Aromatic micelles: toward a third-generation of micelles

Abstract

Micelles are useful and widely applied molecular assemblies, formed from amphiphilic molecules, in water. The majority of amphiphiles possess an alkyl chain as the hydrophobic part. Amphiphiles bearing hydrophilic and hydrophobic polymer chains generate so-called polymeric micelles in water. This review focuses on the recent progress of "aromatic micelles", formed from bent polyaromatic/aromatic amphiphiles, for the development of third-generation micelles. Thanks to multiple host-guest interactions, e.g., the hydrophobic effect and π-π/CH-π interactions, the present micelles display wide-ranging uptake abilities toward various hydrophobic compounds in water. In addition to such host functions, new stimuli-responsive aromatic micelles with pH, light, and redox switches, aromatic oligomer micelles, saccharide-coated aromatic micelles, and related cycloalkane-based micelles were recently developed by our group.

Keywords: aromatic micelle; bent aromatic amphiphile; host-guest interaction; stimuli-responsive; water.

Figure 1.

(Color online) Schematic representation of (a) a conventional micelle and (b) a polymer micelle. (c) Typical amphiphilic molecules and polymers.

Figure 2.

(Color online) (a) Formation of an aromatic micelle from bent aromatic amphiphiles in water. (b) Anthracene-based bent amphiphile AA and its optimized structures (obtained by molecular mechanics (MM) calculation using forcite module, Materials Studio, Dassault Systèmes Co.). (c) Optimized structure of micelle (AA)_n. Modulation of amphiphile AA through (d) functionalization and (e) replacement of the anthracene panels with other panels.

Figure 3.

(Color online) (a) Schematic representation of the incorporation of hydrophobic compounds (e.g., dyes) by aromatic micelle (AA)_n in water. (b) Representative fluorescent dyes, nanocarbons, and (c) metal-complexes incorporated by aromatic micelles.

Figure 4.

(Color online) (a) pH-responsive bent amphiphile AcA and its aromatic micelle with guest releasing ability upon acid addition. (b) Photo-responsive bent amphiphile oAA and the optimized structures (MM calculation) of (c) aromatic micelle (oAA)_n and (d) its host-guest composite including Nile red. (e) Guest releasing ability of micelle (oAA)_n upon light irradiation.

Figure 5.

(Color online) (a) Redox-responsive bent amphiphile PTA and (b) its aromatic micelle capable of reversibly forming a radical micelle upon oxidation.

Figure 6.

(Color online) (a) Formation of an aromatic oligomer micelle from amphiphilic trimers in water. (b) Amphiphilic trimer AT bearing three bent aromatic amphiphiles AA. (c) Formation of host-guest composites from AT and oligothiophenes in water and (d) the optimized structure (MM calculation).

Figure 7.

(Color online) (a) Formation of a saccharide-coated aromatic micelle from bent amphiphiles MA with three mannose groups in water and (b) the optimized structure (MM calculation) of (MA)_n. (c) Fluorescent dyes loaded by the micelle, and the photographs and emission quantum yields of the corresponding host-guest complexes.

Figure 8.

(a) Cyclohexane-based bent amphiphile CHA and the formation of its capsular micelle in water. (b) Multiple uptake of ZnPor by micelle (CHA)_n in water and (c) the optimized structure (MM calculation) of the host-guest composite. (d) Substituent-selective uptake of CuPcX (X = H, F, and Cl).

Figure 9.

(a) Emission properties of trinuclear Au(I)-complex AuPz in solution and in the solid state, and (b) uptake-induced solution-state emission of AuPz by cyclohexane-based micelle (CHA)_n in water and the photograph.

Figure 10.

(Color online) (a) Efficient uptake of metal-organic polyhedra (MOP) by adamantane-based bent amphiphile ADA in water and (b) the optimized structure (MM calculation) of the host-guest composite. (c) Efficient co-uptake of MOP and fluorescent dyes by adamantane-based micelle (ADA)_n in water.