Bulletin of the Chemical Society of Ethiopia

Major and heavy metals contents and health risk assessment of pumpkin peel, flesh and seed by microwave plasma-atomic emission spectroscopy

Abeb Yetesha — 2023-03-06

ABSTRACT. The aim of this study was to determine the levels of major (Na, Mg, K, Ca) and heavy (Cr, Mn, Fe, Ni, Cu, Zn, Cd) metals and health risk assessment of the peel, flesh and seed of pumpkins cultivated in Ethiopia, using microwave plasma-atomic emission spectrometry. Dried powdered samples (0.5 g) were wet digested with 69% HNO₃ and 30% H₂O₂ in microwave digester. The percent recovery for the three parts of pumpkin samples were 90-110%. The mean concentration of metals in pumpkin peel, flesh, seed samples, respectively, were K (27806±9767, 29531±2452, 10667±1133), Ca (5267±2092, 3190±900, 2919±397), Mg (4716±469, 848±349, 4668±413), Fe (158±29, 111±46, 225±56), Na (167±116, 63.1±15, 171±123), Mn (28.9±1.4, 9.61±3.2, 33.4±4.9), Zn (24.2±4.4, 10.6±4.0, 67.5±12.3), Cu (8.14±1.1, 15.1±9.3, 10.8±0.9), Ni (3.79±2.4, 2.14±1.3, 3.44±2.8), Cr (0.28±0.1, 0.36±0.2, 0.69±0.1), Cd (0.24±0.1, 0.46±0.1, 1.39±0.2) mg/kg. The hazard index (HI) of pumpkin flesh and seed indicated ingestion of pumpkin is safe from non-carcinogenic risk. The total cancer risk (CR) due to consumption of pumpkin flesh and seed through Cr and Cd from the three sampling sites are in the range 1.1 x 10^-4-1.8 x 10^-4, indicating a non-risk of exposure to cancer due to the consumption of pumpkin grown in the sampling areas.

KEY WORDS: Pumpkin, Mineral content, Health risk, Microwave plasma-atomic emission spectrometry

Bull. Chem. Soc. Ethiop. 2023, 37(3), 533-551.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.1

Physicochemical properties and microbial load evaluation of raw cow milks of Jimma Town, Ethiopia

Tesfaye Tadesse — 2023-03-06

ABSTRACT. In this study, physicochemical properties and microbial loads of raw and sterilized cow milks of Jimma town, Ethiopia, were investigated. Raw and sterilized milk samples were collected from milk venders and local market, respectively. Standard methods were used for analysis of both physicochemical and microbial loads of the samples. The results of the study showed that physicochemical properties of the studied milk samples were within the recommended values. The total bacteria count (TBC) and coliform count (CC) of raw milk samples were above the recommended values, whereas their values in the sterilized milk sample were comparable with the recommended values. However, the yeast and mould count (YMC) of the studied milk samples were comparable with their recommended values. ANOVA (p < 0.05) results showed the presence of significant differences in the physicochemical properties such as temperature, pH, titratable acidity, total solids, solids not fat, protein, fat, lactose, total bacteria count and coliform count among the studied milk samples. In general, the studied raw and sterilized milk samples had acceptable physicochemical properties. However, the TBC and CC of the raw milk samples were above their respective recommended values, which might be attributed to the low hygienic practices of the venders.

KEYWORDS: Raw and sterilized cow milks, Physicochemical properties, Microbial load

Bull. Chem. Soc. Ethiop. 2023, 37(3), 553-563.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.2

Determination of fatty acids composition by GC-MS and physicochemical parameters of pumpkin (Cucurbita maxima) seed oil cultivated in Ethiopia

Mulu Hagos — 2023-03-06

ABSTRACT. Pumpkin (Cucurbita maxima) seed oil was extracted using petroleum ether and analyzed for fatty acid compositions and physicochemical parameters of the oil. The seeds were found to contain 43.6% (%w/w) oil. Linoleic (50.7%), oleic (18.8%), palmitic (17.9%) and stearic (12.4%) were found as the primary fatty acids in pumpkin seed oil. Physicochemical parameters of pumpkin seed oil were found to be acid value (1.32 mg KOH/g oil), saponification value (191 mg KOH/g oil), iodine value (114 g I₂/100 g), peroxide value (3.6 meq/kg), specific gravity (0.91 g/mL), refractive index (1.47) and viscosity (24.7). According to the study's findings, 50% of the oil contains the essential fatty acid omega-6 (linoleic acid). The high concentration of essential linoleic acid in pumpkin seed oil implies that it is a nutrient-dense food. The physicochemical study of the pumpkin seed oil samples also showed that they were suitable as industrial ingredients for making soap, cosmetics, medications, and food additives, among other things.

KEY WORDS: Pumpkin seed oil, Fatty acids, Oil content, Physicochemical parameters, Gas chromatography-mass spectrometry, Ethiopia

Bull. Chem. Soc. Ethiop. 2023, 37(3), 565-577.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.3

Development of an efficient dispersive liquid-liquid microextraction approach combined with spectrophotometry for determination of antiviral drug, valacyclovir HCl in pharmaceutical formulations

Amal H. Al-Bagawi — 2023-03-07

ABSTRACT. A new, fast, sensitive, simple, and green dispersive liquid–liquid microextraction (DLLME)-based spectrophotometric method for the determination of valacyclovir HCl (VAL) in pure form and pharmaceutical formulations has been developed and validated. The developed method is based on the formation of a coloured product through the reaction of VAL and 1,2-naphthoquine-4-sulfonate (NQS) at pH = 9. The important experimental parameters affecting the extraction efficiency were investigated and optimized. The tiny organic droplets had a wavelength of l = 505 nm. At the optimum conditions, linearity ranged from 0.06 to 2.0 μg/mL, with a linear correlation coefficient of 0.9995. The limits of detection and quantification were 0.02, and 0.06 μg/mL, respectively. The enhancement factor was 36.87. Good recovery as accuracy (99.50%) and relative standard deviation (RSD) as precision were 1.20%, respectively. The developed DLLME method was successfully applied to the determination of VAL in pharmaceutical formulations, and the validity was assessed by applying the standard addition technique. The results obtained by the proposed method for the pure VAL and commercial tablets agreed well with those obtained by the official method.

KEY WORDS: Valacyclovir HCl, Spectrophotometry, 1-2-Naphthoquine-4-sulfonate, Dispersive liquid–liquid microextraction, Pharmaceutical formulations

Bull. Chem. Soc. Ethiop. 2023, 37(3), 579-592.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.4

Adsorption of diazo dye direct red-28 and tetra-azo dye direct black-22 using calcined kaolin in aqueous solutions

Serap Findik — 2023-03-06

ABSTRACT. In this study, the removal of diazo and tetra-azo dyes using calcined kaolin were compared. Direct red-28 (DR-28) and Direct black-22 (DB-22) was chosen as diazo and tetra-azo dyes, respectively. The kaolin obtained from Turkiye and calcined at 200 °C was found to be the most efficient adsorbent. Natural and calcined kaolins were characterized using SEM-EDS, FTIR, TGA, and XRD. The parameters such as, calcination temperature of the kaolin, adsorbent amount, temperature, initial pH, contact time, and initial concentration were studied. It was found that the removal rate of DR-28 was higher than that of DB-22 at the studied conditions. The removal of DR-28 and DB-22 were found to be 90.1% and 46.2% under the following conditions: adsorbent amount: 1.2 g/200 mL, initial concentration: 20 mg/L, original pH, temperature: 20 °C and contact time 120 min. The adsorption of the dyes was fitted to Langmuir isotherm model. The maximum adsorption capacity of calcined kaolin at 200 °C was determined as 5.39 and 3.5 mg/g for DR-28 and DB-22, respectively. The adsorption of DR-28 and DB-22 followed a pseudo-second order model. The thermodynamic study showed that the adsorption of DB-22 onto calcined kaolin was endothermic while that of DR-28 was exothermic.

KEY WORDS: Adsorption, Diazo dye, Tetra-azo dye, Kaolin

Bull. Chem. Soc. Ethiop. 2023, 37(3), 593-610.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.5

Zeolite-x encapsulated Ni(II) and Co(II) complexes with 2,6-pyridine dicarboxylic acid as catalysts for oxidative degradation of atenolol in an aqueous solution

Fatemeh Hassani — 2023-03-06

ABSTRACT. Complexes of Co(II) and Ni(II) with 2,6-pyridine dicarboxylic acid (PydcH₂) have been synthesized in the NaX (zeolite-X) nanopores. The formation of zeolite X encapsulated Co(II) and Ni(II) complexes ([M(pydcH)₂]-NaX, [M = Co(II) and Ni(II])] were confirmed using spectroscopic methods of FT-IR, elemental analysis, XRD, FE-SEM, and TEM. It was affirmed that the encapsulation of complexes in NaX pores was formed without changes in the structure and shape of the zeolite. The oxidative degradation reaction of atenolol with hydrogen peroxide as an oxidant was performed in the presence of synthesized [M(pydcH)₂]-NaX nanocomposites to study their catalytic activity. Therefore, oxidation of atenolol was performed under different conditions of catalyst, temperature, and time. Under optimal conditions, catalysts [Co(pydcH)₂]-NaX and [Ni(pydcH)₂]-NaX showed 82.3% and 71.1% activity of atenolol oxidation, respectively. These catalysts were stable after recovery and were used three more times. The results showed that these catalysts were reusable and had a reduction in the catalytic activity of less than ten percent.

KEY WORDS: Zeolite-X, Nano porosity, Ion-exchange, Degradation of atenolol, 2,6-Pyridine dicarboxylic acid

Bull. Chem. Soc. Ethiop. 2023, 37(3), 611-622.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.6

New tetrapropylammonium tetrabromozincate complex [(C3H7)4N]2ZnBr4(II) - synthesis, spectral, thermal characterization and antioxidant activity

Banupriya Kanagarajan — 2023-03-06

ABSTRACT. The importance of the A₂BX₄ complex (A = bivalent ion, NH₄⁺ and its alkyl radical derivatives; B = bivalent transition metal ion and X = halogen) has increased in recent years due to fascinating physical properties such as ferro elastic, ferroelectric, and corresponding – unequal phases at low temperatures. In modern technologies the use of transistors, ferromagnetic garnets, sensor systems, softener templates, and ultraviolet light, as well as IR solid-state lasers, efficient crystalline materials are expected. A slow evaporation approach at room temperature was used to grow the TPAPBr-Zn [(CH₃CH₂CH₂)₄N]₂ZnBr₄(II) challenging kind A₂BX₄. Elemental analysis, powder diffraction, differential thermal analysis, FT-IR, proton and carbon-13 NMR spectroscopic techniques are used to characterize the synthesized compound. The presence of chemical groups and methylene radical groups in the compound are confirmed by the FT-IR spectra. The presence of an N-propyl group in the molecule is indicated by the nuclear magnetic resonance spectra. Thermogram of the compound reveals two-stage decomposition showing endo followed by exothermic decomposition resulting zinc oxide as an end product. As synthesised compound shown significant inhibitory activity towards free radical.

KEY WORDS: Synthesis, Elemental analysis, Spectroscopic studies, TG analysis, Antioxidant, Tetrapropylammonium tetrabromozincate(II)

Bull. Chem. Soc. Ethiop. 2023, 37(3), 623-631.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.7

Zinc(II) complex of (Z)-4-((4-nitrophenyl)amino)pent-3-en-2-one, a potential antimicrobial agent: synthesis, characterization, antimicrobial screening, DFT calculation and docking study

I. Waziri — 2023-03-06

ABSTRACT. Herein, the synthesis and characterizations of (Z)-4-((4-nitrophenyl)amino)pent-3-en-2-one (HL) ligand and its Zn(II) complex are reported. The compounds were characterized using elemental and thermogravimetric (TGA) analysis, electrochemical studies, FTIR, UV-Vis, ¹H and ¹³C{H}NMR, HRMS, and PXRD techniques. Antimicrobial activity was screened on some Gram-positive and Gram-negative bacteria. DFT predictions were achieved using B3LYP, ωB97XD and M06-2X functional with 6-31+G(d,p) and LANL2DZ basis sets for nonmetallic and metallic atoms, respectively. The therapeutic potentials of the compounds were evaluated based on protein binding affinity, ADME/T and drug-likeness properties. The experimental results revealed the formation of a complex in which two ligands coordinated to the zinc ion in a tetrahedral arrangement through their carbonyl and amino groups. The antimicrobial study showed that the complex possesses higher antimicrobial activity than free ligand and the control (Streptomycin). B3LYP emerged as the best performing functional having yielded the best IR spectra and geometrical parameters relative to the experimental data. The density functional theory (DFT) predictions revealed that the complex is more active than the ligand, and its formation is thermodynamically feasible and exothermic. The docking results revealed that the binding affinities of the compounds are in agreement with the in-vitro data, and they possess drug-like properties.

KEY WORDS: Schiff base, Zinc complex, Antimicrobial, DFT, Docking study

Bull. Chem. Soc. Ethiop. 2023, 37(3), 633-651.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.8

Structure and properties of strontium phosphate glasses modified with aluminum oxide applied as glass ionomer cement

G. El-Damrawi — 2023-03-06

ABSTRACT. Studied glasses in the system 50P₂O₅-(49-x)SrO-1AlF₃-xAl₂O₃ (mol%), 0≤x≤4.5, were prepared via the melt-annealing technique. The prepared samples are transparent amorphous network structures. Glasses are still transparent upon the heat treatment at 540 ºC for 4 hours. ²⁷Al nuclear magnetic resonance (NMR) has been applied to determine the structural role of Al₂O₃. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Vickers hardness (H_v) measurements have been carried out. XRD spectroscopy is used to investigate the glasses' crystalline features. The crystallinity was enhanced via the heat treatment process. Some of investigated strontium phosphate glasses are recommended to be applied in dental applications.

KEY WORDS: NMR, Aluminum oxide, GIC, X-ray diffraction, Strontium phosphate

Bull. Chem. Soc. Ethiop. 2023, 37(3), 653-662.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.9

A simple and low-cost new procedure for synthesis of nickel(II) and cadmium(II) sulfides in situ thiourea metal–chelation precursor

Moamen S. Refat — 2023-03-06

ABSTRACT. Nickel(II) and cadmium(II) sulfides are a promising chemical material in various advanced research areas such as solar cells, supercapacitors, catalysts, and of significant interest for their practical implementations in up to photonics and electronics. Cadmium and nickel sulfides were synthesized with stoichiometries in aqueous media at elevated temperature from Ni(NO₃)₂.6H₂O, NiCl₂.6H₂O, NiSO₄.6H₂O, CdCl₂, Cd(NO₃)₂.4H₂O, CdSO₄.8H₂O and thiourea as a sulfur precursor using a direct chemical reaction. At room temperature an octahedral and tetrahedral geometries result from the reactions between different nickel(II), cadmium(II) and thiourea with the molecular formulas can be presented as [Ni(NH₂CSNH₂)₆]X₂ and [Cd(NH₂CSNH₂)₄]X₂ where X = Cl^-, NO₃^-, SO₄². The novelty of our study is precipitated yellow cadmium sulfide and black nickel sulfide at elevated temperature ~80 ^oC through the molar ratio 1:10 (M²⁺: thiourea) in aqueous media. Infrared spectra, XRD, TEM including EDX, and elemental analysis were used for characterization the metal sulfides products. The average crystalline size of obtained CdS and NiS particles in range 20-25 nm. Different reaction conditions effects were evaluated on the size, morphology and particle size.

KEY WORDS: Nickel and cadmium sulfide, Chelation, Thiourea, XRD, TEM

Bull. Chem. Soc. Ethiop. 2023, 37(3), 663-674.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.10

Synthesis, characterization and DFT studies of Schiff bases of p-methoxysalicylaldehyde

Temitope E. Olalekan — 2023-03-20

ABSTRACT. Five new Schiff bases synthesized by the reaction between 2-(methylthio)aniline derivatives and p-methoxysalicylaldehyde are presented as MtH-1 (R = H), MtH-2 (R = CH₃), MtH-3 (R = OCH₃), MtH-4 (R = Cl) and MtH-5 (R = Br). They were characterized by CHNS analyses, NMR (¹H, ¹³C, DEPT135, COSY and HSQC), FTIR and UV-Vis spectroscopic techniques. FT-IR, elemental analyses and NMR data supported the formation of the Schiff bases, with the chemical shifts of azomethine and phenol protons showing sensitivity to ring substitution. The crystal structure of MtH-1 featured the alignment of the phenyl rings to each other and to the C=N group with dihedral angles >170^o. The DFT calculations corroborated the bond lengths and angles of MtH-1. The HOMO-LUMO energies, dipole moments and other reactivity parameters were calculated. The methyl-substituted MtH-2 was the least polar of the compounds. With calculated energy band gaps of almost 4 eV, the compounds may have applications in the semiconductors field.

Bull. Chem. Soc. Ethiop. 2023, 37(3), 675-688.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.11

KEY WORDS: Schiff bases, p-methoxysalicylaldehyde, Crystal structure, Spectroscopic properties, DFT calculations

Preparation and characterization of vernolic acid methyl ester functionalized ordered mesoporous materials

Yonas Chebude — 2023-03-06

ABSTRACT. Vernonia oil is a naturally epoxidized triglyceride oil extracted from the seed of Vernonia galamensis, a native plant in East Africa. After hydrolysis to vernolic acid (VA) and derivatization, vernolic acid methyl ester (VAME) is synthesized and used to functionalize ordered mesoporous materials (OMM). Al-MCM-41 with Si/Al ratio of 15, pure silica SBA-15 and periodic mesoporous organosilica (PMO) are employed as supports exploring the different surface properties. Following optimization of the VAME/OMM ratios, selected samples, i.e. those with 13% VAME, were impregnated with AgNO₃ in NaBH₄ to obtain Ag-nanoparticles. The final AgVAME-OMM potential catalysts were characterized by transmission electron microscopy, observing an efficient loading of Ag nanoparticles in pure silica SBA-15 with VAME with 500 m² specific surface area and 6 nm pore size.

KEY WORDS: Vernolic acid methyl ester, Vernonia oil, Functionalization, Ordered mesoporous materials, Catalysis

Bull. Chem. Soc. Ethiop. 2023, 37(3), 689-702.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.12

Chemical composition and antibacterial activity of essential oils from selected species of the genus Cucumis in Ethiopia

Teshale Assefa — 2023-03-06

ABSTRACT. Chemical composition of the essential oils obtained by hydrodistillation from various parts of Cucumis ficifolius, Cucumis dipsaceus and Cucumis prophetarum were determined by gas chromatography-mass spectrometry (GC/MS) analysis. Compounds 3,7,11,15-tetramethyl-1-hexadecanol, neophytadiene, and isophytol from leaves, phytol and octacosane from the stems, hentriacontane from the fruits, and octacosane, abietadiene from roots were identified the major constituents of Cucumis ficifolius. Hydrocarbons including Octacosane, tricosane, tetracosane, hentriacontane and hexacosane were the principal components of various parts of Cucumis. dispaceus. While leaves, stems and roots of Cucumis prophetarum contain mainly hentriacontane, neophytadiene and octacosane, respectively. The oils were evaluated for their antibacterial activity using disc diffusion method against four bacterial pathogens including E. coli, P. aeruginosa, S. aureus and S. pyogenes. All tested essential oils were sensitive against the bacterial strains. The essential oil from the leaves of Cucumis dispaceus exhibited the highest inhibition zone against E. coli (11.87±2.42 mm) while the other displayed modest activity compared with the positive control, ceftriaxone. Therefore, the antibacterial activities displayed by the essential oils along with the literature reported for their constituents suggest the use of these plants as an antibacterial agent. Furthermore, the results presented herein also support the traditional use of these plants against bacteria.

KEY WORDS: Cucumis ficifolius, Cucumis dipsaceus, Cucumis prophetarum, Antibacteria

Bull. Chem. Soc. Ethiop. 2023, 37(3), 703-715.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.13

Multi-component reactions for the synthesis of pyrazolo [1,5-a]quinoline derivatives together with their cytotoxic evaluations

Rafat M. Mohareb — 2023-03-06

ABSTRACT. A new approaches for the synthesis of novel pyrazolo[1,5-a]quinazoline 8a-f and pyrazolo[1,5-a]quinazolin-6-one 10a-s and 12a-s derivatives were obtained using 4-(2-phenylhydrazono)-4H-pyrazol-3-amine derivatives 5a-f via their multi-component reactions. The later pyrazole derivatives were prepared via arylhydrazone derivatives 3a-f. The structures of the synthesized compounds were established based on their respective analytical data. On the other hand, the cytotoxic effects of the synthesized compounds were obtained against the six cancer cell lines, namely A549, HT-29, MKN-45, U87MG, SMMC-7721 and, H460 utilizing foretinib as the positive control and the standard MTT assay in vitro. The obtained results showed that compounds 8c, 8f, 10c, 10i, 10l, 10p, 10s, 12c, 12i, 12l, 12p and, 12s were the most cytotoxic compounds. In most cases the presence of the electronegative Cl group enhanced the cytotoxicity of the tested compound.

KEY WORDS: Multi-component reactions, Pyrazolo[1,5-a]quinazoline, Pyrazolo[1,5-a]quinazolin-6-one, Cytotoxicity

Bull. Chem. Soc. Ethiop. 2023, 37(3), 717-734.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.14

Zinc leaching from smithsonite ore in lactic acid solution: Studies on parametric optimization, kinetic and mechanism

Sıla Sadiye Ilhan — 2023-03-06

ABSTRACT. The solubility of low-grade zinc ores with a selective leaching environmentally friendly reagent has become a focus of great interest since zinc and its compounds have found wide application. For this purpose, lactic acid was used to investigate the selective leaching kinetics of smithsonite ore obtained from Kayseri region. The effects of particle size (137.5-725 µm), acid concentration (0.5-5 M), solid/liquid ratio (0.5/250-3/250 g mL^-1), stirring speed (500-800 rpm) and temperature (40-70 °C) parameters on the smithsonite dissolution rate were experimentally studied. The results obtained show that leaching of about 99.8% of zinc is achieved using 425 µm particle size at a reaction temperature of 70 °C for 45 min reaction time with 2 M lactic acid, the solid/liquid ratio of 1/250 g mL^-1 and stirring speed of 600 rpm. The statistical analysis of the experimental data obtained from the parameters revealed that smithsonite dissolution was the surface reaction-controlled with an apparent activation energy of 53.62 kJ.moL^-1. The kinetic model describing the process was found as

KEY WORDS: Smithsonite, Dissolution kinetics, Lactic acid, Zinc lactate

Bull. Chem. Soc. Ethiop. 2023, 37(3), 735-744.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.15

p-Anisidine release study by hydrolysis of Schiff bases in homogeneous media

Awatif Amaria Moulay — 2023-03-06

ABSTRACT. The objective of this work is to study the release of p-anisidine by the hydrolysis of synthesized Schiff bases N-vinylbenzylidene-p-anisidine (Im) as a monomer and its copolymers (Cp₁, Cp₂) with N,N-dimethylacrylamide (DMA). The hydrolysis behavior and kinetics are investigated in homogeneous media composed of ethanol/water (80% v/v) at 37 °C and at pH range of 4.0-10.0. The variation of the concentration over time is measured in thermostatically cells using UV-Vis spectroscopy. The results showed that the imine function hydrolysis obeyed to the first order for all compounds; the experimental kinetic constants are determined and the pH–rate diagram profile is established. It is noticed that the hydrolysis of imine function is extremely dependent on its carrier and the pH medium.

KEY WORDS: p-Anisidine, Copolymer, Schiff base, Hydrolysis, pH–rate diagram, Controlled release

Bull. Chem. Soc. Ethiop. 2023, 37(3), 745-755.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.16

Structural analysis of Val-Trp dipeptide: Molecular mechanics and DFT calculations

Sara Gambar Rahimzade — 2023-03-06

ABSTRACT. The present study of biologically active Val-Trp dipeptide has been performed using computer modeling methods. To search the stable structures the different theoretically possible conformations of this molecule were calculated within molecular mechanics framework. The results showed that two types of conformations, folded and extended, are realized for this compound. Afterwards, the most stable conformations of the Val-Trp dipeptide were optimized using DFT/B3LYP level of theory with 6-31+G(d,p) basis set. The geometry, energy parameters, electronic properties, molecular electrostatic potential (MEP) map, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, chemical reactivity descriptors, nonlinear optical properties such as the electric dipole moment and polarizability were computed and compared for the optimized extended and folded structures of this molecule. The differences in the electronic structure between two characteristic conformations of title dipeptide were revealed. It was found the redistribution of charges as a result of folding of the peptide chain leads to a decrease in the dipole moment of this molecule. The effects of intramolecular hydrogen bonding on geometry of Val-Trp dipeptide were observed.

KEY WORDS: Val-Trp dipeptide, Molecular Mechanics, DFT calculations

Bull. Chem. Soc. Ethiop. 2023, 37(3), 757-770.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.17

Inorganic tin(IV) complexes as photo-stabilizer for PVC

Raghad Haddad — 2023-03-06

ABSTRACT. Five organotin(IV) complexes including captopril (ligand) were employed in small amount as photostabilizers for poly(vinyl chloride) (PVC) when irradiated by UV light. Polymer’s samples were cast into films in order to conduct the UV exposure impact. The photodegradation rate constant (k_d) of blank and organotin(IV) complexes embedded PVC specimens were investigated in this work. The k_d values of filled samples were lower than the blank one, which indicates higher stability of these embedded films. Among these additives, triphenyltin(IV) showed the highest stability effect.

KEY WORDS: PVC, Organotin(IV) complexes, Photostability, Photodegradation, UV light

Bull. Chem. Soc. Ethiop. 2023, 37(3), 771-777. a

DOI: https://dx.doi.org/10.4314/bcse.v37i3.18

Investigation of the effect of some polar organic solvents on the leaching and dissolution kinetics of chalcopyrite in hydrogen peroxide and sulfuric acid solution

Mohamed Taha Osman Abdelraheem — 2023-03-06

ABSTRACT. The effect of acetic acid and ethanol as polar aqueous solvents on sulfuric acid with hydrogen peroxide as an oxidant was studied. A small amount of these polar aqueous solvents significantly improved the copper leaching recovery. The leaching parameters such as temperature, stirring speed, H₂O₂concentration, solid/liquid ratio, H₂SO₄concentration and particle size were examined. About 76.33% as highest Cu extraction was gained with 2 M H₂O₂, 600 rpm stirring speed, 50 °C temperature, 1 M H₂SO₄, 240 min of the reaction and 75 x 53 µm particle size fraction. Further experimental tests were carried out when the stirring speed, solid-to-liquid ratio (S/L), particle size, H₂O₂concentration, temperature and H₂SO₄concentration were kept constant to investigate the effect of ethanol and acetic acid concentration in the range of 0–2 M. The experimental results proved that the copper extraction recovery reached to 99.03% in 180 min of the reaction with 2 M acetic acid. While 2 M of ethanol increased copper extraction recovery up to 100% in 90 min of the leaching time. The dissolution reaction found to be described by mixed kinetic model and activation energy of 54.37 kJ/mol. Addition of acetic acid and ethanol suggested reaction controlled by diffusion across product layer.

KEY WORDS: Hydrogen peroxide, Sulfuric acid, Activation energy, Leaching, Chalcopyrite

Bull. Chem. Soc. Ethiop. 2023, 37(3), 779-788.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.19

Parameters for the conductometric association for lump and nano CoSO4.7H2O in the presence and absence of fuchsin acid in water at different temperature

Mohamed Fathi — 2023-03-06

ABSTRACT. For lump and nanocobalt sulfate (CoSO₄) in pure water, the affiliation and thermodynamic association characteristics were measured at 298.15, 303.15, 308.15, and 313.15 K. Based on the bulk and nano CoSO₄ molar conductance, estimates were made for the parameters of the solvation, such as the activity coefficient, free energy of association, enthalpy of association, association constant, and entropy of association. We discussed about each of these solvation parameters. Two stoichiometric complexes were formed by the interaction of bulk and nano CoSO₄.7H₂O with fuchsin acid: 1:1 and 1:2 In the case of 1:1 (CoSO₄.7H₂O/fuchsin acid) compared to 1:2 (fuchsin acid in pure water as solvent), the complex K_f and ∆G_f are higher, indicating simpler complex formation. The temperature increase resulted in a drop in the formation constants. The complexation's negative ∆G_f values demonstrate that the process of complex synthesis was spontaneous and that the temperature improved the spontaneity.

KEY WORDS: Molar conductance, Association constants, Fuchsin acid, Nano cobalt sulfate salt, Formation constant

Bull. Chem. Soc. Ethiop. 2023, 37(3), 789-804.

DOI: https://dx.doi.org/10.4314/bcse.v37i3.20