Department of Chemistry

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https://univendspace.univen.ac.za/handle/11602/1924

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Browsing Department of Chemistry by Subject "547.7"

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    Application of organic acid functionalized cellulose for batch and aqueous two-phase extraction of sulfonamides from different matrices
    (2025-09-05) Shikweni, Mbuyelo; Mokgehle, T.; Tavengwa, N. T.; Ndou, D. I.
    Antibiotics are among the most widely used drugs globally, with fluoroquinolones, macrolides and sulfonamides being commonly prescribed. Sulfonamides, which form the basis of several sulfa drugs, have significant applications in both medicinal and synthetic organic chemistry. While these substances are effective in their intended uses, their negative environmental impact raises serious concerns. Sulfonamides can have toxic effects on aquatic ecosystems, leading to the disruption of microbial communities, bioaccumulation in organisms and the development of antibiotic resistance. To mitigate these effects, cellulose and its functionalized derivatives were investigated for their ability to adsorb sulfonamides from real wastewater, milk and honey samples. To improve adsorption, cellulose was functionalized with oxalic and adipic acid. The resulting sorbents were then analyzed using FTIR, PXRD and SEM techniques. Based on FTIR analysis the optimal reaction time for cellulose functionalized with adipic acid and oxalic acid via hydrothermal treatment in an autoclave was 1 h at a temperature of 50℃. Furthermore, the FTIR data revealed the emergence of ester moieties from the esterification reaction of carboxyl groups in the organic acids and the hydroxyl groups on cellulose. Based on PXRD analysis for the adipic acid functionalized cellulose contained a hybrid of adipic acid and oxalic acid peaks, indicating functionalization of cellulose. Batch adsorption experiments were conducted using sulfonamide based analytical standards: sulfachloropyradazine and sulfabenzamide, to evaluate the adsorption capability of cellulose and its functionalized derivatives at varying temperature, time, and mass of sorbent. The multivariate based optimal conditions for the adsorption of sulfachloropyradazine and sulfabenzamide using cellulose was 25°C, 180 min and 5 mg and with extraction efficiency of 70 and 51%, respectively. The optimal conditions for adsorption of sulfachloropyradazine and sulfabenzamide using oxalic acid functionalized cellulose was 25°C, 30 min and 50 mg with extraction efficiency of 64 and 75%, respectively. Adsorption of sulfachloropyradazine and sulfabenzamide using adipic acid functionalized cellulose was 25°C, 30 min, and 5 mg with extraction efficiency of 70 and 51%, respectively. Although cellulose functionalized with adipic and oxalic acid showed some influence on the adsorption behavior of sulfachloropyridazine and sulfabenzamide, the adsorption of sulfachloropyridazine was slightly reduced from 70% with unmodified cellulose to 64% with the functionalized form. Functionalizing cellulose with adipic and oxalic acid adds carboxyl and hydroxyl groups, enhancing adsorption of sulfachloropyradazine and sulfabenzamide through stronger hydrogen bonding, electrostatic interactions, and possibly π-π stacking, compared to cellulose. Overall, the functionalization of cellulose with these acids is a promising approach for enhancing the adsorption of sulfonamides which could be applied in wastewater treatment.
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    Stereo-directing effect of molecularly imprinted polymers on cinnamic acids
    (2025-09-05) Maseko, Nontlantla Regina; Mniyakeni-Moleele, S. S,.; Tavengwa, N. T.
    The pursuit of enantiomerically and diastereomerically pure compounds is a paramount concern in pharmaceutical synthesis and various other industries, as different isomers often exhibit drastically different even opposite and toxic biological activities. Traditional separation methods are often inefficient, costly, and environmentally unsustainable, necessitating an exploration of good separation and purification techniques. The study addresses this challenge by exploring, for the first time, the stereo-directing potential of molecularly imprinted polymers (MIPs) in reactions involving cinnamic acid derivatives, specifically focusing on (2E)-3-(4-methoxyphenyl) prop-2-enoic acid (trans-4-methoxy cinnamic acid (t-4MCA)). To the best of our knowledge, no prior studies have reported the synthesis of MIPs using t-4MCA as a template, nor the application of MIPs as catalysts in the Wittig reaction or for the selective separation of cis and trans isomers resulting from photoisomerization. The work represents a novel approach to stereoselective synthesis and purification. MIPs were synthesized via precipitation polymerization using t-4MCA as the template, methacrylic acid (MAA) as the functional monomer, and ethylene glycol dimethacrylate (EEDGMA) as the cross-linker in a 1:4:20 molar ratio. A “dummy” template paracetamol (PCM) was also used to create a comparative MIP. Non-imprinted polymers (NIPs) were synthesized as controls. Complete template removal was verified after 8 washing cycles using UV-VIS spectroscopy. Brunauer-Emmert-Teller (BET), Fourier transform Infra-red (FTIR), thermogravimetric analysis (TGA), and ultraviolet (UV) spectroscopy were employed to characterize the unwashed MIPs, washed MIPS and NIPs. The characterization confirmed the formation of amorphous, mesoporous material with high surface areas, particularly after template removal. The disappearance of the vinyl C=C stretch (1635 cm-1) in the FTIR spectra confirmed complete polymerization while the peaks for the polymer backbone were confirmed by C-H vibrations at ⁓2980 cm-1 and ⁓1451 cm-1. The t-4MCA MIP exhibited a BET surface area of 175.2 m2 g-1 and a pore volumeof 0.190 cm3 g-1, markedly higher than the NIP (7.9 m2 g-1 and 0.009 cm3 g-1). TGA showed maximumdecomposition temperatures of 375oC, 379oC and 389oC for the washed t-4MCA MIP, unwashed t-4MCAMIP, and NIP, respectively, highlighting the good thermal stability of the polymer network. Swellingstudies showed differential swelling behavior dependent on solvent, with acetonitrile showing a highdegree of swelling for MIPs and ethanol for the NIPs. Adsorption studies, optimized using a 5:5 v/v methanol/water washing solution 10 mg of polymer mass, pH 7, and a 60-min contact time, revealed a maximum adsorption capacity (qm) of 3.00 mg g-1, for t-4MCA on the MIP, significantly exceeding that of the NIP (2.60 mg g-1) and PCM MIPs (2.4 mg g-1), with an imprinting factor of 1.14. Selectivity studies using structurally analogues ferulic acid, (E)-3-(4-hydroxyphenyl)prop-2-enoic acid (trans-4-hydroxy cinnamic acid (t-4HCA)), and ethyl (E)-3-(4-methoxyphenyl) acrylate (Et-MOPA) demonstrated a significant cross-reactivity with ferulic acid (k` = 0.356), moderate cross-reactivity with t-4HCA (k` = 2.340) and minimal cross-reactivity with Et-MOPA (k` = 1.635). Optimum photoisomerization of t-4MCA at 3 h resulted in the MIP increasing the reaction rate by a 21.63% increase in the cis isomer proportion. At 12 h, after total equilibration, there was evidence of an increased yield of the cis isomer of almost 10%. The Wittig reaction of 4-methoxybenzaldehyde yielded a percentage cis/trans ratio of 3/97. Crucially, conducting the reaction in the presence of the t-4MCA MIP improved the ratio to 6/94, an increase in the cis isomer ratio. This research demonstrated, for the first time, an attempt at the application of t-4MCA-imprinted MIPs as both selective adsorbents and stereo-directing agents. The MIPs significantly enhanced the proportion of the cis isomer in the photoisomerization reaction and, uniquely, in the Wittig reaction, highlighting their potential for efficient and sustainable production of diastereomerically pure pharmaceuticals and fine chemicals.