Search Results (1,563)

Oxygen-related absorption features provide fundamental constraints for passive atmospheric remote sensing in the reflected-solar spectrum. Because molecular oxygen is well-mixed in the dry atmosphere, O₂ absorption links measured radiance to atmospheric mass, pressure, and effective photon path length, while O₂-O₂ (O₄) collision-induced absorption provides complementary sensitivity to lower-tropospheric photon paths. This review synthesizes the spectroscopic basis, radiative-transfer mechanisms, satellite implementations, retrieval algorithms, and atmospheric applications of O₂ and O₄ measurements from the ultraviolet to the shortwave infrared. Particular emphasis is placed on the O₂ B-band near 687 nm, the O₂ A-band near 760 nm, O₄ bands in the UV–visible range, and the O₂ band near 1.27 µm. These features support retrievals of cloud fraction, cloud pressure, optical centroid pressure, aerosol layer height, surface pressure, dry-air column abundance, and light-path corrections for greenhouse gas observations. We review major algorithmic approaches, including cloud-as-reflecting-boundary models, cloud-as-layer models, DOAS-based retrievals, optimal-estimation frameworks, photon path-length distribution methods, and machine learning or hybrid techniques. Key applications include cloud climatology, aerosol vertical characterization, air mass factor correction, XCO₂ and XCH₄ retrievals, carbon-cycle studies, and multi-mission data integration. Remaining challenges include spectroscopic uncertainty, aerosol and cloud scattering degeneracy, surface bidirectional reflectance, three-dimensional radiative-transfer effects, wavelength-dependent path mismatch, and inconsistent uncertainty characterization. Future progress will depend on improved spectroscopy, active–passive validation, multi-angle polarimetry, physically constrained machine learning, and harmonized multi-mission retrieval frameworks. Full article

Carbonate jade has emerged as a recently recognized commercial variety in the Chinese gemstone market. Systematic gemological and mineralogical investigations on carbonate jade, however, remain very scarce. Three Xinjiang calcite-dominated jade samples were investigated by using Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, microbeam X-ray fluorescence (Micro-XRF) spectrometry, trace element analysis, in situ U-Pb dating, and C-O isotope analysis. The orange-red color originates from staining by hematite and magnetite inclusions, while the green color is produced by d-d electronic transitions of lattice-bound Fe³⁺ and Mn²⁺. The provenance comparison reveals systematic differences in trace element compositions between the Xinjiang carbonate jade and Pakistani Lvwen stone: the Xinjiang samples are characterized by extremely low Cu and Sr contents, whereas the Pakistani Lvwen stone has high Cu, Mn and Sr contents, and low Fe content. The U-Pb age obtained for the Xinjiang carbonate jade sample coincides with a Late Cretaceous rapid cooling event. Enriched light rare earth element (LREE) and C-O isotope (δ¹³C_V-PDB = −1.19–2.21‰, δ¹⁸O_V-SMOW = 15.00–20.01‰) signatures indicate that the carbonate-precipitating fluids were derived from marine carbonate wall rocks. These findings provide new mineralogical and geochemical constraints on the coloration mechanism, provenance, and fluid evolution of carbonate jade from Xinjiang. Full article

The formation and stabilization of silver nanoparticles (AgNPs) in thin films of ionic liquids (ILs) based on long-chain alkylimidazolium cations are demonstrated in this work. IL films were prepared by vacuum thermal evaporation using the Knudsen effusion method onto ITO/glass substrates, leading to the formation of micro- and nanosized structures distributed across the surface. The investigated ILs were symmetrical dialkylimidazolium-based systems: [C₇C₇im][NTf₂], [C₈C₈im][NTf₂], and [C₁₀C₁₀im][NTf₂]. Increasing the alkyl side-chain length of the imidazolium cation resulted in larger droplet domains. AgNPs were subsequently deposited onto the IL films by sputtering. The formation of AgNPs was confirmed by scanning electron microscopy (SEM), ultraviolet (UV)–visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that increasing the alkyl side-chain length promotes more effective confinement and stabilization of AgNPs, leading to improved nanoparticle formation and a narrower size distribution. The temporal stability of the Ag-containing IL films was evaluated under both air exposure and inert argon storage, revealing a strong influence of the surrounding atmosphere on nanoparticle evolution. Among the ILs studied, [C₁₀C₁₀im][NTf₂] exhibited the most favorable behavior for AgNP formation and stabilization, providing a more stable and homogeneous nanoparticle distribution over time. Full article

The primary objective of this study was to compare the contribution of cellular and cell-free filtrates of Serratia marcescens ATCC 9986 to the synthesis of silver nanoparticles, followed by a determination of the inhibitory activity on growth of S. marcescens and E. coli of the obtained biogenic silver nanoparticles. The synthesized silver nanoparticles exhibited maximum absorption at 257 nm and 262 nm when analyzed by ultraviolet–visible spectroscopy (UV–Vis). Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a peak at 3 keV, corresponding to silver nanocrystals. Characterization by TEM, EDX, and IR spectroscopy demonstrated the presence of organic compounds in the nanoparticles. IR analysis revealed the presence of proteins, carbohydrates, carboxylic acids, and other compounds with saturated and unsaturated C-C bonds in the nanoparticles. Silver nanoparticles synthesized using cell-free and cellular filtrates inhibited growth of antibiotic-resistant bacteria E. coli. Moreover, cell-free filtrate of S. marcescens exerted inhibitory activity against E. coli, but not against its source, S. marcescens bacteria. Full article

Natural blue calcite is relatively rare, and its coloration and luminescence mechanisms have not been systematically established. In this study, four natural blue calcite samples from China were comprehensively characterized using mineralogical testing, X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), photoluminescence (PL), and electron paramagnetic resonance (EPR). XRD confirms single-phase trigonal calcite (space group R-3c). EPMA detects minor Mg, Fe, Cu, and Sr, with smaller-radius Mg²⁺, Fe²⁺, and Cu²⁺ being the main contributors to the contraction through isomorphous substitution for Ca²⁺. UV-Vis spectra show characteristic absorptions at 270 nm and 340 nm related to lattice defects with a broad emission band centered at 480 nm in the PL spectra. EPR detects a CO₂⁻ radical center (g = 2.003), and the same signal is also observed in the colorless sample. The colorless sample also contains the same CO₂⁻ radicals, indicating that these radicals alone do not account for the blue coloration. A broad 480 nm blue-violet fluorescence band is observed in the four blue samples under 405 nm excitation. These findings provide a spectroscopic and crystallographic basis for distinguishing natural blue calcite from analogous materials and for understanding the origin of its color and luminescence. Full article

This study aimed to synthesize copper(I) iodide nanoparticles (CuI NPs) through a green route using taxo (banana passion fruit) extract as a natural capping and stabilizing agent, and to evaluate their antimicrobial performance against microorganisms isolated from concrete, together with a preliminary cytotoxicity screening. The obtained nanoparticles were characterized by ultraviolet–visible spectroscopy (UV–Vis), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), dynamic light scattering (DLS), and X-ray diffraction (XRD). UV–Vis spectra recorded in the 200–704 nm range showed a strong absorption band at 224 nm, consistent with electronic transitions associated with nanostructured CuI. FTIR analysis revealed extract-derived biomolecules adsorbed on the nanoparticle surface, with bands assigned to aliphatic C–H, aromatic moieties, and C–O/C–O–C vibrations, supporting the formation of an organic capping layer. DLS analysis showed a mean hydrodynamic diameter of approximately 32 nm in aqueous suspension, whereas TEM revealed particle sizes ranging from 13 to 42 nm. XRD confirmed a predominantly cubic CuI phase, while SEM–EDS identified Cu and I as the main elements, with minor signals attributed to residual organic coating and/or trace species from the synthesis medium. The CuI NPs exhibited antimicrobial activity against microorganisms isolated from medium-strength concrete, producing inhibitory effects at all tested concentrations (0.014, 0.0087, and 0.0035 mol/L). Preliminary cytotoxicity screening using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in human foreskin fibroblast (HFF), human breast adenocarcinoma (MCF7), and human glioblastoma (U251) cell lines showed dose- and time-dependent reductions in metabolic viability. The 1.0 mol/L formulations, particularly the precipitated fraction, produced stronger cytotoxic effects, whereas the 0.1 mol/L formulations, especially the residual fraction, preserved comparatively higher metabolic viability. Overall, these findings suggest that taxo-mediated CuI NPs are promising antimicrobial candidates for concrete biodeterioration control, while further colloidal and biological studies are required to better define their behavior under cell-culture conditions and optimize their safe application. Full article

Hydrophilic osmium(Os)-based redox polymers were designed as electron-transfer mediators for fungal flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH)-based glucose sensors. Poly(vinylimidazole-co-hydroxyethyl acrylate) (PVI-HEA) copolymers with different HEA compositions were synthesized and coordinated with Os(dmo-bpy)₂Cl₂ to prepare PVI-HEA-Os(dmo-bpy)₂Cl₂ redox mediators. The synthesized mediator systems were characterized using ¹H-nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, field emission scanning electron microscopy/energy dispersive spectroscopy, zeta potential analysis, cyclic voltammetry, and electrochemical impedance spectroscopy. The results confirmed the successful formation of Os redox polymer structures and their immobilization on the electrode surface. The electrochemical behavior and glucose sensing performance strongly depended on the PVI-HEA composition. Among the compositions tested, PVI-HEA(3.5:1)-Os(dmo-bpy)₂Cl₂ showed the strongest redox current response, stable aqueous dispersion behavior, and relatively low interfacial charge-transfer resistance. Glucose-sensing measurements using FAD-GDH/mediator-modified electrodes showed linear current responses over the glucose concentration range of 1.25–20 mM. The PVI-HEA(3.5:1)-Os(dmo-bpy)₂Cl₂-based electrode showed the highest sensitivity of 16.18 μA cm⁻² mM⁻¹, which was significantly higher than those observed at lower-HEA compositions. The optimized mediator system also showed selective glucose responses against representative biological interferents, including ascorbic acid, uric acid, dopamine, and serotonin. Stable catalytic current responses were maintained under Human Plasma-Like Medium conditions, suggesting improved matrix tolerance compared to conventional PVI-based Os redox polymers. The improved sensing performance was attributed to the hydrophilic polymer environment introduced by the HEA units, which may facilitate favorable interfacial charge-transfer behavior within the enzyme–mediator layer. The results show that the hydrophilic copolymer composition plays an important role in the electrochemical behavior and glucose sensing performance of Os redox polymer mediators. The proposed PVI-HEA-Os(dmo-bpy)₂Cl₂ system may be a promising candidate for future enzymatic glucose sensing and continuous glucose monitoring-related applications. Full article

Background/Objectives: The green synthesis of gold nanoparticles (AuNPs) using plant-derived flavonoids offers a sustainable alternative to traditional methods. This study aimed to synthesize, characterize, and evaluate the biological activities and cytogenotoxicity of AuNPs functionalized with naringin (NG) and its aglycone, naringenin (NGN). Methods: Synthesis was optimized by varying pH, HAuCl₄ concentration, reagent ratios, temperature, and stirring time. The resulting AuNPs-NG and AuNPs-NGN were characterized via Ultraviolet–Visible (UV–Vis) Spectroscopy, Fourier-Transform Infrared (FTIR) Spectroscopy, Dynamic Light Scattering (DLS), and Scanning Transmission Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (STEM-EDX). Biological potential was assessed through five antioxidant assays, alpha-amylase and alpha-glucosidase inhibition, and antimicrobial screening. Cytogenotoxicity was evaluated using the Allium cepa root meristem model. Results: Optimal synthesis occurred at pH 10 for both flavonoids (NG at 40 °C, NGN at 20 °C). STEM revealed AuNPs-NG were smaller (54.64 ± 13.15 nm) and more polydisperse than AuNPs-NGN (135.52 ± 23.85 nm). Both nanoformulations exhibited superior antioxidant and antidiabetic activities compared to free precursors, with AuNPs-NGN showing the highest potency in inhibiting lipoxygenase (LOX) (EC₅₀ = 9.58 ± 0.74 µg/mL). No antimicrobial activity was detected. In the Allium cepa test, both AuNPs induced concentration-dependent reduction in the mitotic index and triggered predominantly aneugenic chromosomal abnormalities. Conclusions: NG and NGN successfully act as reducing and stabilizing agents for AuNPs, with NGN providing enhanced biological efficacy alongside larger particle sizes. While these biogenic AuNPs show significant therapeutic potential as antioxidant and antidiabetic agents, their concentration-dependent cytogenotoxicity must be carefully considered for biomedical applications. Full article

In this study, pure ZnO and Ho-doped ZnO powders (1 and 2 mol % Ho) were synthesized via hydrothermal and sol–gel methods and evaluated for their tribocatalytic activity toward the degradation of paracetamol, an emerging pharmaceutical contaminant in aquatic environments. Structural, morphological, and optical properties of the obtained materials were investigated by X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. SEM observations revealed pronounced morphology differences between the synthesis routes, with hydrothermally prepared samples exhibiting well-defined rod-like structures. XPS and EPR analyses provided evidence for successful Ho modification of ZnO and the presence of defect-related electronic states associated with Ho doping. The tribocatalytic performance was examined in distilled, tap, and mineral water using friction rods with different geometries in order to assess the influence of synthesis route, Ho concentration, and water composition. Among all the investigated materials, hydrothermally synthesized ZnO doped with 2 mol % Ho exhibited the highest tribocatalytic activity, achieving 96.91% degradation of paracetamol at an initial concentration of 15 mg/L within 24 h. The enhanced performance was attributed to improved charge separation induced by Ho modification, combined with the favorable rod-like morphology of the particles. Higher degradation efficiencies were observed in distilled water compared to tap and mineral water, indicating the important role of dissolved ions during the tribocatalytic process. These findings demonstrate that the synthesis route, Ho doping, and water composition collectively govern the tribocatalytic performance of ZnO-based materials, highlighting their potential for water purification. Full article

The discharge of azo-dye-containing wastewater from textile and related industries represents a major environmental challenge because of the persistence, toxicity, and poor bio-degradability of synthetic dyes. Congo red dye (CR), one of the most widely used azo dyes, poses serious ecological and public health risks when released into aquatic ecosystems. Although numerous biological adsorbents have been investigated for dye removal, the development of sustainable fungal-based nanocomposites with high adsorption efficiency, optimized operational conditions, and verified environmental safety remains limited. Therefore, the present work describes the development and evaluation of a novel Aspergillus terreus–silver oxide nanoparticle (Ag₂O NPs) myco-nanocomposite as a promising eco-friendly biosorbent for CR dye removal from aqueous solutions and real wastewater. Aspergillus terreus (GenBank accession PX920301) isolated from dye-contaminated wastewater, the adsorption efficiencies of dried mycelia, and the myco-nanocomposite were compared. Myco-nanocomposite was characterized using ultraviolet visible spectroscopic analysis (UV/Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). A. terreus–Ag₂O NPs myco-nanocomposite exhibited the highest ad-sorption efficiency 92.73%, adsorption capacity (qe) 118.7 mg/g and lowest CR dye residual by 3.81 mg/L, while A. terreus non-autoclaved dried mycelia recorded 78.28% CR removal, adsorption capacity (qe) 100.2 mg/g and CR dye residual by 11.39 mg/L. Adsorption parameters were optimized using a four-factor Box–Behnken experimental design, producing a highly significant quadratic model (R² = 0.986). The highest optimized conditions were obtained at run 17 in which 100 mg L⁻¹ CR dye, pH 8, 0.05 g adsorbent dosage, and 48 h contact time, with removal efficiency of 96.88%, followed by run 14 using 50 mg L⁻¹ CR dye, pH 6, 0.05 g adsorbent dosage, and 48 h contact time, with removal efficiency of 95.79%. Phytotoxicity and microbial toxicity assays demonstrated that the treated wastewater was environmentally safer than untreated CR dye, exhibiting no inhibitory effects on representative bacteria, yeast, and filamentous fungi while improving wheat seedling growth. Furthermore, application of the myco-nanocomposite to real industrial wastewater achieved 94.92% decolorization. This study provides a sustainable myco-nanocomposite of A. terreus–Ag₂O NPs which represents a promising green technology for the remediation of dye-contaminated industrial effluents and supports the development of environmentally sustainable wastewater management strategies and applicability of reusing treated wastewater. Full article

The study of ancient sculptural polychromy increasingly relies on non-invasive analytical approaches capable of identifying pigments and reconstructing original decorative schemes while preserving the integrity of archaeological objects. This paper presents the investigation of the polychromy, extraordinarily preserved, on two Roman marble statues discovered in the forum of Formia (southern Latium) and currently housed in the National Archaeological Museum of Formia: a togate statue (inv. 147614) and a headless draped female figure (inv. 147680). Both sculptures retain exceptionally well-preserved traces of pigments, offering a rare opportunity to investigate materials and painting techniques applied to Roman marble statuary. The analytical protocol combined multiband imaging (Visible-Induced Luminescence and Ultraviolet Luminescence), optical microscopy, Fiber Optic Reflectance Spectroscopy (FORS), portable X-ray Fluorescence (XRF), and Surface Enhanced Raman Spectroscopy (Raman-SERS) applied to two micro-samples. The analyses allowed the identification of Egyptian blue, iron-based pigments, gilding, and an organic red lake on the palettes used for the statues. Raman-SERS measurements provided additional information on the composition of the organic lake detected on the female statue’s himation, supporting its attribution to a natural vegetal-derived dye, as madder lake. The results highlight the success of integrated non-destructive methodologies for the study of Roman sculptural polychromy and contribute to the reconstruction of complex decorative schemes on marble statuary. Full article

In this study, a series of xFe₂O₃–Na₂O–CaO–SiO₂ glass-ceramics containing 0–28 wt.% Fe₂O₃ were prepared via the conventional melt-quenching technique. The resulting samples, designated S1–S4, were subsequently subjected to thermal treatment and investigated with respect to their structural, thermal, and optical characteristics. Differential scanning calorimetry analysis revealed the influence of the Fe₂O₃ concentration on the glass transition temperature and crystallization behavior of the samples. Structural analysis of the samples revealed that crystalline silicate and iron oxide phases constituted the predominant crystalline phases, with their overall crystallinity being strongly dependent on the Fe₂O₃ content and thermal treatment. Fourier transform infrared spectroscopy evidenced structural modifications of the silicate network induced by iron incorporation, while ultraviolet–visible–near infrared spectroscopy highlighted the presence of Fe²⁺/Fe³⁺ ions and their associated electronic transitions. The results indicate that increasing the Fe₂O₃ content significantly affects the network structure, redox state, and thermal behavior of the glass-ceramic system, leading to enhanced absorption properties. Full article

Melanin is a natural biopolymer with broad biological activities, yet research on melanin from the medicinal fungus Ophiocordyceps sinensis remains insufficient. In this study, two melanin fractions, TZ-a and TZ-b, were isolated from its fermentation products and characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Ultraviolet–Visible spectra (UV-Vis). Their protective effects against UVB-induced damage in keratinocytes and heavy metal (Cd²⁺, Pb²⁺, As³⁺, Hg²⁺) cytotoxicity were evaluated. Both fractions exhibited characteristic melanin peaks but showed structural differences. TZ-a displayed lamellar or needle-like crystals, whereas TZ-b formed block-like aggregates. Both demonstrated good thermal stability. UV-Vis spectra confirmed their typical melanin identity. At 200 μg/mL, TZ-a and TZ-b increased cell viability from ~50% (model) to 80.59% and 82.48%, respectively. Additionally, they elevated the proportion of viable cells within the apoptotic population from 59.11% to 86.08% and 84.79%. Both fractions concentration-dependently alleviated heavy metal-induced cytotoxicity, reduced malondialdehyde levels, and restored glutathione pools. In conclusion, the melanin fractions TZ-a and TZ-b from O. sinensis exhibited photoprotective effects and alleviated heavy metal toxicity. Full article

Background/Objectives: The study addresses the global health challenge posed by multidrug-resistant (MDR) pathogens, highlighting the urgent need for alternative antimicrobial solutions. This study investigated the in vitro antimicrobial and antibiofilm potential of endophytic mediated-synthesized silver nanoparticles (AgNPs). Methods: An endophytic bacterium was isolated from the medicinal plant Commiphora gileadensis in Saudi Arabia and identified as Bacillus subtilis CG1 through 16S rRNA gene sequencing. The bacterium was utilized for the green synthesis of AgNPs, as confirmed by Ultraviolet-visible (UV–Vis) spectroscopy. AgNPs characterization was done using Fourier-transform infrared (FTIR) spectroscopy, Transmission and scanning electron microscopy (TEM and SEM), energy-dispersive X-ray spectroscopy (EDX), and dynamic light scattering (DLS). The antimicrobial efficacy of the fabricated AgNPs was tested against eight clinically relevant pathogens using standard in vitro assays such as the agar disk diffusion method, minimum inhibitory concentration (MIC), minimum bactericidal and fungicidal concentrations (MBC and MFC). Additionally, AgNPs were tested for antibiofilm activity against P. aeruginosa and S. epidermidis. Tested pathogens included Methicillin-Resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Candida auris, Candida albicans, and Candida tropicalis. The antibiofilm efficacy was tested using the Crystal violet assay. Results: UV–Vis spectroscopy confirmed AgNP formation with a characteristic absorption peak at 412 nm. FTIR analysis identified the presence of hydroxyl, nitrile, and alkyne functional groups, which are involved in nanoparticle reduction and stabilization. TEM and SEM revealed predominantly spherical AgNPs with sizes ranging from 17 to 72 nm, while EDX confirmed silver as the major elemental component. DLS analysis showed a Z-average particle size of 113.9 ± 67.75 nm and a zeta potential of −24.2 mV. The synthesized AgNPs exhibited concentration-dependent antimicrobial activity, producing inhibition zones of 10–20 mm at 240 µg/mL. MIC values ranged from 6.25 to 25 µg/mL, whereas MBC and MFC values ranged from 6.25 to 50 µg/mL and 25 to 100 µg/mL, respectively. Moreover, bacterial growth kinetics analysis demonstrated a concentration-dependent inhibition of growth by AgNPs at MIC and sub-MIC concentrations. Additionally, AgNPs demonstrated significant antibiofilm activity against P. aeruginosa and S. epidermidis.Conclusions: Overall, B. subtilis CG1-mediated AgNPs exhibited promising physicochemical properties and antimicrobial and antibiofilm activities, suggesting their potential as alternatives for combating resistant and biofilm-associated infections. Full article

This paper presents the synthesis and characterization of Schiff base ligands (L) derived from NH-pyrazole-indole and their ruthenium(II) complexes of the general formula [Ru(p-cymene)(L)Cl₂]. The structural characterization of the ligands and ruthenium complexes was performed using a range of analytical methods, including infrared spectroscopy (IR), Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, elemental analysis, mass spectrometry(ESI-MS), density functional theory (DFT) calculations, and single-crystal X-ray diffraction crystallography for two of the four synthesized compounds. Schiff base ligands (L) derived from NH-pyrazole-indole and their ruthenium(II) complexes were evaluated against antibiotic-resistant bacteria. The effect of substituting the ligand with methoxy groups on biological activity was assessed. The antibacterial activity, Minimal Inhibitory Concentration (MIC), and Minimal Bactericidal Concentration (MBC) of the free ligands and the ruthenium compounds were measured against six bacterial isolates (Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, Shigella dysenteriae) and two control strains (Enterococcus faecalis ATCC 29212 and Enterobacter cloacae ATCC 13047) from the ESKAPE group of highly antibiotic-resistant pathogens. The free ligands were inactive, whereas all four ruthenium complexes displayed notable antibacterial activity. In particular, compounds Ru3 and Ru4 exhibited higher activity against Staphylococcus aureus than the Trimethoprim control, with MIC values of 15.60 µg/mL, compared with an MIC > 64 µg/mL for Trimethoprim. The activity of those two complexes was similar to that of Gentamicin against this strain. Molecular docking calculations suggested a possible mechanism of action through binding of the complexes to the active site of S. aureus PBP2a. Full article