title: Vesicle formation by L-cysteine-derived unconventional single-tailed amphiphiles in water: a fluorescence, microscopy, and calorimetric investigation.
abstract: Two new L-cysteine-derived zwitterionic amphiphiles with poly(ethylene glycol) methyl ether (mPEG) tail of different chain lengths were synthesized and their surface activity and self-assembly properties were investigated. In aqueous phosphate buffered solution of pH 7.0, the amphiphiles were observed to form stable unilamellar vesicles, the bilayer membrane of which is constituted by the mPEG chains. The vesicle phase was characterized by a number of methods including fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The thermodynamics of self-assembly was also studied by isothermal titration calorimetry through measurements of the standard Gibbs free energy change (ΔG°m), standard enthalpy change (ΔH°m) and standard entropy change (ΔS°m) of micellization. The self-assembly process was found to be entropy-driven, which implies that the mPEG chain behaves like a hydrocarbon tail of conventional surfactants. The effects of pH, temperature, salt, and aging time on the bilayer stability were also investigated. Encapsulation and pH-triggered release of model hydrophobic and hydrophilic drugs is demonstrated.
authors.affiliation: Department of Chemistry, Indian Institute of Technology , Kharagpur 721 302, India.
authors.forename: Rita
authors.initials: R
authors.lastname: Ghosh
authors.forename: Joykrishna
authors.initials: J
authors.lastname: Dey
mesh_terms: D002151:Calorimetry; D003545:Cysteine / Q000737:chemistry*; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D008027:Light; D046529:Microscopy, Electron, Transmission; D015394:Molecular Structure; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D013499:Surface Properties; D013501:Surface-Active Agents / Q000138:chemical synthesis* / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D013501:Surface-Active Agents; D014867:Water; D011092:Polyethylene Glycols; D003545:Cysteine