International Journal of Chemistry

International Journal of Chemistry | Vol. 13, No. 9, September 2022 | pp. 65–72

DOI: 10.46882/2022/IJC/000167

Article Type: Original Research Paper

Title: Validation of an RP-HPLC Method for Quantitative Monitoring of Azithromycin Formulations

Names of Authors: E. O. Effiong¹, L. A. S. dos Santos²*

Authors’ Affiliations:
¹Department of Chemistry, University of Uyo, Uyo, Nigeria.
²Department of Pharmacy, Federal University of Minas Gerais, Belo Horizonte, Brazil.

Abstract: Developing simple, automated, and accurate analytical methods is essential for routine quality monitoring and the detection of counterfeit macrolide antibiotics in commercial pharmacies. This paper describes the development and validation of a rapid Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) method for the quantitative determination of azithromycin in tablet dosage forms. Separation was achieved using a C18 stationary phase column under an isocratic mobile phase composed of acetonitrile-methanol-phosphate buffer (pH 6.5) (45:35:20 v/v/v), at a flow rate of 1.0 mL/min. Eluent monitoring was executed spectrophotometrically at a wavelength maximum of 215 nm. Method validation parameters followed the International Council for Harmonisation (ICH) guidelines. Excellent linearity was established over a concentration range of 2.0 to 50.0 mg/L with a correlation coefficient (R²) of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were determined to be 0.06 mg/L and 0.18 mg/L, respectively. Precision assessments yielded relative standard deviations (RSD) below 1.4%. The validated method was successfully applied to screen six commercial brands, producing recovery percentages between 98.6% and 101.4% with no interference from common excipients.

Keywords: RP-HPLC; Azithromycin; Quantitative analysis; Method validation; Pharmaceuticals; Quality control

Manuscript Timeline: Received: September 02, 2021; Revised: October 12, 2021; Accepted: November 05, 2021; Published: September 09, 2022.

Citation: Effiong, E. O., & dos Santos, L. A. S. (2022). Validation of an RP-HPLC Method for Quantitative Monitoring of Azithromycin Formulations. International Journal of Chemistry, 13(9), 65–72.

International Journal of Chemistry | Vol. 13, No. 10, October 2022 | pp. 73–80

DOI: 10.46882/2022/IJC/000168

Article Type: Original Research Paper

Title: Synthesis, Molecular Docking, and Enzymatic Screening of Novel Quinoline-Linked Chalcone Derivatives

Names of Authors: O. M. Kolawole¹, E. C. J. Smith²*

Authors’ Affiliations:
¹Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria.
²Department of Chemistry, University of Manchester, Manchester, United Kingdom.

Abstract: Inhibiting acetylcholinesterase (AChE) represents a vital clinical strategy for managing Alzheimer's disease by maintaining systemic acetylcholine neurotransmitter levels in brain tissue. In this work, five novel quinoline-linked chalcone derivatives were synthesized via Claisen-Schmidt condensation of quinoline-2-carboxaldehyde with various substituted acetophenones in the presence of potassium hydroxide catalysts. The molecular structures of the synthesized targets were verified using elemental analysis, FT-IR, and ¹H-NMR spectroscopy. In vitro AChE enzyme inhibition assays revealed that compound 3d, bearing a p-chlorosubstituent, possessed the highest inhibitory potency, showing an IC50 value of 7.8 μM compared to the donepezil clinical standard (IC50 = 2.1 μM). To investigate specific binding modes, in silico molecular docking simulations were run inside the catalytic active site of human AChE using AutoDock Vina software. The computational docking models demonstrated that the chalcone carbonyl forms stable hydrogen bonds with Gly121 and Ser203 residues. The quinoline ring extensions fit well into the peripheral anionic site, engaging in significant edge-to-face pi-pi stacking interactions with Trp286. These structural contacts stabilize the ligand-protein topology, explaining the low inhibition constants and presenting a potential scaffold for further antidementia drug design.

Keywords: Quinoline; Chalcones; Acetylcholinesterase; Enzyme inhibition; Molecular docking; Alzheimer's disease

Manuscript Timeline: Received: September 10, 2021; Revised: October 22, 2021; Accepted: November 15, 2021; Published: October 05, 2022.

Citation: Kolawole, O. M., & Smith, E. C. J. (2022). Synthesis, Molecular Docking, and Enzymatic Screening of Novel Quinoline-Linked Chalcone Derivatives. International Journal of Chemistry, 13(10), 73–80.

International Journal of Chemistry | Vol. 13, No. 6, June 2022 | pp. 41–48

DOI: 10.46882/2022/IJC/000164

Article Type: Original Research Paper

Title: Kinetic Studies and Inner-Sphere Mechanisms of the Ceric Sulfate Oxidation of L-Cysteine in Acidic Media

Names of Authors: T. M. Usman¹, F. A. Al-Otaibi²*

Authors’ Affiliations:
¹Department of Chemistry, Bayero University, Kano, Nigeria.
²Department of Chemistry, King Abdulaziz University, Jeddah, Saudi Arabia.

Abstract: The kinetics of transition metal electron transfer reactions involving basic amino acids yield essential data required to map biochemical oxidation paths and structural intermediate transformations. The oxidation of L-cysteine by ceric sulfate [Ce(SO₄)₂] was investigated spectrophotometrically in an aqueous perchloric acid medium at a constant ionic strength of 0.40 M (NaClO₄). The reaction progress was monitored under pseudo-first-order conditions by following the absorbance decay of Cr(VI) at its absorption maximum of 320 nm. The empirical rate law showed a first-order dependence on [ceric sulfate] and a fractional-first-order dependence on [L-cysteine]. The reaction rate increased with rising hydronium ion concentration, revealing an acid-catalyzed pathway driven by the active protonated species. Variations in the dielectric constant of the solvent medium produced significant kinetic shifts, indicating a rate-determining step involving two polar molecular species. Stoichiometric determinations confirmed that 2 moles of L-cysteine consumed 1 mole of ceric sulfate, producing cystine and cerium(III) ions as the primary end products. Thermodynamic activation constants calculated from temperature-dependence datasets using the Eyring equation yielded an enthalpy of activation (delta H*) of 48.5 kJ/mol and an entropy of activation (delta S*) of -104.2 J/mol K, supporting an inner-sphere mechanism.

Keywords: Reaction kinetics; Spectrophotometry; Ceric sulfate; L-cysteine; Activation parameters; Inner-sphere mechanism

Manuscript Timeline: Received: July 10, 2021; Revised: August 20, 2021; Accepted: September 15, 2021; Published: June 03, 2022.

Citation: Usman, T. M., & Al-Otaibi, F. A. (2022). Kinetic Studies and Inner-Sphere Mechanisms of the Ceric Sulfate Oxidation of L-Cysteine in Acidic Media. International Journal of Chemistry, 13(6), 41–48.

International Journal of Chemistry | Vol. 13, No. 11, November 2022 | pp. 81–88

DOI: 10.46882/2022/IJC/000169

Article Type: Original Research Paper

Title: Thermodynamic Modeling, Desorption Kinetics, and Multilayer Adsorption of Reactive Black 5 Dye onto Modified Illite Clay

Names of Authors: A. D. Yusuf¹, M. A. Al-Dosari²*

Authors’ Affiliations:
¹Department of Industrial Chemistry, Federal University of Technology, Yola, Nigeria.
²Department of Chemistry, Qatar University, Doha, Qatar.

Abstract: The release of highly stable anionic reactive dyes like Reactive Black 5 from textile finishing plants causes significant environmental and toxicity hazards in surface aquatic resources. This study examines the adsorptive uptake performance of a surfactant-modified illite clay (SMI) prepared via chemical functionalization with hexadecyltrimethylammonium bromide (HDTMA-Br). The structural parameters of raw and modified clays were characterized using X-ray diffraction (XRD) and FT-IR spectroscopy. Adsorption operations were conducted via batch runs, monitoring changes in contact time, solution pH, initial dye loading concentrations, and system temperatures. The equilibrium datasets fit closely with the Freundlich isotherm model, demonstrating successful multilayer dye attachment onto the hydrophobic surfactant bilayers. Kinetic parameters matched the intra-particle diffusion expressions alongside a pseudo-second-order mechanism, showing that chemisorption reactions controlled the mass transfer rates. Thermodynamic constants showed that the adsorption process was endothermic (delta H° = 21.4 kJ/mol) and caused an increase in system randomness at the solid-solution interface (delta S° = 72.5 J/mol K). Negative values of Gibbs free energy (delta G°) spanning from -2.1 to -5.5 kJ/mol across the 298 to 328 K range confirmed process spontaneity, positioning SMI as an affordable material for industrial dye wastewater treatment.

Keywords: Illite clay; Surfactant modification; Reactive black 5; Adsorption isotherm; Chemisorption; Thermodynamic parameters

Manuscript Timeline: Received: October 02, 2021; Revised: November 15, 2021; Accepted: December 04, 2021; Published: November 09, 2022.

Citation: Yusuf, A. D., & Al-Dosari, M. A. (2022). Thermodynamic Modeling, Desorption Kinetics, and Multilayer Adsorption of Reactive Black 5 Dye onto Modified Illite Clay. International Journal of Chemistry, 13(11), 81–88.

International Journal of Chemistry | Vol. 13, No. 3, March 2022 | pp. 17–24

DOI: 10.46882/2022/IJC/000161

Article Type: Original Research Paper

Title: Adsorptive Sequestration of Hexavalent Chromium Using Thiol-Functionalized Sugarcane Bagasse Biomass

Names of Authors: E. N. Chidi¹, L. M. van der Westhuizen²*

Authors’ Affiliations:
¹Department of Pure and Industrial Chemistry, Nnamdi Azikiwe University, Awka, Nigeria.
²Department of Chemical Engineering, Stellenbosch University, Stellenbosch, South South Africa.

Abstract: Heavy metal contamination of surface waters by industrial chrome plating operations requires the development of low-cost, chemically stable, and highly active biosorption matrices. This investigation reports the adsorptive efficiency of a modified agricultural adsorbent derived from sugarcane bagasse prepared via chemical modification with thioglycolic acid. The chemical transformations and surface porous architectures of the matrix were examined through scanning electron microscopy (SEM) and FT-IR spectroscopy. The analytical data confirmed that the thiolation process successfully integrated sulfur-rich thiol (-SH) functional ligand networks across the cellulosic biomass structure. Batch extraction experiments evaluated parameters of solution pH, equilibrium contact time, adsorbent dosage, and initial Cr(VI) concentrations. Maximum chromium adsorption occurred at an acidic pH of 2.0, using an equilibrium contact period of 90 minutes due to the protonation of surface functional groups. Equilibrium data matched the Langmuir model closely, showing a maximum monolayer adsorption capacity of 54.45 mg/g at 298 K. Sorption kinetics followed a pseudo-second-order model with a high correlation coefficient (R² > 0.998), proving that chemical surface complexation reactions controlled the mass transfer rates. Thermodynamic parameters confirmed process spontaneity and endothermic characteristics, highlighting this modified biomass as an affordable material for industrial water treatment plant design.

Keywords: Sugarcane bagasse; Thiolation; Hexavalent chromium; Adsorption kinetics; Chemisorption; Wastewater treatment

Manuscript Timeline: Received: June 02, 2021; Revised: July 15, 2021; Accepted: August 10, 2021; Published: March 08, 2022.

Citation: Chidi, E. N., & van der Westhuizen, L. M. (2022). Adsorptive Sequestration of Hexavalent Chromium Using Thiol-Functionalized Sugarcane Bagasse Biomass. International Journal of Chemistry, 13(3), 17–24.

International Journal of Chemistry | Vol. 13, No. 12, December 2022 | pp. 89–96

DOI: 10.46882/2022/IJC/000170

Article Type: Original Research Paper

Title: Green Synthesis of Zinc Oxide Nanoparticles Using Leaves Extract of Alchornea cordifolia and Catalytic Degradation of Methyl Orange

Names of Authors: S. I. Musa¹, C. R. de Souza²*

Authors’ Affiliations:
¹Department of Chemistry, University of Jos, Jos, Nigeria.
²Department of Chemical Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

Abstract: The biological synthesis of noble metal and metal oxide nanomaterials using tropical flora presents an eco-friendly and economically sustainable alternative to hazardous chemical reduction pathways. This study describes the green synthesis of stable zinc oxide nanoparticles (ZnO-NPs) utilizing the aqueous leaf extract of Alchornea cordifolia as a powerful reducing and capping agent. The bioreduction process was monitored via UV-Vis spectrophotometry, which revealed a distinct surface plasmon resonance peak at 370 nm, confirming the nucleation of metallic oxides. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses showed highly spherical nanoparticles with an average particle diameter of 18 nm. X-ray diffraction (XRD) patterns confirmed the wurtzite hexagonal crystalline structure of the biosynthesized zinc oxide. Fourier-transform infrared (FT-IR) spectroscopy indicated that water-soluble polyphenols and flavonoids within the leaf matrix were responsible for capping and protecting the ZnO-NPs against structural agglomeration. The catalytic efficiency of the synthesized ZnO-NPs was evaluated by tracking the chemical reduction of methyl orange dye by sodium borohydride (NaBH₄) in an aqueous system under solar exposure. The reaction achieved 96.8% decolorization within 12 minutes. The dye degradation kinetics conformed tightly to the pseudo-first-order kinetic model with a rate constant of 0.295 min⁻¹, indicating excellent catalytic potential for textile wastewater treatment arrays.

Keywords: Zinc oxide nanoparticles; Green synthesis; Alchornea cordifolia; Biosynthesis; Heterogeneous catalysis; Methyl orange

Manuscript Timeline: Received: October 12, 2021; Revised: November 24, 2021; Accepted: December 18, 2021; Published: December 04, 2022.

Citation: Musa, S. I., & de Souza, C. R. (2022). Green Synthesis of Zinc Oxide Nanoparticles Using Leaves Extract of Alchornea cordifolia and Catalytic Degradation of Methyl Orange. International Journal of Chemistry, 13(12), 89–96.