Synthesis of colloidal silver-polyphenols nanocomplexes - physicochemical properties, DFT calculation, modeling of adsorption and antibacterial activity

Abstract The aim of the studies was the investigation of nanocomplexes based on a silver core and attached three polyphenolic compounds belonging to tannins i.e. tannic acid (AgNPs-TA), 3,6-bis- O -di- O -galloyl-1,2,4-tri- O -galloyl- β -D-glucose (AgNPs-RT) and 1,2,3,4,6-penta- O -galloyl- β -D-glucose (AgNPs-PGG). The nanoparticles were characterized using UV-Vis spectroscopy, DLS (dynamic light scattering) and STEM (scanning transmission electron microscopy). Additionally, the molecular modelling connected with the biointerface interactions between tannins and AgNPs were studies carrying out a Monte Carlo search as well as DFT calculation along with the analysis of HOMO and LUMO orbitals were done to better characterize synthesized nanoparticles at the quantum level. The antibacterial activity of AgNPs-TA, AgNPs-RT and AgNPs-PGG was also assessed by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Staphylococcus aureus (MRSA and MSSA) and Escherichia coli . The studies found that synthesized nanocomplexes AgNPs-TA, AgNPs-RT and AgNPs-PGG have the diameter in the range 35–38 nm, possess high stability, large homogeneity and antibacterial activity. The strongest antibacterial potential was observed for AgNPs-RT and AgNPs-PGG nanocomplexes (with the MIC range 0.781–6.25 µg/ml and 0.390628–6.25 µg/ml calculated in relation to AgNPs) while the lowest for pure, non-modified by tannins, AgNPs (with the range 3.125–25 µg/ml). According to the obtained results, it can be concluded that silver-tannin nanoparticles have stronger antibacterial activity in comparison with pure AgNPs. That modification of AgNPs by tannins increases the antibacterial activity of silver nanoparticles.