Polymers for Anion Recognition and Sensing

Solvent effects in anion recognition

Anion recognition is pertinent to a range of environmental, medicinal and industrial applications. Recent progress in the field has relied on advances in synthetic host design to afford a broad range of potent recognition motifs and novel supramolecular structures capable of effective binding both in solution and at derived molecular films. However, performance in aqueous media remains a critical challenge. Understanding the effects of bulk and local solvent on anion recognition by host scaffolds is imperative if effective and selective detection in real-world media is to be viable. This Review seeks to provide a framework within which these effects can be considered both experimentally and theoretically. We highlight proposed models for solvation effects on anion binding and discuss approaches to retain strong anion binding in highly competitive (polar) solvents. The synthetic design principles for exploiting the aforementioned solvent effects are explored.

Thiourea-Based Receptors for Anion Recognition and Signaling

This work reports on two thiourea-based receptors with pyridine and amine units including 1-naphthyl (MT1N) and 4-nytrophenyl (MT4N) as signaling units. For both compounds, their affinity and signaling ability toward various anions of different geometry and basicity in DMSO were studied using UV-vis, fluorescence, and 1H NMR techniques. Anion recognition studies revealed that both MT1N and MT4N have, in general, high affinities toward basic anions. In this regard, a higher acidity of the MT4N receptor was demonstrated. Furthermore, MT4N has a higher affinity for fluoride (log K1 = 5.98) than for the other anions and can effectively detect it through colorimetric changes that can be monitored by the UV-vis technique. The interaction between receptors and anions mainly involves the hydrogens of the amino and thiourea groups of the former. Complementary single-crystal X-ray diffraction studies and molecular modeling at the DFT level were also performed.

Deciphering the Effect of Microstructural Modification in Sodium Alginate-Based Solid Polymer Electrolyte by Unlike Anions

Microstructure modification in sodium alginate (NaAlg)-based solid polymer electrolytes by the perchlorate (ClO4-) and acetate (CH3COO-) anions of sodium salts has been reported. ClO4- participates in the structure-breaking effect via inter/intramolecular hydrogen bond breaking, while CH3COO- changes the amorphous phase, as evident from X-ray diffraction studies. The larger size and negative charge delocalization of ClO4- have a plasticizing effect, resulting in a lower glass transition temperature (Tg) compared to CH3COO-. Decomposition temperature is strongly dependent on the type of anion. Scanning electron microscopy images showed divergent modifications in the surface morphology in both electrolyte systems, with variations in salt content. The mechanical properties of the NaAlg-NaClO4 electrolyte systems are better than those of the NaAlg-CH3 COONa system, indicating weak interactions in the latter. Although most of the studies focus on the cation influence on conductivity, the interaction of the anion and its size certainly have an influence on the properties of solid polymer electrolytes, which will be of interest in the near future for sodium ion-based electrolytes in energy storage devices.

A Two-Dimensional Metallacycle Cross-Linked Switchable Polymer for Fast and Highly Efficient Phosphorylated Peptide Enrichment

The selective and efficient capture of phosphopeptides is critical for comprehensive and in-depth phosphoproteome analysis. Here we report a new switchable two-dimensional (2D) supramolecular polymer that serves as an ideal platform for the enrichment of phosphopeptides. A well-defined, positively charged metallacycle incorporated into the polymer endows the resultant polymer with a high affinity for phosphopeptides. Importantly, the stimuli-responsive nature of the polymer facilitates switchable binding affinity of phosphopeptides, thus resulting in an excellent performance in phosphopeptide enrichment and separation from model proteins. The polymer has a high enrichment capacity (165 mg/g) and detection sensitivity (2 fmol), high enrichment recovery (88%), excellent specificity, and rapid enrichment and separation properties. Additionally, we have demonstrated the capture of phosphopeptides from the tryptic digest of real biosamples, thus illustrating the potential of this polymeric material in phosphoproteomic studies.

Water soluble organic electrochromic materials

Organic materials in electrochromic device applications possess a number of advantages over transition metal oxides like WO3 such as ease of synthesis and tunability, flexibility, and derivability from renewable feedstocks. However, these advantages are offset by the need to use organic solvents in their processing which are often flammable and/or toxic. Therefore, it is of paramount importance to the longterm economic and environmental sustainability of organic electronics research to develop water soluble organic materials. Herein, we describe the advances made in developing water soluble organic electronic materials for electrochromic applications. We here classify electrochromic materials into two broad categories: those that transition between colourless and coloured states (Type I) and those that transition between differently coloured states (Type II). The methods by which organic electrochromes are made water soluble are described in detail along with their potential applications in order to promote research in water soluble organic electronic materials in general.

Electronic and assembly properties of a water-soluble blue naphthalene diimide

Herein we report on the synthesis and characterisation of a water soluble deep blue naphthalene diimide, (ⁱPrNH)₂NDI–V.

Polyaniline–niobium oxide nanohybrids with photocatalytic activity under visible light irradiation

In this study, we reported the production of polyaniline and niobium oxide hybrids synthesized by the direct reaction between a niobium peroxyoxalate complex and anilinium salt in an aqueous medium.

A neutral porous organic polymer host for the recognition of anionic dyes in water

Neutral hosts for the recognition of anionic guests in water remain underdeveloped due to the inherent thermodynamic barrier for desolvation. To address this challenge, we have repurposed crosslinked porous organic polymers (POPs) as hosts. This polymer architecture affords a hydrophobic environment with a densely packed array of urea hydrogen bond donors to cooperatively promote anion desolvation and recognition in water. Using the principles of supramolecular design, we demonstrate through adsorption assays that the resulting Urea-POP-1 can recognize structurally different dyes containing phosphonate, sulfonate, and carboxylate anions in water. Moreover, when compared to Methyl-POP-1, a control POP lacking hydrogen bond donors, we find that the driving force for desolvation and adsorption of each dye is achieved through hydrophobic interactions with the POP backbone and, more importantly, cooperative hydrogen bonding interactions with the urea sidechains. This starting point sets the stage to exploit the modularity of our design to build a family of neutral polymer hosts with tunable pore sizes and anion preferences for fundamental investigations and targeted applications.

Electrochemical Determination of Norepinephrine at Poly (p-aminobenzenesulfonic Acid) Modified Sensor

Objective:

In this study, it was aimed to prepare an electrochemical sensor capable of assigning Norepinephrine in the presence of an interference such as ascorbic acid.

Methods:

A sensitive modified sensor was prepared by electrodeposition of p-aminobenzenesulfonic acid (p-ABSA) to the glassy carbon electrode by cyclic voltammetry. The electrooxidation of Norepinephrine was accomplished by cyclic and differential pulse voltammetry.

Results:

The current values were enhanced and the peak potentials of Norepinephrine and ascorbic acid were separated at the sensor compared to the bare electrode. There was linearity between the oxidation current and concentration of Norepinephrine ranging from 0.5 to 99.8 μM in phosphate buffer solution at pH 7.0. The limit of detection was 10.0 nM and the sensitivity was 0.455 μA/μM.

Conclusion:

The determination of Norepinephrine was successfully performed in real samples such as blood serum and urine at the poly (p-ABSA) sensor. To the best of our knowledge, this is the first study to detect Norepinephrine in the presence of ascorbic acid at poly (p-ABSA) modified sensor in the literature.

Synthesis of Magnetite-Based Polymers as Mercury and Anion Sensors Using Single Electron Transfer-Living Radical Polymerization

In this work, hydrophilic polymers modified with iron oxide nanoparticles, such as iron oxide-poly(2-dimethylaminoethyl methacrylate) [P(DMAEMA)] magnetite-based and iron oxide-poly(acrylamide) [P(AAm)] magnetite-based polymers, were prepared via a single electron transfer-living radical polymerization approach. Bile acid and 2-bromo-2-methylpropionic acid were covalently attached onto the surface of Fe3O4 nanoparticles, and these immobilized magnetite nanoparticles were used as an initiator for the polymerization. The binding capabilities of different ions, such as Hg2+, CN-, Cl-, F-, and NO3 -, were tested using these polymeric sensors monitored by UV-vis spectroscopy. Magnetite-based P(DMAEMA) showed enhanced binding capability due to the presence of tertiary amine groups. In addition, it was possible to easily separate the bound ions from aqueous media using an external magnetic field.

Ion specific fluorescence modulation of polyvinyl alcohol-boronate matrices

Borylated polymers are emerging as valuable chemosensors that can report analyte binding through an array of responses. Condensing aryl boronic acids onto polyvinyl alcohol affords fluorescent polymers that can detect and extract borophilic anions.

On the recognition of chloride, bromide and nitrate anions by anthracene–squaramide conjugated compounds: a computational perspective

Anionic recognition appears in several biological processes. Here, the interaction between anthracene–squaramide conjugated compounds and Cl⁻, Br⁻ and NO₃⁻ anions has been explored using density functional theory (DFT) calculations.

Supramolecular behaviour and fluorescence of rhodamine-functionalised ROMP polymers

A ROMP platform leading to rhodamine B containing amphiphilic block copolymers, which self-assemble into micelles which are able to sequester molecular dyes and interact with them by energy transfer. The polymer micelles do not interact with DNA.

A novel hydroxyl-containing polyimide as a colorimetric and ratiometric chemosensor for the reversible detection of fluoride ions

A novel hydroxyl-containing polyimide film has been designed and fabricated as a chemosensor for the real-time visualization of F⁻ with high selectivity and sensitivity.

Organotin-based receptors for anions and ion pairs

The field of anion recognition has developed into an area of tremendous significance over the recent decades due to the role of anions in biological and environmental systems, contributing significantly to the more general domain of supramolecular chemistry. So far, a number of receptors have been designed for anion recognition, synthesized and evaluated, most involving hydrogen bonding donors (urea, amide, pyrrole, imidazolium and hydroxyl groups), π-acidic aryl rings, Lewis acidic metals (boron, tin, aluminium, mercury and uranium) and positively charged polyammonium moieties. With the rapid progress in this field, the role of counterions in modulating the binding strength and selectivity of a specific ion has been recognized, leading to the design and discovery of more robust ion pair receptors. Among various recognition strategies that are presently available for anions and ion pairs, the development of Lewis acidic element-based receptors offers an attractive alternative to the hydrogen bond donor-based receptors, by which both anion and Lewis base recognition can be achieved. Consequently, researchers have focused a great deal of attention on such receptors and this sub-branch of recognition chemistry is expanding rapidly. In recent years, the desired selectivity and binding strength have been achieved for various anions by tuning the Lewis acidity through variation of substituents about the metal center. The easy access, rich molecular diversity and strong Lewis acidity of organotin compounds led to the development of organotin-based molecular receptors for anions and ion pairs. This feature article highlights the advances in the design, synthesis and applications of organotin-based receptors, mainly focusing on our group's contributions.

7-Dialkylaminocoumarin Oximates: Small Molecule Fluorescent "Turn-On" Chemosensors for Low-Level Water Content in Aprotic Organic Solvents

The water sensing properties of two efficient two-component fluorescent “turn-on” chemo-sensors based on the 7-dialkylaminocoumarin oxime acid-base equilibrium were investigated. Interestingly, although simple frontier orbital analysis predicts an intramolecular photoinduced electron transfer quenching pathway in conjugated oximates, TD-DFT (Time-dependent density functional theory) quantum chemical calculations support non-radiative dark S₁ excited state deactivation as a fluorescence quenching mechanism. Due to the acid-base sensing mechanism and sensitive “turn-on” fluorescent response, both studied coumarin aldoxime chemosensors exhibit rapid response to low-level water content in polar aprotic solvents, with detection limits comparable to chemodosimeters or chemosensors based on interpolymer π-stacking aggregation.

Furan and Julolidine-Based "Turn-on" Fluorescence Chemosensor for Detection of F- in a Near-Perfect Aqueous Solution

A new fluorescent sensor 1, containing furan and julolidine moieties linked through a Schiff-base, has been synthesized. Distinct "turn-on" fluorescence enhancement of 1 was observed upon the addition of F^- in a near-perfect aqueous solution. The binding capabilities of 1 with F^- were studied by using fluorescent spectroscopic techniques, ESI-mass analysis and NMR titration measurements. The detection limit for the analysis of F^- was found to be 10.02 μM, which is below the WHO guideline (79 μM) for drinking water. Practically, the sensing ability of 1 for F^- was successfully applied in real water samples. The sensing mechanism for F^- was proposed to be the ICT mechanism via the hydrogen bonding, which was well explained by theoretical calculations.

Borinic Acid Polymer: Simplified Synthesis and Enzymatic Biofuel Cell Application

A simplified one-pot and less harmful method has been introduced for the synthesis of borinic acid monomer. The corresponding borinic acid polymer (PBA) has been prepared by reversible addition-fragmentation chain transfer polymerization. Property investigations confirm the characteristics of PBA as a new type of "smart material" in the field of thermo-responsive polymer. The potential application of PBA in the field of enzymatic biofuel cell has been illustrated with a wide open circuit potential of 0.92 V.

Reaction-based probe for hydrogen sulfite: dual-channel and good ratiometric response

We designed and synthesized a new series of intramolecular charge transfer (ICT) molecules (compounds T1, T2 and T3) by attaching various electron-donating thiophene groups to the triphenylamine backbone with aldehyde group as the electron acceptor. Based on the nucleophilic addition reaction between hydrogen sulfite and aldehyde, all compounds could act as ratiometric optical probe for hydrogen sulfite and displayed efficient chromogenic and fluorogenic signaling. Upon the addition of hydrogen sulfite anions, probe T3 displayed apparent fluorescent color changes from yellowish-green to blue, with a large emission wavelength shift (Δλ = 120 nm). T3 responded to hydrogen sulfite with high sensitivity and the detection limit was determined to be as low as 0.9 μM. At the same time, apparent changes in UV-vis spectra could also be observed. By virtue of the special nucleophilic addition reaction with aldehyde, T3 displayed high selectivity over other anions. Copyright © 2016 John Wiley & Sons, Ltd.

Merging thiophene with boron: new building blocks for conjugated materials

Recent advances on the use of thienylborane chemistry for the development of new functional materials are highlighted.

Fluorine substitution effects of halide anion receptors based on the combination of a distinct hydrogen bond and anion–π noncovalent interactions: a theoretical investigation

Fluorine-substitution effects on anion–π interaction were deeply explored, and a more feasible and rational geometric criterion for halide-anion–π contact is established via three inequalities.

Isatin pentafluorophenylhydrazones: interesting conformational change during anion sensing

Easily synthesized and highly efficient F⁻ and CH₃COO⁻ anion sensors based on reversible keto (hydrazo)/enolate (azo) acid–base equilibrium followed by interesting conformational change in solution.

Thermo-responsive behavior of borinic acid polymers: experimental and molecular dynamics studies

The thermo-responsive properties of borinic acid polymers were investigated by experimental and molecular dynamics simulation studies. The homopolymer poly(styrylphenyl(tri-iso-propylphenyl)borinic acid) (PBA) exhibits an upper critical solution temperature (UCST) in polar organic solvents that is tunable over a wide temperature range by addition of small amounts of H2O. The UCST of a 1 mg mL(-1) PBA solution in DMSO can be adjusted from 20 to 100 °C by varying the H2O content from ∼0-2.5%, in DMF from 0 to 100 °C (∼3-17% H2O content), and in THF from 0 to 60 °C (∼4-19% H2O). The UCST increases almost linearly from the freezing point of the solvent with higher freezing point to the boiling point of the solvent with the lower boiling point. The mechanistic aspects of this process were investigated by molecular dynamics simulations. The latter indicate rapid and strong hydrogen-bond formation between BOH moieties and H2O molecules, which serve as crosslinkers to form an insoluble network. Our results suggest that borinic acid-containing polymers are promising as new "smart" materials, which display thermo-responsive properties that are tunable over a wide temperature range.

Borinic acid block copolymers: new building blocks for supramolecular assembly and sensory applications

Borinic acid functional groups were incorporated into block copolymers via RAFT polymerization and their supramolecular assembly and sensor applications were investigated.

Dip in colorimetric fluoride sensing by a chemically engineered polymeric cellulose/bPEI conjugate in the solid state

A novel heterogeneous, selective dip-in sensor for fluoride has been developed by cross-linking oxidized cellulose with branched PEI functionalized with pNO₂-phenyl urea units.

Benzodithieno-imidazole based π-conjugated fluorescent polymer probe for selective sensing of Cu2+

A benzodithieno-imidazole based π-conjugated fluorescent polymer probe shows excellent selectivity towards Cu²⁺ions through fluorescence quenching.

Conjugated oligomers incorporating azulene building blocks – seven- vs. five-membered ring connectivity

The properties of isomeric azulene derivatives based on 7- versus 5-membered ring substitution were examined by the synthesis and characterization of well-defined electroactive oligomers.