Antimicrobial Activity of ε‑Poly‑l‑lysine after Forming a Water-Insoluble Complex with an Anionic Surfactant

ε-Poly-l-lysine (ε-PL) is one of the few homopoly­(amino-acid)­s occurring in nature. ε-PL, which possesses multiple amino groups, is highly soluble in water, where it forms the antimicrobial polycationic chain (PL n+). Although the high water-solubility is advantageous for the use of ε-PL as a food preservative, it has limited the applicability of ε-PL as a biopolymer plastic. Here, we report on the preparation and availability of a water-insoluble complex formed with PL n+ and an anionic surfactant, bis­(2-ethylhexyl) sulfosuccinate (BEHS–, is also commercialized as AOT) anion. The PLn+/BEHS–-complex, which is soluble in organic solvents, was successfully used as a coating material for a cellulose acetate membrane to create a water-resistant antimicrobial membrane. In addition, the thermoplastic PLn+/BEHS–-complex was able to be uniformly mixed with polypropylene by heating, resulting in materials exhibiting antimicrobial activities.