title: Relationship between the mobility of phosphocholine headgroups of liposomes and the hydrophobicity at the membrane interface: a characterization with spectrophotometric measurements.
abstract: In this study, we investigated the dynamics of a membrane interface of liposomes prepared by eight zwitterionic phosphatidylcholines in terms of their headgroup mobility, with spectroscopic methods such as dielectric dispersion analysis (DDA), fluorescence spectroscopy. The DDA measurement is based on the response of the permanent dipole moment to a driving electric field and could give the information on the axial rotational Brownian motion of a headgroup with the permanent dipole moment. This motion depended on kinds of phospholipids, the diameter of the liposomes, and the temperature. The activation energy required to overcome the intermolecular force between headgroups of phospholipids depended on the strength of the interaction between headgroups such as hydrogen bonds and/or dipole-dipole interaction. Hydration at the phosphorous group of phospholipid and the molecular order of lipid membrane impaired the interaction between headgroups. Furthermore, the hydrophobicity of membrane surface increased parallel to the increase in headgroup mobility. It is, therefore, concluded that hydration of headgroup promoted its mobility to make the membrane surface hydrophobic. The lipid membrane in liquid crystalline phase or the lipid membrane with the larger curvature was more hydrophobic.
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Shimanouchi
authors.forename: Masashi
authors.initials: M
authors.lastname: Sasaki
authors.forename: Azusa
authors.initials: A
authors.lastname: Hiroiwa
authors.forename: Noriko
authors.initials: N
authors.lastname: Yoshimoto
authors.forename: Kazuya
authors.initials: K
authors.lastname: Miyagawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Umakoshi
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Kuboi
mesh_terms: D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry*; D008567:Membranes, Artificial; D010713:Phosphatidylcholines / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D008081:Liposomes; D008567:Membranes, Artificial; D010713:Phosphatidylcholines