Metalloporphyrin intercalation in liposome membranes: ESR study |
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Authors: | Dariusz Man Rudolf Słota Małgorzata A Broda Giuseppe Mele Jun Li |
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Institution: | 1.Institute of Physics,Opole University,Opole,Poland;2.Faculty of Chemistry,Opole University,Opole,Poland;3.Dipartimento di Ingegneria dell’Innovazione,Università del Salento,Lecce,Italy;4.Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, The College of Chemistry and Materials Science,Northwest University,Xi’an,China |
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Abstract: | Liposomes characterized by membranes featuring diverse fluidity (liquid-crystalline and/or gel phase), prepared from egg yolk
lecithin (EYL) and dipalmitoylphosphatidylcholine (DPPC), were doped with selected metalloporphyrins and the time-related
structural and dynamic changes within the lipid double layer were investigated. Porphyrin complexes of Mg(II), Mn(III), Fe(III),
Co(II), Ni(II), Cu(II), Zn(II), and the metal-free base were embedded into the particular liposome systems and tested for
350 h at 24°C using the electron spin resonance (ESR) spin probe technique. 5-DOXYL, 12-DOXYL, and 16-DOXYL stearic acid methyl
ester spin labels were applied to explore the interior of the lipid bilayer. Only the 16-DOXYL spin probe detected evident
structural changes inside the lipid system due to porphyrin intercalation. Fluidity of the lipid system and the type of the
porphyrin complex introduced significantly affected the intermolecular interactions, which in certain cases may result in
self-assembly of metalloporphyrin molecules within the liposome membrane, reflected in the presence of new lines in the relevant
ESR spectra. The most pronounced time-related effects were demonstrated by the EYL liposomes (liquid-crystalline phase) when
doped with Mg and Co porphyrins, whereas practically no spectral changes were revealed for the metal-free base and both the
Ni and Zn dopants. ESR spectra of the porphyrin-doped gel phase of DPPC liposomes did not show any extra lines; however, they
indicated the formation of a more rigid lipid medium. Electronic configuration of the porphyrin’s metal center appeared crucial
to the degree of molecular reorganization within the phospholipid bilayer system. |
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