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Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures

Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures
Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures
The addition of saturated fatty acids (FA) to phosphatidylcholine lipids (PC) that have saturated acyl chains has been shown to promote the formation of lyotropic liquid-crystalline phases with negative mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic phases (Im3m, Pn3m) or inverse topology hexagonal phases (H-II), depending on the length of the acyl chains/fatty acid. Here we report a detailed study of the phase behavior of binary mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic acid at limiting hydration, constructed using small-angle X-ray diffraction (SAXD) data. The phase diagrams of both systems show a succession of phases with increasing negative mean curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar Fd3m phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We also propose a method that uses the temperature dependence of the lattice parameters of the H-II phases to estimate the spontaneous radii of curvature (R-0) of the binary mixtures and of the component lipids. Using this method, we calculated the R-0 values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive the formation of inverse phases in PL/FA mixtures. These are -1.8 nm (+/-0.4 nm) for DOPC(OA)(2) and -1.1 nm (+/-0.1 nm) for DOPE(OA)(2). R-0 values estimated in this way allow the quantification of the contribution that different lipid species make to membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins.
0743-7463
3337-3344
Gillams, Richard
89341fe4-db94-4d27-a5be-c092e2e8de5b
Nylander, Tommy
18d94ea0-6456-4eaf-b552-844261a37283
Plivelic, Tomás S.
91447a5e-27c6-4f4b-be41-b6adc466884c
Dymond, Marcus K.
e180765b-039e-47ff-9841-ce6a5123a519
Attard, George
3219075d-2364-4f00-aeb9-1d90f8cd0d36
Gillams, Richard
89341fe4-db94-4d27-a5be-c092e2e8de5b
Nylander, Tommy
18d94ea0-6456-4eaf-b552-844261a37283
Plivelic, Tomás S.
91447a5e-27c6-4f4b-be41-b6adc466884c
Dymond, Marcus K.
e180765b-039e-47ff-9841-ce6a5123a519
Attard, George
3219075d-2364-4f00-aeb9-1d90f8cd0d36

Gillams, Richard, Nylander, Tommy, Plivelic, Tomás S., Dymond, Marcus K. and Attard, George (2014) Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures. Langmuir, 30 (12), 3337-3344. (doi:10.1021/la404275u).

Record type: Article

Abstract

The addition of saturated fatty acids (FA) to phosphatidylcholine lipids (PC) that have saturated acyl chains has been shown to promote the formation of lyotropic liquid-crystalline phases with negative mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic phases (Im3m, Pn3m) or inverse topology hexagonal phases (H-II), depending on the length of the acyl chains/fatty acid. Here we report a detailed study of the phase behavior of binary mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic acid at limiting hydration, constructed using small-angle X-ray diffraction (SAXD) data. The phase diagrams of both systems show a succession of phases with increasing negative mean curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar Fd3m phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We also propose a method that uses the temperature dependence of the lattice parameters of the H-II phases to estimate the spontaneous radii of curvature (R-0) of the binary mixtures and of the component lipids. Using this method, we calculated the R-0 values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive the formation of inverse phases in PL/FA mixtures. These are -1.8 nm (+/-0.4 nm) for DOPC(OA)(2) and -1.1 nm (+/-0.1 nm) for DOPE(OA)(2). R-0 values estimated in this way allow the quantification of the contribution that different lipid species make to membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins.

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More information

e-pub ahead of print date: 7 March 2014
Published date: 1 April 2014
Organisations: Electrochemistry

Identifiers

Local EPrints ID: 395444
URI: http://eprints.soton.ac.uk/id/eprint/395444
ISSN: 0743-7463
PURE UUID: 668173b6-80fd-464a-81ca-6a064e7f41d3
ORCID for Richard Gillams: ORCID iD orcid.org/0000-0002-8597-8723
ORCID for George Attard: ORCID iD orcid.org/0000-0001-8304-0742

Catalogue record

Date deposited: 31 May 2016 08:50
Last modified: 29 Oct 2019 02:07

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