Effects of phosphonium-based ionic liquids on phospholipid membranes studied by small-angle X-ray scattering.
The effects of ionic liquids on model phospholipid membranes were studied by small-angle X-ray scattering, dynamic light scattering (DLS) and zeta potential measurements. Multilamellar 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes and large unilamellar vesicles composed of l-α-phosphatidylcholine (eggPC) and l-α-phosphatidylglycerol (eggPG) (80:20mol%) or eggPC, eggPG, and cholesterol (60:20:20mol%) were used as biomimicking membrane models. The effects of the phosphonium-based ionic liquids: tributylmethylphosphonium acetate, trioctylmethylphosphonium acetate, tributyl(tetradecyl)-phosphonium acetate, and tributyl(tetradecyl)-phosphonium chloride, were compared to those of 1-ethyl-3-methyl-imidazolium acetate. With multilamellar vesicles, the ionic liquids that did not disrupt liposomes decreased the lamellar spacing as a function of concentration. The magnitude of the effect depended on concentration for all studied ionic liquids. Using large unilamellar vesicles, first a slight decrease in the vesicle size, then aggregation of vesicles was observed by DLS for increasing ionic liquid concentrations. At concentrations just below those that caused aggregation of liposomes, large unilamellar vesicles were coated by ionic liquid cations, evidenced by a change in their zeta potential. The ability of phosphonium-based ionic liquids to affect liposomes is related to the length of the hydrocarbon chains in the cation. Generally, the ability of ionic liquids to disrupt liposomes goes hand in hand with inducing disorder in the phospholipid membrane. However, trioctylmethylphosphonium acetate selectively extracted and induced a well-ordered lamellar structure in phospholipids from disrupted cholesterol-containing large unilamellar vesicles. This kind of effect was not seen with any other combination of ionic liquids and liposomes.
Department of Physics, University of Helsinki, P.O.B. 64, 00014 Helsinki, Finland. Electronic address: inkeri.kontro@helsinki.fi.
Inkeri
I
Kontro
Department of Physics, University of Helsinki, P.O.B. 64, 00014 Helsinki, Finland.
Kirsi
K
Svedström
Department of Chemistry, University of Helsinki, P.O.B. 55, 00014 Helsinki, Finland; Institute of Analytical Chemistry of the CAS, v. v. i., Brno, Czechia.
Filip
F
Duša
Department of Physics, University of Helsinki, P.O.B. 64, 00014 Helsinki, Finland.
Patrik
P
Ahvenainen
Department of Chemistry, University of Helsinki, P.O.B. 55, 00014 Helsinki, Finland.
Suvi-Katriina
SK
Ruokonen
Department of Chemistry, University of Helsinki, P.O.B. 55, 00014 Helsinki, Finland.
Joanna
J
Witos
Department of Chemistry, University of Helsinki, P.O.B. 55, 00014 Helsinki, Finland.
Susanne K
SK
Wiedmer
D002784:Cholesterol / Q000737:chemistry; D000067493:Dynamic Light Scattering; D052578:Ionic Liquids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D053838:Scattering, Small Angle; D053835:Unilamellar Liposomes / Q000737:chemistry; D014961:X-Ray Diffraction
D052578:Ionic Liquids; D008081:Liposomes; D009943:Organophosphorus Compounds; D010743:Phospholipids; D053835:Unilamellar Liposomes; D002784:Cholesterol
Dynamic light scattering; Ionic liquids; Liposomes; Saxs