Leishmaniasis is a group of parasitic diseases with the potential to infect more than 1 billion people; however, its treatment is still old and inadequate. In order to contribute to changing this view, this work consisted of the development of complexes derived from M^I metal ions with thioureas, aiming to obtain potential leishmanicidal agents. The thiourea ligands (HL^R) were obtained by reactions of p-toluenesulfohydrazide with R-isothiocyanates and were used in complexation reactions with Ag^I and Au^I, leading to the formation of complexes of composition [M(HL^R)₂]X (M = Ag or Au; X = NO₃⁻ or Cl⁻). All compounds were characterized by FTIR, ¹H NMR, UV-vis, emission spectroscopy and elemental analysis. Some representatives were additionally studied by ESI-MS and single-crystal XRD. Their properties were further analyzed by DFT calculations. Their cytotoxicity on Vero cells and the extracellular leishmanicidal activity on Leishmania infantum and Leishmania braziliensis cells were evaluated. Additionally, the interaction of the complexes with the Old Yellow enzyme of the L. braziliensis (LbOYE) was examined. The biological tests showed that some compounds present remarkable leishmanicidal activity, even higher than that of the standard drug Glucantime, with different selectivity for the two species of Leishmania. Finally, the interaction studies with LbOYE revealed that this enzyme could be one of their biological targets.

The binuclear oxidovanadium(V) complex [{VO(L)}2(μ-O)(μ-H2O)]∙2CH3CN (1), where L2– is the dianion of the Schiff base 2-salicylaldehyde-2-hydroxybenzoylhydrazone, were prepared and characterized by elemental analysis, FTIR, 1H, 13C and 51V NMR. Furthermore, the crystal structure of the compound 1 was determined by single crystal X-ray diffractometry revealing a distorted octahedral O5N-coordination geometry around the V(V) acceptor centers. The vanadium ions are connected by the μ-O2– and the μ-H2O asymmetric bridges located in the edge between the two octahedrons which keeps a distance of 3.194 Å between the two vanadium centers. Crystal data for C32H28N6O10V2 (M =758.48 g/mol): orthorhombic, space group P212121 (no. 19), a = 12.9655(8) Å, b = 14.1902(9) Å, c = 18.4379(10) Å, V = 3392.3(4) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.616 mm-1, Dcalc = 1.485 g/cm3, 18803 reflections measured (3.622° ≤ 2Θ ≤ 56.704°), 8263 unique (Rint = 0.0473, Rsigma = 0.1020) which were used in all calculations. The final R1 was 0.0509 (I > 2σ(I)) and wR2 was 0.1531 (all data). The (VO)2(μ-O)(μ-H2O) core in compound 1 represents a rare case and few examples of similar type have been structurally characterized.

The constant evolution of bacteria makes the search for new and effective bactericidal agents essential. In this context, developing antibacterial compounds with luminescent properties offers a promising strategy to investigate intracellular biochemical processes while simultaneously assessing the drug's effects. In the present work, coordination polymers of composition [{M(L1)2}{M(L1)(H2O)2}]n (M = Sm3+, Gd3+, and Yb3+) were obtained from reactions of their respective lanthanide salts with 1.5 equivalent of the ligand 1,2-diphenylethane-1,2-diylidene)diisonicotinohydrazide (H2L1). The techniques used for characterization of the compounds included FTIR, UV-visible spectroscopy, high-resolution mass spectrometry and single-crystal X-ray diffraction. In addition, emission spectra were obtained at room temperature and at 77 K, along with emission spectra in the presence of oxygen or argon. The antibacterial activity of the compounds was evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and their clinical resistant strains - MRSA (methicillin-resistant Staphylococcus aureus). It was observed that, upon complexation, there was a general increase in the activity, particularly with a more pronounced percentage of inhibition against bacterial biofilms. Additionally, the complex [{Yb(L1)2}{Yb(L1)(H2O)2}]n was used for functionalization of Bi2O3/Bi2S3 nanoparticles, however, a fluorescence suppression was observed for the Yb-containing nanoparticles. Finally, cellular internalization studies demonstrated that the Ln³⁺ polymers alone could be detected inside Vero cells through their luminescence properties. Altogether, these lanthanide complexes present potential for dual-modality biological performance, combining significant antibacterial activity with the ability for intracellular detection.