Ga(III) pyridinecarboxylate complexes: potential analogues of the second generation of therapeutic Ga(III) complexes?

A series of novel Ga(III)-pyridine carboxylates ([Ga(Pic)₃]·H₂O (GaPic; HPic = picolinic acid), H₃O[Ga(Dpic)₂]·H₂O (GaDpic; H₂Dpic = dipicolinic acid), [Ga(Chel)(H₂O)(OH)]₂·4H₂O (GaChel; H₂Chel = chelidamic acid) and [Ga(Cldpic)(H₂O)(OH)]₂ (GaCldpic; H₂Cldpic = 4-chlorodipicolinic acid)) have been synthesized by simple one-step procedure. Vibrational spectroscopy (mid-IR), elemental analysis, thermogravimetric analysis and X-ray diffraction confirmed complexes molecular structure, inter and intramolecular interactions and their influence to spectral and thermal properties. Moreover, complex species speciation was described in Ga(III)-HPic and Ga(III)-H₂Dpic systems by potentiometry and ¹H NMR spectroscopy and mononuclear complex species were determined; [Ga(Pic)₂]⁺ (logβ₀₂₁ = 16.23(6)), [Ga(Pic)₃] (logβ₀₃₁ = 20.86(2)), [Ga(Dpic)₂]^- (logβ₀₂₁ = 15.42(9)) and [Ga(Dpic)₂(OH)]^2- (logβ_-121 = 11.08(4)). To confirm the complexes stability in 1% DMSO (primary solvent for biological testing), timescale ¹H NMR spectra were measured (immediately after dissolution up to 96 h). Antimicrobial activity evaluated by IC₅₀ (0.05 mM) is significant for GaDpic and GaCldpic against difficult to treat and multi-resistant P. aeruginosa. On the other hand, the GaPic complex is most effective against Jurkat, MDA-MB-231 and A2058 cancer cell lines and significantly also decreases the HepG2 cancer cells viability at 75 and 100 μM concentrations in a relatively short time (up to 48 h). In addition, fluorescence measurements have been used to elucidate bovine serum albumin binding activity between ligands, Ga(III) complexes and bovine serum albumin.