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Spectroscopy
Volume 22, Issue 1, Pages 33-41
http://dx.doi.org/10.3233/SPE-2008-0325

Application of spin markers for study of liposome prepared by the modified reverse-phase evaporation method

Danuta Pentak,1 Wiesław W. Sułkowski,1 Agnieszka Wolińska,1 Sławomir Maślanka,1 Barbara Bojko,2 Małgorzata Maciążek,2 Joanna Równicka,2 and Anna Sułkowska2

1Department of Environmental Chemistry and Technology, Institute of Chemistry, University of Silesia, 40-006 Katowice, Poland
2Department of Physical Pharmacy, Medical University of Silesia, 41-200 Sosnowiec, Poland

Copyright © 2008 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The EPR spectroscopy was used to determine the structure and physicochemical properties of liposomes prepared from L-α-phosphatidylcholine dipalmitoyl (DPPC) by the modified reverse-phase evaporation method (mREV). EPR study was carried out in the temperature range from 297 K to 340 K i.e. below and above the phase transition temperature TC of DPPC. On the basis of EPR spectra of spin marker 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) incorporated into the liposome, the parameter f was determined. TEMPO dissolves easily in water and in the fluid lamellar smectic liquid-crystaline phase of lipid bilayer but is largely excluded from the solid, gel-phase. Thus TEMPO can be used to observe the change in the partition between aqueous and fluid lipid regions. The change in the relative value of f as a function of temperature for DPPC shows that, in the presence of water excess, this phospholipids undergoes a transition from a “gel phase” to a lamellar smectic liquid crystalline phase. On the basis of EPR spectra of spin marker 2-(3carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinloxyl (5-DOXYL) incorporated into liposome, the parameter a'N was determined. The isotropic 14N-hyperfine coupling constant a'N of nitroxide spin label depends on the local environmental polarity. The increase of a'N value reflects the rise of polarity of spin label environment. Temperature, cholesterol and pH dependent structural changes were also described.