Biologically relevant silver(i)-n-heterocyclic carbene complexes: synthesis, structure, intramolecular interactions, and applications

Abstract

N-Heterocyclic carbenes (NHCs) complexed with silver represent new, broad-spectrum antimicrobial and anticancer agents, normally with low toxicity profiles, and they provide a range of versatile structures for targeted biological applications. Most of these complexes have shown higher cytotoxicity than cisplatin, a potent anticancer drug. This study reviews the design, synthesis, structural characterization, and biological applications of silver complexes derived from both functionalized and nonfunctionalized NHC ligands. Specifically, silver complexes of functionalized and nonfunctionalized imidazole- and benzimidazole-based NHC systems employed in antimicrobial and anticancer applications are reviewed. Advancements achieved in the use of silver(I)-NHC complexes of miscellaneous azolium ligands, such as 1,2,4-triazole and the heterocycle-fused imidazolium derivative xanthene are also reviewed. Encapsulation of a series of silver-NHC complexes in a polymer-based carrier material represents a promising method for the targeted delivery of silver ions to the infected sites. The advances achieved in this particular area are systematically reviewed in this paper. In general, these preliminary achievements reveal the potential of silver(I)-NHC complexes as efficient antimicrobial and anticancer candidates. NHC ligand design for the formation of mono- and binuclear AgI complexes is reviewed. Particular attention is paid to AgI-NHC complexes that exhibit different biological activities. The effects of different substituents on the structures of the complexes are investigated. AgI complexes with functionalized and nonfunctionalized NHCs are compared.