title: Effect of cholesterol on distribution of stable, hydrophobic perchlorotriphenylmethyl triethylester radical incorporated in lecithin liposomal membranes.
abstract: Perchlorotriphenylmethyl triethylester radical (PTM-TE) is a hydrophobic, stable radical giving a narrow singlet ESR signal with a small satellite signal for (13)C in organic solvents. In order to use PTM-TE as a label of liposomal membranes, its manner of incorporation into liposomal membranes was studied. Two components, broad and narrow signals, were observed on the ESR spectrum of PTM-TE incorporated into liposomal membranes composed of egg yolk phosphatidylcholine (egg-PC). The broad signal was increased by the presence of cholesterol in the membranes. The spectral anisotropy of the broad signal was very small as analyzed with oriented planar multilamellar membranes. The narrow signal increased with an increase in temperature in the absence of cholesterol, whereas only a small increase in the signal was observed in the presence of cholesterol. The g-value and line width of the narrow signal were very close to those of PTM-TE in mineral oil, whose viscosity is close to the microviscosity in the hydrophobic region of egg-PC membranes. On the other hand, the g-value and line width of the broad signal were close to those of solid PTM-TE. These observations indicate that the broad signal observed in liposomes originates from PTM-TE clusters in the membranes. The clusters were dissolved in egg-PC membranes at a PTM-TE/egg-PC molar ratio of less than 0.017. However, the clusters were hardly dissolved in the presence of cholesterol.
authors.affiliation: Laboratory of Analytical Chemistry, Faculty of Pharmaceutical Sciences, Sojo University, Kumamoto, Japan. keizo@ph.sojo-u.ac.jp
authors.forename: Keizo
authors.initials: K
authors.lastname: Takeshita
authors.forename: Shoko
authors.initials: S
authors.lastname: Okazaki
authors.forename: Hisao
authors.initials: H
authors.lastname: Kansui
mesh_terms: D002250:Carbon Radioisotopes / Q000737:chemistry; D002784:Cholesterol / Q000737:chemistry / Q000494:pharmacology*; D016503:Drug Delivery Systems / Q000379:methods*; D004530:Egg Yolk / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004952:Esters / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D054709:Lecithins / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism*; D008567:Membranes, Artificial; D010472:Perchlorates / Q000737:chemistry; D014320:Triphenylmethyl Compounds / Q000737:chemistry
chemical_list: D002250:Carbon Radioisotopes; D004952:Esters; D005609:Free Radicals; D006843:Hydrocarbons, Chlorinated; D054709:Lecithins; D008081:Liposomes; D008567:Membranes, Artificial; D010472:Perchlorates; D014320:Triphenylmethyl Compounds; C560278:perchlorotriphenylmethyl triethylester radical; D002784:Cholesterol