Scielo RSS <![CDATA[South African Journal of Chemistry]]> vol. 70 num. lang. en <![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.