Spontaneous vesiculation of uncharged phospholipid dispersions consisting of lecithin and lysolecithin |
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| Authors: | H Hauser |
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| Institution: | 1. Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seo-dae-mun-gu, Seoul 120-749, Republic of Korea;2. College of Life Science and Bioengineering, Incheon National University, Republic of Korea;3. Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea;4. Institute of Pharmaceutical and Medical Chemistry, University of Muenster, Muenster, Germany;1. Department of Genetic Engineering, School of Biotechnology, Madurai Kamaraj University, Madurai 625021, Tamil Nadu, India;2. Centre of Excellence in Bioinformatics, School of Biotechnology, Madurai Kamaraj University, Madurai 625021, Tamilnadu, India;1. Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia;2. Department of Food Science, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia;3. King Saud University, College of Science, Chemistry Department, Riyadh, Saudi Arabia |
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| Abstract: | The work presented here demonstrates that the phenomenon of spontaneous vesiculation is not restricted to charged lipids and lipid mixtures, but occurs also in isoelectric phospholipid mixtures consisting of egg phosphatidylcholine (EPC) and egg lysophosphatidylcholine (lyso-EPC). 1H high-resolution NMR and freeze-fracture electron microscopy have been used to characterize the mixed EPC/lyso EPC dispersions in excess H2O. The predominant phase in these mixed phospholipid dispersions is smectic (lamellar) at least up to approximately 70% lysophosphatidylcholine. The type of phospholipid aggregate formed in excess H2O depends on the mole ratio diacyl to monoacyl phosphatidylcholine. The dispersive (lytic) action of lysophosphatidylcholine on phosphatidylcholine bilayers becomes effective at lysophospholipid contents in excess of approximately 10%. Large multilamellar liposomes are disrupted and replaced by smaller particles, mainly unilamellar vesicles. Between 30 and 70% lysophosphatidylcholine a significant proportion of the total phospholipid is present as small unilamellar vesicles (SUV) of a diameter of 23 nm (range: 20-70 nm). At even higher lysophosphatidylcholine contents the fraction of phospholipid present as small mixed micelles with a diameter smaller than about 14 nm grows at the expense of the vesicular structures. There is a second effect of increasing the quantity of lysophosphatidylcholine in phosphatidylcholine bilayers: the presence of lysophosphatidylcholine in excess of 10% renders the phospholipid bilayer more permeable to ions as compared to pure phosphatidylcholine bilayers. The key factor in inducing spontaneous vesiculation is probably not the charge but the wedge-like shape of the lysophospholipid molecule. The molecular shape may give rise to an asymmetric distribution of lysophosphatidylcholine between the two halves of the bilayer, thus stabilizing highly curved bilayers as present in SUV. |
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