Doctoral Degrees (Chemistry and Polymer Science)

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Browsing Doctoral Degrees (Chemistry and Polymer Science) by browse.metadata.advisor "Bredenkamp, M. W."

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    Controlled polymerization of amino acid derivatives
    (Stellenbosch : University of Stellenbosch, 2008-03) Van Kralingen, Leon; Bredenkamp, M. W.; Sanderson, Ron D.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
    This dissertation can be broken into two parts comprising different strategies to synthesise novel poly-amino acid based polymers. The use of recently developed nickel(0) and cobalt(0) metal catalysts for the living polymerization of α-amino acid-N-carboxyanhydrides (NCAs) to synthesise novel poly-amino acid polymers, comprising a polar, hydrophilic block and a neutral hydrophobic block, were investigated in the first part of this study. The hydrophilic block was made up of a random sequence of arginine (Arg, R), glycine (Gly, G) and aspartic acid (Asp, D) - poly-RGD. This was followed by a polyleucine (Leu, L) hydrophobic block. Success was limited with this system due to polymer precipitation during the polymerization reaction. Because of this precipitation, the amino acid composition of the hydrophilic block was changed to a random sequence of glutamic acid (Glu, E), cystein (Cys, C) and aspartic acid – poly-ECD. Here also, the success was limited because of polymer precipitation. A novel approach to the synthesis of hybrid poly-amino acid – synthetic polymer materials constitutes the second part of this study. The final polymeric structure can be described as a carboxylic acid functionalized polyethylene glycol (PEG) sheathed polylysine polymer. The technology involves the synthesis of a lysine NCA functionalized at the ε-amino group with an α,ω-bis(carboxymethyl) ether PEG. The distal carboxylic acid group was protected as a benzyl ester during synthesis and subsequent polymerization of the PEG-lysine-NCA macro-monomer. The polymerization was successfully initiated using n-butyl amine to form short homopolymer strands. Copolymerization with lysine-NCA was also achieved as well as the successful initiation using a generation 1.0 dendritic amine initiator, N,N,N’,N’-tetrakis(3-aminopropyl)-1,4-butanediamine (DAB-Am-4). These polymers were characterized by 1H NMR.
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    Self-assembly of new porous materials
    (Stellenbosch : University of Stellenbosch, 2009-03) Jacobs, Tia; Barbour, Leonard J.; Bredenkamp, M. W.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: The primary objective of the work was to prepare and investigate new porous materials using the principles of crystal engineering. Both organic and metal-organic systems were studied and the work can best be divided into two separate sections: 1. The crystal engineering of Dianin’s Compound, a well-known organic host. 2. The design and synthesis of a series of related porous coordination compounds consisting of discrete, dinuclear metallocycles. The first section discusses the synthetic modification of Dianin’s compound in order to engineer a new clathrate host with an altered aperture size. Although this study ultimately failed to isolate the host material in its porous guest-free form, the work led to the discovery of a chiral host framework that aligns guest molecules in a polar fashion, and consequently displays non-linear optical properties. These findings are unprecedented in the long history of crystal engineering of Dianin’s compound and its analogues. This section also describes desorption studies of the new inclusion compound, as well as the known thiol analogue of Dianin’s compound. Systematic characterisation of these desorbed phases has raised interesting fundamental questions about desolvation processes in general. The second section constitutes the major portion of the work. A series of related isostructural coordination metallocycles were synthesised and their structure-property relationships were investigated using a variety of complementary techniques. These metallocyclic compounds all crystallise as solvates in their as-synthesised forms, and different results are obtained upon desolvation of the materials. In each case, desolvation occurs as a single-crystal to single-crystal transformation and three new “seemingly nonporous” porous materials were obtained. A single-crystal diffraction study under various pressures of acetylene and carbon dioxide was conducted for one of the porous metallocycles. This enabled the systematic study of the host deformation with increasing equilibrium pressure (i.e. with increasing guest occupancy). The observed differences in the sorption behaviour for acetylene and carbon dioxide are discussed and rationalised. Gravimetric gas sorption isotherms were also recorded for the three different porous materials and the diffusion of bulkier molecules through the host was also investigated structurally. Finally, a possible gas transport mechanism is postulated for this type of porous material (i.e. seemingly nonporous), and this is supported by thermodynamic and kinetic studies, as well as molecular mechanics and statistical mechanics simulations.
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    Synthesis, structure and coordination chemistry of new monopodal and bipodal thiocarbamic esters and acyl(aroyl)-substituted ureas with Ni(II), Pd(II), Pt(II) and Cu(II)
    (Stellenbosch : Stellenbosch University, 2006-12) Blewett Gavin; Koch, Klaus R.; Bredenkamp, M. W.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: N-acyl(aroyl)-N',N'-dialkylthioureas have resulted in a number of potential industrial and analytical applications within the platinum group metals (PGM) industry. N-acyl(aroyl)thiocarbamic-0-alkyl esters and N-acyl(aroyl)-N',N'-dialkylureas are remarkably similar in connectivity and molecular geometry to the N-acyl(aroyl)-N',N'-dialkylthioureas and are therefore of interest as structural analogues. A systematic study was made of the influence of variation of the N-acyl(aroyl) moiety, as well as the 0-alkyl moiety of N-acyl(aroyl)thiocarbamic-0-alkyl esters, on the coordination geometry of this class of ligand to nickel(II), palladium(II) and platinum(II). Numerous single crystal X-ray analyses were undertaken on both the non-coordinated ligands as well as the resultant complexes in order to elucidate the effect these variations have on the molecular structures and the overall crystal lattices. Particular attention was paid to the effect that these variations have in the solid state on the carbon-nitrogen bond lengths within the non-coordinated ligands as well as the derived metal complexes. A systematic study was also undertaken of the steric and electronic influences of electron rich substituents introduced onto the aroyl moiety of the N-acyl(aroyl)thiocarbamic-0-alkyl esters on the metal-oxygen bond lengths within the derived 0-alkyl-N-aroyl-thiocarbamato complexes. A parallel investigation was carried out on a series of N-acyl(aroyl)-N',N'-dialkylureas to elucidate the effect of the variation from bidentate (S, 0)-donor atoms sets to the ( 0,0 ')-donor atom sets. The molecular structures of several N-acyl(aroyl)-N',N'-dialkylureas as well as several copper(II) complexes thereof were determined and used to investigate the steric and electronic influences the N',N'-dialkyl and N-acyl(aroy) variations within this series have on the coordination of this class of ligand. The resultant scarcity of trans- or anti-( 0, 0 ') chelates was also investigated from an electronic and steric perspective of the ligands and their coordination mode to the metals investigated. The first example of a trans- or anti-( 0, 0 ') copper complex of this class of ligand was successfully isolated and fully characterised. Furthermore, the theme has been expanded to incorporate the preparation and characterisation of bipodal equivalents to the simple monopodal N-acyl(aroyl)thiocarbamic-0-alkyl esters. These bipodal compounds potentially add a 'supramolecular' and 'self assembly' dimension to the Nacyl( aroyl)thiocarbamic-0-alkyl ester motif. The first crystal structures of this type are reported and include an interesting case of polymorphism. The coordination of this class of bipodal ligand to several platinum group metals as well as copper was investigated.
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    Tin-bemiddeling van inositolderivatisering
    (Stellenbosch : Stellenbosch University, 2000-03) Prinsloo, Mare-Loe; Bredenkamp, M. W.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science .
    ENGLISH ABSTRACT: The aim of this thesis is to use tin-mediated reactions to differentiate between the four zones in the myo-inositol ring that consists of five contiguous equatorial and one axial hydroxyl groups. It is expected to give chemical control over the hexitol that can be put to good use in commercializing the phosphate derivatives of myo-inositol that are of pharmaceutical value. As point of departure 1,2-0-cyclohexylidene-myo-inositol (II.I) was synthesized that contains a tetrol with one end adjacent to an axial acetal oxygen and the other end adjacent to an equatorial acetal oxygen. The selective protection of position 3 (Dmyo- inositol) was investigated. Various problems lead to the selective silylation of the acetal at position 5. The silane forms the basis of the subsequent investigation because the cyclitol is now divided into an isolated mono-ol and a trans-diol allowing for easier differentiation between the various hydroxyl groups. It was indeed possible to differentiate the trans-diol from the mono-ol by using carbonylation and allylidenation. Ring closure occurs in both cases. In the carbonylation case the resultant five-membered ring is less stable than that of the allylidene due to the Sp² hybridized carbon atom of the carbonate compared to theSp³ hybridized carbon of the allylidene group. Preliminary work was done on the racerrue 1,2-0-cyclohexylidene-myo-inositol (II.VII) in order to use the acquired technology on the chiral camphor analog. The transition from racemic to chiral proved problematic since the camphor acetal is difficult to prepare and its selective silylation differs from that observed for cyc1ohexylidene. The camphor acetal itself was silylated in the process. (S)-( -)-Camphanic chloride was therefore used as chiral auxiliary in the protection of position six of the racemic 1,2,3,4,5-protected myo-inositol, thus solving the problems encountered in the protection of position six whilst combining the protection and chiral induction steps. The resultant diastereomers could both be used in the synthesis of IP₃ and IP₄ respectively, eliminating the disposal of half ofthe product. This project lead to the development of useful chiral differentially protected myoinositol derivatives, which could be useful in synthesis of various other myo-inositol derivatives. Besides the synthesis of useful chiral differentially protected myo-inositol derivatives, this investigation developed new applications in the tin-mediated derivatization of sugars. The following compounds were synthesized during this investigation. Bold numbers indicates novel compounds.