Metal Ion Recognition Research Articles

An MOF‐Based Luminescent Sensor Array for Pattern Recognition and Quantification of Metal Ions

AbstractThe development of a convenient method for the discrimination of typically quenching metal ions such as Cu2+, Co2+, Ni2+, and Fe3+ is of great interest but still a challenge. By simultaneously incorporating Eu3+ and organic dye 3,3′‐diethyloxacarbocyanine iodide (DOC) into a metal‐organic framework, MOF‐253, a luminescent sensor array MOF‐253⊃Eu3++DOC with three emission centers is generated. Utilizing the diversity of quenching responses of metal ions to the different emission centers, five metal ions including Ag+, Cu2+, Fe3+, Co2+ and Ni2+ can be well distinguished with a discrimination accuracy of 100% at a concentration as low as 60 µm. Subsequently, the binary and ternary mixtures of three metal ions (Fe3+, Co2+, and Ni2+) can also be discriminated successfully. Furthermore, taking Cu2+ and Ag+ as examples, this MOF‐based sensor array can quantify the ion concentration at a low range from 0 to 15 µm. Most probably, this is the first case of simultaneous recognition and quantitation of metal ions in an aqueous solution using an MOF‐based luminescent sensor array. Since a variety of luminescent species including organic dyes and lanthanide ions can be introduced into MOFs to generate multiple‐dimensional luminescence, such strategy will open a new avenue for luminescent sensor assays.

Tetraphenylethylene-based covalent organic frameworks as fluorescent chemosensor for rapid sensitive recognition and selective “turn-on” fluorescence detection of trace-level Al3+ ion

Abstract Tetraphenylethylene-based covalent organic framework (COF-DHTA) was prepared and then well characterized. COF-DHTA processes regular pore structure and high thermal stability. COF-DHTA suspension in DMF displays moderate fluorescence emission in DMF suspension and a highly selective fluorescence “turn-on” response towards Al3+ ions. The fluorescence intensity of COF-DHTA suspension at the emission peak 352 nm exhibits a good linear relationship with the concentration of the added Al3+ ions with a very low detection limit of 0.927 μmol/L. The selective and sensitive fluorescence enhancement recognition and detection for Al3+ ions can be attributed to the coordination of Al3+ ions with N and O atoms on the COF-DHTA and the suppression of photoinduced electron transfer (PET). The results of the N2 adsorption experiment, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation verified the coordination interaction between Al3+ ion and the N and O chelating sites on COF-DHTA. This work may pave the way to reasonable design fluorescent COF chemosensors for the recognition and detection of specific metal ions.

A novel approach towards crown-ether modified polyimides with affinity for alkali metal ions recognition

In the attempt to enlarge the family of imide-based materials suitable for sensor applications, novel five- and six-membered thermostable polyimides functionalized with benzo-15-crown-5 ether side chains were synthesized and thoroughly investigated with regard to their affinity for alkali metal ions recognition. For this purpose, a new diamine monomer containing as receptor triphenylmethane modified with 15-crown-5 ether (called by us crowned TPM) has been synthesized and structurally characterized. For the first time, we brought evidence for the occurrence of a ground-state intermolecular charge transfer (CT) complex between the donor crowned TPM diamine and the acceptor diimide segment which is actually responsible for the polyimides strong light emission in the green to yellow spectral range. All polyimides were electrochemically active in both anodic and cathodic regions, their voltammetric response being consistent with the coplanarity and electron accepting strength of the diimide segment. In the presence of alkali metal ions some changes appeared in the electronic absorption signals, although quite diffuse. Instead, these cations significantly altered the fluorescence response of polyimides in dependence on the excitation wavelength, cation type and polymer structure. These mostly caused the occurrence of a new emission band, when the green or yellow fluorescence turned in blue, thus proving the capability of our polyimides to detect alkali metal ions.

Cobalt oxyhydroxide nanosheets integrating with metal indicator enable sensitive detection of glutathione

Glutathione (GSH) plays a significant role in various biological functions. The fluctuation of GSH level is closely linked to some serious diseases. Currently, the colorimetric detection of GSH is mainly built on the inhibitory effect on the catalytic activity of the developed nanomaterials. However, tedious synthesis of the nanomaterials is always required to control their morphologies for better catalytic activity. Metal indicators are some specific substances capable of chelating metal ions, during which significant color variation can be triggered, making them promising for colorimetric analysis. More importantly, the recognition of metal ions has nothing to do with the structure of the materials. Herein, CoOOH ultrathin nanosheets were prepared via a facile method, which can be easily reduced to Co2+ ions by GSH. After being chelated by metal indicator, a rapid and sensitive sensing platform for GSH detection is established with the distinct color change. As a result, the UV–vis absorbances of Co2+–xylenol orange disodium salt complexes (a typical metal indicator) at 580 nm exhibit good linearity against GSH concentrations from 33 μM to 1.3 mM with the detection limit of 13.7 μM. The developed sensor is further used in the detection of GSH contained in the human serum and an ideal recovery rate is obtained, demonstrating its excellent applicability for the detection of GSH in practical samples.

A multi-responsive pyranone based Schiff base for the selective, sensitive and competent recognition of copper metal ions

Exploring a new multi-responsive pyranone chemosensor capable of sensing copper ions specifically and selectively through colorimetric, UV–Vis absorption and fluorescence methods is of great importance. In this piece of work, a novel pyranone based Schiff base ligand 4-Hydroxy-6-methyl-3-[1-(2-morpholin-4-yl-ethylimino)-ethyl]-pyran-2-one (DM) was synthesized by the condensation of dehydroacetic acid and 4-(2-aminoethyl) morpholine. The structural determination of ligand DM was executed using distinct spectral techniques i.e.,1H NMR, 13C NMR, FT-IR and HR-MS techniques. The reported Schiff base DM showed an immediate colorimetric change from pale yellow to colorless accompanied by a strong change in the UV–Vis absorption band onto the addition of Cu (II) ions. This metal ligand chelation leads a decrease in ICT process. Also the decrease in fluorescence emission intensity of Schiff base DM with Cu (II) ions addition showed its turn-off behavior towards copper ions. Further absorption/ emission titration studies, Job’s plot, HR-MS and 1H NMR titration data designated 2:1 stoichiometric ratio between DM and Cu (II) ions respectively. Density functional theory studies were also performed to authenticate the binding mechanism theoretically. The sensitivity of Schiff base DM towards Cu (II) ions was applicable at every pH conditions and at the same time DM exhibited selectivity towards Cu (II) ions with a negligible interference of other metal ions. DM showed a detection limit of 7.7 nM towards copper ions via fluorescence emission studies. The best part about DM is that it has good stability but showed an instant chemical reversibility when titrated with EDTA solution.

Cover Feature: Synergistic Self‐Assembly of Oxoanions and d‐Block Metal Ions with Heteroditopic Receptors into Triple‐Stranded Helicates (Chem. Eur. J. 63/2020)

In competitive extraction experiments, receptors functionalized with 2,2’-bipyridine (bpy) and o-phenylene-bis(urea) (pbu) binding sites that are interconnected with methylene linker exhibit very high affinity towards CuSO4 in the presence of other divalent first-row transition metal sulfates. Synergistic recognition of divalent d-block metal ions and tetrahedral oxoanions by these receptors induces self-assembly of triple-stranded helicates. More information can be found in the Communication by S. Jansone-Popova et al. on page 14290.

Selective Recognition of Fe3+ by a Simple Schiff Base Chemosensor

A simple and easily synthesized Schiff base chemosensor 1 was prepared by the one-step condensation reaction of 3-acetyl-4-hydroxycoumarin and 1-naphthylamine. The metal ion recognition ability of the chemosensor was measured by UV-Vis spectrophotometer. It demonstrated that its absorbance at 327 nm enhanced upon addition of Fe3+ significantly. The absorption intensities at 327 nm fitted good linear relation (R 2=0.9928) to Fe3+ concentration in DMF. 1 is able to recognize Fe3+ selectively over other ions. The synthesized chemosensor 1 would be useful to detect Fe3+ qualitatively and quantitatively.

Polypyrrole: a reactive and functional conductive polymer for the selective electrochemical detection of heavy metals in water

The last two decades have witnessed attractive, innovative aspects of conductive polymers (CPs) in monitoring environmental pollution. In this regard, CP-based electrode materials were designed for the selective recognition of heavy metal ions in the environment (e.g. waste, river or tap water) or in simulated polluted environmental samples. In this review, the emphasis is on polypyrrole (PPy), an interesting electrosensing electrode material for heavy metals due to its facile preparation, versatile chemistry and physicochemical features. Indeed, health issues raised by metal ion pollutants require an urgent holistic approach for environmental problem solving. In this review, we will summarize the existing knowledge on the use of PPy as electrode material for the detection of heavy metals. We will report strategies of preparation of polypyrrole that exhibit selectivity towards heavy metal ions: (i) choice of dopant, (ii) functionalization of polymer backbone by chelatant groups, and (iii) preparation of ion imprinted polypyrrole. It is clear from this review that dopants could act as chelatant of metal ions and increase the selectivity. Such improvement could also be achieved by copolymerization of pyrrole with pyrrole-bearing chelatant groups (e.g. EDTA-like) or finally by the imprinting technique. The latter imparts artificial receptor sites for the recognition of metal ions combining the shape of the receptor site within the polypyrrole matrix that fit in well with the size of the metal ion, on the one hand, and the receptor site–ion interactions, on the other hand. Regardless, the method employed to design polypyrrole sensing layers for heavy metal nanostructuration seems to definitely improve the sensitivity of polypyrrole-based sensor devices. The review finishes by concluding remarks and indication of possible challenging new directions exploring polypyrrole in tracking occurrence of heavy metal ions in the environment.

Synthesis of antipyrine based organic material for Zn2+ ion sensing and implication in logic gate analysis

The antipyrine linked E allylic ester (BH-AP) ONO tridentate was synthesized, using acetate of Baylis-Hillman Adduct (BH) and antipyrine (AP) through SN2′ allylic substitution reaction.The newly synthesized ligand was characterized using IR and NMR spectroscopy.The ligand BH-AP was analyzed using UV–Visible and fluorescence techniques for its selective metal ion recognition properties. The emission spectroscopy exhibited the sensitivity and selectivity of the sensor for Zn2+ ion by significantly quenching the fluorescence intensity upon excitation at 268 nm. The 1:1 ratio binding stoichiometry and the binding constant value of 4.5796 × 10−6 M−1 were obtained for the ligand BH-AP with Zn2+ion. The appropriate combination of materials-AP, Zn2+and pH found to be suitable for NOR logic gate application.

Tannic acid modified single nanopore with multivalent metal ions recognition and ultra-trace level detection

• A reliable single glass nanopore system that possess specific binding affinities has been developed. • This system could achieve metal ions recognitions and ultra-trace level detection (limit of our detection on Fe 3+ ion can reach 10 −15 M). • Theoretical modeling and experiments demonstrate that the specific binding energies between the functional polyphenol groups and metal ions play an important role in metal ions recognition, which promote a systematical study of polyphenol chemistry in nanoconfined space. Artificial single nanopore as a promising tool for chemical and biological studies, such as ionic detection, DNA sequencing, molecular sensing/separation, nanofluidics and biomimetics, has been attracting great attention. Here we show a reliable functional single glass nanopore system with tannic acid to provide polyphenolic functional groups that possess specific binding affinities able to achieve metal ions recognition and ultra-trace level detection (e.g., limit of Fe 3+ detection is down to 10 −15 M). This system displays fast and high sensing ability features for detecting multivalent metal ions. Theoretical calculation (Gaussian 16) and experiments demonstrate that the specific binding energy between the trihydroxy phenolic groups of the inner surface of the nanopore and multiple metal ions can effectively distinguish trivalent, divalent, and monovalent metal ions. Therefore, our new system could promote a potential to conveniently recognize multivalent metal ions in nanoconfined space, and spark efforts to mimic ionic transport in biological nanopore systems and exploit smart nanofluidic devices.

Cu(I)‐catalyzed azide–alkyne cycloaddition synthesis and fluorescent ion sensor behavior of carbazole‐triazole‐fluorene conjugated polymers

Abstract1,8‐Carbazole‐based conjugated polymers were synthesized by the Cu(I)‐catalyzed azide–alkyne cycloaddition between 1,8‐diethynylcarbazole monomers and 2,7‐diazidofluorene counter comonomers. Successful polymer formation was revealed by conventional techniques, such as gel permeation chromatography and 1H NMR spectroscopy, and the bathochromically shifted absorption with respect to the model monomer. The resulting polymer displayed selective metal ion recognition in terms of fluorescence quenching or the appearance of a new emission peak. The fluorescence chemosensor behavior could be achieved only when the 9H position of the carbazole was unsubstituted. Of the studied metal cations, Sn2+ ions were the most strongly bound to the polymer. The degree of fluorescence quenching was more significant than that of the model monomer, a fact that highlights the use of polymeric chemosensors. Moreover, CN− anion recognition was also demonstrated by the fluorescence recovery of the polymer–Sn2+ ion complex. Overall, this is the first click polymerization of 1,8‐carbazole‐based monomers, and the selective ion sensor behavior was achieved by the characteristic 1,8‐di(triazolyl)carbazole unit. © 2020 Society of Chemical Industry

Molecularly Imprinted Polymers for Selective Recognition and Extraction of Heavy Metal Ions and Toxic Dyes

Contamination triggered by toxic metal ions and dyes is a foremost menace to the environment and its inhabitants. Industries including metal plating, paints, and battery engineering are responsible...

Target Self‐Enhanced Selectivity in Metal‐Specific DNAzymes

AbstractHighly selective recognition of metal ions by rational ligand design is challenging, and simple metal binding by biological ligands is often obscured by nonspecific interactions. In this work, binding‐triggered catalysis is used and metal selectivity is greatly increased by increasing the number of metal ions involved, as exemplified in a series of in vitro selected RNA‐cleaving DNAzymes. The cleavage junction is modified with a glycyl–histidine‐functionalized tertiary amine moiety to provide multiple potential metal coordination sites. DNAzymes that bind 1, 2, and 3 Zn2+ ions, increased their selectivity for Zn2+ over Co2+ ions from approximately 20‐, 1000‐, to 5000‐fold, respectively. This study offers important insights into metal recognition by combining rational ligand design and combinatorial selection, and it provides a set of new DNAzymes with excellent selectivity for Zn2+ ions.

Target Self-Enhanced Selectivity in Metal-Specific DNAzymes.

Highly selective recognition of metal ions by rational ligand design is challenging, and simple metal binding by biological ligands is often obscured by nonspecific interactions. In this work, binding-triggered catalysis is used and metal selectivity is greatly increased by increasing the number of metal ions involved, as exemplified in a series of in vitro selected RNA-cleaving DNAzymes. The cleavage junction is modified with a glycyl-histidine-functionalized tertiary amine moiety to provide multiple potential metal coordination sites. DNAzymes that bind 1, 2, and 3 Zn2+ ions, increased their selectivity for Zn2+ over Co2+ ions from approximately 20-, 1000-, to 5000-fold, respectively. This study offers important insights into metal recognition by combining rational ligand design and combinatorial selection, and it provides a set of new DNAzymes with excellent selectivity for Zn2+ ions.

A Smartphone‐Assisted Sensitive, Selective and Reversible Recognition of Copper Ions in an Aqueous Medium

AbstractA photochromic substituted spiropyran (8‐methoxy‐1,3’,3’‐trimethylspiro[chromene‐2,2’indoline]) was successfully synthesized and its structural integrity was ascertained using spectroscopic methods. Owing to the uniquely positioned methoxy and phenolic groups for potential coordination with a metal ion, it was investigated for the recognition of toxic metal ions. The spiropyran derivative responded to the presence of Cu2+ ions in an aqueous solution by displaying a color change visible to the naked eye (colorless to pink). The color change was witnessed due to the Cu2+ ion‐induced transformation of the closed‐form (spiro) of the substituted spiropyran derivative into an open merocyanine (MC) form, which complexes the Cu2+ ion. The color change was further used for the quantification of Cu2+ ion concentration in water using a smartphone captured digital images via pixel intensity analysis. The spiropyran derivative displayed 0.24±0.01 μM, 0.65±0.06 μM (0.61±0.06 μM using paper strips) as the LOD for Cu2+ ions using UV‐Visible spectroscopy and digital colorimetry, respectively. The density functional theory (DFT) calculations and Job's plot supported the formation of a 2 : 1 (H: G) complex between the spiropyran derivative and copper ions. The time‐dependent DFT (TD‐DFT) investigations were also used to understand the color change during the complex formation, which indicated a good correlation between the experimental and theoretical results at the molecular level.

Synthesis of organosilocane allied N-heteroaryl Schiff base chemosensor for the detection of Cu2+ metal ions and their biological applications

N-Heteroaryl organosilocanes-based chemosensors have been synthesized for the recognition of copper metal ions with excellent selectivity.

Fluorescent pattern recognition of metal ions by nanoparticles of bovine serum albumin as a chemical nose/tongue.

A sensor array mimicking a chemical nose/tongue based on bovine serum albumin nanoparticles (BSANsn) has been developed for the fluorescence pattern recognition of metal ions in biofluids. Three types of BSANsn (BSANs10, BSANs20, and BSANs40) show the same excitation/emission peak at 478/526 nm. According to the differential fluorescence variation, the sensor array shows particular fluorescence response patterns depending upon metal ions. Upon principal component analysis (PCA), it was found that the sensor array can distinguish 18 metal ions clearly at a concentration of as low as 10 μM. Moreover, different concentrations of metal ions and mixed metal ions of diverse kinds or valence states can be differentiated by the sensor in biofluids. In addition, the results were well consistent with those obtained with the traditional ICP-AES method.

Design and synthesis of a tripodal receptor for the selective detection of Fe3+

The tripodalreceptor (Ty) was synthesized from naphthol and tren units.The metal ionrecognition property of the tripodalreceptor Ty was analysed using UV–Visible and fluorescence techniques. The structure of Ty receptor is confirmed by FT-IR and NMR spectral data. The Elemental and surface morphology were determined by EDAX and SEM analysis.Fluorescence analysis revealed a positive selectivity towards Fe3+ ions, in minimal conditions. Thereceptor Ty selectively recognizes Fe3+ ions through fluorescence switch-on process in which a bright green luminescence was observed on binding with Fe3+ ions. Further, thebinding stoichiometry for [Ty-Fe3+] exhibited 1:1 ratio and the binding constant value was found to be 5.1127 × 106 M−1.

Ordinary microfluidic electrodes combined with bulk nanoprobe produce multidimensional electric double-layer capacitances towards metal ion recognition

While multidimensional sensors are powerful platforms towards multitarget analyses, the successive synthesis/fabrication of multiple probes and measurements to each one of these units still damage the device miniaturization, scalability, cost, consumption of samples, operational simplicity, precision, and analysis time. Herein, we describe an electrochemical sensing array that affords the discrimination of metal ions from a single ready-to-use probe and experiment. The sensing probe consisted of commercial stainless-steel capillaries, which defined a microfluidic circuit and acted as electric double-layer parallel capacitors into devices prototyped by a fast, cleanroom-free, and green technique. The probes assured differential responses due to heterogeneous interactions with samples and multichannel capacitance outputs. In addition, we address an effective strategy to further improve the repeatability and recognition ability of the sensor by using oxidized multi-walled carbon nanotubes as a single bulk probe. The nanotubes provided differential electrostatic adsorptions of ions, then increasing the variance of the capacitance responses. The approach was successfully applied in the identification of samples of mineral water, lake, and petroleum according to the presence of metal ions. Using supervised machine learning tasks, the sensor assured reproducible, sensitive, and accurate classification of dozens of lake samples spiked with multiple heavy metals in accordance with their safe limits. Remarkably, simultaneous quantification of the individual concentration of these ions was also possible from universal impedimetric assays by treating the data through multi-output regression. The sensor will be of significance for advanced discriminations from a single ordinary probe and measurement in a direct mode using scalable chips.

An Acridone‐Based Fluorescent Chemosensor for Cationic and Anionic Species, and Its Application for Molecular Logic Operations

AbstractThe metal ion and anion recognition abilities of the newly synthesized acridone derivative having amide and ester groups were studied by UV–vis and fluorescence spectroscopies. The sensor molecule revealed selective recognition toward Ca(II), Hg(II), and fluoride in acetonitrile. Based on X‐ray crystallographic and 1H NMR analyses, intramolecular bifurcated H‐bond is formed between the acridone NH and the amide oxygens in the free receptor. Addition of Ca(II) and Hg(II) induced large fluorescence enhancements and changes in the 1H NMR shifts due to complexation, while fluoride deprotonated the sensor molecule giving rise to a new emission band. Selective sensing of Hg(II) based on absorption changes was also observed, presumably due to the tautomerization of the acridone unit upon complexation. The optical spectroscopic behavior in the presence or absence of Ca(II) and fluoride as chemical inputs provided an opportunity to construct IMP, INH, XOR, and XNOR molecular logic gates as well as a complementary IMP/INH circuit, and integrated logic functions such as a half‐subtractor (XOR/INH combination) and a magnitude comparator (XNOR/INH combination).