Selective cyanide sensing using a Fe(III) complex of pyridoxal-beta alanine Schiff base

Dual channel chemosensor for successive detection of environmentally toxic Pd2+ and CN- ions and its application to cancer cell imaging

BACKGROUND

Detecting and neutralizing Pd2+ ions are a significant challenge due to their cytotoxicity, even at low concentrations. To address this issue, various chemosensors have been designed for advanced detection systems, offering simplicity and the potential to differentiate signals from different analytes. Nonetheless, these chemosensors often suffer from limited emission response and complex synthesis procedures. As a result, the tracking and quantification of residual palladium in biological systems and environments remain challenging tasks, with only a few chemosensing probes available for commercial use.

RESULTS

In this paper, a straightforward approach for the selective detection of Pd2+ ions is proposed, which involves the design, synthesis, and utilization of a propargylated naphthalene-derived probe (E)-N'-((2-(prop-2-yn-1-yloxy)naphthalen-1-yl)methylene)benzohydrazide (NHP). The NHP probe exhibits sensitive dual-channel colorimetry and fluorescence Pd2+ detection over other tested metal ions. The detection process is performed through a catalytic depropargylation reaction, followed by an excited state intramolecular proton transfer (ESIPT) process, the detection limit is as low as 11.58 × 10-7 M under mild conditions. Interestingly, the resultant chemodosimeter adduct (E)-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide (NHH) was employed for the consecutive detection of CN- ions, exhibiting an impressive detection limit of 31.79 × 10-8 M. Validation of both detection processes was achieved through 1H nuclear magnetic resonance and density functional theory calculations. For real-time applications of the NHP and NHH probes, smartphone-assisted detection, and intracellular detection of Pd2+ and CN- ions within HeLa cells were studied.

SIGNIFICANCE

This research presents a novel naphthalene derivative for visually detecting environmentally toxic Pd2+ and CN- ions. The synthesized probe selectively binds to Pd2+, forming a chemodosimeter. It successfully detects CN- ions through colorimetry and fluorimetry, offering a low detection limit and quick response. Notably, it's the first naphthalene-based small molecule to serve as a dual probe for toxic analytes - palladium and cyanide. Moreover, it effectively detects Pd2+ and CN- intracellularly in cancer cells.

Selective Turn-On Fluorescence Sensing of Cyanide Using the Pyridoxal Platform of a Ni(II) Complex

Cyanide is a very toxic pollutant to aquatic life and the environment. Analytical methods for the quantitative assay of cyanide, which are rapid, sensitive (low limit of detection), and cost-effective, are in great demand. Colorimetric and fluorometric methods are ideally suited for this purpose. In this report, we describe a Ni(II) complex containing a pyridoxal platform for the rapid and sensitive fluorometric estimation of cyanide. The square-planar Ni(II) complex, [Ni(L)(N₃)]·3H₂O, where the ligand LH = 4-[(2-dimethylamino-ethylimino)-methyl]-5-hydroxymtheyl-2-methyl-pyridin-3-ol, a Schiff base formed between pyridoxal and (2-dimethylamino)ethyl amine, was synthesized and characterized by various spectroscopic techniques as well as by single-crystal X-ray structure determination. The complex was found to selectively bind CN^- in the presence of other biologically important anions such as F^-, Cl^-, Br^-, I^-, OAc^-, S^2-, NO₃ ^-, PO₄ ^3-, SO₄ ^2-, and H₂PO₄ ^- in tris-HCl/NaCl buffer [pH = 7.4], and it can be monitored by fluorescence turn-on or by UV-visible spectroscopy. The binding constant of the complex with CN^- was estimated to be 2.046 × 10¹⁴ M^-2 and the limit of detection (LOD) was 9 nM, the LOD being considerably lower than the maximum permissible level of cyanide ions (1.9 μM) in drinking water, as recognized by the World Health Organization (WHO). The effects of pH and temperature on the sensing are also investigated. The Ni(II) complex is also found to bind to calf-thymus DNA very strongly, and the apparent binding constant (K _app) was determined to be 1.33 × 10⁷ M^-1 by the fluorescence quenching of the ethidium bromide-DNA adduct by the complex.

Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses

A bis-heteroleptic ruthenium(ii) complex, [Ru(Hdpa)₂(H₂pia)]X₂ (1·X₂; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H₂pia = 2-pycolinamide; OTf⁻ = CF₃SO₃⁻), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl₂·2.5H₂O and 1·F₂·2EtOH revealed essentially identical geometries for the 1²⁺ dication; however, the dihedral angle between the two pyridyl groups in the Hdpa ligands, which represented the degree of bending of the bent conformation, was affected by hydrogen-bonding interactions between the NH group and counterions. In 1·F₂·2EtOH, one of the Hdpa ligands had an unusually smaller dihedral angle (15.8°) than the others (29.9°–35.0°). The two NH groups of each Hdpa ligand and the NH₂ group of the H₂pia ligand in 1²⁺ acted as receptors for F⁻ anion recognition via hydrogen-bonding interactions in a dimethyl sulfoxide (DMSO) solution, and the reaction showed an unambiguous color change in the visible region. Upon the addition of tetra-n-butylammonium fluoride to the red DMSO solution of 1·(OTf)₂·H₂O, the solution turned dark brown. ¹H NMR analysis and absorption spectroscopy of the reaction between 1²⁺ and the added F⁻ anions revealed that the F⁻ anions did not distinguish between the two amino groups of Hdpa and the amide group of H₂pia, although they were in different environments in the DMSO solution. A tris-F-adduct with 1²⁺, 1·F₃⁻, was formed when sufficient F⁻ anions were present in the solution, despite the presence of four NH protons in 1²⁺. Time-dependent DFT calculations of 1²⁺ and 1·F₃⁻ were consistent with their absorption spectra.

A bis-heteroleptic ruthenium(ii) complex; [Ru(Hdpa)₂(H₂pia)]X₂ (1·X₂; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H₂pia = 2-pycolinamide; OTf^– = CF₃SO₃^–) was synthesized and spectroscopically and crystallographically characterized.

Bioimaging agents based on redox-active transition metal complexes

Detecting the fluctuation and distribution of various bioactive species in biological systems is of great importance in determining diseases at their early stages. Metal complex-based probes have attracted considerable attention in bioimaging applications owing to their unique advantages, such as high luminescence, good photostability, large Stokes shifts, low toxicity, and good biocompatibility. In this review, we summarized the development of redox-active transition metal complex-based probes in recent five years with the metal ions of iron, manganese, and copper, which play essential roles in life and can avoid the introduction of exogenous metals into biological systems. The designing principles that afford these complexes with optical or magnetic resonance (MR) imaging properties are elucidated. The applications of the complexes for bioimaging applications of different bioactive species are demonstrated. The current challenges and potential future directions of these probes for applications in biological systems are also discussed.

This review summarizes transition metal complexes as bioimaging agents in optical and magnetic resonance imaging.