A highly selective and sensitive salamo-salen-salamo hybrid fluorometic chemosensor for identification of Zn2+ and the continuous recognition of phosphate anions

A benzimidazole-appended double-armed salamo type fluorescence and colorimetric bifunctional sensor for identification of MnO4- and its applications in actual water samples

The symmetrically double-armed salamo type fluorescent sensor BMS, incorporating benzimidazole units, was designed and synthesized. Showcasing remarkable specificity and responsiveness to MnO4- within a DMSO:H2O (V/V = 9:1, pH = 7.2) Tris-HCl buffer medium, it enabled dual-channel detection of MnO4- through fluorescent and colorimetric changes. Critical experimental parameters, including detection and quantification thresholds (LOD and LOQ) along with binding affinity constants (Ka), were calculated using the Origin software. A rational interaction mechanism between BMS and MnO4- was deduced, based on fluorescence titration, Electrospray Ionization Mass Spectrometry (ESI-MS), Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared Spectroscopy (IR), Stern-Volmer plots, and Density Functional Theory (DFT) computations. Additionally, the sensor BMS was applied to monitor MnO4- in real water samples. Advancing its practical utility, BMS was fabricated into test strips for the selective detecting of MnO4-.

Recent Advances in Organic Small-Molecule Fluorescent Probes for the Detection of Zinc Ions (Zn2+)

Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn2+ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn2+ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn2+ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn2+ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn2+ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn2+.

An unusual highly sensitive dual-channel bis(salamo)-like chemical probe for recognizing B4O72-, sensing mechanism, theoretical calculations and practical applications

A bis(salamo)-like chemical sensor H3L ((1E,3E)-2-hydroxy-5-methylisophthalaldehyde O,O -di(3-((((E)-(2-hydroxynaphthalen-1-yl)methylene)amino)oxy)propyl) dioxime) was constructed. H3L is capable of recognizing B4O72- in H2O/DMF (1:9, v/v) solution by both fluorescent and colorimetric channels, bright green fluorescence was turned on when B4O72- was added to H3L and changed from colorless to yellow in natural light. The detection limit was 3.21 × 10-8 M. The identification has good anti-interfering ability, quickly responsive time (5 S) and broad pH detecting range (pH = 5-12). The mechanism of action was determined by 1H NMR titration, infrared spectrometry, HRMS spectra and further elucidated by theory calculations. The fluorescence imaging of bean sprouts and spiked recovery assays of actual water samples demonstrated the practical use of sensor H3L for the detection of B4O72-, which is expected to have applications for the detection of B4O72- in plants and the environment.

Turn-On Solid-State Fluorescent Determination of Zinc Ion by Quinoline-Based Covalent Organic Framework

A new quinoline-based COF (covalent organic framework), obtained by Povarov reaction, containing 2,6-diisopropylphenyl moieties as substituents over the heterocyclic ring is described for detecting Zn2+ in aqueous solution. The introduction of the mentioned bulky phenyl rings into the network favors an increase of the distance between the reticular sheets and their arrangement, obtaining a new material with an alternating AB type stacking. The new material exhibits good selectivity to detect Zn2+ by fluorescence emission in aqueous solutions up to a concentration of 1.2 × 10-4 m of the metal ion. In order to have a deeper insight into the interaction between the COF and the zinc cation, a thorough spectroscopical, microscopical, and theoretical study is also presented and discussed in this communication.

A unique N-heterocyclic oligo(N,O-donor) salamo-Ni(II)-based probe for highly selective fluorescence detection of Cr2O72

A unique fluorescent probe Ni-DAS was developed by a nitrogenous heterocyclic oligo(N,O-donor) salamo-based compound DAS. DAS exhibits AIE and ESIPT effects which are extremely infrequent in salamo-based multi-oxime compounds. In addition, Ni-DAS can be used as a fluorescent probe with high selectivity and sensitivity to recognize Cr2O72- in DMF with 80 % water content, which enhances the value of the probe for application in real environments, and outperforms most similar molecular fluorescence probes. The probe Ni-DAS can recognize Cr2O72- by oxidative hydrolysis of C = N bonds, which promotes further research on theory of C = N bond hydrolysis, and the binding ratio and recognition mechanism were verified and supported by relevant theoretical calculations (DFT & MESP). The experiments showed that the probe Ni-DAS can be used for ion detection in real environments. It provides a new strategy for the oxidative hydrolysis of C = N bond and the structure of salamo-based compounds with AIE nature, and offers new ideas for study ion recognition and acidity detection.

Spectroscopic and theoretical studies on a novel bis(salamo)-like probe for highly effective fluorimetric-colorimetric identification of Fe3+ and Cu2+ in aquo-organic medium

A novel bis(salamo)-type sensor FT for fluorescence-colorimetric recognition of Fe3+/Cu2+ has been created, which revealed significant fluorescent performance and colorimetric sensing ability for Cu2+ and Fe3+ ions, superior to other related competitive metal ions. Interestingly, the binding of the FT probe with Cu2+ ions manifested an instant color change from colorless to red in sunlight, which is detectable by the naked-eye, and a fluorescence turn-off response under UV light for Fe3+ and Cu2+. The results demonstrated that the probe exhibits better sensitivity, greater affinity and lower limit of detection leading to quick response time in an aquo-organic medium. The excited state property of the FT probe and in the presence of Cu2+/Fe3+ was evaluated on the basis of DFT & TD-DFT results. Furthermore, test strips have been provided for convenient monitoring of Cu2+ and Fe3+ ions by naked eye and fluorescence method.

A symmetric bis(salamo)-like fluorescent chemosensor for identifying HCO3- and CO32- and its application

In this work, we successfully designed and synthesized a methoxydisubstituted bis(salamo)-type fluorescent chemical sensor BS, which can be applied as a highly sensitive and selective fluorescence probe for HCO3- and CO32- detection. The LODs of HCO3- and CO32- were experimentally calculated to be 5.4068 × 10-8 M and 4.4517 × 10-8 M, respectively. After relevant experiments, the sensing mechanism was investigated. Moreover, the application of the sensor in practice is explored, and the sensor BS can be loaded on portable test strips for ion detection. In the field of ion detection, salamo-like chemical sensors have been less studied compared to other sensor molecules, especially for the recognition and detection of anions. Therefore, this study will to some extent contribute to expanding the application of salamo-like compounds.

A single 8-hydroxyquinoline-appended bile acid fluorescent probe obtained by click chemistry for solvent-dependent and distinguishable sensing of zinc(II) and cadmium(II)

Construction of fluorescent probes for zinc ion (Zn2+ ) and cadmium ion (Cd2+ ) is significant for the safety of humans. However, the discriminating recognition of Zn2+ and Cd2+ by a single probe remains challenging owing to their similar properties. Herein, a novel deoxycholic acid derivative containing 8-hydroxyquinoline fluorophore has been facilely synthesized through click chemistry to form a clamp-like probe. Using its perfect bonding cavity from 1,2,3-triazole and quinoline, this molecule showed favorable solvent-dependent fluorescent responses and distinguished Zn2+ and Cd2+ in different solvents. In ethanol aqueous solution, it displayed good selectivity and ratiometric fluorescence to Zn2+ with 30 nm spectroscopic red-shifts. In acetonitrile aqueous solution, it exhibited good selectivity and ratiometric fluorescence to Cd2+ with 18 nm spectroscopic red-shifts. Moreover, the unique microstructural features of the probe in assembly were used to reflect its recognition processes. Due to its merits of low detection limit and instant response time, the probe was utilized for sensing Zn2+ and Cd2+ in water, beer and urine with high accuracy. Meanwhile, this probe served as a handy tool and was employed to obtain inexpensive test strips for the prompt and semiqualitative analysis of Zn2+ and Cd2+ with the naked eye.

A fluorescent Salamo-Salen-Salamo-Zn(II) sensor for bioimaging and biosensing H2PO4- in Zebrafish and plants

A newly designed and synthesized Salamo-Salen-Salamo-Zn(II) complex sensor (sensor ZT) was extensively explored for anion sensing studies. The selectivity and sensitivity of the sensor ZT towards H2PO4- ions were based on ICT and CHEF effects, and via displacement pathways in DMSO/H2O (9:1, v/v) medium in the presence of other anions like, PO43-, HPO42- and P2O74- in a short time, separately. The prepared ZT sensor has excellent association constant and low detection lines. The sensing mechanism and binding mode of the sensor were studied by UV-Vis spectroscopy, HR-MS, 1H NMR titration and theory calculations (DFT & TD-DFT) for analytes. The time response and stability of the sensor are also given. Meanwhile, the sensor ZT can be widely used as a simple and effective solid-state optical sensor to detect H2PO4- by intuitive fluorescence changes. In addition, besides the environment can be used as a powerful instrument for detecting H2PO4-, based on the good biocompatibility and tissue permeability of ZT, effectively monitoring H2PO4- in cellular distribution by confocal microscopy using Zebrafish and bean sprout.

Coordination-Driven Salamo-Salen-Salamo-Type Multinuclear Transition Metal(II) Complexes: Synthesis, Structure, Luminescence, Transformation of Configuration, and Nuclearity Induced by the Acetylacetone Anion

A flexible polydentate Salamo-Salen-Salamo hybrid ligand H₄L was designed and synthesized, which has rich pockets (salamo and salen pockets) so that it may have fascinating coordination patterns with transition metal(II) ions. Four multinuclear transition metal(II) complexes, novel butterfly-shaped homotetranuclear [Ni₄(L)(μ₁-OAc)₂(μ_1,3-OAc)₂(H₂O)_0.5(CH₃CH₂OH)_3.5]·4CH₃CH₂OH (1), helical homotrinuclear [Zn₃(L)(μ₁-OAc)₂]·2CH₃CH₂OH (2), double-helical homotrinuclear [Cu₂(H₂L)₂]·2CH₃CN (3), and mononuclear [Ni(H₂L)]·1.5CH₃COCH₃ (4), have been synthesized and characterized by single-crystal X-ray diffraction. The effects of different anions [OAc^- and (O₂C₅H₇)^2-] on the complexation behavior of H₄L with transition metal(II) ions were studied by UV-vis spectrophotometry. The fluorescent properties of the four complexes were studied with zebrafish, which are expected to be a potential light-emitting material. Ultimately, interaction region indicator (IRI) valuations, Hirshfeld surface analyses, density functional theory (DFT & TD-DFT), electrostatic potential analyses (ESP), and simulations were carried out to further demonstrate the weak interactions and electronic properties of the free ligand and its four complexes.