Synthesis and characterization of new palladium (II) and silver (I) thiosemicarbazone derived by acenaphthenequinone complexes and their antimicrobial activity

Abstract

The ability of substituted acenaphthenequinone-thiosemicarbazones to do complexation with Pd(II) and Ag(I) salts was investigated. The obtained Pd(II) 5a-f and Ag(I) 7a-f complexes showed that ligation was occurred during the reaction of two equivalents of the ligands with one equivalent of the metal salts. In case of Pd complexes 5a-f, two moles of HCl were eliminated during complexation process. Whereas direct ligation was occurred during complexation of one mole of AgNO3 and two moles of ligands to form the corresponding cationic-anionic salts 7a-f. IR, NMR, and UV–vis spectra were used to deduce the structure of the formed metal complexes. X-ray structure analysis proved the syn-form of bis(bidentate) structure of Pd complex 5e, as Pd showed a square planar coordination with two sulfur and two nitrogen atoms. The cationic-anionic nature of silver complexes was revealed by molar conductance. UV–visible spectra were also investigated by means of Time-Dependent Density-Functional Theory (TD-DFT) computations. The obtained metal complexes were also investigated asantibacterial and antifungal agents. Compounds 5f, 5e, 7d, and 7f were found to be the most active and effective against the four bacterial strains, with compound 7f having the most potent action. Compound 7f (R = 3-OMe-Ph) showed MIC values of 0.066, 0.018, 0.018, and 0.033 µg/mL against B. subtilis, S. aureus, E. coli, and K. pneumoniae, respectively. For compound 7d (R = Benzyl), the MIC values are found as 0.028, 0.057, 0.028, and 0.028 µg/mL against the same previous bacterial strains. Compounds 5d, 5e, 7c, and 7f demonstrated promising antifungal activity against C. albicans with MIC values of 0.029, 0.023, 0.018, and 0.027 µg/ml, respectively, when compared to the reference fluconazole, which had a MIC value of 0.020 µg/ml. Compound 7f revealed inhibitory activity of E. coli DNA gyrase (IC50 = 210 ± 15 nM, respectively) being 1.2-folds less potent than the reference novobiocin (IC50 = 170 ± 20 nM).