Synthesis, Characterization And Antimicrobial Activities On Bacteria And Fungi Of Polymeric Quaternary Ammonium Salts

Polymeric quaternary ammonium salts have high antimicrobial abilities and some uniqueproperties compared with inorganic and natural antimicrobial agents, such as high chemicalstability, low residual toxicity, lasting anmicrobial effect. However, there are few researcheson the “structure–antimicrobial activity” relationships of the polymeric quaternary ammoniumsalts. From this perspective, this paper discusses the synthesis, characterization andantimicrobial activities against bacteria and phytopathogenic fungi of two new polymericquaternary ammonium salts with different structures and compositions. The main work andresults are described below.First, we synthesize a series of acrylamide quaternary ammonium salts monomers (QDmonomers), homopolymers (PQD polymers) and copolymers (PQDC copolymers) from thereaction of N-dimethylamine propyl methacrylamide (DMAPMA) with halogenated reagents(n-butyl bromide (BB),1-bromohexane (HEB) and benzyl chloride (BC)), then wecharacterize their antimicrobial activities against gram-positive bacteria (S. albus),gram-negative bacteria (E. coli) and phytopathogenic fungi (R. solani and FocR4). The resultsreveal that the antibacterial and antifungal activities of acrylamide quaternary ammoniumsalts polymers are far better than monomers and with a benzyl group linked to the nitrogenatom, acrylamide quaternary ammonium salts polymers have the best antimicrobial effect; thecopolymers obatained from acrylamide quaternary ammonium salts monomers and acrylatemonomers have better antimicrobial activities than acrylamide quaternary ammonium saltshomopolymers.On this basis, we design and synthesize a new polymeric quaternary ammonium salt(dimethylaminopropyl benzyl chloride grafted polydimethylsiloxane, short for polysiloxanequaternary ammonium salts, PDMS-g-BC) from a more hydrophobic polydimethylsiloxanebackbone to substitute polyacrylamide backbone. Compared with polyacrylamide quaternaryammonium salts (PQD homopolymers and PQDC copolymers)，the minimum inhibitoryconcentration (MIC) of PDMS-g-BC against E. Coli is lower, which means incorporating a more hydrophobic backbone in polymers can strengthen the antimicrobial activities ofpolymeric quaternary ammonium salts. The antibacterial and antifungal activities ofPDMS-g-BC are affected by molecular weight and cationic content: when the molecularweight is about2500g/mol and cationic content is about20%, PDMS-g-BC shows greatantimicrobial activities against E. coli and FocR4, which can be compared to commonly usedbroad-spectrum microbicide benzalkonium chloride (dodecyl dimethyl benzyl ammoniumchloride).