Anti-Mold Activities of Cationic Oligomeric Surfactants

Molds are persistent and harmful but receive far less research attention compared with pathogenic bacteria. With the increase in microbial resistance to single-chain surfactant antimicrobial agents, it is crucial to investigate how surfactant structures affect the antimicrobial activity of surfactants. Here, we have studied the antimold efficacy of a series of oligomeric cationic quaternary ammonium surfactants at varying oligomerization levels with or without dynamic covalent imine bonds. Four common molds are chosen as representatives: A. niger, T. viride, C. globosum, and P. funiculosum. The minimum fungicidal concentration (MFC) results indicate that the dynamic covalent surfactants in solution display stronger antimold activity than the surfactants of the same oligomerization degree without imine bonds, and the antimold activity decreases as the oligomerization degree increases. The superior fungicidal efficacy of imine-based surfactants in solution is attributed to their longer hydrophobic chains and benzene rings, which enhance the interactions with mold membranes, causing perforation and membrane disruption. Nonetheless, the higher oligomerization degree reduces antimold effectiveness due to the formation of overly stable aggregates, which lower the concentration of free molecular monomers released from aggregates and may accumulate on mold spore membranes. However, on fabric surfaces, the surfactants with a higher oligomerization degree show stronger antimold performance. The multiple hydrophobic chains and cationic headgroups result in greater surfactant adsorption and stronger antimildew activity. Moreover, the reversibility of the imine-based surfactants plays a significant role in reducing the likelihood of resistance. This work is helpful to construct antimicrobial agents with broad-spectrum activity and a weak resistance potential.