Site-Selective Binding of Peripheral Chiral Guests Induces Stereospecificity in A₄L₆ Tetrahedral Anion Cages

Abstract

Herein we report an unprecedented chiral induction of anion-coordination-driven tetrahedra (A4L6-type) by peripheral guests, S-, R-α-methylcholine and S-, R-β-methylcholine, which are bound along the tetrahedral edges in a highly site-specific fashion. This “peripheral templation”, which has proven indispensable for the formation of tetrahedral structure, is also an effective approach to encoding chiral information to the tetrahedron. Moreover, the site-selective binding of chiral choline derivatives to the anion cage with induced one-handedness may imply applications of such metal-free, labile systems in the study of biological processes such as selective recognition of structurally similar molecules.

Outside the box: quantifying interactions of anions with the exterior surface of a cationic coordination cage

“…13 Raymond and co-workers have shown how the interaction of tetraphenyborate with a cage exterior surface was driven by quite different thermodynamic effects than binding in the central cavity; 14 and Wu's group have shown how hydrogen-bonded cages, formed using urea / phosphate interactions instead of metal/ligand dative bonds, can be switched between different structural types based on interaction of the cage surfaces with counter-ions of different size and shape. 15 Interaction of solvent molecules and counter-ions with the exterior surfaces of a pair of isostructural tetrahehedral cages bearing different charges has recently been studied in detail by Stelson and co-workers. 16 Overall, the importance of interactions of the exterior surface of cages with species in the surrounding medium is becoming more appreciated as being as important as the more obvious interactions associated with cavity-bound guests -a particular focus of host-guest chemistry that has been with us since the first complexes of crown ethers with alkali metal ions.…”

Acid‐Tolerant Sulfate Tetrahedral Cages from Anion‐Coordination‐Driven Assembly

“…The number of H‐bonds for oxygen atoms is between 2 and 4, and each sulfate ion is coordinated by 11 or 12 H‐bonds. In particular, the isolation of complexes 3 a and 3 a’ reveals the significant role of “peripheral templates” in stabilizing the tetrahedral structure [3g,14] . The H‐bonding of sulfate in all these complexes (av.…”

“…Such metal‐free, multiple hydrogen‐bonded systems can be readily assembled and disassembled under mild conditions and be directly monitored by NMR spectroscopy. They exhibit flexible interactions that lead to adaptive guest binding, and the nonspherical shape of some anions (e. g., PO 4 3− ) allows specific asymmetry in the assemblies [3g,h] …”

Combining a Titanium–Organic Cage and a Hydrogen‐Bonded Organic Cage for Highly Effective Third‐Order Nonlinear Optics

“…Among them, M 4 L 6 ‐ and M 4 L 4 ‐type tetrahedral cages have been intensely investigated because they are relatively easy to prepare and display interesting host–guest properties [10–17] . As another new type of supramolecular ensemble, hydrogen‐bonded organic cages (HOCs) have only emerged very recently [18–22] . So far only several tetrahedral HOCs have been reported by Wu et al [20–22] .…”

“…[10][11][12][13][14][15][16][17] As another new type of supramolecular ensemble, hydrogenbonded organic cages (HOCs) have only emerged very recently. [18][19][20][21][22] So far only several tetrahedral HOCs have been reported by Wu et al [20][21][22] What is more, the cooperative self-assembly of MOCs and HOCs into mixed co-crystal system has never been explored.…”