Assembly of Acidic Amphiphiles into Inverted Hexagonal Phases Using an l-Alanine-Based Surfactant as a Structure-Directing Agent

Abstract

Several taper-shaped, Brønsted acidic amphiphiles containing an amide linkage near the headgroup were synthesized with the goal of generating acidic, inverted hexagonal (HII) lyotropic liquid crystal (LLC) phases that can be stabilized by polymerization. These polymerizable acidic amphiphiles were synthesized by reacting the acyl chloride of 3,4,5-tris(11‘-acryloxyundecyloxy)benzoic acid with several amino acids (l-alanine, β-alanine, l-phenylalanine) and 2-aminoethanesulfonic acid. Of these derivatives, only the l-alanine derivative (1) was found to form the HII phase, using N,N-dimethylformamide as the hydrophilic solvent. To our knowledge, this is one of the rare examples (if not the only example) of a Brønsted acidic amphiphile capable of forming a high-curvature LLC phase. Monomer 1 was also found to be able to direct the formation of the other amide-containing acidic derivatives into the HII phase when blended together. IR analysis revealed that intermolecular amide H-bonding near the headgroup plays a major role in the LLC assembly and structure-directing behavior of these systems.

Recent Advances in the Design of Polymerizable Lyotropic Liquid‐Crystal Assemblies for Heterogeneous Catalysis and Selective Separations

“…4a) was designed and synthesized. [38] Monomer 1 was chosen as the starting point for a sulfonic acid derivative because 1 contains acrylate groups which are not susceptible to acid-catalyzed cationic polymerization, as opposed to the styryl groups on 2 and 3. [39] Unfortunately, it was found that 4 does not form a well-defined H II with water or dimethyl formamide (DMF), but rather a mixture of L and H II phases (Fig.…”

“…4a). [38] We rationalized that extensive hydrogen bonding (H-bonding) of the sulfonic acid headgroup with surrounding water molecules increases the effective size of the hydrophilic headgroup, thereby perturbing the taper shape needed to form H II phases. Alternatively, the presence of the unsubstituted flexible ethyl tether may also have been detrimental to forming the desired taper shape required for H IIphase formation.…”

“…4b) forms a well-defined H II phase, even though 5 contains a poor self-ionizing headgroup (COOH), and the parent carboxylic acid of 1 does not show any LLC behavior. [38] Powder X-ray diffraction (XRD) showed that a mixture of L-alanine derivative 5 with 12 wt.-% DMF exhibits a d-spacing pattern characteristic of an H II phase (1:1/ 3 p :1/ 7 p ..., with the 1/ 4 p peak systematically absent). This XRD pattern is retained even after photopolymerization (Fig.…”

“…[38] Given the structural similarity of 4 and 5, we envisioned that it might be possible to blend the two monomers and use 5 to direct the LLC-phase formation of 4 via amide H-bonding. Using 5 as a "structure-directing agent", we managed to template mixtures of 4 and 5 into a well-defined H II phase with ratios of up to 5:1 (mol/mol), respectively, without observable phase separation (Fig.…”

The Equilibrium of Phosphatidylcholine–Amino Acid System in Monolayer at the Air/water Interface

“…Interesting study on aggregation properties of amino acid amphiphiles has been reported by Huang and co-workers [9]. Acidic amphiphiles based on L-alanine surfactant with specific structuredirecting properties have been explored by Gin and co-workers [10]. New materials such as gel emulsions from these amphiphiles for specific applications have been achieved [11].…”