South African Journal of Chemistry 2019-02-26T12:43:06+00:00 Prof. Luke Chimuka Open Journal Systems <p>The journal publishes short communications, full research papers and review articles in all branches of chemistry.</p><p>Other websites associated with this journal: <a title="" href="" target="_blank"></a> </p> Kinetics and Mechanism of Oxidation of N-acetyl-d-penicillamine in Acidified Iodate and Aqueous Iodine 2019-02-26T12:43:02+00:00 Kudzanai Chipiso Trang Duca Reuben H. Simoyia <p>The oxidation of the biologically-active thiol, N-acetyl-d-penicillamine (NDPen) by acidified iodate and aqueous iodine has been studied. The stoichiometry of the reaction is 1:1 in which the thiol (RSH) is oxidized to its sulfonic acid (RSO<sub>3</sub>H) without cleavage of the C-S bond. In excess acidified iodate the reaction displayed a short induction period, followed by formation of aqueous iodine. Overall stoichiometry in excess iodate was 6:5: 6 IO<sub>3</sub> –+5RSH+6H<sup>+</sup>→5 RSO<sub>3</sub>H+3I<sub>2</sub>(aq)+3H<sub>2</sub>O. The direct reaction of aqueous iodine and was relatively fast, over within 100 ms and had a stoichiometry of 1:3: 3 I<sub>2</sub>(aq) + RSH+3H<sub>2</sub>O →RSO<sub>3</sub>H+6 I<sup>–</sup> + 6 H<sup>+</sup>. The reaction is essentially diffusion-controlled and our stopped-flow with a mixing time limitation of 1.00 ms could only catch the reaction of the last iodine molecule. This reaction is, however, strongly inhibited by the product of reaction, I<sup>– </sup>. This is due to the formation of the relatively inert triiodide anion: I2(aq)+I<sup>–</sup>→I<sub>3</sub> –. Mass spectrometry results showed that the reaction proceeds through the sulfinic acid with negligible stabilization of the sulfenic acid. In excess of reductant, the dimeric species is the favoured product due to a rapid condensation-type reaction between the electrophilic unstable sulfenic acid and unreacted thiol.</p><p><strong>Keywords:</strong> Biological thiols, bioactivation, oxidations, oxyhalogen chemistry.</p> 2019-02-26T00:00:00+00:00 Copyright (c) Photocatalytic Activity of MOF-derived Cu<sub>2</sub>O/Cu/C/Ag Porous Composites 2019-02-26T12:43:03+00:00 Wei Chang Dandan Zheng Chaosheng Zhao Yixin Yang <p>Cu<sub>2</sub>O/Cu/C/Ag porous composite was synthesized by heat-treatment and wet-chemical method using a typical metal-organic framework (Cu-BTC) as precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and ultraviolet-visible spectroscopy (UV-vis). The results showed that the original<br />structure of Cu-BTC was retained by high temperature calcination in nitrogen atmosphere. Uniform doping of Cu, C and Ag provided a triple trapping of photogenerated electron hole pairs and the Cu<sub>2</sub>O/Cu/C/Ag exhibited an enhanced photocatalytic activity for degradation of Congo Red under visible light irradiation. Heat-treatment of the MOFs with high temperature is a<br />facile and effective way for preparation of photocatalytic composite with desirable properties.</p><p><br /><strong>Keywords</strong>: Photocatalyst, cuprous oxide, dye degradation, Cu-BTC.</p> Copyright (c) Production and Characterization of Carbon Molecular Sieves from Bituminous Lafia-Obi Nasarawa Coal by Pore Size Modification with Spent Engine Oil 2019-02-26T12:43:04+00:00 E. Bala O.R. Momoh B.O. Aderemi B.J. El-Yakubu <p>In this work, a carbon molecular sieve (CMS) was produced from a bituminous Lafia-Obi Nasarawa coal. An initial activated carbon (AC) sample was prepared via chemical activation from the coal, from which the CMS samples were then produced through heat treatment processes and carbon deposition fromspent engine oil. Spent engine oil was pyrolyzed in order to deposit carbon at the pore mouth of coal-based AC to yield CMS. The effect of reaction temperature and holding time variation on the surface area, micropore pore volume and pore size of CMS was studied. Reaction temperature was varied at 400, 550 and 700 °C while holding time was varied at 30 and 60 min. The Brunauer–Emmett–Teller (BET) method was used to calculate the surface areas, while the Dubinin–Radushkevich (DR) and Horváth-Kawazoe (HK) methods were used to determine the micropore<br />volumes and pore sizes of the AC and CMS, respectively. The CMS sample with the largest BET surface area (5.824 m2 g–1), DR micropore volume (0.172 cm3 g–1) and HK pore size (6.317 Å) were obtained at 700 °C reaction temperature and 60 min holding time. In addition to this, a molecular sieving ability test to separate benzene from a mixture of benzene and o-xylene in solution was carried out on the AC and CMS, with the CMS having a selective benzene percentage uptake of 61.36 %.</p><p><br /><strong>Keywords</strong>: Activated carbon (AC), carbon molecular sieves (CMS), carbon deposition, reaction temperature, holding time.</p> 2019-02-26T00:00:00+00:00 Copyright (c) Comparative Effects of Silver Nanoparticles, Sucrose and Sodium Chloride as Osmotic Solutions for Tomato Slices: Antioxidant Activity, Microbial Quality and Modelling with Polynomial Regression Model 2019-02-26T12:43:05+00:00 Luqmon Azeez Agbaje Lateef Abideen A. Wahab Ayoade L. Adejumo Kawthar Raji <p>This study has reported comparative effects of silver nanoparticles (AgNPs), sucrose and sodium chloride as osmotic solutions on antioxidant activity and microbial quality of 10 mm tomato slices. 40 g of tomato slices were dehydrated osmotically (OD) at different temperatures (60, 70 and 80 °C) and time (30, 60, 90, 120 150 and 180 min).Water loss, solid impregnation, water and solid diffusivities of tomato slices were found to increase with increase in solution temperatures and concentrations with AgNPs having the greatest influence. Antioxidant activities using 2,2-diphenyl-1-picrylhydrazyl increased with increase in solution concentrations but decreased with increase in temperature. Three-wayANOVA(R2=0.998) revealed additive statistically significant effects of osmotic agents, concentrations and temperatures on antioxidant activity; F(8,54)=67.854,P=0.00. Polynomial regression analysis with response surface methodology validated experiments such that for each unit increase in concentration and temperature, antioxidant activity increased with good coefficients of determination; sucrose (R2 = 0.87), NaCl, (R2 = 0.89) and<br />AgNPs (R2 = 0.91). Potato dextrose and nutrient agars were used for isolating and identifying microorganisms in OD tomato slices. Tomato slices dehydrated with AgNPs had the highest microbial inhibition of fungi with growth occurring after 7 days, unlike in treatments with sucrose and NaCl where fungal growth appeared after 2 and 5 days, respectively. Aspergillus niger was the most prevalent fungus. It can be concluded that AgNPs may serve as a viable means to dehydrate and preserve tomatoes without loss of antioxidant activity.</p><p><br /><strong>Keywords</strong>: Osmotic dehydration, polynomial regression, response surface, antioxidant activity, three-way ANOVA, silver nanoparticles.</p> 2019-02-26T00:00:00+00:00 Copyright (c)