Synthesis of Ag and Cu-chitosan metal-polymer nanocomposites in supercritical carbon dioxide medium and study of their structure and antimicrobial activity

Abstract

This paper is dedicated to the design of efficient antimicrobial pharmaceuticals based on chitosan. Chitosan with a deacetylation degree of 0.98 preliminarily treated with supercritical carbon dioxide (scCO2) was impregnated with organometallic complexes (silver cyclooctadiene(hexafluoroacetylacetonate) and copper hexafluoroacetylacetonate) from an scCO2 solution followed by reduction with hydrogen to form metal-chitosan composites. Their structure was studied by small-angle X-ray scattering (SAXS). A narrow virtually monodisperse size distribution with a preferable particle size of 1–3 nm was found for silver and a wider polymodal size distribution with a particle size of up to 1–40 nm was revealed for copper. An X-ray fluorescent analysis showed the content of silver and copper metal to be 6 and 4.6%, respectively. The composites prepared by fluid technology were tested for antimicrobial activity toward bacteria S. epidermidis, E. coli, and a spore form of bacteria B. cereus in comparison with Cu2+-chitosan complexes obtained by the routine solution procedure. Ag0-chitosan nanocomposites were found to show bactericidal activity toward all the noted bacteria and spore forms, whereas Cu2+-chitosan complexes exhibit bacteriostatic activity toward the above bacteria and a lack of bactericidal properties toward the spore forms. The reasons for the bactericidal activity of the prepared composites are discussed.