Heterocyclic thioamide/phosphine mixed-ligand silver(I) complexes: Synthesis, molecular structures, DNA-binding properties and antibacterial activity

Abstract Five silver(I) mixed-ligand complexes containing a heterocyclic thioamide or thioamidate (mtdztH = 5-methyl-1,3,4-thiadiazole-2-thiol or atdztH = 5-amino-1,3,4-thiadiazole-2-thiol or mqzH = 2-mercapto-4(3H)-quinazolinone) and triphenylphosphine (PPh 3 ) have been synthesized and structurally characterized. Four of these compounds, namely [AgCl(PPh 3 ) 2 (mtdztH)] ( 1 ), [AgCl(PPh 3 ) 2 (mqzH)] ( 2 ), [Ag(PPh 3 ) 3 (mtdzt)] ( 3 ) and [Ag(PPh 3 ) 3 (atdzt)] ( 4 ) reveal a distorted tetrahedral coordination environment, while [Ag(PPh 3 ) 2 (atdzt)] ( 5 ) adopts a trigonal planar arrangement. The interaction of the compounds with calf-thymus DNA was monitored via UV–Vis spectroscopy, DNA-viscosity measurements and their competition with ethidium bromide for the DNA-intercalation sites studied by fluorescence emission spectroscopy. The affinity of all the silver(I) complexes for the interaction with CT DNA is high and takes place via an intercalative mode. The new complexes show in vitro antibacterial activity against certain Gram-positive ( Bacillus subtilis, Bacillus cereus, Staphylococcus aureus ) bacterial strains, but are inactive against the Gram-negative Escherichia coli . Interestingly, higher activity was detected for the trigonal planar compound compared to its tetrahedrally coordinated counterparts.