Visualization and Quantification of Transmembrane Ion Transport into Giant Unilamellar Vesicles

Abstract

Transmembrane ion transporters (ionophores) are widely investigated as supramolecular agents with potential for biological activity. Tests are usually performed in synthetic membranes that are assembled into large unilamellar vesicles (LUVs). However transport must be followed through bulk properties of the vesicle suspension, because LUVs are too small for individual study. An alternative approach is described whereby ion transport can be revealed and quantified through direct observation. The method employs giant unilamellar vesicles (GUVs), which are 20-60 mm in diameter and readily imaged by light microscopy. This allows characterization of individual GUVs containing transporter molecules, followed by studies of transport through fluorescence emission from encapsulated indicators. The method provides new levels of certainty and relevance, given that the GUVs are similar in size to living cells. It has been demonstrated using a highly active anion carrier, and should aid the development of compounds for treating channelopathies such as cystic fibrosis.

Diphenylethylenediamine-Based Potent Anionophores: Transmembrane Chloride Ion Transport and Apoptosis Inducing Activities

“…Thioureas are also good hydrogen bond donor for Cl − ions and have lower pK a values of the N−H protons. 30 To have strong regulation capability over the localized concentration and suitable positioning of the lipophilic ion-recognition moieties, preorganized scaffolds such as cholapods, diureidodecalins, tris(aminomethyl)benzene, and others have been employed as synthetic Cl − ion transporters. 22,24,31−33 The presence of these preorganized scaffolds enhances the anion transport efficiency of these thiourea derivatives by many-fold because of its fixed binding site to form stable complex and lowering of ΔG value of the ion binding process.…”

Fluorescence quenching in β-cyclodextrin vesicles: membrane confinement and host-guest interactions

“…Vesicles are widely used as models for biological membranes. 8,9 Vesicles can encapsulate water-soluble molecules in the aqueous interior and incorporate hydrophobic molecules into the bilayer membrane. Synthetic amphiphiles used to form vesicles can additionally include a binding motif which selectively binds complementary molecules.…”

Droplet-Templated Synthetic Cells

“…There has been a vast amount of studies of the fabrication of vesicles through assembly of amphiphilic lipids, polymers, peptides, and dendrimers. [52][53][54][55][56][57] The resultant vesicles, polymersomes, peptosomes, and dendrimersomes open the path from compartmentalized reactors to synthetic cells. It is worth noting that for artificially assembled lipid vesicles to better mimic the cellular membrane, the lipid bilayer asymmetry (i.e., the difference in the lipid composition between the inner and outer monolayers) and the associated physical properties should be considered.…”