STUDIA CHEMIA - Issue no.4 / 2024 - Table of contents

This work aimed to investigate the effect of ZrO2 addition on the structural and mechanical properties of an experimental dental porcelain (DP) prepared from natural raw materials. ZrO2 was added in different amounts (1, 3, and 5 wt.%) to the DP mass with the initial composition of 80 wt.% feldspar, 15 wt.% quartz, and 5 wt.% kaolin, obtained by sintering the mixture at 1200 ºC. The raw materials and raw materials mixture were analyzed by laser diffraction to obtain the typical particle size distribution (PSD). Subsequently, the obtained phases in the elaborated samples were investigated by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and microhardness tests. The structural analyses revealed that the obtained DP mainly comprised quartz and amorphous phases. In addition, certain peaks of weak corresponding to mullite and zirconia were detected. The measured Vickers microhardness (VMH) of DP sintered at 1200 °C was 794.07±106.56 kgf/mm2, which is comparable with those reported for conventional porcelains. Moreover, ZrO2 addition leads to an overall increase of the VMH, with the best value of 912.91±30.76 kgf/mm2 obtained for the sample with 5 wt.% ZrO2. In conclusion, the DP studied here exhibits good mechanical properties and could be potentially used in restorative dentistry.

Keywords: dental porcelain, zirconia, structural analyses, Vickers microhardness

In this study, we investigate the electrochemical properties of a novel copper complex (CuL2) derived from the Schiff base ligand N-3-bromopropylsalicylaldimine (LH). We also examine its interaction with chicken blood double-stranded DNA (cb-ds DNA) in phosphate buffer solution (PB) at physiological pH 7.2 using cyclic voltammetry (CV) techniques. The interaction mechanism of nitrite with CuL2, involving the CuII/CuI redox system, is explored. The CuL2 complex was electropolymerized on glassy carbon (GC) and fluorine tin oxide (FTO). The morphology of PolyCuL2 formed on FTO was analyzed using scanning electron microscopy (SEM) and its elemental composition determined by EDX analysis. The modified electrode polyCuL2/GC exhibited efficient catalytic activity for the electroreduction of oxygen (O2) in homogeneous electrocatalytic media. The binding constant (Kb) of the DNA-CuL2 adduct, determined from CV measurements, was found to be 1.33×105, closely matching the value obtained from molecular docking studies (1.75×105). Docking studies indicate that the CuL2 complex binds to DNA in the minor groove binding mode. The anodic peak potential shift in the negative direction suggests an electrostatic interaction between CuL2 and DNA.

Keywords: Copper(II) complex; Electro-polymerization; catalytic reduction; DNA binding affinity; AutoDock

Rifampin (Rif) is usually applied as first-line anti-tubercular drugs but has limited bioavailability. Herein, Rif-loaded ethyl cellulose (EC) composites was designed and fabricated by electrospray to improve therapy effectiveness and duration. A novel stable disk-like drug delivery system was prepared, and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric (TG) analysis as well as in vitro release tests in phosphate buffer solution (PBS) at pH= 4.0 and pH= 7.4. The SEM results suggested EC/Rif composites had uniform circular surface and particle size distribution with an average size ranged from 7.11 μm to 7.37 μm. Rif can be physically and molecularly dispersed and incorporated into the EC matrix, as confirmed by the XRD, FTIR, DSC, and TG results. At pH 7.4, the rate of Rif release in EC/Rif composites improved with the increasing Rif content. For EC/Rif sample with equal mass ratio, the highest cumulative release of Rif reached 64.6% at the end of 24 h, while at pH 4.0 the Rif release was slower to 24.8% at 24h. These results suggested that EC/Rif composites fabricated by electrospray could be a promising strategy for controlling Rif delivery.

Keywords: ethyl cellulose; rifampicin; electrospray; amorphous, drug delivery

The objective of this study is to evaluate the pozzolanic activity of metakaolin, glass powder and silica powder for use in cementitious mortars. Thus, metakaolin was produced by calcination at 700 °C of a clay soil from Burkina composed of kaolinite (62 wt.%), quartz (30 wt.%) and goethite (6 wt.%). Glass powder consists of amorphous silica and silica powder essentially contains quartz. The chemical characterization of materials showed that the metakaolin and the silica powder belong to the category of type F pozzolans while the silica powder would be type N. The lime saturation test reveals low kinetics of lime fixation by the silica powder. On the other hand, the rate of lime fixation by metakaolin and glass powder increases with treatment time. The pozzolanic index of metakaolin and glass powder at 28 and 90 days is higher than the minimum value of 75% required by the ASTM C618 standard. The presence of metakaolin and glass powder within the cement matrix improves the compressive strength of the resulting mortars due to their good pozzolanic reactivity inducing the formation of calcium silicates hydrated (CSH). Metakaolin and glass powder are therefore suitable for replacing cement in the production of mortars in the construction field.

Keywords: Glass powder, Metakaolin, Silica powder, Cementitious mortars, Compressive strength.

Miconazole nitrate containing soaps were formulated using one commercially available soap base and three cold process soap bases with various lipids. The aim of our work was to investigate the antimicrobial activity and physicochemical properties of the obtained formulations. The water loss and hardness of the soaps was determined 1, 2, 4 and 9 weeks after preparation. The pH and foamability were determined after 9 weeks of curing time. Two Gram-positive, four Gram-negative bacteria and two yeast (Candida spp.) strains were used in the microbial study. The miconazole content was determined with HPLC-UV analysis. Antimicrobial assay showed that all medicated soaps were effective against Candida albicans. The API had minimal influence on the physicochemical properties (water loss, pH, foamability and consistency) of the soaps. All soaps possessed good lathering properties and an alkaline pH (9.2-11.3). The miconazole content of the soaps varied from 2.72 % to 5.12 % as revealed by HPLC-UV analysis.

Keywords: miconazole, medicated soap, Candida albicans, olive oil.

Enzyme immobilization (covalent or noncovalent) on solid supports such as nanomaterials, resins or polymers can enhance the enzyme activity-, and selectivity, improving their stability. The present research is focused on the non-covalent immobilization of lipase B from Candida antarctica (CaL-B) into polyvinyl alcohol (PVA) nanofibers via electrospinning with the aim to prepare a stable and reusable biocatalyst compatible with organic reaction media. Polymer solutions of 8, 10 and 12 w/w % concentrations were used to investigate the effect of the polymer concentration on the biocatalyst’s activity. The immobilized enzyme amount was determined using the Bradford assay, while structural characterization was performed by transmission electron microscopy. The immobilized enzyme preparates were tested in the enzymatic kinetic resolution of (rac)-1-phenylethanol and its halogenated derivatives through transesterification with vinyl acetate in batch mode. The highest conversion was obtained in case of CaL-B entrapped in electrospun nanofibers prepared from 10 w/w % PVA solution (noted as 10%–PVA–CaL-B) and its high stability was confirmed in recycling experiments. It was found that after the 5th cycle the biocatalyst maintained 88% of its initial activity.

Keywords: CaL-B, immobilization, electrospinning, PVA, (rac)-1-phenylethanol, EKR.

This study aimed to evaluate the kinetic interactions between clozapine (CLZ) and the fluoroquinolone antibiotics ciprofloxacin and norfloxacin using a systematic three-step compartmental modelling approach. Clozapine, primarily metabolized by CYP1A2 and CYP3A4, is known to exhibit altered kinetics when co-administered with fluoroquinolones due to their inhibitory effect on CYP1A2. The proposed models evaluated the absorption, distribution, metabolism, and elimination (ADME) of clozapine and its active metabolite, N-desmethyl clozapine (CLZ-M), under both reference conditions and in the presence of these antibiotics. The selected kinetic models demonstrated a strong correlation between experimental data and predictions (R² > 0.96), providing robust insights into the mechanisms underlying these interactions. Ciprofloxacin and norfloxacin significantly affected CLZ's presystemic and systemic metabolism, with ciprofloxacin altering relative bioavailability more prominently. These findings emphasize the necessity of dose adjustments for clozapine in clinical practice to mitigate potential adverse effects due to modified drug exposure when co-administered with fluoroquinolones. This study offers a mechanistic framework for understanding complex drug-drug interactions and optimizing dosing strategies in combined therapeutic regimens.

Keywords: kinetic modelling, drug-drug interaction, preclinical study, clozapine, fluoroquinolone antibiotics.

Cholinesterase inhibitors are valuable compounds that can be used in many different therapeutic applications, including Alzheimer’s disease. Carbonic anhydrase (CA) inhibitors constitute a pharmacological intervention employed for the management and alleviation of various medical conditions, including glaucoma, idiopathic intracranial hypertension. Turkey has a large and diverse flora, home to thousands of plant species. Hundreds of compounds of medicinal importance have been identified from the many plants in this flora. In this study, the inhibitory properties of seven different plant extracts on CA I and II, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes were investigated. The tested extracts showed AChE inhibitory activity with values ranging from 1.26 to 4.20 μg/mL, BChE inhibitory activity with values ranging from 1.32 to 4.24 μg/mL, CA I inhibitory activity with values ranging from 0.74 to 1.82 μg/mL and CA II inhibitory activity with values ranging from 0.033 to 0.067 μg/mL. The extract of Zosima absinthifolia showed a very active inhibition profile against both AChE and BChE (IC50 1.26 ± 0.01 μg/mL for AChE and 1.32 ± 0.02 μg/mL for BChE). The results indicate that these extracts are potent cholinesterases inhibitors and specifically Zosima absinthifolia extract could be evaluated for further studies.

Keywords: enzyme inhibition, Turkey flora, Zosima absinthifolia

The primary objective of this investigation was to assess the total polyphenolic content (TPC), identify and quantify individual polyphenols, and evaluate their radical scavenging activity (RSA), as well as determine the mineral composition in stem extracts from nine distinct Vitis vinifera varieties. The total phenolic content in grape stem extracts ranged from 34.87 to 76.95 mg gallic acid equivalents (GAE) per gram of dry weight (d.w.). These extracts exhibited significant free radical scavenging activity, ranging from 0.344 to 0.898 mmol Trolox equivalents (TE) per gram d.w. Stem extracts were predominantly characterized by flavan-3-ols, flavonols, and phenolic acids. Catechin and quercetin-3-glucuronide were identified as the most abundant components, with concentrations of up to 1.858 mg/g d.w. and 1.315 mg/g d.w., respectively. Potassium (K) emerged as the most abundant element in all samples, with content ranging from 7.297 mg/g d.w. to 16.695 mg/g d.w., followed by calcium (Ca), phosphorus (P), and magnesium (Mg).

Keywords: Vitis vinifera, stem extracts, flavonols, potassium.

The paper presents the AMS (accelerator mass spectrometry) radiocarbon dating investigation of the historic Derby Boab Tree from Derby, Kimberley, Australia. This well-known boab (Adansonia gregorii) is often considered a prison tree, where Aboriginal prisoners were temporarily incarcerated in its cavity. According to recent research, the Derby Boab Tree was never used as a prison tree. The boab has a closed ring-shaped structure, with 3 perfectly fused stems enclosing a false cavity. A number of six punctiform wood samples, the size of a grain of sand were collected from the cavity door wall. The radiocarbon date of the oldest dated punctiform sample was 1285 ± 21 BP, a value which corresponds to a calibrated age of 1185 ± 20 calendar years. This result indicates that the age of the Derby Boab Tree is 1250 ± 50 years. This is the first accurate dating result of a boab and demonstrates that the species is a millennial angiosperm.

Keywords: AMS radiocarbon dating, Adansonia gregorii, dendrochronology, Australia, age determination, false cavity.

The anaerobic digestion of animal manure is a promising treatment solution allowing its partial conversion to energy, in the form of biogas. Anaerobic digestion technology is thus considered not only as a way to solve environmental problems, but also as a potential source of energy, while also contributing to solving economic and social problems. This research investigates the potential of poultry, cattle and pig wastes for biogas production through the anaerobic digestion process. A number of 15 recipes had been prepared and studied, each consisting of a mixture of organic materials with a concentration of 10% total solids (animal waste, vegetable waste, food waste), in different proportions. The raw material mixtures (representing the substrates) respected a C/N ratio between 15 and 25. The substrate composition influence on the production of biogas was investigated. Different types of animal manure have been found to produce varying rates of biogas, with certain types yielding higher or more stable levels. In this installation, efficient biogas production was observed after seven days of anaerobic digestion, with the most effective mixtures being those with a higher proportion of grass.

Keywords: animal waste, organic waste, anaerobic digestion, biogas, agro-food byproducts.

This work investigates the possible usage of tomato pomace biomass (TPB) as support for metabolic quantities of copper. Thus, biosorption potential of natural and biodegradable matrix formed from tomato residue, in suspension form was explored. The effect of biomass quantity, Cu(II) concentration and temperature were assessed. Analysis of Fourier-transform infrared (FTIR) spectrum, scanning electron microscopy (SEM) images and elemental analysis suggested that the organic functional groups take part in the Cu (II) biosorption process, and some surface modifications and appearance of cavities onto the TPB surface were observed after biosorption. Experimental data were analysed in terms of pseudo-first order, pseudo-second order, intraparticle diffusion and external diffusion kinetic models. The results showed that the biosorption process of Cu(II) ions followed well pseudo-second order kinetics. The biosorption data of Cu(II) ions at 295 K are fitted to Langmuir, Freundlich, Dubinin–Radushkevich (D–R) and Temkin isotherms. Biosorption of Cu(II) onto TPB followed the Freundlich isotherm model (R2 = 0.93) with the maximum biosorption capacity of 2.05 mg/g. In conclusion, TPB showed appropriate adsorption capacity, 0.5 g of this biomaterial, as powder, containing Cu(II), could be used as a dietary supplement in order to supply the daily copper demand of the organism.

Keywords: Lycopersicon esculentum, tomato pomace biomass, Cu(II), lycopene, biosorption, dietary supplement

This study presents an analysis of In Vitro-In Vivo Correlation (IVIVC) for pentoxifylline modified-release tablets, with a focus on deriving robust predictive models. In vitro dissolution tests were conducted in three pH media (1.2, 4.5, and 6.8) to simulate various gastrointestinal conditions. Data was collected under fed conditions from a bioequivalence (BE) study. The modeling and calculations were performed using Phoenix WinNonlin® version 8.4 software, enabling estimation of drug absorption kinetics. A Level A IVIVC model was employed for each in vivo data to establish a direct and reliable correlation between the in vitro dissolution profiles and the in vivo pharmacokinetic data. The determination coefficient (R²) exceeded 0.97, demonstrating a high degree of predictability and robustness in the established IVIVC.

Keywords: In Vitro – In Vivo Correlations (IVIVCs), pentoxifylline, in vitro dissolution, bioequivalence, Level A Correlation