The bactericidal activity of positively charged chitosans and derivatives is normally related to their electrostatic interaction with the negatively charged bacteria membranes, but a direct proof of this correlation remains elusive. In this study, we determined the bactericidal activity for 5 quaternized chitosans (TMCs) and managed to isolate the parameter which is the most relevant for the activity. Several pieces of evidence, from different physicochemical characterizations, are presented to support this claim. In this way, we confirm that activity of TMCs with sulfate, acetate and halide counter-ions against <i>Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive)</i> bacteria correlates well with the availability of N-quaternized groups in the TMCs. N,N,N-trimethyl chitosan sulfate (TMCS) and N,N,N-trimethyl chitosan acetate (TMCAc) exhibited the highest activities as a possible consequence of the delocalized π system presence. This delocalized π system has the lowest unoccupied molecular orbital (LUMO) placed at the edges of the molecules thus making it possible for the ions to interact with methyl groups of quaternized amine, withdrawing electron density. Such interaction decreases the inductive effect of methyl groups on the positive nitrogen site in the quaternized amine, resulting in an effectively higher charge density on the N-quaternized sites. Among the TMCs with halide counter-ions, larger activity was observed for N,N,N-trimethyl chitosan chloride (TMCCl), whereas N,N,N-trimethyl chitosan iodide (TMCI) and N,N,N-trimethyl chitosan bromide (TMCBr) displayed lower and similar values to each other. This result is consistent with the shielding of N-quaternized groups inferred from chemical shifts for the halide counter-ions in the 1H-NMR spectra. Moreover, we demonstrate that TMCs with distinct bactericidal activities can also be classified according to their vibrational spectral features using principal component analysis (PCA). Generally, these physicochemical characterization approaches represent a predictive tool for the bactericidal activity of chitosans derivatives.

Availability of N-quaternized groups determines the bactericide activity of N,N,N-trimethyl chitosan salts

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.