Biogenic Metal Transformations from Plectranthus amboinicus: Complexes, Nanoparticles, and Therapeutic Applications

Green synthesis of metal complexes and metal oxide nanoparticles offers promising antimicrobial, antioxidant, and anticancer properties. Their efficacy hinges on precise control of preparation methods and reaction conditions, which influence particle size and shape. Due to their nanoscale dimensions, these materials can penetrate and destroy target cells, positioning them as potential future therapeutics. Using plant extracts reduces costs and enhances efficiency, though many green methods remain experimental and require strict control for optimal results.

Copper, zinc, and manganese complexes were synthesised by reacting these metals with flavonoids extracted from Plectranthus amboinicus, identified via LC-MS/MS. Corresponding metal oxide nanoparticles were produced from methanolic extracts. Characterisation utilised UV-Vis, FT-IR, XRD, ¹H NMR, and FESEM. Antimicrobial activity was assessed against four bacteria and one fungus using agar diffusion; antioxidant activity via DPPH and ABTS assays; and anticancer effects on AML (WTS-1) and Calu-3 lung cancer cells (SRB assay). Flow cytometry analysed apoptosis mechanisms.

Diagnostic analyses confirmed successful synthesis of metal complexes and oxide nanoparticles. UV-Vis spectra showed characteristic peaks; FT-IR identified M-O bonds. XRD and FESEM revealed nanoscale sizes and diverse morphologies. EDX indicated elemental composition differences; higher carbon content was observed in complexes compared to nanoparticles. Copper complexes were most effective antimicrobial agents, outperforming antibiotics like clindamycin and ampicillin. Conversely, copper oxide nanoparticles exhibited superior antioxidant and anticancer activities, inducing apoptosis in cancer cells.

Green synthesis using Plectranthus amboinicus effectively produced nanoscale metal complexes and oxide nanoparticles suitable for therapeutic applications. Their demonstrated biological activities-antimicrobial, antioxidant, and anticancer-alongside apoptosis induction, underscore their potential as promising drug candidates. Further research is warranted to optimise these green methods for clinical use.