Antifungal activity of chitosan-metal organic frameworks against Aspergillus niger and Candida Albicans Gideon Kirui , Edwin Shigwenya Madivoli, Dennis Mwanza Nzilu, Walyambillah Waudo, Patrick Gachoki Kareru Chemistry Department, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya Antifungal resistance and the health hazard associated with the use of synthetic fungicides necessitate the need to develop new antifungals. This study, therefore, sought to develop a chitosan metal-organic framework (Cs-MOF) containing copper and zinc particles with antifungal activity. The Cs-MOF was prepared by first isolating chitosan (Cs) from Hermetia illucens (black soldier fly) followed by periodate oxidation to introduce carbonyl groups (C=O) in its structure for complexing copper and zinc ions. Metal salts were then heated with terephthalic acid in dimethylformamide followed by Cs loading after which glycine (Gly) was anchored to unreacted C=O groups in Cs-MOF to obtain Cs-MOF-Gly. X-ray fluorescence (XRF) and Energy-dispersive X-ray (EDX) spectroscopy data indicated the removal of extractives and purity of Cs and MOFs, while C=O vibrational bands using Fourier-Transform Infrared Spectroscopy (FTIR) were proof of Cs oxidation, MOFs synthesis and modification. Scanning Electronic Microscopy (SEM) images of Cs-MOF-OCs were rougher than Cs-MOF indicative of successful modification. The phase purity and crystallinity of Cs, MOF, and Cs-MOF were analyzed using XRD which further confirmed our findings. Using the Plate count method, Cs-MOF-Gly showed more antifungal activity against Aspergillus niger and Candida albicans than Cs-MOF and also when compared to Cs and Pirimiphos-methyl as standards. Glycine hastens the interaction with fungal membrane amino groups via covalent bonds. This interaction combined with the synergistic antimicrobial effect of Cs, Gly, and metal ions compromises the integrity of the fungal membrane as a protective layer. The Cs-MOF and Cs-MOF-Gly showed effective antifungal activity via a “pronounced killing effect” caused by the gradual release of the metal ions as the framework structure slowly biodegrades. This release resulted in the diffusion of metal ions through the fungal membrane hence the activity of Cs-MOF and Cs-MOF-Gly which implies they can control this fungus during postharvest thereby preventing losses . References 1. Akinremi, C. A., Adeogun, A. I., Poupin, M., & Huddersman, K. (2021). Chitosan-Terephthalic Acid-Magnetic Composite Beads for Effective Removal of the Acid Blue Dye from Aqueous Solutions: Kinetics, Isotherm, and Statistical Modeling. ACS Omega , 6 (45), 30499–30514. 2. Dong, W., Yang, L., & Huang, Y. (2017). Glycine post-synthetic modification of MIL-53(Fe) metal–organic framework with enhanced and stable peroxidase-like activity for sensitive glucose biosensing. Talanta , 167 , 359–366. 3. Gikonyo, B., Liu, F., De, S., Journet, C., Marichy, C., & Fateeva, A. (2022). Investigating the vapour phase synthesis of copper terephthalate metal organic framework thin films by atomic/molecular layer deposition. Dalton Transactions, 52(1), 211–217. 4. Matveevskaya, V. V, Pavlov, D. I., Ryadun, A. A., Fedin, V. P., & Potapov, A. S. (2023). Synthesis, Crystal Structure, and Luminescent Sensing Properties of a Supramolecular 3D Zinc(II) Metal–Organic Framework with Terephthalate and Bis(imidazol-1-yl)methane Linkers. Inorganics, 11(7), 264.
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