STUDIA CHEMIA - Issue no.1 / 2024 - Table of contents

The high elastomer content of the crumb rubber powder obtained from the processing of used tires increases the interest for its valorization when modifying road bitumen in order to improve its elastic characteristics. Sulfur cross-linking of elastomer chains reduces the dispersion of the crumb rubber in the road bitumen during the modification process. A novel approach was explored, involving the partial desulfurization of rubber powder using a natural zeolitic catalyst, clinoptilolite, modified in its acid form. The catalytic desulfurization of the powder was carried out in a batch system at a temperature of 280°C for 6 hours in the presence of high aromaticity solvents. The catalysts’ high acidity facilitated the conversion of rubber powder effectively, reaching a more suitable form to use in improving road bitumen.

Keywords: natural zeolite, desulfurization, crumb rubber

Four deciduous woody feedstocks (Casuarina equisetifolia L., Eucalyptus globulus, Wrightia tinctoria, and Neolamarika cadamba) were subjected to the Hydrothermal Carbonization (HTC) process inside a 50 mL stainless steel hydrothermal reactor at varying temperatures (180°C, 215°C, and 250°C), while keeping water-to-feedstock ratio (6:1 v/w%) and residence time (1.5 h) constant. The mass yield and energy yield of the resulting biomass were calculated as parameters for energy intensification. Characterization of the biomass, biochar, and bio-oil was conducted using elemental analysis, SEM, and GC–MS. Interestingly, the mass yield of biochar decreased with increasing temperature, but it significantly improved the energy densification ratio, with a minimum of 1.06 observed for Neolamarika cadamba biomass at 180°C and a maximum of 1.23 observed for Eucalyptus globulus biomass at 250°C. Moreover, detailed analysis of the bio-oil obtained at 250°C using GC-MS revealed the presence of a diverse range of fine chemicals, including benzyl, carboxylic acid, ester, methyl, phenol, pyrrole, nitro, and aliphatic hydrocarbons. These findings suggest that the HTC process can be optimized to tailor the production of specific value-added chemicals from lignocellulosic woody biomass.

Keywords: Hydrothermal carbonization (HTC), Biomass, Bio-oil, Biochar, Fine chemicals

This work was undertaken to study the electrodeposition of tungsten from the Na2WO4-B2O3 system in the molten state. The measurement of the EMF being made with platinum-oxygen indicator and tungsten relative electrodes versus platinum-oxygen. Experiment due to dependencies of the platinum-oxygen potential and tungsten electrodes on the B2O3 concentration, are validate by the forming of ditungstate ions W2O72- in the high temperature ionic liquids (HTILs).The electroreduction process of the active species, is controlled by the diffusion; the rate of formation of the active species does not limit the electrode process; Polarization, in galvanostatic and potentiodynamic mode, have highlighted the fact that charge transfer is reversible. In the Na2WO4-B2O3 melt (acid-basic character), in a narrow potential range and at a controlled process potential, the electroreduction of tungsten from its dimeric form is possible due to the multielectronic processes that take place at the electrode surface. This study played an important role in the evolution tungsten coatings; the corrosion potentials of electrodes (copper, nickel, steel) plated with tungsten, were also measured. In this study, the influence of some parameters (temperature, electrolysis time, cathodic current density, B2O3 concentration) on the cathodic structure and composition was quantified, determining the optimal conditions of the reverse electrodeposition.

Keywords: Tungstate, Borate, Ionic liquid, Electrodeposition, Voltammetry

The effects of thallium(Ⅰ) ions on the surface morphology, cathode current efficiency, cathode potential, polarization behavior, and electrochemical impedance spectroscopy of zinc electrowinning were studied by scanning electron microscopy and electrochemical measurements. The results showed that with increasing thallium(Ⅰ) ion concentration in the electrolyte, the hydrogen evolution reaction and the galvanic effect produced during zinc electrowinning increased. When the concentration of thallium(Ⅰ) ions in the electrolyte was 0.6 mg L-1, the exchange current density of the zinc electrowinning process was maximum and the polarization was minimum. At this time, the Rct of the equivalent circuit was minimum, the CPE value was minimum, and the charge transfer rate was maximum. The cathodic current efficiency decreased from 80% to 55% when the thallium(Ⅰ) ion concentration was 1.5 mg L-1. The presence of thallium(Ⅰ) ions also affected the surface macro- and microstructure of the zinc deposits. This result confirmed that thallium(Ⅰ) ions have a significant negative influence on the electrowinning of zinc.

Keywords: Zinc electrowinning; Thallium(Ⅰ) ions; Cathodic current efficiency; Cathodic polarization; Electrochemical impedance spectroscopy

The objective of the study was to assess the biological functions and chemical composition of Malva sylvestris L. from Ida Mountain of Turkiye, a medicinal plant used for a variety of therapeutic applications. The antioxidant (DPPH, ABTS, Iron (II) chelate activity), enzyme inhibition (acetylcholinesterase), and cytotoxic properties of methanol extracts prepared from leaves and flowers were investigated. The chemical composition of the extracts was evaluated in terms of spectrophotometric (total phenol and total flavonoid) and chromatographic (HPLC) techniques. IC50 value of the DPPH radical scavenging effect of the flower extract, with the highest total phenol and flavonoid content, was found to be 0.5 mg/mL. The ABTS radical scavenging effect was 2.56 mmol/ L Trolox. While the extracts’ chelating activity was not as great as that of EDTA, the enzyme inhibition of the flower extract was determined to be 37.67%. Flower extract was shown to have the most cytotoxic activity in both Hela and Hep G2 cell lines. In HPLC analysis; amounts of the detected phenolic compounds were determined, and method validation was performed. This research has given us a better understanding of the traditional use of the M. sylvestris plant from Turkiye, which stands out for its therapeutic properties.

Keywords: M. sylvestris; Malvaceae; antioxidant; anticholinesterase activity; cytotoxic activity

The activation of muscle pyruvate kinase (PK) increases the conversion of phosphoenolpyruvate (PEP) to pyruvate, which results in the production of ATP. This is critical for supplying the energy needed for muscle contraction. In this study, we synthesized 1,4-dihydropyridine/pyridine compounds bearing tetrazole and 1,3,4-oxadiazole groups by using Hantzsch method and characterized by FT-IR spectroscopy, elemental analysis, and 1H and 13C NMR and studied PK activation, ADME, and molecular docking. The studies revealed that all original synthesized compounds activated PK and AC50 (half-maximal activating concentration) values of the compounds were extremely effective (1.30 μM to 14.65 μM).

Keywords: Rabbit Muscle Pyruvate Kinase, Tetrazole, 1,3,4-oxadiazole

Some parts of agro-wastes (pomace meal) are used for animal food containing variability in composition (proteins, dietary fibres, carbohydrates, polyphenols, minerals). Paper aim was to evaluate some nutraceutical bioactive compounds from pomace meal for use as animal feed additives. Studied meals are pomace obtained from solid remains of grapes and sea buckthorn after juice pressing, as well as flaxseed and rapeseed after oil pressing. HPLC methods were used to determine some carbohydrates (glucose, fructose, sucrose, maltose), organic acids (oxalic, citric, tartaric, malic), flavonoids (catechin, epicatechin, rutin, quercetin, luteolin) and phenolic acids (gallic, vanillic, caffeic, p-coumaric, ferulic). The content of total polyphenolic compounds and the antioxidant activity (DPPH and ABTS assays) of the pomace meals were evaluated by spectrophotometry. The results obtained show that the carbohydrates quantities (mg/100 g) in pomace meals were between 2943.31 (grapeseed) and 3210.11 (rapeseed). Sea buckthorn contains the most important amount of total organic acids of 8078.89 mg/100 g. Also, the highest quantities (mg/100 g) of total polyphenolic compounds were found in grapeseed (10789) and flaxseed (8537), respectively. These findings indicate a good source of carbohydrates, organic acids and polyphenols (phenolic acids and flavonoids) therefore these meals can be used as animal feed additives.

Keywords: bioactive compounds, animal feed additives, HPLC, total phenolic compounds, antioxidant activity

This study reports the identification of volatile organic compounds (VOCs) and the phenolic composition for these medicinal plants: lemon balm (Melissa officinalis), lavender (Lavandula angustifolia), and elderflower (Sambucus nigra). The HS-SPME-GC-MS hyphenated technique was used to investigate the volatiles from the three plants in fresh and dried forms. The essential oils were obtained by hydrodistillation technique, followed by GC-MS analysis. Additionally, HPLC-UV/VIS detection was used to identify the phenolic compounds of these plants. The majority compounds identified in the fresh, dried and oil of lemon balm were Z-beta-ocimene, citronellal, citronellol, b-caryophyllene, (E)-citral, (Z)-citral and geraniol respectively. The aerial part of lavender contains mainly linalool, linalyl acetate, beta-myrcene, trans-beta-ocimene, lavandulyl acetate and caryophyllene. The most compounds identified in the fresh flowers of elderflower were linalool, cis-beta-ocimene, linalool oxide (II) pyran, cis-3-hexenyl isovalerate, while in the dry flowers the majority compounds were linalool oxide (II) pyran, cis-3-hexenyl isovalerate and hexenyl tiglate. The essential oil was rich in n-hexadecanoic acid, linoleic acid, and heneicosane. Majority phenolic compounds identified in the analysed species were vanillic, sinapic, ferulic, and p-coumaric acids, while the predominant flavonoids were rutin, quercetin and epicatechin. The profile of VOCs represents an indicator in the valorisation of medicinal plants.

Keywords: medicinal plants, volatile organic compounds (VOCs), phenolic compounds, HS-SPME-GC-MS, HPLC-UV/VIS

This study presents the extraction of essential oils and volatiles of Eryngium planum (E. planum) by classical hydrodistillation (HD), ultrasound-assisted hydrodistillation (UAHD) and headspace solid-phase microextraction (HS-SPME). The GC-MS analysis showed that the essential oil of E. planum obtained by UAHD contains the following majority compounds: β-copaene (11.97%), cis-chrysanthenyl acetate (10.14%), (E)-β-farnesene (6.79%), γ-gurjunene (6.53%), caryophyllene (5.73%), germacrene B (3.93%), (+)-cis-verbenol,2-methylpropionate (2.87%), β-selinene (2.73%). The GC-MS analysis showed that E. planum volatiles extracted by HS-SPME contains as majority compounds: cis-chrysanthenyl acetate (30.39%), (E)-β-farnesene (11.71%), γ-maaliene (7.69%), β-elemene (7.26%), caryophyllene (6.5%), β-selinene (4.72%), δ-cadinene (4.72%), β-copaene (4.61%), α-pinene (4.51%), γ-muurolene (2.98%). By using the UAHD method, the yield of E. planum oil was increased by 27.27% compared with the classical HD method. The essential oil of E. planum showed an excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus.

Keywords: Eryngium planum, essential oils, ultrasound-assisted hydrodistillation (UAHD), headspace solid-phase microextraction (HS-SPME), antimicrobial activity

In the present study, phenolic compounds, antioxidant activities, DNA cleavage and binding effects of Vincetoxicum tmoleum (Vt) collected from west of Anatolia (Manisa city) were investigated. Antioxidant potentials of the extracts were characterized with their total phenolic and flavonoid contents, DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and FRAP (ferric reducing antioxidant power assay) tests. Besides, the DNA cleavage and binding features of V. tmoleum extract were studied using pBR322 DNA and CT-DNA, respectively. Phenolic compounds of the extract were analyzed by high performance liquid chromatography (HPLC-DAD). As a result, V. tmoleum methanol extract was found to have the high total phenolic and total flavonoid content and antioxidant effect. Strong positive correlations were also found between DPPH and TFC (r = 0.995; p < 0.01), and TPC (r = 0.989;p < 0.01), ABTS (r = 0.994;p < 0.01) and FRAP(r=0,995; p < 0.01). Methanol extract of V. tmoleum had large amounts of p-coumaric acid, ferulic acid and protocatechuic acid. While V. tmoleum samples showed weak DNA cleavage activity, they showed DNA binding activity at 50 μM concentration, that is, the potential to be an intercalation agent in this concentration

Keywords: Vincetoxicum tmoleum, antioxidant activity, DNA cleavage, HPLC-DAD

The major fatty acids present in cosmetics are the unsaturated fatty acids from triglycerides, especially essential fatty acids: linoleic acid (omega-6) and α-linolenic acid (omega-3).The purpose of the study was to develop a simple and precise gas chromatography-flame ionization detection method, using an OPTIMA-WAX (macrogol 20000) capillary GC column (30m x 0.32mm x 0.25μm) with a run time of 17min, for the analysis of fatty acids composition from vegetable oils and macerated oils. The method was validated for quantifying four major fatty acids: palmitic, stearic, oleic and linoleic acids, as methyl esters. The quantification was performed by internal standardization, using the methyl ester of nonadecanoic acid as internal standard. The esterification reaction was carried out on a magnetic stirrer at a temperature of 80°C and with continuous stirring, in hermetically sealed vials.

Keywords: fatty acid, vegetable oils, gas-chromatography, method validation

The use of natural materials derived from biomass or biodegradable polymer materials can be one of the solutions to be considered in reducing environmental pollution problems. In addition, some polymers have been shown to be biocompatible and thus beneficial in biomedical applications. Therefore, within the framework of this study, we will present the results of the application of lanthanide-borohydride systems (Nd(BH4)3(THF)3) combined with n-butylethyl magnesium in the block copolymerization of conjugated dienes (myrcene-styrene) and a conjugated diene with a polar monomer (L-lactide) for the synthesis of bio-sourced elastomers. The analysis of copolymers resulting from the copolymerization between myrcene and styrene shows that it is possible to insert up to 9.9% of styrene. Moreover, the stereoselectivity (1,4-trans) of the myrcene motif has not significantly changed, even in the presence of a significant amount of styrene in the reaction medium. The presence of the copolymer was confirmed by the observation of a peak at 146 ppm which corresponds to the ipso carbon of styrene.

Keywords: coordination polymerization, β-myrcene, styrene, L-lactide, biomass, elastomers.

Wild bilberry, blackcurrant and blackberry fruit pomaces obtained after industrial juice processing were extracted in water, 1% citric acid, 40%, 60% and 80% (v/v) aqueous ethanol using two extraction methods: maceration and ultrasound-assisted extraction. The total phenolics content (TPC), total anthocyanins content (TAC), and DPPH radical scavenging activity (RSA) were quantified in the extracts. TPC was about 2.3-3.2 times higher in ethanolic extracts as compared with the water extracts. The extracts made in 60% aqueous ethanol showed the highest values of TPC, TAC and RSA irrespective of extraction method and pomace matrix while water and 1% aqueous citric acid were very little effective in recovering anthocyanins and phenolic compounds. Bilberry pomace extracts made in 60% ethanol using maceration presented the highest TAC (585.21 mg CGE/L), TPC (3381.82 mg GAE/L) and RSA (2.05 mmol Trolox/l). The results showed that bilberry, blackcurrant and blackberry fruit pomaces can be a valuable source of bioactive compounds to be used in food supplements and functional foods.

Keywords: fruit pomaces, extraction, total phenolics content, total anthocyanins content, DPPH radical scavenging activity, correlations