South African Journal of Chemistry - Volume 58, Issue 1, 2005
Volumes & issues
Volume 58, Issue 1, 2005
Designer Ligands. Part 13. Synthesis and Catalytic Activity of Transition Metal Complexes of a Macrocyclic LigandSource: South African Journal of Chemistry 58, pp 1 –3 (2005)More Less
Source: South African Journal of Chemistry 58, pp 4 –8 (2005)More Less
A procedure for fabricating an enzyme electrode has been described based on the effective immobilization of horseradish peroxidase (HRP) to a nano-scaled particulate silver (nano-Ag)-modified platinum electrode with polyvinyl butyral (PVB) as the matrix. The hydrogen peroxide concentration was determined in the presence of azure C as a mediator to transfer electrons between the electrode and HRP. The HRP immobilized on colloidal Ag was stable and retained its biological activity. The biosensor displayed excellent electrocatalytic activity to the reduction of H2O2. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of experimental variables such as the operating potential of the working electrode, mediator concentration, pH and temperature of the measuring solution were investigated for optimum analytical performance by using an amperometric method. Linear calibration for H2O2; was obtained in the range 2.0 x 10-6 to 6.0 x 10-3 M under the optimized conditions. The sensor was highly sensitive to H2O2 with a detection limit of 1.0 x 10-6 M and the sensor achieved 95% of the steady-state current within 5 s. The sensor exhibited high sensitivity and stability.
Source: South African Journal of Chemistry 58, pp 9 –15 (2005)More Less
The electronic spectra of 11 cobalamin complexes were analysed by Gaussian analysis. It is shown that the αβ-region of the spectrum, sometimes attributed to a forbidden π → 960;* transition and its vibrational fine structure actually consists of several overlapping transitions, of which between three and five could be resolved in each spectrum. The γ-band region could be successfully modelled in each case with three overlapping transitions. It is shown that there is no fundamental difference between the 'typical' and 'atypical' spectra of the cobalamins, and that the difference in appearance is merely a consequence of the relative positions of the γ-region components of the spectrum. The electronic transitions of the cobalamins move to longer wavelengths as the donor power of the axial ligand increases. This cis influence, as measured by the average position of the Gaussian components of the αβ-region, correlates with the trans influence, as measured by the Co-N bond length to the trans dimethylbenzimidazole ligand of the corrins.
Source: South African Journal of Chemistry 58, pp 16 –24 (2005)More Less
Some properties of the monomeric binary hydrides of the elements of the first two rows of the periodic table have been determined using ab initio molecular orbital theory. The properties in question are the energetic, structural, electronic, topological and vibrational characteristics. In general, a gradual convergence towards the experimental values of these properties with systematic extension of the basis set has been observed. The well-known periodic trends in most of the properties have been confirmed. This study serves as a calibration set of data for an exhaustive search for the properties of the dimers of the hydrides, and for all the 1:1 binary complexes formed from among them, to be presented in forthcoming publications.
Solubility of crystalline nonelectrolyte solutes in organic solvents : mathematical correlation of 3-chlorobenzoic acid solubilities with the Abraham solvation parameter modelSource: South African Journal of Chemistry 58, pp 25 –29 (2005)More Less
The Abraham solvation parameter model is used to calculate the numerical values of the solute descriptors for 3-chlorobenzoic acid from experimental solubilities in organic solvents. The mathematical correlations take the form of
log (CS/CW) = c + e.E + s.S + a.A + b.B + v.V
log (CS/CG) = c + e.E + s.S + a.A + b.B + l.L
where CS and CW refer to the solute solubility in the organic solvent and water, respectively, CG is a gas phase concentration, E is the solute excess molar refraction, V is the McGowan volume of the solute, A and B are measures of the solute hydrogen-bond acidity and hydrogen-bond basicity, S denotes the solute dipolarity/polarizability descriptor, and L is the logarithm of the solute gas phase dimensionless Ostwald partition coefficient into hexadecane at 298 K. The remaining symbols in the above expressions are known solvent coefficients, which have been determined previously for a large number of gas/solvent and water/solvent systems. The Abraham solvation parameter model was found to describe the experimental solubility data and published literature partitioning data of 3-chlorobenzoic acid to within an overall standard deviation of 0.083 log units.
Source: South African Journal of Chemistry 58, pp 30 –36 (2005)More Less
Chromium(III) and chromium(VI) compounds play an important role in natural oxidation processes in terrestrial and atmospheric water. During the oxidation of SO2, peroxodisulphate is formed as an intermediate. In acidic and neutral solutions, peroxodisulphate oxidizes chromium(III) very slowly. This reaction rate is markedly enhanced by silver ions, resulting in a reaction rate that allows the reaction to be studied conveniently under laboratory conditions. The kinetics of the Cr(III)/Ag(I)/S2O82- reaction system were studied as a function of different Cr(III), Ag(I) and S2O82- concentrations, temperature and pressure. The formation of Cr(VI) was observed as a first-order process at high [Cr(III)] and as a zero-order process at low [Cr(III)]. An induction period was observed in both cases. For the first-order process, reaction rates were found to be independent of [Cr(III)], linearly dependent on [Ag+] and independent of [S2O82-]. The activation enthalpy (∆H≠) was calculated as 56 ± 5 kJ mol-1, the activation entropy (∆S≠) as -136 ± 16 J K-1 mol-1 and the activation volume as -5.8 ± 0.7 cm3 mol-1. At low [Cr(III)], the reaction rate was independent of [Cr(III)], linearly dependent on S2O82-] and non-linearly dependent on [Ag+], reaching a limiting value at high [Ag+;]. The activation enthalpy (∆H≠) was calculated as 61± 5 kJ mol-1, the activation entropy (∆S≠) as -119±15 J K-1 mol-1 and the activation volume as -1.7±0.1 cm3 mol-1. A mechanism involving the reversible formation of a silver-peroxodisulphate complex that decomposes into oxidizing intermediates is proposed. The empirical observations can be adequately described by this mechanism.
Source: South African Journal of Chemistry 58, pp 37 –40 (2005)More Less
The synthesis of four novel trishomocubane amino acid derivatives is described. The hydantoin precursor and bis-Boc protected hydantoin (>95% yield) were previously reported. A mild hydrolysis of the bis-Boc hydantoin with lithium hydroxide at room temperature quantitatively yielded the corresponding novel cage amino acid. The cage amino acid was characterized as the Fmoc derivative. Although the Fmoc amino acid is partially deprotected after three weeks in a refrigerator, it is stable enough for use in Solid Phase Peptide Synthesis (SPPS). The Fmoc cage amino acid was converted to the acid fluoride with cyanuric fluoride. The acid fluoride is required for activation of the cage amino acid in SPPS. Esterification of the sterically hindered trishomocubane amino acid is also reported, indicating sufficient reactivity of the acid function for potential use in SPPS.
Source: South African Journal of Chemistry 58, pp 41 –45 (2005)More Less
α-Santonin 3 was successfully converted into a biologically active compound 5b containing an endoperoxide group through a photo-oxygenation approach as a single isomer. It was found that the singlet oxygen afforded the isomer produced by attack from the sterically-hindered face of cyclohexadiene derivative 4. Evidence to this end is presented based on NOE results and the products formed in the photo-oxygenation reaction, as well as the in vitro testing of 5b for antimalarial activity.
Source: South African Journal of Chemistry 58, pp 46 –52 (2005)More Less
Ultramarine pigments are aluminosilicate-based and contain sulphur-based chromophores. Self-consistent-field Hartree-Fock and Moller-Plesset second order perturbation theory were applied to determine the relative stability of S2, S2-., S22-, and S3, S3-., S32-. The singly charged species was found to be the most stable in both sets. The transition from green to blue ultramarine is thought to be the transformation of the doubly charged species to the singly charged species and is known to be exothermic. Modelling studies supported this hypothesis. The open, C2v, isomer was found to be the most stable for the S3-. molecule, which is the blue chromophore in ultramarine. The closed, D3h, geometry represents a transition state. The S4 molecule is the most likely chromophore in ultramarine red; however the specific isomer is uncertain. Under the assumption that S4 was formed by a concerted reaction between S3-. and S+., a Woodward-Hoffmann analysis of the molecular orbitals of S3-. and S+. supported the formation of the puckered square S4, pyramidal S4, double triangle S4, and gauche S4 chain isomers. The gauche S4 chain is the most likely isomer in ultramarine red.
Study on the solid phase extraction and spectrophotometric determination of mercury in water and biological samples with 5-(p-aminobenzylidene)-thiorhodanineSource: South African Journal of Chemistry 58, pp 53 –56 (2005)More Less
This paper presents the synthesis and application of 5-(p-aminobenzylidene)-thiorhodanine (ABTR) as a new chromogenic reagent for the determination of mercury. Based on the rapid reaction of mercury(II) with ABTR and the solid phase extraction of the coloured chelate with a C18 disk, a highly sensitive, selective and rapid method for the determination of mercury has been developed. In the presence of pH 3.5 sodium acetate-acetic acid buffer solution and emulsifier-OP medium, ABTR reacted with mercury(II) to form a red chelate in a molar ratio 1:2 (mercury to ABTR). This chelate was enriched by solid phase extraction with a C18 disk and eluted from the disk with dimethyl formamide (DMF). An enrichment factor of 50 was achieved. The molar absorptivity of the chelate in DMF was found to be 1.21 x 105 L mol-1 cm-1 at 555 nm. Beer's law was obeyed in the range of 0.01~ 3 µg mL-1. The relative standard deviation for eleven replicates with a concentration of 0.01 µg mL-1 was 1.98%. This method was applied with good results to the determination of mercury in water and biological samples.
Simultaneous determination of palladium and platinum by on-line enrichment and HPLC with 4-(2-hydroxynaphthalene-1-ylmethylene)-thiazolidine-2, 5-dithione as pre-column derivatization reagentSource: South African Journal of Chemistry 58, pp 57 –60 (2005)More Less
In this paper, a new reagent, 4-(2-hydroxy-naphthalene-1-ylmethylene)-thiazolidine-2, 5-dithione (HNMTD) was synthesized. A new method for the simultaneous determination of palladium and platinum ions as metal-HNMTD chelates was developed using high performance liquid chromatography equipped with an on-line enrichment technique. Prior to chromatography the palladium and platinum ions were derivatized with HNMTD to coloured chelate complexes. The Pd-HNMTD and Pt-HNMTD complexes were then enriched on an enrichment column (ZORBAX Reversed Phase Stable Bound C18, 4.6 x 10 mm, 1.8 µm) using a buffer solution of 0.05 mol L-1 sodium acetate-acetic acid buffer (pH 3.8) as mobile phase. After the enrichment was completed, the retained chelates were back-flushed to the analytical column. The separation of chelates on the analytical column (ZORBAX Reversed Phase Stable Bound C18, 4.6 x 50 mm, 1.8 µm) was satisfactory when 72% methanol (containing 0.05 mol L-1 of pH 3.8 sodium acetate-acetic acid buffer salt and 0.1% of TritonX-100) was used as mobile phase. The Pt-HNMTD and Pd-HNMTD chelates were separated completely within 2 min. The detection limits (S/N = 3) for palladium and platinum were 1.2 ng L-1 and 1.4 ng L-1, respectively. The method was applied with good results to the determination of palladium and platinum in water and urine samples.
Measurements of polycyclic aromatic hydrocarbons and genotoxicity in soot deposited at a toll plaza near Durban, South AfricaSource: South African Journal of Chemistry 58, pp 61 –66 (2005)More Less
This research was designed to examine the presence of polycyclic aromatic hydrocarbons (PAHs) in soot deposited at the Mariannhill toll plaza situated on the N3 highway in KwaZulu-Natal, South Africa. Samples were collected from the toll plaza either by scraping the toll booth walls and surrounding areas, or by wiping the surfaces with cotton wool swabs. The organic component was separated by ultrasonic extraction into dichloromethane and analysed for PAHs by reverse phase high performance liquid chromatography with both fluorescence and ultraviolet detection. The genotoxicity was investigated by means of two bacterial assays: the Ames test and the SOS Chromotest. A number of PAHs were identified and genotoxic activity was observed in both of the assays.
Supported liquid membrane extraction of anabolic androgenic compounds in biological matrices and detection by LC-ESI-MSSource: South African Journal of Chemistry 58, pp 67 –73 (2005)More Less
A sample work-up and enrichment technique involving the use of supported liquid membrane (SLM) and detection by high performance liquid chromatography coupled to a mass spectrometer operating under positive ion electrospray mode (LC-PI-ESI-MS) has been developed for the determination of six anabolic androgenic compounds in different biomatrices; mainly urine, kidney, liver and milk. Anabolic androgenic compounds analysed included 17α-trenbolone, 17β-trenbolone, 19-nortestosterone, testosterone, 4-androstene-3, 17-dione and testosterone benzoate. Several factors affecting the extraction efficiency during SLM enrichment, such as donor pH were studied. The detection limits (DL) were 0.08 µg L-1 for 4-androstene-3, 17-dione, 0.7 ng L-1 19-testosterone, 1.1 ng L-1 for testosterone, 0.1 ng L-1 for 17β-trenbolone, 1.6 ng L-1 for 17α-trenbolene and 0.03µg L-1 for testosterone benzoate. Modification at C17 in the structures of 4-androstene-3, 17-dione and testosterone benzoate affected their recoveries with SLM and explained their observed high detection limits.
Source: South African Journal of Chemistry 58, pp 74 –81 (2005)More Less
2, 3-Dihydro-2-propyl-3-propylimino-9-thioxo-pyrrolo[3, 4-b]quinolin-1-one reacts with an aliphatic primary, secondary or tertiary amine to forma 1:1 substrate:amine (thiolate) complex. It also readily undergoes S-alkylation (with diazomethane or with an alkyl halide), S-acetylation (with acetic anhydride), hydrogenolysis (Raney nickel) with removal of sulphur, and acid-catalysed hydrolysis (with selective replacement of the 3-propylimino function by oxygen). Two novel di-(pyrrolo[3, 4-b] quinolinyl) sulphide reaction products are described and their structures established. Treatment of these 'dimers' and related 9-alkylthio-substituted pyrroloquinolines with an aliphatic amine provides a convenient access to 'simple' or 'mixed' 2-alkyl-9-alkylamino-3-alkylimino-pyrroloquinoline derivatives. Preliminary antimicrobial (in vitro) tests indicate that: (a) the weak antimicrobial activity of the aforementioned 9-thioxo-pyrroloquinoline substrate against three selected Gram-positive pathogens is significantly enhanced in its amine complexes, and by the presence of a 6-fluoro atom in the quinoline moiety, and (b) that substitution of the 4-oxo-function in 4-oxo-3-quinolinecarboxylic acids by an ethylimino group leads to a marked reduction in antimicrobial properties.
The determination of degradation products of lewisite and / or mustard gas in water by high performance liquid chromatographySource: South African Journal of Chemistry 58, pp 82 –85 (2005)More Less
Lewisite (L) and mustard gas (HD) are highly toxic vesicant warfare agents that are very sparingly soluble in water and thereby converted quantitatively to the stable and soluble degradation products 2-chlorovinylarsonous acid (CVAA), 2-chloro vinylarsonic acid (CVAOA), 2, 2'-dihydroxyethyl sulphide and 2, 2'-dichlorodiethyl sulphoxide. A new method based on reversed-phase high performance liquid chromatography (RP-HPLC) has been developed for the simultaneous detection of CVAOA, CVAA, 2, 2'-dichlorodiethyl sulphoxide, 2, 2'-dihydroxyethyl sulphide. The effects of eluent and pH on the separation efficiency were studied. UV spectra of CVAOA, CVAA, 2, 2'-dichlorodiethyl sulphoxide and 2, 2'-dihydroxyethyl sulphide were recorded. Good separation was achieved by HPLC using a 250 x 4.6 mm column with 5 µm ODS C18 after optimization of all relevant parameters. The calibration curves of CVAOA, CVAA, 2, 2'-dichlorodiethyl sulphoxide and 2, 2'-dihydroxyethyl sulphide showed high linearity over a concentration range of 5-500, 2-500, 5-500, 50-1000 mg L-1, respectively. The detection limits at a signal-to-noise ratio of 3 were 0.001, 0.2, 2, 20mgL-1. The method may be beneficial for studying the distribution of lewisite- and/or mustard gas and their degradation products in the environment.
Mechanism of oxidation of brilliant cresyl blue with acidic chlorite and hypochlorous acid. A kinetic approachSource: South African Journal of Chemistry 58, pp 86 –92 (2005)More Less
The kinetics and mechanism of oxidation of brilliant cresyl blue (7-amino-3-diethylamino-8-methyl-phenoxazine chloride) (BB+) by chlorite in the presence of acid is reported. Under [H+]0 > [ClO2-]0 > [BB+]0 conditions, the oxidation reaction followed pseudo first-order kinetics with respect to BB+. During the reaction, chlorite ion disproportionates, resulting in accumulation of chlorine dioxide. The overall reaction is third-order with first-order dependence on both H+ and ClO2- ions. The rate coefficient for the overall reaction is (0.158 ± 0.003) l2 mol-2 s-1. The stoichiometry of the reaction is 2BB+ + 7ClO2- + 2H+ --> 2P + 2CH3COOH + 4ClO2 + 3Cl- where P=7-amino-3-ethylamino-8-methyl-phenoxazine-10-N-oxide, and it varied with the initial concentrations of chlorite and acid. Near neutral pH, the hypochlorite-initiated oxidation of BB+ proceeded through two second-order pathways, one driven by OCl- ion and the other by HOCl. The latter reaction is much faster, with k=(1.26 ± 0.04) x 103 l mol-1 s-1. At low pH, the reaction was much faster and had first-order dependence on the concentrations of BB+, H+ and HOCl. Ru(III) catalysed the BB+-chlorite reaction with efficiency and the kinetics of the catalysed reaction are reported. Ru(III) had a catalytic constant, kCAT=1.2 x 106 l3 mol-3 s-1. The activation parameters for both uncatalysed and catalysed reactions were also reported. The kinetic profiles of the title reaction were computed using the proposed 11-step mechanism and Simkine software. The simulated curves agreed well with the experimental curves.
Synthesis of indoles : tetrahydropyrazino[1, 2-a]indole-1, 4-dione and pyrazino[1, 2-a]indole-6, 13-diones from piperazine-2, 5-dionesSource: South African Journal of Chemistry 58, pp 93 –97 (2005)More Less
The readily available piperazine-2, 5-dione has been used to prepare both 1:1 (1-3), with stereotopic methylene protons; and 2:1 (4-6) arylmethylenepiperazine-2, 5-diones in above average yields. The halo-derivatives, 1, 4 and 5 were cyclized to pyrazino[1, 2-a]indoles, 7-9, using copper bronze. Indole compounds 7 and 9 were further treated, separately, with lithium aluminium hydride, sodium borohydride, lithium hydroxide monohydrate and butyl lithium to yield 2-substituted indoles 10-13.
Volumetric and viscometric studies of molecular interactions in binary N, N-dimethylacetamide + benzyl alcohol mixtures at different temperaturesSource: South African Journal of Chemistry 58, pp 98 –104 (2005)More Less
The densities, ρ, and viscosities, η, of pure N, N-dimethylacetamide (DMA) and benzyl alcohol (BA), and nine of their binary mixtures covering the entire composition range have been measured at 25, 30, 35, 40 and 45°C. The experimental ρ and η values were correlated with composition and temperature by using some empirical relations. The excess volumes, VE, deviation in viscosities, ∆η, excess Gibbs energies of activation of viscous flow, ∆G*E, and paal molar volumes, Vo1 and Vo2, of DMA in BA and BA in DMA, respectively, at infinite dilution have been evaluated from the experimental data. The variations of these parameters with composition and temperature indicate the presence of specific interactions, namely hydrogen bonding and dipole-dipole forces between unlike molecules, which decrease with rise in temperature. Furthermore, the enthalpies, ∆H*, and entropies, ∆S*, of activation of viscous flow have also been obtained by using the Eyring viscosity equation and fitting the results to some empirical relations. The ∆H* values were found to be dependent on temperature. The dependencies of ∆H* and ∆S* on the compositions of the mixtures have been discussed.
Excess enthalpies of mixing of binary mixtures of NaCl, KCl, NaBr and KBr in mixed ternary solvent systems at 298.15 KSource: South African Journal of Chemistry 58, pp 105 –109 (2005)More Less
Excess enthalpies of mixing for six possible binary combinations of solutions of NaCl, KCl, NaBr and KBr in mixed ternary solvents composed of formamide, 1, 4-dioxane and water have been determined using a flow microcalorimeter at constant ionic strengths of 0.500 and 1.000 mol kg-1 at 298.15 K. Unlike the case of water, the data do not support Young's cross square rule. Pitzer's virial coefficient theory has been utilized to obtain binary and ternary interaction parameters, i.e. θH and φH. The data were also analysed in terms of the Friedman model and it was found that interactions between solvated ions are dictated not only by coulombic interactions but also by appreciable asymmetric effects.
Source: South African Journal of Chemistry 58, pp 110 –115 (2005)More Less
The effect of the addition of NaOH or KOH on commercial Degussa Titania P25 was investigated using TEM, Raman and in situ Raman spectroscopy. Treatment of titania with conc. NaOH generated a tubular material corresponding to a sodium titanate. An in situ Raman study on the sodium titanate nanotubes as a function of temperature revealed that the titanate structure was stable up to 700°C. Raman spectra of the titanate nanotubes after acid treatment, showed that the titanate structure was retained and EDX analysis revealed only trace amounts of sodium (0.3%) left in the material. HRTEM data are also consistent with the synthesis of protonated titanate nanotubes. An in situ Raman study of protonated titanate nanotubes as a function of temperature showed that the material was stable up to 150°C, while anatase appeared at T > 300°C. An in situ Raman study of the protonated titanate nanotubes produced from KOH as a function of temperature showed that the shape and size of the nanotubes prepared from NaOH and KOH are similar although rutile formation at 1000°C was different. A proposal for the formation of tubular titanates (and anatase) is given.