International Journal of Chemistry

International Journal of Chemistry | Vol. 8, No. 8, August 2017 | pp. 57–64

DOI: 10.46882/2017/IJC/000107

Article Type: Original Research Paper

Title: Green Corrosion Inhibition of Carbon Steel in Acidic Medium Using Fruit Extract of Solanum melongena

Names of Authors: M. A. Haruna¹, S. K. Bhattacharya²*

Authors’ Affiliations:
¹Department of Chemistry, Federal University of Technology, Minna, Nigeria.
²Department of Chemistry, Indian Institute of Technology, Kharagpur, India.

Abstract: The utilization of toxic synthetic chemical inhibitors in industrial acid descaling operations creates substantial environmental and safety hazards, driving research into sustainable green alternatives. The corrosion mitigation performance of the aqueous fruit extract of Solanum melongena (SM-Extract) on carbon steel in 0.5 M H₂SO₄ was investigated via gravimetric weight loss and electrochemical test protocols. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were recorded across varying inhibitor dosages (0.2 to 2.0 g/L) and system temperatures (303 to 333 K). Weight loss metrics revealed that protection efficiency increased with extract concentration, peaking at 91.4% at a dose of 2.0 g/L. Polarization diagrams established that SM-Extract functions as a mixed-type inhibitor, suppressing both anodic iron dissolution and cathodic hydrogen gas evolution pathways. EIS scans confirmed that charge-transfer resistance (Rct) increased with higher extract amounts, indicating the formation of a robust organic protective film on the steel face. The adsorption behavior of the bioactive compounds conformed to the Langmuir isotherm model, yielding a negative standard free energy of adsorption (delta G°ads = -20.8 kJ/mol), denoting a spontaneous physical adsorption mechanism driven by the presence of rich plant anthocyanins.

Keywords: Carbon steel; Corrosion inhibition; Solanum melongena; Electrochemical impedance spectroscopy; Polarization; Adsorption isotherm

Manuscript Timeline: Received: August 14, 2016; Revised: September 25, 2016; Accepted: October 15, 2016; Published: August 03, 2017.

Citation: Haruna, M. A., & Bhattacharya, S. K. (2017). Green Corrosion Inhibition of Carbon Steel in Acidic Medium Using Fruit Extract of Solanum melongena. International Journal of Chemistry, 8(8), 57–64.

International Journal of Chemistry | Vol. 8, No. 9, September 2017 | pp. 65–72

DOI: 10.46882/2017/IJC/000108

Article Type: Original Research Paper

Title: Development and Validation of an RP-HPLC Method for Quantitative Monitoring of Amoxicillin 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 beta-lactam 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 amoxicillin in capsule dosage forms. Separation was achieved using a C18 stationary phase column under an isocratic mobile phase composed of phosphate buffer (pH 4.0)-acetonitrile (85:15 v/v), at a flow rate of 1.0 mL/min. Eluent monitoring was executed spectrophotometrically at a wavelength maximum of 230 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 amoxicillin brands, producing recovery percentages between 98.6% and 101.4% with no interference from common excipients.

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

Manuscript Timeline: Received: September 02, 2016; Revised: October 12, 2016; Accepted: November 05, 2016; Published: September 09, 2017.

Citation: Effiong, E. O., & dos Santos, L. A. S. (2017). Development and Validation of an RP-HPLC Method for Quantitative Monitoring of Amoxicillin Formulations. International Journal of Chemistry, 8(9), 65–72.

International Journal of Chemistry | Vol. 8, No. 10, October 2017 | pp. 73–80

DOI: 10.46882/2017/IJC/000109

Article Type: Original Research Paper

Title: Synthesis, Molecular Docking, and In Vitro Enzymatic Evaluation of Novel Indole-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 indole-linked chalcone derivatives were synthesized via Claisen-Schmidt condensation of indole-3-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 indole 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: Indole; Chalcones; Acetylcholinesterase; Enzyme inhibition; Molecular docking; Alzheimer's disease

Manuscript Timeline: Received: September 10, 2016; Revised: October 22, 2016; Accepted: November 15, 2016; Published: October 05, 2017.

Citation: Kolawole, O. M., & Smith, E. C. J. (2017). Synthesis, Molecular Docking, and In Vitro Enzymatic Evaluation of Novel Indole-Linked Chalcone Derivatives. International Journal of Chemistry, 8(10), 73–80.

International Journal of Chemistry | Vol. 8, No. 11, November 2017 | pp. 81–88

DOI: 10.46882/2017/IJC/000110

Article Type: Original Research Paper

Title: Thermodynamic Modeling, Desorption Kinetics, and Multilayer Adsorption of Acid Blue 25 Dye onto Modified Smectite 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 anthraquinone dyes like Acid Blue 25 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 smectite clay (SMS) 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 SMS as an affordable material for industrial dye wastewater treatment.

Keywords: Smectite clay; Surfactant modification; Acid blue 25; Adsorption isotherm; Chemisorption; Thermodynamic parameters

Manuscript Timeline: Received: October 02, 2016; Revised: November 15, 2016; Accepted: December 04, 2016; Published: November 09, 2017.

Citation: Yusuf, A. D., & Al-Dosari, M. A. (2017). Thermodynamic Modeling, Desorption Kinetics, and Multilayer Adsorption of Acid Blue 25 Dye onto Modified Smectite Clay. International Journal of Chemistry, 8(11), 81–88.

International Journal of Chemistry | Vol. 8, No. 2, February 2017 | pp. 9–16

DOI: 10.46882/2017/IJC/000101

Article Type: Original Research Paper

Title: Synthesis, Luminescent Properties, and Fluorimetric Detection of Nitroaromatic Explosives Using Novel Terbium(III) β-Diketone Complexes

Names of Authors: A. O. Balogun¹, J. E. Kim²*

Authors’ Affiliations:
¹Department of Chemistry, University of Ilorin, Ilorin, Nigeria.
²Department of Chemistry, Seoul National University, Seoul, South Korea.

Abstract: Rare-earth coordination materials displaying highly sensitive photoluminescent behaviors are increasingly sought for chemical sensor fabrications due to their sharp emission bands and high signal-to-noise ratios. This study reports the synthesis, material characterization, and analytical sensor optimization of a novel terbium(III) complex using 2-thenoyltrifluoroacetone and 1,10-phenanthroline ligands. Structural configurations were verified using elemental analysis, molar conductance, and Fourier-transform infrared (FT-IR) spectroscopy. Analytical calculations confirmed a 1:3:1 metal-to-ligand stoichiometric coordination pattern, conforming to the formula [Tb(TTA)₃(phen)]. Molar conductivity tests in acetonitrile confirmed a completely non-electrolytic layout. Photoluminescence scanning at room temperature showed intense green monochromatic emission peaks at 545 nm, corresponding to the characteristic ⁵D₄ to ⁷F₅ electronic transition of the central Tb(III) ion. The analytical potential of the complex as a fluorimetric sensor for trace nitroaromatic explosives was evaluated in aqueous media. The introduction of picric acid caused immediate, highly selective luminescence quenching of the green emission intensity. The fluorimetric quenching behavior followed the Stern-Volmer relationship with a high quenching constant (Ksv) of 4.5 x 10⁴ M⁻¹ and a low limit of detection (LOD) of 0.18 μM, pointing to a photoinduced electron transfer pathway.

Keywords: Terbium complexes; Rare earth elements; Photoluminescence; Fluorimetric sensor; Nitroaromatic explosives; Stern-Volmer relation

Manuscript Timeline: Received: May 12, 2016; Revised: June 25, 2016; Accepted: July 18, 2016; Published: February 04, 2017.

Citation: Balogun, A. O., & Kim, J. E. (2017). Synthesis, Luminescent Properties, and Fluorimetric Detection of Nitroaromatic Explosives Using Novel Terbium(III) β-Diketone Complexes. International Journal of Chemistry, 8(2), 9–16.

International Journal of Chemistry | Vol. 7, No. 1, January 2016 | pp. 1–8

DOI: 10.46882/2016/IJC/000088

Article Type: Original Research Paper

Title: Development and Validation of a Spectrophotometric Method for Quantitative Determination of Norfloxacin in Pharmaceutical Tablets

Names of Authors: E. O. Effiong¹, J. M. S. Cardoso²*

Authors’ Affiliations:
¹Department of Chemistry, University of Uyo, Uyo, Nigeria.
²Department of Pharmacy, University of Coimbra, Coimbra, Portugal.

Abstract: Developing rapid, low-cost analytical protocols is essential for routine quality monitoring and the detection of substandard antibiotic formulations in clinical testing laboratories. This paper describes the development and validation of a simple UV-Vis spectrophotometric method for the quantification of norfloxacin in tablet dosage forms. The analytical procedure relied on the reaction of norfloxacin with 2,4-dinitrophenylhydrazine in an acidic medium, generating a highly stable yellow-colored hydrazone derivative monitored spectrophotometrically at its absorption maximum of 420 nm. Method validation parameters followed the International Council for Harmonisation (ICH) guidelines. Excellent linearity was established over a concentration range of 2.0 to 25.0 mg/L with a correlation coefficient (R²) of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were determined to be 0.08 mg/L and 0.24 mg/L, respectively. Precision assessments yielded relative standard deviations (RSD) below 1.8%. The validated method was successfully applied to screen five commercial brands of norfloxacin tablets, producing recovery percentages between 98.6% and 101.4% with no interference from common tablet excipients, making it suitable for routine quality control setups.

Keywords: UV-Vis spectrophotometry; Norfloxacin; Chemical derivation; Method validation; Pharmaceuticals; Quality control

Manuscript Timeline: Received: May 02, 2015; Revised: June 15, 2015; Accepted: July 20, 2015; Published: January 03, 2016.

Citation: Effiong, E. O., & Cardoso, J. M. S. (2016). Development and Validation of a Spectrophotometric Method for Quantitative Determination of Norfloxacin in Pharmaceutical Tablets. International Journal of Chemistry, 7(1), 1–8.