STUDIA CHEMIA - Issue no.2 / 2022 - Table of contents

Isopropanol could be an additive or substitute for diesel fuel due to some of its key properties. Viscosity influences the atomization and spray formation, affecting the combustion process and the emission of diesel engine. Experimental data of viscosity of diesel fuel + isopropanol and biodiesel + isopropanol mixtures over the entire composition range at five temperatures (288.15, 293.15, 303.15, 313.15 and 323.15 K) are presented. Based on experimental data, the ability of predictive and correlative models to estimate the viscosity of the studied systems was tested. The best accuracy in viscosity estimation at a desired temperature is given by a polynomial equation, followed by Grunberg-Nissan equation. The value of Grunberg-Nissan interaction parameter G12 increases with temperature increasing, following a trend described by a polynomial equation. Negative values for deviation in viscosity were obtained for diesel fuel + isopropanol mixtures and positive values for biodiesel + isopropanol mixtures. The best fit with viscosity experimental data for viscosity dependence on temperature was provided by Vogel model.

Keywords: viscosity, biodiesel, isopropanol, diesel, viscosity models

In this research composite based on zirconia and graphite was synthesized using the sol-gel method. Aim of this research is to activate and increase the photocatalytic activity of ZrO2 by combining with graphite-based material. Our results show that we obtained material that can remove both cationic and anionic dyes by sorption and photocatalytic processes. Obtained composite is very effective in sorption of RB19 with up to 100% removal. Photocatalytic activity of composite is higher than pristine GO and goes up to 100% for RB19 degradation and about 50% degradation of MB. These results are promising and present an excellent base for further research.

Keywords: Composite, Zirconia, Graphite, Methylene blue, Reactive blue 19, Sorption, Photocatalysis, UV degradation

The modified natural phosphate of djebel onk was investigated for the removal of cationic textile dye Methylene blue (MB) from aqueous solution. The modified natural phosphate rock powder (MNP) was characterized by means of XRD, IR spectroscopic and thermal analysis. Adsorption studies were carried out under various parameters such as pH, contact time, initial dye concentration and temperature. The equilibrium data were analyzed using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models, the results of modeling adsorption of Methylene blue (MB) on modified natural phosphate rock (MNP) show that the Langmuir model present a good coefficient of correlation compared to other models. The kinetics of adsorption were best described by pseudo-second order and the thermodynamic parameters (ΔH°, ΔS° and ΔG°) of the adsorption were also evaluated. The adsorption process was found not-spontaneous and exothermic.

Keywords: Algerian phosphate, adsorption, methylene blue, isotherme

We investigated the phase structure, magnetic properties, corrosion resistance, microstructure of 1.4541 (V2A) stainless steel through X-ray diffraction (XRD), magnetic measurement device, gravimetric/electrochemical methods, metallographic microscopy. Corrosion resistance was evaluated in natural seawaters of Mediterranean, Black and Aegean seas. The results show that crystal structure and specific magnetic characteristics are resistant to corrosion action of all seawaters at a temperature of 295 K. The greatest corrosive effect on studied alloy has the Mediterranean Seawater, corrosion penetration is about 0.1290 mm/year. Microscopy confirmed corrosion data.

Keywords: text, Stainless steel, Sea waters, Corrosion, Micrography, XRD analyses, Magnetization.

Present day scientific research is focused on the identification of renewable and clean alternatives to fossil fuels, with hydrogen being a promising energy source that fulfills both requirements. Given this context, the current work investigates the water splitting electrocatalytic properties of two hydrothermally synthesized transition metal oxides: MnO2 and Fe3O4. Electrodes were obtained by modifying graphite substrates with suspensions in ethanol containing the catalytic materials as such or in compositions, and their activity for the O2 and H2 evolution reactions (OER and HER) was studied in alkaline medium. Out of the MnO2-based electrodes, the one modified with the suspension containing 2 mg MnO2, 1 mg Carbon Black and 10 μL Nafion solution displayed an OER overpotential (ηO2) value, at i = 10 mA/cm2, of 0.53 V, while the one manufactured using the suspension with 4 mg MnO2 and 10 μL Nafion solution showed a HER overpotential (ηH2) of 0.427 V (at i = -10 mA/cm2). From the Fe3O4-based electrodes, the one modified with the suspension containing 2 mg Fe3O4 and 2 mg Carbon Black evidenced the highest catalytic activity for both reactions (ηO2 = 0.51 V and ηH2 = 0.43 V).

Keywords: water splitting, oxygen evolution reaction, hydrogen evolution reaction, metal oxide, electrocatalysis

The quality of a cosmetic cream is evaluated by classical methods in specific authorized laboratories by periodically measuring the physicochemical and microbiological quality indicators of the basic emulsions. This paper aims to use systems theory to study cosmetic emulsions by establishing mathematical models that correlate the existing dependencies between different quality indicators. The main parameters that allow the quantification of the stability of the emulsions were monitored in time: the evaporation residue, the pH, the total number of germs, staphylococcus aureus, pseudomonas aeruginosa and the concentration of the active ingredients. Mathematical models were obtained with adequacy indicators that meet the requirements of a good approximation and that can be used as models for control and prediction of stability in the short and medium term, for the types of creams based on the recipes of the emulsions studied.

Keywords: emulsion, quality indicator of cosmetic creams, mathematical model

Tomato is one of the most consumed foodstuffs around the world and major dietary source of lycopene. The main objectives of this study were evaluation of antioxidant activity, using DPPH, ABTS, FRAP, TRP and CUPRAC assays, as well as total phenolic, total flavonoid, lycopene and β-carotene content in 30 tomato and cherry tomato cultivars commonly consumed in Serbia. Tomato with the highest total phenol and total flavonoid content was tomato Indigo Rose (17.56 mg GAE g-1 DW and 30.30 mg RE g-1 DW, respectively), which showed excellent antioxidant characteristics. Total lycopene content was lower in yellow tomato species compared to the red ones, and the highest lycopene content was 0.283 mg g-1 DW for tomato Red Pearl Big. Cluster analysis yields dendrogram, separating tomato and cherry tomato cultivars into three statistically significant clusters ((Dlink / Dmax)×100 < 50).

Keywords: Tomato, Antioxidant characteristics, Bioactive compounds, PCA, Cluster analysis

Bentonites refer to the class of argilliferous folded silicate rocks, which as a whole have such common characteristics, as dispersion (fragmentation), colloidal properties, propensity to wetness, and adsorption properties. The importance of this paper, as it follows from the conclusion, is connected with the study of synthesizing of magnetic clay composites which have high adsorption capacity, as well as with systematization of their properties. Bentonite magnetic composites are among those which can be stabilized using sodium alginate. Magnetic composites synthesized on the basis of bentonite showed the proportion of magnetite corresponding to the proportion of Fe in the composition of the initial clays. Sodium alginate-based stabilization method is an effective one for bentonite magnetic composites.

Keywords: bentonite, iron impurities, magnetic composite

The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of Kizimkazi Big tree and Kizimkazi II baobab, two large African baobabs from Zanzibar, Tanzania. Unfortunately, both baobabs toppled and died in 2018 and 2020, during violent storms. The investigation of the two baobabs evinced that the first of them, which was also the biggest tree of Tanzania, consisted of 5 stems, out of which 2 were false ones, and had a closed ring-shaped structure. The second baobab was composed of 4 fused stems and had a cluster structure. Several wood samples were collected from the two baobabs. Seven segments were extracted from the samples and dated by radiocarbon. The oldest segment from Kizimkazi Big tree had a radiocarbon date of 312 ± 18 BP, corresponding to a calibrated age of 380 ± 10 calendar years. According to dating results, the Kizimkazi Big tree died at the age of 400 ± 25 years. The oldest segment from Kizimkazi II baobab had a radiocarbon date of 137 ± 17 BP, corresponding to a calibrated age of 190 ± 10 calendar years. This value indicates that the Kizimkazi II baobab was 250 ± 25 years old when it died.

Keywords: AMS radiocarbon dating, Adansonia digitata, dendrochronology, age determination, multiple stems, false cavity.

This study aimed to synthesize novel unsymmetrical urea derivatives containing biologically active tryptamine and phenethylamines and investigate their inhibition effects on human carbonic anhydrase (hCA) I and II isozymes as well as acetylcholinesterase (AChE). For this purpose, five different N,N'-dialkyl urea derivatives 18-22 were synthesized from tryptamine and substituted 2-phenethylamine. According to the results of inhibition, all of the synthesized urea derivatives effectively inhibited both hCA (I - II) and AChE enzymes at micromolar concentrations. The IC50 values for these molecules were determined to be in the range of 1.214-2.281 μM for hCA-I, 0.888-2.984 μM for hCA-II, and 0.309-0.816 μM for AChE. The most potent inhibitors against hCA-I and hCA-II isozymes are compound 18 (IC50: 1.214 μM; Ki: 0.984 ± 0.277 μM) and compound 19 (IC50: 0.888 μM, Ki: 0.564 ± 0.019 μM), respectively. Furthermore, compound 20 (IC50: 0.309 M and Ki: 0.470 ± 0.039 M) is the most effective AChE inhibitor. Molecular docking studies of compounds with the most effective inhibition were performed. The estimated binding energy values for compounds 18, 19, and 20 were calculated to be −7.81, -7.34, and -8.20 kcal/mol, respectively. Finally, the ADME studies were determined these compounds' physicochemical and pharmacokinetic descriptors and drug-like properties./p>

Keywords: biological activity, tryptamine, phenethylamine, toxicology, molecular docking, ADME

Silica nanoparticles were covered with a thin layer of chitosan to obtain a positive surface charge. The resulting silica/chitosan nanoparticles were characterized using zeta potential and particle size analysis before being electrophoretically deposited on zinc substrates to obtain an anticorrosive coating. The uniformity of the resulting layers was studied by optical and scanning electron microscopy. The anticorrosive properties were determined using potentiodynamic polarization and electrochemical impedance spectroscopy. Results show non-uniform deposits of nanoparticles. Nevertheless, the electrochemical measurements point to a relatively significant corrosion inhibition efficiency of the coating (ca. 60-80%) which increases with the time of deposition.

Keywords: chitosan, silica nanoparticles, electrophoretic deposition, zinc, corrosion

A spectacular 2D Halogen Bond Organic Framework (XBOF) was prepared by the mechanochemical solvent-drop grinding method (SCD) starting from 2,7-dipyridylfluorene and 1,3,5-trifluoro-2,4,6-triiodobenzene tectons. The formation of the supramolecular assembly was proved by powder X-ray diffraction measurements and the structural details were collected from the single crystal X-ray diffraction investigations.

Keywords: N···I and I···F halogen bonds, XBOFs, dipyridylfluorene, 1,3,5- trifluoro-2,4,6-triiodobenzene, single crystal X-ray diffraction structure