Water-Soluble Palladium Complexes with 1,10-Phenanthroline—Synthetic Aspects, Crystal Structure, DNA-Binding and In Vitro Antibacterial Evaluation

Obtaining water-soluble palladium complexes capable of interacting with DNA is an important synthetic task in medicinal chemistry. The interaction of [Pd(phen)(OAc)2] (phen = 1,10-phenanthroline) with pivalic acid (tBuCOOH) and trifluoromethanesulfonic acid (HOTf) leads to the formation of the molecular complex [Pd(phen)(OOCtBu)2] (1) and the ionic complex [Pd(phen)(H2O)2]Otf2 (2), respectively. Complex 1 is highly soluble in water and stable in solution for 48 h. When complex 2 is boiled in water, it undergoes hydrolysis to form the binuclear hydroxo-bridged complex [Pd2(phen)2(μ-OH)2]Otf2 (3). According to X-ray diffraction data, the crystal lattices of 1–3 are stabilized by numerous intermolecular hydrogen bonds and π-π stacking interactions. The interaction of 1 and 2 with DNA in vitro (in 0.005 M NaCl solution) was studied using UV spectroscopy, low-gradient viscometry, and DNA melting analysis. It was shown that both compounds interact with DNA, and the binding is accompanied by the intercalation of the phenanthroline ligand at low concentrations in the DNA solution. An increase in their concentration leads to an alternative binding mode—palladium–DNA interaction causes a decrease in the DNA molecular coil size due to electrostatic interaction and/or palladium coordination to DNA bases. The difference between the binding of compounds 1 and 2 to DNA is that 2 can coordinate to N-bases, unlike complex 1. The antibacterial properties of the complexes have been studied in vitro against E. coli, P. aeruginosa, and S. aureus.