] At high temperatures, I 1 /I 3 (1.1 at 55°C) approaches the typical values for micelles. For example, Hashimoto and Thomas [11] have measured a value of 1.16 for sodium dodecyl sulfate micelles.…”

mentioning

confidence: 81%

Supramolecular Structures Generated by a p‐tert‐Butylphenyl‐amide Derivative of Cholic Acid: From Vesicles to Molecular Tubes

et al. 2007

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The formation of supramolecular structures initiated by a p‐tert‐butylphenyl‐amide derivative of cholic acid is investigated. The initial spherical vesicles, with a rather low effective bending constant, collapse into necklaces that self‐transform into tubules of small diameter. Finally, molecular tubes are generated (see figure). During the process, the geometrical constraints of fixed surface area and fixed enclosed volume are obeyed.

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“…When dissolved in water, above its T m and at low concentration (up to about 1 mM), DODAX molecules associate spontaneously as large unilamellar vesicles, whose physical and thermal properties have already been reported [7,[11][12][13]. At higher concentrations, however, they tend to associate as more complex structures.…”

mentioning

confidence: 87%

“…The surfactant tails form different microdomains, which are sensitive to spectroscopic probes like fluorescence [11] or electron spin resonance probes [13]. The effects of NaCl and NaBr on the uspscan DSC thermograms of 5.0 mM DODABr in aqueous dispersions are shown in Figs.…”

Section: Effects Of Ionic Strength and Counterion On The Thermotropicmentioning

confidence: 99%

The effect of ionic strength on the structural organization of dioctadecyldimethylammonium bromide in aqueous solution

Feitosa¹,

Barreleiro

2004

Surface and Colloid Science

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IntroductionDioctadecyldimethylammonium salts (DODAX, X being usually Br -or Cl -) are long (C 18 ) double chain cationic surfactants which associate in water, above the gel-to-liquid-crystalline phase transition temperature, T m , as bilayer structures (T m =45°C, for DODABr) [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The molecular organization of DODAX depends on the surfactant concentration, the temperature and the solvent condition. Since DODAX molecules are poorly soluble in water at room temperature, energy-input-based methods are required to form high-curvature vesicles. The most common vesicle preparation protocols consist of sonicating [8] or extruding [14] the homogeneous surfactant aqueous dispersion, or dissolving the surfactant in an appropriate organic solvent (e.g., chloroform, dichloromethane or ethanol) and then injecting it in the desired solvent (usually water or electrolytic aqueous solution) above the evaporation temperature of the organic solvent [8]. These protocols usually introduce contaminants in the surfactant dispersion. Exceptions are bath sonication and extrusion since the flask or syringe containing the dispersion may be sealed or isolated, but the loss of surfactant, retained in the extrusion membrane, is a problem to be overcome. Thus, the formation of spontaneous vesicles seems to be the best way to form vesicles with good control of Abstract High-curvature and stabilized vesicles of dioctadecyldimethylammonium bromide (DODABr) can be formed spontaneously in aqueous electrolytic solution. It is shown by cryo-transmission electron microscopy that 5.0 mM DODABr molecules associate in water at a temperature above its gel-to-liquidcrystalline phase transition temperature (T m »45°C) in a variety of complex bilayer structures. However, in the presence of NaCl the preferred structures formed are unilamellar and bilamellar vesicles with high curvature and the dispersion is polydisperse in size and geometry, but the main vesicle population contains spherical, flattened and smoothed structures. It is, however, less polydisperse than the corresponding salt-free dispersion, and the size polydispersity and the vesicle curvature radius tend to decrease with NaCl concentration. Long cylindrical bilamellar vesicles, with a very thin water layer separating the bilayers are also formed in the presence of 10 mM NaCl. The effect of the ionic strength on T m , obtained by differential scanning calorimetry, is shown to depend on the nature of the counterion: Br -decreases, whereas Cl -increases T m of DODABr, indicating different affinity of these counterions for the vesicle surfaces.Progr Colloid Polym Sci (2004) 128: 163-168 DOI 10.1007/b97125 Ó Springer-Verlag 2004 Eloi

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Phase behavior of synthetic amphiphile vesicles investigated by calorimetry and fluorescence methods

Cited by 38 publications

References 10 publications

Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

Supramolecular Structures Generated by a p‐tert‐Butylphenyl‐amide Derivative of Cholic Acid: From Vesicles to Molecular Tubes

The effect of ionic strength on the structural organization of dioctadecyldimethylammonium bromide in aqueous solution

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