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.

Enhanced anion recognition by ammonium [2]catenane functionalisation of a halogen bonding acyclic receptor.

Ammonium-dibenzo[24]crown-8 [2]catenane functionalisation of a 3,5-bis-iodotriazole-pyridine motif produces a potent halogen bonding (XB) receptor capable of binding anions in aqueous-acetone solvent mixtures of up to 20% water. Exploiting the kinetically inert nature of the mechanically bonded cationic ammonium [2]catenane substituents, the XB receptor is demonstrated to exhibit superior anion recognition behaviour in comparison to labile sodium cation complexed bis-benzo[15]crown-5 XB and HB triazole-pyridine heteroditopic receptor analogues.

Supramolecular self-assembled polymeric nanospheres based on hydrazino naphthalimide functionalised pillar[5]arene for long chain aldehyde detection.

A novel fluorescent sensor HNP5A is constructed consisting of bis-hydrazine naphthalimide decorated pillar[5]arene. Interestingly, this sensor possessed the potential for sensitive and selective detection of long-chain aldehydes, particularly nonanal (C9), and subsequently formed supramolecular pseudorotaxane polymeric nanoparticles inducing a strong fluorescence enhancement. In addition, this as-produced HNP5A⊂C9 exhibited an unexpected reduction of Ag+ to produce AgNPs in an aqueous system and the resulting AgNPs-HNP5A⊂C9 demonstrated a significant fluorescence enhancement under metal-enhanced fluorescence (MEF) behaviour.

Exploitations of Schiff's test and iodoform test for an effective quality assessment of alcohol-based hand sanitizers.

In the period of the corona virus disease 2019 (COVID-19) outbreak, an alcohol-based hand sanitizer is one of the most in-demand products for disinfection purposes. Two major concerns are adulteration of methanol, which causes toxicity to human health, and the concentration of legal alcohol in hand sanitizers due to their effect on antivirus. In this work, the first report of the entire quality assessment of alcohol-based hand sanitizers in terms of detection of methanol adulteration and quantification of ethanol is presented. Detection of adulterated methanol is carried out based on Schiff's reagent after the oxidation of methanol to formaldehyde, giving a bluish-purple solution to detect at 591 nm. In cases where a colorless solution is observed, an iodoform reaction with turbidimetric detection is then performed for quantitative analysis of legal alcohol (ethanol or isopropanol). To comply with the regulation of quality assessment of alcohol-based hand sanitizers, a regulation chart with four safety zones is also presented, employing a combination of two developed tests. The coordinates of a point (x, y) obtained from the two tests are extrapolated to the safety zone in the regulation chart. The regulation chart also showed consistency of analytical results as compared with the gas chromatography-flame ionization detector.

A microplate spectrophotometric method for analysis of indole-3-carbinol in dietary supplements using p-dimethylaminocinnamaldehyde (DMACA) as a chromogenic reagent.

This work presents the development of a microplate spectrophotometric method for determination of indole-3-carbinol in dietary supplements. The colorimetric procedure is based on the reaction of indole-3-carbinol with the p-dimethylaminocinnamaldehyde (DMACA) reagent under acidic conditions. The absorbance of the colored product measured at 675 nm was used to determine the target analyte. To achieve optimal spectrophotometric performance, the DMACA reagent concentration, the hydrochloric acid concentration, and the reaction time were optimized. The developed technique performed well under the optimal conditions, with a linear calibration range of 30 to 300 mg L-1 and a high correlation coefficient (r2 = 0.9954). The limit of detection and limit of quantification were 7.8 mg L-1 and 26.2 mg L-1, respectively. This approach demonstrated good repeatability (intra- and inter-day precision) with a % RSD lower than 9.4%, good accuracy with acceptable relative recoveries in the range of 98 to 106%, and high sample throughput (24 detection per min). This simple, rapid, and multi-sample analysis approach for routine analysis of indole-3-carbinol has the potential to be used for the quality control of dietary supplements.

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.

Chalcogen Bonding Ion-Pair Cryptand Host Discrimination of Potassium Halide Salts.

A series of chalcogen, halogen and hydrogen bonding heteroditopic macrobicyclic cryptands are reported and their potassium halide ion-pair recognition properties investigated. Saliently, the co-bound potassium cation was determined to be crucial in switching on the bromide and iodide recognition properties of the respective cryptand receptor. Importantly, the nature of the sigma-hole mediated interaction employed in the anion recognition component is demonstrated to significantly augment the ion-pair binding behaviour, markedly so for the halogen bonding analogue. Most notably the incorporation of a chelating chalcogen bonding donor motif significantly improves the selectivity towards KBr over KI, relative to halogen and hydrogen bonding analogues.

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.

Chalcogen Bond Mediated Enhancement of Cooperative Ion-Pair Recognition.

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5-bis-triazole pyridine structure covalently linked to benzo-15-crown-5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi-nuclear 1 H, 13 C, 125 Te and 19 F NMR, ion pair binding investigations reveal sodium cation-benzo-crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred-fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.

Uniform Cu/chitosan beads as a green and reusable catalyst for facile synthesis of imines via oxidative coupling reaction.

A nonprecious metal and biopolymer-based catalyst, Cu/chitosan beads, has been successfully prepared by using a software-controlled flow system. Uniform, spherical Cu/chitosan beads can be obtained with diameters in millimeter-scale and narrow size distribution (0.78 ± 0.04 mm). The size and morphology of the Cu/chitosan beads are reproducible due to high precision of the flow rate. In addition, the application of the Cu/chitosan beads as a green and reusable catalyst has been demonstrated using a convenient and efficient protocol for the direct synthesis of imines via the oxidative self- and cross-coupling of amines (24 examples) with moderate to excellent yields. Importantly, the beads are stable and could be reused more than ten times without loss of the catalytic performance. Furthermore, because of the bead morphology, the Cu/chitosan catalyst has greatly simplified recycling and workup procedures.

A Potent Halogen-Bonding Donor Motif for Anion Recognition and Anion Template Mechanical Bond Synthesis.

The covalent attachment of electron deficient perfluoroaryl substituents to a bis-iodotriazole pyridinium group produces a remarkably potent halogen bonding donor motif for anion recognition in aqueous media. Such a motif also establishes halogen bonding anion templation as a highly efficient method for constructing a mechanically interlocked molecule in unprecedented near quantitative yield. The resulting bis-perfluoroaryl substituted iodotriazole pyridinium axle containing halogen bonding [2]rotaxane host exhibits exceptionally strong halide binding affinities in competitive 50 % water containing aqueous media, by a factor of at least three orders of magnitude greater in comparison to a hydrogen bonding rotaxane host analogue. These observations further champion and advance halogen bonding as a powerful tool for recognizing anions in aqueous media.

A Bis-Triazacyclononane Tris-Pyridyl N9 -Azacryptand "Beer Can" Receptor for Complexation of Alkali Metal and Lead(II) Cations.

A new bis-triazacyclononane tris-pyridyl N9 -azacryptand ligand is prepared via a convenient one-pot [2+3] condensation reaction between triazacyclononane and 2,6-bis(bromomethyl) pyridine in the presence of M2 CO3 (M=Li, Na, K). The proton, lithium, sodium, potassium and lead(II) complexes of the ligand are characterised in the solid state. Preliminary solution-phase competition experiments indicate that the cryptand ligand preferentially binds lead(II) in the presence of sodium, calcium, potassium and zinc cations in methanol solution.

Strong and Selective Halide Anion Binding by Neutral Halogen-Bonding [2]Rotaxanes in Wet Organic Solvents.

The design and construction of neutral interlocked host molecules for anion recognition are rare. Using an active-metal template approach, the preparation of a family of neutral halogen bonding (XB) rotaxanes containing two, three and four iodotriazole groups integrated into the macrocycle and axle components is achieved. In spite of the interlocked hosts' neutrality, such rotaxane systems are capable of binding halide anions strongly and selectively in wet organic solvent mixtures. Importantly, halide-binding strength and selectivity can be modulated by varying the number and position of the halogen bond donor iodotriazole groups within the interlocked cavity; the rotaxane containing the largest number of halogen bond donor groups exhibits the highest halide anion-binding affinities. By varying the percentage of water content in the solvent, neutral XB donor-mediated anion-binding strength is also demonstrated to be highly sensitive to solvent polarity.