Dinuclear gallium(III) complex with 1,3-propanediamine-N, N'-diacetate

In this study, a tetradentate 1,3-propanediamine-N,N′-diacetate (1,3-pdda$^{2−}$) was utilized for the synthesis of a dinuclear gallium(III) complex, uns-cis-[Ga(1,3-pdda)(µ-OH)]$_2cdot$2H$_2$O (1). Complex 1 was characterized using IR and NMR ($^1$H and $^{13}$C) spectroscopy, and its crystal structure was determined by single-crystal X-ray diffraction analysis. Both Ga(III) ions in Complex 1 exhibit octahedral geometry, with each ion coordinated by two nitrogen and two oxygen atoms from the 1,3-pdda$^{2–}$ ligand, as well as two oxygen atoms from the bridging hydroxyl groups. IR and NMR ($^1$H and $^{13}$C) spectra were simulated using DFT methods, showing a high degree of correlation with experimental data. Hirshfeld surface analysis provided insights into intermolecular interactions, with H⋯O and H⋯H interactions contributing significantly to the crystal stability. The antimicrobial potential of Complex 1 was evaluated alongside previously synthesized gallium(III) complexes, Na[Ga(1,3-pdta)]·3H$_2$O (2) and Ba[Ga(1,3-pndta)]2·3H$_2$O (3), with 1,3-pdta$^{4−}$ (1,3-propanediamine-N,N,N′,N′-tetraacetate) and 1,3-pndta$^{4−}$ ((±)-1,3-pentanediamine-N,N,N′,N′-tetraacetate), respectively. Among all the tested microbial species, the gallium(III) complexes have shown selective activity against Pseudomonas aeruginosa PAO1 strain and were able to reduce pyocyanin production by 40–43% in the clinical isolate BK25H of this bacterium. Moreover, Complexes 1–3 can modulate the quinolone-mediated quorum sensing system in P. aeruginosa PAO1. Interaction studies with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) were conducted to evaluate the binding affinity and mode of interaction of Complex 1 with key biomolecules, aiming to assess its potential for transport via serum proteins and its safety profile in terms of DNA interactions. Spectrofluorimetric experiments and molecular docking revealed that Complex 1 binds strongly to the Site I on BSA, with weaker interactions at the Site II. While spectrofluorimetric studies showed that Complex 1 has a slight affinity for minor groove binding or intercalation to ct-DNA, docking studies suggested some minor groove binding, especially in larger DNA sequences, with enhanced stabilization in 10-bp-DNA through hydrogen and carbon bonds.