New duel fluorescent "on-off" and colorimetric sensor for Copper(II): Copper(II) binds through N coordination and pi cation interaction to sensor

Sensing of Co2+ and Cu2+ Ions Using Dimethylamino-functionalized Poly(azomethine-1,3,4-oxadiazole)s

The ability of OxT and OxFl azomethines to recognize metal ions in THF solutions was investigated using UV-vis absorption techniques. Various metal ions, including Cd2+, Hg2+, Co2+, Sn2+, Cu2+, Ni2+, Zn2+ and Ag+, were tested. The absorption spectra revealed two distinct π-π* transition bands in the 273-278 nm and 330-346 nm wavelength ranges. Additionally, OxFl displayed an absorption peak at 309 nm, attributed to the fluorene group. Spectral titrations were used to study the fluorescence behavior in the presence of these metal ions. The results showed significant quenching with Co2+ and Cu2+ ions, while other metal ions had minimal effects on the fluorescence intensity. The quenching mechanism was further analyzed using the Stern-Volmer and Lehrer equations, and the binding constants ( K b fl ) were calculated using the Benesi-Hildebrand relations. The results confirm that Co2+ has a 1:2 stoichiometry and Cu2+ has a 1:1 stoichiometry, indicating the strong affinity of OxFl and OxT for these ions. The negative values of ΔG (Gibbs free energy) suggest that complex formation occurs spontaneously at room temperature.

Recent Development on Copper-Sensor and its Biological Applications: A Review

Metal ion recognition is one of the most prospective research topics in the field of chemical sensors due to its wide range of clinical, biological and environmental applications. In this context, hydrazones are well known compounds that exhibit metal sensing and several biological properties due to the presence of N=CH- bond. Some of the biological properties includes anti-cancer, anti-tumor, anti-oxidant, anti-microbial activities. Hydrazones are also used as a ligand to detect metal ion as well as to generate metal complexes that exhibit medicinal properties. Thus, in recent years, many attempts were made to develop novel ligands with enhanced metal sensing and medicinal properties. In this review, some of the recent development on the hydrazones and their copper complexes are covered from the last few years from 2015-2023. These includes significance of copper ions, synthesis, biological properties, mechanism and metal sensing properties of some of the copper complexes were discussed.

A novel dehydroabietic acid-based multifunctional fluorescent probe for the detection and bioimaging of Cu2+/Zn2+/ClO. Analyst 2023;148:1867-1876. [PMID: 36942689 DOI: 10.1039/d3an00001j]

A multifunctional dehydroabietic acid-based fluorescent probe (CPS) was designed and synthesized by introducing the 2,6-bis(1H-benzo[d]imidazol-2-yl)phenol fluorophore. The probe CPS could selectively recognize Cu²⁺, Zn²⁺ and ClO^- ions from other analytes, and it showed fluorescence quenching behavior toward Cu²⁺ and a ratiometric response to Zn²⁺ and ClO^- by changing from green fluorescence to blue and cyan, respectively. The detection limits toward Cu²⁺, Zn²⁺ and ClO^- ions were 3.8 nM, 0.253 μM and 0.452 μM, respectively. In addition, CPS presented many fascinating merits, such as high selectivity, a short response time (15-20 s), a wide pH range (3-10) and high photostability. The sensing mechanisms of CPS were verified by ¹H-NMR, ESI-MS, FT-IR and Job's plot methods. Meanwhile, CPS exhibited satisfactory detection performance in water samples. More importantly, the probe could be applied as a promising tool for visual bioimaging of three ions in living cells and zebrafishes.

Fluorescent Sensors for Hg2+ and Cu2+ Based on Condensation Products of 4H-1,2,4 Triazole-4-Amine and Carboxylated Benzoic Acids

Mercury (Hg) causes serious health issues in its all forms. Deficiency as well as excess of copper ion (Cu²⁺) in human body is hazardous. A series of four compounds have been derived from carboxylated benzoic acids (benzoic acid, isophthalic acid, terephthalic acid and phthalic acid) and 4H-1,2,4 triazole-4-amine and characterized. Fluorescence detection of Hg²⁺ was recorded by the derivates with benzoic acid and isophthalic acid while the derivatives of terephthalic acid and phthalic acid detect Cu²⁺ by fluorescence "off" mode. Metal ions like Li⁺, Na⁺, K⁺, Zn²⁺, Al³⁺, Mg²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Pb²⁺ and Hg²⁺ found not to interfere. The stoichiometry of binding is 1:1 for the benzoic acid derivative with Hg²⁺ while it is 1:2 for the other three derivatives. The binding constants are ca. 10^-4.5 between the sensors and Hg²⁺ or Cu²⁺ and detection limits are around 10^-5.5 M. DFT calculation provided optimized geometries of the sensors and confirmed the stoichiometry of binding with Hg²⁺/Cu²⁺.

Highly Sensitive and Selective Spiropyran-Based Sensor for Copper(II) Quantification

The metal-binding capabilities of the spiropyran family of molecular switches have been explored for several purposes from sensing to optical circuits. Metal-selective sensing has been of great interest for applications ranging from environmental assays to industrial quality control, but sensitive metal detection for field-based assays has been elusive. In this work, we demonstrate colorimetric copper sensing at low micromolar levels. Dimethylamine-functionalized spiropyran (SP1) was synthesized and its metal-sensing properties were investigated using UV-vis spectrophotometry. The formation of a metal complex between SP1 and Cu²⁺ was associated with a color change that can be observed by the naked eye as low as ≈6 μM and the limit of detection was found to be 0.11 μM via UV-vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0-20 μM Cu²⁺) with high selectivity for Cu²⁺ ions over biologically and environmentally relevant metals such as Na⁺, K⁺, Mn²⁺, Ca²⁺, Zn²⁺, Co²⁺, Mg²⁺, Ni²⁺, Fe³⁺, Cd²⁺, and Pb²⁺. Since the color change accompanying SP1-Cu²⁺ complex formation could be detected at low micromolar concentrations, SP1 could be viable for field testing of trace Cu²⁺ ions.

Condensation Product of p-anisaldehyde and L-phenylalanine: Fluorescent "on-off" Sensor for Cu2+ and IMPLICATION Logic Gate

(Z)-2-(4-methoxybenzylideneamino)-3-phenylpropanoic acid (L) synthesized by condensation of p-anisaldehyde and L-phenylalanine acts as selective fluorescent as well as voltammetric sensor for Cu²⁺ in 2:1 (v/v) CH₃OH:H₂O. The fluorescence intensity of L (λ_max 425 nm) is quenched ca. 65% by Cu²⁺. Metal ions - Li⁺, Na⁺, K⁺, Al³⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Mn²⁺, Ni²⁺ and Pb²⁺ do not interfere. The binding constant and the detection limits were calculated to be 0.56 × 10² M^-1 and 10^-6 M respectively. DFT and TDDFT calculations confirmed 2:1 binding stoichiometry between L and Cu²⁺ obtained from fluorescence data. The interaction between L and Cu²⁺ is reversible for many cycles with respect to ethylenediamine tetraacetate anion (EDTA^2-) which results in IMPLICATION logic gate.

Re-usage of the Waste Drug as Molecular Chemosensor for Fe3+ Ion: Application towards Fluorescent Ink

Herein, a novel notion is used to reuse an expired drug namely Telmisartan (Sensor 2) to optically sense the Fe³⁺ metal ion. Direct re-usage of the drug avoided wearisome procedures of synthesis, hence proved the method as simple and economic. Sensor 2 found highly stable in the temperature range 25-75 °C. Relative fluorescence was almost the same even after 35 days of observation. There were no significant changes in wavelength even after adding different concentrations of FeCl₃, which shows the high stability of the compound. The value of Limit of Detection (LOD) observed was 34.2 nM. FTIR studies confirmed the presence of carboxylic group. The method of fluorescence quenching was used to detect the Fe³⁺ ion. The association between Sensor 2 and Fe³⁺ was analyzed using Benesi-Hildebrand relation. Positive deviation from the linearity of S-V plots suggested that the quenching was not purely dynamic. Further, this deviation was analyzed by the sphere of action quenching model. To investigate whether the quenching is diffusion limited, we applied the finite sink approximation model and deduced that quenching is due to both static and dynamic processes. Due to the high fluorescence property of the molecule, it was successfully tested to be used as fluorescent ink.

A Spectroscopic Study of Xanthene Dyes on a Polystyrene Surface: an Investigation of Ion-π Interactions at Polymer Interfaces

Thin films of three differently charged xanthene dyes: rhodamine 6G (Rh6G, cationic), fluorescein 27 (F27, neutral), and disodium fluorescein (DSF, anionic) were cast onto a polystyrene (PS) coated glass substrate to investigate ion-π interactions. Absorbance spectroscopy was used to determine the aggregation state of the dyes on the PS surface. Deconvolution of the spectra of films revealed multiple peaks for all dyes assigned to isolated monomers, aggregates, and complexes between the dye and the polymer substrate. The shift of the low energy peak relative to the monomer peak was used as an indication of interaction strength of that species with the PS π system, which followed the trend of Rh6G > DSF > F27. Increase in the interaction energy is attributed to stabilization from ion-π interactions. Steady-state emission spectra and excited state lifetime measurements were performed on all films. The formation of a weakly emissive exciplex was found for Rh6G and DSF, consistent with ion-π interactions, but no evidence of an exciplex is found for the F27 films.

A New Schiff Base Based Fluorescent Sensor for Al(III) Based on 2-Hydroxyacetophenone and o-Phenylenediamine

A simple Schiff base (L) based on 2-hydroxyacetophenone and o-phenylenediamine was prepared which acts as an effective fluorescent sensor for Al³⁺ with ca. 9.0 fold enhancement in fluorescence intensity and detection limit 10^-4.3 M. L can quite clearly distinguish Al³⁺ over other metal ions Zn²⁺, Hg²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ca²⁺, K⁺, Li⁺, Na⁺ and Fe³⁺. Cyclic voltammogram and square wave voltammogram of L shows a significant change on interaction with Al³⁺. Spectroscopic data and DFT calculations confirm 1:1 interaction between L and Al³⁺ which is reversible with respect to Na₂EDTA.

The Design and Synthesis of Fluorescent Coumarin Derivatives and Their Study for Cu2+ Sensing with an Application for Aqueous Soil Extracts

A series of fluorescent coumarin derivatives 2a–e were systematically designed, synthesized and studied for their Cu²⁺ sensing performance in aqueous media. The sensitivities and selectivities of the on-to-off fluorescent Cu²⁺ sensing signal were in direct correlation with the relative arrangements of the heteroatoms within the coordinating moieties of these coumarins. Probes 2b and 2d exhibited Cu²⁺ concentration dependent and selective fluorescence quenching, with linear ranges of 0–80 μM and 0–10 μM, and limits of detection of 0.14 μM and 0.38 μM, respectively. Structural changes of 2b upon Cu²⁺ coordination were followed by fluorescence titration, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), mass spectrometry, and single crystal X-ray diffraction on the isolated Cu²⁺-coumarin complex. The results revealed a 1:1 stoichiometry between 2b and Cu²⁺, and that the essential structural features for Cu²⁺-selective coordination are the coumarin C=O and a three-bond distance between the amide NH and heterocyclic N. Probe 2b was also used to determine copper (II) levels in aqueous soil extracts, with recovery rates over 80% when compared to the standard soil analysis method: inductively coupled plasma-mass spectrometry (ICP-MS).

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu²⁺ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The detection limit of WM toward Cu²⁺ was 1.84 × 10^-7 M, which was lower than the concentration of Cu²⁺ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu²⁺ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu²⁺.

Condensation Product of 4-Methoxybenzaldehyde and Ethylenediamine: "Off-On" Fluorescent Sensor for Cerium(III)

The condensation product (L) of 4-methoxybenzaldehyde and ethylenediamine has been synthesised and characterised. L showed a 21 times enhancement in fluorescence intensity on interaction with Ce³⁺ in CH₃OH at λ_max = 360 nm when excited with 270 nm photons. Metal ions K⁺, Na⁺, Al³⁺, Co²⁺, Hg²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Mg²⁺ and Ca²⁺ do not interfere. The stoichiometry of binding and the binding constants were determined from spectroscopic data and found to be 1:1 and 10^4.8 M respectively. The detection limit was found to be 10^-5.2 M. The protonation/de-protonation of water molecules coordinated to Ce³⁺ was found to show interesting behaviour on the fluorescence of L:Ce³⁺.

Dual-Analyte Fluorescent Sensor Based on [5]Helicene Derivative with Super Large Stokes Shift for the Selective Determinations of Cu2+ or Zn2+ in Buffer Solutions and Its Application in a Living Cell

A new fluorescent sensor, M201-DPA, based on [5]helicene derivative was utilized as dual-analyte sensor for determination of Cu²⁺ or Zn²⁺ in different media and different emission wavelengths. The sensor could provide selective and bifunctional determination of Cu²⁺ in HEPES buffer containing Triton-X100 and Zn²⁺ in Tris buffer/methanol without interference from each other and other ions. In HEPES buffer, M201-DPA demonstrated the selective ON-OFF fluorescence quenching at 524 nm toward Cu²⁺. On the other hand, in Tris buffer/methanol, M201-DPA showed the selective OFF-ON fluorescence enhancement upon the addition of Zn²⁺, which was specified by the hypsochromic shift at 448 nm. Additionally, M201-DPA showed extremely large Stokes shifts up to ∼150 nm. By controlling the concentration of Zn²⁺ and Cu²⁺ in a living cell, the imaging of a HepG2 cellular system was performed, in which the fluorescence of M201-DPA in the blue channel was decreased upon addition of Cu²⁺ and was enhanced in UV channel upon addition of Zn²⁺. The detection limits of M201-DPA for Cu²⁺ and Zn²⁺ in buffer solutions were 5.6 and 3.8 ppb, respectively. Importantly, the Cu²⁺ and Zn²⁺ detection limits of the developed sensors were significantly lower than permitted Cu²⁺ and Zn²⁺ concentrations in drinking water as established by the U.S. EPA and WHO.

Remarkable colorimetric sensing behavior of pyrazole-based chemosensor towards Cu(ii) ion detection: synthesis, characterization and theoretical investigations

We report the synthesis of a new imine based ligand, 3-((3-methoxybenzylidene)amino)-1H-pyrazol-5-ol (HL) and its Cu(ii) complexes in 2 : 1 (HL : metal) and 1 : 1 : 1 (HL : metal : HQ) stoichiometric ratio using 8-hydroxyquinoline (HQ) as an additional bidentate ligand. The synthesized ligand (HL) and its Cu(ii) complexes (1 and 2) are structurally characterized using FT-IR, electronic absorption and emission, NMR and MS techniques. Furthermore, the complexation of Cu2+ with HL leads to the immediate formation of brown colour solution which indicates that HL can act as simple colorimetric sensor for Cu2+ ions. We further investigated that the sensor could selectively bind to the Cu2+ ions even in the presence of competitive ions such as Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Ag+ and Na+ ions in aqueous solutions which was studied by electronic absorption spectroscopy. The HL ligand has been investigated for its reactive properties by density functional theory (DFT) calculations. Quantum molecular descriptors describing local reactive properties have been calculated in order to identify the most reactive molecule sites of title compounds. DFT calculations encompassed molecular electrostatic potential (MEP), local average ionization energies (ALIE), Fukui functions and bond dissociation energies for hydrogen abstraction (H-BDE).

A peptide-based multifunctional fluorescent probe for Cu2+, Hg2+ and biothiols

A peptide-based fluorescent probe (Dansyl-His-Pro-Gly-Trp-NH₂, D-P4) bearing the dansyl fluorophore and tryptophan residue has been developed for the detection of Hg²⁺, Cu²⁺ and biothiols (–SH).

Near-infrared aza-BODIPY fluorescent probe for selective Cu2+detection and its potential in living cell imaging

A near-infrared (NIR) fluorescent sensor1composed of an aza-boron-dipyrromethene (aza-BODIPY) core covalently bound to two di-2-picolylamine moieties was prepared for Cu²⁺detection in aqueous solutions.

Exploration of an easily synthesized fluorescent probe for detecting copper in aqueous samples

Bonding behavior and spectral response studies of an easily synthesized fluorescent probe for the detection of Cu²⁺ ions and CuO NPs in aqueous samples.

A new simple Schiff base fluorescence "on" sensor for Al3+ and its living cell imaging

The simple Schiff base (Z)-N-benzylidenenaphthalen-1-amine (L) acts as an effective fluorescence sensor for Al(3+) by "off-on" mode, and ca. 42 times enhancement in fluorescence intensity is observed. The detection limit of L towards Al(3+) is observed to be 5 × 10(-5) M. UV/Visible and fluorescence data as well as DFT calculations confirm 1:3 coordination between Al(3+) and L through N atoms in a pyramidal shape. L is employed for imaging the Al(3+) ion in living biological cells and for the determination of the Al(3+) ion in bovine serum albumin.