Novel Composite Plastics Containing Silver(I) Acylpyrazolonato Additives Display Potent Antimicrobial Activity by Contact

Abstract

New silver(I) acylpyrazolonato derivatives displaying a mononuclear, polynuclear, or ionic nature, as a function of the ancillary azole ligands used in the synthesis, have been fully characterized by thermal analysis, solution NMR spectroscopy, solid-state IR and NMR spectroscopies, and X-ray diffraction techniques. These derivatives have been embedded in polyethylene (PE) matrix, and the antimicrobial activity of the composite materials has been tested against three bacterial strains (E. coli, P. aeruginosa, and S. aureus): Most of the composites show antimicrobial action comparable to PE embedded with AgNO3 . Tests by contact and release tests for specific migration of silver from PE composites clearly indicate that, at least in the case of the PE, for composites containing polynuclear silver(I) additives, the antimicrobial action is exerted by contact, without release of silver ions. Moreover, PE composites can be re-used several times, displaying the same antimicrobial activity. Membrane permeabilization studies and induced reactive oxygen species (ROS) generation tests confirm the disorganization of bacterial cell membranes. The cytotoxic effect, evaluated in CD34(+) cells by MTT (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazoliumbromide) and CFU (colony forming units) assays, indicates that the PE composites do not induce cytotoxicity in human cells. Studies of ecotoxicity, based on the test of Daphnia magna, confirm tolerability of the PE composites by higher organisms and exclude the release of Ag(+) ions in sufficient amounts to affect water environment.

Preparation and Characterization of Silver(I) Ethylcellulose Thin Films as Potential Food Packaging Materials

“… Molecular structure of complexes 1 and 2 (a) and molecular dimers of complex 2 formed by N−H…O and C−H…F hydrogen bonds (b) reproduced from reported data …”

“…In particular, Ag nanoparticles (AgNPs) and Ag‐based molecular derivatives owing to their established antimicrobial potential against bacterial strains, results to be the most used agents to promote the formation of active food packaging materials Ag is a metal known for its broad‐spectrum antibiotic and antimicrobial activity against Gram‐positive and Gram‐negative bacteria, fungi, protozoa and certain viruses . As reported, the microbicide action seems to be directly related to the amount of highly reactive Ag(I) ions released, interacting with negatively charged proteins RNA and DNA . While the use of AgNPs as carrier for Ag(I) ions in their antibacterial activity, when added into polymers, seems to enhance their efficacy of the derived active packaging, unfortunately many issues persist in their use, since few information available regarding both their human metabolism and bioaccumulation in the environment are still available .…”

“…In the search of new Ag‐based additives, recently Ag(I) coordination complexes have attracted a great deal of attention for their important antibacterial action exhibited against numerous bacterial families . Novel composite antimicrobial polyethylene materials have been prepared by embedding as antimicrobial additives in a polyethylene matrix Ag(I) substituted acylpyrazolonate complexes .…”

“…In continuation with our previous studies, the goal of this work is to prepare and to investigate novel Ag active packaging materials, based on a natural derived polymer, EC, and selected antimicrobial Ag(I) acylpyrazolonato complexes. Indeed, these new class of Ag(I) complexes based on acylpyrazolone ligands are found to be highly toxic to microorganisms, being tested on different antibacterial families, but not against higher organisms, and benign in aqueous environments . The EC‐ n x ( n =complexes 1 and 2 , x=a–c, weight ratios n :EC) new materials herein reported are obtained through various preparation methods as transparent films.…”

Application of metal − organic frameworks

“…The silver additives form agglomerates with dimensions 10 − 100 µm on the polyethylene surface, without changing the elastic and thermal properties of the composites with respect to unloaded polyethylene. Finally, none of the composites is toxic against higher organisms …”