A new lawsone azo-dye for optical sensing of Fe3+ and Cu2+ and their DFT study

A new lawsone-based azo-dye 2-hydroxy-3-((pyridin-2-ylmethyl)diazenyl)naphthalene-1,4-dione (1) was synthesized and applied for sensing of metal ions. Receptor 1 showed selective fluorescent and colorimetric response for the detection of Cu²⁺ and Fe³⁺ over other tested metal ions. The fluorescence intensity of 1 was significantly quenched allowing detection of Fe³⁺ and Cu²⁺ down to 0.61 and 6.06 μM, respectively. The binding has been established by fluorescence spectroscopic method. Receptor 1 provided a 1?:?1 binding scaffold for recognition of Fe³⁺ and Cu²⁺ ions with the association constant of 3.33 × 10⁶ and 3.33 × 10⁵ M^?1, respectively. The B3LYP/6-31G/LANL2DZ method was employed for the optimization of 1 and 1·Fe³⁺ and 1·Cu²⁺.     

Iron(III)‐Selective Chelation‐Enhanced Fluorescence Sensing for In Vivo Imaging Applications

A “turn‐on” pattern Fe³⁺‐selective fluorescent sensor was synthesized and characterized that showed high fluorescence discrimination of Fe³⁺ over Fe²⁺ and other tested ions. With a 62‐fold fluorescence enhancement towards Fe³⁺, the probe was employed to detect Fe³⁺ in vivo in HeLa cells and Caenorhabditis elegans, and it was also successfully used to elucidate Fe³⁺ enrichment and exchange infected by innexin3 (Inx3) in hemichannel‐closed Sf9 cells.     

Anthrone-spirolactam and quinoline hybrid based sensor for selective fluorescent detection of Fe3+ ions

The synthesis of a novel, and highly selective Fe³⁺ ion sensor based on anthrone-spirolactam and its quinoline hybrid ligand is reported. The designed ligand displayed selective detection of Fe³⁺ ions with enhanced fluorescence emission. The complexation of Fe³⁺ ion led to a red shift of 32 nm from 420 nm to 452 nm, and a several fold increase in intensity with fluorescent green emission. The complexation (detection) of Fe³⁺ ions with ligand resulted in chelation enhanced fluorescence and intramolecular charge transfer through the inhibition of C=N isomerization. This hybrid sensor shows high sensitivity and selectivity, spontaneous response, and works on a wide pH range a minimum detection limit of 6.83 × 10⁻⁸ M. Importantly, the sensor works through the fluorescence turn-on mechanism that overcomes the paramagnetic effect of Fe³⁺ ions. The binding mechanism between the ligand and the Fe³⁺ ions was established from the Job's plot method, optical studies, Fourier transfor infrared spectroscopy, NMR titration, fluorescence life-time studies, and density functional theory optimization. The sensor displayed excellent results in the quantification of Fe³⁺ ions from real water samples. Furthermore, due to its biocompatibility nature, fluorescent spotting of Fe³⁺ ions in live cells revealed its bioimaging applications.     

Enhanced Performance of CNT‐doped Imine Based Receptors as Fe(III) Sensor Using Potentiometry and Voltammetry

A highly sensitive and selective potentiometric and voltammteric assay for the detection of Fe³⁺ using (E)‐3‐((2‐(2‐(2‐aminoethylamino) ethylamino) ethylimino)methyl)‐4H‐chromen‐4‐one (IFE(III)) ionophore was developed. To demonstrate the ion‐to‐electron transfer ability of MWCNT, these were incorporated in the ion‐selective membrane and response characteristics of Fe³⁺ electrode was compared with those of the traditional ion selective electrode. The electrode showed an improved Nernstian slope, lower detection limit, response time of less than 5 s and working in a pH range of 3.0 to 8.0. Differential pulse voltammetric studies were performed for IFE(III)‐Fe³⁺ complex in DMSO solvent medium at glassy carbon (GC) electrode. A linear relationship between the cathodic peak current and concentration of Fe³⁺ was observed in the range of 1.6×10^?5 to 4.4×10^?5 mol/L with a detection limit of 5.2×10^?8 mol/L. The electrode shows remarkable selectivity for Fe³⁺ ions over alkali, alkaline earth, transition and heavy metal ions. The optimized electrode was successfully applied for the determination of Fe³⁺ ion in different real‐life samples using potentiometric technique. Theoretical calculations were used to support the complexation behavior of Fe³⁺ with IFE(III).     

Facile synthesis of tough metallosupramolecular hydrogels by using phosphates as temporary ligands of ferric ions to avoid inhibition of polymerization

Forming carboxyl-Fe³⁺ coordination bonds as physical crosslinks is an effective strategy to develop tough hydrogels. Considering the inhibition of ferric ions on free-radical polymerization, these coordination bonds cannot be formed during the reaction, and a soaking process of preformed hydrogels is usually required for mechanical enhancement, resulting in uncontrollable gradient structure, long preparation time, and unnecessary waste of metallic ions. A facile strategy is reported here to prepare tough metallosupramolecular hydrogels by polymerization and in situ formation of coordination bonds with phosphates as the temporal ligands of Fe³⁺ ions. The phosphate ligands in the precursor solution form coordination complexes with the Fe³⁺ ions, which avoids the inhibition and ensures the polymerization. After swelling the resultant hydrogel in water, the ligands are substituted by carboxyl groups of the gel matrix due to the variation of local pH. The equilibrated hydrogel with carboxyl-Fe³⁺ coordination bonds as the physical crosslinks possesses excellent mechanical properties that can be tuned over a wide range by adjusting the polymer compositions and the concentrations of phosphate ligands and Fe³⁺ ions. This strategy should be applicable to other systems to enable synthesis of functional hydrogels with Fe³⁺ ions as the additive toward specific applications in engineering and biomedical fields.     

Naked-eye detection of Cu (II) and Fe (III) based on a Schiff Base Ruthenium complex with nicotinohydrazide

A cyclometalated ruthenium (II) complex 1 [(Ru (Phen)₂(Pbznh)]⁺ PF₆⁻ (Phen = 1,10-phenanthroline and Pbznh = N-(4-(pyridine-2-yl)benzylidene) nicotinohydrazide) with nicotinohydrazide as a functional group was synthesized and characterized. Changes of its absorption spectra and color induced by Cu²⁺ and Fe³⁺ were systematic investigated. The results demonstrated that complex 1 could be served as a colorimetric probe to fast, selective and sensitive detection of Cu²⁺ and Fe³⁺ both in acetonitrile and filter paper based strips. Upon addition of Cu²⁺ and Fe³⁺ to solution of probe 1 , solution color changed from pink to colorless and light yellow respectively, and their corresponding detection limit were calculated to be 3.26 × 10⁻⁸ M and 3.12 × 10⁻⁷ M. Moreover, color of test papers with 1 changed from pink to colorless/yellow when Cu²⁺/Fe³⁺ were dropwise added. Therefore, it can be used as a desirable ‘naked-eye’ indicator candidate for Cu²⁺ and Fe³⁺.     

Highly Fe selective ratiometric fluorescent probe based on imine-linked benzimidazole

We synthesized a novel benzimidazole-based fluorescent receptor bearing imine linkages with two sets of sp² nitrogens, and investigated its binding properties toward various metal ions. The receptor exhibited a shift in emission band upon binding with Fe³⁺ ions, and no such significant response was noticed in other metal ions. The receptor shows a property of selective ratiometric fluorescent probe of Fe³⁺ ions without interferences of the background metal ions.     

Green synthesis of fluorescent carbon dots from Kumquat (Fortunella margarita) for detection of Fe3+ ions in aqueous solution

In this study, kumquat was first time used for synthesizing carbon dot structures (CDs) with the hydrothermal method. These newly synthesized CDs was characterized structurally and optically. The ion sensor application of the new CDs was carried out using 20 different metal ions. It was observed that CDs have high selectivity only for Fe³⁺ ions among the metal ions studied. Detection limit for Fe³⁺ ions was calculated as 0.70 µM. The results showed that these new CDs are highly selective against Fe³⁺ ions and have a very short response time such as 0.5 min. The Fe³⁺ ions selectivity of CDs was tested on real (tap water) samples. The results exhibited that this new CDs, obtained with green synthesis from Kumquat fruit without using chemical agents in one-pot simple and economical process, can be used as fluorometric sensor for detection of Fe³⁺ ions with high selectivity and sensitivity, low detection limit and rapid response time.

     

1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxynaphthalene as chemo-sensor for Fe in aqueous HEPES buffer based on colour changes observable with the naked eye

A new glucose-based C2-derivatized colorimetric chemo-sensor (L₁) has been synthesized by a one-step condensation of glucosamine and 2-hydroxy-1-naphthaldehyde for the recognition of transition metal ions. Among the eleven metal ions studied, viz., Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺, L₁ results in visual colour change only in the presence of Fe²⁺, Fe³⁺and Cu²⁺ in methanol. However, in an aqueous HEPES buffer (pH 7.2) it is only the Fe³⁺ that gives a distinct visual colour change even in the presence of other metal ions, up to a concentration of 280 ppb. The changes have been explained based on the complex formed, and the composition has been determined to be 2:1 between L₁ and Fe³⁺ based on Job’s plot as well as ESI MS. The structure of the proposed complex has been derived based on HF/6-31G calculations.     

Fine tuning of a solvatochromic fluorophore for selective determination of Fe: a new type of benzimidazole-based anthracene-coupled receptor

We synthesized a novel benzimidazole-based, anthracene-coupled fluorescent receptor capable of recognizing and estimating the concentrations of Fe³⁺ in semi-aqueous solution by ratiometric estimation. Our sensor can be made highly selective for Fe³⁺ over other metal ions by changing the solvent composition.     

A highly selective fluorescent probe for nanomolar detection of ferric ions in the living cells and aqueous media

A dipodal fluorescent probe 3, with imine and hydroxyl moieties as binding sites, has been synthesized and characterized with spectroscopic methods, single-crystal X-ray techniques, and DFT. The synthesized probe 3 (φ = 0.0028) showed highly sensitive and highly specific fluorescent ‘turn-on’ effect (λ_em = 453 nm) for the 1:1 binding with Fe³⁺ ions to form probe 3.Fe³⁺ complex (φ = 0.203) in semi-aqueous medium (acetonitrile:water (50:50; v/v)) and live cells. The 1:1 binding stoichiometry of probe 3 and Fe³⁺ ions was proposed by DFT calculations and confirmed by the NMR spectroscopy, crystal structures of probe 3 and 3.Fe³⁺ complex, and mass spectrum of probe 3.Fe³⁺ complex. The stability of probe 3.Fe³⁺ complex in a wide pH range (pH 2–12) and reversibility for binding with Fe³⁺ ions in the presence of EDTA indicates that it can be an effective chemosensor for the detection of Fe³⁺ ions in various samples, including living cells. Importantly, with the LOD of 21.5 nM for the detection of Fe³⁺ ions, probe 3 did not show any interference from potentially competing ions even at a 1:3 ratio, indicates its biocompatibility. The nanomolar limit of detection (21.5 nM), cell permeability, and low cytotoxicity allows the probe 3 to be an excellent tool for the live-cell imaging and detection of ferric ions in live cells.     

Novel hexacentered phosphazene compound as selective Fe3+ ions sensor with high quantum yield: Synthesis and application

A novel compound hexa-rhodamine substituted phosphazene (HRP) with six active centers on a cyclotriphosphazene ring was synthesized using the alkyne-azide “click” reaction. The structure of HRP was characterized using spectroscopic techniques. The optical sensor properties of HRP for metal ions were investigated using UV-Vis and Fluorescence spectroscopy. It was determined that HRP is a selective sensor with colorimetric and fluorescent properties for Fe³⁺ ions. Limit of detection (LOD) of HRP was determined as 6.94?×?10^?9 M using fluorescence intensities in the presence of different concentrations of Fe³⁺ ions. It was determined that HRP-Fe³⁺ complex has high quantum yield and excellent photostability.     

Colorimetric detection of iron ions (III) based on the highly sensitive plasmonic response of the N-acetyl-l-cysteine-stabilized silver nanoparticles

We report here a facile colorimetric sensor based on the N-acetyl-l-cysteine (NALC)-stabilized Ag nanoparticles (NALC–Ag NPs) for detection of Fe³⁺ ions in aqueous solution. The Ag NPs with an average diameter of 6.55 ± 1.0 nm are successfully synthesized through a simple method using sodium borohydride as reducing agent and N-acetyl-l-cysteine as protecting ligand. The synthesized silver nanoparticles show a strong surface plasmon resonance (SPR) around 400 nm and the SPR intensity decreases with the increasing of Fe³⁺ concentration in aqueous solution. Based on the linear relationship between SPR intensity and concentration of Fe³⁺ ions, the as-synthesized water-soluble silver nanoparticles can be used for the sensitive and selective detection of Fe³⁺ ions in water with a linear range from 80 nM to 80 μM and a detection limit of 80 nM. On the basis of the experimental results, a new detection mechanism of oxidation–reduction reaction between Ag NPs and Fe³⁺ ions is proposed, which is different from previously reported mechanisms. Moreover, the NALC–Ag NPs could be applied to the detection of Fe³⁺ ions in real environmental water samples.     

Development of Fluorescent Film Sensors Based on Electropolymerization for Iron(III) Ion Detection

Two electroactive materials, M1 and M2 , are synthesized and their fluorescent electropolymerized (EP) films are prepared and used to detect metal ions. From the tested metal ions, M1 and M2 are demonstrated to be sensitive and selective for Fe³⁺ ions. In particular, M2 exhibits higher sensitivity towards Fe³⁺ ions. The fluorescent detection ranges from 10^?5 M to 4×10^?4 M . The excellent performance of the EP fluorescent films is mainly due to the strong metal‐chelated properties of M2 and the intrinsic porous cross‐linked‐network microstructure of the EP films. This study, thus, provides a promising Fe³⁺ sensing candidate and a potential preparation method for fluorescent sensing films.     

2-Aminopyridine derivative as fluorescence ‘On–Off’ molecular switch for selective detection of Fe3+/Hg2+

2-Amino-6-methyl-4-phenyl-nicotinonitrile 1, a 2-aminopyridine-based fluorescent compound, was found to be a fluorescent chemosensor for the detection of Fe³⁺ and Hg²⁺ ions over a number of other metal ions. Compound 1 was synthesized in one step using a multicomponent reaction, and characterized using common spectroscopic tools. During Fe³⁺/Hg²⁺ sensing the compound 1 followed a ‘switch-off’ mechanism. Further, compound 1 could sense Fe³⁺ over Hg²⁺ by its distinct absorption and fluorescence quenching behaviors. 1:1 complex formation of 1 with Fe³⁺ and Hg²⁺ was clearly understood from Job’s plot. The present work brings additional evidence on the importance of multicomponent reactions which could lead to the development of fluorescence chemosensor in one step for the selective detection of biologically important metal ions.     

Selective detection of phosphaphenanthrenecontaining luminophors with aggregation-induced emission enhancement to transition metal ions

Transition metal ions (Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Hg²⁺, Ag⁺, Fe³⁺) in water are used to quench emission of 2-(6-oxido-6H-dibenz 〈c,e〉 〈1,2〉 oxaphosphorin-6-yl)-1,4-phenylene-bis(p-pentyloxylbenzoate)s (MD5) with aggregation-induced emission enhancement (AIEE) in water-acetonitrile (AN) mixture (80:20 by volume). Among all metal ions, Fe³⁺ exhibits the highest quenching efficiency on AIEE of MD5 even when the concentration of Fe³⁺ is lower than 1×10⁻⁶ mol/L. The quenching efficiency of Hg²⁺ is lower than that of Fe³⁺ at the same concentration, though MD5 is used to detect Hg²⁺ efficiently, too. To other metal ions, low quenching efficiency has few relations with a wider concentration range. The UV absorbance spectra show only red shift of absorbance wavelength in the presence of Hg²⁺ and Fe³⁺, which indicates a salt-induced Jaggregation. SEM photos reveal larger aggregation and morphological change of nanoparticles of MD5 in water containing Hg²⁺ and Fe³⁺, which reduce the surface area of MD5 emission for further aggregation. The selective quenching effect of transition metal ions to emission of MD5 has a potential application in chemical sensors of some metal ions.     

Synthesis of a conjugated polymer for sensing ferric/ferrous cations based on dual responses

A conjugated polymer (PPETE-RB) with poly[p-(phenylene ethynylene)-alt-(thienylene-ethynylene)] (PPETE) as the backbone with pendant rhodamine B (RB) groups in the close-ring spirolactam form was synthesized. With long spacer between backbone and pedant groups as well as long solubilizing side chains, the polymer possesses good solubility in most organic solvents and relatively large molecular weight. The fluorescence of the conjugated polymer in THF exhibited selective dual responses upon adding Fe³⁺/Fe²⁺ but negligible response upon other cations. The emission around 481 nm (excited at 360 nm) decreased and that around 571 nm (excited at 520 nm) emerged and increased when increasing the concentration of iron ions. The responses to Fe³⁺ and Fe²⁺ are very similar. The limits of detection were found to fall in between 6 μM and 8 μM. The mechanism study showed that the quenching around 481 nm was due to the inner filter effect (IFE) between the Fe³⁺/Fe²⁺ and PPETE-RB; while that enhancement around 571 nm could be attributed to the formation of fluorescent ring-open structure from nonfluorescent spirolactam of pedant RB group upon Fe³⁺/Fe²⁺. Such dual and opposite responses provided more reliable information than single response for sensing applications.     

Drawing with Iron on a Gel Containing a Supramolecular Siderophore

Guanosine‐5′‐hydroxamic acid ( 3 ) forms hydrogels when mixed with guanosine ( 1 ) and KCl. The 5′‐hydroxamic acid (HA) unit is pH‐responsive and also chelates Fe³⁺. When gels are prepared under basic conditions, the 5′‐HA groups are deprotonated and the anionic hydrogel binds cationic thiazole orange (TO), signaled by enhanced fluorescence. The HA nucleoside 3 , when immobilized in the G‐quartet gel, acts as a supramolecular siderophore to form red complexes with Fe³⁺. We patterned the hydrogel's surface with FeCl₃, by hand and by using a 3D printer. Patterns form instantly, are visible by eye, and can be erased using vitamin C. This hydrogel, combining self‐assembled G‐quartet and siderophore–Fe³⁺ motifs, is strong, can be molded into different shapes, and is stable on the bench or under salt water.     

A highly selective coumarin-based chemosensor for the sequential detection of Fe3+ and pyrophosphate and its application in living cell imaging

A new chemosensor based on coumarin FB has been designed and synthesized for the detection of Fe³⁺ and PPi. FB displayed a high affinity to Fe³⁺ in the presence of other competing cations. The resulting FB-Fe³⁺ complex displayed highly sensitivity to PPi via Fe³⁺ displacement approach. The Fe³⁺ and PPi recognition processes is rapid and reversible, the detection limits of FB to Fe³⁺ and FB-Fe³⁺ complex to PPi were estimated to be 8.73?×?10^?8?M and 1.25?×?10^?8?M, respectively. The good biocompatibility of FB enables the investigation of fluorescent response for Fe³⁺ and PPi in living cells by confocal microscope. A B3LYP/6-31G(d,p) basis set was employed for optimization of FB and FB-Fe³⁺ complex.     

A Bis‐Oxime Derivative of Diaza‐18‐Crown‐6 as an Ionophore for Silver Ion

A new pendant‐arm derivative of diaza‐18‐crown‐6, containing two oxime donor groups, has been synthesized and incorporated into a polyvinyl chloride (PVC) membrane ion‐selective electrode. The electrode shows selectivity for Ag⁺ ion, with a near Nernstian response. Pb²⁺, Cu²⁺, Hg²⁺, and Tl⁺ are major interfering ions, with Cd²⁺ having minor interference. The electrode shows no potentiometric response for the ions Mg²⁺, Al³⁺, K⁺, Ca²⁺, Ni²⁺, Fe³⁺, and La³⁺, and is responsive to H⁺ at pH<6.