Editorial: Supramolecular Metal-Based Entities for Biomedical and Biological Applications

Fabrication of Host-Guest Complexes between Adamantane-Functionalized 1,3,4-Oxadiazoles and β-Cyclodextrin with Improved Control Efficiency against Intractable Plant Bacterial Diseases

Supramolecular chemistry provides huge potentials and opportunities in agricultural pest management. In an attempt to develop highly bioactive, eco-friendly, and biocompatible supramolecular complexes for managing intractable plant bacterial diseases, herein, a type of interesting adamantane-functionalized 1,3,4-oxadiazole was rationally prepared to facilitate the formation of supramolecular complexes via β-cyclodextrin-adamantane host-guest interactions. Initial antibacterial screening revealed that most of these adamantane-decorated 1,3,4-oxadiazoles were obviously bioactive against three typically destructive phytopathogens. The lowest EC₅₀ values could reach 0.936 (III₁₈), 0.889 (III₁₈), and 2.10 (III₁₉) μg/mL against the corresponding Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa). Next, the representative supramolecular binary complex III₁₈@β-CD (binding mode 1:1) was successfully fabricated and characterized by ¹H nuclear magnetic resonance (NMR), isothermal titration calorimetry (ITC), high-resolution mass spectrometry (HRMS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Eventually, correlative water solubility and foliar surface wettability were significantly improved after the formation of host-guest assemblies. In vivo antibacterial evaluation found that the achieved supramolecular complex could distinctly alleviate the disease symptoms and promote the control efficiencies against rice bacterial blight (from 34.6-35.7% (III₁₈) to 40.3-43.6% (III₁₈@β-CD)) and kiwi canker diseases (from 41.0-42.3% (III₁₈) to 53.9-68.0% (III₁₈@β-CD)) at 200 μg/mL (active ingredient). The current study can provide a feasible platform and insight for constructing biocompatible supramolecular assemblies for managing destructive bacterial infections in agriculture.

Modular synthesis of antimalarial quinoline-based PGM metallarectangles

A new ditopic, quinoline-based ligand L (7-chloro-4-(pyridin-4-yl)quinoline) was synthesized via a Suzuki cross-coupling reaction. The ligand was utilized to synthesize the corresponding half-sandwich iridium(III) and ruthenium(II) binuclear complexes (1c and 1d) and the subsequent metallarectangles (2c, 2d, 3c, and 3d), via [2 + 2] coordination-driven self-assembly. Single-crystal X-ray diffraction confirmed the proposed molecular structure of the binuclear complex [{IrCl₂(Cp*)}₂(μ-L)] (1c) and DFT calculations were used to predict the optimized geometry of the rectangular nature of [{Ir(μ-Cl)(Cp*)}₄(μ-L)₂](CF₃SO₃)₄ (2c). All of the metallarectangles were isolated as their triflate salts and characterized using various spectroscopic (¹H, ¹³C{¹H}, DOSY NMR, and IR spectroscopy) and analytical techniques (ESI-MS). The synthesized compounds were screened against the NF54 chloroquine-sensitive (CQS) and K1 chloroquine-resistant (CQR) strains of Plasmodium falciparum. Incorporation of the ubiquitous quinoline core and metal complexation significantly enhanced the in vitro biological activity, with an increase in the nuclearity correlating with an increase in the resultant antiplasmodial activity. This was observed across both parasitic strains, alluding to the potential of supramolecular metallarectangles to act as antiplasmodial agents. Inhibition of haemozoin formation was considered a potential mechanism of action and selected metallarectangles exhibit β-haematin inhibition activity with near comparable activity to chloroquine.

Covalent Post-Assembly Modification: A Synthetic Multipurpose Tool in Supramolecular Chemistry

The use of covalent post-assembly modification (PAM) in supramolecular chemistry has grown significantly in recent years, to the point where PAM is now a versatile synthesis tool for tuning, modulating, and expanding the functionality of self-assembled complexes and materials. PAM underpins supramolecular template-synthesis strategies, enables modular derivatization of supramolecular assemblies, permits the covalent 'locking' of unstable structures, and can trigger controlled structural transformations between different assembled morphologies. This Review discusses key examples of PAM spanning a range of material classes, including discrete supramolecular complexes, self-assembled soft nanostructures and hierarchically ordered polymeric and framework materials. As such, we hope to highlight how PAM has continued to evolve as a creative and functional addition to the synthetic chemist's toolbox for constructing bespoke self-assembled complexes and materials.