Volumetric Studies Of Lecithin-Water Dispersions
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Date
2007-03
Authors
Yeap, Pei Koon
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Abstract
Volumetric studies of lecithin-water dispersions were carried out. A literature
review of liposomes and their applications in various areas of science and medicine
was presented to illustrate the importance of research studies on liposomes. The main
objectives of this present study are to determine accurately the density of the lecithin
dispersions and the density of the lecithin in the dispersions, as well as to elucidate the
molecular packing structure of the liposomes in the lecithin dispersions. To achieve this
aim, sizes of liposomes were estimated via turbidity measurements, while the density of
the lecithin dispersions were determined accurately over a temperature range from 25
°C to 55°C using a digital density meter. Further studies on the effects of ions were
similarly investigated. The estimation of the liposome sizes in different lecithin
dispersions supported the observation that prolonged sonication typically produced
small unilamellar liposomes. The density of the lecithin in the dispersions was
calculated and the value was found to be comparable to the value in the dry state
(1.056 g cm-\ Nevertheless, the value was found to be slightly higher for dispersions
with higher concentrations of lecithin. This observation was further confirmed by the
calculated values of the effective molecular volume of lecithin, which were smaller for
higher concentrations of lecithin in the dispersions. Temperature dependence studies
of density demonstrated the presence of a thermotropic phase transition at about 40°C
to 45 DC. With the addition of Ca2+ ions or Na+ ions to the lecithin dispersions, the
density of the lecithin dispersions and the density of the lecithin in the dispersions
increased. However, the effective molecular volume of lecithin in the dispersions
decreased. The above effects were more pronounced with the addition of Ca2+ ions
compared to the addition of Na+ ions, thus probably indicating that Ca2+ ions pack the
lecithin molecules in the dispersions even tighter when compared to that of Na+ ions.
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Keywords
To determine accurately the density of the lecithin dispersions , and the density of the lecithin in the dispersions