Tunable Ag@SiO2 core-shell nanocomposites for broad spectrum antibacterial applications

Silica encapsulated silver nanoparticle core-shell nanocomposites of tunable dimensions were synthesised via a one-pot reverse microemulsion route to achieve controlled release of Ag+ ions for broad spectrum antibacterial application. Silver release rates and bactericidal efficacy against Gram-positive and Gram-negative bacteria, S. aureus and P. aeruginosa respectively, were inversely proportional to nanoparticle core diameter (3-8 nm) and silica shell (7-14 nm) thickness, and readily tuned through a facile hydrothermal etching protocol employing a PVP stabiliser to introduce mesoporosity

Convenient syntheses of cyanuric chloride-derived NHC ligands, their Ag(i) and Au(i) complexes and antimicrobial activity

Convenient syntheses of mono- and bis-imidazolium 1,3,5-triazine derivatives bearing piperidine and morpholine substituents are reported. In situ deprotonation of the mono-imidazolium salts and reaction with Ag2O or Au(tht)Cl (tht = tetrahydrothiophene) precursors affords the corresponding Ag(NHC) Cl and Au(NHC) Cl carbene complexes. In the presence of Ag(I) or Au(I) salts the bis-imidazolium pincers eliminate the imidazolium group to afford -OMe or -NMe2 substituted triazines depending on the solvent used. In solution, the Ag(I) and Au(I) complexes show a barrier to rotation about the C-triazine-N-amine bonds, with calculated Delta G(not equal) barriers in the region of 70 kJ mol(-1). Single crystal X-ray structures of several of the proligands and their corresponding Ag(I) and Au(I) complexes were obtained. These universally reveal an extended, rigidly planar pi-conjugated network between the triazine core, imidazolium/imidazolylidene substituents and exocyclic amine functions, to which the origin of the rotational barrier observed in solution is attributed. Only very weak N-triazine-metal interactions are observed in the solid state, as indicated by small deviations of the C-NHC-Ag-Cl bond angles from 180 degrees and also supported by DFT calculations on the Ag(NHC) Cl complex (NHC = 4,6-dipiperidinyl-2-methylimidazolylidene triazine). Preliminary antimicrobial susceptibility studies against five microorganisms (methicillin resistant Staphylococcus aureus NCTC 13277, S. aureus NCTC 6571, Pseudomonas aeruginosa NCTC 10662, Proteus mirabilis NCTC 11938 and Candida albicans ATCC 90028) show that the above triazine-based Ag-NHC complexes are active antimicrobial and antifungal agents