Selective Capture of Ni2+Ions by Naphthalene- and Coumarin-Substituted Dithiolenes

Coumarin-Synthetic Methodologies, Pharmacology, and Application as Natural Fluorophore

Coumarins are secondary metabolites made up of benzene and α-pyrone rings fused together that can potentially treat various ailments, including cancer, metabolic, and degenerative disorders. Coumarins are a diverse category of both naturally occurring as well as synthesized compounds with numerous biological and therapeutic properties. Coumarins as fluorophores play a key role in fluorescent labeling of biomolecules, metal ion detection, microenvironment polarity detection, and pH detection. This review provides a detailed insight into the characteristics of coumarins as well as their biosynthesis in plants and metabolic pathways. Various synthetic strategies for coumarin core involving both conventional and green methods have been discussed comparing advantages and disadvantages of each method. Conventional methods discussed are Pechmann, Knoevenagel, Perkin, Wittig, Kostanecki, Buchwald-Hartwig, and metal-induced coupling reactions such as Heck and Suzuki, as well as green approaches involving microwave or ultrasound energy. Various pharmacological applications of coumarin derivatives are discussed in detail. The structural features and conditions responsible for influencing the fluorescence of coumarin core are also elaborated.

Amino-coumarin-based colorimetric and fluorescent chemosensors capable of discriminating Co2+, Ni2+, and Cu2+ ions in solution and potential utilization as a paper-based device

New chemosensors, L1-L3, based on the coumarin Schiff base scaffold with substituent modifications, have been designed and synthesized. The chemosensors L1-L3 exhibited the absorbance and fluorescence spectral changes that can discriminate Co²⁺, Ni²⁺, and Cu²⁺ ions. Sensor L1 demonstrated the ability to respond to Co²⁺, Ni²⁺, and Cu²⁺ ions. Remarkably, the slight modification of substituent on L2 has been observed to cause selective binding to Ni²⁺ and Cu²⁺ ions while L3 can specifically detect Cu²⁺ ions. The in-situ formation of metal and ligand complexes was determined by Job's plot analysis. The limit of detection and the sensing ability of all probes are estimated to be within the range of safe drinking water. Incorporation of the sensing compounds into a paper-based detection system using a laminated paper-based analytical device (LPAD) was demonstrated and found to be consistent to those obtained from the batchwise solution measurements.

Photoconducting Devices with Response in the Visible-Near-Infrared Region Based on Neutral Ni Complexes of Aryl-1,2-dithiolene Ligands

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)₂]^x- [Ar-edt^2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1^x-), 2-naphthyl (2^x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.

A Mixed-Valence Tetra-Nuclear Nickel Dithiolene Complex: Synthesis, Crystal Structure, and the Lability of Its Nickel Sulfur Bonds

In this study, by employing a common synthetic protocol, an unusual and unexpected tetra-nuclear nickel dithiolene complex was obtained. The synthesis of the [Ni4(ecpdt)6]2− dianion (ecpdt = (Z)-3-ethoxy-3-oxo-1-phenylprop-1-ene-1,2-bis-thiolate) with two K+ as counter ions was then intentionally reproduced. The formation of this specific complex is attributed to the distinct dithiolene precursor used and the combination with the then coordinated counter ion in the molecular solid-state structure, as determined by X-ray diffraction. K2[Ni4(ecpdt)6] was further characterized by ESI-MS, FT-IR, UV-Vis, and cyclic voltammetry. The tetra-nuclear complex was found to have an uncommon geometry arising from the combination of four nickel centers and six dithiolene ligands. In the center of the arrangement, suspiciously long Ni–S distances were found, suggesting that the tetrameric structure can be easily split into two identical dimeric fragments or two distinct groups of monomeric fragments, for instance, upon dissolving. A proposed variable magnetism in the solid-state and in solution due to the postulated dissociation was confirmed. The Ni–S bonds of the “inner” and “outer” nickel centers differed concurrently with their coordination geometries. This observation also correlates with the fact that the complex bears two anionic charges requiring the four nickel centers to be present in two distinct oxidation states (2 × +2 and 2 × +3), i.e., to be hetero-valent. The different coordination geometries observed, together with the magnetic investigation, allowed the square planar “outer” geometry to be assigned to d8 centers, i.e., Ni2+, while the Ni3+ centers (d7) were in a square pyramidal geometry with longer Ni–S distances due to the increased number of donor atoms and interactions.

Selective binding of Ni2+ and Cu2+ metal ions with naphthazarin esters isolated from Arnebia euchroma

Naphthazarin esters (C1-C4) isolated from the roots of Arnebia euchroma are found as skilled dual chemosensors for Ni²⁺ and Cu²⁺ among Pb²⁺ , Na²⁺ , K²⁺ , Hg²⁺ , Mg²⁺ , and Ca²⁺ metal ions. C1-C4 esters exhibited a red shift of 54 nm with Ni²⁺ and 30 nm with Cu²⁺ metal ions in absorption. There is a formation of red-shifted bands between 517 and 613 nm in the absorption spectrum of C1-C4 sensors on binding with Ni²⁺ and Cu²⁺ ions. The addition of Ni²⁺ and Cu²⁺ ions to sensors C1-C4 stimulates a remarkable color change from reddish pink to purple and light blue, respectively. These color changes can be identified with the naked eye. The significant downfield shifts of CO and OH peaks in nuclear magnetic resonance (NMR) spectrum confirm the chelation as binding mechanism. With ultraviolet-visble and NMR studies, it is found that C1-C4 esters possessed notable selectivity and sensitivity toward Ni²⁺ and Cu²⁺ over other metal ions.

A dual-responsive colorimetric probe for the detection of Cu2+ and Ni2+ species in real water samples and human serum

The monitoring of heavy transition metals has increasingly attracted great attention because they pollute the environment and have unique physiological functions. Chemosensors are useful tools for monitoring heavy transition metals due to their simple visualization, excellent sensitivity and high selectivity. Herein, we have developed a novel chemosensor for the detection of water-soluble Cu2+ and Ni2+ species with different mechanisms, and low detection limits of 2.1 nM for Cu2+ and 1.2 nM for Ni2+ were obtained. The colorimetric probe CPH has been applied to qualitative and quantitative detection of Cu2+ and Ni2+ species in real samples.

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.

Crystal structure of 1-ethyl-3-(2-oxo-1,3-di-thiol-4-yl)quinoxalin-2(1H)-one

The title compound I, C13H10N2O2S2, crystallizes in the monoclinic space group C2/c with eight mol-ecules in the unit cell. Excluding for the ethyl substituent, the mol-ecule of I adopts a nearly coplanar conformation (r.m.s. deviations is 0.058 Å), which is supported by the intra-molecular C-H⋯O hydrogen-bonding inter-action between the two ring systems [C⋯O = 2.859 (3) Å]. In the crystal, the mol-ecules form dimeric associates via two bifurcated C-H⋯O hydrogen-bonding inter-actions between an ene hydrogen atom and a carbonyl functional group of an adjacent mol-ecule [C⋯O = 3.133 (3) Å] and vice versa. The crystal structure is further stabilized by a three-dimensional network of weak hydrogen bonds between one mol-ecule and six adjacent mol-ecules as well as offset π-π stacking. The combination of the quinoxaline 2(1H)-one moiety with the di-thio-carbonate moiety extends the aromaticity of the quinoxaline scaffold towards the substituent as well as influencing the π-system of the quinoxaline. The title compound is the direct precursor for a di-thiol-ene ligand mimicking the natural cofactor ligand molybdopterin.

Synthesis, characterization and oxygen atom transfer reactivity of a pair of Mo(iv)O- and Mo(vi)O2-enedithiolate complexes – a look at both ends of the catalytic transformation

A novel pair of mono-oxo and di-oxo bis-dithiolene molybdenum complexes were synthesized, characterized and catalytically investigated as models for a molybdenum dependent oxidoreductase.