Thiazole sulfonamide based ratiometric fluorescent chemosensor with a large spectral shift for zinc sensing

A new thiazole sulfonamide (TTP, 1) based Zn²⁺ selective intrinsic chemosensor has been synthesized and investigated. The chemosensor shows a selective fluorescence enhancement (3.0 fold) with Zn²⁺ over biologically relevant cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) and biologically non-relevant cations (Cd²⁺) in an aqueous ethanol system. It produces an increase in the quantum yield and a longer emission wavelength shift (64 nm) on Zn²⁺ binding with the potential of a ratiometric assay.     

Simple imine linked colorimetric and fluorescent receptor for sensing Zn ions in aqueous medium based on inhibition of ESIPT mechanism

Herein, we report the highly selective binding of Zn²⁺ ion by the salicylaldimine based Schiff base chromogenic receptor 1 [(N,N′-bis (salicylidine)-o-phenylenediamine]. Receptor 1 senses Zn²⁺ ion in aqueous medium by colorimetric and fluorescent response in the presence of other metal ions like Pb²⁺, Hg²⁺, Sn²⁺, Cd²⁺. Receptor 1 on binding with Zn²⁺ ion exhibits fluorescence enhancement which is due to the inhibition of the (ESIPT) mechanism.     

Thiazole-based chemosensor: synthesis and ratiometric fluorescence sensing of zinc

A new ratiometric and selective fluorescent chemosensor (1), based on thiazole for quantification of zinc ions in aqueous ethanol, was synthesized and investigated. The mechanism of fluorescence was based on the cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT).     

A dual-response fluorescent probe for Zn and Al detection in aqueous media: pH-dependent selectivity and practical application

A Schiff base-type fluorescent probe (1) consist of 2-hydroxynaphthaldehyde and glutamide moieties has been designed and synthesized for detection Zn²⁺ and Al³⁺. The probe shows pH dependent dual-selectivity for Zn²⁺ and Al³⁺ in Tris-HCl buffer, viz. that can selectively recognized Zn²⁺ at pH 7.4 and Al³⁺ at pH 6.0, respectively. From Job's plots and MS data, the stoichiometric ratios of the probe with Zn²⁺ and Al³⁺ appeared to be 1:1 and 2:1, respectively. The probe can detect as low as 5.5 × 10⁻⁸ M⁻¹ Zn²⁺ and 1.27 × 10⁻⁷ M⁻¹ Al³⁺, whereas respective association constants are 4.27 × 10⁴ M⁻¹ and 3.50 × 10⁹ M⁻¹. Furthermore, it is also confirmed that the probe has good cell-permeability and could thus be used to selectively sense intracellular Zn²⁺ and Al³⁺ by bioimaging in different pH environment. Finally the probe has been used successfully for determination of the analytes in real drug samples.     

Molecular fluorescent probe for Zn based on 2-(2-nitrostyryl)-8-methoxyquinoline

A fluorescent Zn²⁺ sensor based on the 2-(2-nitrostyryl)-8-methoxyquinoline (2-nitroSQ) has been designed, synthesized, and characterized by various spectral techniques. The designed fluorophore displays high selectivity, sensitive fluorescence enhancement (13-fold), and strong binding affinity toward Zn²⁺ among the various biologically significant metal ions examined in ACN-H₂O (9:1, v/v).     

A chemosensor showing discriminating fluorescent response for highly selective and nanomolar detection of Cu and Zn and its application in molecular logic gate

A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu²⁺ and Zn²⁺ in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn²⁺ and Cu²⁺ ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu²⁺ and Zn²⁺ ions, respectively. Further, we have effectively utilized the two metal ions (Cu²⁺ and Zn²⁺) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm.     

Synthesis of 1,8-naphthyridine and BF2-based isomers and their application in fluorogenic sensing Cd

A series of isomers were synthesized and identified, two isomers of which were developed as the dual-channel fluorescent probe toward Cd²⁺. BF₂ dissociates from the probe upon reaction with CdCl₂, demonstrating a new approach for sensing Cd²⁺.     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.     

Exploiting the deprotonation mechanism for the design of ratiometric and colorimetric Zn fluorescent chemosensor with a large red-shift in emission

The design, synthesis, and photophysical evaluation of a new naphthalimide-based fluorescent chemosensor, N-butyl-4-[di-(2-picolyl)amino]-5-(2-picolyl)amino-1,8-naphthalimide (1), were described for the detection of Zn²⁺ in aqueous acetonitrile solution at pH 7.0. Probe 1 showed absorption at 451 nm and a strong fluorescence emission at 537 nm (Φ_F=0.33). The capture of Zn²⁺ by the receptor resulted in the deprotonation of the secondary amine conjugated to 1,8-naphthalimide so that the electron-donating ability of the N atom would be greatly enhanced; thus probe 1 showed a 56 nm red-shift in absorption (507 nm) and fluorescence spectra (593 nm, Φ_F=0.14), respectively, from which one could sense Zn²⁺ ratiometrically and colorimetrically. The deprotonated complex, [(1-H)/Zn]⁺, was calculated at m/z 619.1800 and measured at m/z 618.9890. In contrast to these results, the emission of 1 was thoroughly quenched by Cu²⁺, Co²⁺, and Ni²⁺. The addition of other metal ions such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Mn²⁺, Al³⁺, Cd²⁺, Hg²⁺, Ag⁺, and Pb²⁺ produced a nominal change in the optical properties of 1 due to their low affinity to probe 1. This means that probe 1 has a very high fluorescent imaging selectivity to Zn²⁺ among metal ions.     

A novel small molecule fluorescent sensor for Zn2+ based on pyridine-pyridone scaffold

The development of a water-soluble and small molecular weight fluorescent probe, 3-(4-methoxyphenyl)-4-(methylsulfanyl)-6-(pyridin-2-yl)pyridin-2(1H)-one (3), for detecting Zn²⁺ based on pyridine-pyridone skeleton is reported. We observed a clear chelation enhanced fluorescence effect of 3 in the presence of Zn²⁺. Other fluorescent properties of 3 are discussed.     

A label-free and signal-on supersandwich fluorescent platform for Hg sensing

A label-free supersandwich fluorescent assay was demonstrated for the first time by taking Hg²⁺ as a detection candidate. The principle of the proposed supersandwich fluorescent platform is based on the formation of supersandwich structure by T-Hg²⁺-T coordination and the fluorescence enhancement of the intercalated Genefinder (GF) in double strand DNA (dsDNA). Such supersandwich fluorescent DNA sensor exhibits a linear range of 10–300 nM for the detection of Hg²⁺, with a detection limit of 2.5 nM on the basis of the 3σ/slope (σ represents the standard deviation of the blank samples), which is well below the permit of the U.S. Environmental Protection Agency (<10 nM). The detection can be fulfilled in less than 10 min. The proposed mix-and-detect fluorescent platform exhibits excellent sensitivity, selectivity, and convenient manipulation. The assay was successfully used to detect Hg²⁺ in the lake water samples, which suggested its potential in practical samples.     

Four Zn(II)/Cd(II) coordination polymers derived from isomeric benzenedicarboxylates and 1,6-bis(triazol)hexane ligand: synthesis,crystal structure,and luminescent properties

Four coordination polymers, [Zn(o-bdc)(bth)_0.5(H₂O)] _n (1), [Cd(o-bdc)(bth)_0.5(H₂O)] _n (2), [Zn(m-bdc)(bth)] _n (3), and [Cd(p-bdc)(bth)?·?(H₂O)₂] _n (4) (where o-bdc?=?1,2-benzenedicarboxylate, m-bdc?=?1,3-benzenedicarboxylate, p-bdc?=?1,4-benzenedicarboxylate, and bth?=?1,6-bis(triazol)hexane), have been hydrothermally synthesized and structurally characterized. Both 1 and 2 are isostructural, featuring two binodal architectures: (6³)(6⁵·8) topology in terms of o-bdc and Zn^II/Cd^II as three- and four-connected nodes. Complex 3 shows a 2-D (4,4) network with the Zn?···?Zn?···?Zn angle of 57.84°, whereas 4 exhibits planar 2-D (4,4) network. These 2-D networks of 3 and 4 are extended by supramolecular interactions, such as CH?···?π/π–π stacking and hydrogen-bonding into 3-D architecture. A structural comparison of these complexes demonstrates that the dicarboxylate building blocks with different dispositions of the carboxyl site play a key role in governing the coordination motifs as well as 3-D supramolecular lattices. Solid-state properties such as photoluminescence and thermal stabilities of 1–4 have also been studied.     

Ratiometric fluorescent determination of Zn(II): a new class of tripodal receptor using mixed imine and amide linkages

We synthesized a novel receptor with a unique combination of sp² nitrogen (-CHN-) and carbonyl groups from amide linkages. These two moieties are judiciously incorporated into the receptor design such that these sites simultaneous binding a metal ion may generate a stable five-member ring. The receptor has been used to selectively detect Zn²⁺ through changes in the fluorescence spectra. Upon Zn²⁺ binding with the receptor, the fluorescence band shifted to enhance fluorescence intensity, allowing ratiometric determination of Zn²⁺ concentration.     

A highly selective visual and fluorescent sensor for Pb2+ and Zn2+ and crystal structure of Cu2+ complex based-on a novel single-armed Salamo-type bisoxime

A novel single-armed Salamo-type bisoximes (H₄L) has been designed and synthesised. An obvious colour change from yellow (H₄L) to pale pink (HL-Pb²⁺) which can be visually observed by the naked eye in visible light. H₄L can act as a fluorescent sensor for ratiometric recognition of Zn²⁺ with high selectivity and sensitivity. Crystallographic data of the [Cu(HL)(μ-OAc)Cu] reveals that the two Cu²⁺ ions are both penta-coordinated with square pyramidal geometries, and forms a 2D supramolecular plane structure by hydrogen bonding interactions.     

Study on the synthesis of novel fluorescent macrocyclic sensors and their sensitive properties for Cu2+ and Fe3+ in aqueous solution

In this work, we synthesised and characterised three novel fluorescence macrocyclic sensors containing optically active dansyl groups. The studies for the interaction of the synthesised compounds with various mental ions (Li⁺, Na⁺, K⁺, Ag⁺, Mg²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Zn²⁺, Co²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Cr³⁺, Al³⁺, Fe³⁺) were performed by fluorescence titration, Job’s plot, ESI-MS and DFT calculations. The results showed that the sensors 1a–1c displayed selective recognition for Cu²⁺ and Fe³⁺ ions and formed stoichiometry 1:1 complex through PET mechanism in DMSO/H₂O solution (1:1, v/v, pH 7.4 of HEPES). The binding constant (K) and detection limit were calculated.     

Thermal investigations of nitrate-hydrates and deuterates of Ca2+, Cd2+ and Mg2+

DTA and DSC were used to study the thermal behaviour of Ca(NO₃)₂·4H₂O, Cd(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O and their deuterated analogues. Evidence was found concerning the process of melting of the initial hydrates and deuterates, followed by a one-stage dehydration of the melt to vield the respective anhydrous salt. T _m, ΔH _m ^o , ΔS _m ^o and ΔH _deh ^o were determined and the ΔH _f ^o values for the investigated hydrates were calculated from the ΔH _deh ^o data.

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Zusammenfassung DTA und DSC wurden zur Untersuchung des thermischen Verhaltens von Ca(NO₃)₂·4H₂O, Cd(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O und ihrer deuterierten Analoge eingesetzt. Man fand Aussagen bezüglich des Schmelzvorganges der Ausgangshydrate und Deuterate, gefolgt von einer Einschritt-Dehydratation der Schmelze unter Bildung der entsprechenden wasserfreien Salze. T _m, ΔH _m ^o , ΔS _m ^o und ΔH _deh ^o wurden ermittelt und die ΔH _f ^o Werte für die untersuchten Hydrate wurden anhand der ΔH _deh ^o berechnet.

     

Sodium polyacrylate as a binding agent in diffusive gradients in thin-films technique for the measurement of Cu and Cd in waters

An aqueous solution containing sodium polyacrylate (PA, 0.0030 M) was used in diffusive gradients in thin-films technique (DGT) to measure DGT-labile Cu²⁺ and Cd²⁺ concentrations. The DGT devices (PA DGT) were validated in four types of solutions, including synthetic river waters containing metal ions with or without complexing EDTA, natural river water (Hun River, Shenyang, China) spiked with Cu²⁺ and Cd²⁺, and an industrial wastewater (Shenyang, China). Results showed that only free metal ions were measured by PA DGT, recovery = 98.79% for Cu²⁺ and recovery = 97.80% for Cd²⁺ in solutions containing only free metal ions, recovery = 51.02% for Cu²⁺ and recovery = 51.92% for Cd²⁺ in solution with metal/EDTA molar ratio of 2:1 and recovery = 0 in solutions with metal/EDTA molar ratio of 1:1 and 1:2. These indicated that the complexes of Cu-EDTA and Cd-EDTA were DGT-inert or not DGT-labile. The DGT performance in spiked river water (recovery = 8.47% for Cu²⁺ and recovery = 27.48% for Cd²⁺) and in industrial wastewater (recovery = 14.16% for Cd²⁺) were also investigated. Conditional stability constants (log K) of PA-Cu and PA-Cd complexes were determined as 6.98 and 5.61, respectively, indicating strong interaction between PA and the metals.     

Cd2+ and Zn2+ Complexes with 2,4,6‐Tri(2‐pyridyl)‐s‐Triazine and Terephthalate for Rapid,High‐Capacity Adsorption of Congo Red

Three crystal complexes were designed and synthesised through the solvothermal method, with Cu²⁺, Zn²⁺, and Cd²⁺ ions as the metal centres and 2,4,6‐tri(2‐pyridyl)‐s‐triazine (TPTZ) and terephthalate (BDC²⁻) as the ligands. Their compositions were determined to be Cd(TPTZ)Cl₂ (Cd‐MOF), {[Zn(TPTZ)(BDC)] ⋅ 3H₂O}_n (Zn‐MOF), and Cu₂(PCA)₂(BDC)(H₂O)₂ (Cu‐MOF) (PCA⁻=2‐pyridinium amide), respectively. Cd‐MOF can adsorb 90 % of Congo red (CR) in 10 s at room temperature and atmospheric pressure, and CR removal was complete at 20 s over a wide pH range. The adsorption capacity for CR reached 1440 mg g⁻¹ in 5 min. Selective adsorption was demonstrated in mixed dyes. The adsorption kinetic data agree well with the pseudo‐second‐order kinetic model. The Temkin model was successfully used to evaluate the adsorption isotherms of CR on Cd‐MOF at room temperature, suggesting that adsorption occurs through a hybrid of monolayer and multilayer mechanisms.     

Graphene quantum dots with Zn2+ and Ni2+ conjugates can cleave supercoiled DNA

Graphene quantum dots (GQDs), inheriting the superb property of graphene oxide, possess smaller lateral size and high biocompatibility, thus having potential in biomedical applications. We previously discovered that GQDs, combining with Cu²⁺ ions, could cleave DNA primarily through an oxidative pathway; yet, oxidative DNA cleavage is not practically preferred in biology. In this work, we explore the DNA cleavage ability of GQDs with Zn²⁺ and Ni²⁺. Zn²⁺ and Ni²⁺ alone are incapable of cleaving supercoiled DNA, but when combining with the GQDs, Zn²⁺ and Ni²⁺ exhibit DNA cleavage activity. However, the activity of these two systems is much lower than that of GQDs/Cu²⁺, and GQDs/Ni²⁺ is less active than GQDs/Zn²⁺. The functional mechanism of GQDs/Ni²⁺ and GQDs/Zn²⁺ is different from that of GQDs/Cu²⁺. The GQDs play a key role in the two systems; the redox inactive Zn²⁺ and Ni²⁺ ions assist to generate the oxidative species that eventually lead to the DNA cleavage. The current results together with our previous result indicate that GQDs together with metal ions can cleave supercoiled DNA, and their cleavage activities depend on the properties of metal ions: for redox active metal ions, metal ions play key roles, for redox inactive metal ions, GQDs are dominant.     

Ratiometric fluorescent and colorimetric sensors for Cu based on 4,5-disubstituted-1,8-naphthalimide and sensing cyanide via Cu displacement approach

Two 4,5-disubstituted-1,8-naphthalimide derivatives 1 and 2 were synthesized as ratiometric fluorescent and colorimetric sensors for Cu²⁺, respectively. In 100% aqueous solutions of 1, the presence of Cu²⁺ induces a strong and increasing fluorescent emission centered at 478 nm at the expense of the fluorescent emission of 1 centered at 534 nm. Compound 2 senses Cu²⁺ by means of a colorimetric (primrose yellow to pink) method with a thorough quench in emission attributed to the deprotonation of the secondary amine conjugated to the naphthalimide fluorophore. 1-Cu²⁺ and 2-Cu²⁺ sense cyanide in ratiometric way via colorimetric and fluorescent changes.