In vitro biological studies of heteroleptic Ag(I) and Cu(I) unsymmetrical N,N′-diarylformamidine dithiocarbamate phosphine complexes; the effect of the metal center

Abstract

A series of five dithiocarbamate and their respective Ag(I) and Cu(I) triphenylphosphine complexes of the general formula [Ag/Cu(PPh3)2L] were synthesized and characterized. The dithiocarbamate ligands were synthesized from formamidines with substituents in the 2 and/or 6 positions of the phenyl rings, intentionally keeping substituents on one ring different from those of the second phenyl ring while investigating the structure-activity relationship of Ag(I) and Cu(I) dithiocarbamate complexes. All Ag(I) and Cu(I) complexes with the general formula [Ag(PPh3)2L] (1–5) or [Cu(PPh3)2L] (6–10), displayed distorted tetrahedral geometry around the metal centers with coordination via two S atoms of the dithiocarbamate ligand and two P atoms from the PPh3 units. Complexes 1–5 showed better inhibition values against Gram-positive, Staphylococcus aureus (methicillin resistant) and Staphylococcus aureus than the standard used, ciprofloxacin. Complexes 1 and 2 generally had good activity against all bacterial strains but were not active against Salmonella typhimurium. All Cu(I) complexes were either of low activity or inactive against all bacterial strains tested. Complex 2 was found to be more active with IC50 values of 1.34 × 10−3 mM and 0.25 mM as agents for antioxidant activity against DPPH and NO free radical scavengers, respectively. The metal center played a vital role in their biological activity as the Ag(I) complexes displayed better antibacterial and antioxidant activity than Cu(I) complexes.