Scielo RSS <![CDATA[South African Journal of Chemistry]]> vol. 63 num. lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Cyclohexenones through addition of ethyl acetoacetate to 3-aryl-1-(thiophen-3-yl)prop-2-en-1-one derivatives</b>]]> Chalcone derivatives 3a-i: containing a thiophene ring were prepared by the condensation of 1-(thiophen-3-yl)ethanone with aromatic aldehydes in excellent yields. The Michael addition of ethyl acetoacetate 4 to chalcone derivatives 3a-i: resulted in the formation of nine novel ethyl 6-aryl-4-(3-thienyl)cyclohex-3-en-2-one-1-carboxylate derivatives 6a-i <![CDATA[<b>Effects of copper exchange levels on complexation of ammonia in Cu (II)-exchanged X zeolite</b>]]> Copper (Il)-exchanged faujasite-X zeolites at various loadings of copper per unit cell of zeolites were prepared and then exposed to ammonia. The copper ammine complexes of the various copper levels per unit cell were characterized and analyzed by a combination of diffuse reflectance, X-ray powder diffraction, FT-infrared spectroscopy, electron paramagnetic resonance and nuclear magnetic resonance spectroscopic methods. At low copper exchange levels (<5 copper atoms per unit cell), the major complex is [Cu(Ozeo)2(NH3)2]2+ and it is strongly bound to the zeolite framework walls at single four ring sites (site III). Above five copper atoms per unit cell, the major complex becomes [Cu(NH3)4]2+ and it is least interacting with the zeolite framework walls. The [Cu(NH3)4]2+ complex which was formed at higher copper levels per unit cell was most favoured by the presence of maximal amount of ammonia. <![CDATA[<b>Characterization and oxidative addition reactions of different rhodium and iridium triazolato complexes</b>]]> A number of different rhodium(I) and iridium(I) triazolato complexes and their oxidative addition products (triazolate = 3,5-bis(pyridine-2-yl)-1,2,4-triazolate (bpt-) and 4-amino-3,5-bis(pyridine-2-yl)-1,2,4-triazolate (bpt-NH-)) were prepared and characterized by means of IR and ¹H NMR spectroscopy, elemental analysis and computational chemistry methods. The oxidative addition reactions of these complexes with iodomethane in different solvents indicated simple second-order kinetics with the faster reactions in the more polar solvents (1.44(7) x 10-2 L mol-1 s-1 in dichloromethane compared with 9.2(5) x 10-4 L mol-1 s-1 in benzene for iridium bpt-NH). ¹H NMR data and density functional theory calculations illustrate that the coordination of the metal centre in [M(bpt-NH)(cod)] (M = Rh or Ir) occurs via the amine moiety and a nitrogen of a pyridine ring. <![CDATA[<b>Kinetics of the adsorption of bovine serum albumin of white wine model solutions onto activated carbon and alumina</b>]]> This study investigates the kinetics of adsorption of bovine serum albumin, BSA, in white wine model solutions onto activated carbon, AC, and alumina, AL. Pseudo-first order and pseudo-second order models were applied to determine the rate and mechanism of adsorption of the white wine protein during the haze removal process. The results showed that the average amount of adsorbed BSA onto AC was 1.10 ± 0.07 times higher than that onto AL. Statistical analysis by two-way ANOVA showed no significant difference in the amount of BSA adsorbed onto the two adsorbents, but a statistically significant difference existed in the amount adsorbed by variation of incubation time. A positive correlation exists between the amounts of BSA adsorbed onto AC and AL. The kinetics of the adsorption were found to be based on the assumption of an intra-particle diffusion-controlled pseudo-second order mechanism, with adsorption rate constants being higher at lower adsorbate concentrations. <![CDATA[<b>Synthesis and characterization of new bis-symmetrical adipoyl, terepthaloyl, chiral diimido-di-L-alanine diesters and chiral phthaloyl-L-alanine ester of tripropoxy <i>p</i>-<i>tert</i>-butyl calix[4]arene and study of their hosting ability for alanine and Na<sup>+</sup></b>]]> Bis-symmetrical tripropoxy p-tert-butyl calix[4]arene esters were prepared from the reaction of tripropoxy calix[4]arene (1HPr3) with di-acyl chlorides as bridges in the presence of sodium hydride. The esters, which were synthesized from L-alanine acyl chloride derivatives, are optically active. In all of these esters, calix[4]arene cavities have a pinched cone conformation. The structures of these esters were confirmed by FT-IR, ¹H NMR and 13C NMR spectroscopy, elemental analysis and ion positive FAB mass spectrometry. <![CDATA[<b>1,5-bis (2-hydroxyphenyl)pent-1,4-diene-3-one: A lead compound for the development of broad-spectrum antibacterial agents</b>]]> A systematic and comparative study has been made starting from a naturally-occurring chalcone nucleus to design effective antibacterial agents. The present investigation established 1,5-bis(2-hydroxyphenyl)pent-1,4-diene-3-one (lc)asalead compound with potential against a panel of pathogenic bacterial strains, Staphylococcus (coagulase negative), Escherichia coli, Pseudomonas aeruginosa, Acenetobacter sp. and Klebsiella pneumoniae. Gentamycine and tetracycline were used as reference drugs. The mode of antibacterial action of 1c was also studied by scanning electron microscopy, which showed membrane disruption and cell lysis of the organisms during the exposure of the tested compound. In vitro toxicity tests demonstrated that all the bioactive compounds showed far less toxicity against human erythrocytes. <![CDATA[<b>Alum-promoted synthesis of 1,8-dioxo-octahydroxanthenes in water</b>]]> A new and efficient method to synthesize a 3,3,6,6,9-aryl-1,8-dioxo-octahydroxanthene derivative using alum as catalyst was performed in aqueous media. This method has several advantages such as environmental friendliness, high yields and simple workup procedure. <![CDATA[<b>The oxidation of rhenium(III) by dioxygen in the presence of tri- and tetradentate N,O-donor ligands</b>]]> The oxidation of trans-[ReCl3(MeCN)(PPh3)2] by dioxygen in the presence of the potentially tridentate N2O-donor ligand 2-[((2-pyridinylmethyl)amino)methyl]phenol (Hham) in ethanol led to the formation of the hydrogen-bonded oxorhenium(V) dimer [ReOCl2(ham)]2. With the potentially tetradentate N2O2-chelate N,N-bis(2-hydroxybenzyl)-aminomethylpyridine (H2hap), the '4 + 1' complex [ReOCl(hap)] was isolated. Both compounds were characterized by ¹Ή NMR and infrared spectroscopy, and X-ray crystallography. <![CDATA[<b>Simultaneous multi-element electrothermal atomic absorption determination using a low resolution CCD spectrometer and continuum light source: The concept and methodology</b>]]> A low resolution CCD spectrometer with continuum light source and fast-heated graphite tube atomizer was employed for simultaneous multi-element determination by electrothermal atomic absorption spectrometry (SMET AAS). The sample vaporization pulse was monitored by fast scanning of vapour spectra within the 190-410 nm wavelength range; absorption was measured at the CCD pixels corresponding to atomic resonance lines; function absorbance vs. concentration of atomic vapour was automatically linearized, and the modified signals integrated. The setup consisted of a D2 or Xe arc lamp, a spectral instrument with a half-width of transmittance profile 120 pm, a linear CCD array attached to a PC and a tube atomizer furnished with a carbon fibre collector. In the experiments simultaneous determination of 18 elements was performed in the mixed solutions at the mg L-1 to L-1 level, within 4-4.5 orders of magnitude linear concentration range. About 1-2 min was needed for the measurement and calculation. Limits of detection (LOD) for individual elements were 1.5-2 orders of magnitude higher than those in the single element ET AAS, but similar or below those in flame AAS. Further reduction of LODs and correction of possible spectral and chemical interferences are associated with optimization of the light source and atomization programme and modification of the calculation algorithm. <![CDATA[<b>Synthesis of nitrogen-doped carbon nanotubes with layered double hydroxides containing iron, cobalt or nickel as catalyst precursors</b>]]> Nitrogen-doped carbon nanotubes (CNx) were synthesized by the catalytic chemical vapour deposition of ethylenediamine with layered double hydroxides (LDHs) containing iron, cobalt or nickel as catalyst precursors at 650 °C. The catalytically active metal particles were obtained by calcination of LDHs followed by reduction. X-ray diffraction was used to characterize the structures of the precursors and their calcined products. Transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the grown CNx. The results show that the CNx grown with Mg2 Fe-LDH as catalyst precursor have abamboo-like morphology and large diameter, while hollow tubes are obtained with CoMgAl- and NiMgAl-LDH as catalyst precursors. The CNx grown with CoMgAl-LDH have the highest N-doped content and the CNx grown with NiMgAl-LDH have the highest degree of graphitization among these three products. <![CDATA[<b>A DFT and NBO analysis of the bonding in titanocenyl complexes containing a five-membered L,L'-cyclic ligand: L,L' = O,O'; S,S' or Se,Se'</b>]]> An NBO analysis of the electron distribution in the DFT-optimized geometries of different Cp2TiIV(L,L'-BID) complexes with L,L'-BID = dioxolene, dithiolene or diselenolene, showed that a large degree of folding along the L...L axis is needed for sufficient Ti←L π-donation. The out of plane folding for maximum Ti←L π donation increases with larger Ti-L bond lengths: Cp2TiIV(O,O'-BID) (~35 °) < Cp2TiIV(S,S'-BID) (47 ° average) < Cp2TiIV(Se,Se'-BID) (50 ° average). <![CDATA[<b>Grade 12 achievement rating scales in the new National Senior Certificate as indication of preparedness for tertiary chemistry</b>]]> There has been much discussion on the impact of the new curricula for Grades 10-12 on the preparedness for tertiary studies of the 2009 cohort in subjects such as mathematics, chemistry and physics. Using the Chemical Competence Test that was developed and refined earlier, we have evaluated the proficiencies of incoming students to determine the shifts in preparedness for tertiary chemistry that occurred after students wrote the National Senior Certificate (NSC) in South Africa for the first time in 2008. Data were collected in 2009 for first-time entering students at the Universities of Pretoria (UP) (N = 828) and Cape Town (UCT) (N = 315) and compared with that of students who were educated according to the former National Education curriculum (NATED 550) (2005: N UP+UCT = 776). The raw score results showed a decline in proficiency in all topics, and significantly reduced skills development, with mastery of acids and bases showing the most serious decline. Rasch analysis of the data indicated that a 12 percentage point shift in preparedness occurred in 2009 compared with 2005. The contribution to this shift of a mismatch between the new NSC rating scale and the one used previously was also investigated. The implications of the findings for selection and placement and teaching of first year chemistry courses are discussed. <![CDATA[<b>Selective bromination of 4-chloro-1-indanone and synthesis of (4-chloro-2, 3-dihydro-1<i>H</i>-indene-2-yl)methanamine</b>]]> The synthesis of 4-chloro-1-indanone in four steps from 2-chlorobenzaldehyde was investigated. Bromination of this compound under various conditions occurred in the cyclopentanone ring, producing mono- and dibromo derivatives. Cyanation of 2-bromo-4-chloro-1-indanone followed by reduction gave (4-chloro-2, 3-dihydro-1H-indene-2-yl)methanamine in quantitative yield. <![CDATA[<b>The synthesis of substituted piperazine-cholesterol conjugates for use as components of nucleic acid transfection lipoplexes</b>]]> A small library of cholesterol-piperazine conjugates were synthesized by the reaction of cholesteryl chloroformate with a set of substituted piperazines in dichloromethane at room temperature. The conjugates, all obtained in good to excellent yields, were synthesized to be key components of nucleic acid transfection lipoplexes. <![CDATA[<b>Imidazole-based vanadium complexes as haloperoxidase models for oxidation reactions</b>]]> Four imidazole-bound oxovanadium(IV) haloperoxidase model complexes were prepared. Two heterogeneous catalysts were prepared by first linking imidazole-4-carboxylic acid or 1-methylimidazole-2-carboxylic acid to chloromethylated polystyrene and subsequently reacting these polymer-anchored ligands with vanadyl sulphate. Two homogeneous catalysts were prepared by reaction vanadyl sulphate with the free ligands. The activity of the catalysts was evaluated for the hydrogen peroxide facilitated oxidation of styrene and ethylbenzene and thioanisole. A maximum conversion of 99.9 % for styrene and 10.6 % for ethylbenzene was achieved. Excellent conversions of thioanisole (100 %) were obtained under mild room temperature conditions. The heterogeneous catalysts also proved to be recyclable for this reaction, with no appreciable loss in activity even after three catalytic cycles. The haloperoxidase activity was evaluated spectrophotometrically by following the bromination of phenol red to bromophenol blue. All four catalysts proved effective in catalysing this process. <![CDATA[<b>Natural products research in South Africa: End of an era on land or the beginning of an endless opportunity in the sea?</b>]]> South African organic chemistry is deeply rooted in a rich history of natural product chemistry research with the secondary metabolites emanating from South Africa's unique floral kingdoms dominating this research for nearly a century. However, South Africa's terrestrial biodiversity is exceeded by an even greater diversity of marine flora and fauna occurring off its coast, which remain a relatively untapped source of novel biomolecules with unrealized pharmaceutical and agrochemical potential. Examples of the seemingly endless opportunities arising from exploration of the diverse bioactivities of South African plant and marine natural products, together with their semi-synthetic analogues, are presented here. <![CDATA[<b>Synthesis and biological evaluation of some novel 2-mercaptobenzothiazoles carrying 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole moieties</b>]]> Several 2-mercaptobenzothiazole derivatives containing 1,3,4-oxadiazoles, 1,2,4-triazoles and 1,3,4-thiadiazoles at the second position were synthesized. Some of these synthesized compounds were evaluated for their in vivo analgesic, anti-inflammatory, acute toxicity and ulcerogenic actions. Some of the tested compounds showed significant analgesic and anti-inflammatory activities. Two of the compounds showed significant gastrointestinal protection compared to the standard drug diclofenac sodium. The compounds were also tested for their in vitro antimicrobial activity with most displaying selective activity against the Gram-negative bacteria Pseudomonas aeruginosa. In the present investigation the tested compounds did not possess antifungal activity. <![CDATA[<b>Synthesis, spectroscopic and pharmacological studies of bivalent copper, zinc and mercury complexes of thiourea</b>]]> A series of metal complexes of Cu(II), Zn(II) and Hg(II) having the general composition [M(L)2X2] [where L = thiourea; M = Cu(II), Zn(II) or Hg(II) and X = Cl-, NO3- or CH3COO-] have been synthesized. All the metal complexes were characterized by elemental chemical analysis, molar conductance, magnetic susceptibility measurements and IR spectroscopy. Cu(II) complexes were additionally characterized by electronic and EPR spectral studies. The IR spectral data suggests the involvement of sulphur atom in coordination to the central metal ion. On the basis of spectral studies square planar geometry has been assigned to Cu(II) complexes except [Cu(L)2(CH3COO-)2] which exhibits six coordinated tetragonal geometry. However, all Zn(II) and Hg(II) complexes exhibited tetrahedral geometry. Furthermore, to achieve a better pharmacological profile, thiourea and its metal complexes were screened for in vitro antimicrobial activity against the human pathogenic bacteria Staphylococcus aureus, Staphylococcus epidermides, Escherichia coli and Pseudomonas aeruginosa and against the fungi Candida albicans and Aspergillus niger. Thiourea and its metal complexes were also screened for in vivo anti-inflammatory activity. Thiourea did not exhibit antibacterial activity but showed antifungal activity. However, it is important to note that the Cu(II), Zn(II) and Hg(II) complexes of thiourea exhibited antibacterial and enhanced antifungal activity. Neither thiourea nor its metal complexes exhibited anti-inflammatory activity. <![CDATA[<b>Alternative dissolution methods for analysis of niobium containing samples</b>]]> Inductively coupled plasma optical emission spectrometry was applied for the qualitative and quantitative analyses of the different high purity Nb containing samples such as Nb metal, Nb2O5 and NbF5. Microwave-assisted digestion of the Nb compounds with concentrated H2SO4 in PTFE vessels produced Nb recoveries of 99.90 ± 0.08 % for Nb metal, 98.8 ± 0.7 % for Nb2O5 and 100.7 ± 0.4 % for NbF5. Fusion of Nb2O5 with Li2B4O7 flux and the subsequent dissolution of the melt with concentrated H2SO4 resulted in the precipitation of H3BO3 under these conditions. Methanol was added to the reaction mixture to convert the boric acid into the volatile methyl ester in an effort to remove the excess H3BO3. This procedure yielded a recovery of 103±2%for the pure Nb2O5 sample. <![CDATA[<b>Iodination of alcohols over Keggin-type heteropoly compounds: A simple, selective and expedient method for the synthesis of alkyl lodides</b>]]> Different catalysts derived from Keggin-type heteropoly compounds were prepared and their catalytic activities have been compared in the iodination of benzyl alcohol with KI under mild reaction conditions. A high catalytic activity was found over tungstophosphoric acid supported on silica and titania. The effect of catalyst loading, iodine source and the nature of substituents on the aromatic ring of benzyl alcohol were investigated. Finally, several competitive reactions were studied between structurally diverse alcohols. This protocol provides a mild and expedient way for the conversion of various alcohols to their corresponding alkyl iodides with high selectivity. <![CDATA[<b>Synthesis, characterization and antimicrobial studies of some novel 1,3,4-thiadiazolium-2-thiolate derivatives</b>]]> In this study, ten new 5-substituted-3-[4,6-di(morpholine-4-yl)-1,3,5-triazine-2-yl]-1,3,5-thiadiazolium-2-thiolate 6(a-j) were prepared via a five step procedure from the starting material 1,3,5-triazine (1). Structures of all synthesized compounds were confirmed by spectral data and elemental analyses. Newly synthesized compounds were tested for their antibacterial and antifungal activities against some important bacterial and fungal species. Some of the compounds were found to be moderately active against the tested organisms. <![CDATA[<b>Electrocatalytic activity of electropolymerized cobalt tetraaminophthalocyanine film modified electrode towards 6-mercaptopurine and 2-mercaptobenzimidazole</b>]]> The electrocatalytic activity of electropolymerized cobalt tetraaminophthalocyanine (poly-CoTAPc) film modified on the glassy carbon electrode (GCE) towards 6-mercaptopurine (6MP) and 2-Mercaptobenzimidazole (MBI) was studied. Comparing with the case at the unmodified GCE, the poly-CoTAPc film decreased the overpotential of oxidation of 6MP (1.0 x 10-3 mol L-1) and MBI (1.0 x 10-3 mol L-1) by 335 and 189 mV, respectively, and increased the peak current by about 3 and 2 times, respectively, while the reduction potential of the disulphide product of previous oxidation of 6MP shifted positively by 312 mV and the peak current increased by 40 times in 0.1 mol L-1 phosphate buffer solution (PBS, pH = 2.0). The poly-CoTAPc film exhibited efficiently electrocatalytic activity for 6MP and MBI with relatively high sensitivity, stability and long-life. <![CDATA[<b>An investigation of the interaction between resazurin and Cd<sup>2+</sup> and Zn<sup>2+</sup> ions in aqueous medium</b>]]> The voltammetric behaviour of resazurin in the presence of Cd2+ and Zn2+ ions at a hanging mercury drop electrode (HMDE) was investigated by using square wave voltammetry (SWV), cyclic voltammetry (CV) and adsorptive square wave voltammetry (AdsSWV). The interaction of resazurin with Cd2+ and Zn2+ starts above pH 4 and seems to be completed at pH 5.2 with Cd2+ ions and at pH 7.5 with Zn2+ ions. A new peak appears at -0.93 V in the presence of Cd2+ and at -1.07 V in the presence of Zn2+. These peaks may be attributed to M2+-resazurin complexes and the logarithm of their stability constant was determined where log β14 = 4.22 for Cd2+-resazurin and log β1:1 = 4.74 for Zn2+-resazurin. Cyclic voltammetry was used to characterize the redox mechanism and to calculate voltammetric data of M2+-resazurin complexes. The amount of adsorbed M2+-resazurin complexes on the mercury drop electrode surface (Γ) is calculated as 5.48 x 10-12 mol cm-2 for Cd2+-resazurin and 1.10 x 10-11 mol cm-2 for Zn2+-resazurin. The voltammetric data were compared with the data obtained using spectrophotometric methods and were observed to be in good agreement. <![CDATA[<b>Alum an efficient catalyst for Erlenmeyer synthesis</b>]]> A new and efficient method to synthesize azlactone derivatives using alum as catalyst was performed in the absence of additional solvent. This method is environmentally friendly and affords the product azlactones in high yields after simple workup. <![CDATA[<b>Interaction of hydroxyproline with bivalent metal ions in chemical and biological systems</b>]]> A recent technique involving the use of paper electrophoresis is described for the study of equilibria in binary complex systems in solution. The stability constants of the ML and ML2 complex species of some metal ions, namely beryllium(II) and cobalt(II), with hydroxyproline were determined in 0.1 mol L-1 perchloric acid and a temperature of 35 °C. The logarithm stability constants of the ML and ML2 complexes of hydroxyproline were found to be 7.39 ± 0.07 and 5.90 ± 0.03, and 4.73 ± 0.08 and 3.71 ± 0.11 for the beryllium(II) and cobalt(II) complexes, respectively. <![CDATA[<b>Synthesis, characterization and thermal studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of some Schiff bases derived from 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4 triazine</b>]]> Co(II), Ni(II), Cu(II) and Zn(II) Complexes of bidentate Schiff bases derived from the condensation of 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4-triazine with 4-fluoro benzaldehyde and 2-acetyl furan were synthesized and characterized by various physico-chemical techniques. A square planar geometry was suggested for Cu(II) and octahedral geometry proposed for Co(II), Ni(II) and Zn(II). TG curves indicated that the complexes decompose in three to four steps. The presence of coordinated water in metal complexes was confirmed by thermal and IR data of the complexes. <![CDATA[<b>Euphorbias of South Africa: Two new phorbol esters from <i>Euphorbia bothae</i></b>]]> Two known phorbol esters, 12-deoxyphorbol-13-isobutyrate-20-acetate (1) and 12-deoxyphorbol-13-(2-methylbutyrate)-20-acetate (2), and two new phorbol esters, 12-deoxyphorbol-13-isobutyrate-16-angelate-20-acetate (3) and 12-deoxyphorbol-13-(2-methylbutyrate)-16-angelate-20-acetate (4), were isolated from the endemic South African plant Euphorbia bothae. Standard spectroscopic techniques were used to elucidate the structures of all four compounds. The interaction of 1-4 with opioid receptors was explored in an attempt to explain the unexplained stupor occasionally observed in herbivores browsing on E. bothae. <![CDATA[<b>Coordination of the bidentate ligands 2,2'-dipyridylamine, 1-phenyl-1,3-butadione and <i>N</i>'-(propan-2-ylidene)benzohydrazide to rhenium(III)</b>]]> The reaction of trans-[ReCl3(MeCN)(PPh3)2] with 1-phenyl-1,3-butadione (Hbat), 2,2'-dipyridylamine (dpa), and 1-(2-hydroxy-phenyl)ethanone benzoylhydrazone (Hhaep) under nitrogen led to the respective complexes cis-[ReIII Cl2(bat)(PPh3)2], fac-[ReIII Cl3(dpa)(PPh3)] and cis-[ReV OCl2(meb)(PPh3)] (meb = N'-(propan-2-ylidene)benzohydrazide). All the complexes were characterized by ¹H NMR and infrared spectroscopy, and X-ray crystallography. <![CDATA[<b>Hydrogen bonding patterns in a series of 3-spirocyclic oxindoles</b>]]> The crystal structures of the new compounds spiro[cyclohexane-1,3'-indol]-2'(1'H)-one (1), (rel-1R,2S)-spiro[bicyclo[2.2.1] heptane-2,3'-indol]-2'(1'H)-one (2) and spiro[indole-3,2'-tricyclo[,7)]decan]-2(1H)-one (3) have been determined by low temperature single crystal X-ray diffraction. The effects of substitution on the hydrogen bonding pattern is compared between all three compounds. <![CDATA[<b>Simple, efficient and green synthesis of oximes under ultrasound irradiation</b>]]> The condensation of aldehydes and ketones with hydroxylamine hydrochloride gives oximes in 81-95 % yields in water and EtOH under ultrasound irradiation. Compared to conventional methods, the main advantages of the present procedure are milder reaction conditions, shorter reaction times and higher yields. <![CDATA[<b>Synthesis of (S)-3-aminoethyl-1,2,3,4-tetrahydroisoquinoline (TIQ-diamine) <i>via</i> the Mitsunobu protocol</b>]]> The synthesis of (S)-3-Aminoethyl-1,2,3,4-tetrahydroisoquinoline (TIQ-diamine) was successfully achieved via the Mitsunobu protocol. The method from earlier reports utilizing aminolysis of commercially available TIQ-amino methyl ester, and reduction of the amide, proved to be inadequate for preparation of TIQ-diamines. The modified route requires three additional steps and consequently rendered three novel intermediates, which were furnished under mild conditions. <![CDATA[<b>Polyaniline/SiO<sub>2</sub> catalyzed one-pot synthesis of tetrahydrobenzo[<i>b</i>]pyran derivatives</b>]]> Polyaniline/SiO2 is an efficient catalyst for the synthesis of tetrahydrobenzo[b]pyran derivatives from a one-pot, three component, condensation of aldehydes, malononitrile and dimedone at room temperature. This protocol has several advantages such as high yield, a simple work up procedure, low toxicity and easy recovery and reusability of the catalytic material. The catalyst has been readily prepared and characterized by means of thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). <![CDATA[<b>The determination of <sup>11</sup>B/<sup>10</sup>B and <sup>87</sup>Sr/<sup>86</sup>Sr isotope ratios by quadrupole-based ICP-MS for the fingerprinting of South African wine</b>]]> The 11B/10B and 87Sr/86Sr isotope ratios in wines and soils of four major South African wine-producing regions have been determined by quadrupole-based ICP-MS in order to establish a fingerprint for origin verification of the wines. The 11B/10B isotope ratio was found to be a useful tool to distinguish among the wines of the selected wine regions. In addition, the use of B isotope ratios together with elemental concentrations of selected indicator elements as independent variables in a linear discriminant analysis procedure was shown to be a highly successful method to classify wine according to geographical origin. A good correlation between the B and Sr isotope ratios in wine and its provenance soil was found. Both wine and soil samples were prepared using microwave-assisted digestion followed by the isolation of boron and strontium from the sample matrix through element-specific ion exchange. Isotope ratio measurements with good precision, ~0.1 % RSD, for both boron and strontium have been obtained. The 87Sr/86Sr ratio showed limited potential as an indicator of provenance in the wine-producing regions included in this study, since the wines of only one region could be distinguished from the others. <![CDATA[<b>Kinetics and mechanism of formation of S-nitrosocysteine</b>]]> The kinetics and mechanism of the nitrosation of cysteine by nitrous acid has been studied in acidic medium. The stoichiometry of the reaction is strictly 1:1, with the formation of one mole of S-nitrosocysteine (CySNO) from one mole of nitrous acid. Only two nitrosating agents were detected: nitrous acid itself and protonated nitrous acid which is the hydrated form of the nitrosonium cation, NO+. Nitric oxide itself was not detected as a nitrosant. The bimolecular rate constant for the direct nitrosation of cysteine by nitrous acid was determined to be 6.4 ± 1.1 L mol-1 s-1, while nitrosation by the nitrosonium cation has a rate constant of 6.8 x 10³ L mol-1 s-1. CySNO is short-lived, and decomposes completely to cystine and nitric oxide within 100 s in the presence of micromolar quantities of Cu(II) ions. Since the physiological environment contains many metal ions and metalloenzymes, it is unlikely that CySNO will be an effective carrier of NO. <![CDATA[<b>Degradation of endosulfan I and endosulfan II in the aquatic environment: A proposed enzymatic kinetic model that takes into account adsorption/desorption of the pesticide by colloidal and/or sediment particles</b>]]> The rate of degradation of the a and β isomers of endosulfan, endosulfan I and endosulfan II in distilled water and river water containing river sediment, were investigated over a period of 90 days. An immediate loss of 18 % endosulfan I and 22 % endosulfan II from the water phase of the river water containing river sediment was observed as a result of adsorption by the sediment. Subsequently biphasic linear rates of degradation were observed for both endosulfan I and II in the water phase, as well as the sediment phase of the experiment. Minimal degradation was observed in the distilled water control. An enzymatic kinetic model is presented showing that the biphasic linear rates are consistent with microbial degradation of free and colloidal particle-adsorbed pesticide in the water phase, and colloidal particle- and sediment particle-adsorbed pesticide in the sediment phase of the experiment. The estimation of the biphasic rates of degradation of the pesticide in the water and sediment phases of the system, and the factors affecting the rates of degradation, are discussed. <![CDATA[<b>An environmentally friendly solvent-free synthesis of 3,4-dihydropyrimidinones using a <i>p</i>-aminobenzene sulfonic acid catalyzed Biginelli reaction</b>]]> Anhydrous p-aminobenzene sulphonic acid mediated solvent-free protocol is described for the synthesis of dihydropyrimidi-nones by the cyclocondensation of aldehydes, β-ketoesters and urea/thiourea. Yields obtained are significantly higher than those obtained utilizing classical Biginelli reaction conditions. <![CDATA[<b>Ph<sub>3</sub>P catalyzed synthesis of alkyl 2-(4-oxopyridin-1(4<i>H</i>)-yl)acrylates by nucleophilic addition to alkyl propiolates</b>]]> 4-Hydroxypyridine undergoes a smooth reaction with alkyl propiolates in the presence of triphenylphosphine to produce α and β-substituted alkyl acrylate products. When the reaction was performed with 4-hydroxyquinoline only α-substituted alkyl acrylates were obtained. <![CDATA[<b>Synthesis and characterization of ethyl 2-methyl-7-oxo-7<i>H</i>-isoxazolo[2,3-</b><b>α</b><b> </b><b>]pyrimidine-6-carboxylate derivatives</b>]]> Reactions of 5-methylisoxazol-3-amine with diethyl ethoxymethylenemalonate derivatives are described. By this method ethyl 2-methyl-7-oxo-7H-isoxazolo[2,3-a]pyrimidine-6-carboxylate derivatives were prepared and characterized. <![CDATA[<b>Poly(ethylene)glycol/AlCl<sub>3</sub> as a green and reusable system in the synthesis of</b><b> </b><b>α</b> ,<b>'</b><b>α</b><b>-bis(substituted-benzylidene) cycloalkanones</b>]]> Aluminum chloride has been found to be a highly efficient catalyst for the aldol condensation of aldehydes and cycloketones in poly(ethylene)glycol 400 at room temperature. The reaction is very fast, clean and environmentally benign for the synthesis of a variety of α,α'-bis(substituted-benzylidene) cycloalkanones.