A simple method for improving the optical properties of a dimetallic coordination fluorescent chemosensor for adenosine triphosphate

The selectivity and sensitivity of [Zn₂(9,10-bis[(2,2-dipicolylamino)methyl]anthracene)]⁴⁺ (1) were enhanced by eliminating its intrinsic fluorescence with the introduction of pyrocatechol violet. An ensemble ([Zn₂(9,10-bis[(2,2-dipicolylamino)methyl]anthracene)(pyrocatechol violet)]²⁺) can easily detect less than 1 μM of ATP and can discriminate between ATP and various other anions including adenosine diphosphate (ADP).     

L-Arginine and zinc ion effect on recognition and hydrolysis rate of adenosine 5′-triphosphate

Zn²⁺ can interact with adenosine 5′-triphosphate (ATP) by electrostatic and coordination interactions, and the interaction sites between Zn²⁺ and ATP vary at different pH in the ATP–Zn²⁺ binary system. Non-covalent interactions exist between the carboxyl of arginine (Arg) and Zn²⁺, which led to competition between ATP and Arg to interact with Zn²⁺ in the ATP–Zn²⁺–Arg ternary system. Kinetics studies show that the hydrolysis rate constant of ATP in the ATP–Zn²⁺ binary system was 2.44?×?10^?2?min^?1, about 11-fold faster than that (2.27?×?10^?3?min^?1) in the ATP–Zn²⁺–Arg ternary system. This may be attributed to coordination interactions between the carboxyl of Arg and Zn²⁺ and the decreased activity of zinc ion toward the phosphate groups via nucleophilic attack. A mechanism that the hydrolysis occurred through an addition–elimination mechanism is proposed.     

Three new turn-on fluorescent sensors for the selective detection of Zn2+: Synthesis,properties and DFT studies

The design and synthesis of three new 1,8-naphthalimide-based fluorescent sensors (1–3) for the detection of Zn²⁺ in aqueous solution is described. The structural architect of these sensors contains 1,8-naphthalimide scaffold as a fluorophore attached to 2,2′-dipicolylamine (DPA) and bis(2-quinolinylmethyl)amine (DQA) receptors through an amide linkage. The addition of Zn²⁺ to the solutions of sensors (1–3) led to enhanced fluorescence intensity, ranging between 2.5 and 14 folds. At physiological pH (pH = 7.4), these sensors exhibited high selectivities for Zn²⁺ over a wide range of competing metal cations, displaying high sensitivities with a limit of detections of 120, 81.7 and 79.2 nM, respectively. This suggests that these sensors can detect chronic Zn²⁺ concentration for freshwater (>1.84 μM), designated by the U.S. Environmental Protection Agency. DFT simulations performed on the more stable stacked conformations of unbound and Zn²⁺ bounded states suggested that the latter display higher density of excited states than the unbound sensors. Moreover, the stacked conformer of sensor 3 was significantly more stable as compared to sensors 1 and 2, which was attributed to a stronger Van Der Waals (VDW) interaction between DQA and 1,8-naphthalimide. The Zn²⁺ binding leads to enhanced electronic coupling between the HOMOs and LUMOs, making excited states more populated which then undergoes geometric relaxation before emitting light and relaxing back to the ground states. The lower energy separation (5.0 eV) between the HOMO and the first Zn²⁺ d-orbital in sensor 3 as compared to sensors 1 and 2 results in enhanced density of the generated states and subsequently higher intensity upon binding with Zn²⁺.     

Gadolinium(III)–fluorescein complex as a dual modal probe for MRI and fluorescence zinc sensing

A bimodal imaging Gd–Zpy probe based on magnetic resonance imaging and fluorescence sensing has been synthesized and characterized. Gd–Zpy features a bright green emission and a turn-on fluorescent response manner with high sensitivity for Zn²⁺ in aqueous solution and is able to luminescent imaging intracellular Zn²⁺ levels within living cells. It exhibits a 130% increase of the longitudinal relaxation time and a 115% increase of transverse relaxive time upon addition of Zn²⁺. The results demonstrated that the incorporating of the fluorescein dye having the efficient chelators within a high-spin Gd³⁺ system was a powerful approach to achieve dual modal probes for MRI and fluorescence sensing.     

A novel highly selective ratiometric fluorescent sensor for relay recognition of Zn2+ and H2PO4−

A novel fluorescent sensor (AQTF1) based on the N-(quinolin-8-yl) tetrahydrofuran-2-carboxamide was designed and synthesized. This new sensor demonstrated high selectivity for the Zn²⁺ without the interference from Cd²⁺. The detection limit of this probe was calculated to be 10.8 nM for Zn²⁺. The in situ prepared AQTF1-Zn²⁺ complex was used for detection of H₂PO₄^? and displayed good selectivity from the common anions. Furthermore, the AQTF1 displayed good ratiometric response for the relay recognition for Zn²⁺ and H₂PO₄^?.     

Fluorescent sensing of pyrophosphate and ATP in 100% aqueous solution using a fluorescein derivative and Mn

A new fluorescein derivative has been synthesized for the detection of pyrophosphate (PPi) and ATP in 100% aqueous solution. Chemosensor 1 in the presence of Mn²⁺ (2.5 equiv) displayed selective fluorescent enhancements with PPi and ATP at pH 7.4. among the anions examined. The association constant of 1 in the presence of Mn²⁺ with PPi and ATP was calculated as 4.2 × 10⁴ and 3.5 × 10⁴ M⁻¹.     

A new acridine derivative as a fluorescent chemosensor for zinc ions in an 100% aqueous solution: a comparison of binding property with anthracene derivative

A new acridine derivative was synthesized as a fluorescent chemosensor for Zn²⁺ in an 100% aqueous solution. Compound 1 displayed a selective CHEF (chelation enhanced fluorescence) effect with Zn²⁺, on the other hand, a similar anthracene derivative 2 did not display any significant change with the metal ions examined.     

A novel carbazole-based ratiometric fluorescent sensor for Zn recognition through excimer formation and application of the resultant complex for colorimetric recognition of oxalate through IDAs

A new carbazole-based Zn²⁺ selective fluorescent sensor L has been developed. In CH₃CN/H₂O (1:1, v/v, HEPES 10 mM, pH=7.4) solution, L displays selective and ratiometric responses to Zn²⁺ through excimer formation. The Zn²⁺ recognition process has good anti-interference ability over other metal ions. The dinuclear complex Zn₂L₂ was further used as a receptor for oxalate. Through constructing a chemosensing ensemble with chromeazurol S, colorimetric recognition of oxalate in water solution was achieved via indicator displacement assays. The oxalate recognition process exhibits obvious color changes from blue to yellow and is naked eye detectable.     

Coumarin-based fluorescent chemosensor for the selective quantification of Zn2+ and AcO− in an aqueous solution and living cells

In this work, we report a novel fluorescence chemosensor HM based on the coumarin fluorophore for the quantification of Zn²⁺ and AcO^?. HM specifically binds to Zn²⁺ in the presence of other competing cations, and evident changes in UV–vis and fluorescence spectra in HEPES buffer are noticed. The in situ generated HM-Zn²⁺ complex solution exhibit a high selectivity toward AcO^? via Zn²⁺ displacement approach. The detection limits of HM for Zn²⁺ and HM-Zn²⁺ for AcO^? were estimated to be 7.24 × 10^?8 M and 9.41 × 10^?8 M, respectively. HM and the resultant complex HM-Zn²⁺ exhibit low cytotoxicity and cell-membrane permeability, which makes them capable of Zn²⁺ and AcO^? imaging in living Hep G2 cells. A B3LYP/6-31G(d,p) basis set was employed for optimization of HM and HM-Zn²⁺ complex.     

Synthesis,Crystal Structure and Characterization of 3d–4d–4f Heterometallic Clusters Based on Super Tetrahedron Anions

Five heterometallic complexes were prepared in aqueous solution at 3–5 °C and characterized by elemental analyses, inductively coupled plasma analysis, IR spectra, UV–Vis spectra, powder X-ray diffraction and X-ray single-crystal diffraction. Complex 1–5 all contain 4d–4f super tetrahedron cluster anions, which are constructed by Ln^III ions (Ln = Nd^III, Pr^III), [MoO₄]^2? and [Mo₇O₂₄]^6? anions. Differences among 1–5 lie on the assembly of super tetrahedron anions by excess Ln^III and TM^II (TM = Co^II, Ni^II, Cu^II or Zn^II), which generates bigger cluster anions (complex 1–4) or anions with 1D infinite structure (complex 5). The assemble styles for synthons mentioned above show with capped style, head-to-head linking style or side-by-side linking style.     

Fluorescence properties of polyamines bearing two terminal quinoline fragments in water

Fluorescence properties of polyamines bearing two terminal quinoline fragments with different polyamine chain length, such as ethylenediamine (L0), diethylenetriamine (L1), and triethylenetetramine (L2), have been studied in water. These ligands show Zn²⁺-induced fluorescence enhancement, while showing almost no enhancement with other cations. However, stability constants for Zn²⁺ coordination and fluorescence response against Zn²⁺ depend strongly on the polyamine chain length. The chain length also affects the fluorescence wavelength. The Zn²⁺-L1 and Zn²⁺-L2 complexes show emission at 410 nm, while Zn²⁺-L0 complexes show a blue-shifted emission at 375 nm due to the partial charge transfer from the excited state quinoline to the Zn²⁺ center.     

A highly selective diarylethene chemosensor for dual channel recognition of CN− and Zn2+ and its application

A novel diarylethene chemosensor comprising 3-aminobenzofuran-2-carboxamide Schiff base (1O) was synthesized and the photophysical and sensing behaviors of 1O were further investigated. Importantly, the introduction of electron-withdrawing group to 1O made the sensor an efficient tool for detection of toxic cyanide even in the presence of other plausible interfering anions including fluoride and acetate. In particular, addition of CN^? to 1O visibly changes the color from colorless to orange-red, which can be observed by the naked eye. Apart from this, it also exhibited an outstanding fluorometric sensing toward Zn²⁺ with high selectivity and sensitivity. Moreover, the remarkable spectral responses of the devised sensor prompted us to fabricate molecular logic circuit. Furthermore, the sensor was successfully applied to the detection of CN^? on test strips and silica coated microslides, and the methods were very simple to operate without resorting to any spectroscopic instrumentation. In addition, the 1O can also effectively detect CN^? and Zn²⁺ in actual water samples.     

A novel BF<Subscript>2</Subscript>–curcumin-based fluorescent chemosensor for detection of Cu<Superscript>2+</Superscript> in aqueous solution and living cells

A novel BF₂–curcumin-based chemosensor 1, namely monopicolinate of BF₂–curcumin complex, was designed, synthesized and applied for the detection of Cu²⁺ in aqueous buffer solution and living cells. Sensor 1 exhibited sensitive naked-eye color change toward Cu²⁺ from blue to pink in TBS solution and the detection limit was estimated to be 0.12 µM. The selectivity of sensor 1 for Cu²⁺ was high over competing metal ions (Ag⁺, Cu⁺, Hg²⁺, Mg²⁺, Ca²⁺, Co²⁺, Zn²⁺, Mn²⁺, Ni²⁺, Fe²⁺ and Fe³⁺). Based on the experimental results, the sensing mechanism was proposed for the Cu²⁺ triggered hydrolysis of 1 to BF₂–curcumin which has unique chromogenic and fluorogenic properties. Compared with other chemosensors with a similar mechanism, chemosensor 1 had a comparatively large Stokes shift and the emission wavelength was close to NIR. Moreover, cell imaging investigations indicated that sensor 1 has the potential to be applied for practical Cu²⁺ detection in biological systems.     

Fluorescent sensors based on controllable conformational change for discrimination of Zn2+ over Cd2+

A new coumarin-derived imine IC1 was designed for highly selective sensing of Zn²⁺ over Cd²⁺ ions in aqueous solution based on a controllable CN isomerization mechanism. Methyl as a fine controllable unit was incorporated into IC1 to tune the conformational change of imine and thus significantly improve its selectivity to Zn²⁺ compared with methyl-free imine IC2. Sensor IC1 was also utilized to image intracellular Zn²⁺ ions in HepG2 cells with a good performance.     

A bifunctional probe for Al3+ and Zn2+ based on diarylethene with an ethylimidazo[2,1-b]thiazole-6-hydrazide unit

A new diarylethene with ethylimidazo[2,1-b]thiazole-6-hydrazide unit was synthesized, and its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of lights and metal ions in methanol. This new diarylethene exhibited high selectivity and sensitivity toward Al³⁺ and Zn²⁺. The addition of Al³⁺ and Zn²⁺ displayed excellent colorimetric response behaviour with the concomitant color change from colorless to yellow, which could be easily observed by the naked eye. Upon addition of Al³⁺, the fluorescence intensity was enhanced by 180–fold and the emission peak of 1O–Al³⁺ blue-shifted by 15?nm accompanied with a color change from colorless to bright blue. In contrast, when stimulated with Zn²⁺, its fluorescence intensity was enhanced by 35–fold and the emission peak of 1O–Zn²⁺ red-shifted by 16?nm with an evident color change from black to bright green. The LOD for Al³⁺ and Zn²⁺ were determined to be 2.97?×?10^?9?mol?L^?1 and 5.98?×?10^?9?mol?L^?1, respectively. Moreover, a logic circuit was constructed with the fluorescence intensity as the output signal responding to the light and chemical species as the inputs.     

A new turn-on fluorescence probe for Zn in aqueous solution and imaging application in living cells

We designed and synthesized a new pyrazoline-based turn-on fluorescence probe for Zn²⁺ by the reaction of chalcone and thiosemicarbazide. The structure of the probe was characterized by IR, NMR and HRMS spectroscopy. The probe (L) exhibits high selectivity and sensitivity for detecting Zn²⁺ in buffered EtOH/HEPES solution (EtOH/HEPES = 1/1, pH 7.2) with 80-fold fluorescence enhancement, which is superior to previous reports. Job’s plot analysis revealed 1:1 stoichiometry between probe L and Zn²⁺ ions. The association constant estimated by the Benesi–Hildebrand method and the detection limit were 3.92 × 10³ M⁻¹ and 5.2 × 10⁻⁷ M, respectively. A proposed binding mode was confirmed by ¹H NMR titration experiments and density functional theory (DFT) calculations. The probe is cell-permeable and stable at the physiological pH range in biological systems. Because of its fast response to Zn²⁺, the probe can monitor Zn²⁺ in living cells. Moreover, the selective binding of L and Zn²⁺ was reversible with the addition of EDTA in buffered EtOH/HEPES solution and Zn²⁺ could be imaged in SH-SY5Y neuron cells.     

Metallovesicular catalytic hydrolysis of p-nitrophenyl picolinate catalyzed by zinc(II) complexes of pyridyl ligands in vesicular solution

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the Zn(II) complexes of 6-(n-butyloxymethyl)-2-(hydroxymethyl)pyridine and 6-(n-dodecyloxymethyl)-2-(hydroxymethyl)pyridine was kinetically investigated by observation of the rates of release of p-nitrophenol in a vesicular solution at different pH values and temperatures. A 1:1 ligand:Zn²⁺ stoichiometry was found to produce the most active species based on a kinetic version of the Job plot analysis. Experimental results also showed that the complex formed from ligand 2 and Zn²⁺ exhibited a more remarkable rate acceleration effect on the hydrolysis of PNPP in vesicular solution than that formed from ligand 1 and Zn²⁺.     

A highly selective ratiometric fluorescent chemosensor for Zn2+ ion based on a polyimine macrocycle

A new ratiometric fluorescent chemosensor based on a polyimine macrocycle ligand 1 has been synthesized. The chemosensor can exhibit a pronounced fluorescence response and high selectivity to Zn²⁺ ion over other 15 metal ions, including Cd²⁺. Sensor 1 appears an emission peak at 370 nm. Upon the addition of Zn²⁺ ion, the typical emission peak for 1 at 370 nm is obviously quenched, but a new emission peak at around 470 nm appears and shows a large enhancement due to the formation of a 1:1 Zn²⁺-1 complex. In addition, there is a good linear relationship between the fluorescence ratio I_470nm/I_370nm and the concentration of Zn²⁺, which makes a ratiometric assay of Zn²⁺ ion possible.     

The physicochemical properties of complexones,tetrapyridylporphin derivatives

We synthesized complexones based on tetrapyridylporphin (I), namely, tetra(pyridinium-4-N-carboxymethylene) porphin tetrachloride (II), tetra(pyridinium-4-N-carboxymethylene)porphin tetrabromide (III), complete ethyl ester of (pyridinium-4-N-carboxymethylene)porphin tetrachloride (IV), and tetra(pyridinium- 4-N-methyl)porphin tetraiodide (V). Data on the electronic absorption spectra of the compounds, the enthalpies of their solution in water, and the enthalpies of complex formation with copper(II) and zinc acetates were obtained, and the acid properties of the ligands and their stability under thermooxidative destruction conditions were studied. The conclusion was drawn that the enthalpy of solution of complexone-porphyrins in water was determined by the strength of their crystal lattices and, when different anions (Cl^?, Br^?, and I^?) were present, by the difference of the enthalpies of their hydration. As distinct from Cu²⁺, complex formation between Zn²⁺ and porphyrin ligands occurred with sensible energy expenditures likely caused by the electronic inconsistency between the zinc cation and porphyrin ligands. The stability of water-soluble porphyrins to thermooxidative destruction was limited by temperatures of 200–260°C.