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1.
Chem Phys Lipids ; 145(2): 63-71, 2007 Feb.
Article En | MEDLINE | ID: mdl-17118350

Small unilamellar liposomes were made of dipalmitoyl-phosphatidylcholine and dioleoyl-phosphatidylcholine, and photosensitized by a symmetrically or an asymmetrically substituted glycosilated tetraphenyl-porphyrin derivative. As differential scanning calorimetry and electron paramagnetic resonance spectroscopy (EPR) revealed these porphyrin derivatives were localized in different depth within the lipid bilayer. Both porphyrin derivatives were able to induce photoreaction and consequent structural changes in the membrane. 5-, 12-, or 16-doxyl stearic acid labeled lipid bilayers were applied and the efficiency of photoinduced reaction was followed by the decay of their EPR signal amplitude. Light dose-dependent destruction of nitroxide radical proved to be dependent on the position of spin label. In this process the porphyrin localized in closer connection with the double bond of unsaturated fatty acid was more effective. EPR signal decay was also dependent on the unsaturated fatty acid content of the liposome and the oxygen saturation of the solvent.


1,2-Dipalmitoylphosphatidylcholine/chemistry , Galactosides/chemistry , Glucosides/chemistry , Lipid Bilayers/chemistry , Liposomes/chemistry , Phosphatidylcholines/chemistry , Photosensitizing Agents/chemistry , Porphyrins/chemistry , Calorimetry, Differential Scanning , Cyclic N-Oxides , Electron Spin Resonance Spectroscopy , Light , Membrane Fluidity , Spin Labels
2.
J Photochem Photobiol B ; 79(2): 83-8, 2005 May 13.
Article En | MEDLINE | ID: mdl-15878112

The effect of the symmetry and polarity of the porphyrin molecules on their membrane localization and interaction with membrane lipids were investigated by electron paramagnetic resonance (EPR). For this purpose, two glycoconjugated tetraphenyl porphyrin derivatives were selected, respectively, symmetrically and asymmetrically substituted. Small unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and spin labeled stearic acids were prepared. The spin probe was located at the 5th or 7th or 12th or 16th position of the hydrocarbon chain in order to monitor various regions of the lipid bilayer. EPR spectra of porphyrin-free and porphyrin-bound liposomes were recorded at various temperatures below and above the phase transition temperature of DPPC. The effect on membrane fluidity proved to be stronger with the asymmetrical porphyrin derivative than with the symmetrical one. The rigidity increased when the spin label was near lipid head groups. The difference observed between control and porphyrin-treated samples when measured below the main lipid transition temperature disappeared at higher temperature. When the spin label was near the end of the hydrophobic tails, the symmetrical porphyrin derivative caused increase in fluidity, while the asymmetrical one slightly decreased it. To explain this phenomenon we propose that the asymmetrical derivative exerts a stronger ordering effect caused by its fluorophenyl group located at the level of the lipid heads, which is attenuated to the hydrophobic tails. The perturbing effect of the symmetric derivative could not lead to similar extent of ordering at the head groups and looses the hydrocarbon chains deeper in the membrane.


1,2-Dipalmitoylphosphatidylcholine/chemistry , Liposomes/chemistry , Porphyrins/chemistry , Electron Spin Resonance Spectroscopy , Glycosylation , Molecular Structure , Phase Transition , Temperature
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