STUDIA CHEMIA - Issue no.2 / 2024 - Table of contents

Partially stabilized zirconia (PSZ) ceramics are one of the most important materials used for different applications like thermal barrier coatings, refractories, oxygen-permeating membranes, and dental and bone implants. In this work, the structural, morphological, and optical properties of bulk Mg-PSZ, Ca-PSZ, and Ce-PSZ, prepared by solid state reaction at high temperature, were comparatively evaluated. Laser diffraction analyses revealed particles by thousands orders of magnitude larger compared to crystallite sizes determined from X-ray powder diffraction (XRPD), more evidenced in the case of Ca-PSZ. The structural analyses indicated the presence of both m- and t-ZrO2 phases, in different ratios, depending on the doping cation. The scanning electron microscopy (SEM) micrographs confirmed the homogenous distribution of the elements through mixed oxides. Further, optical properties evaluated in terms of ultraviolet–visible diffuse reflectance spectroscopy (UV-VIS DRS) revealed that the doped ZrO2 samples showed a smaller bandgap compared with pure ZrO2, which may be due to the incorporation of magnesia, calcia or ceria in the ZrO2 matrix. The maximum bandgap reduction of ZrO2 was observed on Ca-PSZ, having a value of 3.52 eV.

Keywords: partially stabilized zirconia, solid state reaction, structural properties, optical properties

The aim of the presented research was to synthesize and characterize via elemental analysis, HRMS, thermogravimetric analysis, FTIR and EPR a novel series of transition metal complexes of Cu(II), Co(II), Ni(II) and Mn(II) with β-L-aspartyl-cyclohexyl amide as ligand. The HRMS recorded spectra confirm the obtaining of new compounds. The changes in the FTIR spectra of the metal complexes, compared to the ligand, support the complexation process. The thermal stability of the ligand and its metal complexes was discussed in the 20-8000C temperature range, in air atmosphere. In all of the studied complexes, the aspartyl amide acts as a bidentate ligand, its coordination involving the carboxylate oxygen and the nitrogen atom belonging to the free amino group of the amino acid. Metal complexes are formed in the 1:2 (Metal:Ligand) ratio as found by the elemental analysis. Except the free ligand, all the metal complexes are hydrating with water molecules, and the thermal stability of these suggested whether the water molecules are inside or outside the coordination sphere. The shape of EPR spectrum for copper complex at room temperature suggests the presence of CuN2O2 monomeric species with a rhombic distortion around the metallic ion. The results indicate that their stability range obeys the Irving-Williams series.

Keywords: L-aspartic acid, aspartyl amide, metal complexes, thermal behavior, spectroscopic studies

The dispersion of crumb rubber in road bitumen is essential for enhancing the elasticity of asphalt coatings. However, elastomer cross-linking through vulcanization can reduce the colloidal stability of bitumen. This study aims to enhance compatibility by partially devulcanizing crumb rubber using a pulverulent catalyst, specifically phosphomolybdic acid, in a batch reactor at 270°C. The use of a molybdenum-based catalyst is preferred due to its effectiveness in catalyzing the devulcanization process. Additionally, further conditioning of the catalyst through grinding optimizes contact with crumb rubber, enhancing catalyst activity and improving overall compatibility with road bitumen.

Keywords: crumb rubber, desulfurization, molybdenum catalysts

The inhibitory ability of the boiling extracts from the groats of Fagopyrum esculentum on the corrosion of mild steel EN Fe37-3FN in 0.5 M hydrochloric acid and 0.5 M sulphuric acid media was investigated using gravimetric, electrochemical, and EIS methods. It was shown that the addition of 100 mg/l of the Fagopyrum esculentum groat extract reduces the corrosion rate by 50%, and that of of 1 g/l and more – by 75%. The adsorption of the extract components on a steel surface follows the Langmuir adsorption model, and the nature of adsorption is physical. The Fagopyrum esculentum groats extract shows itself as perspective and environmentally friendly substance for reducing the steel corrosion rate in acidic environments.

Keywords: Fagopyrum esculentum, common buckwheat, acid medium corrosion inhibition, gravimetric study, electrochemical study, Langmuir adsorption isotherm.

The purpose of this work was to prove the enrichment of sunflower oil with active principles (polyphenolic acids, flavones, flavonoids) from plants, using the ultrasounds-assisted extraction (UAE) process. The analytical technique used for qualitative characterization of the UAE samples is thin layer chromatography (TLC), a relatively simple technique, which under certain separation and detection conditions highlights the bioactive components of the plants studied in our study. UV-VIS spectrophotometry was used to evaluate the level of flavonoids. The UAE samples in sunflower oil were also characterized by determining the alpha-tocopherol content through a gas-cromatographic method (GC-MS), and by evaluating the antioxidant activity through an indirect DPPH spectrophotometric method. The oily plants extracts were obtained to be used as raw material in the formulation of a dermato-cosmetic product, and thus the characterisation performed herein is very useful in supporting the effects of the above-mentioned products.

Keywords: sunflower oil, ultrasound-assisted extraction, TLC, UV-VIS, GC-MS

Currently, gold nanoparticles (GNPs) are considered an ideal delivery system due to their physiological stability, high bioactivity, and controlled release of biological component. Our primary objective was to comprehend the behavior of gold nanoparticles obtained with specific natural compounds in the gastrointestinal tract. We investigated the conduct of GNPs synthesized with natural compounds from Cornus mas L. (GNPs-CM) or Sambucus nigra (GNPs-E) fruits, during the oral, gastric, and intestinal phases of the in vitro simulated gastrointestinal digestion. Additionally, we assessed their antioxidant capacity, phenolic content, and their potential to mitigate damages caused by nitro-oxidative stress after each phase of in vitro digestion. Results indicated that both GNPs-CM and GNPs-E maintained stability throughout simulated digestion, with some observed differences between them. Upon measuring antioxidant capacity, the GNPs-CM exhibited the lowest percentage of inhibition from hydrogen donor measurements (12.08%) after the simulated intestinal phase. Conversely, the GNPs-E displayed the highest inhibition percentage (65.3%) after the simulated oral phase. Concerning phenolic content, GNPs-CM showed a polyphenol content of 39.53 mg of gallic acid equivalents (GAE)/L, decreasing during gastrointestinal phases. GNPs-Eexhibited a polyphenol content of 100.99 mg GAE /l, also decreasing during gastrointestinal phases.

Keywords: gold nanoparticles, simulated gastrointestinal digestion, Cornus mas L., Sambucus nigra L., nitro oxidative stress, antioxidant capacity, phenolic content.

Coal auto-oxidation is an undesirable chemical phenomenon that occurs due to the interaction of coal with atmospheric oxygen, a phenomenon that takes place during the coal life cycle, from the extraction moment until it is used. Thus, it is imperative to understand this process not only for the prevention of coal autoignition in the mining industry, but also for the optimization of the coal storage. The aim of this work was to assess the chemical behavior such as the oxidation, self-heating, and auto-ignition characteristics of coal in Oltenia Basin, Romania during its storage period. The hydrogen peroxide oxidation testing was used to determine the auto-oxidation tendency of lignite, while for the monitoring of coal quality during the storage process, coal samples were taken from a coal stack after 0, 5, 10, 20 and 30 days of storage and analyzed regarding the moisture (39,71%), ash content (35.21 – 37,11%), calorific value (1940 – 1875 kcal/kg), and volatile compounds (36.71 – 37,27%). A good correlation between the autoxidation and the content of volatile matter was observed. Compared to the initial values measured in initial coal samples (day 0), the carbon content and the superior calorific value decreased, while the ash content increased after a period of 30 days of storage.Thus, it can be concluded that knowing the self-ignition characteristic of lignites is important both for managing coal stocks and for evaluating the impact that coal storage can have on the environment.

Keywords: coal oxidation, lignite auto-oxidation, coal oxygen absorbtion, coal quality degradation, Oltenia basin

The article discloses the AMS (accelerator mass spectrometry) radiocarbon dating results of the well-known African baobab of Dalkut, Dhofar Governorate, Oman. The investigation shows that the baobab has a cluster structure and is composed of 3 perfectly fused stems. Three wood samples were collected from primary branches and one sample was collected from the exterior of a stem. Eight tiny segments were extracted from the samples and dated by radiocarbon. The oldest dated sample segment, which originates from a primary branch of the southern stem, had a radiocarbon date of 590 ± 18 BP, which corresponds to a calibrated age of 685 ± 15 years. This result indicates that the southern stem of the baobab of Dalkut is 800 ± 30 years old. According to other radiocarbon dating results, the two northern stems are younger and emerged from the southern stem around 550 years ago. The tree of Dalkut is a solitary baobab. The nearest baobab is over 150 km away, to the north.

Keywords: AMS radiocarbon dating, Adansonia digitata, Oman, multiple stems, age determination

Non-covalent interactions involving element-hydrogen contacts are a central part in supramolecular chemistry and play essential roles in biomolecular structure. Reported here is a systematic computational analysis of such interactions within XHn---YHm dimers, where X and Y are C, Si, N, P, O, S, F and Cl, respectively. Two functionals are employed – the widely used BP86 and the M06-2X functional especially designed for describing noncovalent interactions. The interaction energies are found to be correlated with charge separation to a degree of 80%, suggesting that these noncovalent interactions can be reasonably explained/predicted by their electrostatic component. Energy decomposition analyses on the other hand suggest that correlation effects are the underlying root of the interaction. The rarely discussed intermolecular vibrations are also analyzed and noted to sometimes intercede in the typical observation windows for molecular spectroscopy. Moreover, in some cases notable effects of the non-covalent interactions are noted upon internal vibrations of the partners.

Keywords: hydracid, binary acid, noncovalent, DFT, supramolecular

Variation of common bean (Phaseolus vulgaris L.) core collection was assessed based on the main nutritive and bioactive components. Nutritional profile was described for each cultivar and landrace. Protein content was in the familiar range for common bean (19.6-31.6%). Detected variability for potassium, sulphur, iron and zinc was 7.78, 16.7, 14.99, and 40.17%, respectively. Total phenolic content ranged from 1.8 to 14.1 mg GAE /g DW, with high variation (CV = 41.3%). Likewise, antioxidant tests DPPH, ABTS and FRAP had high, genotype-based, CV in range 29-46%. With the application of PCA and cluster analysis, better insight in underlying germplasm structure was acknowledged, as well accession’s grouping based on the studied traits. Cultivars Vulkan and Panonski tetovac, breeding line HR45, landraces L24, L92, L119, L120, and L125 had larger amounts of iron, nitrogen, and proteins. Elevated phenolic content was observed in cultivars Balkan and Spinel, as well as landraces L19, L29, L41 and L60. In addition, cultivar Royal Dutch was recognized for higher levels of zinc, and higher antioxidant capacity revealed by DPPH, ABTS, and FRAP assays. Therefore, these tests could be used in the selection of the accessions for breeding for nutritive quality enhancing.

Keywords: nutritive value, bioactive compounds, variability, landraces, cultivars