Effects of the PEG molecular weight of a PEG-lipid and cholesterol on PEG chain flexibility on liposome surfaces

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 474; pp. 63 - 70
• Main Authors: Abe, Kozue, Higashi, Kenjirou, Watabe, Keiko, Kobayashi, Ai, Limwikrant, Waree, Yamamoto, Keiji, Moribe, Kunikazu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.06.2015
• Subjects: Cholesterol; Flexibility; Liposome; NMR; PEG molecular weight; Liposome; NMR; PEG molecular weight; Flexibility; Cholesterol
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2015.03.006

•PEG chains with larger molecular weights on liposome surface were more flexible.•Enhanced lipid lateral diffusion by cholesterol increased PEG chain flexibility.•Uniform distribution of cholesterol in lipid bilayer made PEG chain more flexible. A variable-temperature 1H NMR study was performed to investigate the effects of the molecular weight of poly(ethylene glycol) (PEG) in PEG-lipids and cholesterol addition to the lipid bilayer on PEG chain flexibility at the liposomal surface. PEG-lipids, i.e., l-α-distearoylphosphatidylethanolamine (DSPE)-PEG, with PEG molecular weights of 750, 2000, and 5000 were modified to liposomes of ca. 100nm. The 1H NMR peak of PEG in DSPE-PEG was overlapped by broad and sharp peaks, corresponding to rigid and flexible PEG components, respectively. When the PEG molecular weight was increased, the PEG peak became sharp, indicating that long-chain PEGs were more flexible on the liposome surface. The proportion of flexible components projecting into the water phase increased as the PEG chain length increased. Peak sharpening also occurred when the cholesterol content was increased from 0 to 30mol%, demonstrating that cholesterol incorporation into the lipid bilayer enhanced the PEG chain flexibility. In addition, the PEG chain flexibility significantly increased when cholesterol was delocalized in the lipid bilayer at concentrations above 20mol%. Lateral diffusion of the lipid with the presence of cholesterol in the lipid bilayer significantly affected the PEG chain flexibility.