This review aims to analyze the emerging number of studies on biological media that describe the unexpected effects of different natural bioactive antioxidants. Hormetic effects, with a biphasic response depending on the dose, or activities that are apparently non-dose-dependent, have been described for compounds such as resveratrol, curcumin, ferulic acid or linoleic acid, among others. The analysis of the reported studies confirms the incidence of these types of effects, which should be taken into account by researchers, discarding initial interpretations of imprecise methodologies or measurements. The incidence of these types of effects should enhance research into the different mechanisms of action, particularly those studied in the field of basic research, that will help us understand the causes of these unusual behaviors, depending on the dose, such as the inactivation of the signaling pathways of the immune defense system. Antioxidative and anti-inflammatory activities in biological media should be addressed in ways that go beyond a mere statistical approach. In this work, some of the research pathways that may explain the understanding of these activities are revised, paying special attention to the ability of the selected bioactive compounds (curcumin, resveratrol, ferulic acid and linoleic acid) to form metal complexes and the activity of these complexes in biological media.

2,5-furandicarboxaldehyde (DFF) is one of the most promising biomass-based building blocks for the synthesis of biobased polymers. DFF can be obtained from 5-hydroxymethylfurfural (HMF), a fructose derivate, and it is a key molecule in the sequence of reactions of furan chemistry to develop biobased plastics. In this frame, four manganese(III)–Schiff base complexes 1–4 have been obtained. The general formula for the complexes, MnLⁿ(OCN)(H₂O/CH₃OH)_m (Lⁿ being the Schiff base ligands L¹–L⁴, formed as the result of the condensation of different substituted hydroxybenzaldehydes with diverse diamines, and m = 1–3), has been confirmed by characterization through different analytical and spectroscopic techniques. X-ray crystallographic studies for 1 and 2 showed tetragonally distorted octahedral structures, where the Schiff base was placed in the equatorial coordination positions of the Mn(III) ion. Complexes 1 and 2 behaved as efficient catalysts in the oxidation of HMF to DFF in an electrolytic reaction at pH 8.5, with phosphate buffer at room temperature, with conversion rates of 70–80%. On the other hand, complexes 3 and 4, where the axial position was sterically less accessible, yielded only an 11% conversion of HMF to DFF. The results indicate that a correct selection of metal complexes allows the development of a new efficient way to obtain DFF.

In this work, we present the design and synthesis of the bisthiosemicarbazone ligand H₃L^Me by means of an iminic condensation reaction between 2-hydroxyisophthalaldehyde and 4-methyl-3-thiosemicarbazide. This ligand is bicompartmental, pentadentate [N₂S₂O] and potentially trianionic. The presence of a spacer constituted by a phenol group facilitates the coordination of transition metal ions, giving rise to a great variety of structures. To confirm the purity of the ligand, different characterization techniques were employed, including elemental analysis, mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance. The acquisition of suitable crystals of H₃L^Me allowed us to analyze its structure through X-ray diffraction studies.

Azine compounds have recently gained significant attention due to the interesting properties that they display, which could be relevant in fields such as Pharmacology and Material Sciences. These types of ligands stand out in Coordination Chemistry because of the facilities that they exhibit that make it easy to coordinate transition and post-transition metal ions. Furthermore, to the azine skeleton (C=N-N=C), the addition of other donor atoms such as sulfur, oxygen or phosphorus in the ligand increases the coordination possibilities. In this sense, we are interested in azine ligands as precursors of novel metallosupramolecular architectures. The research herein reported is focused on the synthesis and characterization of a potentially tetradentate [P₂O₂] organic phosphine-azine ligand (LP). The addition of the phosphine group to the azine skeleton allows for the stabilization of soft metal ions and the assembly of functional structures. The azine ligand LP⁸ has been prepared by a condensation reaction between two equivalents of (diphenylphosphino)benzaldehyde and one equivalent of azine monohydrate, and it was fully characterized by using several techniques such as elemental analysis, mass spectrometry, infrared spectroscopy, ¹H NMR spectroscopy and X-ray diffraction.

The increase in the investigation of different self-assembled architectures derived from thiosemicarbazone ligands can be attributed to the numerous functional metallosupramolecular architectures with practical applications that can be obtained. The potentially tetradentate organic bisthiosemicarbazone ligand H₂L possesses two flexible bidentate [NS] domains separated by a short and rigid spacer, which could stabilize several metal ions and thus different metallosupramolecular architectures. H₂L was prepared by the reaction between two equivalents of N-ethylhydrazinecarbothioamide and one equivalent of 1,1′,1″-(benzene-1,3,5-triyl)tris(ethan-1-one) and was fully studied using several techniques, including X-ray diffraction.

A potentially dianionic symmetric bisthiosemicarbazone ligand H₂L^Et has been prepared by a condensation reaction between two equivalents of 4-N-ethyl-3-thiosemicarbazide and one equivalent of 4,4′-methylenebis(acetophenone). The crystal structures obtained from solvents with different donor abilities were studied. The recrystallization of H₂L^Et from methanol and dimethylsulfoxide enables the isolation of single crystals suitable for the X-ray diffraction studies of [H₂L^Et] 1 and [H₂L^Et]·CH₃SOCH₃2, respectively. This study shows that the solvent does not affect the macrostructure but influences the microstructure of the ethyl-substituted bisthiosemicarbazone ligand H₂L^Et.