Redox Stability Of Complexes Research Articles

New mononuclear gold(III) complexes: Synthesis, characterization, kinetic, mechanistic, DNA/BSA/HSA binding, DFT and molecular docking studies

Five new gold(III) complexes, with general formula [Au(NN)Cl2]+ for complexes 1–3 and [Au(NN)2]3+ for complexes 4–5 (where NN is 3-((2-((5-phenyl-1H-pyrazol-3-yl)methoxy)naphthalene-3-yloxy)methyl)-5-phenyl-1H-pyrazole – L1, (3-((2-((5-phenyl-1H-pyrazol-3-yl)methoxy) phenoxy)methyl)-5-phenyl-1H-pyrazole – L2, (3-((2-((5-naphthalen-2-yl)-1H-pyrazol-3-yl)methoxy)phenoxy)methyl)-5-(naphthalen-3-yl)-1H-pyrazole – L3), were synthesized and characterized by elemental analysis, 1H NMR, IR, UV–Vis, ESI-MS and conductometry. Also, ligand L2 was characterized by X-ray analysis. Stability of complexes in water and in Hepes buffer was confirmed by UV–Vis. Kinetics and mechanism of the substitution reactions of 1–3 with guanosine-5′-monophosphate (5′-GMP), glutathione (GSH) and.l-Methionine (l-Met) were studied by stopped-flow technique. Obtained results have shown that complex 1 is the most reactive, while the reactivity of the nucleophiles decreases in order: GSH > 5′-GMP > l-Met. Calculated values of the entropy of activation support an associative mechanism. Redox stability of complexes 1–3 was investigated in the presence of the same biomolecules by cyclic voltametry. Obtained voltammograms showed reduction of gold(III) up to gold(0). DNA binding studies in the presence of ethidium bromide (EB) and 2-(4-hydroxyphenyl)-5-[5-(4-methylpipera-zine-1yl)-benzimidazo-2-yl]-benzimidazole (HOE) were performed by UV–Vis, fluorescence spectroscopy and viscosity measurements, in order to assess the binding mode. The results showed that gold(III) complexes interact with calf-thymus (CT-DNA) via covalently binding mode rather than via intercalation. Also, all complexes shown high values of binding constants for the interactions with bovine serum albumin (BSA) and human serum albumin (HSA). Furthermore, the binding studies with CT-DNA and BSA/HSA were supported by molecular docking. The strong connection between structure and reactivity of gold(III) complexes toward biologically important molecules was confirmed.

Synthesis, characterization, DFT study, DNA/BSA-binding affinity, and cytotoxicity of some dinuclear and trinuclear gold(III) complexes.

In this study, we have synthesized a series of dinuclear and trinuclear gold(III) complexes of the general formula [Au2(N-N)Cl6] (1-3) for dinuclear and [Au3(N-N)2Cl8]+ (4-6) for trinuclear compounds, respectively, in which N-N is a bidentate ligand (1,4-diaminobutane; 1,6-diaminohexane or 1,8-diaminooctane). These complexes were characterized by elemental analysis, molar conductivity, and spectroscopic techniques (IR, UV-Vis, 1H NMR, ESI-MS). We performed DFT calculations to get insight into the geometry of the studies complexes. DNA-binding studies were performed by UV-Vis spectrophotometry and fluorescence spectroscopy. The results of competitive reactions between gold(III) complexes and ethidium bromide (EB) towards DNA have shown that selected complexes can displace EB from DNA-EB adduct. In addition, these experiments confirm that polynuclear gold(III) complexes interact with DNA covalently or via intercalation. Furthermore, high values of binding constants of gold(III) complexes towards bovine serum albumin (BSA) protein indicate good binding affinity. In addition, redox stability of complexes in the presence of DNA/BSA was confirmed by cyclic voltammetry. Results of the interactions between gold(III) complexes with DNA/BSA were discussed in reference to molecular docking data obtain by Molegro virtual docker. The cytotoxic activity of synthesized gold(III) complexes was evaluated on human breast cancer cell line (MDA-MB-231), human colorectal cancer cell line (HCT-116), and normal human lung fibroblast cell line (MRC-5). All complexes dose-dependently reduced cancer and normal cells viabilities, with significant cytotoxic effects (IC50 < 25μM) for trinuclear gold(III) complexes (4, 5) on HCT-116 cells.

Structure and redox stability of [Au(III)(X^N^X)PR3] complexes (X = C or N) in aqueous solution: The role of phosphine auxiliary ligand

The choice of the auxiliary ligand in Au(III) complexes is of paramount importance in tuning their reactivity and biological activity. Tertiary phosphines are one of the most used auxiliary ligands in gold compounds, due to their stereo-electronic properties that confer stability and lipophilicity to these metallodrugs. The redox stability of [Au(III)(C^N^C)PR3]+ (A) (C^N^C = 2,6-diphenylpyridine) and [Au(III)(N^N^N)PR3]3+ (N^N^N = 2,2′:6′,2″-terpyridine) (B) complexes (where R is the phosphine substituent groups with different steric and electronic properties) was herein investigated for a set of 41 phosphines, using the predicted standard reduction potential (εo) for Au(III)/Au(I) electrochemical system as reference. For the complexes A, εo spread over 829 mV and all values were negative, whereas for the complexes B εo were positive and covered a narrower range of 507 mV. The phosphines with high buried volume (%Vbur ≥ 32%) decrease the complex stability despite being strong σ-donors. Both steric and electronic properties were used as molecular descriptors to build quantitative structure-property relationships (QSPR), which showed that the %Vbur plays the major role on the redox stability of the studied Au(III) complexes. For complexes B where the phosphine affects both Au(III) and Au(I) forms, the steric impact is more pronounced on the Au(I) reduced species. The electron-donating ability of phosphines is also important and plays a greater role on the redox stability of complexes B than complexes A. These outcomes are certainly useful to predict the redox stability of Au(III) complexes which, in turn, should affect their chemical reactivity against biological targets.

Inclusion of relativistic effects into ZDO methods. II. Solavation of metal complexes

AbstractThe quasirelativistic CNDO/1 method has been in investigating the geometry, electronic structure, and redox stability of metal complexes. The systems of [Co(NH3)6]q and [MCl4]q, M being Ni, Pd, and Pt, have been studied. A modified Germer model of solvation has been implemented into the method. This yields reliable results on the redox stability of complexes in aqueous solutions. The calculated excitation energies resemble the electronic spectra of [MCl4]2− complexes.