Silver nanoparticles doped with silver cations and stabilized with maleic acid copolymers: specific structure and antimicrobial properties

Abstract

Combined composites containing silver nanoparticles and silver cations were proposed. Water-soluble complexes of silver nanoparticles (AgNPs) stabilized by copolymers of maleic acid with ethylene or N-vinylpyrrolidone were doped with silver cations in a molar ratio of 0.3–1.0 relative to the maleic acid units. The specificity of the complexation of silver ions by a silver nanoparticle shell was revealed using instrumental methods of analysis – X-ray photoelectron spectroscopy and IR spectroscopy. It was found that at equimolar loads of the copolymer with silver cations, complexes with a cyclic structure are formed, in which Ag⁺ binds to both carboxyl groups of the maleic acid residue by a coordination-ionic bond. The study demonstrated that the obtained colloidal solutions of AgNPs and their composites with cationic silver were active against a wide range of planktonic forms of opportunistic microorganisms – Gram-positive and Gram-negative microorganisms, and yeast-like fungi. It was found that the silver cations introduced into the system reduce the charge of the polymer matrix and potentiate the activity of the preparation of AgNPs, acting as an “adjuvant”. The calculated values of the fractional inhibitory concentration indexes for all composites and all tested microorganisms were in the range of 0.5–1.0, which indicates an additive interaction of the antimicrobial components of the composites – silver nanoparticles and silver cations.