The effect of cobalt precursor (nitrate, acetate and chloride salts) on the catalyst reducibility and dispersion, as well as the catalytic activity of the Fischer-Tropsch (FT) synthesis, of boron-modified titania-supported cobalt catalysts (0.1%B/10%Co/TiO<sub>2</sub>) has been investigated. FT studies were performed on both calcined and uncalcined catalysts prepared from the three cobalt sources. The
uncalcined nitrate catalyst showed a higher activity for FT synthesis compared to the uncalcined acetate and chloride catalysts.
For the calcined catalysts, the acetate and nitrate catalysts exhibited higher FT activity. The low activity associated with the
chloride catalyst related to poisoning by residual chloride ions. Calcination was found to enhance the extent of cobalt bulk
reduction and FT activity for all three of the catalysts. The FT reaction rate increased with increasing percentage cobalt dispersion
while the turnover frequency (TOF) was found be near independent of cobalt source.
The voltammetric determination of benzimidazole anthelmintics at a glassy carbon rotating-disk electrode modified with
poly(3-methylthiophene) is presented. The purpose of surface modification was to improve the sensitivity and limits of detection
for determination of the compounds in a standard mixture. Thus, five compounds, namely thiabendazole, mebendazole,
albendazole, fenbendazole and oxibendazole have been studied using square wave voltammetry. It has been possible to resolve
four of the compounds, mebendazole, fenbendazole, oxibendazole and thiabendazole, in a mixture. Investigations of a number of
parameters, including the mode of potential application, cathodic reduction versus anodic oxidation, the type of electrode, effect
of pH and speed of electrode rotation, among others, are reported.
The reaction of iodine (acceptor) and nickel(II) acetylacetonate (donor) was studied photometrically in different solvents such as chloroform, dichloromethane and carbon tetrachloride at room temperature. The results indicate the formation of a 1 : 1 charge-transfer complex in each solvent and the iodine complex is formulated as the triiodide species [Ni(acac)<sub>2</sub>]<sub>2</sub>I<sup>+</sup>.I<sub>3</sub><sup>-</sup>, based
on the characteristic electronic absorptions of the I<sub>3</sub><sup>-</sup> ion at 361 and 285 nm, as well as on the far infrared absorption bands
characteristic of the I<sub>3</sub><sup>-</sup> ion with C<sub>2v</sub> symmetry. These bands are observed at 132, 101 and 84 cm<sup>-1</sup> and are assigned to <span style='font-family:Symbol'>n</span><sub>a</sub>(I-I), <span style='font-family:Symbol'>n</span><sub>s</sub>(I-I)
and <span style='font-family:Symbol'>d</span>(I<sub>3</sub><sup>-</sup>), respectively. The values of the equilibrium constant (K), absorptivity (<span style='font-family:Symbol'>e</span>) and oscillator strength (<span style='font-family:"Monotype Corsiva"'>f</span>) of the iodine
complex are shown to be strongly dependent on the type of solvent used. The important role played by the solvent is suggested to
be mainly due to the interaction of the ionic complex with the solvent. The proposed structure of the new solid triiodide
charge-transfer complex reported in this study is further supported by thermal and mid-infrared measurements.
The trace element content of clinkers (and possibly of cements) can be used to identify the manufacturing factory. The Mg, Sr, Ba, Mn, Ti, Zr, Zn and V content of clinkers give detailed information for the determination of the origin of clinkers produced in different factories. However, for the analysis of such complex data there is a need for algorithmic tools for the visualization and
clustering of the samples. This paper proposes a new approach for this purpose. The analytical data are transformed into a twodimensional latent space by factor analysis (probabilistic principal component analysis) and dendograms are constructed for
cluster formation. The classification of South African clinkers is used as an illustrative example for the approach.
The reaction of potassium salts of RNHCSSK with 2-chloro-1-(3-methyl-3-phenylcyclobutyl)ethan-1-one in ethanol at 78-80°C
afforded new 1, 3-thiazole-2(3<i>H</i>)-thiones containing 1, 1, 3-trisubstituted cyclobutane rings at C-4. The antimicrobial activities of
these compounds were also investigated against seven different microorganisms, and some of them were found to be active
against several of the microorganisms at higher concentrations.
The major electron-impact mass fragmentation patterns exhibited by 2-(<I>N, N</I>-dialkylamino)-4<I>H</I>-1-benzopyran-4-ones and -naphthopyran-4-ones have been explored using a combination of low-resolution, high-resolution and <I>B/E</I> linked-scan data.
Treatment of the title substrate with propylamine yielded 2-propyl-9-propylamino-3-propylimino-2, 3-dihydro-pyrrolo[3, 4-b]
quinolin-1-one (15%) and a S-containing product (63%). The latter is inferred (from its spectral and chemical properties) to be a
(1:1) complex of 2-propyl-3-propylimino-9-thioxo-2, 3, 4, 9-tetrahydro-pyrrolo[3, 4-b]quinolin-1-one (derived via an unusual
S-rearrangement) with propylamine. The propylamine in the complex is removed by acid or thermally to provide the aforementioned
9-thioxo component which structure was substantiated froma X-ray crystal analysis. Aminolysis of the title substrate with
ethylamine afforded the analogous ethyl-substituted products.
The zeolite, Na-P1, was synthesized from fly ash samples originating from coal-fired power stations in South Africa by hydrothermal treatment of the raw ash with concentrated aqueous NaOH solutions. The zeolite was then further modified by acid leaching at elevated temperatures. This resulted in the formation of a novel high surface-area solid. Spectroscopic and potentiometric investigations into the surface properties of both solids indicate that acid-base properties are most likely due to the presence of <u>=</u>AlOH- and <u>=</u>SiOH-type surface groups. Surface protonation constants for the various solids (unmodified ash, base-modified ash, acid-etched zeolitic product) are reported. Metal sorption studies were performed for cadmium and copper. It is suggested that the zeolitic product sorbs copper and cadmium by an ion exchange mechanism instead of a surface complexation mechanism, whereas the high surface-area solid, formed after acid etching, sorbs these metals <I>via</I> a surface complexation mechanism. Metal adsorption constants for the formation of <u>=</u>XOMOH species on the surface of the last mentioned solid for use in speciation models are reported.
The outcome from aminolysis of 3, 3, 9-trichlorothieno[3, 4-b]quinolinone with an alkylamine is dependent on the reaction conditions and extraneous reagents employed. A variety of hitherto unreported products can be obtained and include 4-chloro-2- alkylthiocarbamoyl-quinoline-3-carboxylic acid alkylamides, 9-chloro-2-alkyl-3- alkylimino-pyrrolo[3, 4-b]quinolines, 9-chloro-2-alkyl-3-thioxo-pyrrolo[3, 4-b]-quinolines, 2-alkyl-3-alkylimino-9-thioxo-pyrrolo[3, 4-b]quinolines, and 2-alkyl-9-alkylamino-3-alkylimino-pyrrolo[3, 4-b]quinolines. The spectral (1H NMR, HRMS) and chemical properties and the structures of the products are described and discussed, and possible mechanistic pathways leading to their formation are presented.
In practical sessions students lack sufficient time or opportunity for deep processing of information. If the signal to noise ratio is too low, it can obscure the 'chemical message' which the lecturer is trying to convey. This study reports on an action research driven attempt to improve on a Hess's Law experiment, well known in most first year curricula. Data collected in 2000 indicated that students struggled primarily because there were toomanypractical demands to allow them to focus on the concepts involved. The exercise was thus divided into two sessions in 2001, the first to address the issues related to techniques required, the second, similar to the experiment in 2000. Analysis of data collected in 2001 shows that the changes made a significant impact on the
effectiveness of the laboratory session.
An amperometric glutamate biosensor was developed using screen-printed carbon electrodes bulk-modified with MnO<sub>2</sub> (5%, m:m) onto which glutamate oxidase was immobilized via Nafion<sup>(R)</sup> film entrapment. The analytical performance of the biosensor was assessed in a flow injection mode and peak heights of the current response were used to evaluate results. Best responses were recorded at an applied potential of 440 mV (<I>vs</I> Ag/AgCl) a flow rate of 0.2 mL min<sup>-1</sup>, and a pH of 7.75 of the carrier (0.1 mol L<sup>-1</sup> phosphate buffer). The calibration curve exhibited linearity in the concentration range 10-160 mg L<sup>-1</sup>, with a detection limit (as 3<SPAN lang=AF
style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN
style="mso-char-type: symbol; mso-symbol-font: Symbol">s</SPAN></SPAN> value) of 1.7mg L<sup>-1</sup>, and a relative standard deviation 3.3% (c=20 mg L<sup>-1</sup>, <I>n</I>=10). This biosensor was used for the determination of monosodium glutamate in food seasonings, and the values obtained were similar to those obtained with spectrophotometry. The biosensor exhibited extraordinary stability when left on the FI system at a flow rate of 0.1 mL min<sup>-1</sup> at room temperature retaining 50% of the original response towards glutamate even after 65 days. Stored in the working buffer for more than 60 days, the same biosensor showed extended linear range, 20-710 mg L<sup>-1</sup>. This 'aged' (stored) biosensor was used to determine monosodium glutamate in food seasonings and gave similar result to those obtained with a freshly prepared biosensor.
Single crystal X-ray analysis of a spiroterpenoid rearrangement product has revealed that its structure is, in fact, isomeric with the structure proposed previously - an observation that has significant mechanistic implications.