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Crystal structures of two vancomycin complexes with phosphate and N-acetyl–d-Ala (AcDA) were determined. Each complex involves two crystallographically independent vancomycin molecules (V1 and V2) in the asymmetric unit, which form a usually observed back-to-back arranged vancomycin dimer V1–V2 with two disaccharide chains packed in a head-to-head manner, but only one of the two ligand-binding sites is occupied. Comparison of the published crystal structures of low-affinity (small in molecular size) ligand complexes of vancomycin with high-affinity (large) ligand complexes reveals that when the high-affinity ligand binds, three structural factors (hydrogen-bonding interactions between the two peptide-backbones and hydrophobic intra-dimer sugar–ring and ring (face)–ring (edge) interactions) work to enhance the stabilization of the back-to-back dimer-interface, an important factor that is believed to promote antibacterial activity. It has also been revealed, by examining the high-affinity ligand complexes (including N-acetyl–d-Ala–d-Ala), that sugar–ligand interaction could cause different affinities of the two halves of the dimer; this is a factor responsible for the failure of the ligand binding to V1 in the AcDA complex. Possible scenarios for the formation of vancomycin complexes with low-affinity as well as high-affinity ligands are presented.

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The movement of supramolecular self-assemblies has been induced by the application of external stimuli that cause a shift to non-equilibrium conditions. However, few supramolecular chemical systems exist in which multiple different functions are associated with movement. Herein, we observed multiple phase transition of micrometer-sized lauronitrile oil droplets in a solution of cationic surfactants with aniline skeletons in the presence of metal ions. These dynamics include tactic motion and subsequent formation of aggregates with membrane structures, in a linear-type channel. These dynamic behaviors result from variations in the interfacial tension at the droplet surface and the chemical compositions owing to the interactions between system components. The current findings may provide a methodology for designing molecular systems in which multi-step phase transitions of supramolecular selfassemblies are coupled to movement in non-equilibrium conditions.