Fig. 5
The presence of dendrimer seems to play a key-role producing higher antibacterial activity as compared to Cu0/NaMt and Ag0/NaMt. This can be due to a higher metal dispersion within the dendrimer entanglement bearing OH groups that act as chelating agents (Lewis base) through their oxygen atoms. This was well supported by a marked increase in the inhibition zone diameter (Table S1). These data also revealed that both Cu0 and Cu2+ are more effective than both silver forms. This can be explained by an easier release of copper (both zero and bivalent forms) in the liquid media due to lower BE shifts (as measured by XPS), as compared to silver. Also, copper is more reactive than silver, generating oxygen reactive species (ROS) as in Fenton-like and Haber-Weiss processes. Other possible contributions should be ascribed to lower amounts: (i) of inserted Ag0 atoms probably because of the lower reduction level of Ag+ cations and (ii) of dispersed Ag+ cation, chelated and stabilized by the polyol moiety. This was supported by SEM images (Fig. 1.a ) that show large amount of non-dispersed rod-like silver salt crystals indicating a rigorous concordance between the material characterization data and antibacterial activity. Highest antibacterial ability was observed against Gram-positive B. subtilis, as illustrated by the largest inhibition zone diameter of 2.73±0.17cm (Table S1).This can be due to the very structure of the Bacillus cell wall with peptidoglycan multilayers and an abundant amount of pores that confers them more sensitivity to reactive species as compared to Gram-negative E. coli (Fu et al., 2015).