Jason Y. C. Lim

Chalcogen Bonding Macrocycles and [2]Rotaxanes for Anion Recognition

Electron-deficient heavy chalcogen atoms contain Lewis acidic σ-holes which are able to form attractive supramolecular interactions, known as chalcogen bonding (ChB), with Lewis bases. However, their potential in solution-phase anion binding applications is only just beginning to be realized in simple acyclic systems. Herein, we explore the 5-(methylchalcogeno)-1,2,3-triazole (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. Other than being chemically robust enough to be incorporated into macrocyclic structures, thereby significantly expanding the scope and complexity of ChB host systems, we also demonstrate, by 1H NMR and DFT calculations, that the chalcogen atoms oriented within the macrocycle cavity are able to chelate copper(I) endotopically. Exploiting this property, the first examples of mechanically interlocked [2]rotaxanes containing ChB-donor groups are prepared via an active metal template strategy. Solution-phase 1H NMR and molecular modeling studies provide compelling evidence for the dominant influence of ChB in anion binding by these interlocked host systems. In addition, unprecedented charge-assisted ChB-mediated anion binding was also studied in aqueous solvent mixtures, which revealed considerable differences in anion recognition behavior in comparison with chalcogen-free host analogues. Moreover, DFT calculations and molecular dynamics simulations in aqueous solvent mixtures indicate that the selectivity is determined by the different hydrophilic characters of the anions allied to the hydration of the binding units in the presence of the anions. Exploiting the NMR-active nuclei of the ChB-donor chalcogen atoms, heteronuclear 77Se and 125Te NMR were used to directly study how anion recognition influences the local electronic environment of the chalcogen atoms in the mechanically bonded rotaxane binding sites in organic and aqueous solvent mixtures.

A pyrrole-containing cleft-type halogen bonding receptor for oxoanion recognition and sensing in aqueous solvent media

The synthesis and anion binding properties of a novel pyrrole-containing dicationic halogen bonding (XB) motif is described. When incorporated into an acyclic cleft-type receptor, rare selectivity for tetrahedral oxoanions (H2PO4− and SO42−) over halides is observed in aqueous solvent media.

Thermodynamics of Anion Binding by Chalcogen Bonding Receptors

The application of chalcogen bonding (ChB) to anion recognition is an underdeveloped area of host-guest supramolecular chemistry. The chemical instability of heavier chalcogen derivatives may in part be responsible for the lack of progress. Herein, the synthesis of a new structurally simple, tellurium-based ChB binding motif is reported, the robust stability of which has enabled the thermodynamic properties for ChB halide anion binding in polar aprotic and wet protic organic solvent media to be elucidated. The thermodynamic data reveals how the subtle interplay between ChB host, anion guest and solvent dictates halide binding selectivity and affinity trends. These findings help to provide a deeper insight into the nature of the ChB-anion interaction.