Preparation, Structural Characterization, Electrochemistry, and Sensing Properties toward Anions and Cations of Ferrocene-Triazole Derivatives

Ferrocenyl-triazole complexes and their use in heavy metal cation sensing

Complexes tris((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (3), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (6), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)ether (7), and 1-ferrocenyl-1H-1,2,3-triazol-4-yl)methanamine (9) were synthesized using the copper-catalyzed click reaction. Complexes 3, 6, 7, and 9 were characterized using NMR (1H and 13{1H}) and IR spectroscopy, elemental analysis, and mass spectrometry. Structures of 3, 7, and 9 in the solid state were determined using single-crystal X-ray diffraction. It was found that the triazole rings were planar and slightly twisted with respect to the cyclopentadienyl groups attached to them. Chains and 3D network structures were observed due to the presence of π⋯π and C-H⋯N interactions between the cyclopentadienyl and triazole ligands. A reversible redox behavior of the Fc groups between 239 and 257 mV with multicycle stability was characteristic for all the compounds, revealing that the electrochemically generated species Fc+ remained soluble in dichloromethane. Electrochemical sensor tests demonstrated the applicability of all the complexes to enhance the quantification sensing behavior of the screen-printed carbon electrode (SPCE) toward Cd2+, Pb2+, and Cu2+ ions.

Electronic Coupling in 1,2,3-Triazole Bridged Ferrocenes and Its Impact on Reactive Oxygen Species Generation and Deleterious Activity in Cancer Cells

Mixed-valence (MV) binuclear ferrocenyl compounds have long been studied as models for testing theories of electron transfer and in attempts to design molecular-scale electronic devices (e.g., molecular wires). In contrary to that, far less attention has been paid to MV binuclear ferrocenes as anticancer agents. Herein, we discuss the synthesis of six 1,2,3-triazole ferrocenyl compounds for combined (spectro)electrochemical, electron paramagnetic resonance (EPR), computational, and anticancer activity studies. Our synthetic approach was based on the copper-catalyzed 1,3-dipolar azide–alkyne cycloaddition reaction and enabled us to obtain in one step compounds bearing either one, two, or three ferrocenyl entities linked to the common 1,2,3-triazole core. Thus, two series of complexes were obtained, which pertain to derivatives of 3′-azido-3′-deoxythymidine (AZT) and 3-azidopropionylferrocene, respectively. Based on the experimental and theoretical data, the two mono-oxidized species corresponding to binuclear AZT and trinuclear 3-azidopropionylferrocene complexes have been categorized as class II mixed-valence according to the classification proposed by Robin and Day. Of importance is the observation that these two compounds are more active against human A549 and H1975 non-small-cell lung cancer cells than their congeners, which do not show MV characteristics. Moreover, the anticancer activity of MV species competes or surpasses, dependent on the cell line, the activity of reference anticancer drugs such as cisplatin, tamoxifen, and 5-fluorouracil. The most active from the entire series of compounds was the binuclear thymidine derivative with the lowest IC₅₀ value of 5 ± 2 μM against lung H1975 cancer cells. The major mechanism of antiproliferative activity for the investigated MV compounds is based on reactive oxygen species generation in cancer cells. This hypothesis was substantiated by EPR spin-trapping experiments and the observation of decreased anticancer activity in the presence of N-acetyl cysteine (NAC) free-radical scavenger.

The 1,2,3-triazole bridged bi- and triferrocenyl compounds were prepared via a “click” reaction. Their corresponding mono-oxidized forms have been categorized as class II MV species. The biferrocenyl thymidine derivative showed remarkable anticancer activity against human A549 and H1975 cancer cells and negligible activity against nonmalignant human BEAS-2B cells. The anticancer activity mechanism is mainly due to ROS generation, and it originates from the combination of electronic coupling and the thymidine moiety, combined all together in one molecular scaffold.

Continuous and Polarization-Tuned Redox Capacitive Anion Sensing at Electroactive Interfaces

Continuous, real-time ion sensing is of great value across various environmental and medical scenarios but remains underdeveloped. Herein, we demonstrate the potential of redox capacitance spectroscopy as a sensitive and highly adaptable ion sensing methodology, exemplified by the continuous flow sensing of anions at redox-active halogen bonding ferrocenylisophthalamide self-assembled monolayers. Upon anion binding, the redox distribution of the electroactive interface, and its associated redox capacitance, are reversibly modulated, providing a simple and direct sensory readout. Importantly, the redox capacitance can be monitored at a freely chosen, constant electrode polarization, providing a facile means of tuning both the sensor analytical performance and the anion binding affinity, by up to 1 order of magnitude. In surpassing standard voltammetric methods in terms of analytical performance and adaptability, these findings pave the way for the development of highly sensitive and uniquely tunable ion sensors. More generally, this methodology also serves as a powerful and unprecedented means of simultaneously modulating and monitoring the thermodynamics and kinetics of host-guest interactions at redox-active interfaces.

Enhanced voltammetric anion sensing at halogen and hydrogen bonding ferrocenyl SAMs

Halogen bonding mediated electrochemical anion sensing has very recently been established as a potent platform for the selective and sensitive detection of anions, although the principles that govern binding and subsequent signal transduction remain poorly understood. Herein we address this challenge by providing a comprehensive study of novel redox-active halogen bonding (XB) and hydrogen bonding (HB) ferrocene-isophthalamide-(iodo)triazole receptors in solution and at self-assembled monolayers (SAMs). Under diffusive conditions the sensory performance of the XB sensor was significantly superior. In molecular films the XB and HB binding motifs both display a notably enhanced, but similar, response to specific anions. Importantly, the enhanced response of these films is rationalised by a consideration of the (interfacial) dielectric microenvironment. These effects, and the resolved relationship between anion binding and signal transduction, underpin an improved fundamental understanding of anion sensing at redox-active interfaces which will benefit not just the development of more potent, real-life relevant, sensors but also new tools to study host–guest interactions at interfaces.

Surface enhancement effects in the sensing of anions at redox-active molecular films are investigated in detail and rationalised based on a consideration of the dielectric binding microenvironment.

New ferrocene-triazole derivatives for multisignaling detection of Cu2+ in aqueous medium and their antibacterial activity

Ferrocene-based naphthalene or quinoline receptors 1-4 linked by triazole were designed and synthesized. Their recognition properties of metal cations have been investigated systematically in aqueous environment. Upon addition 1 equiv. of Cu²⁺ ion, receptors 1 (C₂₃H₁₉FeN₃O) and 2 (C₂₂H₁₈FeN₄O) showed fluorescent turn-off, enhanced absorption and color variations. At the same time, receptor 1 also caused the perturbation of redox potential after addition 1 equiv. of Cu²⁺ ion. Therefore, receptors 1 and 2 behaved as naked-eye chemosensors and fluorescent probes for Cu²⁺ without interference by other ions and with low detection limit. In addition, receptor 1 could also be considered electrochemical sensor for Cu²⁺ having excellent sensitivity and selectivity. However, increasing the molecules flexibility resulted in the lower selectivity of ion recognition in the case of receptors 3 (C₂₄H₂₁FeN₃O) and 4 (C₂₃H₂₀FeN₄O). Furthermore, this series of compounds were nontoxicity and receptor 1 exhibited certain antibacterial activity.

Oxidation-Induced Differentially Selective Turn-On Fluorescence via Photoinduced Electron Transfer Based on a Ferrocene-Appended Coumarin-Quinoline Platform: Application in Cascaded Molecular Logic

Differentially selective molecular sensors that exhibit differential response toward multiple analytes are cost-effective and in high demand for various practical applications. A novel, highly differentially selective electrochemical and fluorescent chemosensor, 5, based on a ferrocene-appended coumarin-quinoline platform has been designed and synthesized. Our designed probe is very specific toward Fe³⁺ via a reversible redox process, whereas it detects Cu²⁺ via irreversible oxidation. Interestingly, it exhibits differential affinity toward the Cu⁺ ion via complexation. High-resolution mass spectrometry, ¹H NMR titration, and IR spectral studies revealed the formation of a bidentate Cu⁺ complex involving an O atom of the amide group attached to the quinoline ring and a N atom of imine unit, and this observation was further supported by quantum-chemical calculations. The metal binding responses were further investigated by UV-vis, fluorescence spectroscopy, and electrochemical analysis. Upon the addition of Fe³⁺ and Cu²⁺ ions, the fluorescence emission of probe 5 shows a "turn-on" signal due to inhibition of the photoinduced electron transfer (PET) process from a donor ferrocene unit to an excited-state fluorophore. The addition of sodium l-ascorbate (LAS) as a reducing agent causes fluorescence "turn off" for the Fe³⁺ ion because of reemergence of the PET process but not for the Cu²⁺ ion because it oxidizes the ferrocene unit to a ferrocenium ion with its concomitant reduction to Cu⁺, which further complexes with 5. Thermodynamic calculations using the Weller equation along with density functional theory calculations validate the feasibility of the PET process. A unique combination of Fe³⁺, LAS, and Cu²⁺ ions has been used to produce a molecular system demonstrating combinational "AND-OR" logic operation.

Scalable Synthesis of Functionalized Ferrocenyl Azides and Amines Enabled by Flow Chemistry

A scalable access to functionalized ferrocenyl azides has been realized in flow. By halogen-lithium exchange of ferrocenyl halides and trapping with tosyl azide, a variety of functionalized ferrocenyl azides were obtained in high yields. To allow a scalable preparation of these potentially explosive compounds, a flow protocol was developed accelerating the reaction time to minutes and circumventing accumulation of potentially hazardous intermediates. The corresponding ferrocenyl amines were then prepared by a reliable reduction process.

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

Synthesis and Evaluation of Antifungal and Antitrypanosomastid Activities of Symmetrical 1,4-Disubstituted-1,2,3-Bistriazoles Obtained by CuAAC Conditions

BACKGROUND

The trypanosomatids, such as the protozoan Leishmania spp., have a demand by ergosterol, which is not present in the membrane from mammal cells. The suppression of the synthesis of ergosterol would be a new target of compounds with leishmanicidal activity, and bistriazole has shown trypanocidal activity by this mechanism. The incidence of fungal infections has increased at an alarming rate over the last decades. This is related both to the growing population of immune-compromised individuals and to the emergence of strains that are resistant to available antifungals. Therefore, there is a challenge for the search of potential new antifungal agents.

OBJECTIVE

The study aimed to synthesize 1,4-disubstituted-1,2,3-bistriazoles by optimized copper( I)-catalyzed alkyne-azide cycloaddition (CuAAC) and evaluate their antifungal and antitrypanosomastid activities.

METHOD

The synthesis of symmetrical bistriazoles with diazides as spacers was planned to be performed following the CuAAC reaction strategy. For evaluation of best conditions for the synthesis of symmetrical bistriazoles hex-1-yne 2 was chosen as leading compound, and a variety of catalysts were employed, choosing (3:1) alkyne:diazide stoichiometric relationship employing CuSO4.5H2O as the best condition. For the preparation of diversity in the synthesis of symmetrical bistriazoles, a 1,3-diazide-propan-2-ol 1a and 1,3-diazidepropane 1b were reacted with seven different alkynes, furnishing eleven symmetrical bistriazoles 9-13a,b and 14a. All compounds were essayed to cultures of promastigotes of L. amazonensis (1 x 106 cells mL-1) in the range of 0.10 - 40.00 µg mL-1 and incubated at 25ºC. After 72 h of incubation, the surviving parasites were counted. For antifungal assay, the minimum inhibitory concentrations (MIC) for yeasts and filamentous fungi were determined. Each compound was tested in 10 serial final concentrations (64 to 0.125 µg mL-1).

RESULTS

Eleven 1,4-disubstituted-1,2,3-bistriazoles were synthesized and their structures were confirmed by IR, 1H and 13C-NMR and Mass spectral analysis. The antifungal and antitrypanosomastid activities were evaluated. The best result to antifungal activity was reached by bistriazole 11a that showed the same MIC of fluconazole (32 µg mL-1) against Candida krusei ATCC 6258, an emerging and potentially multidrug-resistant fungal pathogen. Due to their intrinsically biological activity versatility, five derivatives compounds showed leishmanicidal inhibitory activity between 15.0 and 20.0% at concentrations of 20 and 40.0 µg mL-1. Among these compounds the derivative 13a showed best IC50 value of 63.34 µg mL-1 (182.86 µM).

CONCLUSION

The preliminary and promising results suggest that bistriazole derivatives, especially compound 13a, could represent an innovative scaffold for further studies and development of new antifungal and anti-parasitic drug candidates.

Water-soluble ferrocene complexes (WFCs) functionalized silica nanospheres for WFC delivery in HepG2 tumor therapy

Silica-encapsulated nanospheres of water-soluble ferrocene complexes WFCs@SiO₂ and WFCs@SiO₂@glutaraldehyde (GA) were first synthesized by a facile inverse-microemulsion method. The surface functional groups, particle size, and morphologies of nanospheres were characterized by IR spectra, UV-vis absorption spectra, dynamic light scattering (DLS) and SEM images. Single-crystal X-ray diffraction was used to confirm the molecular structure of free ferrocenyl-pyrazol ligand (L) and three WFCs, namely, [Ni(C₂₂H₁₄F₆FeN₄O₄)(H₂O)₄] (5a), [Mg(C₂₂H₁₄F₆FeN₄O₄)(H₂O)₄]·3H₂O (5b), and [Ba(C₂₂H₁₄F₆FeN₄O₄)(H₂O)₃] (5c). The electrochemical properties of 5a-5c were explored by cyclic voltammetry. The WFCs-loading capacities of 5a-5c in WFCs@SiO₂ were found to be 38.4, 38.2, and 38.1 μg/mg, respectively. Cell studies under two drug delivery modes (free diffusion and endocytosis) were carried out by MTT cell-survival assays and morphological observation of HepG2 cells. It's interesting that the cytotoxicity of WFCs against HepG2 was increased by applying silica nanocarriers. Compared to WFCs@SiO₂, the modification of GA on the spherical surface provided not only the better water-dispersity but also additional functional groups for further modification of other pharmacophores. The novel nanocarrier system for WFC delivery present a novel concept-of-proof method to protect varieties of affordable metal-based anticancer agents in physiological conditions and provided experimental basis for future studies focusing on drug delivery of other WFCs.

Synthesis and structural characterization of electrochemically reversible bisferrocenes containing bis(acyl-thiourea)s: enantiomers and conformers

Enantiomeric and conformational isomers of chiral bisferrocenyl-modified bis(acyl-thiourea)s; their crystal packing and electrochemically reversible redox reaction properties.

Synthesis of bi- and bis-1,2,3-triazoles by copper-catalyzed Huisgen cycloaddition: A family of valuable products by click chemistry

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction, also known as click chemistry, has become a useful tool for the facile formation of 1,2,3-triazoles. Specifically, the utility of this reaction has been demonstrated by the synthesis of structurally diverse bi- and bis-1,2,3-triazoles. The present review focuses on the synthesis of such bi- and bistriazoles and the importance of using copper-promoted click chemistry (CuAAC) for such transformations. In addition, the application of bitriazoles and the related CuAAAC reaction in different fields, including medicinal chemistry, coordination chemistry, biochemistry, and supramolecular chemistry, have been highlighted.

Pyrenyl-functionalized ferrocenes for multisignaling recognition of anions

New pyrenyl-functionalized ferrocenes for fluorescence and electrochemical dual sensing of anions in organic solution are introduced.

Synthesis, Electrochemical, and Thermal Properties of [3]Ferrocenophane-Containing Chalcone Derivatives

[3]Ferrocenophane-containing chalcone derivatives with benzene ring (3a–3d) or naphthalene ring (3e–3f) were synthesized and characterized. The potentials for [3]ferrocenophane-containing chalcones cathodically shifted ~70–80 mV compared with those of ferrocene-containing chalcones, indicating easier oxidation by loss of an electron for the former. The thermal behaviours of the prepared compounds were studied by differential scanning calorimetry and polarizing optical microscopy. Compound 3f with terminal alkyl chain of 14 carbon atoms displayed mesophases, whereas other compounds were non-mesomorphic and showed either crystal polymorphic phase transitions or simple melting and freezing process in the heating and cooling cycles.

Heterobimetallic complexes with redox-active mesoionic carbenes as metalloligands: electrochemical properties, electronic structures and catalysis

Electronic structures and redox-induced catalysis are presented with the first example of heterobimetallic ferrocenyl–Au(i) complexes with mesoionic carbenes.

Imine modified ZnO nanoparticles: a luminescent chemodosimeter for Al3+ and S2− ions based on ligand displacement reaction

A novel fluorescent chemosensor for rapid recognition of Al³⁺ and S²⁻ ions using imine capped ZnO nanoparticles in aqueous media.

A simple and highly selective 2,2-diferrocenylpropane-based multi-channel ion pair receptor for Pb2+ and HSO4−

A 2,2-diferrocenylpropane-based multi-channel ion pair receptor 1 was designed and structurally characterized. It was a “naked-eye-detectable” chemosensor towards Pb²⁺ and HSO₄⁻ with excellent selectivity and sensitivity.

Halogen bonding-enhanced electrochemical halide anion sensing by redox-active ferrocene receptors

The first redox-active halogen bonding anion receptors display larger electrochemical voltammetric responses to halide binding compared to their hydrogen bonding analogues.