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).