Bi- and trinuclear copper(I) compounds of 2,2,5,5-tetramethyl-imidazolidine-4-thione and 1,2-bis(diphenylphosphano)ethane: Synthesis, crystal structures, in vitro and in silico study of antibacterial activity and interaction with DNA and albumins

Abstract

Herein we report on the synthesis, molecular structures, DNA-binding properties and antibacterial activity of four new copper(I) mixed-ligand complexes obtained by reacting copper(I) halides or [Cu(CH3CN)4](BF4) with 1,2-bis(diphenylphosphano)ethane (dppe) and 2,2,5,5-tetramethylimidazolidine-4-thione (tmimdtH). Depending on the nature of the halide, the resulting compounds adopt two different structural motifs. Thus, using CuCl or CuBr, doubly dppe-bridged symmetrical dimmers of type [(κ-S-tmimdtH)XCu(μ-dppe)2CuX(κ-S-tmimdtH)] are formed, while in the case of CuI, a rare example of a trinuclear complex was isolated, in which the Cu atom of a CuI(tmimdtH) moiety is linked by two bridging dppe units with the two Cu atoms of a cluster-type Cu2I2(dppe) core. On the other hand, [Cu(CH3CN)4](BF4) reacts with the anion of tmimdtH in the presence of dppe to form a binuclear complex consisting of two (dppe)Cu(tmimdt) units linked together by the P atoms of a dppe bridging ligand. The complexes show significant in vitro antibacterial activity against certain bacterial strains. An intercalative mode is suggested as the most probable interaction fashion of the compounds with calf-thymus (CT) DNA, monitored directly via UV–vis spectroscopy, DNA-viscosity measurements and indirectly via their competition with ethidium bromide for DNA as studied by fluorescence emission spectroscopy. The binding of the complexes to human (HSA) and bovine serum albumin (BSA) is tight. In order to explain the described in vitro activity of the compounds, we adopted molecular docking studies on the crystal structure of HSA, BSA, CT DNA and DNA-gyrase.