title: Calorimetry and cryo-transmission electron microscopic studies of PEG2000-grafted liposomes.
abstract: The phase behavior of poly(ethylene glycol) grafted liposomes (PEG-liposomes) was investigated by differential scanning calorimetry (DSC), dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM). PEG-liposomes were prepared from mixtures of dipalmitoyl phosphatidylcholine (DPPC) and distearoyl phosphatidylethanolamine with a covalently attached PEG molecular weight of 2000 (DSPE-PEG2000). From the results of DLS measurements, the coexistence of PEG-liposomes and small molecular assemblies were confirmed at mole fractions of DSPE-PEG2000 above about 0.1. Moreover, it was confirmed that small molecular assemblies were disk micelles by cryo-TEM. However, the phase transition enthalpies of PEG-liposomes were hardly changed according to the DSC measurement, though the mole fraction of the PEG lipid increased. From these results, it was suggested that the phase transition enthalpies hardly changed despite mixed micelles being formed because the bilayer structure of the disk micelle maintains high cooperativity between the DPPC molecules.
authors.affiliation: College of Pharmacy, Nihon University, Chiba, Japan. khashiza@pha.nihon-u.ac.jp
authors.forename: Kaname
authors.initials: K
authors.lastname: Hashizaki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Taguchi
authors.forename: Koji
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Saito
authors.forename: Naotake
authors.initials: N
authors.lastname: Ogawa
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D002151:Calorimetry / Q000379:methods; D008081:Liposomes / Q000737:chemistry*; D008823:Micelles; D008854:Microscopy, Electron / Q000379:methods; D008970:Molecular Weight; D044367:Phase Transition; D010714:Phosphatidylethanolamines / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D008081:Liposomes; D008823:Micelles; D010714:Phosphatidylethanolamines; C038089:1,2-distearoylphosphatidylethanolamine; D015060:1,2-Dipalmitoylphosphatidylcholine; D011092:Polyethylene Glycols