Scielo RSS <![CDATA[South African Journal of Chemistry]]> http://www.scielo.org.za/rss.php?pid=0379-435020190001&lang=pt vol. 72 num. lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Kinetics and Mechanism of Oxidation of N-acetyl-d-penicillamine in Acidified lodate and Aqueous Iodine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100001&lng=pt&nrm=iso&tlng=pt 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 (RSO3H) 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 6:5:6IO3- + 5RSH + 6H+ ® 5 RSO3H + 3I2(aq) + 3 H2O. The direct reaction of aqueous iodine and was relatively fast, over within 100 ms and had a stoichiometry of 1:3:3 I2(aq) + RSH + 3H2O ® RSO3H + 6 I- + 6H+. 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-. This is due to the formation of the relatively inert triiodide anion: I2(aq) + I- ® I3-. 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. <![CDATA[<b>Photocatalytic Activity of MOF-derived Cu<sub>2</sub>O/Cu/C/Ag Porous Composites</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100002&lng=pt&nrm=iso&tlng=pt Cu2O/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 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 Cu2O/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 facile and effective way for preparation of photocatalytic composite with desirable properties. <![CDATA[<b>Production and Characterization of Carbon Molecular Sieves from Bituminous Lafia-Obi Nasarawa Coal by Pore Size Modification with Spent Engine Oil</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100003&lng=pt&nrm=iso&tlng=pt 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 from spent 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 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 A) 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 %. <![CDATA[<b>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</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100004&lng=pt&nrm=iso&tlng=pt 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 (30,60,90,120150 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-way ANOVA (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 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. <![CDATA[<b>Kinetics of Oxidation of Triaryl Methane Dye, Brilliant Blue-R with Chlorine Dioxide</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100005&lng=pt&nrm=iso&tlng=pt The fast decolourization of multi-purpose dye, Brilliant blue (BB-) oxidized by chlorine dioxide was investigated using the stopped flow technique under varied pH conditions by monitoring its oxidation kinetics. The products were identified and reaction mechanism is described, which is confirmed by kinetic simulations. Under [ClO2]0 > [OH-]0 > [BB-]0 conditions, the oxidation kinetics showed first-order dependence on BB- and chlorine dioxide. The overall second-order rate coefficient enhanced with increasing pH, and values were 30.2 ± 0.2 M-1 s-1,42.5 ± 0.8 M-1 s-1 and 117.9 ± 0.8 M-1 s-1 at pH 7.0,8.0 and 9.0, respectively. In the pH range 7.0 to 9.0, the catalytic constant for [OH-] catalyzed reaction was 9.0 X 10(6) M-2 s-1 with energy of activation of 50.06 kJ mol-1. Observed negative entropy of activation of -658.73 J K-1 mol-1 suggests the formation a compact transient activated complex. <![CDATA[<b>Determination of Phytocomponents of Twenty-one Varieties of Smokeless Tobacco using Gas Chromatography-Mass Spectroscopy (GC-MS)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100006&lng=pt&nrm=iso&tlng=pt Smokeless tobacco (ST) leaves are being consumed by millions in Middle Eastern countries including Saudi Arabia, Sudan and Yemen, where the locally manufactured form is called shammah. We intended to explore and compare the phytocomponents of 21 different varieties of shammah that are commonly available in different cities of Jazan province of Saudi Arabia using gas chromatography-mass spectroscopy (GC-MS). A total of 61 different constituents were tentatively identified in these samples including both hazardous and non-hazardous compounds. Solvents of different polarity, such as petroleum ether, chloroform, ethanol and water were used to prepare the extracts. Interestingly, a number of new and unusual constituents were identified in some samples. N-methoxycarbonyl-amphetamine was detected as 6.76 %, 4.88 % and 2.58 % of total compounds in Khadrah, Arishi and Sudani shammah samples, respectively. Similarly, the presence of caffeine (0.44-1.41 %) in Adani cold from Jazan city and Abu Arish and Adani hot shammah from Abu Arish suggested the possibility of adulteration. Extremely hazardous arsenic and benzopyran derivatives were present in Sudani shammah from Sabya in small but significant amounts. Furthermore, carcinogenic components were also detected in significant amounts which indicate a relation between ST amounts used and different types of cancer, especially oral cancer. Chemometric hierarchical cluster analysis (HCA) revealed the existence of sufficient differences between samples from different extracts based on the polarity and dendrograms. <![CDATA[<b>Air Sampling: A Mini-denuder Sampling Device for Direct Desorption in an Inlet of a Gas Chromatograph for the Analyses of Airborne Gaseous Phase Pollutants and Airborne Particulate Phase Pollutants</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100007&lng=pt&nrm=iso&tlng=pt We introduce a compact mini-denuder air sampling device consisting of a regular gas chromatograph (GC) inlet liner for the simultaneous concentration of separate airborne gaseous and particulate phases in a single-step. Denuder materials are thermally desorbed in a regular inlet of a GC using routine equipment available in any chromatography laboratory. The simplicity of the technique makes it ideal for resource-poor laboratories. <![CDATA[<b>Molecularly Imprinted Polymer Solid Phase Extraction followed by High-Performance Liquid Chromatography as an Efficient and Sensitive Technique for Determination of Meropenem in Human Plasma and Urine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100008&lng=pt&nrm=iso&tlng=pt A new and selective sorbent for molecularly imprinted polymer solid-phase extraction (MIP-SPE) was prepared to extract meropenem from plasma and urine samples. The extracted analyte was analyzed by high-performance liquid chromatography (HPLC) coupled with photodiode array detection. Methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, azobisisobutyronitrile (AIBN) as an initiator and meropenem as a template molecule were used for the MIP preparation. Imprinted meropenem molecule was removed from the polymeric structure using acetonitrile in water (1:9, v/v), as the eluent solvent. Under the optimized conditions, the limit of detection (LOD) and limit of quantification (LOQ) were 35 and 120μg L-1, respectively. The developed MIP-SPE method demonstrates that it could be applied for the determination of meropenem in plasma and urine samples. <![CDATA[<b>Understanding How Chemistry Teachers Transform Stoichiometry Concepts at Secondary Level in Lesotho</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100009&lng=pt&nrm=iso&tlng=pt This qualitative study sought to investigate how secondary level chemistry teachers transform and represent subject matter knowledge (SMK). The study drew its theoretical framework from the notion of Pedagogical Content Knowledge (PCK) that foregrounds the teachers' ability to transform and represent SMK for students to understand the content presented. Seven qualified chemistry teachers participated in this study which used questionnaires, follow-up interviews, and lesson observations to collect data. The teachers were observed teaching the topic of stoichiometry to grade 11 students. Data analysis started with a coding system that resulted in themes of meanings suggested by teachers. The results show that chemistry teachers participating in the study were aware of different teaching strategies but their choice of those strategies was not informed by an attempt to transform the concepts. It is argued that teachers' failure to transform concepts will have a negative impact on students' understanding of these concepts. <![CDATA[<b>A Liquid-Solid Two-phase Flow Computational Fluid Dynamic Modelling of the Operational Characteristics Effects on the Cleaning Time of a Circulating Flow Loop</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100010&lng=pt&nrm=iso&tlng=pt Flow loops and computational fluid dynamics are the main research approaches for resolving the hole-cleaning problems. Cutting transport phenomena can be considered as a Computational Fluid Dynamic (CFD) model by using Eulerian assumptions for the turbulent liquid-solid flow in concentric annuli. The effect of time along with the main operational characteristics on the hole-cleaning phenomena is not negligible but recent studies have had paid little attention to it. Poor near bit cleaning causes many problems such as bit balling, decline in the rate of penetration, pipe sticking, etc. In addition to the effect of inclination, drill pipe rotary speed, cutting size, nozzle velocity and fluid viscosity as well as the effect of the bit nozzle arrangement on the cutting transport process were discussed. The results demonstrate that at a critical inclination angle of 30 degrees the cutting transport is inefficient. For all sections, the effect of drill pipe rotary speed was negligible at high velocities. In the horizontal section, at low flow rates and high drill pipe rotation speeds, Newtonian viscous fluids or water has no effect on the time needed for initial hole-cleaning butby removing the drill pipe rotation speed in similar conditions, a dramatic influence on time is observed. In inclined annuli, increasing the cuttings size and decreasing the nozzle velocity result in having no cutting in the output. Under critical inclination (30 degrees) the effect of the nozzle angle pattern on the hole-cleaning time is negligible. However, for a vertical annulus, the nozzle angle significantly influences the cutting transport. The best performance is obtained when the nozzle angle was perpendicular to the drill pipe axes. <![CDATA[<b>Co-encapsulation of Rifampicin and Isoniazid in Crude Soybean Lecithin Liposomes</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100011&lng=pt&nrm=iso&tlng=pt Despite the well-known anti-mycobacterial actions of isoniazid (INH) and rifampicin (RIF), the clinical success of tuberculosis (TB) therapy requires prolonged administration of multiple drugs in high doses, which often result in frequent adverse effects and low patient adherence. Although liposomes are promising candidates for controlled delivery of anti-TB drug, the high cost of synthetic and highly purified natural lipids currently used in liposomal technology might preclude the universal application of therapeutic liposomes. This work aimed at evaluating the potential of a cost-effective lipid material, crude soybean lecithin (CL), to co-encapsulate RIF and INH for liposomal dual delivery. RIF was encapsulated in CL-liposomes with/without cholesterol using film hydration method, after which INH was incorporated using a freeze-thawing technique. Dynamic light scattering, differential scanning calorimetry, X-ray diffraction and dialysis were used for liposome characterization. Liposomes containing CL alone (CLL) exhibited 90 % encapsulation efficiency for RIF and 59 % for INH. The mean size and surface charge of CLL were 1114 nm and -63 mV respectively. In addition, CLL showed a controlled release profile for the co-encapsulated drugs. CLL would be promising vehicles for macrophage-targeting drug delivery. The present findings demonstrate the feasibility of using CL for preparation of combination products for liposomal delivery. <![CDATA[<b>Selective Removal of Organonitrogen Compounds in Fuel using Functional Polybenzimidazole Nanofibres: A Combined Experimental and Theoretical Study</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100012&lng=pt&nrm=iso&tlng=pt Organonitrogen compounds present in fuel oils are deleterious to the environment as well as refining catalysts. Herein, functional polybenzimidazole (PBI) nanofibres fabricated in the presence of N-compounds (nitrogen-containing compounds) were employed for the selective adsorption of quinoline, pyrimidine and carbazole, largely found in diesel fuel. Adsorption capacities of 11.5 mg g-1,11.8 mg g-1 and 11.0 mg g-1 were observed for pyrimidine, carbazole and quinoline, respectively. Density functional theory (DFT) studies indicated π-π interactions/stacking and hydrogen bond interactions between the nitrogen atom of N-compounds and PBI. The study clearly shows the potential of PBI material use for the selective removal of organonitrogen compounds in fuels. <![CDATA[<b>Mononuclear Schiff Base Complexes Derived from 5-Azophenylsalicylaldehyde with Co(II), Ni(II) Ions: Synthesis, Characterization, Electrochemical Study and Antibacterial Properties</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100013&lng=pt&nrm=iso&tlng=pt In the present research, 1,2-di[N-2-phenylthio-5-azophenylsalicylidene]ethane (H2L¹, 1,3-di[N-2-phenylthio-5-azophenylsali-cylidene]propane(H2L²) and 1,4-di[N-2-phenylthio-5-azophenylsalicylidene]butane (H2L³) were synthesized. ML¹,ML² and ML³ complexes were prepared through the reaction of H2L¹,H2L² and H2L³ with Ni(II) and Co(II) acetate salts. The prepared ligands and their complexes were characterized with FT-IR, ¹H-NMR, elemental analysis, conductivity and magnetic measurements, ESI-mass, UV-Vis spectroscopy and cyclic voltammetry. The complexes had monomeric structure according to the mass spectral data. All of the complexes had a six-coordinated octahedral geometry. The electrochemical behavior of the ligands, Ni(II) and Co(II) complexes was investigated by CV in DMF under argon atmosphere. The results show that the coordination of Ni(II) causes the ligands to be deactivated. The voltammogram of Co(II) complexes shows that the reduction of CoL¹ is harder than CoL³ and CoL² is inactive. Their antibacterial activity was investigated and the complexes exhibited better antibacterial activity than the free ligands against selective bacteria. <![CDATA[<b>Development of a Thiol-capped Core/Shell Quantum Dot Sensor for Acetaminophen</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100014&lng=pt&nrm=iso&tlng=pt Acetaminophen (AC) is a frequently used pharmaceutical which has been detected in water systems and is of concern due to its potential environmental impacts. In this study, three quantum dot (QD)-ligand systems, namely L-cysteine (L-cys)-, N-acetyl-L-cysteine (NAC)- and glutathione (GSH)-capped CdSe/ZnS quantum dots, were synthesized and tested for the fluorescence detection of acetaminophen. Among the synthesized aqueous core/shell quantum dots, L-cys-CdSe/ZnS QDs were found to be optimal with high sensitivity for the fluorescence detection of acetaminophen. The L-cys-CdSe/ZnS QDs were of a zinc blende crystal structure and displayed excellent fluorescence intensity and photostability and provided a photoluminescence quantum yield of 77 % . The fluorescence of L-cys-CdSe/ZnS QDs was enhanced by the introduction of AC enabling the development of a fast and simple method for the detection of AC. Under optimal conditions, F-F0 was linearly proportional to the concentration of AC from 3.0-100 nmol L-1 with limits of detection and quantification of 1.6 and 5.3 nmol L-1, respectively. Some related pharmaceutical compounds including epinephrine hydrochloride (EP), L-ascorbic acid (AA), uric acid (UA), dopamine hydrochloride (DA) and 4-aminophenol (4-AP) did not interfere with the sensing of AC. The probe was also successfully applied in the determination of AC in tap and river water matrices. <![CDATA[<b>Calcination of Precipitated Calcium Carbonate with Surfactant-assisted Agglomeration - A Non-isothermal Topochemical Approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100015&lng=pt&nrm=iso&tlng=pt It has been shown that precipitated calcium carbonate prepared by surfactant-assisted agglomeration (PCC-SAA) provided higher capacity for the carbon dioxide capture during calcination carbonation cycling as compared to commercially available calcium carbonate. It was also shown previously that the capacity was maintained over multiple cycles while commercially available calcium carbonate significantly lost its capacity. In order to understand the differences in the calcination behaviour of the PCC-SAA sample as compared to the commercially available laboratory-grade calcium carbonate (AC) sample, a non-isothermal topochemical approach was adopted to delineate the various controlling mechanisms for calcination of CaCO3. Activation energies were calculated using iso-conversional methods such as Friedman's method, the KSA method, and the FWO method. In addition, the mechanism was identified at different heating rates by applying the Malek's method and evaluated in some cases using the JMA kinetics. Finally, four mechanisms were used to calculate the pre-exponential (frequency factor). Some key differences such as the initiation temperature, and mechanisms were found between the two samples. Generally, it was found that the differences in the two samples were primarily due to the structural causes. It was observed that the initiation temperature for CaCO3 decomposition, activation energies and mechanisms were a function of the heating rates. D2 or D4 was identified as the controlling mechanisms at lower temperatures for the PCC-SAA sample in contrast to JMA (n > 1) kinetics for the higher heating rates. For the AC sample, 3D diffusion process appears to control the calcination of the AC sample. <![CDATA[<b>Liquid Chromatographic Determination of Dexamethasone and Fluoroquinolones; <i>in vitro </i>Study</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100016&lng=pt&nrm=iso&tlng=pt A precise, accurate and sensitive liquid chromatographic method is presented for the simultaneous analysis of moxifloxacin, levofloxacin, ciprofloxacin and dexamethasone in reference drugs, ophthalmic dosage form and in physiological fluids. Separation was achieved on a C1(8)analytical column with acetonitrile-phosphate buffer (35:65 v/v) as mobile phase which was pumped isocratically at a flow rate of 1.0 mL min-1 and monitored at 254 nm wavelength. The calibration curve was linear in range of 40-10 000 ng mL-1. Test results in pharmaceutical and physiological samples showed excellent drug recovery (96.5-102.3 %) with good precision (0.81-2.3 % RSD). Test results were linear to sample concentration and correlation coefficient was more than 0.9990. The small value of quantification and detection levels showed the method to be sensitive enough for use in clinical and industrial investigations of all the mentioned drugs. <![CDATA[<b>Caffeine and Ciprofloxacin Adsorption from Water onto Clinoptilolite: Linear Isotherms, Kinetics, Thermodynamic and Mechanistic Studies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100017&lng=pt&nrm=iso&tlng=pt In this study, clinoptilolite was used to sequester ciprofloxacin (CIP) and caffeine (CAF), two emergent contaminants, from aqueous solution using batch equilibration method and the effects of contact time, pH, initial contaminant concentration, temperature and adsorbent dosage investigated and herein reported. The adsorption kinetics was described by the pseudo-second-order model (PSO) and pore diffusion was not the sole operative rate-controlling step as depicted by the intraparticle diffusion model. The equilibrium data were modelled using three linear forms of Langmuir equation and Freundlich model and was best fitted by the Lineweaver-Burk linearization of Langmuir equation (type-1). Linearization is shown to induce errors that may lead to discrepancies in parameter values estimation. The derived thermodynamic functions revealed the adsorption processes are exothermic, spontaneous and physical in nature. The adsorption mechanism of CIP is strongly controlled by electrostatic interactions while CAF adsorption is weakly affected by changes in pH. The findings demonstrate that clinoptilolite in its unmodified form is a potential low-cost and eco-friendly adsorbent for removal of pharma-ceutically active ingredients from water. <![CDATA[<b>An Investigation into the Corrosion Rates of Inconel 600</b><b>™</b><b> in Different Corrosive Solutions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100018&lng=pt&nrm=iso&tlng=pt Inconel 600™, an austenitic high nickel alloy, has relatively low corrosion properties and is used extensively for aerospace and nuclear engineering applications. Other applications include exposure of the material to caustic and acidic environments and possible use in prosthetic implants. Electrochemical techniques, which include potentiodynamic polarization and polarization resistance, provide a means to rapidly determine the corrosion rates and the suitability of the alloy in a specific corrosive environment. The results from these two techniques were used to determine the corrosion rates as well as other thermodynamic properties for the alloy exposed to various strong and weak acids, salt and Ringer's solution. The results showed slight differences in the corrosion rates determined by the two electrochemical techniques, with those from the polarization resistance technique being on average larger. The corrosion activation energies determined for the alloy in different solutions were indicative of the corrosion rates with some anomalies in values for results observed in the 10 % acetic acid solution. The microstructural composition of the alloy was also investigated by SEM-EDS and showed peculiar inclusions that can contribute to an acceleration of the corrosion rates. <![CDATA[<b>Concentration of Total Mercury in Convenience Fish Products and Cooked Fish</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100019&lng=pt&nrm=iso&tlng=pt Convenience fish products are very popular culinary items among South African customers because they do not require any preliminary preparation before cooking. To the best of our knowledge, convenience fish products had never been a subject of analysis for mercury (Hg) content in South Africa. A Zeeman Mercury Analyzer was used for direct determination of Hg in these products after thermal decomposition of samples followed by atomic absorption detection. The Hg concentrations in convenience fish products, namely 'Hake crumbed AA portions' and 'Hake AA portions' was found to be at a very low level (8.2 ± 1.1 ng g-1), and in the other convenience fish products 'Fish bites' and 'Battered mince portions' it was in the range of 48-64 ng g-1. In 'ready to eat' deep-fried fish, the concentrations of Hg varied in a much wider range (from 55 to 306 ng g-1). To estimate the health risk associated with Hg in these products, the safe amount of cooked in-store fish and convenience fish products have been calculated. <![CDATA[<b>Combining Alkali and Peroxide for Pretreatment of Sugarcane Wastes, Bagasse and Trash, for Bioethanol Synthesis</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100020&lng=pt&nrm=iso&tlng=pt The use of agricultural waste material in the production of bioethanol can provide an alternative to fossil fuels that is renewable and readily available. This research sought to use a combination of chemical pretreatments to make available reducing sugars from sugarcane bagasse and trash for fermentation into bioethanol. A combination of alkali and peroxide was used. These results indicate that pretreatment with alkali peroxide is quite effective in reducing the levels of hemicellulose sugars and lignin in particular. The slight changes in cellulose quantities are an indication that alkali peroxide preatreatment conserves the quantities of cellulose and does not result in a loss in cellulose as compared to other pretreatment processes such as acid hydrolysis. The drawback is that this can also mean that the crystalline structure of the cellulose was not disturbed, which could slow down downstream processes of enzyme hydrolysis and subsequent fermentation. The pretreated bagasse contained significantly higher levels cellulose of 48 % and 63 % after pretreatment with 3 % and 5 % alkali peroxide, respectively. This represents a 28 % increase and a 70 % increase, respectively, in available exposed cellulose for use in further processes of enzyme hydrolysis and fermentation. <![CDATA[<b>Synthesis of Indeno[1,2-<em>b</em>]benzofurans using TPAB as Highly Efficient and Recoverable Catalyst</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100021&lng=pt&nrm=iso&tlng=pt Herein we report the synthesis of some novel indeno[1,2-b]benzofuran derivatives by reaction of ninhydrin with cyclic 1,3-dicarbonyl compounds including cyclopentane-1,3-dione, cyclohexane-1,3-dione, dimedone, 4,4-dimethylcyclohexane-1,3-dione, meldrum's acid, barbituric acid, thiobarbituric acid, 1,3-dimethylbarbituric acid and indane-1,3-dione. We also used tetra-propylammonium bromide (TPAB) as an organocatalyst. <![CDATA[<b>Experimental, Statistical Modelling and Molecular Dynamics Simulation Concept of <i>Sapium ellipticum </i>Leaf Extract as Corrosion Inhibitor for Carbon Steel in Acid Environment</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100022&lng=pt&nrm=iso&tlng=pt The inhibitive performance of Sapium ellipticum leaf extract as green corrosion inhibitor for carbon steel in varying concentrations in hydrochloric acid has been investigated. To determine the adsorption strength and phenomenon of inhibition, density functional theory was adopted to model the molecular structure of the extract. Also to evaluate the inhibition efficiency weight loss, electrochemical method and statistical modelling was employed. Optimum inhibition efficiency of 89 % was achieved from electrochemical study atconditions of 1.5 g L-1 SE concentration, temperature of 303 K and 1M HCl, respectively. The electrochemical study signifies that the phenomenon of inhibition is under mixed control and the inhibition process is in accordance with Langmuir isotherm. Fourier transform infrared spectroscopy (FTIR) of the corrosion particles and surface examination (SEM) confirms the existence of the protective film on the metal surface through the adsorption of extract species. <![CDATA[<b>Molecular Structure, FT-IR, NMR (<sup>13</sup>C/<sup>1</sup>H), UV-Vis Spectroscopy and DFT Calculations on (2Z, 5Z)-3-N(4-Methoxy phenyl)-2-N'(4-methoxy phenyl imino)-5-((E)-3-(2-nitrophenyl)allylidene) thiazolidin-4-one</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100023&lng=pt&nrm=iso&tlng=pt In this study, some molecular properties of (2Z, 5Z)-3-N(4-methoxy phenyl)-2-N'(4-methoxy phenyl imino)-5-((E)-3-(2-nitro-phenyl) allylidene) thiazolidin-4-one (MNTZ) are evaluated using a combination of spectroscopic characterization (FT-IR, ¹H and 13C NMR chemical shifts) and theoretical calculations. Molecular geometry, vibrational wavenumbers, gauge-independent atomic orbital (GIAO), ¹H and 13C chemical shift values and NBO analysis are investigated using B3LYP and PBE functionals with the 6-31G(d,p) basis set in the ground state. The calculated geometrical parameters and vibrational spectra are compared to available experimental data and each vibrational frequency is assigned on the basis of potential energy distribution (PED). The electronic transitions are calculated using time-dependent density functional theory (TDDFT). The energy band gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies are obtained by computing the frontier molecular orbitals using the B3LYP/6-31G(d,p) and PBE/6-31G(d,p) levels along with the global reactivity descriptors. Mulliken atomic charges and molecular electrostatic potential (MEP) are simulated using both functionals to find more reactive sites for electrophilic and nucleophilic attack. Finally, the thermodynamic functions (heat capacity, entropy, and enthalpy) from spectroscopic data are obtained and discussed in the range of 100-1000 K. <![CDATA[<b>Kinetic Approach to Determine 3-Amino Methyl Hexanoic Acid in Pharmaceutical Formulations</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100024&lng=pt&nrm=iso&tlng=pt A simple and sensitive colorimetric spectrophotometric method based on application of chemical kinetics was produced and developed for the quantitative determination of 3-amino methyl hexanoic acid (pregabalin) in bulk and pharmaceutical preparations. Ninhydrin, a chromogenic agent was reacted with pregabalin at 70 °C and the absorbance was measured at 575 nm and kinetic correlation was evaluated between absorbance and time. The initial-rate, rate-constant and fixed-time (80 min) methods were employed for the estimation of pregabalin in the range of 10-30ug mL-1 which showed good correlation &gt;0.9990 in all three cases with LOQ values ranging from 1.2-1.5 mL-1and LOD values ranging from 0.76-0.95 mL-1. Method validation was carried out using ICH recommendations and the variables were evaluated and optimized. The newly developed method has useful applications to determine pregabalin in pharmaceutical formulation with good recovery (98.38 to 102.12 %t) and precision (RSD < 1.4 %). Standard free energy changes and association constant were found to be 1.212 X 10³ and -4.747, respectively, as determined by the Benesi-Hildebrand equation. <![CDATA[<b>2,4-Dioxo-1,3-diazaspiro[4,5]decane-3-sulfonic Acid as a Novel Solid Phase Halogen-free Acid Catalyst: Preparation, Characterization and Evaluation</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100025&lng=pt&nrm=iso&tlng=pt N-sulfonated cyclohexylhydantoin (NSCH), a new N-sulfonic acid compound, was prepared and characterized using FT-IR, NMR, 13C NMR, UV-Vis and TGA analysis. The potential catalyst efficiency was examined, using synthesis of chromene, xanthene and hydroquinoline derivatives under solvent-free conditions. All of the examined model reactions gave excellent yields, and required short reaction times. Simple catalyst preparation and work-up under mild reaction condition, with low cost and the ability to recover the catalyst for reuse without significant loss of activity are some of the notable advantages of the introduced catalyst. <![CDATA[<b>The South African Journal of Chemistry 1918-2018: A Celebration</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100026&lng=pt&nrm=iso&tlng=pt In celebration of the centenary of the first publication of the South African Journal of Chemistry, the history of the Journal is traced, with reference to the personalities involved in its development and its relationship with the South African Chemical Institute. The impact of online publishing on the format of the Journal and the ways in which the handling of submitted manuscripts have changed over time are discussed. Some statistics are presented illustrating the changing topicality of the various chemistry disciplines over time, as well as the expansion of the potential pool of authors arising from the internationalization of the scientific publishing field. Reference is also made to the quantitative measures by which the integrity and international acceptance of the Journal are judged. <![CDATA[<b>Un-functionalized Gold Nanoparticles as a Simple Colorimetric Probe for Sensitive and Selective Detection of Dopamine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100027&lng=pt&nrm=iso&tlng=pt A dopamine (DA) colorimetric probe based on the growth and aggregation of un-functionalized gold nanoparticles (AuNPs) is reported. Upon addition of AuNPs to dopamine at various concentrations, the shape, size and colour change of the nanoparticles results in spectral shifts to higher wavelengths and hence colour change is the mode of detection. The colour change can be easily observed by the naked eye from as low as 5.0 nM DA, even under sub-optimal conditions. Under optimal pH conditions the calculated limit of detection was 2.5 nM (3σ). The probe was successfully applied to whole blood sample and showed good selectivity and sensitivity towards DA. The simple, sensitive and selective probe could be an excellent alternative for on-site and immediate detection of DA without the use of instrumentation and would thus be useful for rapid diagnostic applications. <![CDATA[<b>Structural and Morphological Behaviour and Study of the Colorimetric and Reflective Properties of Commercial Inorganic Pigments</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100028&lng=pt&nrm=iso&tlng=pt Characterization of colourful materials must include reflective, spectroscopic and colorimetric properties. Therefore, powder commercial pigments (Xadrez®) were investigated to identify their structure, morphology, composition and real colour, in order to use them as patterns to new materials. Results from X-ray diffraction, X-ray fluorescence spectroscopy and electronic spectros-copy indicated the compounds that give colour to the pigments brown, red, yellow and black as, generally, iron oxides, in the phases hematite (a-Fe2O3), goethite (a-FeOOH) and magnesium ferrite (MgFe2O4), in different proportions. Meanwhile, blue and green pigments contained copper phthalocyanine and other compounds responsible for their colour. Commercial pigments presented different degrees of solar reflectance: the highest value was 44.7 % to white pigment and the lowest 2.2 % to black pigment. Colorimetric data made it possible to calculate the real colour of the pigments, using the free software of ColorMine library, and, then, to assess the colour of new synthetic pigments. <![CDATA[<b>Control of Electric Dipole Moment using Deformation induced by Functionalization of (5, 0) Zigzag Carbon Nanotubes as Gigahertz Oscillators</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100029&lng=pt&nrm=iso&tlng=pt Electric dipole moment (EDM) required for the relative motion of carbon nanotube (CNT) walls in nanoelectromechanical systems (NEMS) such as actuators and oscillators is studied by functionalization. Pristine (5,0) zigzag carbon nanotube with little inherent electric dipole moment (ì) were deformed by adding three -OH functional groups to its end rims. The properties of eight yielded isomers are studied. The Gibbs free energy calculations demonstrate that the eight structures are more stable than pristine CNT. The induced deformation resulted in charge imbalances which developed large electric dipole moments for each case. The values of dipole moments produced for all cases are calculated. The bandgap energy, conductivity, density of state (DOS) and IR spectra of these structures are also computed and analyzed. The study revealed that the location of the -OH positioning (site selectivity) which gives rise to different degrees of deformation has a significant impact on all of the above parameters, especially the magnitude and direction of the electric dipole moment. The functionalization produced large ì of about 6.9 D for 60 carbon atoms nanotube which is higher than in the previous study. Applying an external electric field to the isomers causes the CNTs with large dipole moments to either get attracted or repelled and hence physical movement or oscillation of the nanotube occurs. The frequency of this oscillation is in gigahertz scale. <![CDATA[<b>Speciation Study of L-ascorbic Acid and its Chelated Cu(II) & Ni(II) Complexes: an Experimental and Theoretical Model of Complex Formation</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100030&lng=pt&nrm=iso&tlng=pt Different species of L-ascorbic acid and their corresponding complex formation ability with Cu(II) and Ni(II) metal ions in aqueous medium has been studied in the pH range from 2.0-12.5. The stability constants of different complexes of Cu(II) and Ni(II) with the bidentate ligand, L-ascorbic acid were determined theoretically using MINIQUARD software. Speciation of ligand and complex of Cu(II)/Ni(II) ascorbate were experimentally investigated by the titration method in solution within this pH range. Different Cu (II) and Ni(II)-L-ascorbic acid species percentages with variation of pH were calculated within the studied pH range with the help of another computer programs SIM and SPECIES. Different species distribution diagrams and the equilibria for the formation of the species were also investigated and at higher pH, ML2 species was found to be the major species in the case of both the metal complexes. All the theoretical possible structures of Cu(II) and Ni(II) complexes with L-ascorbic acid were optimized and square pyramidal and square planer geometry have been evaluated for Cu(II) and Ni(II) respectively by Gaussian09 software. Their corresponding HOMO-LUMO energy and reactivity parameters such as chemical hardness (ç), ionization potential (I), electron affinity (A), electro negativity (χ), chemical potential («), electrophilicity index (ω) have been calculated in order to provide a better understanding of the electronic structure of complexes with the experimental results. <![CDATA[<b>Solvent Extraction of a South African Bituminous Coal using a Model Biomass-derived Phenolic Mixture</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502019000100031&lng=pt&nrm=iso&tlng=pt A model biomass-derived phenolic mixture was investigated for its solvent ability for extraction of a South African bituminous coal at temperatures of 300-360 °C. A previous study showed that phenol gave the highest extraction yield of 49.5 wt. % (daf) for bituminous coal at 360 °C, with an oil yield of 26.3 wt. % (daf). The phenolic products produced from sweet sorghum bagasse via an alkaline liquefaction process were identified and reported earlier and a model biomass-derived phenolic mixture was formulated, evaluated and results used in this study. The model mixture gave an extraction yield of 37.1 wt. % (daf) and oil yield of 16.9 wt. % (daf) at 360 °C. This solvent mixture was found to be less effective for high extraction yields when compared to phenol at mild temperatures. This could be due to phenol being a better hydrogen carrier than the solvent mixture during the internal redistribution of hydrogen in the coal. The infrared spectroscopy results of the coal and extraction products obtained using the model mixtures showed similar functional groups. These results demonstrate that the use of a model biomass-derived phenolic mixture has the potential to depolymerize coal and produce high-value chemicals from coal.