Low Molecular Weight Shuttle Molecules Enhance Polychloramide Antimicrobial Activity.

Area of Science:

• Polymer Chemistry
• Antimicrobial Agents
• Biocidal Activity

Background:

• Water-soluble polymers with antimicrobial properties are of interest for disinfection applications.
• Chlorination of polymers can impart biocidal activity, but efficacy can be influenced by formulation.
• The role of small molecules in modulating the activity of immobilized antimicrobials requires investigation.

Purpose of the Study:

• To investigate the influence of succinimide (SI), 5,5-dimethylhydantoin (DMH), and 3-(hydroxymethyl)-5,5-dimethylhydantoin (HDMH) on the biocidal activity of chlorinated polyamides.
• To understand the mechanism by which these small molecules affect antimicrobial efficacy.
• To assess the potential for these molecules to exaggerate antimicrobial testing results.

Main Methods:

• Synthesis of a chlorinated, water-soluble polyamide.
• Treatment of the polymer with NaOCl to achieve chlorination.
• Testing the biocidal activity of the chlorinated polymer against *Escherichia coli* and *Staphylococcus aureus* in the presence and absence of SI, DMH, and HDMH.
• Solution studies to investigate chlorine transfer from the polymer to small molecules.

Main Results:

• Succinimide (SI), 5,5-dimethylhydantoin (DMH), and 3-(hydroxymethyl)-5,5-dimethylhydantoin (HDMH) significantly increased the biocidal activity of chlorinated polyamides.
• Chlorinated polyamides showed increased activity against planktonic *Escherichia coli* and *Staphylococcus aureus* when these compounds were present.
• Oxidative chlorine was observed to transfer spontaneously from aqueous polychloramides to small molecules, with succinimide being the most effective shuttle.

Conclusions:

• SI, DMH, and HDMH act as shuttles, extracting oxidative chlorine from polymer chloramides and delivering it more efficiently to microbial surfaces.
• Succinimide demonstrated the highest efficacy as a chlorine shuttle among the tested compounds.
• The presence of low molecular weight soluble molecules in antimicrobial testing solutions can lead to an overestimation of the effectiveness of polymer-based or immobilized antimicrobial agents.