Synthesis of Two Coumarin-Derived Schiff Bases and Investigation of theirs Selectivity for Zn2+

Stability Constant and Potentiometric Sensitivity of Heavy Metal-Organic Fluorescent Compound Complexes: QSPR Models for Prediction and Design of Novel Coumarin-like Ligands

Industrial wastewater often consists of toxic chemicals and pollutants, which are extremely harmful to the environment. Heavy metals are toxic chemicals and considered one of the major hazards to the aquatic ecosystem. Analytical techniques, such as potentiometric methods, are some of the methods to detect heavy metals in wastewaters. In this work, the quantitative structure-property relationship (QSPR) was applied using a range of machine learning techniques to predict the stability constant (logβ_ML) and potentiometric sensitivity (PS_ML) of 200 ligands in complexes with the heavy metal ions Cu²⁺, Cd²⁺, and Pb²⁺. In result, the logβML models developed for four ions showed good performance with square correlation coefficients (R²) ranging from 0.80 to 1.00 for the training and 0.72 to 0.85 for the test sets. Likewise, the PSML displayed acceptable performance with an R² of 0.87 to 1.00 for the training and 0.73 to 0.95 for the test sets. By screening a virtual database of coumarin-like structures, several new ligands bearing the coumarin moiety were identified. Three of them, namely NEW02, NEW03, and NEW07, showed very good sensitivity and stability in the metal complexes. Subsequent quantum-chemical calculations, as well as physicochemical/toxicological profiling were performed to investigate their metal-binding ability and developability of the designed sensors. Finally, synthesis schemes are proposed to obtain these three ligands with major efficiency from simple resources. The three coumarins designed clearly demonstrated capability to be suitable as good florescent chemosensors towards heavy metals. Overall, the computational methods applied in this study showed a very good performance as useful tools for designing novel fluorescent probes and assessing their sensing abilities.

A Novel Benzimidazole-Based Chemosensor for Fluorometric Determination of Zinc Ions

A simple and novel Schiff base chemosensor (BMHM) based on benzimidazole was synthesized. In ethanol-water (1:1, v/v) medium on varying concentrations of Zn²⁺ chemosensor exhibited a strong and quick turn on fluorescence response. The Zn²⁺ recognition was based on the Chelation-enhanced fluorescence effect. The binding constant and limit of detection for BMHM-Zn²⁺ complexation were estimated to be 7.99 × 104 M^-1 and 0.148 µM, respectively. The extreme fluorescent enhancement caused by Zn²⁺ binding in chemosensor BMHM occurred at a pH range of 6-7. The practical use of chemosensor BMHM was tested by determination of Zn²⁺ in real water samples and comparing the results with the data obtained using high resolution inductively coupled plasma mass spectrometry.

A facile sonochemical protocol for synthesis of 3-amino- and 4-amino-1,2,4-triazole derived Schiff bases as potential antibacterial agents

A facile method has been developed for the synthesis of Schiff bases derived from substituted and unsubstituted 3-amino- and 4-amino-1,2,4-triazoles. Condensation of the aminotrizoles with a variety of aromatic aldehydes afforded desired Schiff bases in excellent yields in 3-5 minutes of exposure to ultra-sound. The synthesized compounds were characterized by means of IR, 1HNMR and Mass spectrometry. The synthesized compounds were also screened for their antibacterial potential against Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Staphylococcus aureus and Bacillus subtilis) strains.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Synthesis, DNA Binding, and Molecular Docking Studies of Dimethylaminobenzaldehyde-Based Bioactive Schiff Bases

A new series of p-dimethylaminobenzaldehyde derivatives were tested for therapeutic potential by exploring their properties through characterization. The derivatives were synthesized by 1 : 1 condensation reaction of p-dimethylaminobenzaldehyde and substituted amines. The synthesized compounds 1–8 were characterized by different characterization techniques including IR, mass, 1H NMR, and 13C NMR spectroscopy, elemental analysis, and mass spectrometry. Furthermore, binding of these Schiff bases to Ct-DNA was examined by absorption spectroscopy, fluorescence quenching, circular dichroic, viscosity measurement, molecular docking, and molecular dynamics simulation methods. Schiff bases were tested for antimicrobial activity against bacterial species Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus by the disc diffusion method. The pharmacological treatment of Schiff bases showed that 1–8 have promising potential against tested bacterial strains. The molecular docking study of the target compounds was also carried out against B-DNA dodecamer d(CGCGAATTCGCG)2, and it has been found that 1–8 can bind to Ct-DNA via an intercalative mode. DPPH free radical and hydrogen peroxide scavenging assays were employed to assess the antioxidant potential of synthesized Schiff bases.

Aggregation-Induced Emission-Based Sensing Platform for Selective Detection of Zn2+ : Experimental and Theoretical Investigations

Fluorescent chemosensors with aggregation induced emission enhancement (AIEE) emerge as promising tools in the field of sensing materials. Herein, we report the design, synthesis and applicability of a Schiff base chemosensor 1-(benzo[1,3]dioxol-4-ylmethylene-hydrazonomethyl)-naphthalen-2-ol (Hbdhn) of AIE characteristics that exhibits highly effective and selective response towards Zn²⁺ . The sensing effect of Hbdhn was evaluated by means of absorption/emission spectra and corresponding underlying photophysical mechanisms were proposed based on extensive quantum-chemical (TD)DFT calculations. The aggregated states in different DMSO/H₂ O ratios and in a presence of Zn²⁺ were examined by fluorescence lifetime measurements, dynamic light scattering and scanning electron microscopy studies. The bioimaging abilities of Hbdhn were evaluated for Zn²⁺ in HepG2 cancer cells. The results demonstrate instant, stable in time and reproducible, colorimetric turn-on response with superb selectivity and sensitivity of Hbdhn towards Zn²⁺ , based on chelation enhanced fluorescence mechanism. AIEE improves further Hbdhn properties, leading to strong, long-lived fluorescence, with appearance of rod-like particles, in 90 % of water in DMSO and only 10 % of water in DMSO in the presence of Zn²⁺ . All these features combined with successful biomaging studies make Hbdhn one of the most promising candidate for practical applications among recently proposed related systems.