Objectives: The antimicrobial, oxidative activities, and ecotoxicity of synthesized silver-loaded zeolites (X and ZSM-5(MFI), Si-to-Al ratios 12 and 25) were studied, linking antimicrobial properties to material structure and released active silver species. Methods: The materials were characterized by SEM, EDX, TEM, and XRPD. All materials, with a silver content of 1–3%wt for the Ss and about 35%wt for the X-zeolites, were tested against Escherichia coli and Staphylococcus aureus. Redox activity was studied in physiological (pH 7.4/37 °C) and optimal (pH 8.5/37 °C) conditions in chemiluminescent model systems. In the ecotoxicity tests, we used Daphnia magna. Results: A proportional correlation was observed between the bactericidal effect of and the silver content in the zeolites. AgX with a Si/Al ratio of ~1.23 and 35% silver showed a higher antimicrobial efficiency, particularly against Gram-negative E. coli versus Gram-positive S. aureus. The concentration thresholds were as follows: AgXas had a bactericidal effect at 0.003 g/L⁻¹, with an MIC at 0.0015 m/L⁻¹ for E. coli; SA25-Ag, AgXcl, AgXrc had a bactericidal effect at 2.5 g/L⁻¹. The bacteria were more resilient than Daphnia magna, which showed a 90–100% lethality at Ag–zeolite concentrations of 0.00625 to 0.0125 g/L⁻¹. AgXas and AgXrc demonstrated strong reactive oxygen species generation at both the physiological and optimal pH, explaining their bactericidal effects. In general, the tested materials showed an inhibition of the generated reactive oxygen species depending on the model system and conditions. Conclusions: The silver species leached from the new materials explain their higher oxidation and bactericidal activity. While suitable for stringently controlled biological applications, their release into the environment, in concentrations higher than 0.01g/L⁻¹, should be avoided.

The present work deals with the sol–gel synthesis of silica–poly (vinylpyrrolidone) hybrid materials. The nanohybrids (Si-PVP) have been prepared using an acidic catalyst at ambient temperature. Tetramethyl ortosilane (TMOS) was used as a silica precursor. Poly (vinylpyrrolidone) (PVP) was introduced into the reaction mixture as a solution in ethanol with a concentration of 20%. The XRD established that the as-prepared material is amorphous. The IR and ²⁹Si MAS NMR spectra proved the formation of a polymerized silica network as well as the hydrogen bonding interactions between the silica matrix and OH hydrogens of the silanol groups. The TEM showed spherical particle formation along with increased agglomeration tendency. The efficacy of SiO₂/PVP nanoparticles as a potential antimicrobial agent against a wide range of bacteria was evaluated as bacteriostatic, using agar diffusion and spot tests. Combined effects of hybrid nanomaterial and antibiotics could significantly reduce the bactericidal concentrations of both the antibiotic and the particles, and they could also eliminate the antibiotic resistance of the pathogen. The registered prooxidant activity of the newly synthesized material was confirmative and explicatory for the antibacterial properties of the tested substance and its synergetic combination with antibiotics. The effect of new hybrid material on Crustacea Daphnia magna was also estimated as harmless under concentration of 0.1 mg/mL.

Vaya (Ramsar site, protected area and Natura 2000 site) is the biggest natural lake in Bulgaria and the shallowest Black Sea coastal lake, which during the last decades has undergone significant changes and was included as critically endangered in the Red List of Bulgarian Wetlands. Our studies were conducted during the summer and autumn months of three years - 2004-2006. The paper presents results on the phytoplankton abundance (numbers, biomass and carbon content) in combination with the indices of species diversity, evenness and dominance. Phytoplankton abundance was extremely high (average values of 1135 × 106 cells/L for the quantity and of 46 mg/L for the biomass) and increased in the end of the studied period (years 2005-2006), when decrease of species diversity and increase of the dominance index values were detected. The carbon content of the phytoplankton was at an average value of 9.7 mg/L and also increased from 2004 to 2006. Cyanoprokaryota dominated in the formation of the total carbon content of the phytoplankton, in its numbers (88%-97.8%), and in the biomass (62%-87.9%). All data on phytoplankton abundance and structural parameters in Vaya confirm the hypertrophic status of the lake and reflect the general negative trend in its development.

Background: The present work is devoted to the biological effects of sol–gel-derived silica (Si)–copper (Cu) nanomaterials. Methods and Results: Tetraethyl orthosilane (TEOS) was used as a silica precursor; copper was introduced as a solution in ethanol with Cu(OH)₂. The obtained samples were denoted as Si/Cu (gel) and Si/Cu/500 (500 °C heat-treated). Their phase formation and morphology were studied by XRD and SEM. The antibacterial activity was tested by two Gram-positive bacteria, three Gram-negative bacteria, and two types of eukaryotic species. Most bacteria were more sensitive to Si/Cu/500 materials than to Si/Cu (gel). The yeasts were more sensitive to Si/Cu (gel). The new nanomaterials were tested for oxidant activity at pH 7.4 (physiological) and pH 8.5 (optimal) in three model systems by the chemiluminescent method. They significantly inhibited the generation of free radicals and ROS. This result underlines their potential as regulators of the free radical processes in living systems. The epithelial tumor cell lines appeared more sensitive than the non-transformed fibroblasts, likely due to their metabolic activity and proliferation rates, leading to greater accumulation of the substances. Using Daphnia magna, the ecotoxicity study showed that the LC₅₀ was reached at 1 mg/L of Si/Cu/500. Si/Cu (gel) was more toxic. Conclusions: Our results reveal the potential of these nanohybrids to be applied in living, eukaryotic systems. The cytotoxicity evaluation showed higher tolerance of normal, non-transformed cells, in concurrence with the oxidation tests.

Silica–poly (vinylpyrrolidone) hybrid material was prepared using the sol–gel method. Tetramethyl ortosilane (TMOS) was used as a silica precursor. XRD analysis established that the as-prepared material is amorphous. The morphological structure of the final product was determined by the incorporated PVP. The UV–Vis analysis showed that the obtained hybrid exhibited absorption in the ultraviolet range. The antimicrobial activity of the SiO₂/15PVP hybrid material was tested on Staphylococcus epidermidis ATCC 14990, Salmonella typhimurium ATCC BAA-2162, Candida albicans, and Saccharomyces cerevisiae in combination with the following antibiotics: Vancomycin for Gram-positive bacteria, Ciprofloxacin for Gram-negative bacteria, and Nystatin for yeast. The results confirmed a concentration-dependent synergistic effect of the antibiotic in combination with the TM15/PVP hybrid particles, especially at their highest concentration of 100 mg/mL on Gram-positive bacteria and for the Gram-negative Salmonella. On Candida albicans ATCC 18804 and Saccharomyces cerevisiae CCY 21-6-3, the effect was synergistic again, and a fungicidal effect was observed at 6.25 and 1.50 mg/mL for the antibiotic concentration and concentrations of hybrid material at 100 mg/mL. The toxicity on Daphnia magna was also tested. The registered prooxidant activity of SiO₂/15PVP shows possible applications at very low concentrations. The obtained results demonstrate the possibility of clinical implementations of the newly synthesized hybrid material.

Objective: The objective of our study was to synthesize and characterize silica–copper nanomaterials and to evaluate their biological properties (antibacterial, redox, cytotoxic, and ecotoxic) for potential applications. Methods and Results: Si/Cu-based materials were prepared by a sol–gel method. They were characterized by XRD, UV-Vis, and SEM-EDS. The antibacterial activity of the materials was evaluated against Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium), and yeasts (Candida albicans, Saccharomyces cerevisiae). The nanomaterial that was calcined at 500 °C exhibited greater antibacterial efficacy compared to the gel form. S. typhimurium demonstrated the highest susceptibility, whereas S. aureus and P. aeruginosa were the most resistant of the tested bacteria. Both yeasts exhibited comparable sensitivity (MBC = 1.0 mg/mL). The redox activity of both nanomaterials was tested at pH 7.4 (physiological) and 8.5 (optimal) by the activated chemiluminescent method. The nanocomposites significantly inhibited the free-radical and ROS generation. This presents them as redox regulators in living systems. The cytotoxic effects in normal BEAS-2B and tumor A549 human cell lines were assessed microscopically and by the cell viability neutral red uptake assay, CC₅₀ being evaluated. The observed effects suggest moderate, similar cytotoxicity in both cell lines. The ecotoxicity study using Daphnia magna showed an LC₅₀ of ~7–8 mg/L about Si/Cu/500. The LC₅₀ for Si/Cu (gel) was lower than 0.25 mg/L, indicating an increase in toxicity with increased exposure time. Conclusions: Possible applications of the newly synthesized nanomaterials include antimicrobial coatings, drug delivery systems, antioxidant additives in various formulations, and water purification.