Pathway-Dependent Phase Transitions of Supramolecular Self-assemblies Containing Cationic Amphiphiles with Azobenzene and Disulfide Groups.

There have been several attempts to construct supramolecular chemical systems that mimic the phase transitions in living systems. However, most of these phase transitions are one-to-one and induced by one stimulus or chemical; there have been few reports on the pathway-dependent phase transition of supramolecular self-assemblies in multi-step. To induce multistep phase transitions, molecular crystals were prepared that contained a cationic amphiphile bearing azobenzene and disulfide groups. A reducing agent caused the crystals to become vesicles, and adjacent, non-touching vesicles fused under UV and subsequent visible light. Adding a reducing agent to the worm-like aggregates that were generated after UV irradiation of the original crystals resulted in the growth of sheet-like aggregates. 1 H NMR and fluorescence anisotropy measurements showed that a series of phase transitions was induced by changes in the phase structures from molecular conversions of the reactive amphiphiles. The multiple pathway-dependent phase transitions of supramolecular self-assemblies can provide a methodology for developing new stimuli-responsive materials that exhibit the desirable properties under specific circumstances from a systems chemistry viewpoint.

Construction of Supramolecular Systems That Achieve Lifelike Functions.

The Nobel Prize in Chemistry was awarded in 1987 and 2016 for research in supramolecular chemistry on the "development and use of molecules with structure-specific interactions of high selectivity" and the "design and production of molecular machines", respectively. This confirmed the explosive development of supramolecular chemistry. In addition, attempts have been made in systems chemistry to embody the complex functions of living organisms as artificial non-equilibrium chemical systems, which have not received much attention in supramolecular chemistry. In this review, we explain recent developments in supramolecular chemistry through four categories: stimuli-responsiveness, time evolution, dissipative self-assembly, and hierarchical expression of functions. We discuss the development of non-equilibrium supramolecular systems, including the use of molecules with precisely designed properties, to achieve functions found in life as a hierarchical chemical system.

pH-Tolerant giant vesicles composed of cationic lipids with imine linkages and oleic acids.

Giant vesicles (GVs) have attracted attention as functional materials because they can encapsulate both hydrophilic and hydrophobic compounds. For next generation functional GVs, both tolerance and stimuli-sensitivity are needed. So far, vesicles tolerant to acidic or basic conditions were generated using a mixture of cationic lipids and fatty acids. Here, to create functional GVs that are tolerant to a wide pH range but sensitively respond at below a specific pH, the behaviour of GVs composed of a cationic lipid with an imine bond and oleic acid was investigated. Even though the GVs prepared by the film swelling method were tolerant to strongly acidic conditions, GVs without oleic acid gradually shrank, accompanied by the generation of oil droplets at the same pH. 1H NMR analysis revealed that during hydration of the film, the imine bond hydrolysed to provide a cationic surfactant and an oil component in the presence of oleic acid due to its own Lewis basicity, suggesting the dissociation of oleic acid. The results of fluorescence spectroscopy using an environment-responsive probe and IR spectroscopy indicated that the GV tolerance originated from the intermolecular interactions of cationic lipids and anionic oleate.