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Issue 1, 2013
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Reverse self-assembly of lipid onions induced by gadolinium and calcium ions

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Abstract

Self-assembly of lipids in water is well-known to result in nanostructures such as vesicles in dilute solution. In contrast, self-assembly in nonpolar organic solvents (oils) is much less established and there are hardly any known routes to forming structures such as reverse vesicles. Here, we build such structures based on our surprising recent discovery that salts can influence self-assembly of lipids in oil. We induce the self-assembly of nanoscale multilamellar vesicles (“onions”) in cyclohexane and toluene by combining the saturated phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), with salts of di- or trivalent cations like calcium (Ca2+) or gadolinium (Gd3+) in the absence of water. DMPC–Gd3+ onions can be seen by a transmission electron microscope (TEM) without additional staining. They have sizes between ∼100 and 400 nm and have 6–18 concentric bilayer shells (lamellae) that are uniformly spaced. The presence of lamellae is further confirmed by small-angle X-ray scattering (SAXS), from which we find the inter-lamellar spacing to be 6.0 nm. The formation of reverse onions is driven by the binding of these multivalent cations with the lipid headgroups, which in turn brings adjacent lipids close and causes a tighter packing of the lipid tails. Evidence for such binding is provided by the cation-induced lowering of the lipid melting temperature.

Graphical abstract: Reverse self-assembly of lipid onions induced by gadolinium and calcium ions

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Publication details

The article was received on 05 Jul 2012, accepted on 20 Sep 2012 and first published on 16 Oct 2012


Article type: Paper
DOI: 10.1039/C2SM26565F
Soft Matter, 2013,9, 200-207

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    Reverse self-assembly of lipid onions induced by gadolinium and calcium ions

    H. Lee, K. Hashizaki, K. Diehn and S. R. Raghavan, Soft Matter, 2013, 9, 200
    DOI: 10.1039/C2SM26565F

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