Physicochemical interactions of selected natural phenolic compounds at the surface of gold nanoparticles

Abstract

In this research endeavour, we investigated the potential of two significant plant materials, G. glabra and G. Africana, as sources of bioactive phenolic structures and reducing agents for the synthesis of UNICAP gold nanoparticles. The roots of G. glabra underwent exhaustive extraction with aqueous methanol, leading to the isolation and identification of 22 compounds. Notably, compound 11 was identified for the first time in this study. The compounds included naringenin 4′-O-glucoside (1), butin (2), liquiritin (3), liquiritin apioside (4), abyssinone (5), glabrol (6), isoliquiritin (7), neoisoliquiritin (8), isoliquiritin apioside (9), licuraside (10), and others. Neuroprotective evaluations revealed inhibitory effects on caspase 3/7 activities induced by MPP+ for both G. glabra total extract (TE) and specific compounds (1, 7, 11, 16, and 20), marking the first report of compound 11 and the neuroprotective activity of certain phenolic constituents from G. glabra. Six isolated compounds, namely liquiritin (3), isoliquiritin (7), neoisoliquiritin (8), liquiritin apioside (4), isoliquiritin apioside (9), and glabridin (19), demonstrated robust reducing power in the synthesis of AuNPs. Characterization of the synthesized AuNPs included UV, zeta sizer, HRTEM, and IR analyses, with stability assessments in various biological media. In vitro studies on cytotoxicity and anti-inflammatory activities using the RAW 264.7 macrophage cell line indicated inhibitory effects on cell proliferation and inflammatory activity for various compounds and their corresponding AuNP conjugates. G. Africana total extract, upon chromatographic purification, yielded eight compounds, including the novel compound 8. Cytotoxicity evaluations against HepG2 and SH-SY5Y cancer cell lines revealed potent activities for compounds 7 and 8. Compound 7 induced apoptosis through the activation of caspases 9 and 3, while compound 8 demonstrated a significant decrease in all tested caspases. These findings provide insights into the heightened toxicity of G. Africana towards sheep liver, potentially explaining the observed damage upon plant ingestion. Furthermore, three isolated compounds (4, 5, and 7) from G. Africana exhibited strong reducing capability and formed stable AuNPs. Characterization of the synthesized NPs, along with assessments of antioxidant capacity and cytotoxicity against cancer cell lines, indicated a notable reduction in the toxic effects of capping agents when in NP conjugate form.