Preparation of high antimicrobial activity thiourea chitosan–Ag+ complex

Thiourea chitosan was prepared by the reaction of chitosan with ammonium thiocyanate in ethanol. Thiourea chitosan was characterized by FT-IR, 13C NMR, and elemental analysis; XPS confirmed that in thiourea chitosan–Ag+ complex, S atoms coordinated to silver ions and were the major electron donors; O atoms also coordinated to silver ions and they were another electron donors next to S atoms. N atoms did not take part in coordination. Thiourea chitosan–Ag+ complex overcomes the instability of Ag+. Antimicrobial activities of the complex was evaluated against six species of bacteria and molds. The complex showed a wide spectrum of antimicrobial activities, whose MIC values against bacteria were 20 times lower than those of chitosan, 100 times lower than those of sodium diacetate and 200 times lower than those of sodium benzoate, respectively; the complex has a better antibacterial activity than antifungal activity.