Photo-Controlled Reversible Uptake and Release of a Modified Sulfamethoxazole Antibiotic Drug from a Pillar[5]arene Cross-Linked Gelatin Hydrogel.

Pillararene cross-linked gelatin hydrogels were designed and synthesized to control the uptake and release of antibiotics using light. A suite of characterization techniques ranging from spectroscopy (FT-IR, 1H and 13C NMR, and MAS NMR), X-ray crystallographic analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) was employed to investigate the physicochemical properties of hydrogels. The azobenzene-modified sulfamethoxazole (Azo-SMX) antibiotic was noncovalently incorporated into the hydrogel via supramolecular host-guest interactions to afford the A-hydrogel. While in its ground state, the Azo-SMX guest has a trans configuration structure and forms a thermodynamically stable inclusion complex with the pillar[5]arene motif in the hydrogel matrix. When the A-hydrogel was exposed to 365 nm UV light, Azo-SMX underwent a photoisomerization reaction. This changed the structure of Azo-SMX from trans to cis, and the material was released into the environment. The Azo-SMX released from the hydrogel was effective against both Gram-positive and Gram-negative bacteria. Importantly, the A-hydrogel exhibited a striking difference in antibacterial activity when applied to bacterial colonies in the presence and absence of UV light, highlighting the switchable antibacterial activity of A-hydrogel aided by light. In addition, all hydrogels containing pillar[5]arenes have demonstrated biocompatibility and effectiveness as scaffolds for biological and medical purposes.

Switchable Metal-Ion Selectivity in Sulfur-Functionalised Pillar[5]arenes and Their Host-Guest Complexes.

Nucleophilic substitution of pertosylated pillar[5]arene (P-OTs) with commercially available sulfur containing nucleophiles (KSCN, KSAc, and thiophenol), yields a series of sulfur-functionalised pillar[5]arenes. DLS results and SEM images imply that these pillararene macrocycles self-assemble in acetonitrile solution, while X-ray crystallographic evidence suggests solvent-dependent assembly in the solid state. The nature of the sulfur substituents decorating the rim of the pillararene controls binding affinities towards organic guest encapsulations within the cavity and dictates metal-ion binding properties through the formation of favorable S-M2+ coordination bonds outside the cavity, as determined by 1 H NMR and fluorescence spectroscopic experiments. Addition of a dinitrile guest containing a bis-triazole benzene spacer (btn) induced formation of pseudorotaxane host-guest complexes. Fluorescence emission signals from these discrete macrocycles were significantly attenuated in the presence of either Hg2+ or Cu2+ in solution. Analogous titrations utilizing the corresponding pseudorotaxanes alter the binding selectivity and improve fluorescence sensing sensitivity. In addition, preliminary liquid-liquid extraction studies indicate that the macrocycles facilitate the transfer of Cu2+ from the aqueous to the organic phase in comparison to extraction without pillar[5]arene ligands.

Neutral isocyanide-templated assembly of pillar[5]arene [2] and [3]pseudorotaxanes.

Unprecedented pillar[5]arene-isocyanide pseudorotaxane complexes are reported. Extensive 1H-NMR experiments reveal remarkably strong binding affinities of alkyl diisocyanide guests (Ka > 105 M-1 in CDCl3) by pillar[5]arenes. Characterised by multinuclear 1H and 13C-NMR spectroscopy and single-crystal X-ray diffraction, it is demonstrated that pillar[5]arenes are capable of encapsulating a series of alkyl diisocyanides wherein either [2]- or [3]pseudorotaxanes can be formed by varying the alkyl chain length. Moreover, electron-deficient aryl isocyanides, are demonstrated to form inclusion complexes within the cavities of pillar[5]arenes stabilised by multiple C-H⋯π interactions.

Selective Extraction, Recovery, and Sensing of Hydroquinone Mediated by a Supramolecular Pillar[5]quinone Quinhydrone Charge-Transfer Complex.

Intermolecular interactions between an electron-rich aromatic hydroquinone (HQ) with its electron deficient counterpart, benzoquinone (BQ), result in the formation of a quinhydrone charge-transfer complex. Herein, we report a novel quinhydrone-type complex between pillar[5]quinone (P[5]Q) and HQ. Characterized by a suite of spectroscopic techniques including 1H NMR, UV-visible, and FTIR together with PXRD, SEM, BET, CV, and DFT modeling studies, the stability of the complex is determined to be due to an electron-proton transfer reaction coupled with a complementary donor-acceptor interaction. The selectivity of P[5]Q toward HQ over other dihydroxybenzene isomers allows for not only the naked-eye detection of HQ but also its selective liquid-liquid extraction and recovery from aqueous media.

Charge neutral halogen bonding tetradentate-iodotriazole macrocycles capable of anion recognition and sensing in highly competitive aqueous media.

A series of neutral tetradentate halogen bonding (XB) macrocycles, comprising of two bis-iodotriazole XB donors were synthesised in 60-70% yields via a stepwise CuAAC-mediated cyclisation strategy. Extensive 1H NMR anion titration experiments reveal halide binding affinities are critically dependent on the substitution pattern of the xylyl spacer unit. The meta-substituted macrocycle remarkably displays cooperative tetradentate XB-halide anion recognition in highly competitive 40% aqueous-organic D2O/acetone-d6 (40 : 60, v/v) solvent mixtures. Integration of para-xylyl and naphthyl spacer units generates extended macrocyclic cavities, capable of selective oxalate recognition. Furthermore, preliminary fluorescence exeperiments reveal dicarboxylate specific sensing can be achieved through monitoring of the naphthylene centred emission.

Pertosylated pillar[5]arene: self-template assisted synthesis and supramolecular polymer formation.

A facile synthesis of decatosylate pillar[5]arene 1 is reported in excellent yield (>70%). The high yield is attributed to a self-template effect of the pendant tosylate arms. The X-ray crystal structure shows the formation of a linear supramolecular polymer, stabilised by intermolecular pillar[5]arene-tosylate inclusion complexes. These polymeric arrays persist in solution and form rod-like microfibril nanostructures evidenced by SEM.