Scielo RSS <![CDATA[South African Journal of Chemistry]]> vol. 70 num. lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Understanding the Precipitated Calcium Carbonate (PCC) Production Mechanism and Its Characteristics in the Liquid-Gas System Using Milk of Lime (MOL) Suspension</b>]]> This study investigates the effect of operating variables and influence of milk of lime (MOL) conditions in PCC using a modified reactor. The variables includes: Ca(OH)2 feed concentration at 0.5 M-2.0 M and CO2 flow rates at 224.0 mL min-1 and 379.5 mL min-1, on the particle morphology and size in the gas-liquid route precipitation. The particle morphology and texture as well as the chemical content were sufficiently authenticated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray fluorescence (XRF). Experimental data show that lower concentration (<1.0 M) favoured the formation of rhombohedra calcite crystals with the particle size below 100 nm. However, increase in concentration and gas flow rate yielded a coarser crystal particles. Two polymorphs were produced at1Mreactant, i.e. rhombohedra calcite with CO2 flow rate of 224 mL min-1 and prismatic calcite at 380 mL min-1. Molarities higher than 1 M yielded a coarser prismatic crystals, and also has a tendency to crystallize into scalenohedron species especially with higher reactant concentration. <![CDATA[<b>Lanthanide(III) complexes with tridentate Schiff base ligand, antioxidant activity and X-ray crystal structures of the Nd(III) and Sm(III) complexes</b>]]> The tridentate N4-type Schiff base was synthesized from the condensation reaction of 2-hydrazinopyridine and pyridine-2-carbaldehyde. Neodymium and Samarium complexes were isolated when the corresponding nitrate salt was added to the solution of the ligand. The isolated compounds were characterized by elemental analyses, IR study, room temperature magnetic measurements and single X-ray crystal diffraction of the two crystals. Both complexes crystallize in the monoclinic system with space group P21/c.The cell parameters of the Nd complex are a = 11.0927(8)Å,b = 17.9926 (13) Å, c = 11.9395(9) Å and β = 115.274(5) ° while the Sm complex shows parameters cell of a = 11.0477(8) Å, b = 17.9254(13) Å, c = 11.9149(8) Å and β = 115.489(5) °. The X-ray study reveals isotopic Nd/Sm binuclear structures were each metal ion is nine-coordinated in the same fashion. Both metal centers have distorted tricapped trigonal prism geometry, with the Schiff base acting as tridentate ligand. The DPPH· radical scavenging effects of the Schiff base ligand and its Ln(III) complexes were screened. The Ln(III) complexes were significantly more efficient in quenching DPPH· than the free Schiff base ligand. <![CDATA[<b>Chemical and nutritional compositions of flame of forest (Delonix regia) seeds and seed oil</b>]]> The seeds of Delonix regia were investigated for proximate, antinutrient, mineral, amino acid and vitamins compositions while the physicochemical properties, fatty acids and acylglycerols of its oil were also determined. Moisture, crude fibre, ash, crude fat, crude protein, carbohydrate, tannin, oxalate and saponin were 10.12 ± 0.59 %, 14.6 ± 0.44 %, 1.03 ± 0.02 %, 17.16 ± 0.15 %, 8.75 ± 0.04 %, 48.34 %, 1.28 ± 0.02 mg g-1,2.57 ± 0.02 mg g-1, and 2.89 ± 0.02 mg g-1, respectively. The seed contained 1604.0 ± 0.1 mg 100 g-1 Na, 1144.0 ± 0.2 mg 100 g-1 Fe, 920.0 ± 0.6 mg 100 g-1 Zn, 284.0 ± 0.1 mg 100 g-1 Mn, 114.0 ± 0.1 mg 100 g-1 Cu, 9.1 ± 0.1 mg 100 g-1 K, 4.1 ± 0.1 mg 100 g-1 P, 4.0 ± 0.1 mg 100 g-1 Mg, and 1.5 ± 0.1 mg 100 g-1 Ca. The ratios of Na/K and Ca/P were 176.26 and 0.37, respectively. Glutamic acid (147.95 mg g-1 protein) and methionine (10.87 mg g-1 protein) were the most and least abundant amino acids, respectively. The oil was liquid at room temperature, sweet-smelling, amber and had high saponification (203.40 ± 6.72 mg KOH g-1) and iodine (121.03 ± 3.02 g 100 g-1) values. The most abundant fatty acids in the oil followed the order; linoleic acid (C18:2, 37.1 %) > palmitic acid (C16:0,23.90 %) > stearic acid (C18:0,8.20 %) > linolenic (C18:3, 7.6 %) > oleic (C18:1A„ 4.91 %) > ricinoleic acid (C18:1,4.50 %). The ratio of saturated to unsaturated fatty acids was 0.83. Vitamin E (33.68 mg 100 g-1) and triacylglycerols (96.62 %) accounted for the highest contributions to vitamins and acylglycerols, respectively, in the oil. These results showed that the seeds were nutritive and good for both nutrition and industrial uses. <![CDATA[<b>Lead pollution of shooting range soils</b>]]> A total of eight military shooting ranges were used for this study. Soil samples were collected at each of the eight shooting ranges at the berm, target line, 50 and 100 m from berm. In all of the shooting ranges investigated the highest total lead (Pb) concentrations were found in the berm soils. Elevated Pb concentrations of 38 406.87 mg kg-1 were found in the berm soils of TAB shooting range. Most of the shooting range soils contained high levels of Pb in the range above 2000 mg kg-1 far exceeding the United States Environmental Protection Agency (USEPA) critical value of 400 mg kg-1. The predominant weathering products in these shooting ranges were cerussite (PbCO3) and hydrocerussite (Pb3(CO3)2(OH)2). The Synthetic Precipitation Leaching Procedure (SPLP) Pb concentrations exceeded the USEPA 0.015 mg kg-1 critical level of hazardous waste indicating possible contamination of surface and groundwater. <![CDATA[<b>Experimental sensing and density functional theory study of an ionic liquid mediated carbon nanotube modified carbon-paste electrode for electrochemical detection of metronidazole</b>]]> A new highly sensitive sensor was prepared for metronidazole (MNZ) employing single-walled carbon nanotube (SWCNT) and 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). The utilization of IL as a binder in the paste increased the response of the electrode. The performance of the obtained carbon paste electrode was examined by differential pulse voltammetry. Various factors like electrode composition, types of supporting electrolyte, pH, stirring rate, scan rate were studied and optimized. The modified sensor demonstrated high recognition ability and sensitivity for MNZ when compared with the unmodified sensor. Moreover, the sensor also demonstrated good stability and acceptable reproducibility for the determination of MNZ. In the optimum experimental conditions, the current response of the electrochemical sensor studied for metronidazole solution and linearity was obtained in the range of 5.00 X 10-5 to 5.00 X 10-3 mg L-1, with a detection limit of 1.238 X 10-5 mg L-1. The method was successfully used for the analysis of MNZ in the milk and egg samples with acceptable recoveries of 90.33-108.0 %. In addition, the non-covalent interactions of the metronidazole with the SWCNT were investigated employing the density functional theory (DFT) method. <![CDATA[<b>Effect of benzamide on the corrosion inhibition of mild steel in sulphuric acid</b>]]> The effect of benzamide as a chemical inhibitor on mild steel corrosion in 0.5M H2SO4 was studied at ambient temperature. The experimental work was performed with gravimetric and potentiostatic polarization measurement methods. Potentiostatic polarization measurement was performed with a potentiostat (Autolab PGSTAT 30 ECO CHIMIE) interfaced with a computer for data acquisition and analysis. The benzamide inhibitor achieved very effective corrosion inhibition of the steel specimens in the H2SO4 test medium. The inhibition performance increased with increasing concentration of the inhibitor. Benzamide's best performance was achieved with the 4 g 200 mL-1 H2SO4 concentration and closely followed by the 3 g 200 mL-1 of the H2SO4.In 0.5 M H2SO4, the 4 g and 3 g 200 mL-1 H2SO4 gave the optimal performance with weight loss of 2.99 g at 480 h of the experiment, respectively. The corrosion rate for 4 g's was 6.4 mm yr-1. The experiment also achieved polarization resistance values of 3.98 and 2.37E + 01Ω; corrosion rate, CR, of 7.48E + 00and1.26E + 01 mm yr¹ and current density (Icorr) values of 6.45E-04 and 1.08E - 03 A cm-2, respectively. The corrosion inhibition efficiency values are, respectively, 60 and 70 % for both 3 g and 4 g 200 mL-1 H2SO4 concentrations at 48 h. Results of ba and bc indicated a mixed type inhibitor. Benzamide adsorption on the steel's surface obeys the Freundlich adsorption isotherm. <![CDATA[<b>Novel silver-doped NiTiO<sub>3</sub>: auto-combustion synthesis, characterization and photovoltaic measurements</b>]]> Novel silver-doped nickel titanate nanoparticles (Ag-NiTiO3) were successfully prepared via a sol-gel method in the presence of stearyl alcohol as the capping agent and solvent. The formation of pure crystallized nickel titanate and silver-doped nickel titanate was occurred when the precursor was heat-treated at 700 °C in air for 150 and 60 min, respectively. The structural, morphological, and optical properties of obtained products were characterized by techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Energy dispersive X-ray microanalysis (EDX), ultraviolet-visible (UV-vis), and scanning electron microscopy (SEM). The magnetic property of the prepared Ag-NiTiO3 nanoparticles was also investigated with vibrating sample magnetometer (VSM). To fabricate a FTO/TiO2/Ag-NiTiO3/Pt-FTO solar cell, Ag-NiTiO3 film was directly deposited on top of the TiO2 prepared by electrophoresis deposition method. Furthermore, solar cell result indicates that an inexpensive solar cell could be developed by the synthesized Ag-NiTiO3 nanoparticles. <![CDATA[<b>Synthesis, spectroscopic and DFT Characterization of 4<em>β</em>-(4-<em>tert</em>-Butylphenoxy)phthalocyanine positional isomers for non-linear optical absorption</b>]]> In this work the synthesis, spectral characterization and non-linear optical properties of metal-free 4y/-(4-ferf-butyl-phenoxy)phthalocyanine isomers are described and compared to the previously reported alpha derivative. The second-order nonlinear optical properties of the phthalocyanine isomers were investigated using the Z-scan technique and compared to the theoretical data obtained from density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. Z-scan results indicated strong non-linear behaviour, revealing reverse saturable absorption (RSA) profiles for all four isomers. The experimental Bexp values showed the following trend: C4h (9.31 X 10(10) mMW¹)>D2h (7.89 X 10(10) mMW-1)>Cs (7.32 X 10-10 mMW-1)>C2v (1.77 X 10-10 mMW-1). These results were similar to that obtained with the 4a-(4-to-f-butylphenoxy)phthalo-cyanines as the C2v and Cs isomers were found to have the lowest Bexp values compared to other symmetries. The 4ß-(4-tert-butylphenoxy)phthalocyanine C4h isomer was found to show better non-linear optical properties compared to all other isomers. <![CDATA[<b>ICH guidelines-compliant HPLC-UV method for pharmaceutical quality control and therapeutic drug monitoring of the multi-targeted tyrosine kinase inhibitor pazopanib</b>]]> In this study, an HPLC method with ultraviolet (UV) detection was developed and validated for determination of pazopanib (PAZ), a multi-targeted tyrosine kinase (TK) inhibitor in bulk drug, tablets formulation, and in human plasma. Oxamniquine (OXA) was used as internal standard (IS). The analytical column used for the separation was Nucleosil CN with dimensions (i.d. 250 X 4.6 mm and particle size 5 μπι). The separation was carried out in isocratic mode with mobile phase constituting acetonitrile:100 mM sodium acetate buffer (pH 4.5); 40:60, v/v. The developed method was linear in the concentration range of 2-12 μg mL-1 and had a correlation coefficient (r = 0.9998, n = 6). The limits of detection and quantitation (LOD and LOQ) were 0.27 and 0.82 μg mL-1, respectively. The relative standard deviations for the inter- and intra-assay precisions were below 3.61 % and the accuracy of the method was 96.69-104.15 %. The degradation products were resolved from the intact drug, proving the stability-indicating property of the proposed method. The recovery values were 100.17-103.98 % (± 1.81-4.02) for determination of PAZ in human plasma. The results indicated the versatility of the new method in estimation of PAZ during pharmaceutical quality control (QC) and therapeutic drug monitoring (TDM). <![CDATA[<b>Great South African molecules: the case for mycothiol</b>]]> South Africa has one of the oldest chemical societies in the world and has a long history of natural products, synthetic, and medicinal chemistry yet the visibility of molecules discovered or synthesized in South Africa is very low. Is this because South African scientists are incapable of discovering influential and celebrated molecules, or is there inadequate publicity of such discoveries? Perspective profiles on the discovery and scope of research on 'Great South African Molecules' should be a good start to redress this state of affairs. One such molecule deserving publicity is the antioxidant mycothiol which is produced by mycobacteria. This is a molecule of interest not only because of its medicinal potential in the fight against tuberculosis, but also from synthetic methodology and enzyme inhibition studies. This review aims to illuminate the scope of research in mycothiol chemistry for the purpose of promoting multidisciplinary investigations related to this South African molecule. <![CDATA[<b>Lyapunov exponents and the Belousov-Zhabotinsky oscillator: an interactive computational approach</b>]]> The Belousov-Zhabotinsky (BZ) chemical oscillator is the most studied oscillator. It has been modelled on the basis of single-step mechanisms which have been continuously refined since the seminal manuscript by Field, Koros and Noyes in 1972. This manuscript reports on a unique way of modelling the global dynamics of the oscillator by assuming that the BZ oscillator has shown chaotic behaviour. The unique mathematical definition of chaos is very stringent, and, in this manuscript, we attempt to trace this unique exotic behaviour by the use of 'onto' maps of the interval onto itself which are known to exhaustively show a universal sequence of states that has all the hallmarks of chaotic behaviour. A series of one-humped maps of the interval display, through iterations and subsequent symbolic dynamics, a universal sequence of steps that commence with period-doubling, culminating in chaotic behaviour at some accumulation point of an appropriate bifurcation parameter. We put this theory to the test for the BZ oscillator in this manuscript by selecting a unique continuous map of the interval. This was then decomposed by an iterative treatment. Metric entropy and subsequent arbiter of chaotic behaviour was determined by evaluation of Lyapunov exponents which were then compared to observed BZ oscillator states. Our proposed map satisfactorily modelled the global dynamics of the BZ oscillator; predicted period-doubling, and a regime after a critical bifurcation parameter, where chaotic sequences were dense. We also produce, in the Addendum, an iterative MatLab procedure that any reader can utilize to reveal the type of states and behaviour reported here. <![CDATA[<b>Synthesis of Fluorescent Poly(coumarin-triazoles) via a CuAAC 'click' reaction</b>]]> We describe a new fluorescent polymer system based on a coumarin-triazole functionality. The non-fluorescent 3-azido-coumarin-alkyne monomers are polymerized in a step-growth manner via a Cu (I)-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction. The process involves the conversion of a quenching azide group to 1,2,3-triazole in the monomer that leads to an increase in the intensity of fluorescence in the new polymer. The solubility and photophysical properties of the polymer were enhanced through co-polymerization with an aliphatic co-monomer. <![CDATA[<b>Electronic effects of group fragments on the XPS of Fe 2p and 3p photoelectron lines of ferrocenyl-containing chalcones</b>]]> A series of ferrocenyl-containing chalcones, Fc-CO-CH=CH-C6H4R, with the R-group on the /wa-position on the phenyl ring and R = OCH3(1), CH3(2), C6H5 (3), tBu (4), H(5), Br (6) and CF3(7) were subjected to an X-ray photoelectron spectroscopy (XPS) study. The linear relationships obtained between the Gordy-scale group electronegativity of molecular fragment R, xR, and the maximum binding energies of the Fe 2p3/2 and the Fe 3p3/2 photoelectron lines, confirmed communication between the iron atom of the ferrocene moiety and the molecular fragments, R, of 1-7. These relationships illustrated that the influence of the electronic properties of the molecular fragments are more pronounced in the Fe 3p photoelectron lines than in the Fe 2p photoelectron lines. <![CDATA[<b>Extraction and Pre-concentration of Phthalic Acid Esters from Aqueous Solutions using Agitation-assisted Dispersed Binary Solvents Microextraction</b>]]> As the search for efficient, affordable and environmentally friendly extraction methods continues, miniaturized solvent techniques are receiving considerable attention due to their simplicity, efficiency and fast extraction rates. Herein we report application of a modified dispersive liquid-liquid microextraction through the introduction of a second extracting solvent in place of a disperser solvent leading to a much improved organic solvent recovery after the extraction of phthalic acid esters from aqueous solutions. The method employs a 75 μL binary mixture of ethylacetate and tetrachloromethane with a 3:1 ratio, extraction time of 20 seconds, and 10 % NaCl. The method demonstrates sufficient linearity (R² > 0.9866) and repeatability (%RSD £ 12.5, for n = 15) with the estimated LOD in the range (0.01-0.05 ng mL-1) using the S/N approach. The method demonstrated significant enrichment factors averaging about 2100 with headspace and about 3000 and increase of over 40 % without headspace, indicating the importance of reduced headspace volume in this approach, especially if the ionic strength is increased. However, the method yielded a significantly wide range of recoveries (65-115 %) when applied to the analysis of spiked soil samples when coupled to hot-water extraction. However, this may notbe entirely attributable to the extraction approach but rather heat-induced hydrolysis during the hot-water dissolution, prior to the proposed organic extraction method. <![CDATA[<b>Austenite and forging effects on 18Cr-18Mn stainless steel impedance</b>]]> The influence of the austenite phase (gamma iron dissolved in carbon) in the corrosion resistance of 18Cr-18Mn steel was studied. The percentage of austenite in the steel was calculated using the (Cr eq/Ni eq) equation. In order to obtain the impedance value of the steel exposed to a corrosive saline environment, Bode diagrams were obtained at 8,16 and 24 hours of exposure. The results obtained indicate that an increase of the austenite phase in the steel, also produces an increase in various steel properties, such as steel impedance and polarization resistance (Rp). On the other hand, it was observed that the impedance value of the forged 18Cr-18Mn steel increases when the steel is immersed in a saline solution. <![CDATA[<b>Physicochemical characterization and <i>In vitro </i>evaluation of the sun protection factor of cosmetic products made from natural clay material</b>]]> Clay has been widely used as photo protectants in rural places of South Africa. Recently, there are wide range of products which are marketed in South Africa as clay cosmetics which are used for photo protection. In this work, in vitro determination of the sun protection factor (SPF) of newly formulated cosmetics produced from natural clay material from the Bizana region in the Eastern Cape Province of South Africa was performed by spectrophotometric means. The SPF values found for clay material, face cream, foundation, face mask and scrub were 1.18,18.33,13.71, 6.74 and 9.53, respectively. The same materials were characterized using thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM) equipped with energy dispersive spectrometry (EDS) and inductively coupled plasma (ICP). Based on FTIR, XRD, XRF and SEM-EDS results, kaolinite, goethite and quartz were the major minerals found in the clay. Toxic elements such as mercury and cadmium were not detected during ICP analysis; however, traces of lead (0.72-2.14 mg kg-1) and arsenic (0.49-0.69 mg kg-1) were found in cosmetic products. The results obtained in this study indicate that the cosmetic products manufactured from clay have sun protection ability. <![CDATA[<b>Synthesis and photocatalytic activity of monolithic Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub></b>]]> The monolithic Fe2O3/TiO2 composites were synthesized via a one-pot sol-gel process with titanium tetrachloride as a Ti source and ferric chloride as a Fe source. The monolithic Fe2O3/TiO2 composites were characterized by scanning electron microscopy, powder XRD, N2/adsorption-desorption, fluorescence and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Fe2O3/TiO2 composites were evaluated by degradation of bisphenol A. The results indicated that, with the doping of Fe, the surface area of the monolithic Fe2O/TiO2 increased, the forbidden band width decreased and the electron-hole recombination rate decreased. The monolithic Fe2O3/TiO2 composite with Fe/Ti molar ratio of 0.03 had the best photocatalytic activity for degradation of bisphenol A. <![CDATA[<b>Synthesis of some 5-[2-Aryl-2-oxoethyl]-1,3-dimethylpyrimidine-2,4,6-trione derivatives by a one-pot, three-component reaction</b>]]> This study reports the reduction of α,β-unsaturated ketones 4a-g, formed by condensation of arylglyoxals 2a-g with 1,3-dimethylbarbituric acid (3) by L-cysteine (5) in the presence of phosphotungstic acid as a catalyst. This reaction leads to the formation of 5-[2-aryl-2-oxoethyl ]-1,3-dimethylpyrimidine-2,4,6-triones 6a-g, with no sign of any heterocyclic product formation. The structure of compound 6f was confirmed by X-ray crystallography. <![CDATA[<b>Effects of precursor salt on colloidal cobalt oxyhydroxides composition and its application in non-enzymatic glucose</b>]]> Colloidal cobalt oxyhydroxide [CoO(OH)] has been prepared from precursors cobalt acetate and cobalt nitrate. The cobalt colloids (Co.Acetate and Co.Nitrate) were characterized by simultaneous thermogravimetric/differential thermal analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared and electronic spectroscopy. Characterization data indicated the presence of counter ions (CH3COO- and NO3-), likely intercalated within the structure of the colloidal cobalt. The platinum working electrode chemically modified with cobalt colloid was studied by cyclic voltammetry in alkaline solution [0.5 M, NaOH], which revealed differences in the reproducibility and stability of the electroactive material. The colloidal Co.Nitrate modified electrode was applied to the non-enzymatic glucose (Glu) electrooxidation in the concentration range from 7.2 to 21.9 X 10(8) mol L-1. The limits of detection (5.87 X 10 8 mol L-1) and quantitation (1.96 X 10 7 mol L-1) calculated suggest that colloidal Co.Nitrate has the potential to be used as a sensor for low glucose concentration.