Scielo RSS <![CDATA[South African Journal of Chemistry]]> vol. 65 num. lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>An efficient and convenient protocol for the synthesis of optically active 1,2,4-triazolo-[3,4-b]-[1,3,4]-thiadiazole, 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives having L-Amino acid moieties</b>]]> A series of novelbis triazolothiadiazole, 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives attached to L-amino acid moieties were synthesized in good yields using a simple and practical method. The structure of all synthesized compounds was confirmed by IR, ¹H NMR, 13C NMR spectroscopy and elemental analysis. <![CDATA[<b>Facile synthesis of 2-(1,3-benzoxazol/benzothiazol-2-yl)-3<i>H</i>-benzo[f]chromen-3-one as blue fluorescent brighteners</b>]]> A novel synthetic method was developed to prepare new fluorescent 2-(1,3-benzoxazol/benzothiazol-2-yl)-3H-benzo [f]chromen-3-one derivatives 3a-p by the Knoevenagel condensation between 2-hydroxy-1-naphthaldehyde and benzothiazole-2-yl-aceatates or N-methyl benzoxazole-2-yl-acetates using choline chloride/urea ionic liquid as a green catalyst. The results of fluorescence studies revealed that all the compounds show moderate to low emission intensities and are expressed in the form of quantum yields. <![CDATA[<b>A highly efficient solvent-free acetalization of aldehydes to 1,1-diacetates catalyzed by SiO<sub>2</sub>-Pr-SO<sub>3</sub>H</b>]]> 1,1-Diacetates are prepared in excellent yields from aldehydes and acetic anhydride under solvent-free conditions at room temperature in short reaction times using catalytic amount of sulfonic acid functionalized silica (SiO2-Pr-SO3H) which could be easily handled and removed from the mixture of reaction. <![CDATA[<b>Pre-concentration of toxic metals using electrospun amino-functionalized nylon-6 nanofibre sorbent</b>]]> This paper presents a new approach for pre-concentrating toxic metals (As, Cd, Ni and Pb) in aqueous environments using an amino-functionalized electrospun nanofibre sorbent. The sorbent, composed of nanofibres of average diameter 80 ± 10 nm and specific surface area of 58 m² g-1, exhibited fast adsorption kinetics (<20 min) for As, Cd, Ni and Pb. The optimal pH for the uptake of As, Cd, Ni and Pb were 5.5, 6.0, 6.5 and 11, respectively. The adsorption process best fitted the Freundlich isotherm and followed the first-order kinetics. The highest pre-concentration achieved using the sorbent was 41.99 (Ni in treated wastewater). The capacity of the sorbent to pre-concentrate the toxic metals was compared with those of aqua regia and HNO3+H2O2 digestions. The pre-concentration factors achieved for Cd in river water samples can be ranked as aqua regia digestion (0.73) &gt; adsorption (0.34) &gt; HNO3+H2O2 (0.23) digestion. A similar trend was observed for Ni in river water as well as Ni and Cd in tap water samples. Pb ions in the river water samples were pre-concentrated slightly better using the two digestion methods (pre-concentration factors ~22) compared to adsorption method (pre-concentration factor ~21). The use of the electrospun amino-functionalized nanofibre sorbentpresents an efficientand cost-effective alternative for pre-concentration of toxic metals in aqueous environments. <![CDATA[<b>Comparison of tetrahydroisoquinoline (TIQ) thiazole and oxazoline ligands for asymmetric Henry reactions</b>]]> A series of novel C¹ symmetric thiazole ligands with a tetrahydroisoquinoline (TIQ) backbone were synthesized. Their application in the catalytic asymmetric Henry reaction was investigated with comparison to a corresponding TIQ oxazoline ligand. The Cu(II)-oxazoline complex was more reactive and furnished moderate enantioselectivities up to 61:36 (syn:anti) with 75:25 diastereomeric excess, while the Cu(II)-thiazole complexes had lower selectivity. This is the first example where a direct comparison between an N, N-type thiazole and oxazoline ligands has been studied. <![CDATA[<b>Synthesis and antibacterial activity of some 5,5'-(1,4-phenylene)-bis-1,3,4-oxadiazole and bis-1,2,4-triazole derivatives as precursors of new <i>S</i>-nucleosides</b>]]> Five compounds, namely 5,5'-benzene-1,4-diylbis(1,3,4-oxadiazole-2-thiol)6 and 5,5'-benzene-1,4-diylbis(1H-1,2,4-triazole-3-thiol) 7a and its derivatives 7b-d were synthesized. Two related S-nucleosides 9 and 10 have been prepared from 6 and 7a Some of these synthesized compounds were tested in vitro by spotting on Mueller Hinton Agar medium against some Gram-positive bacteria, Staphylococcus aureus and Enterococcus faecalis and three Gram-negative bacteria Escherichia coli, Pseudomonasaeruginosa, Pseudomonas fluorescens and compared with the known antibiotics cephalosporin (cefotaxim) and gentamycin. Compound 6: showed significant inhibitory activity against Gram-positive E. faecalis and Gram-negative E. coli bacteria while the others have shown variable inhibition activity. <![CDATA[<b>Rapid synthesis of 2-substituted-2,3-dihydro-4(1<i>H</i>)-quinazolinones using boric acid or sodium dihydrogen phosphate under solvent-free conditions</b>]]> Two efficient and convenient methods have been described for synthesis of 2-substituted-2,3-dihydro-4(1H)-quinazolinone derivatives by one-pot condensation of 2-anthranilamide with aldehydes or ketones in the presence of a catalytic amount of boric acid or sodium dihydrogen phosphate under solvent-free conditions. The attractive features of these processes are short reaction times, easy isolation of products, excellent yields and an environmental friendly procedure. <![CDATA[<b>The synthesis of nitrogen-doped multiwalled carbon nanotubes using an Fe-Co/CaCO<sub>3</sub> catalyst</b>]]> A CVD method was used to prepare high-quality nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) using acetonitrile as the nitrogen and carbon source and acetylene as a carbon source over an Fe-Co/CaCO3 catalyst in the temperature range 700-850 °C. This represents a continuation of earlier work in which Fe-Co on CaCO3 was used to make undoped carbon nanotubes. The effect of synthesis parameters (growth temperature and CH3CN vaporization temperature) on the yield, size, quality, morphology and thermal stability of the N-MWCNTs was studied. The resulting materials were characterized by TEM, SEM, TGA, BET, XPS, CN elemental analysis and Raman spectroscopy. TEM analysis revealed that the nanotubes exhibit bamboo-like structures with rough surfaces and a relatively uniform diameter. The bamboo compartment distance decreased with increase in synthesis temperature due to the increased nitrogen content in N-MWCNTs. The SEM examination showed that at high synthesis temperatures carbon spheres (CSs) with chain-like morphology and large sizes were also formed along with the N-MWCNTs. The XPS and CN elemental analysis revealed that nitrogen atoms were successfully doped into the carbon walls. The amount of nitrogen incorporated in the N-MWCNTs varied with increasing growth time and CH3CN vaporization temperature. <![CDATA[<b>GC-MS analysis and antimicrobial activities of the non-polar extracts of <i>Mundulea sericea</i></b>]]> The composition of the non-polar extracts of the leaves, stem bark and twigs of Mundulea sericea (Fabaceae) were analyzed using GC-MS. Eight, five and eleven components were identified from the leaves, twigs and stem bark extract, respectively. The major components were identified as: caryophyllene (43.6 %) and cadina-3,9-diene (29.7 %) in the leaf extract, amorphene (34.4 %) and valencene (17.9 %) in the stem bark extract and isoledene (29.0 %) and α-gurjunene (22.4 %) from the twig extract. Sesquiterpenes were the major abundant components in the non-polar extracts. The leaf, stem bark and twig extracts showed weak antibacterial and antifungal activities. <![CDATA[<b>The transposing of isomer yields in the methanolyses of <i>N</i>-substituted quinolinimides by triethylamine</b>]]> The effect of triethylamine in transposing the respective yields of the two isomeric esters ensuing from the methanolysis of N-substituted quinolinimides is described and is rationalized with a mechanism. <![CDATA[<b>Functionalization of a natural biopolymer with aliphatic polyamines and its sorption properties for vanadium removal from aqueous solutions</b>]]> A low-cost natural adsorbent, Moringa oleifera, was investigated as a potential alternative for currently costly methods of removing vanadium from contaminated aqueous solutions. The unmodified bark was characterized using techniques such as N2-BET, SEM, XRD and FTIR spectroscopy, CHNS elemental determination and AA spectroscopy. Results showed a relatively small surface area, motivating surface functionalization to enhance adsorption capacity. Chemical modification was performed using four aliphatic polyamines: ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). The modified bark was characterized and then investigated to determine its efficiency in removing VO2+ from aqueous solutions. The bark had a mesoporous amorphous structure and was enriched with N and S groups. FTIR absorption frequencies also revealed that polyamines were indeed immobilized on the adsorbent surface. The polyamine density was calculated and was in the order of EDA>DETA>TETA>TEPA, whereas the adsorption efficiency with VO2+ was in the order DETA>EDA>TETA>TEPA. Adsorbent amination was enhanced by up to 26 % and adsorption performance improved by up to 155 %. It was, therefore, concluded that chemical modification of M. oleifera using polyamines enhances adsorption of VO2+ from aqueous solutions. This can, thus, preconcentrate VO2+ in the bark leading to its use as a good water purifier. <![CDATA[<b>Ionic liquid 3-methyl-1-sulphonic acid imidazolium chloride {[Msim]Cl}: A highly efficient, mild and green catalyst for the synthesis of <b><i>β</i></b>-acetamido ketones</b>]]> Bronstedacidic ionic liquid 3-methyl-1-sulphonic acid imidazolium chloride {[Msim]Cl} is utilized as a highly efficient, inexpensive, mild and green catalyst for the synthesis of β-acetamido ketones by the one-pot multi-component coupling between acetophenones, arylaldehydes, acetonitrile and acetyl chloride at room temperature. Under these conditions, the title compounds are produced in high to excellent yields and in relatively short reaction times. In addition, this method is superior to reported methods, for the synthesis of β-acetamido ketones and is applicable for the synthesis of tris(β-acetamido ketone). <![CDATA[<b>Highly active, carbon-supported, PdSn nano-core, partially covered with Pt, as catalysts for methanol oxidation</b>]]> Carbon-supported, Pt partially covered, PdSn alloy nanoparticles (Pt-PdSn/C) were synthesized via a metathetical reaction of PdSn alloy nanoparticles, and a platinum precursor. The electrochemical activity was evaluated by methanol oxidation. The Pt-PdSn/C catalysts were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CV). TEM showed that Pt grows layer-by-layer on the surface of PdSn cores and the thickness of the Pt shell is 0.2 nm, about 1-2 monolayers thick. Cyclic voltammetry results showed that PdSn/C nanoparticles, partially covered by Pt, have a better electrocatalystic performance than conventional PtRu/C and PtPdSn/C catalysts. Electrochemical active surface areas of the Pt-PdSn/C was 2.30 times larger than that of PtRu/C and 1.8 times higher than that of PtPdSn/C catalysts. The results showed that a metathetical reaction is an efficient way of preparing, low Pt loading, highly active electrocatalyst, for methanol oxidation, thus offering great potential for producing Pt-based electrocatalyst for direct methanol fuel cells on a large scale. <![CDATA[<b>Novel O^N^N pyrazolyl-imine and imidazolyl-imine pincer palladium complexes as Heck coupling catalysts</b>]]> Five pyrazolyl and imidazolyl compounds, 2,4-di-tert-butyl-6-[2-pyrazol-1-yl-ethylimino-methyl]-phenol (L1), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L2), 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3), 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L4) and 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L5) were synthesized by condensation of the appropriate 2-hydroxybenzaldehyde and the corresponding alkylamine. Reactions of L1-L5 with either [Pd(NCMe)2Cl2] or [Pd(COD)MeCl] led to in situ deprotonation of the phenolic-OH proton to afford the pincer palladium complexes [Pd(L1)Cl] (1), [Pd(L1)Me] (2), [Pd(L2)Cl] (3), [Pd(L3)Cl] (4), [Pd(L4)Cl] (5) and [Pd(L5)Cl] (6). The tridentate coordination modes of the ligands were confirmed by the solid state structures of 1, 2, 3 and 4.H2O: Complexes 1-6 catalyzed the Heck coupling reactions of iodobenzene and butylacrylate. In addition, complex 4 catalyzed the Heck coupling reaction of butyl acrylate and bromobenzene; giving conversions as high as 70 %. <![CDATA[<b>Study of cyclization of diphenylacetals derived from L-rhamnose and L-fucose: A theoretical approach</b>]]> This work aimed to study the configuration of two mono-tosyl-diphenylacetals, highly flexible molecules derived from L-ramnose and L-fucose, by means of the Monte Carlo conformational search method. The energy of the conformers established by this method and calculated by using the molecular mechanics force field (MMFF) permitted to establish a first conformational space. The geometry of the conformers was optimized by using the semi-empirical AM1 and the density functional B3LYP/DGDZVP methods. We were able to explain the different final products recovered from the reaction of the diphenylacetals derived from L-rhamnose and L-fucose with tosyl chloride, in a pyridine solution. On the other hand, obtaining cyclical compounds by intramolecular cyclization could be an attractive pathway for the synthesis of furanosides. <![CDATA[<b>Convenient reduction of carbonyl compounds to their corresponding alcohols with NaBH<sub>4</sub>/(NH<sub>4</sub>)<sub>2</sub>C<sub>2</sub>O<sub>4</sub> system</b>]]> Sodium borohydride (0.4-1.5 equivalents) in the presence of ammonium oxalate (0.2 equivalents) reduces varieties of organic carbonyl compounds such as aldehydes, ketones, acyloins, a-diketones and α,β-unsaturated carbonyl compounds to their corresponding alcohols. Reduction reactions were carried out in acetonitrile in high to excellent yields of products. The chemoselective reduction of aldehydes over ketones was accomplished successfully with this reducing system. In addition, regioselectivity and exclusive 1,2-reduction of conjugated carbonyl compounds to their corresponding allylic alcohols in high to excellent yields was achieved successfully with this reducing system. <![CDATA[<b>Effects of deposited metallic silver on nano-ZnO for the environmental purification of dye pollutants</b>]]> Silver-deposited nano-ZnO samples with different Ag loadings were prepared by a one-pot solvothermal method. The structure, physico-chemical and optical properties of the products were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PLS). The experimental results show that the prepared nanometer zinc oxide powders have a narrow size distribution of 40-60 nm, and their crystal forms can be assigned to hexagonal wurtzite structures. Moreover, the photocatalytic activity of the samples was examined by using photocatalytic oxidation of methylene blue (MB), as a model reaction, and the effects of the noble metal content on the photocatalytic activity were investigated. The results indicate that the photocatalytic activity of the ZnO nanoparticles can be greatly improved by depositing appropriate amounts of noble metal on their surfaces. In addition, a mechanism was proposed in order to account for the enhanced activity. It is evident that the effective lifetime of photogenerated holes is prolonged by electron-trapping of the metallic silver on the surface of the ZnO nanoparticles. The metal deposits serve as electron sinks, which lead to an enhanced rate of dioxygen reduction, facilitating the generation of hydroxyl radicals, and thereby increasing the photocatalytic activity. <![CDATA[<b>The facile synthesis of <i>N</i>-aryl isoxazolones as DNA intercalators under solvent-free conditions using microwave irradiation</b>]]> The reaction of chloroheterocycles with some isoxazolones under microwave irradiation and under solvent-free conditions to give the corresponding mono isoxazolinyl derivatives is reported. The main advantages of this method are: (I) elimination of the nitrogen gas (N2), (II) solvent-free conditions, (III) microwave irradiation, (IV) avoiding the use of silica gel for purification of the products, and (v) higher and shorter reaction times. These compounds have potential applications as DNA intercalators. <![CDATA[<b>Synthesis and NMR elucidation of novel pentacycloundecane-derived peptides</b>]]> Herein we report the synthesis and NMR elucidation of five novel pentacycloundecane (PCU)-derived short peptides as potential HIV protease inhibitors. ¹H and 13C spectral analysis show major overlapping of methine resonance of the PCU 'cage' thereby making it extremely difficult to assign the NMR signals. Attachment of short peptides to the cage at position C-8/C-11 results in conformational differences of the peptide side chains due to diastereomeric interactions between the cage skeleton and the chiral side chains. The use of two-dimensional NMR techniques proved to be highly effective in the elucidation of such systems. <![CDATA[<b>A molecular dynamics study of lunasin</b>]]> Lunasin, a 43 amino acid peptide, suppresses chemically induced transformations in mammalian cells and skin carcinogenesis in mice. This peptide has also been reported to exhibit very good bioavailability after its oral administration. However, despite its biological and medicinal significance, the exact three-dimensional (3D) structure of lunasinis thus far not yet fully characterized. Thus this work is aimed at exploring the conformational profile of lunasin,using classical molecular dynamics (MD) simulations at the time scale of 300 ns. The results obtained from the MD trajectory reveal that lunasin has a strong propensity to exhibit three characteristic a helical bundles in its structure supported by residues His5-Cys10, Cys22-Ile30 and Asp35-Asp41. The reported cell adhesion motif (Arg-Gly-Asp) of lunasin responsible for its binding to cell chromatin, on other hand, did not exhibit any characteristic secondary feature. The structural information obtained from the current study could be useful to better understand the bioactive conformation of lunasin. <![CDATA[<b>Hydrothermal synthesis of CdWO<sub>4</sub> nanorods and their photoluminescence properties</b>]]> CdWO4 nanorods with wolframite structure were synthesized in the presence of the surfactant SDBS by a hydrothermal method, and characterized by a variety of techniques. The obtained products are CdWO4 nanorods with length of 0.8-2.5 µm and width of 50-250 nm. The surfactant SDBS plays a key role in the formation of the CdWO4 nanorods. The pH value impacts on crystallinity of the products. The PL properties of the CdWO4 nanorods prepared under different conditions were studied. The intensity of the PL emissions of the samples increases with crystallinity and aspect ratio of the CdWO4 nanorods. <![CDATA[<b>SnO<sub>2</sub>/SiO<sub>2</sub> nanocomposite catalyzed one-pot, four-component synthesis of 2-amino-3-cyanopyridines</b>]]> An efficient and rapid protocol for the synthesis of 2-amino-3-cyanopyridines by the cyclocondensation reaction of aromatic aldehydes, methyl ketones, malononitrile and ammonium acetate catalyzed by SnO2/SiO2 nanocomposite material at refluxed condition in ethanol was investigated. Nanocomposite (SnO2/SiO2) catalytic material has been synthesized by using the sol-gel method. The prepared catalytic materials were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmer-Teller (BET) surface area, and temperature-programmed desorption of ammonia (NH3-TPD). Advantages of the present method include a simple work-up procedure, high yields of the products, low toxicity and easy recovery and reusability of the catalytic materials. <![CDATA[<b>Dodecatungstocobaltate and Sn (IV)-substituted polyoxometalate: Preparation, characterization and catalytic performances in solventless synthesis of bis(indolyl)methanes</b>]]> Electrophilic substitution reaction of indole with various aldehydes and cyclohexanone were carried out in the presence of electron-transfer (K5CoW12O40.3H2O) and green Lewis acid ([(n-C4H9)4N]3PMo2W9(Sn4+.H2O)O39) catalysts. These catalysts were characterized by N2-adsorption measurements, FT-IR, UV-Vis, 31P NMR, TGA, cyclic voltammetry and elemental analysis. Mechanisms for their catalytic activity are proposed. Both of these catalysts can be recovered and reused. <![CDATA[<b>Utilization of ionic liquids for the separation of organic liquids from industrial effluents</b>]]> The recovery of aromatic organic solvents from mixtures containing aliphatic compounds has economic as well as environmental significance. This is so because viable methods have not been established for the recovery from mixtures in which the components of value are 20 % (v/v) or less. In the light of this, we investigated the efficacy of selected ionic liquids to recover aromatic solvents from prepared mixtures. We used 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4] and 1-ethyl-3-methyl-pyridinium ethyl sulfate [EMpy][EtSO4] to separate and recover aromatic hydrocarbons (less than 10 % (v/v)) from aromatic/ aliphatic hydrocarbon mixtures, namely, benzene, toluene, ethyl benzene and o-xylene (BTEX) from «-heptane at 40 °C. The same aromatic components were used with «-hexane as an alkane and 1-ethyl-3-methylpyridinium ethyl sulfate [EMpy][EtSO4] as an ionic liquid. The concentrations of the aromatic components used were in the range of 2.5-10 % (v/v) for the following multi-systems at 40 °C: • Benzene + toluene + ethyl benzene + o-xylene + n-heptane + [EMIM][EtSO4]. • Benzene + toluene + ethyl benzene + o-xylene + n-hexane + [EMIM][EtSO4]. • Benzene + toluene + ethyl benzene + o-xylene + n-hexane + [EMpy][EtSO4]. The % removal of each aromatic, the ionic liquid selectivity trend, as well as its lifetime, and the distribution pattern of aromatic components in the ionic liquid obtained by gas chromatography were used to determine the capability of [EMIM][EtSO4] and [EMpy][EtSO4] as extracting solvents for low concentration BTEX. <![CDATA[<b>Spectral and thermal characterization and antimicrobial effect of 3-(5-H/Me/Cl/NO<sub>2</sub>-1<i>H</i>-benzimidazol-2-yl)-benzene-1,2-diols and some transition metal complexes</b>]]> 3-(5-H/Me/Cl/NO2-1H-benzimidazol-2-yl)-benzene-1,2-diols (HL X; X = 1-4) ligands and HL3 complexes with Fe(NO3)3, Cu(NO3)2, Co(NO3)2, Zn(NO3)2 have been synthesized and characterized. The structural representations of the compounds are proposed on the basis of elemental analysis, molar conductivity, TGA, mass, FT-IR, ¹H- and 13C-NMR spectrometry. All of the complexes are 1:1 electrolyte and have 1:1 M:L ratio except that of Cu(II).All of the complexes present fluorescence, the Co(II) complex showing the highest fluorescence intensity and the highest emission wavelength in comparison to the other complexes. Antibacterial activities of the ligands and the complexes formed by the HL3 ligand were evaluated using the disk diffusion method against six bacteria and Candida albicans. HL1, HL2, HL3 and [Cu(HL3)(L3)(H2O)2](NO3)-H2O show considerable antimicrobial activity toward S. epidermidis and C. albicans. <![CDATA[<b>Assessment of levels of V, Cr, Mn, Sr, Cd, Pb and U in bovine meat</b>]]> Pollution of the environment with heavy metals can be a serious problem. In South Africa, particularly, there are many sources of heavy metals, often due to smelter and mining activities. This has led to toxic metals in the environment that directly affect air, water and food. The presence of heavy metal residues in foodstuffs is potentially hazardous to humans and animals. Heavy metals accumulate in certain organs, particularly in the liver and kidney. The objective of this study was to determine the levels of V Cr, Mn, Sr, Cd, Pb and U in bovine organs and tissues obtained from polluted areas of North West Province, South Africa. Bovine liver, kidney, muscle, fat and bone samples were freeze-dried, homogenized and mineralized using a microwave-assisted digestion system. The levels were quantified using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). A bovine muscle (NIST-RM 8414) and bovine liver, reference material (NIST-RM 1577b), were also analyzed and results agreed with certified values. The study revealed accumulation of Sr in bone, Cd, Pb and U in kidney and bone, Mn in liver and, V and Cr in kidney tissues of cattle. <![CDATA[<b>Electrochemical oxidation of phenol using a flow-through micro-porous lead dioxide/lead cell</b>]]> The electrochemical oxidation of phenol to benzoquinone followed by the reduction to hydroquinone and catechol was demonstrated by constructing a three-dimensional porous micro-flow cell from lead dioxide and lead. The electrodes were made by using the principles of curing and formation of lead oxide material that are common in the construction of the electrodes used in lead-acid batteries. This resulted in highly porous electrodes that can allow the reactant solution to flow through them in series, without the risk of having the products being oxidized again at the anode that usually occurs in a simple undivided cell. In this study, a 50 mM solution of phenol in a 60 % acetonitrile and water mixture was used that contained 2 % sulphuric acid. The reactant solution would flow through the anode porous material oxidizing the phenol to benzoquinone. The benzoquinone in solution would then flow through the cathode porous material and reduce to catechol and hydroquinone. The study showed that almost all of the phenol could be converted in one continuous flow process in using a relatively low cost electrochemical micro-flow cell that can be easily scaled up to accommodate larger volumes and concentrations by using electrode manufacturing principles used in the lead-acid battery industry. <![CDATA[<b>Oxo and oxofree rhenium(V) complexes with N,O-donor Schiff bases</b>]]> The reaction between cis-[ReV O2I(PPh3)2] and H3duo (N-(2-hydroxybenzylidene)-5-amino-1,3-dimethyl uracil) led to the formation of the oxofree, imido compound, trans-[ReV(ddd)(Hduo)(PPh3)2]I (1) (H2ddd = 5,6-diamino-1,3-dimethyluracil). An oxo complex, cis-[ReV(bcp)OCl2(PPh3)](2) [Hbcp = N-(2-hydroxybenzylidene)-benzothiazole] was isolated from the reaction of trans-[ReO V Cl3(PPh3)2]with Hbcp. The crystal structures of the compounds were determined by single crystal X-ray diffraction. <![CDATA[<b>Impact of metals on secondary metabolites production and plant morphology in vetiver grass <i>(Chrysopogon zizanioides)</i></b>]]> The impact of selected metals on the production of phenolic compounds was investigated in a pot trial experiment. One-month-old vetiver grass (Chrysopogon zizanioides) seedlings were exposed to different concentrations (0, 10, 50, 100, and 500 ppm) of As, Cr, Cu, Fe, Ni, Pb and Zn. All the plants except for those treated with As tolerated up to 500 ppm as they did not show any signs of stress such as wilting or necrosis. A significant decrease (>35 %) in the length of the plants treated with As, compared to the control, was observed at 50 ppm which further decreased with increasing As concentration. A serious case of phytotoxicity was observed at 500 ppm As as the plant could not survive. Total soluble phenolics content in vetiver plants increased with increasing concentration of metals in the growth medium. The amount of the cell wall-bound phenolics (2.01 to 5.84 mg GAE g-1 DW) was higher than the total soluble phenolics (1.13 to 2.14 mg GAE g-1 dry weight DW) and both increased with increasing metal concentrations. Morphological changes associated with metal-induced stress were also examined with a scanning electron microscope which revealed thickened cell walls, loss of cell shape, reduction of intercellular space and the closure of stomata in leaves of metal-exposed plants. <![CDATA[<b>Ternary complexes of some divalent metal ions with potentially tridentate ligands in dioxane-water mixtures</b>]]> Chemical speciation of mixed ligand complexes of Ca(II), Mg(II) and Zn(II) with L-histidine and L-glutamic acid have been studied in varying concentrations (0.0-60.0 % v/v) of 1, 4-dioxane-water mixtures maintaining an ionic strength of 0.16 mol L-1 sodium chloride at 303.0 K. Titrations were carried out in the presence of different relative concentrations (M:L:X = 1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5) of metal (M) to L-histidine (L) to L-glutamic acid (X) with sodium hydroxide. Stability constants of ternary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The predominant species detected were ML2XH2, MLXH2 and MLX2 for Ca(II), Mg(II) and Zn(II). The formation and distribution of different species with relative concentrations of metal and ligands with varying pH are represented in the form of distribution diagrams. The influence of the solvent on the speciation is discussed in terms of the dielectric constant of the medium. <![CDATA[<b>FeCl<sub>3</sub>.nano SiO<sub>2</sub>: An efficient heterogeneous nano catalyst for the synthesis of 14-aryl-14<i>H</i>-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes under solvent-free conditions</b>]]> A novel, efficient and eco-friendly procedure for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydroxanthenes is described through one-pot condensation of 2-naphthol and dimedone with aryl aldehydes in the presence of nano silica-supported ferric chloride under solvent-free conditions. The present approach offers several advantages such as short reaction times, high yields, easy purification, recovery and reusability of the catalyst. <![CDATA[<b>Preparation of Mg-doped Ce-Zr solid catalysts and their catalytic potency for the synthesis of 5-arylidene-2,4-thiazolidinediones <i>via</i> Knoevenagel condensation</b>]]> A series of Mg-doped Ce-Zr mixed oxides with different molar ratios were prepared by a simple co-precipitation method. The surface characterization of these materials were investigated by means of XRD, FT-IR, SEM-EDS, CO2-TPD and BET techniques. The catalytic activity of the prepared materials was tested by synthesizing of 5-arylidene-2,4-thiazolidinedione derivatives via a Knoevenagel condensation using aromatic aldehydes and 2,4-thiazolidinedione in ethanol:water medium. The best catalytic activity was obtained with Ce1Mg0.6Zr0.4O2. The particle size or crystallite size was estimated using the Debye-Scherrer equation. Addition of MgO to the Ce-Zr mixed metal oxides affected both particle size and catalytic activity. <![CDATA[<b>Nano-Fe<sub>3</sub>O<sub>4</sub>/O<sub>2</sub>: Green, magnetic and reusable catalytic system for the synthesis of benzimidazoles</b>]]> Magnetic nano-Fe3O4 was applied in the presence of atmospheric air as a green, efficient, heterogeneous and reusable catalytic system for the synthesis of benzimidazoles via the reactions of o-phenylenediamine (1 eq) with aryl aldehydes (1 eq) in excellent yields (85-97 %) and short reaction times (30-100 min) with a proposed mechanism. <![CDATA[<b>Development and application of solid phase extraction method for polycyclic aromatic hydrocarbons in water samples in Johannesburg area, South Africa</b>]]> A solid phase extraction (SPE) technique has been developed for the quantitative determination of polyaromatic hydrocarbons (PAHs) in aqueous samples. The SPE technique involved extraction of PAHs from a 100 mL sample containing 10 % methanol as a modifier onto C18 cartridges. 40 % methanol in water was used as conditioning solvent, and 3 mL acetone:THF (1:1) as eluting solvent. After eluting, the extract was reduced to 1 mL under nitrogen and then analyzed by GC-MS. The extraction was optimized for the addition of organic modifier, sample load volume, conditioning solvent, washing solvent and eluting solvent. In order to evaluate the practical applicability of SPE technique, water samples were spiked with the PAHs to give final sample concentrations between 3 and 7µg L-1. Enrichment factors of 81-135 were achieved with relative standard deviations (RSDs) of less than 6 %. Recoveries obtained ranged from 81 to 135 %. Detection limits ranged from 20.0-52.0 ng L-1. The optimized method was validated by analyzing certified reference materials. The optimized method was then applied to spiked real river samples in and around the Johannesburg area, South Africa. The concentrations obtained varied from 22.0 to 1040.0 ng L-1. The RSDs were between 2.3 and 13 %. The overall order of PAHs levels was: phenanthrene > acenaphthene > naphthalene > fluoranthene > pyrene. <![CDATA[<b>Heterogenization of some PNP ligands for the oligomerization of ethylene</b>]]> Bis(diphenylphosphino)amine ligands were supported on Merrifield's resin and tested in catalytic ethylene oligomerization reactions with a chromium source. The supported ligands were characterized via IR, solid-state NMR, SEM and TGA-DSC. In order to compare activity of the supported and unsupported ligands, homogeneous bis(diphenylphosphino)amine ligands were synthesized and characterized via NMR, elemental analysis, IR and GC-MS. Oligomerization reactions were carried out in a Parr pressure reactor using Cr(acac)3 as the precursor and MMAO-3A as the activator. The system with the homogeneous ligands proved active in the tetramerization of ethylene, with the selectivity of 1-octene in the C8 fraction being comparable with that mentioned in literature (>98 wt%). When comparing the homogeneous ligands with their heterogeneous counterparts, the latter showed a four-fold drop in activity compared to their homogeneous counterparts. The selectivity towards the main product, 1-octene, was less than 10 wt%. These supported ligands created a system that favoured the formation of C6 products more than any other product, with C6 cyclics (methylcyclopentane and methylenecyclopentane) being the most dominant, probably due to steric effects caused by the polymer chain. <![CDATA[<b>Synthesis and antitumour activity of gold(I) and silver(I) complexes of hydrazine-bridged diphosphine ligands</b>]]> A known synthetic route was used to prepare two known hydrazine-bridged phosphine ligands and four new ligands with variable groups on the hydrazine bridge (methyl and ethyl), as well as positions on the aryl phosphine groups (phenyl, methoxyphenyl, dimethylaminophenyl). A range of gold(I) and silver(I) complexes were synthesized utilizing these phosphine ligands. Both the phosphine-bridged dimetal and cationic bis(diphosphine) metal complexes were isolated. An interesting phenomenon of the spontaneous oxidation of gold(I) to gold(III) (and reduction of gold(IIII) to gold(I)) upon complexation with ((N,N-dimethyl)-4-aminophenyl)dialkylhydrazine ligands is described. Thirteen of the synthesized complexes were subjected to anticancer activity screening against HeLa, Jurkat, A2780, cisplatin-resistant A2780, CoLo 320 DM and MCF7. Most of the complexes were found to inhibit the cancerous cells at low µM concentrations and in some cases nM concentrations. Two of the complexes were tested for their ability to reduce the mitochondrial membrane potential of PBMC cells as a possible mechanism of action of anticancer activity. <![CDATA[<b>Synthesis of novel thieno[3,2-b]quinolines and thieno[3,2-d][1,3]thiazoles</b>]]> New heterocyclic 2-Aryl-9-chloro-5,6,7,8-tetrahydrothieno[3,2-b]quinoline derivatives [Aryl-CTTQ] ( 2a-e ) and 5-arylthieno[3,2-d][1,3]thiazol-2-amine derivatives[Aryl-TZA] ( 6a-e )were achieved in good yields starting from 5-aryl-3-aminothiophene-2-carboxylic acid ( 1a-c ). <![CDATA[<b>Syntheses, protonation constants and antimicrobial activity of 2-substituted <i>N</i>-alkylimidazole derivatives</b>]]> A series of N-alkylimidazole-2-carboxylic acid, N-alkylimidazole-2-carboxaldehyde and N-alkylimidazole-2-methanol derivatives [alkyl = benzyl, methyl, ethyl, propyl, butyl, heptyl, octyl and decyl] have been synthesized and the protonation constants determined. The antimicrobial properties of the compounds were tested against Gram-negative (Escherichi coli), Gram-positive (Staphylococcus aureus & Bacillus subtilis subsp. spizizenii) bacterial strains and yeast (C. albicans). Both the disk diffusion and broth microdilution methods for testing the antimicrobial activity showed that N-alkylation of imidazole with longer alkyl chains and the substitution with low pKa group at 2-position resulted in enhanced antimicrobial activity. Particularly, the N-alkylimidazole-2-carboxylic acids exhibited the best antimicrobial activity due to the low pKa of the carboxylic acid moiety. Generally, all the N-alkylimidazole derivatives were most active against the Gram-positive bacteria [S. aureus (MIC = 5-160 mL-1) and B. subtilis subsp. spizizenii (5-20 mL-1)], with the latter more susceptible. All the compounds showed poor antimicrobial activity against both Gram-negative (E. coli, MIC = 0.15 to >2500 mL-1) bacteria and all the compounds were inactive against the yeast (Candida albicans). <![CDATA[<b>Fabrication of perovskite-type oxide BaPbO<sub>3</sub> nanoparticles and their efficiency in photodegradation of methylene blue</b>]]> BaPbO3 perovskite was prepared by the sol-gel method. The physical and chemical properties of catalyst were characterized by XRD, TEM, SEM, EDX and IR techniques. The photocatalytic activity of the sample was evaluated by photocatalytic decomposition of methylene blue (MB) dye under UV irradiation. The results of XRD indicate that the perovskite-type oxide (BaPbO3) is crystal at 700 °C. The XRD, TEM and SEM revealed that BaPbO3 particles are prepared in the nano-size regime. The results show that the degradation efficiency of methylene blue (MB) by BaPbO3 is higher than rutile under similar conditions. <![CDATA[<b>The use of an experimental design approach to investigate the interactions of additives used in the making of the negative plate in lead-acid batteries</b>]]> When a conventional starting, lighting and ignition (SLI) lead acid battery is exposed to a high rate partial state of charge (HRPSoC) cycling, it would experience a build-up of irreversible PbSO4 on the negative plate, resulting in capacity loss and electrode damage. The addition of certain graphites to the negative paste mix has proven to be successful in reducing this effect. This study looked at using statistical design of experimental (DoE) principles to observe interactions between two graphite types and a nanocarbon together with other additives, such as BaSO4 and Vanisperse, to a negative paste mixture. The response factors considered were in relation to their effect on the battery's cold cranking ability (CCA) at -18 °C, the HRPSoC and its active material utilization. Typical flooded nominal 8 Ah test cells were assembled in a reverse ratio build,with three positive and two negative plates, with three types of added carbons (flake graphite, natural graphite and nanocarbon) added to the negative paste mixture at a two-level design. The study showed the usefulness of a statistical DoE approach in the effective use of additives that are included to the negative plate paste mixture, where there are interactions between the amounts of added carbon, BaSO4 and Vanisperse, with respect to the responses of CCA and HRPSoC, that do not necessarily act independently - based on their amounts - on the performance of the active material. The study also showed that there are correlations between certain response factors, such as the number of achievable cycles within a HRPSoC test sequence, and the type of added carbon. <![CDATA[<b>Speciation studies of some toxic metal complexes of glycylglycine in propylene glycol-water mixtures</b>]]> The formation equilibria of complexes of Pb(II), Cd(II) and Hg(II) with glycylglycine were investigated pH-metrically in propylene glycol-water mixtures (0-60 % v/v) at 303 K and an ionic strength of 0.16 mol L-1. The dominant species detected were ML+ and ML2H2²+ for Pb(II); MLH²+ and ML2H+ for Cd(II) and ML+,ML2 and ML2H+ are for Hg(II). The appropriateness of the experimental conditions was verified by introducing errors deliberately in the concentrations of ingredients and volume of the solution. The models containing different numbers of species were refined by using the computer program MINIQUAD75. Selection of the best fit chemical models was based on statistical parameters. The trend in variation of stability constants of the complexes with dielectric constant of the medium was attributed to electrostatic and non-electrostatic forces. Distribution diagrams and plausible equilibria for the formation and possible structures of the complex species are presented. <![CDATA[<b>Pb(II) and Mn(II) supermolecular polymers of bipy and (4-chlorophenyloxy) acetate anions: Syntheses, structure and fluorescence properties</b>]]> Two new supermolecular polymers of the formula [Pb4L8(2,2'-bipy)4] 1 and [MnL2(4,4'-bipy)] 2 [HL = (4-chlorophenyloxy)acetic acid] have been synthesized and characterized by X-ray single crystal diffraction analysis, elemental analysis, fluorescence spectroscopy method and electrochemical analysis. Complex 1 is a multinuclear dimmer in which four Pb ions are linked together by the L ligands. In complex 2: , each carboxyl of L bridges two Mn ions to form infinite Mn-O-C-O rods. Both in complex 1 and complex 2: , π-π stacking and van der Waals' interactions make the two complexes stable, 3-D, supermolecular polymers. This work will contribute to the design and synthesis of fluorescent, supramolecular polymers. <![CDATA[<b>A convenient and direct route to 1,2-dichlorovinylphosphine oxides <i>via</i> copper-catalyzed addition of H-phosphine oxides to 1,2-dichloroethyne</b>]]> An efficient, convenient and inexpensive CuI-catalyzed method for the synthesis of 1,2-dichlorovinylphosphine oxides from substituted phosphites, diphenylphosphine oxide and 1,2-dichloroethyne has been developed in moderate-good yields, and the reactions provided mainly regioselective anti addition products. <![CDATA[<b>Synthesis and antimicrobial activity of the essential oil compounds (<i>E</i>)- and (<i>Z</i>)-3-hexenyl nonanoate and two analogues</b>]]> The synthesis of (E)- and (Z)-3-hexenyl nonanoate, known constituents of essential oil containing plants, and two related compounds is reported. These compounds were assembled from nonanoyl chloride or nonanoic acid and the respective alcohols. In particular, it was found that the use of triethylamine as a co-solvent was necessary to avoid acid-mediated isomerization of the alkenes, which resulted in an inseparable mixture of products. The antimicrobial activity of the four hexenyl and hexyl nonanoate compounds was undertaken using microdilution minimum inhibitory concentration (MIC) analysis against eight test microorganisms. All four compounds demonstrated activity, with (E)-3-hexenyl nonanoate 1B: having the highest inhibition (MIC value of 0.45 mg mL-1) against Pseudomonas aeruginosa ATCC 27858. Furthermore, this compound demonstrated the highest broad-spectrum activity (mean MIC value of 1.24 ± 0.50 mg mL-1) with noteworthy activity against all pathogens tested.