Search Results (254)

Developing molecular electrocatalysts with controllable and predictable properties remains a central challenge in hydrogen evolution reaction (HER) catalysis. Herein, four Sb(III) corrole complexes (1–4) bearing zero to three p-cyano-substituted meso-phenyl groups (-CN Ph) were synthesized to investigate the effect of electron-withdrawing substituents on their catalytic HER performance, in which complexes 2–4 are newly reported. All prepared complexes were well characterized via UV–vis, NMR, HRMS, and XPS. SEM–EDS and UV–vis analyses indicated their uniform dispersion and excellent stability under organic and neutral aqueous solvent electrolysis conditions. When using TsOH as the proton source in DMF, complex 4 exhibited the highest activity with a TOF of 42.19 s⁻¹ at an overpotential of 895 mV. In mixed aqueous–organic media, the Faradaic efficiency of complex 4 reached 85.5%. The HER activity increases with the increasing number of cyano groups, and this observation has been rationalized via DFT calculations, which indicates a ligand-centered reduction and supports a possible ECEC pathway for the HER. These results highlight that cyano functionalization can modulate the electronic properties of Sb(III) corroles, thereby enhancing HER performance. This is helpful for designing efficient Sb(III) corrole-based HER catalysts. Full article

The increasing demand for rapid identification of bacteria capable of degrading environmentally relevant organic compounds highlights the need for scalable and selective analytical tools. Cupriavidus necator catabolizes several hydroxybenzoic acids, including 2-hydroxybenzoate (salicylate, 2-HBA), 4-hydroxybenzoate (4-HBA), and 3-hydroxybenzoate (3-HBA), funneling them into central aromatic catabolism via monooxygenation to 2,5-dihydroxybenzoate (gentisate, 2,5-dHBA) and 3,4-dihydroxybenzoate (protocatechuate, 3,4-dHBA) followed by the oxidative cleavage reaction, enabling complete conversion to tricarboxylic acid (TCA) cycle intermediates. To quantify how readily C. necator is able to activate catabolic genes in response to hydroxybenzoic acid, an extracellular ligand, we applied an approach centered on a transcription-factor (TF)-based biosensor that combines ligand-bound regulator activity with a fluorescent reporter. This approach allowed to evaluate the ligand sensitivity by determining gene activation threshold AC_min and half-maximal effective concentration EC₅₀. Amongst studied hydroxybenzoic acids, 2-HBA and 4-HBA sensors from C. necator showed very low thresholds 4.8 and 2.4 μM and EC₅₀ values of 19.91 and 13.06 μM, indicating high sensitivity to these compounds and implicating a scavenging characteristic of associated catabolism. This study shows that the TF-based-biosensor approach applied for mapping functional sensing ranges of hydroxybenzoates combined with the research and informatics of catabolism can advance our understanding of how gene expression regulation systems have evolved to respond differentially to the availability and concentration of carbon sources. Furthermore, it can inform metabolic engineering strategies in the prevention of premature pathway activation or in predicting competitive substrate hierarchies in complex mixed environments. Full article

This paper presents accurate TD-DFT calculations for several mixed-ligand gold(III) complexes with ligands including Cl⁻, Br⁻, I⁻, OH⁻, and NH₃. The calculated results show excellent agreement with available experimental data. The spectral shapes are determined by charge transfer transitions, which are systematically influenced by the ligand’s position in the spectrochemical series. The main vertical electron transitions and the molecular orbitals involved are identified and discussed. Furthermore, the results indicate that the iodide-containing gold(III) complexes, [AuCl₂I₂]⁻ and [AuI(OH)₃]⁻, are viable candidates for practical synthesis. Full article

Uranium isotopic composition of shallow groundwater in the Jabal Sayid-Mahd Adhab area of western Saudi Arabia was investigated to evaluate geochemical changes resulting from water-rock interactions. The wide range of uranium concentrations (0.75–29.3 ppb) and ²³⁴U/²³⁸U activity ratios (1.11–3.11) reflect variable redox and uranium dissolution conditions across the aquifer. Samples with high uranium concentrations but low activity ratios suggest a recent release of uranium from mineral phases, which is further enhanced by the presence of fluoride ions. Fluoride’s strong reactivity aids in uranium dissolution by forming stable uranyl-fluoride complexes under open-system leaching conditions. Conversely, higher isotopic ratios in low-uranium samples suggest longer water-rock interaction and preferential leaching of ²³⁴U by alpha-recoil processes. The positive correlation between uranium and salinity parameters further indicates that uranium enrichment is linked to increased ionic strength and the abundance of complex ligands. The relationship between activity ratio ²³⁴U/²³⁸U (AR) and 1/U in the studied samples indicates that uranium behavior in the shallow aquifer is dominated by open-system leaching, with local binary mixing superimposed in a few sites. The findings emphasize that uranium isotopic composition is a valuable tool for identifying localized groundwater mixing and assessing the hydrogeochemical impacts of nearby mineralized areas on the aquifer system. These results represent an essential baseline for future environmental monitoring and for evaluating potential temporal changes in uranium behavior. Full article

(This paper presents the synthesis of a novel copper(II) metal complex with ethyl (2-(methylcarbamoyl)phenyl)carbamate and 3-methylquinazoline-2,4(1H,3H)-dione. The characterization of the compound was conducted through various techniques, including melting point determination, microwave plasma atomic emission spectrometry (MP-AES) for Cu, attenuated total reflection (ATR), IR, ¹H NMR, and ¹³C NMR spectroscopy. The coordination compound was obtained after mixing water solutions of the metal salt and the ligand dissolved in DMSO and water solutions of NaOH, in a metal-to-ligand-to-base ratio of 1:2:2. The ligand and the metal chloride were brought into the reaction at room temperature in DMSO and H₂O as solvents, respectively. The results indicate the successful formation of a stable mixed-ligand Cu(II) coordination compound involving N,O-donor ligands. Based on the obtained data, we assumed that the ligands are coordinated through N- and O-donor atoms. Spectroscopic data suggested that the ligand (3-methylquinazoline-2,4(1H,3H)-dione), by using (NaOH), coordinated to a metal ion as a monodentate ligand through the nitrogen atom of the NH group and ethyl (2-(methylcarbamoyl)phenyl)carbamate coordinated in a bidentate fashion through the N- and O-donor atoms of ester group. Additionally, two hydroxyl groups were bridged for two metal ions into the formed dimer structure. Full article

For complexation of mRNA into polyplexes, double-pH-responsive lipo-xenopeptides (XP), comprising tetraethylene pentamino succinic acid (Stp) and lipoamino fatty acids (LAFs), were combined with PEGylated lipids, either DMG-PEG 2 kDa (DMG-PEG) or azido-group-containing DSPE-PEG 2 kDa (DSPE-PEG-N3), to increase colloidal stability and to facilitate ligand-mediated targeted mRNA delivery. LAF-XPs mixed with DMG-PEG at low (1.5% and 3%) molar ratios improved colloidal stability and retained transfection efficiency. PEGylation also enabled the formulation of otherwise unstable carrier complexes and prevented aggregation induced by salt, proteins, and serum. PEGylation of more positively charged Stp-LAF₂ mRNA polyplexes decreased fibrinogen adsorption. More neutral, LAF-rich Stp-LAF₄ polyplexes exhibited low fibrinogen binding without PEGylation. Intravenous administration of these stabilized mRNA complexes demonstrated enhanced biosafety while preserving transfection efficiency. DSPE-PEG-N3 was selected for cell targeting after strain-promoted azide-alkyne cycloaddition (SPAAC)-mediated click-coupling of DBCO-modified ligands. Higher PEG ratios (10% and 20%) provided effective shielding but reduced transfection efficiency, a drawback known as the “PEG dilemma”. Functionalization with an EGFR-targeting ligand restored transfection in EGFR-positive cell lines in a ligand-specific manner. High transfection efficiency is consistent with a lipophilic-to-hydrophilic polarity switch of LAF-XP carriers upon endosomal protonation, triggering dissociation of the PEG lipids and deshielding of the polyplex. Full article

Anthraquinones are molecules with numerous biological properties that can act as DNA intercalators and topoisomerase IIa inhibitors. In this work, the development of technetium-99m radiotracers was pursued via the technetium-tricarbonyl “2 + 1” mixed-ligand approach, fac-[^99mTc][Tc^I(CO)₃(NN′)(N)]⁺, with a (N,N′) bidentate chelator and a N co-ligand. In one approach, the ligands used were 2,2′-bipyridine (bpy) and N-functionalized-imidazole, where imidazole was conjugated to an anthraquinone moiety. In the other approach, 2-picolylamine and imidazole were used as the mixed-ligand system, where picolylamine was conjugated to an anthraquinone moiety. The synthesis of the ligands was achieved by reaction of 2-picolylamine with a suitably functionalized anthraquinone (Aqpa) or anthrapyrazole (Appa) and imidazole with a suitably functionalized anthraquinone (Aqim). The rhenium reference compounds, fac-[Re^I(CO)₃(bpy)(Aqim)]⁺ with bpy as a bidentate chelator and fac-[Re^I(CO)₃(Aqpa or Appa)(Im)]⁺, with imidazole (Im) as a co-ligand, were synthesized and characterized with spectroscopic methods. The radiotracer technetium-99m complexes fac-[^99mTc][Tc(CO)₃(bpy)(Aqim)]⁺ and fac-[^99mTc][Tc(CO)₃(Aqpa or Appa)(Im)]⁺ were prepared and characterized with standard methods. The purified radiotracers displayed high stability (≥90%) after incubation 24 h in 1 mM L-histidine or rat plasma. The tracers’ cell uptake was evaluated in vitro in CT-26 cells, and their pharmacokinetic properties and tumor uptake were evaluated in vivo in CT26-tumor-bearing mice. The “2 + 1” technetium-tricarbonyl approach leads to in vitro stable tracers, and this mixed-ligand system shows promise for further evaluation. Full article

The photocatalytic reduction of carbon dioxide (CO₂) into energy-dense fuels using visible light provides a sustainable approach for solar-to-chemical energy transformation. Among the diverse metal molecular systems developed, ruthenium (II) (Ru(II)) complexes have emerged as promising catalysts due to their superior redox properties, strong visible light absorption, and customizable ligand structures. This review explores recent advances in Ru(II)-catalyzed CO₂ photoreduction, with particular attention given to catalyst design strategies, mechanistic pathways, and system integration methodologies. Key configurations, including photosensitizer/catalyst (PS/Cat) mixed systems, covalently bonded dyads, and hybrid/supramolecular frameworks, are evaluated in terms of efficiency, turnover numbers (TON), and selectivity. A critical analysis of challenges such as competing H₂ generation, inefficient charge transfer, and limited long-term stability is presented. Emerging trends toward the use of pincer ligands, transition metal integration, and self-photosensitizing frameworks are discussed as potential approaches for improving efficiency. Overall, this review offers insights into the structural and mechanistic features driving CO₂ photoreduction and provides perspectives for the rational design of next-generation Ru-based photocatalytic systems for efficient solar CO₂ conversion and the photocatalytic reduction of carbon dioxide (CO₂) into energy-dense fuels using visible light. Full article

This research prepared and characterised novel mixed coordination complexes derived from escitalopram with eugenol and curcumin to form (L₁) and (L₂), respectively. The complexes were prepared via Williamson ether synthesis and analysed by FTIR, UV–Vis, ¹H-NMR spectroscopy, elemental analysis, molar conductivity, and magnetic susceptibility. The results confirmed their octahedral geometries. Magnetic investigation reported high-spin configurations for Mn(II), Co(II), and Ni(II) complexes, whereas Cu(II) exhibited a distorted octahedral arrangement with characteristic d–d transitions. In addition, the calculation of Density functional theory (DFT) provided more insight into the detailed structural and electronic properties of the new ligand and its complexes. Antimicrobial compounds were evaluated against Escherichia coli, Staphylococcus aureus, and Candida albicans through the agar well diffusion method. The reported results revealed that Cobalt complexes showed antimicrobial activity followed by Copper (Cu), Nickel (Ni) and Manganese(Mn) complexes, respectively, due to an increase in Co-lipophilicity, which leads to improved diffusion through microbial cell membranes. The research findings confirmed that escitalopram-based mixed ligands coordinate with transition metals and could have significant biological applications. Full article

Understanding how redox-active ligands coordinate to metal centers of different oxidation states is essential for applications ranging from metal remediation and recycling to drug discovery. In this study, coordination complexes of nickel(II), copper(II), and zinc(II) chloride salts were synthesized by mixing the salts with either arylazoformamide (AAF) or arylazothioformamide (ATF) ligands in toluene or methanol. The AAF and ATF ligands coordinate through their 1,3-heterodienes, N=N–C=O and N=N–C=S, respectively, and, due to their known strong binding, the piperidine and pyrrolidine formamide units were selected, as was the electron-donating methoxy group on the aryl ring. A total of 12 complexes were obtained, representing potential chelation events from ligand-driven oxidation of zerovalent metals and/or coordination of oxidized metal salts. The X-ray crystallography revealed a range of coordination patterns. Notably, the Cu(II)Cl₂ complexes, in the presence of ATF, produce [ATF-CuCl]₂ dimers, supporting a potential reduction event at the copper, while other metals with ATF and all metals with AAF remain in the 2+ oxidation state. Hirshfeld analysis was performed on all complexes, and it was found that most interactions across the complexes were dominated by H…H, followed by Cl…H/H…Cl, with metals showing very little to no interaction with other atoms. Spectroscopic techniques such as UV–VIS absorption, NMR (when diamagnetic), and FTIR, in addition to electrochemical studies support the metal–ligand coordination. Full article

This study investigates the corrosion inhibition efficiency of [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] and its Zn and Cu complexes for mild steel in 1.0 M HCl. The ligand was selected for its non-toxic profile and high electron density, favoring strong adsorption onto the metal surface. Electrochemical methods, including EIS, PDP, LPR, and CASP, were employed to evaluate the inhibitors’ performance. The results showed a significant decrease in corrosion current density and increased polarization resistance, with the Zn complex achieving the highest inhibition efficiency (93.8%). EIS fitting confirmed the formation of a protective film with high charge transfer and film resistance. Surface analyses by SEM and EDS revealed smoother steel morphology and inhibitor adsorption. XPS confirmed the presence of Fe³⁺, Zn²⁺and Cu²⁺ oxides, as well as all active inhibitor elements on the surface, supporting a mixed inhibition mechanism. The enhanced performance of the metal complexes is attributed to synergistic effects between the metal ions and the heterocyclic ligand, offering a promising strategy for the design of effective and environmentally friendly corrosion inhibitors. Full article

Three new complexes of Hg(II), with the general formulas [Hg₂(ox)₂(NA)₄]_n·3nH₂O (1), [Hg(NO₃)₂(NA)₂(H₂O)₂]·2NA (2), and [Hg₂(SO₄)₂(H₂O)₂(NA)₄]·6H₂O (3), where ox = oxalate and NA = nicotinamide, were synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, and fluorescence spectra. For complex (2), ¹³C and ¹H NMR spectra were recorded. Thermogravimetric analysis was also performed for complexes (1) and (2). Single crystal X-ray diffraction shows that in the polymeric complex (1) and the binuclear complex (3), the Hg(II) ions are hexacoordinated, whereas in the mononuclear complex (2), Hg(II) is octacoordinated. In complex (1), each oxalate group acts in a µ₄ coordination manner, the basal plan being made up by four oxygen atoms belonging to the two oxalate ligands, while the nicotinamide molecules occupy the axial positions. In complex (2), the nitrate groups coordinate in a bidentate chelating mode, whereas in complex (3), each sulphate ligand acts in a bidentate chelating–bis monodentate bridging manner. Full article

We report the mode of interaction of copper(II) ions with tyrosine (Tyr, L) in binary and ternary systems with Ado, AMP, ADP, and ATP (L’) as second ligands in an aqueous solution. The composition and overall stability constants of the complexes formed were determined using the potentiometric method. The coordination sites were identified through spectroscopic (VIS, EPR, IR) methods, as well as DFT and computational–molecular modeling. In the binary Cu(II)/Tyr system, the main reaction centers of the ligand molecule involved in the interactions with copper(II) ions are nitrogen (-NH₂ group), as well as oxygen atoms (-COO⁻ group), as confirmed, for example, by comparing the mode of coordination in the CuH₂(Tyr)₂ species and the [CuH₂(Tyr)₂(H₂O)] × 1.5H₂O solid complex obtained. In the ternary Cu(II)/L/L’ systems, MLHxL’ and mixed MLL’ protonated complexes are formed. Only in the ATP system were no MLL’(OH)_x hydroxocomplexes found. An increase in the number of phosphate groups in ADP and ATP molecules has no effect on their participation in the coordination in ternary species, and these ligands interact just like in binary species (i.e., in ADP, both α- and β-phosphate groups, and in ATP, only the γ-phosphate group). It was observed that the introduction of a second ligand into the Cu(II)/Tyr system did not change, over the entire pH range studied, the tyrosine coordination mode. Full article

Cyclen-based ligands are among the most preferred ones in radiopharmacy, where they are mainly applied for transferring radioisotopes through the human body. A crucial criterion is the stability of their metal–ligand complexes, which depends on the stabilization of the free ligand in solution. However, these flexible ligands can have numerous conformations, and for a reliable evaluation of the dissociation energy, the most stable one(s) in solution must be known. In the present study, the low-energy conformational space of four anionic (2-) cyclen-based ligands has been elucidated in aqueous solution by a joint molecular mechanics (MM)/Density Functional Theory (DFT) procedure. The results revealed a significant preference for C₂ symmetric structures, more or less resembling the arrangements in their metal complexes. The computed dissociation energies agree with the experimentally found stability trend for the Pb²⁺ complexes with ligands containing picolinate pendant arms. For complexes with mixed donor groups (carboxyl, amide, pyridine), significant thermodynamic stabilities were predicted. Full article