Unusual phosphatidylcholine lipid phase behavior in the ionic liquid ethylammonium nitrate

Livia Salvati Manni; Caitlin Davies; Kathleen Wood; Salvatore Assenza; Rob Atkin; Gregory G Warr

doi:10.1016/j.jcis.2023.03.161

Unusual phosphatidylcholine lipid phase behavior in the ionic liquid ethylammonium nitrate

J Colloid Interface Sci. 2023 Aug:643:276-281. doi: 10.1016/j.jcis.2023.03.161. Epub 2023 Apr 5.

Authors

Livia Salvati Manni¹, Caitlin Davies², Kathleen Wood³, Salvatore Assenza⁴, Rob Atkin⁵, Gregory G Warr⁶

Affiliations

¹ School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia; School of Environmental and Life Sciences, University of Newcastle, Callaghan 2308, NSW, Australia.
² School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia.
³ Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organization, New Illawarra Road, Lucas Heights, NSW 2234, Australia.
⁴ Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain; Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain; Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Madrid, Spain.
⁵ School of Molecular Sciences, The University of Western Australia, Perth, WA 6009, Australia.
⁶ School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia. Electronic address: gregory.warr@sydney.edu.au.

PMID: 37068361
DOI: 10.1016/j.jcis.2023.03.161

Abstract

Hypothesis: The forces that govern lipid self-assembly ionic liquids are similar to water, but their different balance can result in unexpected behaviour.

Experiments: The self-assembly behaviour and phase equilibria of two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), in the most common protic ionic liquid, ethylammonium nitrate (EAN) have been investigated as function of composition and temperature by small- and wide-angle X-ray scattering (SAXS/WAXS) and small-angle neutron scattering (SANS).

Findings: Both lipids form unusual self-assembly structures and show complex and unexpected phase behaviour unlike that seen in water; DSPC undergoes a gel L_β to crystalline L_c phase transition on warming, while POPC forms worm-like micelles L₁ upon dilution. This surprising phase behaviour is attributed to the large size of the EAN ions that solvate the lipid headgroup compared to water changing amphiphile packing. Weaker H-bonding between EAN and lipid headgroups also contributes. These results provide new insight for the design of lipid based nanostructured materials in ionic liquids with atypical properties.

Keywords: Ionic liquids; LIPID self-assembly; Phospholipids; Small angle X-ray scattering; Small angle neutron scattering.