Search Results (8)

2,8-Dithia-5-aza-2,6-pyridinophane (L1) has been used as a receptor unit in the construction of the conjugated redox chemosensor 5-ferrocenylmethyl-2,8-dithia-5-aza-2,6-pyridinophane (L3). In order to further explore the coordination chemistry of L1, and comparatively, that of its structural analogue 2,11-dithia-5,8-diaza-2,6-pyridinophane (L2), featuring two secondary nitrogen atoms in the macrocyclic unit, the crystal structures of the new synthesised complexes [Pb(L1)(ClO₄)₂]·½CH₃CN, [Cu(L2)](ClO₄)₂·CH₃CN and [Cd(L2)(NO₃)]NO₃ were determined by X-ray diffraction analysis. The electrochemical response of L3 towards the metal ions Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ was investigated by cyclic voltammetry (CV) in CH₂Cl₂/CH₃CN 0.25:1 (v/v) mixture. Upon addition to L3 of increasing amounts of the aforementioned metal cations, the wave corresponding to the Fc⁺/Fc redox couple of the un-complexed L3 was gradually replaced by a new reversible wave at more positive potentials and corresponding to the Fc⁺/Fc redox couple of the complexed ligand. The maximum anodic shift of the ferrocene oxidation wave is observed in the presence of Pb²⁺ (230 mV), to which corresponds a reaction coupling efficiency (RCE) value as large as 7.9 × 10³. The response selectivity of L3 is discussed in reference to the optical selectivity observed for conjugated chemosensors featuring L1 as receptor unit and different fluorogenic fragments as signalling units. Full article

Over the past few decades, interest in the fast and sensitive recognition and detection of molecules and ions with biological and/or environmental relevance has increased. Therefore, the search for new molecules capable of coordinating these analytes is an important topic of investigation, especially concerning those with an optical response (via color or fluorescence changes). Thiosemicarbazones are versatile organic compounds due to their wide range of biological activities and interesting optical, electronic and redox properties. Additionally, they possess various binding sites, whose complexing ability can be tuned by the introduction of substituents of different electronic character. Having this in mind, we report the synthesis of a new thiosemicarbazone derivative functionalized with a quinoline moiety. The new compound was characterized by ¹H and ¹³C NMR, UV-vis absorption and fluorescence spectroscopies. Moreover, a preliminary chemosensory study was undertaken in acetonitrile solutions in the presence of relevant ions with biological, medicinal and environmental relevance, showing that this receptor has potential application as a fluorimetric chemosensor. Full article

2,4,5-Trisubstituted imidazole derivatives with heteroaromatic groups are versatile heterocyclic compounds exhibiting a wide range of biological activities, as well as very interesting thermal, optical, electronic, and redox properties. In recent years, this type of imidazole derivatives has been explored as colorimetric and fluorimetric chemosensors due to their ability to coordinate with ions of biological and environmental relevance. In order to continue the work developed by the research group, we report the synthesis and characterization using usual spectroscopic techniques (NMR, absorption and emission spectroscopies) of a new imidazole derivative, substituted at position 2 of the imidazole with an 8-hydroxy-quinoline group. Furthermore, to complement the characterization of the synthesized imidazole, a preliminary study as an optical chemosensor was carried out in acetonitrile in the presence of ions with biological, medicinal, and environmental relevance. Full article

Metal–organic frameworks (MOFs), as a class of crystalline hybrid architectures, consist of metal ions and organic ligands and have displayed great potential in luminescent sensing applications due to their tunable structures and unique photophysical properties. Until now, many studies have been reported on the development of MOF-based luminescent sensors, which can be classified into two major categories: MOF chemosensors based on reversible host–guest interactions and MOF chemodosimeters based on the irreversible reactions between targets with a probe. In this review, we summarize the recently developed luminescent MOF-based chemodosimeters for various analytes, including H₂S, HClO, biothiols, fluoride ions, redox-active biomolecules, Hg²⁺, and CN⁻. In addition, some remaining challenges and future perspectives in this area are also discussed. Full article

γ-Glutamyl-cysteinyl-glycine (GSH) plays a critical role in maintaining redox homeostasis in biological systems and a decrease in its cellular levels is associated with diseases. Existing fluorescence-based chemosensors for GSH acts as irreversible reaction-based probes that exhibit a maximum fluorescence (‘turn-on’) once the reaction is complete, regardless of the actual concentration of GSH. A reversible, reaction-based ‘turn-off’ probe (1) is reported here to sense the decreasing levels of GSH, a situation known to occur at the onset of various diseases. The more fluorescent merocyanine (MC) isomer of 1 exists in aqueous solution and this reacts with GSH to induce formation of the ring-closed spiropyran (SP) isomer, with a measurable decrease in absorbance and fluorescence (‘turn-off’). Sensor 1 has good aqueous solubility and shows an excellent selectivity for GSH over other biologically relevant metal ions and aminothiol analytes. The sensor permeates HEK 293 cells and an increase in fluorescence is observed on adding buthionine sulfoximine, an inhibitor of GSH synthesis. Full article

Conducting polymer (CP) hybrids, which combine CPs with heterogeneous species, have shown strong potential as electrical transducers in chemosensors. The charge transport properties of CPs are based on chemical redox reactions and provide various chemo-electrical signal transduction mechanisms. Combining CPs with other functional materials has provided opportunities to tailor their major morphological and physicochemical properties, often resulting in enhanced sensing performance. The hybrids can provide an enlarged effective surface area for enhanced interaction and chemical specificity to target analytes via a new signal transduction mechanism. Here, we review a selection of important CPs, including polyaniline, polypyrrole, polythiophene and their derivatives, to fabricate versatile organic and inorganic hybrid materials and their chemo-electrical sensing performance. We focus on what benefits can be achieved through material hybridization in the sensing application. Moreover, state-of-the-art trends in technologies of CP hybrid sensors are discussed, as are limitations and challenges. Full article

[m.n] Multinuclear ferrocenophanes prepared by aza-Wittig reaction of bisiminophosphoranes derived from 1,1'-diazidoferrocene and isophthaladelhyde or 2,5-diformylthiophene, behave as efficient electrochemical and chromogenic chemosensor molecules for Zn²⁺, Pb²⁺, and Hg²⁺ metal cations. Whereas the OSWV of receptor 3, bearing two m-phenylene units in the bridges, display one oxidation peak, receptor 4 incorporating two thiophene rings in the bridges, exhibits two well-separated oxidation peaks. In both receptors only the addition of Zn²⁺, Pb²⁺, and Hg²⁺ metal cations induced a remarkable anodic shift of ferrocene/ferrocenium redox couple. Likewise, in the absorption spectra of these receptors the low energy band is red-shifted by Δλ = 165 − 209 nm, and these changes promoted a significant color changes which could be used for the naked eye detection of these metal cations. The coordination modes for two representative cases were unveiled by DFT calculations that show an unsual coordination in the [4₂Pb]²⁺ complex with the Pb²⁺ cation in a distorted cubic N₄S₄ donor cage. Full article

In an effort to develop new ruthenium(II) complexes, this work describes the design, synthesis and characterization of a ruthenium(II) functionalized phenanthroline complex with extended π-conjugation. The ligand were L₁ (4,7-bis(2,3-dimethylacrylic acid)-1,10-phenanthroline), synthesized by a direct aromatic substitution reaction, and L₂ (4,7-bis(trianthracenyl-2,3-dimethylacrylic acid)-1,10-phenanthroline), which was synthesized by the dehalogenation of halogenated aromatic compounds using a zero-valent palladium cross-catalyzed reaction in the absence of magnesium-diene complexes and/or cyclooctadienyl nickel (0) catalysts to generate a new carbon-carbon bond (C-C bond) polymerized hydrocarbon units. The ruthenium complex [RuL₁L₂(NCS)₂] showed improved photophysical properties (red-shifted metal-to-ligand charge-transfer transition absorptions and enhanced molar extinction coefficients), luminescence and interesting electrochemical properties. Cyclic and square wave voltammetry revealed five major redox processes. The number of electron(s) transferred by the ruthenium complex was determined by chronocoulometry in each case. The results show that processes I, II and III are multi-electron transfer reactions while processes IV and V involved one-electron transfer reaction. The photophysical property of the complex makes it a promising candidate in the design of chemosensors and photosensitizers, while its redox-active nature makes the complex a potential mediator of electron transfer in photochemical processes. Full article