This study screened phytochemicals to determine their total polyphenols content (TPC) by Folin-Ciocalteu reagents and to evaluate antioxidant activity using DPPH scavenging, ABTS cation decolorization, and reducing power assays of various extracts of Symplocos cochinchinensis leaves. A correlation between TPC and antioxidant activity was analysed by Pearson’s method. The results indicated that S. cochinchinensisleaves contained triterpenoids, alkaloids, anthraglycosides, flavonoids, anthocyanosides, proanthocyanidins, polyphenols, tannins, saponins, polyuronics, and reducing agents. All extracts had antioxidant properties with the ethyl acetate fraction exhibiting the highest antioxidant capacity, which had the lowest IC50 in DPPH (83.33 μg/ml), an ABTS of 46.21 μg/ml, and EC50 of 69.10 μg/ml in reducing power. There was a significant negative correlation between the TPC in S. cochinchinensis leaf extracts and their IC50 and EC50 values of antioxidant activity. It was suggested that S. cochinchinensis leaves have a great potential for antioxidant activity based on its high total polyphenol content and potential for use as a traditional treatment
Ag/SiO2 colloidal nanocomposites (NCs) were prepared through the semi-continuous chemical reduction of silver ions on a silica surface; NaBH4 was used as a primary reducing agent, while carboxymethyl cellulose (CMC) served as a secondary reductant and a stabilizer at low temperature. Silver nanoparticles (AgNPs) of an average diameter of 3.89±0.18 nm were uniformly and densely dispersed on the SiO2 surface, forming 218.6-nm-sized Ag/SiO2 NCs. The zeta potential of the Ag/SiO2 NCs (−92.6 mV) was more negative than that of silica (−24 mV), indicating their high long-term stability. Furthermore, their proposed formation mechanism was confirmed via Fourier transform infrared spectroscopy. Then, the bactericidal effect of the Ag/SiO2 was evaluated based on their minimal inhibitory concentration (MIC) against Ralstonia solanacearum 15 (R. solanacearum 15); it was 62.5 ppm, much lower than that of conventional AgNPs (500 ppm). Therefore, these highly stable Ag/SiO2 colloidal NCs with more effective antibacterial activity than conventional AgNPs are a promising nanopesticide in agriculture.
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