Green Biosynthesis and Bioactivity Assessment of AgNPs and NaNPs from Pycnanthus angolensis Sap: Experimental and Computational Validation of Ethnomedicinal Use

Abstract

Background: Nanoparticles are materials with at least one dimension ranging between one and 100 nanometers, and at this scale, they display unique physical, chemical, and biological properties distinct from their bulk counterparts. Objective: To synthesise and characterise silver and sodium nanoparticles from plant sap, evaluate their antimicrobial and antioxidant properties, and provide scientific validation for the traditional use of sodium chloride in herbal cough remedies. Methodology: In this study, Silver (AgNPS) and sodium (NaNPS) nanoparticles were synthesised and characterised using ultraviolet (UV), Fourier Transform Infrared (FT-IR) spectroscopy, and gas chromatography–mass spectrometry (GC-MS). Their biological activities were evaluated against Staphylococcus aureus and Aspergillus niger, while antioxidant potential was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Density Functional Theory (DFT) calculations at the B3LYP/6-31G level were employed to estimate the HOMO–LUMO energy gap and related global reactivity parameters. Results: Two major compounds were identified: 2-(4-hydroxy-3-methoxyphenyl)propanamide (73.05%) and 4,4'-[(2R,3S)-2,3-dimethylbutane-1,4-diyl]bis(2-methoxyphenol) (26.95%). Antimicrobial screening revealed inhibition zones of 19 mm for NaNPS and 10 mm for AgNPS against S. aureus. Radical scavenging activity followed the trend NaNPS > crude sap > AgNPS. Theoretical studies indicated that 4,4'-[(2R,3S)-2,3-dimethylbutane-1,4-diyl]bis(2-methoxyphenol) is more potent than the major constituent, 2-(4-hydroxy-3-methoxyphenyl)propanamide. Conclusion/Recommendations: The findings provide scientific justification for the traditional use of sodium chloride (NaCl, common salt) in the preparation of this plant’s sap for cough remedies. Given the superior bioactivity of the minor compound 4,4'-[(2R,3S)-2,3-dimethylbutane-1,4-diyl]bis(2-methoxyphenol) predicted by DFT calculations, isolation and structure-activity relationship studies of this compound should be prioritised to develop more potent antimicrobial and antioxidant agents for pharmaceutical applications.