Characterization and comparative antioxidant study of calcium oxide and zinc nanoparticles mediated by Annona muricata leaves

Abstract

In this study, the leaf extract of Annona muricata was employed as an eco-friendly reducing and capping agent for the synthesis of calcium-oxide nanoparticles (CaONPs) and zinc nanoparticles (ZnNPs). Phytochemical screening revealed significant levels of total flavonoids (173.5 mg QE/100 g), total phenolics (52.97 mg GAE/100 g), tannins (19.1 mg TAE/100 g), triterpenes (12.94 mg OAE/100 g), starch (10.14%), coumarins (5.62 mg CE/100 g), and reducing sugars (4.66%), indicating that the extract possessed sufficient bioactive compounds. The nanoparticles were characterized by UV–visible, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy, and energy-dispersive X-ray analysis. ZnNPs showed maximum absorption at 304 nm, with an irregular shape, and an average particle size of 3.68 nm, whereas CaONPs absorbed at 294 nm, with an oval shape and an average size of 4.09 nm. The FTIR spectra of ZnNPs showed peaks at 3448, 2928, 2850, 1620, and 567 cm⁻¹, assigned to O–H, C–H of CH3, C–H of CH₂, C = C, and Zn–O groups, respectively. For CaONPs, peaks at 3387, 2854, 1438, 1060, and 702 cm⁻¹ were attributed to O–H, C–H of CH₂, Ca–O, and C–O groups. Antioxidant activity, assessed using 2,2-diphenyl-1-picrylhydrazyl, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), Ferric reducing antioxidant power, and phosphomolybdate assay, increased with concentration from 0.2 to 1.0 mg/mL. ZnNPs exhibited stronger activity, with IC₅₀ values of 0.17 mg/mL and 0.233 mg/mL for DPPH and ABTS, 8.13 mg GAE/g for FRAP, and 59.14 mg AAE/g for TAC, while CaONPs showed a notable FRAP activity of 16.99 mg GAE/g. These findings highlight ZnNPs as promising plant-mediated antioxidant agents.