A highly sensitive fluorogenic “turn-on” chemosensor for the recognition of Cd2+ based on a hybrid purine-quinoline Schiff base

Sensitive fluorescence detection of glyphosate and glufosinate ammonium pesticides by purine-hydrazone-Cu2+ complex

Organophosphorus pesticides play an important role as broad-spectrum inactivating herbicides in agriculture. Developing a method for rapid and efficient organophosphorus pesticides detection is still urgent due to the increasing concern on food safety. An organo-probe (ZDA), synthesized by purine hydrazone derivative and 2,2'-dipyridylamine derivative, was applied in sensitive recognition of Cu2+ with detection limit of 300 nM. Mechanism study via density functional theory (DFT) and job's plot experiment revealed that ZDA and Cu2+ ions form a 1:2 complex quenching the fluorescence emission. Moreover, this fluorescent complex ZDA-Cu2+ was applicable for detecting glyphosate and glufosinate ammonium following fluorescence enhancement mechanism, with detection limits of 11.26 nM and 11.5 nM, respectively. Meanwhile, ZDA-Cu2+ was effective and sensitive when it is used for pesticide detection, reaching the maximum value and stabilizing in 1 min. Finally, the ZDA-Cu2+ probe could also be tolerated in cell assay environment, implying potential bio-application.

Synthesis and application of purine-based fluorescence probe for continuous recognition of Cu2+ and glyphosate

In this study, a novel fluorescent sensor, N,N-dimethyl-4-((2-(8-m-ethyl-9-(naphthalen-1-yl)-9H-purin-6-yl)hydrazineylidene)methyl)aniline(PHA), which was constructed via Schiff base reaction of purine derivatives and dimethylaminobenzaldehyde. This probe showed significant selective fluorescence quenching of Cu2+, and accompanying with an increase in Cu2+ concentration and a change in solution color from colorless to yellow. The outstanding features of PHA include low detection limit (0.429 μM), strong anti-interference ability and fast response time. We further investigated the chelation mechanism of PHA and Cu2+ by Job's plot experiment, density generalization theory (DFT), and the probe PHA can form a 1:2 complex with Cu2+ ions, leading to a fluorescence quenching process, thus realizing the rapid detection of Cu2+. In addition, this new fluorescent sensor [PHA-Cu2+] can be used to detect pesticide residues in solution. When the [PHA-Cu2+] system was mixed with glyphosate solution, that a fluorescence recovering was observed. This may be because glyphosate chelates more strongly with Cu2+ ions, making the copper ions dissociated from the [PHA-Cu2+] system. The detection limit of the fluorescent sensor [PHA-Cu2+] for glyphosate was 18.77 nM. Finally, the sensor system has been successfully applied in fluorescence imaging of glyphosate in living cells.

Easily synthesizable molecular probe for the nanomolar level detection of Cd2+ in near aqueous media: Theoretical investigations and live cell imaging

The present investigation highlights a quinoline-based small molecule probe (DEQ) for the detection of Cd2+ among other metal ions in near-aqueous media. The probe DEQ and its Cd2+ complex (DEQ-Cd) have been synthesized and characterized by all possible spectroscopic methods. The weakly emissive DEQ showed its strong emission in the presence of Cd2+, which is attributed to the photoinduced electron transfer (PET) along with the chelation-enhanced fluorescence (CHEF) mechanism. The 1:1 binding mode between ligand and Cd2+ is confirmed by single crystal XRD analysis, which is further supported by Job's plot and HRMS. The detection limit of the probe to recognize Cd2+ was found to be as low as 89 nM. Furthermore, DEQ can act as a reversible fluorescence probe with the off-on-off mechanism by the alternative addition of Cd2+ and EDTA. DFT and TD-DFT studies exposed the proposed mechanism after Cd2+ insertion and the obtained results for electronic spectra are in line with the experimental results. The response towards pH was quite interesting and allowed us to study its application in live cell imaging. With all the positive results, the proposed ligand DEQ can be used as a potential probe for the detection of Cd2+ in real-life applications.

Versatile applications of transition metal incorporating quinoline Schiff base metal complexes: An overview

Since the last decade, research on quinoline Schiff base metal complexes has risen substantially due to their versatile applications across many significant fields. Schiff bases are also known as azomethines, aldimines, and imines. Quinoline Schiff base-derived metal complexes are intriguing to study topics. These complexes are employed in biological, analytical, and catalytic fields. Researchers have found that Schiff bases are more biologically active when coordinated with metal ions. Research in the biological sciences has shown that heterocyclic compounds like quinoline and its derivatives are important. Because of their broad spectrum of activity, quinoline derivatives have been discovered to be effective therapeutic agents for various disorders. Even though various classical synthetic pathways mentioned in the literature are still in use, there is an urgent need for a new, more effective method that is safer for the environment, has a higher yield, generates less hazardous waste, and is easier to use. This highlights the critical need for a safe, eco-friendly approach to quinoline scaffold synthesis. This review focuses exclusively on Schiff base metal complexes derived from quinoline, fabricated and studied in the past ten years, and having anticancer, antibacterial, antifungal, antioxidant, antidiabetic, antiproliferative, DNA-intercalation, and cytotoxic activities.

A novel fluorescence probe for the recognition of Cd2+ and its application

A facile fluorescence probe BQBH was synthesized and investigated on its spectrum property. The result showed that the BQBH had high sensitivity and selectivity for Cd²⁺ with lowest detection determined as 0.14 μM by fluorescence response. The 1: 1 binding ratio between BQBH and Cd²⁺ was determined by Job's plot, and the binding details were further confirmed by ¹H NMR titration, FT-IR spectrum and HRMS analysis. The applications including on test paper, smart phone and cell image were all also investigated.

The Novel Fluorescent Probe Toward Yttrium(III) and its Bioimaging

In this paper, the novel fluorescence probe XP based on Schiff-base was designed, synthesized and characterized, which could detect Y³⁺selectively and sensitively. The recognition mechanism of XP toward Y³⁺ was studied by Job's plot and HRMS. It was investigated that stoichiometric ratio of the probe XP conjugated with Y³⁺ was 1:2. And the detection limit was calculated as 0.30 μM. In addition, Y³⁺ was recognized by the test paper made from XP. And the probe XP could detect  Y³⁺ selectively in Caenorhabditis elegans and the main organs of mice. Thus, XP was considered to have some potential for application in bioimaging.

A new naphthalimide-picolinohydrazide derived fluorescent "turn-on" probe for hypersensitive detection of Al3+ ions and applications of real water analysis and bio-imaging

The development of high-selective chemosensors for trace Al³⁺ detection in the ecosystem is crucially importance due to its detrimental effects. In this work, a simple Schiff-base fluorescent probe NPP derived from naphthalimide and picolinohydrazide was rationally designed and prepared for efficient detection of Al³⁺. NPP exhibited prominent sensing behaviors toward Al³⁺ with low detection limit (LOD) (39 nM), rapid response time (1 min), strong binding affinity (4.02 × 10⁴), good anti-interference characteristics and visual detection. Binding ratio of NPP-Al³⁺ complex was determined to be 1:1 by Job's plot analysis. In addition, the chelation mechanism of NPP with Al³⁺ ions was proposed and substantiated by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT), IR spectrum and ¹H NMR titration experiments. Furthermore, this "signal-on" probe NPP was efficiently utilized as a promising indicator for Al³⁺ detection in environmental and biological samples.

Naphthalimide appended isoquinoline fluorescent probe for specific detection of Al3+ ions and its application in living cell imaging

Herein, a novel Schiff base fluorescent probe NIQ based on naphthalimide and iso-quinoline units has been readily prepared for the selective detection of Al³⁺ ions. The obviously visible color changes and prominent fluorescence enhancement were observed upon the addition of Al³⁺ to NIQ, which could be attributed to the complexation of NIQ with Al³⁺ and thus leading to the inhibition of photo-induced electron transfer (PET) and the chelation-enhanced fluorescence (CHEF) progress. The limit of detection (LOD) was 52 nM that was far below the standard recommended by the WHO. Binding ratio (1:1) of NIQ with Al³⁺ ions was supported by Job's plot. The binding constant of NIQ for Al³⁺ were calculated to be 3.27 × 10⁵ M^-1 on the basis of benesi-Hildebrand plot. The plausible binding mechanism for NIQ towards Al³⁺ ions was evidenced by the density functional theory (DFT) and ¹H NMR titration experiment. Furthermore, this "turn-on" probe NIQ has been successfully applied as a biomarker for imaging the Al³⁺ ions in living cells.

A novel reversible fluorescent probe based on naphthalimide for sequential detection of aluminum (Al3+) and fluoride (F-) ions and its applications

A new Schiff base fluorescent probe NBP derived from the one-step condensation strategy of 2-butyl-6-hydroxy-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-5-carbaldehyde and N-(2-(hydrazinecarbonyl)phenyl)benzamide was synthesized and characterized. NBP exhibited high selectivity toward Al³⁺ along with naked-eye color changes and prominent fluorescence enhancement. The limit of detection (LOD) of NBP toward Al³⁺ was detected to be 80 nM. The binding ratio of NBP with Al³⁺ ions was obtained as 1 : 2 on the basis of Job's plot with the association constant K_a value of 4.22 × 10¹⁰ M^-1/2. The plausible complexation mechanism of NBP toward Al³⁺ ions was validated by the density functional theory (DFT) and IR spectrum. In addition, in situ formed "NBP + Al³⁺" could be utilized as the second sensor for selective recognition of F^-via fluorescence quenching with a low detection limit (44 nM). Furthermore, the cell imaging experiments of probe NBP in HeLa cells have successfully demonstrated that NBP could serve as an indicator for monitoring Al³⁺ ions in living cells. On top of that, NBP could be used to prepare simple test paper strips for quickly and qualitatively detecting a trace amount of Al³⁺ ions in a visible manner.