Browsing by Author "Smith, Michael-Phillip"

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    The effect of hydrogen bonding on foldamer self-assembly
    (Stellenbosch : Stellenbosch University, 2023-02) Smith, Michael-Phillip; Klumperman, Bert; Pfukwa, Rueben; van Otterlo, Willem; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Foldamers are chain molecules (oligomer or polymers) that fold into a conformationally ordered state when in solution. These polymers have been shown to have applications in host-guest chemistry, catalysis, and show great promise as responsive gel polymers. In previous literature, a large para-aryl triazole foldamer system with a diameter of 30 Å was developed and studied by Klumperman and co-workers. The foldamer’s superhelical structures (helixes made of helixes) were shown to be unstable. Where the structures would collapse (forming spherical objects made of secondary structure helixes) at high percentage solvent compositions of the selective solvent (water) in the non-selective solvent (Dimethylformamide, (DMF)). This was hypothesized to have occurred because of the polymer being poorly solubilized in solution. A library of polymers with varying amounts of hydrogen bond acceptors incorporated within the monomeric units was therefore synthesized and successfully characterized. The properties of the said library of polymers were then investigated via DLS (dynamic light scattering), LD (linear dichroism), CD (circular dichroism), and UV/Vis spectroscopy (ultraviolet-visible light spectroscopy). It was determined that the polymers with hydrogen bonding moieties incorporated within the monomeric units, would not fold with a change in solvent composition, instead, the polymers would form a conglomerated mass of polymer chains. This may be a result of two factors; firstly, although the hydrogen bonding was expected to increase the stabilization of the helical structure (simulated via molecular dynamic calculations), the amount of hydrogen bonding groups incorporated within the polymers could be too great and inhibited the polymers’ ability to fold. Secondly, the polymers may have not folded as the molecular weights of the polymers may have not been sufficiently large enough to induce folding (polymer length would need to be 42 kDa). To confirm this hypothesis, ultrapure monomers would need to be synthesized (according to a new synthetic procedure) and a new polymerization methodology would need to be developed for the hydrogen bonding containing monomers to ensure higher molecular weights are easily achieved. In the future, it would be ideal to investigate other streamlined methods to achieve the synthesis of the polymeric systems developed in this thesis, this would enable for the effective investigation of the properties of this system without having such synthetic hurdles as was encountered in this work. For example, the development of a triphenylphosphine-free methodology for a Sonagashira-Hagihara coupling reaction. It would also be ideal to develop another method of polymerization for the hydrogen bond-containing systems as the current polymerization technique may have not yielded polymer with high enough molecular weights to confirm that low molecular weights of the polymer systems were inhibiting the folding process. In addition, it would be ideal to develop another methodology to acquire ultrapure monomer as this is a step growth polymerization and any impurities would drastically impact the molecular weight acquired.
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    Facile synthesis of a C4-symmetrical inherently chiral calix[4]arene†
    (Royal Society of Chemistry, 2021-09) Hodson, Luke; Visagie, Kevin J.; Smith, Michael-Phillip; Loots, Leigh; Kuter, David; Snayer, Tregen M.
    Inherently chiral calix[4]arenes with C4-symmetry are extremely rare and difficult to synthesise, severely hampering any effort to expand on their potential as chiral supramolecular catalysts and building blocks. Herein we report a reaction of a tetracarbamate calix[4]arene with NBS which results in a high yield of an inherently chiral calix[4]arenes with C4-symmetry. Furthermore, employing a chiral N-Boc proline moiety allows for separation of the diastereomers formed, thus obtaining the pure enantiomers after hydrolysis. The enantiomers could be assigned based on the CD spectra and DFT calculated values.