Scielo RSS <![CDATA[South African Journal of Chemistry]]> http://www.scielo.org.za/rss.php?pid=0379-435020150001&lang=es vol. 68 num. lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>A rapid and sensitive LC-MS/MS method for the determination of multi-class residues of antibiotics in chicken liver</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100001&lng=es&nrm=iso&tlng=es A very sensitive, simple and cost-effective liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method for the determination of multi-class antibiotics in chicken liver was developed. The drugs under consideration were sulfaguanidine and sulfamethazole, trimethoprim, tetracycline, chlortetracycline and tylosin. Linear calibrations were established for all the analytes and the R² values ranged between 0.9990 and 0.9997. The limits of quantitation (LOQs) varied between 0.025 and 78.8 μg kg-1. The limit of detections (LODs) were better than those that have been reported for the same antibiotics in many instances in other studies and ranged between 0.010-31.5 μg kg-1 with the sulfonamides exhibiting lower sensitivity compared to others. This was attributed to poor response factors, low S/N ratios and matrix interferences. A contrast between the relative responses towards mass spectrometer and ultra-violate/visible (UV/VIS) detection of the analytes is also reported. Sulfonamides exhibited higher response factors towards UV/VIS than mass spectrometer detection and the opposite was true for the rest of the analytes. <![CDATA[<b>Ring-opening polymerization of lactides by (pyrazol-1-ylmethyl)pyridine Zn(II) and Cu(II) complexes: Kinetics, mechanism and tacticity studies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100002&lng=es&nrm=iso&tlng=es The kinetics, mechanism and polymer microstructure studies of ring-opening polymerization (ROP) of lactides (LA) by Zn(II) and Cu(II) complexes of (pyrazolylmethyl)pyridine ligands, 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2-(3,5-diphenylpyrazol-1-ylmethyl)pyridine (L2) is described. The complexes [Zn(Ac)2(L1)] (1), [Cu(Ac)2(L1)] (2), [Zn(Ac)2(L2)] (3) and [Cu2(Ac)4(L2)2](4) form active initiators in the ROP of D,L-LA and L-LA monomers. Generally Zn(II) complexes 1 and 3 exhibit higher activities compared to the corresponding Cu(II) complexes 2 and 4. Polymerization kinetics of D,L-LA show higher rates compared to the L-LA reactions. All the polymerization reactions follow pseudo first-order kinetics with respect to monomer while 1 shows second-order dependency on the polymerization reactions. Molecular weights of the polymers range from 813 g mol-1 to 9207 g mol-1 and exhibit relatively narrow molecular weight distributions between 1.2 to 1.6. While poly(D,L-LA) are predominantly atactic, poly(L-LA) are largely isotactic. All polymerization reactions proceed through coordination insertion mechanism followed by hydrolysis of the end groups. <![CDATA[<b>A solvent-free synthesis of polyhydroquinolines <i>via</i> Hantzsch multicomponent condensation catalyzed by nanomagnetic-supported sulfonic acid</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100003&lng=es&nrm=iso&tlng=es A simple and efficient procedure for the synthesis of polyhydroquinolines was developed, involving a one-pot four-component Hantzsch condensation of aromatic aldehydes, 1,3-cyclohexanediones, alkyl acetoacetate and ammonium acetate in the presence of a catalytic amount of nanomagnetic-supported sulfonic acid under solvent-free conditions. The method offers several advantages including high yields, short reaction times, a simple work-up procedure and catalyst reusability for several runs. Furthermore, easy isolation of the catalyst from the reaction mixture was enabled by use of an external magnet. <![CDATA[<b>Kinetics and mechanism of the ligand exchange reaction between tetradentate schiff base N,N'-ethylen-bis (salicylaldimine) and Ni(N,N'-propylen-bis(salicylaldimine))</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100004&lng=es&nrm=iso&tlng=es Visible spectrophotometry is used to study the kinetics of ligand exchange in the system Ni(salpn)/H2salen with or without triethylamine (NEt3) and H2O in dimethylformamide (DMF) solvent at 25 ± 0.1 °C and 0.01 M NaNO3 [H2salen and H2salpn are N,N'-ethylen-bis(salicylaldimine) and N,N'-propylen-bis(salicylaldimine), respectively]. It was found that the reaction rate is of the first-order with respect to Ni(salpn). In addition, the effect of NEt3 and H2O on the rate of the reaction was examined. The rate of the ligand exchange reaction was accelerated by adding NEt3 to the reaction mixture. However, the ligand exchange rate was not changed by adding H2O to the mixture reaction. The effects of NEt3 and H2O on the ligand exchange rate show that deprotonation/protonation of the H2salen ligand and anionic form of H2salen is important. On the basis of these results, the reaction mechanism is discussed. <![CDATA[<b>Synthesis and NMR elucidation of novel octa-amino acid resorcin[4]arenes derivatives</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100005&lng=es&nrm=iso&tlng=es The synthesis of nine novel protected amino acid cavitands is reported. All have four pendant M-undecyl chains and 'headgroups' connected by a two-carbon spacer at eight positions on the aromatic rings. The amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine and lysine. The structures of the compounds were elucidated using one and two-dimensional NMR techniques which verified that all octa-substituted cavitands have symmetrical C2v conformation at room temperature. These compounds have potential synthetic ion channel applications. <![CDATA[<b>Isolation, characterization and x-ray structure determination of the schiff base ligand: 5-methyl-2-phenyl-4-[phenyl-(4-phenyl-thiazol-2-ylamino)-methylene]-2,4-dihydro-pyrazol-3-one</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100006&lng=es&nrm=iso&tlng=es The structure of the amine tautomer of the new Schiff base derived from 4-benzoyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one (2) and 4-phenyl-thiazol-2-ylamine (3) was confirmed by means of single crystal X-ray diffraction. The title compound (4) was synthesized and crystals were grown from a mixture of dichloromethane and n-hexane (1:3). Single crystal X-ray diffraction analysis show that the structure is primarily stabilized by strong intramolecular N3-H3A-O1 hydrogen bonds [N3-H3A = 0.883(19) Ẳ, H3A-O1 = 1.925(18) Ẳ, N3-O1 = 2.6901(13) A, with an angle for N3-H3A-O1 = 144.1(17) °] and this leads to the formation of a pseudo nine-membered hydrogen bonded pattern. Elemental analysis, FTIR and NMR analyses have been employed to characterize the crystal. <![CDATA[<b>Kinetic and thermodynamic studies of the adsorption of Cr(VI) onto some selected local adsorbents</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100007&lng=es&nrm=iso&tlng=es In this study, locally available biomasses obtained from avocado kernel seeds (AKS), Juniperus procera sawdust (JPS) and papaya peels (PP) were investigated as adsorbents for the removal of Cr(VI). The study employed a batch method to investigate the efficiency of the adsorbents. Parameters that influence adsorption such as: pH, adsorbent dose, initial concentration of Cr(VI), contact time and temperature have been studied. Optimum parameters for the adsorption of 5 mg L-1 Cr(VI) were: pH:1, adsorbent dose: 0.5 g, contact time: 160 min and temperature: 313 K. The equilibrium data was best fitted to the Freundlich adsorption isotherm model. The results of kinetic models showed that the pseudo-second-order kinetic model was found to correlate well to the experimental data. The results of thermodynamic parameters showed that the adsorption process is feasible. The positive values of the entropy change suggest increased randomness at solid-liquid interfaces during the adsorption. The efficiencies of the adsorbents towards the removal of chromium from real samples were also examined and were found to remove chromium from waste water. <![CDATA[<b>A facile and practical <i>p</i>-Toluenesulfonic acid catalyzed route to dicoumarols containing an Aroyl group</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100008&lng=es&nrm=iso&tlng=es New and known dicoumarols may be efficiently synthesized employing p-toluenesulfonic acid (p-TSA) as a solid acid catalyst from the reaction of 4-hydroxycoumarin with aryl glyoxal in water. This method offers direct access to structurally diverse coumarin derivatives in moderate to good yields (up to 65%). A total of five new compounds were synthesized. <![CDATA[<b>Determination of Leachable Vanadium (V) in sediment</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100009&lng=es&nrm=iso&tlng=es A method for speciation of vanadium in solid samples was developed for quantification of vanadium( + 5) in solid samples of sediment Certified Reference Materials (CRM) PACS-2 and MESS-3 (Trace Elements in Sediments) of known total vanadium content. The method relies on a classical analytical chemistry procedure based on leaching water-insoluble vanadium( + 5) compounds from the solid state into solution using Na2CO3 followed by electrothermal atomic absorption spectrometry (ET-AAS) detection. The total amount content of vanadium was determined after complete digestion of the CRMs and found to be 132 ± 5 and 245 ±12 μg g-1 in PACS-2 and MESS-3, respectively, in good agreement with the certified values of 133±6 μg g-1 and 243 ± 12 μg g-1. The concentrations of vanadium(+5) were determined to be 25 ± 3 μg g-1 and 13 ± 2 μg g-1 in PACS-2 and MESS-3, respectively. These results were verified by the method of standard additions for which quantitative recoveries (100±2 and 97 ± 3 %, one standard deviation, n = 3) were obtained for spikes added to PACS-2 and MESS-3, respectively. Approximately 18.8 % of the total vanadium content of PACS-2 and 5.3 % in MESS-3 is in the form of vanadium(+5) species. <![CDATA[<b>Selective adsorption of uranium (VI) on NaHCO<sub>3</sub> leached composite γ-Methacryloxypropyltrimethoxysilane coated magnetic Ion-imprinted polymers prepared by precipitation polymerization</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100010&lng=es&nrm=iso&tlng=es Ion imprinted nano-magnetic composite polymers for selective removal of hexavalent uranium were prepared by a precipitation polymerization technique in the presence of γ-methacryloxypropyltrimethoxysilane (γ-MPS) coated magnetite and other pre-polymerization reagents. The synthesized magnetic polymers were then leached with NaHCO3 to produce magnetic ion imprinted polymers (IIPs) with fabricated adsorption sites complementary to the uranyl ions in terms of size and shape. Several parameters were investigated to obtain conditions which gave the optimum adsorption of the uranyl onto the magnetic IIPs and their corresponding controls, magnetic ion non-imprinted polymers (NIPs). The optimum amount of magnetic sorbent, initial concentration and contact time were 50 mg, 2.5 mg L-1 and 45 min, respectively. The adsorption capacity of the magnetic IIP (1.15 ± 0.01 mg g-1) was higher than that of the magnetic NIP (0.93 ± 0.02 mg g-1). This indicated that the former had a somewhat higher affinity for U(VI) than the later. The magnetic polymers also displayed good selectivity of the order: U(VI) > Ni(II) > Mg(II). After six cycles of use, the magnetic polymers illustrated good stability and reusability. <![CDATA[<b>Extraction of cerium (IV) using di-n-butylsulfoxide in chloroform from nitric acid and determination with arsenazo (III) as chromogenic Reagent</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100011&lng=es&nrm=iso&tlng=es A new and advantageous extraction procedure was developed for extraction of cerium (IV) from nitric acid with di-n-butylsulfoxide (DBSO) in perchloric acid. The extracted Ce (IV) was determined spectrophotometrically using 0.01 % solution of arsenazo-III in 3 M per-chloric acid. Various parameters such as equilibration time, metal ion concentration, effect of temperature and diverse ions on the extraction of the Ce (IV) were established. U (VI), Th (IV) and Pb (II) interfere whereas only phosphate and fluoride suppress the extraction among anions. The stoichiometric composition of the cerium complex with DBSO was determined by slope analysis and found to be 1:4. The process of extraction was found to be exothermic. Deionized water was the most appropriate solvent for back extraction of cerium. This method is easier and more sensitive than many of the reported procedures. <![CDATA[<b>Evaluation of six sample preparation methods for determination of trace metals in lubricating oils using inductively coupled plasma-optical emission spectrometry</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100012&lng=es&nrm=iso&tlng=es Quantification of trace elements in used lubricating oil forms a vital part in monitoring engine conditions and impact on the environment. In this study, inductively coupled plasma-optical emission spectrometry (ICP-OES) was employed for the determination of Ag, Ba, Cu, Mn and Ni in used lubricating oils. Methodology was developed so as to minimize the oil's carbonaceous matter and its effect on viscosity. Accordingly, six oil sample preparation techniques (xylene dilution, detergent emulsion, microwave digestion, dry-ashing, wet-ashing and ultrasonic extraction) were investigated for their efficiency. Optimization of the factors influencing ultrasonic-assisted extraction and ICP-OES operating parameters enabled quantification of the trace metals in oils. Limits of detection (3Sb/m), in the ng g-1 range, were obtained for each element of interest using each method investigated. The validity of the methodologies studied was confirmed through the analysis of quality control (QC) samples. Analyte recoveries, ranging from 48.3 to 106 %, were obtained. Evaluation of the analytical methods studied with regard to accuracy, precision, LOD, linearity, applicability for routine analysis, preparation time and cost was made. Based on these evaluations, ultrasonic extraction has a clear advantage in terms of accuracy, applicability for routine analysis, time and cost of sample preparation. <![CDATA[<b>Kinetics and mechanism of the oxidation of Coomassie Brilliant Blue-R dye by hypochlorite and role of acid therein</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100013&lng=es&nrm=iso&tlng=es The kinetics of the oxidation of a triphenylmethane dye, Brilliant Blue-R (BB- Na+), in aqueous solutionby hypochlorite as a function of pH was investigated. While the degradation of dye obeyed pseudo-first-order kinetics, the oxidation of the dye occurred through two competitive reactions facilitated by [OCl-] and [HOCl]. Both reactions exhibited first-order dependence on [OCl-] and [HOCl], respectively, but the hypochlorous acid initiated reaction was about ten times faster. The relative importance of the two paths rested on the pH-dependent concentrations of hypochlorite and hypochlorous acid. The overall second-order rate constants for the OCl- and HOCl initiated reactions are 1.2 ± 0.2 M-1 s-1 and 22.2 ±1.2 M-1 s-1, respectively. The reaction energy parameters were determined as Ea = 35.5 kJ mol-1, ∆H‡ = 33.1 kJ mol-1 and ∆S‡ = -191.9 J K-1 mol-1 for the OCl- driven oxidation; and Ea = 26.8 kJ mol-1, ∆H‡ = 29.3 kJ mol-1 and ∆S‡ = -204.6 J K-1 mol-1 for the HOCl facilitated reaction. The governing rate law and probable reaction mechanism were elucidated and validated by simulation. The three main oxidation products were 4-(4-ethoxyphenylamino)benzoic acid, 3-[(ethyl-hydroxyamino)methyl]benzene sulfonic acid and 6'-chloro-5'-hydroxy-bicyclohexylidene-2,5,2'-triene-4,4'-dione. <![CDATA[<b>Ultra performance liquid chromatography tandem mass spectrometric method development and validation for determination of neratinib in human plasma</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100014&lng=es&nrm=iso&tlng=es This study was designed to develop and validate a UPLC-MS/MS method for quantification of neratinib in human plasmsa. Neratinib is an irreversible tyrosine kinase inhibitor against the pan-ErbB (ErbB-1, -2, -4) receptor. UPLC-MS/MS is an excellent analytical methodology for rapid biomedical analysis, decreasing the time for analysis and maintaining good efficiency. Crizotinib was used as internal standard (IS). Samples where extracted by plasma protein precipitation (PPT) procedure with acetonitrile and methanol and analysis was performed on a C18 Acquity UPLC BEH TM column. The ion transitions where recorded in positive ion multiple reaction monitoring mode m/z 557.51 → 112.17 for neratinib and m/z 450.0 → 260.0 for IS. The mobile phase used was methanol:water: formic acid (70:30:0.1 %, v/v/v) with a flow rate of 0.3 mL min-1. The linearity of the assay was found to be 4-500 ng mL-1 for neratinib in human plasma with lower limit of quatification of 4 ng mL-1. The intra- and inter-assay precision relative standard deviations did not exceed 10.99 and mean extraction recovery was found to be 69.12 ± 3.58. <![CDATA[<b>Study of preparation and properties on polymer-modified magnetite nanoparticles</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100015&lng=es&nrm=iso&tlng=es In this paper, polyacrylamide (PAM)-modified magnetite (Fe3O4) nanoparticles were prepared by in situ polymerization in aqueous solution. The particle size, morphology, crystal phase and magnetic properties were measured utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. The size distribution and stability of the nano-particles in aqueous solution were evaluated using the laser particle size analyzer and ultraviolet-visible spectroscopy (UV-vis). The influences of the dose of acrylamide (AM) and the pH value on the particle size and stability were also examined. The results showed that the Fe3O4 nanoparticles possessed superparamagnetic property and super dispersion stability in aqueous solution after PAM modification. <![CDATA[<b>Inhibition effect of deanol on mild steel corrosion in dilute sulphuric acid</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100016&lng=es&nrm=iso&tlng=es The influence of deanol on the corrosion behaviour of mild steel in dilute sulphuric acid with sodium chloride addition was studied by means of mass-loss, potentiodynamic polarization, electrode potential monitoring, scanning electron microscopy and statistical analysis. Results show that deanol performed excellently with a maximum inhibition efficiency of 97.9 % obtained from the mass loss technique and 98.23 % from the potentiodynamic polarization tests at the maximum deanol concentration evaluated. Polarization studies show that the amino alcohol is a cathodic type inhibitor. Adsorption of deanol on the steel surface was observed to obey the Langmuir and Frumkin adsorption isotherms. Scanning electron microscopy studies confirmed the corrosion protection property of deanol to be through adsorption on the mild steel surface while statistical evaluation showed the overwhelming influence and significance of inhibitor concentration on inhibition efficiency compared with exposure time. <![CDATA[<b>Adsorption of Rhodamine B dye from aqueous solution on <i>Irvingia gabonensis </i>biomass: Kinetics and thermodynamics studies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100017&lng=es&nrm=iso&tlng=es Raw Irvingia gabonenses (dika nut) (DN) and its acid-treated form (ADN) were used for the uptake of rhodamine B (RhB) dye from aqueous solution. The adsorbents were characterized by Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and scanning electron microscopy (SEM). The adsorbents were found to have characteristic functional groups such as -OH, C-N and C=O. SEM revealed that acid treatment resulted in the development of several pore sizes. Sorption data fitted the Freundlich adsorption isotherm better than the Langmuir isotherm. The maximum sorption capacities, q max, obtained from the Langmuir adsorption isotherm were 212.77 and 232 mg g-1 for DN and ADN, respectively. The pseudo-second-order kinetics model was observed to fit the adsorption data. Solution pH and temperature significantly influenced the adsorption process and negative values of DG° suggest that the sorption process was spontaneous and feasible. Intraparticle diffusion mainly controlled the uptake of RhB onto DN and ADN; however, boundary layer diffusion also occurred in the RhB-ADN system. The desorption efficiency of RhB from the adsorbents was tested with a number of eluents. The eluents were found to follow the order: H2O>CH3COOH>HCl and CH3COOH>HCl>H2O for DN and ADN, respectively. <![CDATA[<b>Application of ultrasound-assisted emulsification microextraction followed by gas chromatography for determination of oxadiazon in water and soil samples</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100018&lng=es&nrm=iso&tlng=es In this study, a simple and efficient ultrasound-assisted emulsification microextraction (USAEME) method combined with gas chromatography (GC) was developed for the preconcentration and determination of oxadiazon in water and soil samples. In this method, fine droplets of toluene were formed and dispersed in the sample with the help of ultrasonic waves which accelerated the formation of a fine cloudy solution without using disperser solvents. Several factors influencing the extraction efficiency, such as the nature and volume of organic solvent, extraction temperature, ionic strength and centrifugation time, were investigated and optimized. Using optimum extraction conditions a detection limit of 0.1 μg L-1 and a good linearity in a calibration range of 0.25-250 μg L-1 were achieved for the analyte in a river water sample. This proposed method was successfully applied to the analysis of oxadiazon in water and soil samples. <![CDATA[<b>Synthesis and characterization of 5-substituted 1<i>H</i>-tetrazoles in the presence of nano-TiCl<sub>4</sub>.SiO<sub>2</sub></b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100019&lng=es&nrm=iso&tlng=es Nano-TiCl4.SiO2 was found to be an extremely efficient catalyst for the preparation of 5-substituted 1H-tetrazole derivatives. Nano-TiCl4.SiO2 is a solid Lewis-acid was synthesized by the reaction of nano-SiO2 and TiCl4. The structure characterization of this acid was achieved with X-ray diffraction, thermogravimetric analysis and electron microscopy. The synthesis of the catalyst is simple and environmentally benign with a good yield. Furthermore, the catalyst is conveniently recoverable and was reused for at least three times. The antimicrobial activities of the synthetic compounds were also determined by both micro dilution methods as recommended by the Clinical Laboratory Standard Institute, but unfortunately did not exhibit antibacterial activities at the highest concentration (256 μL mL-1). Further studies are still needed to investigate the potential biological activities of these compounds against other diseases. <![CDATA[<b>Synthesis and photocatalytic activity of Zn<sub>x</sub>Cd<sub>1-x</sub>S/TiO<sub>2 </sub>heterostructures nanofibre prepared by combining electrospinning and hydrothermal method</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100020&lng=es&nrm=iso&tlng=es The Zn xCd1-xS/TiO2 hierarchical heterostructures were successfully fabricated by combining electrospinning technology and hydrothermal methods. The morphology, crystallinity, composition and band gap of Zn xCd1-xS/TiO2 were characterized by SEM, XRD, EDS, and UV-vis diffuse reflectance spectroscopy. The results indicated the sulphur concentration had a significant influence on the composition and morphology of the products. The values of the band gap energy for Zn xCd1-xS/TiO2 varied from 2.33 to 2.66 eV with the change of sulphur concentration. When the molar ratio of S/Ti was 0.96, the Zn xCd1xS/TiO2 hierarchical heterostructures exhibited enhanced visible light photocatalytic behaviour for the decomposition of Rhodamine B (RhB) under visible light irradiation. The photocatalytic degradation of RhB followed first-order reaction kinetics. <![CDATA[<b>Solid state NMR characterization and adsorption properties of lignocellulose-clinoptilolite composites prepared with siloxanes coupling agents</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100021&lng=es&nrm=iso&tlng=es This study reports the preparation of lignocellulose-clinoptilolite composites by means of N-terminated siloxanes as coupling agents, after acid hydrolysis. Reactions were carried out in the presence of dibutyltin dilaurate as catalyst by reacting lignocellulose modified with the coupling agents and clinoptilolite at 140 °C in DMF under nitrogen atmosphere. The light in weight and fluffy composites obtained were characterized by FT-IR, XRD, TGA, SEM and Solid State NMR. Results depicted possible chemical interactions between the two materials (lignocellulose and clinoptilolite). Used as adsorbents, the composites showed to be good candidates for the removal of used motor oil from aqueous solution, with up to 92 mg g-1 of chemical oxygen demand removed. <![CDATA[<b>Multiwalled carbon nanotube-titania nanocomposites: Understanding nano-structural parameters and functionality in dye-sensitized solar cells</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100022&lng=es&nrm=iso&tlng=es Nanocomposites consisting of multiwalled carbon nanotubes and titania were synthesized by two methods, namely, sol-gel and chemical vapour deposition (CVD) methods. The work takes advantage of the bridging ability of nanotechnology between macromolecules and the solid state process in engineering alternative nanomaterials for various applications including solar cell fabrication. Physical and chemical characterization of the mesoporous nanocomposites from the two synthetic methods were investigated using Raman spectroscopy, thermogravimetric analysis, Fourier transformation infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, surface characterization and X-ray diffraction analysis. Physicochemical properties in the nanocomposites such as thermal stability, pore volume, crystallinity and surface area were observed to be a subject of MWCNT: titania ratios and synthetic methods. From the CVD synthetic method, observed attributes include more uniform and smoother coating; better crystallinity and larger pore width than sol-gel method. On the other hand, nanocomposites from sol-gel synthetic method had larger surface areas, were more defective and less thermally stable than those from CVD. Nanocomposites by the CVD method performed 39.2 % more efficient than those from sol-gel in light-harvesting experiments. The study shows that the nanocomposites synthesized were more effective than titania alone when the cheaper natural dye, Eosin B, was used. This highlights the great potential of typical nanomaterials in improving the performances of titania in DSSCs as well as lowering the cost of the ultimate devices. <![CDATA[<b>Removal of uranium from aqueous solutions using ammonium-modified zeolite</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100023&lng=es&nrm=iso&tlng=es Batch experiments were conducted to study the effects of contact time, pH (3 to 8), initial concentration, presence of carbonate, sulphate, and competing ions (Fe³+,Ca²+,Sr²+,Mg²+) on the adsorption of U(VI) on ammonium-modified zeolite (AMZ). The structural features of the modified zeolite were assessed by Fourier Transform Infra Red Spectroscopy (FTIR) while the metal content was determined by Inductively Coupled Plasma Optical Emission Specroscopy (ICP-OES). The removal of uranium was effective and maximal under acidic conditions (pH 3 to 5). The kinetics of adsorption of U-nitrate and U-sulphate on AMZ were described by the pseudo-second-order model (R² ≥ 0.9820). In the presence of SO4²" and CO3(2-), a significant reduction of 67.88 % and 71.63 %, respectively, in uranium uptake was observed. The distribution coefficient, K D(L g-1), was in the order of: U-nitrate (1.116) > U-sulphate (0.029) > U-carbonate (0.019), suggesting that AMZ had a high affinity for U-nitrate. The presence of Fe³+ enhanced the removal of U(VI) from U-nitrate, U-sulphate and U-carbonate by 20.18 %, 72.48 % and 82.43 %, respectively, while the presence of Ca²+,Mg²+ and Sr²+ reduced the removal to 19.57 %, 31.60 % and 23.65 %, respectively. AMZ is an effective adsorbent for uranium removal from aqueous solutions dominated by nitrate, carbonate and sulphate. <![CDATA[<b>The oxidation of dibenzothiophene using oxidovanadium(IV)-containing nanofibres as catalyst</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100024&lng=es&nrm=iso&tlng=es Polyvinylbenzylchloride nanofibres were fabricated by the electrospinning technique and subsequently functionalized with a tetradentate ligand, 2,2'-(1E',1'E)-(1,2-phenykenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)bis(4-aminophenol). VO²+ was then incorporated into the nanofibres to produce the catalyst VO-fibres. Microanalysis, TG and FT-IR were used for the characterization of VO-fibre, and EPR also confirmed the presence of oxidovanadium(IV) within the nanofibres. Oxidation of dibenzothiophene (DBT) was investigated by varying the catalyst amount, substrate amount, oxidant and temperature, and the progress of oxidation was followed with a gas chromatograph fitted with a flame ionization detector. An increase in the amount of oxidant caused an increase in the amount of dibenzothiophene sulfone (DBTO2), while a decrease in the quantity of dibenzothiophene resulted in an increase in the overall yield of dibenzothiophene sulfone under a constant temperature and oxidant (H2O2) concentration. Dibenzothiophene sulfone was confirmed as the oxidation product through ¹H-NMR spectroscopy and single crystal X-ray diffraction. <![CDATA[<b>Plume characterization of a typical South African braai</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100025&lng=es&nrm=iso&tlng=es To braai is part of the South African heritage that transcends ethnic barriers and socio-economic groups. In this paper, a comprehensive analysis of atmospheric gaseous and aerosol species within a plume originating from a typical South African braai is presented. Braai experiments were conducted at Welgegund - a comprehensively equipped regional background atmospheric air quality and climate change monitoring station. Five distinct phases were identified during the braai. Sulphur dioxide (SO2), nitrogen oxides (NOx) and carbon monoxide (CO) increased significantly, while ozone (O3) did not increase notably. Aromatic and alkane volatile organic compounds were determined, with benzene exceeding the 2015 South African one-year ambient air quality limit. A comparison of atmospheric PM10 (particulate matter of an aerodynamic diameter <10μm) concentrations with the 24-hour ambient limit indicated that PM10 is problematic during the meat grilling phase. From a climatic point of view, relatively high single scattering albedo (ωo) indicated a cooling aerosol direct effect, while periods with lower ωocoincided with peak black carbon (BC) emissions. The highest trace metal concentrations were associated with species typically present in ash. The lead (Pb) concentration was higher than the annual ambient air quality limit. Sulphate (SO4(2-)-), calcium (Ca²+) and magnesium (Mg²+) were the dominant water-soluble species present in the aerosols. The largest number of organic aerosol compounds was in the PM25-1 fraction, which also had the highest semi-quantified concentration. The results indicated that a recreational braai does not pose significant health risks. However, the longer exposure periods that are experienced by occupational vendors, will significantly increase health risks. <![CDATA[<b>A kinetic insight into the activation of <em>n</em>-octane with alkaline-earth metal hydroxyapatites</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100026&lng=es&nrm=iso&tlng=es Alkaline-earth metal hydroxyapatites are prepared by the co-precipitation method and characterized using XRD, ICP NH3-TPD, SEM-EDX, TEM and N2 physisorption analysis. The metal present in the hydroxyapatite influences the acidity of the catalyst. Oxidative dehydrogenation reactions carried out in a continuous flow fixed bed reactor showed that the selectivity towards desired products was dependent on the alkaline-earth metal in the hydroxyapatite. All hydroxyapatite catalysts showed high selectivity towards carbon oxides, followed by cracked products, octenes and aromatics. The highest selectivity and turnover numbers towards C8 products and a high specific rate was shown by Sr-HAp. The activation of Η-octane over these catalysts followed the Eley-Rideal mechanism. <![CDATA[<b>Modelling the effects of competing anions on fluoride removal by functionalized polyacrylonitrile coated with iron oxide nanoparticles</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100027&lng=es&nrm=iso&tlng=es Fe2O3 nano particles supported on functionalized poly-acrylonitrile was prepared. PAN-oxime-nano Fe2O3 was characterized by XRD, FTIR and TEM and used for fluoride adsorption. The adsorption capacity increased with increasing initial fluoride concentration and reaction time. Fluoride-removal performance of PAN-oxime-nano Fe2O3 was also tested in the presence of various competing anions usually found in drinking water. Competitive sorption between fluoride and competing anions showed a minimum preference for chloride counterions. Carbonate was the greatest competitor for fluoride removal followed by phosphate and sulphate. Counterion presence decreased fluoride adsorption capacity in order of CO3(2-)&gt; PO4(3-) &gt; SO4(2-) &gt; Cl-. The presence of anions at various concentrations decreased fluoride adsorption capacity on PAN-oxime-nano Fe2O3 by 1.22 to 6.51 mg g-1. Effects of each two anions exist simultaneously in aqueous solution on fluoride adsorption was investigated using Tukey's test (called also a pairwise comparison). Tukey's HSD results indicate that the differences between various pairs of anions are significant (P < 0.05), except for chloride-sulphate (P = 0.08). In the design of PAN-oxime-nano Fe2O3 for environmental applications, the strong influence of the counter ions must be considered. <![CDATA[<b>Kinetic and thermodynamic studies of charge-transfer complex formation between imipramine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (ddq) in acetonitrile and dichloromethane solutions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100028&lng=es&nrm=iso&tlng=es Spectro-kinetic studies revealed the formation of charge-transfer (CT) complex of Imipramine as an electron donor with π acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile and dichloromethane solutions. The resulted CT complexes exhibit spectra that were remarkably different from those of the donor and acceptor. The stoichiometry of the resulting complex was found to be 1:1 by the method of Job's continuous variation. The formation constants and thermodynamic parameters of the resulting electron-donor-acceptor (DA) complexes were determined by Benesi-Hildebrand and van't Hoff equations, respectively. The time-dependent spectra recorded after mixing donor and acceptor has been related to an immediate formation of DA complex, which is followed by two relatively slow consecutive reactions. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance-time data to appropriate equations. The activation parameters, i.e. activation energy, enthalpy, and entropy of activation were computed from temperature dependence of the rate constants. The observed results afford evidence concerning the critical role of solvent polarity on the kinetics and stability of the resulting charge transfer complexes. The ionization potential of the donor in the two solvents was estimated and compared with the theoretical values. <![CDATA[<b>A simple polarimetry technique for predicting the absolute configuration of the preferred enantiomer in chiral host-guest inclusion complexes</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100029&lng=es&nrm=iso&tlng=es A method for predicting the configuration of the preferred guest enantiomer in an inclusion complex with an optically pure hosl compound was developed. The method involves simply measuring the optical rotation of the host-guest inclusion complex as a whole, by means of polarimetry, and using this value in a calculation in order to obtain information about the guest configuration. The availability of standard optically pure guest materials is not required, nor is the isolation of the guest species from the host crystal, resulting in an attractive, inexpensive, rapid and simple procedure for this purpose. <![CDATA[<b>New pyridazinium-based ionic liquids: An eco-friendly ultrasound-assisted synthesis, characterization and biological activity</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100030&lng=es&nrm=iso&tlng=es An eco-friendly ultrasound-assisted procedure was developed for the preparation of a series of novel pyridazinium ionic liquids (ILs) 1-8. The structures of the novel ILs were established based on their FT-IR, ¹H, 13C NMR and mass spectra. Furthermore, the antimicrobial and anticancer activities of ILs 1-8 have been also investigated. The results of these screening experiments revealed that the ILs exhibited good to moderate antibacterial activity, such as IL 7, compared with standard drugs. Some of the newly synthesized ILs were also tested in vitro against human hepatocellular carcinoma (HEPG2), human breast adenocarcinoma (MCF7) and human colon carcinoma (HCT116) cell lines. Among the synthesized ILs, IL 8 was found to exhibit promising antiproliferative effects and produced the lowest IC50 values among the tested ILs. <![CDATA[<b>Adsorption of Mercury(II) onto activated carbons derived from <i>Theobroma cacao </i>pod husk</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100031&lng=es&nrm=iso&tlng=es Activated carbon prepared from Theobroma cacao pod husk was used as a low-costbiosorbent for the removal of mercury(II) from aqueous solutions. The influence of pH and contact time on the adsorption was investigated by conducting a series of batch adsorption experiments. The equilibrium data were fitted to the Langmuir and Freundlich isotherm models. The Langmuir isotherm was found to best describe the experimental data. The amount adsorbed increased with increasing temperature. The maximum adsorption capacity of mercury was found to be 10(5) ng g-1 for an initial mercury concentration of 100 ppb. The kinetics of adsorption were modelled by means of the Lagergren-first-order and pseudo-second-order models. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that pore diffusion played an important role in the adsorption, and intra-particle diffusion was the rate-limiting step during the first 30 min. A FTIR study revealed that the carbonyl and sulfur functional groups present on the surface of the adsorbing material were involved in chemical interaction with mercury(II). <![CDATA[<b>An inquiry-based practical curriculum for organic chemistry as preparation for industry and postgraduate research</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100032&lng=es&nrm=iso&tlng=es This paper describes the development of a new practical curriculum for third-year organic chemistry to replace the recipe-based approach typically used in undergraduate teaching laboratories. The new curriculum consists of an inquiry-based project set in a simulated industrial context preceded by two scaffolding experiments to prepare students for the task. The industrial project requires students to evaluate experimentally three multi-step synthetic routes to a given target based on cost, technical challenge and environmental impact in order to make a recommendation as to which route the 'company' should use to synthesize the compound. The project equips students with technical skills suitable for both postgraduate research and industry, and develops metacognition and understanding through the use of the jig-saw cooperative learning strategy and reflection. The students were found to engage with the practical work at a deep intellectual level, demonstrating that contextualized inquiry-based laboratory teaching afforded an improved quality of learning. In addition, the reported practical curriculum made a difficult subject accessible and even popular, to some measure grew the students' ability in all desired graduate attributes and resulted in the establishment of a professional identity for individual students. <![CDATA[<b>A comparison of adsorption equilibrium, kinetics and thermodynamics of aqueous phase clomazone between faujasite X and a natural zeolite from Kenya</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502015000100033&lng=es&nrm=iso&tlng=es In this study, a well-studied synthetic faujasite X (FAU-X) zeolite and a recently discovered natural zeolite material from Kenya (NZ-K) were compared for their efficiency in removal of clomazone, a herbicide and water contaminant, from aqueous solution. The adsorption kinetics, isotherms and thermodynamics parameters were investigated. Equilibrium sorption data were describable by both the Langmuir and Freundlich models. The adsorption kinetics obeyed the pseudo-second-order kinetic law while pore diffusion was not the sole operating rate determining step. The derived thermodynamic parameters, namely AG and AH, indicated the adsorption process was feasible, spontaneous and exothermic for the natural zeolite and non-spontaneous for the synthetic zeolite via a physical and chemical process, respectively. The natural zeolite proved to be a suitable low-cost adsorbent for clomazone removal with removal efficiency above 70 %, five-fold more efficient than faujasite X.