Compounds

Mn and Fe complexes of ethylene cross-bridged tetraazamacrocycles, known to retain their reactive metal ions even under harsh aqueous conditions due to the rigidity and topological constraint of the ligands, with methyl, allyl and benzyl pendant arms were electrostatically fixed to a commercial cation exchange resin, and their effectiveness and recyclability in the bleaching of organic dyes, namely, methyl orange, methylene blue and rhodamine B, were determined. These molecular Mn and Fe tetraazamacrocycle catalysts have been previously reported as homogeneous solution phase catalysts for bleaching organic dyes, but could not be feasibly recovered for multiple cycles of dye bleaching. Herein, we report the potential of these resin-fixed solid-state metal complex catalysts in the degradation of organic dyes. The Mn catalysts were faster in the first cycle of dye bleaching, but their bleaching rate slowed considerably (to about 10% on average) in additional cycles. In contrast, the Fe catalysts were slower in the first cycle of dye bleaching, but were able to bleach dyes for up to five cycles while retaining more of their original reactivity (30–50% on average), suggesting their potential recyclability. Thus, these resin-fixed tetraazamacrocyclic metal complex catalysts, when coupled with the demonstrated rechargeability of the resin with fresh catalyst, may one day be effectively used for water purification applications. SEM and optical microscopy images demonstrated the robustness of the resin bead across multiple cycles, while EDS experiments confirmed the continued presence of Mn and Fe on the bead surface after multiple cycles.

Background: Increasing antimicrobial resistance has directed studies toward investigating the antimicrobial activity of thymol, as well as the antibiofilm and antioxidant potential of its emulsions (with Tween 80) against multidrug-resistant (MDR) K. pneumoniae isolates. Methods: A microdilution assay was used to estimate thymol’s antibacterial potential against 10 clinical isolates (labeled 1–10). The dynamic light scattering technique was used to measure the particle size diameter (Zavg) of formulated emulsions. The antibiofilm potential of emulsions was assessed in vitro using a crystal violet assay and ex vivo on a surgical drain through a colony-forming unit assay. Antioxidant activity was screened by using the DPPH assay. Results: The MIC values were ≤1.5 mg/mL for strains 1 and 7 and <0.5 mg/mL for the other strains. Emulsions E_250:500, E_250:750, E_300:750, and E_500:750 were stable and homogeneous, with a Zavg of approx. 200 nm (128.4 ± 0.8 nm for E_250:750). These emulsions significantly reduced the biofilm biomass of strains 3 and 7 (50.6–74.32% and 34.60–59.8% of inhibition, respectively), with the strongest activity observed for E_250:500 and E_500:750. Antibiofilm potential was confirmed ex vivo, with E_500:750 showing the highest efficacy (ΔLogCFU 2.60 and 2.68 for strains 3 and 7). E_250:750 demonstrated the highest capacity to neutralize the DPPH• radical. Conclusions: Thymol and its emulsions exhibited antibacterial and antibiofilm activity against MDR K. pneumoniae isolates, along with the proven antioxidant properties of the emulsions.

α-Fe_2−4xZ_3xO₃ (Z = Ce, Ru) nanoparticles were synthesized via a conventional solid-state reaction route. X-Ray diffraction analysis confirmed that all compositions crystallize in the single-phase hexagonal hematite (α-Fe₂O₃) structure, with no detectable secondary phases. Cerium substitution resulted in a pronounced reduction in crystallite size accompanied by a progressive narrowing of the optical band gap, which decreased to approximately 1.73 eV at higher Ce contents. The optical properties were further investigated through absorption coefficient, optical transmittance, and complex refractive index analyses, revealing that cerium-doped hematite exhibits enhanced light-harvesting capability, highlighting its strong potential for optoelectronic and solar-energy conversion applications. Magnetic hysteresis measurements on α-Fe_2−4xRu_3xO₃ samples showed a systematic increase in both coercive field (H_c) and remanent magnetization (M_r) with increasing Ru concentration. This magnetic hardening behavior is attributed to strengthened magnetocrystalline and shape anisotropy induced by Ru incorporation into the hematite lattice. Mössbauer spectroscopy confirmed the presence of Fe³⁺ and Ru⁴⁺ species, providing valuable insight into the oxidation states and local magnetic environments within the corundum-type structure.