title: Structural characterization of diC14-amidine, a pH-sensitive cationic lipid used for transfection.
abstract: The structure of N-t-butyl-N'-tetradecyl-3-tetradecylaminopropionamidine (diC(14)-amidine) cationic vesicles, used for transfection, was investigated at different pH values and ionic strengths, through the analysis of the electron spin resonance (ESR) spectra of spin labels. Phospholipid derivatives, spin labeled at the 5th and 16th C-atoms along the hydrocarbon chain, incorporated in diC(14)-amidine bilayers, show that the bilayer structure is highly sensitive to the pH value of the medium, due to the two titratable groups present in the amphiphile. Compared with samples at higher pH values, the double charged diC(14)-amidine at pH 3 presents a rather non-organized bilayer gel phase, and a much lower gel-fluid temperature transition, in accord with a strong headgroup electrostatic repulsion. In addition, the structure was found to be highly dependent on the ionic strength of the medium. However, pH 3 diC(14)-amidine bilayer, in the fluid phase, was found to be slightly more closely packed than those at pH 7.4 or 9.0, which are less charged. Parallel to that, the larger isotropic hyperfine splitting measured for nitroxides in the center of the pH 3 diC(14)-amidine bilayer suggests a higher membrane polarity for the highly charged low pH sample.
authors.affiliation: Instituto de Física, Universidade de S. Paulo, CP 66318, CEP 05315-970, S. Paulo, SP, Brazil.
authors.forename: Carlos R
authors.initials: CR
authors.lastname: Benatti
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Ruysschaert
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Lamy
mesh_terms: D000578:Amidines / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*; D009994:Osmolar Concentration; D044367:Phase Transition; D013113:Spin Labels; D014162:Transfection
chemical_list: D000578:Amidines; D002247:Carbon Isotopes; D008051:Lipid Bilayers; D008081:Liposomes; C089665:N-t-butyl-n'-tetradecyl-3-tetradecylaminopropionamidine; D013113:Spin Labels