Abstract
Nine new complexes with camphor imine or camphor sulfonimine ligands were synthesized and analytically and spectroscopically characterized, aiming to identify the key parameters that drive the antibacterial activity of the complexes with metal cores and imine substituents with distinct electronic and steric characteristics. The antimicrobial activity of all complexes was evaluated by determining their minimum inhibitory concentrations (MIC) against the Gram-negative Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, and Burkholderia contaminans IST408, and the Gram-positive Staphylococcus aureus Newman. Camphor imine complexes based on the hydroxyl silver center ({Ag(OH)}) typically perform better than those based on the nitrate silver center ({Ag(NO3)}), while ligands prone to establish hydrogen bonding facilitate interactions with the bacterial cell surface structures. A different trend is observed for the silver camphor sulfonimine complexes that are almost non-sensitive to the nature of the metal cores {Ag(OH)} or {Ag(NO3)} and display low sensitivity to the Y substituent. The antibacterial activities of the Ag(I) camphor sulfonimine complexes are higher than those of the camphor imine analogues. All the complexes display higher activity towards Gram-negative strains than towards the Gram-positive strain.
Highlights
New antimicrobials are urgently needed to overcome the increasing resistance of bacteria to existing antibiotics
The antibacterial activity of all complexes was evaluated against Gram-negative E. coli ATCC25922, P. aeruginosa 477, B. contaminans IST408, and Gram-positive S. aureus Newman through determination of the minimum inhibitory concentration (MIC)
The antibacterial activities of the Ag(I) camphor imine (Series a, b, and c) and camphor sulfonimine imine (Series d, e, and f) complexes were evaluated against E. coli, P. aeruginosa, B. contaminans, and S. aureus through determination of minimum inhibitory concentrations (MIC) values
Summary
New antimicrobials are urgently needed to overcome the increasing resistance of bacteria to existing antibiotics. Threats to human health include the emergence of multi-resistance among common microbial human pathogens, but of emerging new pathogens, as is the case of SARS-COV2. These health threats create a worldwide challenge and pressure to the discovery and development of new antimicrobials, a domain that has not been intensively pursued by the pharma industry in the last decades [3]. Over the two last decades, research focused on the search for potential antimicrobial properties of silver coordination compounds raised considerably. Several sets of camphor imine ([Ag(NO3)(XC10H14NY)] (X= O or N, Series a), [Ag(OC10H14NY)2((μ-O)] (Series b), [Ag(OH)(OC10H14NY)2] (Series c)), and camphor sulfonimine complexes ([Ag(NO3)(O2SNC10H14NY)2] (Series d), [Ag(OH)(O2 SNC10H14NY)2] (Series e), and [Ag(OH)(O2SNC10H14NY)] (Series f)) were synthesized, analytically and spectroscopically characterized, and their antibacterial activities determined, in order to get insights into the effect of structural changes at the camphor ligand or inner sphere on the antibacterial properties of the complexes
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