Abstract
Keratitis treatment has become more complicated due to the emergence of bacterial or fungal pathogens with enhanced antibiotic resistance. The pharmaceutical applications of N-heterocyclic carbene complexes have received remarkable attention due to their antimicrobial properties. In this paper, the new precursor, 3,3′-(p-phenylenedimethylene) bis{1-(2- methyl-allyl)imidazolium} bromide (1a) and its analogous PF6 salt (1b) were synthesized. Furthermore, silver(I) and gold(I) -N-heterocyclic carbene (NHC) complexes [Ag2LBr2/Au2LBr2; 2a/3a], [(Ag2L2)(PF6)2/(Au2L2)(PF6)2; 2b/3b] were developed from their corresponding ligands. All compounds were screened for their antimicrobial activities against multiple keratitis-associated human eye pathogens, including bacteria and fungi. Complexes 2a and 3a showed highest activity, and the effectiveness of 3a was also studied, focusing eradication of pathogen biofilm. Furthermore, the structures of 1a, 2a and 3b were determined using single crystal X-ray analysis, 2b and 3a were optimized theoretically. The mechanism of action of 3a was evaluated by scanning electron microscopy and docking experiments, suggesting that its target is the cell membrane. In summary, 3a may be helpful in developing antimicrobial therapies in patients suffering from keratitis-associated eye infections caused by multidrug-resistant pathogens.
Highlights
Keratitis is a common corneal infection in tropical areas of the world
Keratitis can develope from fungal (Candida, Aspergillus, Fusarium etc.) and bacterial (Staphylococcus aureus, Pseudomonas aeruginosa etc.) infections, especially those caused by the use of contact lenses or by eye injuries [1,2]
In the case of 2a, the carbenic signal appeared at 178.2 ppm in the 13CNMR spectra, and a downfield shift of 38.9 ppm in comparison to free imidazolium salt was observed after complexation
Summary
Keratitis is a common corneal infection in tropical areas of the world. This kind of infection is quite dangerous, and in many cases can lead to permanent blindness, specially if not diagnosed promptly and treated effectively. Hindi et al [6] summarized the antimicrobial activities of several NHCs showing clear benefits, but demonstrated the need for higher amounts in order to obtain effective pathogen control. NHCs are in a versatile ligand class which has the advantage of easy manipulation. They have the ability to bind to metals and can be readily functionalized [7]. An interesting aspect of silver (I)-NHC complexes is the aggregation of silver (I) centers by argentophilic attraction with Ag–Ag separations [10] shorter than the sum of their van der Waals radii
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