Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study

Physical properties and cytotoxicity of Cu(II) and Zn(II) complexes with a TMS-substituted indolo[2,3-c]quinoline-derived Schiff base

The incorporation of non-native chemical elements, such as silicon, into drug molecules has gained significant attention as a strategy to broaden the chemical space in medicinal chemistry and develop novel drug candidates. Traditionally, research has focused on the isosteric replacement of a carbon atom with silicon ("silicon switch") in known drug structures or the attachment of a trimethylsilyl (TMS) group to biologically active scaffolds. In this study, a TMS-substituted indoloquinoline-based Schiff base (HLTMS) and its corresponding metal complexes, Cu(HLTMS)Cl2 (1) and Zn(HLTMS)Cl2 (2), were synthesized and comprehensively characterized using elemental analysis, spectroscopic techniques (IR, UV-vis, 1H and 13C NMR for HLTMS and 2), ESI mass spectrometry and single-crystal X-ray diffraction (SC-XRD) for 1 and electron diffraction (ED) for 2. The attachment of the TMS group enhanced the lipophilicity of HLTMS, while complex formation with Cu(II) substantially improved the antiproliferative activity. Exploitation of their intrinsic fluorescence to investigate cellular uptake and intracellular localization in cancer cells was impeded by limited solubility. Both HLTMS and 2 were found to generate reactive oxygen species under cell-free conditions in accord with their redox activity established by cyclic voltammetry. The photochemical activity of the indolo[2,3-c]quinoline-based proligand HLTMS and its complexes 1 and 2 has been disclosed. The compounds exhibited significant toxicity on various human cancer cells and disrupted the mitochondrial membrane potential, suggesting the contribution of mitochondrial dysfunction, triggered by HLTMS and its metal complexes, to their toxic effects. These findings highlight the potential of TMS-substituted Schiff bases as promising anticancer drug candidates.

Antioxidant effect, DNA-binding, and transport of the flavonoid acacetin influenced by the presence of redox-active Cu(II) ion: Spectroscopic and in silico study

Acacetin (AC) is a natural polyphenol from the group of flavonoids. It is well established that the behavior of flavonoids depends on the presence of redox-active substances; therefore, we aim to investigate their biological activity following the interaction with Cu(II) ion. Our study demonstrates that AC can effectively bind Cu(II) ions, as confirmed by UV-Vis and EPR spectroscopy as well as DFT calculations. AC appears as a potent scavenger against the model ABTS radical cation by itself, but this ability is significantly limited upon Cu(II) coordination. The possible mild synergistic effect of AC in the presence of vitamin C and glutathione was also shown by the ABTS•+ test. In contrast, an inhibitory effect was observed in the presence of Cu(II) ions. The equimolar addition of AC to the model Fenton-like system containing Cu(II) did not have a noticeable effect on the concentration of hydroxyl radicals produced, but in its excess the formation of •OH decreased, as proved by EPR spin trapping. Absorption titrations and gel electrophoresis revealed effective binding to calf thymus (CT)-DNA with a stronger interaction for the Cu(II)-AC complex. The detailed mode of binding to biomolecules was described using molecular docking and molecular dynamics. Obtained results indicate that the double helix of DNA unwinds after interaction with the Cu(II)-AC complex. Fluorescence spectroscopy, employing human serum albumin (HSA), suggested a potential transport capacity for both AC and its Cu(II) complex.

Albumin-based nanocarriers loaded with novel Zn(II)-thiosemicarbazone compounds chart a new path for precision breast cancer therapy

This study explores the therapeutic potential of albumin-bound Zn(II)-thiosemicarbazone compounds (Alb-ZnTcA, Alb-ZnTcB) against breast cancer cells. Previous research indicates that these compounds hinder cancer cell proliferation by blocking DNA synthesis, promoting oxidative stress to induce apoptosis, and disrupting the cell cycle to inhibit cellular division. This study focuses on the loading and characterization of these potentially chemically unstable compounds on bovine serum albumin-based nanocarriers. Accordingly, unlike previous studies using albumin nanoparticles, in this study, ultraviolet light was used to precisely bind the therapeutic agent to albumin during the integration of thiosemicarbazones, achieving controlled nanoparticle size to control nanoparticle size. The mean diameter of Alb-ZnTcA nanoparticles was 32 nm, while Alb-ZnTcB exhibited an average diameter of 43 nm. Notably, Alb-ZnTcA displayed the highest cytotoxicity toward breast cancer cells, suggesting an optimal size for cellular uptake. Additionally, albumin-bound compounds showed enhanced cytotoxicity at lower concentrations, potentially minimizing adverse side effects. Apoptosis analysis indicated that both Alb-ZnTcA and Alb-ZnTcB induce cell death predominantly through apoptosis, effectively preventing the uncontrolled proliferation of cancer cells. These findings demonstrate the potential of Zn(II)-thiosemicarbazone compounds loaded on albumin-based nanocarriers for breast cancer treatment. The increased potency of Alb-ZnTcA and Alb-ZnTcB compared to free compounds, along with their ability to activate apoptotic signaling pathways in MCF-7 breast cancer cells, highlights a promising approach for future cancer therapies. This study suggests that albumin-bound Zn(II)-thiosemicarbazone compounds could offer a targeted and effective strategy in breast cancer treatment, leveraging the advantages of nanocarrier-based delivery systems.

Apatite-Forming Ability and Visible Light-Enhanced Antibacterial Activity of CuO-Supported TiO2 Formed on Titanium by Chemical and Thermal Treatments

Titanium with apatite-forming ability as well as antibacterial activity is useful as a component of antibacterial dental implants. When Ti was subjected to hydrogen peroxide (H2O2), copper acetate (Cu(OAc)2), and heat (H2O2-Cu(OAc)2-heat) treatments, a network structure of anatase and rutile titanium dioxide (TiO2) and fine copper oxide (CuO) particles was formed on the Ti surface. The resulting samples accumulated a dense and uniform apatite layer on the surface when incubated in simulated body fluid and showed enhanced antibacterial activity against Escherichia coli and Staphylococcus aureus under visible-light irradiation. Electron spin resonance spectra of H2O2-Cu(OAc)2-heat-treated samples showed that hydroxyl radicals (·OH) were generated from the samples, and the concentration of ·OH increased with increasing Cu concentration of the Cu(OAc)2 solution. The enhanced antibacterial activity of these samples under visible-light irradiation may be attributable to the generation of ·OH from samples. These results suggest that Ti implants obtained using H2O2-Cu(OAc)2-heat treatments and subjected to regular or on-demand visible-light irradiation may provide a decreased risk of peri-implantitis.

Hydration and bactericidal activity of nanometer- and micrometer-sized particles of rock salt-type Mg1-xCuxO oxides

Copper substitution together with nano-structuring are applied with the aim to increase the bactericidal performances of the rocksalt-type MgO oxide. The partial substitution of magnesium ions with Cu²⁺ has been successfully achieved in both micrometer- and nanometer-sized particles of MgO up to 20 mol% in increments of 5 mol%. Microstructural analyses using the Integral Breadth method revealed that the thermal decomposition of the single source precursor Mg_1-xCu_x(OH)_2-2y(CO₃)_y.zH₂O at 400 °C creates numerous defects in 10-20 nm-sized particles of Mg_1-xCu_xO thus obtained. These defects make the surface of nanoparticles highly reactive towards the sorption of water molecules, to the extent that the cubic cell a parameter in as-prepared Mg_1-xCu_xO expands by +0.24% as soon as the nanoparticles are exposed to ambient air (60% RH). The hydration of Mg_1-xCu_xO particles in liquid water is based on a conventional dissolution-precipitation mechanism. Particles of a few microns in size dissolve all the more slowly the higher the copper content and only Mg(OH)₂ starts precipitating after 3 h. In contrast, the dissolution of all 10-20 nm-sized Mg_1-xCu_xO particles is complete over a 3 h period and water suspension only contains 4-12 nm-sized Mg_1-xCu_x(OH)₂ particles after 3 h. Thereby, the bactericidal activity reported for water suspension of Mg_1-xCu_xO nanoparticles depends on the speed at which these nanoparticles dissolve and Mg_1-xCu_x(OH)₂ nanoparticles precipitate in the first 3 h. Only 10 mol% of cupric ions in MgO nanoparticles are sufficient to kill both E. coli and S. aureus with a bactericidal kinetics faster and reductions in viability at 3 h (6.5 Log₁₀ and 2.7 Log₁₀, respectively) higher than the conventional antibacterial agent CuO (4.7 Log₁₀ and 2 Log₁₀ under the same conditions). EPR spin trapping study reveals that "hydroxylated" Mg_0.9Cu_0.1O as well as Mg_0.9Cu_0.1(OH)₂ nanoparticles produce more spin-adducts with highly toxic hydroxyl radicals than their copper-free counterparts. The rapid mass adsorption of Mg_0.9Cu_0.1(OH)₂ nanoparticles onto the cell envelopes following their precipitation together with their ability to produce Reactive Oxygen Species are responsible for the exceptionally high bactericidal activity measured in the course of the hydroxylation of Mg_0.9Cu_0.1O nanoparticles.

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways. Indeed, this matter has already been the focus of a number of published studies and reviews. The aim of the present study was to elucidate the antioxidant vs. prooxidant properties of flavonoids in the presence of the redox-active metal, copper (II) ion, by means of the Fenton reaction. The specific motivation of this work is that, since an increased level of Cu(II) ions is known to be associated with many disease states such as neurological conditions (Alzheimer’s disease) and cancer, any interaction between these ions and flavonoids might affect the outcome of therapeutic uses of the latter. The structure of the Cu-kaempferol complex in DMSO was investigated by means of low temperature EPR spectroscopy, which confirmed the existence of at least two distinct coordination environments around the copper (II) ion. UV vis-spectra of kaempferol and its Cu(II) complex in DMSO revealed an interaction between the 5-OH (A ring) group and the 4-CO (C ring) group of kaempferol with Cu(II) ions. An ABTS assay confirmed that kaempferol acted as an effective radical scavenger, and that this effect was further enhanced in the form of the Cu(II)-kaempferol complex. Quantitative EPR spin trapping experiments, using DMPO as the spin trap, confirmed suppression of the formation of a mixture of hydroxyl, superoxide, and methyl radicals, in a Fenton reaction system, upon coordination of kaempferol to the redox-active Cu(II) ions, by 80% with respect to the free Cu(II) ions. A viscometric study revealed a better DNA-intercalating ability of the Cu-kaempferol complex than for free kaempferol, essential for conferring anticancer activity of these substances. The results of the viscometric measurements were compared with those from a DNA damage study of Cu-kaempferol complexes in a Fenton reaction system, using gel electrophoresis. At low concentrations of kaempferol (Cu–kaempferol ratios of 1:1 and 1:2), a very weak protective effect on DNA was noted, whereas when kaempferol was present in excess, a significant DNA-protective effect was found. This can be explained if the weakly intercalated kaempferol molecules present at the surface of DNA provide protection against attack by ROS that originate from the Fenton reaction involving intercalated Cu(II)-kaempferol complexes. Following the application of ROS scavengers, L-histidine, DMSO, and SOD, gel electrophoresis confirmed the formation of singlet oxygen, hydroxyl radicals, and superoxide radical anions, respectively. We propose that the prooxidant properties of Cu-kaempferol complexes may provide anticancer activity of these substances. When present in excess, kaempferol displays antioxidant properties under Cu-Fenton conditions. This suggests that kaempferol might prove a suitable candidate for the prevention or treatment of oxidative stress related medical conditions that involve a disturbed metabolism of redox metals such as copper, for example, Menkes disease, and neurological disorders, including Alzheimer’s disease. For the potential use of kaempferol in clinical practice, it will be necessary to optimize the dose size and critical age of the patient so that this flavonoid may be beneficial as a preventive drug against cancer and neurological disorders.

Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes

Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.

Synthesis and spectral characterizations of water soluble Cu(ii) complexes containing N-heterocyclic chelates: cell-proliferation, antioxidant and nucleic acid/serum albumin interactions

Water soluble N-heterocyclic copper(ii) complexes were synthesized, characterized and studied their DNA/protein binding interactions, antioxidation and antiproliferative potentials. The complex 4 found to be better than other complexes.

Aspergillus flavus NRRL 3251 Growth, Oxidative Status, and Aflatoxins Production Ability In Vitro under Different Illumination Regimes

Aspergillus flavus is the most important mycotoxin-producing fungus involved in the global episodes of aflatoxin B₁ contamination of crops at both the pre-harvest and post-harvest stages. However, in order to effectively control aflatoxin contamination in crops using antiaflatoxigenic and/or antifungal compounds, some of which are photosensitive, a proper understanding of the photo-sensitive physiology of potential experimental strains need to be documented. The purpose of the study is therefore to evaluate the effect of visible (VIS) light illumination on growth and conidiation, aflatoxin production ability and modulation of A. flavus oxidative status during in vitro experiment. Aflatoxigenic A. flavus strain was inoculated in aflatoxin-inducing YES media and incubated under three different VIS illumination regimes during a 168 h growth period at 29 °C. VIS illumination reduced A. flavus mycelia biomass yield, both during growth on plates and in liquid media, promoted conidiation and increased the aflatoxin production. Furthermore, aflatoxin production increased with increased reactive oxidative species (ROS) levels at 96 h of growth, confirming illumination-driven oxidative stress modulation activity on A. flavus cells.