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Structure of vesicles formed from non-ionic dialkylglycerol poly(oxyethylene) ether surfactants: effect of electrolyte and cholesterol
Five non-ionic dialkylglycerol poly(oxyethylene) ether surfactants, designated 2C m E n (where m, the number of carbons in each alkyl chain = 16 or 18, and n, the number of oxyethylene units = 12, 16 or 17) have been examined for their ability to form vesicles when dispersed in water or in an aqueou...
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Published in: | Chemistry and physics of lipids 2011-07, Vol.164 (5), p.341-350 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Online Access: | Get full text |
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Summary: | Five non-ionic dialkylglycerol poly(oxyethylene) ether surfactants, designated 2C
m
E
n
(where
m, the number of carbons in each alkyl chain
=
16 or 18, and
n, the number of oxyethylene units
=
12, 16 or 17) have been examined for their ability to form vesicles when dispersed in water or in an aqueous solution of 154
mM NaCl, alone or in the presence of 50
mol% cholesterol. Freeze fracture electron microscopy and light scattering showed that regardless of the hydrating fluid, all the non-ionic surfactants, with the exception of 2C
16E
17 and 2C
18E
17, formed vesicles in the absence of cholesterol – 2C
16E
17 and 2C
18E
17 instead formed micellar aggregates. All surfactants, however, formed vesicles in the presence of 50
mol% cholesterol. Small angle neutron scattering studies of the surfactant vesicles enabled the bilayer thickness and repeat distance (
d-spacing) to be determined. The bilayers formed by all the non-ionic surfactants in the absence of cholesterol were surprisingly thin (∼50
Å for the E
12 containing surfactants and ∼64
Å for 2C
18E
16) most likely due to the intrusion of oxyethylene groups into the hydrophobic core of the bilayers. In contrast, however, the non-ionic surfactants exhibited a relatively large
d-spacing of around ∼130–150
Å. The addition of 50
mol% cholesterol had a dramatic effect on the thickness of the vesicle bilayer, increasing its size by 10–20
Å, most probably because of an extrusion of oxyethylene from the hydrophobic region of the bilayer and/or a reduction in the tilt on the surfactant alkyl chains. Additionally the presence of cholesterol in a vesicle tended to reduce slightly both the
d-spacing and the thickness of the water layer separating the bilayers. The presence of NaCl, even at the low concentrations used in the study, did affect the properties of the bilayer such that it reduced the
d-spacing and, in the case of cholesterol-containing systems, also reduced bilayer thickness. |
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ISSN: | 0009-3084 1873-2941 |
DOI: | 10.1016/j.chemphyslip.2011.03.007 |