Modeling of structure-property relationships of polymerizable surfactants with antimicrobial activity

Polymerizable quaternary ammonium salts (PQASs) were synthesized in a previous work and some of them were used as surfactants in the antimicrobial coating of commercial membranes. Herein, the electrostatic charges, maximum length, and aspect ratio of these antibacterial surfactants were calculated with the aim of investigating the relationship between the properties, recognized to control the biocidal activity of these molecules, and the molecular structures. The effect of the water molecules was considered through a quantum and molecular mechanics approach. The correlation between the number of carbons in the main aliphatic chain of PQAS and the above properties was investigated, by finding that the net charge on the ammonium group does not increase as the number of carbons in the aliphatic chain increase. Thus, although this number influences the antibacterial activity of the surfactants, this influence is not correlated with an increase of the ammonium positive charge. Unlike the partial charges, a different trend was obtained for the surfactants' maximum length and aspect ratio in agreement with the experimental behavior. As this modeling does not use empirical or adjustable parameters, it can assist the synthetic plan of new structures for surface functionalization, in order to improve the biofouling resistance of the membranes.