Hydroxy-Substituted Azacalix[4]Pyridines: Synthesis, Structure, and Construction of Functional Architectures

A number of hydroxyl-substituted azacalix[4]pyridines were synthesized using Pd-catalyzed macrocyclic "2+2" and "3+1" coupling methods and the protection-deprotection strategy of hydroxyl group. While the conformation of the these hydroxyl-substituted azacalix[4]pyridines is fluxional in solution, in the solid state, they adopted shape-persistent 1,3-alternate conformations. Besides, X-ray analysis revealed that the existence of hydroxy groups on the para-position of pyridine facilitated the formation of solvent-bridged intermolecular hydrogen bonding for mono-hydroxyl-substituted while partial tautomerization for four-hydroxyl-substituted macrocycles, respectively. Taking the hydroxyl-substituted azacalix[4]pyridines as molecular platforms, multi-macrocycle-containing architectures and functional building blocks were constructed. The self-assembly behavior of the resulting building blocks was investigated in crystalline state.

Anion Transporters Based on Noncovalent Balance including Anion-π, Hydrogen, and Halogen Bonding

Anion transmembrane transport mediated by novel noncovalent interactions is of central interest in supramolecular chemistry. In this work, a series of oxacalix[2]arene[2]triazine-derived transporters 1 and 2 bearing anion-π-, hydrogen-, and halogen-bonding sites in rational proximity were designed and synthesized by a one-pot strategy starting from gallic acid ester derivatives and mono- or di-halogen-substituted triazines. ¹H NMR titrations demonstrated efficient binding of 1 and 2 toward Cl^- and Br^- in solution, giving association constants in the range of 10²-10⁴ M^-1. Cooperation of anion-π, hydrogen, and halogen bonding was revealed as a driving force for anion binding by single-crystal structures of two complexes and density functional theory calculations. Fluorescence assays indicated that compounds 1 are efficient chloride transporters with effective concentrations (EC₅₀) falling in the range of 3.1-7.4 μM and following an order of 1a > 1b > 1c > 1d. The contribution of halogen bonding and cooperative noncovalent bonds to ion transport was then discussed. Significantly, transporters 1 exhibit high anticancer activity. In the presence of 1 and KCl (60 mM), the cell survival of HCT116 reduces to 11.9-24.9% with IC₅₀ values in the range of 52.3-66.4 μM.

Oxacalix[2]arene[2]triazine based ion-pair transporters

Heteracalixaromatics are a new generation of macrocyclic hosts showing a unique structure and versatile recognition properties towards various guests.

2,14-Dithiacalix[4]arene and its homooxa analogues: synthesis and dynamic NMR study of conformational behaviour

Novel homooxa analogues of thiacalix[4]arene possessing up to three different bridging units (–CH₂–, –S– and –CH₂–O–CH₂–) were prepared. The unique structural features allowed for the study offlip-flopmotion of the circular hydrogen bond arrays.

Ultra-sensitive ROS-responsive tellurium-containing polymers

Tellurium-containing polymer micelles are responsive to 100 μM H₂O₂ or 2 Gy gamma radiation, enabling the development of ultra-sensitive ROS-eliminating materials.

Arylpyrrole oligomers as tunable anion receptors

A novel class of oligomeric arylpyrrole receptors has been designed, prepared and analysed for their affinity towards anionic guests.