Synthesis and Characterization of Camphorimine Au(I) Complexes with a Remarkably High Antibacterial Activity towards B. contaminans and P. aeruginosa.

Fourteen new camphorimine Au(I) complexes were synthesized and characterized by spectroscopic (NMR, FTIR) and elemental analysis. The structural arrangement of three selected examples were computed by Density Functional Theory (DFT) showing that the complexes essentially keep the {AuI-CN} unit. The Minimum Inhibition Concentrations (MIC) were assessed for all complexes showing that they are active towards the Gram-negative strains E. coli ATCC25922, P. aeruginosa 477, and B. contaminans IST408 and the Gram-positive strain S. aureus Newman. The complexes display very high activity towards P. aeruginosa 477 and B. contaminans IST408 with selectivity towards B. contaminans. An inverse correlation between the MIC values and the gold content was found for B. contaminans and P. aeruginosa. However, plots of MIC values and Au content for P. aeruginosa 477 and B. contaminans IST408 follow distinct trends. No clear relationship could be established between the MIC values and the redox potentials of the complexes measured by cyclic voltammetry. The MIC values are essentially independent of the redox potentials either cathodic or anodic. The complexes K3[{Au(CN)2}3(A4L)] (8, Y = m-OHC6H4) and K3[{Au(CN)2}3(B2L)]·3H2O (14, Z = p-C6H4) display the lower MIC values for the two strains. In normal fibroblast cells, the IC50 values for the complexes are ca. one order of magnitude lower than their MIC values, although higher than that of the precursor KAu(CN)2.