Self-assembly of regular hollow icosahedra in salt-free catanionic solutions

Abstract

Self-assembled structures having a regular hollow icosahedral form (such as those observed for proteins of virus capsids) can occur as a result of biomineralization processes, but are extremely rare in mineral crystallites. Compact icosahedra made from a boron oxide have been reported, but equivalent structures made of synthetic organic components such as surfactants have not hitherto been observed. It is, however, well known that lipids, as well as mixtures of anionic and cationic single chain surfactants, can readily form bilayers that can adopt a variety of distinct geometric forms: they can fold into soft vesicles or random bilayers (the so-called sponge phase) or form ordered stacks of flat or undulating membranes. Here we show that in salt-free mixtures of anionic and cationic surfactants, such bilayers can self-assemble into hollow aggregates with a regular icosahedral shape. These aggregates are stabilized by the presence of pores located at the vertices of the icosahedra. The resulting structures have a size of about one micrometre and mass of about 1010 daltons, making them larger than any known icosahedral protein assembly or virus capsid. We expect the combination of wall rigidity and holes at vertices of these icosahedral aggregates to be of practical value for controlled drug or DNA release.

Responsive self-assemblies based on fatty acids

“…When the catanionic surfactant is in slight excess, corresponding to intermediate pH values, nanodiscs are formed and the excess of cationic surfactants forms their edges [20]. When the fatty acid is in excess, the pH decreases and facetted vesicles and icosahedra are obtained due to the segregation of the excess of fatty acid molecules [21].…”

“…When 1/2<p<1, bilayers or vesicles are obtained. The nature of the fatty acid and the approach used to disperse it lead to various values of p giving a large variety of fatty acid self-assemblies in aqueous dilute medium (>90 wt.% water) from usual self-assembled morphologies (spherical micelles, worm-like micelles, vesicle and bilayer) to unusual morphologies such as tubes [19], nanodiscs [20], icosahedra [21], buckled membranes [22] or cones [23].…”

Vesicle Origami and the Influence of Cholesterol on Lipid Packing

“…The lipid concentration in the DSC suspensions was determined using a microwave-based phosphate assay. 16 Samples were degassed for at least 30 min prior to DSC scans using a TA degassing station. Scans were run at 0.5°C/min from 5 to 60°C.…”

“…12,13 We give experimental details on d-form vesicles and a triangular vesicular structure that previously was only alluded to on a much larger scale in a review 14 and has been proposed on the basis of computational studies. 15 Together with icosahedral catanionic vesicles 16 and block copolymer cubes, 17 selfassembly vesicle origami comes of age.…”

Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

“…Above the transition temperature, T m , the amphiphile has fluid disordered alkyl chains and vesicles typically exhibit spheroidal shape. Below this temperature, upon crystallization of the chains and the curvature constraints imposed by it, nonspheroidal aggregates can be formed [24][25][26][27][28] (e.g., disks, planar bilayer fragments, lens-shaped vesicles, regular polygon-shaped vesicles, and irregularly faceted vesicles), while reheating restores the spheroidal shape. In two-component catanionic vesicles, segregation has been shown to occur in the frozen state and be responsible for the observed polygonal-shaped vesicles.…”