Petranka Petrova

Cordierite-based ceramics (Mg₂Al₄Si₅O₁₈) were successfully synthesized and comprehensively characterized to evaluate their structural and dielectric behavior for high-temperature electronic applications. Morphological, microstructural and vibrational analyses confirm the high phase purity and structural integrity of the synthesized material. Dielectric measurements reveal high real permittivity (ε′) values at low frequencies and elevated temperatures, mainly attributed to interfacial polarization arising from Schottky-type barriers at grain–grain and surface–volume interfaces, underscoring the crucial influence of heterogeneous interfaces on the dielectric response. The electrical conductivity follows a thermally activated hopping mechanism involving both intra-grain and grain-boundary charge transport. Analysis of the electric modulus formalism provides further insight into relaxation dynamics: the real (M′) and imaginary (M″) components highlight pronounced space-charge effects, with M″ exhibiting a distinct relaxation peak (M″) associated with grain contributions. The systematic shift of this peak toward higher frequencies with increasing temperature indicates enhanced charge-carrier mobility and a strongly thermally activated relaxation process. The frequency-dependent conductivity displays two regimes: a low-frequency plateau corresponding to dc conductivity and a high-frequency dispersive region following a power-law behavior characteristic of hopping conduction, with power-law exponents (α₁ and α₂) markedly lower than unity, confirming the non-Debye character of the relaxation processes. The hopping frequency (ω) increases with temperature, further supporting the thermally activated nature of charge transport. Activation energies extracted from Arrhenius plots of dc conductivity are 0.88 eV for grain boundaries and 0.83 eV for grains, demonstrating that both microstructural regions significantly contribute to the overall conduction process.

Mullite (Al₆Si₂O₁₃), an aluminosilicate with remarkable thermal and dielectric properties, is a promising material for advanced electronic applications. This study focuses on a sintered mullite composite and examines its structural, morphological, dielectric, and electrical properties. X-ray diffraction and scanning electron microscopy analyses confirm a well-defined crystalline structure and a homogeneous microstructure. Impedance spectroscopy measurements reveal a high relative permittivity at low frequencies, dominated by interfacial and jump polarization mechanisms. Electrical conductivity follows Jonscher’s double-power law, reflecting mixed ionic and electronic conduction due to contributions from grains and grain boundaries. Analysis of the Nyquist diagrams shows a marked decrease in resistances with increasing temperature: The grain resistance decreases from 21.87 MΩ to 4.85 MΩ, while that of the grain boundaries decreases from 89.44 MΩ to 5.94 MΩ between 450 °C and 900 °C. In addition, the relative permittivity increases sharply with temperature, from 25 × 10³ to 350 × 10³ at 1 kHz and from 200 to 1 × 10³ at 1 MHz over the same temperature range, highlighting the dominant influence of temperature and low frequencies on polarization mechanisms. These results confirm the strong potential of sintered mullite for electronic applications. The activation energy of the grain and grain boundary were determined to be E_a,g = 0.18 eV and E_a,bg = 0.22 eV, respectively.

Sulfur - containing building blocks represent highly favored scaffolds in various natural or synthetically obtained pharmacologically active molecules. Their diverse functionalities, including thioether, sulfonamide, sulfoxide, and others are often linked with the possibility to inhibit microbial growth and to regulate immune responses. Nowadays, approximately 25 % of all utilized small - molecule pharmaceuticals have been approved as organosulfur drugs or are clinical candidates. Herein, inspired by the medicinal power of such compounds, a series of potential sulfur based ligands against influenza A viruses was obtained by modification of amino group of anti - influenza drugs (rimantadine, amantadine and oseltamivir) and memantine. Furthermore, the structures of novel derivatives bearingversatile sulfur - containing acyl moieties (cysteinyl-, thienyl-) were established by spectroscopic methods (1H NMR, 13C NMR, (ATR)umax, and HRMS). The newly synthesized amides were tested in vitro for antiviral activity against four influenza A viruses (A/Fort Monmouth/1/1947 (H1N1), A/Wuhan/359/1995 (H3N2), A/Jinnan/15/2009 (H1N1), and A/Aichi/2/68 (H3N2). Amongst the evaluated amides 1, 6, and 7 were the most active ones, inhibiting both the A/Fort Monmouth/1/1947 (H1N1) and A/Wuhan/359/1995 (H3N2) influenza virus strains, while amides 3 and 5 showed pronounced antiviral efficacy specifically against the A/Wuhan/359/1995 (H3N2) strain. Moreover, compounds 6 and 7 indicated remarkable inhibitory activity against the oseltamivir-resistant A/Jinnan/15/2009 strain.Furthermore, the hydrolytic stability of desired amides was monitored in two model pH systems that mimic conditions in the stomach, and blood plasma, including pH 1.0, and 7.4, respectively.

Carbon - based materials derived from waste biomass have attracted attention in water treatment applications due to their porous structure, high surface area, and sustainability. In this study, an activated carbon produced from argan shell biomass, an abundant, low - cost byproduct of the Moroccan Argania spinosa tree, was evaluated for the removal of toxic heavy metals from wastewater. Batch adsorption experiments demonstrated that solution pH was an important parameter governing uptake performance. Near - neutral conditions enabled simultaneous and efficient removal of Pb (II), Zn (II), and Cu (II), achieving metal ions sorption of about 90 - 100 % within contact time of 40 min. Under strong acidic conditions (pH 1), metal uptake was inhibited due to surface protonation and competitionfrom excess H+ ions. At mildly alkaline conditions (pH 9), Pb (II) removal remained consistently high, whereas Zn (II) and Cu (II) removal decreased significantly. These findings identify pH 7.0 as the optimized operational parameter for effective and simultaneous removal of Pb (II), Zn (II), and Cu (II).

This research explores the modification of marl by the incorporation of diopside (CaMgSi₂O₆) to develop a composite material with improved dielectric properties, while addressing environmental and economic challenges through the use of abundant natural resources. X-ray fluorescence (XRF) analysis reveals a high silicate content in the raw marl, mainly SiO₂ (68.12%) and Al₂O₃ (12.54%), while laser particle size analysis indicates a homogeneous grain size distribution centered around 100 µm. The composite was synthesized by the solid-state reaction method, achieving good phase homogeneity. X-ray diffraction (XRD) and infrared spectroscopy confirm the incorporation of diopside, while SEM analysis shows a porous morphology with granular aggregates. The modified material has an average particle size of 11.653 µm, optimizing the electrical properties. Impedance spectroscopy demonstrates improved dielectric performance, with accumulated permittivity and reduced losses, which improves energy storage and dissipation. Tests showed the remarkable stability of dielectric properties over a wide frequency range (10 Hz to 10 MHz) and low-temperature dependence. The performance was demonstrated on a single sample with a thickness of 0.63 mm, demonstrating consistent efficiency. These results position the diopside-modified marl as a promising candidate for electrochemical and microelectronic applications.

In the present study, the potential of elemental analysis combined with statistical tools to identify honey origin was evaluated by mineral characterization of 173 honeys of 13 floral types (acacia, fir, spruce, linden, chestnut, lavender, coriander, thistle, honeydew, rosemary, sage, euphorbia and ziziphus plant species) collected from five geographical regions (Slovenia, Croatia, Bulgaria, Turkey, and Morocco). The objective of the study was to accurately and reliably differentiate the mineral composition among honey varieties. The aim was to establish traceability, to ensure product authenticity and to improve quality control measures within the honey industry. For this purpose, 18 major, minor and trace elements were quantified using microwave digestion, followed by ICP-MS measurement. Statistical evaluation of elemental concentration was undertaken using principal component analysis (PCA) to distinguish honey floral types. The research give light on the specific elements that can serve as indicators for determining the geographical and botanical source of honey. Our findings indicate that certain elements, such as Mn, K, and Ca, are primarily influenced by the type of pollen present in the honey, making them indicative of the floral source. On the other hand, levels of Na, Mg, and Fe were found to be more strongly influenced by environmental factors and can be considered as markers of geographical origin. One novel aspect of this research is the exploration of the relationship between honey minerals and honey botanical source. This was achieved through the analysis of chestnut tree samples and a subsequent comparison with the composition of chestnut honey.

Microgreens are receiving increasing attention due to their high content of bioactive components and their importance to human health. These emerging food products can be obtained from the seeds of different plant species, including aromatic herbs. Aromatic microgreens are gaining popularity as new functional food products. In this study, we investigated the effects of different light-emitting diode (LED) lamp spectra on the growth, pigments, nitrates, and osmoprotectant content of microgreens of Ocimum basilicum L., Trigonella foenum-graecum, Anethum graveolens, and Anthriscus cerefolium plants. Three types of artificial LED lamps were used: T0 as artificial white light, T1 as a continuous light-emitting diode with a longer blue wavelength, and T2 as a continuous light-emitting diode with a longer red wavelength. The results obtained showed that the three types of LED light had significant effects on the different parameters studied. In relation to growth parameters, such as fresh weight (FW) and microgreen height (H), the T2 treatment was most effective for fenugreek, dill, and chervil. However, in basil plants, FW and H values were higher under T1 treatment. Regarding nitrate accumulation, both T1 and T2 treatments reduced the content of this nutrient in the different species studied here. Finally, levels of chlorophyll, carotenoid, glucose, proline, and proteins were all higher in plants cultivated under T1 and T2 treatments than in control plants.

Pollution by heavy metals is one of the most serious issues in the world, and the principal sources are manufacturing, fertilizers, mining, pesticides, transport, and wastewater discharge. In this study, the presence of macroelements (Nitrogen (N) and Phosphorus (P)) and heavy metals (Chromium (Cr), Nickel (Ni), Cadmium (Cd), Iron (Fe), Zinc (Zn), Lead (Pb), Cooper (Cu), and Manganese (Mn)) in the green tide caused by the green seaweed Ulva lactuca from Marchica lagoon (NE-Morocco, Mediterranean) was evaluated. The mean values of P and N in the algae were 1773.33 mg·kg ⁻¹ and 44.4 g·kg ⁻¹, respectively. The heavy metals have mean values following this descending sequence: Fe > Mn > Zn > Cu > Ni > Pb > Cr > Cd. This finding has suggested that Ulva has the strongest affinity to Fe and Mn among the metals examined. Mn, Fe, and Pb recorded the highest bioconcentration factors (BCFs), which were 1687, 1656, and 1643, respectively. Regarding their contribution to the Recommended Dietary Allowance (RDA), Fe showed a contribution of 13.58% to the RDA, while that of Mn varied between 4.42 % and 28.42%. The health risk assessment did not indicate any hazard related to the ingestion of Ulva lactuca. Therefore, this study suggests that Ulva lactuca in the Nador lagoon has the potential to bioaccumulate heavy metals and mitigate eutrophication.

Mineral composition of Nigella S. seed variety having Moroccan origin, was determined. The methodology consisted in Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) determination after microwave assisted digestion. The accuracy of the procedure was assured by recovery studies of Nigella seeds samples spiked at different concentration levels. The results revealed that potassium was a predominate element, followed by calcium and magnesium. According to the microelements Moroccan black cumin seeds were good source of iron, zinc and aluminum. A comparative study has indicated variations in mineral content among black cumin seeds with different geographical origin.

A series of seventeen cinnamic acid hybrids (4a_ic_i) were obtained through an amidation of aminoadamantanes (amantadine, rimantadine, and memantine) with mixed anhydride generated from different substituted cinnamic acid and ethyl chloroformate. ¹H NMR, ¹³C NMR, IR, and HRMS were used for the confirmation of the structures of the synthesized hybrids. Moreover, the antioxidant profiles of amides were estimated as per five different in vitro methods: 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid cation radical (ABTS), ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC) assay, and inhibition of Fe(III)/asc induced lipid peroxidation (LP) in brain homogenate. For comparison, caffeic acid (CaffA), known as a potent naturally occurring antioxidant, was used as a reference compound in our study. The results revealed that the most prominent antioxidant activity was demonstrated by compound 4b₂, with excellent CUPRAC, FRAP, scavenging ABTS⁺˙ potential, and inhibition of Fe/ascinduced LP, followed by 4c₆>4a₆>CaffA>4c₅ and 4a₅>4a₇. Overall, the results suggest that the hybrids (4b₂, 4c₆, and 4a₆) consisting of a caffeoyl moiety and lipophilic adamantane core endow the molecules with the higher antioxidant activity than their parent compound (caffeic acid), especially against LP. Thus, these promising antioxidants could have beneficial effects in various pathological conditions, where oxidative stress is implicated.