A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

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.

A pyridine dicarboxylate based hydrazone Schiff base for reversible colorimetric recognition of Ni2+ and PPi

A pyridine dicarboxylate Schiff-base DAS was synthesized for cascade colorimetric recognition of Ni²⁺ and PPi. The selectivity and sensitivity of chemosensor DAS was investigated through colorimetric and UV-vis studies in MeOH-PBS (5 : 1, v/v, pH = 7.4). The chemosensor formed a 2 : 1 complex with Ni²⁺ metal ions with a binding constant of K_a = 3.07 × 10³ M^-2. Besides, a plausible sensing mechanism is confirmed by single crystal X-ray diffraction (SC-XRD), Job's plot and Benesi-Hildebrand plot (B-H plot) experiments. Furthermore, the DAS-Ni²⁺ ensemble formed 'in situ' was used to selectively recognise PPi. The limit of detection (LOD) of DAS for Ni²⁺ was found to be 0.14 μM and that of the DAS-Ni²⁺ ensemble for PPi was found to be 0.33 μM. Also, the potential of the chemosensor has been applied for solid state detection of Ni²⁺ as well as to mimic the 'INHIBIT' logic gate on the addition of Ni²⁺ ions and PPi.

A Bis(Salamo)-Based Fluorogenic Sensor for Highly Selective and Sequential Recognition of Cu2+ and B4O72- Ions in Semi-Aqueous Medium

A new type of multifunctional bis(salamo)-based fluorogenic sensor H₂BS was designed and synthesized. Under the action of V_DMF: V_H2O = 9: 1, the fluorogenic sensor can identify Cu²⁺ and B₄O₇^2-, in which N and O atoms can serve as binding sites for Cu²⁺ and B₄O₇^2-, the stoichiometry of the binding of the fluorogenic sensor H₂BS and Cu²⁺ has been confirmed by titration experiment, working curve, ESI-MS analysis and DFT calculation. The pH response experiment also confirmed that the fluorogenic sensor can recognize Cu²⁺ and B₄O₇^2- in the pH range applicable to the physiological environment. The minimum detection limit of H₂BS for Cu²⁺ and B₄O₇^2- recognition reaches 1.12 × 10^-7 and 5.56 × 10^-8 M, and the fluorogenic sensor H₂BS has been successfully applied to Cu²⁺ detection in actual water samples, and the test strip for detecting Cu²⁺ and B₄O₇^2- was obtained. Meanwhile, the success of the test strip experiment made the fluorogenic sensor H₂BS to recognize Cu²⁺ and B₄O₇^2- widely used in daily life. A new type of salamo-based multifunctional fluorogenic sensor H₂BS was designed and synthesized to identify Cu²⁺ and B₄O₇^2- in aqueous solvent systems. Added Cu²⁺ to H₂BS can cause fluorescence quenching. Further experiments showed that H₂BS and Cu²⁺ form a stable 1:2 complex, while B₄O₇^2- can also cause fluorescence quenching of H₂BS, which is the occurrence of the PET effect. Meanwhile, H₂BS can be used for quantitative detection in the environment and rapid identification in life.

8-Hydroxyquinoline Fluorophore for Sensing of Metal Ions and Anions

Among various known hydroxyquinolines, 8-hydroxyquinoline (8-HQ) is the most prevalent moiety due to excellent property for the formation of the complex with different metal ions and anions, and utilized in a wide variety of applications in pharmacological and medicinal fields. 8-Hydroxyquinoline moiety and its analogues acts as fluorophoric ligands on complex formation with alkali and alkaline as well as transition metal ions and anions, thus, considered as an ideal building block in metallo-supramolecular chemistry for recognition, separation, and quantitative investigation of cations. 8-Hydroxyquinoline moiety is also used in various applications for the advancement of novel fluorescent chemosensors in a wide variety of areas viz., material chemistry, bioorganic chemistry, molecular imaging, analytical chemistry, molecular recognition, medical and biological science communities. The present review emphasises on the progress of sensing properties of 8-HQ centred small-molecule fluorescent chemosensors towards several metal ions viz., Fe³⁺ , Al³⁺ , Ag⁺ , Hg²⁺ , Cu²⁺ , Pd²⁺ , Zn²⁺ , Cr³⁺ , Cd²⁺ , Mn²⁺ , Ca²⁺ , and K⁺ and anions such as F^- , CN^- and PPi, from 2008 to 2020, because of their sensitivity and selectivity in terms of diverse colour changes for different species. This critical and comprehensive review might facilitate the improvement of more prevailing chemosensors for future exciting and broad applications.

Overview on developed synthesis procedures of coumarin heterocycles

Considering highly valuable biological and pharmaceutical properties of coumarins, the synthesis of these heterocycles has been considered for many organic and pharmaceutical chemists. This review includes the recent research in synthesis methods of coumarin systems, investigating their biological properties and describing the literature reports for the period of 2016 to the middle of 2020. In this review, we have classified the contents based on co-groups of coumarin ring. These reported methods are carried out in the classical and non-classical conditions particularly under green condition such as using green solvent, catalyst and other procedures.

Selective immediate detection of Cu2+ by a pH-sensitive rhodamine-based fluorescence probe in breast cancer cell-line

A biocompatible fluorogenic chemosensor (N-(3-carboxy acryloyl)) rhodamine B (RHA) comprising a furan-2,5-dione receptor and a rhodamine fluorophore via an iminohydrazine crosslinker has been prepared for more scrutinizing optical properties and utilization in molecular imaging of living cells. The consequences indicated that RHA not only is a good pH indicator in acidic media but also can be used as a great sensitive fluoroionophore with high selectivity. The fluorescence emission of the molecule RHA is quite stable in the presence of 15 diverse cations, 18 anions (especially H₂PO₄^-, S², and F^-), and 5 amino acids with the different functional group as a model, except Cu²⁺ ions with observable emission intensity changing. The Cu²⁺ probe has a dual functional effect, an "on-off" mechanism in solvent media, and an "off-on" mechanism in Phosphate Buffered Saline (PBS) in acidic pH conditions. The detection limits for Cu²⁺ in acetone-water media was 0.69 μM and 0.18 μM in pH = 5.0. Moreover, RHA can fluorescently and colorimetrically image Cu²⁺ ions in acidic and neutral pH with low cytotoxicity in living cells.

A coumarin-containing Schiff base fluorescent probe with AIE effect for the copper(ii) ion

A novel coumarin-derived Cu²⁺-selective Schiff base fluorescent “turn-off” chemosensor CTPE was successfully obtained, which showed an AIE effect. It could identify Cu²⁺ by quenching its fluorescence. The lower limit of detection was 0.36 μM. CTPE can act as a highly selective and sensitive fluorescence probe for detecting Cu²⁺.

A novel coumarin-derived Schiff base fluorescent “turn-off” chemosensor with AIE effect showed selectivity towards Cu²⁺. The recognition mechanism is presented.

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.

A fluorescent and colorimetric probe based on naphthalene diimide and its high sensitivity towards copper ions when used as test strips

Herein, a red fluorescent and colorimetric probe (NDI-Py) based on naphthalene diimide was designed and synthesized, which exhibited rapid response, high sensitivity and selectivity towards copper ions, and the detection limit was as low as 0.97 μM in solution. Furthermore, NDI-Py demonstrated a strong red emission in the aggregated state because of its non-planar structure. Thus, it can act as a test strip to conveniently monitor copper ions with the detection limit as low as 2.0 μM.

A red fluorescent and colorimetric probe (NDI-Py) exhibited high selectivity and sensitivity towards copper ions both in solution and on silica gel plates.