Synthesis, characterization and antimicrobial activity of novel Pd(II) complexes with athracenylbased Schiff bases

Four new Schiff bases, one well-known Schiff base, and five new Pd(II) complexes were synthesized, characterized, and evaluated in their antimicrobial activities. New ligands were synthesized in the reaction of 9-anthracenecarboxaldehyde and phenylenediamines (4-methyl-1,2-phenylenediamine, 4-chloro-1,2-phenylenediamine, 4,5-dimethyl-1,2-phenylenediamine, and methyl 3,4-diaminobenzoate). The chemical structures of all synthesized compounds were confirmed using standard NMR and IR spectroscopy, and MS spectrometry, as well as molar conductivity measurements, while their purity was evaluated by elemental analysis. The antimicrobial activities of these novel compounds were assessed in vitro against a representative panel of microbial strains. The test organisms included three Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, and Enterococcus faecalis), four Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis, and Enterobacter aerogenes), and a single yeast strain (Candida albicans ATCC 10231), selected to assess antifungal activity. The assay included two commercial antibiotics, streptomycin and chloramphenicol, as positive controls to ensure assay validity and enable comparative analysis of antimicrobial activity. The free ligands exhibited limited antimicrobial activity, while the metal complexes demonstrated significantly enhanced, broader-spectrum activity. Complex C2 (with N,N’-(4-methyl-1,2-phenylene)bis(1-(anthracen-9- yl)methanimine)) showed the best activity, surpassing the standard antibiotics streptomycin and chloramphenicol in several cases.