Chemotherapeutic metal-based compounds are effective anticancer agents; however, their cytotoxic profile and significant side effects limit their wide application. Natural products, especially flavonoids, are a prominent alternative source of anticancer agents that can be used as ligands for the generation of new bioactive complexes with metal ions of known biochemical and pharmacological activities. Herein, we present the synthesis and detailed structural and physicochemical characterizations of three novel complex assemblies of Ga(III) with the flavonoid chrysin and the ancillary aromatic chelators 1,10-phenanthroline, 2,2′-bipyridine and imidazole. The complexes constitute the only crystallographically characterized structures having a metal core from the boron group elements and a flavonoid as the ligand. The in vitro biological evaluation of the three complexes in a series of cancer cell lines of different origin established their cytotoxicity and ROS generating potential. In particular, the Ga(III)–chrysin–imidazole complex displayed the highest anticancer efficacy against all cancer cell lines with IC₅₀ values in the low micromolar range (<1.18 μM), a result worth further investigation.

Four Cu^I and three Ag^I mixed–ligand complexes containing a heterocyclic pyrimidine-type thione (pymtH = pyrimidine-2-thione or dmpymtH = 4,6-dimethyl-pyrimidine-2-thione) and triphenylphosphine (PPh₃) have been synthesized and structurally characterized. All copper and two of the silver compounds, namely [Cu(PPh₃)₂(pymtH)₂]BF₄ (1), [Cu(PPh₃)₃(pymtH)]BF₄ (2), [Cu(PPh₃)₂(dmpymtH)₂]BF₄ (3), [Cu(PPh₃)₃(dmpymtH)]BF₄ (4), [Ag(PPh₃)₃(pymtH)]NO₃ (5) and [Ag(PPh₃)₃(dmpymtH)]NO₃ (6), reveal a tetrahedral coordination environment while [Ag(PPh₃)₂(pymtH)]NO₃ (7) preferentially adopts a trigonal planar arrangement. The stoichiometry of the isolated silver complexes does not always follow the respective stoichiometries of the synthetic procedures. The photophysical properties of all the isolated products have been evaluated. In solution, phosphine derived emission is detected while in the solid state only [Cu(PPh₃)₃(dmpymtH)]BF₄ (4) emits from a state of different parentage. All of the complexes were also tested for in vitro antibacterial activity against four bacterial strains and for anti-inflammatory activity by measuring lipoxygenase inhibition activity.

Five palladium(II) complexes of substituted salicylaldehydes (X-saloH, X = 4-Et₂N (for 1), 3,5-diBr (for 2), 3,5-diCl (for 3), 5-F (for 4) or 4-OMe (for 5)) bearing the general formula [Pd(X-salo)₂] were synthesized and structurally characterized. The crystal structure of complex [Pd(4-Et₂N-salo)₂] was determined by single-crystal X-ray crystallography. The complexes can scavenge 1,1-diphenyl-picrylhydrazyl and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radicals and reduce H₂O₂. They are active against two Gram-positive (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative (Escherichia coli and Xanthomonas campestris) bacterial strains. The complexes interact strongly with calf-thymus DNA via intercalation, as deduced by diverse techniques and via the determination of their binding constants. Complexes interact reversibly with bovine and human serum albumin. Complementary insights into their possible mechanisms of bioactivity at the molecular level were provided by molecular docking calculations, exploring in silico their ability to bind to calf-thymus DNA, Escherichia coli and Staphylococcus aureus DNA-gyrase, 5-lipoxygenase, and membrane transport lipid protein 5-lipoxygenase-activating protein, contributing to the understanding of the role complexes 1–5 can play both as antioxidant and antibacterial agents. Furthermore, in silico predictive tools have been employed to study the chemical reactivity, molecular properties and drug-likeness of the complexes, and also the drug-induced changes of gene expression profile (as protein- and mRNA-based prediction results), the sites of metabolism, the substrate/metabolite specificity, the cytotoxicity for cancer and non-cancer cell lines, the acute rat toxicity, the rodent organ-specific carcinogenicity, the anti-target interaction profiles, the environmental ecotoxicity, and finally the activity spectra profile of the compounds.

Five neutral zinc(II) complexes of 3-bromo-5-chloro-salicylaldehyde (3-Br-5-Cl-saloH) were synthesized in the absence or presence of the nitrogen-donor co-ligands 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neoc), or 2,2′-bipyridylamine (bipyam) and were characterized by various techniques. The obtained complexes were [Zn(3-Br-5-Cl-salo)₂(H₂O)₂] (1), [Zn(3-Br-5-Cl-salo)₂(bipy)] (2), [Zn(3-Br-5-Cl-salo)₂(phen)] (3), [Zn(3-Br-5-Cl-salo)₂(neoc)] (4) and [Zn(3-Br-5-Cl-salo)₂(bipyam)] (5). The crystal structures of complexes 1 and 3 were determined by single-crystal X-ray crystallography. The interaction of the compounds with calf-thymus DNA takes place via intercalation. The compounds may moderately cleave pBR322 plasmid DNA at a concentration of 500 μM. The compounds may bind tightly and reversibly to serum albumins. The antioxidant activity of the compounds was examined towards 1,1-diphenyl-picrylhydrazyl and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radicals and H₂O₂. The antimicrobial potency of the compounds was investigated against Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633, Escherichia coli NCTC 29212 and Xanthomonas campestris ATCC 1395.