No description available.

The study of rapid cleavage of organophosphate esters by metal ions is of great interest as it is the most important reaction in both biological and environmental sciences. A good understanding of organophosphate hydrolysis by metal ions is important as it can be exploited in formulation of useful detoxifying agents for organophosphate contaminants in the environment. The knowledge can also help in developing effective artificial enzymes. The hydrolysis of 4-NPP in the presence of Ferrous and Ferric ions in o/w microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the 4-nitrophenolate ion produced in the reaction aliquots with time. The order of effectiveness of the ME media towards the hydrolysis of 4-NPP was found to be CME > AME > aqueous in the presence of Fe(II), Fe(III) and Prussian blue at neutral pH. In comparison with individual metal ions used in the investigation, it was found that polymetallic Prussian blue showed enhanced rate of hydrolysis. The degree of effectiveness is as follows; Prussian blue (insoluble) > Prussian blue (soluble) > Fe(III) > Fe(II). The result of the present investigation enriches our understanding of the possible roles polymetallic ions play in hydrolysis reactions and the effect of different reaction media. The reactions mimic the roles of purple acid phosphatases in the hydrolysis of phosphate esters. The application of the above systems for environmental decontamination of organophosphates is also envisaged. / Chemistry / M.Sc.(Chemistry)

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: A series of di- and mono-substituted acyl(aroyl) thioureas were examined for the extraction and transportation of Au(III). Two-phase metal ion extraction experiments were employed to investigate the extraction behaviour of these ligands. The effect of varying ligand concentration on the extraction trend of these ligands was investigated. The results show that the different substituent groups on the benzoyl ring can affect the extraction pattern of the metal. Furthermore, the alkyl substituents on the thiourea moiety and varying the ligand concentration have an influence on the percentage of metal ion extracted. With the exception of the H2L2(N,N-di-propyl-N'- benzoylthiourea ) ligand the di-alkyl substituted thioureas were more efficient for the metal ion extraction than the mono-alkyl ligands. In almost all the experimental set ups there was reduction of the Au(lIl) to Au(l) and Au(O) but it was more pronounced with HL3 (N,N-di-(2-hydroxyethyl)-N'-benzoylthiourea). Transport experiments were also conducted, the experimental set up for transportation was a concentric type cell involving a 3-phase system - 2 aqueous phases ( source and receiving phase) separated by a chloroform membrane incorporating the ligand. The transport results however only gave a satisfactory result of about 5% of gold transported by the HL1 (N,N-dibutyl-N'-benzoylthiourea). All other ligands attempted resulted in metal ion being present in the organic phase, but no metal ion present in the receiving phase. To help drive the transport of the metal ion to the receiving phase CN-, S203 2- and perchloric acid were incorporated into the receiving phase. The transport results were not enhanced with these substances being present in the aqueous receiving phase. The aqueous source and receiving phases were analyzed by flame atomic absorption spectroscopy (FAAS). Finally the N,N-diethyl-N'-camphanoylthiourea (HL10) ligand and its complex with Au(l) were synthesised. Single crystals of the complex were grown for X-ray crystallography and the crystal and molecular structure of the complex was determined. The complex crystallizes in the monoclinic space group P21. The cell parameters are a = 10.7356(7)A b = 16.3443(11)A c = 10.9268(7)A f3 = 103.1450(10t , and final R-factor of 1.76%. The coordination sphere around Au(l) shows a nearly linear arrangement of sulphur and chloride. / AFRIKAANSE OPSOMMING: In hierdie proefskrif is In aantal mono- en di-gesubstitueerde asiel(ariel) thioureums ondersoek vir die transportasie en ekstraksie van Au(III). Twee-fase metaalioon vloeistof-vloeistof ekstraksie eksperimente is gebruik om die ekstraksie patroon van hierdie ligande te ondersoek. Die effek van verskillende ligand konsentrasies op die ekstraksie neiging van hierdie ligande is ondersoek. Resultate toon dat die verskillende substituente op die benziel ring die ekstraksie patroon van die metaalioon beïnvloed. Verder, is gevind dat die alkiel substituente op die thioureum saam met varierende ligand konsentrasies geensins die metaalioon ekstraksie beïnvloed nie. Met die uitsondering van H2L2 (N,N-dipropiel-N'-benzielthioureum) is die di-alkiel gesubstitueerde ligande meer effektief vir metaalioon ekstraksie in vergelyking met die mono-alkiel ligande. In baie van die eksperimente is In reduksie van Au(llI) na Au(l) en Au(O) gesien en dit is baie duidelik met ligand HL3 (N,N-di(2- hidroksie-etiel)N'-benzielthioureum). Alle waterige fases is ge-analiseer met gebruik van Atoomabsorpsie Spektroskopie (AAS). Transportasie eksperimente is ook uitgevoer met gebruik van In drie-fase selsisteem. Twee waterige fases (bron- en ontvang-fase) is geskei met die chloroform membraan fase wat die ligande bevat. Hierdie eksperimente het net In 5% Au(lll) transportasie getoon met HL1(N,N-dibutiel-N'-benzielthioureum). Daar was geen transportasie van Au(lIl) met enige van die ander ligande. Analise van die twee waterige fases het getoon dat die metaalioon eindelik goed ge-ekstraeer is en is teenwoordig in die membraan fase. Om die transportasie van Au(lIl) aan te spoor, is CN-, s2ol- en perchloorsuur in die ontvang-fase geinkorporeer. Die resultate was geensins beïnvloed nie. N,N-di-etiel-N'-kamfonielthioureum (HL10)ligande en die kompleks daarvan met Au(l) is ook gesintetiseer. Enkel-kristalle van die kompleks is verkry en X-straal kristallografiese analiese is onderneem. Hierdie kompleks kristalliseer in die monokliniese ruimtegroep P21,met a =10.7356(7)Á, b=16.3443(11)Á, c=10.9268(7)Á en ~=103.1450(10t. Die finale R-faktor is 1.76%. Die koordinasie om Au(l) toon In liniêre geometrie met swael en chloor.

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

A dissertation submitted to the Faculty of Science University of the Witwatersrand, Johannesburg for the degree of Master of Science. Johannesburg, 1994. / Molecular mechanics calculations are used to interpret and predict metal ion discrimination by coordinating ligands. Of particular interest are chelates exhibiting characteristics that Single them out for potential medical application; Selectivity patterns for several series of ligands are investigated with the help of strain energy profiles as a function of metal-donor atom bond distance. Ligands include simple; open-chain oxygen- and nitrogen-donors ana triaza- and tetraazamacrocyeles. Results are compared with X-ray crystallographic and solution data. Factors such as chelate ring size, conformational flexibility and preferred metal coordination geometry are found to influence metal specificity. Addition of pendent donor groups to macrocyoles leads to rigid structures and selectivity predictions according to cavity size. Interpretation of specific. metal ion recognition by polyetner antibiotics is attempted. Structural and steric factors are probed as possible determinants of metal choice. both covalent and ionic bonding models are explored. The covalent approach results in predictions of metal selectivity which correlate with mown selectivity patterns. Unfortunately, inability to optimise force field parameters in the ionic bonding approach forced us to abandon this model. The main force field used is the TRIPOS (1992,1993) force field. It performs well in calculations involving a univariate scanning technique but has to be modified to obtain reasonable structure reproduction with the large antibiotics, Errors in thermodynamic data predictions are obtained, nonbonding parameters have yet to be properly parameterized and the allocation of partial atomic charges warrants closer examination . All of these factors contribute to the poor performance of the force field when ionic interactions between metal and donor atoms of the polyethers are assumed. / AC2017

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / In this dissertation, the synthesis of nitrogen doped carbon nanotubes (N-CNTs) was performed successfully, using a floating catalyst chemical vapour deposition (CVD) method. Fe(CO)5 was utilized as the catalyst and acetonitrile and toluene as nitrogen and carbon sources respectively. Two different procedures were used to add reagents to the reactor: an injection method and a bubbling method. The effect of nitrogen concentration and physical parameters such as reaction temperature, gas flow rate on the morphology, crystallinity and thermal stability of the tubes was studied. The synthesized materials were characterized by means of Raman spectroscopy, TGA and TEM analyses. The presence of nitrogen was confirmed by the presence of the bamboo formations in the tubes by TEM. A comparison of the data from the numerous reactions revealed that N-CNTs can be made from Fe(CO)5 and acetonitrile. Further the main conclusions achieved using the injection method were: i) the maximum number of tubes with bamboo structure were made using on acetonitrile concentration of 15%, ii) The best growth temperature to make N-CNTs was 850 oC, iii) An increase in acetonitrile concentration decreased the yield of NCNTs and iv) Tubes with the narrowest outer diameters were made using an acetonitrile concentration of 15%.

In this project the link between species in solution and the solid state was considered. This is relevant due to the many applications in life where there is this interchange between solid and solution state, for example drug design, environmental metal speciation and the manufacture of materials that are in contact with solution (such as outdoor surface coatings, containers and so on). Complexation of two metal ions, namely cadmium(II) and bismuth(III), was studied. With bismuth showing so much promise in medicinal applications it was pertinent to investigate this interchange since the intake of medication is generally in the solid form which then converts to solution species as it dissolves in the body where it becomes active. For cadmium it is mainly the environmental concerns which we are faced with that call for the examination of speciation of complexes in solution, as well as their disposition upon precipitation or crystallization. A correlation was found between solution species and the complex that was isolated in the crystalline form with regards to pH for a number of metal-ligand species. We show how the results from solution experiments (achieved using direct current polarography) and those of crystalline complexes can complement each other when using species distribution diagrams as the intermediary. The distribution of species can be varied by changing the concentration and ligand-to-metal ratio at which the species distribution diagram is plotted. It is this characteristic which allows the solution and crystalline complexes – which are achieved using differing experimental conditions – to be correlated. The speciation diagram for a metal-ligand system, calculated using formation constants derived from solutions studies, was used in most instances to target specific species for their growth in the solid state. In some cases the solid state structure was used to confirm a suspected solution species, and in others the result was used to identify minor solution species which cannot be detected by the techniques used in determining formation constants. Further, we show that doing solution experiments at a range of temperatures can also aid in elucidating these minor species. The growth of crystalline species at low pH was important for this work because the pH titrations used for solution experiments were conducted from below pH 2 where the diffusion junction potential is large and changing. An in-situ witness ion was incorporated into the experiment to monitor the shifts due to the diffusion junction potential so that they could be compensated for. Additionally, for bismuth-ligand systems, hydrolysis and complexation with nitrates occurs in this same pH region. The formation constants and the species identified below pH 2 therefore do carry some uncertainty, so obtaining crystalline complexes of these species provides further confidence in their prediction in solution.