Silver(I)−Imidazole Cyclophane gem-Diol Complexes Encapsulated by Electrospun Tecophilic Nanofibers:  Formation of Nanosilver Particles and Antimicrobial Activity

Silver(I)-imidazole cyclophane gem-diol complex, 3 Ag2C36 N10(O)4(2+)2(x)-, where x = OH- or CO3(2-), was synthesized and well characterized. The minimum inhibition concentration tests showed that the aqueous form of 3 is 2 times less effective as an antibiotic than 0.5% AgNO3, with about the same amount of silver. The antimicrobial activity of 3 was enhanced when encapsulated into Tecophilic polymer by electrospinning to obtain mats made of nano-fibers. The fiber mats released nanosilver particles, which in turn sustained the antimicrobial activity of the mats over a long period of time. The rate of bactericidal activity of 3 was greatly improved by encapsulation, and the amount of silver used was much reduced. The amount of silver contained in the fiber mat of 3, with 75% of 3 and 25% Tecophilic, was 8 times less than that in 0.5% AgNO3 and 5 times lower than that in silver sulfadiazine cream 1%. The fiber mat was found to kill S. aureus at the same rate as 0.5% AgNO3, with zero colonies on an agar plate, and about 6 times faster than silver sulfadiazine cream. The silver mats were found effective against E. coli, P. aeruginosa, S. aureus, C. albicans, A. niger, and S. cerevisiae. Transmission electron microscopy and scanning electron microscopy were used to characterize the fiber mats. The acute toxicity of the ligand (imidazolium cyclophane gem-diol dichloride) was assessed by intravenous administration to rats, with an LD 50 of 100 mg/kg of rat.