Preparation of Polyethylene Composites Containing Silver(I) Acylpyrazolonato Additives and SAR Investigation of their Antibacterial Activity

Novel composite materials PEn(n= 1–9) have been prepared by an easily up-scalable embedding procedure of three different families of Ag(I) acylpyrazolonato complexes in polyethylene (PE) matrix. In details, PE1–PE3composites contain polynuclear [Ag(QR)]ncomplexes, PE4–PE6contain mononuclear [Ag(QR)(L)m] complexes and PE7–PE9are loaded with mononuclear [Ag(QR) (PPh3)2] complexes, respectively (where L = 1-methylimidazole or 2-ethylimidazole, m= 1 or 2, and HQR= 1-phenyl-3-methyl-4-RC(O)-5-pyrazolone, where in detail HQfb, R = −CF2CF2CF3; HQcy, R = −cyclo-C6H11; HQbe, R = −C(H)C(CH3)2). The PEncomposites, prepared by using a 1:1000 w/w silver additive/polyethylene ratio, have been characterized in bulk by IR spectroscopy and TGA analyses, which confirmed that the properties of polyethylene matrix are essentially unchanged. AFM, SEM, and EDX surface techniques show that silver additives form agglomerates with dimensions 10–100 μm on the polyethylene surface, with a slight increment of surface roughness of pristine plastic within 50 nm. However, the elastic properties of the composites are essentially the same of PE. The antibacterial activity of all composites has been tested against three bacterial strains (E. coli, P. aeruginosaand S. aureus) and results show that two classes of composites, PE1–PE3and PE4–PE6, display high and persistent bactericidal and bacteriostatic activity, comparable to PE embedded with AgNO3. By contrast, composites PE7–PE9exhibit a reduced antibacterial action. Contact and release tests in several conditions for specific migration of Ag+from plastics, indicate a very limited but time persistent release of silver ions from PE1–PE6composites, thus suggesting that they are potential antibacterial materials for future applications. Instead, PE7–PE9almost do not release silver, only trace levels of silver ions being detected, in accordance with their reduced antibacterial action. None of the composites is toxic against higher organisms, as confirmed by D. magnatest of ecotoxicity.