Catanionic Tubules with Tunable Charge

Abstract

The three-dimensional structures with nanoscopic dimensions that are yielded by the self-assembly of lipids and surfactants are of particular interest for their applications in nanotechnology. In these applications, the possibility of controlling the charge of the particles allows the regulation of fundamental aspects, such as the ability of the particles to load molecules (drugs, DNA, proteins, etc.), to aggregate, and to penetrate membranes. Within the possible surfactant supramolecular architectures, tubular structures have recently drawn much research interest.[1] The main reason is that micro-and nanoscopic tubules have many interesting potential applications in nanotechnology, involving for example catalysis, selective separations, [2] sensors, electronic, electrochemical, and field emission devices, [3] tissue engineering, [4] and preparations of template nanostructured materials [5] or of prospective nanoscopic networks.[6] Because of this interest, several families of compounds have been studied that selfassemble in tubules, [7] for example phospholipids, [8] glycolipids, [9] peptides, [5,10] polymers, [11] bile salts, [12] and rationally designed amphiphiles.[13]Herein, we report on the preparation of tubules in aqueous solutions of mixed cationic and anionic amphiphiles, whose compositions and charges can be tuned by controlling the stoichiometry of the mixtures. In particular, it was found that a very dilute mixture of anionic (ACD) and cationic (CCD) derivatives of the bile salt sodium cholate (Scheme 1) forms tubules over the whole range of the investigated anionic/cationic surfactant molar ratio. An interval within this wide range was found in which variation of the tubule composition and charge occurs.Mixtures of anionic and cationic surfactants in water have been extensively investigated for many years; [14] however, the behavior described herein has never been observed. Commonly, in conditions similar to those adopted in this work, domains of cationic and anionic rich vesicles and micelles can be recognized in the phase diagram of these systems. Twophase regions and precipitates around the equimolar composition are observed as well. [15] Details of the syntheses of ACD and CCD are given in the Supporting Information. Two sets of mixtures of ACD and CCD were prepared with total surfactant concentrations (c T ) of 0.80 and 0.40 mm, as reported in the Experimental Section. In view of the thermal stability of the previously studied pure ACD tubules, [16] the samples were measured at 40 8C. The mixture composition is reported as molar fraction of each surfactant defined as X i = n i /n tot (where n i and n tot are the number of moles of the component i (CCD or ACD) and of the total surfactant, respectively).The 0.4 and 0.8 mm solutions of neat ACD and CCD are transparent ( Figure S1 in the Supporting Information). Transmission electron microscopy (TEM) images of these samples did not show any aggregate structure even after aging (3 months). Moreover, critical aggregation concentrations of around 0.4 ...

Sphere–Tubule Superstructures through Supramolecular and Supracolloidal Assembly Pathways

“…Hereby, we present an alternative route to create different hybrid superstructures, combining both supramolecular and supracolloidal assembly pathways. In a stepwise approach, rationally designed bile salt derivative amphiphilic molecules were in a first step used to form tubular supramolecular aggregates . A controlled supracolloidal assembly of these aggregates was induced in a second step by exploiting the interactions with spherical microgels used as linkers.…”

Wormlike reverse micelles in lecithin/bile salt/water mixtures in oil

“…The tubes have cross section diameters spanning a wide range of values (3-450 nm) [9,19,[27][28][29][30][31][32][33][34] and sometimes they form through appealing pH [35,36] or temperature responsive aggregations [37]. Mixed tubes with tunable composition and related features such as charge [38] and sizes [39] can sometimes be prepared. The unconventional amphiphilic molecular structure of BSs dictates also remarkable abilities as carriers across tissues and membranes of many compounds (e.g.…”

Crystal Structure of a Cationic Bile Salt Derivative ([3β,5β,7α,12α]-3-(2-naphthyloylamino)-7,12-dihydroxycholan-24-triethylammonium iodide)

“…The functionality of bile acids allows the synthesis of several cationic derivatives [5][6][7]. Many of them form gels [8][9][10] and also show a similar ability for the solubilization of cholesterol as that of natural bile salts [10].…”