Differential scanning calorimetry |
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Authors: | A M Samuni D J A Crommelin N J Zuidam Y Barenholz |
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Institution: | (1) Department of Biochemistry, Hebrew University-Hadassah Medical School, P.O. Box 12272, 91120 Jerusalem, Israel;(2) Department of Pharmaceutics, Utrecht University for Pharmaceutical Sciences (UIPS) participant in the research school Groningen — Utrecht Institute for Drug Exploration (GUIDE), Faculty of Pharmacy, Utrecht University, Utrecht, The Netherlands |
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Abstract: | This study was aimed to investigate the physicochemical changes induced in 200 nm extruded oligolamellar DPPC:DPPG (10:1)
liposomes by freezing, followed by γ-irradiation, in the absence and presence of 5 mM stable cyclic nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1-oxyl
(Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol). The characterization is based on the use of differential
scanning calorimetry (DSC) and was aimed to differentiate the contribution of freezing and γ-irradiation in the presence and
absence of nitroxides. Liposomal preparations of DPPC/DPPG which have sub-, pre- and main-phase transitions in the temperature
range (0°C<T
m<50°C) were used.
Our results show that: (1) freezing modified and induced fusion to MLV as well as fission to SUV, (2) freezing did not fully
prevent the radiation-induced changes in the thermotropic characteristics of the liposomes, and (3) Tempo and Tempol did not
prevent the changes in thermotropic behavior caused as a result of freezing of the liposomal dispersion. These results demonstrate
that DSC is a powerful and sensitive tool in both physical and chemical studies of lipid assemblies.
This work was supported in part by the Szold Foundation, Jerusalem, Israel and United State-Israel Binational Science Foundation
(grant 95/318 to Y.B.). |
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Keywords: | DSC γ -irradiation liposomes liposome freezing oxidative damage |
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