A binuclear silver complex with l-buthionine sulfoximine: synthesis, spectroscopic characterization, DFT studies and antibacterial assays

Abstract

A binuclear silver(I) complex with the amino acid L-buthionine sulfoximine (BSO) of composition Ag₂C₈H₁₆N₂O₃S was synthesized and characterized by chemical and spectroscopic measurements, and DFT (density functional theory) studies. Solid-state ¹³C nuclear magnetic resonance (SSNMR) and infrared vibrational spectroscopy (IR) analyses indicate the coordination of the nitrogen and carboxylate groups of the amino acid moiety to one of the silver atoms, while coordination to the second silver atom occurs through the nitrogen of the sulfoximine group. ESI-QTOF-MS measurements show the maintenance of the binuclear structure in solution. DFT studies confirm the proposed structure as a minimum of the potential energy surface (PES) with calculations of the hessians showing no imaginary frequencies. Raman spectroscopic measurements of the [Ag₂(BSO)] complex led to the assignments of the Ag–N bonds. Biological assays of BSO and [Ag₂(BSO)] were performed by the well-diffusion method over Staphyloccocus aureus (Gram-positive), Escherichia coli and Pseudomonas aeruginosa (Gram-negative) bacterial strains. The ligand was inactive under the tested concentration (100 μg mL⁻¹). The [Ag₂(BSO)] complex was active against the Gram-negative and Gram-positive bacteria tested, with MIC values of 3.125 μg mL⁻¹.