Cooperative Self-Assembly at Interfaces and its Impact on Long Range Molecular Orientation

The prominence of molecular self-assembly in chemical and biochemical processes related to sensing, electro-optical applications, and cellular mechanisms motivates fundamental studies of self-assembly processes. Here, we study how biomolecules and organic compounds interact at interfaces to cooperatively self-assemble into organized structures. In particular we are interested in understanding how liquid crystals (LCs), capable of forming anisotropic phases, behave under varying interfacial conditions. First, we systematically decreased the monolayer coverage of long chain alkylsilanes to study the interplay between surface energy and hydrocarbon chain density. Next, we studied the molecular mechanisms of how nucleic acids influenced interfacial molecular orientation at surfactant laden aqueous/LC interfaces. These studies motivated subsequent exploration of how bio-molecular interactions involving aptamers might induce LC reorientations. Finally, we explored ways to use receptor-mediated liposome fusion to induce LC reorientations at the aqueous/LC interface. The findings presented here elucidate the molecular mechanisms that dictate LC reorientations capable of signal transduction in molecular sensing. For example, studies at the solid/LC and aqueous/LC interface revealed that a relatively low sub-monolayer coverage (~11%) of long alkyl chains can induce homeotropic alignment of calamitic LCs. Furthermore, when hydrophobic polyanions adsorb to aqueous/LC interfaces with an alkyl chain coverage close to this threshold, a LC reorientation to a planar/tilted LC alignment occurred. Experiments revealed that the interaction between exposed hydrophobic moieties and the LC were of critical importance toward inducing this LC reorientation. Furthermore, when specific binding events (i.e. DNA hybridization, aptamer-ligand binding) were used to modulate the hydrophobic exposure of biomolecules at LC interfaces, the LC alignment was correlated with the hydrophobic exposure. Finally, we designed and characterized aqueous/LC interfaces that inhibited the spontaneous fusion of liposomes and the non-specific adsorption of macromolecular proteins, enabling receptor-mediated (i.e. DNA hybridization) liposome fusion. These studies advance the understanding of molecular mechanisms that dictate LC alignment and provide examples of how liquid crystal reorientations can be exploited for molecular bio-sensing. Thus we have used a range of organic and bio-molecular species to gain a better understanding of the self-assembly processes that dictate LC alignment at solid/LC and aqueous/LC interfaces