Highly selective and sensitive colorimetric probe for Al3+ and Fe3+ metal ions based on 2-aminoquinolin-3-yl phenyl hydrazone Schiff base

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al3+ ion

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al3+ could clearly be demonstrated on the filter paper test strips.

Sulfonamide functionalized silica nano-composite: characterization and fluorescence "turn-on" detection of Fe3+ ions in aqueous samples

We have synthesized novel sulfonamide-based nano-composite (SAN) for selective and sensitive detection of Fe³⁺ ions in aqueous samples. Morphological characterization of SAN was carried out with TGA, FT-IR, UV-Vis, ninhydrin assay, FE-SEM, pXRD, BET, EDX, and elemental analysis. The sensing nature, effect of pH, sensor concentration and response time analysis were accomplished with the help of emission spectral studies and SAN was assessed as "turn-on" emission detector for the biologically important Fe³⁺ ions. Here, the LOD and LOQ were computed to be 26.68 nM and 88.93 nM, respectively, and it was found to be much lower than the permissible limit of Fe³⁺ ions in drinking water. The accuracy of the sensor (SAN) was determined by testing the aqueous samples spiked with known concentrations of Fe³⁺ ions and results demonstrated 98.00-99.66% recovery, which made SAN a reliable, selective and sensitive chemosensor for the quantification of Fe³⁺ ions in fully aqueous media.

Oxadiazole Schiff Base as Fe3+ Ion Chemosensor: "Turn-off" Fluorescent, Biological and Computational Studies

Compound, (E)-5-(4-((thiophen-2-ylmethylene)amino)phenyl)-1,3,4-oxadiazole-2-thiol (3) was synthesized via condensation reaction of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol with thiophene-2-carbaldehyde in ethanol. For the synthesis and structural confirmation the FT-IR, ¹H, ¹³C-NMR, UV-visible spectroscopy, and mass spectrometry were carried out. The long-term stability of the probe (3) was validated by the experimental as well as theoretical studies. The sensing behaviour of the compound 3 was monitored with various metal ions (Ca²⁺, Cr³⁺, Fe³⁺, Co²⁺, Mg²⁺, Na⁺, Ni²⁺, K⁺) using UV- Vis. and fluorescence spectroscopy techniques by various methods (effect of pH and density functional theory) which showing the most potent sensing behaviour with iron. Job's plot analysis confirmed the binding stoichiometry ratio 1:1 of Fe³⁺ ion and compound 3. The limit of detection (LOD), the limit of quantification (LOQ), and association constant (K_a) were calculated as 0.113 µM, 0.375 µM, and 5.226 × 10⁵ respectively. The sensing behavior was further confirmed through spectroscopic techniques (FT-IR and ¹H-NMR) and DFT calculations. The intercalative mode of binding of oxadiazole derivative 3 with Ct-DNA was supported through UV-Vis spectroscopy, fluorescence spectroscopy, viscosity, cyclic voltammetry, and circular dichroism measurements. The binding constant, Gibb's free energy, and stern-volmer constant were find out as 1.24 × 10⁵, -29.057 kJ/mol, and 1.82 × 10⁵ respectively. The cleavage activity of pBR322 plasmid DNA was also observed at 3 × 10^-5 M concentration of compound 3. The computational binding score through molecular docking study was obtained as -7.4 kcal/mol. Additionally, the antifungal activity for compound 3 was also screened using broth dilution and disc diffusion method against C. albicans strain. The synthesized compound 3 showed good potential scavenging antioxidant activity against DPPH and H₂O₂ free radicals.

Development of a fluorescent probe for detecting Al3+ in cooked wheaten food based on phosphonic acid group functionalized polythiophene derivatives

As an unnecessary trace element, the content of aluminium in biological systems should be strictly controlled. Therefore, it was necessary to develop a convenient method for detection of aluminium ions. In this study, a fluorescent probe based on polythiophene derivatives was developed and used to detect Al³⁺ in Chinese traditional pasta. The fluorescence of this probe showed a significant decrease in hexamethylenetetramine-HCl buffer solution (pH 5) when Al³⁺ was present. In addition, the probe exhibited good sensitivity and selectivity to Al³⁺ over other metal ions when EDTA was used as the masking agent. Fluorescence intensity had a good linear relationship with the Al³⁺ concentration in the range 0.1-10 μM and the limit of detection for Al³⁺ was 39 nM. Furthermore, the probe was successfully applied to detect Al³⁺ in food samples and the results were consistent with ICP-AES.

Highly sensitive naphthalimide based Schiff base for the fluorimetric detection of Fe3

A simple 1,8-naphthalimide based Schiff base probe (E)-6-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2-(2-morpholinoethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NDSM) has been designed and synthesized for the specific detection of Fe3+ based on a fluorimetric mode. The absorbance of NDSM at 360 nm increased significantly in acetonitrile : water (7 : 3, v/v) medium only in the presence of Fe3+ ions with a visible colour change from yellow to golden yellow. Likewise, fluorescence emission intensity at 531 nm was almost wholly quenched in the presence of Fe3+. However, other competitive ions influenced insignificantly or did not affect the optical properties of NDSM. Lysosome targetability was expected from NDSM due to the installation of a basic morpholine unit. The LOD was found to be 0.8 μM with a response time of seconds. The fluorescence reversibility of NDSM + Fe3+ was established with complexing agent EDTA. Fe3+ influences the optical properties of NDSM by complexing with it, which blocks C[double bond, length as m-dash]N isomerization in addition to the ICT mechanism. The real-time application of Fe3+ was demonstrated in test paper-based detection, by the construction of a molecular logic gate, quantification of Fe3+ in water samples and fluorescence imaging of Fe3+.

New Schiff bases of 2-(quinolin-8-yloxy)acetohydrazide and their Cu(ii), and Zn(ii) metal complexes: their in vitro antimicrobial potentials and in silico physicochemical and pharmacokinetics properties

The purpose of this work was to prepare Schiff base ligands containing quinoline moiety and using them for preparing Cu(ii) and Zn(ii) complexes. Four bidentate Schiff base ligands (SL1–SL4) with quinoline hydrazine scaffold and a series of mononuclear Cu(ii) and Zn(ii) complexes were successfully prepared and characterized. The in vitro antibacterial and antifungal potential experimentation revealed that the ligands exhibited moderate antibacterial activity against the Gram-positive bacterial types and were inactive against the Gram-negative bacteria and the fungus strains. The metal complexes showed some enhancement in the activity against the Gram-positive bacterial strains and were inactive against the Gram-negative bacteria and the fungus strains similar to the parent ligands. The complex [Cu(SL1)2] was the most toxic compound against both Gram-positive S. aureus and E. faecalis bacteria. The in silico physicochemical investigation revealed that the ligand SL4 showed highest in silico absorption (82.61%) and the two complexes [Cu(SL4)2] and [Zn(SL4)2] showed highest in silico absorption with 56.23% for both compounds. The in silico pharmacokinetics predictions showed that the ligands have high gastrointestinal (GI) absorption and the complexes showed low GI absorption. The ligands showed a good bioavailability score of 0.55 where the complexes showed moderate to poor bioavailability.

Synthesis, biological evaluation, theoretical investigations, docking study and ADME parameters of some 1,4-bisphenylhydrazone derivatives as potent antioxidant agents and acetylcholinesterase inhibitors

Five 1,4-bisphenylhydrazone derivatives (1-5) were successfully synthesized and evaluated for their antioxidant and acetylcholinesterase inhibitory activities. The antioxidant activity has been carried out using DPPH, ABTS, CUPRAC and superoxide radical scavenging methods. All the compounds showed a very good antioxidant activity compared to that of the standards used. Compound 1 was found to be the best antioxidant agent with IC₅₀ values lower or comparable to that of the standards. The acetylcholinesterase inhibitory activity has been evaluated using a modified Ellman's assay. The obtained results indicate that compound 2 is the best acetylcholinesterase inhibitor with a low IC₅₀ value comparable to that of the galantamine. In addition, DFT calculations have been performed to determine in which mechanism the synthesized hydrazones follow to scavenge free radicals. Molecular docking study was performed for compound 2, and its interaction modes with the enzyme acetylcholinesterase were determined. As a result, a strong interaction between this compound and the active site of AChE enzyme was revealed. Finally, ADME properties of the synthesized compounds were also studied and showed good drug-like properties.