Eleven new complexes of general formula [Ag(NO3)(L-Y)2] corresponding to Ag(I) camphorimine complexes [Ag(NO3)(OC10H14NY)2] (Y=NMe2 (1); OH (2); C6H5 (3); 4-MeC6H4, (4); 3,5-(CH3)2C6H3 (5); 3-OHC6H4, (6); 3-ClC6H4 (7); 4-ClC6H4 (8); 4-FC6H4 (9); 4-CF3C6H4 (10)) and the camphor sulfonylimine complex [Ag(NO3)(O2SNC10H14NY)2] (Y=NH2) were synthesized/characterized and their structural properties and antibacterial activity studied to gain insights into the structure-antimicrobial activity relationships. Five of the complexes were selected as representative examples and structures were optimized by Density Functional Theory calculations. The results show that the imine substituents (Y) at the camphor ligands drive the structure of the complexes from distorted octahedral to trigonal prismatic or linear ionic while the effect of the sulfonylimine ring does not appreciably affects the geometry of the complex. The lipophilicity and polarity which are important parameters concerning the biological activity of the complexes are also high dependent of the characteristics of the camphor ligands. The redox properties of the complexes studied by cyclic voltammetry showed that their reduction potentials are essentially independent of their electronic and steric properties. The antibacterial activity of all the complexes, against Gram-positive (S. aureus Newman) and Gram-negative (Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, Burkholderia contaminans IST408) strains was evaluated through calculation of MIC values. Results show that complexes with camphor imine ligands (1-10) that combine high lipophilicity with low dipolar moment (3-5) exhibit enhanced antibacterial activity. The ability to establish hydrogen bonding emerged as an important contribution to the antibacterial activity of the camphor sulphonylimine complex 11 (Y=NH2).
Keywords: Antibacterials; Camphorimines; Gram-negative bacteria; Gram-positive bacteria; Silver complexes; Structure-activity relationships.
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