UV-Curable Contact Active Benzophenone Terminated Quaternary Ammonium Antimicrobials for Applications in Polymer...

A series of UV active benzophenone ([C₆H₅COC₆H₄-O-(CH₂)_n-N⁺Me₂R][X^-]; 4, R = C₁₂H₂₅, n = 3, X^- = Br^-; 5a-c, R = C₁₈H₃₇, n = 3, X^- = Cl^-, Br^-, I^-; 6a-c, R = C₁₈H₃₇, n = 4, X^- = Cl^-, Br^-, I^-; 7a-c, R = C₁₈H₃₇, n = 6, X^- = Cl^-, Br^-, I^-) terminated C₁₂ and C₁₈ quaternary ammonium salts (QACs) were prepared by thermal or microwave-driven Menshutkin protocols of the appropriate benzophenone alkyl halide (1a-c, 2a-c, 3a-c) with the corresponding dodecyl- or octadecyl N,N-dimethylamine. All new compounds were characterized by NMR spectroscopy, HRMS spectrometry, and, in one instance (4), by single-crystal X-ray crystallography. Representative C₁₂ and C₁₈ benzophenone QACs were formulated into 1% (w/v) water or water/ethanol-based aerosol spray coatings and then UV-cured onto plastic substrates (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyether ether ketone) with exposure to low to moderate doses of UV (20-30 J cm^-2). Confirmation as to the presence of the coatings was detected by advancing water contact angle measurements, which revealed a more hydrophilic surface after coating. Further confirmation was gained by X-ray photoelectron spectroscopy analysis, time of flight secondary ion mass spectrometry, and bromophenol blue staining, all of which showed the presence of the attached quaternary ammonium molecule. Analysis of surfaces treated with the C₁₈ benzophenone 5b by atomic force microscopy and surface profilometry revealed a coating thickness of ∼350 nm. The treated samples along with controls were then evaluated for their antimicrobial efficacy against Gram-positive (Arthrobacter sp., Listeria monocytogenes) and Gram-negative (Pseudomonas aeruginosa) bacteria at a solid/air interface using the large drop inoculum protocol; this technique gave no evidence for cell adhesion after a 3 h time frame. These antimicrobial materials show promise for their use as coatings on plastic biomedical devices with the aim of preventing biofilm formation and preventing the spread of hospital acquired infections.