Denise de Oliveira Silva

Unusual Structural Features in the Lysozyme Derivative of the Tetrakis(acetato)chloridodiruthenium(II,III) Complex

The reaction between the paddle-wheel tetrakis(acetato)chloridodiruthenium(II,III) complex, [Ru2(μ-O2CCH3)4Cl] and hen egg-white lysozyme (HEWL) was investigated through ESI-MS and UV/Vis spectroscopy and the formation of a stable metal-protein adduct was unambiguously demonstrated. Remarkably, the diruthenium core is conserved in the adduct while two of the four acetate ligands are released. The crystal structure of this diruthenium-protein derivative was subsequently solved through X-ray diffraction analysis to 2.1 Å resolution. The structural data are in agreement with the solution results. It was found that HEWL binds two diruthenium moieties, at Asp101 and Asp119, respectively, with the concomitant release of two acetate ligands from each diruthenium center.

Inhibition of C6 rat glioma proliferation by [Ru2Cl(Ibp)4] depends on changes in p21, p27, Bax/Bcl2 ratio and mitochondrial membrane potential

The ruthenium compound [Ru(2)Cl(Ibp)(4)] (or RuIbp) has been reported to cause significantly greater inhibition of C6 glioma cell proliferation than the parent HIbp. The present study determined the effects of 0-72h exposure to RuIbp upon C6 cell cycle distribution, mitochondrial membrane potential, reactive species generation and mRNA and protein expression of E2F1, cyclin D1, c-myc, pRb, p21, p27, p53, Ku70, Ku80, Bax, Bcl2, cyclooxygenase 1 and 2 (COX1 and COX2). The most significant changes in mRNA and protein expression were seen for the cyclin-dependent kinase inhibitors p21 and p27 which were both increased (p<0.05). The marked decrease in mitochondrial membrane potential (p<0.01) and modest increase in apoptosis was accompanied by a decrease in anti-apoptotic Bcl2 expression and an increase in pro-apoptotic Bax expression (p<0.05). Interestingly, COX1 expression was increased in response to a significant loss of prostaglandin E(2) production (p<0.001), most likely due to the intracellular action of Ibp. Future studies will investigate the efficacy of this novel ruthenium-ibuprofen complex in human glioma cell lines in vitro and both rat and human glioma cells growing under orthotopic conditions in vivo.

The novel ruthenium-gamma-linolenic complex [Ru(2)(aGLA)(4)Cl] inhibits C6 rat glioma cell proliferation and induces changes in mitochondrial membrane potential, increased reactive oxygen species generation and apoptosis in vitro.

The present study reports the synthesis of a novel compound with the formula [Ru2(aGLA)4Cl] according to elemental analyses data, referred to as Ru2GLA. The electronic spectra of Ru2GLA is typical of a mixed valent diruthenium(II,III) carboxylate. Ru2GLA was synthesized with the aim of combining and possibly improving the anti‐tumour properties of the two active components ruthenium and γ‐linolenic acid (GLA). The properties of Ru2GLA were tested in C6 rat glioma cells by analysing cell number, viability, lipid droplet formation, apoptosis, cell cycle distribution, mitochondrial membrane potential and reactive oxygen species. Ru2GLA inhibited cell proliferation in a time and concentration dependent manner. Nile Red staining suggested that Ru2GLA enters the cells and ICP‐AES elemental analysis found an increase in ruthenium from <0.02 to 425 mg/Kg in treated cells. The sub‐G1 apoptotic cell population was increased by Ru2GLA (22 ± 5.2%) when analysed by FACS and this was confirmed by Hoechst staining of nuclei. Mitochondrial membrane potential was decreased in the presence of Ru2GLA (44 ± 2.3%). In contrast, the cells which maintained a high mitochondrial membrane potential had an increase (18 ± 1.5%) in reactive oxygen species generation. Both decreased mitochondrial membrane potential and increased reactive oxygen species generation may be involved in triggering apoptosis in Ru2GLA exposed cells. The EC50 for Ru2GLA decreased with increasing time of exposure from 285 µM at 24 h, 211 µM at 48 h to 81 µM at 72 h. In conclusion, Ru2GLA is a novel drug with antiproliferative properties in C6 glioma cells and is a potential candidate for novel therapies in gliomas. Copyright

Preparação de compostos de alumínio a partir da bauxita: considerações sobre alguns aspectos envolvidos em um experimento didático

Aluminum metal and aluminum compounds have many applications in several branches of the industry and in our daily lives. The most important raw material for aluminum and its manufactured compounds is bauxite, a rock constituted mainly by aluminum hydroxides minerals. In this work, a didactic experiment aiming the preparation of alumina and potassium alum starting from bauxite is proposed for undergraduate students. Both compounds are of great commercial, scientific and historical interest. The experiment involves applications of important chemical principles such as acid-base and precipitation. Some chemical properties and uses of aluminum compounds are also illustrated.

Thermodynamics of Axial Substitution and Kinetics of Reactions with Amino Acids for the Paddlewheel Complex Tetrakis(acetato)chloridodiruthenium(II,III)

The known paddlewheel, tetrakis(acetato)chloridodiruthenium(II,III), offers a versatile synthetic route to a novel class of antitumor diruthenium(II,III) metallo drugs, where the equatorial ligands are nonsteroidal anti-inflammatory carboxylates. This complex was studied here as a soluble starting prototype model for antitumor analogues to elucidate the reactivity of the [Ru(2)(CH(3)COO)(4)](+) framework. Thermodynamic studies on equilibration reactions for axial substitution of water by chloride and kinetic studies on reactions of the diaqua complexes with the amino acids glycine, cysteine, histidine, and tryptophan were performed. The standard thermodynamic reaction parameters ΔH°, ΔS°, and ΔV° were determined and showed that both of the sequential axial substitution reactions are enthalpy driven. Kinetic rate laws and rate constants were determined for the axial substitution reactions of coordinated water by the amino acids that gave the corresponding aqua(amino acid)-Ru(2) substituted species. The results revealed that the [Ru(2)(CH(3)COO)(4)](+) paddlewheel framework remained stable during the axial ligand substitution reactions and was also mostly preserved in the presence of the amino acids.

Kinetic and mechanistic studies on reactions of diruthenium(II,III) with biologically relevant reducing agents

Diruthenium(ii,iii)-tetracarboxylates have shown promising anticancer properties as metallotherapeutics. On the basis of the role that bio-reducing agents may play on the mode of action of ruthenium-based anticancer drugs, we performed detailed kinetic studies on the reaction of ascorbic acid and glutathione with the [Ru2(RCOO)4](+) paddlewheel framework by using the non-drug, diaqua complex ion [Ru2(CH3COO)4(H2O)2](+). In the presence of the reducing agents, the diaqua-Ru2 species first undergo a ligand substitution reaction by which the axially-coordinated water is displaced by the reducing agent. In both cases, this reaction is followed by an intra-molecular electron transfer process during which the metal-metal center is reduced from Ru2(5+) to Ru2(4+) and the reducing agent is oxidized. Product analyses were performed with the application of ESI-MS and (1)H-NMR techniques. Rate and activation parameters are reported for the different reaction steps.

Axially-modified paddlewheel diruthenium(II,III)-ibuprofenato metallodrugs and the influence of the structural modification on U87MG and A172 human glioma cell proliferation, apoptosis, mitosis and migration

The metallodrug chloridotetrakis(ibuprofenato)diruthenium(II,III) ([Ru2(Ibp)4Cl] or RuIbpCl (1), Ibp=carboxylate anion derived from the non-steroidal anti-inflammatory drug ibuprofen) has shown promising results in vitro and in vivo, which point to its potential as an inhibitor of glioma tumour growth in vivo. In order to get insight into the influence of structural changes on the biological response of the metallodrug, the [Ru2(Ibp)4] metal-metal multiply bonded paddlewheel unit was modified for the axial ligand. Two new analogues, [Ru2(Ibp)4(CF3SO3)] (2) and [Ru2(Ibp)4(EtOH)2]PF6 (3), were synthesized and fully characterized by elemental analysis, ESI-MS, vibrational (FTIR, Raman) and electronic (UV/VIS/NIR) spectroscopy, magnetic susceptibility, molar conductivity measurements, and thermal analysis. RuIbpCl was re-prepared and complementary characterization to previous work was performed. The three axially-modified RuIbp metallodrugs were compared for their effects on U87MG and A172 human glioma cell proliferation, apoptosis, mitosis, and cell migration in vitro. The results provide evidence that the chloride ligand in RuIbpCl may play key role in the mode of action of the metallodrug, since the best results for antiproliferative activity were found for (1) in both types of human glioma cells. All the metallodrugs, (1), (2) and (3), were uptaken by the cells, and were shown to cause increase on number of apoptotic cells and decrease on number of mitotic cells. Additionally, the RuIbp metallodrugs were capable of inhibiting cell migration process in both human glioma cell lines. These data are extremely promising as drugs which can inhibit both cell proliferation/mitosis and inhibit cell migration could target two major chemotherapeutic targets in high grade gliomas.

Spectroscopic studies on interactions of the tetrakis(acetato)chloridodiruthenium(II,III) complex and the Ru2(II,III)-NSAID-derived metallodrugs of ibuprofen and ketoprofen with human serum albumin

Diruthenium paddlewheel-structured complexes bearing a Ru2(II,III) multiply bonded core show promising potential in medicinal chemistry. This work reports studies on the interactions of the tetrakis(acetato)chloridodiruthenium(II,III) complex (RuAc), [Ru2(μ-O2CCH3)4Cl], and the corresponding Ru2(II,III)-non-steroidal anti-inflammatory drug (NSAID) metallodrugs of the NSAIDs ibuprofen (RuIbp) and ketoprofen (RuKet) with the human serum albumin (HSA). Circular dichroism (CD) studies showed that the three Ru2 complexes interact with the HSA and induce conformational changes on the secondary structure of the protein. The reaction of the RuAc complex with the protein was monitored and the RuAc/HSA binding constant was estimated on the basis of electronic absorption spectroscopy data. Fluorescence emission spectroscopy studies were performed for all the Ru2 complex/HSA systems and the Stern–Volmer constants and the thermodynamic parameters were determined for the RuAc/HSA binding. Mass spectrometry data confirmed the presence of the Ru2 complexes in the protein phase after ultrafiltration. The studies suggest that the nature of the RuAc binding to the HSA is distinct from that of the derived RuIbp and RuKet metallodrugs. Electrostatic forces, accompanied by coordination of the metal to the amino acid side chains of the protein, seem to be the main forces acting in the RuAc/HSA binding, while non-covalent/hydrophobic forces might be predominant in the Ru2-NSAID metallodrug/protein interactions. The findings suggest that the HSA protein might be a potential carrier in the blood plasma for the Ru2(II,III)-NSAID metallodrugs. Graphical abstract

Interaction of chitosan beads with a copper–naproxen metallodrug

This manuscript reports a novel hybrid system containing a copper-drug entrapped into the chitosan biopolymer. Chitosan beads (CTb) were prepared and investigated for interaction with a copper metallodrug (CuNpx) of the naproxen (HNpx) non-steroidal anti-inflammatory drug. The loading capacity of CTb for CuNpx suggests a sponge-like behavior for copper-drug entrapping at a CuNpx concentration range from 10−4 to 10−2 mol L−1. A novel CTb/CuNpx hybrid material formed by the copper-drug loaded into chitosan beads was prepared and characterized by elemental analysis, scanning electron microscopy, electronic absorption spectroscopy, FTIR spectroscopy, X-ray diffractometry and thermal analysis. The CTb/CuNpx hybrid material was coated with Acrycoat S100, and its behavior in gastric/intestinal pH simulated solutions was investigated to verify potential releasing properties. The coated beads showed a capacity to release naproxen in a sustained release manner for at least 24 h.

Structure, spectroscopy and electrochemistry of the bis(2,2′-bipyridine)(salicylato)ruthenium(II) complex

The bis(2,2′-bipyridine)(salicylato)ruthenium(II) complex has been prepared and characterized by means of single crystal X-ray diffraction, electrochemistry and resonance Raman spectroscopy. The electronic bands in the visible region have been assigned to Ru–bipy charge-transfer transitions and discussed in terms of ZINDO/S semiempirical calculations. Spectroelectrochemical measurements have been performed in order to elucidate the nature of the electrochemical waves in the cyclic voltammograms. The green complex generated by oxidation of the complex at 0.25 V has been isolated, revealing substantial ruthenium–salicylate electronic mixing, as deduced from the corresponding resonance Raman spectra. Further oxidations at 1.2 and 1.4 V have been observed and ascribed to hydroxylation of the salicylate semiquinone ligand in the complex.