Design, synthesis and biological activities of gold-conjugated piperazine-dithiocarbamates: Antimicrobial and tyrosinase inhibitory activities

In this study, a set of piperazine-derived dithiocarbamate ligands (1a-6a) and the corresponding gold nanoparticle (NP)–conjugated derivatives (AuLNPs) (1b-6b) were synthesized and characterized by 1H and 13C NMR, MALDI-TOF, FTIR. The bioactive potential of the synthesized products was also screened for antimicrobial, antioxidant and tyrosinase inhibition activities. The free ligands showed mild to moderate activity against three fungi and six bacteria strains, but association with gold led to marked improvements in the biological activities of some derivatives. The AuLNPs, especially, exhibited enhanced effectiveness against both Gram-positive as well as Candida species. Derivative 2b was the most effective compound in all compounds tested, showing the strongest tyrosinase inhibiting activity (IC₅₀ = 0.51 ± 0.01 mg/mL) and it was among the substances that yielded the best results in antioxidant tests (DPPH, ABTS, CUPRAC). The computational findings generally supported the experimental results, suggesting that smaller energy band gaps and moderate softness may contribute to the observed activity. These findings show that gold nanoparticle conjugation plays an important role in modulating the biological activity of the ligands.