Effect of O-substitution in imidazole based Zn(II) dual fluorescent probes in the light of arsenate detection in potable water: a combined experimental and theoretical approach

A thiazole-based colorimetric and photoluminescent chemosensors for As3+ ions detection: Density functional theory, test strips, real samples, and bioimaging applications

A Schiff-base Ethyl (E)-2-(3-((2-carbamothioylhydrazono)methyl)-4-hydroxyphenyl)-4-methylthiazole-5-carboxylate (TZTS) dual functional colorimetric and photoluminescent chemosensor which includes thiazole and thiosemicarbazide has been synthesized to detect arsenic (As3+) ions selectively in DMSO: H2O (7:3, v/v) solvent system. The molecular structure of the probe was characterized via FT-IR, 1H, and 13C NMR & HRMS analysis. Interestingly, the probe exhibits a remarkable and specific colorimetric and photoluminescence response to As3+ ions when exposed to various metal cations. The absorption spectral changes of TZTS were observed upon the addition of As3+ ions, with a naked eye detectable color change from colorless to yellow color. Additionally, the chemosensor (TZTS) exhibited a new absorption band at 412 nm and emission enhancements in photoluminescence at 528 nm after adding As3+ ions. The limit of detection (LOD) for As3+ ions was calculated to be 16.5 and 7.19 × 10-9 M by the UV-visible and photoluminescent titration methods, respectively. The underlying mechanism and experimental observations have been comprehensively elucidated through techniques such as Job's plot, Benesi-Hildebrand studies, and density functional theory (DFT) calculations. For practical application, the efficient determination of As3+ ions were accomplished using a spike and recovery approach applied to real water samples. In addition, the developed probe was successfully employed in test strip applications, allowing for the naked-eye detection of arsenic ions. Moreover, fluorescence imaging experiments of As3+ ions in the breast cancer cell line (MCF-7) demonstrated their practical applications in biological systems. Consequently, these findings highlight the significant potential of the TZTS sensor for detecting As3+ ions in environmental analysis systems.

Biochemical Resistivity against Free Radicals and Microbes: Cooperative Action of Zn(II)/Imidazole in Phosphoesterase-Mediated Cell Death

This work delivers a targeted synthesis of four isostructural O-substituted imidazole-based zinc(II) complexes, namely, [Zn2(L1)2(I)2](DMF) (1), [Zn2(L2)2(I)2](DMF) (2), [Zn2(L1)2(Br)2] (3), and [Zn2(L2)2(Br)2] (4), derived from homologous Schiff-base ligands HL1 and HL2 to explore their impact on free radicals, microbes, and dephosphorylation of phosphoesters. The antioxidant activity of all complexes was checked by various radical scavenging assays (ABTS+•, DPPH•, and H2O2 radical quenching). Among them, complex 2 showed superior radical quenching activity, as indicated by its lowest EC50 value and thus maximum antioxidative capability. Again, antibacterial assays against several Gram-positive and Gram-negative bacteria were conducted to evaluate the zone of inhibition. The minimum bactericidal concentration and minimum inhibitory concentration values from the microdilution method for all complexes revealed complex 3 to have maximum potency against Gram-positive bacteria. The P-O bond hydrolysis in the phospholipid chain caused by the hydrolytic phosphoesterase activity of the Zn(II)-complexes plays a crucial role in cell membrane rupture. A model substrate 4-PNPP was used to explain the potency of monomeric Zn(II) complex (3) for cell penetration over dimeric one (2) with a proper mechanism. Furthermore, a heme model substrate, Fe(TPP)Cl, has been introduced with the most potent complex 3 and has spectrophotometric evidence for covalent interaction with imidazole and Fe(III) that can disrupt the nitric oxide dioxygenase function of flavohemoglobin, leading to bacterial cell death. To our knowledge, this is the first case to report a novel mechanism of antimicrobial action where both the metal and the ligand are cooperatively involved in bacterial cell death. The main goal of this work is to invent multifunctional therapeutics as well as the proper chemical rationalization of biological processes using mechanistic approaches, which includes investigating the roles of halides, imidazoles, and solution-phase structural variations of complexes..

Research Progress in Fluorescent Probes for Arsenic Species

Arsenic is a toxic non-metallic element that is widely found in nature. In addition, arsenic and arsenic compounds are included in the list of Group I carcinogens and toxic water pollutants. Therefore, rapid and efficient methods for detecting arsenic are necessary. In the past decade, a variety of small molecule fluorescent probes have been developed, which has been widely recognized for their rapidness, efficiency, convenience and sensitivity. With the development of new nanomaterials (AuNPs, CDs and QDs), organic molecules and biomolecules, the conventional detection of arsenic species based on fluorescence spectroscopy is gradually transforming from the laboratory to the portable kit. Therefore, in view of the current research status, this review introduces the research progress of both traditional and newly developed fluorescence spectrometry based on novel materials for arsenic detection, and discusses the potential of this technology in the rapid screening and field testing of water samples contaminated with arsenic. The review also discusses the problems that still exist in this field, as well as the expectations.

Experimental and Theoretical Studies of the Optical Properties of the Schiff Bases and Their Materials Obtained from o-Phenylenediamine

Two macrocyclic Schiff bases derived from o-phenylenediamine and 2-hydroxy-5-methylisophthalaldehyde L1 or 2-hydroxy-5-tert-butyl-1,3-benzenedicarboxaldehyde L2, respectively, were obtained and characterized by X-ray crystallography and spectroscopy (UV-vis, fluorescence and IR). X-ray crystal structure determination and DFT calculations for compounds confirmed their geometry in solution and in the solid phase. Moreover, intermolecular interactions in the crystal structure of L1 and L2 were analyzed using 3D Hirshfeld surfaces and the related 2D fingerprint plots. The 3D Hirschfeld analyses show that the most numerous interactions were found between hydrogen atoms. A considerable number of such interactions are justified by the presence of bulk tert-butyl groups in L2. The luminescence of L1 and L2 in various solvents and in the solid state was studied. In general, the quantum efficiency between 0.14 and 0.70 was noted. The increase in the quantum efficiency with the solvent polarity in the case of L1 was observed (λex = 350 nm). For L2, this trend is similar, except for the chloroform. In the solid state, emission was registered at 552 nm and 561 nm (λex = 350 nm) for L1 and L2, respectively. Thin layers of the studied compounds were deposited on Si(111) by the spin coating method or by thermal vapor deposition and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), spectroscopic ellipsometry and fluorescence spectroscopy. The ellipsometric analysis of thin materials obtained by thermal vapor deposition showed that the band-gap energy was 3.45 ± 0.02 eV (359 ± 2 nm) and 3.29 ± 0.02 eV (377 ± 2 nm) for L1/Si and L2/Si samples, respectively. Furthermore, the materials of the L1/Si and L2/Si exhibited broad emission. This feature can allow for using these compounds in LED diodes.

ZnAl2O4 Nanomaterial as a Naked-Eye Arsenate Sensor: A Combined Experimental and Computational Mechanistic Approach

Raising public awareness over the emerging health risk due to intake of arsenic-contaminated potable water is a matter of great concern. Exploration of cost-effective, self-testing kits is a substantial way to reach out to the masses and detect the presence of arsenate in water. With this agenda, a photoluminescent Mannich base Zn(II) complex (ZnMC = [Zn₂(ML)₂]·(ClO₄)₂·(H₂O); HML = Mannich base ligand) has been synthesized, and its dinuclearity was verified with single-crystal X-ray diffraction structural analysis. Among a range of anions, ZnMC was found to detect arsenate selectively by showing a turn-off emission with a color change from bright green to dark under UV light. The real-life applicability of the ZnMC probe is somewhat restricted to only sensing of arsenate, but not its removal owing to the fact of its homogeneity. Considering the efficacy of ZnMC as well as a need for its easy removal from water, slight modification has been done with chloride ions in the form of ZnMC″ (=[Zn₂(ML)₂(Cl)₂]), and finally, an interface between homogeneous and heterogeneous solid support has been explored with a strategic fabrication of ZnMC″ grafted ZnAl₂O₄, named as ZAZ nanomaterial. This not only imparts successful segregation of arsenate from drinking water but also provides naked-eye detection under ambient light as well as UV light. Thermodynamic parameters associated with the binding of arsenate to ZnMC and ZAZ have been evaluated through isothermal calorimetric (ITC) measurements. Steady-state and time-resolved fluorescence titration study, absorption titration study, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and computational calculations have been performed to get deep insights into the sensing properties. Proper justification of the sensing mechanism is the highlight of this work. ZAZ nanomaterial has been exploited to produce a self-test paper kit for arsenate detection with a limit of 9.86 ppb, which potentially enables applications in environmental monitoring.