Evaluation of the antioxidant activity of nanostructured systems containing Cordia verbenacea extract

Solid lipid nanoparticles (SLNs) offer potential carriers for bioactive plant extracts, while green synthesis uses phytochemicals to reduce and stabilize metallic nanoparticles (GUNAWAN and BOONKANOKWONG, 2024). This study evaluated silver nanoparticles (AgNPs) synthesized using standardized Cordia verbenacea extract (CvSE), alongside SLNs containing the same extract, focusing on phytochemical composition, characterization, and antioxidant activity. AgNP synthesis conditions were optimized by varying CvSE concentrations (1, 2, and 4 mg mL⁻¹), silver nitrate concentrations (5, 7, and 10 mmol L⁻¹), pH (3, 5, 9, and 11), and temperature and reaction time. The selected conditions were 4 mg mL⁻¹ CvSE, 7 mmol L⁻¹ AgNO₃, pH 11, and 50 °C for 30 minutes. SLNs were produced by homogenizing stearic acid and soy lecithin with CvSE, followed by hot emulsification, cooling, filtration, freezing, and lyophilization, adapting the lipid nanoparticle preparation approach described by GOKCE et al. (2012). Total polyphenols were measured using Folin–Ciocalteu reagent, and flavonoids were quantified using an aluminum chloride method. Antioxidant activity was evaluated through DPPH radical scavenging and ferric reducing antioxidant power (FRAP), following RUFINO et al. (2010). Fourier-transform infrared spectroscopy (FTIR) and electron microscopy were used for characterization. AgNPs were spherical, measuring 9–17 nm, and displayed a surface plasmon band at 420–450 nm. CvSE scavenged 80.84 ± 0.84% of DPPH radicals at 4 mg mL⁻¹, whereas AgNPs achieved 68.23 ± 0.35%. AgNP FRAP activity was 1,117.44 ± 23.65 μM Trolox equivalents g⁻¹ and was statistically equivalent to CvSE. Total polyphenols measured 750.30 ± 27.07 mg gallic acid equivalents g⁻¹ in AgNPs and 522.63 ± 114.26 mg g⁻¹ in CvSE. Flavonoid contents were comparable: 234.92 ± 13.92 and 249.92 ± 25.91 mg rutin equivalents g⁻¹, respectively. These findings suggest that phytochemicals remained associated with the nanoparticles. SLNs were spherical, with sizes of 85–100 nm. FTIR bands at 1699 and 1021 cm⁻¹ indicated carbonyl- and C–O-associated groups. SLN DPPH scavenging increased from 2.19 ± 0.02% before release to 18.5 ± 4.89% after release. Released samples contained 558.17 ± 22.19 mg gallic acid equivalents g⁻¹ polyphenols and 630.75 ± 25.17 mg rutin equivalents g⁻¹ flavonoids. Overall, both systems warrant further investigation as potential platforms for topical antioxidant delivery and phonophoresis. However, antioxidant responses differed between formulations, emphasizing that composition, accessibility, and release behavior may influence activity. Further work should assess particle size distribution, encapsulation efficiency, storage stability, release kinetics, cytocompatibility, and efficacy before therapeutic claims or clinical translation. These results provide a basis for comparing metallic nanomaterials with lipid carriers containing extract.

Funding: Laboratory of Green Nanobiotechnology and Natural Products and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES),