Scielo RSS <![CDATA[South African Journal of Chemistry]]> vol. 73 num. lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Photocatalytic Degradation of Direct Red 16 Dye using Ag/Ag<sub>3</sub>VO<sub>4</sub>/AgVO<sub>3</sub>/GO Nanocomposite</b>]]> In this research, synthesized Ag NPs/Ag3VO4/AgVO3/GO was applied as a visible-light sensitive photocatalyst for photocatalytic degradation of Direct Red 16 dye (DR16) from aqueous solutions. The synthesized nanocomposite was analyzed by XRD, FESEM, TEM, EDX and Dot mapping. The effect of DR16 dye concentration, AgNPs/Ag3VO4/AgVO3/GO dosage, time and pH on photocatalytic removal of DR16 were studied. Results revealed thatpH, dosage and DR16 concentration are more important parameters than time on photocatalytic removal of the dye. The results indicate that 58.98 % of DR16 removal was obtained under the following optimized conditions: DR16 concentration = 32 mg L-1; Ag NPs/Ag3VO4/AgVO3/GO dosage = 0.2 g 50 mL-1; pH = 4.5; 300 W visible light for 155 min. So, it was concluded that the new nanocomposite can be used as an efficient visible-light photocatalyst for degradation of Direct Red 16 dye. <![CDATA[<b>The Activities of the Eastern Province Section of the South African Chemical Institute 1935-1965</b>]]> This article traces the activities of the Eastern Province (EP) Section of the South African Chemical Institute (SACI) from its founding in 1935 to the formation of the University of Port Elizabeth in 1965. The EP Section was only the third Section of the Institute to be formed in South Africa and was very active with regular meetings being scheduled. These meetings dealtpredominantly with industrial and applied chemistry topics, indicating very strong interaction between industry and the Chemical Institute. Pure academic topics were presented under the auspices of the Chemistry Department of Rhodes University in Grahamstown (Makhanda). During this period, the EP Section hosted three National Conventions and produced two Presidents of SACI. <![CDATA[<b>C-H activation</b><b>: </b><b>a Critical Evaluation of a Published Method and its Application Towards Inherently Chiral Calix[4]arenes</b>]]> C-H activation offers an intriguing access into inherently chiral calix[4]arenes, but has been little explored in the literature. In this article, we report our investigation into a published C-H activation method that uses carbamates to direct a palladium catalyzed C-H activation and subsequent reaction with N-bromosuccinimide. However, we show that this report is unfortunately flawed on a number of points. An earlier reported study revealed the more likely S E Ar mechanism of the bromination reaction, which did not involve palladium catalysis. We nevertheless employed the S E Ar bromination in an attempt to form inherently chiral calix[4]arenes, using a chiral (+)-menthyl carbamate as a directing group. Unfortunately, although the reaction was high yielding, the diastereomers formed were inseparable and we were unable to quantify their ratio. Subsequent removal of the chiral (+)-menthyl carbamate, returned a small positive optical rotation, suggesting that at least a level of asymmetric induction was achieved in the bromination to afford a non-racemic product. <![CDATA[<b>Flower of <i>Typha latifolia </i>as a Low-cost Adsorbent for Quantitative Uptake of Multiclass Pesticide Residues from Contaminated Waters</b>]]> The quantitative removal of atrazine, diazinon, chlorothalonil, ametryn, chlorpytrifos and dimethametryn from contaminated water was studied using flower of the Typha latifolia. The surface chemistry of this adsorbent was analyzed by FT-IR and the adsorption efficiency was studied using batch adsorption technique. The potential experimental parameters studied were pH (5-9), the dose of adsorbent (0.1-0.5 g), contact time (100-140 min), shaking speed (100-300 rpm) and initial pesticide concentration (3.15-100 jug L-1). The effects of concentration and contact time at the optimum conditions were used to study equilibrium and kinetic models for pesticide sorption. Results of the sorption equilibria were found to fit better to the Langmuir isotherm model than the Freundlich adsorption model indicating monolayer homogeneous surface conditions. On the other hand, kinetics of all pesticides sorption on the adsorbent was well defined by the pseudo-second-order model. The results obtained showed that the use of this plant be considered as one of the promising, natural, easily accessible and low-cost adsorbent for efficient and quantitative removal of pesticides from contaminated water. <![CDATA[<b>Formation of 3,3,4-Trimethyl-1,7-dibromonorbornane-2-one: a Spectroscopic and Computational Study</b>]]> The structure and origin of the major by-product in the synthesis of 8-bromocamphor from (+)-3,3,8-tribromocamphor has been confirmed using NMR, coset and single crystal X-ray analysis and DFT-level computational techniques. <![CDATA[<b>Ultrasound Promoted Stereoselective Synthesis of 2,3-Dihydrobenzofuran Appended Chalcones at Ambient Temperature</b>]]> In the present investigation, an ultrasound promoted the synthesis of a series of (£)-3-(2,3-dihydrobenzofuran 5-yl)-1-(aryl)prop-2-en-1-one derivatives from 2,3-dihydrobenzofuran-5-carbaldehyde and various aromatic ketones under clean conditions. The application of ultrasound irradiation in organic reactions is one of the incredible tools of green chemistry as reactions can be carried out rapidly under neat conditions. A library of a novel (E)-3-(2,3-dihydrobenzofuran-5-yl)-1-(aryl)prop-2-en-1-one chalcone derivatives were synthesized in good to excellent yield under ultrasonic irradiation. The structures of all synthesized chalcone derivatives synthesized in this study have been established by using FT-IR, ¹H NMR, 13C NMR, and HRMS techniques. The stereochemistry around C=C in the chalcones was shown to be trans by 'HNMR (Jab = 15.5Hz). The benefits of the present synthesis include mild reaction conditions, high yield, purification by non-chromatographic strategy and short reaction times, demonstrating the significance of this protocol in terms of waste reduction and energy efficiency. <![CDATA[<b>A Spectroscopic, Thermodynamic and Molecular Docking Study of the Binding Mechanism of Dapoxetine with Calf Thymus DNA</b>]]> Dapoxetine is a selective serotonin reuptake inhibitor, used to treat premature ejaculation in men. Dapoxetine may interact with the DNA and hence this study investigated dapoxetine and calf thymus DNA (ctDNA) binding interaction. The interaction study of ligands to DNA is of importance in the development of molecular probes and therapeutic agents. Spectroscopic techniques including spectrofluorometry and spectrophotometry were employed to study this interaction. Fluorescence studies indicated a static quenching mechanism between dapoxetine and ctDNA. Groove binding was suggested as the mode of interaction between dapoxetine and ctDNA based on UV absorption, circular dichroism (CD) spectroscopy, iodide quenching and molecular docking studies. The studies conducted at three different temperatures 298,303 and 310 K indicated a strong binding interaction at higher temperatures. Thermodynamic studies conducted indicated involvement of hydrophobic interaction between ctDNA and dapoxetine and were entropy-driven. Ethidium bromide probe study suggested that dapoxetine does not bind to ctDNA in an intercalative fashion. Iodide quenching studies further proved the non-intercalative binding of ctDNA with dapoxetine. Ionic strength studies conducted ruled out the electrostatic binding mechanism between ctDNA and dapoxetine. Molecular docking analysis performed for the dapoxetine with calf thymus DNA (ctDNA) interaction and confirmed minor groove binding of dapoxetine to ctDNA. The study helped to reveal the binding interaction mechanism between dapoxetine and ctDNA. <![CDATA[<b>Effect of <i>Telfaira occidentalis </i>Leaf Extract on Packed Cell Volume in Rats with Malaria-induced Anaemia</b>]]> The bioactive ingredients in most malarial drugs only reduce plasmodium load during chemotherapy. No anti-malarial drug replenishes the red blood cells destroyed by Plasmodium. This creates a need to incorporate bioactive components with haematinic property in malaria therapy. This study aimed to assess the effect of T. occidentalis leaf extract on packed cell volume (PCV) of rats with malaria-induced anaemia. Anaemia was induced in the rats by inoculating them with Plasmodium berghei. The effect of the plant extract on the PCV of the rats was determined alongside a negative and a positive control. Also, the effect of varying doses of the extract on PCV of the rats was determined. T. occidentalis leaf extract produced a 22 % increase in the post-inoculation PCV of rats. The negative and positive control groups showed a 37 % and 25 % decrease, respectively, in PCV Also, PCV increased with increase in extract dose administered. <![CDATA[<b>A Novel Biopolymer-based Nanomagnetic Catalyst for the Synthesis of 4H-pyran and Tetrahydro-4H-chromene Derivatives</b>]]> In the present study, we have designed and synthesized a new magnetically recoverable, nanocatalyst of Ag/Fe3O4@starch. The successful synthesis and the structure of the nanocatalyst were confirmed and evaluated with several analytical techniques including XRD, EDX, VSM, FT-IR, TEM and TGA. The impact and efficiency of Ag/Fe3O4@starch were successfully investigated in the one-pot synthesis of desired 4H-pyrans and tetrahydro-4H-chromenes using three-component condensation of various aldehydes, malononitrile, and 1,3-diketoesters or cyclic 1,3-diketones. The magnetic nanocatalyst was easily recovered and reused with high catalytic activity even after up to five runs. <![CDATA[<b>Synthesis and Characterization of Zeolites Produced by Ultrasonication of Coal Fly Ash/NaOH Slurry Filtrates</b>]]> Studies were conducted to determine if crystalline zeolites could be obtained from the filtrates of coal fly ash (CFA)/NaOH slurries through sonication. The CFA/NaOH slurries were obtained by aging CFA in 3 M NaOH for 24 h at 50 °C using a solid/ liquid (S/L) ratio of 15 g/120 mL. FT-IR studies indicated that the 'Lo' regime ultrasonicated zeolite had higher intensities than that of the 'Hi' frequency ultrasonicated zeolite. The bands associated with the 'Lo' regime ultrasonicated zeolite were observed at 1066 cm-1,1400 cm-1 and 3600 cm-1, which were identified as Si-O asymmetric stretch, Al-O asymmetric stretch, O-Hbend and O-H asymmetric stretch, respectively. Based on PXRD studies, the zeolitic phases were most intense for the 90 min ultrasonicated zeolite. Powder X-ray diffraction studies showed that the phases initially in CFA, such as quartz and aluminosilicate, were converted into gismodine zeolite Na-P1. Morphological changes were seen as ultrasonication period was increased. At short ultrasonication times, irregularly shaped fused-like grain structures were observed, while at longer times separate grain-like structures became more apparent. Energy dispersive X-ray spectroscopy studies on the 90 min ultrasonicated zeolite indicated the presence of Na, O, Si and Al, which were important building-blocks for the zeolites. <![CDATA[<b>Surface-modified Water Hyacinth <i>(Eichhornia crassipes) </i>over Activated Carbon for Wastewater Treatment: A Comparative Account</b>]]> Finding an economical, efficient and easy handling alternative for commercial grade activated charcoal (AC) in textile wastewater treatment is a dire need. To address this, a noxious weed water hyacinth (WH) has been explored as a 'biosorbent' for the decolorization of the hazardous textile dye, Remazol Brilliant Red 3BS (RBR 3BS) in wastewater. A novel surface modification has been carried out using the quaternary ammonium salt, N-Cetyl-N,N,N-trimethyl ammonium bromide, to enhance the dye decolorization capacity of raw WH. The impact of several process parameters, viz. pH, dosage of adsorbent, temperature, concentration and contact time have been examined. Batch adsorption studies, kinetic-thermodynamics, isothermal modelling and error analysis have been studied to ascertain the efficacy of the adsorbent. A comparison of the results has been carried out with activated carbon (AC). Surface-modified WH showed the highest dye uptake of 104.26 mg g-1, at 27 °C, which was about 10 times more than that of AC. Isothermal, kinetic and thermodynamic studies were conducted for identification of adsorption type taking place for dye-adsorbent systems. Energy of activation was 8.65 kJ mol-1 for treated WH and 8.98 kJ mol-1 for AC. It was proven that surface-modified WH had a high capability to replace AC for adsorption treatments. <![CDATA[<b>The Quality Control of Alcoholic Components of Disinfectants by a Simple Colour Test</b>]]> The identity and quality of liquid components for disinfectants, preferentially isopropyl alcohol and ethanol, can be determined with the naked eye using solvatochromic dyes and comparing their colour with a colour scale. Thus, any confusion with toxic methanol or other solvents can be excluded, as can also the application of raw materials in insufficient concentration or incorrect formulations. The production of a quick and easy to use simple low-cost test kit is described. <![CDATA[<b>Synthesis, Characterization and Application of a Molecularly Imprinted Polymer in Selective Adsorption of Abacavir from Polluted Water</b>]]> Abacavir is an antiretroviral drug (ARVD), which has been identified as a water pollutant. To find a selective adsorbent for its extraction from water, a molecularly imprinted polymer (MIP) is proposed for its selective uptake. A 24-hour bulk polymerization process was performed for imprinting abacavir with aliquat 336 and ethylene glycol dimethacrylate, as functional monomer and cross-linking agent, respectively. Uptake of abacavir from 10 mL of aqueous solutions was performed with 40 mg of MIP at pH 5 within 60 min of contact time. MIP selectively adsorbed abacavir from water in the presence of other ARVDs (tenofovir disoproxil and efavirenz). The maximum adsorption capacity obtained for abacavir was 5.98 mg g-1. The adsorption mechanism was best described by the Freundlich isotherm and pseudo-second-order kinetic model, which were translated to multilayer coverage and chemisorption influenced by electrostatic attractions, respectively. The extraction efficiencies achieved for abacavir in wastewater influent, effluent and estuarine water were 67,74 and 76 %, respectively. The synthesized MIP can be reused at least 10 consecutive times for adsorption of abacavir from polluted water without losing its extraction efficiency. This is the first study to report the application of aliquat 336 as the functional monomer in the synthesis of MIP for selective extraction of abacavir from water. <![CDATA[<b>Optimization of X-ray Fluorescence Calibration through the Introduction of Synthetic Standards for the Determination of Mineral Sands Oxides</b>]]> An XRF spectrometer traditionally requires its methods to be calibrated using certified reference materials (CRMs). This means choosing from a limited selection of CRMs, which are costly and not widely available. This article examines the application of synthetic oxide standards made from commercially available high purity compounds for the calibration of an XRF spectrometer. Enabling itto analyze for major, minor and trace elements (Mg, Al, Si, PP Hf, Ca, Ti, Zr, Fe, Th, U) in heavy mineral sands processing. Calibration standards were synthesized by mixing pure compounds and mineral sands reference materials, to mimic matrices similar to that of the routine samples and cover the required analytical range. The aliquots were mixed in % fractions and fused with a 1:9 sample/borate dilution to make glass beads. The optimized calibration was validated as per SANAS TR 26-02 criteria for linearity, working range, limit of detection (LOD) and quantification (LOQ), precision and accuracy. The correlation coefficients (r²) of the resulting calibration curves were &gt;0.999, showing excellent linearity. The working range for all the calibration lines was satisfactory. The LOD and LOQ values for all the lines were low enough to prevent extrapolation below the lowest calibration point. The precision of the calibration was sufficiently high, and the accuracy was of adequate quality with z(MAD) <2. These observations support the successful synthesis and use of a well-selected set of synthetic standards. Additionally, it has been successfully utilized to analyze a variety of heavy mineral sands samples. <![CDATA[<b>Computer-Aided: Modelled Sustainable Hybrid Catalysts for a Nano-drug Delivery System</b>]]> We evaluated a hybrid catalytic power source for less invasive internal electroporation with better tissue reach than the widely used and more invasive external electroporation. We modelled how open-circuit voltage optimizes platinum-loading in catalysts to improve the electrochemical activity (ECA) possible from bioelectrogenesis through these systems and address the high costs of nano-drug delivery systems. The effects of the catalysts' convective flux and proton concentration were modelled for an enzyme (glucose oxidase) biofuel cell that was fed glucose substrate at a current rate under isothermal physiological conditions. Glucose concentrations were varied relative to anode catalyst loading models with 0.1-0.5 mg cm-2 platinum and alloyed (Pt-Ru-Ni) with a narrow particle size distribution. Using the free (solvation) electron model, bioelectrochemical activity (BECA) and a high open circuit voltage were generated by 5.5,10 and 20 mM glucose with 20 kU L-1 glucose oxidase at 37 °C. BECA (glucose oxidase), on its own, produced pulses of various intensities for nano-microsecond durations whereas the hybrid BECA-ECA (glucose oxidase and platinum) anode catalyst provided sustainable pulses of microseconds-minute durations. Enhanced catalysis with the hybrid BECA-ECA's open circuit voltage favours compatibility of a hybrid-powered nano-drug delivery system for internal electroporation. <![CDATA[<b>Efficient Removal of Sulfamethoxazole onto Sugarcane Bagasse-derived Biochar: Two and Three-parameter Isotherms, Kinetics and Thermodynamics</b>]]> In this work, bagasse, an agricultural waste was used for the development of environmentally benign biochar (CBG) and the thermal pyrolysis product applied for adsorption of sulfamethoxazole (SMX) from water using a batch technique. The pseudo-first-order model best described the adsorption kinetics. Equilibrium adsorption data were modelled using six two-parameter and five three-parameter isotherm equations and the best-fitting models obtained using five error functions. The Sips isotherm best predicted the equilibrium data with an estimated adsorption capacity of 128.8 mg g-1. Error analysis showed that three-parameter isotherms best explained the experimental data. The thermodynamic functions, viz. enthalpy (AH = -24.72 kJ mol-1), Gibbs free energy (AG = -15.67 kJ mol-1), entropy (AS = 32.65 kJ mol-1), showed that the reaction is spontaneous and exothermic. The mechanism of adsorption involved charge-assisted hydrogen bonding (-)CAHB. The amount of CBG required for the removal of 99 % of SMX in a given volume of effluent was predicted. The results attest that CBG is an effective low-cost adsorbent for SMX adsorption. <![CDATA[<b>Understanding the Link Between the Detection Limit and the Energy Stability of Two Quercetin-Antimony Complexes by Means of Conceptual DFT</b>]]> In view of the importance of quercetin and its derivatives in trace metal analyses, two organometallic complexes formed between quercetin (Q) and quercetin-5-sulfonic acid (QSA) with antimony metal, were theoretically studied via density functional theory (DFT) calculations. In this study, the concept of detection limit in electroanalysis was correlated to quantum chemical calculations for antimony trace analysis in aqueous solution by using Q and QSA as ligands. Based on two previous reports, the study was carried out experimentally using polarography where the working electrode was a dropping mercury electrode. The DFT calculations were performed with B3LYP and LSDA functionals as implemented in Gaussian 09 program and by employing the 6-31G(d) and 3-21G(d) basis sets, respectively. The results show a very strong relationship between the total energy of antimony complexes and the detection limit; thus, the more stable complex has a better detection limit value. Based on the Fukui functions, the calculated parameters such as local nucleophilicity indices and HOMO-1 electronic density of the ligands show a high interaction of antimony ion (III) with quercetin-5-sulfonic acid than that with quercetin. This finding was in good accord with the experimental results. <![CDATA[<b>Anti-corrosion Behaviour of Expired Tobramycin Drug on Carbon Steel in Acidic Medium</b>]]> The anti-corrosion behaviour of the expired Tobramycin (ETo) drug for carbon steel in 2 M HCl solution was investigated by thermometric methods (Thermo), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results obtained from Thermo, PDP and EIS show that the level of anti-corrosion behaviour is in direct association to the ETo application. The model of adsorption isotherm fitted Langmuir, confirming a chemical adsorption system. The SEM image of carbon steel immersed in optimum concentration of ETo has confirmed the film formation on the carbon steel surface. The PDP technique, indicated by the Tafel plots, demonstrated that the ETo inhibitor acted as a mixed-type inhibitor. The results obtained from activation energy, Ea, the quantity of heat adsorbed, Qads, and standard free energy of adsorption, AG°ads, show a chemical adsorption mechanism of the ETo inhibitor. <![CDATA[<b>Templated Cross-linked Nanoporous Starch</b>]]> Nanoporous starch materials were successfully prepared by a sustainable synthetic process. In this method, some available economic cationic, anionic and nonionic templates like CTAB, SDS and Tween 80 in the presence of borax, as a green and low-cost cross-linker, were used to synthesize the desired cross-linked nanoporous starch in the aqueous phase at relatively low temperature. The obtained materials were characterized by SEM, FT-IR, TGA, DSC and N2 adsorption/desorption methods. While SEM analysis confirmed the porous nature of the materials, BET measurement showed that the materials can have a specific surface area of 65 m² g-1. Cross-linked nanoporous starch was found to be an efficient, inexpensive, easy to prepare, green adsorbent in the removal of methylene blue and methyl orange from wastewater. The synthesized material was found to be highly efficient in controlled adsorption and desorption of ciprofloxacin, which can be applied in drug delivery.