Tubular and lamellar hydrogen-bonding molecular assemblies of isophthalic acid derivatives bearing a -CONHCnH2 n +1 chain

Abstract

Isophthalic acid derivatives (CnIP), bearing alkylamide chains (-CONHCnH2n+1: n = 6, 10, 14, and 18) at the 5-position that can participate in hydrogen bonding, were prepared and evaluated for their hydrogen-bonding molecular assembly structures for organogelation and liquid crystal formation. The hydrogen-bonding carboxylic acid (-COOH) groups form a ring-shaped (CnIP)6 hexamer or a one-dimensional (1D) zig-zag (CnIP)∞ chain. Although neither organogelation nor liquid crystal formation was observed in the isophthalic acid derivative bearing an alkoxy (-OC14H29) chain, C14IP and C18IP derivatives could form both organogel and liquid crystal states through intermolecular N-H⋯O = amide-type hydrogen-bonding interactions. A discotic hexagonal columnar liquid crystal (Colh) phase was observed in hydrated (C14IP)6·(H2O)n and (C18IP)6·(H2O)n, whereas a lamella-type liquid crystal (La) phase was confirmed in the unhydrated C18IP. In the Colh phase, O-H⋯O hydrogen-bonding ring-shaped (C14IP)6 and (C18IP)6 hexamers assembled to form the tubular molecular assembly stabilized by intermolecular-N-H⋯O = hydrogen-bonding interactions along the tube growth direction, where H2O molecules were contained within the hydrophilic space. On the other hand, the N-H⋯O = hydrogen-bonding interactions between the 1D zig-zag (CnIP)∞ chains formed a layer-type molecular assembly of the La-phase in the absence of water molecules.