Air/Water Interfacial Monolayer Assembly of Peptide-Conjugated Liquid-Crystalline Molecules

Abstract

Abstract Potential applications of functional liquid crystals such as biosensors strongly rely on control of the molecular orientation at interfaces. However, little knowledge regarding detailed molecular arrangements at such interfaces is available. In this work, two-dimensional self-assembling behavior at air/water interfaces of two types of amphiphilic mesogens with different peptide chains, arginine-glycine-aspartic acid and glycine-glycine-aspartic acid is investigated. Surface pressure–mean molecular area isotherms indicate that both bioconjugated mesogens are in the liquid expanded state to high surface compression conditions. The monolayer thickness of 16–19 Å derived by atomic force microscopic images is much smaller than the molecular length of ∼50 Å of a completely stretched motif. This implies that the bioconjugated molecules align in an inflected manner where tetraethylene glycol connecting hydrophobic rigid-rod and hydrophilic peptides is the inflection point. Contact angles of water for substrate surface with monolayers remarkably change depending on the surface pressure at the substrate transfer. This can be explained by the varied molecular arrangements with surface compression at the air/water interfaces. Understanding of molecular orientation at air/water interfaces is of fundamental importance for study of the ordering of liquid crystals at various other interfaces, leading to the design and further development of functional liquid-crystalline molecules for attractive sensor platforms.