title: Lipid chain length effect on the phase behaviour of PCs/PEG:2000-PEs mixtures. A spin label electron spin resonance and spectrophotometric study.
abstract: Spin-label electron spin resonance (ESR) spectroscopy and spectrophotometry at fixed wavelength are used to study fully hydrated aqueous dispersions of phosphatidylcholines (PCs) with poly(ethylene glycol:2000)-phosphatidylethanolamines (PEG:2000-PEs). PEG:2000-PE is a micelle-forming polymer-lipid that is extensively used for increasing the lifetime of PC liposomes in the blood circulation through a steric stabilisation effect. The PC lipids and the PEG:2000-PE polymer-lipids have the same acyl chain length of either dimiristoyl (DM) or distearoyl (DS) chains. DMPC/PEG:2000-DMPE and DSPC/PEG:2000-DSPE mixtures were investigated over the entire range of relative compositions (0-100 mol%). In both dispersions, the low-temperature conventional spin label ESR spectra and the temperature dependence of the absorbance at 400 nm give an indication of the conversion from lamellae to micelles with increasing PEG:2000-PEs content. The physical state of the lipid assemblies, lamellar or micellar, is dependent not only on PEG:2000-PEs content, but also on the length of hydrocarbon chain of the lipid matrix. Micellisation is attained more readily in dispersions with longer hydrocarbon chains (i.e. in DSPC/PEG:2000-DSPE mixtures) than in those with shorter acyl chains (i.e. in DMPC/PEG:2000-DMPE mixtures). Saturation transfer ESR (ST-ESR) and absorbance measurements reflect the disaggregation of the bilayers and a reduction in the size of the lipid aggregates by PEG:2000-PEs at low content.
authors.affiliation: Dipartimento di Fisica and Unità INFM, Università della Calabria, Ponte P. Bucci, Cubo 31 C, I-87030 Arcavacata di (CS), Rende, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Belsito
authors.forename: R
authors.initials: R
authors.lastname: Bartucci
authors.forename: L
authors.initials: L
authors.lastname: Sportelli
mesh_terms: D004355:Drug Stability; D004578:Electron Spin Resonance Spectroscopy; D008081:Liposomes; D008823:Micelles; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D011092:Polyethylene Glycols / Q000737:chemistry* / Q000378:metabolism; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D008081:Liposomes; D008823:Micelles; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D011092:Polyethylene Glycols