Pseudo[3]rotaxane and [3]Rotaxane of Per(5-carboxy-5-dehydroxymethyl)-Cyclodextrins Utilizing Carboxylic Acid Dimer as Recognition Units

The formation of pseudo[3]rotaxane using dimers of per(5-carboxy-5-dehydroxymethyl)-cyclodextrins as ring components and secondary ammoniums as an axle is presented. This supramolecule is formed by the unique interaction of circularly arranged carboxylic acid dimers acting as hydrogen bonding acceptors covering the axle moiety. On these grounds, we could achieve the synthesis of the [3]rotaxane by capping the terminal groups through thiol-ene reactions.

Amide cyclodextrin that recognises monophosphate anions in harmony with water molecules

Anion recognition in water by synthetic host molecules is a popular and challenging topic. It has been considered difficult because the water molecules compete for the recognition units. In this study, we have successfully created a novel macrocycle that achieves precise recognition through multipoint hydrogen bonding in harmony with water molecules. Specifically, an N-methylpyridinium amide β-cyclodextrin (β-CD) derivative 1(OTf)7 was synthesized, whose amide groups are directly attached to each pyranose ring. The pyridinium amide CD encapsulated a monophosphate anion in water, but it did not show interactions with sulfonates or carboxylates, thus a remarkable selectivity was demonstrated. Two monophosphates with different substituents, phenyl phosphate (PhOPO3 2-) and adamantyl phosphate (AdOPO3 2-), exhibited interesting contrasting pictures in the inclusion process, which were revealed by a combination of NOESY experiments, ITC measurements, and MD simulations. PhOPO3 2- was positioned slightly "upper" (closer to the pyridinium amide side) in 17+ with the oxygen atom of the phosphate ester R-O-P involved in the hydrogen bonds with the amide N-H, and configurational entropy plays a key role in the inclusion. Meanwhile, AdOPO3 2- was positioned "lower" (closer to the methoxy rim of CD) with the terminal -PO3 2- forming hydrogen bonds with the amides, and the hydrophobic effect is a major contributing driving force of the inclusion. The molecular design presented herein to achieve the precise recognition in water and clarification of the detailed mechanisms including the hydration phenomenon greatly contribute to the development of functional molecules that work in aqueous environments.

Formation of a Metallomacrocycle Possessing Nitrogen Donors Assembled in the Cavity and Unique Water Clusters

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

Rotaxane formation by an allosteric pseudomacrocyclic anion receptor utilising kinetically labile copper(i) coordination properties

A pseudomacrocyclic receptor with hydrogen bonding units spontaneously generates a rotaxane with an anionic axle possessing large end groups.