Layered assembly of cationic and anionic supramolecular polymers

Abstract

The chemical synthesis and the supramolecular assembly of an aromatic oligoamine are described. The self-assembly of the cationic oligomers in aqueous solution leads to the formation of vesicular objects. The assembly process of the oligomers is monitored by absorption and fluorescence spectroscopy and the formed vesicles are characterized by atomic force and transmission electron microscopy. The electrostatic complementarity of anionic supramolecular polymers sheets and the cationic vesicles is used for a layered assembly process.

Scheme 1. Synthesis of the 3,6-disubstituted phenanthrene trimer with amine-bridges (N-Phe3).

Fig. 1. UV-vis spectra of N-Phe3 (1 μM) in ethanol (black) and in an aqueous medium (10 mM sodium acetate buffer pH 4.7, containing 10 vol% ethanol) at 75 °C (red) and 15 °C (blue).

Fig. 2. AFM images of self-assembled structures obtained from amine-oligomer N-Phe3 at 1 μM and 10 μM sample concentrations (images A and B, respectively). Conditions: 10 mM sodium acetate buffer (pH 4.7), 10 vol% ethanol.

Fig. 3. Graphical illustration of vesicle formation by N-Phe3. Blue dots indicate amines, red dots hydroxyl groups. A bilayer of trimers has a calculated height of ∼6 nm.

Fig. 4. TEM images of vesicles assembled from N-Phe3 (left: 3 μM; right: 5 μM). Conditions as in Fig. 2.

Fig. 5. Graphical illustration of the electrostatic layered assembly preparation. (A) Py3 self-assembles into negatively charged sheets (blue) and N-Phe3 into positively charged vesicles (grey). (B) First the Py3-sheet (blue) is adsorbed on the substrate (APTES-modified mica, brown), followed by the adsorption of N-Phe3-vesicles (grey).

Fig. 6. Electrostatic assembly starting with Py3 sheets and leading to a two-layered structure. Left: Graphical illustration of layering; middle and right: AFM images and height profiles. Conditions: 1st layer 2 μM Py3, 10 mM sodium phosphate (pH 7.1), 10 mM NaCl and 10 vol% ethanol; 2nd layer 10 μM N-Phe3, 10 mM sodium acetate buffer (pH 4.7) and 10 vol% ethanol.