Silver(I) and Thioether-bis(pyrazolyl)methane Ligands: The Correlation between Ligand Functionalization and Coordination Polymer Architecture

This work examines the crystal structures of 15 Ag­(I) complexes with thioether functionalized bis­(pyrazolyl)­methane derivatives to rationalize the influence of the ligand on the formation of (a) coordination polymers (CPs), (b) oligonuclear (hexameric and dinuclear) complexes, and (c) mononuclear complexes. It was previously reported how this ligand class could generate microporous architectures with permanent porosity. Some ligand modifications could induce a cavity size modulation while preserving the same overall architecture. The bis­(pyrazolyl)­methane scaffold can be easily functionalized with various structural fragments; hence the structural outcomes were studied in this work using various ligand modifications and Ag­(I) salts. In particular, six new ligand classes were prepared with the following features: (1) The steric hindrance on the pyrazole rings L^3,3′Me, L^5,5′Me, L^5,3′Me, L^CF3, and L^Br was modified. (2) The steric hindrance was reduced on the peripheral thioether group: L^SMe. (3) Finally, the presence of fluorine and bromine atoms in L^CF3 and L^Br offered the possibility to expand the type of interaction with respect to the ligands based on hydrocarbon substituents (CH₃, phenyl, naphthyl). The effect of the anions was explored using different Ag­(I) precursors such as AgPF₆, AgBF₄, AgCF₃SO₃, or AgNO₃. A comparison of the crystal structures allowed for the tentative identification of the type of substituents able to induce the formation of CPs having permanent porosity to include a symmetric and moderate steric hindrance on the pyrazolyl moieties (four CH₃) and an aromatic and preorganized thioether moiety. An asymmetric steric hindrance on the pyrazole groups led to the formation of more varied structural types. Overall, the most frequently reported structural motifs are the porous hexameric systems and the molecular chains

Oxidative Stress Induced by Copper and Iron Complexes with 8‑Hydroxyquinoline Derivatives Causes Paraptotic Death of HeLa Cancer Cells

Here, we report the antiproliferative/cytotoxic properties of 8-hydroxyquinoline (8-HQ) derivatives on HeLa cells in the presence of transition metal ions (Cu²⁺, Fe³⁺, Co²⁺, Ni²⁺). Two series of ligands were tested, the arylvinylquinolinic <b>L1–L8</b> and the arylethylenequinolinic <b>L9</b>–<b>L16</b>, which can all interact with metal ions by virtue of the N,O donor set of 8-HQ; however, only <b>L9</b>–<b>L16</b> are flexible enough to bind the metal in a multidentate fashion, thus exploiting the additional donor functions. <b>L1</b>–<b>L16</b> were tested for their cytotoxicity on HeLa cancer cells, both in the absence and in the presence of copper. Among them, the symmetric <b>L14</b> exhibits the highest differential activity between the ligand alone (IC₅₀ = 23.7 μM) and its copper complex (IC₅₀ = 1.8 μM). This latter, besides causing a significant reduction of cell viability, is associated with a considerable accumulation of the metal inside the cells. Metal accumulation is also observed when the cells are incubated with <b>L14</b> complexed with other late transition metal ions (Fe³⁺, Co²⁺, Ni²⁺), although the biological response of HeLa cells is different. In fact, while Ni/<b>L14</b> and Co/<b>L14</b> exert a cytostatic effect, both Cu/<b>L14</b> and Fe/<b>L14</b> trigger a caspase-independent paraptotic process, which results from the induction of a severe oxidative stress and the unfolded protein response