Anion Sensors Research Articles

Conjugated polymers applicable to colorimetric and fluorescent anion detection

A reliable and practical method that allows simple and rapid anion detection has been in increasing demand because anions are recognized as important analytes in diverse fields. As a candidate to satisfy the above requirements, optical anion sensors have recently attracted much attention, and thus many efforts have been made to develop materials for sensor applications. This article reviews recent progress in the design and fabrication of conjugated polymer-based anion sensors. The validity of polymer-based anion sensors has been verified through the evaluation of colorimetric and fluorescent responses for a series of conjugated polymers with different binding sites and varied pendant structures. Through rational molecular design of the sensor polymers, certain structures have been found to possess desirable anion detection abilities, including enhanced binding affinity, strict size specificity and applicability to anions in an aqueous environment. Thus, the demonstration described in this focused review could provide useful insight not only for anion detection chemistry but also for polymer and supramolecular chemistry. Because of importance of anions as analyte in diverse fields, a reliable and practical method that allows simple and rapid anion detection has been in increasing demand. To satisfy this requirement, many efforts have been made to develop optical anion sensor materials for sensor applications. This article reviews recent progress in the design and fabrication of conjugated polymer-based anion sensors. Through rational molecular design of the sensor polymers, certain structures have been found to possess desirable anion detection abilities, including enhanced binding affinity, strict size specificity and applicability to anions in an aqueous environment.

Acylthiourea derivatives as colorimetric sensors for anions: Synthesis, characterization and spectral behaviors

Several acylthioureas have been synthesized to develop colorimetric sensors for detection of biologically important anions. UV–vis titration experiments indicated that the absorbance values have a good linear relationship with concentration of anions when the anions were added in AR-1, AR-4 and AR-6 sensor molecules. The detection limit to AcO− and F− is 5×10−6mol/L when the concentration of receptors are 2×10−5mol/L. Especially, compounds AR-1 and AR-4, decorated with strong electron-withdrawing NO2 substituent, showed augmented anion sensing properties, being capable of naked-eye detecting of F− and AcO− when the water content is lower than 15%. The recognition details of anion sensing were also assessed using 1H NMR technique and confirmed that the basic anions induced deprotonation of N–H.

The potential of ion mobility mass spectrometry for tuning synthetic host guest systems: A case study using novel zinc(II)dipicolylamine anion sensors

Synthetic approaches to produce scaffolds that will act as efficient biosensors have been the subject of considerable research efforts in recent years. The preparation of host complexes which will specifically bind a given guest necessitates structural analysis of the potential complexes formed, as well as an assessment of the strength of the binding interaction. A challenge to the down-stream analytical scientist is to develop a rapid method that can probe the strength of binding, and the architecture of the complex. In this work we apply nano-ESI MS and Drift Tube ion mobility mass spectrometry (DT IM-MS) to examine host guest interactions. We present data on 5 cyclic peptide bis(ZnII-dipicolylamines) which have been systematically designed as potential molecular biosensors for pyrophosphate (PPi). The competition of the macrocycles for PPi compared with other small anions is investigated. Mass spectrometry provides the stoichiometry of the complex, and the proportion of complex preserved into the mass spectrometer correlates with solution phase data. We find the macrocycles have a higher affinity for PPi than for ATP or pyrocatechol violet (PV). The absolute scale of affinity from mass spectrometry is less (4–5 Log Ka) than that found in solution (4–9 Log Ka), but within the series of macrocycles trend in relative affinities are comparable. DT IM-MS shows that the collision cross sections (DTCCSHe) of the macrocycles are unchanged on binding PPi, indicating that the anion is within the designed binding pocket. We also find that binding has tightened the conformation of the macrocycle, as revealed from analysis of the collision cross section distributions (DTCCSDHe), where for 4/5 of the macrocycles there is a significant decrease in FWHM. Molecular mechanics (MMFF94) and semi empirical methods (ONIOM PM6:B3LYP/aug-cc-pvDZ) were used to generate candidate geometries for 4 to support our assertions on the nature of the binding pocket in the uncomplexed host, and to provide a route for improvement in the design.

Substituent effects on anion sensing of salicylidene Schiff base derivatives: Tuning sensitivity and selectivity

A series of colorimetric anion sensors using the salicylidene Schiff bases with different substituents, including electron donating group (tert-butyl, in sensor 2), conjugated group (naphthyl, in sensor 3) and electron withdrawing group (chlorine, in sensor 4), respectively, have been developed. The substituents can not only impact chromogenic signal output, but also tune the sensitivity and selectivity of the anion sensing by their specific electron push–pull features. In particular, both 1 (without substituent) and 2 show high selectivity for F− over Cl−, Br−, I−, AcO− and H2PO4−, but the sensitivity of 2 is poorer than 1 due to the effect of electron donating groups. Sensor 3 exhibits higher sensitivity for F− than 1, but it is disturbed by the weak response to AcO− and H2PO4−. Sensor 4 has the highest sensitivity for F−, but shows the significant response to AcO− and H2PO4−, which also decreases the selectivity for F−. Finally, analytical applications of 1 for the detection of F− in aqueous medium and toothpaste have been studied.

Expanded Porphyrin-Anion Supramolecular Assemblies: Environmentally Responsive Sensors for Organic Solvents and Anions.

Porphyrins have been used frequently to construct supramolecular assemblies. In contrast, noncovalent ensembles derived from expanded porphyrins, larger congeners of naturally occurring tetrapyrrole macrocycles, are all but unknown. Here we report a series of expanded porphyrin-anion supramolecular assemblies. These systems display unique environmentally responsive behavior. Addition of polar organic solvents or common anions to the ensembles leads to either a visible color change, a change in the fluorescence emission features, or differences in solubility. The actual response, which could be followed easily by the naked eye, was found to depend on the specifics of the assembly, as well as the choice of analyte. Using the ensembles of this study, it proved possible to differentiate between common solvents, such as diethyl ether, THF, ethyl acetate, acetone, alcohol, acetonitrile, DMF, and DMSO, identify complex solvent systems, as well as distinguish between the fluoride, chloride, bromide, nitrate, and sulfate anions.

Microwave-assisted synthesis of photoluminescent glutathione-capped Au/Ag nanoclusters: A unique sensor-on-a-nanoparticle for metal ions, anions, and small molecules

Even though great advances have been achieved in the synthesis of luminescent metal nanoclusters, it is still challenging to develop metal nanoclusters with high quantum efficiency as well as multiple sensing functionalities. Here, we demonstrate the rapid preparation of glutathione-capped Au/Ag nanoclusters (GS-Au/Ag NCs) using microwave irradiation and their unique sensing capacities. Compared to bare GS-Au NCs, the doped Au/Ag NCs possess an enhanced quantum yield (7.8% compared to 2.2% for GS-Au NCs). Several characterization techniques were used to elucidate the atomic composition, particulate character, and electronic structure of the fabricated NCs. According to the X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectra, a significant amount of Au exists in the oxidized state as Au(I), and the Ag atoms are positively charged. In contrast to those nanoclusters that detect only one analyte, the GS-Au/Ag NCs can be used as a versatile sensor for metal ions, anions, and small molecules. In this manner, the NCs can be regarded as a unique sensor-on-a-nanoparticle.

TDDFT study on the sensing mechanism of a fluorescent sensor for fluoride anion: Inhibition of the ESPT process

The fluoride-sensing mechanism of a reported salicylaldehyde-based sensor (J. Photochem. Photobiol. B 2014, 138, 75) has been investigated by the TDDFT method. The present theoretical study indicates that there is an excited-state proton transfer (ESPT) process from the phenolic O–H moiety to the neighbor N atom in the sensor. The added fluoride anion could capture the proton in the O–H moiety and the corresponding phenolic anion is formed, which could inhibit the ESPT process. The experimental UV/Vis and fluorescence spectra are well reproduced by the calculated vertical excitation energies. Frontier molecular orbital analysis indicates that the local excited state of phenolic anion is responsible for its enhanced fluorescence. Due to this reason, the sensor can be used to sense fluoride anion by monitoring the fluorescent change.

Panchromatic Borane–aza‐BODIPY Conjugate: Synthesis, Intriguing Optical Properties, and Selective Fluorescent Sensing of Fluoride Anions

AbstractA new triarylborane–aza‐BODIPY conjugate is reported. The compound consists of two blue emissive dimesitylarylborane moieties and a near‐infrared (NIR) emissive aza‐BOIDPY core and shows panchromatic absorption spanning approximately 300–800 nm. DFT computational studies suggest limited electronic communication between the individual fluorophore units. Hence, the partial energy transfer from blue fluorophore triarylborane to NIR chromophore aza‐BODIPY unit leads to a broad dual‐emissive feature covering a large part of visible and NIR region. Furthermore, the broadband emissive compound can act as a selective sensor for fluoride anion as a result of fluorescence quenching response in both visible and NIR spectral regions.

Synthesis, biological activity, DNA binding and anion sensors, molecular structure and quantum chemical studies of a novel bidentate Schiff base derived from 3,5-bis(triflouromethyl)aniline and salicylaldehyde

Synthesis, biological activity, spectroscopic and crystallographic characterization and density functional theory (DFT) studies of the Schiff base 3,5-bis(triflouromethyl)aniline and salicylaldehyde are reported. It crystallizes as a monoclinic space group P21/c with a=7.7814(3)Å, b=26.8674(9)Å, c=7.4520(2)Å, V=1379.98(8), Z=4, Dc=1.6038gcm−3, and μ=0.156mm−1. The molecular structure obtained from X-ray single-crystal analysis of the investigated compound in the ground state was compared using Hartree–Fock (HF) and density functional theory (DFT) with the functionals B3LYP and B1B95 using the 6-311++G(d,p) basis set. The antimicrobial activities of the compound were investigated for its minimum inhibitory concentration (MIC). The interaction of the Schiff base with calf thymus DNA was investigated using UV–visible spectra. The colorimetric response of the Schiff base receptors in DMSO was investigated before and after the addition of an equivalent amount of each anion to evaluate the anion recognition properties.

A colorimetric and absorption ratiometric anion sensor based on indole & hydrazide binding units

A colorimetric and absorption ratiometric anion sensor (L) based on indole and hydrazide binding units was designed and synthesized, and its recognition & sensing properties towards different anions were studied by naked-eye observations, UV–vis and 1H NMR titration spectra. Sensor L could selectively recognize biologically important F−, AcO− and H2PO4− in DMSO over other anions, along with a significant change in its color and absorption spectrum, resulting from the formation of corresponding 1:2 (L/F−) and 1:1 (L/AcO− and L/H2PO4−) complexes. The 1H NMR titration experiments proved that sensor L experienced deprotonation of NH fragment and produced [HF2]− species, whereas a stable H-bonding complex was formed in the presence of AcO− and H2PO4−.

Segmented conjugated macromolecules containing silicon and boron: ADMET synthesis and luminescent properties

Boron- and silicon-containing conjugated homo- and copolymers could be synthesized using acyclic diene metathesis (ADMET) condensation of bis-styryl monomers. Both, tri-and tetra-coordinated boron monomers were successfully polymerized forming homopolymers, or random copolymers (if polymerized together with a silicon containing co-monomer). Polymer molecular weights Mn were measured at ∼6000 to 15,000 g/mol (NMR end group analysis) with molecular weight distributions Mw/Mn ∼1.8 to 2.2. The polymers absorbed at λmax ∼317 to 406 nm and emitted at λmax ∼370 to 494 nm with fluorescent quantum efficiencies ∼24 to 48%. The copolymer with tri-coordinate boron showed highly efficient fluorescence quenching in the presence of fluoride ions at ratios boron/fluoride ∼5/1, demonstrating its potential as anion sensor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1707–1718

An Amide-Functionalized Dynamic Metal-Organic Framework Exhibiting Visual Colorimetric Anion Exchange and Selective Uptake of Benzene over Cyclohexane.

A novel porous metal-organic framework (MOF) architecture is formed by a neutral amide-functionalized ligand and copper(II). Upon desolvation, this compound undergoes a dynamic structural transformation from a one-dimensional (1D) porous phase to a two-dimensional (2D) non-porous phase that shows selective uptake of benzene over cyclohexane. The as-synthesized compound also acts as a visual colorimetric anion sensor for thiocyanate.

Anion binding with urea and thiourea derivatives

Abstract The importance of anion receptors is a reflection of the ubiquitousness of anions, their functions in biological and industrial processes, as well as their behaviour as pollutants. In the immense field of anion receptor chemistry which has expanded greatly in the past few decades, one of the most prominent binding sites is (thio)urea. The simple synthesis of diverse (thio)urea derivatives, their possibility to form two H-bonds with anions and a promising selectivity with anions of complementary geometry are factors that gave rise to a plethora of studies reporting new organic molecules with different properties and applicability. This review includes the most important examples of (thio)urea receptors from the very beginning, until present. Many authors have used (thio)urea moieties in the computer-aided design of anion sensors, which was then followed by their synthesis, and utilization in the photophysical characterization of host–guest systems, and studies in the transport of ions and ion pairs through membranes. These endeavours led to their successful utilization in the fields of crystal engineering and development of functional materials. Characterization of supramolecular systems and investigations of the complexation thermodynamics has been conducted by use of different analytical and physico-chemical methods. Consequently, it is highly beneficial to summarize all aspects of anion recognition by (thio)ureas within one review article. This critical review containing 386 references classifies (thio)urea derivatives, published from 1990 to 2015, with respect to the complexity of the receptors and the number of urea groups in the molecule.

An anion sensor based on an organic field effect transistor.

We propose an organic field effect transistor (OFET)-based sensor design as a new and innovative platform for anion detection. OFETs could be fabricated on low-cost plastic film substrates using printing technologies, suggesting that OFETs can potentially be applied to practical supramolecular anion sensor devices in the near future.

Colorimetric and fluorimetric response of Schiff base molecules towards fluoride anion, solution test kit fabrication, logical interpretations and DFT-D3 study.

Two newly synthesized Schiff base molecules are herein reported as anion sensors. -NO2 substituted receptor (P1) is comparatively more acidic and can sense F(-), OAc(-) and H2PO4(-), whereas -CN substituted receptor (P2) is less acidic and is selective for F(-) only. Reversible UV-Vis response for both receptors with F(-) can mimic multiple logic gate functions, and several complex electronic circuits based on XNOR, XOR, OR, AND, NOT and NOR logic operations with 'Write-Read-Erase-Read' options have been executed. Interesting 'turn on and off' fluorescence responses were noticed for the receptors with F(-). Intracellular F(-) detection as a diagnosis of non-skeletal fluorosis was successful using a fluorescence microscope with Candida albicans (prokaryotic cell, a diploid fungus) and pollen grains of Tecoma stans (eukaryotic cell) incubated in 10(-6) M fluoride-contaminated hand-pump water collected from Bankura, West Bengal, India. Furthermore, a solution test kit was fabricated for easy and selective detection of F(-) in an aqueous solvent.

A series of homonuclear lanthanide coordination polymers based on a fluorescent conjugated ligand: syntheses, luminescence and sensor for pollutant chromate anion

Series of homonuclear lanthanide coordination polymers incorporating conjugated ligand have been fabricated successfully and characterized systematically.

A recyclable, fluorescent, and colorimetric sensor for fluoride anion in water using a crosslinked polymer functionalized with hydroxyl quinolinium

A crosslinked polymer-based recyclable, fluorescent, and colorimetric sensor for F− in water.

Voltammetric Sensor for Fluoride Ions Using Diphenylether Derivatives Supported by NMR and Theoretical Studies

Compounds 3-(2,4-dinitrophenoxy)phenol (L1) and 3-(2-nitrophenoxy)phenol (L2) were synthesized with high yield and characterized by spectroscopic techniques. The complexation behavior of L1 and L2 for different anionic species (CN−, F−, Cl−, Br−, AcO−, I−, HSO4−, OH−, H2PO4−, ClO4−) in acetonitrile medium were investigated. L1 showed high degree of selectivity for fluoride over other anions. This selectivity could be easily observed by the naked eye, indicating that L1 is a potential colorimetric sensor for fluoride anion. Differential pulse voltammetry of both the ligands showed complete quenching of anodic peaks at 1.16 V for L1 and 1.34 V for L2 upon the addition of 1 equivalent fluoride ions. The proposed mechanism of anion detection is supported by theoretical calculations, UV studies and NMR titrations.

Tris(triazole) tripodal receptors as selective probes for citrate anion recognition and multichannel transition and heavy metal cation sensing.

The three-armed pyrenyl-triazole receptor 1 behaves as a highly selective fluorescent molecular sensor for citrate anions over similar carboxylates such as malate or tartrate. In addition, this receptor senses Cu(2+) cations through absorption and emission channels even in the presence of Hg(2+) metal cations. The related three-armed ferrocenyl-triazole receptor 2 behaves as a highly selective dual (redox and chromogenic) chemosensor molecule for Pb(2+) metal cations.

A highly selective SBA-15 supported fluorescent “turn-on” sensor for the fluoride anion

TSBA (or ASBA) remained stable upon prolonged exposure to UV light (losing ∼0.12% of its fluorescence intensity), and was highly selective towards F− over other common anions (Cl−, Br−, I−, HPO42−, ACO−, and NO3−).