Selective Complexation and Transport of Europium Ions at the Interface of Vesicles

Abstract

The aim of the present work was to design functionalized lipidic membranes that can selectively interact with lanthanide ions at the interface and to exploit the interaction between membranes induced by this molecular-recognition process with a view to building up self-assembled vesicles or controlling the permeability of the membrane to lanthanide ions. Amphiphilic molecules bearing a beta-diketone unit as head group were synthesized and incorporated into phospholipidic vesicles. Binding of Eu(III) ions to the amphiphilic ligand can lead to formation of a complex involving ligands of the same vesicle membrane (intravesicular complex) or of two different vesicles (intervesicular complex). The effect of Eu(III) ions on vesicle behavior was studied by complementary techniques such as fluorimetry, light scattering, and electron microscopy. The formation of an intravesicular luminescent Eu/beta-diketone ligand (1/2) complex was demonstrated. The linear increase in the binding constant with increasing concentration of ligands in the membrane revealed a cooperative effect of the ligands distributed in the vesicle membrane. The luminescence of this complex can be exploited to monitor the kinetics of complexation at the interface of the vesicles, as well as ion transport across the membrane. By encapsulation of 2,6-dipicolinic acid (DPA) as a competing ligand which forms a luminescent Eu/DPA complex, the kinetics of ion transport across the membrane could be followed. These functional vesicles were shown to be an efficient system for the selective transport of Eu(III) ions across a membrane with assistance by beta-diketone ligands.

Janus dendrimersomes coassembled from fluorinated, hydrogenated, and hybrid Janus dendrimers as models for cell fusion and fission

“…Both processes, which are involved in cell uptake, secretion, communication, and division for instance, are vital for the survival and proliferation of cells and are driven by various proteins (31)(32)(33). Synthetic models of vesicle fusion have been reported previously in giant liposome and polymeric vesicle systems, often with the aid of various ligands and ions replicating the roles of proteins in biological systems (34)(35)(36)(37)(38)(39). Additionally, vesicle fusion has been modeled with computer simulations for both unilamellar and multilamellar vesicles (40)(41)(42)(43)(44).…”

Time scales of membrane fusion revealed by direct imaging of vesicle fusion with high temporal resolution

“…In the first fusion protocol, we used giant unilamellar vesicles made of conventional lipidegg phosphatidylcholine (egg-PC) or lecithin. We functionalized these egg-PC vesicles by incorporating lipid-like molecules with ␤-diketone ''head groups'' (28). A micropipette was used to inject a solution of EuCl 3 locally over a population of vesicles or directly into the area of contact between two giant vesicles that were trapped and displaced by two additional micropipettes (see Fig.…”

“…When injected over vesicles in contact, EuCl 3 induced adhesion. In addition, Eu 3ϩ is known to form a coordination complex with ␤-diketone groups in a 1:2 ion-to-ligand ratio (28). When the complex of one europium ion and two or more ligands is formed between two adjacent membranes, fusion is triggered (a possible mechanism for this interaction on the molecular level is shown in Fig.…”

“…29. The membranes used for micropipette manipulation contained a small fraction (Յ0.5 mol%) of amphiphilic ␤-diketone ligands (28). The vesicles were swelled in 0.2 M sucrose and subsequently diluted 40 times into 0.2 M glucose solution (some of the vesicle samples used for electrofusion were diluted in glucose solutions containing NaCl).…”

“…Recently, the action of fusion proteins has been mimicked by synthetic ligand molecules that are connected to lipid-like membrane anchors (18,27). In the present study, we used amphiphilic ligands with a ␤-diketone head group that can be cross-linked by Eu 3ϩ ions (28).…”