The design, synthesis, and antibacterial activity of ferrocene-based long-chain quaternary ammonium salts

Abstract

The paper described the synthesis a series of novel long-chain quaternary ammonium salts based on ferrocene carboxylic acid. The structures of these salts were characterized through ¹H NMR, ¹³C NMR, HRMS (ESI), and UV–Vis. Their electrochemical behavior was evaluated through cyclic voltammetry, and the surface properties were assessed by measuring surface tension and conductivity. Additionally, the antimicrobial effects of the target molecules were tested against both Gram-positive bacteria (S. aureus) and Gram-negative bacteria (Escherichia coli). The activity results indicated that increasing the length of the alkyl chain in the compounds significantly decreased the critical micelle concentration and greatly enhanced the antimicrobial efficacy. Furthermore, the introduction of ferrocene improved the antibacterial activity of the compounds against S. aureus. Structurally, the Gemini-type compound FcCnNNCnFc, featuring a single-chain FcCnN linked by a hexyl group, exhibited a pronounced decrease in critical micelle concentration and a significant improvement in antimicrobial activity. These ferrocene-containing quaternary ammonium salt compounds proposed showed promising potential alternatives for antimicrobial agents or surfactants used in industrial applications.